1 accept_memory= [MM] 2 Format: { eager | lazy } 3 default: lazy 4 By default, unaccepted memory is accepted lazily to 5 avoid prolonged boot times. The lazy option will add 6 some runtime overhead until all memory is eventually 7 accepted. In most cases the overhead is negligible. 8 For some workloads or for debugging purposes 9 accept_memory=eager can be used to accept all memory 10 at once during boot. 11 12 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 13 Advanced Configuration and Power Interface 14 Format: { force | on | off | strict | noirq | rsdt | 15 copy_dsdt | nospcr } 16 force -- enable ACPI if default was off 17 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 18 off -- disable ACPI if default was on 19 noirq -- do not use ACPI for IRQ routing 20 strict -- Be less tolerant of platforms that are not 21 strictly ACPI specification compliant. 22 rsdt -- prefer RSDT over (default) XSDT 23 copy_dsdt -- copy DSDT to memory 24 nocmcff -- Disable firmware first mode for corrected 25 errors. This disables parsing the HEST CMC error 26 source to check if firmware has set the FF flag. This 27 may result in duplicate corrected error reports. 28 nospcr -- disable console in ACPI SPCR table as 29 default _serial_ console on ARM64 30 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 31 "acpi=nospcr" are available 32 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 33 are available 34 35 See also Documentation/power/runtime_pm.rst, pci=noacpi 36 37 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 38 Format: <int> 39 2: use 2nd APIC table, if available 40 1,0: use 1st APIC table 41 default: 0 42 43 acpi_backlight= [HW,ACPI] 44 { vendor | video | native | none } 45 If set to vendor, prefer vendor-specific driver 46 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 47 of the ACPI video.ko driver. 48 If set to video, use the ACPI video.ko driver. 49 If set to native, use the device's native backlight mode. 50 If set to none, disable the ACPI backlight interface. 51 52 acpi_force_32bit_fadt_addr [ACPI,EARLY] 53 force FADT to use 32 bit addresses rather than the 54 64 bit X_* addresses. Some firmware have broken 64 55 bit addresses for force ACPI ignore these and use 56 the older legacy 32 bit addresses. 57 58 acpica_no_return_repair [HW, ACPI] 59 Disable AML predefined validation mechanism 60 This mechanism can repair the evaluation result to make 61 the return objects more ACPI specification compliant. 62 This option is useful for developers to identify the 63 root cause of an AML interpreter issue when the issue 64 has something to do with the repair mechanism. 65 66 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 67 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 68 Format: <int> 69 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 70 debug output. Bits in debug_layer correspond to a 71 _COMPONENT in an ACPI source file, e.g., 72 #define _COMPONENT ACPI_EVENTS 73 Bits in debug_level correspond to a level in 74 ACPI_DEBUG_PRINT statements, e.g., 75 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 76 The debug_level mask defaults to "info". See 77 Documentation/firmware-guide/acpi/debug.rst for more information about 78 debug layers and levels. 79 80 Enable processor driver info messages: 81 acpi.debug_layer=0x20000000 82 Enable AML "Debug" output, i.e., stores to the Debug 83 object while interpreting AML: 84 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 85 Enable all messages related to ACPI hardware: 86 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 87 88 Some values produce so much output that the system is 89 unusable. The "log_buf_len" parameter may be useful 90 if you need to capture more output. 91 92 acpi_enforce_resources= [ACPI] 93 { strict | lax | no } 94 Check for resource conflicts between native drivers 95 and ACPI OperationRegions (SystemIO and SystemMemory 96 only). IO ports and memory declared in ACPI might be 97 used by the ACPI subsystem in arbitrary AML code and 98 can interfere with legacy drivers. 99 strict (default): access to resources claimed by ACPI 100 is denied; legacy drivers trying to access reserved 101 resources will fail to bind to device using them. 102 lax: access to resources claimed by ACPI is allowed; 103 legacy drivers trying to access reserved resources 104 will bind successfully but a warning message is logged. 105 no: ACPI OperationRegions are not marked as reserved, 106 no further checks are performed. 107 108 acpi_force_table_verification [HW,ACPI,EARLY] 109 Enable table checksum verification during early stage. 110 By default, this is disabled due to x86 early mapping 111 size limitation. 112 113 acpi_irq_balance [HW,ACPI] 114 ACPI will balance active IRQs 115 default in APIC mode 116 117 acpi_irq_nobalance [HW,ACPI] 118 ACPI will not move active IRQs (default) 119 default in PIC mode 120 121 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 122 Format: <irq>,<irq>... 123 124 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 125 use by PCI 126 Format: <irq>,<irq>... 127 128 acpi_mask_gpe= [HW,ACPI] 129 Due to the existence of _Lxx/_Exx, some GPEs triggered 130 by unsupported hardware/firmware features can result in 131 GPE floodings that cannot be automatically disabled by 132 the GPE dispatcher. 133 This facility can be used to prevent such uncontrolled 134 GPE floodings. 135 Format: <byte> or <bitmap-list> 136 137 acpi_no_auto_serialize [HW,ACPI] 138 Disable auto-serialization of AML methods 139 AML control methods that contain the opcodes to create 140 named objects will be marked as "Serialized" by the 141 auto-serialization feature. 142 This feature is enabled by default. 143 This option allows to turn off the feature. 144 145 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 146 kernels. 147 148 acpi_no_static_ssdt [HW,ACPI,EARLY] 149 Disable installation of static SSDTs at early boot time 150 By default, SSDTs contained in the RSDT/XSDT will be 151 installed automatically and they will appear under 152 /sys/firmware/acpi/tables. 153 This option turns off this feature. 154 Note that specifying this option does not affect 155 dynamic table installation which will install SSDT 156 tables to /sys/firmware/acpi/tables/dynamic. 157 158 acpi_no_watchdog [HW,ACPI,WDT] 159 Ignore the ACPI-based watchdog interface (WDAT) and let 160 a native driver control the watchdog device instead. 161 162 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 163 Pass the RSDP address to the kernel, mostly used 164 on machines running EFI runtime service to boot the 165 second kernel for kdump. 166 167 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 168 Format: To spoof as Windows 98: ="Microsoft Windows" 169 170 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 171 of 2 which is mandated by ACPI 6) as the supported ACPI 172 specification revision (when using this switch, it may 173 be necessary to carry out a cold reboot _twice_ in a 174 row to make it take effect on the platform firmware). 175 176 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 177 acpi_osi="string1" # add string1 178 acpi_osi="!string2" # remove string2 179 acpi_osi=!* # remove all strings 180 acpi_osi=! # disable all built-in OS vendor 181 strings 182 acpi_osi=!! # enable all built-in OS vendor 183 strings 184 acpi_osi= # disable all strings 185 186 'acpi_osi=!' can be used in combination with single or 187 multiple 'acpi_osi="string1"' to support specific OS 188 vendor string(s). Note that such command can only 189 affect the default state of the OS vendor strings, thus 190 it cannot affect the default state of the feature group 191 strings and the current state of the OS vendor strings, 192 specifying it multiple times through kernel command line 193 is meaningless. This command is useful when one do not 194 care about the state of the feature group strings which 195 should be controlled by the OSPM. 196 Examples: 197 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 198 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 199 can make '_OSI("Windows 2000")' TRUE. 200 201 'acpi_osi=' cannot be used in combination with other 202 'acpi_osi=' command lines, the _OSI method will not 203 exist in the ACPI namespace. NOTE that such command can 204 only affect the _OSI support state, thus specifying it 205 multiple times through kernel command line is also 206 meaningless. 207 Examples: 208 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 209 FALSE. 210 211 'acpi_osi=!*' can be used in combination with single or 212 multiple 'acpi_osi="string1"' to support specific 213 string(s). Note that such command can affect the 214 current state of both the OS vendor strings and the 215 feature group strings, thus specifying it multiple times 216 through kernel command line is meaningful. But it may 217 still not able to affect the final state of a string if 218 there are quirks related to this string. This command 219 is useful when one want to control the state of the 220 feature group strings to debug BIOS issues related to 221 the OSPM features. 222 Examples: 223 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 224 '_OSI("Module Device")' FALSE. 225 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 226 '_OSI("Module Device")' TRUE. 227 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 228 equivalent to 229 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 230 and 231 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 232 they all will make '_OSI("Windows 2000")' TRUE. 233 234 acpi_pm_good [X86] 235 Override the pmtimer bug detection: force the kernel 236 to assume that this machine's pmtimer latches its value 237 and always returns good values. 238 239 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 240 Format: { level | edge | high | low } 241 242 acpi_skip_timer_override [HW,ACPI,EARLY] 243 Recognize and ignore IRQ0/pin2 Interrupt Override. 244 For broken nForce2 BIOS resulting in XT-PIC timer. 245 246 acpi_sleep= [HW,ACPI] Sleep options 247 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 248 s4_nohwsig, old_ordering, nonvs, 249 sci_force_enable, nobl } 250 See Documentation/power/video.rst for information on 251 s3_bios and s3_mode. 252 s3_beep is for debugging; it makes the PC's speaker beep 253 as soon as the kernel's real-mode entry point is called. 254 s4_hwsig causes the kernel to check the ACPI hardware 255 signature during resume from hibernation, and gracefully 256 refuse to resume if it has changed. This complies with 257 the ACPI specification but not with reality, since 258 Windows does not do this and many laptops do change it 259 on docking. So the default behaviour is to allow resume 260 and simply warn when the signature changes, unless the 261 s4_hwsig option is enabled. 262 s4_nohwsig prevents ACPI hardware signature from being 263 used (or even warned about) during resume. 264 old_ordering causes the ACPI 1.0 ordering of the _PTS 265 control method, with respect to putting devices into 266 low power states, to be enforced (the ACPI 2.0 ordering 267 of _PTS is used by default). 268 nonvs prevents the kernel from saving/restoring the 269 ACPI NVS memory during suspend/hibernation and resume. 270 sci_force_enable causes the kernel to set SCI_EN directly 271 on resume from S1/S3 (which is against the ACPI spec, 272 but some broken systems don't work without it). 273 nobl causes the internal blacklist of systems known to 274 behave incorrectly in some ways with respect to system 275 suspend and resume to be ignored (use wisely). 276 277 acpi_use_timer_override [HW,ACPI,EARLY] 278 Use timer override. For some broken Nvidia NF5 boards 279 that require a timer override, but don't have HPET 280 281 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 282 kernel's map of available physical RAM. 283 284 agp= [AGP] 285 { off | try_unsupported } 286 off: disable AGP support 287 try_unsupported: try to drive unsupported chipsets 288 (may crash computer or cause data corruption) 289 290 ALSA [HW,ALSA] 291 See Documentation/sound/alsa-configuration.rst 292 293 alignment= [KNL,ARM] 294 Allow the default userspace alignment fault handler 295 behaviour to be specified. Bit 0 enables warnings, 296 bit 1 enables fixups, and bit 2 sends a segfault. 297 298 align_va_addr= [X86-64] 299 Align virtual addresses by clearing slice [14:12] when 300 allocating a VMA at process creation time. This option 301 gives you up to 3% performance improvement on AMD F15h 302 machines (where it is enabled by default) for a 303 CPU-intensive style benchmark, and it can vary highly in 304 a microbenchmark depending on workload and compiler. 305 306 32: only for 32-bit processes 307 64: only for 64-bit processes 308 on: enable for both 32- and 64-bit processes 309 off: disable for both 32- and 64-bit processes 310 311 alloc_snapshot [FTRACE] 312 Allocate the ftrace snapshot buffer on boot up when the 313 main buffer is allocated. This is handy if debugging 314 and you need to use tracing_snapshot() on boot up, and 315 do not want to use tracing_snapshot_alloc() as it needs 316 to be done where GFP_KERNEL allocations are allowed. 317 318 allow_mismatched_32bit_el0 [ARM64,EARLY] 319 Allow execve() of 32-bit applications and setting of the 320 PER_LINUX32 personality on systems where only a strict 321 subset of the CPUs support 32-bit EL0. When this 322 parameter is present, the set of CPUs supporting 32-bit 323 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 324 and hot-unplug operations may be restricted. 325 326 See Documentation/arch/arm64/asymmetric-32bit.rst for more 327 information. 328 329 amd_iommu= [HW,X86-64] 330 Pass parameters to the AMD IOMMU driver in the system. 331 Possible values are: 332 fullflush - Deprecated, equivalent to iommu.strict=1 333 off - do not initialize any AMD IOMMU found in 334 the system 335 force_isolation - Force device isolation for all 336 devices. The IOMMU driver is not 337 allowed anymore to lift isolation 338 requirements as needed. This option 339 does not override iommu=pt 340 force_enable - Force enable the IOMMU on platforms known 341 to be buggy with IOMMU enabled. Use this 342 option with care. 343 pgtbl_v1 - Use v1 page table for DMA-API (Default). 344 pgtbl_v2 - Use v2 page table for DMA-API. 345 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 346 nohugepages - Limit page-sizes used for v1 page-tables 347 to 4 KiB. 348 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 349 to 4KiB/2Mib/1GiB. 350 351 352 amd_iommu_dump= [HW,X86-64] 353 Enable AMD IOMMU driver option to dump the ACPI table 354 for AMD IOMMU. With this option enabled, AMD IOMMU 355 driver will print ACPI tables for AMD IOMMU during 356 IOMMU initialization. 357 358 amd_iommu_intr= [HW,X86-64] 359 Specifies one of the following AMD IOMMU interrupt 360 remapping modes: 361 legacy - Use legacy interrupt remapping mode. 362 vapic - Use virtual APIC mode, which allows IOMMU 363 to inject interrupts directly into guest. 364 This mode requires kvm-amd.avic=1. 365 (Default when IOMMU HW support is present.) 366 367 amd_pstate= [X86,EARLY] 368 disable 369 Do not enable amd_pstate as the default 370 scaling driver for the supported processors 371 passive 372 Use amd_pstate with passive mode as a scaling driver. 373 In this mode autonomous selection is disabled. 374 Driver requests a desired performance level and platform 375 tries to match the same performance level if it is 376 satisfied by guaranteed performance level. 377 active 378 Use amd_pstate_epp driver instance as the scaling driver, 379 driver provides a hint to the hardware if software wants 380 to bias toward performance (0x0) or energy efficiency (0xff) 381 to the CPPC firmware. then CPPC power algorithm will 382 calculate the runtime workload and adjust the realtime cores 383 frequency. 384 guided 385 Activate guided autonomous mode. Driver requests minimum and 386 maximum performance level and the platform autonomously 387 selects a performance level in this range and appropriate 388 to the current workload. 389 390 amd_prefcore= 391 [X86] 392 disable 393 Disable amd-pstate preferred core. 394 395 amijoy.map= [HW,JOY] Amiga joystick support 396 Map of devices attached to JOY0DAT and JOY1DAT 397 Format: <a>,<b> 398 See also Documentation/input/joydev/joystick.rst 399 400 analog.map= [HW,JOY] Analog joystick and gamepad support 401 Specifies type or capabilities of an analog joystick 402 connected to one of 16 gameports 403 Format: <type1>,<type2>,..<type16> 404 405 apc= [HW,SPARC] 406 Power management functions (SPARCstation-4/5 + deriv.) 407 Format: noidle 408 Disable APC CPU standby support. SPARCstation-Fox does 409 not play well with APC CPU idle - disable it if you have 410 APC and your system crashes randomly. 411 412 apic [APIC,X86-64] Use IO-APIC. Default. 413 414 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 415 Change the output verbosity while booting 416 Format: { quiet (default) | verbose | debug } 417 Change the amount of debugging information output 418 when initialising the APIC and IO-APIC components. 419 420 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 421 Format: { bsp (default) | all | none } 422 bsp: External NMI is delivered only to CPU 0 423 all: External NMIs are broadcast to all CPUs as a 424 backup of CPU 0 425 none: External NMI is masked for all CPUs. This is 426 useful so that a dump capture kernel won't be 427 shot down by NMI 428 429 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 430 apicmaintimer. Useful when your PIT timer is totally 431 broken. 432 433 autoconf= [IPV6] 434 See Documentation/networking/ipv6.rst. 435 436 apm= [APM] Advanced Power Management 437 See header of arch/x86/kernel/apm_32.c. 438 439 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 440 Format: { "0" | "1" } 441 See security/apparmor/Kconfig help text 442 0 -- disable. 443 1 -- enable. 444 Default value is set via kernel config option. 445 446 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 447 Format: <io>,<irq>,<nodeID> 448 449 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 450 32 bit applications. 451 452 arm64.nobti [ARM64] Unconditionally disable Branch Target 453 Identification support 454 455 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 456 support 457 458 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 459 Set instructions support 460 461 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 462 Monitoring support 463 464 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 465 support 466 467 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 468 support 469 470 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 471 Extension support 472 473 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 474 Extension support 475 476 ataflop= [HW,M68k] 477 478 atarimouse= [HW,MOUSE] Atari Mouse 479 480 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 481 EzKey and similar keyboards 482 483 atkbd.reset= [HW] Reset keyboard during initialization 484 485 atkbd.set= [HW] Select keyboard code set 486 Format: <int> (2 = AT (default), 3 = PS/2) 487 488 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 489 keyboards 490 491 atkbd.softraw= [HW] Choose between synthetic and real raw mode 492 Format: <bool> (0 = real, 1 = synthetic (default)) 493 494 atkbd.softrepeat= [HW] 495 Use software keyboard repeat 496 497 audit= [KNL] Enable the audit sub-system 498 Format: { "0" | "1" | "off" | "on" } 499 0 | off - kernel audit is disabled and can not be 500 enabled until the next reboot 501 unset - kernel audit is initialized but disabled and 502 will be fully enabled by the userspace auditd. 503 1 | on - kernel audit is initialized and partially 504 enabled, storing at most audit_backlog_limit 505 messages in RAM until it is fully enabled by the 506 userspace auditd. 507 Default: unset 508 509 audit_backlog_limit= [KNL] Set the audit queue size limit. 510 Format: <int> (must be >=0) 511 Default: 64 512 513 bau= [X86_UV] Enable the BAU on SGI UV. The default 514 behavior is to disable the BAU (i.e. bau=0). 515 Format: { "0" | "1" } 516 0 - Disable the BAU. 517 1 - Enable the BAU. 518 unset - Disable the BAU. 519 520 baycom_epp= [HW,AX25] 521 Format: <io>,<mode> 522 523 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 524 Format: <io>,<mode> 525 See header of drivers/net/hamradio/baycom_par.c. 526 527 baycom_ser_fdx= [HW,AX25] 528 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 529 Format: <io>,<irq>,<mode>[,<baud>] 530 See header of drivers/net/hamradio/baycom_ser_fdx.c. 531 532 baycom_ser_hdx= [HW,AX25] 533 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 534 Format: <io>,<irq>,<mode> 535 See header of drivers/net/hamradio/baycom_ser_hdx.c. 536 537 bdev_allow_write_mounted= 538 Format: <bool> 539 Control the ability to open a mounted block device 540 for writing, i.e., allow / disallow writes that bypass 541 the FS. This was implemented as a means to prevent 542 fuzzers from crashing the kernel by overwriting the 543 metadata underneath a mounted FS without its awareness. 544 This also prevents destructive formatting of mounted 545 filesystems by naive storage tooling that don't use 546 O_EXCL. Default is Y and can be changed through the 547 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 548 549 bert_disable [ACPI] 550 Disable BERT OS support on buggy BIOSes. 551 552 bgrt_disable [ACPI,X86,EARLY] 553 Disable BGRT to avoid flickering OEM logo. 554 555 blkdevparts= Manual partition parsing of block device(s) for 556 embedded devices based on command line input. 557 See Documentation/block/cmdline-partition.rst 558 559 boot_delay= [KNL,EARLY] 560 Milliseconds to delay each printk during boot. 561 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 562 and you may also have to specify "lpj=". Boot_delay 563 values larger than 10 seconds (10000) are assumed 564 erroneous and ignored. 565 Format: integer 566 567 bootconfig [KNL,EARLY] 568 Extended command line options can be added to an initrd 569 and this will cause the kernel to look for it. 570 571 See Documentation/admin-guide/bootconfig.rst 572 573 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 574 bttv.radio= Most important insmod options are available as 575 kernel args too. 576 bttv.pll= See Documentation/admin-guide/media/bttv.rst 577 bttv.tuner= 578 579 bulk_remove=off [PPC] This parameter disables the use of the pSeries 580 firmware feature for flushing multiple hpte entries 581 at a time. 582 583 c101= [NET] Moxa C101 synchronous serial card 584 585 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 586 Sometimes CPU hardware bugs make them report the cache 587 size incorrectly. The kernel will attempt work arounds 588 to fix known problems, but for some CPUs it is not 589 possible to determine what the correct size should be. 590 This option provides an override for these situations. 591 592 carrier_timeout= 593 [NET] Specifies amount of time (in seconds) that 594 the kernel should wait for a network carrier. By default 595 it waits 120 seconds. 596 597 ca_keys= [KEYS] This parameter identifies a specific key(s) on 598 the system trusted keyring to be used for certificate 599 trust validation. 600 format: { id:<keyid> | builtin } 601 602 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 603 algorithm. Accepted values range from 0 to 7 604 inclusive. See arch/mips/include/asm/pgtable-bits.h 605 for platform specific values (SB1, Loongson3 and 606 others). 607 608 ccw_timeout_log [S390] 609 See Documentation/arch/s390/common_io.rst for details. 610 611 cgroup_disable= [KNL] Disable a particular controller or optional feature 612 Format: {name of the controller(s) or feature(s) to disable} 613 The effects of cgroup_disable=foo are: 614 - foo isn't auto-mounted if you mount all cgroups in 615 a single hierarchy 616 - foo isn't visible as an individually mountable 617 subsystem 618 - if foo is an optional feature then the feature is 619 disabled and corresponding cgroup files are not 620 created 621 {Currently only "memory" controller deal with this and 622 cut the overhead, others just disable the usage. So 623 only cgroup_disable=memory is actually worthy} 624 Specifying "pressure" disables per-cgroup pressure 625 stall information accounting feature 626 627 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 628 Format: { { controller | "all" | "named" } 629 [,{ controller | "all" | "named" }...] } 630 Like cgroup_disable, but only applies to cgroup v1; 631 the blacklisted controllers remain available in cgroup2. 632 "all" blacklists all controllers and "named" disables 633 named mounts. Specifying both "all" and "named" disables 634 all v1 hierarchies. 635 636 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 637 Format: { "true" | "false" } 638 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 639 640 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 641 Format: <string> 642 nosocket -- Disable socket memory accounting. 643 nokmem -- Disable kernel memory accounting. 644 nobpf -- Disable BPF memory accounting. 645 646 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 647 Format: { "0" | "1" } 648 See security/selinux/Kconfig help text. 649 0 -- check protection applied by kernel (includes 650 any implied execute protection). 651 1 -- check protection requested by application. 652 Default value is set via a kernel config option. 653 Value can be changed at runtime via 654 /sys/fs/selinux/checkreqprot. 655 Setting checkreqprot to 1 is deprecated. 656 657 cio_ignore= [S390] 658 See Documentation/arch/s390/common_io.rst for details. 659 660 clearcpuid=X[,X...] [X86] 661 Disable CPUID feature X for the kernel. See 662 arch/x86/include/asm/cpufeatures.h for the valid bit 663 numbers X. Note the Linux-specific bits are not necessarily 664 stable over kernel options, but the vendor-specific 665 ones should be. 666 X can also be a string as appearing in the flags: line 667 in /proc/cpuinfo which does not have the above 668 instability issue. However, not all features have names 669 in /proc/cpuinfo. 670 Note that using this option will taint your kernel. 671 Also note that user programs calling CPUID directly 672 or using the feature without checking anything 673 will still see it. This just prevents it from 674 being used by the kernel or shown in /proc/cpuinfo. 675 Also note the kernel might malfunction if you disable 676 some critical bits. 677 678 clk_ignore_unused 679 [CLK] 680 Prevents the clock framework from automatically gating 681 clocks that have not been explicitly enabled by a Linux 682 device driver but are enabled in hardware at reset or 683 by the bootloader/firmware. Note that this does not 684 force such clocks to be always-on nor does it reserve 685 those clocks in any way. This parameter is useful for 686 debug and development, but should not be needed on a 687 platform with proper driver support. For more 688 information, see Documentation/driver-api/clk.rst. 689 690 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 691 [Deprecated] 692 Forces specified clocksource (if available) to be used 693 when calculating gettimeofday(). If specified 694 clocksource is not available, it defaults to PIT. 695 Format: { pit | tsc | cyclone | pmtmr } 696 697 clocksource= Override the default clocksource 698 Format: <string> 699 Override the default clocksource and use the clocksource 700 with the name specified. 701 Some clocksource names to choose from, depending on 702 the platform: 703 [all] jiffies (this is the base, fallback clocksource) 704 [ACPI] acpi_pm 705 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 706 pxa_timer,timer3,32k_counter,timer0_1 707 [X86-32] pit,hpet,tsc; 708 scx200_hrt on Geode; cyclone on IBM x440 709 [MIPS] MIPS 710 [PARISC] cr16 711 [S390] tod 712 [SH] SuperH 713 [SPARC64] tick 714 [X86-64] hpet,tsc 715 716 clocksource.arm_arch_timer.evtstrm= 717 [ARM,ARM64,EARLY] 718 Format: <bool> 719 Enable/disable the eventstream feature of the ARM 720 architected timer so that code using WFE-based polling 721 loops can be debugged more effectively on production 722 systems. 723 724 clocksource.verify_n_cpus= [KNL] 725 Limit the number of CPUs checked for clocksources 726 marked with CLOCK_SOURCE_VERIFY_PERCPU that 727 are marked unstable due to excessive skew. 728 A negative value says to check all CPUs, while 729 zero says not to check any. Values larger than 730 nr_cpu_ids are silently truncated to nr_cpu_ids. 731 The actual CPUs are chosen randomly, with 732 no replacement if the same CPU is chosen twice. 733 734 clocksource-wdtest.holdoff= [KNL] 735 Set the time in seconds that the clocksource 736 watchdog test waits before commencing its tests. 737 Defaults to zero when built as a module and to 738 10 seconds when built into the kernel. 739 740 cma=nn[MG]@[start[MG][-end[MG]]] 741 [KNL,CMA,EARLY] 742 Sets the size of kernel global memory area for 743 contiguous memory allocations and optionally the 744 placement constraint by the physical address range of 745 memory allocations. A value of 0 disables CMA 746 altogether. For more information, see 747 kernel/dma/contiguous.c 748 749 cma_pernuma=nn[MG] 750 [KNL,CMA,EARLY] 751 Sets the size of kernel per-numa memory area for 752 contiguous memory allocations. A value of 0 disables 753 per-numa CMA altogether. And If this option is not 754 specified, the default value is 0. 755 With per-numa CMA enabled, DMA users on node nid will 756 first try to allocate buffer from the pernuma area 757 which is located in node nid, if the allocation fails, 758 they will fallback to the global default memory area. 759 760 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 761 [KNL,CMA,EARLY] 762 Sets the size of kernel numa memory area for 763 contiguous memory allocations. It will reserve CMA 764 area for the specified node. 765 766 With numa CMA enabled, DMA users on node nid will 767 first try to allocate buffer from the numa area 768 which is located in node nid, if the allocation fails, 769 they will fallback to the global default memory area. 770 771 cmo_free_hint= [PPC] Format: { yes | no } 772 Specify whether pages are marked as being inactive 773 when they are freed. This is used in CMO environments 774 to determine OS memory pressure for page stealing by 775 a hypervisor. 776 Default: yes 777 778 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 779 Sets the size of memory pool for coherent, atomic dma 780 allocations, by default set to 256K. 781 782 com20020= [HW,NET] ARCnet - COM20020 chipset 783 Format: 784 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 785 786 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 787 Format: <io>[,<irq>] 788 789 com90xx= [HW,NET] 790 ARCnet - COM90xx chipset (memory-mapped buffers) 791 Format: <io>[,<irq>[,<memstart>]] 792 793 condev= [HW,S390] console device 794 conmode= 795 796 con3215_drop= [S390,EARLY] 3215 console drop mode. 797 Format: y|n|Y|N|1|0 798 When set to true, drop data on the 3215 console when 799 the console buffer is full. In this case the 800 operator using a 3270 terminal emulator (for example 801 x3270) does not have to enter the clear key for the 802 console output to advance and the kernel to continue. 803 This leads to a much faster boot time when a 3270 804 terminal emulator is active. If no 3270 terminal 805 emulator is used, this parameter has no effect. 806 807 console= [KNL] Output console device and options. 808 809 tty<n> Use the virtual console device <n>. 810 811 ttyS<n>[,options] 812 ttyUSB0[,options] 813 Use the specified serial port. The options are of 814 the form "bbbbpnf", where "bbbb" is the baud rate, 815 "p" is parity ("n", "o", or "e"), "n" is number of 816 bits, and "f" is flow control ("r" for RTS or 817 omit it). Default is "9600n8". 818 819 See Documentation/admin-guide/serial-console.rst for more 820 information. See 821 Documentation/networking/netconsole.rst for an 822 alternative. 823 824 <DEVNAME>:<n>.<n>[,options] 825 Use the specified serial port on the serial core bus. 826 The addressing uses DEVNAME of the physical serial port 827 device, followed by the serial core controller instance, 828 and the serial port instance. The options are the same 829 as documented for the ttyS addressing above. 830 831 The mapping of the serial ports to the tty instances 832 can be viewed with: 833 834 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 835 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 836 837 In the above example, the console can be addressed with 838 console=00:04:0.0. Note that a console addressed this 839 way will only get added when the related device driver 840 is ready. The use of an earlycon parameter in addition to 841 the console may be desired for console output early on. 842 843 uart[8250],io,<addr>[,options] 844 uart[8250],mmio,<addr>[,options] 845 uart[8250],mmio16,<addr>[,options] 846 uart[8250],mmio32,<addr>[,options] 847 uart[8250],0x<addr>[,options] 848 Start an early, polled-mode console on the 8250/16550 849 UART at the specified I/O port or MMIO address, 850 switching to the matching ttyS device later. 851 MMIO inter-register address stride is either 8-bit 852 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 853 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 854 to be equivalent to 'mmio'. 'options' are specified in 855 the same format described for ttyS above; if unspecified, 856 the h/w is not re-initialized. 857 858 hvc<n> Use the hypervisor console device <n>. This is for 859 both Xen and PowerPC hypervisors. 860 861 { null | "" } 862 Use to disable console output, i.e., to have kernel 863 console messages discarded. 864 This must be the only console= parameter used on the 865 kernel command line. 866 867 If the device connected to the port is not a TTY but a braille 868 device, prepend "brl," before the device type, for instance 869 console=brl,ttyS0 870 For now, only VisioBraille is supported. 871 872 console_msg_format= 873 [KNL] Change console messages format 874 default 875 By default we print messages on consoles in 876 "[time stamp] text\n" format (time stamp may not be 877 printed, depending on CONFIG_PRINTK_TIME or 878 `printk_time' param). 879 syslog 880 Switch to syslog format: "<%u>[time stamp] text\n" 881 IOW, each message will have a facility and loglevel 882 prefix. The format is similar to one used by syslog() 883 syscall, or to executing "dmesg -S --raw" or to reading 884 from /proc/kmsg. 885 886 consoleblank= [KNL] The console blank (screen saver) timeout in 887 seconds. A value of 0 disables the blank timer. 888 Defaults to 0. 889 890 coredump_filter= 891 [KNL] Change the default value for 892 /proc/<pid>/coredump_filter. 