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_PCI_COMPONENT 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 PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM[,BITNUM...] [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [KNL,CMA] 595 Sets the size of kernel global memory area for 596 contiguous memory allocations and optionally the 597 placement constraint by the physical address range of 598 memory allocations. A value of 0 disables CMA 599 altogether. For more information, see 600 kernel/dma/contiguous.c 601 602 cma_pernuma=nn[MG] 603 [ARM64,KNL] 604 Sets the size of kernel per-numa memory area for 605 contiguous memory allocations. A value of 0 disables 606 per-numa CMA altogether. And If this option is not 607 specificed, the default value is 0. 608 With per-numa CMA enabled, DMA users on node nid will 609 first try to allocate buffer from the pernuma area 610 which is located in node nid, if the allocation fails, 611 they will fallback to the global default memory area. 612 613 cmo_free_hint= [PPC] Format: { yes | no } 614 Specify whether pages are marked as being inactive 615 when they are freed. This is used in CMO environments 616 to determine OS memory pressure for page stealing by 617 a hypervisor. 618 Default: yes 619 620 coherent_pool=nn[KMG] [ARM,KNL] 621 Sets the size of memory pool for coherent, atomic dma 622 allocations, by default set to 256K. 623 624 com20020= [HW,NET] ARCnet - COM20020 chipset 625 Format: 626 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 627 628 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 629 Format: <io>[,<irq>] 630 631 com90xx= [HW,NET] 632 ARCnet - COM90xx chipset (memory-mapped buffers) 633 Format: <io>[,<irq>[,<memstart>]] 634 635 condev= [HW,S390] console device 636 conmode= 637 638 console= [KNL] Output console device and options. 639 640 tty<n> Use the virtual console device <n>. 641 642 ttyS<n>[,options] 643 ttyUSB0[,options] 644 Use the specified serial port. The options are of 645 the form "bbbbpnf", where "bbbb" is the baud rate, 646 "p" is parity ("n", "o", or "e"), "n" is number of 647 bits, and "f" is flow control ("r" for RTS or 648 omit it). Default is "9600n8". 649 650 See Documentation/admin-guide/serial-console.rst for more 651 information. See 652 Documentation/networking/netconsole.rst for an 653 alternative. 654 655 uart[8250],io,<addr>[,options] 656 uart[8250],mmio,<addr>[,options] 657 uart[8250],mmio16,<addr>[,options] 658 uart[8250],mmio32,<addr>[,options] 659 uart[8250],0x<addr>[,options] 660 Start an early, polled-mode console on the 8250/16550 661 UART at the specified I/O port or MMIO address, 662 switching to the matching ttyS device later. 663 MMIO inter-register address stride is either 8-bit 664 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 665 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 666 to be equivalent to 'mmio'. 'options' are specified in 667 the same format described for ttyS above; if unspecified, 668 the h/w is not re-initialized. 669 670 hvc<n> Use the hypervisor console device <n>. This is for 671 both Xen and PowerPC hypervisors. 672 673 If the device connected to the port is not a TTY but a braille 674 device, prepend "brl," before the device type, for instance 675 console=brl,ttyS0 676 For now, only VisioBraille is supported. 677 678 console_msg_format= 679 [KNL] Change console messages format 680 default 681 By default we print messages on consoles in 682 "[time stamp] text\n" format (time stamp may not be 683 printed, depending on CONFIG_PRINTK_TIME or 684 `printk_time' param). 685 syslog 686 Switch to syslog format: "<%u>[time stamp] text\n" 687 IOW, each message will have a facility and loglevel 688 prefix. The format is similar to one used by syslog() 689 syscall, or to executing "dmesg -S --raw" or to reading 690 from /proc/kmsg. 691 692 consoleblank= [KNL] The console blank (screen saver) timeout in 693 seconds. A value of 0 disables the blank timer. 694 Defaults to 0. 695 696 coredump_filter= 697 [KNL] Change the default value for 698 /proc/<pid>/coredump_filter. 699 See also Documentation/filesystems/proc.rst. 700 701 coresight_cpu_debug.enable 702 [ARM,ARM64] 703 Format: <bool> 704 Enable/disable the CPU sampling based debugging. 705 0: default value, disable debugging 706 1: enable debugging at boot time 707 708 cpuidle.off=1 [CPU_IDLE] 709 disable the cpuidle sub-system 710 711 cpuidle.governor= 712 [CPU_IDLE] Name of the cpuidle governor to use. 713 714 cpufreq.off=1 [CPU_FREQ] 715 disable the cpufreq sub-system 716 717 cpufreq.default_governor= 718 [CPU_FREQ] Name of the default cpufreq governor or 719 policy to use. This governor must be registered in the 720 kernel before the cpufreq driver probes. 721 722 cpu_init_udelay=N 723 [X86] Delay for N microsec between assert and de-assert 724 of APIC INIT to start processors. This delay occurs 725 on every CPU online, such as boot, and resume from suspend. 726 Default: 10000 727 728 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 729 Format: 730 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 731 732 crashkernel=size[KMG][@offset[KMG]] 733 [KNL] Using kexec, Linux can switch to a 'crash kernel' 734 upon panic. This parameter reserves the physical 735 memory region [offset, offset + size] for that kernel 736 image. If '@offset' is omitted, then a suitable offset 737 is selected automatically. 738 [KNL, X86-64] Select a region under 4G first, and 739 fall back to reserve region above 4G when '@offset' 740 hasn't been specified. 741 See Documentation/admin-guide/kdump/kdump.rst for further details. 742 743 crashkernel=range1:size1[,range2:size2,...][@offset] 744 [KNL] Same as above, but depends on the memory 745 in the running system. The syntax of range is 746 start-[end] where start and end are both 747 a memory unit (amount[KMG]). See also 748 Documentation/admin-guide/kdump/kdump.rst for an example. 749 750 crashkernel=size[KMG],high 751 [KNL, X86-64] range could be above 4G. Allow kernel 752 to allocate physical memory region from top, so could 753 be above 4G if system have more than 4G ram installed. 754 Otherwise memory region will be allocated below 4G, if 755 available. 756 It will be ignored if crashkernel=X is specified. 757 crashkernel=size[KMG],low 758 [KNL, X86-64] range under 4G. When crashkernel=X,high 759 is passed, kernel could allocate physical memory region 760 above 4G, that cause second kernel crash on system 761 that require some amount of low memory, e.g. swiotlb 762 requires at least 64M+32K low memory, also enough extra 763 low memory is needed to make sure DMA buffers for 32-bit 764 devices won't run out. Kernel would try to allocate at 765 at least 256M below 4G automatically. 766 This one let user to specify own low range under 4G 767 for second kernel instead. 768 0: to disable low allocation. 769 It will be ignored when crashkernel=X,high is not used 770 or memory reserved is below 4G. 771 772 cryptomgr.notests 773 [KNL] Disable crypto self-tests 774 775 cs89x0_dma= [HW,NET] 776 Format: <dma> 777 778 cs89x0_media= [HW,NET] 779 Format: { rj45 | aui | bnc } 780 781 dasd= [HW,NET] 782 See header of drivers/s390/block/dasd_devmap.c. 783 784 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 785 (one device per port) 786 Format: <port#>,<type> 787 See also Documentation/input/devices/joystick-parport.rst 788 789 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 790 time. See 791 Documentation/admin-guide/dynamic-debug-howto.rst for 792 details. Deprecated, see dyndbg. 793 794 debug [KNL] Enable kernel debugging (events log level). 795 796 debug_boot_weak_hash 797 [KNL] Enable printing [hashed] pointers early in the 798 boot sequence. If enabled, we use a weak hash instead 799 of siphash to hash pointers. Use this option if you are 800 seeing instances of '(___ptrval___)') and need to see a 801 value (hashed pointer) instead. Cryptographically 802 insecure, please do not use on production kernels. 803 804 debug_locks_verbose= 805 [KNL] verbose self-tests 806 Format=<0|1> 807 Print debugging info while doing the locking API 808 self-tests. 809 We default to 0 (no extra messages), setting it to 810 1 will print _a lot_ more information - normally 811 only useful to kernel developers. 812 813 debug_objects [KNL] Enable object debugging 814 815 no_debug_objects 816 [KNL] Disable object debugging 817 818 debug_guardpage_minorder= 819 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 820 parameter allows control of the order of pages that will 821 be intentionally kept free (and hence protected) by the 822 buddy allocator. Bigger value increase the probability 823 of catching random memory corruption, but reduce the 824 amount of memory for normal system use. The maximum 825 possible value is MAX_ORDER/2. Setting this parameter 826 to 1 or 2 should be enough to identify most random 827 memory corruption problems caused by bugs in kernel or 828 driver code when a CPU writes to (or reads from) a 829 random memory location. Note that there exists a class 830 of memory corruptions problems caused by buggy H/W or 831 F/W or by drivers badly programing DMA (basically when 832 memory is written at bus level and the CPU MMU is 833 bypassed) which are not detectable by 834 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 835 tracking down these problems. 836 837 debug_pagealloc= 838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 839 enables the feature at boot time. By default, it is 840 disabled and the system will work mostly the same as a 841 kernel built without CONFIG_DEBUG_PAGEALLOC. 842 Note: to get most of debug_pagealloc error reports, it's 843 useful to also enable the page_owner functionality. 844 on: enable the feature 845 846 debugfs= [KNL] This parameter enables what is exposed to userspace 847 and debugfs internal clients. 848 Format: { on, no-mount, off } 849 on: All functions are enabled. 850 no-mount: 851 Filesystem is not registered but kernel clients can 852 access APIs and a crashkernel can be used to read 853 its content. There is nothing to mount. 854 off: Filesystem is not registered and clients 855 get a -EPERM as result when trying to register files 856 or directories within debugfs. 857 This is equivalent of the runtime functionality if 858 debugfs was not enabled in the kernel at all. 859 Default value is set in build-time with a kernel configuration. 860 861 debugpat [X86] Enable PAT debugging 862 863 decnet.addr= [HW,NET] 864 Format: <area>[,<node>] 865 See also Documentation/networking/decnet.rst. 866 867 default_hugepagesz= 868 [HW] The size of the default HugeTLB page. This is 869 the size represented by the legacy /proc/ hugepages 870 APIs. In addition, this is the default hugetlb size 871 used for shmget(), mmap() and mounting hugetlbfs 872 filesystems. If not specified, defaults to the 873 architecture's default huge page size. Huge page 874 sizes are architecture dependent. See also 875 Documentation/admin-guide/mm/hugetlbpage.rst. 876 Format: size[KMG] 877 878 deferred_probe_timeout= 879 [KNL] Debugging option to set a timeout in seconds for 880 deferred probe to give up waiting on dependencies to 881 probe. Only specific dependencies (subsystems or 882 drivers) that have opted in will be ignored. A timeout of 0 883 will timeout at the end of initcalls. This option will also 884 dump out devices still on the deferred probe list after 885 retrying. 886 887 dfltcc= [HW,S390] 888 Format: { on | off | def_only | inf_only | always } 889 on: s390 zlib hardware support for compression on 890 level 1 and decompression (default) 891 off: No s390 zlib hardware support 892 def_only: s390 zlib hardware support for deflate 893 only (compression on level 1) 894 inf_only: s390 zlib hardware support for inflate 895 only (decompression) 896 always: Same as 'on' but ignores the selected compression 897 level always using hardware support (used for debugging) 898 899 dhash_entries= [KNL] 900 Set number of hash buckets for dentry cache. 901 902 disable_1tb_segments [PPC] 903 Disables the use of 1TB hash page table segments. This 904 causes the kernel to fall back to 256MB segments which 905 can be useful when debugging issues that require an SLB 906 miss to occur. 907 908 stress_slb [PPC] 909 Limits the number of kernel SLB entries, and flushes 910 them frequently to increase the rate of SLB faults 911 on kernel addresses. 912 913 disable= [IPV6] 914 See Documentation/networking/ipv6.rst. 915 916 hardened_usercopy= 917 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 918 hardening is enabled for this boot. Hardened 919 usercopy checking is used to protect the kernel 920 from reading or writing beyond known memory 921 allocation boundaries as a proactive defense 922 against bounds-checking flaws in the kernel's 923 copy_to_user()/copy_from_user() interface. 924 on Perform hardened usercopy checks (default). 925 off Disable hardened usercopy checks. 926 927 disable_radix [PPC] 928 Disable RADIX MMU mode on POWER9 929 930 radix_hcall_invalidate=on [PPC/PSERIES] 931 Disable RADIX GTSE feature and use hcall for TLB 932 invalidate. 933 934 disable_tlbie [PPC] 935 Disable TLBIE instruction. Currently does not work 936 with KVM, with HASH MMU, or with coherent accelerators. 937 938 disable_cpu_apicid= [X86,APIC,SMP] 939 Format: <int> 940 The number of initial APIC ID for the 941 corresponding CPU to be disabled at boot, 942 mostly used for the kdump 2nd kernel to 943 disable BSP to wake up multiple CPUs without 944 causing system reset or hang due to sending 945 INIT from AP to BSP. 946 947 perf_v4_pmi= [X86,INTEL] 948 Format: <bool> 949 Disable Intel PMU counter freezing feature. 950 The feature only exists starting from 951 Arch Perfmon v4 (Skylake and newer). 952 953 disable_ddw [PPC/PSERIES] 954 Disable Dynamic DMA Window support. Use this 955 to workaround buggy firmware. 956 957 disable_ipv6= [IPV6] 958 See Documentation/networking/ipv6.rst. 959 960 disable_mtrr_cleanup [X86] 961 The kernel tries to adjust MTRR layout from continuous 962 to discrete, to make X server driver able to add WB 963 entry later. This parameter disables that. 964 965 disable_mtrr_trim [X86, Intel and AMD only] 966 By default the kernel will trim any uncacheable 967 memory out of your available memory pool based on 968 MTRR settings. This parameter disables that behavior, 969 possibly causing your machine to run very slowly. 970 971 disable_timer_pin_1 [X86] 972 Disable PIN 1 of APIC timer 973 Can be useful to work around chipset bugs. 974 975 dis_ucode_ldr [X86] Disable the microcode loader. 976 977 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 978 this option disables the debugging code at boot. 979 980 dma_debug_entries=<number> 981 This option allows to tune the number of preallocated 982 entries for DMA-API debugging code. One entry is 983 required per DMA-API allocation. Use this if the 984 DMA-API debugging code disables itself because the 985 architectural default is too low. 986 987 dma_debug_driver=<driver_name> 988 With this option the DMA-API debugging driver 989 filter feature can be enabled at boot time. Just 990 pass the driver to filter for as the parameter. 991 The filter can be disabled or changed to another 992 driver later using sysfs. 993 994 driver_async_probe= [KNL] 995 List of driver names to be probed asynchronously. 996 Format: <driver_name1>,<driver_name2>... 997 998 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 999 Broken monitors, graphic adapters, KVMs and EDIDless 1000 panels may send no or incorrect EDID data sets. 1001 This parameter allows to specify an EDID data sets 1002 in the /lib/firmware directory that are used instead. 1003 Generic built-in EDID data sets are used, if one of 1004 edid/1024x768.bin, edid/1280x1024.bin, 1005 edid/1680x1050.bin, or edid/1920x1080.bin is given 1006 and no file with the same name exists. Details and 1007 instructions how to build your own EDID data are 1008 available in Documentation/admin-guide/edid.rst. An EDID 1009 data set will only be used for a particular connector, 1010 if its name and a colon are prepended to the EDID 1011 name. Each connector may use a unique EDID data 1012 set by separating the files with a comma. An EDID 1013 data set with no connector name will be used for 1014 any connectors not explicitly specified. 1015 1016 dscc4.setup= [NET] 1017 1018 dt_cpu_ftrs= [PPC] 1019 Format: {"off" | "known"} 1020 Control how the dt_cpu_ftrs device-tree binding is 1021 used for CPU feature discovery and setup (if it 1022 exists). 1023 off: Do not use it, fall back to legacy cpu table. 1024 known: Do not pass through unknown features to guests 1025 or userspace, only those that the kernel is aware of. 1026 1027 dump_apple_properties [X86] 1028 Dump name and content of EFI device properties on 1029 x86 Macs. Useful for driver authors to determine 1030 what data is available or for reverse-engineering. 1031 1032 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1033 <module>.dyndbg[="val"] 1034 Enable debug messages at boot time. See 1035 Documentation/admin-guide/dynamic-debug-howto.rst 1036 for details. 1037 1038 nopku [X86] Disable Memory Protection Keys CPU feature found 1039 in some Intel CPUs. 1040 1041 <module>.async_probe [KNL] 1042 Enable asynchronous probe on this module. 1043 1044 early_ioremap_debug [KNL] 1045 Enable debug messages in early_ioremap support. This 1046 is useful for tracking down temporary early mappings 1047 which are not unmapped. 1048 1049 earlycon= [KNL] Output early console device and options. 1050 1051 When used with no options, the early console is 1052 determined by stdout-path property in device tree's 1053 chosen node or the ACPI SPCR table if supported by 1054 the platform. 1055 1056 cdns,<addr>[,options] 1057 Start an early, polled-mode console on a Cadence 1058 (xuartps) serial port at the specified address. Only 1059 supported option is baud rate. If baud rate is not 1060 specified, the serial port must already be setup and 1061 configured. 1062 1063 uart[8250],io,<addr>[,options] 1064 uart[8250],mmio,<addr>[,options] 1065 uart[8250],mmio32,<addr>[,options] 1066 uart[8250],mmio32be,<addr>[,options] 1067 uart[8250],0x<addr>[,options] 1068 Start an early, polled-mode console on the 8250/16550 1069 UART at the specified I/O port or MMIO address. 1070 MMIO inter-register address stride is either 8-bit 1071 (mmio) or 32-bit (mmio32 or mmio32be). 1072 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1073 to be equivalent to 'mmio'. 'options' are specified 1074 in the same format described for "console=ttyS<n>"; if 1075 unspecified, the h/w is not initialized. 1076 1077 pl011,<addr> 1078 pl011,mmio32,<addr> 1079 Start an early, polled-mode console on a pl011 serial 1080 port at the specified address. The pl011 serial port 1081 must already be setup and configured. Options are not 1082 yet supported. If 'mmio32' is specified, then only 1083 the driver will use only 32-bit accessors to read/write 1084 the device registers. 1085 1086 meson,<addr> 1087 Start an early, polled-mode console on a meson serial 1088 port at the specified address. The serial port must 1089 already be setup and configured. Options are not yet 1090 supported. 1091 1092 msm_serial,<addr> 1093 Start an early, polled-mode console on an msm serial 1094 port at the specified address. The serial port 1095 must already be setup and configured. Options are not 1096 yet supported. 1097 1098 msm_serial_dm,<addr> 1099 Start an early, polled-mode console on an msm serial 1100 dm port at the specified address. The serial port 1101 must already be setup and configured. Options are not 1102 yet supported. 1103 1104 owl,<addr> 1105 Start an early, polled-mode console on a serial port 1106 of an Actions Semi SoC, such as S500 or S900, at the 1107 specified address. The serial port must already be 1108 setup and configured. Options are not yet supported. 1109 1110 rda,<addr> 1111 Start an early, polled-mode console on a serial port 1112 of an RDA Micro SoC, such as RDA8810PL, at the 1113 specified address. The serial port must already be 1114 setup and configured. Options are not yet supported. 1115 1116 sbi 1117 Use RISC-V SBI (Supervisor Binary Interface) for early 1118 console. 1119 1120 smh Use ARM semihosting calls for early console. 1121 1122 s3c2410,<addr> 1123 s3c2412,<addr> 1124 s3c2440,<addr> 1125 s3c6400,<addr> 1126 s5pv210,<addr> 1127 exynos4210,<addr> 1128 Use early console provided by serial driver available 1129 on Samsung SoCs, requires selecting proper type and 1130 a correct base address of the selected UART port. The 1131 serial port must already be setup and configured. 1132 Options are not yet supported. 1133 1134 lantiq,<addr> 1135 Start an early, polled-mode console on a lantiq serial 1136 (lqasc) port at the specified address. The serial port 1137 must already be setup and configured. Options are not 1138 yet supported. 1139 1140 lpuart,<addr> 1141 lpuart32,<addr> 1142 Use early console provided by Freescale LP UART driver 1143 found on Freescale Vybrid and QorIQ LS1021A processors. 1144 A valid base address must be provided, and the serial 1145 port must already be setup and configured. 1146 1147 ec_imx21,<addr> 1148 ec_imx6q,<addr> 1149 Start an early, polled-mode, output-only console on the 1150 Freescale i.MX UART at the specified address. The UART 1151 must already be setup and configured. 1152 1153 ar3700_uart,<addr> 1154 Start an early, polled-mode console on the 1155 Armada 3700 serial port at the specified 1156 address. The serial port must already be setup 1157 and configured. Options are not yet supported. 1158 1159 qcom_geni,<addr> 1160 Start an early, polled-mode console on a Qualcomm 1161 Generic Interface (GENI) based serial port at the 1162 specified address. The serial port must already be 1163 setup and configured. Options are not yet supported. 1164 1165 efifb,[options] 1166 Start an early, unaccelerated console on the EFI 1167 memory mapped framebuffer (if available). On cache 1168 coherent non-x86 systems that use system memory for 1169 the framebuffer, pass the 'ram' option so that it is 1170 mapped with the correct attributes. 1171 1172 linflex,<addr> 1173 Use early console provided by Freescale LINFlexD UART 1174 serial driver for NXP S32V234 SoCs. A valid base 1175 address must be provided, and the serial port must 1176 already be setup and configured. 1177 1178 earlyprintk= [X86,SH,ARM,M68k,S390] 1179 earlyprintk=vga 1180 earlyprintk=sclp 1181 earlyprintk=xen 1182 earlyprintk=serial[,ttySn[,baudrate]] 1183 earlyprintk=serial[,0x...[,baudrate]] 1184 earlyprintk=ttySn[,baudrate] 1185 earlyprintk=dbgp[debugController#] 1186 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1187 earlyprintk=xdbc[xhciController#] 1188 1189 earlyprintk is useful when the kernel crashes before 1190 the normal console is initialized. It is not enabled by 1191 default because it has some cosmetic problems. 1192 1193 Append ",keep" to not disable it when the real console 1194 takes over. 1195 1196 Only one of vga, efi, serial, or usb debug port can 1197 be used at a time. 1198 1199 Currently only ttyS0 and ttyS1 may be specified by 1200 name. Other I/O ports may be explicitly specified 1201 on some architectures (x86 and arm at least) by 1202 replacing ttySn with an I/O port address, like this: 1203 earlyprintk=serial,0x1008,115200 1204 You can find the port for a given device in 1205 /proc/tty/driver/serial: 1206 2: uart:ST16650V2 port:00001008 irq:18 ... 1207 1208 Interaction with the standard serial driver is not 1209 very good. 1210 1211 The VGA and EFI output is eventually overwritten by 1212 the real console. 1213 1214 The xen output can only be used by Xen PV guests. 1215 1216 The sclp output can only be used on s390. 1217 1218 The optional "force" to "pciserial" enables use of a 1219 PCI device even when its classcode is not of the 1220 UART class. 1221 1222 edac_report= [HW,EDAC] Control how to report EDAC event 1223 Format: {"on" | "off" | "force"} 1224 on: enable EDAC to report H/W event. May be overridden 1225 by other higher priority error reporting module. 1226 off: disable H/W event reporting through EDAC. 1227 force: enforce the use of EDAC to report H/W event. 1228 default: on. 1229 1230 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1231 ekgdboc=kbd 1232 1233 This is designed to be used in conjunction with 1234 the boot argument: earlyprintk=vga 1235 1236 This parameter works in place of the kgdboc parameter 1237 but can only be used if the backing tty is available 1238 very early in the boot process. For early debugging 1239 via a serial port see kgdboc_earlycon instead. 1240 1241 edd= [EDD] 1242 Format: {"off" | "on" | "skip[mbr]"} 1243 1244 efi= [EFI] 1245 Format: { "debug", "disable_early_pci_dma", 1246 "nochunk", "noruntime", "nosoftreserve", 1247 "novamap", "no_disable_early_pci_dma" } 1248 debug: enable misc debug output. 