1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_EVENTS 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> or <bitmap-list> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 229 s4_nohwsig, old_ordering, nonvs, 230 sci_force_enable, nobl } 231 See Documentation/power/video.rst for information on 232 s3_bios and s3_mode. 233 s3_beep is for debugging; it makes the PC's speaker beep 234 as soon as the kernel's real-mode entry point is called. 235 s4_hwsig causes the kernel to check the ACPI hardware 236 signature during resume from hibernation, and gracefully 237 refuse to resume if it has changed. This complies with 238 the ACPI specification but not with reality, since 239 Windows does not do this and many laptops do change it 240 on docking. So the default behaviour is to allow resume 241 and simply warn when the signature changes, unless the 242 s4_hwsig option is enabled. 243 s4_nohwsig prevents ACPI hardware signature from being 244 used (or even warned about) during resume. 245 old_ordering causes the ACPI 1.0 ordering of the _PTS 246 control method, with respect to putting devices into 247 low power states, to be enforced (the ACPI 2.0 ordering 248 of _PTS is used by default). 249 nonvs prevents the kernel from saving/restoring the 250 ACPI NVS memory during suspend/hibernation and resume. 251 sci_force_enable causes the kernel to set SCI_EN directly 252 on resume from S1/S3 (which is against the ACPI spec, 253 but some broken systems don't work without it). 254 nobl causes the internal blacklist of systems known to 255 behave incorrectly in some ways with respect to system 256 suspend and resume to be ignored (use wisely). 257 258 acpi_use_timer_override [HW,ACPI] 259 Use timer override. For some broken Nvidia NF5 boards 260 that require a timer override, but don't have HPET 261 262 add_efi_memmap [EFI; X86] Include EFI memory map in 263 kernel's map of available physical RAM. 264 265 agp= [AGP] 266 { off | try_unsupported } 267 off: disable AGP support 268 try_unsupported: try to drive unsupported chipsets 269 (may crash computer or cause data corruption) 270 271 ALSA [HW,ALSA] 272 See Documentation/sound/alsa-configuration.rst 273 274 alignment= [KNL,ARM] 275 Allow the default userspace alignment fault handler 276 behaviour to be specified. Bit 0 enables warnings, 277 bit 1 enables fixups, and bit 2 sends a segfault. 278 279 align_va_addr= [X86-64] 280 Align virtual addresses by clearing slice [14:12] when 281 allocating a VMA at process creation time. This option 282 gives you up to 3% performance improvement on AMD F15h 283 machines (where it is enabled by default) for a 284 CPU-intensive style benchmark, and it can vary highly in 285 a microbenchmark depending on workload and compiler. 286 287 32: only for 32-bit processes 288 64: only for 64-bit processes 289 on: enable for both 32- and 64-bit processes 290 off: disable for both 32- and 64-bit processes 291 292 alloc_snapshot [FTRACE] 293 Allocate the ftrace snapshot buffer on boot up when the 294 main buffer is allocated. This is handy if debugging 295 and you need to use tracing_snapshot() on boot up, and 296 do not want to use tracing_snapshot_alloc() as it needs 297 to be done where GFP_KERNEL allocations are allowed. 298 299 allow_mismatched_32bit_el0 [ARM64] 300 Allow execve() of 32-bit applications and setting of the 301 PER_LINUX32 personality on systems where only a strict 302 subset of the CPUs support 32-bit EL0. When this 303 parameter is present, the set of CPUs supporting 32-bit 304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 305 and hot-unplug operations may be restricted. 306 307 See Documentation/arm64/asymmetric-32bit.rst for more 308 information. 309 310 amd_iommu= [HW,X86-64] 311 Pass parameters to the AMD IOMMU driver in the system. 312 Possible values are: 313 fullflush - Deprecated, equivalent to iommu.strict=1 314 off - do not initialize any AMD IOMMU found in 315 the system 316 force_isolation - Force device isolation for all 317 devices. The IOMMU driver is not 318 allowed anymore to lift isolation 319 requirements as needed. This option 320 does not override iommu=pt 321 force_enable - Force enable the IOMMU on platforms known 322 to be buggy with IOMMU enabled. Use this 323 option with care. 324 325 amd_iommu_dump= [HW,X86-64] 326 Enable AMD IOMMU driver option to dump the ACPI table 327 for AMD IOMMU. With this option enabled, AMD IOMMU 328 driver will print ACPI tables for AMD IOMMU during 329 IOMMU initialization. 330 331 amd_iommu_intr= [HW,X86-64] 332 Specifies one of the following AMD IOMMU interrupt 333 remapping modes: 334 legacy - Use legacy interrupt remapping mode. 335 vapic - Use virtual APIC mode, which allows IOMMU 336 to inject interrupts directly into guest. 337 This mode requires kvm-amd.avic=1. 338 (Default when IOMMU HW support is present.) 339 340 amijoy.map= [HW,JOY] Amiga joystick support 341 Map of devices attached to JOY0DAT and JOY1DAT 342 Format: <a>,<b> 343 See also Documentation/input/joydev/joystick.rst 344 345 analog.map= [HW,JOY] Analog joystick and gamepad support 346 Specifies type or capabilities of an analog joystick 347 connected to one of 16 gameports 348 Format: <type1>,<type2>,..<type16> 349 350 apc= [HW,SPARC] 351 Power management functions (SPARCstation-4/5 + deriv.) 352 Format: noidle 353 Disable APC CPU standby support. SPARCstation-Fox does 354 not play well with APC CPU idle - disable it if you have 355 APC and your system crashes randomly. 356 357 apic= [APIC,X86] Advanced Programmable Interrupt Controller 358 Change the output verbosity while booting 359 Format: { quiet (default) | verbose | debug } 360 Change the amount of debugging information output 361 when initialising the APIC and IO-APIC components. 362 For X86-32, this can also be used to specify an APIC 363 driver name. 364 Format: apic=driver_name 365 Examples: apic=bigsmp 366 367 apic_extnmi= [APIC,X86] External NMI delivery setting 368 Format: { bsp (default) | all | none } 369 bsp: External NMI is delivered only to CPU 0 370 all: External NMIs are broadcast to all CPUs as a 371 backup of CPU 0 372 none: External NMI is masked for all CPUs. This is 373 useful so that a dump capture kernel won't be 374 shot down by NMI 375 376 autoconf= [IPV6] 377 See Documentation/networking/ipv6.rst. 378 379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 380 Limit apic dumping. The parameter defines the maximal 381 number of local apics being dumped. Also it is possible 382 to set it to "all" by meaning -- no limit here. 383 Format: { 1 (default) | 2 | ... | all }. 384 The parameter valid if only apic=debug or 385 apic=verbose is specified. 386 Example: apic=debug show_lapic=all 387 388 apm= [APM] Advanced Power Management 389 See header of arch/x86/kernel/apm_32.c. 390 391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 392 Format: <io>,<irq>,<nodeID> 393 394 arm64.nobti [ARM64] Unconditionally disable Branch Target 395 Identification support 396 397 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 398 support 399 400 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 401 support 402 403 ataflop= [HW,M68k] 404 405 atarimouse= [HW,MOUSE] Atari Mouse 406 407 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 408 EzKey and similar keyboards 409 410 atkbd.reset= [HW] Reset keyboard during initialization 411 412 atkbd.set= [HW] Select keyboard code set 413 Format: <int> (2 = AT (default), 3 = PS/2) 414 415 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 416 keyboards 417 418 atkbd.softraw= [HW] Choose between synthetic and real raw mode 419 Format: <bool> (0 = real, 1 = synthetic (default)) 420 421 atkbd.softrepeat= [HW] 422 Use software keyboard repeat 423 424 audit= [KNL] Enable the audit sub-system 425 Format: { "0" | "1" | "off" | "on" } 426 0 | off - kernel audit is disabled and can not be 427 enabled until the next reboot 428 unset - kernel audit is initialized but disabled and 429 will be fully enabled by the userspace auditd. 430 1 | on - kernel audit is initialized and partially 431 enabled, storing at most audit_backlog_limit 432 messages in RAM until it is fully enabled by the 433 userspace auditd. 434 Default: unset 435 436 audit_backlog_limit= [KNL] Set the audit queue size limit. 437 Format: <int> (must be >=0) 438 Default: 64 439 440 bau= [X86_UV] Enable the BAU on SGI UV. The default 441 behavior is to disable the BAU (i.e. bau=0). 442 Format: { "0" | "1" } 443 0 - Disable the BAU. 444 1 - Enable the BAU. 445 unset - Disable the BAU. 446 447 baycom_epp= [HW,AX25] 448 Format: <io>,<mode> 449 450 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 451 Format: <io>,<mode> 452 See header of drivers/net/hamradio/baycom_par.c. 453 454 baycom_ser_fdx= [HW,AX25] 455 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 456 Format: <io>,<irq>,<mode>[,<baud>] 457 See header of drivers/net/hamradio/baycom_ser_fdx.c. 458 459 baycom_ser_hdx= [HW,AX25] 460 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 461 Format: <io>,<irq>,<mode> 462 See header of drivers/net/hamradio/baycom_ser_hdx.c. 463 464 blkdevparts= Manual partition parsing of block device(s) for 465 embedded devices based on command line input. 466 See Documentation/block/cmdline-partition.rst 467 468 boot_delay= Milliseconds to delay each printk during boot. 469 Values larger than 10 seconds (10000) are changed to 470 no delay (0). 471 Format: integer 472 473 bootconfig [KNL] 474 Extended command line options can be added to an initrd 475 and this will cause the kernel to look for it. 476 477 See Documentation/admin-guide/bootconfig.rst 478 479 bert_disable [ACPI] 480 Disable BERT OS support on buggy BIOSes. 481 482 bgrt_disable [ACPI][X86] 483 Disable BGRT to avoid flickering OEM logo. 484 485 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 486 bttv.radio= Most important insmod options are available as 487 kernel args too. 488 bttv.pll= See Documentation/admin-guide/media/bttv.rst 489 bttv.tuner= 490 491 bulk_remove=off [PPC] This parameter disables the use of the pSeries 492 firmware feature for flushing multiple hpte entries 493 at a time. 494 495 c101= [NET] Moxa C101 synchronous serial card 496 497 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 498 Sometimes CPU hardware bugs make them report the cache 499 size incorrectly. The kernel will attempt work arounds 500 to fix known problems, but for some CPUs it is not 501 possible to determine what the correct size should be. 502 This option provides an override for these situations. 503 504 carrier_timeout= 505 [NET] Specifies amount of time (in seconds) that 506 the kernel should wait for a network carrier. By default 507 it waits 120 seconds. 508 509 ca_keys= [KEYS] This parameter identifies a specific key(s) on 510 the system trusted keyring to be used for certificate 511 trust validation. 512 format: { id:<keyid> | builtin } 513 514 cca= [MIPS] Override the kernel pages' cache coherency 515 algorithm. Accepted values range from 0 to 7 516 inclusive. See arch/mips/include/asm/pgtable-bits.h 517 for platform specific values (SB1, Loongson3 and 518 others). 519 520 ccw_timeout_log [S390] 521 See Documentation/s390/common_io.rst for details. 522 523 cgroup_disable= [KNL] Disable a particular controller or optional feature 524 Format: {name of the controller(s) or feature(s) to disable} 525 The effects of cgroup_disable=foo are: 526 - foo isn't auto-mounted if you mount all cgroups in 527 a single hierarchy 528 - foo isn't visible as an individually mountable 529 subsystem 530 - if foo is an optional feature then the feature is 531 disabled and corresponding cgroup files are not 532 created 533 {Currently only "memory" controller deal with this and 534 cut the overhead, others just disable the usage. So 535 only cgroup_disable=memory is actually worthy} 536 Specifying "pressure" disables per-cgroup pressure 537 stall information accounting feature 538 539 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 540 Format: { { controller | "all" | "named" } 541 [,{ controller | "all" | "named" }...] } 542 Like cgroup_disable, but only applies to cgroup v1; 543 the blacklisted controllers remain available in cgroup2. 544 "all" blacklists all controllers and "named" disables 545 named mounts. Specifying both "all" and "named" disables 546 all v1 hierarchies. 547 548 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 549 Format: <string> 550 nosocket -- Disable socket memory accounting. 551 nokmem -- Disable kernel memory accounting. 552 553 checkreqprot [SELINUX] Set initial checkreqprot flag value. 554 Format: { "0" | "1" } 555 See security/selinux/Kconfig help text. 556 0 -- check protection applied by kernel (includes 557 any implied execute protection). 558 1 -- check protection requested by application. 559 Default value is set via a kernel config option. 560 Value can be changed at runtime via 561 /sys/fs/selinux/checkreqprot. 562 Setting checkreqprot to 1 is deprecated. 563 564 cio_ignore= [S390] 565 See Documentation/s390/common_io.rst for details. 566 clk_ignore_unused 567 [CLK] 568 Prevents the clock framework from automatically gating 569 clocks that have not been explicitly enabled by a Linux 570 device driver but are enabled in hardware at reset or 571 by the bootloader/firmware. Note that this does not 572 force such clocks to be always-on nor does it reserve 573 those clocks in any way. This parameter is useful for 574 debug and development, but should not be needed on a 575 platform with proper driver support. For more 576 information, see Documentation/driver-api/clk.rst. 577 578 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 579 [Deprecated] 580 Forces specified clocksource (if available) to be used 581 when calculating gettimeofday(). If specified 582 clocksource is not available, it defaults to PIT. 583 Format: { pit | tsc | cyclone | pmtmr } 584 585 clocksource= Override the default clocksource 586 Format: <string> 587 Override the default clocksource and use the clocksource 588 with the name specified. 589 Some clocksource names to choose from, depending on 590 the platform: 591 [all] jiffies (this is the base, fallback clocksource) 592 [ACPI] acpi_pm 593 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 594 pxa_timer,timer3,32k_counter,timer0_1 595 [X86-32] pit,hpet,tsc; 596 scx200_hrt on Geode; cyclone on IBM x440 597 [MIPS] MIPS 598 [PARISC] cr16 599 [S390] tod 600 [SH] SuperH 601 [SPARC64] tick 602 [X86-64] hpet,tsc 603 604 clocksource.arm_arch_timer.evtstrm= 605 [ARM,ARM64] 606 Format: <bool> 607 Enable/disable the eventstream feature of the ARM 608 architected timer so that code using WFE-based polling 609 loops can be debugged more effectively on production 610 systems. 611 612 clocksource.max_cswd_read_retries= [KNL] 613 Number of clocksource_watchdog() retries due to 614 external delays before the clock will be marked 615 unstable. Defaults to two retries, that is, 616 three attempts to read the clock under test. 617 618 clocksource.verify_n_cpus= [KNL] 619 Limit the number of CPUs checked for clocksources 620 marked with CLOCK_SOURCE_VERIFY_PERCPU that 621 are marked unstable due to excessive skew. 622 A negative value says to check all CPUs, while 623 zero says not to check any. Values larger than 624 nr_cpu_ids are silently truncated to nr_cpu_ids. 625 The actual CPUs are chosen randomly, with 626 no replacement if the same CPU is chosen twice. 627 628 clocksource-wdtest.holdoff= [KNL] 629 Set the time in seconds that the clocksource 630 watchdog test waits before commencing its tests. 631 Defaults to zero when built as a module and to 632 10 seconds when built into the kernel. 633 634 clearcpuid=BITNUM[,BITNUM...] [X86] 635 Disable CPUID feature X for the kernel. See 636 arch/x86/include/asm/cpufeatures.h for the valid bit 637 numbers. Note the Linux specific bits are not necessarily 638 stable over kernel options, but the vendor specific 639 ones should be. 640 Also note that user programs calling CPUID directly 641 or using the feature without checking anything 642 will still see it. This just prevents it from 643 being used by the kernel or shown in /proc/cpuinfo. 644 Also note the kernel might malfunction if you disable 645 some critical bits. 646 647 cma=nn[MG]@[start[MG][-end[MG]]] 648 [KNL,CMA] 649 Sets the size of kernel global memory area for 650 contiguous memory allocations and optionally the 651 placement constraint by the physical address range of 652 memory allocations. A value of 0 disables CMA 653 altogether. For more information, see 654 kernel/dma/contiguous.c 655 656 cma_pernuma=nn[MG] 657 [ARM64,KNL,CMA] 658 Sets the size of kernel per-numa memory area for 659 contiguous memory allocations. A value of 0 disables 660 per-numa CMA altogether. And If this option is not 661 specificed, the default value is 0. 662 With per-numa CMA enabled, DMA users on node nid will 663 first try to allocate buffer from the pernuma area 664 which is located in node nid, if the allocation fails, 665 they will fallback to the global default memory area. 666 667 cmo_free_hint= [PPC] Format: { yes | no } 668 Specify whether pages are marked as being inactive 669 when they are freed. This is used in CMO environments 670 to determine OS memory pressure for page stealing by 671 a hypervisor. 672 Default: yes 673 674 coherent_pool=nn[KMG] [ARM,KNL] 675 Sets the size of memory pool for coherent, atomic dma 676 allocations, by default set to 256K. 677 678 com20020= [HW,NET] ARCnet - COM20020 chipset 679 Format: 680 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 681 682 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 683 Format: <io>[,<irq>] 684 685 com90xx= [HW,NET] 686 ARCnet - COM90xx chipset (memory-mapped buffers) 687 Format: <io>[,<irq>[,<memstart>]] 688 689 condev= [HW,S390] console device 690 conmode= 691 692 console= [KNL] Output console device and options. 693 694 tty<n> Use the virtual console device <n>. 695 696 ttyS<n>[,options] 697 ttyUSB0[,options] 698 Use the specified serial port. The options are of 699 the form "bbbbpnf", where "bbbb" is the baud rate, 700 "p" is parity ("n", "o", or "e"), "n" is number of 701 bits, and "f" is flow control ("r" for RTS or 702 omit it). Default is "9600n8". 703 704 See Documentation/admin-guide/serial-console.rst for more 705 information. See 706 Documentation/networking/netconsole.rst for an 707 alternative. 708 709 uart[8250],io,<addr>[,options] 710 uart[8250],mmio,<addr>[,options] 711 uart[8250],mmio16,<addr>[,options] 712 uart[8250],mmio32,<addr>[,options] 713 uart[8250],0x<addr>[,options] 714 Start an early, polled-mode console on the 8250/16550 715 UART at the specified I/O port or MMIO address, 716 switching to the matching ttyS device later. 717 MMIO inter-register address stride is either 8-bit 718 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 719 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 720 to be equivalent to 'mmio'. 'options' are specified in 721 the same format described for ttyS above; if unspecified, 722 the h/w is not re-initialized. 723 724 hvc<n> Use the hypervisor console device <n>. This is for 725 both Xen and PowerPC hypervisors. 726 727 { null | "" } 728 Use to disable console output, i.e., to have kernel 729 console messages discarded. 730 This must be the only console= parameter used on the 731 kernel command line. 732 733 If the device connected to the port is not a TTY but a braille 734 device, prepend "brl," before the device type, for instance 735 console=brl,ttyS0 736 For now, only VisioBraille is supported. 737 738 console_msg_format= 739 [KNL] Change console messages format 740 default 741 By default we print messages on consoles in 742 "[time stamp] text\n" format (time stamp may not be 743 printed, depending on CONFIG_PRINTK_TIME or 744 `printk_time' param). 745 syslog 746 Switch to syslog format: "<%u>[time stamp] text\n" 747 IOW, each message will have a facility and loglevel 748 prefix. The format is similar to one used by syslog() 749 syscall, or to executing "dmesg -S --raw" or to reading 750 from /proc/kmsg. 751 752 consoleblank= [KNL] The console blank (screen saver) timeout in 753 seconds. A value of 0 disables the blank timer. 754 Defaults to 0. 755 756 coredump_filter= 757 [KNL] Change the default value for 758 /proc/<pid>/coredump_filter. 759 See also Documentation/filesystems/proc.rst. 760 761 coresight_cpu_debug.enable 762 [ARM,ARM64] 763 Format: <bool> 764 Enable/disable the CPU sampling based debugging. 765 0: default value, disable debugging 766 1: enable debugging at boot time 767 768 cpuidle.off=1 [CPU_IDLE] 769 disable the cpuidle sub-system 770 771 cpuidle.governor= 772 [CPU_IDLE] Name of the cpuidle governor to use. 773 774 cpufreq.off=1 [CPU_FREQ] 775 disable the cpufreq sub-system 776 777 cpufreq.default_governor= 778 [CPU_FREQ] Name of the default cpufreq governor or 779 policy to use. This governor must be registered in the 780 kernel before the cpufreq driver probes. 781 782 cpu_init_udelay=N 783 [X86] Delay for N microsec between assert and de-assert 784 of APIC INIT to start processors. This delay occurs 785 on every CPU online, such as boot, and resume from suspend. 786 Default: 10000 787 788 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 789 Format: 790 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 791 792 crashkernel=size[KMG][@offset[KMG]] 793 [KNL] Using kexec, Linux can switch to a 'crash kernel' 794 upon panic. This parameter reserves the physical 795 memory region [offset, offset + size] for that kernel 796 image. If '@offset' is omitted, then a suitable offset 797 is selected automatically. 798 [KNL, X86-64] Select a region under 4G first, and 799 fall back to reserve region above 4G when '@offset' 800 hasn't been specified. 801 See Documentation/admin-guide/kdump/kdump.rst for further details. 802 803 crashkernel=range1:size1[,range2:size2,...][@offset] 804 [KNL] Same as above, but depends on the memory 805 in the running system. The syntax of range is 806 start-[end] where start and end are both 807 a memory unit (amount[KMG]). See also 808 Documentation/admin-guide/kdump/kdump.rst for an example. 809 810 crashkernel=size[KMG],high 811 [KNL, X86-64] range could be above 4G. Allow kernel 812 to allocate physical memory region from top, so could 813 be above 4G if system have more than 4G ram installed. 814 Otherwise memory region will be allocated below 4G, if 815 available. 816 It will be ignored if crashkernel=X is specified. 817 crashkernel=size[KMG],low 818 [KNL, X86-64] range under 4G. When crashkernel=X,high 819 is passed, kernel could allocate physical memory region 820 above 4G, that cause second kernel crash on system 821 that require some amount of low memory, e.g. swiotlb 822 requires at least 64M+32K low memory, also enough extra 823 low memory is needed to make sure DMA buffers for 32-bit 824 devices won't run out. Kernel would try to allocate at 825 at least 256M below 4G automatically. 826 This one let user to specify own low range under 4G 827 for second kernel instead. 828 0: to disable low allocation. 829 It will be ignored when crashkernel=X,high is not used 830 or memory reserved is below 4G. 831 832 cryptomgr.notests 833 [KNL] Disable crypto self-tests 834 835 cs89x0_dma= [HW,NET] 836 Format: <dma> 837 838 cs89x0_media= [HW,NET] 839 Format: { rj45 | aui | bnc } 840 841 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call 842 handling. When switched on, additional debug data is 843 printed to the console in case a hanging CPU is 844 detected, and that CPU is pinged again in order to try 845 to resolve the hang situation. 846 0: disable csdlock debugging (default) 847 1: enable basic csdlock debugging (minor impact) 848 ext: enable extended csdlock debugging (more impact, 849 but more data) 850 851 dasd= [HW,NET] 852 See header of drivers/s390/block/dasd_devmap.c. 853 854 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 855 (one device per port) 856 Format: <port#>,<type> 857 See also Documentation/input/devices/joystick-parport.rst 858 859 debug [KNL] Enable kernel debugging (events log level). 860 861 debug_boot_weak_hash 862 [KNL] Enable printing [hashed] pointers early in the 863 boot sequence. If enabled, we use a weak hash instead 864 of siphash to hash pointers. Use this option if you are 865 seeing instances of '(___ptrval___)') and need to see a 866 value (hashed pointer) instead. Cryptographically 867 insecure, please do not use on production kernels. 868 869 debug_locks_verbose= 870 [KNL] verbose locking self-tests 871 Format: <int> 872 Print debugging info while doing the locking API 873 self-tests. 874 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 875 (no extra messages), setting it to -1 (all bits set) 876 will print _a_lot_ more information - normally only 877 useful to lockdep developers. 878 879 debug_objects [KNL] Enable object debugging 880 881 no_debug_objects 882 [KNL] Disable object debugging 883 884 debug_guardpage_minorder= 885 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 886 parameter allows control of the order of pages that will 887 be intentionally kept free (and hence protected) by the 888 buddy allocator. Bigger value increase the probability 889 of catching random memory corruption, but reduce the 890 amount of memory for normal system use. The maximum 891 possible value is MAX_ORDER/2. Setting this parameter 892 to 1 or 2 should be enough to identify most random 893 memory corruption problems caused by bugs in kernel or 894 driver code when a CPU writes to (or reads from) a 895 random memory location. Note that there exists a class 896 of memory corruptions problems caused by buggy H/W or 897 F/W or by drivers badly programing DMA (basically when 898 memory is written at bus level and the CPU MMU is 899 bypassed) which are not detectable by 900 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 901 tracking down these problems. 902 903 debug_pagealloc= 904 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 905 enables the feature at boot time. By default, it is 906 disabled and the system will work mostly the same as a 907 kernel built without CONFIG_DEBUG_PAGEALLOC. 908 Note: to get most of debug_pagealloc error reports, it's 909 useful to also enable the page_owner functionality. 910 on: enable the feature 911 912 debugfs= [KNL] This parameter enables what is exposed to userspace 913 and debugfs internal clients. 914 Format: { on, no-mount, off } 915 on: All functions are enabled. 916 no-mount: 917 Filesystem is not registered but kernel clients can 918 access APIs and a crashkernel can be used to read 919 its content. There is nothing to mount. 920 off: Filesystem is not registered and clients 921 get a -EPERM as result when trying to register files 922 or directories within debugfs. 923 This is equivalent of the runtime functionality if 924 debugfs was not enabled in the kernel at all. 925 Default value is set in build-time with a kernel configuration. 926 927 debugpat [X86] Enable PAT debugging 928 929 decnet.addr= [HW,NET] 930 Format: <area>[,<node>] 931 See also Documentation/networking/decnet.rst. 932 933 default_hugepagesz= 934 [HW] The size of the default HugeTLB page. This is 935 the size represented by the legacy /proc/ hugepages 936 APIs. In addition, this is the default hugetlb size 937 used for shmget(), mmap() and mounting hugetlbfs 938 filesystems. If not specified, defaults to the 939 architecture's default huge page size. Huge page 940 sizes are architecture dependent. See also 941 Documentation/admin-guide/mm/hugetlbpage.rst. 942 Format: size[KMG] 943 944 deferred_probe_timeout= 945 [KNL] Debugging option to set a timeout in seconds for 946 deferred probe to give up waiting on dependencies to 947 probe. Only specific dependencies (subsystems or 948 drivers) that have opted in will be ignored. A timeout of 0 949 will timeout at the end of initcalls. This option will also 950 dump out devices still on the deferred probe list after 951 retrying. 952 953 dell_smm_hwmon.ignore_dmi= 954 [HW] Continue probing hardware even if DMI data 955 indicates that the driver is running on unsupported 956 hardware. 957 958 dell_smm_hwmon.force= 959 [HW] Activate driver even if SMM BIOS signature does 960 not match list of supported models and enable otherwise 961 blacklisted features. 962 963 dell_smm_hwmon.power_status= 964 [HW] Report power status in /proc/i8k 965 (disabled by default). 966 967 dell_smm_hwmon.restricted= 968 [HW] Allow controlling fans only if SYS_ADMIN 969 capability is set. 970 971 dell_smm_hwmon.fan_mult= 972 [HW] Factor to multiply fan speed with. 973 974 dell_smm_hwmon.fan_max= 975 [HW] Maximum configurable fan speed. 976 977 dfltcc= [HW,S390] 978 Format: { on | off | def_only | inf_only | always } 979 on: s390 zlib hardware support for compression on 980 level 1 and decompression (default) 981 off: No s390 zlib hardware support 982 def_only: s390 zlib hardware support for deflate 983 only (compression on level 1) 984 inf_only: s390 zlib hardware support for inflate 985 only (decompression) 986 always: Same as 'on' but ignores the selected compression 987 level always using hardware support (used for debugging) 988 989 dhash_entries= [KNL] 990 Set number of hash buckets for dentry cache. 991 992 disable_1tb_segments [PPC] 993 Disables the use of 1TB hash page table segments. This 994 causes the kernel to fall back to 256MB segments which 995 can be useful when debugging issues that require an SLB 996 miss to occur. 997 998 stress_slb [PPC] 999 Limits the number of kernel SLB entries, and flushes 1000 them frequently to increase the rate of SLB faults 1001 on kernel addresses. 1002 1003 disable= [IPV6] 1004 See Documentation/networking/ipv6.rst. 1005 1006 hardened_usercopy= 1007 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1008 hardening is enabled for this boot. Hardened 1009 usercopy checking is used to protect the kernel 1010 from reading or writing beyond known memory 1011 allocation boundaries as a proactive defense 1012 against bounds-checking flaws in the kernel's 1013 copy_to_user()/copy_from_user() interface. 1014 on Perform hardened usercopy checks (default). 1015 off Disable hardened usercopy checks. 