893 See also Documentation/filesystems/proc.rst. 894 895 coresight_cpu_debug.enable 896 [ARM,ARM64] 897 Format: <bool> 898 Enable/disable the CPU sampling based debugging. 899 0: default value, disable debugging 900 1: enable debugging at boot time 901 902 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 903 Format: 904 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 905 906 cpuidle.off=1 [CPU_IDLE] 907 disable the cpuidle sub-system 908 909 cpuidle.governor= 910 [CPU_IDLE] Name of the cpuidle governor to use. 911 912 cpufreq.off=1 [CPU_FREQ] 913 disable the cpufreq sub-system 914 915 cpufreq.default_governor= 916 [CPU_FREQ] Name of the default cpufreq governor or 917 policy to use. This governor must be registered in the 918 kernel before the cpufreq driver probes. 919 920 cpu_init_udelay=N 921 [X86,EARLY] Delay for N microsec between assert and de-assert 922 of APIC INIT to start processors. This delay occurs 923 on every CPU online, such as boot, and resume from suspend. 924 Default: 10000 925 926 cpuhp.parallel= 927 [SMP] Enable/disable parallel bringup of secondary CPUs 928 Format: <bool> 929 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 930 the parameter has no effect. 931 932 crash_kexec_post_notifiers 933 Only jump to kdump kernel after running the panic 934 notifiers and dumping kmsg. This option increases 935 the risks of a kdump failure, since some panic 936 notifiers can make the crashed kernel more unstable. 937 In configurations where kdump may not be reliable, 938 running the panic notifiers could allow collecting 939 more data on dmesg, like stack traces from other CPUS 940 or extra data dumped by panic_print. Note that some 941 configurations enable this option unconditionally, 942 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 943 944 crashkernel=size[KMG][@offset[KMG]] 945 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 946 upon panic. This parameter reserves the physical 947 memory region [offset, offset + size] for that kernel 948 image. If '@offset' is omitted, then a suitable offset 949 is selected automatically. 950 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 951 under 4G first, and fall back to reserve region above 952 4G when '@offset' hasn't been specified. 953 See Documentation/admin-guide/kdump/kdump.rst for further details. 954 955 crashkernel=range1:size1[,range2:size2,...][@offset] 956 [KNL] Same as above, but depends on the memory 957 in the running system. The syntax of range is 958 start-[end] where start and end are both 959 a memory unit (amount[KMG]). See also 960 Documentation/admin-guide/kdump/kdump.rst for an example. 961 962 crashkernel=size[KMG],high 963 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 964 above 4G. 965 Allow kernel to allocate physical memory region from top, 966 so could be above 4G if system have more than 4G ram 967 installed. Otherwise memory region will be allocated 968 below 4G, if available. 969 It will be ignored if crashkernel=X is specified. 970 crashkernel=size[KMG],low 971 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 972 When crashkernel=X,high is passed, kernel could allocate 973 physical memory region above 4G, that cause second kernel 974 crash on system that require some amount of low memory, 975 e.g. swiotlb requires at least 64M+32K low memory, also 976 enough extra low memory is needed to make sure DMA buffers 977 for 32-bit devices won't run out. Kernel would try to allocate 978 default size of memory below 4G automatically. The default 979 size is platform dependent. 980 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 981 --> arm64: 128MiB 982 --> riscv: 128MiB 983 --> loongarch: 128MiB 984 This one lets the user specify own low range under 4G 985 for second kernel instead. 986 0: to disable low allocation. 987 It will be ignored when crashkernel=X,high is not used 988 or memory reserved is below 4G. 989 990 cryptomgr.notests 991 [KNL] Disable crypto self-tests 992 993 cs89x0_dma= [HW,NET] 994 Format: <dma> 995 996 cs89x0_media= [HW,NET] 997 Format: { rj45 | aui | bnc } 998 999 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1000 function call handling. When switched on, 1001 additional debug data is printed to the console 1002 in case a hanging CPU is detected, and that 1003 CPU is pinged again in order to try to resolve 1004 the hang situation. The default value of this 1005 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1006 Kconfig option. 1007 1008 dasd= [HW,NET] 1009 See header of drivers/s390/block/dasd_devmap.c. 1010 1011 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1012 (one device per port) 1013 Format: <port#>,<type> 1014 See also Documentation/input/devices/joystick-parport.rst 1015 1016 debug [KNL,EARLY] Enable kernel debugging (events log level). 1017 1018 debug_boot_weak_hash 1019 [KNL,EARLY] Enable printing [hashed] pointers early in the 1020 boot sequence. If enabled, we use a weak hash instead 1021 of siphash to hash pointers. Use this option if you are 1022 seeing instances of '(___ptrval___)') and need to see a 1023 value (hashed pointer) instead. Cryptographically 1024 insecure, please do not use on production kernels. 1025 1026 debug_locks_verbose= 1027 [KNL] verbose locking self-tests 1028 Format: <int> 1029 Print debugging info while doing the locking API 1030 self-tests. 1031 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1032 (no extra messages), setting it to -1 (all bits set) 1033 will print _a_lot_ more information - normally only 1034 useful to lockdep developers. 1035 1036 debug_objects [KNL,EARLY] Enable object debugging 1037 1038 debug_guardpage_minorder= 1039 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1040 parameter allows control of the order of pages that will 1041 be intentionally kept free (and hence protected) by the 1042 buddy allocator. Bigger value increase the probability 1043 of catching random memory corruption, but reduce the 1044 amount of memory for normal system use. The maximum 1045 possible value is MAX_PAGE_ORDER/2. Setting this 1046 parameter to 1 or 2 should be enough to identify most 1047 random memory corruption problems caused by bugs in 1048 kernel or driver code when a CPU writes to (or reads 1049 from) a random memory location. Note that there exists 1050 a class of memory corruptions problems caused by buggy 1051 H/W or F/W or by drivers badly programming DMA 1052 (basically when memory is written at bus level and the 1053 CPU MMU is bypassed) which are not detectable by 1054 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1055 help tracking down these problems. 1056 1057 debug_pagealloc= 1058 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1059 enables the feature at boot time. By default, it is 1060 disabled and the system will work mostly the same as a 1061 kernel built without CONFIG_DEBUG_PAGEALLOC. 1062 Note: to get most of debug_pagealloc error reports, it's 1063 useful to also enable the page_owner functionality. 1064 on: enable the feature 1065 1066 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1067 userspace and debugfs internal clients. 1068 Format: { on, no-mount, off } 1069 on: All functions are enabled. 1070 no-mount: 1071 Filesystem is not registered but kernel clients can 1072 access APIs and a crashkernel can be used to read 1073 its content. There is nothing to mount. 1074 off: Filesystem is not registered and clients 1075 get a -EPERM as result when trying to register files 1076 or directories within debugfs. 1077 This is equivalent of the runtime functionality if 1078 debugfs was not enabled in the kernel at all. 1079 Default value is set in build-time with a kernel configuration. 1080 1081 debugpat [X86] Enable PAT debugging 1082 1083 default_hugepagesz= 1084 [HW] The size of the default HugeTLB page. This is 1085 the size represented by the legacy /proc/ hugepages 1086 APIs. In addition, this is the default hugetlb size 1087 used for shmget(), mmap() and mounting hugetlbfs 1088 filesystems. If not specified, defaults to the 1089 architecture's default huge page size. Huge page 1090 sizes are architecture dependent. See also 1091 Documentation/admin-guide/mm/hugetlbpage.rst. 1092 Format: size[KMG] 1093 1094 deferred_probe_timeout= 1095 [KNL] Debugging option to set a timeout in seconds for 1096 deferred probe to give up waiting on dependencies to 1097 probe. Only specific dependencies (subsystems or 1098 drivers) that have opted in will be ignored. A timeout 1099 of 0 will timeout at the end of initcalls. If the time 1100 out hasn't expired, it'll be restarted by each 1101 successful driver registration. This option will also 1102 dump out devices still on the deferred probe list after 1103 retrying. 1104 1105 delayacct [KNL] Enable per-task delay accounting 1106 1107 dell_smm_hwmon.ignore_dmi= 1108 [HW] Continue probing hardware even if DMI data 1109 indicates that the driver is running on unsupported 1110 hardware. 1111 1112 dell_smm_hwmon.force= 1113 [HW] Activate driver even if SMM BIOS signature does 1114 not match list of supported models and enable otherwise 1115 blacklisted features. 1116 1117 dell_smm_hwmon.power_status= 1118 [HW] Report power status in /proc/i8k 1119 (disabled by default). 1120 1121 dell_smm_hwmon.restricted= 1122 [HW] Allow controlling fans only if SYS_ADMIN 1123 capability is set. 1124 1125 dell_smm_hwmon.fan_mult= 1126 [HW] Factor to multiply fan speed with. 1127 1128 dell_smm_hwmon.fan_max= 1129 [HW] Maximum configurable fan speed. 1130 1131 dfltcc= [HW,S390] 1132 Format: { on | off | def_only | inf_only | always } 1133 on: s390 zlib hardware support for compression on 1134 level 1 and decompression (default) 1135 off: No s390 zlib hardware support 1136 def_only: s390 zlib hardware support for deflate 1137 only (compression on level 1) 1138 inf_only: s390 zlib hardware support for inflate 1139 only (decompression) 1140 always: Same as 'on' but ignores the selected compression 1141 level always using hardware support (used for debugging) 1142 1143 dhash_entries= [KNL] 1144 Set number of hash buckets for dentry cache. 1145 1146 disable_1tb_segments [PPC,EARLY] 1147 Disables the use of 1TB hash page table segments. This 1148 causes the kernel to fall back to 256MB segments which 1149 can be useful when debugging issues that require an SLB 1150 miss to occur. 1151 1152 disable= [IPV6] 1153 See Documentation/networking/ipv6.rst. 1154 1155 disable_radix [PPC,EARLY] 1156 Disable RADIX MMU mode on POWER9 1157 1158 disable_tlbie [PPC] 1159 Disable TLBIE instruction. Currently does not work 1160 with KVM, with HASH MMU, or with coherent accelerators. 1161 1162 disable_ddw [PPC/PSERIES,EARLY] 1163 Disable Dynamic DMA Window support. Use this 1164 to workaround buggy firmware. 1165 1166 disable_ipv6= [IPV6] 1167 See Documentation/networking/ipv6.rst. 1168 1169 disable_mtrr_cleanup [X86,EARLY] 1170 The kernel tries to adjust MTRR layout from continuous 1171 to discrete, to make X server driver able to add WB 1172 entry later. This parameter disables that. 1173 1174 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1175 By default the kernel will trim any uncacheable 1176 memory out of your available memory pool based on 1177 MTRR settings. This parameter disables that behavior, 1178 possibly causing your machine to run very slowly. 1179 1180 disable_timer_pin_1 [X86,EARLY] 1181 Disable PIN 1 of APIC timer 1182 Can be useful to work around chipset bugs. 1183 1184 dis_ucode_ldr [X86] Disable the microcode loader. 1185 1186 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1187 this option disables the debugging code at boot. 1188 1189 dma_debug_entries=<number> 1190 This option allows to tune the number of preallocated 1191 entries for DMA-API debugging code. One entry is 1192 required per DMA-API allocation. Use this if the 1193 DMA-API debugging code disables itself because the 1194 architectural default is too low. 1195 1196 dma_debug_driver=<driver_name> 1197 With this option the DMA-API debugging driver 1198 filter feature can be enabled at boot time. Just 1199 pass the driver to filter for as the parameter. 1200 The filter can be disabled or changed to another 1201 driver later using sysfs. 1202 1203 reg_file_data_sampling= 1204 [X86] Controls mitigation for Register File Data 1205 Sampling (RFDS) vulnerability. RFDS is a CPU 1206 vulnerability which may allow userspace to infer 1207 kernel data values previously stored in floating point 1208 registers, vector registers, or integer registers. 1209 RFDS only affects Intel Atom processors. 1210 1211 on: Turns ON the mitigation. 1212 off: Turns OFF the mitigation. 1213 1214 This parameter overrides the compile time default set 1215 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1216 disabled when other VERW based mitigations (like MDS) 1217 are enabled. In order to disable RFDS mitigation all 1218 VERW based mitigations need to be disabled. 1219 1220 For details see: 1221 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1222 1223 driver_async_probe= [KNL] 1224 List of driver names to be probed asynchronously. * 1225 matches with all driver names. If * is specified, the 1226 rest of the listed driver names are those that will NOT 1227 match the *. 1228 Format: <driver_name1>,<driver_name2>... 1229 1230 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1231 Broken monitors, graphic adapters, KVMs and EDIDless 1232 panels may send no or incorrect EDID data sets. 1233 This parameter allows to specify an EDID data sets 1234 in the /lib/firmware directory that are used instead. 1235 An EDID data set will only be used for a particular 1236 connector, if its name and a colon are prepended to 1237 the EDID name. Each connector may use a unique EDID 1238 data set by separating the files with a comma. An EDID 1239 data set with no connector name will be used for 1240 any connectors not explicitly specified. 1241 1242 dscc4.setup= [NET] 1243 1244 dt_cpu_ftrs= [PPC,EARLY] 1245 Format: {"off" | "known"} 1246 Control how the dt_cpu_ftrs device-tree binding is 1247 used for CPU feature discovery and setup (if it 1248 exists). 1249 off: Do not use it, fall back to legacy cpu table. 1250 known: Do not pass through unknown features to guests 1251 or userspace, only those that the kernel is aware of. 1252 1253 dump_apple_properties [X86] 1254 Dump name and content of EFI device properties on 1255 x86 Macs. Useful for driver authors to determine 1256 what data is available or for reverse-engineering. 1257 1258 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1259 <module>.dyndbg[="val"] 1260 Enable debug messages at boot time. See 1261 Documentation/admin-guide/dynamic-debug-howto.rst 1262 for details. 1263 1264 early_ioremap_debug [KNL,EARLY] 1265 Enable debug messages in early_ioremap support. This 1266 is useful for tracking down temporary early mappings 1267 which are not unmapped. 1268 1269 earlycon= [KNL,EARLY] Output early console device and options. 1270 1271 When used with no options, the early console is 1272 determined by stdout-path property in device tree's 1273 chosen node or the ACPI SPCR table if supported by 1274 the platform. 1275 1276 cdns,<addr>[,options] 1277 Start an early, polled-mode console on a Cadence 1278 (xuartps) serial port at the specified address. Only 1279 supported option is baud rate. If baud rate is not 1280 specified, the serial port must already be setup and 1281 configured. 1282 1283 uart[8250],io,<addr>[,options[,uartclk]] 1284 uart[8250],mmio,<addr>[,options[,uartclk]] 1285 uart[8250],mmio32,<addr>[,options[,uartclk]] 1286 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1287 uart[8250],0x<addr>[,options] 1288 Start an early, polled-mode console on the 8250/16550 1289 UART at the specified I/O port or MMIO address. 1290 MMIO inter-register address stride is either 8-bit 1291 (mmio) or 32-bit (mmio32 or mmio32be). 1292 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1293 to be equivalent to 'mmio'. 'options' are specified 1294 in the same format described for "console=ttyS<n>"; if 1295 unspecified, the h/w is not initialized. 'uartclk' is 1296 the uart clock frequency; if unspecified, it is set 1297 to 'BASE_BAUD' * 16. 1298 1299 pl011,<addr> 1300 pl011,mmio32,<addr> 1301 Start an early, polled-mode console on a pl011 serial 1302 port at the specified address. The pl011 serial port 1303 must already be setup and configured. Options are not 1304 yet supported. If 'mmio32' is specified, then only 1305 the driver will use only 32-bit accessors to read/write 1306 the device registers. 1307 1308 liteuart,<addr> 1309 Start an early console on a litex serial port at the 1310 specified address. The serial port must already be 1311 setup and configured. Options are not yet supported. 1312 1313 meson,<addr> 1314 Start an early, polled-mode console on a meson serial 1315 port at the specified address. The serial port must 1316 already be setup and configured. Options are not yet 1317 supported. 1318 1319 msm_serial,<addr> 1320 Start an early, polled-mode console on an msm serial 1321 port at the specified address. The serial port 1322 must already be setup and configured. Options are not 1323 yet supported. 1324 1325 msm_serial_dm,<addr> 1326 Start an early, polled-mode console on an msm serial 1327 dm port at the specified address. The serial port 1328 must already be setup and configured. Options are not 1329 yet supported. 1330 1331 owl,<addr> 1332 Start an early, polled-mode console on a serial port 1333 of an Actions Semi SoC, such as S500 or S900, at the 1334 specified address. The serial port must already be 1335 setup and configured. Options are not yet supported. 1336 1337 rda,<addr> 1338 Start an early, polled-mode console on a serial port 1339 of an RDA Micro SoC, such as RDA8810PL, at the 1340 specified address. The serial port must already be 1341 setup and configured. Options are not yet supported. 1342 1343 sbi 1344 Use RISC-V SBI (Supervisor Binary Interface) for early 1345 console. 1346 1347 smh Use ARM semihosting calls for early console. 1348 1349 s3c2410,<addr> 1350 s3c2412,<addr> 1351 s3c2440,<addr> 1352 s3c6400,<addr> 1353 s5pv210,<addr> 1354 exynos4210,<addr> 1355 Use early console provided by serial driver available 1356 on Samsung SoCs, requires selecting proper type and 1357 a correct base address of the selected UART port. The 1358 serial port must already be setup and configured. 1359 Options are not yet supported. 1360 1361 lantiq,<addr> 1362 Start an early, polled-mode console on a lantiq serial 1363 (lqasc) port at the specified address. The serial port 1364 must already be setup and configured. Options are not 1365 yet supported. 1366 1367 lpuart,<addr> 1368 lpuart32,<addr> 1369 Use early console provided by Freescale LP UART driver 1370 found on Freescale Vybrid and QorIQ LS1021A processors. 1371 A valid base address must be provided, and the serial 1372 port must already be setup and configured. 1373 1374 ec_imx21,<addr> 1375 ec_imx6q,<addr> 1376 Start an early, polled-mode, output-only console on the 1377 Freescale i.MX UART at the specified address. The UART 1378 must already be setup and configured. 1379 1380 ar3700_uart,<addr> 1381 Start an early, polled-mode console on the 1382 Armada 3700 serial port at the specified 1383 address. The serial port must already be setup 1384 and configured. Options are not yet supported. 1385 1386 qcom_geni,<addr> 1387 Start an early, polled-mode console on a Qualcomm 1388 Generic Interface (GENI) based serial port at the 1389 specified address. The serial port must already be 1390 setup and configured. Options are not yet supported. 1391 1392 efifb,[options] 1393 Start an early, unaccelerated console on the EFI 1394 memory mapped framebuffer (if available). On cache 1395 coherent non-x86 systems that use system memory for 1396 the framebuffer, pass the 'ram' option so that it is 1397 mapped with the correct attributes. 1398 1399 linflex,<addr> 1400 Use early console provided by Freescale LINFlexD UART 1401 serial driver for NXP S32V234 SoCs. A valid base 1402 address must be provided, and the serial port must 1403 already be setup and configured. 1404 1405 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1406 earlyprintk=vga 1407 earlyprintk=sclp 1408 earlyprintk=xen 1409 earlyprintk=serial[,ttySn[,baudrate]] 1410 earlyprintk=serial[,0x...[,baudrate]] 1411 earlyprintk=ttySn[,baudrate] 1412 earlyprintk=dbgp[debugController#] 1413 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1414 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1415 earlyprintk=xdbc[xhciController#] 1416 earlyprintk=bios 1417 1418 earlyprintk is useful when the kernel crashes before 1419 the normal console is initialized. It is not enabled by 1420 default because it has some cosmetic problems. 1421 1422 Use "nocfg" to skip UART configuration, assume 1423 BIOS/firmware has configured UART correctly. 1424 1425 Append ",keep" to not disable it when the real console 1426 takes over. 1427 1428 Only one of vga, serial, or usb debug port can 1429 be used at a time. 1430 1431 Currently only ttyS0 and ttyS1 may be specified by 1432 name. Other I/O ports may be explicitly specified 1433 on some architectures (x86 and arm at least) by 1434 replacing ttySn with an I/O port address, like this: 1435 earlyprintk=serial,0x1008,115200 1436 You can find the port for a given device in 1437 /proc/tty/driver/serial: 1438 2: uart:ST16650V2 port:00001008 irq:18 ... 1439 1440 Interaction with the standard serial driver is not 1441 very good. 1442 1443 The VGA output is eventually overwritten by 1444 the real console. 1445 1446 The xen option can only be used in Xen domains. 1447 1448 The sclp output can only be used on s390. 1449 1450 The bios output can only be used on SuperH. 1451 1452 The optional "force" to "pciserial" enables use of a 1453 PCI device even when its classcode is not of the 1454 UART class. 1455 1456 edac_report= [HW,EDAC] Control how to report EDAC event 1457 Format: {"on" | "off" | "force"} 1458 on: enable EDAC to report H/W event. May be overridden 1459 by other higher priority error reporting module. 1460 off: disable H/W event reporting through EDAC. 1461 force: enforce the use of EDAC to report H/W event. 1462 default: on. 1463 1464 edd= [EDD] 1465 Format: {"off" | "on" | "skip[mbr]"} 1466 1467 efi= [EFI,EARLY] 1468 Format: { "debug", "disable_early_pci_dma", 1469 "nochunk", "noruntime", "nosoftreserve", 1470 "novamap", "no_disable_early_pci_dma" } 1471 debug: enable misc debug output. 1472 disable_early_pci_dma: disable the busmaster bit on all 1473 PCI bridges while in the EFI boot stub. 1474 nochunk: disable reading files in "chunks" in the EFI 1475 boot stub, as chunking can cause problems with some 1476 firmware implementations. 1477 noruntime : disable EFI runtime services support 1478 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1479 attribute may cause the kernel to reserve the 1480 memory range for a memory mapping driver to 1481 claim. Specify efi=nosoftreserve to disable this 1482 reservation and treat the memory by its base type 1483 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1484 novamap: do not call SetVirtualAddressMap(). 1485 no_disable_early_pci_dma: Leave the busmaster bit set 1486 on all PCI bridges while in the EFI boot stub 1487 1488 efi_no_storage_paranoia [EFI,X86,EARLY] 1489 Using this parameter you can use more than 50% of 1490 your efi variable storage. Use this parameter only if 1491 you are really sure that your UEFI does sane gc and 1492 fulfills the spec otherwise your board may brick. 1493 1494 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1495 that is to be dynamically loaded by Linux. If there are 1496 multiple variables with the same name but with different 1497 vendor GUIDs, all of them will be loaded. See 1498 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1499 1500 1501 eisa_irq_edge= [PARISC,HW] 1502 See header of drivers/parisc/eisa.c. 1503 1504 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1505 Format: ekgdboc=kbd 1506 1507 This is designed to be used in conjunction with 1508 the boot argument: earlyprintk=vga 1509 1510 This parameter works in place of the kgdboc parameter 1511 but can only be used if the backing tty is available 1512 very early in the boot process. For early debugging 1513 via a serial port see kgdboc_earlycon instead. 1514 1515 elanfreq= [X86-32] 1516 See comment before function elanfreq_setup() in 1517 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1518 1519 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1520 Specifies physical address of start of kernel core 1521 image elf header and optionally the size. Generally 1522 kexec loader will pass this option to capture kernel. 1523 See Documentation/admin-guide/kdump/kdump.rst for details. 1524 1525 enable_mtrr_cleanup [X86,EARLY] 1526 The kernel tries to adjust MTRR layout from continuous 1527 to discrete, to make X server driver able to add WB 1528 entry later. This parameter enables that. 1529 1530 enable_timer_pin_1 [X86] 1531 Enable PIN 1 of APIC timer 1532 Can be useful to work around chipset bugs 1533 (in particular on some ATI chipsets). 1534 The kernel tries to set a reasonable default. 1535 1536 enforcing= [SELINUX] Set initial enforcing status. 1537 Format: {"0" | "1"} 1538 See security/selinux/Kconfig help text. 1539 0 -- permissive (log only, no denials). 1540 1 -- enforcing (deny and log). 1541 Default value is 0. 1542 Value can be changed at runtime via 1543 /sys/fs/selinux/enforce. 1544 1545 erst_disable [ACPI] 1546 Disable Error Record Serialization Table (ERST) 1547 support. 1548 1549 ether= [HW,NET] Ethernet cards parameters 1550 This option is obsoleted by the "netdev=" option, which 1551 has equivalent usage. See its documentation for details. 1552 1553 evm= [EVM] 1554 Format: { "fix" } 1555 Permit 'security.evm' to be updated regardless of 1556 current integrity status. 1557 1558 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1559 stages so cover more early boot allocations. 1560 Please note that as side effect some optimizations 1561 might be disabled to achieve that (e.g. parallelized 1562 memory initialization is disabled) so the boot process 1563 might take longer, especially on systems with a lot of 1564 memory. Available with CONFIG_PAGE_EXTENSION=y. 1565 1566 failslab= 1567 fail_usercopy= 1568 fail_page_alloc= 1569 fail_skb_realloc= 1570 fail_make_request=[KNL] 1571 General fault injection mechanism. 1572 Format: <interval>,<probability>,<space>,<times> 1573 See also Documentation/fault-injection/. 1574 1575 fb_tunnels= [NET] 1576 Format: { initns | none } 1577 See Documentation/admin-guide/sysctl/net.rst for 1578 fb_tunnels_only_for_init_ns 1579 1580 floppy= [HW] 1581 See Documentation/admin-guide/blockdev/floppy.rst. 1582 1583 forcepae [X86-32] 1584 Forcefully enable Physical Address Extension (PAE). 1585 Many Pentium M systems disable PAE but may have a 1586 functionally usable PAE implementation. 1587 Warning: use of this parameter will taint the kernel 1588 and may cause unknown problems. 1589 1590 fred= [X86-64] 1591 Enable/disable Flexible Return and Event Delivery. 1592 Format: { on | off } 1593 on: enable FRED when it's present. 1594 off: disable FRED, the default setting. 1595 1596 ftrace=[tracer] 1597 [FTRACE] will set and start the specified tracer 1598 as early as possible in order to facilitate early 1599 boot debugging. 1600 1601 ftrace_boot_snapshot 1602 [FTRACE] On boot up, a snapshot will be taken of the 1603 ftrace ring buffer that can be read at: 1604 /sys/kernel/tracing/snapshot. 1605 This is useful if you need tracing information from kernel 1606 boot up that is likely to be overridden by user space 1607 start up functionality. 1608 1609 Optionally, the snapshot can also be defined for a tracing 1610 instance that was created by the trace_instance= command 1611 line parameter. 1612 1613 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1614 1615 The above will cause the "foo" tracing instance to trigger 1616 a snapshot at the end of boot up. 1617 1618 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1619 ,<instance>=2(orig_cpu)] 1620 [FTRACE] will dump the trace buffers on oops. 1621 If no parameter is passed, ftrace will dump global 1622 buffers of all CPUs, if you pass 2 or orig_cpu, it 1623 will dump only the buffer of the CPU that triggered 1624 the oops, or the specific instance will be dumped if 1625 its name is passed. Multiple instance dump is also 1626 supported, and instances are separated by commas. Each 1627 instance supports only dump on CPU that triggered the 1628 oops by passing 2 or orig_cpu to it. 1629 1630 ftrace_dump_on_oops=foo=orig_cpu 1631 1632 The above will dump only the buffer of "foo" instance 1633 on CPU that triggered the oops. 1634 1635 ftrace_dump_on_oops,foo,bar=orig_cpu 1636 1637 The above will dump global buffer on all CPUs, the 1638 buffer of "foo" instance on all CPUs and the buffer 1639 of "bar" instance on CPU that triggered the oops. 1640 1641 ftrace_filter=[function-list] 1642 [FTRACE] Limit the functions traced by the function 1643 tracer at boot up. function-list is a comma-separated 1644 list of functions. This list can be changed at run 1645 time by the set_ftrace_filter file in the debugfs 1646 tracing directory. 1647 1648 ftrace_notrace=[function-list] 1649 [FTRACE] Do not trace the functions specified in 1650 function-list. This list can be changed at run time 1651 by the set_ftrace_notrace file in the debugfs 1652 tracing directory. 1653 1654 ftrace_graph_filter=[function-list] 1655 [FTRACE] Limit the top level callers functions traced 1656 by the function graph tracer at boot up. 1657 function-list is a comma-separated list of functions 1658 that can be changed at run time by the 1659 set_graph_function file in the debugfs tracing directory. 1660 1661 ftrace_graph_notrace=[function-list] 1662 [FTRACE] Do not trace from the functions specified in 1663 function-list. This list is a comma-separated list of 1664 functions that can be changed at run time by the 1665 set_graph_notrace file in the debugfs tracing directory. 1666 1667 ftrace_graph_max_depth=<uint> 1668 [FTRACE] Used with the function graph tracer. This is 1669 the max depth it will trace into a function. This value 1670 can be changed at run time by the max_graph_depth file 1671 in the tracefs tracing directory. default: 0 (no limit) 1672 1673 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1674 devices by scanning the firmware to infer the 1675 consumer/supplier relationships. This feature is 1676 especially useful when drivers are loaded as modules as 1677 it ensures proper ordering of tasks like device probing 1678 (suppliers first, then consumers), supplier boot state 1679 clean up (only after all consumers have probed), 1680 suspend/resume & runtime PM (consumers first, then 1681 suppliers). 1682 Format: { off | permissive | on | rpm } 1683 off -- Don't create device links from firmware info. 1684 permissive -- Create device links from firmware info 1685 but use it only for ordering boot state clean 1686 up (sync_state() calls). 1687 on -- Create device links from firmware info and use it 1688 to enforce probe and suspend/resume ordering. 1689 rpm -- Like "on", but also use to order runtime PM. 1690 1691 fw_devlink.strict=<bool> 1692 [KNL,EARLY] Treat all inferred dependencies as mandatory 1693 dependencies. This only applies for fw_devlink=on|rpm. 1694 Format: <bool> 1695 1696 fw_devlink.sync_state = 1697 [KNL,EARLY] When all devices that could probe have finished 1698 probing, this parameter controls what to do with 1699 devices that haven't yet received their sync_state() 1700 calls. 1701 Format: { strict | timeout } 1702 strict -- Default. Continue waiting on consumers to 1703 probe successfully. 1704 timeout -- Give up waiting on consumers and call 1705 sync_state() on any devices that haven't yet 1706 received their sync_state() calls after 1707 deferred_probe_timeout has expired or by 1708 late_initcall() if !CONFIG_MODULES. 1709 1710 gamecon.map[2|3]= 1711 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1712 support via parallel port (up to 5 devices per port) 1713 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1714 See also Documentation/input/devices/joystick-parport.rst 1715 1716 gamma= [HW,DRM] 1717 1718 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1719 Format: off | on 1720 default: on 1721 1722 gather_data_sampling= 1723 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1724 mitigation. 1725 1726 Gather Data Sampling is a hardware vulnerability which 1727 allows unprivileged speculative access to data which was 1728 previously stored in vector registers. 1729 1730 This issue is mitigated by default in updated microcode. 1731 The mitigation may have a performance impact but can be 1732 disabled. On systems without the microcode mitigation 1733 disabling AVX serves as a mitigation. 1734 1735 force: Disable AVX to mitigate systems without 1736 microcode mitigation. No effect if the microcode 1737 mitigation is present. Known to cause crashes in 1738 userspace with buggy AVX enumeration. 1739 1740 off: Disable GDS mitigation. 1741 1742 gbpages [X86] Use GB pages for kernel direct mappings. 1743 1744 gcov_persist= [GCOV] When non-zero (default), profiling data for 1745 kernel modules is saved and remains accessible via 1746 debugfs, even when the module is unloaded/reloaded. 1747 When zero, profiling data is discarded and associated 1748 debugfs files are removed at module unload time. 1749 1750 goldfish [X86] Enable the goldfish android emulator platform. 1751 Don't use this when you are not running on the 1752 android emulator 1753 1754 gpio-mockup.gpio_mockup_ranges 1755 [HW] Sets the ranges of gpiochip of for this device. 1756 Format: <start1>,<end1>,<start2>,<end2>... 1757 gpio-mockup.gpio_mockup_named_lines 1758 [HW] Let the driver know GPIO lines should be named. 1759 1760 gpt [EFI] Forces disk with valid GPT signature but 1761 invalid Protective MBR to be treated as GPT. If the 1762 primary GPT is corrupted, it enables the backup/alternate 1763 GPT to be used instead. 1764 1765 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1766 the "Enable 0" bit of the configuration register. 1767 Format: 0 | 1 1768 Default: 0 1769 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1770 the "Enable 0" bit of the configuration register. 1771 Format: 0 | 1 1772 Default: 0 1773 grcan.select= [HW] Select which physical interface to use. 1774 Format: 0 | 1 1775 Default: 0 1776 grcan.txsize= [HW] Sets the size of the tx buffer. 1777 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1778 Default: 1024 1779 grcan.rxsize= [HW] Sets the size of the rx buffer. 