1249 disable_early_pci_dma: disable the busmaster bit on all 1250 PCI bridges while in the EFI boot stub. 1251 nochunk: disable reading files in "chunks" in the EFI 1252 boot stub, as chunking can cause problems with some 1253 firmware implementations. 1254 noruntime : disable EFI runtime services support 1255 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1256 attribute may cause the kernel to reserve the 1257 memory range for a memory mapping driver to 1258 claim. Specify efi=nosoftreserve to disable this 1259 reservation and treat the memory by its base type 1260 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1261 novamap: do not call SetVirtualAddressMap(). 1262 no_disable_early_pci_dma: Leave the busmaster bit set 1263 on all PCI bridges while in the EFI boot stub 1264 1265 efi_no_storage_paranoia [EFI; X86] 1266 Using this parameter you can use more than 50% of 1267 your efi variable storage. Use this parameter only if 1268 you are really sure that your UEFI does sane gc and 1269 fulfills the spec otherwise your board may brick. 1270 1271 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1272 Add arbitrary attribute to specific memory range by 1273 updating original EFI memory map. 1274 Region of memory which aa attribute is added to is 1275 from ss to ss+nn. 1276 1277 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1278 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1279 attribute is added to range 0x100000000-0x180000000 and 1280 0x10a0000000-0x1120000000. 1281 1282 If efi_fake_mem=8G@9G:0x40000 is specified, the 1283 EFI_MEMORY_SP(0x40000) attribute is added to 1284 range 0x240000000-0x43fffffff. 1285 1286 Using this parameter you can do debugging of EFI memmap 1287 related features. For example, you can do debugging of 1288 Address Range Mirroring feature even if your box 1289 doesn't support it, or mark specific memory as 1290 "soft reserved". 1291 1292 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1293 that is to be dynamically loaded by Linux. If there are 1294 multiple variables with the same name but with different 1295 vendor GUIDs, all of them will be loaded. See 1296 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1297 1298 1299 eisa_irq_edge= [PARISC,HW] 1300 See header of drivers/parisc/eisa.c. 1301 1302 elanfreq= [X86-32] 1303 See comment before function elanfreq_setup() in 1304 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1305 1306 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1307 Specifies physical address of start of kernel core 1308 image elf header and optionally the size. Generally 1309 kexec loader will pass this option to capture kernel. 1310 See Documentation/admin-guide/kdump/kdump.rst for details. 1311 1312 enable_mtrr_cleanup [X86] 1313 The kernel tries to adjust MTRR layout from continuous 1314 to discrete, to make X server driver able to add WB 1315 entry later. This parameter enables that. 1316 1317 enable_timer_pin_1 [X86] 1318 Enable PIN 1 of APIC timer 1319 Can be useful to work around chipset bugs 1320 (in particular on some ATI chipsets). 1321 The kernel tries to set a reasonable default. 1322 1323 enforcing [SELINUX] Set initial enforcing status. 1324 Format: {"0" | "1"} 1325 See security/selinux/Kconfig help text. 1326 0 -- permissive (log only, no denials). 1327 1 -- enforcing (deny and log). 1328 Default value is 0. 1329 Value can be changed at runtime via 1330 /sys/fs/selinux/enforce. 1331 1332 erst_disable [ACPI] 1333 Disable Error Record Serialization Table (ERST) 1334 support. 1335 1336 ether= [HW,NET] Ethernet cards parameters 1337 This option is obsoleted by the "netdev=" option, which 1338 has equivalent usage. See its documentation for details. 1339 1340 evm= [EVM] 1341 Format: { "fix" } 1342 Permit 'security.evm' to be updated regardless of 1343 current integrity status. 1344 1345 failslab= 1346 fail_page_alloc= 1347 fail_make_request=[KNL] 1348 General fault injection mechanism. 1349 Format: <interval>,<probability>,<space>,<times> 1350 See also Documentation/fault-injection/. 1351 1352 floppy= [HW] 1353 See Documentation/admin-guide/blockdev/floppy.rst. 1354 1355 force_pal_cache_flush 1356 [IA-64] Avoid check_sal_cache_flush which may hang on 1357 buggy SAL_CACHE_FLUSH implementations. Using this 1358 parameter will force ia64_sal_cache_flush to call 1359 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1360 1361 forcepae [X86-32] 1362 Forcefully enable Physical Address Extension (PAE). 1363 Many Pentium M systems disable PAE but may have a 1364 functionally usable PAE implementation. 1365 Warning: use of this parameter will taint the kernel 1366 and may cause unknown problems. 1367 1368 ftrace=[tracer] 1369 [FTRACE] will set and start the specified tracer 1370 as early as possible in order to facilitate early 1371 boot debugging. 1372 1373 ftrace_dump_on_oops[=orig_cpu] 1374 [FTRACE] will dump the trace buffers on oops. 1375 If no parameter is passed, ftrace will dump 1376 buffers of all CPUs, but if you pass orig_cpu, it will 1377 dump only the buffer of the CPU that triggered the 1378 oops. 1379 1380 ftrace_filter=[function-list] 1381 [FTRACE] Limit the functions traced by the function 1382 tracer at boot up. function-list is a comma separated 1383 list of functions. This list can be changed at run 1384 time by the set_ftrace_filter file in the debugfs 1385 tracing directory. 1386 1387 ftrace_notrace=[function-list] 1388 [FTRACE] Do not trace the functions specified in 1389 function-list. This list can be changed at run time 1390 by the set_ftrace_notrace file in the debugfs 1391 tracing directory. 1392 1393 ftrace_graph_filter=[function-list] 1394 [FTRACE] Limit the top level callers functions traced 1395 by the function graph tracer at boot up. 1396 function-list is a comma separated list of functions 1397 that can be changed at run time by the 1398 set_graph_function file in the debugfs tracing directory. 1399 1400 ftrace_graph_notrace=[function-list] 1401 [FTRACE] Do not trace from the functions specified in 1402 function-list. This list is a comma separated list of 1403 functions that can be changed at run time by the 1404 set_graph_notrace file in the debugfs tracing directory. 1405 1406 ftrace_graph_max_depth=<uint> 1407 [FTRACE] Used with the function graph tracer. This is 1408 the max depth it will trace into a function. This value 1409 can be changed at run time by the max_graph_depth file 1410 in the tracefs tracing directory. default: 0 (no limit) 1411 1412 fw_devlink= [KNL] Create device links between consumer and supplier 1413 devices by scanning the firmware to infer the 1414 consumer/supplier relationships. This feature is 1415 especially useful when drivers are loaded as modules as 1416 it ensures proper ordering of tasks like device probing 1417 (suppliers first, then consumers), supplier boot state 1418 clean up (only after all consumers have probed), 1419 suspend/resume & runtime PM (consumers first, then 1420 suppliers). 1421 Format: { off | permissive | on | rpm } 1422 off -- Don't create device links from firmware info. 1423 permissive -- Create device links from firmware info 1424 but use it only for ordering boot state clean 1425 up (sync_state() calls). 1426 on -- Create device links from firmware info and use it 1427 to enforce probe and suspend/resume ordering. 1428 rpm -- Like "on", but also use to order runtime PM. 1429 1430 gamecon.map[2|3]= 1431 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1432 support via parallel port (up to 5 devices per port) 1433 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1434 See also Documentation/input/devices/joystick-parport.rst 1435 1436 gamma= [HW,DRM] 1437 1438 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1439 Format: off | on 1440 default: on 1441 1442 gcov_persist= [GCOV] When non-zero (default), profiling data for 1443 kernel modules is saved and remains accessible via 1444 debugfs, even when the module is unloaded/reloaded. 1445 When zero, profiling data is discarded and associated 1446 debugfs files are removed at module unload time. 1447 1448 goldfish [X86] Enable the goldfish android emulator platform. 1449 Don't use this when you are not running on the 1450 android emulator 1451 1452 gpt [EFI] Forces disk with valid GPT signature but 1453 invalid Protective MBR to be treated as GPT. If the 1454 primary GPT is corrupted, it enables the backup/alternate 1455 GPT to be used instead. 1456 1457 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1458 the "Enable 0" bit of the configuration register. 1459 Format: 0 | 1 1460 Default: 0 1461 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1462 the "Enable 0" bit of the configuration register. 1463 Format: 0 | 1 1464 Default: 0 1465 grcan.select= [HW] Select which physical interface to use. 1466 Format: 0 | 1 1467 Default: 0 1468 grcan.txsize= [HW] Sets the size of the tx buffer. 1469 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1470 Default: 1024 1471 grcan.rxsize= [HW] Sets the size of the rx buffer. 1472 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1473 Default: 1024 1474 1475 gpio-mockup.gpio_mockup_ranges 1476 [HW] Sets the ranges of gpiochip of for this device. 1477 Format: <start1>,<end1>,<start2>,<end2>... 1478 1479 hardlockup_all_cpu_backtrace= 1480 [KNL] Should the hard-lockup detector generate 1481 backtraces on all cpus. 1482 Format: 0 | 1 1483 1484 hashdist= [KNL,NUMA] Large hashes allocated during boot 1485 are distributed across NUMA nodes. Defaults on 1486 for 64-bit NUMA, off otherwise. 1487 Format: 0 | 1 (for off | on) 1488 1489 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1490 1491 hd= [EIDE] (E)IDE hard drive subsystem geometry 1492 Format: <cyl>,<head>,<sect> 1493 1494 hest_disable [ACPI] 1495 Disable Hardware Error Source Table (HEST) support; 1496 corresponding firmware-first mode error processing 1497 logic will be disabled. 1498 1499 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1500 size of <nn>. This works even on boxes that have no 1501 highmem otherwise. This also works to reduce highmem 1502 size on bigger boxes. 1503 1504 highres= [KNL] Enable/disable high resolution timer mode. 1505 Valid parameters: "on", "off" 1506 Default: "on" 1507 1508 hlt [BUGS=ARM,SH] 1509 1510 hpet= [X86-32,HPET] option to control HPET usage 1511 Format: { enable (default) | disable | force | 1512 verbose } 1513 disable: disable HPET and use PIT instead 1514 force: allow force enabled of undocumented chips (ICH4, 1515 VIA, nVidia) 1516 verbose: show contents of HPET registers during setup 1517 1518 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1519 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1520 1521 hugetlb_cma= [HW] The size of a cma area used for allocation 1522 of gigantic hugepages. 1523 Format: nn[KMGTPE] 1524 1525 Reserve a cma area of given size and allocate gigantic 1526 hugepages using the cma allocator. If enabled, the 1527 boot-time allocation of gigantic hugepages is skipped. 1528 1529 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1530 If this follows hugepagesz (below), it specifies 1531 the number of pages of hugepagesz to be allocated. 1532 If this is the first HugeTLB parameter on the command 1533 line, it specifies the number of pages to allocate for 1534 the default huge page size. See also 1535 Documentation/admin-guide/mm/hugetlbpage.rst. 1536 Format: <integer> 1537 1538 hugepagesz= 1539 [HW] The size of the HugeTLB pages. This is used in 1540 conjunction with hugepages (above) to allocate huge 1541 pages of a specific size at boot. The pair 1542 hugepagesz=X hugepages=Y can be specified once for 1543 each supported huge page size. Huge page sizes are 1544 architecture dependent. See also 1545 Documentation/admin-guide/mm/hugetlbpage.rst. 1546 Format: size[KMG] 1547 1548 hung_task_panic= 1549 [KNL] Should the hung task detector generate panics. 1550 Format: 0 | 1 1551 1552 A value of 1 instructs the kernel to panic when a 1553 hung task is detected. The default value is controlled 1554 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1555 option. The value selected by this boot parameter can 1556 be changed later by the kernel.hung_task_panic sysctl. 1557 1558 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1559 terminal devices. Valid values: 0..8 1560 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1561 If specified, z/VM IUCV HVC accepts connections 1562 from listed z/VM user IDs only. 1563 1564 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1565 which allow the hypervisor to 'idle' the 1566 guest on lock contention. 1567 1568 keep_bootcon [KNL] 1569 Do not unregister boot console at start. This is only 1570 useful for debugging when something happens in the window 1571 between unregistering the boot console and initializing 1572 the real console. 1573 1574 i2c_bus= [HW] Override the default board specific I2C bus speed 1575 or register an additional I2C bus that is not 1576 registered from board initialization code. 1577 Format: 1578 <bus_id>,<clkrate> 1579 1580 i8042.debug [HW] Toggle i8042 debug mode 1581 i8042.unmask_kbd_data 1582 [HW] Enable printing of interrupt data from the KBD port 1583 (disabled by default, and as a pre-condition 1584 requires that i8042.debug=1 be enabled) 1585 i8042.direct [HW] Put keyboard port into non-translated mode 1586 i8042.dumbkbd [HW] Pretend that controller can only read data from 1587 keyboard and cannot control its state 1588 (Don't attempt to blink the leds) 1589 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1590 i8042.nokbd [HW] Don't check/create keyboard port 1591 i8042.noloop [HW] Disable the AUX Loopback command while probing 1592 for the AUX port 1593 i8042.nomux [HW] Don't check presence of an active multiplexing 1594 controller 1595 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1596 controllers 1597 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1598 i8042.reset [HW] Reset the controller during init, cleanup and 1599 suspend-to-ram transitions, only during s2r 1600 transitions, or never reset 1601 Format: { 1 | Y | y | 0 | N | n } 1602 1, Y, y: always reset controller 1603 0, N, n: don't ever reset controller 1604 Default: only on s2r transitions on x86; most other 1605 architectures force reset to be always executed 1606 i8042.unlock [HW] Unlock (ignore) the keylock 1607 i8042.kbdreset [HW] Reset device connected to KBD port 1608 1609 i810= [HW,DRM] 1610 1611 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1612 indicates that the driver is running on unsupported 1613 hardware. 1614 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1615 does not match list of supported models. 1616 i8k.power_status 1617 [HW] Report power status in /proc/i8k 1618 (disabled by default) 1619 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1620 capability is set. 1621 1622 i915.invert_brightness= 1623 [DRM] Invert the sense of the variable that is used to 1624 set the brightness of the panel backlight. Normally a 1625 brightness value of 0 indicates backlight switched off, 1626 and the maximum of the brightness value sets the backlight 1627 to maximum brightness. If this parameter is set to 0 1628 (default) and the machine requires it, or this parameter 1629 is set to 1, a brightness value of 0 sets the backlight 1630 to maximum brightness, and the maximum of the brightness 1631 value switches the backlight off. 1632 -1 -- never invert brightness 1633 0 -- machine default 1634 1 -- force brightness inversion 1635 1636 icn= [HW,ISDN] 1637 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1638 1639 ide-core.nodma= [HW] (E)IDE subsystem 1640 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1641 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1642 .cdrom .chs .ignore_cable are additional options 1643 See Documentation/ide/ide.rst. 1644 1645 ide-generic.probe-mask= [HW] (E)IDE subsystem 1646 Format: <int> 1647 Probe mask for legacy ISA IDE ports. Depending on 1648 platform up to 6 ports are supported, enabled by 1649 setting corresponding bits in the mask to 1. The 1650 default value is 0x0, which has a special meaning. 1651 On systems that have PCI, it triggers scanning the 1652 PCI bus for the first and the second port, which 1653 are then probed. On systems without PCI the value 1654 of 0x0 enables probing the two first ports as if it 1655 was 0x3. 1656 1657 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1658 Claim all unknown PCI IDE storage controllers. 1659 1660 idle= [X86] 1661 Format: idle=poll, idle=halt, idle=nomwait 1662 Poll forces a polling idle loop that can slightly 1663 improve the performance of waking up a idle CPU, but 1664 will use a lot of power and make the system run hot. 1665 Not recommended. 1666 idle=halt: Halt is forced to be used for CPU idle. 1667 In such case C2/C3 won't be used again. 1668 idle=nomwait: Disable mwait for CPU C-states 1669 1670 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1671 Format: { strict | legacy | 2008 | relaxed } 1672 Default: strict 1673 1674 Choose which programs will be accepted for execution 1675 based on the IEEE 754 NaN encoding(s) supported by 1676 the FPU and the NaN encoding requested with the value 1677 of an ELF file header flag individually set by each 1678 binary. Hardware implementations are permitted to 1679 support either or both of the legacy and the 2008 NaN 1680 encoding mode. 1681 1682 Available settings are as follows: 1683 strict accept binaries that request a NaN encoding 1684 supported by the FPU 1685 legacy only accept legacy-NaN binaries, if supported 1686 by the FPU 1687 2008 only accept 2008-NaN binaries, if supported 1688 by the FPU 1689 relaxed accept any binaries regardless of whether 1690 supported by the FPU 1691 1692 The FPU emulator is always able to support both NaN 1693 encodings, so if no FPU hardware is present or it has 1694 been disabled with 'nofpu', then the settings of 1695 'legacy' and '2008' strap the emulator accordingly, 1696 'relaxed' straps the emulator for both legacy-NaN and 1697 2008-NaN, whereas 'strict' enables legacy-NaN only on 1698 legacy processors and both NaN encodings on MIPS32 or 1699 MIPS64 CPUs. 1700 1701 The setting for ABS.fmt/NEG.fmt instruction execution 1702 mode generally follows that for the NaN encoding, 1703 except where unsupported by hardware. 1704 1705 ignore_loglevel [KNL] 1706 Ignore loglevel setting - this will print /all/ 1707 kernel messages to the console. Useful for debugging. 1708 We also add it as printk module parameter, so users 1709 could change it dynamically, usually by 1710 /sys/module/printk/parameters/ignore_loglevel. 1711 1712 ignore_rlimit_data 1713 Ignore RLIMIT_DATA setting for data mappings, 1714 print warning at first misuse. Can be changed via 1715 /sys/module/kernel/parameters/ignore_rlimit_data. 1716 1717 ihash_entries= [KNL] 1718 Set number of hash buckets for inode cache. 1719 1720 ima_appraise= [IMA] appraise integrity measurements 1721 Format: { "off" | "enforce" | "fix" | "log" } 1722 default: "enforce" 1723 1724 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1725 The builtin appraise policy appraises all files 1726 owned by uid=0. 1727 1728 ima_canonical_fmt [IMA] 1729 Use the canonical format for the binary runtime 1730 measurements, instead of host native format. 1731 1732 ima_hash= [IMA] 1733 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1734 | sha512 | ... } 1735 default: "sha1" 1736 1737 The list of supported hash algorithms is defined 1738 in crypto/hash_info.h. 1739 1740 ima_policy= [IMA] 1741 The builtin policies to load during IMA setup. 1742 Format: "tcb | appraise_tcb | secure_boot | 1743 fail_securely" 1744 1745 The "tcb" policy measures all programs exec'd, files 1746 mmap'd for exec, and all files opened with the read 1747 mode bit set by either the effective uid (euid=0) or 1748 uid=0. 1749 1750 The "appraise_tcb" policy appraises the integrity of 1751 all files owned by root. 1752 1753 The "secure_boot" policy appraises the integrity 1754 of files (eg. kexec kernel image, kernel modules, 1755 firmware, policy, etc) based on file signatures. 1756 1757 The "fail_securely" policy forces file signature 1758 verification failure also on privileged mounted 1759 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1760 flag. 1761 1762 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1763 Load a policy which meets the needs of the Trusted 1764 Computing Base. This means IMA will measure all 1765 programs exec'd, files mmap'd for exec, and all files 1766 opened for read by uid=0. 1767 1768 ima_template= [IMA] 1769 Select one of defined IMA measurements template formats. 1770 Formats: { "ima" | "ima-ng" | "ima-sig" } 1771 Default: "ima-ng" 1772 1773 ima_template_fmt= 1774 [IMA] Define a custom template format. 1775 Format: { "field1|...|fieldN" } 1776 1777 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1778 Format: <min_file_size> 1779 Set the minimal file size for using asynchronous hash. 1780 If left unspecified, ahash usage is disabled. 1781 1782 ahash performance varies for different data sizes on 1783 different crypto accelerators. This option can be used 1784 to achieve the best performance for a particular HW. 1785 1786 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1787 Format: <bufsize> 1788 Set hashing buffer size. Default: 4k. 1789 1790 ahash performance varies for different chunk sizes on 1791 different crypto accelerators. This option can be used 1792 to achieve best performance for particular HW. 1793 1794 init= [KNL] 1795 Format: <full_path> 1796 Run specified binary instead of /sbin/init as init 1797 process. 1798 1799 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1800 for working out where the kernel is dying during 1801 startup. 1802 1803 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1804 initcall functions. Useful for debugging built-in 1805 modules and initcalls. 1806 1807 initrd= [BOOT] Specify the location of the initial ramdisk 1808 1809 initrdmem= [KNL] Specify a physical address and size from which to 1810 load the initrd. If an initrd is compiled in or 1811 specified in the bootparams, it takes priority over this 1812 setting. 1813 Format: ss[KMG],nn[KMG] 1814 Default is 0, 0 1815 1816 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1817 zeroes. 1818 Format: 0 | 1 1819 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1820 1821 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1822 Format: 0 | 1 1823 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1824 1825 init_pkru= [X86] Specify the default memory protection keys rights 1826 register contents for all processes. 0x55555554 by 1827 default (disallow access to all but pkey 0). Can 1828 override in debugfs after boot. 1829 1830 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1831 Format: <irq> 1832 1833 int_pln_enable [X86] Enable power limit notification interrupt 1834 1835 integrity_audit=[IMA] 1836 Format: { "0" | "1" } 1837 0 -- basic integrity auditing messages. (Default) 1838 1 -- additional integrity auditing messages. 1839 1840 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1841 on 1842 Enable intel iommu driver. 1843 off 1844 Disable intel iommu driver. 1845 igfx_off [Default Off] 1846 By default, gfx is mapped as normal device. If a gfx 1847 device has a dedicated DMAR unit, the DMAR unit is 1848 bypassed by not enabling DMAR with this option. In 1849 this case, gfx device will use physical address for 1850 DMA. 1851 forcedac [X86-64] 1852 With this option iommu will not optimize to look 1853 for io virtual address below 32-bit forcing dual 1854 address cycle on pci bus for cards supporting greater 1855 than 32-bit addressing. The default is to look 1856 for translation below 32-bit and if not available 1857 then look in the higher range. 1858 strict [Default Off] 1859 With this option on every unmap_single operation will 1860 result in a hardware IOTLB flush operation as opposed 1861 to batching them for performance. 1862 sp_off [Default Off] 1863 By default, super page will be supported if Intel IOMMU 1864 has the capability. With this option, super page will 1865 not be supported. 1866 sm_on [Default Off] 1867 By default, scalable mode will be disabled even if the 1868 hardware advertises that it has support for the scalable 1869 mode translation. With this option set, scalable mode 1870 will be used on hardware which claims to support it. 1871 tboot_noforce [Default Off] 1872 Do not force the Intel IOMMU enabled under tboot. 1873 By default, tboot will force Intel IOMMU on, which 1874 could harm performance of some high-throughput 1875 devices like 40GBit network cards, even if identity 1876 mapping is enabled. 1877 Note that using this option lowers the security 1878 provided by tboot because it makes the system 1879 vulnerable to DMA attacks. 1880 nobounce [Default off] 1881 Disable bounce buffer for untrusted devices such as 1882 the Thunderbolt devices. This will treat the untrusted 1883 devices as the trusted ones, hence might expose security 1884 risks of DMA attacks. 