1016 1017 disable_radix [PPC] 1018 Disable RADIX MMU mode on POWER9 1019 1020 radix_hcall_invalidate=on [PPC/PSERIES] 1021 Disable RADIX GTSE feature and use hcall for TLB 1022 invalidate. 1023 1024 disable_tlbie [PPC] 1025 Disable TLBIE instruction. Currently does not work 1026 with KVM, with HASH MMU, or with coherent accelerators. 1027 1028 disable_cpu_apicid= [X86,APIC,SMP] 1029 Format: <int> 1030 The number of initial APIC ID for the 1031 corresponding CPU to be disabled at boot, 1032 mostly used for the kdump 2nd kernel to 1033 disable BSP to wake up multiple CPUs without 1034 causing system reset or hang due to sending 1035 INIT from AP to BSP. 1036 1037 disable_ddw [PPC/PSERIES] 1038 Disable Dynamic DMA Window support. Use this 1039 to workaround buggy firmware. 1040 1041 disable_ipv6= [IPV6] 1042 See Documentation/networking/ipv6.rst. 1043 1044 disable_mtrr_cleanup [X86] 1045 The kernel tries to adjust MTRR layout from continuous 1046 to discrete, to make X server driver able to add WB 1047 entry later. This parameter disables that. 1048 1049 disable_mtrr_trim [X86, Intel and AMD only] 1050 By default the kernel will trim any uncacheable 1051 memory out of your available memory pool based on 1052 MTRR settings. This parameter disables that behavior, 1053 possibly causing your machine to run very slowly. 1054 1055 disable_timer_pin_1 [X86] 1056 Disable PIN 1 of APIC timer 1057 Can be useful to work around chipset bugs. 1058 1059 dis_ucode_ldr [X86] Disable the microcode loader. 1060 1061 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1062 this option disables the debugging code at boot. 1063 1064 dma_debug_entries=<number> 1065 This option allows to tune the number of preallocated 1066 entries for DMA-API debugging code. One entry is 1067 required per DMA-API allocation. Use this if the 1068 DMA-API debugging code disables itself because the 1069 architectural default is too low. 1070 1071 dma_debug_driver=<driver_name> 1072 With this option the DMA-API debugging driver 1073 filter feature can be enabled at boot time. Just 1074 pass the driver to filter for as the parameter. 1075 The filter can be disabled or changed to another 1076 driver later using sysfs. 1077 1078 driver_async_probe= [KNL] 1079 List of driver names to be probed asynchronously. 1080 Format: <driver_name1>,<driver_name2>... 1081 1082 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1083 Broken monitors, graphic adapters, KVMs and EDIDless 1084 panels may send no or incorrect EDID data sets. 1085 This parameter allows to specify an EDID data sets 1086 in the /lib/firmware directory that are used instead. 1087 Generic built-in EDID data sets are used, if one of 1088 edid/1024x768.bin, edid/1280x1024.bin, 1089 edid/1680x1050.bin, or edid/1920x1080.bin is given 1090 and no file with the same name exists. Details and 1091 instructions how to build your own EDID data are 1092 available in Documentation/admin-guide/edid.rst. An EDID 1093 data set will only be used for a particular connector, 1094 if its name and a colon are prepended to the EDID 1095 name. Each connector may use a unique EDID data 1096 set by separating the files with a comma. An EDID 1097 data set with no connector name will be used for 1098 any connectors not explicitly specified. 1099 1100 dscc4.setup= [NET] 1101 1102 dt_cpu_ftrs= [PPC] 1103 Format: {"off" | "known"} 1104 Control how the dt_cpu_ftrs device-tree binding is 1105 used for CPU feature discovery and setup (if it 1106 exists). 1107 off: Do not use it, fall back to legacy cpu table. 1108 known: Do not pass through unknown features to guests 1109 or userspace, only those that the kernel is aware of. 1110 1111 dump_apple_properties [X86] 1112 Dump name and content of EFI device properties on 1113 x86 Macs. Useful for driver authors to determine 1114 what data is available or for reverse-engineering. 1115 1116 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1117 <module>.dyndbg[="val"] 1118 Enable debug messages at boot time. See 1119 Documentation/admin-guide/dynamic-debug-howto.rst 1120 for details. 1121 1122 nopku [X86] Disable Memory Protection Keys CPU feature found 1123 in some Intel CPUs. 1124 1125 <module>.async_probe [KNL] 1126 Enable asynchronous probe on this module. 1127 1128 early_ioremap_debug [KNL] 1129 Enable debug messages in early_ioremap support. This 1130 is useful for tracking down temporary early mappings 1131 which are not unmapped. 1132 1133 earlycon= [KNL] Output early console device and options. 1134 1135 When used with no options, the early console is 1136 determined by stdout-path property in device tree's 1137 chosen node or the ACPI SPCR table if supported by 1138 the platform. 1139 1140 cdns,<addr>[,options] 1141 Start an early, polled-mode console on a Cadence 1142 (xuartps) serial port at the specified address. Only 1143 supported option is baud rate. If baud rate is not 1144 specified, the serial port must already be setup and 1145 configured. 1146 1147 uart[8250],io,<addr>[,options] 1148 uart[8250],mmio,<addr>[,options] 1149 uart[8250],mmio32,<addr>[,options] 1150 uart[8250],mmio32be,<addr>[,options] 1151 uart[8250],0x<addr>[,options] 1152 Start an early, polled-mode console on the 8250/16550 1153 UART at the specified I/O port or MMIO address. 1154 MMIO inter-register address stride is either 8-bit 1155 (mmio) or 32-bit (mmio32 or mmio32be). 1156 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1157 to be equivalent to 'mmio'. 'options' are specified 1158 in the same format described for "console=ttyS<n>"; if 1159 unspecified, the h/w is not initialized. 1160 1161 pl011,<addr> 1162 pl011,mmio32,<addr> 1163 Start an early, polled-mode console on a pl011 serial 1164 port at the specified address. The pl011 serial port 1165 must already be setup and configured. Options are not 1166 yet supported. If 'mmio32' is specified, then only 1167 the driver will use only 32-bit accessors to read/write 1168 the device registers. 1169 1170 liteuart,<addr> 1171 Start an early console on a litex serial port at the 1172 specified address. The serial port must already be 1173 setup and configured. Options are not yet supported. 1174 1175 meson,<addr> 1176 Start an early, polled-mode console on a meson serial 1177 port at the specified address. The serial port must 1178 already be setup and configured. Options are not yet 1179 supported. 1180 1181 msm_serial,<addr> 1182 Start an early, polled-mode console on an msm serial 1183 port at the specified address. The serial port 1184 must already be setup and configured. Options are not 1185 yet supported. 1186 1187 msm_serial_dm,<addr> 1188 Start an early, polled-mode console on an msm serial 1189 dm port at the specified address. The serial port 1190 must already be setup and configured. Options are not 1191 yet supported. 1192 1193 owl,<addr> 1194 Start an early, polled-mode console on a serial port 1195 of an Actions Semi SoC, such as S500 or S900, at the 1196 specified address. The serial port must already be 1197 setup and configured. Options are not yet supported. 1198 1199 rda,<addr> 1200 Start an early, polled-mode console on a serial port 1201 of an RDA Micro SoC, such as RDA8810PL, at the 1202 specified address. The serial port must already be 1203 setup and configured. Options are not yet supported. 1204 1205 sbi 1206 Use RISC-V SBI (Supervisor Binary Interface) for early 1207 console. 1208 1209 smh Use ARM semihosting calls for early console. 1210 1211 s3c2410,<addr> 1212 s3c2412,<addr> 1213 s3c2440,<addr> 1214 s3c6400,<addr> 1215 s5pv210,<addr> 1216 exynos4210,<addr> 1217 Use early console provided by serial driver available 1218 on Samsung SoCs, requires selecting proper type and 1219 a correct base address of the selected UART port. The 1220 serial port must already be setup and configured. 1221 Options are not yet supported. 1222 1223 lantiq,<addr> 1224 Start an early, polled-mode console on a lantiq serial 1225 (lqasc) port at the specified address. The serial port 1226 must already be setup and configured. Options are not 1227 yet supported. 1228 1229 lpuart,<addr> 1230 lpuart32,<addr> 1231 Use early console provided by Freescale LP UART driver 1232 found on Freescale Vybrid and QorIQ LS1021A processors. 1233 A valid base address must be provided, and the serial 1234 port must already be setup and configured. 1235 1236 ec_imx21,<addr> 1237 ec_imx6q,<addr> 1238 Start an early, polled-mode, output-only console on the 1239 Freescale i.MX UART at the specified address. The UART 1240 must already be setup and configured. 1241 1242 ar3700_uart,<addr> 1243 Start an early, polled-mode console on the 1244 Armada 3700 serial port at the specified 1245 address. The serial port must already be setup 1246 and configured. Options are not yet supported. 1247 1248 qcom_geni,<addr> 1249 Start an early, polled-mode console on a Qualcomm 1250 Generic Interface (GENI) based serial port at the 1251 specified address. The serial port must already be 1252 setup and configured. Options are not yet supported. 1253 1254 efifb,[options] 1255 Start an early, unaccelerated console on the EFI 1256 memory mapped framebuffer (if available). On cache 1257 coherent non-x86 systems that use system memory for 1258 the framebuffer, pass the 'ram' option so that it is 1259 mapped with the correct attributes. 1260 1261 linflex,<addr> 1262 Use early console provided by Freescale LINFlexD UART 1263 serial driver for NXP S32V234 SoCs. A valid base 1264 address must be provided, and the serial port must 1265 already be setup and configured. 1266 1267 earlyprintk= [X86,SH,ARM,M68k,S390] 1268 earlyprintk=vga 1269 earlyprintk=sclp 1270 earlyprintk=xen 1271 earlyprintk=serial[,ttySn[,baudrate]] 1272 earlyprintk=serial[,0x...[,baudrate]] 1273 earlyprintk=ttySn[,baudrate] 1274 earlyprintk=dbgp[debugController#] 1275 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1276 earlyprintk=xdbc[xhciController#] 1277 1278 earlyprintk is useful when the kernel crashes before 1279 the normal console is initialized. It is not enabled by 1280 default because it has some cosmetic problems. 1281 1282 Append ",keep" to not disable it when the real console 1283 takes over. 1284 1285 Only one of vga, efi, serial, or usb debug port can 1286 be used at a time. 1287 1288 Currently only ttyS0 and ttyS1 may be specified by 1289 name. Other I/O ports may be explicitly specified 1290 on some architectures (x86 and arm at least) by 1291 replacing ttySn with an I/O port address, like this: 1292 earlyprintk=serial,0x1008,115200 1293 You can find the port for a given device in 1294 /proc/tty/driver/serial: 1295 2: uart:ST16650V2 port:00001008 irq:18 ... 1296 1297 Interaction with the standard serial driver is not 1298 very good. 1299 1300 The VGA and EFI output is eventually overwritten by 1301 the real console. 1302 1303 The xen option can only be used in Xen domains. 1304 1305 The sclp output can only be used on s390. 1306 1307 The optional "force" to "pciserial" enables use of a 1308 PCI device even when its classcode is not of the 1309 UART class. 1310 1311 edac_report= [HW,EDAC] Control how to report EDAC event 1312 Format: {"on" | "off" | "force"} 1313 on: enable EDAC to report H/W event. May be overridden 1314 by other higher priority error reporting module. 1315 off: disable H/W event reporting through EDAC. 1316 force: enforce the use of EDAC to report H/W event. 1317 default: on. 1318 1319 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1320 ekgdboc=kbd 1321 1322 This is designed to be used in conjunction with 1323 the boot argument: earlyprintk=vga 1324 1325 This parameter works in place of the kgdboc parameter 1326 but can only be used if the backing tty is available 1327 very early in the boot process. For early debugging 1328 via a serial port see kgdboc_earlycon instead. 1329 1330 edd= [EDD] 1331 Format: {"off" | "on" | "skip[mbr]"} 1332 1333 efi= [EFI] 1334 Format: { "debug", "disable_early_pci_dma", 1335 "nochunk", "noruntime", "nosoftreserve", 1336 "novamap", "no_disable_early_pci_dma" } 1337 debug: enable misc debug output. 1338 disable_early_pci_dma: disable the busmaster bit on all 1339 PCI bridges while in the EFI boot stub. 1340 nochunk: disable reading files in "chunks" in the EFI 1341 boot stub, as chunking can cause problems with some 1342 firmware implementations. 1343 noruntime : disable EFI runtime services support 1344 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1345 attribute may cause the kernel to reserve the 1346 memory range for a memory mapping driver to 1347 claim. Specify efi=nosoftreserve to disable this 1348 reservation and treat the memory by its base type 1349 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1350 novamap: do not call SetVirtualAddressMap(). 1351 no_disable_early_pci_dma: Leave the busmaster bit set 1352 on all PCI bridges while in the EFI boot stub 1353 1354 efi_no_storage_paranoia [EFI; X86] 1355 Using this parameter you can use more than 50% of 1356 your efi variable storage. Use this parameter only if 1357 you are really sure that your UEFI does sane gc and 1358 fulfills the spec otherwise your board may brick. 1359 1360 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1361 Add arbitrary attribute to specific memory range by 1362 updating original EFI memory map. 1363 Region of memory which aa attribute is added to is 1364 from ss to ss+nn. 1365 1366 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1367 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1368 attribute is added to range 0x100000000-0x180000000 and 1369 0x10a0000000-0x1120000000. 1370 1371 If efi_fake_mem=8G@9G:0x40000 is specified, the 1372 EFI_MEMORY_SP(0x40000) attribute is added to 1373 range 0x240000000-0x43fffffff. 1374 1375 Using this parameter you can do debugging of EFI memmap 1376 related features. For example, you can do debugging of 1377 Address Range Mirroring feature even if your box 1378 doesn't support it, or mark specific memory as 1379 "soft reserved". 1380 1381 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1382 that is to be dynamically loaded by Linux. If there are 1383 multiple variables with the same name but with different 1384 vendor GUIDs, all of them will be loaded. See 1385 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1386 1387 1388 eisa_irq_edge= [PARISC,HW] 1389 See header of drivers/parisc/eisa.c. 1390 1391 elanfreq= [X86-32] 1392 See comment before function elanfreq_setup() in 1393 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1394 1395 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1396 Specifies physical address of start of kernel core 1397 image elf header and optionally the size. Generally 1398 kexec loader will pass this option to capture kernel. 1399 See Documentation/admin-guide/kdump/kdump.rst for details. 1400 1401 enable_mtrr_cleanup [X86] 1402 The kernel tries to adjust MTRR layout from continuous 1403 to discrete, to make X server driver able to add WB 1404 entry later. This parameter enables that. 1405 1406 enable_timer_pin_1 [X86] 1407 Enable PIN 1 of APIC timer 1408 Can be useful to work around chipset bugs 1409 (in particular on some ATI chipsets). 1410 The kernel tries to set a reasonable default. 1411 1412 enforcing [SELINUX] Set initial enforcing status. 1413 Format: {"0" | "1"} 1414 See security/selinux/Kconfig help text. 1415 0 -- permissive (log only, no denials). 1416 1 -- enforcing (deny and log). 1417 Default value is 0. 1418 Value can be changed at runtime via 1419 /sys/fs/selinux/enforce. 1420 1421 erst_disable [ACPI] 1422 Disable Error Record Serialization Table (ERST) 1423 support. 1424 1425 ether= [HW,NET] Ethernet cards parameters 1426 This option is obsoleted by the "netdev=" option, which 1427 has equivalent usage. See its documentation for details. 1428 1429 evm= [EVM] 1430 Format: { "fix" } 1431 Permit 'security.evm' to be updated regardless of 1432 current integrity status. 1433 1434 failslab= 1435 fail_usercopy= 1436 fail_page_alloc= 1437 fail_make_request=[KNL] 1438 General fault injection mechanism. 1439 Format: <interval>,<probability>,<space>,<times> 1440 See also Documentation/fault-injection/. 1441 1442 fb_tunnels= [NET] 1443 Format: { initns | none } 1444 See Documentation/admin-guide/sysctl/net.rst for 1445 fb_tunnels_only_for_init_ns 1446 1447 floppy= [HW] 1448 See Documentation/admin-guide/blockdev/floppy.rst. 1449 1450 force_pal_cache_flush 1451 [IA-64] Avoid check_sal_cache_flush which may hang on 1452 buggy SAL_CACHE_FLUSH implementations. Using this 1453 parameter will force ia64_sal_cache_flush to call 1454 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1455 1456 forcepae [X86-32] 1457 Forcefully enable Physical Address Extension (PAE). 1458 Many Pentium M systems disable PAE but may have a 1459 functionally usable PAE implementation. 1460 Warning: use of this parameter will taint the kernel 1461 and may cause unknown problems. 1462 1463 ftrace=[tracer] 1464 [FTRACE] will set and start the specified tracer 1465 as early as possible in order to facilitate early 1466 boot debugging. 1467 1468 ftrace_boot_snapshot 1469 [FTRACE] On boot up, a snapshot will be taken of the 1470 ftrace ring buffer that can be read at: 1471 /sys/kernel/tracing/snapshot. 1472 This is useful if you need tracing information from kernel 1473 boot up that is likely to be overridden by user space 1474 start up functionality. 1475 1476 ftrace_dump_on_oops[=orig_cpu] 1477 [FTRACE] will dump the trace buffers on oops. 1478 If no parameter is passed, ftrace will dump 1479 buffers of all CPUs, but if you pass orig_cpu, it will 1480 dump only the buffer of the CPU that triggered the 1481 oops. 1482 1483 ftrace_filter=[function-list] 1484 [FTRACE] Limit the functions traced by the function 1485 tracer at boot up. function-list is a comma-separated 1486 list of functions. This list can be changed at run 1487 time by the set_ftrace_filter file in the debugfs 1488 tracing directory. 1489 1490 ftrace_notrace=[function-list] 1491 [FTRACE] Do not trace the functions specified in 1492 function-list. This list can be changed at run time 1493 by the set_ftrace_notrace file in the debugfs 1494 tracing directory. 1495 1496 ftrace_graph_filter=[function-list] 1497 [FTRACE] Limit the top level callers functions traced 1498 by the function graph tracer at boot up. 1499 function-list is a comma-separated list of functions 1500 that can be changed at run time by the 1501 set_graph_function file in the debugfs tracing directory. 1502 1503 ftrace_graph_notrace=[function-list] 1504 [FTRACE] Do not trace from the functions specified in 1505 function-list. This list is a comma-separated list of 1506 functions that can be changed at run time by the 1507 set_graph_notrace file in the debugfs tracing directory. 1508 1509 ftrace_graph_max_depth=<uint> 1510 [FTRACE] Used with the function graph tracer. This is 1511 the max depth it will trace into a function. This value 1512 can be changed at run time by the max_graph_depth file 1513 in the tracefs tracing directory. default: 0 (no limit) 1514 1515 fw_devlink= [KNL] Create device links between consumer and supplier 1516 devices by scanning the firmware to infer the 1517 consumer/supplier relationships. This feature is 1518 especially useful when drivers are loaded as modules as 1519 it ensures proper ordering of tasks like device probing 1520 (suppliers first, then consumers), supplier boot state 1521 clean up (only after all consumers have probed), 1522 suspend/resume & runtime PM (consumers first, then 1523 suppliers). 1524 Format: { off | permissive | on | rpm } 1525 off -- Don't create device links from firmware info. 1526 permissive -- Create device links from firmware info 1527 but use it only for ordering boot state clean 1528 up (sync_state() calls). 1529 on -- Create device links from firmware info and use it 1530 to enforce probe and suspend/resume ordering. 1531 rpm -- Like "on", but also use to order runtime PM. 1532 1533 fw_devlink.strict=<bool> 1534 [KNL] Treat all inferred dependencies as mandatory 1535 dependencies. This only applies for fw_devlink=on|rpm. 1536 Format: <bool> 1537 1538 gamecon.map[2|3]= 1539 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1540 support via parallel port (up to 5 devices per port) 1541 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1542 See also Documentation/input/devices/joystick-parport.rst 1543 1544 gamma= [HW,DRM] 1545 1546 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1547 Format: off | on 1548 default: on 1549 1550 gcov_persist= [GCOV] When non-zero (default), profiling data for 1551 kernel modules is saved and remains accessible via 1552 debugfs, even when the module is unloaded/reloaded. 1553 When zero, profiling data is discarded and associated 1554 debugfs files are removed at module unload time. 1555 1556 goldfish [X86] Enable the goldfish android emulator platform. 1557 Don't use this when you are not running on the 1558 android emulator 1559 1560 gpio-mockup.gpio_mockup_ranges 1561 [HW] Sets the ranges of gpiochip of for this device. 1562 Format: <start1>,<end1>,<start2>,<end2>... 1563 gpio-mockup.gpio_mockup_named_lines 1564 [HW] Let the driver know GPIO lines should be named. 1565 1566 gpt [EFI] Forces disk with valid GPT signature but 1567 invalid Protective MBR to be treated as GPT. If the 1568 primary GPT is corrupted, it enables the backup/alternate 1569 GPT to be used instead. 1570 1571 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1572 the "Enable 0" bit of the configuration register. 1573 Format: 0 | 1 1574 Default: 0 1575 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1576 the "Enable 0" bit of the configuration register. 1577 Format: 0 | 1 1578 Default: 0 1579 grcan.select= [HW] Select which physical interface to use. 1580 Format: 0 | 1 1581 Default: 0 1582 grcan.txsize= [HW] Sets the size of the tx buffer. 1583 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1584 Default: 1024 1585 grcan.rxsize= [HW] Sets the size of the rx buffer. 1586 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1587 Default: 1024 1588 1589 hardlockup_all_cpu_backtrace= 1590 [KNL] Should the hard-lockup detector generate 1591 backtraces on all cpus. 1592 Format: 0 | 1 1593 1594 hashdist= [KNL,NUMA] Large hashes allocated during boot 1595 are distributed across NUMA nodes. Defaults on 1596 for 64-bit NUMA, off otherwise. 1597 Format: 0 | 1 (for off | on) 1598 1599 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1600 1601 hd= [EIDE] (E)IDE hard drive subsystem geometry 1602 Format: <cyl>,<head>,<sect> 1603 1604 hest_disable [ACPI] 1605 Disable Hardware Error Source Table (HEST) support; 1606 corresponding firmware-first mode error processing 1607 logic will be disabled. 1608 1609 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1610 size of <nn>. This works even on boxes that have no 1611 highmem otherwise. This also works to reduce highmem 1612 size on bigger boxes. 1613 1614 highres= [KNL] Enable/disable high resolution timer mode. 1615 Valid parameters: "on", "off" 1616 Default: "on" 1617 1618 hlt [BUGS=ARM,SH] 1619 1620 hpet= [X86-32,HPET] option to control HPET usage 1621 Format: { enable (default) | disable | force | 1622 verbose } 1623 disable: disable HPET and use PIT instead 1624 force: allow force enabled of undocumented chips (ICH4, 1625 VIA, nVidia) 1626 verbose: show contents of HPET registers during setup 1627 1628 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1629 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1630 1631 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation 1632 of gigantic hugepages. Or using node format, the size 1633 of a CMA area per node can be specified. 1634 Format: nn[KMGTPE] or (node format) 1635 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1636 1637 Reserve a CMA area of given size and allocate gigantic 1638 hugepages using the CMA allocator. If enabled, the 1639 boot-time allocation of gigantic hugepages is skipped. 1640 1641 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1642 If this follows hugepagesz (below), it specifies 1643 the number of pages of hugepagesz to be allocated. 1644 If this is the first HugeTLB parameter on the command 1645 line, it specifies the number of pages to allocate for 1646 the default huge page size. If using node format, the 1647 number of pages to allocate per-node can be specified. 1648 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1649 Format: <integer> or (node format) 1650 <node>:<integer>[,<node>:<integer>] 1651 1652 hugepagesz= 1653 [HW] The size of the HugeTLB pages. This is used in 1654 conjunction with hugepages (above) to allocate huge 1655 pages of a specific size at boot. The pair 1656 hugepagesz=X hugepages=Y can be specified once for 1657 each supported huge page size. Huge page sizes are 1658 architecture dependent. See also 1659 Documentation/admin-guide/mm/hugetlbpage.rst. 1660 Format: size[KMG] 1661 1662 hugetlb_free_vmemmap= 1663 [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP 1664 enabled. 1665 Allows heavy hugetlb users to free up some more 1666 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1667 Format: { on | off (default) } 1668 1669 on: enable the feature 1670 off: disable the feature 1671 1672 Built with CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON=y, 1673 the default is on. 1674 1675 This is not compatible with memory_hotplug.memmap_on_memory. 1676 If both parameters are enabled, hugetlb_free_vmemmap takes 1677 precedence over memory_hotplug.memmap_on_memory. 1678 1679 hung_task_panic= 1680 [KNL] Should the hung task detector generate panics. 1681 Format: 0 | 1 1682 1683 A value of 1 instructs the kernel to panic when a 1684 hung task is detected. The default value is controlled 1685 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1686 option. The value selected by this boot parameter can 1687 be changed later by the kernel.hung_task_panic sysctl. 1688 1689 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1690 terminal devices. Valid values: 0..8 1691 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1692 If specified, z/VM IUCV HVC accepts connections 1693 from listed z/VM user IDs only. 1694 1695 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1696 which allow the hypervisor to 'idle' the 1697 guest on lock contention. 1698 1699 keep_bootcon [KNL] 1700 Do not unregister boot console at start. This is only 1701 useful for debugging when something happens in the window 1702 between unregistering the boot console and initializing 1703 the real console. 1704 1705 i2c_bus= [HW] Override the default board specific I2C bus speed 1706 or register an additional I2C bus that is not 1707 registered from board initialization code. 1708 Format: 1709 <bus_id>,<clkrate> 1710 1711 i8042.debug [HW] Toggle i8042 debug mode 1712 i8042.unmask_kbd_data 1713 [HW] Enable printing of interrupt data from the KBD port 1714 (disabled by default, and as a pre-condition 1715 requires that i8042.debug=1 be enabled) 1716 i8042.direct [HW] Put keyboard port into non-translated mode 1717 i8042.dumbkbd [HW] Pretend that controller can only read data from 1718 keyboard and cannot control its state 1719 (Don't attempt to blink the leds) 1720 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1721 i8042.nokbd [HW] Don't check/create keyboard port 1722 i8042.noloop [HW] Disable the AUX Loopback command while probing 1723 for the AUX port 1724 i8042.nomux [HW] Don't check presence of an active multiplexing 1725 controller 1726 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1727 controllers 1728 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1729 i8042.reset [HW] Reset the controller during init, cleanup and 1730 suspend-to-ram transitions, only during s2r 1731 transitions, or never reset 1732 Format: { 1 | Y | y | 0 | N | n } 1733 1, Y, y: always reset controller 1734 0, N, n: don't ever reset controller 1735 Default: only on s2r transitions on x86; most other 1736 architectures force reset to be always executed 1737 i8042.unlock [HW] Unlock (ignore) the keylock 1738 i8042.kbdreset [HW] Reset device connected to KBD port 1739 i8042.probe_defer 1740 [HW] Allow deferred probing upon i8042 probe errors 1741 1742 i810= [HW,DRM] 1743 1744 i915.invert_brightness= 1745 [DRM] Invert the sense of the variable that is used to 1746 set the brightness of the panel backlight. Normally a 1747 brightness value of 0 indicates backlight switched off, 1748 and the maximum of the brightness value sets the backlight 1749 to maximum brightness. If this parameter is set to 0 1750 (default) and the machine requires it, or this parameter 1751 is set to 1, a brightness value of 0 sets the backlight 1752 to maximum brightness, and the maximum of the brightness 1753 value switches the backlight off. 1754 -1 -- never invert brightness 1755 0 -- machine default 1756 1 -- force brightness inversion 1757 1758 icn= [HW,ISDN] 1759 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1760 1761 ide-core.nodma= [HW] (E)IDE subsystem 1762 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1763 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1764 .cdrom .chs .ignore_cable are additional options 1765 See Documentation/ide/ide.rst. 1766 1767 ide-generic.probe-mask= [HW] (E)IDE subsystem 1768 Format: <int> 1769 Probe mask for legacy ISA IDE ports. Depending on 1770 platform up to 6 ports are supported, enabled by 1771 setting corresponding bits in the mask to 1. The 1772 default value is 0x0, which has a special meaning. 1773 On systems that have PCI, it triggers scanning the 1774 PCI bus for the first and the second port, which 1775 are then probed. On systems without PCI the value 1776 of 0x0 enables probing the two first ports as if it 1777 was 0x3. 1778 1779 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1780 Claim all unknown PCI IDE storage controllers. 1781 1782 idle= [X86] 1783 Format: idle=poll, idle=halt, idle=nomwait 1784 Poll forces a polling idle loop that can slightly 1785 improve the performance of waking up a idle CPU, but 1786 will use a lot of power and make the system run hot. 1787 Not recommended. 1788 idle=halt: Halt is forced to be used for CPU idle. 1789 In such case C2/C3 won't be used again. 1790 idle=nomwait: Disable mwait for CPU C-states 1791 1792 idxd.sva= [HW] 1793 Format: <bool> 1794 Allow force disabling of Shared Virtual Memory (SVA) 1795 support for the idxd driver. By default it is set to 1796 true (1). 