1780 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1781 Default: 1024 1782 1783 hardened_usercopy= 1784 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1785 hardening is enabled for this boot. Hardened 1786 usercopy checking is used to protect the kernel 1787 from reading or writing beyond known memory 1788 allocation boundaries as a proactive defense 1789 against bounds-checking flaws in the kernel's 1790 copy_to_user()/copy_from_user() interface. 1791 The default is determined by 1792 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1793 on Perform hardened usercopy checks. 1794 off Disable hardened usercopy checks. 1795 1796 hardlockup_all_cpu_backtrace= 1797 [KNL] Should the hard-lockup detector generate 1798 backtraces on all cpus. 1799 Format: 0 | 1 1800 1801 hashdist= [KNL,NUMA] Large hashes allocated during boot 1802 are distributed across NUMA nodes. Defaults on 1803 for 64-bit NUMA, off otherwise. 1804 Format: 0 | 1 (for off | on) 1805 1806 hd= [EIDE] (E)IDE hard drive subsystem geometry 1807 Format: <cyl>,<head>,<sect> 1808 1809 hest_disable [ACPI] 1810 Disable Hardware Error Source Table (HEST) support; 1811 corresponding firmware-first mode error processing 1812 logic will be disabled. 1813 1814 hibernate= [HIBERNATION] 1815 noresume Don't check if there's a hibernation image 1816 present during boot. 1817 nocompress Don't compress/decompress hibernation images. 1818 no Disable hibernation and resume. 1819 protect_image Turn on image protection during restoration 1820 (that will set all pages holding image data 1821 during restoration read-only). 1822 1823 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1824 used with hibernation. 1825 Format: { lzo | lz4 } 1826 Default: lzo 1827 1828 lzo: Select LZO compression algorithm to 1829 compress/decompress hibernation image. 1830 1831 lz4: Select LZ4 compression algorithm to 1832 compress/decompress hibernation image. 1833 1834 hibernate.pm_test_delay= 1835 [HIBERNATION] 1836 Sets the number of seconds to remain in a hibernation test 1837 mode before resuming the system (see 1838 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 1839 is set. Default value is 5. 1840 1841 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 1842 size of <nn>. This works even on boxes that have no 1843 highmem otherwise. This also works to reduce highmem 1844 size on bigger boxes. 1845 1846 highres= [KNL] Enable/disable high resolution timer mode. 1847 Valid parameters: "on", "off" 1848 Default: "on" 1849 1850 hlt [BUGS=ARM,SH] 1851 1852 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 1853 Format: <string> 1854 This allows setting the system's hostname during early 1855 startup. This sets the name returned by gethostname. 1856 Using this parameter to set the hostname makes it 1857 possible to ensure the hostname is correctly set before 1858 any userspace processes run, avoiding the possibility 1859 that a process may call gethostname before the hostname 1860 has been explicitly set, resulting in the calling 1861 process getting an incorrect result. The string must 1862 not exceed the maximum allowed hostname length (usually 1863 64 characters) and will be truncated otherwise. 1864 1865 hpet= [X86-32,HPET] option to control HPET usage 1866 Format: { enable (default) | disable | force | 1867 verbose } 1868 disable: disable HPET and use PIT instead 1869 force: allow force enabled of undocumented chips (ICH4, 1870 VIA, nVidia) 1871 verbose: show contents of HPET registers during setup 1872 1873 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1874 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1875 1876 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 1877 If this follows hugepagesz (below), it specifies 1878 the number of pages of hugepagesz to be allocated. 1879 If this is the first HugeTLB parameter on the command 1880 line, it specifies the number of pages to allocate for 1881 the default huge page size. If using node format, the 1882 number of pages to allocate per-node can be specified. 1883 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1884 Format: <integer> or (node format) 1885 <node>:<integer>[,<node>:<integer>] 1886 1887 hugepagesz= 1888 [HW,EARLY] The size of the HugeTLB pages. This is 1889 used in conjunction with hugepages (above) to 1890 allocate huge pages of a specific size at boot. The 1891 pair hugepagesz=X hugepages=Y can be specified once 1892 for each supported huge page size. Huge page sizes 1893 are architecture dependent. See also 1894 Documentation/admin-guide/mm/hugetlbpage.rst. 1895 Format: size[KMG] 1896 1897 hugepage_alloc_threads= 1898 [HW] The number of threads that should be used to 1899 allocate hugepages during boot. This option can be 1900 used to improve system bootup time when allocating 1901 a large amount of huge pages. 1902 The default value is 25% of the available hardware threads. 1903 1904 Note that this parameter only applies to non-gigantic huge pages. 1905 1906 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 1907 of gigantic hugepages. Or using node format, the size 1908 of a CMA area per node can be specified. 1909 Format: nn[KMGTPE] or (node format) 1910 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1911 1912 Reserve a CMA area of given size and allocate gigantic 1913 hugepages using the CMA allocator. If enabled, the 1914 boot-time allocation of gigantic hugepages is skipped. 1915 1916 hugetlb_cma_only= 1917 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 1918 try to allocate from the CMA areas. 1919 1920 This option does nothing if hugetlb_cma= is not also 1921 specified. 1922 1923 hugetlb_free_vmemmap= 1924 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 1925 enabled. 1926 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 1927 Allows heavy hugetlb users to free up some more 1928 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1929 Format: { on | off (default) } 1930 1931 on: enable HVO 1932 off: disable HVO 1933 1934 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 1935 the default is on. 1936 1937 Note that the vmemmap pages may be allocated from the added 1938 memory block itself when memory_hotplug.memmap_on_memory is 1939 enabled, those vmemmap pages cannot be optimized even if this 1940 feature is enabled. Other vmemmap pages not allocated from 1941 the added memory block itself do not be affected. 1942 1943 hung_task_panic= 1944 [KNL] Should the hung task detector generate panics. 1945 Format: 0 | 1 1946 1947 A value of 1 instructs the kernel to panic when a 1948 hung task is detected. The default value is controlled 1949 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1950 option. The value selected by this boot parameter can 1951 be changed later by the kernel.hung_task_panic sysctl. 1952 1953 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1954 terminal devices. Valid values: 0..8 1955 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1956 If specified, z/VM IUCV HVC accepts connections 1957 from listed z/VM user IDs only. 1958 1959 hv_nopvspin [X86,HYPER_V,EARLY] 1960 Disables the paravirt spinlock optimizations 1961 which allow the hypervisor to 'idle' the guest 1962 on lock contention. 1963 1964 hw_protection= [HW] 1965 Format: reboot | shutdown 1966 1967 Hardware protection action taken on critical events like 1968 overtemperature or imminent voltage loss. 1969 1970 i2c_bus= [HW] Override the default board specific I2C bus speed 1971 or register an additional I2C bus that is not 1972 registered from board initialization code. 1973 Format: 1974 <bus_id>,<clkrate> 1975 1976 i2c_touchscreen_props= [HW,ACPI,X86] 1977 Set device-properties for ACPI-enumerated I2C-attached 1978 touchscreen, to e.g. fix coordinates of upside-down 1979 mounted touchscreens. If you need this option please 1980 submit a drivers/platform/x86/touchscreen_dmi.c patch 1981 adding a DMI quirk for this. 1982 1983 Format: 1984 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 1985 Where <val> is one of: 1986 Omit "=<val>" entirely Set a boolean device-property 1987 Unsigned number Set a u32 device-property 1988 Anything else Set a string device-property 1989 1990 Examples (split over multiple lines): 1991 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 1992 touchscreen-inverted-y 1993 1994 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 1995 touchscreen-size-y=1080:touchscreen-inverted-y: 1996 firmware-name=gsl1680-vendor-model.fw:silead,home-button 1997 1998 i8042.debug [HW] Toggle i8042 debug mode 1999 i8042.unmask_kbd_data 2000 [HW] Enable printing of interrupt data from the KBD port 2001 (disabled by default, and as a pre-condition 2002 requires that i8042.debug=1 be enabled) 2003 i8042.direct [HW] Put keyboard port into non-translated mode 2004 i8042.dumbkbd [HW] Pretend that controller can only read data from 2005 keyboard and cannot control its state 2006 (Don't attempt to blink the leds) 2007 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2008 i8042.nokbd [HW] Don't check/create keyboard port 2009 i8042.noloop [HW] Disable the AUX Loopback command while probing 2010 for the AUX port 2011 i8042.nomux [HW] Don't check presence of an active multiplexing 2012 controller 2013 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2014 controllers 2015 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2016 i8042.reset [HW] Reset the controller during init, cleanup and 2017 suspend-to-ram transitions, only during s2r 2018 transitions, or never reset 2019 Format: { 1 | Y | y | 0 | N | n } 2020 1, Y, y: always reset controller 2021 0, N, n: don't ever reset controller 2022 Default: only on s2r transitions on x86; most other 2023 architectures force reset to be always executed 2024 i8042.unlock [HW] Unlock (ignore) the keylock 2025 i8042.kbdreset [HW] Reset device connected to KBD port 2026 i8042.probe_defer 2027 [HW] Allow deferred probing upon i8042 probe errors 2028 2029 i810= [HW,DRM] 2030 2031 i915.invert_brightness= 2032 [DRM] Invert the sense of the variable that is used to 2033 set the brightness of the panel backlight. Normally a 2034 brightness value of 0 indicates backlight switched off, 2035 and the maximum of the brightness value sets the backlight 2036 to maximum brightness. If this parameter is set to 0 2037 (default) and the machine requires it, or this parameter 2038 is set to 1, a brightness value of 0 sets the backlight 2039 to maximum brightness, and the maximum of the brightness 2040 value switches the backlight off. 2041 -1 -- never invert brightness 2042 0 -- machine default 2043 1 -- force brightness inversion 2044 2045 ia32_emulation= [X86-64] 2046 Format: <bool> 2047 When true, allows loading 32-bit programs and executing 32-bit 2048 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2049 boot time. When false, unconditionally disables IA32 emulation. 2050 2051 icn= [HW,ISDN] 2052 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2053 2054 2055 idle= [X86,EARLY] 2056 Format: idle=poll, idle=halt, idle=nomwait 2057 2058 idle=poll: Don't do power saving in the idle loop 2059 using HLT, but poll for rescheduling event. This will 2060 make the CPUs eat a lot more power, but may be useful 2061 to get slightly better performance in multiprocessor 2062 benchmarks. It also makes some profiling using 2063 performance counters more accurate. Please note that 2064 on systems with MONITOR/MWAIT support (like Intel 2065 EM64T CPUs) this option has no performance advantage 2066 over the normal idle loop. It may also interact badly 2067 with hyperthreading. 2068 2069 idle=halt: Halt is forced to be used for CPU idle. 2070 In such case C2/C3 won't be used again. 2071 2072 idle=nomwait: Disable mwait for CPU C-states 2073 2074 idxd.sva= [HW] 2075 Format: <bool> 2076 Allow force disabling of Shared Virtual Memory (SVA) 2077 support for the idxd driver. By default it is set to 2078 true (1). 2079 2080 idxd.tc_override= [HW] 2081 Format: <bool> 2082 Allow override of default traffic class configuration 2083 for the device. By default it is set to false (0). 2084 2085 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2086 Format: { strict | legacy | 2008 | relaxed | emulated } 2087 Default: strict 2088 2089 Choose which programs will be accepted for execution 2090 based on the IEEE 754 NaN encoding(s) supported by 2091 the FPU and the NaN encoding requested with the value 2092 of an ELF file header flag individually set by each 2093 binary. Hardware implementations are permitted to 2094 support either or both of the legacy and the 2008 NaN 2095 encoding mode. 2096 2097 Available settings are as follows: 2098 strict accept binaries that request a NaN encoding 2099 supported by the FPU 2100 legacy only accept legacy-NaN binaries, if supported 2101 by the FPU 2102 2008 only accept 2008-NaN binaries, if supported 2103 by the FPU 2104 relaxed accept any binaries regardless of whether 2105 supported by the FPU 2106 emulated accept any binaries but enable FPU emulator 2107 if binary mode is unsupported by the FPU. 2108 2109 The FPU emulator is always able to support both NaN 2110 encodings, so if no FPU hardware is present or it has 2111 been disabled with 'nofpu', then the settings of 2112 'legacy' and '2008' strap the emulator accordingly, 2113 'relaxed' straps the emulator for both legacy-NaN and 2114 2008-NaN, whereas 'strict' enables legacy-NaN only on 2115 legacy processors and both NaN encodings on MIPS32 or 2116 MIPS64 CPUs. 2117 2118 The setting for ABS.fmt/NEG.fmt instruction execution 2119 mode generally follows that for the NaN encoding, 2120 except where unsupported by hardware. 2121 2122 ignore_loglevel [KNL,EARLY] 2123 Ignore loglevel setting - this will print /all/ 2124 kernel messages to the console. Useful for debugging. 2125 We also add it as printk module parameter, so users 2126 could change it dynamically, usually by 2127 /sys/module/printk/parameters/ignore_loglevel. 2128 2129 ignore_rlimit_data 2130 Ignore RLIMIT_DATA setting for data mappings, 2131 print warning at first misuse. Can be changed via 2132 /sys/module/kernel/parameters/ignore_rlimit_data. 2133 2134 ihash_entries= [KNL] 2135 Set number of hash buckets for inode cache. 2136 2137 ima_appraise= [IMA] appraise integrity measurements 2138 Format: { "off" | "enforce" | "fix" | "log" } 2139 default: "enforce" 2140 2141 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2142 The builtin appraise policy appraises all files 2143 owned by uid=0. 2144 2145 ima_canonical_fmt [IMA] 2146 Use the canonical format for the binary runtime 2147 measurements, instead of host native format. 2148 2149 ima_hash= [IMA] 2150 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2151 | sha512 | ... } 2152 default: "sha1" 2153 2154 The list of supported hash algorithms is defined 2155 in crypto/hash_info.h. 2156 2157 ima_policy= [IMA] 2158 The builtin policies to load during IMA setup. 2159 Format: "tcb | appraise_tcb | secure_boot | 2160 fail_securely | critical_data" 2161 2162 The "tcb" policy measures all programs exec'd, files 2163 mmap'd for exec, and all files opened with the read 2164 mode bit set by either the effective uid (euid=0) or 2165 uid=0. 2166 2167 The "appraise_tcb" policy appraises the integrity of 2168 all files owned by root. 2169 2170 The "secure_boot" policy appraises the integrity 2171 of files (eg. kexec kernel image, kernel modules, 2172 firmware, policy, etc) based on file signatures. 2173 2174 The "fail_securely" policy forces file signature 2175 verification failure also on privileged mounted 2176 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2177 flag. 2178 2179 The "critical_data" policy measures kernel integrity 2180 critical data. 2181 2182 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2183 Load a policy which meets the needs of the Trusted 2184 Computing Base. This means IMA will measure all 2185 programs exec'd, files mmap'd for exec, and all files 2186 opened for read by uid=0. 2187 2188 ima_template= [IMA] 2189 Select one of defined IMA measurements template formats. 2190 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2191 "ima-sigv2" } 2192 Default: "ima-ng" 2193 2194 ima_template_fmt= 2195 [IMA] Define a custom template format. 2196 Format: { "field1|...|fieldN" } 2197 2198 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2199 Format: <min_file_size> 2200 Set the minimal file size for using asynchronous hash. 2201 If left unspecified, ahash usage is disabled. 2202 2203 ahash performance varies for different data sizes on 2204 different crypto accelerators. This option can be used 2205 to achieve the best performance for a particular HW. 2206 2207 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2208 Format: <bufsize> 2209 Set hashing buffer size. Default: 4k. 2210 2211 ahash performance varies for different chunk sizes on 2212 different crypto accelerators. This option can be used 2213 to achieve best performance for particular HW. 2214 2215 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2216 Target Selection(ITS) bug in Intel CPUs. Updated 2217 microcode is also required for a fix in IBPB. 2218 2219 on: Enable mitigation (default). 2220 off: Disable mitigation. 2221 force: Force the ITS bug and deploy default 2222 mitigation. 2223 vmexit: Only deploy mitigation if CPU is affected by 2224 guest/host isolation part of ITS. 2225 stuff: Deploy RSB-fill mitigation when retpoline is 2226 also deployed. Otherwise, deploy the default 2227 mitigation. 2228 2229 For details see: 2230 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2231 2232 init= [KNL] 2233 Format: <full_path> 2234 Run specified binary instead of /sbin/init as init 2235 process. 2236 2237 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2238 for working out where the kernel is dying during 2239 startup. 2240 2241 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2242 initcall functions. Useful for debugging built-in 2243 modules and initcalls. 2244 2245 initramfs_async= [KNL] 2246 Format: <bool> 2247 Default: 1 2248 This parameter controls whether the initramfs 2249 image is unpacked asynchronously, concurrently 2250 with devices being probed and 2251 initialized. This should normally just work, 2252 but as a debugging aid, one can get the 2253 historical behaviour of the initramfs 2254 unpacking being completed before device_ and 2255 late_ initcalls. 2256 2257 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2258 2259 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2260 load the initrd. If an initrd is compiled in or 2261 specified in the bootparams, it takes priority over this 2262 setting. 2263 Format: ss[KMG],nn[KMG] 2264 Default is 0, 0 2265 2266 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2267 zeroes. 2268 Format: 0 | 1 2269 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2270 2271 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2272 Format: 0 | 1 2273 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2274 2275 init_pkru= [X86] Specify the default memory protection keys rights 2276 register contents for all processes. 0x55555554 by 2277 default (disallow access to all but pkey 0). Can 2278 override in debugfs after boot. 2279 2280 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2281 Format: <irq> 2282 2283 int_pln_enable [X86] Enable power limit notification interrupt 2284 2285 integrity_audit=[IMA] 2286 Format: { "0" | "1" } 2287 0 -- basic integrity auditing messages. (Default) 2288 1 -- additional integrity auditing messages. 2289 2290 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2291 on 2292 Enable intel iommu driver. 2293 off 2294 Disable intel iommu driver. 2295 igfx_off [Default Off] 2296 By default, gfx is mapped as normal device. If a gfx 2297 device has a dedicated DMAR unit, the DMAR unit is 2298 bypassed by not enabling DMAR with this option. In 2299 this case, gfx device will use physical address for 2300 DMA. 2301 strict [Default Off] 2302 Deprecated, equivalent to iommu.strict=1. 2303 sp_off [Default Off] 2304 By default, super page will be supported if Intel IOMMU 2305 has the capability. With this option, super page will 2306 not be supported. 2307 sm_on 2308 Enable the Intel IOMMU scalable mode if the hardware 2309 advertises that it has support for the scalable mode 2310 translation. 2311 sm_off 2312 Disallow use of the Intel IOMMU scalable mode. 2313 tboot_noforce [Default Off] 2314 Do not force the Intel IOMMU enabled under tboot. 2315 By default, tboot will force Intel IOMMU on, which 2316 could harm performance of some high-throughput 2317 devices like 40GBit network cards, even if identity 2318 mapping is enabled. 2319 Note that using this option lowers the security 2320 provided by tboot because it makes the system 2321 vulnerable to DMA attacks. 2322 2323 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2324 0 disables intel_idle and fall back on acpi_idle. 2325 1 to 9 specify maximum depth of C-state. 2326 2327 intel_pstate= [X86,EARLY] 2328 disable 2329 Do not enable intel_pstate as the default 2330 scaling driver for the supported processors 2331 active 2332 Use intel_pstate driver to bypass the scaling 2333 governors layer of cpufreq and provides it own 2334 algorithms for p-state selection. There are two 2335 P-state selection algorithms provided by 2336 intel_pstate in the active mode: powersave and 2337 performance. The way they both operate depends 2338 on whether or not the hardware managed P-states 2339 (HWP) feature has been enabled in the processor 2340 and possibly on the processor model. 2341 passive 2342 Use intel_pstate as a scaling driver, but configure it 2343 to work with generic cpufreq governors (instead of 2344 enabling its internal governor). This mode cannot be 2345 used along with the hardware-managed P-states (HWP) 2346 feature. 2347 force 2348 Enable intel_pstate on systems that prohibit it by default 2349 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2350 instead of acpi-cpufreq may disable platform features, such 2351 as thermal controls and power capping, that rely on ACPI 2352 P-States information being indicated to OSPM and therefore 2353 should be used with caution. This option does not work with 2354 processors that aren't supported by the intel_pstate driver 2355 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2356 no_hwp 2357 Do not enable hardware P state control (HWP) 2358 if available. 2359 hwp_only 2360 Only load intel_pstate on systems which support 2361 hardware P state control (HWP) if available. 2362 support_acpi_ppc 2363 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2364 Description Table, specifies preferred power management 2365 profile as "Enterprise Server" or "Performance Server", 2366 then this feature is turned on by default. 2367 per_cpu_perf_limits 2368 Allow per-logical-CPU P-State performance control limits using 2369 cpufreq sysfs interface 2370 no_cas 2371 Do not enable capacity-aware scheduling (CAS) on 2372 hybrid systems 2373 2374 intremap= [X86-64,Intel-IOMMU,EARLY] 2375 on enable Interrupt Remapping (default) 2376 off disable Interrupt Remapping 2377 nosid disable Source ID checking 2378 no_x2apic_optout 2379 BIOS x2APIC opt-out request will be ignored 2380 nopost disable Interrupt Posting 2381 posted_msi 2382 enable MSIs delivered as posted interrupts 2383 2384 iomem= Disable strict checking of access to MMIO memory 2385 strict regions from userspace. 2386 relaxed 2387 2388 iommu= [X86,EARLY] 2389 2390 off 2391 Don't initialize and use any kind of IOMMU. 2392 2393 force 2394 Force the use of the hardware IOMMU even when 2395 it is not actually needed (e.g. because < 3 GB 2396 memory). 2397 2398 noforce 2399 Don't force hardware IOMMU usage when it is not 2400 needed. (default). 2401 2402 biomerge 2403 panic 2404 nopanic 2405 merge 2406 nomerge 2407 2408 soft 2409 Use software bounce buffering (SWIOTLB) (default for 2410 Intel machines). This can be used to prevent the usage 2411 of an available hardware IOMMU. 2412 2413 [X86] 2414 pt 2415 [X86] 2416 nopt 2417 [PPC/POWERNV] 2418 nobypass 2419 Disable IOMMU bypass, using IOMMU for PCI devices. 2420 2421 [X86] 2422 AMD Gart HW IOMMU-specific options: 2423 2424 <size> 2425 Set the size of the remapping area in bytes. 2426 2427 allowed 2428 Overwrite iommu off workarounds for specific chipsets 2429 2430 fullflush 2431 Flush IOMMU on each allocation (default). 2432 2433 nofullflush 2434 Don't use IOMMU fullflush. 2435 2436 memaper[=<order>] 2437 Allocate an own aperture over RAM with size 2438 32MB<<order. (default: order=1, i.e. 64MB) 2439 2440 merge 2441 Do scatter-gather (SG) merging. Implies "force" 2442 (experimental). 2443 2444 nomerge 2445 Don't do scatter-gather (SG) merging. 2446 2447 noaperture 2448 Ask the IOMMU not to touch the aperture for AGP. 2449 2450 noagp 2451 Don't initialize the AGP driver and use full aperture. 2452 2453 panic 2454 Always panic when IOMMU overflows. 2455 2456 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2457 Format: { "0" | "1" } 2458 0 - Try to allocate a 32-bit DMA address first, before 2459 falling back to the full range if needed. 2460 1 - Allocate directly from the full usable range, 2461 forcing Dual Address Cycle for PCI cards supporting 2462 greater than 32-bit addressing. 2463 2464 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2465 Format: { "0" | "1" } 2466 0 - Lazy mode. 2467 Request that DMA unmap operations use deferred 2468 invalidation of hardware TLBs, for increased 2469 throughput at the cost of reduced device isolation. 2470 Will fall back to strict mode if not supported by 2471 the relevant IOMMU driver. 2472 1 - Strict mode. 2473 DMA unmap operations invalidate IOMMU hardware TLBs 2474 synchronously. 2475 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2476 Note: on x86, strict mode specified via one of the 2477 legacy driver-specific options takes precedence. 2478 2479 iommu.passthrough= 2480 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2481 Format: { "0" | "1" } 2482 0 - Use IOMMU translation for DMA. 2483 1 - Bypass the IOMMU for DMA. 2484 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2485 2486 io7= [HW] IO7 for Marvel-based Alpha systems 2487 See comment before marvel_specify_io7 in 2488 arch/alpha/kernel/core_marvel.c. 2489 2490 io_delay= [X86,EARLY] I/O delay method 2491 0x80 2492 Standard port 0x80 based delay 2493 0xed 2494 Alternate port 0xed based delay (needed on some systems) 2495 udelay 2496 Simple two microseconds delay 2497 none 2498 No delay 2499 2500 ip= [IP_PNP] 2501 See Documentation/admin-guide/nfs/nfsroot.rst. 2502 2503 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2504 IPC identifiers from 32,768 to 16,777,216. 2505 2506 ipe.enforce= [IPE] 2507 Format: <bool> 2508 Determine whether IPE starts in permissive (0) or 2509 enforce (1) mode. The default is enforce. 2510 2511 ipe.success_audit= 2512 [IPE] 2513 Format: <bool> 2514 Start IPE with success auditing enabled, emitting 2515 an audit event when a binary is allowed. The default 2516 is 0. 2517 2518 irqaffinity= [SMP] Set the default irq affinity mask 2519 The argument is a cpu list, as described above. 2520 2521 irqchip.gicv2_force_probe= 2522 [ARM,ARM64,EARLY] 2523 Format: <bool> 2524 Force the kernel to look for the second 4kB page 2525 of a GICv2 controller even if the memory range 2526 exposed by the device tree is too small. 2527 2528 irqchip.gicv3_nolpi= 2529 [ARM,ARM64,EARLY] 2530 Force the kernel to ignore the availability of 2531 LPIs (and by consequence ITSs). Intended for system 2532 that use the kernel as a bootloader, and thus want 2533 to let secondary kernels in charge of setting up 2534 LPIs. 2535 2536 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2537 Enables support for pseudo-NMIs in the kernel. This 2538 requires the kernel to be built with 2539 CONFIG_ARM64_PSEUDO_NMI. 2540 2541 irqfixup [HW] 2542 When an interrupt is not handled search all handlers 2543 for it. Intended to get systems with badly broken 2544 firmware running. 2545 2546 irqpoll [HW] 2547 When an interrupt is not handled search all handlers 2548 for it. Also check all handlers each timer 2549 interrupt. Intended to get systems with badly broken 2550 firmware running. 2551 2552 isapnp= [ISAPNP] 2553 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2554 2555 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2556 [Deprecated - use cpusets instead] 2557 Format: [flag-list,]<cpu-list> 2558 2559 Specify one or more CPUs to isolate from disturbances 2560 specified in the flag list (default: domain): 2561 2562 nohz 2563 Disable the tick when a single task runs as well as 2564 disabling other kernel noises like having RCU callbacks 2565 offloaded. This is equivalent to the nohz_full parameter. 2566 2567 A residual 1Hz tick is offloaded to workqueues, which you 2568 need to affine to housekeeping through the global 2569 workqueue's affinity configured via the 2570 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2571 by using the 'domain' flag described below. 2572 2573 NOTE: by default the global workqueue runs on all CPUs, 2574 so to protect individual CPUs the 'cpumask' file has to 2575 be configured manually after bootup. 2576 2577 domain 2578 Isolate from the general SMP balancing and scheduling 2579 algorithms. Note that performing domain isolation this way 2580 is irreversible: it's not possible to bring back a CPU to 2581 the domains once isolated through isolcpus. It's strongly 2582 advised to use cpusets instead to disable scheduler load 2583 balancing through the "cpuset.sched_load_balance" file. 2584 It offers a much more flexible interface where CPUs can 2585 move in and out of an isolated set anytime. 2586 2587 You can move a process onto or off an "isolated" CPU via 2588 the CPU affinity syscalls or cpuset. 2589 <cpu number> begins at 0 and the maximum value is 2590 "number of CPUs in system - 1". 2591 2592 managed_irq 2593 2594 Isolate from being targeted by managed interrupts 2595 which have an interrupt mask containing isolated 2596 CPUs. The affinity of managed interrupts is 2597 handled by the kernel and cannot be changed via 2598 the /proc/irq/* interfaces. 2599 2600 This isolation is best effort and only effective 2601 if the automatically assigned interrupt mask of a 2602 device queue contains isolated and housekeeping 2603 CPUs. If housekeeping CPUs are online then such 2604 interrupts are directed to the housekeeping CPU 2605 so that IO submitted on the housekeeping CPU 2606 cannot disturb the isolated CPU. 2607 2608 If a queue's affinity mask contains only isolated 2609 CPUs then this parameter has no effect on the 2610 interrupt routing decision, though interrupts are 2611 only delivered when tasks running on those 2612 isolated CPUs submit IO. IO submitted on 2613 housekeeping CPUs has no influence on those 2614 queues. 2615 2616 The format of <cpu-list> is described above. 2617 2618 iucv= [HW,NET] 2619 2620 ivrs_ioapic [HW,X86-64] 2621 Provide an override to the IOAPIC-ID<->DEVICE-ID 2622 mapping provided in the IVRS ACPI table. 2623 By default, PCI segment is 0, and can be omitted. 2624 2625 For example, to map IOAPIC-ID decimal 10 to 2626 PCI segment 0x1 and PCI device 00:14.0, 2627 write the parameter as: 2628 ivrs_ioapic=10@0001:00:14.0 2629 2630 Deprecated formats: 2631 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2632 write the parameter as: 2633 ivrs_ioapic[10]=00:14.0 2634 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2635 PCI device 00:14.0 write the parameter as: 2636 ivrs_ioapic[10]=0001:00:14.0 2637 2638 ivrs_hpet [HW,X86-64] 2639 Provide an override to the HPET-ID<->DEVICE-ID 2640 mapping provided in the IVRS ACPI table. 2641 By default, PCI segment is 0, and can be omitted. 2642 2643 For example, to map HPET-ID decimal 10 to 2644 PCI segment 0x1 and PCI device 00:14.0, 2645 write the parameter as: 2646 ivrs_hpet=10@0001:00:14.0 2647 2648 Deprecated formats: 2649 * To map HPET-ID decimal 0 to PCI device 00:14.0 2650 write the parameter as: 2651 ivrs_hpet[0]=00:14.0 2652 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2653 PCI device 00:14.0 write the parameter as: 2654 ivrs_ioapic[10]=0001:00:14.0 2655 2656 ivrs_acpihid [HW,X86-64] 2657 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2658 mapping provided in the IVRS ACPI table. 2659 By default, PCI segment is 0, and can be omitted. 2660 2661 For example, to map UART-HID:UID AMD0020:0 to 2662 PCI segment 0x1 and PCI device ID 00:14.5, 2663 write the parameter as: 2664 ivrs_acpihid=AMD0020:0@0001:00:14.5 2665 2666 Deprecated formats: 2667 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2668 PCI device ID 00:14.5, write the parameter as: 2669 ivrs_acpihid[00:14.5]=AMD0020:0 2670 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2671 PCI device ID 00:14.5, write the parameter as: 2672 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2673 2674 js= [HW,JOY] Analog joystick 2675 See Documentation/input/joydev/joystick.rst. 2676 2677 kasan_multi_shot 2678 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2679 report on every invalid memory access. Without this 2680 parameter KASAN will print report only for the first 2681 invalid access. 2682 2683 keep_bootcon [KNL,EARLY] 2684 Do not unregister boot console at start. This is only 2685 useful for debugging when something happens in the window 2686 between unregistering the boot console and initializing 2687 the real console. 2688 2689 keepinitrd [HW,ARM] See retain_initrd. 2690 2691 kernelcore= [KNL,X86,PPC,EARLY] 2692 Format: nn[KMGTPE] | nn% | "mirror" 2693 This parameter specifies the amount of memory usable by 2694 the kernel for non-movable allocations. The requested 2695 amount is spread evenly throughout all nodes in the 2696 system as ZONE_NORMAL. The remaining memory is used for 2697 movable memory in its own zone, ZONE_MOVABLE. In the 2698 event, a node is too small to have both ZONE_NORMAL and 2699 ZONE_MOVABLE, kernelcore memory will take priority and 2700 other nodes will have a larger ZONE_MOVABLE. 2701 2702 ZONE_MOVABLE is used for the allocation of pages that 2703 may be reclaimed or moved by the page migration 2704 subsystem. Note that allocations like PTEs-from-HighMem 2705 still use the HighMem zone if it exists, and the Normal 2706 zone if it does not. 2707 2708 It is possible to specify the exact amount of memory in 2709 the form of "nn[KMGTPE]", a percentage of total system 2710 memory in the form of "nn%", or "mirror". If "mirror" 2711 option is specified, mirrored (reliable) memory is used 2712 for non-movable allocations and remaining memory is used 2713 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2714 are exclusive, so you cannot specify multiple forms. 