1885 1886 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1887 0 disables intel_idle and fall back on acpi_idle. 1888 1 to 9 specify maximum depth of C-state. 1889 1890 intel_pstate= [X86] 1891 disable 1892 Do not enable intel_pstate as the default 1893 scaling driver for the supported processors 1894 passive 1895 Use intel_pstate as a scaling driver, but configure it 1896 to work with generic cpufreq governors (instead of 1897 enabling its internal governor). This mode cannot be 1898 used along with the hardware-managed P-states (HWP) 1899 feature. 1900 force 1901 Enable intel_pstate on systems that prohibit it by default 1902 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1903 instead of acpi-cpufreq may disable platform features, such 1904 as thermal controls and power capping, that rely on ACPI 1905 P-States information being indicated to OSPM and therefore 1906 should be used with caution. This option does not work with 1907 processors that aren't supported by the intel_pstate driver 1908 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1909 no_hwp 1910 Do not enable hardware P state control (HWP) 1911 if available. 1912 hwp_only 1913 Only load intel_pstate on systems which support 1914 hardware P state control (HWP) if available. 1915 support_acpi_ppc 1916 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1917 Description Table, specifies preferred power management 1918 profile as "Enterprise Server" or "Performance Server", 1919 then this feature is turned on by default. 1920 per_cpu_perf_limits 1921 Allow per-logical-CPU P-State performance control limits using 1922 cpufreq sysfs interface 1923 1924 intremap= [X86-64, Intel-IOMMU] 1925 on enable Interrupt Remapping (default) 1926 off disable Interrupt Remapping 1927 nosid disable Source ID checking 1928 no_x2apic_optout 1929 BIOS x2APIC opt-out request will be ignored 1930 nopost disable Interrupt Posting 1931 1932 iomem= Disable strict checking of access to MMIO memory 1933 strict regions from userspace. 1934 relaxed 1935 1936 iommu= [X86] 1937 off 1938 force 1939 noforce 1940 biomerge 1941 panic 1942 nopanic 1943 merge 1944 nomerge 1945 soft 1946 pt [X86] 1947 nopt [X86] 1948 nobypass [PPC/POWERNV] 1949 Disable IOMMU bypass, using IOMMU for PCI devices. 1950 1951 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1952 Format: { "0" | "1" } 1953 0 - Lazy mode. 1954 Request that DMA unmap operations use deferred 1955 invalidation of hardware TLBs, for increased 1956 throughput at the cost of reduced device isolation. 1957 Will fall back to strict mode if not supported by 1958 the relevant IOMMU driver. 1959 1 - Strict mode (default). 1960 DMA unmap operations invalidate IOMMU hardware TLBs 1961 synchronously. 1962 1963 iommu.passthrough= 1964 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1965 Format: { "0" | "1" } 1966 0 - Use IOMMU translation for DMA. 1967 1 - Bypass the IOMMU for DMA. 1968 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1969 1970 io7= [HW] IO7 for Marvel-based Alpha systems 1971 See comment before marvel_specify_io7 in 1972 arch/alpha/kernel/core_marvel.c. 1973 1974 io_delay= [X86] I/O delay method 1975 0x80 1976 Standard port 0x80 based delay 1977 0xed 1978 Alternate port 0xed based delay (needed on some systems) 1979 udelay 1980 Simple two microseconds delay 1981 none 1982 No delay 1983 1984 ip= [IP_PNP] 1985 See Documentation/admin-guide/nfs/nfsroot.rst. 1986 1987 ipcmni_extend [KNL] Extend the maximum number of unique System V 1988 IPC identifiers from 32,768 to 16,777,216. 1989 1990 irqaffinity= [SMP] Set the default irq affinity mask 1991 The argument is a cpu list, as described above. 1992 1993 irqchip.gicv2_force_probe= 1994 [ARM, ARM64] 1995 Format: <bool> 1996 Force the kernel to look for the second 4kB page 1997 of a GICv2 controller even if the memory range 1998 exposed by the device tree is too small. 1999 2000 irqchip.gicv3_nolpi= 2001 [ARM, ARM64] 2002 Force the kernel to ignore the availability of 2003 LPIs (and by consequence ITSs). Intended for system 2004 that use the kernel as a bootloader, and thus want 2005 to let secondary kernels in charge of setting up 2006 LPIs. 2007 2008 irqchip.gicv3_pseudo_nmi= [ARM64] 2009 Enables support for pseudo-NMIs in the kernel. This 2010 requires the kernel to be built with 2011 CONFIG_ARM64_PSEUDO_NMI. 2012 2013 irqfixup [HW] 2014 When an interrupt is not handled search all handlers 2015 for it. Intended to get systems with badly broken 2016 firmware running. 2017 2018 irqpoll [HW] 2019 When an interrupt is not handled search all handlers 2020 for it. Also check all handlers each timer 2021 interrupt. Intended to get systems with badly broken 2022 firmware running. 2023 2024 isapnp= [ISAPNP] 2025 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2026 2027 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2028 [Deprecated - use cpusets instead] 2029 Format: [flag-list,]<cpu-list> 2030 2031 Specify one or more CPUs to isolate from disturbances 2032 specified in the flag list (default: domain): 2033 2034 nohz 2035 Disable the tick when a single task runs. 2036 2037 A residual 1Hz tick is offloaded to workqueues, which you 2038 need to affine to housekeeping through the global 2039 workqueue's affinity configured via the 2040 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2041 by using the 'domain' flag described below. 2042 2043 NOTE: by default the global workqueue runs on all CPUs, 2044 so to protect individual CPUs the 'cpumask' file has to 2045 be configured manually after bootup. 2046 2047 domain 2048 Isolate from the general SMP balancing and scheduling 2049 algorithms. Note that performing domain isolation this way 2050 is irreversible: it's not possible to bring back a CPU to 2051 the domains once isolated through isolcpus. It's strongly 2052 advised to use cpusets instead to disable scheduler load 2053 balancing through the "cpuset.sched_load_balance" file. 2054 It offers a much more flexible interface where CPUs can 2055 move in and out of an isolated set anytime. 2056 2057 You can move a process onto or off an "isolated" CPU via 2058 the CPU affinity syscalls or cpuset. 2059 <cpu number> begins at 0 and the maximum value is 2060 "number of CPUs in system - 1". 2061 2062 managed_irq 2063 2064 Isolate from being targeted by managed interrupts 2065 which have an interrupt mask containing isolated 2066 CPUs. The affinity of managed interrupts is 2067 handled by the kernel and cannot be changed via 2068 the /proc/irq/* interfaces. 2069 2070 This isolation is best effort and only effective 2071 if the automatically assigned interrupt mask of a 2072 device queue contains isolated and housekeeping 2073 CPUs. If housekeeping CPUs are online then such 2074 interrupts are directed to the housekeeping CPU 2075 so that IO submitted on the housekeeping CPU 2076 cannot disturb the isolated CPU. 2077 2078 If a queue's affinity mask contains only isolated 2079 CPUs then this parameter has no effect on the 2080 interrupt routing decision, though interrupts are 2081 only delivered when tasks running on those 2082 isolated CPUs submit IO. IO submitted on 2083 housekeeping CPUs has no influence on those 2084 queues. 2085 2086 The format of <cpu-list> is described above. 2087 2088 iucv= [HW,NET] 2089 2090 ivrs_ioapic [HW,X86-64] 2091 Provide an override to the IOAPIC-ID<->DEVICE-ID 2092 mapping provided in the IVRS ACPI table. For 2093 example, to map IOAPIC-ID decimal 10 to 2094 PCI device 00:14.0 write the parameter as: 2095 ivrs_ioapic[10]=00:14.0 2096 2097 ivrs_hpet [HW,X86-64] 2098 Provide an override to the HPET-ID<->DEVICE-ID 2099 mapping provided in the IVRS ACPI table. For 2100 example, to map HPET-ID decimal 0 to 2101 PCI device 00:14.0 write the parameter as: 2102 ivrs_hpet[0]=00:14.0 2103 2104 ivrs_acpihid [HW,X86-64] 2105 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2106 mapping provided in the IVRS ACPI table. For 2107 example, to map UART-HID:UID AMD0020:0 to 2108 PCI device 00:14.5 write the parameter as: 2109 ivrs_acpihid[00:14.5]=AMD0020:0 2110 2111 js= [HW,JOY] Analog joystick 2112 See Documentation/input/joydev/joystick.rst. 2113 2114 nokaslr [KNL] 2115 When CONFIG_RANDOMIZE_BASE is set, this disables 2116 kernel and module base offset ASLR (Address Space 2117 Layout Randomization). 2118 2119 kasan_multi_shot 2120 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2121 report on every invalid memory access. Without this 2122 parameter KASAN will print report only for the first 2123 invalid access. 2124 2125 keepinitrd [HW,ARM] 2126 2127 kernelcore= [KNL,X86,IA-64,PPC] 2128 Format: nn[KMGTPE] | nn% | "mirror" 2129 This parameter specifies the amount of memory usable by 2130 the kernel for non-movable allocations. The requested 2131 amount is spread evenly throughout all nodes in the 2132 system as ZONE_NORMAL. The remaining memory is used for 2133 movable memory in its own zone, ZONE_MOVABLE. In the 2134 event, a node is too small to have both ZONE_NORMAL and 2135 ZONE_MOVABLE, kernelcore memory will take priority and 2136 other nodes will have a larger ZONE_MOVABLE. 2137 2138 ZONE_MOVABLE is used for the allocation of pages that 2139 may be reclaimed or moved by the page migration 2140 subsystem. Note that allocations like PTEs-from-HighMem 2141 still use the HighMem zone if it exists, and the Normal 2142 zone if it does not. 2143 2144 It is possible to specify the exact amount of memory in 2145 the form of "nn[KMGTPE]", a percentage of total system 2146 memory in the form of "nn%", or "mirror". If "mirror" 2147 option is specified, mirrored (reliable) memory is used 2148 for non-movable allocations and remaining memory is used 2149 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2150 are exclusive, so you cannot specify multiple forms. 2151 2152 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2153 Format: <Controller#>[,poll interval] 2154 The controller # is the number of the ehci usb debug 2155 port as it is probed via PCI. The poll interval is 2156 optional and is the number seconds in between 2157 each poll cycle to the debug port in case you need 2158 the functionality for interrupting the kernel with 2159 gdb or control-c on the dbgp connection. When 2160 not using this parameter you use sysrq-g to break into 2161 the kernel debugger. 2162 2163 kgdboc= [KGDB,HW] kgdb over consoles. 2164 Requires a tty driver that supports console polling, 2165 or a supported polling keyboard driver (non-usb). 2166 Serial only format: <serial_device>[,baud] 2167 keyboard only format: kbd 2168 keyboard and serial format: kbd,<serial_device>[,baud] 2169 Optional Kernel mode setting: 2170 kms, kbd format: kms,kbd 2171 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2172 2173 kgdboc_earlycon= [KGDB,HW] 2174 If the boot console provides the ability to read 2175 characters and can work in polling mode, you can use 2176 this parameter to tell kgdb to use it as a backend 2177 until the normal console is registered. Intended to 2178 be used together with the kgdboc parameter which 2179 specifies the normal console to transition to. 2180 2181 The name of the early console should be specified 2182 as the value of this parameter. Note that the name of 2183 the early console might be different than the tty 2184 name passed to kgdboc. It's OK to leave the value 2185 blank and the first boot console that implements 2186 read() will be picked. 2187 2188 kgdbwait [KGDB] Stop kernel execution and enter the 2189 kernel debugger at the earliest opportunity. 2190 2191 kmac= [MIPS] Korina ethernet MAC address. 2192 Configure the RouterBoard 532 series on-chip 2193 Ethernet adapter MAC address. 2194 2195 kmemleak= [KNL] Boot-time kmemleak enable/disable 2196 Valid arguments: on, off 2197 Default: on 2198 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2199 the default is off. 2200 2201 kprobe_event=[probe-list] 2202 [FTRACE] Add kprobe events and enable at boot time. 2203 The probe-list is a semicolon delimited list of probe 2204 definitions. Each definition is same as kprobe_events 2205 interface, but the parameters are comma delimited. 2206 For example, to add a kprobe event on vfs_read with 2207 arg1 and arg2, add to the command line; 2208 2209 kprobe_event=p,vfs_read,$arg1,$arg2 2210 2211 See also Documentation/trace/kprobetrace.rst "Kernel 2212 Boot Parameter" section. 2213 2214 kpti= [ARM64] Control page table isolation of user 2215 and kernel address spaces. 2216 Default: enabled on cores which need mitigation. 2217 0: force disabled 2218 1: force enabled 2219 2220 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2221 Default is 0 (don't ignore, but inject #GP) 2222 2223 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2224 Default is false (don't support). 2225 2226 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2227 KVM MMU at runtime. 2228 Default is 0 (off) 2229 2230 kvm.nx_huge_pages= 2231 [KVM] Controls the software workaround for the 2232 X86_BUG_ITLB_MULTIHIT bug. 2233 force : Always deploy workaround. 2234 off : Never deploy workaround. 2235 auto : Deploy workaround based on the presence of 2236 X86_BUG_ITLB_MULTIHIT. 2237 2238 Default is 'auto'. 2239 2240 If the software workaround is enabled for the host, 2241 guests do need not to enable it for nested guests. 2242 2243 kvm.nx_huge_pages_recovery_ratio= 2244 [KVM] Controls how many 4KiB pages are periodically zapped 2245 back to huge pages. 0 disables the recovery, otherwise if 2246 the value is N KVM will zap 1/Nth of the 4KiB pages every 2247 minute. The default is 60. 2248 2249 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2250 Default is 1 (enabled) 2251 2252 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2253 for all guests. 2254 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2255 2256 kvm-arm.vgic_v3_group0_trap= 2257 [KVM,ARM] Trap guest accesses to GICv3 group-0 2258 system registers 2259 2260 kvm-arm.vgic_v3_group1_trap= 2261 [KVM,ARM] Trap guest accesses to GICv3 group-1 2262 system registers 2263 2264 kvm-arm.vgic_v3_common_trap= 2265 [KVM,ARM] Trap guest accesses to GICv3 common 2266 system registers 2267 2268 kvm-arm.vgic_v4_enable= 2269 [KVM,ARM] Allow use of GICv4 for direct injection of 2270 LPIs. 2271 2272 kvm_cma_resv_ratio=n [PPC] 2273 Reserves given percentage from system memory area for 2274 contiguous memory allocation for KVM hash pagetable 2275 allocation. 2276 By default it reserves 5% of total system memory. 2277 Format: <integer> 2278 Default: 5 2279 2280 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2281 (virtualized MMU) support on capable Intel chips. 2282 Default is 1 (enabled) 2283 2284 kvm-intel.emulate_invalid_guest_state= 2285 [KVM,Intel] Enable emulation of invalid guest states 2286 Default is 0 (disabled) 2287 2288 kvm-intel.flexpriority= 2289 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2290 Default is 1 (enabled) 2291 2292 kvm-intel.nested= 2293 [KVM,Intel] Enable VMX nesting (nVMX). 2294 Default is 0 (disabled) 2295 2296 kvm-intel.unrestricted_guest= 2297 [KVM,Intel] Disable unrestricted guest feature 2298 (virtualized real and unpaged mode) on capable 2299 Intel chips. Default is 1 (enabled) 2300 2301 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2302 CVE-2018-3620. 2303 2304 Valid arguments: never, cond, always 2305 2306 always: L1D cache flush on every VMENTER. 2307 cond: Flush L1D on VMENTER only when the code between 2308 VMEXIT and VMENTER can leak host memory. 2309 never: Disables the mitigation 2310 2311 Default is cond (do L1 cache flush in specific instances) 2312 2313 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2314 feature (tagged TLBs) on capable Intel chips. 2315 Default is 1 (enabled) 2316 2317 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2318 affected CPUs 2319 2320 The kernel PTE inversion protection is unconditionally 2321 enabled and cannot be disabled. 2322 2323 full 2324 Provides all available mitigations for the 2325 L1TF vulnerability. Disables SMT and 2326 enables all mitigations in the 2327 hypervisors, i.e. unconditional L1D flush. 2328 2329 SMT control and L1D flush control via the 2330 sysfs interface is still possible after 2331 boot. Hypervisors will issue a warning 2332 when the first VM is started in a 2333 potentially insecure configuration, 2334 i.e. SMT enabled or L1D flush disabled. 2335 2336 full,force 2337 Same as 'full', but disables SMT and L1D 2338 flush runtime control. Implies the 2339 'nosmt=force' command line option. 2340 (i.e. sysfs control of SMT is disabled.) 2341 2342 flush 2343 Leaves SMT enabled and enables the default 2344 hypervisor mitigation, i.e. conditional 2345 L1D flush. 2346 2347 SMT control and L1D flush control via the 2348 sysfs interface is still possible after 2349 boot. Hypervisors will issue a warning 2350 when the first VM is started in a 2351 potentially insecure configuration, 2352 i.e. SMT enabled or L1D flush disabled. 2353 2354 flush,nosmt 2355 2356 Disables SMT and enables the default 2357 hypervisor mitigation. 2358 2359 SMT control and L1D flush control via the 2360 sysfs interface is still possible after 2361 boot. Hypervisors will issue a warning 2362 when the first VM is started in a 2363 potentially insecure configuration, 2364 i.e. SMT enabled or L1D flush disabled. 2365 2366 flush,nowarn 2367 Same as 'flush', but hypervisors will not 2368 warn when a VM is started in a potentially 2369 insecure configuration. 2370 2371 off 2372 Disables hypervisor mitigations and doesn't 2373 emit any warnings. 2374 It also drops the swap size and available 2375 RAM limit restriction on both hypervisor and 2376 bare metal. 2377 2378 Default is 'flush'. 2379 2380 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2381 2382 l2cr= [PPC] 2383 2384 l3cr= [PPC] 2385 2386 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2387 disabled it. 2388 2389 lapic= [X86,APIC] Do not use TSC deadline 2390 value for LAPIC timer one-shot implementation. Default 2391 back to the programmable timer unit in the LAPIC. 2392 Format: notscdeadline 2393 2394 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2395 in C2 power state. 2396 2397 libata.dma= [LIBATA] DMA control 2398 libata.dma=0 Disable all PATA and SATA DMA 2399 libata.dma=1 PATA and SATA Disk DMA only 2400 libata.dma=2 ATAPI (CDROM) DMA only 2401 libata.dma=4 Compact Flash DMA only 2402 Combinations also work, so libata.dma=3 enables DMA 2403 for disks and CDROMs, but not CFs. 2404 2405 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2406 libata.ignore_hpa=0 keep BIOS limits (default) 2407 libata.ignore_hpa=1 ignore limits, using full disk 2408 2409 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2410 when set. 2411 Format: <int> 2412 2413 libata.force= [LIBATA] Force configurations. The format is comma 2414 separated list of "[ID:]VAL" where ID is 2415 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2416 matching port, link or device. Basically, it matches 2417 the ATA ID string printed on console by libata. If 2418 the whole ID part is omitted, the last PORT and DEVICE 2419 values are used. If ID hasn't been specified yet, the 2420 configuration applies to all ports, links and devices. 2421 2422 If only DEVICE is omitted, the parameter applies to 2423 the port and all links and devices behind it. DEVICE 2424 number of 0 either selects the first device or the 2425 first fan-out link behind PMP device. It does not 2426 select the host link. DEVICE number of 15 selects the 2427 host link and device attached to it. 2428 2429 The VAL specifies the configuration to force. As long 2430 as there's no ambiguity shortcut notation is allowed. 2431 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2432 The following configurations can be forced. 2433 2434 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2435 Any ID with matching PORT is used. 2436 2437 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2438 2439 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2440 udma[/][16,25,33,44,66,100,133] notation is also 2441 allowed. 2442 2443 * [no]ncq: Turn on or off NCQ. 2444 2445 * [no]ncqtrim: Turn off queued DSM TRIM. 2446 2447 * nohrst, nosrst, norst: suppress hard, soft 2448 and both resets. 2449 2450 * rstonce: only attempt one reset during 2451 hot-unplug link recovery 2452 2453 * dump_id: dump IDENTIFY data. 2454 2455 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2456 2457 * disable: Disable this device. 2458 2459 If there are multiple matching configurations changing 2460 the same attribute, the last one is used. 2461 2462 memblock=debug [KNL] Enable memblock debug messages. 2463 2464 load_ramdisk= [RAM] [Deprecated] 2465 2466 lockd.nlm_grace_period=P [NFS] Assign grace period. 2467 Format: <integer> 2468 2469 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2470 Format: <integer> 2471 2472 lockd.nlm_timeout=T [NFS] Assign timeout value. 2473 Format: <integer> 2474 2475 lockd.nlm_udpport=M [NFS] Assign UDP port. 2476 Format: <integer> 2477 2478 lockdown= [SECURITY] 2479 { integrity | confidentiality } 2480 Enable the kernel lockdown feature. If set to 2481 integrity, kernel features that allow userland to 2482 modify the running kernel are disabled. If set to 2483 confidentiality, kernel features that allow userland 2484 to extract confidential information from the kernel 2485 are also disabled. 2486 2487 locktorture.nreaders_stress= [KNL] 2488 Set the number of locking read-acquisition kthreads. 2489 Defaults to being automatically set based on the 2490 number of online CPUs. 2491 2492 locktorture.nwriters_stress= [KNL] 2493 Set the number of locking write-acquisition kthreads. 2494 2495 locktorture.onoff_holdoff= [KNL] 2496 Set time (s) after boot for CPU-hotplug testing. 2497 2498 locktorture.onoff_interval= [KNL] 2499 Set time (s) between CPU-hotplug operations, or 2500 zero to disable CPU-hotplug testing. 2501 2502 locktorture.shuffle_interval= [KNL] 2503 Set task-shuffle interval (jiffies). Shuffling 2504 tasks allows some CPUs to go into dyntick-idle 2505 mode during the locktorture test. 2506 2507 locktorture.shutdown_secs= [KNL] 2508 Set time (s) after boot system shutdown. This 2509 is useful for hands-off automated testing. 2510 2511 locktorture.stat_interval= [KNL] 2512 Time (s) between statistics printk()s. 2513 2514 locktorture.stutter= [KNL] 2515 Time (s) to stutter testing, for example, 2516 specifying five seconds causes the test to run for 2517 five seconds, wait for five seconds, and so on. 2518 This tests the locking primitive's ability to 2519 transition abruptly to and from idle. 2520 2521 locktorture.torture_type= [KNL] 2522 Specify the locking implementation to test. 2523 2524 locktorture.verbose= [KNL] 2525 Enable additional printk() statements. 2526 2527 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2528 Format: <irq> 2529 2530 loglevel= All Kernel Messages with a loglevel smaller than the 2531 console loglevel will be printed to the console. It can 2532 also be changed with klogd or other programs. The 2533 loglevels are defined as follows: 2534 2535 0 (KERN_EMERG) system is unusable 2536 1 (KERN_ALERT) action must be taken immediately 2537 2 (KERN_CRIT) critical conditions 2538 3 (KERN_ERR) error conditions 2539 4 (KERN_WARNING) warning conditions 2540 5 (KERN_NOTICE) normal but significant condition 2541 6 (KERN_INFO) informational 2542 7 (KERN_DEBUG) debug-level messages 2543 2544 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2545 in bytes. n must be a power of two and greater 2546 than the minimal size. The minimal size is defined 2547 by LOG_BUF_SHIFT kernel config parameter. There is 2548 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2549 that allows to increase the default size depending on 2550 the number of CPUs. See init/Kconfig for more details. 2551 2552 logo.nologo [FB] Disables display of the built-in Linux logo. 2553 This may be used to provide more screen space for 2554 kernel log messages and is useful when debugging 2555 kernel boot problems. 2556 2557 lp=0 [LP] Specify parallel ports to use, e.g, 2558 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2559 lp=reset first parallel port). 'lp=0' disables the 2560 lp=auto printer driver. 'lp=reset' (which can be 2561 specified in addition to the ports) causes 2562 attached printers to be reset. Using 2563 lp=port1,port2,... specifies the parallel ports 2564 to associate lp devices with, starting with 2565 lp0. A port specification may be 'none' to skip 2566 that lp device, or a parport name such as 2567 'parport0'. Specifying 'lp=auto' instead of a 2568 port specification list means that device IDs 2569 from each port should be examined, to see if 2570 an IEEE 1284-compliant printer is attached; if 2571 so, the driver will manage that printer. 2572 See also header of drivers/char/lp.c. 2573 2574 lpj=n [KNL] 2575 Sets loops_per_jiffy to given constant, thus avoiding 2576 time-consuming boot-time autodetection (up to 250 ms per 2577 CPU). 