1797 1798 idxd.tc_override= [HW] 1799 Format: <bool> 1800 Allow override of default traffic class configuration 1801 for the device. By default it is set to false (0). 1802 1803 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1804 Format: { strict | legacy | 2008 | relaxed } 1805 Default: strict 1806 1807 Choose which programs will be accepted for execution 1808 based on the IEEE 754 NaN encoding(s) supported by 1809 the FPU and the NaN encoding requested with the value 1810 of an ELF file header flag individually set by each 1811 binary. Hardware implementations are permitted to 1812 support either or both of the legacy and the 2008 NaN 1813 encoding mode. 1814 1815 Available settings are as follows: 1816 strict accept binaries that request a NaN encoding 1817 supported by the FPU 1818 legacy only accept legacy-NaN binaries, if supported 1819 by the FPU 1820 2008 only accept 2008-NaN binaries, if supported 1821 by the FPU 1822 relaxed accept any binaries regardless of whether 1823 supported by the FPU 1824 1825 The FPU emulator is always able to support both NaN 1826 encodings, so if no FPU hardware is present or it has 1827 been disabled with 'nofpu', then the settings of 1828 'legacy' and '2008' strap the emulator accordingly, 1829 'relaxed' straps the emulator for both legacy-NaN and 1830 2008-NaN, whereas 'strict' enables legacy-NaN only on 1831 legacy processors and both NaN encodings on MIPS32 or 1832 MIPS64 CPUs. 1833 1834 The setting for ABS.fmt/NEG.fmt instruction execution 1835 mode generally follows that for the NaN encoding, 1836 except where unsupported by hardware. 1837 1838 ignore_loglevel [KNL] 1839 Ignore loglevel setting - this will print /all/ 1840 kernel messages to the console. Useful for debugging. 1841 We also add it as printk module parameter, so users 1842 could change it dynamically, usually by 1843 /sys/module/printk/parameters/ignore_loglevel. 1844 1845 ignore_rlimit_data 1846 Ignore RLIMIT_DATA setting for data mappings, 1847 print warning at first misuse. Can be changed via 1848 /sys/module/kernel/parameters/ignore_rlimit_data. 1849 1850 ihash_entries= [KNL] 1851 Set number of hash buckets for inode cache. 1852 1853 ima_appraise= [IMA] appraise integrity measurements 1854 Format: { "off" | "enforce" | "fix" | "log" } 1855 default: "enforce" 1856 1857 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1858 The builtin appraise policy appraises all files 1859 owned by uid=0. 1860 1861 ima_canonical_fmt [IMA] 1862 Use the canonical format for the binary runtime 1863 measurements, instead of host native format. 1864 1865 ima_hash= [IMA] 1866 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1867 | sha512 | ... } 1868 default: "sha1" 1869 1870 The list of supported hash algorithms is defined 1871 in crypto/hash_info.h. 1872 1873 ima_policy= [IMA] 1874 The builtin policies to load during IMA setup. 1875 Format: "tcb | appraise_tcb | secure_boot | 1876 fail_securely | critical_data" 1877 1878 The "tcb" policy measures all programs exec'd, files 1879 mmap'd for exec, and all files opened with the read 1880 mode bit set by either the effective uid (euid=0) or 1881 uid=0. 1882 1883 The "appraise_tcb" policy appraises the integrity of 1884 all files owned by root. 1885 1886 The "secure_boot" policy appraises the integrity 1887 of files (eg. kexec kernel image, kernel modules, 1888 firmware, policy, etc) based on file signatures. 1889 1890 The "fail_securely" policy forces file signature 1891 verification failure also on privileged mounted 1892 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1893 flag. 1894 1895 The "critical_data" policy measures kernel integrity 1896 critical data. 1897 1898 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1899 Load a policy which meets the needs of the Trusted 1900 Computing Base. This means IMA will measure all 1901 programs exec'd, files mmap'd for exec, and all files 1902 opened for read by uid=0. 1903 1904 ima_template= [IMA] 1905 Select one of defined IMA measurements template formats. 1906 Formats: { "ima" | "ima-ng" | "ima-sig" } 1907 Default: "ima-ng" 1908 1909 ima_template_fmt= 1910 [IMA] Define a custom template format. 1911 Format: { "field1|...|fieldN" } 1912 1913 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1914 Format: <min_file_size> 1915 Set the minimal file size for using asynchronous hash. 1916 If left unspecified, ahash usage is disabled. 1917 1918 ahash performance varies for different data sizes on 1919 different crypto accelerators. This option can be used 1920 to achieve the best performance for a particular HW. 1921 1922 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1923 Format: <bufsize> 1924 Set hashing buffer size. Default: 4k. 1925 1926 ahash performance varies for different chunk sizes on 1927 different crypto accelerators. This option can be used 1928 to achieve best performance for particular HW. 1929 1930 init= [KNL] 1931 Format: <full_path> 1932 Run specified binary instead of /sbin/init as init 1933 process. 1934 1935 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1936 for working out where the kernel is dying during 1937 startup. 1938 1939 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1940 initcall functions. Useful for debugging built-in 1941 modules and initcalls. 1942 1943 initramfs_async= [KNL] 1944 Format: <bool> 1945 Default: 1 1946 This parameter controls whether the initramfs 1947 image is unpacked asynchronously, concurrently 1948 with devices being probed and 1949 initialized. This should normally just work, 1950 but as a debugging aid, one can get the 1951 historical behaviour of the initramfs 1952 unpacking being completed before device_ and 1953 late_ initcalls. 1954 1955 initrd= [BOOT] Specify the location of the initial ramdisk 1956 1957 initrdmem= [KNL] Specify a physical address and size from which to 1958 load the initrd. If an initrd is compiled in or 1959 specified in the bootparams, it takes priority over this 1960 setting. 1961 Format: ss[KMG],nn[KMG] 1962 Default is 0, 0 1963 1964 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1965 zeroes. 1966 Format: 0 | 1 1967 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1968 1969 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1970 Format: 0 | 1 1971 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1972 1973 init_pkru= [X86] Specify the default memory protection keys rights 1974 register contents for all processes. 0x55555554 by 1975 default (disallow access to all but pkey 0). Can 1976 override in debugfs after boot. 1977 1978 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1979 Format: <irq> 1980 1981 int_pln_enable [X86] Enable power limit notification interrupt 1982 1983 integrity_audit=[IMA] 1984 Format: { "0" | "1" } 1985 0 -- basic integrity auditing messages. (Default) 1986 1 -- additional integrity auditing messages. 1987 1988 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1989 on 1990 Enable intel iommu driver. 1991 off 1992 Disable intel iommu driver. 1993 igfx_off [Default Off] 1994 By default, gfx is mapped as normal device. If a gfx 1995 device has a dedicated DMAR unit, the DMAR unit is 1996 bypassed by not enabling DMAR with this option. In 1997 this case, gfx device will use physical address for 1998 DMA. 1999 strict [Default Off] 2000 Deprecated, equivalent to iommu.strict=1. 2001 sp_off [Default Off] 2002 By default, super page will be supported if Intel IOMMU 2003 has the capability. With this option, super page will 2004 not be supported. 2005 sm_on 2006 Enable the Intel IOMMU scalable mode if the hardware 2007 advertises that it has support for the scalable mode 2008 translation. 2009 sm_off 2010 Disallow use of the Intel IOMMU scalable mode. 2011 tboot_noforce [Default Off] 2012 Do not force the Intel IOMMU enabled under tboot. 2013 By default, tboot will force Intel IOMMU on, which 2014 could harm performance of some high-throughput 2015 devices like 40GBit network cards, even if identity 2016 mapping is enabled. 2017 Note that using this option lowers the security 2018 provided by tboot because it makes the system 2019 vulnerable to DMA attacks. 2020 2021 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2022 0 disables intel_idle and fall back on acpi_idle. 2023 1 to 9 specify maximum depth of C-state. 2024 2025 intel_pstate= [X86] 2026 disable 2027 Do not enable intel_pstate as the default 2028 scaling driver for the supported processors 2029 passive 2030 Use intel_pstate as a scaling driver, but configure it 2031 to work with generic cpufreq governors (instead of 2032 enabling its internal governor). This mode cannot be 2033 used along with the hardware-managed P-states (HWP) 2034 feature. 2035 force 2036 Enable intel_pstate on systems that prohibit it by default 2037 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2038 instead of acpi-cpufreq may disable platform features, such 2039 as thermal controls and power capping, that rely on ACPI 2040 P-States information being indicated to OSPM and therefore 2041 should be used with caution. This option does not work with 2042 processors that aren't supported by the intel_pstate driver 2043 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2044 no_hwp 2045 Do not enable hardware P state control (HWP) 2046 if available. 2047 hwp_only 2048 Only load intel_pstate on systems which support 2049 hardware P state control (HWP) if available. 2050 support_acpi_ppc 2051 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2052 Description Table, specifies preferred power management 2053 profile as "Enterprise Server" or "Performance Server", 2054 then this feature is turned on by default. 2055 per_cpu_perf_limits 2056 Allow per-logical-CPU P-State performance control limits using 2057 cpufreq sysfs interface 2058 2059 intremap= [X86-64, Intel-IOMMU] 2060 on enable Interrupt Remapping (default) 2061 off disable Interrupt Remapping 2062 nosid disable Source ID checking 2063 no_x2apic_optout 2064 BIOS x2APIC opt-out request will be ignored 2065 nopost disable Interrupt Posting 2066 2067 iomem= Disable strict checking of access to MMIO memory 2068 strict regions from userspace. 2069 relaxed 2070 2071 iommu= [X86] 2072 off 2073 force 2074 noforce 2075 biomerge 2076 panic 2077 nopanic 2078 merge 2079 nomerge 2080 soft 2081 pt [X86] 2082 nopt [X86] 2083 nobypass [PPC/POWERNV] 2084 Disable IOMMU bypass, using IOMMU for PCI devices. 2085 2086 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. 2087 Format: { "0" | "1" } 2088 0 - Try to allocate a 32-bit DMA address first, before 2089 falling back to the full range if needed. 2090 1 - Allocate directly from the full usable range, 2091 forcing Dual Address Cycle for PCI cards supporting 2092 greater than 32-bit addressing. 2093 2094 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour 2095 Format: { "0" | "1" } 2096 0 - Lazy mode. 2097 Request that DMA unmap operations use deferred 2098 invalidation of hardware TLBs, for increased 2099 throughput at the cost of reduced device isolation. 2100 Will fall back to strict mode if not supported by 2101 the relevant IOMMU driver. 2102 1 - Strict mode. 2103 DMA unmap operations invalidate IOMMU hardware TLBs 2104 synchronously. 2105 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2106 Note: on x86, strict mode specified via one of the 2107 legacy driver-specific options takes precedence. 2108 2109 iommu.passthrough= 2110 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 2111 Format: { "0" | "1" } 2112 0 - Use IOMMU translation for DMA. 2113 1 - Bypass the IOMMU for DMA. 2114 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2115 2116 io7= [HW] IO7 for Marvel-based Alpha systems 2117 See comment before marvel_specify_io7 in 2118 arch/alpha/kernel/core_marvel.c. 2119 2120 io_delay= [X86] I/O delay method 2121 0x80 2122 Standard port 0x80 based delay 2123 0xed 2124 Alternate port 0xed based delay (needed on some systems) 2125 udelay 2126 Simple two microseconds delay 2127 none 2128 No delay 2129 2130 ip= [IP_PNP] 2131 See Documentation/admin-guide/nfs/nfsroot.rst. 2132 2133 ipcmni_extend [KNL] Extend the maximum number of unique System V 2134 IPC identifiers from 32,768 to 16,777,216. 2135 2136 irqaffinity= [SMP] Set the default irq affinity mask 2137 The argument is a cpu list, as described above. 2138 2139 irqchip.gicv2_force_probe= 2140 [ARM, ARM64] 2141 Format: <bool> 2142 Force the kernel to look for the second 4kB page 2143 of a GICv2 controller even if the memory range 2144 exposed by the device tree is too small. 2145 2146 irqchip.gicv3_nolpi= 2147 [ARM, ARM64] 2148 Force the kernel to ignore the availability of 2149 LPIs (and by consequence ITSs). Intended for system 2150 that use the kernel as a bootloader, and thus want 2151 to let secondary kernels in charge of setting up 2152 LPIs. 2153 2154 irqchip.gicv3_pseudo_nmi= [ARM64] 2155 Enables support for pseudo-NMIs in the kernel. This 2156 requires the kernel to be built with 2157 CONFIG_ARM64_PSEUDO_NMI. 2158 2159 irqfixup [HW] 2160 When an interrupt is not handled search all handlers 2161 for it. Intended to get systems with badly broken 2162 firmware running. 2163 2164 irqpoll [HW] 2165 When an interrupt is not handled search all handlers 2166 for it. Also check all handlers each timer 2167 interrupt. Intended to get systems with badly broken 2168 firmware running. 2169 2170 isapnp= [ISAPNP] 2171 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2172 2173 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2174 [Deprecated - use cpusets instead] 2175 Format: [flag-list,]<cpu-list> 2176 2177 Specify one or more CPUs to isolate from disturbances 2178 specified in the flag list (default: domain): 2179 2180 nohz 2181 Disable the tick when a single task runs. 2182 2183 A residual 1Hz tick is offloaded to workqueues, which you 2184 need to affine to housekeeping through the global 2185 workqueue's affinity configured via the 2186 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2187 by using the 'domain' flag described below. 2188 2189 NOTE: by default the global workqueue runs on all CPUs, 2190 so to protect individual CPUs the 'cpumask' file has to 2191 be configured manually after bootup. 2192 2193 domain 2194 Isolate from the general SMP balancing and scheduling 2195 algorithms. Note that performing domain isolation this way 2196 is irreversible: it's not possible to bring back a CPU to 2197 the domains once isolated through isolcpus. It's strongly 2198 advised to use cpusets instead to disable scheduler load 2199 balancing through the "cpuset.sched_load_balance" file. 2200 It offers a much more flexible interface where CPUs can 2201 move in and out of an isolated set anytime. 2202 2203 You can move a process onto or off an "isolated" CPU via 2204 the CPU affinity syscalls or cpuset. 2205 <cpu number> begins at 0 and the maximum value is 2206 "number of CPUs in system - 1". 2207 2208 managed_irq 2209 2210 Isolate from being targeted by managed interrupts 2211 which have an interrupt mask containing isolated 2212 CPUs. The affinity of managed interrupts is 2213 handled by the kernel and cannot be changed via 2214 the /proc/irq/* interfaces. 2215 2216 This isolation is best effort and only effective 2217 if the automatically assigned interrupt mask of a 2218 device queue contains isolated and housekeeping 2219 CPUs. If housekeeping CPUs are online then such 2220 interrupts are directed to the housekeeping CPU 2221 so that IO submitted on the housekeeping CPU 2222 cannot disturb the isolated CPU. 2223 2224 If a queue's affinity mask contains only isolated 2225 CPUs then this parameter has no effect on the 2226 interrupt routing decision, though interrupts are 2227 only delivered when tasks running on those 2228 isolated CPUs submit IO. IO submitted on 2229 housekeeping CPUs has no influence on those 2230 queues. 2231 2232 The format of <cpu-list> is described above. 2233 2234 iucv= [HW,NET] 2235 2236 ivrs_ioapic [HW,X86-64] 2237 Provide an override to the IOAPIC-ID<->DEVICE-ID 2238 mapping provided in the IVRS ACPI table. For 2239 example, to map IOAPIC-ID decimal 10 to 2240 PCI device 00:14.0 write the parameter as: 2241 ivrs_ioapic[10]=00:14.0 2242 2243 ivrs_hpet [HW,X86-64] 2244 Provide an override to the HPET-ID<->DEVICE-ID 2245 mapping provided in the IVRS ACPI table. For 2246 example, to map HPET-ID decimal 0 to 2247 PCI device 00:14.0 write the parameter as: 2248 ivrs_hpet[0]=00:14.0 2249 2250 ivrs_acpihid [HW,X86-64] 2251 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2252 mapping provided in the IVRS ACPI table. For 2253 example, to map UART-HID:UID AMD0020:0 to 2254 PCI device 00:14.5 write the parameter as: 2255 ivrs_acpihid[00:14.5]=AMD0020:0 2256 2257 js= [HW,JOY] Analog joystick 2258 See Documentation/input/joydev/joystick.rst. 2259 2260 nokaslr [KNL] 2261 When CONFIG_RANDOMIZE_BASE is set, this disables 2262 kernel and module base offset ASLR (Address Space 2263 Layout Randomization). 2264 2265 kasan_multi_shot 2266 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2267 report on every invalid memory access. Without this 2268 parameter KASAN will print report only for the first 2269 invalid access. 2270 2271 keepinitrd [HW,ARM] 2272 2273 kernelcore= [KNL,X86,IA-64,PPC] 2274 Format: nn[KMGTPE] | nn% | "mirror" 2275 This parameter specifies the amount of memory usable by 2276 the kernel for non-movable allocations. The requested 2277 amount is spread evenly throughout all nodes in the 2278 system as ZONE_NORMAL. The remaining memory is used for 2279 movable memory in its own zone, ZONE_MOVABLE. In the 2280 event, a node is too small to have both ZONE_NORMAL and 2281 ZONE_MOVABLE, kernelcore memory will take priority and 2282 other nodes will have a larger ZONE_MOVABLE. 2283 2284 ZONE_MOVABLE is used for the allocation of pages that 2285 may be reclaimed or moved by the page migration 2286 subsystem. Note that allocations like PTEs-from-HighMem 2287 still use the HighMem zone if it exists, and the Normal 2288 zone if it does not. 2289 2290 It is possible to specify the exact amount of memory in 2291 the form of "nn[KMGTPE]", a percentage of total system 2292 memory in the form of "nn%", or "mirror". If "mirror" 2293 option is specified, mirrored (reliable) memory is used 2294 for non-movable allocations and remaining memory is used 2295 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2296 are exclusive, so you cannot specify multiple forms. 2297 2298 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2299 Format: <Controller#>[,poll interval] 2300 The controller # is the number of the ehci usb debug 2301 port as it is probed via PCI. The poll interval is 2302 optional and is the number seconds in between 2303 each poll cycle to the debug port in case you need 2304 the functionality for interrupting the kernel with 2305 gdb or control-c on the dbgp connection. When 2306 not using this parameter you use sysrq-g to break into 2307 the kernel debugger. 2308 2309 kgdboc= [KGDB,HW] kgdb over consoles. 2310 Requires a tty driver that supports console polling, 2311 or a supported polling keyboard driver (non-usb). 2312 Serial only format: <serial_device>[,baud] 2313 keyboard only format: kbd 2314 keyboard and serial format: kbd,<serial_device>[,baud] 2315 Optional Kernel mode setting: 2316 kms, kbd format: kms,kbd 2317 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2318 2319 kgdboc_earlycon= [KGDB,HW] 2320 If the boot console provides the ability to read 2321 characters and can work in polling mode, you can use 2322 this parameter to tell kgdb to use it as a backend 2323 until the normal console is registered. Intended to 2324 be used together with the kgdboc parameter which 2325 specifies the normal console to transition to. 2326 2327 The name of the early console should be specified 2328 as the value of this parameter. Note that the name of 2329 the early console might be different than the tty 2330 name passed to kgdboc. It's OK to leave the value 2331 blank and the first boot console that implements 2332 read() will be picked. 2333 2334 kgdbwait [KGDB] Stop kernel execution and enter the 2335 kernel debugger at the earliest opportunity. 2336 2337 kmac= [MIPS] Korina ethernet MAC address. 2338 Configure the RouterBoard 532 series on-chip 2339 Ethernet adapter MAC address. 2340 2341 kmemleak= [KNL] Boot-time kmemleak enable/disable 2342 Valid arguments: on, off 2343 Default: on 2344 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2345 the default is off. 2346 2347 kprobe_event=[probe-list] 2348 [FTRACE] Add kprobe events and enable at boot time. 2349 The probe-list is a semicolon delimited list of probe 2350 definitions. Each definition is same as kprobe_events 2351 interface, but the parameters are comma delimited. 2352 For example, to add a kprobe event on vfs_read with 2353 arg1 and arg2, add to the command line; 2354 2355 kprobe_event=p,vfs_read,$arg1,$arg2 2356 2357 See also Documentation/trace/kprobetrace.rst "Kernel 2358 Boot Parameter" section. 2359 2360 kpti= [ARM64] Control page table isolation of user 2361 and kernel address spaces. 2362 Default: enabled on cores which need mitigation. 2363 0: force disabled 2364 1: force enabled 2365 2366 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2367 Default is 0 (don't ignore, but inject #GP) 2368 2369 kvm.eager_page_split= 2370 [KVM,X86] Controls whether or not KVM will try to 2371 proactively split all huge pages during dirty logging. 2372 Eager page splitting reduces interruptions to vCPU 2373 execution by eliminating the write-protection faults 2374 and MMU lock contention that would otherwise be 2375 required to split huge pages lazily. 2376 2377 VM workloads that rarely perform writes or that write 2378 only to a small region of VM memory may benefit from 2379 disabling eager page splitting to allow huge pages to 2380 still be used for reads. 2381 2382 The behavior of eager page splitting depends on whether 2383 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2384 disabled, all huge pages in a memslot will be eagerly 2385 split when dirty logging is enabled on that memslot. If 2386 enabled, eager page splitting will be performed during 2387 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2388 cleared. 2389 2390 Eager page splitting currently only supports splitting 2391 huge pages mapped by the TDP MMU. 2392 2393 Default is Y (on). 2394 2395 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2396 Default is false (don't support). 2397 2398 kvm.nx_huge_pages= 2399 [KVM] Controls the software workaround for the 2400 X86_BUG_ITLB_MULTIHIT bug. 2401 force : Always deploy workaround. 2402 off : Never deploy workaround. 2403 auto : Deploy workaround based on the presence of 2404 X86_BUG_ITLB_MULTIHIT. 2405 2406 Default is 'auto'. 2407 2408 If the software workaround is enabled for the host, 2409 guests do need not to enable it for nested guests. 2410 2411 kvm.nx_huge_pages_recovery_ratio= 2412 [KVM] Controls how many 4KiB pages are periodically zapped 2413 back to huge pages. 0 disables the recovery, otherwise if 2414 the value is N KVM will zap 1/Nth of the 4KiB pages every 2415 period (see below). The default is 60. 2416 2417 kvm.nx_huge_pages_recovery_period_ms= 2418 [KVM] Controls the time period at which KVM zaps 4KiB pages 2419 back to huge pages. If the value is a non-zero N, KVM will 2420 zap a portion (see ratio above) of the pages every N msecs. 2421 If the value is 0 (the default), KVM will pick a period based 2422 on the ratio, such that a page is zapped after 1 hour on average. 2423 2424 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2425 Default is 1 (enabled) 2426 2427 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2428 for all guests. 2429 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2430 2431 kvm-arm.mode= 2432 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2433 2434 none: Forcefully disable KVM. 2435 2436 nvhe: Standard nVHE-based mode, without support for 2437 protected guests. 2438 2439 protected: nVHE-based mode with support for guests whose 2440 state is kept private from the host. 2441 Not valid if the kernel is running in EL2. 2442 2443 Defaults to VHE/nVHE based on hardware support. Setting 2444 mode to "protected" will disable kexec and hibernation 2445 for the host. 2446 2447 kvm-arm.vgic_v3_group0_trap= 2448 [KVM,ARM] Trap guest accesses to GICv3 group-0 2449 system registers 2450 2451 kvm-arm.vgic_v3_group1_trap= 2452 [KVM,ARM] Trap guest accesses to GICv3 group-1 2453 system registers 2454 2455 kvm-arm.vgic_v3_common_trap= 2456 [KVM,ARM] Trap guest accesses to GICv3 common 2457 system registers 2458 2459 kvm-arm.vgic_v4_enable= 2460 [KVM,ARM] Allow use of GICv4 for direct injection of 2461 LPIs. 2462 2463 kvm_cma_resv_ratio=n [PPC] 2464 Reserves given percentage from system memory area for 2465 contiguous memory allocation for KVM hash pagetable 2466 allocation. 2467 By default it reserves 5% of total system memory. 2468 Format: <integer> 2469 Default: 5 2470 2471 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2472 (virtualized MMU) support on capable Intel chips. 2473 Default is 1 (enabled) 2474 2475 kvm-intel.emulate_invalid_guest_state= 2476 [KVM,Intel] Disable emulation of invalid guest state. 2477 Ignored if kvm-intel.enable_unrestricted_guest=1, as 2478 guest state is never invalid for unrestricted guests. 2479 This param doesn't apply to nested guests (L2), as KVM 2480 never emulates invalid L2 guest state. 2481 Default is 1 (enabled) 2482 2483 kvm-intel.flexpriority= 2484 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2485 Default is 1 (enabled) 2486 2487 kvm-intel.nested= 2488 [KVM,Intel] Enable VMX nesting (nVMX). 2489 Default is 0 (disabled) 2490 2491 kvm-intel.unrestricted_guest= 2492 [KVM,Intel] Disable unrestricted guest feature 2493 (virtualized real and unpaged mode) on capable 2494 Intel chips. Default is 1 (enabled) 2495 2496 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2497 CVE-2018-3620. 2498 2499 Valid arguments: never, cond, always 2500 2501 always: L1D cache flush on every VMENTER. 2502 cond: Flush L1D on VMENTER only when the code between 2503 VMEXIT and VMENTER can leak host memory. 2504 never: Disables the mitigation 2505 2506 Default is cond (do L1 cache flush in specific instances) 2507 2508 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2509 feature (tagged TLBs) on capable Intel chips. 2510 Default is 1 (enabled) 2511 2512 l1d_flush= [X86,INTEL] 2513 Control mitigation for L1D based snooping vulnerability. 2514 2515 Certain CPUs are vulnerable to an exploit against CPU 2516 internal buffers which can forward information to a 2517 disclosure gadget under certain conditions. 2518 2519 In vulnerable processors, the speculatively 2520 forwarded data can be used in a cache side channel 2521 attack, to access data to which the attacker does 2522 not have direct access. 2523 2524 This parameter controls the mitigation. The 2525 options are: 2526 2527 on - enable the interface for the mitigation 2528 2529 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2530 affected CPUs 2531 2532 The kernel PTE inversion protection is unconditionally 2533 enabled and cannot be disabled. 2534 2535 full 2536 Provides all available mitigations for the 2537 L1TF vulnerability. Disables SMT and 2538 enables all mitigations in the 2539 hypervisors, i.e. unconditional L1D flush. 2540 2541 SMT control and L1D flush control via the 2542 sysfs interface is still possible after 2543 boot. Hypervisors will issue a warning 2544 when the first VM is started in a 2545 potentially insecure configuration, 2546 i.e. SMT enabled or L1D flush disabled. 2547 2548 full,force 2549 Same as 'full', but disables SMT and L1D 2550 flush runtime control. Implies the 2551 'nosmt=force' command line option. 2552 (i.e. sysfs control of SMT is disabled.) 2553 2554 flush 2555 Leaves SMT enabled and enables the default 2556 hypervisor mitigation, i.e. conditional 2557 L1D flush. 2558 2559 SMT control and L1D flush control via the 2560 sysfs interface is still possible after 2561 boot. Hypervisors will issue a warning 2562 when the first VM is started in a 2563 potentially insecure configuration, 2564 i.e. SMT enabled or L1D flush disabled. 2565 2566 flush,nosmt 2567 2568 Disables SMT and enables the default 2569 hypervisor mitigation. 2570 2571 SMT control and L1D flush control via the 2572 sysfs interface is still possible after 2573 boot. Hypervisors will issue a warning 2574 when the first VM is started in a 2575 potentially insecure configuration, 2576 i.e. SMT enabled or L1D flush disabled. 2577 2578 flush,nowarn 2579 Same as 'flush', but hypervisors will not 2580 warn when a VM is started in a potentially 2581 insecure configuration. 2582 2583 off 2584 Disables hypervisor mitigations and doesn't 2585 emit any warnings. 2586 It also drops the swap size and available 2587 RAM limit restriction on both hypervisor and 2588 bare metal. 2589 2590 Default is 'flush'. 2591 2592 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2593 2594 l2cr= [PPC] 2595 2596 l3cr= [PPC] 2597 2598 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2599 disabled it. 2600 2601 lapic= [X86,APIC] Do not use TSC deadline 2602 value for LAPIC timer one-shot implementation. Default 2603 back to the programmable timer unit in the LAPIC. 2604 Format: notscdeadline 2605 2606 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2607 in C2 power state. 2608 2609 libata.dma= [LIBATA] DMA control 2610 libata.dma=0 Disable all PATA and SATA DMA 2611 libata.dma=1 PATA and SATA Disk DMA only 2612 libata.dma=2 ATAPI (CDROM) DMA only 2613 libata.dma=4 Compact Flash DMA only 2614 Combinations also work, so libata.dma=3 enables DMA 2615 for disks and CDROMs, but not CFs. 2616 2617 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2618 libata.ignore_hpa=0 keep BIOS limits (default) 2619 libata.ignore_hpa=1 ignore limits, using full disk 2620 2621 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2622 when set. 2623 Format: <int> 2624 2625 libata.force= [LIBATA] Force configurations. The format is comma- 2626 separated list of "[ID:]VAL" where ID is 2627 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2628 matching port, link or device. Basically, it matches 2629 the ATA ID string printed on console by libata. If 2630 the whole ID part is omitted, the last PORT and DEVICE 2631 values are used. If ID hasn't been specified yet, the 2632 configuration applies to all ports, links and devices. 