2715 2716 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2717 Format: <Controller#>[,poll interval] 2718 The controller # is the number of the ehci usb debug 2719 port as it is probed via PCI. The poll interval is 2720 optional and is the number seconds in between 2721 each poll cycle to the debug port in case you need 2722 the functionality for interrupting the kernel with 2723 gdb or control-c on the dbgp connection. When 2724 not using this parameter you use sysrq-g to break into 2725 the kernel debugger. 2726 2727 kgdboc= [KGDB,HW] kgdb over consoles. 2728 Requires a tty driver that supports console polling, 2729 or a supported polling keyboard driver (non-usb). 2730 Serial only format: <serial_device>[,baud] 2731 keyboard only format: kbd 2732 keyboard and serial format: kbd,<serial_device>[,baud] 2733 Optional Kernel mode setting: 2734 kms, kbd format: kms,kbd 2735 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2736 2737 kgdboc_earlycon= [KGDB,HW,EARLY] 2738 If the boot console provides the ability to read 2739 characters and can work in polling mode, you can use 2740 this parameter to tell kgdb to use it as a backend 2741 until the normal console is registered. Intended to 2742 be used together with the kgdboc parameter which 2743 specifies the normal console to transition to. 2744 2745 The name of the early console should be specified 2746 as the value of this parameter. Note that the name of 2747 the early console might be different than the tty 2748 name passed to kgdboc. It's OK to leave the value 2749 blank and the first boot console that implements 2750 read() will be picked. 2751 2752 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 2753 kernel debugger at the earliest opportunity. 2754 2755 kho= [KEXEC,EARLY] 2756 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 2757 Enables or disables Kexec HandOver. 2758 "0" | "off" | "n" - kexec handover is disabled 2759 "1" | "on" | "y" - kexec handover is enabled 2760 2761 kho_scratch= [KEXEC,EARLY] 2762 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 2763 Defines the size of the KHO scratch region. The KHO 2764 scratch regions are physically contiguous memory 2765 ranges that can only be used for non-kernel 2766 allocations. That way, even when memory is heavily 2767 fragmented with handed over memory, the kexeced 2768 kernel will always have enough contiguous ranges to 2769 bootstrap itself. 2770 2771 It is possible to specify the exact amount of 2772 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 2773 where the first parameter defines the size of a low 2774 memory scratch area, the second parameter defines 2775 the size of a global scratch area and the third 2776 parameter defines the size of additional per-node 2777 scratch areas. The form "nn%" defines scale factor 2778 (in percents) of memory that was used during boot. 2779 2780 kmac= [MIPS] Korina ethernet MAC address. 2781 Configure the RouterBoard 532 series on-chip 2782 Ethernet adapter MAC address. 2783 2784 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 2785 Valid arguments: on, off 2786 Default: on 2787 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2788 the default is off. 2789 2790 kprobe_event=[probe-list] 2791 [FTRACE] Add kprobe events and enable at boot time. 2792 The probe-list is a semicolon delimited list of probe 2793 definitions. Each definition is same as kprobe_events 2794 interface, but the parameters are comma delimited. 2795 For example, to add a kprobe event on vfs_read with 2796 arg1 and arg2, add to the command line; 2797 2798 kprobe_event=p,vfs_read,$arg1,$arg2 2799 2800 See also Documentation/trace/kprobetrace.rst "Kernel 2801 Boot Parameter" section. 2802 2803 kpti= [ARM64,EARLY] Control page table isolation of 2804 user and kernel address spaces. 2805 Default: enabled on cores which need mitigation. 2806 0: force disabled 2807 1: force enabled 2808 2809 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 2810 CONFIG_KUNIT to be set to be fully enabled. The 2811 default value can be overridden via 2812 KUNIT_DEFAULT_ENABLED. 2813 Default is 1 (enabled) 2814 2815 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2816 Default is 0 (don't ignore, but inject #GP) 2817 2818 kvm.eager_page_split= 2819 [KVM,X86] Controls whether or not KVM will try to 2820 proactively split all huge pages during dirty logging. 2821 Eager page splitting reduces interruptions to vCPU 2822 execution by eliminating the write-protection faults 2823 and MMU lock contention that would otherwise be 2824 required to split huge pages lazily. 2825 2826 VM workloads that rarely perform writes or that write 2827 only to a small region of VM memory may benefit from 2828 disabling eager page splitting to allow huge pages to 2829 still be used for reads. 2830 2831 The behavior of eager page splitting depends on whether 2832 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2833 disabled, all huge pages in a memslot will be eagerly 2834 split when dirty logging is enabled on that memslot. If 2835 enabled, eager page splitting will be performed during 2836 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2837 cleared. 2838 2839 Eager page splitting is only supported when kvm.tdp_mmu=Y. 2840 2841 Default is Y (on). 2842 2843 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 2844 If enabled, KVM will enable virtualization in hardware 2845 when KVM is loaded, and disable virtualization when KVM 2846 is unloaded (if KVM is built as a module). 2847 2848 If disabled, KVM will dynamically enable and disable 2849 virtualization on-demand when creating and destroying 2850 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 2851 number of VMs. 2852 2853 Enabling virtualization at module load avoids potential 2854 latency for creation of the 0=>1 VM, as KVM serializes 2855 virtualization enabling across all online CPUs. The 2856 "cost" of enabling virtualization when KVM is loaded, 2857 is that doing so may interfere with using out-of-tree 2858 hypervisors that want to "own" virtualization hardware. 2859 2860 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2861 Default is false (don't support). 2862 2863 kvm.nx_huge_pages= 2864 [KVM] Controls the software workaround for the 2865 X86_BUG_ITLB_MULTIHIT bug. 2866 force : Always deploy workaround. 2867 off : Never deploy workaround. 2868 auto : Deploy workaround based on the presence of 2869 X86_BUG_ITLB_MULTIHIT. 2870 2871 Default is 'auto'. 2872 2873 If the software workaround is enabled for the host, 2874 guests do need not to enable it for nested guests. 2875 2876 kvm.nx_huge_pages_recovery_ratio= 2877 [KVM] Controls how many 4KiB pages are periodically zapped 2878 back to huge pages. 0 disables the recovery, otherwise if 2879 the value is N KVM will zap 1/Nth of the 4KiB pages every 2880 period (see below). The default is 60. 2881 2882 kvm.nx_huge_pages_recovery_period_ms= 2883 [KVM] Controls the time period at which KVM zaps 4KiB pages 2884 back to huge pages. If the value is a non-zero N, KVM will 2885 zap a portion (see ratio above) of the pages every N msecs. 2886 If the value is 0 (the default), KVM will pick a period based 2887 on the ratio, such that a page is zapped after 1 hour on average. 2888 2889 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 2890 KVM/SVM. Default is 1 (enabled). 2891 2892 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 2893 a.k.a. Two-Dimensional Page Tables. Default is 1 2894 (enabled). Disable by KVM if hardware lacks support 2895 for NPT. 2896 2897 kvm-arm.mode= 2898 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 2899 operation. 2900 2901 none: Forcefully disable KVM. 2902 2903 nvhe: Standard nVHE-based mode, without support for 2904 protected guests. 2905 2906 protected: Mode with support for guests whose state is 2907 kept private from the host, using VHE or 2908 nVHE depending on HW support. 2909 2910 nested: VHE-based mode with support for nested 2911 virtualization. Requires at least ARMv8.4 2912 hardware (with FEAT_NV2). 2913 2914 Defaults to VHE/nVHE based on hardware support. Setting 2915 mode to "protected" will disable kexec and hibernation 2916 for the host. To force nVHE on VHE hardware, add 2917 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 2918 command-line. 2919 "nested" is experimental and should be used with 2920 extreme caution. 2921 2922 kvm-arm.vgic_v3_group0_trap= 2923 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 2924 system registers 2925 2926 kvm-arm.vgic_v3_group1_trap= 2927 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 2928 system registers 2929 2930 kvm-arm.vgic_v3_common_trap= 2931 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 2932 system registers 2933 2934 kvm-arm.vgic_v4_enable= 2935 [KVM,ARM,EARLY] Allow use of GICv4 for direct 2936 injection of LPIs. 2937 2938 kvm-arm.wfe_trap_policy= 2939 [KVM,ARM] Control when to set WFE instruction trap for 2940 KVM VMs. Traps are allowed but not guaranteed by the 2941 CPU architecture. 2942 2943 trap: set WFE instruction trap 2944 2945 notrap: clear WFE instruction trap 2946 2947 kvm-arm.wfi_trap_policy= 2948 [KVM,ARM] Control when to set WFI instruction trap for 2949 KVM VMs. Traps are allowed but not guaranteed by the 2950 CPU architecture. 2951 2952 trap: set WFI instruction trap 2953 2954 notrap: clear WFI instruction trap 2955 2956 kvm_cma_resv_ratio=n [PPC,EARLY] 2957 Reserves given percentage from system memory area for 2958 contiguous memory allocation for KVM hash pagetable 2959 allocation. 2960 By default it reserves 5% of total system memory. 2961 Format: <integer> 2962 Default: 5 2963 2964 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 2965 a.k.a. Two-Dimensional Page Tables. Default is 1 2966 (enabled). Disable by KVM if hardware lacks support 2967 for EPT. 2968 2969 kvm-intel.emulate_invalid_guest_state= 2970 [KVM,Intel] Control whether to emulate invalid guest 2971 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 2972 as guest state is never invalid for unrestricted 2973 guests. This param doesn't apply to nested guests (L2), 2974 as KVM never emulates invalid L2 guest state. 2975 Default is 1 (enabled). 2976 2977 kvm-intel.flexpriority= 2978 [KVM,Intel] Control KVM's use of FlexPriority feature 2979 (TPR shadow). Default is 1 (enabled). Disable by KVM if 2980 hardware lacks support for it. 2981 2982 kvm-intel.nested= 2983 [KVM,Intel] Control nested virtualization feature in 2984 KVM/VMX. Default is 1 (enabled). 2985 2986 kvm-intel.unrestricted_guest= 2987 [KVM,Intel] Control KVM's use of unrestricted guest 2988 feature (virtualized real and unpaged mode). Default 2989 is 1 (enabled). Disable by KVM if EPT is disabled or 2990 hardware lacks support for it. 2991 2992 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2993 CVE-2018-3620. 2994 2995 Valid arguments: never, cond, always 2996 2997 always: L1D cache flush on every VMENTER. 2998 cond: Flush L1D on VMENTER only when the code between 2999 VMEXIT and VMENTER can leak host memory. 3000 never: Disables the mitigation 3001 3002 Default is cond (do L1 cache flush in specific instances) 3003 3004 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3005 Identification feature (tagged TLBs). Default is 1 3006 (enabled). Disable by KVM if hardware lacks support 3007 for it. 3008 3009 l1d_flush= [X86,INTEL,EARLY] 3010 Control mitigation for L1D based snooping vulnerability. 3011 3012 Certain CPUs are vulnerable to an exploit against CPU 3013 internal buffers which can forward information to a 3014 disclosure gadget under certain conditions. 3015 3016 In vulnerable processors, the speculatively 3017 forwarded data can be used in a cache side channel 3018 attack, to access data to which the attacker does 3019 not have direct access. 3020 3021 This parameter controls the mitigation. The 3022 options are: 3023 3024 on - enable the interface for the mitigation 3025 3026 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3027 affected CPUs 3028 3029 The kernel PTE inversion protection is unconditionally 3030 enabled and cannot be disabled. 3031 3032 full 3033 Provides all available mitigations for the 3034 L1TF vulnerability. Disables SMT and 3035 enables all mitigations in the 3036 hypervisors, i.e. unconditional L1D flush. 3037 3038 SMT control and L1D flush control via the 3039 sysfs interface is still possible after 3040 boot. Hypervisors will issue a warning 3041 when the first VM is started in a 3042 potentially insecure configuration, 3043 i.e. SMT enabled or L1D flush disabled. 3044 3045 full,force 3046 Same as 'full', but disables SMT and L1D 3047 flush runtime control. Implies the 3048 'nosmt=force' command line option. 3049 (i.e. sysfs control of SMT is disabled.) 3050 3051 flush 3052 Leaves SMT enabled and enables the default 3053 hypervisor mitigation, i.e. conditional 3054 L1D flush. 3055 3056 SMT control and L1D flush control via the 3057 sysfs interface is still possible after 3058 boot. Hypervisors will issue a warning 3059 when the first VM is started in a 3060 potentially insecure configuration, 3061 i.e. SMT enabled or L1D flush disabled. 3062 3063 flush,nosmt 3064 3065 Disables SMT and enables the default 3066 hypervisor mitigation. 3067 3068 SMT control and L1D flush control via the 3069 sysfs interface is still possible after 3070 boot. Hypervisors will issue a warning 3071 when the first VM is started in a 3072 potentially insecure configuration, 3073 i.e. SMT enabled or L1D flush disabled. 3074 3075 flush,nowarn 3076 Same as 'flush', but hypervisors will not 3077 warn when a VM is started in a potentially 3078 insecure configuration. 3079 3080 off 3081 Disables hypervisor mitigations and doesn't 3082 emit any warnings. 3083 It also drops the swap size and available 3084 RAM limit restriction on both hypervisor and 3085 bare metal. 3086 3087 Default is 'flush'. 3088 3089 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3090 3091 l2cr= [PPC] 3092 3093 l3cr= [PPC] 3094 3095 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3096 disabled it. 3097 3098 lapic= [X86,APIC] Do not use TSC deadline 3099 value for LAPIC timer one-shot implementation. Default 3100 back to the programmable timer unit in the LAPIC. 3101 Format: notscdeadline 3102 3103 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3104 in C2 power state. 3105 3106 libata.dma= [LIBATA] DMA control 3107 libata.dma=0 Disable all PATA and SATA DMA 3108 libata.dma=1 PATA and SATA Disk DMA only 3109 libata.dma=2 ATAPI (CDROM) DMA only 3110 libata.dma=4 Compact Flash DMA only 3111 Combinations also work, so libata.dma=3 enables DMA 3112 for disks and CDROMs, but not CFs. 3113 3114 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3115 libata.ignore_hpa=0 keep BIOS limits (default) 3116 libata.ignore_hpa=1 ignore limits, using full disk 3117 3118 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3119 when set. 3120 Format: <int> 3121 3122 libata.force= [LIBATA] Force configurations. The format is a comma- 3123 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3124 PORT and DEVICE are decimal numbers matching port, link 3125 or device. Basically, it matches the ATA ID string 3126 printed on console by libata. If the whole ID part is 3127 omitted, the last PORT and DEVICE values are used. If 3128 ID hasn't been specified yet, the configuration applies 3129 to all ports, links and devices. 3130 3131 If only DEVICE is omitted, the parameter applies to 3132 the port and all links and devices behind it. DEVICE 3133 number of 0 either selects the first device or the 3134 first fan-out link behind PMP device. It does not 3135 select the host link. DEVICE number of 15 selects the 3136 host link and device attached to it. 3137 3138 The VAL specifies the configuration to force. As long 3139 as there is no ambiguity, shortcut notation is allowed. 3140 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3141 The following configurations can be forced. 3142 3143 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3144 Any ID with matching PORT is used. 3145 3146 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3147 3148 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3149 udma[/][16,25,33,44,66,100,133] notation is also 3150 allowed. 3151 3152 * nohrst, nosrst, norst: suppress hard, soft and both 3153 resets. 3154 3155 * rstonce: only attempt one reset during hot-unplug 3156 link recovery. 3157 3158 * [no]dbdelay: Enable or disable the extra 200ms delay 3159 before debouncing a link PHY and device presence 3160 detection. 3161 3162 * [no]ncq: Turn on or off NCQ. 3163 3164 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3165 3166 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3167 3168 * [no]trim: Enable or disable (unqueued) TRIM. 3169 3170 * trim_zero: Indicate that TRIM command zeroes data. 3171 3172 * max_trim_128m: Set 128M maximum trim size limit. 3173 3174 * [no]dma: Turn on or off DMA transfers. 3175 3176 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3177 3178 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3179 commands that are not a multiple of 16 bytes. 3180 3181 * [no]dmalog: Enable or disable the use of the 3182 READ LOG DMA EXT command to access logs. 3183 3184 * [no]iddevlog: Enable or disable access to the 3185 identify device data log. 3186 3187 * [no]logdir: Enable or disable access to the general 3188 purpose log directory. 3189 3190 * max_sec_128: Set transfer size limit to 128 sectors. 3191 3192 * max_sec_1024: Set or clear transfer size limit to 3193 1024 sectors. 3194 3195 * max_sec_lba48: Set or clear transfer size limit to 3196 65535 sectors. 3197 3198 * external: Mark port as external (hotplug-capable). 3199 3200 * [no]lpm: Enable or disable link power management. 3201 3202 * [no]setxfer: Indicate if transfer speed mode setting 3203 should be skipped. 3204 3205 * [no]fua: Disable or enable FUA (Force Unit Access) 3206 support for devices supporting this feature. 3207 3208 * dump_id: Dump IDENTIFY data. 3209 3210 * disable: Disable this device. 3211 3212 If there are multiple matching configurations changing 3213 the same attribute, the last one is used. 3214 3215 load_ramdisk= [RAM] [Deprecated] 3216 3217 lockd.nlm_grace_period=P [NFS] Assign grace period. 3218 Format: <integer> 3219 3220 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3221 Format: <integer> 3222 3223 lockd.nlm_timeout=T [NFS] Assign timeout value. 3224 Format: <integer> 3225 3226 lockd.nlm_udpport=M [NFS] Assign UDP port. 3227 Format: <integer> 3228 3229 lockdown= [SECURITY,EARLY] 3230 { integrity | confidentiality } 3231 Enable the kernel lockdown feature. If set to 3232 integrity, kernel features that allow userland to 3233 modify the running kernel are disabled. If set to 3234 confidentiality, kernel features that allow userland 3235 to extract confidential information from the kernel 3236 are also disabled. 3237 3238 locktorture.acq_writer_lim= [KNL] 3239 Set the time limit in jiffies for a lock 3240 acquisition. Acquisitions exceeding this limit 3241 will result in a splat once they do complete. 3242 3243 locktorture.bind_readers= [KNL] 3244 Specify the list of CPUs to which the readers are 3245 to be bound. 3246 3247 locktorture.bind_writers= [KNL] 3248 Specify the list of CPUs to which the writers are 3249 to be bound. 3250 3251 locktorture.call_rcu_chains= [KNL] 3252 Specify the number of self-propagating call_rcu() 3253 chains to set up. These are used to ensure that 3254 there is a high probability of an RCU grace period 3255 in progress at any given time. Defaults to 0, 3256 which disables these call_rcu() chains. 3257 3258 locktorture.long_hold= [KNL] 3259 Specify the duration in milliseconds for the 3260 occasional long-duration lock hold time. Defaults 3261 to 100 milliseconds. Select 0 to disable. 3262 3263 locktorture.nested_locks= [KNL] 3264 Specify the maximum lock nesting depth that 3265 locktorture is to exercise, up to a limit of 8 3266 (MAX_NESTED_LOCKS). Specify zero to disable. 3267 Note that this parameter is ineffective on types 3268 of locks that do not support nested acquisition. 3269 3270 locktorture.nreaders_stress= [KNL] 3271 Set the number of locking read-acquisition kthreads. 3272 Defaults to being automatically set based on the 3273 number of online CPUs. 3274 3275 locktorture.nwriters_stress= [KNL] 3276 Set the number of locking write-acquisition kthreads. 3277 3278 locktorture.onoff_holdoff= [KNL] 3279 Set time (s) after boot for CPU-hotplug testing. 3280 3281 locktorture.onoff_interval= [KNL] 3282 Set time (s) between CPU-hotplug operations, or 3283 zero to disable CPU-hotplug testing. 3284 3285 locktorture.rt_boost= [KNL] 3286 Do periodic testing of real-time lock priority 3287 boosting. Select 0 to disable, 1 to boost 3288 only rt_mutex, and 2 to boost unconditionally. 3289 Defaults to 2, which might seem to be an 3290 odd choice, but which should be harmless for 3291 non-real-time spinlocks, due to their disabling 3292 of preemption. Note that non-realtime mutexes 3293 disable boosting. 3294 3295 locktorture.rt_boost_factor= [KNL] 3296 Number that determines how often and for how 3297 long priority boosting is exercised. This is 3298 scaled down by the number of writers, so that the 3299 number of boosts per unit time remains roughly 3300 constant as the number of writers increases. 3301 On the other hand, the duration of each boost 3302 increases with the number of writers. 3303 3304 locktorture.shuffle_interval= [KNL] 3305 Set task-shuffle interval (jiffies). Shuffling 3306 tasks allows some CPUs to go into dyntick-idle 3307 mode during the locktorture test. 3308 3309 locktorture.shutdown_secs= [KNL] 3310 Set time (s) after boot system shutdown. This 3311 is useful for hands-off automated testing. 3312 3313 locktorture.stat_interval= [KNL] 3314 Time (s) between statistics printk()s. 3315 3316 locktorture.stutter= [KNL] 3317 Time (s) to stutter testing, for example, 3318 specifying five seconds causes the test to run for 3319 five seconds, wait for five seconds, and so on. 3320 This tests the locking primitive's ability to 3321 transition abruptly to and from idle. 3322 3323 locktorture.torture_type= [KNL] 3324 Specify the locking implementation to test. 3325 3326 locktorture.verbose= [KNL] 3327 Enable additional printk() statements. 3328 3329 locktorture.writer_fifo= [KNL] 3330 Run the write-side locktorture kthreads at 3331 sched_set_fifo() real-time priority. 3332 3333 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3334 Format: <irq> 3335 3336 loglevel= [KNL,EARLY] 3337 All Kernel Messages with a loglevel smaller than the 3338 console loglevel will be printed to the console. It can 3339 also be changed with klogd or other programs. The 3340 loglevels are defined as follows: 3341 3342 0 (KERN_EMERG) system is unusable 3343 1 (KERN_ALERT) action must be taken immediately 3344 2 (KERN_CRIT) critical conditions 3345 3 (KERN_ERR) error conditions 3346 4 (KERN_WARNING) warning conditions 3347 5 (KERN_NOTICE) normal but significant condition 3348 6 (KERN_INFO) informational 3349 7 (KERN_DEBUG) debug-level messages 3350 3351 log_buf_len=n[KMG] [KNL,EARLY] 3352 Sets the size of the printk ring buffer, in bytes. 3353 n must be a power of two and greater than the 3354 minimal size. The minimal size is defined by 3355 LOG_BUF_SHIFT kernel config parameter. There 3356 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3357 parameter that allows to increase the default size 3358 depending on the number of CPUs. See init/Kconfig 3359 for more details. 3360 3361 logo.nologo [FB] Disables display of the built-in Linux logo. 3362 This may be used to provide more screen space for 3363 kernel log messages and is useful when debugging 3364 kernel boot problems. 3365 3366 lp=0 [LP] Specify parallel ports to use, e.g, 3367 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3368 lp=reset first parallel port). 'lp=0' disables the 3369 lp=auto printer driver. 'lp=reset' (which can be 3370 specified in addition to the ports) causes 3371 attached printers to be reset. Using 3372 lp=port1,port2,... specifies the parallel ports 3373 to associate lp devices with, starting with 3374 lp0. A port specification may be 'none' to skip 3375 that lp device, or a parport name such as 3376 'parport0'. Specifying 'lp=auto' instead of a 3377 port specification list means that device IDs 3378 from each port should be examined, to see if 3379 an IEEE 1284-compliant printer is attached; if 3380 so, the driver will manage that printer. 3381 See also header of drivers/char/lp.c. 3382 3383 lpj=n [KNL] 3384 Sets loops_per_jiffy to given constant, thus avoiding 3385 time-consuming boot-time autodetection (up to 250 ms per 3386 CPU). 0 enables autodetection (default). To determine 3387 the correct value for your kernel, boot with normal 3388 autodetection and see what value is printed. Note that 3389 on SMP systems the preset will be applied to all CPUs, 3390 which is likely to cause problems if your CPUs need 3391 significantly divergent settings. An incorrect value 3392 will cause delays in the kernel to be wrong, leading to 3393 unpredictable I/O errors and other breakage. Although 3394 unlikely, in the extreme case this might damage your 3395 hardware. 3396 3397 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3398 3399 lsm=lsm1,...,lsmN 3400 [SECURITY] Choose order of LSM initialization. This 3401 overrides CONFIG_LSM, and the "security=" parameter. 3402 3403 machtype= [Loongson] Share the same kernel image file between 3404 different yeeloong laptops. 3405 Example: machtype=lemote-yeeloong-2f-7inch 3406 3407 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3408 will bring up during bootup. maxcpus=n : n >= 0 limits 3409 the kernel to bring up 'n' processors. Surely after 3410 bootup you can bring up the other plugged cpu by executing 3411 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3412 only takes effect during system bootup. 3413 While n=0 is a special case, it is equivalent to "nosmp", 3414 which also disables the IO APIC. 3415 3416 max_loop= [LOOP] The number of loop block devices that get 3417 (loop.max_loop) unconditionally pre-created at init time. The default 3418 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3419 of statically allocating a predefined number, loop 3420 devices can be requested on-demand with the 3421 /dev/loop-control interface. 3422 3423 mce= [X86-{32,64}] 3424 3425 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3426 3427 off 3428 disable machine check 3429 3430 no_cmci 3431 disable CMCI(Corrected Machine Check Interrupt) that 3432 Intel processor supports. Usually this disablement is 3433 not recommended, but it might be handy if your 3434 hardware is misbehaving. 3435 3436 Note that you'll get more problems without CMCI than 3437 with due to the shared banks, i.e. you might get 3438 duplicated error logs. 3439 3440 dont_log_ce 3441 don't make logs for corrected errors. All events 3442 reported as corrected are silently cleared by OS. This 3443 option will be useful if you have no interest in any 3444 of corrected errors. 3445 3446 ignore_ce 3447 disable features for corrected errors, e.g. 3448 polling timer and CMCI. All events reported as 3449 corrected are not cleared by OS and remained in its 3450 error banks. 3451 3452 Usually this disablement is not recommended, however 3453 if there is an agent checking/clearing corrected 3454 errors (e.g. BIOS or hardware monitoring 3455 applications), conflicting with OS's error handling, 3456 and you cannot deactivate the agent, then this option 3457 will be a help. 3458 3459 no_lmce 3460 do not opt-in to Local MCE delivery. Use legacy method 3461 to broadcast MCEs. 3462 3463 bootlog 3464 enable logging of machine checks left over from 3465 booting. Disabled by default on AMD Fam10h and older 3466 because some BIOS leave bogus ones. 3467 3468 If your BIOS doesn't do that it's a good idea to 3469 enable though to make sure you log even machine check 3470 events that result in a reboot. On Intel systems it is 3471 enabled by default. 3472 3473 nobootlog 3474 disable boot machine check logging. 3475 3476 monarchtimeout (number) 3477 sets the time in us to wait for other CPUs on machine 3478 checks. 0 to disable. 3479 3480 bios_cmci_threshold 3481 don't overwrite the bios-set CMCI threshold. This boot 3482 option prevents Linux from overwriting the CMCI 3483 threshold set by the bios. Without this option, Linux 3484 always sets the CMCI threshold to 1. Enabling this may 3485 make memory predictive failure analysis less effective 3486 if the bios sets thresholds for memory errors since we 3487 will not see details for all errors. 3488 3489 recovery 3490 force-enable recoverable machine check code paths 3491 3492 Everything else is in sysfs now. 3493 3494 3495 md= [HW] RAID subsystems devices and level 3496 See Documentation/admin-guide/md.rst. 3497 3498 mdacon= [MDA] 3499 Format: <first>,<last> 3500 Specifies range of consoles to be captured by the MDA. 3501 3502 mds= [X86,INTEL,EARLY] 3503 Control mitigation for the Micro-architectural Data 3504 Sampling (MDS) vulnerability. 3505 3506 Certain CPUs are vulnerable to an exploit against CPU 3507 internal buffers which can forward information to a 3508 disclosure gadget under certain conditions. 3509 3510 In vulnerable processors, the speculatively 3511 forwarded data can be used in a cache side channel 3512 attack, to access data to which the attacker does 3513 not have direct access. 3514 3515 This parameter controls the MDS mitigation. The 3516 options are: 3517 3518 full - Enable MDS mitigation on vulnerable CPUs 3519 full,nosmt - Enable MDS mitigation and disable 3520 SMT on vulnerable CPUs 3521 off - Unconditionally disable MDS mitigation 3522 3523 On TAA-affected machines, mds=off can be prevented by 3524 an active TAA mitigation as both vulnerabilities are 3525 mitigated with the same mechanism so in order to disable 3526 this mitigation, you need to specify tsx_async_abort=off 3527 too. 3528 3529 Not specifying this option is equivalent to 3530 mds=full. 3531 3532 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3533 3534 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3535 Must be specified, otherwise memory size will be 0. 3536 3537 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3538 of memory Amount of memory to be used in cases 3539 as follows: 3540 3541 1 for test; 3542 2 when the kernel is not able to see the whole system memory; 3543 3 memory that lies after 'mem=' boundary is excluded from 3544 the hypervisor, then assigned to KVM guests. 3545 4 to limit the memory available for kdump kernel. 3546 3547 [ARC,MICROBLAZE] - the limit applies only to low memory, 3548 high memory is not affected. 3549 3550 [ARM64] - only limits memory covered by the linear 3551 mapping. The NOMAP regions are not affected. 3552 3553 [X86] Work as limiting max address. Use together 3554 with memmap= to avoid physical address space collisions. 3555 Without memmap= PCI devices could be placed at addresses 3556 belonging to unused RAM. 3557 3558 Note that this only takes effects during boot time since 3559 in above case 3, memory may need be hot added after boot 3560 if system memory of hypervisor is not sufficient. 3561 3562 mem=nn[KMG]@ss[KMG] 3563 [ARM,MIPS,EARLY] - override the memory layout 3564 reported by firmware. 3565 Define a memory region of size nn[KMG] starting at 3566 ss[KMG]. 3567 Multiple different regions can be specified with 3568 multiple mem= parameters on the command line. 3569 3570 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3571 memory. 3572 3573 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3574 3575 memchunk=nn[KMG] 3576 [KNL,SH] Allow user to override the default size for 3577 per-device physically contiguous DMA buffers. 3578 3579 memhp_default_state=online/offline/online_kernel/online_movable 3580 [KNL] Set the initial state for the memory hotplug 3581 onlining policy. If not specified, the default value is 3582 set according to the 3583 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3584 options. 3585 See Documentation/admin-guide/mm/memory-hotplug.rst. 3586 3587 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3588 E820 memory map, as specified by the user. 3589 Such memmap=exactmap lines can be constructed based on 3590 BIOS output or other requirements. See the memmap=nn@ss 3591 option description. 3592 3593 memmap=nn[KMG]@ss[KMG] 3594 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3595 Region of memory to be used is from ss to ss+nn. 3596 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3597 which limits max address to nn[KMG]. 3598 Multiple different regions can be specified, 3599 comma delimited. 3600 Example: 3601 memmap=100M@2G,100M#3G,1G!1024G 3602 3603 memmap=nn[KMG]#ss[KMG] 3604 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3605 Region of memory to be marked is from ss to ss+nn. 3606 3607 memmap=nn[KMG]$ss[KMG] 3608 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3609 Region of memory to be reserved is from ss to ss+nn. 3610 Example: Exclude memory from 0x18690000-0x1869ffff 3611 memmap=64K$0x18690000 3612 or 3613 memmap=0x10000$0x18690000 3614 Some bootloaders may need an escape character before '$', 3615 like Grub2, otherwise '$' and the following number 3616 will be eaten. 3617 3618 memmap=nn[KMG]!ss[KMG,EARLY] 3619 [KNL,X86] Mark specific memory as protected. 3620 Region of memory to be used, from ss to ss+nn. 3621 The memory region may be marked as e820 type 12 (0xc) 3622 and is NVDIMM or ADR memory. 3623 3624 memmap=<size>%<offset>-<oldtype>+<newtype> 3625 [KNL,ACPI,EARLY] Convert memory within the specified region 3626 from <oldtype> to <newtype>. If "-<oldtype>" is left 3627 out, the whole region will be marked as <newtype>, 3628 even if previously unavailable. If "+<newtype>" is left 3629 out, matching memory will be removed. Types are 3630 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3631 3 = ACPI, 12 = PRAM. 3632 3633 memory_corruption_check=0/1 [X86,EARLY] 3634 Some BIOSes seem to corrupt the first 64k of 3635 memory when doing things like suspend/resume. 3636 Setting this option will scan the memory 3637 looking for corruption. Enabling this will 3638 both detect corruption and prevent the kernel 3639 from using the memory being corrupted. 3640 However, its intended as a diagnostic tool; if 3641 repeatable BIOS-originated corruption always 3642 affects the same memory, you can use memmap= 3643 to prevent the kernel from using that memory. 3644 3645 memory_corruption_check_size=size [X86,EARLY] 3646 By default it checks for corruption in the low 3647 64k, making this memory unavailable for normal 3648 use. Use this parameter to scan for 3649 corruption in more or less memory. 