0 enables autodetection (default). To determine 2578 the correct value for your kernel, boot with normal 2579 autodetection and see what value is printed. Note that 2580 on SMP systems the preset will be applied to all CPUs, 2581 which is likely to cause problems if your CPUs need 2582 significantly divergent settings. An incorrect value 2583 will cause delays in the kernel to be wrong, leading to 2584 unpredictable I/O errors and other breakage. Although 2585 unlikely, in the extreme case this might damage your 2586 hardware. 2587 2588 ltpc= [NET] 2589 Format: <io>,<irq>,<dma> 2590 2591 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2592 2593 lsm=lsm1,...,lsmN 2594 [SECURITY] Choose order of LSM initialization. This 2595 overrides CONFIG_LSM, and the "security=" parameter. 2596 2597 machvec= [IA-64] Force the use of a particular machine-vector 2598 (machvec) in a generic kernel. 2599 Example: machvec=hpzx1 2600 2601 machtype= [Loongson] Share the same kernel image file between 2602 different yeeloong laptops. 2603 Example: machtype=lemote-yeeloong-2f-7inch 2604 2605 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2606 than or equal to this physical address is ignored. 2607 2608 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2609 will bring up during bootup. maxcpus=n : n >= 0 limits 2610 the kernel to bring up 'n' processors. Surely after 2611 bootup you can bring up the other plugged cpu by executing 2612 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2613 only takes effect during system bootup. 2614 While n=0 is a special case, it is equivalent to "nosmp", 2615 which also disables the IO APIC. 2616 2617 max_loop= [LOOP] The number of loop block devices that get 2618 (loop.max_loop) unconditionally pre-created at init time. The default 2619 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2620 of statically allocating a predefined number, loop 2621 devices can be requested on-demand with the 2622 /dev/loop-control interface. 2623 2624 mce [X86-32] Machine Check Exception 2625 2626 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2627 2628 md= [HW] RAID subsystems devices and level 2629 See Documentation/admin-guide/md.rst. 2630 2631 mdacon= [MDA] 2632 Format: <first>,<last> 2633 Specifies range of consoles to be captured by the MDA. 2634 2635 mds= [X86,INTEL] 2636 Control mitigation for the Micro-architectural Data 2637 Sampling (MDS) vulnerability. 2638 2639 Certain CPUs are vulnerable to an exploit against CPU 2640 internal buffers which can forward information to a 2641 disclosure gadget under certain conditions. 2642 2643 In vulnerable processors, the speculatively 2644 forwarded data can be used in a cache side channel 2645 attack, to access data to which the attacker does 2646 not have direct access. 2647 2648 This parameter controls the MDS mitigation. The 2649 options are: 2650 2651 full - Enable MDS mitigation on vulnerable CPUs 2652 full,nosmt - Enable MDS mitigation and disable 2653 SMT on vulnerable CPUs 2654 off - Unconditionally disable MDS mitigation 2655 2656 On TAA-affected machines, mds=off can be prevented by 2657 an active TAA mitigation as both vulnerabilities are 2658 mitigated with the same mechanism so in order to disable 2659 this mitigation, you need to specify tsx_async_abort=off 2660 too. 2661 2662 Not specifying this option is equivalent to 2663 mds=full. 2664 2665 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2666 2667 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2668 Amount of memory to be used in cases as follows: 2669 2670 1 for test; 2671 2 when the kernel is not able to see the whole system memory; 2672 3 memory that lies after 'mem=' boundary is excluded from 2673 the hypervisor, then assigned to KVM guests. 2674 2675 [X86] Work as limiting max address. Use together 2676 with memmap= to avoid physical address space collisions. 2677 Without memmap= PCI devices could be placed at addresses 2678 belonging to unused RAM. 2679 2680 Note that this only takes effects during boot time since 2681 in above case 3, memory may need be hot added after boot 2682 if system memory of hypervisor is not sufficient. 2683 2684 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2685 memory. 2686 2687 memchunk=nn[KMG] 2688 [KNL,SH] Allow user to override the default size for 2689 per-device physically contiguous DMA buffers. 2690 2691 memhp_default_state=online/offline 2692 [KNL] Set the initial state for the memory hotplug 2693 onlining policy. If not specified, the default value is 2694 set according to the 2695 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2696 option. 2697 See Documentation/admin-guide/mm/memory-hotplug.rst. 2698 2699 memmap=exactmap [KNL,X86] Enable setting of an exact 2700 E820 memory map, as specified by the user. 2701 Such memmap=exactmap lines can be constructed based on 2702 BIOS output or other requirements. See the memmap=nn@ss 2703 option description. 2704 2705 memmap=nn[KMG]@ss[KMG] 2706 [KNL] Force usage of a specific region of memory. 2707 Region of memory to be used is from ss to ss+nn. 2708 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2709 which limits max address to nn[KMG]. 2710 Multiple different regions can be specified, 2711 comma delimited. 2712 Example: 2713 memmap=100M@2G,100M#3G,1G!1024G 2714 2715 memmap=nn[KMG]#ss[KMG] 2716 [KNL,ACPI] Mark specific memory as ACPI data. 2717 Region of memory to be marked is from ss to ss+nn. 2718 2719 memmap=nn[KMG]$ss[KMG] 2720 [KNL,ACPI] Mark specific memory as reserved. 2721 Region of memory to be reserved is from ss to ss+nn. 2722 Example: Exclude memory from 0x18690000-0x1869ffff 2723 memmap=64K$0x18690000 2724 or 2725 memmap=0x10000$0x18690000 2726 Some bootloaders may need an escape character before '$', 2727 like Grub2, otherwise '$' and the following number 2728 will be eaten. 2729 2730 memmap=nn[KMG]!ss[KMG] 2731 [KNL,X86] Mark specific memory as protected. 2732 Region of memory to be used, from ss to ss+nn. 2733 The memory region may be marked as e820 type 12 (0xc) 2734 and is NVDIMM or ADR memory. 2735 2736 memmap=<size>%<offset>-<oldtype>+<newtype> 2737 [KNL,ACPI] Convert memory within the specified region 2738 from <oldtype> to <newtype>. If "-<oldtype>" is left 2739 out, the whole region will be marked as <newtype>, 2740 even if previously unavailable. If "+<newtype>" is left 2741 out, matching memory will be removed. Types are 2742 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2743 3 = ACPI, 12 = PRAM. 2744 2745 memory_corruption_check=0/1 [X86] 2746 Some BIOSes seem to corrupt the first 64k of 2747 memory when doing things like suspend/resume. 2748 Setting this option will scan the memory 2749 looking for corruption. Enabling this will 2750 both detect corruption and prevent the kernel 2751 from using the memory being corrupted. 2752 However, its intended as a diagnostic tool; if 2753 repeatable BIOS-originated corruption always 2754 affects the same memory, you can use memmap= 2755 to prevent the kernel from using that memory. 2756 2757 memory_corruption_check_size=size [X86] 2758 By default it checks for corruption in the low 2759 64k, making this memory unavailable for normal 2760 use. Use this parameter to scan for 2761 corruption in more or less memory. 2762 2763 memory_corruption_check_period=seconds [X86] 2764 By default it checks for corruption every 60 2765 seconds. Use this parameter to check at some 2766 other rate. 0 disables periodic checking. 2767 2768 memtest= [KNL,X86,ARM,PPC] Enable memtest 2769 Format: <integer> 2770 default : 0 <disable> 2771 Specifies the number of memtest passes to be 2772 performed. Each pass selects another test 2773 pattern from a given set of patterns. Memtest 2774 fills the memory with this pattern, validates 2775 memory contents and reserves bad memory 2776 regions that are detected. 2777 2778 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2779 Valid arguments: on, off 2780 Default (depends on kernel configuration option): 2781 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2782 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2783 mem_encrypt=on: Activate SME 2784 mem_encrypt=off: Do not activate SME 2785 2786 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2787 for details on when memory encryption can be activated. 2788 2789 mem_sleep_default= [SUSPEND] Default system suspend mode: 2790 s2idle - Suspend-To-Idle 2791 shallow - Power-On Suspend or equivalent (if supported) 2792 deep - Suspend-To-RAM or equivalent (if supported) 2793 See Documentation/admin-guide/pm/sleep-states.rst. 2794 2795 meye.*= [HW] Set MotionEye Camera parameters 2796 See Documentation/admin-guide/media/meye.rst. 2797 2798 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2799 Multi-Function General Purpose Timers on AMD Geode 2800 platforms. 2801 2802 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2803 the BIOS has incorrectly applied a workaround. TinyBIOS 2804 version 0.98 is known to be affected, 0.99 fixes the 2805 problem by letting the user disable the workaround. 2806 2807 mga= [HW,DRM] 2808 2809 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2810 physical address is ignored. 2811 2812 mini2440= [ARM,HW,KNL] 2813 Format:[0..2][b][c][t] 2814 Default: "0tb" 2815 MINI2440 configuration specification: 2816 0 - The attached screen is the 3.5" TFT 2817 1 - The attached screen is the 7" TFT 2818 2 - The VGA Shield is attached (1024x768) 2819 Leaving out the screen size parameter will not load 2820 the TFT driver, and the framebuffer will be left 2821 unconfigured. 2822 b - Enable backlight. The TFT backlight pin will be 2823 linked to the kernel VESA blanking code and a GPIO 2824 LED. This parameter is not necessary when using the 2825 VGA shield. 2826 c - Enable the s3c camera interface. 2827 t - Reserved for enabling touchscreen support. The 2828 touchscreen support is not enabled in the mainstream 2829 kernel as of 2.6.30, a preliminary port can be found 2830 in the "bleeding edge" mini2440 support kernel at 2831 https://repo.or.cz/w/linux-2.6/mini2440.git 2832 2833 mitigations= 2834 [X86,PPC,S390,ARM64] Control optional mitigations for 2835 CPU vulnerabilities. This is a set of curated, 2836 arch-independent options, each of which is an 2837 aggregation of existing arch-specific options. 2838 2839 off 2840 Disable all optional CPU mitigations. This 2841 improves system performance, but it may also 2842 expose users to several CPU vulnerabilities. 2843 Equivalent to: nopti [X86,PPC] 2844 kpti=0 [ARM64] 2845 nospectre_v1 [X86,PPC] 2846 nobp=0 [S390] 2847 nospectre_v2 [X86,PPC,S390,ARM64] 2848 spectre_v2_user=off [X86] 2849 spec_store_bypass_disable=off [X86,PPC] 2850 ssbd=force-off [ARM64] 2851 l1tf=off [X86] 2852 mds=off [X86] 2853 tsx_async_abort=off [X86] 2854 kvm.nx_huge_pages=off [X86] 2855 2856 Exceptions: 2857 This does not have any effect on 2858 kvm.nx_huge_pages when 2859 kvm.nx_huge_pages=force. 2860 2861 auto (default) 2862 Mitigate all CPU vulnerabilities, but leave SMT 2863 enabled, even if it's vulnerable. This is for 2864 users who don't want to be surprised by SMT 2865 getting disabled across kernel upgrades, or who 2866 have other ways of avoiding SMT-based attacks. 2867 Equivalent to: (default behavior) 2868 2869 auto,nosmt 2870 Mitigate all CPU vulnerabilities, disabling SMT 2871 if needed. This is for users who always want to 2872 be fully mitigated, even if it means losing SMT. 2873 Equivalent to: l1tf=flush,nosmt [X86] 2874 mds=full,nosmt [X86] 2875 tsx_async_abort=full,nosmt [X86] 2876 2877 mminit_loglevel= 2878 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2879 parameter allows control of the logging verbosity for 2880 the additional memory initialisation checks. A value 2881 of 0 disables mminit logging and a level of 4 will 2882 log everything. Information is printed at KERN_DEBUG 2883 so loglevel=8 may also need to be specified. 2884 2885 module.sig_enforce 2886 [KNL] When CONFIG_MODULE_SIG is set, this means that 2887 modules without (valid) signatures will fail to load. 2888 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2889 is always true, so this option does nothing. 2890 2891 module_blacklist= [KNL] Do not load a comma-separated list of 2892 modules. Useful for debugging problem modules. 2893 2894 mousedev.tap_time= 2895 [MOUSE] Maximum time between finger touching and 2896 leaving touchpad surface for touch to be considered 2897 a tap and be reported as a left button click (for 2898 touchpads working in absolute mode only). 2899 Format: <msecs> 2900 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2901 reporting absolute coordinates, such as tablets 2902 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2903 reporting absolute coordinates, such as tablets 2904 2905 movablecore= [KNL,X86,IA-64,PPC] 2906 Format: nn[KMGTPE] | nn% 2907 This parameter is the complement to kernelcore=, it 2908 specifies the amount of memory used for migratable 2909 allocations. If both kernelcore and movablecore is 2910 specified, then kernelcore will be at *least* the 2911 specified value but may be more. If movablecore on its 2912 own is specified, the administrator must be careful 2913 that the amount of memory usable for all allocations 2914 is not too small. 2915 2916 movable_node [KNL] Boot-time switch to make hotplugable memory 2917 NUMA nodes to be movable. This means that the memory 2918 of such nodes will be usable only for movable 2919 allocations which rules out almost all kernel 2920 allocations. Use with caution! 2921 2922 MTD_Partition= [MTD] 2923 Format: <name>,<region-number>,<size>,<offset> 2924 2925 MTD_Region= [MTD] Format: 2926 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2927 2928 mtdparts= [MTD] 2929 See drivers/mtd/parsers/cmdlinepart.c 2930 2931 multitce=off [PPC] This parameter disables the use of the pSeries 2932 firmware feature for updating multiple TCE entries 2933 at a time. 2934 2935 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2936 2937 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2938 2939 boundary - index of last SLC block on Flex-OneNAND. 2940 The remaining blocks are configured as MLC blocks. 2941 lock - Configure if Flex-OneNAND boundary should be locked. 2942 Once locked, the boundary cannot be changed. 2943 1 indicates lock status, 0 indicates unlock status. 2944 2945 mtdset= [ARM] 2946 ARM/S3C2412 JIVE boot control 2947 2948 See arch/arm/mach-s3c2412/mach-jive.c 2949 2950 mtouchusb.raw_coordinates= 2951 [HW] Make the MicroTouch USB driver use raw coordinates 2952 ('y', default) or cooked coordinates ('n') 2953 2954 mtrr_chunk_size=nn[KMG] [X86] 2955 used for mtrr cleanup. It is largest continuous chunk 2956 that could hold holes aka. UC entries. 2957 2958 mtrr_gran_size=nn[KMG] [X86] 2959 Used for mtrr cleanup. It is granularity of mtrr block. 2960 Default is 1. 2961 Large value could prevent small alignment from 2962 using up MTRRs. 2963 2964 mtrr_spare_reg_nr=n [X86] 2965 Format: <integer> 2966 Range: 0,7 : spare reg number 2967 Default : 1 2968 Used for mtrr cleanup. It is spare mtrr entries number. 2969 Set to 2 or more if your graphical card needs more. 2970 2971 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2972 2973 netdev= [NET] Network devices parameters 2974 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2975 Note that mem_start is often overloaded to mean 2976 something different and driver-specific. 2977 This usage is only documented in each driver source 2978 file if at all. 2979 2980 nf_conntrack.acct= 2981 [NETFILTER] Enable connection tracking flow accounting 2982 0 to disable accounting 2983 1 to enable accounting 2984 Default value is 0. 2985 2986 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2987 See Documentation/admin-guide/nfs/nfsroot.rst. 2988 2989 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2990 See Documentation/admin-guide/nfs/nfsroot.rst. 2991 2992 nfsrootdebug [NFS] enable nfsroot debugging messages. 2993 See Documentation/admin-guide/nfs/nfsroot.rst. 2994 2995 nfs.callback_nr_threads= 2996 [NFSv4] set the total number of threads that the 2997 NFS client will assign to service NFSv4 callback 2998 requests. 2999 3000 nfs.callback_tcpport= 3001 [NFS] set the TCP port on which the NFSv4 callback 3002 channel should listen. 3003 3004 nfs.cache_getent= 3005 [NFS] sets the pathname to the program which is used 3006 to update the NFS client cache entries. 3007 3008 nfs.cache_getent_timeout= 3009 [NFS] sets the timeout after which an attempt to 3010 update a cache entry is deemed to have failed. 3011 3012 nfs.idmap_cache_timeout= 3013 [NFS] set the maximum lifetime for idmapper cache 3014 entries. 3015 3016 nfs.enable_ino64= 3017 [NFS] enable 64-bit inode numbers. 3018 If zero, the NFS client will fake up a 32-bit inode 3019 number for the readdir() and stat() syscalls instead 3020 of returning the full 64-bit number. 3021 The default is to return 64-bit inode numbers. 3022 3023 nfs.max_session_cb_slots= 3024 [NFSv4.1] Sets the maximum number of session 3025 slots the client will assign to the callback 3026 channel. This determines the maximum number of 3027 callbacks the client will process in parallel for 3028 a particular server. 3029 3030 nfs.max_session_slots= 3031 [NFSv4.1] Sets the maximum number of session slots 3032 the client will attempt to negotiate with the server. 3033 This limits the number of simultaneous RPC requests 3034 that the client can send to the NFSv4.1 server. 3035 Note that there is little point in setting this 3036 value higher than the max_tcp_slot_table_limit. 3037 3038 nfs.nfs4_disable_idmapping= 3039 [NFSv4] When set to the default of '1', this option 3040 ensures that both the RPC level authentication 3041 scheme and the NFS level operations agree to use 3042 numeric uids/gids if the mount is using the 3043 'sec=sys' security flavour. In effect it is 3044 disabling idmapping, which can make migration from 3045 legacy NFSv2/v3 systems to NFSv4 easier. 3046 Servers that do not support this mode of operation 3047 will be autodetected by the client, and it will fall 3048 back to using the idmapper. 3049 To turn off this behaviour, set the value to '0'. 3050 nfs.nfs4_unique_id= 3051 [NFS4] Specify an additional fixed unique ident- 3052 ification string that NFSv4 clients can insert into 3053 their nfs_client_id4 string. This is typically a 3054 UUID that is generated at system install time. 3055 3056 nfs.send_implementation_id = 3057 [NFSv4.1] Send client implementation identification 3058 information in exchange_id requests. 3059 If zero, no implementation identification information 3060 will be sent. 3061 The default is to send the implementation identification 3062 information. 3063 3064 nfs.recover_lost_locks = 3065 [NFSv4] Attempt to recover locks that were lost due 3066 to a lease timeout on the server. Please note that 3067 doing this risks data corruption, since there are 3068 no guarantees that the file will remain unchanged 3069 after the locks are lost. 3070 If you want to enable the kernel legacy behaviour of 3071 attempting to recover these locks, then set this 3072 parameter to '1'. 3073 The default parameter value of '0' causes the kernel 3074 not to attempt recovery of lost locks. 3075 3076 nfs4.layoutstats_timer = 3077 [NFSv4.2] Change the rate at which the kernel sends 3078 layoutstats to the pNFS metadata server. 3079 3080 Setting this to value to 0 causes the kernel to use 3081 whatever value is the default set by the layout 3082 driver. A non-zero value sets the minimum interval 3083 in seconds between layoutstats transmissions. 3084 3085 nfsd.nfs4_disable_idmapping= 3086 [NFSv4] When set to the default of '1', the NFSv4 3087 server will return only numeric uids and gids to 3088 clients using auth_sys, and will accept numeric uids 3089 and gids from such clients. This is intended to ease 3090 migration from NFSv2/v3. 3091 3092 nmi_debug= [KNL,SH] Specify one or more actions to take 3093 when a NMI is triggered. 3094 Format: [state][,regs][,debounce][,die] 3095 3096 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3097 Format: [panic,][nopanic,][num] 3098 Valid num: 0 or 1 3099 0 - turn hardlockup detector in nmi_watchdog off 3100 1 - turn hardlockup detector in nmi_watchdog on 3101 When panic is specified, panic when an NMI watchdog 3102 timeout occurs (or 'nopanic' to not panic on an NMI 3103 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3104 To disable both hard and soft lockup detectors, 3105 please see 'nowatchdog'. 3106 This is useful when you use a panic=... timeout and 3107 need the box quickly up again. 3108 3109 These settings can be accessed at runtime via 3110 the nmi_watchdog and hardlockup_panic sysctls. 3111 3112 netpoll.carrier_timeout= 3113 [NET] Specifies amount of time (in seconds) that 3114 netpoll should wait for a carrier. By default netpoll 3115 waits 4 seconds. 3116 3117 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3118 emulation library even if a 387 maths coprocessor 3119 is present. 3120 3121 no5lvl [X86-64] Disable 5-level paging mode. Forces 3122 kernel to use 4-level paging instead. 3123 3124 nofsgsbase [X86] Disables FSGSBASE instructions. 3125 3126 no_console_suspend 3127 [HW] Never suspend the console 3128 Disable suspending of consoles during suspend and 3129 hibernate operations. Once disabled, debugging 3130 messages can reach various consoles while the rest 3131 of the system is being put to sleep (ie, while 3132 debugging driver suspend/resume hooks). This may 3133 not work reliably with all consoles, but is known 3134 to work with serial and VGA consoles. 3135 To facilitate more flexible debugging, we also add 3136 console_suspend, a printk module parameter to control 3137 it. Users could use console_suspend (usually 3138 /sys/module/printk/parameters/console_suspend) to 3139 turn on/off it dynamically. 3140 3141 novmcoredd [KNL,KDUMP] 3142 Disable device dump. Device dump allows drivers to 3143 append dump data to vmcore so you can collect driver 3144 specified debug info. Drivers can append the data 3145 without any limit and this data is stored in memory, 3146 so this may cause significant memory stress. Disabling 3147 device dump can help save memory but the driver debug 3148 data will be no longer available. This parameter 3149 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3150 is set. 3151 3152 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3153 caches in the slab allocator. Saves per-node memory, 3154 but will impact performance. 3155 3156 noalign [KNL,ARM] 3157 3158 noaltinstr [S390] Disables alternative instructions patching 3159 (CPU alternatives feature). 3160 3161 noapic [SMP,APIC] Tells the kernel to not make use of any 3162 IOAPICs that may be present in the system. 3163 3164 noautogroup Disable scheduler automatic task group creation. 3165 3166 nobats [PPC] Do not use BATs for mapping kernel lowmem 3167 on "Classic" PPC cores. 3168 3169 nocache [ARM] 3170 3171 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3172 3173 nodelayacct [KNL] Disable per-task delay accounting 3174 3175 nodsp [SH] Disable hardware DSP at boot time. 3176 3177 noefi Disable EFI runtime services support. 3178 3179 noexec [IA-64] 3180 3181 noexec [X86] 3182 On X86-32 available only on PAE configured kernels. 3183 noexec=on: enable non-executable mappings (default) 3184 noexec=off: disable non-executable mappings 3185 3186 nosmap [X86,PPC] 3187 Disable SMAP (Supervisor Mode Access Prevention) 3188 even if it is supported by processor. 3189 3190 nosmep [X86,PPC] 3191 Disable SMEP (Supervisor Mode Execution Prevention) 3192 even if it is supported by processor. 3193 3194 noexec32 [X86-64] 3195 This affects only 32-bit executables. 3196 noexec32=on: enable non-executable mappings (default) 3197 read doesn't imply executable mappings 3198 noexec32=off: disable non-executable mappings 3199 read implies executable mappings 3200 3201 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3202 3203 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3204 register save and restore. The kernel will only save 3205 legacy floating-point registers on task switch. 3206 3207 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3208 3209 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3210 Equivalent to smt=1. 3211 3212 [KNL,X86] Disable symmetric multithreading (SMT). 3213 nosmt=force: Force disable SMT, cannot be undone 3214 via the sysfs control file. 3215 3216 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3217 (bounds check bypass). With this option data leaks are 3218 possible in the system. 3219 3220 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3221 the Spectre variant 2 (indirect branch prediction) 3222 vulnerability. System may allow data leaks with this 3223 option. 3224 3225 nospec_store_bypass_disable 3226 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3227 3228 noxsave [BUGS=X86] Disables x86 extended register state save 3229 and restore using xsave. The kernel will fallback to 3230 enabling legacy floating-point and sse state. 