2633 2634 If only DEVICE is omitted, the parameter applies to 2635 the port and all links and devices behind it. DEVICE 2636 number of 0 either selects the first device or the 2637 first fan-out link behind PMP device. It does not 2638 select the host link. DEVICE number of 15 selects the 2639 host link and device attached to it. 2640 2641 The VAL specifies the configuration to force. As long 2642 as there's no ambiguity shortcut notation is allowed. 2643 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2644 The following configurations can be forced. 2645 2646 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2647 Any ID with matching PORT is used. 2648 2649 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2650 2651 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2652 udma[/][16,25,33,44,66,100,133] notation is also 2653 allowed. 2654 2655 * [no]ncq: Turn on or off NCQ. 2656 2657 * [no]ncqtrim: Turn off queued DSM TRIM. 2658 2659 * nohrst, nosrst, norst: suppress hard, soft 2660 and both resets. 2661 2662 * rstonce: only attempt one reset during 2663 hot-unplug link recovery 2664 2665 * dump_id: dump IDENTIFY data. 2666 2667 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2668 2669 * disable: Disable this device. 2670 2671 If there are multiple matching configurations changing 2672 the same attribute, the last one is used. 2673 2674 memblock=debug [KNL] Enable memblock debug messages. 2675 2676 load_ramdisk= [RAM] [Deprecated] 2677 2678 lockd.nlm_grace_period=P [NFS] Assign grace period. 2679 Format: <integer> 2680 2681 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2682 Format: <integer> 2683 2684 lockd.nlm_timeout=T [NFS] Assign timeout value. 2685 Format: <integer> 2686 2687 lockd.nlm_udpport=M [NFS] Assign UDP port. 2688 Format: <integer> 2689 2690 lockdown= [SECURITY] 2691 { integrity | confidentiality } 2692 Enable the kernel lockdown feature. If set to 2693 integrity, kernel features that allow userland to 2694 modify the running kernel are disabled. If set to 2695 confidentiality, kernel features that allow userland 2696 to extract confidential information from the kernel 2697 are also disabled. 2698 2699 locktorture.nreaders_stress= [KNL] 2700 Set the number of locking read-acquisition kthreads. 2701 Defaults to being automatically set based on the 2702 number of online CPUs. 2703 2704 locktorture.nwriters_stress= [KNL] 2705 Set the number of locking write-acquisition kthreads. 2706 2707 locktorture.onoff_holdoff= [KNL] 2708 Set time (s) after boot for CPU-hotplug testing. 2709 2710 locktorture.onoff_interval= [KNL] 2711 Set time (s) between CPU-hotplug operations, or 2712 zero to disable CPU-hotplug testing. 2713 2714 locktorture.shuffle_interval= [KNL] 2715 Set task-shuffle interval (jiffies). Shuffling 2716 tasks allows some CPUs to go into dyntick-idle 2717 mode during the locktorture test. 2718 2719 locktorture.shutdown_secs= [KNL] 2720 Set time (s) after boot system shutdown. This 2721 is useful for hands-off automated testing. 2722 2723 locktorture.stat_interval= [KNL] 2724 Time (s) between statistics printk()s. 2725 2726 locktorture.stutter= [KNL] 2727 Time (s) to stutter testing, for example, 2728 specifying five seconds causes the test to run for 2729 five seconds, wait for five seconds, and so on. 2730 This tests the locking primitive's ability to 2731 transition abruptly to and from idle. 2732 2733 locktorture.torture_type= [KNL] 2734 Specify the locking implementation to test. 2735 2736 locktorture.verbose= [KNL] 2737 Enable additional printk() statements. 2738 2739 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2740 Format: <irq> 2741 2742 loglevel= All Kernel Messages with a loglevel smaller than the 2743 console loglevel will be printed to the console. It can 2744 also be changed with klogd or other programs. The 2745 loglevels are defined as follows: 2746 2747 0 (KERN_EMERG) system is unusable 2748 1 (KERN_ALERT) action must be taken immediately 2749 2 (KERN_CRIT) critical conditions 2750 3 (KERN_ERR) error conditions 2751 4 (KERN_WARNING) warning conditions 2752 5 (KERN_NOTICE) normal but significant condition 2753 6 (KERN_INFO) informational 2754 7 (KERN_DEBUG) debug-level messages 2755 2756 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2757 in bytes. n must be a power of two and greater 2758 than the minimal size. The minimal size is defined 2759 by LOG_BUF_SHIFT kernel config parameter. There is 2760 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2761 that allows to increase the default size depending on 2762 the number of CPUs. See init/Kconfig for more details. 2763 2764 logo.nologo [FB] Disables display of the built-in Linux logo. 2765 This may be used to provide more screen space for 2766 kernel log messages and is useful when debugging 2767 kernel boot problems. 2768 2769 lp=0 [LP] Specify parallel ports to use, e.g, 2770 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2771 lp=reset first parallel port). 'lp=0' disables the 2772 lp=auto printer driver. 'lp=reset' (which can be 2773 specified in addition to the ports) causes 2774 attached printers to be reset. Using 2775 lp=port1,port2,... specifies the parallel ports 2776 to associate lp devices with, starting with 2777 lp0. A port specification may be 'none' to skip 2778 that lp device, or a parport name such as 2779 'parport0'. Specifying 'lp=auto' instead of a 2780 port specification list means that device IDs 2781 from each port should be examined, to see if 2782 an IEEE 1284-compliant printer is attached; if 2783 so, the driver will manage that printer. 2784 See also header of drivers/char/lp.c. 2785 2786 lpj=n [KNL] 2787 Sets loops_per_jiffy to given constant, thus avoiding 2788 time-consuming boot-time autodetection (up to 250 ms per 2789 CPU). 0 enables autodetection (default). To determine 2790 the correct value for your kernel, boot with normal 2791 autodetection and see what value is printed. Note that 2792 on SMP systems the preset will be applied to all CPUs, 2793 which is likely to cause problems if your CPUs need 2794 significantly divergent settings. An incorrect value 2795 will cause delays in the kernel to be wrong, leading to 2796 unpredictable I/O errors and other breakage. Although 2797 unlikely, in the extreme case this might damage your 2798 hardware. 2799 2800 ltpc= [NET] 2801 Format: <io>,<irq>,<dma> 2802 2803 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2804 2805 lsm=lsm1,...,lsmN 2806 [SECURITY] Choose order of LSM initialization. This 2807 overrides CONFIG_LSM, and the "security=" parameter. 2808 2809 machvec= [IA-64] Force the use of a particular machine-vector 2810 (machvec) in a generic kernel. 2811 Example: machvec=hpzx1 2812 2813 machtype= [Loongson] Share the same kernel image file between 2814 different yeeloong laptops. 2815 Example: machtype=lemote-yeeloong-2f-7inch 2816 2817 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2818 than or equal to this physical address is ignored. 2819 2820 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2821 will bring up during bootup. maxcpus=n : n >= 0 limits 2822 the kernel to bring up 'n' processors. Surely after 2823 bootup you can bring up the other plugged cpu by executing 2824 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2825 only takes effect during system bootup. 2826 While n=0 is a special case, it is equivalent to "nosmp", 2827 which also disables the IO APIC. 2828 2829 max_loop= [LOOP] The number of loop block devices that get 2830 (loop.max_loop) unconditionally pre-created at init time. The default 2831 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2832 of statically allocating a predefined number, loop 2833 devices can be requested on-demand with the 2834 /dev/loop-control interface. 2835 2836 mce [X86-32] Machine Check Exception 2837 2838 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2839 2840 md= [HW] RAID subsystems devices and level 2841 See Documentation/admin-guide/md.rst. 2842 2843 mdacon= [MDA] 2844 Format: <first>,<last> 2845 Specifies range of consoles to be captured by the MDA. 2846 2847 mds= [X86,INTEL] 2848 Control mitigation for the Micro-architectural Data 2849 Sampling (MDS) vulnerability. 2850 2851 Certain CPUs are vulnerable to an exploit against CPU 2852 internal buffers which can forward information to a 2853 disclosure gadget under certain conditions. 2854 2855 In vulnerable processors, the speculatively 2856 forwarded data can be used in a cache side channel 2857 attack, to access data to which the attacker does 2858 not have direct access. 2859 2860 This parameter controls the MDS mitigation. The 2861 options are: 2862 2863 full - Enable MDS mitigation on vulnerable CPUs 2864 full,nosmt - Enable MDS mitigation and disable 2865 SMT on vulnerable CPUs 2866 off - Unconditionally disable MDS mitigation 2867 2868 On TAA-affected machines, mds=off can be prevented by 2869 an active TAA mitigation as both vulnerabilities are 2870 mitigated with the same mechanism so in order to disable 2871 this mitigation, you need to specify tsx_async_abort=off 2872 too. 2873 2874 Not specifying this option is equivalent to 2875 mds=full. 2876 2877 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2878 2879 mem=nn[KMG] [HEXAGON] Set the memory size. 2880 Must be specified, otherwise memory size will be 0. 2881 2882 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2883 Amount of memory to be used in cases as follows: 2884 2885 1 for test; 2886 2 when the kernel is not able to see the whole system memory; 2887 3 memory that lies after 'mem=' boundary is excluded from 2888 the hypervisor, then assigned to KVM guests. 2889 4 to limit the memory available for kdump kernel. 2890 2891 [ARC,MICROBLAZE] - the limit applies only to low memory, 2892 high memory is not affected. 2893 2894 [ARM64] - only limits memory covered by the linear 2895 mapping. The NOMAP regions are not affected. 2896 2897 [X86] Work as limiting max address. Use together 2898 with memmap= to avoid physical address space collisions. 2899 Without memmap= PCI devices could be placed at addresses 2900 belonging to unused RAM. 2901 2902 Note that this only takes effects during boot time since 2903 in above case 3, memory may need be hot added after boot 2904 if system memory of hypervisor is not sufficient. 2905 2906 mem=nn[KMG]@ss[KMG] 2907 [ARM,MIPS] - override the memory layout reported by 2908 firmware. 2909 Define a memory region of size nn[KMG] starting at 2910 ss[KMG]. 2911 Multiple different regions can be specified with 2912 multiple mem= parameters on the command line. 2913 2914 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2915 memory. 2916 2917 memchunk=nn[KMG] 2918 [KNL,SH] Allow user to override the default size for 2919 per-device physically contiguous DMA buffers. 2920 2921 memhp_default_state=online/offline 2922 [KNL] Set the initial state for the memory hotplug 2923 onlining policy. If not specified, the default value is 2924 set according to the 2925 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2926 option. 2927 See Documentation/admin-guide/mm/memory-hotplug.rst. 2928 2929 memmap=exactmap [KNL,X86] Enable setting of an exact 2930 E820 memory map, as specified by the user. 2931 Such memmap=exactmap lines can be constructed based on 2932 BIOS output or other requirements. See the memmap=nn@ss 2933 option description. 2934 2935 memmap=nn[KMG]@ss[KMG] 2936 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 2937 Region of memory to be used is from ss to ss+nn. 2938 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2939 which limits max address to nn[KMG]. 2940 Multiple different regions can be specified, 2941 comma delimited. 2942 Example: 2943 memmap=100M@2G,100M#3G,1G!1024G 2944 2945 memmap=nn[KMG]#ss[KMG] 2946 [KNL,ACPI] Mark specific memory as ACPI data. 2947 Region of memory to be marked is from ss to ss+nn. 2948 2949 memmap=nn[KMG]$ss[KMG] 2950 [KNL,ACPI] Mark specific memory as reserved. 2951 Region of memory to be reserved is from ss to ss+nn. 2952 Example: Exclude memory from 0x18690000-0x1869ffff 2953 memmap=64K$0x18690000 2954 or 2955 memmap=0x10000$0x18690000 2956 Some bootloaders may need an escape character before '$', 2957 like Grub2, otherwise '$' and the following number 2958 will be eaten. 2959 2960 memmap=nn[KMG]!ss[KMG] 2961 [KNL,X86] Mark specific memory as protected. 2962 Region of memory to be used, from ss to ss+nn. 2963 The memory region may be marked as e820 type 12 (0xc) 2964 and is NVDIMM or ADR memory. 2965 2966 memmap=<size>%<offset>-<oldtype>+<newtype> 2967 [KNL,ACPI] Convert memory within the specified region 2968 from <oldtype> to <newtype>. If "-<oldtype>" is left 2969 out, the whole region will be marked as <newtype>, 2970 even if previously unavailable. If "+<newtype>" is left 2971 out, matching memory will be removed. Types are 2972 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2973 3 = ACPI, 12 = PRAM. 2974 2975 memory_corruption_check=0/1 [X86] 2976 Some BIOSes seem to corrupt the first 64k of 2977 memory when doing things like suspend/resume. 2978 Setting this option will scan the memory 2979 looking for corruption. Enabling this will 2980 both detect corruption and prevent the kernel 2981 from using the memory being corrupted. 2982 However, its intended as a diagnostic tool; if 2983 repeatable BIOS-originated corruption always 2984 affects the same memory, you can use memmap= 2985 to prevent the kernel from using that memory. 2986 2987 memory_corruption_check_size=size [X86] 2988 By default it checks for corruption in the low 2989 64k, making this memory unavailable for normal 2990 use. Use this parameter to scan for 2991 corruption in more or less memory. 2992 2993 memory_corruption_check_period=seconds [X86] 2994 By default it checks for corruption every 60 2995 seconds. Use this parameter to check at some 2996 other rate. 0 disables periodic checking. 2997 2998 memory_hotplug.memmap_on_memory 2999 [KNL,X86,ARM] Boolean flag to enable this feature. 3000 Format: {on | off (default)} 3001 When enabled, runtime hotplugged memory will 3002 allocate its internal metadata (struct pages) 3003 from the hotadded memory which will allow to 3004 hotadd a lot of memory without requiring 3005 additional memory to do so. 3006 This feature is disabled by default because it 3007 has some implication on large (e.g. GB) 3008 allocations in some configurations (e.g. small 3009 memory blocks). 3010 The state of the flag can be read in 3011 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3012 Note that even when enabled, there are a few cases where 3013 the feature is not effective. 3014 3015 This is not compatible with hugetlb_free_vmemmap. If 3016 both parameters are enabled, hugetlb_free_vmemmap takes 3017 precedence over memory_hotplug.memmap_on_memory. 3018 3019 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest 3020 Format: <integer> 3021 default : 0 <disable> 3022 Specifies the number of memtest passes to be 3023 performed. Each pass selects another test 3024 pattern from a given set of patterns. Memtest 3025 fills the memory with this pattern, validates 3026 memory contents and reserves bad memory 3027 regions that are detected. 3028 3029 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3030 Valid arguments: on, off 3031 Default (depends on kernel configuration option): 3032 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 3033 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 3034 mem_encrypt=on: Activate SME 3035 mem_encrypt=off: Do not activate SME 3036 3037 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 3038 for details on when memory encryption can be activated. 3039 3040 mem_sleep_default= [SUSPEND] Default system suspend mode: 3041 s2idle - Suspend-To-Idle 3042 shallow - Power-On Suspend or equivalent (if supported) 3043 deep - Suspend-To-RAM or equivalent (if supported) 3044 See Documentation/admin-guide/pm/sleep-states.rst. 3045 3046 meye.*= [HW] Set MotionEye Camera parameters 3047 See Documentation/admin-guide/media/meye.rst. 3048 3049 mfgpt_irq= [IA-32] Specify the IRQ to use for the 3050 Multi-Function General Purpose Timers on AMD Geode 3051 platforms. 3052 3053 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3054 the BIOS has incorrectly applied a workaround. TinyBIOS 3055 version 0.98 is known to be affected, 0.99 fixes the 3056 problem by letting the user disable the workaround. 3057 3058 mga= [HW,DRM] 3059 3060 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 3061 physical address is ignored. 3062 3063 mini2440= [ARM,HW,KNL] 3064 Format:[0..2][b][c][t] 3065 Default: "0tb" 3066 MINI2440 configuration specification: 3067 0 - The attached screen is the 3.5" TFT 3068 1 - The attached screen is the 7" TFT 3069 2 - The VGA Shield is attached (1024x768) 3070 Leaving out the screen size parameter will not load 3071 the TFT driver, and the framebuffer will be left 3072 unconfigured. 3073 b - Enable backlight. The TFT backlight pin will be 3074 linked to the kernel VESA blanking code and a GPIO 3075 LED. This parameter is not necessary when using the 3076 VGA shield. 3077 c - Enable the s3c camera interface. 3078 t - Reserved for enabling touchscreen support. The 3079 touchscreen support is not enabled in the mainstream 3080 kernel as of 2.6.30, a preliminary port can be found 3081 in the "bleeding edge" mini2440 support kernel at 3082 https://repo.or.cz/w/linux-2.6/mini2440.git 3083 3084 mitigations= 3085 [X86,PPC,S390,ARM64] Control optional mitigations for 3086 CPU vulnerabilities. This is a set of curated, 3087 arch-independent options, each of which is an 3088 aggregation of existing arch-specific options. 3089 3090 off 3091 Disable all optional CPU mitigations. This 3092 improves system performance, but it may also 3093 expose users to several CPU vulnerabilities. 3094 Equivalent to: nopti [X86,PPC] 3095 kpti=0 [ARM64] 3096 nospectre_v1 [X86,PPC] 3097 nobp=0 [S390] 3098 nospectre_v2 [X86,PPC,S390,ARM64] 3099 spectre_v2_user=off [X86] 3100 spec_store_bypass_disable=off [X86,PPC] 3101 ssbd=force-off [ARM64] 3102 l1tf=off [X86] 3103 mds=off [X86] 3104 tsx_async_abort=off [X86] 3105 kvm.nx_huge_pages=off [X86] 3106 no_entry_flush [PPC] 3107 no_uaccess_flush [PPC] 3108 3109 Exceptions: 3110 This does not have any effect on 3111 kvm.nx_huge_pages when 3112 kvm.nx_huge_pages=force. 3113 3114 auto (default) 3115 Mitigate all CPU vulnerabilities, but leave SMT 3116 enabled, even if it's vulnerable. This is for 3117 users who don't want to be surprised by SMT 3118 getting disabled across kernel upgrades, or who 3119 have other ways of avoiding SMT-based attacks. 3120 Equivalent to: (default behavior) 3121 3122 auto,nosmt 3123 Mitigate all CPU vulnerabilities, disabling SMT 3124 if needed. This is for users who always want to 3125 be fully mitigated, even if it means losing SMT. 3126 Equivalent to: l1tf=flush,nosmt [X86] 3127 mds=full,nosmt [X86] 3128 tsx_async_abort=full,nosmt [X86] 3129 3130 mminit_loglevel= 3131 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 3132 parameter allows control of the logging verbosity for 3133 the additional memory initialisation checks. A value 3134 of 0 disables mminit logging and a level of 4 will 3135 log everything. Information is printed at KERN_DEBUG 3136 so loglevel=8 may also need to be specified. 3137 3138 module.sig_enforce 3139 [KNL] When CONFIG_MODULE_SIG is set, this means that 3140 modules without (valid) signatures will fail to load. 3141 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3142 is always true, so this option does nothing. 3143 3144 module_blacklist= [KNL] Do not load a comma-separated list of 3145 modules. Useful for debugging problem modules. 3146 3147 mousedev.tap_time= 3148 [MOUSE] Maximum time between finger touching and 3149 leaving touchpad surface for touch to be considered 3150 a tap and be reported as a left button click (for 3151 touchpads working in absolute mode only). 3152 Format: <msecs> 3153 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3154 reporting absolute coordinates, such as tablets 3155 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3156 reporting absolute coordinates, such as tablets 3157 3158 movablecore= [KNL,X86,IA-64,PPC] 3159 Format: nn[KMGTPE] | nn% 3160 This parameter is the complement to kernelcore=, it 3161 specifies the amount of memory used for migratable 3162 allocations. If both kernelcore and movablecore is 3163 specified, then kernelcore will be at *least* the 3164 specified value but may be more. If movablecore on its 3165 own is specified, the administrator must be careful 3166 that the amount of memory usable for all allocations 3167 is not too small. 3168 3169 movable_node [KNL] Boot-time switch to make hotplugable memory 3170 NUMA nodes to be movable. This means that the memory 3171 of such nodes will be usable only for movable 3172 allocations which rules out almost all kernel 3173 allocations. Use with caution! 3174 3175 MTD_Partition= [MTD] 3176 Format: <name>,<region-number>,<size>,<offset> 3177 3178 MTD_Region= [MTD] Format: 3179 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3180 3181 mtdparts= [MTD] 3182 See drivers/mtd/parsers/cmdlinepart.c 3183 3184 multitce=off [PPC] This parameter disables the use of the pSeries 3185 firmware feature for updating multiple TCE entries 3186 at a time. 3187 3188 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 3189 3190 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 3191 3192 boundary - index of last SLC block on Flex-OneNAND. 3193 The remaining blocks are configured as MLC blocks. 3194 lock - Configure if Flex-OneNAND boundary should be locked. 3195 Once locked, the boundary cannot be changed. 3196 1 indicates lock status, 0 indicates unlock status. 3197 3198 mtdset= [ARM] 3199 ARM/S3C2412 JIVE boot control 3200 3201 See arch/arm/mach-s3c/mach-jive.c 3202 3203 mtouchusb.raw_coordinates= 3204 [HW] Make the MicroTouch USB driver use raw coordinates 3205 ('y', default) or cooked coordinates ('n') 3206 3207 mtrr_chunk_size=nn[KMG] [X86] 3208 used for mtrr cleanup. It is largest continuous chunk 3209 that could hold holes aka. UC entries. 3210 3211 mtrr_gran_size=nn[KMG] [X86] 3212 Used for mtrr cleanup. It is granularity of mtrr block. 3213 Default is 1. 3214 Large value could prevent small alignment from 3215 using up MTRRs. 3216 3217 mtrr_spare_reg_nr=n [X86] 3218 Format: <integer> 3219 Range: 0,7 : spare reg number 3220 Default : 1 3221 Used for mtrr cleanup. It is spare mtrr entries number. 3222 Set to 2 or more if your graphical card needs more. 3223 3224 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3225 3226 netdev= [NET] Network devices parameters 3227 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3228 Note that mem_start is often overloaded to mean 3229 something different and driver-specific. 3230 This usage is only documented in each driver source 3231 file if at all. 3232 3233 nf_conntrack.acct= 3234 [NETFILTER] Enable connection tracking flow accounting 3235 0 to disable accounting 3236 1 to enable accounting 3237 Default value is 0. 3238 3239 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3240 See Documentation/admin-guide/nfs/nfsroot.rst. 3241 3242 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3243 See Documentation/admin-guide/nfs/nfsroot.rst. 3244 3245 nfsrootdebug [NFS] enable nfsroot debugging messages. 3246 See Documentation/admin-guide/nfs/nfsroot.rst. 3247 3248 nfs.callback_nr_threads= 3249 [NFSv4] set the total number of threads that the 3250 NFS client will assign to service NFSv4 callback 3251 requests. 3252 3253 nfs.callback_tcpport= 3254 [NFS] set the TCP port on which the NFSv4 callback 3255 channel should listen. 3256 3257 nfs.cache_getent= 3258 [NFS] sets the pathname to the program which is used 3259 to update the NFS client cache entries. 3260 3261 nfs.cache_getent_timeout= 3262 [NFS] sets the timeout after which an attempt to 3263 update a cache entry is deemed to have failed. 3264 3265 nfs.idmap_cache_timeout= 3266 [NFS] set the maximum lifetime for idmapper cache 3267 entries. 3268 3269 nfs.enable_ino64= 3270 [NFS] enable 64-bit inode numbers. 3271 If zero, the NFS client will fake up a 32-bit inode 3272 number for the readdir() and stat() syscalls instead 3273 of returning the full 64-bit number. 3274 The default is to return 64-bit inode numbers. 3275 3276 nfs.max_session_cb_slots= 3277 [NFSv4.1] Sets the maximum number of session 3278 slots the client will assign to the callback 3279 channel. This determines the maximum number of 3280 callbacks the client will process in parallel for 3281 a particular server. 3282 3283 nfs.max_session_slots= 3284 [NFSv4.1] Sets the maximum number of session slots 3285 the client will attempt to negotiate with the server. 3286 This limits the number of simultaneous RPC requests 3287 that the client can send to the NFSv4.1 server. 3288 Note that there is little point in setting this 3289 value higher than the max_tcp_slot_table_limit. 3290 3291 nfs.nfs4_disable_idmapping= 3292 [NFSv4] When set to the default of '1', this option 3293 ensures that both the RPC level authentication 3294 scheme and the NFS level operations agree to use 3295 numeric uids/gids if the mount is using the 3296 'sec=sys' security flavour. In effect it is 3297 disabling idmapping, which can make migration from 3298 legacy NFSv2/v3 systems to NFSv4 easier. 3299 Servers that do not support this mode of operation 3300 will be autodetected by the client, and it will fall 3301 back to using the idmapper. 3302 To turn off this behaviour, set the value to '0'. 3303 nfs.nfs4_unique_id= 3304 [NFS4] Specify an additional fixed unique ident- 3305 ification string that NFSv4 clients can insert into 3306 their nfs_client_id4 string. This is typically a 3307 UUID that is generated at system install time. 3308 3309 nfs.send_implementation_id = 3310 [NFSv4.1] Send client implementation identification 3311 information in exchange_id requests. 3312 If zero, no implementation identification information 3313 will be sent. 3314 The default is to send the implementation identification 3315 information. 3316 3317 nfs.recover_lost_locks = 3318 [NFSv4] Attempt to recover locks that were lost due 3319 to a lease timeout on the server. Please note that 3320 doing this risks data corruption, since there are 3321 no guarantees that the file will remain unchanged 3322 after the locks are lost. 3323 If you want to enable the kernel legacy behaviour of 3324 attempting to recover these locks, then set this 3325 parameter to '1'. 3326 The default parameter value of '0' causes the kernel 3327 not to attempt recovery of lost locks. 3328 3329 nfs4.layoutstats_timer = 3330 [NFSv4.2] Change the rate at which the kernel sends 3331 layoutstats to the pNFS metadata server. 3332 3333 Setting this to value to 0 causes the kernel to use 3334 whatever value is the default set by the layout 3335 driver. A non-zero value sets the minimum interval 3336 in seconds between layoutstats transmissions. 3337 3338 nfsd.inter_copy_offload_enable = 3339 [NFSv4.2] When set to 1, the server will support 3340 server-to-server copies for which this server is 3341 the destination of the copy. 3342 3343 nfsd.nfsd4_ssc_umount_timeout = 3344 [NFSv4.2] When used as the destination of a 3345 server-to-server copy, knfsd temporarily mounts 3346 the source server. It caches the mount in case 3347 it will be needed again, and discards it if not 3348 used for the number of milliseconds specified by 3349 this parameter. 3350 3351 nfsd.nfs4_disable_idmapping= 3352 [NFSv4] When set to the default of '1', the NFSv4 3353 server will return only numeric uids and gids to 3354 clients using auth_sys, and will accept numeric uids 3355 and gids from such clients. This is intended to ease 3356 migration from NFSv2/v3. 3357 3358 3359 nmi_backtrace.backtrace_idle [KNL] 3360 Dump stacks even of idle CPUs in response to an 3361 NMI stack-backtrace request. 3362 3363 nmi_debug= [KNL,SH] Specify one or more actions to take 3364 when a NMI is triggered. 3365 Format: [state][,regs][,debounce][,die] 3366 3367 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3368 Format: [panic,][nopanic,][num] 3369 Valid num: 0 or 1 3370 0 - turn hardlockup detector in nmi_watchdog off 3371 1 - turn hardlockup detector in nmi_watchdog on 3372 When panic is specified, panic when an NMI watchdog 3373 timeout occurs (or 'nopanic' to not panic on an NMI 3374 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3375 To disable both hard and soft lockup detectors, 3376 please see 'nowatchdog'. 3377 This is useful when you use a panic=... timeout and 3378 need the box quickly up again. 3379 3380 These settings can be accessed at runtime via 3381 the nmi_watchdog and hardlockup_panic sysctls. 3382 3383 netpoll.carrier_timeout= 3384 [NET] Specifies amount of time (in seconds) that 3385 netpoll should wait for a carrier. By default netpoll 3386 waits 4 seconds. 3387 3388 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3389 emulation library even if a 387 maths coprocessor 3390 is present. 3391 3392 no5lvl [X86-64] Disable 5-level paging mode. Forces 3393 kernel to use 4-level paging instead. 3394 3395 nofsgsbase [X86] Disables FSGSBASE instructions. 3396 3397 no_console_suspend 3398 [HW] Never suspend the console 3399 Disable suspending of consoles during suspend and 3400 hibernate operations. Once disabled, debugging 3401 messages can reach various consoles while the rest 3402 of the system is being put to sleep (ie, while 3403 debugging driver suspend/resume hooks). This may 3404 not work reliably with all consoles, but is known 3405 to work with serial and VGA consoles. 3406 To facilitate more flexible debugging, we also add 3407 console_suspend, a printk module parameter to control 3408 it. Users could use console_suspend (usually 3409 /sys/module/printk/parameters/console_suspend) to 3410 turn on/off it dynamically. 