3650 3651 memory_corruption_check_period=seconds [X86,EARLY] 3652 By default it checks for corruption every 60 3653 seconds. Use this parameter to check at some 3654 other rate. 0 disables periodic checking. 3655 3656 memory_hotplug.memmap_on_memory 3657 [KNL,X86,ARM] Boolean flag to enable this feature. 3658 Format: {on | off (default)} 3659 When enabled, runtime hotplugged memory will 3660 allocate its internal metadata (struct pages, 3661 those vmemmap pages cannot be optimized even 3662 if hugetlb_free_vmemmap is enabled) from the 3663 hotadded memory which will allow to hotadd a 3664 lot of memory without requiring additional 3665 memory to do so. 3666 This feature is disabled by default because it 3667 has some implication on large (e.g. GB) 3668 allocations in some configurations (e.g. small 3669 memory blocks). 3670 The state of the flag can be read in 3671 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3672 Note that even when enabled, there are a few cases where 3673 the feature is not effective. 3674 3675 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 3676 Format: <integer> 3677 default : 0 <disable> 3678 Specifies the number of memtest passes to be 3679 performed. Each pass selects another test 3680 pattern from a given set of patterns. Memtest 3681 fills the memory with this pattern, validates 3682 memory contents and reserves bad memory 3683 regions that are detected. 3684 3685 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3686 Valid arguments: on, off 3687 Default: off 3688 mem_encrypt=on: Activate SME 3689 mem_encrypt=off: Do not activate SME 3690 3691 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3692 for details on when memory encryption can be activated. 3693 3694 mem_sleep_default= [SUSPEND] Default system suspend mode: 3695 s2idle - Suspend-To-Idle 3696 shallow - Power-On Suspend or equivalent (if supported) 3697 deep - Suspend-To-RAM or equivalent (if supported) 3698 See Documentation/admin-guide/pm/sleep-states.rst. 3699 3700 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3701 the BIOS has incorrectly applied a workaround. TinyBIOS 3702 version 0.98 is known to be affected, 0.99 fixes the 3703 problem by letting the user disable the workaround. 3704 3705 mga= [HW,DRM] 3706 3707 microcode.force_minrev= [X86] 3708 Format: <bool> 3709 Enable or disable the microcode minimal revision 3710 enforcement for the runtime microcode loader. 3711 3712 mini2440= [ARM,HW,KNL] 3713 Format:[0..2][b][c][t] 3714 Default: "0tb" 3715 MINI2440 configuration specification: 3716 0 - The attached screen is the 3.5" TFT 3717 1 - The attached screen is the 7" TFT 3718 2 - The VGA Shield is attached (1024x768) 3719 Leaving out the screen size parameter will not load 3720 the TFT driver, and the framebuffer will be left 3721 unconfigured. 3722 b - Enable backlight. The TFT backlight pin will be 3723 linked to the kernel VESA blanking code and a GPIO 3724 LED. This parameter is not necessary when using the 3725 VGA shield. 3726 c - Enable the s3c camera interface. 3727 t - Reserved for enabling touchscreen support. The 3728 touchscreen support is not enabled in the mainstream 3729 kernel as of 2.6.30, a preliminary port can be found 3730 in the "bleeding edge" mini2440 support kernel at 3731 https://repo.or.cz/w/linux-2.6/mini2440.git 3732 3733 mitigations= 3734 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 3735 CPU vulnerabilities. This is a set of curated, 3736 arch-independent options, each of which is an 3737 aggregation of existing arch-specific options. 3738 3739 Note, "mitigations" is supported if and only if the 3740 kernel was built with CPU_MITIGATIONS=y. 3741 3742 off 3743 Disable all optional CPU mitigations. This 3744 improves system performance, but it may also 3745 expose users to several CPU vulnerabilities. 3746 Equivalent to: if nokaslr then kpti=0 [ARM64] 3747 gather_data_sampling=off [X86] 3748 indirect_target_selection=off [X86] 3749 kvm.nx_huge_pages=off [X86] 3750 l1tf=off [X86] 3751 mds=off [X86] 3752 mmio_stale_data=off [X86] 3753 no_entry_flush [PPC] 3754 no_uaccess_flush [PPC] 3755 nobp=0 [S390] 3756 nopti [X86,PPC] 3757 nospectre_bhb [ARM64] 3758 nospectre_v1 [X86,PPC] 3759 nospectre_v2 [X86,PPC,S390,ARM64] 3760 reg_file_data_sampling=off [X86] 3761 retbleed=off [X86] 3762 spec_rstack_overflow=off [X86] 3763 spec_store_bypass_disable=off [X86,PPC] 3764 spectre_bhi=off [X86] 3765 spectre_v2_user=off [X86] 3766 srbds=off [X86,INTEL] 3767 ssbd=force-off [ARM64] 3768 tsx_async_abort=off [X86] 3769 3770 Exceptions: 3771 This does not have any effect on 3772 kvm.nx_huge_pages when 3773 kvm.nx_huge_pages=force. 3774 3775 auto (default) 3776 Mitigate all CPU vulnerabilities, but leave SMT 3777 enabled, even if it's vulnerable. This is for 3778 users who don't want to be surprised by SMT 3779 getting disabled across kernel upgrades, or who 3780 have other ways of avoiding SMT-based attacks. 3781 Equivalent to: (default behavior) 3782 3783 auto,nosmt 3784 Mitigate all CPU vulnerabilities, disabling SMT 3785 if needed. This is for users who always want to 3786 be fully mitigated, even if it means losing SMT. 3787 Equivalent to: l1tf=flush,nosmt [X86] 3788 mds=full,nosmt [X86] 3789 tsx_async_abort=full,nosmt [X86] 3790 mmio_stale_data=full,nosmt [X86] 3791 retbleed=auto,nosmt [X86] 3792 3793 mminit_loglevel= 3794 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 3795 parameter allows control of the logging verbosity for 3796 the additional memory initialisation checks. A value 3797 of 0 disables mminit logging and a level of 4 will 3798 log everything. Information is printed at KERN_DEBUG 3799 so loglevel=8 may also need to be specified. 3800 3801 mmio_stale_data= 3802 [X86,INTEL,EARLY] Control mitigation for the Processor 3803 MMIO Stale Data vulnerabilities. 3804 3805 Processor MMIO Stale Data is a class of 3806 vulnerabilities that may expose data after an MMIO 3807 operation. Exposed data could originate or end in 3808 the same CPU buffers as affected by MDS and TAA. 3809 Therefore, similar to MDS and TAA, the mitigation 3810 is to clear the affected CPU buffers. 3811 3812 This parameter controls the mitigation. The 3813 options are: 3814 3815 full - Enable mitigation on vulnerable CPUs 3816 3817 full,nosmt - Enable mitigation and disable SMT on 3818 vulnerable CPUs. 3819 3820 off - Unconditionally disable mitigation 3821 3822 On MDS or TAA affected machines, 3823 mmio_stale_data=off can be prevented by an active 3824 MDS or TAA mitigation as these vulnerabilities are 3825 mitigated with the same mechanism so in order to 3826 disable this mitigation, you need to specify 3827 mds=off and tsx_async_abort=off too. 3828 3829 Not specifying this option is equivalent to 3830 mmio_stale_data=full. 3831 3832 For details see: 3833 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 3834 3835 <module>.async_probe[=<bool>] [KNL] 3836 If no <bool> value is specified or if the value 3837 specified is not a valid <bool>, enable asynchronous 3838 probe on this module. Otherwise, enable/disable 3839 asynchronous probe on this module as indicated by the 3840 <bool> value. See also: module.async_probe 3841 3842 module.async_probe=<bool> 3843 [KNL] When set to true, modules will use async probing 3844 by default. To enable/disable async probing for a 3845 specific module, use the module specific control that 3846 is documented under <module>.async_probe. When both 3847 module.async_probe and <module>.async_probe are 3848 specified, <module>.async_probe takes precedence for 3849 the specific module. 3850 3851 module.enable_dups_trace 3852 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 3853 this means that duplicate request_module() calls will 3854 trigger a WARN_ON() instead of a pr_warn(). Note that 3855 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 3856 will always be issued and this option does nothing. 3857 module.sig_enforce 3858 [KNL] When CONFIG_MODULE_SIG is set, this means that 3859 modules without (valid) signatures will fail to load. 3860 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3861 is always true, so this option does nothing. 3862 3863 module_blacklist= [KNL] Do not load a comma-separated list of 3864 modules. Useful for debugging problem modules. 3865 3866 mousedev.tap_time= 3867 [MOUSE] Maximum time between finger touching and 3868 leaving touchpad surface for touch to be considered 3869 a tap and be reported as a left button click (for 3870 touchpads working in absolute mode only). 3871 Format: <msecs> 3872 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3873 reporting absolute coordinates, such as tablets 3874 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3875 reporting absolute coordinates, such as tablets 3876 3877 movablecore= [KNL,X86,PPC,EARLY] 3878 Format: nn[KMGTPE] | nn% 3879 This parameter is the complement to kernelcore=, it 3880 specifies the amount of memory used for migratable 3881 allocations. If both kernelcore and movablecore is 3882 specified, then kernelcore will be at *least* the 3883 specified value but may be more. If movablecore on its 3884 own is specified, the administrator must be careful 3885 that the amount of memory usable for all allocations 3886 is not too small. 3887 3888 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 3889 NUMA nodes to be movable. This means that the memory 3890 of such nodes will be usable only for movable 3891 allocations which rules out almost all kernel 3892 allocations. Use with caution! 3893 3894 MTD_Partition= [MTD] 3895 Format: <name>,<region-number>,<size>,<offset> 3896 3897 MTD_Region= [MTD] Format: 3898 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3899 3900 mtdparts= [MTD] 3901 See drivers/mtd/parsers/cmdlinepart.c 3902 3903 mtouchusb.raw_coordinates= 3904 [HW] Make the MicroTouch USB driver use raw coordinates 3905 ('y', default) or cooked coordinates ('n') 3906 3907 mtrr=debug [X86,EARLY] 3908 Enable printing debug information related to MTRR 3909 registers at boot time. 3910 3911 mtrr_chunk_size=nn[KMG,X86,EARLY] 3912 used for mtrr cleanup. It is largest continuous chunk 3913 that could hold holes aka. UC entries. 3914 3915 mtrr_gran_size=nn[KMG,X86,EARLY] 3916 Used for mtrr cleanup. It is granularity of mtrr block. 3917 Default is 1. 3918 Large value could prevent small alignment from 3919 using up MTRRs. 3920 3921 mtrr_spare_reg_nr=n [X86,EARLY] 3922 Format: <integer> 3923 Range: 0,7 : spare reg number 3924 Default : 1 3925 Used for mtrr cleanup. It is spare mtrr entries number. 3926 Set to 2 or more if your graphical card needs more. 3927 3928 multitce=off [PPC] This parameter disables the use of the pSeries 3929 firmware feature for updating multiple TCE entries 3930 at a time. 3931 3932 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3933 3934 netdev= [NET] Network devices parameters 3935 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3936 Note that mem_start is often overloaded to mean 3937 something different and driver-specific. 3938 This usage is only documented in each driver source 3939 file if at all. 3940 3941 netpoll.carrier_timeout= 3942 [NET] Specifies amount of time (in seconds) that 3943 netpoll should wait for a carrier. By default netpoll 3944 waits 4 seconds. 3945 3946 nf_conntrack.acct= 3947 [NETFILTER] Enable connection tracking flow accounting 3948 0 to disable accounting 3949 1 to enable accounting 3950 Default value is 0. 3951 3952 nfs.cache_getent= 3953 [NFS] sets the pathname to the program which is used 3954 to update the NFS client cache entries. 3955 3956 nfs.cache_getent_timeout= 3957 [NFS] sets the timeout after which an attempt to 3958 update a cache entry is deemed to have failed. 3959 3960 nfs.callback_nr_threads= 3961 [NFSv4] set the total number of threads that the 3962 NFS client will assign to service NFSv4 callback 3963 requests. 3964 3965 nfs.callback_tcpport= 3966 [NFS] set the TCP port on which the NFSv4 callback 3967 channel should listen. 3968 3969 nfs.delay_retrans= 3970 [NFS] specifies the number of times the NFSv4 client 3971 retries the request before returning an EAGAIN error, 3972 after a reply of NFS4ERR_DELAY from the server. 3973 Only applies if the softerr mount option is enabled, 3974 and the specified value is >= 0. 3975 3976 nfs.enable_ino64= 3977 [NFS] enable 64-bit inode numbers. 3978 If zero, the NFS client will fake up a 32-bit inode 3979 number for the readdir() and stat() syscalls instead 3980 of returning the full 64-bit number. 3981 The default is to return 64-bit inode numbers. 3982 3983 nfs.idmap_cache_timeout= 3984 [NFS] set the maximum lifetime for idmapper cache 3985 entries. 3986 3987 nfs.max_session_cb_slots= 3988 [NFSv4.1] Sets the maximum number of session 3989 slots the client will assign to the callback 3990 channel. This determines the maximum number of 3991 callbacks the client will process in parallel for 3992 a particular server. 3993 3994 nfs.max_session_slots= 3995 [NFSv4.1] Sets the maximum number of session slots 3996 the client will attempt to negotiate with the server. 3997 This limits the number of simultaneous RPC requests 3998 that the client can send to the NFSv4.1 server. 3999 Note that there is little point in setting this 4000 value higher than the max_tcp_slot_table_limit. 4001 4002 nfs.nfs4_disable_idmapping= 4003 [NFSv4] When set to the default of '1', this option 4004 ensures that both the RPC level authentication 4005 scheme and the NFS level operations agree to use 4006 numeric uids/gids if the mount is using the 4007 'sec=sys' security flavour. In effect it is 4008 disabling idmapping, which can make migration from 4009 legacy NFSv2/v3 systems to NFSv4 easier. 4010 Servers that do not support this mode of operation 4011 will be autodetected by the client, and it will fall 4012 back to using the idmapper. 4013 To turn off this behaviour, set the value to '0'. 4014 4015 nfs.nfs4_unique_id= 4016 [NFS4] Specify an additional fixed unique ident- 4017 ification string that NFSv4 clients can insert into 4018 their nfs_client_id4 string. This is typically a 4019 UUID that is generated at system install time. 4020 4021 nfs.recover_lost_locks= 4022 [NFSv4] Attempt to recover locks that were lost due 4023 to a lease timeout on the server. Please note that 4024 doing this risks data corruption, since there are 4025 no guarantees that the file will remain unchanged 4026 after the locks are lost. 4027 If you want to enable the kernel legacy behaviour of 4028 attempting to recover these locks, then set this 4029 parameter to '1'. 4030 The default parameter value of '0' causes the kernel 4031 not to attempt recovery of lost locks. 4032 4033 nfs.send_implementation_id= 4034 [NFSv4.1] Send client implementation identification 4035 information in exchange_id requests. 4036 If zero, no implementation identification information 4037 will be sent. 4038 The default is to send the implementation identification 4039 information. 4040 4041 nfs4.layoutstats_timer= 4042 [NFSv4.2] Change the rate at which the kernel sends 4043 layoutstats to the pNFS metadata server. 4044 4045 Setting this to value to 0 causes the kernel to use 4046 whatever value is the default set by the layout 4047 driver. A non-zero value sets the minimum interval 4048 in seconds between layoutstats transmissions. 4049 4050 nfsd.inter_copy_offload_enable= 4051 [NFSv4.2] When set to 1, the server will support 4052 server-to-server copies for which this server is 4053 the destination of the copy. 4054 4055 nfsd.nfs4_disable_idmapping= 4056 [NFSv4] When set to the default of '1', the NFSv4 4057 server will return only numeric uids and gids to 4058 clients using auth_sys, and will accept numeric uids 4059 and gids from such clients. This is intended to ease 4060 migration from NFSv2/v3. 4061 4062 nfsd.nfsd4_ssc_umount_timeout= 4063 [NFSv4.2] When used as the destination of a 4064 server-to-server copy, knfsd temporarily mounts 4065 the source server. It caches the mount in case 4066 it will be needed again, and discards it if not 4067 used for the number of milliseconds specified by 4068 this parameter. 4069 4070 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4071 See Documentation/admin-guide/nfs/nfsroot.rst. 4072 4073 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4074 See Documentation/admin-guide/nfs/nfsroot.rst. 4075 4076 nfsrootdebug [NFS] enable nfsroot debugging messages. 4077 See Documentation/admin-guide/nfs/nfsroot.rst. 4078 4079 nmi_backtrace.backtrace_idle [KNL] 4080 Dump stacks even of idle CPUs in response to an 4081 NMI stack-backtrace request. 4082 4083 nmi_debug= [KNL,SH] Specify one or more actions to take 4084 when a NMI is triggered. 4085 Format: [state][,regs][,debounce][,die] 4086 4087 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4088 Format: [panic,][nopanic,][rNNN,][num] 4089 Valid num: 0 or 1 4090 0 - turn hardlockup detector in nmi_watchdog off 4091 1 - turn hardlockup detector in nmi_watchdog on 4092 rNNN - configure the watchdog with raw perf event 0xNNN 4093 4094 When panic is specified, panic when an NMI watchdog 4095 timeout occurs (or 'nopanic' to not panic on an NMI 4096 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4097 To disable both hard and soft lockup detectors, 4098 please see 'nowatchdog'. 4099 This is useful when you use a panic=... timeout and 4100 need the box quickly up again. 4101 4102 These settings can be accessed at runtime via 4103 the nmi_watchdog and hardlockup_panic sysctls. 4104 4105 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4106 emulation library even if a 387 maths coprocessor 4107 is present. 4108 4109 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4110 Forces kernel to use 3-level paging instead. 4111 4112 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4113 kernel to use 4-level paging instead. 4114 4115 noalign [KNL,ARM] 4116 4117 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4118 IOAPICs that may be present in the system. 4119 4120 noapictimer [APIC,X86] Don't set up the APIC timer 4121 4122 noautogroup Disable scheduler automatic task group creation. 4123 4124 nocache [ARM,EARLY] 4125 4126 no_console_suspend 4127 [HW] Never suspend the console 4128 Disable suspending of consoles during suspend and 4129 hibernate operations. Once disabled, debugging 4130 messages can reach various consoles while the rest 4131 of the system is being put to sleep (ie, while 4132 debugging driver suspend/resume hooks). This may 4133 not work reliably with all consoles, but is known 4134 to work with serial and VGA consoles. 4135 To facilitate more flexible debugging, we also add 4136 console_suspend, a printk module parameter to control 4137 it. Users could use console_suspend (usually 4138 /sys/module/printk/parameters/console_suspend) to 4139 turn on/off it dynamically. 4140 4141 no_debug_objects 4142 [KNL,EARLY] Disable object debugging 4143 4144 nodsp [SH] Disable hardware DSP at boot time. 4145 4146 noefi [EFI,EARLY] Disable EFI runtime services support. 4147 4148 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4149 4150 noexec32 [X86-64] 4151 This affects only 32-bit executables. 4152 noexec32=on: enable non-executable mappings (default) 4153 read doesn't imply executable mappings 4154 noexec32=off: disable non-executable mappings 4155 read implies executable mappings 4156 4157 no_file_caps Tells the kernel not to honor file capabilities. The 4158 only way then for a file to be executed with privilege 4159 is to be setuid root or executed by root. 4160 4161 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4162 4163 nofsgsbase [X86] Disables FSGSBASE instructions. 4164 4165 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4166 register save and restore. The kernel will only save 4167 legacy floating-point registers on task switch. 4168 4169 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4170 4171 no_hash_pointers 4172 [KNL,EARLY] 4173 Force pointers printed to the console or buffers to be 4174 unhashed. By default, when a pointer is printed via %p 4175 format string, that pointer is "hashed", i.e. obscured 4176 by hashing the pointer value. This is a security feature 4177 that hides actual kernel addresses from unprivileged 4178 users, but it also makes debugging the kernel more 4179 difficult since unequal pointers can no longer be 4180 compared. However, if this command-line option is 4181 specified, then all normal pointers will have their true 4182 value printed. This option should only be specified when 4183 debugging the kernel. Please do not use on production 4184 kernels. 4185 4186 nohibernate [HIBERNATION] Disable hibernation and resume. 4187 4188 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4189 busy wait in do_idle() and not use the arch_cpu_idle() 4190 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4191 to be effective. This is useful on platforms where the 4192 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4193 correctly or when doing power measurements to evaluate 4194 the impact of the sleep instructions. This is also 4195 useful when using JTAG debugger. 4196 4197 nohpet [X86] Don't use the HPET timer. 4198 4199 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4200 4201 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4202 4203 nohz= [KNL] Boottime enable/disable dynamic ticks 4204 Valid arguments: on, off 4205 Default: on 4206 4207 nohz_full= [KNL,BOOT,SMP,ISOL] 4208 The argument is a cpu list, as described above. 4209 In kernels built with CONFIG_NO_HZ_FULL=y, set 4210 the specified list of CPUs whose tick will be stopped 4211 whenever possible. The boot CPU will be forced outside 4212 the range to maintain the timekeeping. Any CPUs 4213 in this list will have their RCU callbacks offloaded, 4214 just as if they had also been called out in the 4215 rcu_nocbs= boot parameter. 4216 4217 Note that this argument takes precedence over 4218 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4219 4220 noinitrd [RAM] Tells the kernel not to load any configured 4221 initial RAM disk. 4222 4223 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4224 remapping. 4225 [Deprecated - use intremap=off] 4226 4227 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4228 4229 noiotrap [SH] Disables trapped I/O port accesses. 4230 4231 noirqdebug [X86-32] Disables the code which attempts to detect and 4232 disable unhandled interrupt sources. 4233 4234 noisapnp [ISAPNP] Disables ISA PnP code. 4235 4236 nokaslr [KNL,EARLY] 4237 When CONFIG_RANDOMIZE_BASE is set, this disables 4238 kernel and module base offset ASLR (Address Space 4239 Layout Randomization). 4240 4241 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4242 fault handling. 4243 4244 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4245 4246 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4247 4248 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4249 4250 nomce [X86-32] Disable Machine Check Exception 4251 4252 nomfgpt [X86-32] Disable Multi-Function General Purpose 4253 Timer usage (for AMD Geode machines). 4254 4255 nomodeset Disable kernel modesetting. Most systems' firmware 4256 sets up a display mode and provides framebuffer memory 4257 for output. With nomodeset, DRM and fbdev drivers will 4258 not load if they could possibly displace the pre- 4259 initialized output. Only the system framebuffer will 4260 be available for use. The respective drivers will not 4261 perform display-mode changes or accelerated rendering. 4262 4263 Useful as error fallback, or for testing and debugging. 4264 4265 nomodule Disable module load 4266 4267 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4268 shutdown the other cpus. Instead use the REBOOT_VECTOR 4269 irq. 4270 4271 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4272 pagetables) support. 4273 4274 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4275 4276 nopku [X86] Disable Memory Protection Keys CPU feature found 4277 in some Intel CPUs. 4278 4279 nopti [X86-64,EARLY] 4280 Equivalent to pti=off 4281 4282 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4283 Disables the PV optimizations forcing the guest to run 4284 as generic guest with no PV drivers. Currently support 4285 XEN HVM, KVM, HYPER_V and VMWARE guest. 4286 4287 nopvspin [X86,XEN,KVM,EARLY] 4288 Disables the qspinlock slow path using PV optimizations 4289 which allow the hypervisor to 'idle' the guest on lock 4290 contention. 4291 4292 norandmaps Don't use address space randomization. Equivalent to 4293 echo 0 > /proc/sys/kernel/randomize_va_space 4294 4295 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4296 with UP alternatives 4297 4298 noresume [SWSUSP] Disables resume and restores original swap 4299 space. 4300 4301 no-scroll [VGA] Disables scrollback. 4302 This is required for the Braillex ib80-piezo Braille 4303 reader made by F.H. Papenmeier (Germany). 4304 4305 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4306 4307 nosmap [PPC,EARLY] 4308 Disable SMAP (Supervisor Mode Access Prevention) 4309 even if it is supported by processor. 4310 4311 nosmep [PPC64s,EARLY] 4312 Disable SMEP (Supervisor Mode Execution Prevention) 4313 even if it is supported by processor. 4314 4315 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4316 and disable the IO APIC. legacy for "maxcpus=0". 4317 4318 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4319 Equivalent to smt=1. 4320 4321 [KNL,X86,PPC,S390] Disable symmetric multithreading (SMT). 4322 nosmt=force: Force disable SMT, cannot be undone 4323 via the sysfs control file. 4324 4325 nosoftlockup [KNL] Disable the soft-lockup detector. 4326 4327 nospec_store_bypass_disable 4328 [HW,EARLY] Disable all mitigations for the Speculative 4329 Store Bypass vulnerability 4330 4331 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4332 history injection) vulnerability. System may allow data leaks 4333 with this option. 4334 4335 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4336 (bounds check bypass). With this option data leaks are 4337 possible in the system. 4338 4339 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4340 for the Spectre variant 2 (indirect branch 4341 prediction) vulnerability. System may allow data 4342 leaks with this option. 4343 4344 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4345 Disable paravirtualized steal time accounting. steal time 4346 is computed, but won't influence scheduler behaviour 4347 4348 nosync [HW,M68K] Disables sync negotiation for all devices. 4349 4350 no_timer_check [X86,APIC] Disables the code which tests for broken 4351 timer IRQ sources, i.e., the IO-APIC timer. This can 4352 work around problems with incorrect timer 4353 initialization on some boards. 4354 4355 no_uaccess_flush 4356 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4357 4358 novmcoredd [KNL,KDUMP] 4359 Disable device dump. Device dump allows drivers to 4360 append dump data to vmcore so you can collect driver 4361 specified debug info. Drivers can append the data 4362 without any limit and this data is stored in memory, 4363 so this may cause significant memory stress. Disabling 4364 device dump can help save memory but the driver debug 4365 data will be no longer available. This parameter 4366 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4367 is set. 4368 4369 no-vmw-sched-clock 4370 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4371 scheduler clock and use the default one. 4372 4373 nowatchdog [KNL] Disable both lockup detectors, i.e. 4374 soft-lockup and NMI watchdog (hard-lockup). 4375 4376 nowb [ARM,EARLY] 4377 4378 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4379 4380 NOTE: this parameter will be ignored on systems with the 4381 LEGACY_XAPIC_DISABLED bit set in the 4382 IA32_XAPIC_DISABLE_STATUS MSR. 4383 4384 noxsave [BUGS=X86] Disables x86 extended register state save 4385 and restore using xsave. The kernel will fallback to 4386 enabling legacy floating-point and sse state. 4387 4388 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4389 register states. The kernel will fall back to use 4390 xsave to save the states. By using this parameter, 4391 performance of saving the states is degraded because 4392 xsave doesn't support modified optimization while 4393 xsaveopt supports it on xsaveopt enabled systems. 4394 4395 noxsaves [X86] Disables xsaves and xrstors used in saving and 4396 restoring x86 extended register state in compacted 4397 form of xsave area. The kernel will fall back to use 4398 xsaveopt and xrstor to save and restore the states 4399 in standard form of xsave area. By using this 4400 parameter, xsave area per process might occupy more 4401 memory on xsaves enabled systems. 4402 4403 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4404 could support. nr_cpus=n : n >= 1 limits the kernel to 4405 support 'n' processors. It could be larger than the 4406 number of already plugged CPU during bootup, later in 4407 runtime you can physically add extra cpu until it reaches 4408 n. So during boot up some boot time memory for per-cpu 4409 variables need be pre-allocated for later physical cpu 4410 hot plugging. 4411 4412 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4413 4414 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4415 Disable NUMA, Only set up a single NUMA node 4416 spanning all memory. 4417 4418 numa=fake=<size>[MG] 4419 [KNL, ARM64, RISCV, X86, EARLY] 4420 If given as a memory unit, fills all system RAM with 4421 nodes of size interleaved over physical nodes. 4422 4423 numa=fake=<N> 4424 [KNL, ARM64, RISCV, X86, EARLY] 4425 If given as an integer, fills all system RAM with N 4426 fake nodes interleaved over physical nodes. 4427 4428 numa=fake=<N>U 4429 [KNL, ARM64, RISCV, X86, EARLY] 4430 If given as an integer followed by 'U', it will 4431 divide each physical node into N emulated nodes. 4432 4433 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4434 4435 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4436 soft-reserved memory partitioning. 4437 4438 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4439 NUMA balancing. 4440 Allowed values are enable and disable 4441 4442 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4443 'node', 'default' can be specified 4444 This can be set from sysctl after boot. 4445 See Documentation/admin-guide/sysctl/vm.rst for details. 4446 4447 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4448 See Documentation/core-api/debugging-via-ohci1394.rst for more 4449 info. 4450 4451 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4452 Rather than timing out after 20 ms if an EC 4453 command is not properly ACKed, override the length 4454 of the timeout. We have interrupts disabled while 4455 waiting for the ACK, so if this is set too high 4456 interrupts *may* be lost! 4457 4458 omap_mux= [OMAP] Override bootloader pin multiplexing. 4459 Format: <mux_mode0.mode_name=value>... 4460 For example, to override I2C bus2: 4461 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4462 4463 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4464 4465 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4466 4467 boundary - index of last SLC block on Flex-OneNAND. 4468 The remaining blocks are configured as MLC blocks. 4469 lock - Configure if Flex-OneNAND boundary should be locked. 4470 Once locked, the boundary cannot be changed. 4471 1 indicates lock status, 0 indicates unlock status. 4472 4473 oops=panic [KNL,EARLY] 4474 Always panic on oopses. Default is to just kill the 4475 process, but there is a small probability of 4476 deadlocking the machine. 4477 This will also cause panics on machine check exceptions. 4478 Useful together with panic=30 to trigger a reboot. 4479 4480 page_alloc.shuffle= 4481 [KNL] Boolean flag to control whether the page allocator 4482 should randomize its free lists. This parameter can be 4483 used to enable/disable page randomization. The state of 4484 the flag can be read from sysfs at: 4485 /sys/module/page_alloc/parameters/shuffle. 4486 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4487 4488 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4489 Storage of the information about who allocated 4490 each page is disabled in default. With this switch, 4491 we can turn it on. 4492 on: enable the feature 4493 4494 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4495 poisoning on the buddy allocator, available with 4496 CONFIG_PAGE_POISONING=y. 4497 off: turn off poisoning (default) 4498 on: turn on poisoning 4499 4500 page_reporting.page_reporting_order= 4501 [KNL] Minimal page reporting order 4502 Format: <integer> 4503 Adjust the minimal page reporting order. The page 4504 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4505 4506 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4507 timeout > 0: seconds before rebooting 4508 timeout = 0: wait forever 4509 timeout < 0: reboot immediately 4510 Format: <timeout> 4511 4512 panic_on_taint= [KNL,EARLY] 4513 Bitmask for conditionally calling panic() in add_taint() 4514 Format: <hex>[,nousertaint] 4515 Hexadecimal bitmask representing the set of TAINT flags 4516 that will cause the kernel to panic when add_taint() is 4517 called with any of the flags in this set. 4518 The optional switch "nousertaint" can be utilized to 4519 prevent userspace forced crashes by writing to sysctl 4520 /proc/sys/kernel/tainted any flagset matching with the 4521 bitmask set on panic_on_taint. 4522 See Documentation/admin-guide/tainted-kernels.rst for 4523 extra details on the taint flags that users can pick 4524 to compose the bitmask to assign to panic_on_taint. 4525 4526 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4527 on a WARN(). 4528 4529 panic_print= Bitmask for printing system info when panic happens. 4530 User can chose combination of the following bits: 4531 bit 0: print all tasks info 4532 bit 1: print system memory info 4533 bit 2: print timer info 4534 bit 3: print locks info if CONFIG_LOCKDEP is on 4535 bit 4: print ftrace buffer 4536 bit 5: print all printk messages in buffer 4537 bit 6: print all CPUs backtrace (if available in the arch) 4538 bit 7: print only tasks in uninterruptible (blocked) state 4539 *Be aware* that this option may print a _lot_ of lines, 4540 so there are risks of losing older messages in the log. 4541 Use this option carefully, maybe worth to setup a 4542 bigger log buffer with "log_buf_len" along with this. 4543 4544 parkbd.port= [HW] Parallel port number the keyboard adapter is 4545 connected to, default is 0. 4546 Format: <parport#> 4547 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4548 0 for XT, 1 for AT (default is AT). 4549 Format: <mode> 4550 4551 parport= [HW,PPT] Specify parallel ports. 0 disables. 