3231 3232 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3233 register states. The kernel will fall back to use 3234 xsave to save the states. By using this parameter, 3235 performance of saving the states is degraded because 3236 xsave doesn't support modified optimization while 3237 xsaveopt supports it on xsaveopt enabled systems. 3238 3239 noxsaves [X86] Disables xsaves and xrstors used in saving and 3240 restoring x86 extended register state in compacted 3241 form of xsave area. The kernel will fall back to use 3242 xsaveopt and xrstor to save and restore the states 3243 in standard form of xsave area. By using this 3244 parameter, xsave area per process might occupy more 3245 memory on xsaves enabled systems. 3246 3247 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3248 wfi(ARM) instruction doesn't work correctly and not to 3249 use it. This is also useful when using JTAG debugger. 3250 3251 no_file_caps Tells the kernel not to honor file capabilities. The 3252 only way then for a file to be executed with privilege 3253 is to be setuid root or executed by root. 3254 3255 nohalt [IA-64] Tells the kernel not to use the power saving 3256 function PAL_HALT_LIGHT when idle. This increases 3257 power-consumption. On the positive side, it reduces 3258 interrupt wake-up latency, which may improve performance 3259 in certain environments such as networked servers or 3260 real-time systems. 3261 3262 nohibernate [HIBERNATION] Disable hibernation and resume. 3263 3264 nohz= [KNL] Boottime enable/disable dynamic ticks 3265 Valid arguments: on, off 3266 Default: on 3267 3268 nohz_full= [KNL,BOOT,SMP,ISOL] 3269 The argument is a cpu list, as described above. 3270 In kernels built with CONFIG_NO_HZ_FULL=y, set 3271 the specified list of CPUs whose tick will be stopped 3272 whenever possible. The boot CPU will be forced outside 3273 the range to maintain the timekeeping. Any CPUs 3274 in this list will have their RCU callbacks offloaded, 3275 just as if they had also been called out in the 3276 rcu_nocbs= boot parameter. 3277 3278 noiotrap [SH] Disables trapped I/O port accesses. 3279 3280 noirqdebug [X86-32] Disables the code which attempts to detect and 3281 disable unhandled interrupt sources. 3282 3283 no_timer_check [X86,APIC] Disables the code which tests for 3284 broken timer IRQ sources. 3285 3286 noisapnp [ISAPNP] Disables ISA PnP code. 3287 3288 noinitrd [RAM] Tells the kernel not to load any configured 3289 initial RAM disk. 3290 3291 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3292 remapping. 3293 [Deprecated - use intremap=off] 3294 3295 nointroute [IA-64] 3296 3297 noinvpcid [X86] Disable the INVPCID cpu feature. 3298 3299 nojitter [IA-64] Disables jitter checking for ITC timers. 3300 3301 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3302 3303 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3304 fault handling. 3305 3306 no-vmw-sched-clock 3307 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3308 clock and use the default one. 3309 3310 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3311 accounting. steal time is computed, but won't 3312 influence scheduler behaviour 3313 3314 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3315 3316 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3317 3318 noltlbs [PPC] Do not use large page/tlb entries for kernel 3319 lowmem mapping on PPC40x and PPC8xx 3320 3321 nomca [IA-64] Disable machine check abort handling 3322 3323 nomce [X86-32] Disable Machine Check Exception 3324 3325 nomfgpt [X86-32] Disable Multi-Function General Purpose 3326 Timer usage (for AMD Geode machines). 3327 3328 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3329 shutdown the other cpus. Instead use the REBOOT_VECTOR 3330 irq. 3331 3332 nomodule Disable module load 3333 3334 nopat [X86] Disable PAT (page attribute table extension of 3335 pagetables) support. 3336 3337 nopcid [X86-64] Disable the PCID cpu feature. 3338 3339 norandmaps Don't use address space randomization. Equivalent to 3340 echo 0 > /proc/sys/kernel/randomize_va_space 3341 3342 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3343 with UP alternatives 3344 3345 nordrand [X86] Disable kernel use of the RDRAND and 3346 RDSEED instructions even if they are supported 3347 by the processor. RDRAND and RDSEED are still 3348 available to user space applications. 3349 3350 noresume [SWSUSP] Disables resume and restores original swap 3351 space. 3352 3353 no-scroll [VGA] Disables scrollback. 3354 This is required for the Braillex ib80-piezo Braille 3355 reader made by F.H. Papenmeier (Germany). 3356 3357 nosbagart [IA-64] 3358 3359 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3360 3361 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3362 and disable the IO APIC. legacy for "maxcpus=0". 3363 3364 nosoftlockup [KNL] Disable the soft-lockup detector. 3365 3366 nosync [HW,M68K] Disables sync negotiation for all devices. 3367 3368 nowatchdog [KNL] Disable both lockup detectors, i.e. 3369 soft-lockup and NMI watchdog (hard-lockup). 3370 3371 nowb [ARM] 3372 3373 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3374 3375 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3376 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3377 Some features depend on CPU0. Known dependencies are: 3378 1. Resume from suspend/hibernate depends on CPU0. 3379 Suspend/hibernate will fail if CPU0 is offline and you 3380 need to online CPU0 before suspend/hibernate. 3381 2. PIC interrupts also depend on CPU0. CPU0 can't be 3382 removed if a PIC interrupt is detected. 3383 It's said poweroff/reboot may depend on CPU0 on some 3384 machines although I haven't seen such issues so far 3385 after CPU0 is offline on a few tested machines. 3386 If the dependencies are under your control, you can 3387 turn on cpu0_hotplug. 3388 3389 nps_mtm_hs_ctr= [KNL,ARC] 3390 This parameter sets the maximum duration, in 3391 cycles, each HW thread of the CTOP can run 3392 without interruptions, before HW switches it. 3393 The actual maximum duration is 16 times this 3394 parameter's value. 3395 Format: integer between 1 and 255 3396 Default: 255 3397 3398 nptcg= [IA-64] Override max number of concurrent global TLB 3399 purges which is reported from either PAL_VM_SUMMARY or 3400 SAL PALO. 3401 3402 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3403 could support. nr_cpus=n : n >= 1 limits the kernel to 3404 support 'n' processors. It could be larger than the 3405 number of already plugged CPU during bootup, later in 3406 runtime you can physically add extra cpu until it reaches 3407 n. So during boot up some boot time memory for per-cpu 3408 variables need be pre-allocated for later physical cpu 3409 hot plugging. 3410 3411 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3412 3413 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3414 Allowed values are enable and disable 3415 3416 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3417 'node', 'default' can be specified 3418 This can be set from sysctl after boot. 3419 See Documentation/admin-guide/sysctl/vm.rst for details. 3420 3421 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3422 See Documentation/core-api/debugging-via-ohci1394.rst for more 3423 info. 3424 3425 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3426 Rather than timing out after 20 ms if an EC 3427 command is not properly ACKed, override the length 3428 of the timeout. We have interrupts disabled while 3429 waiting for the ACK, so if this is set too high 3430 interrupts *may* be lost! 3431 3432 omap_mux= [OMAP] Override bootloader pin multiplexing. 3433 Format: <mux_mode0.mode_name=value>... 3434 For example, to override I2C bus2: 3435 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3436 3437 oprofile.timer= [HW] 3438 Use timer interrupt instead of performance counters 3439 3440 oprofile.cpu_type= Force an oprofile cpu type 3441 This might be useful if you have an older oprofile 3442 userland or if you want common events. 3443 Format: { arch_perfmon } 3444 arch_perfmon: [X86] Force use of architectural 3445 perfmon on Intel CPUs instead of the 3446 CPU specific event set. 3447 timer: [X86] Force use of architectural NMI 3448 timer mode (see also oprofile.timer 3449 for generic hr timer mode) 3450 3451 oops=panic Always panic on oopses. Default is to just kill the 3452 process, but there is a small probability of 3453 deadlocking the machine. 3454 This will also cause panics on machine check exceptions. 3455 Useful together with panic=30 to trigger a reboot. 3456 3457 page_alloc.shuffle= 3458 [KNL] Boolean flag to control whether the page allocator 3459 should randomize its free lists. The randomization may 3460 be automatically enabled if the kernel detects it is 3461 running on a platform with a direct-mapped memory-side 3462 cache, and this parameter can be used to 3463 override/disable that behavior. The state of the flag 3464 can be read from sysfs at: 3465 /sys/module/page_alloc/parameters/shuffle. 3466 3467 page_owner= [KNL] Boot-time page_owner enabling option. 3468 Storage of the information about who allocated 3469 each page is disabled in default. With this switch, 3470 we can turn it on. 3471 on: enable the feature 3472 3473 page_poison= [KNL] Boot-time parameter changing the state of 3474 poisoning on the buddy allocator, available with 3475 CONFIG_PAGE_POISONING=y. 3476 off: turn off poisoning (default) 3477 on: turn on poisoning 3478 3479 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3480 timeout > 0: seconds before rebooting 3481 timeout = 0: wait forever 3482 timeout < 0: reboot immediately 3483 Format: <timeout> 3484 3485 panic_print= Bitmask for printing system info when panic happens. 3486 User can chose combination of the following bits: 3487 bit 0: print all tasks info 3488 bit 1: print system memory info 3489 bit 2: print timer info 3490 bit 3: print locks info if CONFIG_LOCKDEP is on 3491 bit 4: print ftrace buffer 3492 bit 5: print all printk messages in buffer 3493 3494 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3495 Format: <hex>[,nousertaint] 3496 Hexadecimal bitmask representing the set of TAINT flags 3497 that will cause the kernel to panic when add_taint() is 3498 called with any of the flags in this set. 3499 The optional switch "nousertaint" can be utilized to 3500 prevent userspace forced crashes by writing to sysctl 3501 /proc/sys/kernel/tainted any flagset matching with the 3502 bitmask set on panic_on_taint. 3503 See Documentation/admin-guide/tainted-kernels.rst for 3504 extra details on the taint flags that users can pick 3505 to compose the bitmask to assign to panic_on_taint. 3506 3507 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3508 on a WARN(). 3509 3510 crash_kexec_post_notifiers 3511 Run kdump after running panic-notifiers and dumping 3512 kmsg. This only for the users who doubt kdump always 3513 succeeds in any situation. 3514 Note that this also increases risks of kdump failure, 3515 because some panic notifiers can make the crashed 3516 kernel more unstable. 3517 3518 parkbd.port= [HW] Parallel port number the keyboard adapter is 3519 connected to, default is 0. 3520 Format: <parport#> 3521 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3522 0 for XT, 1 for AT (default is AT). 3523 Format: <mode> 3524 3525 parport= [HW,PPT] Specify parallel ports. 0 disables. 3526 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3527 Use 'auto' to force the driver to use any 3528 IRQ/DMA settings detected (the default is to 3529 ignore detected IRQ/DMA settings because of 3530 possible conflicts). You can specify the base 3531 address, IRQ, and DMA settings; IRQ and DMA 3532 should be numbers, or 'auto' (for using detected 3533 settings on that particular port), or 'nofifo' 3534 (to avoid using a FIFO even if it is detected). 3535 Parallel ports are assigned in the order they 3536 are specified on the command line, starting 3537 with parport0. 3538 3539 parport_init_mode= [HW,PPT] 3540 Configure VIA parallel port to operate in 3541 a specific mode. This is necessary on Pegasos 3542 computer where firmware has no options for setting 3543 up parallel port mode and sets it to spp. 3544 Currently this function knows 686a and 8231 chips. 3545 Format: [spp|ps2|epp|ecp|ecpepp] 3546 3547 pause_on_oops= 3548 Halt all CPUs after the first oops has been printed for 3549 the specified number of seconds. This is to be used if 3550 your oopses keep scrolling off the screen. 3551 3552 pcbit= [HW,ISDN] 3553 3554 pcd. [PARIDE] 3555 See header of drivers/block/paride/pcd.c. 3556 See also Documentation/admin-guide/blockdev/paride.rst. 3557 3558 pci=option[,option...] [PCI] various PCI subsystem options. 3559 3560 Some options herein operate on a specific device 3561 or a set of devices (<pci_dev>). These are 3562 specified in one of the following formats: 3563 3564 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3565 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3566 3567 Note: the first format specifies a PCI 3568 bus/device/function address which may change 3569 if new hardware is inserted, if motherboard 3570 firmware changes, or due to changes caused 3571 by other kernel parameters. If the 3572 domain is left unspecified, it is 3573 taken to be zero. Optionally, a path 3574 to a device through multiple device/function 3575 addresses can be specified after the base 3576 address (this is more robust against 3577 renumbering issues). The second format 3578 selects devices using IDs from the 3579 configuration space which may match multiple 3580 devices in the system. 3581 3582 earlydump dump PCI config space before the kernel 3583 changes anything 3584 off [X86] don't probe for the PCI bus 3585 bios [X86-32] force use of PCI BIOS, don't access 3586 the hardware directly. Use this if your machine 3587 has a non-standard PCI host bridge. 3588 nobios [X86-32] disallow use of PCI BIOS, only direct 3589 hardware access methods are allowed. Use this 3590 if you experience crashes upon bootup and you 3591 suspect they are caused by the BIOS. 3592 conf1 [X86] Force use of PCI Configuration Access 3593 Mechanism 1 (config address in IO port 0xCF8, 3594 data in IO port 0xCFC, both 32-bit). 3595 conf2 [X86] Force use of PCI Configuration Access 3596 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3597 the function, IO port 0xCFA, also 8-bit, sets 3598 bus number. The config space is then accessed 3599 through ports 0xC000-0xCFFF). 3600 See http://wiki.osdev.org/PCI for more info 3601 on the configuration access mechanisms. 3602 noaer [PCIE] If the PCIEAER kernel config parameter is 3603 enabled, this kernel boot option can be used to 3604 disable the use of PCIE advanced error reporting. 3605 nodomains [PCI] Disable support for multiple PCI 3606 root domains (aka PCI segments, in ACPI-speak). 3607 nommconf [X86] Disable use of MMCONFIG for PCI 3608 Configuration 3609 check_enable_amd_mmconf [X86] check for and enable 3610 properly configured MMIO access to PCI 3611 config space on AMD family 10h CPU 3612 nomsi [MSI] If the PCI_MSI kernel config parameter is 3613 enabled, this kernel boot option can be used to 3614 disable the use of MSI interrupts system-wide. 3615 noioapicquirk [APIC] Disable all boot interrupt quirks. 3616 Safety option to keep boot IRQs enabled. This 3617 should never be necessary. 3618 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3619 primary IO-APIC for bridges that cannot disable 3620 boot IRQs. This fixes a source of spurious IRQs 3621 when the system masks IRQs. 3622 noioapicreroute [APIC] Disable workaround that uses the 3623 boot IRQ equivalent of an IRQ that connects to 3624 a chipset where boot IRQs cannot be disabled. 3625 The opposite of ioapicreroute. 3626 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3627 routing table. These calls are known to be buggy 3628 on several machines and they hang the machine 3629 when used, but on other computers it's the only 3630 way to get the interrupt routing table. Try 3631 this option if the kernel is unable to allocate 3632 IRQs or discover secondary PCI buses on your 3633 motherboard. 3634 rom [X86] Assign address space to expansion ROMs. 3635 Use with caution as certain devices share 3636 address decoders between ROMs and other 3637 resources. 3638 norom [X86] Do not assign address space to 3639 expansion ROMs that do not already have 3640 BIOS assigned address ranges. 3641 nobar [X86] Do not assign address space to the 3642 BARs that weren't assigned by the BIOS. 3643 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3644 assigned automatically to PCI devices. You can 3645 make the kernel exclude IRQs of your ISA cards 3646 this way. 3647 pirqaddr=0xAAAAA [X86] Specify the physical address 3648 of the PIRQ table (normally generated 3649 by the BIOS) if it is outside the 3650 F0000h-100000h range. 3651 lastbus=N [X86] Scan all buses thru bus #N. Can be 3652 useful if the kernel is unable to find your 3653 secondary buses and you want to tell it 3654 explicitly which ones they are. 3655 assign-busses [X86] Always assign all PCI bus 3656 numbers ourselves, overriding 3657 whatever the firmware may have done. 3658 usepirqmask [X86] Honor the possible IRQ mask stored 3659 in the BIOS $PIR table. This is needed on 3660 some systems with broken BIOSes, notably 3661 some HP Pavilion N5400 and Omnibook XE3 3662 notebooks. This will have no effect if ACPI 3663 IRQ routing is enabled. 3664 noacpi [X86] Do not use ACPI for IRQ routing 3665 or for PCI scanning. 3666 use_crs [X86] Use PCI host bridge window information 3667 from ACPI. On BIOSes from 2008 or later, this 3668 is enabled by default. If you need to use this, 3669 please report a bug. 3670 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3671 If you need to use this, please report a bug. 3672 routeirq Do IRQ routing for all PCI devices. 3673 This is normally done in pci_enable_device(), 3674 so this option is a temporary workaround 3675 for broken drivers that don't call it. 3676 skip_isa_align [X86] do not align io start addr, so can 3677 handle more pci cards 3678 noearly [X86] Don't do any early type 1 scanning. 3679 This might help on some broken boards which 3680 machine check when some devices' config space 3681 is read. But various workarounds are disabled 3682 and some IOMMU drivers will not work. 3683 bfsort Sort PCI devices into breadth-first order. 3684 This sorting is done to get a device 3685 order compatible with older (<= 2.4) kernels. 3686 nobfsort Don't sort PCI devices into breadth-first order. 3687 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3688 tuning and use the BIOS-configured MPS defaults. 3689 pcie_bus_safe Set every device's MPS to the largest value 3690 supported by all devices below the root complex. 3691 pcie_bus_perf Set device MPS to the largest allowable MPS 3692 based on its parent bus. Also set MRRS (Max 3693 Read Request Size) to the largest supported 3694 value (no larger than the MPS that the device 3695 or bus can support) for best performance. 3696 pcie_bus_peer2peer Set every device's MPS to 128B, which 3697 every device is guaranteed to support. This 3698 configuration allows peer-to-peer DMA between 3699 any pair of devices, possibly at the cost of 3700 reduced performance. This also guarantees 3701 that hot-added devices will work. 3702 cbiosize=nn[KMG] The fixed amount of bus space which is 3703 reserved for the CardBus bridge's IO window. 3704 The default value is 256 bytes. 3705 cbmemsize=nn[KMG] The fixed amount of bus space which is 3706 reserved for the CardBus bridge's memory 3707 window. The default value is 64 megabytes. 3708 resource_alignment= 3709 Format: 3710 [<order of align>@]<pci_dev>[; ...] 3711 Specifies alignment and device to reassign 3712 aligned memory resources. How to 3713 specify the device is described above. 3714 If <order of align> is not specified, 3715 PAGE_SIZE is used as alignment. 3716 A PCI-PCI bridge can be specified if resource 3717 windows need to be expanded. 3718 To specify the alignment for several 3719 instances of a device, the PCI vendor, 3720 device, subvendor, and subdevice may be 3721 specified, e.g., 12@pci:8086:9c22:103c:198f 3722 for 4096-byte alignment. 3723 ecrc= Enable/disable PCIe ECRC (transaction layer 3724 end-to-end CRC checking). 3725 bios: Use BIOS/firmware settings. This is the 3726 the default. 3727 off: Turn ECRC off 3728 on: Turn ECRC on. 3729 hpiosize=nn[KMG] The fixed amount of bus space which is 3730 reserved for hotplug bridge's IO window. 3731 Default size is 256 bytes. 3732 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3733 reserved for hotplug bridge's MMIO window. 3734 Default size is 2 megabytes. 3735 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3736 reserved for hotplug bridge's MMIO_PREF window. 3737 Default size is 2 megabytes. 3738 hpmemsize=nn[KMG] The fixed amount of bus space which is 3739 reserved for hotplug bridge's MMIO and 3740 MMIO_PREF window. 3741 Default size is 2 megabytes. 3742 hpbussize=nn The minimum amount of additional bus numbers 3743 reserved for buses below a hotplug bridge. 3744 Default is 1. 3745 realloc= Enable/disable reallocating PCI bridge resources 3746 if allocations done by BIOS are too small to 3747 accommodate resources required by all child 3748 devices. 3749 off: Turn realloc off 3750 on: Turn realloc on 3751 realloc same as realloc=on 3752 noari do not use PCIe ARI. 3753 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3754 do not use PCIe ATS (and IOMMU device IOTLB). 3755 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3756 only look for one device below a PCIe downstream 3757 port. 3758 big_root_window Try to add a big 64bit memory window to the PCIe 3759 root complex on AMD CPUs. Some GFX hardware 3760 can resize a BAR to allow access to all VRAM. 3761 Adding the window is slightly risky (it may 3762 conflict with unreported devices), so this 3763 taints the kernel. 3764 disable_acs_redir=<pci_dev>[; ...] 3765 Specify one or more PCI devices (in the format 3766 specified above) separated by semicolons. 3767 Each device specified will have the PCI ACS 3768 redirect capabilities forced off which will 3769 allow P2P traffic between devices through 3770 bridges without forcing it upstream. Note: 3771 this removes isolation between devices and 3772 may put more devices in an IOMMU group. 3773 force_floating [S390] Force usage of floating interrupts. 3774 nomio [S390] Do not use MIO instructions. 3775 norid [S390] ignore the RID field and force use of 3776 one PCI domain per PCI function 3777 3778 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3779 Management. 3780 off Disable ASPM. 3781 force Enable ASPM even on devices that claim not to support it. 3782 WARNING: Forcing ASPM on may cause system lockups. 3783 3784 pcie_ports= [PCIE] PCIe port services handling: 3785 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3786 even if the platform doesn't give the OS permission to 3787 use them. This may cause conflicts if the platform 3788 also tries to use these services. 3789 dpc-native Use native PCIe service for DPC only. May 3790 cause conflicts if firmware uses AER or DPC. 3791 compat Disable native PCIe services (PME, AER, DPC, PCIe 3792 hotplug). 3793 3794 pcie_port_pm= [PCIE] PCIe port power management handling: 3795 off Disable power management of all PCIe ports 3796 force Forcibly enable power management of all PCIe ports 3797 3798 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3799 nomsi Do not use MSI for native PCIe PME signaling (this makes 3800 all PCIe root ports use INTx for all services). 3801 3802 pcmv= [HW,PCMCIA] BadgePAD 4 3803 3804 pd_ignore_unused 3805 [PM] 3806 Keep all power-domains already enabled by bootloader on, 3807 even if no driver has claimed them. This is useful 3808 for debug and development, but should not be 3809 needed on a platform with proper driver support. 3810 3811 pd. [PARIDE] 3812 See Documentation/admin-guide/blockdev/paride.rst. 3813 3814 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3815 boot time. 3816 Format: { 0 | 1 } 3817 See arch/parisc/kernel/pdc_chassis.c 3818 3819 percpu_alloc= Select which percpu first chunk allocator to use. 3820 Currently supported values are "embed" and "page". 3821 Archs may support subset or none of the selections. 3822 See comments in mm/percpu.c for details on each 3823 allocator. This parameter is primarily for debugging 3824 and performance comparison. 3825 3826 pf. [PARIDE] 3827 See Documentation/admin-guide/blockdev/paride.rst. 3828 3829 pg. [PARIDE] 3830 See Documentation/admin-guide/blockdev/paride.rst. 3831 3832 pirq= [SMP,APIC] Manual mp-table setup 3833 See Documentation/x86/i386/IO-APIC.rst. 3834 3835 plip= [PPT,NET] Parallel port network link 3836 Format: { parport<nr> | timid | 0 } 3837 See also Documentation/admin-guide/parport.rst. 3838 3839 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3840 Override pmtimer IOPort with a hex value. 