3411 3412 novmcoredd [KNL,KDUMP] 3413 Disable device dump. Device dump allows drivers to 3414 append dump data to vmcore so you can collect driver 3415 specified debug info. Drivers can append the data 3416 without any limit and this data is stored in memory, 3417 so this may cause significant memory stress. Disabling 3418 device dump can help save memory but the driver debug 3419 data will be no longer available. This parameter 3420 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3421 is set. 3422 3423 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3424 caches in the slab allocator. Saves per-node memory, 3425 but will impact performance. 3426 3427 noalign [KNL,ARM] 3428 3429 noaltinstr [S390] Disables alternative instructions patching 3430 (CPU alternatives feature). 3431 3432 noapic [SMP,APIC] Tells the kernel to not make use of any 3433 IOAPICs that may be present in the system. 3434 3435 noautogroup Disable scheduler automatic task group creation. 3436 3437 nobats [PPC] Do not use BATs for mapping kernel lowmem 3438 on "Classic" PPC cores. 3439 3440 nocache [ARM] 3441 3442 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3443 3444 delayacct [KNL] Enable per-task delay accounting 3445 3446 nodsp [SH] Disable hardware DSP at boot time. 3447 3448 noefi Disable EFI runtime services support. 3449 3450 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3451 3452 noexec [IA-64] 3453 3454 noexec [X86] 3455 On X86-32 available only on PAE configured kernels. 3456 noexec=on: enable non-executable mappings (default) 3457 noexec=off: disable non-executable mappings 3458 3459 nosmap [X86,PPC] 3460 Disable SMAP (Supervisor Mode Access Prevention) 3461 even if it is supported by processor. 3462 3463 nosmep [X86,PPC64s] 3464 Disable SMEP (Supervisor Mode Execution Prevention) 3465 even if it is supported by processor. 3466 3467 noexec32 [X86-64] 3468 This affects only 32-bit executables. 3469 noexec32=on: enable non-executable mappings (default) 3470 read doesn't imply executable mappings 3471 noexec32=off: disable non-executable mappings 3472 read implies executable mappings 3473 3474 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3475 3476 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3477 register save and restore. The kernel will only save 3478 legacy floating-point registers on task switch. 3479 3480 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3481 3482 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings. 3483 3484 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3485 Equivalent to smt=1. 3486 3487 [KNL,X86] Disable symmetric multithreading (SMT). 3488 nosmt=force: Force disable SMT, cannot be undone 3489 via the sysfs control file. 3490 3491 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3492 (bounds check bypass). With this option data leaks are 3493 possible in the system. 3494 3495 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3496 the Spectre variant 2 (indirect branch prediction) 3497 vulnerability. System may allow data leaks with this 3498 option. 3499 3500 nospec_store_bypass_disable 3501 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3502 3503 no_uaccess_flush 3504 [PPC] Don't flush the L1-D cache after accessing user data. 3505 3506 noxsave [BUGS=X86] Disables x86 extended register state save 3507 and restore using xsave. The kernel will fallback to 3508 enabling legacy floating-point and sse state. 3509 3510 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3511 register states. The kernel will fall back to use 3512 xsave to save the states. By using this parameter, 3513 performance of saving the states is degraded because 3514 xsave doesn't support modified optimization while 3515 xsaveopt supports it on xsaveopt enabled systems. 3516 3517 noxsaves [X86] Disables xsaves and xrstors used in saving and 3518 restoring x86 extended register state in compacted 3519 form of xsave area. The kernel will fall back to use 3520 xsaveopt and xrstor to save and restore the states 3521 in standard form of xsave area. By using this 3522 parameter, xsave area per process might occupy more 3523 memory on xsaves enabled systems. 3524 3525 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait 3526 in do_idle() and not use the arch_cpu_idle() 3527 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 3528 to be effective. This is useful on platforms where the 3529 sleep(SH) or wfi(ARM,ARM64) instructions do not work 3530 correctly or when doing power measurements to evalute 3531 the impact of the sleep instructions. This is also 3532 useful when using JTAG debugger. 3533 3534 no_file_caps Tells the kernel not to honor file capabilities. The 3535 only way then for a file to be executed with privilege 3536 is to be setuid root or executed by root. 3537 3538 nohalt [IA-64] Tells the kernel not to use the power saving 3539 function PAL_HALT_LIGHT when idle. This increases 3540 power-consumption. On the positive side, it reduces 3541 interrupt wake-up latency, which may improve performance 3542 in certain environments such as networked servers or 3543 real-time systems. 3544 3545 no_hash_pointers 3546 Force pointers printed to the console or buffers to be 3547 unhashed. By default, when a pointer is printed via %p 3548 format string, that pointer is "hashed", i.e. obscured 3549 by hashing the pointer value. This is a security feature 3550 that hides actual kernel addresses from unprivileged 3551 users, but it also makes debugging the kernel more 3552 difficult since unequal pointers can no longer be 3553 compared. However, if this command-line option is 3554 specified, then all normal pointers will have their true 3555 value printed. This option should only be specified when 3556 debugging the kernel. Please do not use on production 3557 kernels. 3558 3559 nohibernate [HIBERNATION] Disable hibernation and resume. 3560 3561 nohz= [KNL] Boottime enable/disable dynamic ticks 3562 Valid arguments: on, off 3563 Default: on 3564 3565 nohz_full= [KNL,BOOT,SMP,ISOL] 3566 The argument is a cpu list, as described above. 3567 In kernels built with CONFIG_NO_HZ_FULL=y, set 3568 the specified list of CPUs whose tick will be stopped 3569 whenever possible. The boot CPU will be forced outside 3570 the range to maintain the timekeeping. Any CPUs 3571 in this list will have their RCU callbacks offloaded, 3572 just as if they had also been called out in the 3573 rcu_nocbs= boot parameter. 3574 3575 noiotrap [SH] Disables trapped I/O port accesses. 3576 3577 noirqdebug [X86-32] Disables the code which attempts to detect and 3578 disable unhandled interrupt sources. 3579 3580 no_timer_check [X86,APIC] Disables the code which tests for 3581 broken timer IRQ sources. 3582 3583 noisapnp [ISAPNP] Disables ISA PnP code. 3584 3585 noinitrd [RAM] Tells the kernel not to load any configured 3586 initial RAM disk. 3587 3588 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3589 remapping. 3590 [Deprecated - use intremap=off] 3591 3592 nointroute [IA-64] 3593 3594 noinvpcid [X86] Disable the INVPCID cpu feature. 3595 3596 nojitter [IA-64] Disables jitter checking for ITC timers. 3597 3598 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3599 3600 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3601 fault handling. 3602 3603 no-vmw-sched-clock 3604 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3605 clock and use the default one. 3606 3607 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3608 accounting. steal time is computed, but won't 3609 influence scheduler behaviour 3610 3611 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3612 3613 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3614 3615 noltlbs [PPC] Do not use large page/tlb entries for kernel 3616 lowmem mapping on PPC40x and PPC8xx 3617 3618 nomca [IA-64] Disable machine check abort handling 3619 3620 nomce [X86-32] Disable Machine Check Exception 3621 3622 nomfgpt [X86-32] Disable Multi-Function General Purpose 3623 Timer usage (for AMD Geode machines). 3624 3625 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3626 shutdown the other cpus. Instead use the REBOOT_VECTOR 3627 irq. 3628 3629 nomodeset Disable kernel modesetting. DRM drivers will not perform 3630 display-mode changes or accelerated rendering. Only the 3631 system framebuffer will be available for use if this was 3632 set-up by the firmware or boot loader. 3633 3634 Useful as fallback, or for testing and debugging. 3635 3636 nomodule Disable module load 3637 3638 nopat [X86] Disable PAT (page attribute table extension of 3639 pagetables) support. 3640 3641 nopcid [X86-64] Disable the PCID cpu feature. 3642 3643 norandmaps Don't use address space randomization. Equivalent to 3644 echo 0 > /proc/sys/kernel/randomize_va_space 3645 3646 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3647 with UP alternatives 3648 3649 nordrand [X86] Disable kernel use of the RDRAND and 3650 RDSEED instructions even if they are supported 3651 by the processor. RDRAND and RDSEED are still 3652 available to user space applications. 3653 3654 noresume [SWSUSP] Disables resume and restores original swap 3655 space. 3656 3657 no-scroll [VGA] Disables scrollback. 3658 This is required for the Braillex ib80-piezo Braille 3659 reader made by F.H. Papenmeier (Germany). 3660 3661 nosbagart [IA-64] 3662 3663 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3664 3665 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3666 3667 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3668 and disable the IO APIC. legacy for "maxcpus=0". 3669 3670 nosoftlockup [KNL] Disable the soft-lockup detector. 3671 3672 nosync [HW,M68K] Disables sync negotiation for all devices. 3673 3674 nowatchdog [KNL] Disable both lockup detectors, i.e. 3675 soft-lockup and NMI watchdog (hard-lockup). 3676 3677 nowb [ARM] 3678 3679 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3680 3681 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3682 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3683 Some features depend on CPU0. Known dependencies are: 3684 1. Resume from suspend/hibernate depends on CPU0. 3685 Suspend/hibernate will fail if CPU0 is offline and you 3686 need to online CPU0 before suspend/hibernate. 3687 2. PIC interrupts also depend on CPU0. CPU0 can't be 3688 removed if a PIC interrupt is detected. 3689 It's said poweroff/reboot may depend on CPU0 on some 3690 machines although I haven't seen such issues so far 3691 after CPU0 is offline on a few tested machines. 3692 If the dependencies are under your control, you can 3693 turn on cpu0_hotplug. 3694 3695 nps_mtm_hs_ctr= [KNL,ARC] 3696 This parameter sets the maximum duration, in 3697 cycles, each HW thread of the CTOP can run 3698 without interruptions, before HW switches it. 3699 The actual maximum duration is 16 times this 3700 parameter's value. 3701 Format: integer between 1 and 255 3702 Default: 255 3703 3704 nptcg= [IA-64] Override max number of concurrent global TLB 3705 purges which is reported from either PAL_VM_SUMMARY or 3706 SAL PALO. 3707 3708 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3709 could support. nr_cpus=n : n >= 1 limits the kernel to 3710 support 'n' processors. It could be larger than the 3711 number of already plugged CPU during bootup, later in 3712 runtime you can physically add extra cpu until it reaches 3713 n. So during boot up some boot time memory for per-cpu 3714 variables need be pre-allocated for later physical cpu 3715 hot plugging. 3716 3717 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3718 3719 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only 3720 set up a single NUMA node spanning all memory. 3721 3722 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 3723 NUMA balancing. 3724 Allowed values are enable and disable 3725 3726 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3727 'node', 'default' can be specified 3728 This can be set from sysctl after boot. 3729 See Documentation/admin-guide/sysctl/vm.rst for details. 3730 3731 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3732 See Documentation/core-api/debugging-via-ohci1394.rst for more 3733 info. 3734 3735 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3736 Rather than timing out after 20 ms if an EC 3737 command is not properly ACKed, override the length 3738 of the timeout. We have interrupts disabled while 3739 waiting for the ACK, so if this is set too high 3740 interrupts *may* be lost! 3741 3742 omap_mux= [OMAP] Override bootloader pin multiplexing. 3743 Format: <mux_mode0.mode_name=value>... 3744 For example, to override I2C bus2: 3745 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3746 3747 oops=panic Always panic on oopses. Default is to just kill the 3748 process, but there is a small probability of 3749 deadlocking the machine. 3750 This will also cause panics on machine check exceptions. 3751 Useful together with panic=30 to trigger a reboot. 3752 3753 page_alloc.shuffle= 3754 [KNL] Boolean flag to control whether the page allocator 3755 should randomize its free lists. The randomization may 3756 be automatically enabled if the kernel detects it is 3757 running on a platform with a direct-mapped memory-side 3758 cache, and this parameter can be used to 3759 override/disable that behavior. The state of the flag 3760 can be read from sysfs at: 3761 /sys/module/page_alloc/parameters/shuffle. 3762 3763 page_owner= [KNL] Boot-time page_owner enabling option. 3764 Storage of the information about who allocated 3765 each page is disabled in default. With this switch, 3766 we can turn it on. 3767 on: enable the feature 3768 3769 page_poison= [KNL] Boot-time parameter changing the state of 3770 poisoning on the buddy allocator, available with 3771 CONFIG_PAGE_POISONING=y. 3772 off: turn off poisoning (default) 3773 on: turn on poisoning 3774 3775 page_reporting.page_reporting_order= 3776 [KNL] Minimal page reporting order 3777 Format: <integer> 3778 Adjust the minimal page reporting order. The page 3779 reporting is disabled when it exceeds (MAX_ORDER-1). 3780 3781 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3782 timeout > 0: seconds before rebooting 3783 timeout = 0: wait forever 3784 timeout < 0: reboot immediately 3785 Format: <timeout> 3786 3787 panic_print= Bitmask for printing system info when panic happens. 3788 User can chose combination of the following bits: 3789 bit 0: print all tasks info 3790 bit 1: print system memory info 3791 bit 2: print timer info 3792 bit 3: print locks info if CONFIG_LOCKDEP is on 3793 bit 4: print ftrace buffer 3794 bit 5: print all printk messages in buffer 3795 bit 6: print all CPUs backtrace (if available in the arch) 3796 *Be aware* that this option may print a _lot_ of lines, 3797 so there are risks of losing older messages in the log. 3798 Use this option carefully, maybe worth to setup a 3799 bigger log buffer with "log_buf_len" along with this. 3800 3801 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3802 Format: <hex>[,nousertaint] 3803 Hexadecimal bitmask representing the set of TAINT flags 3804 that will cause the kernel to panic when add_taint() is 3805 called with any of the flags in this set. 3806 The optional switch "nousertaint" can be utilized to 3807 prevent userspace forced crashes by writing to sysctl 3808 /proc/sys/kernel/tainted any flagset matching with the 3809 bitmask set on panic_on_taint. 3810 See Documentation/admin-guide/tainted-kernels.rst for 3811 extra details on the taint flags that users can pick 3812 to compose the bitmask to assign to panic_on_taint. 3813 3814 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3815 on a WARN(). 3816 3817 crash_kexec_post_notifiers 3818 Run kdump after running panic-notifiers and dumping 3819 kmsg. This only for the users who doubt kdump always 3820 succeeds in any situation. 3821 Note that this also increases risks of kdump failure, 3822 because some panic notifiers can make the crashed 3823 kernel more unstable. 3824 3825 parkbd.port= [HW] Parallel port number the keyboard adapter is 3826 connected to, default is 0. 3827 Format: <parport#> 3828 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3829 0 for XT, 1 for AT (default is AT). 3830 Format: <mode> 3831 3832 parport= [HW,PPT] Specify parallel ports. 0 disables. 3833 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3834 Use 'auto' to force the driver to use any 3835 IRQ/DMA settings detected (the default is to 3836 ignore detected IRQ/DMA settings because of 3837 possible conflicts). You can specify the base 3838 address, IRQ, and DMA settings; IRQ and DMA 3839 should be numbers, or 'auto' (for using detected 3840 settings on that particular port), or 'nofifo' 3841 (to avoid using a FIFO even if it is detected). 3842 Parallel ports are assigned in the order they 3843 are specified on the command line, starting 3844 with parport0. 3845 3846 parport_init_mode= [HW,PPT] 3847 Configure VIA parallel port to operate in 3848 a specific mode. This is necessary on Pegasos 3849 computer where firmware has no options for setting 3850 up parallel port mode and sets it to spp. 3851 Currently this function knows 686a and 8231 chips. 3852 Format: [spp|ps2|epp|ecp|ecpepp] 3853 3854 pata_legacy.all= [HW,LIBATA] 3855 Format: <int> 3856 Set to non-zero to probe primary and secondary ISA 3857 port ranges on PCI systems where no PCI PATA device 3858 has been found at either range. Disabled by default. 3859 3860 pata_legacy.autospeed= [HW,LIBATA] 3861 Format: <int> 3862 Set to non-zero if a chip is present that snoops speed 3863 changes. Disabled by default. 3864 3865 pata_legacy.ht6560a= [HW,LIBATA] 3866 Format: <int> 3867 Set to 1, 2, or 3 for HT 6560A on the primary channel, 3868 the secondary channel, or both channels respectively. 3869 Disabled by default. 3870 3871 pata_legacy.ht6560b= [HW,LIBATA] 3872 Format: <int> 3873 Set to 1, 2, or 3 for HT 6560B on the primary channel, 3874 the secondary channel, or both channels respectively. 3875 Disabled by default. 3876 3877 pata_legacy.iordy_mask= [HW,LIBATA] 3878 Format: <int> 3879 IORDY enable mask. Set individual bits to allow IORDY 3880 for the respective channel. Bit 0 is for the first 3881 legacy channel handled by this driver, bit 1 is for 3882 the second channel, and so on. The sequence will often 3883 correspond to the primary legacy channel, the secondary 3884 legacy channel, and so on, but the handling of a PCI 3885 bus and the use of other driver options may interfere 3886 with the sequence. By default IORDY is allowed across 3887 all channels. 3888 3889 pata_legacy.opti82c46x= [HW,LIBATA] 3890 Format: <int> 3891 Set to 1, 2, or 3 for Opti 82c611A on the primary 3892 channel, the secondary channel, or both channels 3893 respectively. Disabled by default. 3894 3895 pata_legacy.opti82c611a= [HW,LIBATA] 3896 Format: <int> 3897 Set to 1, 2, or 3 for Opti 82c465MV on the primary 3898 channel, the secondary channel, or both channels 3899 respectively. Disabled by default. 3900 3901 pata_legacy.pio_mask= [HW,LIBATA] 3902 Format: <int> 3903 PIO mode mask for autospeed devices. Set individual 3904 bits to allow the use of the respective PIO modes. 3905 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 3906 All modes allowed by default. 3907 3908 pata_legacy.probe_all= [HW,LIBATA] 3909 Format: <int> 3910 Set to non-zero to probe tertiary and further ISA 3911 port ranges on PCI systems. Disabled by default. 3912 3913 pata_legacy.probe_mask= [HW,LIBATA] 3914 Format: <int> 3915 Probe mask for legacy ISA PATA ports. Depending on 3916 platform configuration and the use of other driver 3917 options up to 6 legacy ports are supported: 0x1f0, 3918 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 3919 of individual ports can be disabled by setting the 3920 corresponding bits in the mask to 1. Bit 0 is for 3921 the first port in the list above (0x1f0), and so on. 3922 By default all supported ports are probed. 3923 3924 pata_legacy.qdi= [HW,LIBATA] 3925 Format: <int> 3926 Set to non-zero to probe QDI controllers. By default 3927 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 3928 3929 pata_legacy.winbond= [HW,LIBATA] 3930 Format: <int> 3931 Set to non-zero to probe Winbond controllers. Use 3932 the standard I/O port (0x130) if 1, otherwise the 3933 value given is the I/O port to use (typically 0x1b0). 3934 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 3935 0 otherwise. 3936 3937 pata_platform.pio_mask= [HW,LIBATA] 3938 Format: <int> 3939 Supported PIO mode mask. Set individual bits to allow 3940 the use of the respective PIO modes. Bit 0 is for 3941 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 3942 allowed by default. 3943 3944 pause_on_oops= 3945 Halt all CPUs after the first oops has been printed for 3946 the specified number of seconds. This is to be used if 3947 your oopses keep scrolling off the screen. 3948 3949 pcbit= [HW,ISDN] 3950 3951 pcd. [PARIDE] 3952 See header of drivers/block/paride/pcd.c. 3953 See also Documentation/admin-guide/blockdev/paride.rst. 3954 3955 pci=option[,option...] [PCI] various PCI subsystem options. 3956 3957 Some options herein operate on a specific device 3958 or a set of devices (<pci_dev>). These are 3959 specified in one of the following formats: 3960 3961 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3962 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3963 3964 Note: the first format specifies a PCI 3965 bus/device/function address which may change 3966 if new hardware is inserted, if motherboard 3967 firmware changes, or due to changes caused 3968 by other kernel parameters. If the 3969 domain is left unspecified, it is 3970 taken to be zero. Optionally, a path 3971 to a device through multiple device/function 3972 addresses can be specified after the base 3973 address (this is more robust against 3974 renumbering issues). The second format 3975 selects devices using IDs from the 3976 configuration space which may match multiple 3977 devices in the system. 3978 3979 earlydump dump PCI config space before the kernel 3980 changes anything 3981 off [X86] don't probe for the PCI bus 3982 bios [X86-32] force use of PCI BIOS, don't access 3983 the hardware directly. Use this if your machine 3984 has a non-standard PCI host bridge. 3985 nobios [X86-32] disallow use of PCI BIOS, only direct 3986 hardware access methods are allowed. Use this 3987 if you experience crashes upon bootup and you 3988 suspect they are caused by the BIOS. 3989 conf1 [X86] Force use of PCI Configuration Access 3990 Mechanism 1 (config address in IO port 0xCF8, 3991 data in IO port 0xCFC, both 32-bit). 3992 conf2 [X86] Force use of PCI Configuration Access 3993 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3994 the function, IO port 0xCFA, also 8-bit, sets 3995 bus number. The config space is then accessed 3996 through ports 0xC000-0xCFFF). 3997 See http://wiki.osdev.org/PCI for more info 3998 on the configuration access mechanisms. 3999 noaer [PCIE] If the PCIEAER kernel config parameter is 4000 enabled, this kernel boot option can be used to 4001 disable the use of PCIE advanced error reporting. 4002 nodomains [PCI] Disable support for multiple PCI 4003 root domains (aka PCI segments, in ACPI-speak). 4004 nommconf [X86] Disable use of MMCONFIG for PCI 4005 Configuration 4006 check_enable_amd_mmconf [X86] check for and enable 4007 properly configured MMIO access to PCI 4008 config space on AMD family 10h CPU 4009 nomsi [MSI] If the PCI_MSI kernel config parameter is 4010 enabled, this kernel boot option can be used to 4011 disable the use of MSI interrupts system-wide. 4012 noioapicquirk [APIC] Disable all boot interrupt quirks. 4013 Safety option to keep boot IRQs enabled. This 4014 should never be necessary. 4015 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4016 primary IO-APIC for bridges that cannot disable 4017 boot IRQs. This fixes a source of spurious IRQs 4018 when the system masks IRQs. 4019 noioapicreroute [APIC] Disable workaround that uses the 4020 boot IRQ equivalent of an IRQ that connects to 4021 a chipset where boot IRQs cannot be disabled. 4022 The opposite of ioapicreroute. 4023 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4024 routing table. These calls are known to be buggy 4025 on several machines and they hang the machine 4026 when used, but on other computers it's the only 4027 way to get the interrupt routing table. Try 4028 this option if the kernel is unable to allocate 4029 IRQs or discover secondary PCI buses on your 4030 motherboard. 4031 rom [X86] Assign address space to expansion ROMs. 4032 Use with caution as certain devices share 4033 address decoders between ROMs and other 4034 resources. 4035 norom [X86] Do not assign address space to 4036 expansion ROMs that do not already have 4037 BIOS assigned address ranges. 4038 nobar [X86] Do not assign address space to the 4039 BARs that weren't assigned by the BIOS. 4040 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4041 assigned automatically to PCI devices. You can 4042 make the kernel exclude IRQs of your ISA cards 4043 this way. 4044 pirqaddr=0xAAAAA [X86] Specify the physical address 4045 of the PIRQ table (normally generated 4046 by the BIOS) if it is outside the 4047 F0000h-100000h range. 4048 lastbus=N [X86] Scan all buses thru bus #N. Can be 4049 useful if the kernel is unable to find your 4050 secondary buses and you want to tell it 4051 explicitly which ones they are. 4052 assign-busses [X86] Always assign all PCI bus 4053 numbers ourselves, overriding 4054 whatever the firmware may have done. 4055 usepirqmask [X86] Honor the possible IRQ mask stored 4056 in the BIOS $PIR table. This is needed on 4057 some systems with broken BIOSes, notably 4058 some HP Pavilion N5400 and Omnibook XE3 4059 notebooks. This will have no effect if ACPI 4060 IRQ routing is enabled. 4061 noacpi [X86] Do not use ACPI for IRQ routing 4062 or for PCI scanning. 4063 use_crs [X86] Use PCI host bridge window information 4064 from ACPI. On BIOSes from 2008 or later, this 4065 is enabled by default. If you need to use this, 4066 please report a bug. 4067 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4068 If you need to use this, please report a bug. 4069 routeirq Do IRQ routing for all PCI devices. 4070 This is normally done in pci_enable_device(), 4071 so this option is a temporary workaround 4072 for broken drivers that don't call it. 4073 skip_isa_align [X86] do not align io start addr, so can 4074 handle more pci cards 4075 noearly [X86] Don't do any early type 1 scanning. 4076 This might help on some broken boards which 4077 machine check when some devices' config space 4078 is read. But various workarounds are disabled 4079 and some IOMMU drivers will not work. 4080 bfsort Sort PCI devices into breadth-first order. 4081 This sorting is done to get a device 4082 order compatible with older (<= 2.4) kernels. 4083 nobfsort Don't sort PCI devices into breadth-first order. 4084 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4085 tuning and use the BIOS-configured MPS defaults. 4086 pcie_bus_safe Set every device's MPS to the largest value 4087 supported by all devices below the root complex. 4088 pcie_bus_perf Set device MPS to the largest allowable MPS 4089 based on its parent bus. Also set MRRS (Max 4090 Read Request Size) to the largest supported 4091 value (no larger than the MPS that the device 4092 or bus can support) for best performance. 4093 pcie_bus_peer2peer Set every device's MPS to 128B, which 4094 every device is guaranteed to support. This 4095 configuration allows peer-to-peer DMA between 4096 any pair of devices, possibly at the cost of 4097 reduced performance. This also guarantees 4098 that hot-added devices will work. 4099 cbiosize=nn[KMG] The fixed amount of bus space which is 4100 reserved for the CardBus bridge's IO window. 4101 The default value is 256 bytes. 4102 cbmemsize=nn[KMG] The fixed amount of bus space which is 4103 reserved for the CardBus bridge's memory 4104 window. The default value is 64 megabytes. 4105 resource_alignment= 4106 Format: 4107 [<order of align>@]<pci_dev>[; ...] 4108 Specifies alignment and device to reassign 4109 aligned memory resources. How to 4110 specify the device is described above. 4111 If <order of align> is not specified, 4112 PAGE_SIZE is used as alignment. 4113 A PCI-PCI bridge can be specified if resource 4114 windows need to be expanded. 4115 To specify the alignment for several 4116 instances of a device, the PCI vendor, 4117 device, subvendor, and subdevice may be 4118 specified, e.g., 12@pci:8086:9c22:103c:198f 4119 for 4096-byte alignment. 4120 ecrc= Enable/disable PCIe ECRC (transaction layer 4121 end-to-end CRC checking). 4122 bios: Use BIOS/firmware settings. This is the 4123 the default. 4124 off: Turn ECRC off 4125 on: Turn ECRC on. 4126 hpiosize=nn[KMG] The fixed amount of bus space which is 4127 reserved for hotplug bridge's IO window. 4128 Default size is 256 bytes. 4129 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4130 reserved for hotplug bridge's MMIO window. 4131 Default size is 2 megabytes. 4132 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4133 reserved for hotplug bridge's MMIO_PREF window. 4134 Default size is 2 megabytes. 4135 hpmemsize=nn[KMG] The fixed amount of bus space which is 4136 reserved for hotplug bridge's MMIO and 4137 MMIO_PREF window. 4138 Default size is 2 megabytes. 4139 hpbussize=nn The minimum amount of additional bus numbers 4140 reserved for buses below a hotplug bridge. 4141 Default is 1. 4142 realloc= Enable/disable reallocating PCI bridge resources 4143 if allocations done by BIOS are too small to 4144 accommodate resources required by all child 4145 devices. 4146 off: Turn realloc off 4147 on: Turn realloc on 4148 realloc same as realloc=on 4149 noari do not use PCIe ARI. 4150 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 4151 do not use PCIe ATS (and IOMMU device IOTLB). 4152 pcie_scan_all Scan all possible PCIe devices. Otherwise we 4153 only look for one device below a PCIe downstream 4154 port. 4155 big_root_window Try to add a big 64bit memory window to the PCIe 4156 root complex on AMD CPUs. Some GFX hardware 4157 can resize a BAR to allow access to all VRAM. 4158 Adding the window is slightly risky (it may 4159 conflict with unreported devices), so this 4160 taints the kernel. 