4552 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4553 Use 'auto' to force the driver to use any 4554 IRQ/DMA settings detected (the default is to 4555 ignore detected IRQ/DMA settings because of 4556 possible conflicts). You can specify the base 4557 address, IRQ, and DMA settings; IRQ and DMA 4558 should be numbers, or 'auto' (for using detected 4559 settings on that particular port), or 'nofifo' 4560 (to avoid using a FIFO even if it is detected). 4561 Parallel ports are assigned in the order they 4562 are specified on the command line, starting 4563 with parport0. 4564 4565 parport_init_mode= [HW,PPT] 4566 Configure VIA parallel port to operate in 4567 a specific mode. This is necessary on Pegasos 4568 computer where firmware has no options for setting 4569 up parallel port mode and sets it to spp. 4570 Currently this function knows 686a and 8231 chips. 4571 Format: [spp|ps2|epp|ecp|ecpepp] 4572 4573 pata_legacy.all= [HW,LIBATA] 4574 Format: <int> 4575 Set to non-zero to probe primary and secondary ISA 4576 port ranges on PCI systems where no PCI PATA device 4577 has been found at either range. Disabled by default. 4578 4579 pata_legacy.autospeed= [HW,LIBATA] 4580 Format: <int> 4581 Set to non-zero if a chip is present that snoops speed 4582 changes. Disabled by default. 4583 4584 pata_legacy.ht6560a= [HW,LIBATA] 4585 Format: <int> 4586 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4587 the secondary channel, or both channels respectively. 4588 Disabled by default. 4589 4590 pata_legacy.ht6560b= [HW,LIBATA] 4591 Format: <int> 4592 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4593 the secondary channel, or both channels respectively. 4594 Disabled by default. 4595 4596 pata_legacy.iordy_mask= [HW,LIBATA] 4597 Format: <int> 4598 IORDY enable mask. Set individual bits to allow IORDY 4599 for the respective channel. Bit 0 is for the first 4600 legacy channel handled by this driver, bit 1 is for 4601 the second channel, and so on. The sequence will often 4602 correspond to the primary legacy channel, the secondary 4603 legacy channel, and so on, but the handling of a PCI 4604 bus and the use of other driver options may interfere 4605 with the sequence. By default IORDY is allowed across 4606 all channels. 4607 4608 pata_legacy.opti82c46x= [HW,LIBATA] 4609 Format: <int> 4610 Set to 1, 2, or 3 for Opti 82c611A on the primary 4611 channel, the secondary channel, or both channels 4612 respectively. Disabled by default. 4613 4614 pata_legacy.opti82c611a= [HW,LIBATA] 4615 Format: <int> 4616 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4617 channel, the secondary channel, or both channels 4618 respectively. Disabled by default. 4619 4620 pata_legacy.pio_mask= [HW,LIBATA] 4621 Format: <int> 4622 PIO mode mask for autospeed devices. Set individual 4623 bits to allow the use of the respective PIO modes. 4624 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4625 All modes allowed by default. 4626 4627 pata_legacy.probe_all= [HW,LIBATA] 4628 Format: <int> 4629 Set to non-zero to probe tertiary and further ISA 4630 port ranges on PCI systems. Disabled by default. 4631 4632 pata_legacy.probe_mask= [HW,LIBATA] 4633 Format: <int> 4634 Probe mask for legacy ISA PATA ports. Depending on 4635 platform configuration and the use of other driver 4636 options up to 6 legacy ports are supported: 0x1f0, 4637 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4638 of individual ports can be disabled by setting the 4639 corresponding bits in the mask to 1. Bit 0 is for 4640 the first port in the list above (0x1f0), and so on. 4641 By default all supported ports are probed. 4642 4643 pata_legacy.qdi= [HW,LIBATA] 4644 Format: <int> 4645 Set to non-zero to probe QDI controllers. By default 4646 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4647 4648 pata_legacy.winbond= [HW,LIBATA] 4649 Format: <int> 4650 Set to non-zero to probe Winbond controllers. Use 4651 the standard I/O port (0x130) if 1, otherwise the 4652 value given is the I/O port to use (typically 0x1b0). 4653 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4654 0 otherwise. 4655 4656 pata_platform.pio_mask= [HW,LIBATA] 4657 Format: <int> 4658 Supported PIO mode mask. Set individual bits to allow 4659 the use of the respective PIO modes. Bit 0 is for 4660 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4661 allowed by default. 4662 4663 pause_on_oops=<int> 4664 Halt all CPUs after the first oops has been printed for 4665 the specified number of seconds. This is to be used if 4666 your oopses keep scrolling off the screen. 4667 4668 pcbit= [HW,ISDN] 4669 4670 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 4671 4672 Some options herein operate on a specific device 4673 or a set of devices (<pci_dev>). These are 4674 specified in one of the following formats: 4675 4676 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4677 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4678 4679 Note: the first format specifies a PCI 4680 bus/device/function address which may change 4681 if new hardware is inserted, if motherboard 4682 firmware changes, or due to changes caused 4683 by other kernel parameters. If the 4684 domain is left unspecified, it is 4685 taken to be zero. Optionally, a path 4686 to a device through multiple device/function 4687 addresses can be specified after the base 4688 address (this is more robust against 4689 renumbering issues). The second format 4690 selects devices using IDs from the 4691 configuration space which may match multiple 4692 devices in the system. 4693 4694 earlydump dump PCI config space before the kernel 4695 changes anything 4696 off [X86] don't probe for the PCI bus 4697 bios [X86-32] force use of PCI BIOS, don't access 4698 the hardware directly. Use this if your machine 4699 has a non-standard PCI host bridge. 4700 nobios [X86-32] disallow use of PCI BIOS, only direct 4701 hardware access methods are allowed. Use this 4702 if you experience crashes upon bootup and you 4703 suspect they are caused by the BIOS. 4704 conf1 [X86] Force use of PCI Configuration Access 4705 Mechanism 1 (config address in IO port 0xCF8, 4706 data in IO port 0xCFC, both 32-bit). 4707 conf2 [X86] Force use of PCI Configuration Access 4708 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4709 the function, IO port 0xCFA, also 8-bit, sets 4710 bus number. The config space is then accessed 4711 through ports 0xC000-0xCFFF). 4712 See http://wiki.osdev.org/PCI for more info 4713 on the configuration access mechanisms. 4714 noaer [PCIE] If the PCIEAER kernel config parameter is 4715 enabled, this kernel boot option can be used to 4716 disable the use of PCIE advanced error reporting. 4717 nodomains [PCI] Disable support for multiple PCI 4718 root domains (aka PCI segments, in ACPI-speak). 4719 nommconf [X86] Disable use of MMCONFIG for PCI 4720 Configuration 4721 check_enable_amd_mmconf [X86] check for and enable 4722 properly configured MMIO access to PCI 4723 config space on AMD family 10h CPU 4724 nomsi [MSI] If the PCI_MSI kernel config parameter is 4725 enabled, this kernel boot option can be used to 4726 disable the use of MSI interrupts system-wide. 4727 noioapicquirk [APIC] Disable all boot interrupt quirks. 4728 Safety option to keep boot IRQs enabled. This 4729 should never be necessary. 4730 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4731 primary IO-APIC for bridges that cannot disable 4732 boot IRQs. This fixes a source of spurious IRQs 4733 when the system masks IRQs. 4734 noioapicreroute [APIC] Disable workaround that uses the 4735 boot IRQ equivalent of an IRQ that connects to 4736 a chipset where boot IRQs cannot be disabled. 4737 The opposite of ioapicreroute. 4738 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4739 routing table. These calls are known to be buggy 4740 on several machines and they hang the machine 4741 when used, but on other computers it's the only 4742 way to get the interrupt routing table. Try 4743 this option if the kernel is unable to allocate 4744 IRQs or discover secondary PCI buses on your 4745 motherboard. 4746 rom [X86] Assign address space to expansion ROMs. 4747 Use with caution as certain devices share 4748 address decoders between ROMs and other 4749 resources. 4750 norom [X86] Do not assign address space to 4751 expansion ROMs that do not already have 4752 BIOS assigned address ranges. 4753 nobar [X86] Do not assign address space to the 4754 BARs that weren't assigned by the BIOS. 4755 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4756 assigned automatically to PCI devices. You can 4757 make the kernel exclude IRQs of your ISA cards 4758 this way. 4759 pirqaddr=0xAAAAA [X86] Specify the physical address 4760 of the PIRQ table (normally generated 4761 by the BIOS) if it is outside the 4762 F0000h-100000h range. 4763 lastbus=N [X86] Scan all buses thru bus #N. Can be 4764 useful if the kernel is unable to find your 4765 secondary buses and you want to tell it 4766 explicitly which ones they are. 4767 assign-busses [X86] Always assign all PCI bus 4768 numbers ourselves, overriding 4769 whatever the firmware may have done. 4770 usepirqmask [X86] Honor the possible IRQ mask stored 4771 in the BIOS $PIR table. This is needed on 4772 some systems with broken BIOSes, notably 4773 some HP Pavilion N5400 and Omnibook XE3 4774 notebooks. This will have no effect if ACPI 4775 IRQ routing is enabled. 4776 noacpi [X86] Do not use ACPI for IRQ routing 4777 or for PCI scanning. 4778 use_crs [X86] Use PCI host bridge window information 4779 from ACPI. On BIOSes from 2008 or later, this 4780 is enabled by default. If you need to use this, 4781 please report a bug. 4782 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4783 If you need to use this, please report a bug. 4784 use_e820 [X86] Use E820 reservations to exclude parts of 4785 PCI host bridge windows. This is a workaround 4786 for BIOS defects in host bridge _CRS methods. 4787 If you need to use this, please report a bug to 4788 <linux-pci@vger.kernel.org>. 4789 no_e820 [X86] Ignore E820 reservations for PCI host 4790 bridge windows. This is the default on modern 4791 hardware. If you need to use this, please report 4792 a bug to <linux-pci@vger.kernel.org>. 4793 routeirq Do IRQ routing for all PCI devices. 4794 This is normally done in pci_enable_device(), 4795 so this option is a temporary workaround 4796 for broken drivers that don't call it. 4797 skip_isa_align [X86] do not align io start addr, so can 4798 handle more pci cards 4799 noearly [X86] Don't do any early type 1 scanning. 4800 This might help on some broken boards which 4801 machine check when some devices' config space 4802 is read. But various workarounds are disabled 4803 and some IOMMU drivers will not work. 4804 bfsort Sort PCI devices into breadth-first order. 4805 This sorting is done to get a device 4806 order compatible with older (<= 2.4) kernels. 4807 nobfsort Don't sort PCI devices into breadth-first order. 4808 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4809 tuning and use the BIOS-configured MPS defaults. 4810 pcie_bus_safe Set every device's MPS to the largest value 4811 supported by all devices below the root complex. 4812 pcie_bus_perf Set device MPS to the largest allowable MPS 4813 based on its parent bus. Also set MRRS (Max 4814 Read Request Size) to the largest supported 4815 value (no larger than the MPS that the device 4816 or bus can support) for best performance. 4817 pcie_bus_peer2peer Set every device's MPS to 128B, which 4818 every device is guaranteed to support. This 4819 configuration allows peer-to-peer DMA between 4820 any pair of devices, possibly at the cost of 4821 reduced performance. This also guarantees 4822 that hot-added devices will work. 4823 cbiosize=nn[KMG] The fixed amount of bus space which is 4824 reserved for the CardBus bridge's IO window. 4825 The default value is 256 bytes. 4826 cbmemsize=nn[KMG] The fixed amount of bus space which is 4827 reserved for the CardBus bridge's memory 4828 window. The default value is 64 megabytes. 4829 resource_alignment= 4830 Format: 4831 [<order of align>@]<pci_dev>[; ...] 4832 Specifies alignment and device to reassign 4833 aligned memory resources. How to 4834 specify the device is described above. 4835 If <order of align> is not specified, 4836 PAGE_SIZE is used as alignment. 4837 A PCI-PCI bridge can be specified if resource 4838 windows need to be expanded. 4839 To specify the alignment for several 4840 instances of a device, the PCI vendor, 4841 device, subvendor, and subdevice may be 4842 specified, e.g., 12@pci:8086:9c22:103c:198f 4843 for 4096-byte alignment. 4844 ecrc= Enable/disable PCIe ECRC (transaction layer 4845 end-to-end CRC checking). Only effective if 4846 OS has native AER control (either granted by 4847 ACPI _OSC or forced via "pcie_ports=native") 4848 bios: Use BIOS/firmware settings. This is the 4849 the default. 4850 off: Turn ECRC off 4851 on: Turn ECRC on. 4852 hpiosize=nn[KMG] The fixed amount of bus space which is 4853 reserved for hotplug bridge's IO window. 4854 Default size is 256 bytes. 4855 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4856 reserved for hotplug bridge's MMIO window. 4857 Default size is 2 megabytes. 4858 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4859 reserved for hotplug bridge's MMIO_PREF window. 4860 Default size is 2 megabytes. 4861 hpmemsize=nn[KMG] The fixed amount of bus space which is 4862 reserved for hotplug bridge's MMIO and 4863 MMIO_PREF window. 4864 Default size is 2 megabytes. 4865 hpbussize=nn The minimum amount of additional bus numbers 4866 reserved for buses below a hotplug bridge. 4867 Default is 1. 4868 realloc= Enable/disable reallocating PCI bridge resources 4869 if allocations done by BIOS are too small to 4870 accommodate resources required by all child 4871 devices. 4872 off: Turn realloc off 4873 on: Turn realloc on 4874 realloc same as realloc=on 4875 noari do not use PCIe ARI. 4876 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 4877 do not use PCIe ATS (and IOMMU device IOTLB). 4878 pcie_scan_all Scan all possible PCIe devices. Otherwise we 4879 only look for one device below a PCIe downstream 4880 port. 4881 big_root_window Try to add a big 64bit memory window to the PCIe 4882 root complex on AMD CPUs. Some GFX hardware 4883 can resize a BAR to allow access to all VRAM. 4884 Adding the window is slightly risky (it may 4885 conflict with unreported devices), so this 4886 taints the kernel. 4887 disable_acs_redir=<pci_dev>[; ...] 4888 Specify one or more PCI devices (in the format 4889 specified above) separated by semicolons. 4890 Each device specified will have the PCI ACS 4891 redirect capabilities forced off which will 4892 allow P2P traffic between devices through 4893 bridges without forcing it upstream. Note: 4894 this removes isolation between devices and 4895 may put more devices in an IOMMU group. 4896 config_acs= 4897 Format: 4898 <ACS flags>@<pci_dev>[; ...] 4899 Specify one or more PCI devices (in the format 4900 specified above) optionally prepended with flags 4901 and separated by semicolons. The respective 4902 capabilities will be enabled, disabled or 4903 unchanged based on what is specified in 4904 flags. 4905 4906 ACS Flags is defined as follows: 4907 bit-0 : ACS Source Validation 4908 bit-1 : ACS Translation Blocking 4909 bit-2 : ACS P2P Request Redirect 4910 bit-3 : ACS P2P Completion Redirect 4911 bit-4 : ACS Upstream Forwarding 4912 bit-5 : ACS P2P Egress Control 4913 bit-6 : ACS Direct Translated P2P 4914 Each bit can be marked as: 4915 '0' – force disabled 4916 '1' – force enabled 4917 'x' – unchanged 4918 For example, 4919 pci=config_acs=10x@pci:0:0 4920 would configure all devices that support 4921 ACS to enable P2P Request Redirect, disable 4922 Translation Blocking, and leave Source 4923 Validation unchanged from whatever power-up 4924 or firmware set it to. 4925 4926 Note: this may remove isolation between devices 4927 and may put more devices in an IOMMU group. 4928 force_floating [S390] Force usage of floating interrupts. 4929 nomio [S390] Do not use MIO instructions. 4930 norid [S390] ignore the RID field and force use of 4931 one PCI domain per PCI function 4932 notph [PCIE] If the PCIE_TPH kernel config parameter 4933 is enabled, this kernel boot option can be used 4934 to disable PCIe TLP Processing Hints support 4935 system-wide. 4936 4937 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 4938 Management. 4939 off Don't touch ASPM configuration at all. Leave any 4940 configuration done by firmware unchanged. 4941 force Enable ASPM even on devices that claim not to support it. 4942 WARNING: Forcing ASPM on may cause system lockups. 4943 4944 pcie_ports= [PCIE] PCIe port services handling: 4945 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 4946 even if the platform doesn't give the OS permission to 4947 use them. This may cause conflicts if the platform 4948 also tries to use these services. 4949 dpc-native Use native PCIe service for DPC only. May 4950 cause conflicts if firmware uses AER or DPC. 4951 compat Disable native PCIe services (PME, AER, DPC, PCIe 4952 hotplug). 4953 4954 pcie_port_pm= [PCIE] PCIe port power management handling: 4955 off Disable power management of all PCIe ports 4956 force Forcibly enable power management of all PCIe ports 4957 4958 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 4959 nomsi Do not use MSI for native PCIe PME signaling (this makes 4960 all PCIe root ports use INTx for all services). 4961 4962 pcmv= [HW,PCMCIA] BadgePAD 4 4963 4964 pd_ignore_unused 4965 [PM] 4966 Keep all power-domains already enabled by bootloader on, 4967 even if no driver has claimed them. This is useful 4968 for debug and development, but should not be 4969 needed on a platform with proper driver support. 4970 4971 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 4972 boot time. 4973 Format: { 0 | 1 } 4974 See arch/parisc/kernel/pdc_chassis.c 4975 4976 percpu_alloc= [MM,EARLY] 4977 Select which percpu first chunk allocator to use. 4978 Currently supported values are "embed" and "page". 4979 Archs may support subset or none of the selections. 4980 See comments in mm/percpu.c for details on each 4981 allocator. This parameter is primarily for debugging 4982 and performance comparison. 4983 4984 pirq= [SMP,APIC] Manual mp-table setup 4985 See Documentation/arch/x86/i386/IO-APIC.rst. 4986 4987 plip= [PPT,NET] Parallel port network link 4988 Format: { parport<nr> | timid | 0 } 4989 See also Documentation/admin-guide/parport.rst. 4990 4991 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4992 Override pmtimer IOPort with a hex value. 4993 e.g. pmtmr=0x508 4994 4995 pmu_override= [PPC] Override the PMU. 4996 This option takes over the PMU facility, so it is no 4997 longer usable by perf. Setting this option starts the 4998 PMU counters by setting MMCR0 to 0 (the FC bit is 4999 cleared). If a number is given, then MMCR1 is set to 5000 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5001 remains 0. 5002 5003 pm_debug_messages [SUSPEND,KNL] 5004 Enable suspend/resume debug messages during boot up. 5005 5006 pnp.debug=1 [PNP] 5007 Enable PNP debug messages (depends on the 5008 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5009 via /sys/module/pnp/parameters/debug. We always show 5010 current resource usage; turning this on also shows 5011 possible settings and some assignment information. 5012 5013 pnpacpi= [ACPI] 5014 { off } 5015 5016 pnpbios= [ISAPNP] 5017 { on | off | curr | res | no-curr | no-res } 5018 5019 pnp_reserve_irq= 5020 [ISAPNP] Exclude IRQs for the autoconfiguration 5021 5022 pnp_reserve_dma= 5023 [ISAPNP] Exclude DMAs for the autoconfiguration 5024 5025 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5026 Ranges are in pairs (I/O port base and size). 5027 5028 pnp_reserve_mem= 5029 [ISAPNP] Exclude memory regions for the 5030 autoconfiguration. 5031 Ranges are in pairs (memory base and size). 5032 5033 ports= [IP_VS_FTP] IPVS ftp helper module 5034 Default is 21. 5035 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5036 may be specified. 5037 Format: <port>,<port>.... 5038 5039 possible_cpus= [SMP,S390,X86] 5040 Format: <unsigned int> 5041 Set the number of possible CPUs, overriding the 5042 regular discovery mechanisms (such as ACPI/FW, etc). 5043 5044 powersave=off [PPC] This option disables power saving features. 5045 It specifically disables cpuidle and sets the 5046 platform machine description specific power_save 5047 function to NULL. On Idle the CPU just reduces 5048 execution priority. 5049 5050 ppc_strict_facility_enable 5051 [PPC,ENABLE] This option catches any kernel floating point, 5052 Altivec, VSX and SPE outside of regions specifically 5053 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5054 There is some performance impact when enabling this. 5055 5056 ppc_tm= [PPC,EARLY] 5057 Format: {"off"} 5058 Disable Hardware Transactional Memory 5059 5060 preempt= [KNL] 5061 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5062 none - Limited to cond_resched() calls 5063 voluntary - Limited to cond_resched() and might_sleep() calls 5064 full - Any section that isn't explicitly preempt disabled 5065 can be preempted anytime. Tasks will also yield 5066 contended spinlocks (if the critical section isn't 5067 explicitly preempt disabled beyond the lock itself). 5068 lazy - Scheduler controlled. Similar to full but instead 5069 of preempting the task immediately, the task gets 5070 one HZ tick time to yield itself before the 5071 preemption will be forced. One preemption is when the 5072 task returns to user space. 5073 5074 print-fatal-signals= 5075 [KNL] debug: print fatal signals 5076 5077 If enabled, warn about various signal handling 5078 related application anomalies: too many signals, 5079 too many POSIX.1 timers, fatal signals causing a 5080 coredump - etc. 5081 5082 If you hit the warning due to signal overflow, 5083 you might want to try "ulimit -i unlimited". 5084 5085 default: off. 5086 5087 printk.always_kmsg_dump= 5088 Trigger kmsg_dump for cases other than kernel oops or 5089 panics 5090 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5091 default: disabled 5092 5093 printk.console_no_auto_verbose= 5094 Disable console loglevel raise on oops, panic 5095 or lockdep-detected issues (only if lock debug is on). 5096 With an exception to setups with low baudrate on 5097 serial console, keeping this 0 is a good choice 5098 in order to provide more debug information. 5099 Format: <bool> 5100 default: 0 (auto_verbose is enabled) 5101 5102 printk.debug_non_panic_cpus= 5103 Allows storing messages from non-panic CPUs into 5104 the printk log buffer during panic(). They are 5105 flushed to consoles by the panic-CPU on 5106 a best-effort basis. 5107 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5108 Default: disabled 5109 5110 printk.devkmsg={on,off,ratelimit} 5111 Control writing to /dev/kmsg. 5112 on - unlimited logging to /dev/kmsg from userspace 5113 off - logging to /dev/kmsg disabled 5114 ratelimit - ratelimit the logging 5115 Default: ratelimit 5116 5117 printk.time= Show timing data prefixed to each printk message line 5118 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5119 5120 proc_mem.force_override= [KNL] 5121 Format: {always | ptrace | never} 5122 Traditionally /proc/pid/mem allows memory permissions to be 5123 overridden without restrictions. This option may be set to 5124 restrict that. Can be one of: 5125 - 'always': traditional behavior always allows mem overrides. 5126 - 'ptrace': only allow mem overrides for active ptracers. 5127 - 'never': never allow mem overrides. 5128 If not specified, default is the CONFIG_PROC_MEM_* choice. 5129 5130 processor.max_cstate= [HW,ACPI] 5131 Limit processor to maximum C-state 5132 max_cstate=9 overrides any DMI blacklist limit. 5133 5134 processor.nocst [HW,ACPI] 5135 Ignore the _CST method to determine C-states, 5136 instead using the legacy FADT method 5137 5138 profile= [KNL] Enable kernel profiling via /proc/profile 5139 Format: [<profiletype>,]<number> 5140 Param: <profiletype>: "schedule" or "kvm" 5141 [defaults to kernel profiling] 5142 Param: "schedule" - profile schedule points. 5143 Param: "kvm" - profile VM exits. 5144 Param: <number> - step/bucket size as a power of 2 for 5145 statistical time based profiling. 5146 5147 prompt_ramdisk= [RAM] [Deprecated] 5148 5149 prot_virt= [S390] enable hosting protected virtual machines 5150 isolated from the hypervisor (if hardware supports 5151 that). If enabled, the default kernel base address 5152 might be overridden even when Kernel Address Space 5153 Layout Randomization is disabled. 5154 Format: <bool> 5155 5156 psi= [KNL] Enable or disable pressure stall information 5157 tracking. 5158 Format: <bool> 5159 5160 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5161 probe for; one of (bare|imps|exps|lifebook|any). 5162 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5163 per second. 5164 psmouse.resetafter= [HW,MOUSE] 5165 Try to reset the device after so many bad packets 5166 (0 = never). 5167 psmouse.resolution= 5168 [HW,MOUSE] Set desired mouse resolution, in dpi. 5169 psmouse.smartscroll= 5170 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5171 0 = disabled, 1 = enabled (default). 5172 5173 pstore.backend= Specify the name of the pstore backend to use 5174 5175 pti= [X86-64] Control Page Table Isolation of user and 5176 kernel address spaces. Disabling this feature 5177 removes hardening, but improves performance of 5178 system calls and interrupts. 5179 5180 on - unconditionally enable 5181 off - unconditionally disable 5182 auto - kernel detects whether your CPU model is 5183 vulnerable to issues that PTI mitigates 5184 5185 Not specifying this option is equivalent to pti=auto. 5186 5187 pty.legacy_count= 5188 [KNL] Number of legacy pty's. Overwrites compiled-in 5189 default number. 5190 5191 quiet [KNL,EARLY] Disable most log messages 5192 5193 r128= [HW,DRM] 5194 5195 radix_hcall_invalidate=on [PPC/PSERIES] 5196 Disable RADIX GTSE feature and use hcall for TLB 5197 invalidate. 5198 5199 raid= [HW,RAID] 5200 See Documentation/admin-guide/md.rst. 5201 5202 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5203 See Documentation/admin-guide/blockdev/ramdisk.rst. 5204 5205 ramdisk_start= [RAM] RAM disk image start address 5206 5207 random.trust_cpu=off 5208 [KNL,EARLY] Disable trusting the use of the CPU's 5209 random number generator (if available) to 5210 initialize the kernel's RNG. 5211 5212 random.trust_bootloader=off 5213 [KNL,EARLY] Disable trusting the use of the a seed 5214 passed by the bootloader (if available) to 5215 initialize the kernel's RNG. 5216 5217 randomize_kstack_offset= 5218 [KNL,EARLY] Enable or disable kernel stack offset 5219 randomization, which provides roughly 5 bits of 5220 entropy, frustrating memory corruption attacks 5221 that depend on stack address determinism or 5222 cross-syscall address exposures. This is only 5223 available on architectures that have defined 5224 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5225 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5226 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5227 5228 ras=option[,option,...] [KNL] RAS-specific options 5229 5230 cec_disable [X86] 5231 Disable the Correctable Errors Collector, 5232 see CONFIG_RAS_CEC help text. 5233 5234 rcu_nocbs[=cpu-list] 5235 [KNL] The optional argument is a cpu list, 5236 as described above. 5237 5238 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5239 enable the no-callback CPU mode, which prevents 5240 such CPUs' callbacks from being invoked in 5241 softirq context. Invocation of such CPUs' RCU 5242 callbacks will instead be offloaded to "rcuox/N" 5243 kthreads created for that purpose, where "x" is 5244 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5245 for the kthreads that mediate grace periods; and 5246 "N" is the CPU number. This reduces OS jitter on 5247 the offloaded CPUs, which can be useful for HPC 5248 and real-time workloads. It can also improve 5249 energy efficiency for asymmetric multiprocessors. 5250 5251 If a cpulist is passed as an argument, the specified 5252 list of CPUs is set to no-callback mode from boot. 5253 5254 Otherwise, if the '=' sign and the cpulist 5255 arguments are omitted, no CPU will be set to 5256 no-callback mode from boot but the mode may be 5257 toggled at runtime via cpusets. 5258 5259 Note that this argument takes precedence over 5260 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5261 5262 rcu_nocb_poll [KNL] 5263 Rather than requiring that offloaded CPUs 5264 (specified by rcu_nocbs= above) explicitly 5265 awaken the corresponding "rcuoN" kthreads, 5266 make these kthreads poll for callbacks. 5267 This improves the real-time response for the 5268 offloaded CPUs by relieving them of the need to 5269 wake up the corresponding kthread, but degrades 5270 energy efficiency by requiring that the kthreads 5271 periodically wake up to do the polling. 5272 5273 rcutree.blimit= [KNL] 5274 Set maximum number of finished RCU callbacks to 5275 process in one batch. 5276 5277 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5278 Do only a one-line RCU CPU stall warning when 5279 there is an ongoing too-long CSD-lock wait. 5280 5281 rcutree.do_rcu_barrier= [KNL] 5282 Request a call to rcu_barrier(). This is 5283 throttled so that userspace tests can safely 5284 hammer on the sysfs variable if they so choose. 5285 If triggered before the RCU grace-period machinery 5286 is fully active, this will error out with EAGAIN. 5287 5288 rcutree.dump_tree= [KNL] 5289 Dump the structure of the rcu_node combining tree 5290 out at early boot. This is used for diagnostic 5291 purposes, to verify correct tree setup. 5292 5293 rcutree.gp_cleanup_delay= [KNL] 5294 Set the number of jiffies to delay each step of 5295 RCU grace-period cleanup. 5296 5297 rcutree.gp_init_delay= [KNL] 5298 Set the number of jiffies to delay each step of 5299 RCU grace-period initialization. 5300 5301 rcutree.gp_preinit_delay= [KNL] 5302 Set the number of jiffies to delay each step of 5303 RCU grace-period pre-initialization, that is, 5304 the propagation of recent CPU-hotplug changes up 5305 the rcu_node combining tree. 5306 5307 rcutree.jiffies_till_first_fqs= [KNL] 5308 Set delay from grace-period initialization to 5309 first attempt to force quiescent states. 5310 Units are jiffies, minimum value is zero, 5311 and maximum value is HZ. 5312 5313 rcutree.jiffies_till_next_fqs= [KNL] 5314 Set delay between subsequent attempts to force 5315 quiescent states. Units are jiffies, minimum 5316 value is one, and maximum value is HZ. 5317 5318 rcutree.jiffies_till_sched_qs= [KNL] 5319 Set required age in jiffies for a 5320 given grace period before RCU starts 5321 soliciting quiescent-state help from 5322 rcu_note_context_switch() and cond_resched(). 5323 If not specified, the kernel will calculate 5324 a value based on the most recent settings 5325 of rcutree.jiffies_till_first_fqs 5326 and rcutree.jiffies_till_next_fqs. 5327 This calculated value may be viewed in 5328 rcutree.jiffies_to_sched_qs. Any attempt to set 5329 rcutree.jiffies_to_sched_qs will be cheerfully 5330 overwritten. 5331 5332 rcutree.kthread_prio= [KNL,BOOT] 5333 Set the SCHED_FIFO priority of the RCU per-CPU 5334 kthreads (rcuc/N). This value is also used for 5335 the priority of the RCU boost threads (rcub/N) 5336 and for the RCU grace-period kthreads (rcu_bh, 5337 rcu_preempt, and rcu_sched). If RCU_BOOST is 5338 set, valid values are 1-99 and the default is 1 5339 (the least-favored priority). Otherwise, when 5340 RCU_BOOST is not set, valid values are 0-99 and 5341 the default is zero (non-realtime operation). 5342 When RCU_NOCB_CPU is set, also adjust the 5343 priority of NOCB callback kthreads. 5344 5345 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5346 On callback-offloaded (rcu_nocbs) CPUs, 5347 RCU reduces the lock contention that would 5348 otherwise be caused by callback floods through 5349 use of the ->nocb_bypass list. However, in the 5350 common non-flooded case, RCU queues directly to 5351 the main ->cblist in order to avoid the extra 5352 overhead of the ->nocb_bypass list and its lock. 5353 But if there are too many callbacks queued during 5354 a single jiffy, RCU pre-queues the callbacks into 5355 the ->nocb_bypass queue. The definition of "too 5356 many" is supplied by this kernel boot parameter. 5357 5358 rcutree.nohz_full_patience_delay= [KNL] 5359 On callback-offloaded (rcu_nocbs) CPUs, avoid 5360 disturbing RCU unless the grace period has 5361 reached the specified age in milliseconds. 5362 Defaults to zero. Large values will be capped 5363 at five seconds. All values will be rounded down 5364 to the nearest value representable by jiffies. 5365 5366 rcutree.qhimark= [KNL] 5367 Set threshold of queued RCU callbacks beyond which 5368 batch limiting is disabled. 5369 5370 rcutree.qlowmark= [KNL] 5371 Set threshold of queued RCU callbacks below which 5372 batch limiting is re-enabled. 5373 5374 rcutree.qovld= [KNL] 5375 Set threshold of queued RCU callbacks beyond which 5376 RCU's force-quiescent-state scan will aggressively 5377 enlist help from cond_resched() and sched IPIs to 5378 help CPUs more quickly reach quiescent states. 5379 Set to less than zero to make this be set based 5380 on rcutree.qhimark at boot time and to zero to 5381 disable more aggressive help enlistment. 5382 5383 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5384 Set the page-cache refill delay (in milliseconds) 5385 in response to low-memory conditions. The range 5386 of permitted values is in the range 0:100000. 5387 5388 rcutree.rcu_divisor= [KNL] 5389 Set the shift-right count to use to compute 5390 the callback-invocation batch limit bl from 5391 the number of callbacks queued on this CPU. 5392 The result will be bounded below by the value of 5393 the rcutree.blimit kernel parameter. Every bl 5394 callbacks, the softirq handler will exit in 5395 order to allow the CPU to do other work. 5396 5397 Please note that this callback-invocation batch 5398 limit applies only to non-offloaded callback 5399 invocation. Offloaded callbacks are instead 5400 invoked in the context of an rcuoc kthread, which 5401 scheduler will preempt as it does any other task. 5402 5403 rcutree.rcu_fanout_exact= [KNL] 5404 Disable autobalancing of the rcu_node combining 5405 tree. This is used by rcutorture, and might 5406 possibly be useful for architectures having high 5407 cache-to-cache transfer latencies. 