3841 e.g. pmtmr=0x508 3842 3843 pm_debug_messages [SUSPEND,KNL] 3844 Enable suspend/resume debug messages during boot up. 3845 3846 pnp.debug=1 [PNP] 3847 Enable PNP debug messages (depends on the 3848 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3849 via /sys/module/pnp/parameters/debug. We always show 3850 current resource usage; turning this on also shows 3851 possible settings and some assignment information. 3852 3853 pnpacpi= [ACPI] 3854 { off } 3855 3856 pnpbios= [ISAPNP] 3857 { on | off | curr | res | no-curr | no-res } 3858 3859 pnp_reserve_irq= 3860 [ISAPNP] Exclude IRQs for the autoconfiguration 3861 3862 pnp_reserve_dma= 3863 [ISAPNP] Exclude DMAs for the autoconfiguration 3864 3865 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3866 Ranges are in pairs (I/O port base and size). 3867 3868 pnp_reserve_mem= 3869 [ISAPNP] Exclude memory regions for the 3870 autoconfiguration. 3871 Ranges are in pairs (memory base and size). 3872 3873 ports= [IP_VS_FTP] IPVS ftp helper module 3874 Default is 21. 3875 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3876 may be specified. 3877 Format: <port>,<port>.... 3878 3879 powersave=off [PPC] This option disables power saving features. 3880 It specifically disables cpuidle and sets the 3881 platform machine description specific power_save 3882 function to NULL. On Idle the CPU just reduces 3883 execution priority. 3884 3885 ppc_strict_facility_enable 3886 [PPC] This option catches any kernel floating point, 3887 Altivec, VSX and SPE outside of regions specifically 3888 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3889 There is some performance impact when enabling this. 3890 3891 ppc_tm= [PPC] 3892 Format: {"off"} 3893 Disable Hardware Transactional Memory 3894 3895 print-fatal-signals= 3896 [KNL] debug: print fatal signals 3897 3898 If enabled, warn about various signal handling 3899 related application anomalies: too many signals, 3900 too many POSIX.1 timers, fatal signals causing a 3901 coredump - etc. 3902 3903 If you hit the warning due to signal overflow, 3904 you might want to try "ulimit -i unlimited". 3905 3906 default: off. 3907 3908 printk.always_kmsg_dump= 3909 Trigger kmsg_dump for cases other than kernel oops or 3910 panics 3911 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3912 default: disabled 3913 3914 printk.devkmsg={on,off,ratelimit} 3915 Control writing to /dev/kmsg. 3916 on - unlimited logging to /dev/kmsg from userspace 3917 off - logging to /dev/kmsg disabled 3918 ratelimit - ratelimit the logging 3919 Default: ratelimit 3920 3921 printk.time= Show timing data prefixed to each printk message line 3922 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3923 3924 processor.max_cstate= [HW,ACPI] 3925 Limit processor to maximum C-state 3926 max_cstate=9 overrides any DMI blacklist limit. 3927 3928 processor.nocst [HW,ACPI] 3929 Ignore the _CST method to determine C-states, 3930 instead using the legacy FADT method 3931 3932 profile= [KNL] Enable kernel profiling via /proc/profile 3933 Format: [<profiletype>,]<number> 3934 Param: <profiletype>: "schedule", "sleep", or "kvm" 3935 [defaults to kernel profiling] 3936 Param: "schedule" - profile schedule points. 3937 Param: "sleep" - profile D-state sleeping (millisecs). 3938 Requires CONFIG_SCHEDSTATS 3939 Param: "kvm" - profile VM exits. 3940 Param: <number> - step/bucket size as a power of 2 for 3941 statistical time based profiling. 3942 3943 prompt_ramdisk= [RAM] [Deprecated] 3944 3945 prot_virt= [S390] enable hosting protected virtual machines 3946 isolated from the hypervisor (if hardware supports 3947 that). 3948 Format: <bool> 3949 3950 psi= [KNL] Enable or disable pressure stall information 3951 tracking. 3952 Format: <bool> 3953 3954 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3955 probe for; one of (bare|imps|exps|lifebook|any). 3956 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3957 per second. 3958 psmouse.resetafter= [HW,MOUSE] 3959 Try to reset the device after so many bad packets 3960 (0 = never). 3961 psmouse.resolution= 3962 [HW,MOUSE] Set desired mouse resolution, in dpi. 3963 psmouse.smartscroll= 3964 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3965 0 = disabled, 1 = enabled (default). 3966 3967 pstore.backend= Specify the name of the pstore backend to use 3968 3969 pt. [PARIDE] 3970 See Documentation/admin-guide/blockdev/paride.rst. 3971 3972 pti= [X86-64] Control Page Table Isolation of user and 3973 kernel address spaces. Disabling this feature 3974 removes hardening, but improves performance of 3975 system calls and interrupts. 3976 3977 on - unconditionally enable 3978 off - unconditionally disable 3979 auto - kernel detects whether your CPU model is 3980 vulnerable to issues that PTI mitigates 3981 3982 Not specifying this option is equivalent to pti=auto. 3983 3984 nopti [X86-64] 3985 Equivalent to pti=off 3986 3987 pty.legacy_count= 3988 [KNL] Number of legacy pty's. Overwrites compiled-in 3989 default number. 3990 3991 quiet [KNL] Disable most log messages 3992 3993 r128= [HW,DRM] 3994 3995 raid= [HW,RAID] 3996 See Documentation/admin-guide/md.rst. 3997 3998 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3999 See Documentation/admin-guide/blockdev/ramdisk.rst. 4000 4001 ramdisk_start= [RAM] RAM disk image start address 4002 4003 random.trust_cpu={on,off} 4004 [KNL] Enable or disable trusting the use of the 4005 CPU's random number generator (if available) to 4006 fully seed the kernel's CRNG. Default is controlled 4007 by CONFIG_RANDOM_TRUST_CPU. 4008 4009 ras=option[,option,...] [KNL] RAS-specific options 4010 4011 cec_disable [X86] 4012 Disable the Correctable Errors Collector, 4013 see CONFIG_RAS_CEC help text. 4014 4015 rcu_nocbs= [KNL] 4016 The argument is a cpu list, as described above, 4017 except that the string "all" can be used to 4018 specify every CPU on the system. 4019 4020 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4021 the specified list of CPUs to be no-callback CPUs. 4022 Invocation of these CPUs' RCU callbacks will be 4023 offloaded to "rcuox/N" kthreads created for that 4024 purpose, where "x" is "p" for RCU-preempt, and 4025 "s" for RCU-sched, and "N" is the CPU number. 4026 This reduces OS jitter on the offloaded CPUs, 4027 which can be useful for HPC and real-time 4028 workloads. It can also improve energy efficiency 4029 for asymmetric multiprocessors. 4030 4031 rcu_nocb_poll [KNL] 4032 Rather than requiring that offloaded CPUs 4033 (specified by rcu_nocbs= above) explicitly 4034 awaken the corresponding "rcuoN" kthreads, 4035 make these kthreads poll for callbacks. 4036 This improves the real-time response for the 4037 offloaded CPUs by relieving them of the need to 4038 wake up the corresponding kthread, but degrades 4039 energy efficiency by requiring that the kthreads 4040 periodically wake up to do the polling. 4041 4042 rcutree.blimit= [KNL] 4043 Set maximum number of finished RCU callbacks to 4044 process in one batch. 4045 4046 rcutree.dump_tree= [KNL] 4047 Dump the structure of the rcu_node combining tree 4048 out at early boot. This is used for diagnostic 4049 purposes, to verify correct tree setup. 4050 4051 rcutree.gp_cleanup_delay= [KNL] 4052 Set the number of jiffies to delay each step of 4053 RCU grace-period cleanup. 4054 4055 rcutree.gp_init_delay= [KNL] 4056 Set the number of jiffies to delay each step of 4057 RCU grace-period initialization. 4058 4059 rcutree.gp_preinit_delay= [KNL] 4060 Set the number of jiffies to delay each step of 4061 RCU grace-period pre-initialization, that is, 4062 the propagation of recent CPU-hotplug changes up 4063 the rcu_node combining tree. 4064 4065 rcutree.use_softirq= [KNL] 4066 If set to zero, move all RCU_SOFTIRQ processing to 4067 per-CPU rcuc kthreads. Defaults to a non-zero 4068 value, meaning that RCU_SOFTIRQ is used by default. 4069 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4070 4071 rcutree.rcu_fanout_exact= [KNL] 4072 Disable autobalancing of the rcu_node combining 4073 tree. This is used by rcutorture, and might 4074 possibly be useful for architectures having high 4075 cache-to-cache transfer latencies. 4076 4077 rcutree.rcu_fanout_leaf= [KNL] 4078 Change the number of CPUs assigned to each 4079 leaf rcu_node structure. Useful for very 4080 large systems, which will choose the value 64, 4081 and for NUMA systems with large remote-access 4082 latencies, which will choose a value aligned 4083 with the appropriate hardware boundaries. 4084 4085 rcutree.rcu_min_cached_objs= [KNL] 4086 Minimum number of objects which are cached and 4087 maintained per one CPU. Object size is equal 4088 to PAGE_SIZE. The cache allows to reduce the 4089 pressure to page allocator, also it makes the 4090 whole algorithm to behave better in low memory 4091 condition. 4092 4093 rcutree.jiffies_till_first_fqs= [KNL] 4094 Set delay from grace-period initialization to 4095 first attempt to force quiescent states. 4096 Units are jiffies, minimum value is zero, 4097 and maximum value is HZ. 4098 4099 rcutree.jiffies_till_next_fqs= [KNL] 4100 Set delay between subsequent attempts to force 4101 quiescent states. Units are jiffies, minimum 4102 value is one, and maximum value is HZ. 4103 4104 rcutree.jiffies_till_sched_qs= [KNL] 4105 Set required age in jiffies for a 4106 given grace period before RCU starts 4107 soliciting quiescent-state help from 4108 rcu_note_context_switch() and cond_resched(). 4109 If not specified, the kernel will calculate 4110 a value based on the most recent settings 4111 of rcutree.jiffies_till_first_fqs 4112 and rcutree.jiffies_till_next_fqs. 4113 This calculated value may be viewed in 4114 rcutree.jiffies_to_sched_qs. Any attempt to set 4115 rcutree.jiffies_to_sched_qs will be cheerfully 4116 overwritten. 4117 4118 rcutree.kthread_prio= [KNL,BOOT] 4119 Set the SCHED_FIFO priority of the RCU per-CPU 4120 kthreads (rcuc/N). This value is also used for 4121 the priority of the RCU boost threads (rcub/N) 4122 and for the RCU grace-period kthreads (rcu_bh, 4123 rcu_preempt, and rcu_sched). If RCU_BOOST is 4124 set, valid values are 1-99 and the default is 1 4125 (the least-favored priority). Otherwise, when 4126 RCU_BOOST is not set, valid values are 0-99 and 4127 the default is zero (non-realtime operation). 4128 4129 rcutree.rcu_nocb_gp_stride= [KNL] 4130 Set the number of NOCB callback kthreads in 4131 each group, which defaults to the square root 4132 of the number of CPUs. Larger numbers reduce 4133 the wakeup overhead on the global grace-period 4134 kthread, but increases that same overhead on 4135 each group's NOCB grace-period kthread. 4136 4137 rcutree.qhimark= [KNL] 4138 Set threshold of queued RCU callbacks beyond which 4139 batch limiting is disabled. 4140 4141 rcutree.qlowmark= [KNL] 4142 Set threshold of queued RCU callbacks below which 4143 batch limiting is re-enabled. 4144 4145 rcutree.qovld= [KNL] 4146 Set threshold of queued RCU callbacks beyond which 4147 RCU's force-quiescent-state scan will aggressively 4148 enlist help from cond_resched() and sched IPIs to 4149 help CPUs more quickly reach quiescent states. 4150 Set to less than zero to make this be set based 4151 on rcutree.qhimark at boot time and to zero to 4152 disable more aggressive help enlistment. 4153 4154 rcutree.rcu_idle_gp_delay= [KNL] 4155 Set wakeup interval for idle CPUs that have 4156 RCU callbacks (RCU_FAST_NO_HZ=y). 4157 4158 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4159 Set wakeup interval for idle CPUs that have 4160 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4161 Lazy RCU callbacks are those which RCU can 4162 prove do nothing more than free memory. 4163 4164 rcutree.rcu_kick_kthreads= [KNL] 4165 Cause the grace-period kthread to get an extra 4166 wake_up() if it sleeps three times longer than 4167 it should at force-quiescent-state time. 4168 This wake_up() will be accompanied by a 4169 WARN_ONCE() splat and an ftrace_dump(). 4170 4171 rcutree.sysrq_rcu= [KNL] 4172 Commandeer a sysrq key to dump out Tree RCU's 4173 rcu_node tree with an eye towards determining 4174 why a new grace period has not yet started. 4175 4176 rcuperf.gp_async= [KNL] 4177 Measure performance of asynchronous 4178 grace-period primitives such as call_rcu(). 4179 4180 rcuperf.gp_async_max= [KNL] 4181 Specify the maximum number of outstanding 4182 callbacks per writer thread. When a writer 4183 thread exceeds this limit, it invokes the 4184 corresponding flavor of rcu_barrier() to allow 4185 previously posted callbacks to drain. 4186 4187 rcuperf.gp_exp= [KNL] 4188 Measure performance of expedited synchronous 4189 grace-period primitives. 4190 4191 rcuperf.holdoff= [KNL] 4192 Set test-start holdoff period. The purpose of 4193 this parameter is to delay the start of the 4194 test until boot completes in order to avoid 4195 interference. 4196 4197 rcuperf.kfree_rcu_test= [KNL] 4198 Set to measure performance of kfree_rcu() flooding. 4199 4200 rcuperf.kfree_nthreads= [KNL] 4201 The number of threads running loops of kfree_rcu(). 4202 4203 rcuperf.kfree_alloc_num= [KNL] 4204 Number of allocations and frees done in an iteration. 4205 4206 rcuperf.kfree_loops= [KNL] 4207 Number of loops doing rcuperf.kfree_alloc_num number 4208 of allocations and frees. 4209 4210 rcuperf.nreaders= [KNL] 4211 Set number of RCU readers. The value -1 selects 4212 N, where N is the number of CPUs. A value 4213 "n" less than -1 selects N-n+1, where N is again 4214 the number of CPUs. For example, -2 selects N 4215 (the number of CPUs), -3 selects N+1, and so on. 4216 A value of "n" less than or equal to -N selects 4217 a single reader. 4218 4219 rcuperf.nwriters= [KNL] 4220 Set number of RCU writers. The values operate 4221 the same as for rcuperf.nreaders. 4222 N, where N is the number of CPUs 4223 4224 rcuperf.perf_type= [KNL] 4225 Specify the RCU implementation to test. 4226 4227 rcuperf.shutdown= [KNL] 4228 Shut the system down after performance tests 4229 complete. This is useful for hands-off automated 4230 testing. 4231 4232 rcuperf.verbose= [KNL] 4233 Enable additional printk() statements. 4234 4235 rcuperf.writer_holdoff= [KNL] 4236 Write-side holdoff between grace periods, 4237 in microseconds. The default of zero says 4238 no holdoff. 4239 4240 rcutorture.fqs_duration= [KNL] 4241 Set duration of force_quiescent_state bursts 4242 in microseconds. 4243 4244 rcutorture.fqs_holdoff= [KNL] 4245 Set holdoff time within force_quiescent_state bursts 4246 in microseconds. 4247 4248 rcutorture.fqs_stutter= [KNL] 4249 Set wait time between force_quiescent_state bursts 4250 in seconds. 4251 4252 rcutorture.fwd_progress= [KNL] 4253 Enable RCU grace-period forward-progress testing 4254 for the types of RCU supporting this notion. 4255 4256 rcutorture.fwd_progress_div= [KNL] 4257 Specify the fraction of a CPU-stall-warning 4258 period to do tight-loop forward-progress testing. 4259 4260 rcutorture.fwd_progress_holdoff= [KNL] 4261 Number of seconds to wait between successive 4262 forward-progress tests. 4263 4264 rcutorture.fwd_progress_need_resched= [KNL] 4265 Enclose cond_resched() calls within checks for 4266 need_resched() during tight-loop forward-progress 4267 testing. 4268 4269 rcutorture.gp_cond= [KNL] 4270 Use conditional/asynchronous update-side 4271 primitives, if available. 4272 4273 rcutorture.gp_exp= [KNL] 4274 Use expedited update-side primitives, if available. 4275 4276 rcutorture.gp_normal= [KNL] 4277 Use normal (non-expedited) asynchronous 4278 update-side primitives, if available. 4279 4280 rcutorture.gp_sync= [KNL] 4281 Use normal (non-expedited) synchronous 4282 update-side primitives, if available. If all 4283 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4284 rcutorture.gp_normal=, and rcutorture.gp_sync= 4285 are zero, rcutorture acts as if is interpreted 4286 they are all non-zero. 4287 4288 rcutorture.n_barrier_cbs= [KNL] 4289 Set callbacks/threads for rcu_barrier() testing. 4290 4291 rcutorture.nfakewriters= [KNL] 4292 Set number of concurrent RCU writers. These just 4293 stress RCU, they don't participate in the actual 4294 test, hence the "fake". 4295 4296 rcutorture.nreaders= [KNL] 4297 Set number of RCU readers. The value -1 selects 4298 N-1, where N is the number of CPUs. A value 4299 "n" less than -1 selects N-n-2, where N is again 4300 the number of CPUs. For example, -2 selects N 4301 (the number of CPUs), -3 selects N+1, and so on. 4302 4303 rcutorture.object_debug= [KNL] 4304 Enable debug-object double-call_rcu() testing. 4305 4306 rcutorture.onoff_holdoff= [KNL] 4307 Set time (s) after boot for CPU-hotplug testing. 4308 4309 rcutorture.onoff_interval= [KNL] 4310 Set time (jiffies) between CPU-hotplug operations, 4311 or zero to disable CPU-hotplug testing. 4312 4313 rcutorture.read_exit= [KNL] 4314 Set the number of read-then-exit kthreads used 4315 to test the interaction of RCU updaters and 4316 task-exit processing. 4317 4318 rcutorture.read_exit_burst= [KNL] 4319 The number of times in a given read-then-exit 4320 episode that a set of read-then-exit kthreads 4321 is spawned. 4322 4323 rcutorture.read_exit_delay= [KNL] 4324 The delay, in seconds, between successive 4325 read-then-exit testing episodes. 4326 4327 rcutorture.shuffle_interval= [KNL] 4328 Set task-shuffle interval (s). Shuffling tasks 4329 allows some CPUs to go into dyntick-idle mode 4330 during the rcutorture test. 4331 4332 rcutorture.shutdown_secs= [KNL] 4333 Set time (s) after boot system shutdown. This 4334 is useful for hands-off automated testing. 4335 4336 rcutorture.stall_cpu= [KNL] 4337 Duration of CPU stall (s) to test RCU CPU stall 4338 warnings, zero to disable. 4339 4340 rcutorture.stall_cpu_block= [KNL] 4341 Sleep while stalling if set. This will result 4342 in warnings from preemptible RCU in addition 4343 to any other stall-related activity. 4344 4345 rcutorture.stall_cpu_holdoff= [KNL] 4346 Time to wait (s) after boot before inducing stall. 4347 4348 rcutorture.stall_cpu_irqsoff= [KNL] 4349 Disable interrupts while stalling if set. 4350 4351 rcutorture.stall_gp_kthread= [KNL] 4352 Duration (s) of forced sleep within RCU 4353 grace-period kthread to test RCU CPU stall 4354 warnings, zero to disable. If both stall_cpu 4355 and stall_gp_kthread are specified, the 4356 kthread is starved first, then the CPU. 4357 4358 rcutorture.stat_interval= [KNL] 4359 Time (s) between statistics printk()s. 4360 4361 rcutorture.stutter= [KNL] 4362 Time (s) to stutter testing, for example, specifying 4363 five seconds causes the test to run for five seconds, 4364 wait for five seconds, and so on. This tests RCU's 4365 ability to transition abruptly to and from idle. 4366 4367 rcutorture.test_boost= [KNL] 4368 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4369 "Maybe" means test if the RCU implementation 4370 under test support RCU priority boosting. 4371 4372 rcutorture.test_boost_duration= [KNL] 4373 Duration (s) of each individual boost test. 4374 4375 rcutorture.test_boost_interval= [KNL] 4376 Interval (s) between each boost test. 4377 4378 rcutorture.test_no_idle_hz= [KNL] 4379 Test RCU's dyntick-idle handling. See also the 4380 rcutorture.shuffle_interval parameter. 4381 4382 rcutorture.torture_type= [KNL] 4383 Specify the RCU implementation to test. 4384 4385 rcutorture.verbose= [KNL] 4386 Enable additional printk() statements. 4387 4388 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4389 Dump ftrace buffer after reporting RCU CPU 4390 stall warning. 4391 4392 rcupdate.rcu_cpu_stall_suppress= [KNL] 4393 Suppress RCU CPU stall warning messages. 4394 4395 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4396 Suppress RCU CPU stall warning messages and 4397 rcutorture writer stall warnings that occur 4398 during early boot, that is, during the time 4399 before the init task is spawned. 4400 4401 rcupdate.rcu_cpu_stall_timeout= [KNL] 4402 Set timeout for RCU CPU stall warning messages. 4403 4404 rcupdate.rcu_expedited= [KNL] 4405 Use expedited grace-period primitives, for 4406 example, synchronize_rcu_expedited() instead 4407 of synchronize_rcu(). This reduces latency, 4408 but can increase CPU utilization, degrade 4409 real-time latency, and degrade energy efficiency. 4410 No effect on CONFIG_TINY_RCU kernels. 4411 4412 rcupdate.rcu_normal= [KNL] 4413 Use only normal grace-period primitives, 4414 for example, synchronize_rcu() instead of 4415 synchronize_rcu_expedited(). This improves 4416 real-time latency, CPU utilization, and 4417 energy efficiency, but can expose users to 4418 increased grace-period latency. This parameter 4419 overrides rcupdate.rcu_expedited. No effect on 4420 CONFIG_TINY_RCU kernels. 4421 4422 rcupdate.rcu_normal_after_boot= [KNL] 4423 Once boot has completed (that is, after 4424 rcu_end_inkernel_boot() has been invoked), use 4425 only normal grace-period primitives. No effect 4426 on CONFIG_TINY_RCU kernels. 4427 4428 rcupdate.rcu_task_ipi_delay= [KNL] 4429 Set time in jiffies during which RCU tasks will 4430 avoid sending IPIs, starting with the beginning 4431 of a given grace period. Setting a large 4432 number avoids disturbing real-time workloads, 4433 but lengthens grace periods. 4434 4435 rcupdate.rcu_task_stall_timeout= [KNL] 4436 Set timeout in jiffies for RCU task stall warning 4437 messages. Disable with a value less than or equal 4438 to zero. 4439 4440 rcupdate.rcu_self_test= [KNL] 4441 Run the RCU early boot self tests 4442 4443 rdinit= [KNL] 4444 Format: <full_path> 4445 Run specified binary instead of /init from the ramdisk, 4446 used for early userspace startup. See initrd. 4447 4448 rdrand= [X86] 4449 force - Override the decision by the kernel to hide the 4450 advertisement of RDRAND support (this affects 4451 certain AMD processors because of buggy BIOS 4452 support, specifically around the suspend/resume 4453 path). 4454 4455 rdt= [HW,X86,RDT] 4456 Turn on/off individual RDT features. List is: 4457 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4458 mba. 4459 E.g. to turn on cmt and turn off mba use: 4460 rdt=cmt,!mba 4461 4462 reboot= [KNL] 4463 Format (x86 or x86_64): 4464 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4465 [[,]s[mp]#### \ 4466 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4467 [[,]f[orce] 4468 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4469 (prefix with 'panic_' to set mode for panic 4470 reboot only), 4471 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4472 reboot_force is either force or not specified, 4473 reboot_cpu is s[mp]#### with #### being the processor 4474 to be used for rebooting. 4475 4476 refscale.holdoff= [KNL] 4477 Set test-start holdoff period. The purpose of 4478 this parameter is to delay the start of the 4479 test until boot completes in order to avoid 4480 interference. 4481 4482 refscale.loops= [KNL] 4483 Set the number of loops over the synchronization 4484 primitive under test. Increasing this number 4485 reduces noise due to loop start/end overhead, 4486 but the default has already reduced the per-pass 4487 noise to a handful of picoseconds on ca. 2020 4488 x86 laptops. 4489 4490 refscale.nreaders= [KNL] 4491 Set number of readers. The default value of -1 4492 selects N, where N is roughly 75% of the number 4493 of CPUs. A value of zero is an interesting choice. 4494 4495 refscale.nruns= [KNL] 4496 Set number of runs, each of which is dumped onto 4497 the console log. 4498 4499 refscale.readdelay= [KNL] 4500 Set the read-side critical-section duration, 4501 measured in microseconds. 4502 4503 refscale.scale_type= [KNL] 4504 Specify the read-protection implementation to test. 4505 4506 refscale.shutdown= [KNL] 4507 Shut down the system at the end of the performance 4508 test. This defaults to 1 (shut it down) when 4509 rcuperf is built into the kernel and to 0 (leave 4510 it running) when rcuperf is built as a module. 4511 4512 refscale.verbose= [KNL] 4513 Enable additional printk() statements. 4514 4515 relax_domain_level= 4516 [KNL, SMP] Set scheduler's default relax_domain_level. 4517 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4518 4519 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4520 Format: <base1>,<size1>[,<base2>,<size2>,...] 4521 Reserve I/O ports or memory so the kernel won't use 4522 them. If <base> is less than 0x10000, the region 4523 is assumed to be I/O ports; otherwise it is memory. 4524 4525 reservetop= [X86-32] 4526 Format: nn[KMG] 4527 Reserves a hole at the top of the kernel virtual 4528 address space. 4529 4530 reservelow= [X86] 4531 Format: nn[K] 4532 Set the amount of memory to reserve for BIOS at 4533 the bottom of the address space. 4534 4535 reset_devices [KNL] Force drivers to reset the underlying device 4536 during initialization. 4537 4538 resume= [SWSUSP] 4539 Specify the partition device for software suspend 4540 Format: 4541 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4542 4543 resume_offset= [SWSUSP] 4544 Specify the offset from the beginning of the partition 4545 given by "resume=" at which the swap header is located, 4546 in <PAGE_SIZE> units (needed only for swap files). 