4161 disable_acs_redir=<pci_dev>[; ...] 4162 Specify one or more PCI devices (in the format 4163 specified above) separated by semicolons. 4164 Each device specified will have the PCI ACS 4165 redirect capabilities forced off which will 4166 allow P2P traffic between devices through 4167 bridges without forcing it upstream. Note: 4168 this removes isolation between devices and 4169 may put more devices in an IOMMU group. 4170 force_floating [S390] Force usage of floating interrupts. 4171 nomio [S390] Do not use MIO instructions. 4172 norid [S390] ignore the RID field and force use of 4173 one PCI domain per PCI function 4174 4175 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 4176 Management. 4177 off Disable ASPM. 4178 force Enable ASPM even on devices that claim not to support it. 4179 WARNING: Forcing ASPM on may cause system lockups. 4180 4181 pcie_ports= [PCIE] PCIe port services handling: 4182 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 4183 even if the platform doesn't give the OS permission to 4184 use them. This may cause conflicts if the platform 4185 also tries to use these services. 4186 dpc-native Use native PCIe service for DPC only. May 4187 cause conflicts if firmware uses AER or DPC. 4188 compat Disable native PCIe services (PME, AER, DPC, PCIe 4189 hotplug). 4190 4191 pcie_port_pm= [PCIE] PCIe port power management handling: 4192 off Disable power management of all PCIe ports 4193 force Forcibly enable power management of all PCIe ports 4194 4195 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 4196 nomsi Do not use MSI for native PCIe PME signaling (this makes 4197 all PCIe root ports use INTx for all services). 4198 4199 pcmv= [HW,PCMCIA] BadgePAD 4 4200 4201 pd_ignore_unused 4202 [PM] 4203 Keep all power-domains already enabled by bootloader on, 4204 even if no driver has claimed them. This is useful 4205 for debug and development, but should not be 4206 needed on a platform with proper driver support. 4207 4208 pd. [PARIDE] 4209 See Documentation/admin-guide/blockdev/paride.rst. 4210 4211 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 4212 boot time. 4213 Format: { 0 | 1 } 4214 See arch/parisc/kernel/pdc_chassis.c 4215 4216 percpu_alloc= Select which percpu first chunk allocator to use. 4217 Currently supported values are "embed" and "page". 4218 Archs may support subset or none of the selections. 4219 See comments in mm/percpu.c for details on each 4220 allocator. This parameter is primarily for debugging 4221 and performance comparison. 4222 4223 pf. [PARIDE] 4224 See Documentation/admin-guide/blockdev/paride.rst. 4225 4226 pg. [PARIDE] 4227 See Documentation/admin-guide/blockdev/paride.rst. 4228 4229 pirq= [SMP,APIC] Manual mp-table setup 4230 See Documentation/x86/i386/IO-APIC.rst. 4231 4232 plip= [PPT,NET] Parallel port network link 4233 Format: { parport<nr> | timid | 0 } 4234 See also Documentation/admin-guide/parport.rst. 4235 4236 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4237 Override pmtimer IOPort with a hex value. 4238 e.g. pmtmr=0x508 4239 4240 pmu_override= [PPC] Override the PMU. 4241 This option takes over the PMU facility, so it is no 4242 longer usable by perf. Setting this option starts the 4243 PMU counters by setting MMCR0 to 0 (the FC bit is 4244 cleared). If a number is given, then MMCR1 is set to 4245 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 4246 remains 0. 4247 4248 pm_debug_messages [SUSPEND,KNL] 4249 Enable suspend/resume debug messages during boot up. 4250 4251 pnp.debug=1 [PNP] 4252 Enable PNP debug messages (depends on the 4253 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 4254 via /sys/module/pnp/parameters/debug. We always show 4255 current resource usage; turning this on also shows 4256 possible settings and some assignment information. 4257 4258 pnpacpi= [ACPI] 4259 { off } 4260 4261 pnpbios= [ISAPNP] 4262 { on | off | curr | res | no-curr | no-res } 4263 4264 pnp_reserve_irq= 4265 [ISAPNP] Exclude IRQs for the autoconfiguration 4266 4267 pnp_reserve_dma= 4268 [ISAPNP] Exclude DMAs for the autoconfiguration 4269 4270 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 4271 Ranges are in pairs (I/O port base and size). 4272 4273 pnp_reserve_mem= 4274 [ISAPNP] Exclude memory regions for the 4275 autoconfiguration. 4276 Ranges are in pairs (memory base and size). 4277 4278 ports= [IP_VS_FTP] IPVS ftp helper module 4279 Default is 21. 4280 Up to 8 (IP_VS_APP_MAX_PORTS) ports 4281 may be specified. 4282 Format: <port>,<port>.... 4283 4284 powersave=off [PPC] This option disables power saving features. 4285 It specifically disables cpuidle and sets the 4286 platform machine description specific power_save 4287 function to NULL. On Idle the CPU just reduces 4288 execution priority. 4289 4290 ppc_strict_facility_enable 4291 [PPC] This option catches any kernel floating point, 4292 Altivec, VSX and SPE outside of regions specifically 4293 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 4294 There is some performance impact when enabling this. 4295 4296 ppc_tm= [PPC] 4297 Format: {"off"} 4298 Disable Hardware Transactional Memory 4299 4300 preempt= [KNL] 4301 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 4302 none - Limited to cond_resched() calls 4303 voluntary - Limited to cond_resched() and might_sleep() calls 4304 full - Any section that isn't explicitly preempt disabled 4305 can be preempted anytime. 4306 4307 print-fatal-signals= 4308 [KNL] debug: print fatal signals 4309 4310 If enabled, warn about various signal handling 4311 related application anomalies: too many signals, 4312 too many POSIX.1 timers, fatal signals causing a 4313 coredump - etc. 4314 4315 If you hit the warning due to signal overflow, 4316 you might want to try "ulimit -i unlimited". 4317 4318 default: off. 4319 4320 printk.always_kmsg_dump= 4321 Trigger kmsg_dump for cases other than kernel oops or 4322 panics 4323 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4324 default: disabled 4325 4326 printk.console_no_auto_verbose= 4327 Disable console loglevel raise on oops, panic 4328 or lockdep-detected issues (only if lock debug is on). 4329 With an exception to setups with low baudrate on 4330 serial console, keeping this 0 is a good choice 4331 in order to provide more debug information. 4332 Format: <bool> 4333 default: 0 (auto_verbose is enabled) 4334 4335 printk.devkmsg={on,off,ratelimit} 4336 Control writing to /dev/kmsg. 4337 on - unlimited logging to /dev/kmsg from userspace 4338 off - logging to /dev/kmsg disabled 4339 ratelimit - ratelimit the logging 4340 Default: ratelimit 4341 4342 printk.time= Show timing data prefixed to each printk message line 4343 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4344 4345 processor.max_cstate= [HW,ACPI] 4346 Limit processor to maximum C-state 4347 max_cstate=9 overrides any DMI blacklist limit. 4348 4349 processor.nocst [HW,ACPI] 4350 Ignore the _CST method to determine C-states, 4351 instead using the legacy FADT method 4352 4353 profile= [KNL] Enable kernel profiling via /proc/profile 4354 Format: [<profiletype>,]<number> 4355 Param: <profiletype>: "schedule", "sleep", or "kvm" 4356 [defaults to kernel profiling] 4357 Param: "schedule" - profile schedule points. 4358 Param: "sleep" - profile D-state sleeping (millisecs). 4359 Requires CONFIG_SCHEDSTATS 4360 Param: "kvm" - profile VM exits. 4361 Param: <number> - step/bucket size as a power of 2 for 4362 statistical time based profiling. 4363 4364 prompt_ramdisk= [RAM] [Deprecated] 4365 4366 prot_virt= [S390] enable hosting protected virtual machines 4367 isolated from the hypervisor (if hardware supports 4368 that). 4369 Format: <bool> 4370 4371 psi= [KNL] Enable or disable pressure stall information 4372 tracking. 4373 Format: <bool> 4374 4375 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4376 probe for; one of (bare|imps|exps|lifebook|any). 4377 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4378 per second. 4379 psmouse.resetafter= [HW,MOUSE] 4380 Try to reset the device after so many bad packets 4381 (0 = never). 4382 psmouse.resolution= 4383 [HW,MOUSE] Set desired mouse resolution, in dpi. 4384 psmouse.smartscroll= 4385 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4386 0 = disabled, 1 = enabled (default). 4387 4388 pstore.backend= Specify the name of the pstore backend to use 4389 4390 pt. [PARIDE] 4391 See Documentation/admin-guide/blockdev/paride.rst. 4392 4393 pti= [X86-64] Control Page Table Isolation of user and 4394 kernel address spaces. Disabling this feature 4395 removes hardening, but improves performance of 4396 system calls and interrupts. 4397 4398 on - unconditionally enable 4399 off - unconditionally disable 4400 auto - kernel detects whether your CPU model is 4401 vulnerable to issues that PTI mitigates 4402 4403 Not specifying this option is equivalent to pti=auto. 4404 4405 nopti [X86-64] 4406 Equivalent to pti=off 4407 4408 pty.legacy_count= 4409 [KNL] Number of legacy pty's. Overwrites compiled-in 4410 default number. 4411 4412 quiet [KNL] Disable most log messages 4413 4414 r128= [HW,DRM] 4415 4416 raid= [HW,RAID] 4417 See Documentation/admin-guide/md.rst. 4418 4419 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4420 See Documentation/admin-guide/blockdev/ramdisk.rst. 4421 4422 ramdisk_start= [RAM] RAM disk image start address 4423 4424 random.trust_cpu={on,off} 4425 [KNL] Enable or disable trusting the use of the 4426 CPU's random number generator (if available) to 4427 fully seed the kernel's CRNG. Default is controlled 4428 by CONFIG_RANDOM_TRUST_CPU. 4429 4430 random.trust_bootloader={on,off} 4431 [KNL] Enable or disable trusting the use of a 4432 seed passed by the bootloader (if available) to 4433 fully seed the kernel's CRNG. Default is controlled 4434 by CONFIG_RANDOM_TRUST_BOOTLOADER. 4435 4436 randomize_kstack_offset= 4437 [KNL] Enable or disable kernel stack offset 4438 randomization, which provides roughly 5 bits of 4439 entropy, frustrating memory corruption attacks 4440 that depend on stack address determinism or 4441 cross-syscall address exposures. This is only 4442 available on architectures that have defined 4443 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 4444 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4445 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 4446 4447 ras=option[,option,...] [KNL] RAS-specific options 4448 4449 cec_disable [X86] 4450 Disable the Correctable Errors Collector, 4451 see CONFIG_RAS_CEC help text. 4452 4453 rcu_nocbs[=cpu-list] 4454 [KNL] The optional argument is a cpu list, 4455 as described above. 4456 4457 In kernels built with CONFIG_RCU_NOCB_CPU=y, 4458 enable the no-callback CPU mode, which prevents 4459 such CPUs' callbacks from being invoked in 4460 softirq context. Invocation of such CPUs' RCU 4461 callbacks will instead be offloaded to "rcuox/N" 4462 kthreads created for that purpose, where "x" is 4463 "p" for RCU-preempt, "s" for RCU-sched, and "g" 4464 for the kthreads that mediate grace periods; and 4465 "N" is the CPU number. This reduces OS jitter on 4466 the offloaded CPUs, which can be useful for HPC 4467 and real-time workloads. It can also improve 4468 energy efficiency for asymmetric multiprocessors. 4469 4470 If a cpulist is passed as an argument, the specified 4471 list of CPUs is set to no-callback mode from boot. 4472 4473 Otherwise, if the '=' sign and the cpulist 4474 arguments are omitted, no CPU will be set to 4475 no-callback mode from boot but the mode may be 4476 toggled at runtime via cpusets. 4477 4478 rcu_nocb_poll [KNL] 4479 Rather than requiring that offloaded CPUs 4480 (specified by rcu_nocbs= above) explicitly 4481 awaken the corresponding "rcuoN" kthreads, 4482 make these kthreads poll for callbacks. 4483 This improves the real-time response for the 4484 offloaded CPUs by relieving them of the need to 4485 wake up the corresponding kthread, but degrades 4486 energy efficiency by requiring that the kthreads 4487 periodically wake up to do the polling. 4488 4489 rcutree.blimit= [KNL] 4490 Set maximum number of finished RCU callbacks to 4491 process in one batch. 4492 4493 rcutree.dump_tree= [KNL] 4494 Dump the structure of the rcu_node combining tree 4495 out at early boot. This is used for diagnostic 4496 purposes, to verify correct tree setup. 4497 4498 rcutree.gp_cleanup_delay= [KNL] 4499 Set the number of jiffies to delay each step of 4500 RCU grace-period cleanup. 4501 4502 rcutree.gp_init_delay= [KNL] 4503 Set the number of jiffies to delay each step of 4504 RCU grace-period initialization. 4505 4506 rcutree.gp_preinit_delay= [KNL] 4507 Set the number of jiffies to delay each step of 4508 RCU grace-period pre-initialization, that is, 4509 the propagation of recent CPU-hotplug changes up 4510 the rcu_node combining tree. 4511 4512 rcutree.use_softirq= [KNL] 4513 If set to zero, move all RCU_SOFTIRQ processing to 4514 per-CPU rcuc kthreads. Defaults to a non-zero 4515 value, meaning that RCU_SOFTIRQ is used by default. 4516 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4517 4518 But note that CONFIG_PREEMPT_RT=y kernels disable 4519 this kernel boot parameter, forcibly setting it 4520 to zero. 4521 4522 rcutree.rcu_fanout_exact= [KNL] 4523 Disable autobalancing of the rcu_node combining 4524 tree. This is used by rcutorture, and might 4525 possibly be useful for architectures having high 4526 cache-to-cache transfer latencies. 4527 4528 rcutree.rcu_fanout_leaf= [KNL] 4529 Change the number of CPUs assigned to each 4530 leaf rcu_node structure. Useful for very 4531 large systems, which will choose the value 64, 4532 and for NUMA systems with large remote-access 4533 latencies, which will choose a value aligned 4534 with the appropriate hardware boundaries. 4535 4536 rcutree.rcu_min_cached_objs= [KNL] 4537 Minimum number of objects which are cached and 4538 maintained per one CPU. Object size is equal 4539 to PAGE_SIZE. The cache allows to reduce the 4540 pressure to page allocator, also it makes the 4541 whole algorithm to behave better in low memory 4542 condition. 4543 4544 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 4545 Set the page-cache refill delay (in milliseconds) 4546 in response to low-memory conditions. The range 4547 of permitted values is in the range 0:100000. 4548 4549 rcutree.jiffies_till_first_fqs= [KNL] 4550 Set delay from grace-period initialization to 4551 first attempt to force quiescent states. 4552 Units are jiffies, minimum value is zero, 4553 and maximum value is HZ. 4554 4555 rcutree.jiffies_till_next_fqs= [KNL] 4556 Set delay between subsequent attempts to force 4557 quiescent states. Units are jiffies, minimum 4558 value is one, and maximum value is HZ. 4559 4560 rcutree.jiffies_till_sched_qs= [KNL] 4561 Set required age in jiffies for a 4562 given grace period before RCU starts 4563 soliciting quiescent-state help from 4564 rcu_note_context_switch() and cond_resched(). 4565 If not specified, the kernel will calculate 4566 a value based on the most recent settings 4567 of rcutree.jiffies_till_first_fqs 4568 and rcutree.jiffies_till_next_fqs. 4569 This calculated value may be viewed in 4570 rcutree.jiffies_to_sched_qs. Any attempt to set 4571 rcutree.jiffies_to_sched_qs will be cheerfully 4572 overwritten. 4573 4574 rcutree.kthread_prio= [KNL,BOOT] 4575 Set the SCHED_FIFO priority of the RCU per-CPU 4576 kthreads (rcuc/N). This value is also used for 4577 the priority of the RCU boost threads (rcub/N) 4578 and for the RCU grace-period kthreads (rcu_bh, 4579 rcu_preempt, and rcu_sched). If RCU_BOOST is 4580 set, valid values are 1-99 and the default is 1 4581 (the least-favored priority). Otherwise, when 4582 RCU_BOOST is not set, valid values are 0-99 and 4583 the default is zero (non-realtime operation). 4584 When RCU_NOCB_CPU is set, also adjust the 4585 priority of NOCB callback kthreads. 4586 4587 rcutree.rcu_nocb_gp_stride= [KNL] 4588 Set the number of NOCB callback kthreads in 4589 each group, which defaults to the square root 4590 of the number of CPUs. Larger numbers reduce 4591 the wakeup overhead on the global grace-period 4592 kthread, but increases that same overhead on 4593 each group's NOCB grace-period kthread. 4594 4595 rcutree.qhimark= [KNL] 4596 Set threshold of queued RCU callbacks beyond which 4597 batch limiting is disabled. 4598 4599 rcutree.qlowmark= [KNL] 4600 Set threshold of queued RCU callbacks below which 4601 batch limiting is re-enabled. 4602 4603 rcutree.qovld= [KNL] 4604 Set threshold of queued RCU callbacks beyond which 4605 RCU's force-quiescent-state scan will aggressively 4606 enlist help from cond_resched() and sched IPIs to 4607 help CPUs more quickly reach quiescent states. 4608 Set to less than zero to make this be set based 4609 on rcutree.qhimark at boot time and to zero to 4610 disable more aggressive help enlistment. 4611 4612 rcutree.rcu_kick_kthreads= [KNL] 4613 Cause the grace-period kthread to get an extra 4614 wake_up() if it sleeps three times longer than 4615 it should at force-quiescent-state time. 4616 This wake_up() will be accompanied by a 4617 WARN_ONCE() splat and an ftrace_dump(). 4618 4619 rcutree.rcu_unlock_delay= [KNL] 4620 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4621 this specifies an rcu_read_unlock()-time delay 4622 in microseconds. This defaults to zero. 4623 Larger delays increase the probability of 4624 catching RCU pointer leaks, that is, buggy use 4625 of RCU-protected pointers after the relevant 4626 rcu_read_unlock() has completed. 4627 4628 rcutree.sysrq_rcu= [KNL] 4629 Commandeer a sysrq key to dump out Tree RCU's 4630 rcu_node tree with an eye towards determining 4631 why a new grace period has not yet started. 4632 4633 rcuscale.gp_async= [KNL] 4634 Measure performance of asynchronous 4635 grace-period primitives such as call_rcu(). 4636 4637 rcuscale.gp_async_max= [KNL] 4638 Specify the maximum number of outstanding 4639 callbacks per writer thread. When a writer 4640 thread exceeds this limit, it invokes the 4641 corresponding flavor of rcu_barrier() to allow 4642 previously posted callbacks to drain. 4643 4644 rcuscale.gp_exp= [KNL] 4645 Measure performance of expedited synchronous 4646 grace-period primitives. 4647 4648 rcuscale.holdoff= [KNL] 4649 Set test-start holdoff period. The purpose of 4650 this parameter is to delay the start of the 4651 test until boot completes in order to avoid 4652 interference. 4653 4654 rcuscale.kfree_rcu_test= [KNL] 4655 Set to measure performance of kfree_rcu() flooding. 4656 4657 rcuscale.kfree_rcu_test_double= [KNL] 4658 Test the double-argument variant of kfree_rcu(). 4659 If this parameter has the same value as 4660 rcuscale.kfree_rcu_test_single, both the single- 4661 and double-argument variants are tested. 4662 4663 rcuscale.kfree_rcu_test_single= [KNL] 4664 Test the single-argument variant of kfree_rcu(). 4665 If this parameter has the same value as 4666 rcuscale.kfree_rcu_test_double, both the single- 4667 and double-argument variants are tested. 4668 4669 rcuscale.kfree_nthreads= [KNL] 4670 The number of threads running loops of kfree_rcu(). 4671 4672 rcuscale.kfree_alloc_num= [KNL] 4673 Number of allocations and frees done in an iteration. 4674 4675 rcuscale.kfree_loops= [KNL] 4676 Number of loops doing rcuscale.kfree_alloc_num number 4677 of allocations and frees. 4678 4679 rcuscale.nreaders= [KNL] 4680 Set number of RCU readers. The value -1 selects 4681 N, where N is the number of CPUs. A value 4682 "n" less than -1 selects N-n+1, where N is again 4683 the number of CPUs. For example, -2 selects N 4684 (the number of CPUs), -3 selects N+1, and so on. 4685 A value of "n" less than or equal to -N selects 4686 a single reader. 4687 4688 rcuscale.nwriters= [KNL] 4689 Set number of RCU writers. The values operate 4690 the same as for rcuscale.nreaders. 4691 N, where N is the number of CPUs 4692 4693 rcuscale.perf_type= [KNL] 4694 Specify the RCU implementation to test. 4695 4696 rcuscale.shutdown= [KNL] 4697 Shut the system down after performance tests 4698 complete. This is useful for hands-off automated 4699 testing. 4700 4701 rcuscale.verbose= [KNL] 4702 Enable additional printk() statements. 4703 4704 rcuscale.writer_holdoff= [KNL] 4705 Write-side holdoff between grace periods, 4706 in microseconds. The default of zero says 4707 no holdoff. 4708 4709 rcutorture.fqs_duration= [KNL] 4710 Set duration of force_quiescent_state bursts 4711 in microseconds. 4712 4713 rcutorture.fqs_holdoff= [KNL] 4714 Set holdoff time within force_quiescent_state bursts 4715 in microseconds. 4716 4717 rcutorture.fqs_stutter= [KNL] 4718 Set wait time between force_quiescent_state bursts 4719 in seconds. 4720 4721 rcutorture.fwd_progress= [KNL] 4722 Specifies the number of kthreads to be used 4723 for RCU grace-period forward-progress testing 4724 for the types of RCU supporting this notion. 4725 Defaults to 1 kthread, values less than zero or 4726 greater than the number of CPUs cause the number 4727 of CPUs to be used. 4728 4729 rcutorture.fwd_progress_div= [KNL] 4730 Specify the fraction of a CPU-stall-warning 4731 period to do tight-loop forward-progress testing. 4732 4733 rcutorture.fwd_progress_holdoff= [KNL] 4734 Number of seconds to wait between successive 4735 forward-progress tests. 4736 4737 rcutorture.fwd_progress_need_resched= [KNL] 4738 Enclose cond_resched() calls within checks for 4739 need_resched() during tight-loop forward-progress 4740 testing. 4741 4742 rcutorture.gp_cond= [KNL] 4743 Use conditional/asynchronous update-side 4744 primitives, if available. 4745 4746 rcutorture.gp_exp= [KNL] 4747 Use expedited update-side primitives, if available. 4748 4749 rcutorture.gp_normal= [KNL] 4750 Use normal (non-expedited) asynchronous 4751 update-side primitives, if available. 4752 4753 rcutorture.gp_sync= [KNL] 4754 Use normal (non-expedited) synchronous 4755 update-side primitives, if available. If all 4756 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4757 rcutorture.gp_normal=, and rcutorture.gp_sync= 4758 are zero, rcutorture acts as if is interpreted 4759 they are all non-zero. 4760 4761 rcutorture.irqreader= [KNL] 4762 Run RCU readers from irq handlers, or, more 4763 accurately, from a timer handler. Not all RCU 4764 flavors take kindly to this sort of thing. 4765 4766 rcutorture.leakpointer= [KNL] 4767 Leak an RCU-protected pointer out of the reader. 4768 This can of course result in splats, and is 4769 intended to test the ability of things like 4770 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4771 such leaks. 4772 4773 rcutorture.n_barrier_cbs= [KNL] 4774 Set callbacks/threads for rcu_barrier() testing. 4775 4776 rcutorture.nfakewriters= [KNL] 4777 Set number of concurrent RCU writers. These just 4778 stress RCU, they don't participate in the actual 4779 test, hence the "fake". 4780 4781 rcutorture.nocbs_nthreads= [KNL] 4782 Set number of RCU callback-offload togglers. 4783 Zero (the default) disables toggling. 4784 4785 rcutorture.nocbs_toggle= [KNL] 4786 Set the delay in milliseconds between successive 4787 callback-offload toggling attempts. 4788 4789 rcutorture.nreaders= [KNL] 4790 Set number of RCU readers. The value -1 selects 4791 N-1, where N is the number of CPUs. A value 4792 "n" less than -1 selects N-n-2, where N is again 4793 the number of CPUs. For example, -2 selects N 4794 (the number of CPUs), -3 selects N+1, and so on. 4795 4796 rcutorture.object_debug= [KNL] 4797 Enable debug-object double-call_rcu() testing. 4798 4799 rcutorture.onoff_holdoff= [KNL] 4800 Set time (s) after boot for CPU-hotplug testing. 4801 4802 rcutorture.onoff_interval= [KNL] 4803 Set time (jiffies) between CPU-hotplug operations, 4804 or zero to disable CPU-hotplug testing. 4805 4806 rcutorture.read_exit= [KNL] 4807 Set the number of read-then-exit kthreads used 4808 to test the interaction of RCU updaters and 4809 task-exit processing. 4810 4811 rcutorture.read_exit_burst= [KNL] 4812 The number of times in a given read-then-exit 4813 episode that a set of read-then-exit kthreads 4814 is spawned. 4815 4816 rcutorture.read_exit_delay= [KNL] 4817 The delay, in seconds, between successive 4818 read-then-exit testing episodes. 4819 4820 rcutorture.shuffle_interval= [KNL] 4821 Set task-shuffle interval (s). Shuffling tasks 4822 allows some CPUs to go into dyntick-idle mode 4823 during the rcutorture test. 4824 4825 rcutorture.shutdown_secs= [KNL] 4826 Set time (s) after boot system shutdown. This 4827 is useful for hands-off automated testing. 4828 4829 rcutorture.stall_cpu= [KNL] 4830 Duration of CPU stall (s) to test RCU CPU stall 4831 warnings, zero to disable. 4832 4833 rcutorture.stall_cpu_block= [KNL] 4834 Sleep while stalling if set. This will result 4835 in warnings from preemptible RCU in addition 4836 to any other stall-related activity. 4837 4838 rcutorture.stall_cpu_holdoff= [KNL] 4839 Time to wait (s) after boot before inducing stall. 4840 4841 rcutorture.stall_cpu_irqsoff= [KNL] 4842 Disable interrupts while stalling if set. 4843 4844 rcutorture.stall_gp_kthread= [KNL] 4845 Duration (s) of forced sleep within RCU 4846 grace-period kthread to test RCU CPU stall 4847 warnings, zero to disable. If both stall_cpu 4848 and stall_gp_kthread are specified, the 4849 kthread is starved first, then the CPU. 4850 4851 rcutorture.stat_interval= [KNL] 4852 Time (s) between statistics printk()s. 4853 4854 rcutorture.stutter= [KNL] 4855 Time (s) to stutter testing, for example, specifying 4856 five seconds causes the test to run for five seconds, 4857 wait for five seconds, and so on. This tests RCU's 4858 ability to transition abruptly to and from idle. 4859 4860 rcutorture.test_boost= [KNL] 4861 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4862 "Maybe" means test if the RCU implementation 4863 under test support RCU priority boosting. 4864 4865 rcutorture.test_boost_duration= [KNL] 4866 Duration (s) of each individual boost test. 4867 4868 rcutorture.test_boost_interval= [KNL] 4869 Interval (s) between each boost test. 4870 4871 rcutorture.test_no_idle_hz= [KNL] 4872 Test RCU's dyntick-idle handling. See also the 4873 rcutorture.shuffle_interval parameter. 4874 4875 rcutorture.torture_type= [KNL] 4876 Specify the RCU implementation to test. 4877 4878 rcutorture.verbose= [KNL] 4879 Enable additional printk() statements. 4880 4881 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4882 Dump ftrace buffer after reporting RCU CPU 4883 stall warning. 4884 4885 rcupdate.rcu_cpu_stall_suppress= [KNL] 4886 Suppress RCU CPU stall warning messages. 4887 4888 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4889 Suppress RCU CPU stall warning messages and 4890 rcutorture writer stall warnings that occur 4891 during early boot, that is, during the time 4892 before the init task is spawned. 4893 4894 rcupdate.rcu_cpu_stall_timeout= [KNL] 4895 Set timeout for RCU CPU stall warning messages. 4896 4897 rcupdate.rcu_expedited= [KNL] 4898 Use expedited grace-period primitives, for 4899 example, synchronize_rcu_expedited() instead 4900 of synchronize_rcu(). This reduces latency, 4901 but can increase CPU utilization, degrade 4902 real-time latency, and degrade energy efficiency. 4903 No effect on CONFIG_TINY_RCU kernels. 4904 4905 rcupdate.rcu_normal= [KNL] 4906 Use only normal grace-period primitives, 4907 for example, synchronize_rcu() instead of 4908 synchronize_rcu_expedited(). This improves 4909 real-time latency, CPU utilization, and 4910 energy efficiency, but can expose users to 4911 increased grace-period latency. This parameter 4912 overrides rcupdate.rcu_expedited. No effect on 4913 CONFIG_TINY_RCU kernels. 4914 4915 rcupdate.rcu_normal_after_boot= [KNL] 4916 Once boot has completed (that is, after 4917 rcu_end_inkernel_boot() has been invoked), use 4918 only normal grace-period primitives. No effect 4919 on CONFIG_TINY_RCU kernels. 4920 4921 But note that CONFIG_PREEMPT_RT=y kernels enables 4922 this kernel boot parameter, forcibly setting 4923 it to the value one, that is, converting any 4924 post-boot attempt at an expedited RCU grace 4925 period to instead use normal non-expedited 4926 grace-period processing. 4927 4928 rcupdate.rcu_task_collapse_lim= [KNL] 4929 Set the maximum number of callbacks present 4930 at the beginning of a grace period that allows 4931 the RCU Tasks flavors to collapse back to using 4932 a single callback queue. This switching only 4933 occurs when rcupdate.rcu_task_enqueue_lim is 4934 set to the default value of -1. 4935 4936 rcupdate.rcu_task_contend_lim= [KNL] 4937 Set the minimum number of callback-queuing-time 4938 lock-contention events per jiffy required to 4939 cause the RCU Tasks flavors to switch to per-CPU 4940 callback queuing. This switching only occurs 4941 when rcupdate.rcu_task_enqueue_lim is set to 4942 the default value of -1. 4943 4944 rcupdate.rcu_task_enqueue_lim= [KNL] 4945 Set the number of callback queues to use for the 4946 RCU Tasks family of RCU flavors. The default 4947 of -1 allows this to be automatically (and 4948 dynamically) adjusted. This parameter is intended 4949 for use in testing. 4950 4951 rcupdate.rcu_task_ipi_delay= [KNL] 4952 Set time in jiffies during which RCU tasks will 4953 avoid sending IPIs, starting with the beginning 4954 of a given grace period. Setting a large 4955 number avoids disturbing real-time workloads, 4956 but lengthens grace periods. 4957 4958 rcupdate.rcu_task_stall_timeout= [KNL] 4959 Set timeout in jiffies for RCU task stall warning 4960 messages. Disable with a value less than or equal 4961 to zero. 4962 4963 rcupdate.rcu_self_test= [KNL] 4964 Run the RCU early boot self tests 4965 4966 rdinit= [KNL] 4967 Format: <full_path> 4968 Run specified binary instead of /init from the ramdisk, 4969 used for early userspace startup. See initrd. 4970 4971 rdrand= [X86] 4972 force - Override the decision by the kernel to hide the 4973 advertisement of RDRAND support (this affects 4974 certain AMD processors because of buggy BIOS 4975 support, specifically around the suspend/resume 4976 path). 