5408 5409 rcutree.rcu_fanout_leaf= [KNL] 5410 Change the number of CPUs assigned to each 5411 leaf rcu_node structure. Useful for very 5412 large systems, which will choose the value 64, 5413 and for NUMA systems with large remote-access 5414 latencies, which will choose a value aligned 5415 with the appropriate hardware boundaries. 5416 5417 rcutree.rcu_min_cached_objs= [KNL] 5418 Minimum number of objects which are cached and 5419 maintained per one CPU. Object size is equal 5420 to PAGE_SIZE. The cache allows to reduce the 5421 pressure to page allocator, also it makes the 5422 whole algorithm to behave better in low memory 5423 condition. 5424 5425 rcutree.rcu_nocb_gp_stride= [KNL] 5426 Set the number of NOCB callback kthreads in 5427 each group, which defaults to the square root 5428 of the number of CPUs. Larger numbers reduce 5429 the wakeup overhead on the global grace-period 5430 kthread, but increases that same overhead on 5431 each group's NOCB grace-period kthread. 5432 5433 rcutree.rcu_kick_kthreads= [KNL] 5434 Cause the grace-period kthread to get an extra 5435 wake_up() if it sleeps three times longer than 5436 it should at force-quiescent-state time. 5437 This wake_up() will be accompanied by a 5438 WARN_ONCE() splat and an ftrace_dump(). 5439 5440 rcutree.rcu_resched_ns= [KNL] 5441 Limit the time spend invoking a batch of RCU 5442 callbacks to the specified number of nanoseconds. 5443 By default, this limit is checked only once 5444 every 32 callbacks in order to limit the pain 5445 inflicted by local_clock() overhead. 5446 5447 rcutree.rcu_unlock_delay= [KNL] 5448 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5449 this specifies an rcu_read_unlock()-time delay 5450 in microseconds. This defaults to zero. 5451 Larger delays increase the probability of 5452 catching RCU pointer leaks, that is, buggy use 5453 of RCU-protected pointers after the relevant 5454 rcu_read_unlock() has completed. 5455 5456 rcutree.sysrq_rcu= [KNL] 5457 Commandeer a sysrq key to dump out Tree RCU's 5458 rcu_node tree with an eye towards determining 5459 why a new grace period has not yet started. 5460 5461 rcutree.use_softirq= [KNL] 5462 If set to zero, move all RCU_SOFTIRQ processing to 5463 per-CPU rcuc kthreads. Defaults to a non-zero 5464 value, meaning that RCU_SOFTIRQ is used by default. 5465 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5466 5467 But note that CONFIG_PREEMPT_RT=y kernels disable 5468 this kernel boot parameter, forcibly setting it 5469 to zero. 5470 5471 rcutree.enable_rcu_lazy= [KNL] 5472 To save power, batch RCU callbacks and flush after 5473 delay, memory pressure or callback list growing too 5474 big. 5475 5476 rcutree.rcu_normal_wake_from_gp= [KNL] 5477 Reduces a latency of synchronize_rcu() call. This approach 5478 maintains its own track of synchronize_rcu() callers, so it 5479 does not interact with regular callbacks because it does not 5480 use a call_rcu[_hurry]() path. Please note, this is for a 5481 normal grace period. 5482 5483 How to enable it: 5484 5485 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5486 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5487 5488 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5489 disabled by the boot parameter passing 0. 5490 5491 rcuscale.gp_async= [KNL] 5492 Measure performance of asynchronous 5493 grace-period primitives such as call_rcu(). 5494 5495 rcuscale.gp_async_max= [KNL] 5496 Specify the maximum number of outstanding 5497 callbacks per writer thread. When a writer 5498 thread exceeds this limit, it invokes the 5499 corresponding flavor of rcu_barrier() to allow 5500 previously posted callbacks to drain. 5501 5502 rcuscale.gp_exp= [KNL] 5503 Measure performance of expedited synchronous 5504 grace-period primitives. 5505 5506 rcuscale.holdoff= [KNL] 5507 Set test-start holdoff period. The purpose of 5508 this parameter is to delay the start of the 5509 test until boot completes in order to avoid 5510 interference. 5511 5512 rcuscale.kfree_by_call_rcu= [KNL] 5513 In kernels built with CONFIG_RCU_LAZY=y, test 5514 call_rcu() instead of kfree_rcu(). 5515 5516 rcuscale.kfree_mult= [KNL] 5517 Instead of allocating an object of size kfree_obj, 5518 allocate one of kfree_mult * sizeof(kfree_obj). 5519 Defaults to 1. 5520 5521 rcuscale.kfree_rcu_test= [KNL] 5522 Set to measure performance of kfree_rcu() flooding. 5523 5524 rcuscale.kfree_rcu_test_double= [KNL] 5525 Test the double-argument variant of kfree_rcu(). 5526 If this parameter has the same value as 5527 rcuscale.kfree_rcu_test_single, both the single- 5528 and double-argument variants are tested. 5529 5530 rcuscale.kfree_rcu_test_single= [KNL] 5531 Test the single-argument variant of kfree_rcu(). 5532 If this parameter has the same value as 5533 rcuscale.kfree_rcu_test_double, both the single- 5534 and double-argument variants are tested. 5535 5536 rcuscale.kfree_nthreads= [KNL] 5537 The number of threads running loops of kfree_rcu(). 5538 5539 rcuscale.kfree_alloc_num= [KNL] 5540 Number of allocations and frees done in an iteration. 5541 5542 rcuscale.kfree_loops= [KNL] 5543 Number of loops doing rcuscale.kfree_alloc_num number 5544 of allocations and frees. 5545 5546 rcuscale.minruntime= [KNL] 5547 Set the minimum test run time in seconds. This 5548 does not affect the data-collection interval, 5549 but instead allows better measurement of things 5550 like CPU consumption. 5551 5552 rcuscale.nreaders= [KNL] 5553 Set number of RCU readers. The value -1 selects 5554 N, where N is the number of CPUs. A value 5555 "n" less than -1 selects N-n+1, where N is again 5556 the number of CPUs. For example, -2 selects N 5557 (the number of CPUs), -3 selects N+1, and so on. 5558 A value of "n" less than or equal to -N selects 5559 a single reader. 5560 5561 rcuscale.nwriters= [KNL] 5562 Set number of RCU writers. The values operate 5563 the same as for rcuscale.nreaders. 5564 N, where N is the number of CPUs 5565 5566 rcuscale.scale_type= [KNL] 5567 Specify the RCU implementation to test. 5568 5569 rcuscale.shutdown= [KNL] 5570 Shut the system down after performance tests 5571 complete. This is useful for hands-off automated 5572 testing. 5573 5574 rcuscale.verbose= [KNL] 5575 Enable additional printk() statements. 5576 5577 rcuscale.writer_holdoff= [KNL] 5578 Write-side holdoff between grace periods, 5579 in microseconds. The default of zero says 5580 no holdoff. 5581 5582 rcuscale.writer_holdoff_jiffies= [KNL] 5583 Additional write-side holdoff between grace 5584 periods, but in jiffies. The default of zero 5585 says no holdoff. 5586 5587 rcutorture.fqs_duration= [KNL] 5588 Set duration of force_quiescent_state bursts 5589 in microseconds. 5590 5591 rcutorture.fqs_holdoff= [KNL] 5592 Set holdoff time within force_quiescent_state bursts 5593 in microseconds. 5594 5595 rcutorture.fqs_stutter= [KNL] 5596 Set wait time between force_quiescent_state bursts 5597 in seconds. 5598 5599 rcutorture.fwd_progress= [KNL] 5600 Specifies the number of kthreads to be used 5601 for RCU grace-period forward-progress testing 5602 for the types of RCU supporting this notion. 5603 Defaults to 1 kthread, values less than zero or 5604 greater than the number of CPUs cause the number 5605 of CPUs to be used. 5606 5607 rcutorture.fwd_progress_div= [KNL] 5608 Specify the fraction of a CPU-stall-warning 5609 period to do tight-loop forward-progress testing. 5610 5611 rcutorture.fwd_progress_holdoff= [KNL] 5612 Number of seconds to wait between successive 5613 forward-progress tests. 5614 5615 rcutorture.fwd_progress_need_resched= [KNL] 5616 Enclose cond_resched() calls within checks for 5617 need_resched() during tight-loop forward-progress 5618 testing. 5619 5620 rcutorture.gp_cond= [KNL] 5621 Use conditional/asynchronous update-side 5622 normal-grace-period primitives, if available. 5623 5624 rcutorture.gp_cond_exp= [KNL] 5625 Use conditional/asynchronous update-side 5626 expedited-grace-period primitives, if available. 5627 5628 rcutorture.gp_cond_full= [KNL] 5629 Use conditional/asynchronous update-side 5630 normal-grace-period primitives that also take 5631 concurrent expedited grace periods into account, 5632 if available. 5633 5634 rcutorture.gp_cond_exp_full= [KNL] 5635 Use conditional/asynchronous update-side 5636 expedited-grace-period primitives that also take 5637 concurrent normal grace periods into account, 5638 if available. 5639 5640 rcutorture.gp_cond_wi= [KNL] 5641 Nominal wait interval for normal conditional 5642 grace periods (specified by rcutorture's 5643 gp_cond and gp_cond_full module parameters), 5644 in microseconds. The actual wait interval will 5645 be randomly selected to nanosecond granularity up 5646 to this wait interval. Defaults to 16 jiffies, 5647 for example, 16,000 microseconds on a system 5648 with HZ=1000. 5649 5650 rcutorture.gp_cond_wi_exp= [KNL] 5651 Nominal wait interval for expedited conditional 5652 grace periods (specified by rcutorture's 5653 gp_cond_exp and gp_cond_exp_full module 5654 parameters), in microseconds. The actual wait 5655 interval will be randomly selected to nanosecond 5656 granularity up to this wait interval. Defaults to 5657 128 microseconds. 5658 5659 rcutorture.gp_exp= [KNL] 5660 Use expedited update-side primitives, if available. 5661 5662 rcutorture.gp_normal= [KNL] 5663 Use normal (non-expedited) asynchronous 5664 update-side primitives, if available. 5665 5666 rcutorture.gp_poll= [KNL] 5667 Use polled update-side normal-grace-period 5668 primitives, if available. 5669 5670 rcutorture.gp_poll_exp= [KNL] 5671 Use polled update-side expedited-grace-period 5672 primitives, if available. 5673 5674 rcutorture.gp_poll_full= [KNL] 5675 Use polled update-side normal-grace-period 5676 primitives that also take concurrent expedited 5677 grace periods into account, if available. 5678 5679 rcutorture.gp_poll_exp_full= [KNL] 5680 Use polled update-side expedited-grace-period 5681 primitives that also take concurrent normal 5682 grace periods into account, if available. 5683 5684 rcutorture.gp_poll_wi= [KNL] 5685 Nominal wait interval for normal conditional 5686 grace periods (specified by rcutorture's 5687 gp_poll and gp_poll_full module parameters), 5688 in microseconds. The actual wait interval will 5689 be randomly selected to nanosecond granularity up 5690 to this wait interval. Defaults to 16 jiffies, 5691 for example, 16,000 microseconds on a system 5692 with HZ=1000. 5693 5694 rcutorture.gp_poll_wi_exp= [KNL] 5695 Nominal wait interval for expedited conditional 5696 grace periods (specified by rcutorture's 5697 gp_poll_exp and gp_poll_exp_full module 5698 parameters), in microseconds. The actual wait 5699 interval will be randomly selected to nanosecond 5700 granularity up to this wait interval. Defaults to 5701 128 microseconds. 5702 5703 rcutorture.gp_sync= [KNL] 5704 Use normal (non-expedited) synchronous 5705 update-side primitives, if available. If all 5706 of rcutorture.gp_cond=, rcutorture.gp_exp=, 5707 rcutorture.gp_normal=, and rcutorture.gp_sync= 5708 are zero, rcutorture acts as if is interpreted 5709 they are all non-zero. 5710 5711 rcutorture.gpwrap_lag= [KNL] 5712 Enable grace-period wrap lag testing. Setting 5713 to false prevents the gpwrap lag test from 5714 running. Default is true. 5715 5716 rcutorture.gpwrap_lag_gps= [KNL] 5717 Set the value for grace-period wrap lag during 5718 active lag testing periods. This controls how many 5719 grace periods differences we tolerate between 5720 rdp and rnp's gp_seq before setting overflow flag. 5721 The default is always set to 8. 5722 5723 rcutorture.gpwrap_lag_cycle_mins= [KNL] 5724 Set the total cycle duration for gpwrap lag 5725 testing in minutes. This is the total time for 5726 one complete cycle of active and inactive 5727 testing periods. Default is 30 minutes. 5728 5729 rcutorture.gpwrap_lag_active_mins= [KNL] 5730 Set the duration for which gpwrap lag is active 5731 within each cycle, in minutes. During this time, 5732 the grace-period wrap lag will be set to the 5733 value specified by gpwrap_lag_gps. Default is 5734 5 minutes. 5735 5736 rcutorture.irqreader= [KNL] 5737 Run RCU readers from irq handlers, or, more 5738 accurately, from a timer handler. Not all RCU 5739 flavors take kindly to this sort of thing. 5740 5741 rcutorture.leakpointer= [KNL] 5742 Leak an RCU-protected pointer out of the reader. 5743 This can of course result in splats, and is 5744 intended to test the ability of things like 5745 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 5746 such leaks. 5747 5748 rcutorture.n_barrier_cbs= [KNL] 5749 Set callbacks/threads for rcu_barrier() testing. 5750 5751 rcutorture.nfakewriters= [KNL] 5752 Set number of concurrent RCU writers. These just 5753 stress RCU, they don't participate in the actual 5754 test, hence the "fake". 5755 5756 rcutorture.nocbs_nthreads= [KNL] 5757 Set number of RCU callback-offload togglers. 5758 Zero (the default) disables toggling. 5759 5760 rcutorture.nocbs_toggle= [KNL] 5761 Set the delay in milliseconds between successive 5762 callback-offload toggling attempts. 5763 5764 rcutorture.nreaders= [KNL] 5765 Set number of RCU readers. The value -1 selects 5766 N-1, where N is the number of CPUs. A value 5767 "n" less than -1 selects N-n-2, where N is again 5768 the number of CPUs. For example, -2 selects N 5769 (the number of CPUs), -3 selects N+1, and so on. 5770 5771 rcutorture.object_debug= [KNL] 5772 Enable debug-object double-call_rcu() testing. 5773 5774 rcutorture.onoff_holdoff= [KNL] 5775 Set time (s) after boot for CPU-hotplug testing. 5776 5777 rcutorture.onoff_interval= [KNL] 5778 Set time (jiffies) between CPU-hotplug operations, 5779 or zero to disable CPU-hotplug testing. 5780 5781 rcutorture.preempt_duration= [KNL] 5782 Set duration (in milliseconds) of preemptions 5783 by a high-priority FIFO real-time task. Set to 5784 zero (the default) to disable. The CPUs to 5785 preempt are selected randomly from the set that 5786 are online at a given point in time. Races with 5787 CPUs going offline are ignored, with that attempt 5788 at preemption skipped. 5789 5790 rcutorture.preempt_interval= [KNL] 5791 Set interval (in milliseconds, defaulting to one 5792 second) between preemptions by a high-priority 5793 FIFO real-time task. This delay is mediated 5794 by an hrtimer and is further fuzzed to avoid 5795 inadvertent synchronizations. 5796 5797 rcutorture.read_exit_burst= [KNL] 5798 The number of times in a given read-then-exit 5799 episode that a set of read-then-exit kthreads 5800 is spawned. 5801 5802 rcutorture.read_exit_delay= [KNL] 5803 The delay, in seconds, between successive 5804 read-then-exit testing episodes. 5805 5806 rcutorture.reader_flavor= [KNL] 5807 A bit mask indicating which readers to use. 5808 If there is more than one bit set, the readers 5809 are entered from low-order bit up, and are 5810 exited in the opposite order. For SRCU, the 5811 0x1 bit is normal readers, 0x2 NMI-safe readers, 5812 and 0x4 light-weight readers. 5813 5814 rcutorture.shuffle_interval= [KNL] 5815 Set task-shuffle interval (s). Shuffling tasks 5816 allows some CPUs to go into dyntick-idle mode 5817 during the rcutorture test. 5818 5819 rcutorture.shutdown_secs= [KNL] 5820 Set time (s) after boot system shutdown. This 5821 is useful for hands-off automated testing. 5822 5823 rcutorture.stall_cpu= [KNL] 5824 Duration of CPU stall (s) to test RCU CPU stall 5825 warnings, zero to disable. 5826 5827 rcutorture.stall_cpu_block= [KNL] 5828 Sleep while stalling if set. This will result 5829 in warnings from preemptible RCU in addition to 5830 any other stall-related activity. Note that 5831 in kernels built with CONFIG_PREEMPTION=n and 5832 CONFIG_PREEMPT_COUNT=y, this parameter will 5833 cause the CPU to pass through a quiescent state. 5834 Given CONFIG_PREEMPTION=n, this will suppress 5835 RCU CPU stall warnings, but will instead result 5836 in scheduling-while-atomic splats. 5837 5838 Use of this module parameter results in splats. 5839 5840 5841 rcutorture.stall_cpu_holdoff= [KNL] 5842 Time to wait (s) after boot before inducing stall. 5843 5844 rcutorture.stall_cpu_irqsoff= [KNL] 5845 Disable interrupts while stalling if set, but only 5846 on the first stall in the set. 5847 5848 rcutorture.stall_cpu_repeat= [KNL] 5849 Number of times to repeat the stall sequence, 5850 so that rcutorture.stall_cpu_repeat=3 will result 5851 in four stall sequences. 5852 5853 rcutorture.stall_gp_kthread= [KNL] 5854 Duration (s) of forced sleep within RCU 5855 grace-period kthread to test RCU CPU stall 5856 warnings, zero to disable. If both stall_cpu 5857 and stall_gp_kthread are specified, the 5858 kthread is starved first, then the CPU. 5859 5860 rcutorture.stat_interval= [KNL] 5861 Time (s) between statistics printk()s. 5862 5863 rcutorture.stutter= [KNL] 5864 Time (s) to stutter testing, for example, specifying 5865 five seconds causes the test to run for five seconds, 5866 wait for five seconds, and so on. This tests RCU's 5867 ability to transition abruptly to and from idle. 5868 5869 rcutorture.test_boost= [KNL] 5870 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 5871 "Maybe" means test if the RCU implementation 5872 under test support RCU priority boosting. 5873 5874 rcutorture.test_boost_duration= [KNL] 5875 Duration (s) of each individual boost test. 5876 5877 rcutorture.test_boost_holdoff= [KNL] 5878 Holdoff time (s) from start of test to the start 5879 of RCU priority-boost testing. Defaults to zero, 5880 that is, no holdoff. 5881 5882 rcutorture.test_boost_interval= [KNL] 5883 Interval (s) between each boost test. 5884 5885 rcutorture.test_no_idle_hz= [KNL] 5886 Test RCU's dyntick-idle handling. See also the 5887 rcutorture.shuffle_interval parameter. 5888 5889 rcutorture.torture_type= [KNL] 5890 Specify the RCU implementation to test. 5891 5892 rcutorture.verbose= [KNL] 5893 Enable additional printk() statements. 5894 5895 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 5896 Dump ftrace buffer after reporting RCU CPU 5897 stall warning. 5898 5899 rcupdate.rcu_cpu_stall_notifiers= [KNL] 5900 Provide RCU CPU stall notifiers, but see the 5901 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 5902 option's help text. TL;DR: You almost certainly 5903 do not want rcupdate.rcu_cpu_stall_notifiers. 5904 5905 rcupdate.rcu_cpu_stall_suppress= [KNL] 5906 Suppress RCU CPU stall warning messages. 5907 5908 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 5909 Suppress RCU CPU stall warning messages and 5910 rcutorture writer stall warnings that occur 5911 during early boot, that is, during the time 5912 before the init task is spawned. 5913 5914 rcupdate.rcu_cpu_stall_timeout= [KNL] 5915 Set timeout for RCU CPU stall warning messages. 5916 The value is in seconds and the maximum allowed 5917 value is 300 seconds. 5918 5919 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 5920 Set timeout for expedited RCU CPU stall warning 5921 messages. The value is in milliseconds 5922 and the maximum allowed value is 21000 5923 milliseconds. Please note that this value is 5924 adjusted to an arch timer tick resolution. 5925 Setting this to zero causes the value from 5926 rcupdate.rcu_cpu_stall_timeout to be used (after 5927 conversion from seconds to milliseconds). 5928 5929 rcupdate.rcu_cpu_stall_cputime= [KNL] 5930 Provide statistics on the cputime and count of 5931 interrupts and tasks during the sampling period. For 5932 multiple continuous RCU stalls, all sampling periods 5933 begin at half of the first RCU stall timeout. 5934 5935 rcupdate.rcu_exp_stall_task_details= [KNL] 5936 Print stack dumps of any tasks blocking the 5937 current expedited RCU grace period during an 5938 expedited RCU CPU stall warning. 5939 5940 rcupdate.rcu_expedited= [KNL] 5941 Use expedited grace-period primitives, for 5942 example, synchronize_rcu_expedited() instead 5943 of synchronize_rcu(). This reduces latency, 5944 but can increase CPU utilization, degrade 5945 real-time latency, and degrade energy efficiency. 5946 No effect on CONFIG_TINY_RCU kernels. 5947 5948 rcupdate.rcu_normal= [KNL] 5949 Use only normal grace-period primitives, 5950 for example, synchronize_rcu() instead of 5951 synchronize_rcu_expedited(). This improves 5952 real-time latency, CPU utilization, and 5953 energy efficiency, but can expose users to 5954 increased grace-period latency. This parameter 5955 overrides rcupdate.rcu_expedited. No effect on 5956 CONFIG_TINY_RCU kernels. 5957 5958 rcupdate.rcu_normal_after_boot= [KNL] 5959 Once boot has completed (that is, after 5960 rcu_end_inkernel_boot() has been invoked), use 5961 only normal grace-period primitives. No effect 5962 on CONFIG_TINY_RCU kernels. 5963 5964 But note that CONFIG_PREEMPT_RT=y kernels enables 5965 this kernel boot parameter, forcibly setting 5966 it to the value one, that is, converting any 5967 post-boot attempt at an expedited RCU grace 5968 period to instead use normal non-expedited 5969 grace-period processing. 5970 5971 rcupdate.rcu_task_collapse_lim= [KNL] 5972 Set the maximum number of callbacks present 5973 at the beginning of a grace period that allows 5974 the RCU Tasks flavors to collapse back to using 5975 a single callback queue. This switching only 5976 occurs when rcupdate.rcu_task_enqueue_lim is 5977 set to the default value of -1. 5978 5979 rcupdate.rcu_task_contend_lim= [KNL] 5980 Set the minimum number of callback-queuing-time 5981 lock-contention events per jiffy required to 5982 cause the RCU Tasks flavors to switch to per-CPU 5983 callback queuing. This switching only occurs 5984 when rcupdate.rcu_task_enqueue_lim is set to 5985 the default value of -1. 5986 5987 rcupdate.rcu_task_enqueue_lim= [KNL] 5988 Set the number of callback queues to use for the 5989 RCU Tasks family of RCU flavors. The default 5990 of -1 allows this to be automatically (and 5991 dynamically) adjusted. This parameter is intended 5992 for use in testing. 5993 5994 rcupdate.rcu_task_ipi_delay= [KNL] 5995 Set time in jiffies during which RCU tasks will 5996 avoid sending IPIs, starting with the beginning 5997 of a given grace period. Setting a large 5998 number avoids disturbing real-time workloads, 5999 but lengthens grace periods. 6000 6001 rcupdate.rcu_task_lazy_lim= [KNL] 6002 Number of callbacks on a given CPU that will 6003 cancel laziness on that CPU. Use -1 to disable 6004 cancellation of laziness, but be advised that 6005 doing so increases the danger of OOM due to 6006 callback flooding. 6007 6008 rcupdate.rcu_task_stall_info= [KNL] 6009 Set initial timeout in jiffies for RCU task stall 6010 informational messages, which give some indication 6011 of the problem for those not patient enough to 6012 wait for ten minutes. Informational messages are 6013 only printed prior to the stall-warning message 6014 for a given grace period. Disable with a value 6015 less than or equal to zero. Defaults to ten 6016 seconds. A change in value does not take effect 6017 until the beginning of the next grace period. 6018 6019 rcupdate.rcu_task_stall_info_mult= [KNL] 6020 Multiplier for time interval between successive 6021 RCU task stall informational messages for a given 6022 RCU tasks grace period. This value is clamped 6023 to one through ten, inclusive. It defaults to 6024 the value three, so that the first informational 6025 message is printed 10 seconds into the grace 6026 period, the second at 40 seconds, the third at 6027 160 seconds, and then the stall warning at 600 6028 seconds would prevent a fourth at 640 seconds. 6029 6030 rcupdate.rcu_task_stall_timeout= [KNL] 6031 Set timeout in jiffies for RCU task stall 6032 warning messages. Disable with a value less 6033 than or equal to zero. Defaults to ten minutes. 6034 A change in value does not take effect until 6035 the beginning of the next grace period. 6036 6037 rcupdate.rcu_tasks_lazy_ms= [KNL] 6038 Set timeout in milliseconds RCU Tasks asynchronous 6039 callback batching for call_rcu_tasks(). 6040 A negative value will take the default. A value 6041 of zero will disable batching. Batching is 6042 always disabled for synchronize_rcu_tasks(). 6043 6044 rcupdate.rcu_tasks_trace_lazy_ms= [KNL] 6045 Set timeout in milliseconds RCU Tasks 6046 Trace asynchronous callback batching for 6047 call_rcu_tasks_trace(). A negative value 6048 will take the default. A value of zero will 6049 disable batching. Batching is always disabled 6050 for synchronize_rcu_tasks_trace(). 6051 6052 rcupdate.rcu_self_test= [KNL] 6053 Run the RCU early boot self tests 6054 6055 rdinit= [KNL] 6056 Format: <full_path> 6057 Run specified binary instead of /init from the ramdisk, 6058 used for early userspace startup. See initrd. 6059 6060 rdrand= [X86,EARLY] 6061 force - Override the decision by the kernel to hide the 6062 advertisement of RDRAND support (this affects 6063 certain AMD processors because of buggy BIOS 6064 support, specifically around the suspend/resume 6065 path). 6066 6067 rdt= [HW,X86,RDT] 6068 Turn on/off individual RDT features. List is: 6069 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6070 mba, smba, bmec. 6071 E.g. to turn on cmt and turn off mba use: 6072 rdt=cmt,!mba 6073 6074 reboot= [KNL] 6075 Format (x86 or x86_64): 6076 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6077 [[,]s[mp]#### \ 6078 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6079 [[,]f[orce] 6080 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6081 (prefix with 'panic_' to set mode for panic 6082 reboot only), 6083 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6084 reboot_force is either force or not specified, 6085 reboot_cpu is s[mp]#### with #### being the processor 6086 to be used for rebooting. 6087 6088 acpi 6089 Use the ACPI RESET_REG in the FADT. If ACPI is not 6090 configured or the ACPI reset does not work, the reboot 6091 path attempts the reset using the keyboard controller. 6092 6093 bios 6094 Use the CPU reboot vector for warm reset 6095 6096 cold 6097 Set the cold reboot flag 6098 6099 default 6100 There are some built-in platform specific "quirks" 6101 - you may see: "reboot: <name> series board detected. 6102 Selecting <type> for reboots." In the case where you 6103 think the quirk is in error (e.g. you have newer BIOS, 6104 or newer board) using this option will ignore the 6105 built-in quirk table, and use the generic default 6106 reboot actions. 6107 6108 efi 6109 Use efi reset_system runtime service. If EFI is not 6110 configured or the EFI reset does not work, the reboot 6111 path attempts the reset using the keyboard controller. 6112 6113 force 6114 Don't stop other CPUs on reboot. This can make reboot 6115 more reliable in some cases. 6116 6117 kbd 6118 Use the keyboard controller. cold reset (default) 6119 6120 pci 6121 Use a write to the PCI config space register 0xcf9 to 6122 trigger reboot. 6123 6124 triple 6125 Force a triple fault (init) 6126 6127 warm 6128 Don't set the cold reboot flag 6129 6130 Using warm reset will be much faster especially on big 6131 memory systems because the BIOS will not go through 6132 the memory check. Disadvantage is that not all 6133 hardware will be completely reinitialized on reboot so 6134 there may be boot problems on some systems. 6135 6136 6137 refscale.holdoff= [KNL] 6138 Set test-start holdoff period. The purpose of 6139 this parameter is to delay the start of the 6140 test until boot completes in order to avoid 6141 interference. 6142 6143 refscale.lookup_instances= [KNL] 6144 Number of data elements to use for the forms of 6145 SLAB_TYPESAFE_BY_RCU testing. A negative number 6146 is negated and multiplied by nr_cpu_ids, while 6147 zero specifies nr_cpu_ids. 6148 6149 refscale.loops= [KNL] 6150 Set the number of loops over the synchronization 6151 primitive under test. Increasing this number 6152 reduces noise due to loop start/end overhead, 6153 but the default has already reduced the per-pass 6154 noise to a handful of picoseconds on ca. 2020 6155 x86 laptops. 6156 6157 refscale.nreaders= [KNL] 6158 Set number of readers. The default value of -1 6159 selects N, where N is roughly 75% of the number 6160 of CPUs. A value of zero is an interesting choice. 6161 6162 refscale.nruns= [KNL] 6163 Set number of runs, each of which is dumped onto 6164 the console log. 6165 6166 refscale.readdelay= [KNL] 6167 Set the read-side critical-section duration, 6168 measured in microseconds. 6169 6170 refscale.scale_type= [KNL] 6171 Specify the read-protection implementation to test. 6172 6173 refscale.shutdown= [KNL] 6174 Shut down the system at the end of the performance 6175 test. This defaults to 1 (shut it down) when 6176 refscale is built into the kernel and to 0 (leave 6177 it running) when refscale is built as a module. 6178 6179 refscale.verbose= [KNL] 6180 Enable additional printk() statements. 6181 6182 refscale.verbose_batched= [KNL] 6183 Batch the additional printk() statements. If zero 6184 (the default) or negative, print everything. Otherwise, 6185 print every Nth verbose statement, where N is the value 6186 specified. 6187 6188 regulator_ignore_unused 6189 [REGULATOR] 6190 Prevents regulator framework from disabling regulators 6191 that are unused, due no driver claiming them. This may 6192 be useful for debug and development, but should not be 6193 needed on a platform with proper driver support. 6194 6195 relax_domain_level= 6196 [KNL, SMP] Set scheduler's default relax_domain_level. 6197 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6198 6199 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6200 Format: <base1>,<size1>[,<base2>,<size2>,...] 6201 Reserve I/O ports or memory so the kernel won't use 6202 them. If <base> is less than 0x10000, the region 6203 is assumed to be I/O ports; otherwise it is memory. 6204 6205 reserve_mem= [RAM] 6206 Format: nn[KMG]:<align>:<label> 6207 Reserve physical memory and label it with a name that 6208 other subsystems can use to access it. This is typically 6209 used for systems that do not wipe the RAM, and this command 6210 line will try to reserve the same physical memory on 6211 soft reboots. Note, it is not guaranteed to be the same 6212 location. For example, if anything about the system changes 6213 or if booting a different kernel. It can also fail if KASLR 6214 places the kernel at the location of where the RAM reservation 6215 was from a previous boot, the new reservation will be at a 6216 different location. 6217 Any subsystem using this feature must add a way to verify 6218 that the contents of the physical memory is from a previous 6219 boot, as there may be cases where the memory will not be 6220 located at the same location. 6221 6222 The format is size:align:label for example, to request 6223 12 megabytes of 4096 alignment for ramoops: 6224 6225 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6226 6227 reservetop= [X86-32,EARLY] 6228 Format: nn[KMG] 6229 Reserves a hole at the top of the kernel virtual 6230 address space. 6231 6232 reset_devices [KNL] Force drivers to reset the underlying device 6233 during initialization. 6234 6235 resume= [SWSUSP] 6236 Specify the partition device for software suspend 6237 Format: 6238 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6239 6240 resume_offset= [SWSUSP] 6241 Specify the offset from the beginning of the partition 6242 given by "resume=" at which the swap header is located, 6243 in <PAGE_SIZE> units (needed only for swap files). 6244 See Documentation/power/swsusp-and-swap-files.rst 6245 6246 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6247 read the resume files 6248 6249 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6250 Useful for devices that are detected asynchronously 6251 (e.g. USB and MMC devices). 6252 6253 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6254 be accessible via /sys/firmware/initrd. 6255 6256 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6257 Speculative Code Execution with Return Instructions) 6258 vulnerability. 6259 6260 AMD-based UNRET and IBPB mitigations alone do not stop 6261 sibling threads from influencing the predictions of other 6262 sibling threads. For that reason, STIBP is used on pro- 6263 cessors that support it, and mitigate SMT on processors 6264 that don't. 6265 6266 off - no mitigation 6267 auto - automatically select a migitation 6268 auto,nosmt - automatically select a mitigation, 6269 disabling SMT if necessary for 6270 the full mitigation (only on Zen1 6271 and older without STIBP). 6272 ibpb - On AMD, mitigate short speculation 6273 windows on basic block boundaries too. 6274 Safe, highest perf impact. It also 6275 enables STIBP if present. Not suitable 6276 on Intel. 6277 ibpb,nosmt - Like "ibpb" above but will disable SMT 6278 when STIBP is not available. This is 6279 the alternative for systems which do not 6280 have STIBP. 6281 unret - Force enable untrained return thunks, 6282 only effective on AMD f15h-f17h based 6283 systems. 6284 unret,nosmt - Like unret, but will disable SMT when STIBP 6285 is not available. This is the alternative for 6286 systems which do not have STIBP. 6287 6288 Selecting 'auto' will choose a mitigation method at run 6289 time according to the CPU. 6290 6291 Not specifying this option is equivalent to retbleed=auto. 6292 6293 rfkill.default_state= 6294 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6295 etc. communication is blocked by default. 6296 1 Unblocked. 6297 6298 rfkill.master_switch_mode= 6299 0 The "airplane mode" button does nothing. 6300 1 The "airplane mode" button toggles between everything 6301 blocked and the previous configuration. 6302 2 The "airplane mode" button toggles between everything 6303 blocked and everything unblocked. 6304 6305 ring3mwait=disable 6306 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6307 CPUs. 6308 6309 riscv_isa_fallback [RISCV,EARLY] 6310 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6311 falling back to detecting extension support by parsing 6312 "riscv,isa" property on devicetree systems when the 6313 replacement properties are not found. See the Kconfig 6314 entry for RISCV_ISA_FALLBACK. 6315 6316 ro [KNL] Mount root device read-only on boot 6317 6318 rodata= [KNL,EARLY] 6319 on Mark read-only kernel memory as read-only (default). 6320 off Leave read-only kernel memory writable for debugging. 6321 full Mark read-only kernel memory and aliases as read-only 6322 [arm64] 6323 6324 rockchip.usb_uart 6325 [EARLY] 6326 Enable the uart passthrough on the designated usb port 6327 on Rockchip SoCs. When active, the signals of the 6328 debug-uart get routed to the D+ and D- pins of the usb 6329 port and the regular usb controller gets disabled. 6330 6331 root= [KNL] Root filesystem 6332 Usually this is a block device specifier of some kind, 6333 see the early_lookup_bdev comment in 6334 block/early-lookup.c for details. 