4547 See Documentation/power/swsusp-and-swap-files.rst 4548 4549 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4550 read the resume files 4551 4552 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4553 Useful for devices that are detected asynchronously 4554 (e.g. USB and MMC devices). 4555 4556 hibernate= [HIBERNATION] 4557 noresume Don't check if there's a hibernation image 4558 present during boot. 4559 nocompress Don't compress/decompress hibernation images. 4560 no Disable hibernation and resume. 4561 protect_image Turn on image protection during restoration 4562 (that will set all pages holding image data 4563 during restoration read-only). 4564 4565 retain_initrd [RAM] Keep initrd memory after extraction 4566 4567 rfkill.default_state= 4568 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4569 etc. communication is blocked by default. 4570 1 Unblocked. 4571 4572 rfkill.master_switch_mode= 4573 0 The "airplane mode" button does nothing. 4574 1 The "airplane mode" button toggles between everything 4575 blocked and the previous configuration. 4576 2 The "airplane mode" button toggles between everything 4577 blocked and everything unblocked. 4578 4579 rhash_entries= [KNL,NET] 4580 Set number of hash buckets for route cache 4581 4582 ring3mwait=disable 4583 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4584 CPUs. 4585 4586 ro [KNL] Mount root device read-only on boot 4587 4588 rodata= [KNL] 4589 on Mark read-only kernel memory as read-only (default). 4590 off Leave read-only kernel memory writable for debugging. 4591 4592 rockchip.usb_uart 4593 Enable the uart passthrough on the designated usb port 4594 on Rockchip SoCs. When active, the signals of the 4595 debug-uart get routed to the D+ and D- pins of the usb 4596 port and the regular usb controller gets disabled. 4597 4598 root= [KNL] Root filesystem 4599 See name_to_dev_t comment in init/do_mounts.c. 4600 4601 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4602 mount the root filesystem 4603 4604 rootflags= [KNL] Set root filesystem mount option string 4605 4606 rootfstype= [KNL] Set root filesystem type 4607 4608 rootwait [KNL] Wait (indefinitely) for root device to show up. 4609 Useful for devices that are detected asynchronously 4610 (e.g. USB and MMC devices). 4611 4612 rproc_mem=nn[KMG][@address] 4613 [KNL,ARM,CMA] Remoteproc physical memory block. 4614 Memory area to be used by remote processor image, 4615 managed by CMA. 4616 4617 rw [KNL] Mount root device read-write on boot 4618 4619 S [KNL] Run init in single mode 4620 4621 s390_iommu= [HW,S390] 4622 Set s390 IOTLB flushing mode 4623 strict 4624 With strict flushing every unmap operation will result in 4625 an IOTLB flush. Default is lazy flushing before reuse, 4626 which is faster. 4627 4628 sa1100ir [NET] 4629 See drivers/net/irda/sa1100_ir.c. 4630 4631 sbni= [NET] Granch SBNI12 leased line adapter 4632 4633 sched_debug [KNL] Enables verbose scheduler debug messages. 4634 4635 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4636 Allowed values are enable and disable. This feature 4637 incurs a small amount of overhead in the scheduler 4638 but is useful for debugging and performance tuning. 4639 4640 sched_thermal_decay_shift= 4641 [KNL, SMP] Set a decay shift for scheduler thermal 4642 pressure signal. Thermal pressure signal follows the 4643 default decay period of other scheduler pelt 4644 signals(usually 32 ms but configurable). Setting 4645 sched_thermal_decay_shift will left shift the decay 4646 period for the thermal pressure signal by the shift 4647 value. 4648 i.e. with the default pelt decay period of 32 ms 4649 sched_thermal_decay_shift thermal pressure decay pr 4650 1 64 ms 4651 2 128 ms 4652 and so on. 4653 Format: integer between 0 and 10 4654 Default is 0. 4655 4656 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4657 xtime_lock contention on larger systems, and/or RCU lock 4658 contention on all systems with CONFIG_MAXSMP set. 4659 Format: { "0" | "1" } 4660 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4661 1 -- enable. 4662 Note: increases power consumption, thus should only be 4663 enabled if running jitter sensitive (HPC/RT) workloads. 4664 4665 security= [SECURITY] Choose a legacy "major" security module to 4666 enable at boot. This has been deprecated by the 4667 "lsm=" parameter. 4668 4669 selinux= [SELINUX] Disable or enable SELinux at boot time. 4670 Format: { "0" | "1" } 4671 See security/selinux/Kconfig help text. 4672 0 -- disable. 4673 1 -- enable. 4674 Default value is 1. 4675 4676 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4677 Format: { "0" | "1" } 4678 See security/apparmor/Kconfig help text 4679 0 -- disable. 4680 1 -- enable. 4681 Default value is set via kernel config option. 4682 4683 serialnumber [BUGS=X86-32] 4684 4685 shapers= [NET] 4686 Maximal number of shapers. 4687 4688 simeth= [IA-64] 4689 simscsi= 4690 4691 slram= [HW,MTD] 4692 4693 slab_nomerge [MM] 4694 Disable merging of slabs with similar size. May be 4695 necessary if there is some reason to distinguish 4696 allocs to different slabs, especially in hardened 4697 environments where the risk of heap overflows and 4698 layout control by attackers can usually be 4699 frustrated by disabling merging. This will reduce 4700 most of the exposure of a heap attack to a single 4701 cache (risks via metadata attacks are mostly 4702 unchanged). Debug options disable merging on their 4703 own. 4704 For more information see Documentation/vm/slub.rst. 4705 4706 slab_max_order= [MM, SLAB] 4707 Determines the maximum allowed order for slabs. 4708 A high setting may cause OOMs due to memory 4709 fragmentation. Defaults to 1 for systems with 4710 more than 32MB of RAM, 0 otherwise. 4711 4712 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4713 Enabling slub_debug allows one to determine the 4714 culprit if slab objects become corrupted. Enabling 4715 slub_debug can create guard zones around objects and 4716 may poison objects when not in use. Also tracks the 4717 last alloc / free. For more information see 4718 Documentation/vm/slub.rst. 4719 4720 slub_memcg_sysfs= [MM, SLUB] 4721 Determines whether to enable sysfs directories for 4722 memory cgroup sub-caches. 1 to enable, 0 to disable. 4723 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4724 Enabling this can lead to a very high number of debug 4725 directories and files being created under 4726 /sys/kernel/slub. 4727 4728 slub_max_order= [MM, SLUB] 4729 Determines the maximum allowed order for slabs. 4730 A high setting may cause OOMs due to memory 4731 fragmentation. For more information see 4732 Documentation/vm/slub.rst. 4733 4734 slub_min_objects= [MM, SLUB] 4735 The minimum number of objects per slab. SLUB will 4736 increase the slab order up to slub_max_order to 4737 generate a sufficiently large slab able to contain 4738 the number of objects indicated. The higher the number 4739 of objects the smaller the overhead of tracking slabs 4740 and the less frequently locks need to be acquired. 4741 For more information see Documentation/vm/slub.rst. 4742 4743 slub_min_order= [MM, SLUB] 4744 Determines the minimum page order for slabs. Must be 4745 lower than slub_max_order. 4746 For more information see Documentation/vm/slub.rst. 4747 4748 slub_nomerge [MM, SLUB] 4749 Same with slab_nomerge. This is supported for legacy. 4750 See slab_nomerge for more information. 4751 4752 smart2= [HW] 4753 Format: <io1>[,<io2>[,...,<io8>]] 4754 4755 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4756 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4757 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4758 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4759 smsc-ircc2.ircc_irq= [HW] IRQ line 4760 smsc-ircc2.ircc_dma= [HW] DMA channel 4761 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4762 0: Toshiba Satellite 1800 (GP data pin select) 4763 1: Fast pin select (default) 4764 2: ATC IRMode 4765 4766 smt [KNL,S390] Set the maximum number of threads (logical 4767 CPUs) to use per physical CPU on systems capable of 4768 symmetric multithreading (SMT). Will be capped to the 4769 actual hardware limit. 4770 Format: <integer> 4771 Default: -1 (no limit) 4772 4773 softlockup_panic= 4774 [KNL] Should the soft-lockup detector generate panics. 4775 Format: 0 | 1 4776 4777 A value of 1 instructs the soft-lockup detector 4778 to panic the machine when a soft-lockup occurs. It is 4779 also controlled by the kernel.softlockup_panic sysctl 4780 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4781 respective build-time switch to that functionality. 4782 4783 softlockup_all_cpu_backtrace= 4784 [KNL] Should the soft-lockup detector generate 4785 backtraces on all cpus. 4786 Format: 0 | 1 4787 4788 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4789 See Documentation/admin-guide/laptops/sonypi.rst 4790 4791 spectre_v2= [X86] Control mitigation of Spectre variant 2 4792 (indirect branch speculation) vulnerability. 4793 The default operation protects the kernel from 4794 user space attacks. 4795 4796 on - unconditionally enable, implies 4797 spectre_v2_user=on 4798 off - unconditionally disable, implies 4799 spectre_v2_user=off 4800 auto - kernel detects whether your CPU model is 4801 vulnerable 4802 4803 Selecting 'on' will, and 'auto' may, choose a 4804 mitigation method at run time according to the 4805 CPU, the available microcode, the setting of the 4806 CONFIG_RETPOLINE configuration option, and the 4807 compiler with which the kernel was built. 4808 4809 Selecting 'on' will also enable the mitigation 4810 against user space to user space task attacks. 4811 4812 Selecting 'off' will disable both the kernel and 4813 the user space protections. 4814 4815 Specific mitigations can also be selected manually: 4816 4817 retpoline - replace indirect branches 4818 retpoline,generic - google's original retpoline 4819 retpoline,amd - AMD-specific minimal thunk 4820 4821 Not specifying this option is equivalent to 4822 spectre_v2=auto. 4823 4824 spectre_v2_user= 4825 [X86] Control mitigation of Spectre variant 2 4826 (indirect branch speculation) vulnerability between 4827 user space tasks 4828 4829 on - Unconditionally enable mitigations. Is 4830 enforced by spectre_v2=on 4831 4832 off - Unconditionally disable mitigations. Is 4833 enforced by spectre_v2=off 4834 4835 prctl - Indirect branch speculation is enabled, 4836 but mitigation can be enabled via prctl 4837 per thread. The mitigation control state 4838 is inherited on fork. 4839 4840 prctl,ibpb 4841 - Like "prctl" above, but only STIBP is 4842 controlled per thread. IBPB is issued 4843 always when switching between different user 4844 space processes. 4845 4846 seccomp 4847 - Same as "prctl" above, but all seccomp 4848 threads will enable the mitigation unless 4849 they explicitly opt out. 4850 4851 seccomp,ibpb 4852 - Like "seccomp" above, but only STIBP is 4853 controlled per thread. IBPB is issued 4854 always when switching between different 4855 user space processes. 4856 4857 auto - Kernel selects the mitigation depending on 4858 the available CPU features and vulnerability. 4859 4860 Default mitigation: 4861 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4862 4863 Not specifying this option is equivalent to 4864 spectre_v2_user=auto. 4865 4866 spec_store_bypass_disable= 4867 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4868 (Speculative Store Bypass vulnerability) 4869 4870 Certain CPUs are vulnerable to an exploit against a 4871 a common industry wide performance optimization known 4872 as "Speculative Store Bypass" in which recent stores 4873 to the same memory location may not be observed by 4874 later loads during speculative execution. The idea 4875 is that such stores are unlikely and that they can 4876 be detected prior to instruction retirement at the 4877 end of a particular speculation execution window. 4878 4879 In vulnerable processors, the speculatively forwarded 4880 store can be used in a cache side channel attack, for 4881 example to read memory to which the attacker does not 4882 directly have access (e.g. inside sandboxed code). 4883 4884 This parameter controls whether the Speculative Store 4885 Bypass optimization is used. 4886 4887 On x86 the options are: 4888 4889 on - Unconditionally disable Speculative Store Bypass 4890 off - Unconditionally enable Speculative Store Bypass 4891 auto - Kernel detects whether the CPU model contains an 4892 implementation of Speculative Store Bypass and 4893 picks the most appropriate mitigation. If the 4894 CPU is not vulnerable, "off" is selected. If the 4895 CPU is vulnerable the default mitigation is 4896 architecture and Kconfig dependent. See below. 4897 prctl - Control Speculative Store Bypass per thread 4898 via prctl. Speculative Store Bypass is enabled 4899 for a process by default. The state of the control 4900 is inherited on fork. 4901 seccomp - Same as "prctl" above, but all seccomp threads 4902 will disable SSB unless they explicitly opt out. 4903 4904 Default mitigations: 4905 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4906 4907 On powerpc the options are: 4908 4909 on,auto - On Power8 and Power9 insert a store-forwarding 4910 barrier on kernel entry and exit. On Power7 4911 perform a software flush on kernel entry and 4912 exit. 4913 off - No action. 4914 4915 Not specifying this option is equivalent to 4916 spec_store_bypass_disable=auto. 4917 4918 spia_io_base= [HW,MTD] 4919 spia_fio_base= 4920 spia_pedr= 4921 spia_peddr= 4922 4923 split_lock_detect= 4924 [X86] Enable split lock detection 4925 4926 When enabled (and if hardware support is present), atomic 4927 instructions that access data across cache line 4928 boundaries will result in an alignment check exception. 4929 4930 off - not enabled 4931 4932 warn - the kernel will emit rate limited warnings 4933 about applications triggering the #AC 4934 exception. This mode is the default on CPUs 4935 that supports split lock detection. 4936 4937 fatal - the kernel will send SIGBUS to applications 4938 that trigger the #AC exception. 4939 4940 If an #AC exception is hit in the kernel or in 4941 firmware (i.e. not while executing in user mode) 4942 the kernel will oops in either "warn" or "fatal" 4943 mode. 4944 4945 srbds= [X86,INTEL] 4946 Control the Special Register Buffer Data Sampling 4947 (SRBDS) mitigation. 4948 4949 Certain CPUs are vulnerable to an MDS-like 4950 exploit which can leak bits from the random 4951 number generator. 4952 4953 By default, this issue is mitigated by 4954 microcode. However, the microcode fix can cause 4955 the RDRAND and RDSEED instructions to become 4956 much slower. Among other effects, this will 4957 result in reduced throughput from /dev/urandom. 4958 4959 The microcode mitigation can be disabled with 4960 the following option: 4961 4962 off: Disable mitigation and remove 4963 performance impact to RDRAND and RDSEED 4964 4965 srcutree.counter_wrap_check [KNL] 4966 Specifies how frequently to check for 4967 grace-period sequence counter wrap for the 4968 srcu_data structure's ->srcu_gp_seq_needed field. 4969 The greater the number of bits set in this kernel 4970 parameter, the less frequently counter wrap will 4971 be checked for. Note that the bottom two bits 4972 are ignored. 4973 4974 srcutree.exp_holdoff [KNL] 4975 Specifies how many nanoseconds must elapse 4976 since the end of the last SRCU grace period for 4977 a given srcu_struct until the next normal SRCU 4978 grace period will be considered for automatic 4979 expediting. Set to zero to disable automatic 4980 expediting. 4981 4982 ssbd= [ARM64,HW] 4983 Speculative Store Bypass Disable control 4984 4985 On CPUs that are vulnerable to the Speculative 4986 Store Bypass vulnerability and offer a 4987 firmware based mitigation, this parameter 4988 indicates how the mitigation should be used: 4989 4990 force-on: Unconditionally enable mitigation for 4991 for both kernel and userspace 4992 force-off: Unconditionally disable mitigation for 4993 for both kernel and userspace 4994 kernel: Always enable mitigation in the 4995 kernel, and offer a prctl interface 4996 to allow userspace to register its 4997 interest in being mitigated too. 4998 4999 stack_guard_gap= [MM] 5000 override the default stack gap protection. The value 5001 is in page units and it defines how many pages prior 5002 to (for stacks growing down) resp. after (for stacks 5003 growing up) the main stack are reserved for no other 5004 mapping. Default value is 256 pages. 5005 5006 stacktrace [FTRACE] 5007 Enabled the stack tracer on boot up. 5008 5009 stacktrace_filter=[function-list] 5010 [FTRACE] Limit the functions that the stack tracer 5011 will trace at boot up. function-list is a comma separated 5012 list of functions. This list can be changed at run 5013 time by the stack_trace_filter file in the debugfs 5014 tracing directory. Note, this enables stack tracing 5015 and the stacktrace above is not needed. 5016 5017 sti= [PARISC,HW] 5018 Format: <num> 5019 Set the STI (builtin display/keyboard on the HP-PARISC 5020 machines) console (graphic card) which should be used 5021 as the initial boot-console. 5022 See also comment in drivers/video/console/sticore.c. 5023 5024 sti_font= [HW] 5025 See comment in drivers/video/console/sticore.c. 5026 5027 stifb= [HW] 5028 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5029 5030 sunrpc.min_resvport= 5031 sunrpc.max_resvport= 5032 [NFS,SUNRPC] 5033 SunRPC servers often require that client requests 5034 originate from a privileged port (i.e. a port in the 5035 range 0 < portnr < 1024). 5036 An administrator who wishes to reserve some of these 5037 ports for other uses may adjust the range that the 5038 kernel's sunrpc client considers to be privileged 5039 using these two parameters to set the minimum and 5040 maximum port values. 5041 5042 sunrpc.svc_rpc_per_connection_limit= 5043 [NFS,SUNRPC] 5044 Limit the number of requests that the server will 5045 process in parallel from a single connection. 5046 The default value is 0 (no limit). 5047 5048 sunrpc.pool_mode= 5049 [NFS] 5050 Control how the NFS server code allocates CPUs to 5051 service thread pools. Depending on how many NICs 5052 you have and where their interrupts are bound, this 5053 option will affect which CPUs will do NFS serving. 5054 Note: this parameter cannot be changed while the 5055 NFS server is running. 5056 5057 auto the server chooses an appropriate mode 5058 automatically using heuristics 5059 global a single global pool contains all CPUs 5060 percpu one pool for each CPU 5061 pernode one pool for each NUMA node (equivalent 5062 to global on non-NUMA machines) 5063 5064 sunrpc.tcp_slot_table_entries= 5065 sunrpc.udp_slot_table_entries= 5066 [NFS,SUNRPC] 5067 Sets the upper limit on the number of simultaneous 5068 RPC calls that can be sent from the client to a 5069 server. Increasing these values may allow you to 5070 improve throughput, but will also increase the 5071 amount of memory reserved for use by the client. 5072 5073 suspend.pm_test_delay= 5074 [SUSPEND] 5075 Sets the number of seconds to remain in a suspend test 5076 mode before resuming the system (see 5077 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5078 is set. Default value is 5. 5079 5080 svm= [PPC] 5081 Format: { on | off | y | n | 1 | 0 } 5082 This parameter controls use of the Protected 5083 Execution Facility on pSeries. 5084 5085 swapaccount=[0|1] 5086 [KNL] Enable accounting of swap in memory resource 5087 controller if no parameter or 1 is given or disable 5088 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5089 5090 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5091 Format: { <int> | force | noforce } 5092 <int> -- Number of I/O TLB slabs 5093 force -- force using of bounce buffers even if they 5094 wouldn't be automatically used by the kernel 5095 noforce -- Never use bounce buffers (for debugging) 5096 5097 switches= [HW,M68k] 5098 5099 sysctl.*= [KNL] 5100 Set a sysctl parameter, right before loading the init 5101 process, as if the value was written to the respective 5102 /proc/sys/... file. Both '.' and '/' are recognized as 5103 separators. Unrecognized parameters and invalid values 5104 are reported in the kernel log. Sysctls registered 5105 later by a loaded module cannot be set this way. 5106 Example: sysctl.vm.swappiness=40 5107 5108 sysfs.deprecated=0|1 [KNL] 5109 Enable/disable old style sysfs layout for old udev 5110 on older distributions. When this option is enabled 5111 very new udev will not work anymore. When this option 5112 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5113 in older udev will not work anymore. 5114 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5115 the kernel configuration. 5116 5117 sysrq_always_enabled 5118 [KNL] 5119 Ignore sysrq setting - this boot parameter will 5120 neutralize any effect of /proc/sys/kernel/sysrq. 5121 Useful for debugging. 5122 5123 tcpmhash_entries= [KNL,NET] 5124 Set the number of tcp_metrics_hash slots. 5125 Default value is 8192 or 16384 depending on total 5126 ram pages. This is used to specify the TCP metrics 5127 cache size. See Documentation/networking/ip-sysctl.rst 5128 "tcp_no_metrics_save" section for more details. 5129 5130 tdfx= [HW,DRM] 5131 5132 test_suspend= [SUSPEND][,N] 5133 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5134 standby suspend) or "freeze" (for suspend type freeze) 5135 as the system sleep state during system startup with 5136 the optional capability to repeat N number of times. 5137 The system is woken from this state using a 5138 wakeup-capable RTC alarm. 5139 5140 thash_entries= [KNL,NET] 5141 Set number of hash buckets for TCP connection 5142 5143 thermal.act= [HW,ACPI] 5144 -1: disable all active trip points in all thermal zones 5145 <degrees C>: override all lowest active trip points 5146 5147 thermal.crt= [HW,ACPI] 5148 -1: disable all critical trip points in all thermal zones 5149 <degrees C>: override all critical trip points 5150 5151 thermal.nocrt= [HW,ACPI] 5152 Set to disable actions on ACPI thermal zone 5153 critical and hot trip points. 5154 5155 thermal.off= [HW,ACPI] 5156 1: disable ACPI thermal control 5157 5158 thermal.psv= [HW,ACPI] 5159 -1: disable all passive trip points 5160 <degrees C>: override all passive trip points to this 5161 value 5162 5163 thermal.tzp= [HW,ACPI] 5164 Specify global default ACPI thermal zone polling rate 5165 <deci-seconds>: poll all this frequency 5166 0: no polling (default) 5167 5168 threadirqs [KNL] 5169 Force threading of all interrupt handlers except those 5170 marked explicitly IRQF_NO_THREAD. 5171 5172 topology= [S390] 5173 Format: {off | on} 5174 Specify if the kernel should make use of the cpu 5175 topology information if the hardware supports this. 5176 The scheduler will make use of this information and 5177 e.g. base its process migration decisions on it. 5178 Default is on. 5179 5180 topology_updates= [KNL, PPC, NUMA] 5181 Format: {off} 5182 Specify if the kernel should ignore (off) 5183 topology updates sent by the hypervisor to this 5184 LPAR. 5185 5186 torture.disable_onoff_at_boot= [KNL] 5187 Prevent the CPU-hotplug component of torturing 5188 until after init has spawned. 5189 5190 torture.ftrace_dump_at_shutdown= [KNL] 5191 Dump the ftrace buffer at torture-test shutdown, 5192 even if there were no errors. This can be a 5193 very costly operation when many torture tests 5194 are running concurrently, especially on systems 5195 with rotating-rust storage. 5196 5197 tp720= [HW,PS2] 5198 5199 tpm_suspend_pcr=[HW,TPM] 5200 Format: integer pcr id 5201 Specify that at suspend time, the tpm driver 5202 should extend the specified pcr with zeros, 5203 as a workaround for some chips which fail to 5204 flush the last written pcr on TPM_SaveState. 5205 This will guarantee that all the other pcrs 5206 are saved. 5207 5208 trace_buf_size=nn[KMG] 5209 [FTRACE] will set tracing buffer size on each cpu. 5210 5211 trace_event=[event-list] 5212 [FTRACE] Set and start specified trace events in order 5213 to facilitate early boot debugging. The event-list is a 5214 comma separated list of trace events to enable. See 5215 also Documentation/trace/events.rst 5216 5217 trace_options=[option-list] 5218 [FTRACE] Enable or disable tracer options at boot. 5219 The option-list is a comma delimited list of options 5220 that can be enabled or disabled just as if you were 5221 to echo the option name into 5222 5223 /sys/kernel/debug/tracing/trace_options 5224 5225 For example, to enable stacktrace option (to dump the 5226 stack trace of each event), add to the command line: 5227 5228 trace_options=stacktrace 5229 5230 See also Documentation/trace/ftrace.rst "trace options" 5231 section. 5232 5233 tp_printk[FTRACE] 5234 Have the tracepoints sent to printk as well as the 5235 tracing ring buffer. This is useful for early boot up 5236 where the system hangs or reboots and does not give the 5237 option for reading the tracing buffer or performing a 5238 ftrace_dump_on_oops. 5239 5240 To turn off having tracepoints sent to printk, 5241 echo 0 > /proc/sys/kernel/tracepoint_printk 5242 Note, echoing 1 into this file without the 5243 tracepoint_printk kernel cmdline option has no effect. 