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