4977 4978 rdt= [HW,X86,RDT] 4979 Turn on/off individual RDT features. List is: 4980 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4981 mba. 4982 E.g. to turn on cmt and turn off mba use: 4983 rdt=cmt,!mba 4984 4985 reboot= [KNL] 4986 Format (x86 or x86_64): 4987 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 4988 [[,]s[mp]#### \ 4989 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4990 [[,]f[orce] 4991 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4992 (prefix with 'panic_' to set mode for panic 4993 reboot only), 4994 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4995 reboot_force is either force or not specified, 4996 reboot_cpu is s[mp]#### with #### being the processor 4997 to be used for rebooting. 4998 4999 refscale.holdoff= [KNL] 5000 Set test-start holdoff period. The purpose of 5001 this parameter is to delay the start of the 5002 test until boot completes in order to avoid 5003 interference. 5004 5005 refscale.loops= [KNL] 5006 Set the number of loops over the synchronization 5007 primitive under test. Increasing this number 5008 reduces noise due to loop start/end overhead, 5009 but the default has already reduced the per-pass 5010 noise to a handful of picoseconds on ca. 2020 5011 x86 laptops. 5012 5013 refscale.nreaders= [KNL] 5014 Set number of readers. The default value of -1 5015 selects N, where N is roughly 75% of the number 5016 of CPUs. A value of zero is an interesting choice. 5017 5018 refscale.nruns= [KNL] 5019 Set number of runs, each of which is dumped onto 5020 the console log. 5021 5022 refscale.readdelay= [KNL] 5023 Set the read-side critical-section duration, 5024 measured in microseconds. 5025 5026 refscale.scale_type= [KNL] 5027 Specify the read-protection implementation to test. 5028 5029 refscale.shutdown= [KNL] 5030 Shut down the system at the end of the performance 5031 test. This defaults to 1 (shut it down) when 5032 refscale is built into the kernel and to 0 (leave 5033 it running) when refscale is built as a module. 5034 5035 refscale.verbose= [KNL] 5036 Enable additional printk() statements. 5037 5038 refscale.verbose_batched= [KNL] 5039 Batch the additional printk() statements. If zero 5040 (the default) or negative, print everything. Otherwise, 5041 print every Nth verbose statement, where N is the value 5042 specified. 5043 5044 relax_domain_level= 5045 [KNL, SMP] Set scheduler's default relax_domain_level. 5046 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 5047 5048 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 5049 Format: <base1>,<size1>[,<base2>,<size2>,...] 5050 Reserve I/O ports or memory so the kernel won't use 5051 them. If <base> is less than 0x10000, the region 5052 is assumed to be I/O ports; otherwise it is memory. 5053 5054 reservetop= [X86-32] 5055 Format: nn[KMG] 5056 Reserves a hole at the top of the kernel virtual 5057 address space. 5058 5059 reset_devices [KNL] Force drivers to reset the underlying device 5060 during initialization. 5061 5062 resume= [SWSUSP] 5063 Specify the partition device for software suspend 5064 Format: 5065 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 5066 5067 resume_offset= [SWSUSP] 5068 Specify the offset from the beginning of the partition 5069 given by "resume=" at which the swap header is located, 5070 in <PAGE_SIZE> units (needed only for swap files). 5071 See Documentation/power/swsusp-and-swap-files.rst 5072 5073 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 5074 read the resume files 5075 5076 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 5077 Useful for devices that are detected asynchronously 5078 (e.g. USB and MMC devices). 5079 5080 hibernate= [HIBERNATION] 5081 noresume Don't check if there's a hibernation image 5082 present during boot. 5083 nocompress Don't compress/decompress hibernation images. 5084 no Disable hibernation and resume. 5085 protect_image Turn on image protection during restoration 5086 (that will set all pages holding image data 5087 during restoration read-only). 5088 5089 retain_initrd [RAM] Keep initrd memory after extraction 5090 5091 rfkill.default_state= 5092 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 5093 etc. communication is blocked by default. 5094 1 Unblocked. 5095 5096 rfkill.master_switch_mode= 5097 0 The "airplane mode" button does nothing. 5098 1 The "airplane mode" button toggles between everything 5099 blocked and the previous configuration. 5100 2 The "airplane mode" button toggles between everything 5101 blocked and everything unblocked. 5102 5103 rhash_entries= [KNL,NET] 5104 Set number of hash buckets for route cache 5105 5106 ring3mwait=disable 5107 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 5108 CPUs. 5109 5110 ro [KNL] Mount root device read-only on boot 5111 5112 rodata= [KNL] 5113 on Mark read-only kernel memory as read-only (default). 5114 off Leave read-only kernel memory writable for debugging. 5115 5116 rockchip.usb_uart 5117 Enable the uart passthrough on the designated usb port 5118 on Rockchip SoCs. When active, the signals of the 5119 debug-uart get routed to the D+ and D- pins of the usb 5120 port and the regular usb controller gets disabled. 5121 5122 root= [KNL] Root filesystem 5123 See name_to_dev_t comment in init/do_mounts.c. 5124 5125 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 5126 mount the root filesystem 5127 5128 rootflags= [KNL] Set root filesystem mount option string 5129 5130 rootfstype= [KNL] Set root filesystem type 5131 5132 rootwait [KNL] Wait (indefinitely) for root device to show up. 5133 Useful for devices that are detected asynchronously 5134 (e.g. USB and MMC devices). 5135 5136 rproc_mem=nn[KMG][@address] 5137 [KNL,ARM,CMA] Remoteproc physical memory block. 5138 Memory area to be used by remote processor image, 5139 managed by CMA. 5140 5141 rw [KNL] Mount root device read-write on boot 5142 5143 S [KNL] Run init in single mode 5144 5145 s390_iommu= [HW,S390] 5146 Set s390 IOTLB flushing mode 5147 strict 5148 With strict flushing every unmap operation will result in 5149 an IOTLB flush. Default is lazy flushing before reuse, 5150 which is faster. 5151 5152 s390_iommu_aperture= [KNL,S390] 5153 Specifies the size of the per device DMA address space 5154 accessible through the DMA and IOMMU APIs as a decimal 5155 factor of the size of main memory. 5156 The default is 1 meaning that one can concurrently use 5157 as many DMA addresses as physical memory is installed, 5158 if supported by hardware, and thus map all of memory 5159 once. With a value of 2 one can map all of memory twice 5160 and so on. As a special case a factor of 0 imposes no 5161 restrictions other than those given by hardware at the 5162 cost of significant additional memory use for tables. 5163 5164 sa1100ir [NET] 5165 See drivers/net/irda/sa1100_ir.c. 5166 5167 sched_verbose [KNL] Enables verbose scheduler debug messages. 5168 5169 schedstats= [KNL,X86] Enable or disable scheduled statistics. 5170 Allowed values are enable and disable. This feature 5171 incurs a small amount of overhead in the scheduler 5172 but is useful for debugging and performance tuning. 5173 5174 sched_thermal_decay_shift= 5175 [KNL, SMP] Set a decay shift for scheduler thermal 5176 pressure signal. Thermal pressure signal follows the 5177 default decay period of other scheduler pelt 5178 signals(usually 32 ms but configurable). Setting 5179 sched_thermal_decay_shift will left shift the decay 5180 period for the thermal pressure signal by the shift 5181 value. 5182 i.e. with the default pelt decay period of 32 ms 5183 sched_thermal_decay_shift thermal pressure decay pr 5184 1 64 ms 5185 2 128 ms 5186 and so on. 5187 Format: integer between 0 and 10 5188 Default is 0. 5189 5190 scftorture.holdoff= [KNL] 5191 Number of seconds to hold off before starting 5192 test. Defaults to zero for module insertion and 5193 to 10 seconds for built-in smp_call_function() 5194 tests. 5195 5196 scftorture.longwait= [KNL] 5197 Request ridiculously long waits randomly selected 5198 up to the chosen limit in seconds. Zero (the 5199 default) disables this feature. Please note 5200 that requesting even small non-zero numbers of 5201 seconds can result in RCU CPU stall warnings, 5202 softlockup complaints, and so on. 5203 5204 scftorture.nthreads= [KNL] 5205 Number of kthreads to spawn to invoke the 5206 smp_call_function() family of functions. 5207 The default of -1 specifies a number of kthreads 5208 equal to the number of CPUs. 5209 5210 scftorture.onoff_holdoff= [KNL] 5211 Number seconds to wait after the start of the 5212 test before initiating CPU-hotplug operations. 5213 5214 scftorture.onoff_interval= [KNL] 5215 Number seconds to wait between successive 5216 CPU-hotplug operations. Specifying zero (which 5217 is the default) disables CPU-hotplug operations. 5218 5219 scftorture.shutdown_secs= [KNL] 5220 The number of seconds following the start of the 5221 test after which to shut down the system. The 5222 default of zero avoids shutting down the system. 5223 Non-zero values are useful for automated tests. 5224 5225 scftorture.stat_interval= [KNL] 5226 The number of seconds between outputting the 5227 current test statistics to the console. A value 5228 of zero disables statistics output. 5229 5230 scftorture.stutter_cpus= [KNL] 5231 The number of jiffies to wait between each change 5232 to the set of CPUs under test. 5233 5234 scftorture.use_cpus_read_lock= [KNL] 5235 Use use_cpus_read_lock() instead of the default 5236 preempt_disable() to disable CPU hotplug 5237 while invoking one of the smp_call_function*() 5238 functions. 5239 5240 scftorture.verbose= [KNL] 5241 Enable additional printk() statements. 5242 5243 scftorture.weight_single= [KNL] 5244 The probability weighting to use for the 5245 smp_call_function_single() function with a zero 5246 "wait" parameter. A value of -1 selects the 5247 default if all other weights are -1. However, 5248 if at least one weight has some other value, a 5249 value of -1 will instead select a weight of zero. 5250 5251 scftorture.weight_single_wait= [KNL] 5252 The probability weighting to use for the 5253 smp_call_function_single() function with a 5254 non-zero "wait" parameter. See weight_single. 5255 5256 scftorture.weight_many= [KNL] 5257 The probability weighting to use for the 5258 smp_call_function_many() function with a zero 5259 "wait" parameter. See weight_single. 5260 Note well that setting a high probability for 5261 this weighting can place serious IPI load 5262 on the system. 5263 5264 scftorture.weight_many_wait= [KNL] 5265 The probability weighting to use for the 5266 smp_call_function_many() function with a 5267 non-zero "wait" parameter. See weight_single 5268 and weight_many. 5269 5270 scftorture.weight_all= [KNL] 5271 The probability weighting to use for the 5272 smp_call_function_all() function with a zero 5273 "wait" parameter. See weight_single and 5274 weight_many. 5275 5276 scftorture.weight_all_wait= [KNL] 5277 The probability weighting to use for the 5278 smp_call_function_all() function with a 5279 non-zero "wait" parameter. See weight_single 5280 and weight_many. 5281 5282 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 5283 xtime_lock contention on larger systems, and/or RCU lock 5284 contention on all systems with CONFIG_MAXSMP set. 5285 Format: { "0" | "1" } 5286 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 5287 1 -- enable. 5288 Note: increases power consumption, thus should only be 5289 enabled if running jitter sensitive (HPC/RT) workloads. 5290 5291 security= [SECURITY] Choose a legacy "major" security module to 5292 enable at boot. This has been deprecated by the 5293 "lsm=" parameter. 5294 5295 selinux= [SELINUX] Disable or enable SELinux at boot time. 5296 Format: { "0" | "1" } 5297 See security/selinux/Kconfig help text. 5298 0 -- disable. 5299 1 -- enable. 5300 Default value is 1. 5301 5302 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 5303 Format: { "0" | "1" } 5304 See security/apparmor/Kconfig help text 5305 0 -- disable. 5306 1 -- enable. 5307 Default value is set via kernel config option. 5308 5309 serialnumber [BUGS=X86-32] 5310 5311 shapers= [NET] 5312 Maximal number of shapers. 5313 5314 simeth= [IA-64] 5315 simscsi= 5316 5317 slram= [HW,MTD] 5318 5319 slab_merge [MM] 5320 Enable merging of slabs with similar size when the 5321 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 5322 5323 slab_nomerge [MM] 5324 Disable merging of slabs with similar size. May be 5325 necessary if there is some reason to distinguish 5326 allocs to different slabs, especially in hardened 5327 environments where the risk of heap overflows and 5328 layout control by attackers can usually be 5329 frustrated by disabling merging. This will reduce 5330 most of the exposure of a heap attack to a single 5331 cache (risks via metadata attacks are mostly 5332 unchanged). Debug options disable merging on their 5333 own. 5334 For more information see Documentation/vm/slub.rst. 5335 5336 slab_max_order= [MM, SLAB] 5337 Determines the maximum allowed order for slabs. 5338 A high setting may cause OOMs due to memory 5339 fragmentation. Defaults to 1 for systems with 5340 more than 32MB of RAM, 0 otherwise. 5341 5342 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 5343 Enabling slub_debug allows one to determine the 5344 culprit if slab objects become corrupted. Enabling 5345 slub_debug can create guard zones around objects and 5346 may poison objects when not in use. Also tracks the 5347 last alloc / free. For more information see 5348 Documentation/vm/slub.rst. 5349 5350 slub_max_order= [MM, SLUB] 5351 Determines the maximum allowed order for slabs. 5352 A high setting may cause OOMs due to memory 5353 fragmentation. For more information see 5354 Documentation/vm/slub.rst. 5355 5356 slub_min_objects= [MM, SLUB] 5357 The minimum number of objects per slab. SLUB will 5358 increase the slab order up to slub_max_order to 5359 generate a sufficiently large slab able to contain 5360 the number of objects indicated. The higher the number 5361 of objects the smaller the overhead of tracking slabs 5362 and the less frequently locks need to be acquired. 5363 For more information see Documentation/vm/slub.rst. 5364 5365 slub_min_order= [MM, SLUB] 5366 Determines the minimum page order for slabs. Must be 5367 lower than slub_max_order. 5368 For more information see Documentation/vm/slub.rst. 5369 5370 slub_merge [MM, SLUB] 5371 Same with slab_merge. 5372 5373 slub_nomerge [MM, SLUB] 5374 Same with slab_nomerge. This is supported for legacy. 5375 See slab_nomerge for more information. 5376 5377 smart2= [HW] 5378 Format: <io1>[,<io2>[,...,<io8>]] 5379 5380 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5381 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5382 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5383 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5384 smsc-ircc2.ircc_irq= [HW] IRQ line 5385 smsc-ircc2.ircc_dma= [HW] DMA channel 5386 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5387 0: Toshiba Satellite 1800 (GP data pin select) 5388 1: Fast pin select (default) 5389 2: ATC IRMode 5390 5391 smt [KNL,S390] Set the maximum number of threads (logical 5392 CPUs) to use per physical CPU on systems capable of 5393 symmetric multithreading (SMT). Will be capped to the 5394 actual hardware limit. 5395 Format: <integer> 5396 Default: -1 (no limit) 5397 5398 softlockup_panic= 5399 [KNL] Should the soft-lockup detector generate panics. 5400 Format: 0 | 1 5401 5402 A value of 1 instructs the soft-lockup detector 5403 to panic the machine when a soft-lockup occurs. It is 5404 also controlled by the kernel.softlockup_panic sysctl 5405 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5406 respective build-time switch to that functionality. 5407 5408 softlockup_all_cpu_backtrace= 5409 [KNL] Should the soft-lockup detector generate 5410 backtraces on all cpus. 5411 Format: 0 | 1 5412 5413 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5414 See Documentation/admin-guide/laptops/sonypi.rst 5415 5416 spectre_v2= [X86] Control mitigation of Spectre variant 2 5417 (indirect branch speculation) vulnerability. 5418 The default operation protects the kernel from 5419 user space attacks. 5420 5421 on - unconditionally enable, implies 5422 spectre_v2_user=on 5423 off - unconditionally disable, implies 5424 spectre_v2_user=off 5425 auto - kernel detects whether your CPU model is 5426 vulnerable 5427 5428 Selecting 'on' will, and 'auto' may, choose a 5429 mitigation method at run time according to the 5430 CPU, the available microcode, the setting of the 5431 CONFIG_RETPOLINE configuration option, and the 5432 compiler with which the kernel was built. 5433 5434 Selecting 'on' will also enable the mitigation 5435 against user space to user space task attacks. 5436 5437 Selecting 'off' will disable both the kernel and 5438 the user space protections. 5439 5440 Specific mitigations can also be selected manually: 5441 5442 retpoline - replace indirect branches 5443 retpoline,generic - Retpolines 5444 retpoline,lfence - LFENCE; indirect branch 5445 retpoline,amd - alias for retpoline,lfence 5446 eibrs - enhanced IBRS 5447 eibrs,retpoline - enhanced IBRS + Retpolines 5448 eibrs,lfence - enhanced IBRS + LFENCE 5449 5450 Not specifying this option is equivalent to 5451 spectre_v2=auto. 5452 5453 spectre_v2_user= 5454 [X86] Control mitigation of Spectre variant 2 5455 (indirect branch speculation) vulnerability between 5456 user space tasks 5457 5458 on - Unconditionally enable mitigations. Is 5459 enforced by spectre_v2=on 5460 5461 off - Unconditionally disable mitigations. Is 5462 enforced by spectre_v2=off 5463 5464 prctl - Indirect branch speculation is enabled, 5465 but mitigation can be enabled via prctl 5466 per thread. The mitigation control state 5467 is inherited on fork. 5468 5469 prctl,ibpb 5470 - Like "prctl" above, but only STIBP is 5471 controlled per thread. IBPB is issued 5472 always when switching between different user 5473 space processes. 5474 5475 seccomp 5476 - Same as "prctl" above, but all seccomp 5477 threads will enable the mitigation unless 5478 they explicitly opt out. 5479 5480 seccomp,ibpb 5481 - Like "seccomp" above, but only STIBP is 5482 controlled per thread. IBPB is issued 5483 always when switching between different 5484 user space processes. 5485 5486 auto - Kernel selects the mitigation depending on 5487 the available CPU features and vulnerability. 5488 5489 Default mitigation: "prctl" 5490 5491 Not specifying this option is equivalent to 5492 spectre_v2_user=auto. 5493 5494 spec_store_bypass_disable= 5495 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5496 (Speculative Store Bypass vulnerability) 5497 5498 Certain CPUs are vulnerable to an exploit against a 5499 a common industry wide performance optimization known 5500 as "Speculative Store Bypass" in which recent stores 5501 to the same memory location may not be observed by 5502 later loads during speculative execution. The idea 5503 is that such stores are unlikely and that they can 5504 be detected prior to instruction retirement at the 5505 end of a particular speculation execution window. 5506 5507 In vulnerable processors, the speculatively forwarded 5508 store can be used in a cache side channel attack, for 5509 example to read memory to which the attacker does not 5510 directly have access (e.g. inside sandboxed code). 5511 5512 This parameter controls whether the Speculative Store 5513 Bypass optimization is used. 5514 5515 On x86 the options are: 5516 5517 on - Unconditionally disable Speculative Store Bypass 5518 off - Unconditionally enable Speculative Store Bypass 5519 auto - Kernel detects whether the CPU model contains an 5520 implementation of Speculative Store Bypass and 5521 picks the most appropriate mitigation. If the 5522 CPU is not vulnerable, "off" is selected. If the 5523 CPU is vulnerable the default mitigation is 5524 architecture and Kconfig dependent. See below. 5525 prctl - Control Speculative Store Bypass per thread 5526 via prctl. Speculative Store Bypass is enabled 5527 for a process by default. The state of the control 5528 is inherited on fork. 5529 seccomp - Same as "prctl" above, but all seccomp threads 5530 will disable SSB unless they explicitly opt out. 5531 5532 Default mitigations: 5533 X86: "prctl" 5534 5535 On powerpc the options are: 5536 5537 on,auto - On Power8 and Power9 insert a store-forwarding 5538 barrier on kernel entry and exit. On Power7 5539 perform a software flush on kernel entry and 5540 exit. 5541 off - No action. 5542 5543 Not specifying this option is equivalent to 5544 spec_store_bypass_disable=auto. 5545 5546 spia_io_base= [HW,MTD] 5547 spia_fio_base= 5548 spia_pedr= 5549 spia_peddr= 5550 5551 split_lock_detect= 5552 [X86] Enable split lock detection or bus lock detection 5553 5554 When enabled (and if hardware support is present), atomic 5555 instructions that access data across cache line 5556 boundaries will result in an alignment check exception 5557 for split lock detection or a debug exception for 5558 bus lock detection. 5559 5560 off - not enabled 5561 5562 warn - the kernel will emit rate-limited warnings 5563 about applications triggering the #AC 5564 exception or the #DB exception. This mode is 5565 the default on CPUs that support split lock 5566 detection or bus lock detection. Default 5567 behavior is by #AC if both features are 5568 enabled in hardware. 5569 5570 fatal - the kernel will send SIGBUS to applications 5571 that trigger the #AC exception or the #DB 5572 exception. Default behavior is by #AC if 5573 both features are enabled in hardware. 5574 5575 ratelimit:N - 5576 Set system wide rate limit to N bus locks 5577 per second for bus lock detection. 5578 0 < N <= 1000. 5579 5580 N/A for split lock detection. 5581 5582 5583 If an #AC exception is hit in the kernel or in 5584 firmware (i.e. not while executing in user mode) 5585 the kernel will oops in either "warn" or "fatal" 5586 mode. 5587 5588 #DB exception for bus lock is triggered only when 5589 CPL > 0. 5590 5591 srbds= [X86,INTEL] 5592 Control the Special Register Buffer Data Sampling 5593 (SRBDS) mitigation. 5594 5595 Certain CPUs are vulnerable to an MDS-like 5596 exploit which can leak bits from the random 5597 number generator. 5598 5599 By default, this issue is mitigated by 5600 microcode. However, the microcode fix can cause 5601 the RDRAND and RDSEED instructions to become 5602 much slower. Among other effects, this will 5603 result in reduced throughput from /dev/urandom. 5604 5605 The microcode mitigation can be disabled with 5606 the following option: 5607 5608 off: Disable mitigation and remove 5609 performance impact to RDRAND and RDSEED 5610 5611 srcutree.counter_wrap_check [KNL] 5612 Specifies how frequently to check for 5613 grace-period sequence counter wrap for the 5614 srcu_data structure's ->srcu_gp_seq_needed field. 5615 The greater the number of bits set in this kernel 5616 parameter, the less frequently counter wrap will 5617 be checked for. Note that the bottom two bits 5618 are ignored. 5619 5620 srcutree.exp_holdoff [KNL] 5621 Specifies how many nanoseconds must elapse 5622 since the end of the last SRCU grace period for 5623 a given srcu_struct until the next normal SRCU 5624 grace period will be considered for automatic 5625 expediting. Set to zero to disable automatic 5626 expediting. 5627 5628 ssbd= [ARM64,HW] 5629 Speculative Store Bypass Disable control 5630 5631 On CPUs that are vulnerable to the Speculative 5632 Store Bypass vulnerability and offer a 5633 firmware based mitigation, this parameter 5634 indicates how the mitigation should be used: 5635 5636 force-on: Unconditionally enable mitigation for 5637 for both kernel and userspace 5638 force-off: Unconditionally disable mitigation for 5639 for both kernel and userspace 5640 kernel: Always enable mitigation in the 5641 kernel, and offer a prctl interface 5642 to allow userspace to register its 5643 interest in being mitigated too. 5644 5645 stack_guard_gap= [MM] 5646 override the default stack gap protection. The value 5647 is in page units and it defines how many pages prior 5648 to (for stacks growing down) resp. after (for stacks 5649 growing up) the main stack are reserved for no other 5650 mapping. Default value is 256 pages. 5651 5652 stack_depot_disable= [KNL] 5653 Setting this to true through kernel command line will 5654 disable the stack depot thereby saving the static memory 5655 consumed by the stack hash table. By default this is set 5656 to false. 5657 5658 stacktrace [FTRACE] 5659 Enabled the stack tracer on boot up. 5660 5661 stacktrace_filter=[function-list] 5662 [FTRACE] Limit the functions that the stack tracer 5663 will trace at boot up. function-list is a comma-separated 5664 list of functions. This list can be changed at run 5665 time by the stack_trace_filter file in the debugfs 5666 tracing directory. Note, this enables stack tracing 5667 and the stacktrace above is not needed. 5668 5669 sti= [PARISC,HW] 5670 Format: <num> 5671 Set the STI (builtin display/keyboard on the HP-PARISC 5672 machines) console (graphic card) which should be used 5673 as the initial boot-console. 5674 See also comment in drivers/video/console/sticore.c. 5675 5676 sti_font= [HW] 5677 See comment in drivers/video/console/sticore.c. 5678 5679 stifb= [HW] 5680 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5681 5682 strict_sas_size= 5683 [X86] 5684 Format: <bool> 5685 Enable or disable strict sigaltstack size checks 5686 against the required signal frame size which 5687 depends on the supported FPU features. This can 5688 be used to filter out binaries which have 5689 not yet been made aware of AT_MINSIGSTKSZ. 5690 5691 sunrpc.min_resvport= 5692 sunrpc.max_resvport= 5693 [NFS,SUNRPC] 5694 SunRPC servers often require that client requests 5695 originate from a privileged port (i.e. a port in the 5696 range 0 < portnr < 1024). 5697 An administrator who wishes to reserve some of these 5698 ports for other uses may adjust the range that the 5699 kernel's sunrpc client considers to be privileged 5700 using these two parameters to set the minimum and 5701 maximum port values. 5702 5703 sunrpc.svc_rpc_per_connection_limit= 5704 [NFS,SUNRPC] 5705 Limit the number of requests that the server will 5706 process in parallel from a single connection. 5707 The default value is 0 (no limit). 5708 5709 sunrpc.pool_mode= 5710 [NFS] 5711 Control how the NFS server code allocates CPUs to 5712 service thread pools. Depending on how many NICs 5713 you have and where their interrupts are bound, this 5714 option will affect which CPUs will do NFS serving. 5715 Note: this parameter cannot be changed while the 5716 NFS server is running. 5717 5718 auto the server chooses an appropriate mode 5719 automatically using heuristics 5720 global a single global pool contains all CPUs 5721 percpu one pool for each CPU 5722 pernode one pool for each NUMA node (equivalent 5723 to global on non-NUMA machines) 5724 5725 sunrpc.tcp_slot_table_entries= 5726 sunrpc.udp_slot_table_entries= 5727 [NFS,SUNRPC] 5728 Sets the upper limit on the number of simultaneous 5729 RPC calls that can be sent from the client to a 5730 server. Increasing these values may allow you to 5731 improve throughput, but will also increase the 5732 amount of memory reserved for use by the client. 5733 5734 suspend.pm_test_delay= 5735 [SUSPEND] 5736 Sets the number of seconds to remain in a suspend test 5737 mode before resuming the system (see 5738 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5739 is set. Default value is 5. 5740 5741 svm= [PPC] 5742 Format: { on | off | y | n | 1 | 0 } 5743 This parameter controls use of the Protected 5744 Execution Facility on pSeries. 5745 5746 swapaccount=[0|1] 5747 [KNL] Enable accounting of swap in memory resource 5748 controller if no parameter or 1 is given or disable 5749 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5750 5751 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5752 Format: { <int> | force | noforce } 5753 <int> -- Number of I/O TLB slabs 5754 force -- force using of bounce buffers even if they 5755 wouldn't be automatically used by the kernel 5756 noforce -- Never use bounce buffers (for debugging) 5757 5758 switches= [HW,M68k] 5759 5760 sysctl.*= [KNL] 5761 Set a sysctl parameter, right before loading the init 5762 process, as if the value was written to the respective 5763 /proc/sys/... file. Both '.' and '/' are recognized as 5764 separators. Unrecognized parameters and invalid values 5765 are reported in the kernel log. Sysctls registered 5766 later by a loaded module cannot be set this way. 5767 Example: sysctl.vm.swappiness=40 5768 5769 sysfs.deprecated=0|1 [KNL] 5770 Enable/disable old style sysfs layout for old udev 5771 on older distributions. When this option is enabled 5772 very new udev will not work anymore. When this option 5773 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5774 in older udev will not work anymore. 5775 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5776 the kernel configuration. 5777 5778 sysrq_always_enabled 5779 [KNL] 5780 Ignore sysrq setting - this boot parameter will 5781 neutralize any effect of /proc/sys/kernel/sysrq. 5782 Useful for debugging. 5783 5784 tcpmhash_entries= [KNL,NET] 5785 Set the number of tcp_metrics_hash slots. 5786 Default value is 8192 or 16384 depending on total 5787 ram pages. This is used to specify the TCP metrics 5788 cache size. See Documentation/networking/ip-sysctl.rst 5789 "tcp_no_metrics_save" section for more details. 5790 5791 tdfx= [HW,DRM] 5792 5793 test_suspend= [SUSPEND][,N] 5794 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5795 standby suspend) or "freeze" (for suspend type freeze) 5796 as the system sleep state during system startup with 5797 the optional capability to repeat N number of times. 5798 The system is woken from this state using a 5799 wakeup-capable RTC alarm. 5800 5801 thash_entries= [KNL,NET] 5802 Set number of hash buckets for TCP connection 5803 5804 thermal.act= [HW,ACPI] 5805 -1: disable all active trip points in all thermal zones 5806 <degrees C>: override all lowest active trip points 5807 5808 thermal.crt= [HW,ACPI] 5809 -1: disable all critical trip points in all thermal zones 5810 <degrees C>: override all critical trip points 5811 5812 thermal.nocrt= [HW,ACPI] 5813 Set to disable actions on ACPI thermal zone 5814 critical and hot trip points. 