5244 5245 ** CAUTION ** 5246 5247 Having tracepoints sent to printk() and activating high 5248 frequency tracepoints such as irq or sched, can cause 5249 the system to live lock. 5250 5251 traceoff_on_warning 5252 [FTRACE] enable this option to disable tracing when a 5253 warning is hit. This turns off "tracing_on". Tracing can 5254 be enabled again by echoing '1' into the "tracing_on" 5255 file located in /sys/kernel/debug/tracing/ 5256 5257 This option is useful, as it disables the trace before 5258 the WARNING dump is called, which prevents the trace to 5259 be filled with content caused by the warning output. 5260 5261 This option can also be set at run time via the sysctl 5262 option: kernel/traceoff_on_warning 5263 5264 transparent_hugepage= 5265 [KNL] 5266 Format: [always|madvise|never] 5267 Can be used to control the default behavior of the system 5268 with respect to transparent hugepages. 5269 See Documentation/admin-guide/mm/transhuge.rst 5270 for more details. 5271 5272 tsc= Disable clocksource stability checks for TSC. 5273 Format: <string> 5274 [x86] reliable: mark tsc clocksource as reliable, this 5275 disables clocksource verification at runtime, as well 5276 as the stability checks done at bootup. Used to enable 5277 high-resolution timer mode on older hardware, and in 5278 virtualized environment. 5279 [x86] noirqtime: Do not use TSC to do irq accounting. 5280 Used to run time disable IRQ_TIME_ACCOUNTING on any 5281 platforms where RDTSC is slow and this accounting 5282 can add overhead. 5283 [x86] unstable: mark the TSC clocksource as unstable, this 5284 marks the TSC unconditionally unstable at bootup and 5285 avoids any further wobbles once the TSC watchdog notices. 5286 [x86] nowatchdog: disable clocksource watchdog. Used 5287 in situations with strict latency requirements (where 5288 interruptions from clocksource watchdog are not 5289 acceptable). 5290 5291 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5292 value instead. Useful when the early TSC frequency discovery 5293 procedure is not reliable, such as on overclocked systems 5294 with CPUID.16h support and partial CPUID.15h support. 5295 Format: <unsigned int> 5296 5297 tsx= [X86] Control Transactional Synchronization 5298 Extensions (TSX) feature in Intel processors that 5299 support TSX control. 5300 5301 This parameter controls the TSX feature. The options are: 5302 5303 on - Enable TSX on the system. Although there are 5304 mitigations for all known security vulnerabilities, 5305 TSX has been known to be an accelerator for 5306 several previous speculation-related CVEs, and 5307 so there may be unknown security risks associated 5308 with leaving it enabled. 5309 5310 off - Disable TSX on the system. (Note that this 5311 option takes effect only on newer CPUs which are 5312 not vulnerable to MDS, i.e., have 5313 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5314 the new IA32_TSX_CTRL MSR through a microcode 5315 update. This new MSR allows for the reliable 5316 deactivation of the TSX functionality.) 5317 5318 auto - Disable TSX if X86_BUG_TAA is present, 5319 otherwise enable TSX on the system. 5320 5321 Not specifying this option is equivalent to tsx=off. 5322 5323 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5324 for more details. 5325 5326 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5327 Abort (TAA) vulnerability. 5328 5329 Similar to Micro-architectural Data Sampling (MDS) 5330 certain CPUs that support Transactional 5331 Synchronization Extensions (TSX) are vulnerable to an 5332 exploit against CPU internal buffers which can forward 5333 information to a disclosure gadget under certain 5334 conditions. 5335 5336 In vulnerable processors, the speculatively forwarded 5337 data can be used in a cache side channel attack, to 5338 access data to which the attacker does not have direct 5339 access. 5340 5341 This parameter controls the TAA mitigation. The 5342 options are: 5343 5344 full - Enable TAA mitigation on vulnerable CPUs 5345 if TSX is enabled. 5346 5347 full,nosmt - Enable TAA mitigation and disable SMT on 5348 vulnerable CPUs. If TSX is disabled, SMT 5349 is not disabled because CPU is not 5350 vulnerable to cross-thread TAA attacks. 5351 off - Unconditionally disable TAA mitigation 5352 5353 On MDS-affected machines, tsx_async_abort=off can be 5354 prevented by an active MDS mitigation as both vulnerabilities 5355 are mitigated with the same mechanism so in order to disable 5356 this mitigation, you need to specify mds=off too. 5357 5358 Not specifying this option is equivalent to 5359 tsx_async_abort=full. On CPUs which are MDS affected 5360 and deploy MDS mitigation, TAA mitigation is not 5361 required and doesn't provide any additional 5362 mitigation. 5363 5364 For details see: 5365 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5366 5367 turbografx.map[2|3]= [HW,JOY] 5368 TurboGraFX parallel port interface 5369 Format: 5370 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5371 See also Documentation/input/devices/joystick-parport.rst 5372 5373 udbg-immortal [PPC] When debugging early kernel crashes that 5374 happen after console_init() and before a proper 5375 console driver takes over, this boot options might 5376 help "seeing" what's going on. 5377 5378 uhash_entries= [KNL,NET] 5379 Set number of hash buckets for UDP/UDP-Lite connections 5380 5381 uhci-hcd.ignore_oc= 5382 [USB] Ignore overcurrent events (default N). 5383 Some badly-designed motherboards generate lots of 5384 bogus events, for ports that aren't wired to 5385 anything. Set this parameter to avoid log spamming. 5386 Note that genuine overcurrent events won't be 5387 reported either. 5388 5389 unknown_nmi_panic 5390 [X86] Cause panic on unknown NMI. 5391 5392 usbcore.authorized_default= 5393 [USB] Default USB device authorization: 5394 (default -1 = authorized except for wireless USB, 5395 0 = not authorized, 1 = authorized, 2 = authorized 5396 if device connected to internal port) 5397 5398 usbcore.autosuspend= 5399 [USB] The autosuspend time delay (in seconds) used 5400 for newly-detected USB devices (default 2). This 5401 is the time required before an idle device will be 5402 autosuspended. Devices for which the delay is set 5403 to a negative value won't be autosuspended at all. 5404 5405 usbcore.usbfs_snoop= 5406 [USB] Set to log all usbfs traffic (default 0 = off). 5407 5408 usbcore.usbfs_snoop_max= 5409 [USB] Maximum number of bytes to snoop in each URB 5410 (default = 65536). 5411 5412 usbcore.blinkenlights= 5413 [USB] Set to cycle leds on hubs (default 0 = off). 5414 5415 usbcore.old_scheme_first= 5416 [USB] Start with the old device initialization 5417 scheme (default 0 = off). 5418 5419 usbcore.usbfs_memory_mb= 5420 [USB] Memory limit (in MB) for buffers allocated by 5421 usbfs (default = 16, 0 = max = 2047). 5422 5423 usbcore.use_both_schemes= 5424 [USB] Try the other device initialization scheme 5425 if the first one fails (default 1 = enabled). 5426 5427 usbcore.initial_descriptor_timeout= 5428 [USB] Specifies timeout for the initial 64-byte 5429 USB_REQ_GET_DESCRIPTOR request in milliseconds 5430 (default 5000 = 5.0 seconds). 5431 5432 usbcore.nousb [USB] Disable the USB subsystem 5433 5434 usbcore.quirks= 5435 [USB] A list of quirk entries to augment the built-in 5436 usb core quirk list. List entries are separated by 5437 commas. Each entry has the form 5438 VendorID:ProductID:Flags. The IDs are 4-digit hex 5439 numbers and Flags is a set of letters. Each letter 5440 will change the built-in quirk; setting it if it is 5441 clear and clearing it if it is set. The letters have 5442 the following meanings: 5443 a = USB_QUIRK_STRING_FETCH_255 (string 5444 descriptors must not be fetched using 5445 a 255-byte read); 5446 b = USB_QUIRK_RESET_RESUME (device can't resume 5447 correctly so reset it instead); 5448 c = USB_QUIRK_NO_SET_INTF (device can't handle 5449 Set-Interface requests); 5450 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5451 handle its Configuration or Interface 5452 strings); 5453 e = USB_QUIRK_RESET (device can't be reset 5454 (e.g morph devices), don't use reset); 5455 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5456 more interface descriptions than the 5457 bNumInterfaces count, and can't handle 5458 talking to these interfaces); 5459 g = USB_QUIRK_DELAY_INIT (device needs a pause 5460 during initialization, after we read 5461 the device descriptor); 5462 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5463 high speed and super speed interrupt 5464 endpoints, the USB 2.0 and USB 3.0 spec 5465 require the interval in microframes (1 5466 microframe = 125 microseconds) to be 5467 calculated as interval = 2 ^ 5468 (bInterval-1). 5469 Devices with this quirk report their 5470 bInterval as the result of this 5471 calculation instead of the exponent 5472 variable used in the calculation); 5473 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5474 handle device_qualifier descriptor 5475 requests); 5476 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5477 generates spurious wakeup, ignore 5478 remote wakeup capability); 5479 k = USB_QUIRK_NO_LPM (device can't handle Link 5480 Power Management); 5481 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5482 (Device reports its bInterval as linear 5483 frames instead of the USB 2.0 5484 calculation); 5485 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5486 to be disconnected before suspend to 5487 prevent spurious wakeup); 5488 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5489 pause after every control message); 5490 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5491 delay after resetting its port); 5492 Example: quirks=0781:5580:bk,0a5c:5834:gij 5493 5494 usbhid.mousepoll= 5495 [USBHID] The interval which mice are to be polled at. 5496 5497 usbhid.jspoll= 5498 [USBHID] The interval which joysticks are to be polled at. 5499 5500 usbhid.kbpoll= 5501 [USBHID] The interval which keyboards are to be polled at. 5502 5503 usb-storage.delay_use= 5504 [UMS] The delay in seconds before a new device is 5505 scanned for Logical Units (default 1). 5506 5507 usb-storage.quirks= 5508 [UMS] A list of quirks entries to supplement or 5509 override the built-in unusual_devs list. List 5510 entries are separated by commas. Each entry has 5511 the form VID:PID:Flags where VID and PID are Vendor 5512 and Product ID values (4-digit hex numbers) and 5513 Flags is a set of characters, each corresponding 5514 to a common usb-storage quirk flag as follows: 5515 a = SANE_SENSE (collect more than 18 bytes 5516 of sense data, not on uas); 5517 b = BAD_SENSE (don't collect more than 18 5518 bytes of sense data, not on uas); 5519 c = FIX_CAPACITY (decrease the reported 5520 device capacity by one sector); 5521 d = NO_READ_DISC_INFO (don't use 5522 READ_DISC_INFO command, not on uas); 5523 e = NO_READ_CAPACITY_16 (don't use 5524 READ_CAPACITY_16 command); 5525 f = NO_REPORT_OPCODES (don't use report opcodes 5526 command, uas only); 5527 g = MAX_SECTORS_240 (don't transfer more than 5528 240 sectors at a time, uas only); 5529 h = CAPACITY_HEURISTICS (decrease the 5530 reported device capacity by one 5531 sector if the number is odd); 5532 i = IGNORE_DEVICE (don't bind to this 5533 device); 5534 j = NO_REPORT_LUNS (don't use report luns 5535 command, uas only); 5536 l = NOT_LOCKABLE (don't try to lock and 5537 unlock ejectable media, not on uas); 5538 m = MAX_SECTORS_64 (don't transfer more 5539 than 64 sectors = 32 KB at a time, 5540 not on uas); 5541 n = INITIAL_READ10 (force a retry of the 5542 initial READ(10) command, not on uas); 5543 o = CAPACITY_OK (accept the capacity 5544 reported by the device, not on uas); 5545 p = WRITE_CACHE (the device cache is ON 5546 by default, not on uas); 5547 r = IGNORE_RESIDUE (the device reports 5548 bogus residue values, not on uas); 5549 s = SINGLE_LUN (the device has only one 5550 Logical Unit); 5551 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5552 commands, uas only); 5553 u = IGNORE_UAS (don't bind to the uas driver); 5554 w = NO_WP_DETECT (don't test whether the 5555 medium is write-protected). 5556 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5557 even if the device claims no cache, 5558 not on uas) 5559 Example: quirks=0419:aaf5:rl,0421:0433:rc 5560 5561 user_debug= [KNL,ARM] 5562 Format: <int> 5563 See arch/arm/Kconfig.debug help text. 5564 1 - undefined instruction events 5565 2 - system calls 5566 4 - invalid data aborts 5567 8 - SIGSEGV faults 5568 16 - SIGBUS faults 5569 Example: user_debug=31 5570 5571 userpte= 5572 [X86] Flags controlling user PTE allocations. 5573 5574 nohigh = do not allocate PTE pages in 5575 HIGHMEM regardless of setting 5576 of CONFIG_HIGHPTE. 5577 5578 vdso= [X86,SH] 5579 On X86_32, this is an alias for vdso32=. Otherwise: 5580 5581 vdso=1: enable VDSO (the default) 5582 vdso=0: disable VDSO mapping 5583 5584 vdso32= [X86] Control the 32-bit vDSO 5585 vdso32=1: enable 32-bit VDSO 5586 vdso32=0 or vdso32=2: disable 32-bit VDSO 5587 5588 See the help text for CONFIG_COMPAT_VDSO for more 5589 details. If CONFIG_COMPAT_VDSO is set, the default is 5590 vdso32=0; otherwise, the default is vdso32=1. 5591 5592 For compatibility with older kernels, vdso32=2 is an 5593 alias for vdso32=0. 5594 5595 Try vdso32=0 if you encounter an error that says: 5596 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5597 5598 vector= [IA-64,SMP] 5599 vector=percpu: enable percpu vector domain 5600 5601 video= [FB] Frame buffer configuration 5602 See Documentation/fb/modedb.rst. 5603 5604 video.brightness_switch_enabled= [0,1] 5605 If set to 1, on receiving an ACPI notify event 5606 generated by hotkey, video driver will adjust brightness 5607 level and then send out the event to user space through 5608 the allocated input device; If set to 0, video driver 5609 will only send out the event without touching backlight 5610 brightness level. 5611 default: 1 5612 5613 virtio_mmio.device= 5614 [VMMIO] Memory mapped virtio (platform) device. 5615 5616 <size>@<baseaddr>:<irq>[:<id>] 5617 where: 5618 <size> := size (can use standard suffixes 5619 like K, M and G) 5620 <baseaddr> := physical base address 5621 <irq> := interrupt number (as passed to 5622 request_irq()) 5623 <id> := (optional) platform device id 5624 example: 5625 virtio_mmio.device=1K@0x100b0000:48:7 5626 5627 Can be used multiple times for multiple devices. 5628 5629 vga= [BOOT,X86-32] Select a particular video mode 5630 See Documentation/x86/boot.rst and 5631 Documentation/admin-guide/svga.rst. 5632 Use vga=ask for menu. 5633 This is actually a boot loader parameter; the value is 5634 passed to the kernel using a special protocol. 5635 5636 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5637 May slow down system boot speed, especially when 5638 enabled on systems with a large amount of memory. 5639 All options are enabled by default, and this 5640 interface is meant to allow for selectively 5641 enabling or disabling specific virtual memory 5642 debugging features. 5643 5644 Available options are: 5645 P Enable page structure init time poisoning 5646 - Disable all of the above options 5647 5648 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5649 size of <nn>. This can be used to increase the 5650 minimum size (128MB on x86). It can also be used to 5651 decrease the size and leave more room for directly 5652 mapped kernel RAM. 5653 5654 vmcp_cma=nn[MG] [KNL,S390] 5655 Sets the memory size reserved for contiguous memory 5656 allocations for the vmcp device driver. 5657 5658 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5659 Format: <command> 5660 5661 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5662 Format: <command> 5663 5664 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5665 Format: <command> 5666 5667 vsyscall= [X86-64] 5668 Controls the behavior of vsyscalls (i.e. calls to 5669 fixed addresses of 0xffffffffff600x00 from legacy 5670 code). Most statically-linked binaries and older 5671 versions of glibc use these calls. Because these 5672 functions are at fixed addresses, they make nice 5673 targets for exploits that can control RIP. 5674 5675 emulate [default] Vsyscalls turn into traps and are 5676 emulated reasonably safely. The vsyscall 5677 page is readable. 5678 5679 xonly Vsyscalls turn into traps and are 5680 emulated reasonably safely. The vsyscall 5681 page is not readable. 5682 5683 none Vsyscalls don't work at all. This makes 5684 them quite hard to use for exploits but 5685 might break your system. 5686 5687 vt.color= [VT] Default text color. 5688 Format: 0xYX, X = foreground, Y = background. 5689 Default: 0x07 = light gray on black. 5690 5691 vt.cur_default= [VT] Default cursor shape. 5692 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5693 the parameters of the <Esc>[?A;B;Cc escape sequence; 5694 see VGA-softcursor.txt. Default: 2 = underline. 5695 5696 vt.default_blu= [VT] 5697 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5698 Change the default blue palette of the console. 5699 This is a 16-member array composed of values 5700 ranging from 0-255. 5701 5702 vt.default_grn= [VT] 5703 Format: <green0>,<green1>,<green2>,...,<green15> 5704 Change the default green palette of the console. 5705 This is a 16-member array composed of values 5706 ranging from 0-255. 5707 5708 vt.default_red= [VT] 5709 Format: <red0>,<red1>,<red2>,...,<red15> 5710 Change the default red palette of the console. 5711 This is a 16-member array composed of values 5712 ranging from 0-255. 5713 5714 vt.default_utf8= 5715 [VT] 5716 Format=<0|1> 5717 Set system-wide default UTF-8 mode for all tty's. 5718 Default is 1, i.e. UTF-8 mode is enabled for all 5719 newly opened terminals. 5720 5721 vt.global_cursor_default= 5722 [VT] 5723 Format=<-1|0|1> 5724 Set system-wide default for whether a cursor 5725 is shown on new VTs. Default is -1, 5726 i.e. cursors will be created by default unless 5727 overridden by individual drivers. 0 will hide 5728 cursors, 1 will display them. 5729 5730 vt.italic= [VT] Default color for italic text; 0-15. 5731 Default: 2 = green. 5732 5733 vt.underline= [VT] Default color for underlined text; 0-15. 5734 Default: 3 = cyan. 5735 5736 watchdog timers [HW,WDT] For information on watchdog timers, 5737 see Documentation/watchdog/watchdog-parameters.rst 5738 or other driver-specific files in the 5739 Documentation/watchdog/ directory. 5740 5741 watchdog_thresh= 5742 [KNL] 5743 Set the hard lockup detector stall duration 5744 threshold in seconds. The soft lockup detector 5745 threshold is set to twice the value. A value of 0 5746 disables both lockup detectors. Default is 10 5747 seconds. 5748 5749 workqueue.watchdog_thresh= 5750 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5751 warn stall conditions and dump internal state to 5752 help debugging. 0 disables workqueue stall 5753 detection; otherwise, it's the stall threshold 5754 duration in seconds. The default value is 30 and 5755 it can be updated at runtime by writing to the 5756 corresponding sysfs file. 5757 5758 workqueue.disable_numa 5759 By default, all work items queued to unbound 5760 workqueues are affine to the NUMA nodes they're 5761 issued on, which results in better behavior in 5762 general. If NUMA affinity needs to be disabled for 5763 whatever reason, this option can be used. Note 5764 that this also can be controlled per-workqueue for 5765 workqueues visible under /sys/bus/workqueue/. 5766 5767 workqueue.power_efficient 5768 Per-cpu workqueues are generally preferred because 5769 they show better performance thanks to cache 5770 locality; unfortunately, per-cpu workqueues tend to 5771 be more power hungry than unbound workqueues. 5772 5773 Enabling this makes the per-cpu workqueues which 5774 were observed to contribute significantly to power 5775 consumption unbound, leading to measurably lower 5776 power usage at the cost of small performance 5777 overhead. 5778 5779 The default value of this parameter is determined by 5780 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5781 5782 workqueue.debug_force_rr_cpu 5783 Workqueue used to implicitly guarantee that work 5784 items queued without explicit CPU specified are put 5785 on the local CPU. This guarantee is no longer true 5786 and while local CPU is still preferred work items 5787 may be put on foreign CPUs. This debug option 5788 forces round-robin CPU selection to flush out 5789 usages which depend on the now broken guarantee. 5790 When enabled, memory and cache locality will be 5791 impacted. 5792 5793 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5794 default x2apic cluster mode on platforms 5795 supporting x2apic. 5796 5797 x86_intel_mid_timer= [X86-32,APBT] 5798 Choose timer option for x86 Intel MID platform. 5799 Two valid options are apbt timer only and lapic timer 5800 plus one apbt timer for broadcast timer. 5801 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5802 5803 xen_512gb_limit [KNL,X86-64,XEN] 5804 Restricts the kernel running paravirtualized under Xen 5805 to use only up to 512 GB of RAM. The reason to do so is 5806 crash analysis tools and Xen tools for doing domain 5807 save/restore/migration must be enabled to handle larger 5808 domains. 5809 5810 xen_emul_unplug= [HW,X86,XEN] 5811 Unplug Xen emulated devices 5812 Format: [unplug0,][unplug1] 5813 ide-disks -- unplug primary master IDE devices 5814 aux-ide-disks -- unplug non-primary-master IDE devices 5815 nics -- unplug network devices 5816 all -- unplug all emulated devices (NICs and IDE disks) 5817 unnecessary -- unplugging emulated devices is 5818 unnecessary even if the host did not respond to 5819 the unplug protocol 5820 never -- do not unplug even if version check succeeds 5821 5822 xen_legacy_crash [X86,XEN] 5823 Crash from Xen panic notifier, without executing late 5824 panic() code such as dumping handler. 5825 5826 xen_nopvspin [X86,XEN] 5827 Disables the qspinlock slowpath using Xen PV optimizations. 5828 This parameter is obsoleted by "nopvspin" parameter, which 5829 has equivalent effect for XEN platform. 5830 5831 xen_nopv [X86] 5832 Disables the PV optimizations forcing the HVM guest to 5833 run as generic HVM guest with no PV drivers. 5834 This option is obsoleted by the "nopv" option, which 5835 has equivalent effect for XEN platform. 5836 5837 xen_scrub_pages= [XEN] 5838 Boolean option to control scrubbing pages before giving them back 5839 to Xen, for use by other domains. Can be also changed at runtime 5840 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5841 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5842 5843 xen_timer_slop= [X86-64,XEN] 5844 Set the timer slop (in nanoseconds) for the virtual Xen 5845 timers (default is 100000). This adjusts the minimum 5846 delta of virtualized Xen timers, where lower values 5847 improve timer resolution at the expense of processing 5848 more timer interrupts. 5849 5850 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5851 Disables the PV optimizations forcing the guest to run 5852 as generic guest with no PV drivers. Currently support 5853 XEN HVM, KVM, HYPER_V and VMWARE guest. 5854 5855 nopvspin [X86,XEN,KVM] 5856 Disables the qspinlock slow path using PV optimizations 5857 which allow the hypervisor to 'idle' the guest on lock 5858 contention. 5859 5860 xirc2ps_cs= [NET,PCMCIA] 5861 Format: 5862 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5863 5864 xive= [PPC] 5865 By default on POWER9 and above, the kernel will 5866 natively use the XIVE interrupt controller. This option 5867 allows the fallback firmware mode to be used: 5868 5869 off Fallback to firmware control of XIVE interrupt 5870 controller on both pseries and powernv 5871 platforms. Only useful on POWER9 and above. 5872 5873 xhci-hcd.quirks [USB,KNL] 5874 A hex value specifying bitmask with supplemental xhci 5875 host controller quirks. Meaning of each bit can be 5876 consulted in header drivers/usb/host/xhci.h. 5877 5878 xmon [PPC] 5879 Format: { early | on | rw | ro | off } 5880 Controls if xmon debugger is enabled. Default is off. 5881 Passing only "xmon" is equivalent to "xmon=early". 5882 early Call xmon as early as possible on boot; xmon 5883 debugger is called from setup_arch(). 5884 on xmon debugger hooks will be installed so xmon 5885 is only called on a kernel crash. Default mode, 5886 i.e. either "ro" or "rw" mode, is controlled 5887 with CONFIG_XMON_DEFAULT_RO_MODE. 5888 rw xmon debugger hooks will be installed so xmon 5889 is called only on a kernel crash, mode is write, 5890 meaning SPR registers, memory and, other data 5891 can be written using xmon commands. 5892 ro same as "rw" option above but SPR registers, 5893 memory, and other data can't be written using 5894 xmon commands. 5895 off xmon is disabled. 5896