5815 5816 thermal.off= [HW,ACPI] 5817 1: disable ACPI thermal control 5818 5819 thermal.psv= [HW,ACPI] 5820 -1: disable all passive trip points 5821 <degrees C>: override all passive trip points to this 5822 value 5823 5824 thermal.tzp= [HW,ACPI] 5825 Specify global default ACPI thermal zone polling rate 5826 <deci-seconds>: poll all this frequency 5827 0: no polling (default) 5828 5829 threadirqs [KNL] 5830 Force threading of all interrupt handlers except those 5831 marked explicitly IRQF_NO_THREAD. 5832 5833 topology= [S390] 5834 Format: {off | on} 5835 Specify if the kernel should make use of the cpu 5836 topology information if the hardware supports this. 5837 The scheduler will make use of this information and 5838 e.g. base its process migration decisions on it. 5839 Default is on. 5840 5841 topology_updates= [KNL, PPC, NUMA] 5842 Format: {off} 5843 Specify if the kernel should ignore (off) 5844 topology updates sent by the hypervisor to this 5845 LPAR. 5846 5847 torture.disable_onoff_at_boot= [KNL] 5848 Prevent the CPU-hotplug component of torturing 5849 until after init has spawned. 5850 5851 torture.ftrace_dump_at_shutdown= [KNL] 5852 Dump the ftrace buffer at torture-test shutdown, 5853 even if there were no errors. This can be a 5854 very costly operation when many torture tests 5855 are running concurrently, especially on systems 5856 with rotating-rust storage. 5857 5858 torture.verbose_sleep_frequency= [KNL] 5859 Specifies how many verbose printk()s should be 5860 emitted between each sleep. The default of zero 5861 disables verbose-printk() sleeping. 5862 5863 torture.verbose_sleep_duration= [KNL] 5864 Duration of each verbose-printk() sleep in jiffies. 5865 5866 tp720= [HW,PS2] 5867 5868 tpm_suspend_pcr=[HW,TPM] 5869 Format: integer pcr id 5870 Specify that at suspend time, the tpm driver 5871 should extend the specified pcr with zeros, 5872 as a workaround for some chips which fail to 5873 flush the last written pcr on TPM_SaveState. 5874 This will guarantee that all the other pcrs 5875 are saved. 5876 5877 trace_buf_size=nn[KMG] 5878 [FTRACE] will set tracing buffer size on each cpu. 5879 5880 trace_event=[event-list] 5881 [FTRACE] Set and start specified trace events in order 5882 to facilitate early boot debugging. The event-list is a 5883 comma-separated list of trace events to enable. See 5884 also Documentation/trace/events.rst 5885 5886 trace_options=[option-list] 5887 [FTRACE] Enable or disable tracer options at boot. 5888 The option-list is a comma delimited list of options 5889 that can be enabled or disabled just as if you were 5890 to echo the option name into 5891 5892 /sys/kernel/debug/tracing/trace_options 5893 5894 For example, to enable stacktrace option (to dump the 5895 stack trace of each event), add to the command line: 5896 5897 trace_options=stacktrace 5898 5899 See also Documentation/trace/ftrace.rst "trace options" 5900 section. 5901 5902 tp_printk[FTRACE] 5903 Have the tracepoints sent to printk as well as the 5904 tracing ring buffer. This is useful for early boot up 5905 where the system hangs or reboots and does not give the 5906 option for reading the tracing buffer or performing a 5907 ftrace_dump_on_oops. 5908 5909 To turn off having tracepoints sent to printk, 5910 echo 0 > /proc/sys/kernel/tracepoint_printk 5911 Note, echoing 1 into this file without the 5912 tracepoint_printk kernel cmdline option has no effect. 5913 5914 The tp_printk_stop_on_boot (see below) can also be used 5915 to stop the printing of events to console at 5916 late_initcall_sync. 5917 5918 ** CAUTION ** 5919 5920 Having tracepoints sent to printk() and activating high 5921 frequency tracepoints such as irq or sched, can cause 5922 the system to live lock. 5923 5924 tp_printk_stop_on_boot[FTRACE] 5925 When tp_printk (above) is set, it can cause a lot of noise 5926 on the console. It may be useful to only include the 5927 printing of events during boot up, as user space may 5928 make the system inoperable. 5929 5930 This command line option will stop the printing of events 5931 to console at the late_initcall_sync() time frame. 5932 5933 traceoff_on_warning 5934 [FTRACE] enable this option to disable tracing when a 5935 warning is hit. This turns off "tracing_on". Tracing can 5936 be enabled again by echoing '1' into the "tracing_on" 5937 file located in /sys/kernel/debug/tracing/ 5938 5939 This option is useful, as it disables the trace before 5940 the WARNING dump is called, which prevents the trace to 5941 be filled with content caused by the warning output. 5942 5943 This option can also be set at run time via the sysctl 5944 option: kernel/traceoff_on_warning 5945 5946 transparent_hugepage= 5947 [KNL] 5948 Format: [always|madvise|never] 5949 Can be used to control the default behavior of the system 5950 with respect to transparent hugepages. 5951 See Documentation/admin-guide/mm/transhuge.rst 5952 for more details. 5953 5954 trusted.source= [KEYS] 5955 Format: <string> 5956 This parameter identifies the trust source as a backend 5957 for trusted keys implementation. Supported trust 5958 sources: 5959 - "tpm" 5960 - "tee" 5961 If not specified then it defaults to iterating through 5962 the trust source list starting with TPM and assigns the 5963 first trust source as a backend which is initialized 5964 successfully during iteration. 5965 5966 tsc= Disable clocksource stability checks for TSC. 5967 Format: <string> 5968 [x86] reliable: mark tsc clocksource as reliable, this 5969 disables clocksource verification at runtime, as well 5970 as the stability checks done at bootup. Used to enable 5971 high-resolution timer mode on older hardware, and in 5972 virtualized environment. 5973 [x86] noirqtime: Do not use TSC to do irq accounting. 5974 Used to run time disable IRQ_TIME_ACCOUNTING on any 5975 platforms where RDTSC is slow and this accounting 5976 can add overhead. 5977 [x86] unstable: mark the TSC clocksource as unstable, this 5978 marks the TSC unconditionally unstable at bootup and 5979 avoids any further wobbles once the TSC watchdog notices. 5980 [x86] nowatchdog: disable clocksource watchdog. Used 5981 in situations with strict latency requirements (where 5982 interruptions from clocksource watchdog are not 5983 acceptable). 5984 5985 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5986 value instead. Useful when the early TSC frequency discovery 5987 procedure is not reliable, such as on overclocked systems 5988 with CPUID.16h support and partial CPUID.15h support. 5989 Format: <unsigned int> 5990 5991 tsx= [X86] Control Transactional Synchronization 5992 Extensions (TSX) feature in Intel processors that 5993 support TSX control. 5994 5995 This parameter controls the TSX feature. The options are: 5996 5997 on - Enable TSX on the system. Although there are 5998 mitigations for all known security vulnerabilities, 5999 TSX has been known to be an accelerator for 6000 several previous speculation-related CVEs, and 6001 so there may be unknown security risks associated 6002 with leaving it enabled. 6003 6004 off - Disable TSX on the system. (Note that this 6005 option takes effect only on newer CPUs which are 6006 not vulnerable to MDS, i.e., have 6007 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 6008 the new IA32_TSX_CTRL MSR through a microcode 6009 update. This new MSR allows for the reliable 6010 deactivation of the TSX functionality.) 6011 6012 auto - Disable TSX if X86_BUG_TAA is present, 6013 otherwise enable TSX on the system. 6014 6015 Not specifying this option is equivalent to tsx=off. 6016 6017 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6018 for more details. 6019 6020 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 6021 Abort (TAA) vulnerability. 6022 6023 Similar to Micro-architectural Data Sampling (MDS) 6024 certain CPUs that support Transactional 6025 Synchronization Extensions (TSX) are vulnerable to an 6026 exploit against CPU internal buffers which can forward 6027 information to a disclosure gadget under certain 6028 conditions. 6029 6030 In vulnerable processors, the speculatively forwarded 6031 data can be used in a cache side channel attack, to 6032 access data to which the attacker does not have direct 6033 access. 6034 6035 This parameter controls the TAA mitigation. The 6036 options are: 6037 6038 full - Enable TAA mitigation on vulnerable CPUs 6039 if TSX is enabled. 6040 6041 full,nosmt - Enable TAA mitigation and disable SMT on 6042 vulnerable CPUs. If TSX is disabled, SMT 6043 is not disabled because CPU is not 6044 vulnerable to cross-thread TAA attacks. 6045 off - Unconditionally disable TAA mitigation 6046 6047 On MDS-affected machines, tsx_async_abort=off can be 6048 prevented by an active MDS mitigation as both vulnerabilities 6049 are mitigated with the same mechanism so in order to disable 6050 this mitigation, you need to specify mds=off too. 6051 6052 Not specifying this option is equivalent to 6053 tsx_async_abort=full. On CPUs which are MDS affected 6054 and deploy MDS mitigation, TAA mitigation is not 6055 required and doesn't provide any additional 6056 mitigation. 6057 6058 For details see: 6059 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6060 6061 turbografx.map[2|3]= [HW,JOY] 6062 TurboGraFX parallel port interface 6063 Format: 6064 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 6065 See also Documentation/input/devices/joystick-parport.rst 6066 6067 udbg-immortal [PPC] When debugging early kernel crashes that 6068 happen after console_init() and before a proper 6069 console driver takes over, this boot options might 6070 help "seeing" what's going on. 6071 6072 uhash_entries= [KNL,NET] 6073 Set number of hash buckets for UDP/UDP-Lite connections 6074 6075 uhci-hcd.ignore_oc= 6076 [USB] Ignore overcurrent events (default N). 6077 Some badly-designed motherboards generate lots of 6078 bogus events, for ports that aren't wired to 6079 anything. Set this parameter to avoid log spamming. 6080 Note that genuine overcurrent events won't be 6081 reported either. 6082 6083 unknown_nmi_panic 6084 [X86] Cause panic on unknown NMI. 6085 6086 usbcore.authorized_default= 6087 [USB] Default USB device authorization: 6088 (default -1 = authorized except for wireless USB, 6089 0 = not authorized, 1 = authorized, 2 = authorized 6090 if device connected to internal port) 6091 6092 usbcore.autosuspend= 6093 [USB] The autosuspend time delay (in seconds) used 6094 for newly-detected USB devices (default 2). This 6095 is the time required before an idle device will be 6096 autosuspended. Devices for which the delay is set 6097 to a negative value won't be autosuspended at all. 6098 6099 usbcore.usbfs_snoop= 6100 [USB] Set to log all usbfs traffic (default 0 = off). 6101 6102 usbcore.usbfs_snoop_max= 6103 [USB] Maximum number of bytes to snoop in each URB 6104 (default = 65536). 6105 6106 usbcore.blinkenlights= 6107 [USB] Set to cycle leds on hubs (default 0 = off). 6108 6109 usbcore.old_scheme_first= 6110 [USB] Start with the old device initialization 6111 scheme (default 0 = off). 6112 6113 usbcore.usbfs_memory_mb= 6114 [USB] Memory limit (in MB) for buffers allocated by 6115 usbfs (default = 16, 0 = max = 2047). 6116 6117 usbcore.use_both_schemes= 6118 [USB] Try the other device initialization scheme 6119 if the first one fails (default 1 = enabled). 6120 6121 usbcore.initial_descriptor_timeout= 6122 [USB] Specifies timeout for the initial 64-byte 6123 USB_REQ_GET_DESCRIPTOR request in milliseconds 6124 (default 5000 = 5.0 seconds). 6125 6126 usbcore.nousb [USB] Disable the USB subsystem 6127 6128 usbcore.quirks= 6129 [USB] A list of quirk entries to augment the built-in 6130 usb core quirk list. List entries are separated by 6131 commas. Each entry has the form 6132 VendorID:ProductID:Flags. The IDs are 4-digit hex 6133 numbers and Flags is a set of letters. Each letter 6134 will change the built-in quirk; setting it if it is 6135 clear and clearing it if it is set. The letters have 6136 the following meanings: 6137 a = USB_QUIRK_STRING_FETCH_255 (string 6138 descriptors must not be fetched using 6139 a 255-byte read); 6140 b = USB_QUIRK_RESET_RESUME (device can't resume 6141 correctly so reset it instead); 6142 c = USB_QUIRK_NO_SET_INTF (device can't handle 6143 Set-Interface requests); 6144 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 6145 handle its Configuration or Interface 6146 strings); 6147 e = USB_QUIRK_RESET (device can't be reset 6148 (e.g morph devices), don't use reset); 6149 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 6150 more interface descriptions than the 6151 bNumInterfaces count, and can't handle 6152 talking to these interfaces); 6153 g = USB_QUIRK_DELAY_INIT (device needs a pause 6154 during initialization, after we read 6155 the device descriptor); 6156 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 6157 high speed and super speed interrupt 6158 endpoints, the USB 2.0 and USB 3.0 spec 6159 require the interval in microframes (1 6160 microframe = 125 microseconds) to be 6161 calculated as interval = 2 ^ 6162 (bInterval-1). 6163 Devices with this quirk report their 6164 bInterval as the result of this 6165 calculation instead of the exponent 6166 variable used in the calculation); 6167 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 6168 handle device_qualifier descriptor 6169 requests); 6170 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 6171 generates spurious wakeup, ignore 6172 remote wakeup capability); 6173 k = USB_QUIRK_NO_LPM (device can't handle Link 6174 Power Management); 6175 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 6176 (Device reports its bInterval as linear 6177 frames instead of the USB 2.0 6178 calculation); 6179 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 6180 to be disconnected before suspend to 6181 prevent spurious wakeup); 6182 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 6183 pause after every control message); 6184 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 6185 delay after resetting its port); 6186 Example: quirks=0781:5580:bk,0a5c:5834:gij 6187 6188 usbhid.mousepoll= 6189 [USBHID] The interval which mice are to be polled at. 6190 6191 usbhid.jspoll= 6192 [USBHID] The interval which joysticks are to be polled at. 6193 6194 usbhid.kbpoll= 6195 [USBHID] The interval which keyboards are to be polled at. 6196 6197 usb-storage.delay_use= 6198 [UMS] The delay in seconds before a new device is 6199 scanned for Logical Units (default 1). 6200 6201 usb-storage.quirks= 6202 [UMS] A list of quirks entries to supplement or 6203 override the built-in unusual_devs list. List 6204 entries are separated by commas. Each entry has 6205 the form VID:PID:Flags where VID and PID are Vendor 6206 and Product ID values (4-digit hex numbers) and 6207 Flags is a set of characters, each corresponding 6208 to a common usb-storage quirk flag as follows: 6209 a = SANE_SENSE (collect more than 18 bytes 6210 of sense data, not on uas); 6211 b = BAD_SENSE (don't collect more than 18 6212 bytes of sense data, not on uas); 6213 c = FIX_CAPACITY (decrease the reported 6214 device capacity by one sector); 6215 d = NO_READ_DISC_INFO (don't use 6216 READ_DISC_INFO command, not on uas); 6217 e = NO_READ_CAPACITY_16 (don't use 6218 READ_CAPACITY_16 command); 6219 f = NO_REPORT_OPCODES (don't use report opcodes 6220 command, uas only); 6221 g = MAX_SECTORS_240 (don't transfer more than 6222 240 sectors at a time, uas only); 6223 h = CAPACITY_HEURISTICS (decrease the 6224 reported device capacity by one 6225 sector if the number is odd); 6226 i = IGNORE_DEVICE (don't bind to this 6227 device); 6228 j = NO_REPORT_LUNS (don't use report luns 6229 command, uas only); 6230 k = NO_SAME (do not use WRITE_SAME, uas only) 6231 l = NOT_LOCKABLE (don't try to lock and 6232 unlock ejectable media, not on uas); 6233 m = MAX_SECTORS_64 (don't transfer more 6234 than 64 sectors = 32 KB at a time, 6235 not on uas); 6236 n = INITIAL_READ10 (force a retry of the 6237 initial READ(10) command, not on uas); 6238 o = CAPACITY_OK (accept the capacity 6239 reported by the device, not on uas); 6240 p = WRITE_CACHE (the device cache is ON 6241 by default, not on uas); 6242 r = IGNORE_RESIDUE (the device reports 6243 bogus residue values, not on uas); 6244 s = SINGLE_LUN (the device has only one 6245 Logical Unit); 6246 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 6247 commands, uas only); 6248 u = IGNORE_UAS (don't bind to the uas driver); 6249 w = NO_WP_DETECT (don't test whether the 6250 medium is write-protected). 6251 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 6252 even if the device claims no cache, 6253 not on uas) 6254 Example: quirks=0419:aaf5:rl,0421:0433:rc 6255 6256 user_debug= [KNL,ARM] 6257 Format: <int> 6258 See arch/arm/Kconfig.debug help text. 6259 1 - undefined instruction events 6260 2 - system calls 6261 4 - invalid data aborts 6262 8 - SIGSEGV faults 6263 16 - SIGBUS faults 6264 Example: user_debug=31 6265 6266 userpte= 6267 [X86] Flags controlling user PTE allocations. 6268 6269 nohigh = do not allocate PTE pages in 6270 HIGHMEM regardless of setting 6271 of CONFIG_HIGHPTE. 6272 6273 vdso= [X86,SH] 6274 On X86_32, this is an alias for vdso32=. Otherwise: 6275 6276 vdso=1: enable VDSO (the default) 6277 vdso=0: disable VDSO mapping 6278 6279 vdso32= [X86] Control the 32-bit vDSO 6280 vdso32=1: enable 32-bit VDSO 6281 vdso32=0 or vdso32=2: disable 32-bit VDSO 6282 6283 See the help text for CONFIG_COMPAT_VDSO for more 6284 details. If CONFIG_COMPAT_VDSO is set, the default is 6285 vdso32=0; otherwise, the default is vdso32=1. 6286 6287 For compatibility with older kernels, vdso32=2 is an 6288 alias for vdso32=0. 6289 6290 Try vdso32=0 if you encounter an error that says: 6291 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 6292 6293 vector= [IA-64,SMP] 6294 vector=percpu: enable percpu vector domain 6295 6296 video= [FB] Frame buffer configuration 6297 See Documentation/fb/modedb.rst. 6298 6299 video.brightness_switch_enabled= [0,1] 6300 If set to 1, on receiving an ACPI notify event 6301 generated by hotkey, video driver will adjust brightness 6302 level and then send out the event to user space through 6303 the allocated input device; If set to 0, video driver 6304 will only send out the event without touching backlight 6305 brightness level. 6306 default: 1 6307 6308 virtio_mmio.device= 6309 [VMMIO] Memory mapped virtio (platform) device. 6310 6311 <size>@<baseaddr>:<irq>[:<id>] 6312 where: 6313 <size> := size (can use standard suffixes 6314 like K, M and G) 6315 <baseaddr> := physical base address 6316 <irq> := interrupt number (as passed to 6317 request_irq()) 6318 <id> := (optional) platform device id 6319 example: 6320 virtio_mmio.device=1K@0x100b0000:48:7 6321 6322 Can be used multiple times for multiple devices. 6323 6324 vga= [BOOT,X86-32] Select a particular video mode 6325 See Documentation/x86/boot.rst and 6326 Documentation/admin-guide/svga.rst. 6327 Use vga=ask for menu. 6328 This is actually a boot loader parameter; the value is 6329 passed to the kernel using a special protocol. 6330 6331 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 6332 May slow down system boot speed, especially when 6333 enabled on systems with a large amount of memory. 6334 All options are enabled by default, and this 6335 interface is meant to allow for selectively 6336 enabling or disabling specific virtual memory 6337 debugging features. 6338 6339 Available options are: 6340 P Enable page structure init time poisoning 6341 - Disable all of the above options 6342 6343 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 6344 size of <nn>. This can be used to increase the 6345 minimum size (128MB on x86). It can also be used to 6346 decrease the size and leave more room for directly 6347 mapped kernel RAM. 6348 6349 vmcp_cma=nn[MG] [KNL,S390] 6350 Sets the memory size reserved for contiguous memory 6351 allocations for the vmcp device driver. 6352 6353 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 6354 Format: <command> 6355 6356 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 6357 Format: <command> 6358 6359 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 6360 Format: <command> 6361 6362 vsyscall= [X86-64] 6363 Controls the behavior of vsyscalls (i.e. calls to 6364 fixed addresses of 0xffffffffff600x00 from legacy 6365 code). Most statically-linked binaries and older 6366 versions of glibc use these calls. Because these 6367 functions are at fixed addresses, they make nice 6368 targets for exploits that can control RIP. 6369 6370 emulate [default] Vsyscalls turn into traps and are 6371 emulated reasonably safely. The vsyscall 6372 page is readable. 6373 6374 xonly Vsyscalls turn into traps and are 6375 emulated reasonably safely. The vsyscall 6376 page is not readable. 6377 6378 none Vsyscalls don't work at all. This makes 6379 them quite hard to use for exploits but 6380 might break your system. 6381 6382 vt.color= [VT] Default text color. 6383 Format: 0xYX, X = foreground, Y = background. 6384 Default: 0x07 = light gray on black. 6385 6386 vt.cur_default= [VT] Default cursor shape. 6387 Format: 0xCCBBAA, where AA, BB, and CC are the same as 6388 the parameters of the <Esc>[?A;B;Cc escape sequence; 6389 see VGA-softcursor.txt. Default: 2 = underline. 6390 6391 vt.default_blu= [VT] 6392 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 6393 Change the default blue palette of the console. 6394 This is a 16-member array composed of values 6395 ranging from 0-255. 6396 6397 vt.default_grn= [VT] 6398 Format: <green0>,<green1>,<green2>,...,<green15> 6399 Change the default green palette of the console. 6400 This is a 16-member array composed of values 6401 ranging from 0-255. 6402 6403 vt.default_red= [VT] 6404 Format: <red0>,<red1>,<red2>,...,<red15> 6405 Change the default red palette of the console. 6406 This is a 16-member array composed of values 6407 ranging from 0-255. 6408 6409 vt.default_utf8= 6410 [VT] 6411 Format=<0|1> 6412 Set system-wide default UTF-8 mode for all tty's. 6413 Default is 1, i.e. UTF-8 mode is enabled for all 6414 newly opened terminals. 6415 6416 vt.global_cursor_default= 6417 [VT] 6418 Format=<-1|0|1> 6419 Set system-wide default for whether a cursor 6420 is shown on new VTs. Default is -1, 6421 i.e. cursors will be created by default unless 6422 overridden by individual drivers. 0 will hide 6423 cursors, 1 will display them. 6424 6425 vt.italic= [VT] Default color for italic text; 0-15. 6426 Default: 2 = green. 6427 6428 vt.underline= [VT] Default color for underlined text; 0-15. 6429 Default: 3 = cyan. 6430 6431 watchdog timers [HW,WDT] For information on watchdog timers, 6432 see Documentation/watchdog/watchdog-parameters.rst 6433 or other driver-specific files in the 6434 Documentation/watchdog/ directory. 6435 6436 watchdog_thresh= 6437 [KNL] 6438 Set the hard lockup detector stall duration 6439 threshold in seconds. The soft lockup detector 6440 threshold is set to twice the value. A value of 0 6441 disables both lockup detectors. Default is 10 6442 seconds. 6443 6444 workqueue.watchdog_thresh= 6445 If CONFIG_WQ_WATCHDOG is configured, workqueue can 6446 warn stall conditions and dump internal state to 6447 help debugging. 0 disables workqueue stall 6448 detection; otherwise, it's the stall threshold 6449 duration in seconds. The default value is 30 and 6450 it can be updated at runtime by writing to the 6451 corresponding sysfs file. 6452 6453 workqueue.disable_numa 6454 By default, all work items queued to unbound 6455 workqueues are affine to the NUMA nodes they're 6456 issued on, which results in better behavior in 6457 general. If NUMA affinity needs to be disabled for 6458 whatever reason, this option can be used. Note 6459 that this also can be controlled per-workqueue for 6460 workqueues visible under /sys/bus/workqueue/. 6461 6462 workqueue.power_efficient 6463 Per-cpu workqueues are generally preferred because 6464 they show better performance thanks to cache 6465 locality; unfortunately, per-cpu workqueues tend to 6466 be more power hungry than unbound workqueues. 6467 6468 Enabling this makes the per-cpu workqueues which 6469 were observed to contribute significantly to power 6470 consumption unbound, leading to measurably lower 6471 power usage at the cost of small performance 6472 overhead. 6473 6474 The default value of this parameter is determined by 6475 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 6476 6477 workqueue.debug_force_rr_cpu 6478 Workqueue used to implicitly guarantee that work 6479 items queued without explicit CPU specified are put 6480 on the local CPU. This guarantee is no longer true 6481 and while local CPU is still preferred work items 6482 may be put on foreign CPUs. This debug option 6483 forces round-robin CPU selection to flush out 6484 usages which depend on the now broken guarantee. 6485 When enabled, memory and cache locality will be 6486 impacted. 6487 6488 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 6489 default x2apic cluster mode on platforms 6490 supporting x2apic. 6491 6492 xen_512gb_limit [KNL,X86-64,XEN] 6493 Restricts the kernel running paravirtualized under Xen 6494 to use only up to 512 GB of RAM. The reason to do so is 6495 crash analysis tools and Xen tools for doing domain 6496 save/restore/migration must be enabled to handle larger 6497 domains. 6498 6499 xen_emul_unplug= [HW,X86,XEN] 6500 Unplug Xen emulated devices 6501 Format: [unplug0,][unplug1] 6502 ide-disks -- unplug primary master IDE devices 6503 aux-ide-disks -- unplug non-primary-master IDE devices 6504 nics -- unplug network devices 6505 all -- unplug all emulated devices (NICs and IDE disks) 6506 unnecessary -- unplugging emulated devices is 6507 unnecessary even if the host did not respond to 6508 the unplug protocol 6509 never -- do not unplug even if version check succeeds 6510 6511 xen_legacy_crash [X86,XEN] 6512 Crash from Xen panic notifier, without executing late 6513 panic() code such as dumping handler. 6514 6515 xen_nopvspin [X86,XEN] 6516 Disables the qspinlock slowpath using Xen PV optimizations. 6517 This parameter is obsoleted by "nopvspin" parameter, which 6518 has equivalent effect for XEN platform. 6519 6520 xen_nopv [X86] 6521 Disables the PV optimizations forcing the HVM guest to 6522 run as generic HVM guest with no PV drivers. 6523 This option is obsoleted by the "nopv" option, which 6524 has equivalent effect for XEN platform. 6525 6526 xen_no_vector_callback 6527 [KNL,X86,XEN] Disable the vector callback for Xen 6528 event channel interrupts. 6529 6530 xen_scrub_pages= [XEN] 6531 Boolean option to control scrubbing pages before giving them back 6532 to Xen, for use by other domains. Can be also changed at runtime 6533 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 6534 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 6535 6536 xen_timer_slop= [X86-64,XEN] 6537 Set the timer slop (in nanoseconds) for the virtual Xen 6538 timers (default is 100000). This adjusts the minimum 6539 delta of virtualized Xen timers, where lower values 6540 improve timer resolution at the expense of processing 6541 more timer interrupts. 6542 6543 xen.balloon_boot_timeout= [XEN] 6544 The time (in seconds) to wait before giving up to boot 6545 in case initial ballooning fails to free enough memory. 6546 Applies only when running as HVM or PVH guest and 6547 started with less memory configured than allowed at 6548 max. Default is 180. 6549 6550 xen.event_eoi_delay= [XEN] 6551 How long to delay EOI handling in case of event 6552 storms (jiffies). Default is 10. 6553 6554 xen.event_loop_timeout= [XEN] 6555 After which time (jiffies) the event handling loop 6556 should start to delay EOI handling. Default is 2. 6557 6558 xen.fifo_events= [XEN] 6559 Boolean parameter to disable using fifo event handling 6560 even if available. Normally fifo event handling is 6561 preferred over the 2-level event handling, as it is 6562 fairer and the number of possible event channels is 6563 much higher. Default is on (use fifo events). 6564 6565 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 6566 Disables the PV optimizations forcing the guest to run 6567 as generic guest with no PV drivers. Currently support 6568 XEN HVM, KVM, HYPER_V and VMWARE guest. 6569 6570 nopvspin [X86,XEN,KVM] 6571 Disables the qspinlock slow path using PV optimizations 6572 which allow the hypervisor to 'idle' the guest on lock 6573 contention. 6574 6575 xirc2ps_cs= [NET,PCMCIA] 6576 Format: 6577 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6578 6579 xive= [PPC] 6580 By default on POWER9 and above, the kernel will 6581 natively use the XIVE interrupt controller. This option 6582 allows the fallback firmware mode to be used: 6583 6584 off Fallback to firmware control of XIVE interrupt 6585 controller on both pseries and powernv 6586 platforms. Only useful on POWER9 and above. 6587 6588 xive.store-eoi=off [PPC] 6589 By default on POWER10 and above, the kernel will use 6590 stores for EOI handling when the XIVE interrupt mode 6591 is active. This option allows the XIVE driver to use 6592 loads instead, as on POWER9. 6593 6594 xhci-hcd.quirks [USB,KNL] 6595 A hex value specifying bitmask with supplemental xhci 6596 host controller quirks. Meaning of each bit can be 6597 consulted in header drivers/usb/host/xhci.h. 6598 6599 xmon [PPC] 6600 Format: { early | on | rw | ro | off } 6601 Controls if xmon debugger is enabled. Default is off. 6602 Passing only "xmon" is equivalent to "xmon=early". 6603 early Call xmon as early as possible on boot; xmon 6604 debugger is called from setup_arch(). 6605 on xmon debugger hooks will be installed so xmon 6606 is only called on a kernel crash. Default mode, 6607 i.e. either "ro" or "rw" mode, is controlled 6608 with CONFIG_XMON_DEFAULT_RO_MODE. 6609 rw xmon debugger hooks will be installed so xmon 6610 is called only on a kernel crash, mode is write, 6611 meaning SPR registers, memory and, other data 6612 can be written using xmon commands. 6613 ro same as "rw" option above but SPR registers, 6614 memory, and other data can't be written using 6615 xmon commands. 6616 off xmon is disabled. 6617