6335 Alternatively this can be "ram" for the legacy initial 6336 ramdisk, "nfs" and "cifs" for root on a network file 6337 system, or "mtd" and "ubi" for mounting from raw flash. 6338 6339 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6340 mount the root filesystem 6341 6342 rootflags= [KNL] Set root filesystem mount option string 6343 6344 rootfstype= [KNL] Set root filesystem type 6345 6346 rootwait [KNL] Wait (indefinitely) for root device to show up. 6347 Useful for devices that are detected asynchronously 6348 (e.g. USB and MMC devices). 6349 6350 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6351 to show up before attempting to mount the root 6352 filesystem. 6353 6354 rproc_mem=nn[KMG][@address] 6355 [KNL,ARM,CMA] Remoteproc physical memory block. 6356 Memory area to be used by remote processor image, 6357 managed by CMA. 6358 6359 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6360 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6361 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6362 Format: <bool> 6363 6364 rw [KNL] Mount root device read-write on boot 6365 6366 S [KNL] Run init in single mode 6367 6368 s390_iommu= [HW,S390] 6369 Set s390 IOTLB flushing mode 6370 strict 6371 With strict flushing every unmap operation will result 6372 in an IOTLB flush. Default is lazy flushing before 6373 reuse, which is faster. Deprecated, equivalent to 6374 iommu.strict=1. 6375 6376 s390_iommu_aperture= [KNL,S390] 6377 Specifies the size of the per device DMA address space 6378 accessible through the DMA and IOMMU APIs as a decimal 6379 factor of the size of main memory. 6380 The default is 1 meaning that one can concurrently use 6381 as many DMA addresses as physical memory is installed, 6382 if supported by hardware, and thus map all of memory 6383 once. With a value of 2 one can map all of memory twice 6384 and so on. As a special case a factor of 0 imposes no 6385 restrictions other than those given by hardware at the 6386 cost of significant additional memory use for tables. 6387 6388 sa1100ir [NET] 6389 See drivers/net/irda/sa1100_ir.c. 6390 6391 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6392 6393 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6394 Allowed values are enable and disable. This feature 6395 incurs a small amount of overhead in the scheduler 6396 but is useful for debugging and performance tuning. 6397 6398 sched_thermal_decay_shift= 6399 [Deprecated] 6400 [KNL, SMP] Set a decay shift for scheduler thermal 6401 pressure signal. Thermal pressure signal follows the 6402 default decay period of other scheduler pelt 6403 signals(usually 32 ms but configurable). Setting 6404 sched_thermal_decay_shift will left shift the decay 6405 period for the thermal pressure signal by the shift 6406 value. 6407 i.e. with the default pelt decay period of 32 ms 6408 sched_thermal_decay_shift thermal pressure decay pr 6409 1 64 ms 6410 2 128 ms 6411 and so on. 6412 Format: integer between 0 and 10 6413 Default is 0. 6414 6415 scftorture.holdoff= [KNL] 6416 Number of seconds to hold off before starting 6417 test. Defaults to zero for module insertion and 6418 to 10 seconds for built-in smp_call_function() 6419 tests. 6420 6421 scftorture.longwait= [KNL] 6422 Request ridiculously long waits randomly selected 6423 up to the chosen limit in seconds. Zero (the 6424 default) disables this feature. Please note 6425 that requesting even small non-zero numbers of 6426 seconds can result in RCU CPU stall warnings, 6427 softlockup complaints, and so on. 6428 6429 scftorture.nthreads= [KNL] 6430 Number of kthreads to spawn to invoke the 6431 smp_call_function() family of functions. 6432 The default of -1 specifies a number of kthreads 6433 equal to the number of CPUs. 6434 6435 scftorture.onoff_holdoff= [KNL] 6436 Number seconds to wait after the start of the 6437 test before initiating CPU-hotplug operations. 6438 6439 scftorture.onoff_interval= [KNL] 6440 Number seconds to wait between successive 6441 CPU-hotplug operations. Specifying zero (which 6442 is the default) disables CPU-hotplug operations. 6443 6444 scftorture.shutdown_secs= [KNL] 6445 The number of seconds following the start of the 6446 test after which to shut down the system. The 6447 default of zero avoids shutting down the system. 6448 Non-zero values are useful for automated tests. 6449 6450 scftorture.stat_interval= [KNL] 6451 The number of seconds between outputting the 6452 current test statistics to the console. A value 6453 of zero disables statistics output. 6454 6455 scftorture.stutter_cpus= [KNL] 6456 The number of jiffies to wait between each change 6457 to the set of CPUs under test. 6458 6459 scftorture.use_cpus_read_lock= [KNL] 6460 Use use_cpus_read_lock() instead of the default 6461 preempt_disable() to disable CPU hotplug 6462 while invoking one of the smp_call_function*() 6463 functions. 6464 6465 scftorture.verbose= [KNL] 6466 Enable additional printk() statements. 6467 6468 scftorture.weight_single= [KNL] 6469 The probability weighting to use for the 6470 smp_call_function_single() function with a zero 6471 "wait" parameter. A value of -1 selects the 6472 default if all other weights are -1. However, 6473 if at least one weight has some other value, a 6474 value of -1 will instead select a weight of zero. 6475 6476 scftorture.weight_single_wait= [KNL] 6477 The probability weighting to use for the 6478 smp_call_function_single() function with a 6479 non-zero "wait" parameter. See weight_single. 6480 6481 scftorture.weight_many= [KNL] 6482 The probability weighting to use for the 6483 smp_call_function_many() function with a zero 6484 "wait" parameter. See weight_single. 6485 Note well that setting a high probability for 6486 this weighting can place serious IPI load 6487 on the system. 6488 6489 scftorture.weight_many_wait= [KNL] 6490 The probability weighting to use for the 6491 smp_call_function_many() function with a 6492 non-zero "wait" parameter. See weight_single 6493 and weight_many. 6494 6495 scftorture.weight_all= [KNL] 6496 The probability weighting to use for the 6497 smp_call_function_all() function with a zero 6498 "wait" parameter. See weight_single and 6499 weight_many. 6500 6501 scftorture.weight_all_wait= [KNL] 6502 The probability weighting to use for the 6503 smp_call_function_all() function with a 6504 non-zero "wait" parameter. See weight_single 6505 and weight_many. 6506 6507 sdw_mclk_divider=[SDW] 6508 Specify the MCLK divider for Intel SoundWire buses in 6509 case the BIOS does not provide the clock rate properly. 6510 6511 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6512 xtime_lock contention on larger systems, and/or RCU lock 6513 contention on all systems with CONFIG_MAXSMP set. 6514 Format: { "0" | "1" } 6515 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6516 1 -- enable. 6517 Note: increases power consumption, thus should only be 6518 enabled if running jitter sensitive (HPC/RT) workloads. 6519 6520 security= [SECURITY] Choose a legacy "major" security module to 6521 enable at boot. This has been deprecated by the 6522 "lsm=" parameter. 6523 6524 selinux= [SELINUX] Disable or enable SELinux at boot time. 6525 Format: { "0" | "1" } 6526 See security/selinux/Kconfig help text. 6527 0 -- disable. 6528 1 -- enable. 6529 Default value is 1. 6530 6531 serialnumber [BUGS=X86-32] 6532 6533 sev=option[,option...] [X86-64] 6534 6535 debug 6536 Enable debug messages. 6537 6538 nosnp 6539 Do not enable SEV-SNP (applies to host/hypervisor 6540 only). Setting 'nosnp' avoids the RMP check overhead 6541 in memory accesses when users do not want to run 6542 SEV-SNP guests. 6543 6544 shapers= [NET] 6545 Maximal number of shapers. 6546 6547 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6548 Limit apic dumping. The parameter defines the maximal 6549 number of local apics being dumped. Also it is possible 6550 to set it to "all" by meaning -- no limit here. 6551 Format: { 1 (default) | 2 | ... | all }. 6552 The parameter valid if only apic=debug or 6553 apic=verbose is specified. 6554 Example: apic=debug show_lapic=all 6555 6556 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6557 Enabling slab_debug allows one to determine the 6558 culprit if slab objects become corrupted. Enabling 6559 slab_debug can create guard zones around objects and 6560 may poison objects when not in use. Also tracks the 6561 last alloc / free. For more information see 6562 Documentation/mm/slub.rst. 6563 (slub_debug legacy name also accepted for now) 6564 6565 slab_max_order= [MM] 6566 Determines the maximum allowed order for slabs. 6567 A high setting may cause OOMs due to memory 6568 fragmentation. For more information see 6569 Documentation/mm/slub.rst. 6570 (slub_max_order legacy name also accepted for now) 6571 6572 slab_merge [MM] 6573 Enable merging of slabs with similar size when the 6574 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6575 (slub_merge legacy name also accepted for now) 6576 6577 slab_min_objects= [MM] 6578 The minimum number of objects per slab. SLUB will 6579 increase the slab order up to slab_max_order to 6580 generate a sufficiently large slab able to contain 6581 the number of objects indicated. The higher the number 6582 of objects the smaller the overhead of tracking slabs 6583 and the less frequently locks need to be acquired. 6584 For more information see Documentation/mm/slub.rst. 6585 (slub_min_objects legacy name also accepted for now) 6586 6587 slab_min_order= [MM] 6588 Determines the minimum page order for slabs. Must be 6589 lower or equal to slab_max_order. For more information see 6590 Documentation/mm/slub.rst. 6591 (slub_min_order legacy name also accepted for now) 6592 6593 slab_nomerge [MM] 6594 Disable merging of slabs with similar size. May be 6595 necessary if there is some reason to distinguish 6596 allocs to different slabs, especially in hardened 6597 environments where the risk of heap overflows and 6598 layout control by attackers can usually be 6599 frustrated by disabling merging. This will reduce 6600 most of the exposure of a heap attack to a single 6601 cache (risks via metadata attacks are mostly 6602 unchanged). Debug options disable merging on their 6603 own. 6604 For more information see Documentation/mm/slub.rst. 6605 (slub_nomerge legacy name also accepted for now) 6606 6607 slab_strict_numa [MM] 6608 Support memory policies on a per object level 6609 in the slab allocator. The default is for memory 6610 policies to be applied at the folio level when 6611 a new folio is needed or a partial folio is 6612 retrieved from the lists. Increases overhead 6613 in the slab fastpaths but gains more accurate 6614 NUMA kernel object placement which helps with slow 6615 interconnects in NUMA systems. 6616 6617 slram= [HW,MTD] 6618 6619 smart2= [HW] 6620 Format: <io1>[,<io2>[,...,<io8>]] 6621 6622 smp.csd_lock_timeout= [KNL] 6623 Specify the period of time in milliseconds 6624 that smp_call_function() and friends will wait 6625 for a CPU to release the CSD lock. This is 6626 useful when diagnosing bugs involving CPUs 6627 disabling interrupts for extended periods 6628 of time. Defaults to 5,000 milliseconds, and 6629 setting a value of zero disables this feature. 6630 This feature may be more efficiently disabled 6631 using the csdlock_debug- kernel parameter. 6632 6633 smp.panic_on_ipistall= [KNL] 6634 If a csd_lock_timeout extends for more than 6635 the specified number of milliseconds, panic the 6636 system. By default, let CSD-lock acquisition 6637 take as long as they take. Specifying 300,000 6638 for this value provides a 5-minute timeout. 6639 6640 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 6641 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 6642 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 6643 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 6644 smsc-ircc2.ircc_irq= [HW] IRQ line 6645 smsc-ircc2.ircc_dma= [HW] DMA channel 6646 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 6647 0: Toshiba Satellite 1800 (GP data pin select) 6648 1: Fast pin select (default) 6649 2: ATC IRMode 6650 6651 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 6652 (logical CPUs) to use per physical CPU on systems 6653 capable of symmetric multithreading (SMT). Will 6654 be capped to the actual hardware limit. 6655 Format: <integer> 6656 Default: -1 (no limit) 6657 6658 softlockup_panic= 6659 [KNL] Should the soft-lockup detector generate panics. 6660 Format: 0 | 1 6661 6662 A value of 1 instructs the soft-lockup detector 6663 to panic the machine when a soft-lockup occurs. It is 6664 also controlled by the kernel.softlockup_panic sysctl 6665 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 6666 respective build-time switch to that functionality. 6667 6668 softlockup_all_cpu_backtrace= 6669 [KNL] Should the soft-lockup detector generate 6670 backtraces on all cpus. 6671 Format: 0 | 1 6672 6673 sonypi.*= [HW] Sony Programmable I/O Control Device driver 6674 See Documentation/admin-guide/laptops/sonypi.rst 6675 6676 spectre_bhi= [X86] Control mitigation of Branch History Injection 6677 (BHI) vulnerability. This setting affects the 6678 deployment of the HW BHI control and the SW BHB 6679 clearing sequence. 6680 6681 on - (default) Enable the HW or SW mitigation as 6682 needed. This protects the kernel from 6683 both syscalls and VMs. 6684 vmexit - On systems which don't have the HW mitigation 6685 available, enable the SW mitigation on vmexit 6686 ONLY. On such systems, the host kernel is 6687 protected from VM-originated BHI attacks, but 6688 may still be vulnerable to syscall attacks. 6689 off - Disable the mitigation. 6690 6691 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 6692 (indirect branch speculation) vulnerability. 6693 The default operation protects the kernel from 6694 user space attacks. 6695 6696 on - unconditionally enable, implies 6697 spectre_v2_user=on 6698 off - unconditionally disable, implies 6699 spectre_v2_user=off 6700 auto - kernel detects whether your CPU model is 6701 vulnerable 6702 6703 Selecting 'on' will, and 'auto' may, choose a 6704 mitigation method at run time according to the 6705 CPU, the available microcode, the setting of the 6706 CONFIG_MITIGATION_RETPOLINE configuration option, 6707 and the compiler with which the kernel was built. 6708 6709 Selecting 'on' will also enable the mitigation 6710 against user space to user space task attacks. 6711 Selecting specific mitigation does not force enable 6712 user mitigations. 6713 6714 Selecting 'off' will disable both the kernel and 6715 the user space protections. 6716 6717 Specific mitigations can also be selected manually: 6718 6719 retpoline - replace indirect branches 6720 retpoline,generic - Retpolines 6721 retpoline,lfence - LFENCE; indirect branch 6722 retpoline,amd - alias for retpoline,lfence 6723 eibrs - Enhanced/Auto IBRS 6724 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 6725 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 6726 ibrs - use IBRS to protect kernel 6727 6728 Not specifying this option is equivalent to 6729 spectre_v2=auto. 6730 6731 spectre_v2_user= 6732 [X86] Control mitigation of Spectre variant 2 6733 (indirect branch speculation) vulnerability between 6734 user space tasks 6735 6736 on - Unconditionally enable mitigations. Is 6737 enforced by spectre_v2=on 6738 6739 off - Unconditionally disable mitigations. Is 6740 enforced by spectre_v2=off 6741 6742 prctl - Indirect branch speculation is enabled, 6743 but mitigation can be enabled via prctl 6744 per thread. The mitigation control state 6745 is inherited on fork. 6746 6747 prctl,ibpb 6748 - Like "prctl" above, but only STIBP is 6749 controlled per thread. IBPB is issued 6750 always when switching between different user 6751 space processes. 6752 6753 seccomp 6754 - Same as "prctl" above, but all seccomp 6755 threads will enable the mitigation unless 6756 they explicitly opt out. 6757 6758 seccomp,ibpb 6759 - Like "seccomp" above, but only STIBP is 6760 controlled per thread. IBPB is issued 6761 always when switching between different 6762 user space processes. 6763 6764 auto - Kernel selects the mitigation depending on 6765 the available CPU features and vulnerability. 6766 6767 Default mitigation: "prctl" 6768 6769 Not specifying this option is equivalent to 6770 spectre_v2_user=auto. 6771 6772 spec_rstack_overflow= 6773 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 6774 6775 off - Disable mitigation 6776 microcode - Enable microcode mitigation only 6777 safe-ret - Enable sw-only safe RET mitigation (default) 6778 ibpb - Enable mitigation by issuing IBPB on 6779 kernel entry 6780 ibpb-vmexit - Issue IBPB only on VMEXIT 6781 (cloud-specific mitigation) 6782 6783 spec_store_bypass_disable= 6784 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 6785 (Speculative Store Bypass vulnerability) 6786 6787 Certain CPUs are vulnerable to an exploit against a 6788 a common industry wide performance optimization known 6789 as "Speculative Store Bypass" in which recent stores 6790 to the same memory location may not be observed by 6791 later loads during speculative execution. The idea 6792 is that such stores are unlikely and that they can 6793 be detected prior to instruction retirement at the 6794 end of a particular speculation execution window. 6795 6796 In vulnerable processors, the speculatively forwarded 6797 store can be used in a cache side channel attack, for 6798 example to read memory to which the attacker does not 6799 directly have access (e.g. inside sandboxed code). 6800 6801 This parameter controls whether the Speculative Store 6802 Bypass optimization is used. 6803 6804 On x86 the options are: 6805 6806 on - Unconditionally disable Speculative Store Bypass 6807 off - Unconditionally enable Speculative Store Bypass 6808 auto - Kernel detects whether the CPU model contains an 6809 implementation of Speculative Store Bypass and 6810 picks the most appropriate mitigation. If the 6811 CPU is not vulnerable, "off" is selected. If the 6812 CPU is vulnerable the default mitigation is 6813 architecture and Kconfig dependent. See below. 6814 prctl - Control Speculative Store Bypass per thread 6815 via prctl. Speculative Store Bypass is enabled 6816 for a process by default. The state of the control 6817 is inherited on fork. 6818 seccomp - Same as "prctl" above, but all seccomp threads 6819 will disable SSB unless they explicitly opt out. 6820 6821 Default mitigations: 6822 X86: "prctl" 6823 6824 On powerpc the options are: 6825 6826 on,auto - On Power8 and Power9 insert a store-forwarding 6827 barrier on kernel entry and exit. On Power7 6828 perform a software flush on kernel entry and 6829 exit. 6830 off - No action. 6831 6832 Not specifying this option is equivalent to 6833 spec_store_bypass_disable=auto. 6834 6835 split_lock_detect= 6836 [X86] Enable split lock detection or bus lock detection 6837 6838 When enabled (and if hardware support is present), atomic 6839 instructions that access data across cache line 6840 boundaries will result in an alignment check exception 6841 for split lock detection or a debug exception for 6842 bus lock detection. 6843 6844 off - not enabled 6845 6846 warn - the kernel will emit rate-limited warnings 6847 about applications triggering the #AC 6848 exception or the #DB exception. This mode is 6849 the default on CPUs that support split lock 6850 detection or bus lock detection. Default 6851 behavior is by #AC if both features are 6852 enabled in hardware. 6853 6854 fatal - the kernel will send SIGBUS to applications 6855 that trigger the #AC exception or the #DB 6856 exception. Default behavior is by #AC if 6857 both features are enabled in hardware. 6858 6859 ratelimit:N - 6860 Set system wide rate limit to N bus locks 6861 per second for bus lock detection. 6862 0 < N <= 1000. 6863 6864 N/A for split lock detection. 6865 6866 6867 If an #AC exception is hit in the kernel or in 6868 firmware (i.e. not while executing in user mode) 6869 the kernel will oops in either "warn" or "fatal" 6870 mode. 6871 6872 #DB exception for bus lock is triggered only when 6873 CPL > 0. 6874 6875 srbds= [X86,INTEL,EARLY] 6876 Control the Special Register Buffer Data Sampling 6877 (SRBDS) mitigation. 6878 6879 Certain CPUs are vulnerable to an MDS-like 6880 exploit which can leak bits from the random 6881 number generator. 6882 6883 By default, this issue is mitigated by 6884 microcode. However, the microcode fix can cause 6885 the RDRAND and RDSEED instructions to become 6886 much slower. Among other effects, this will 6887 result in reduced throughput from /dev/urandom. 6888 6889 The microcode mitigation can be disabled with 6890 the following option: 6891 6892 off: Disable mitigation and remove 6893 performance impact to RDRAND and RDSEED 6894 6895 srcutree.big_cpu_lim [KNL] 6896 Specifies the number of CPUs constituting a 6897 large system, such that srcu_struct structures 6898 should immediately allocate an srcu_node array. 6899 This kernel-boot parameter defaults to 128, 6900 but takes effect only when the low-order four 6901 bits of srcutree.convert_to_big is equal to 3 6902 (decide at boot). 6903 6904 srcutree.convert_to_big [KNL] 6905 Specifies under what conditions an SRCU tree 6906 srcu_struct structure will be converted to big 6907 form, that is, with an rcu_node tree: 6908 6909 0: Never. 6910 1: At init_srcu_struct() time. 6911 2: When rcutorture decides to. 6912 3: Decide at boot time (default). 6913 0x1X: Above plus if high contention. 6914 6915 Either way, the srcu_node tree will be sized based 6916 on the actual runtime number of CPUs (nr_cpu_ids) 6917 instead of the compile-time CONFIG_NR_CPUS. 6918 6919 srcutree.counter_wrap_check [KNL] 6920 Specifies how frequently to check for 6921 grace-period sequence counter wrap for the 6922 srcu_data structure's ->srcu_gp_seq_needed field. 6923 The greater the number of bits set in this kernel 6924 parameter, the less frequently counter wrap will 6925 be checked for. Note that the bottom two bits 6926 are ignored. 6927 6928 srcutree.exp_holdoff [KNL] 6929 Specifies how many nanoseconds must elapse 6930 since the end of the last SRCU grace period for 6931 a given srcu_struct until the next normal SRCU 6932 grace period will be considered for automatic 6933 expediting. Set to zero to disable automatic 6934 expediting. 6935 6936 srcutree.srcu_max_nodelay [KNL] 6937 Specifies the number of no-delay instances 6938 per jiffy for which the SRCU grace period 6939 worker thread will be rescheduled with zero 6940 delay. Beyond this limit, worker thread will 6941 be rescheduled with a sleep delay of one jiffy. 6942 6943 srcutree.srcu_max_nodelay_phase [KNL] 6944 Specifies the per-grace-period phase, number of 6945 non-sleeping polls of readers. Beyond this limit, 6946 grace period worker thread will be rescheduled 6947 with a sleep delay of one jiffy, between each 6948 rescan of the readers, for a grace period phase. 6949 6950 srcutree.srcu_retry_check_delay [KNL] 6951 Specifies number of microseconds of non-sleeping 6952 delay between each non-sleeping poll of readers. 6953 6954 srcutree.small_contention_lim [KNL] 6955 Specifies the number of update-side contention 6956 events per jiffy will be tolerated before 6957 initiating a conversion of an srcu_struct 6958 structure to big form. Note that the value of 6959 srcutree.convert_to_big must have the 0x10 bit 6960 set for contention-based conversions to occur. 6961 6962 ssbd= [ARM64,HW,EARLY] 6963 Speculative Store Bypass Disable control 6964 6965 On CPUs that are vulnerable to the Speculative 6966 Store Bypass vulnerability and offer a 6967 firmware based mitigation, this parameter 6968 indicates how the mitigation should be used: 6969 6970 force-on: Unconditionally enable mitigation for 6971 for both kernel and userspace 6972 force-off: Unconditionally disable mitigation for 6973 for both kernel and userspace 6974 kernel: Always enable mitigation in the 6975 kernel, and offer a prctl interface 6976 to allow userspace to register its 6977 interest in being mitigated too. 6978 6979 stack_guard_gap= [MM] 6980 override the default stack gap protection. The value 6981 is in page units and it defines how many pages prior 6982 to (for stacks growing down) resp. after (for stacks 6983 growing up) the main stack are reserved for no other 6984 mapping. Default value is 256 pages. 6985 6986 stack_depot_disable= [KNL,EARLY] 6987 Setting this to true through kernel command line will 6988 disable the stack depot thereby saving the static memory 6989 consumed by the stack hash table. By default this is set 6990 to false. 6991 6992 stacktrace [FTRACE] 6993 Enabled the stack tracer on boot up. 6994 6995 stacktrace_filter=[function-list] 6996 [FTRACE] Limit the functions that the stack tracer 6997 will trace at boot up. function-list is a comma-separated 6998 list of functions. This list can be changed at run 6999 time by the stack_trace_filter file in the debugfs 7000 tracing directory. Note, this enables stack tracing 7001 and the stacktrace above is not needed. 7002 7003 sti= [PARISC,HW] 7004 Format: <num> 7005 Set the STI (builtin display/keyboard on the HP-PARISC 7006 machines) console (graphic card) which should be used 7007 as the initial boot-console. 7008 See also comment in drivers/video/console/sticore.c. 7009 7010 sti_font= [HW] 7011 See comment in drivers/video/console/sticore.c. 7012 7013 stifb= [HW] 7014 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7015 7016 strict_sas_size= 7017 [X86] 7018 Format: <bool> 7019 Enable or disable strict sigaltstack size checks 7020 against the required signal frame size which 7021 depends on the supported FPU features. This can 7022 be used to filter out binaries which have 7023 not yet been made aware of AT_MINSIGSTKSZ. 7024 7025 stress_hpt [PPC,EARLY] 7026 Limits the number of kernel HPT entries in the hash 7027 page table to increase the rate of hash page table 7028 faults on kernel addresses. 7029 7030 stress_slb [PPC,EARLY] 7031 Limits the number of kernel SLB entries, and flushes 7032 them frequently to increase the rate of SLB faults 7033 on kernel addresses. 7034 7035 sunrpc.min_resvport= 7036 sunrpc.max_resvport= 7037 [NFS,SUNRPC] 7038 SunRPC servers often require that client requests 7039 originate from a privileged port (i.e. a port in the 7040 range 0 < portnr < 1024). 7041 An administrator who wishes to reserve some of these 7042 ports for other uses may adjust the range that the 7043 kernel's sunrpc client considers to be privileged 7044 using these two parameters to set the minimum and 7045 maximum port values. 7046 7047 sunrpc.svc_rpc_per_connection_limit= 7048 [NFS,SUNRPC] 7049 Limit the number of requests that the server will 7050 process in parallel from a single connection. 7051 The default value is 0 (no limit). 7052 7053 sunrpc.pool_mode= 7054 [NFS] 7055 Control how the NFS server code allocates CPUs to 7056 service thread pools. Depending on how many NICs 7057 you have and where their interrupts are bound, this 7058 option will affect which CPUs will do NFS serving. 7059 Note: this parameter cannot be changed while the 7060 NFS server is running. 7061 7062 auto the server chooses an appropriate mode 7063 automatically using heuristics 7064 global a single global pool contains all CPUs 7065 percpu one pool for each CPU 7066 pernode one pool for each NUMA node (equivalent 7067 to global on non-NUMA machines) 7068 7069 sunrpc.tcp_slot_table_entries= 7070 sunrpc.udp_slot_table_entries= 7071 [NFS,SUNRPC] 7072 Sets the upper limit on the number of simultaneous 7073 RPC calls that can be sent from the client to a 7074 server. Increasing these values may allow you to 7075 improve throughput, but will also increase the 7076 amount of memory reserved for use by the client. 7077 7078 suspend.pm_test_delay= 7079 [SUSPEND] 7080 Sets the number of seconds to remain in a suspend test 7081 mode before resuming the system (see 7082 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7083 is set. Default value is 5. 7084 7085 svm= [PPC] 7086 Format: { on | off | y | n | 1 | 0 } 7087 This parameter controls use of the Protected 7088 Execution Facility on pSeries. 7089 7090 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7091 Format: { <int> [,<int>] | force | noforce } 7092 <int> -- Number of I/O TLB slabs 7093 <int> -- Second integer after comma. Number of swiotlb 7094 areas with their own lock. Will be rounded up 7095 to a power of 2. 7096 force -- force using of bounce buffers even if they 7097 wouldn't be automatically used by the kernel 7098 noforce -- Never use bounce buffers (for debugging) 7099 7100 switches= [HW,M68k,EARLY] 7101 7102 sysctl.*= [KNL] 7103 Set a sysctl parameter, right before loading the init 7104 process, as if the value was written to the respective 7105 /proc/sys/... file. Both '.' and '/' are recognized as 7106 separators. Unrecognized parameters and invalid values 7107 are reported in the kernel log. Sysctls registered 7108 later by a loaded module cannot be set this way. 7109 Example: sysctl.vm.swappiness=40 7110 7111 sysrq_always_enabled 7112 [KNL] 7113 Ignore sysrq setting - this boot parameter will 7114 neutralize any effect of /proc/sys/kernel/sysrq. 7115 Useful for debugging. 7116 7117 tcpmhash_entries= [KNL,NET] 7118 Set the number of tcp_metrics_hash slots. 7119 Default value is 8192 or 16384 depending on total 7120 ram pages. This is used to specify the TCP metrics 7121 cache size. See Documentation/networking/ip-sysctl.rst 7122 "tcp_no_metrics_save" section for more details. 7123 7124 tdfx= [HW,DRM] 7125 7126 test_suspend= [SUSPEND] 7127 Format: { "mem" | "standby" | "freeze" }[,N] 7128 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7129 standby suspend) or "freeze" (for suspend type freeze) 7130 as the system sleep state during system startup with 7131 the optional capability to repeat N number of times. 7132 The system is woken from this state using a 7133 wakeup-capable RTC alarm. 7134 7135 thash_entries= [KNL,NET] 7136 Set number of hash buckets for TCP connection 7137 7138 thermal.act= [HW,ACPI] 7139 -1: disable all active trip points in all thermal zones 7140 <degrees C>: override all lowest active trip points 7141 7142 thermal.crt= [HW,ACPI] 7143 -1: disable all critical trip points in all thermal zones 7144 <degrees C>: override all critical trip points 7145 7146 thermal.off= [HW,ACPI] 7147 1: disable ACPI thermal control 7148 7149 thermal.psv= [HW,ACPI] 7150 -1: disable all passive trip points 7151 <degrees C>: override all passive trip points to this 7152 value 7153 7154 thermal.tzp= [HW,ACPI] 7155 Specify global default ACPI thermal zone polling rate 7156 <deci-seconds>: poll all this frequency 7157 0: no polling (default) 7158 7159 thp_anon= [KNL] 7160 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7161 state is one of "always", "madvise", "never" or "inherit". 7162 Control the default behavior of the system with respect 7163 to anonymous transparent hugepages. 7164 Can be used multiple times for multiple anon THP sizes. 7165 See Documentation/admin-guide/mm/transhuge.rst for more 7166 details. 7167 7168 threadirqs [KNL,EARLY] 7169 Force threading of all interrupt handlers except those 7170 marked explicitly IRQF_NO_THREAD. 7171 7172 thp_shmem= [KNL] 7173 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7174 Control the default policy of each hugepage size for the 7175 internal shmem mount. <policy> is one of policies available 7176 for the shmem mount ("always", "inherit", "never", "within_size", 7177 and "advise"). 7178 It can be used multiple times for multiple shmem THP sizes. 7179 See Documentation/admin-guide/mm/transhuge.rst for more 7180 details. 7181 7182 topology= [S390,EARLY] 7183 Format: {off | on} 7184 Specify if the kernel should make use of the cpu 7185 topology information if the hardware supports this. 7186 The scheduler will make use of this information and 7187 e.g. base its process migration decisions on it. 7188 Default is on. 7189 7190 torture.disable_onoff_at_boot= [KNL] 7191 Prevent the CPU-hotplug component of torturing 7192 until after init has spawned. 7193 7194 torture.ftrace_dump_at_shutdown= [KNL] 7195 Dump the ftrace buffer at torture-test shutdown, 7196 even if there were no errors. This can be a 7197 very costly operation when many torture tests 7198 are running concurrently, especially on systems 7199 with rotating-rust storage. 7200 7201 torture.verbose_sleep_frequency= [KNL] 7202 Specifies how many verbose printk()s should be 7203 emitted between each sleep. The default of zero 7204 disables verbose-printk() sleeping. 7205 7206 torture.verbose_sleep_duration= [KNL] 7207 Duration of each verbose-printk() sleep in jiffies. 7208 7209 tpm.disable_pcr_integrity= [HW,TPM] 7210 Do not protect PCR registers from unintended physical 7211 access, or interposers in the bus by the means of 7212 having an integrity protected session wrapped around 7213 TPM2_PCR_Extend command. Consider this in a situation 7214 where TPM is heavily utilized by IMA, thus protection 7215 causing a major performance hit, and the space where 7216 machines are deployed is by other means guarded. 7217 7218 tpm_suspend_pcr=[HW,TPM] 7219 Format: integer pcr id 7220 Specify that at suspend time, the tpm driver 7221 should extend the specified pcr with zeros, 7222 as a workaround for some chips which fail to 7223 flush the last written pcr on TPM_SaveState. 7224 This will guarantee that all the other pcrs 7225 are saved. 7226 7227 tpm_tis.interrupts= [HW,TPM] 7228 Enable interrupts for the MMIO based physical layer 7229 for the FIFO interface. By default it is set to false 7230 (0). For more information about TPM hardware interfaces 7231 defined by Trusted Computing Group (TCG) see 7232 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7233 7234 tp_printk [FTRACE] 7235 Have the tracepoints sent to printk as well as the 7236 tracing ring buffer. This is useful for early boot up 7237 where the system hangs or reboots and does not give the 7238 option for reading the tracing buffer or performing a 7239 ftrace_dump_on_oops. 7240 7241 To turn off having tracepoints sent to printk, 7242 echo 0 > /proc/sys/kernel/tracepoint_printk 7243 Note, echoing 1 into this file without the 7244 tp_printk kernel cmdline option has no effect. 7245 7246 The tp_printk_stop_on_boot (see below) can also be used 7247 to stop the printing of events to console at 7248 late_initcall_sync. 7249 7250 ** CAUTION ** 7251 7252 Having tracepoints sent to printk() and activating high 7253 frequency tracepoints such as irq or sched, can cause 7254 the system to live lock. 7255 7256 tp_printk_stop_on_boot [FTRACE] 7257 When tp_printk (above) is set, it can cause a lot of noise 7258 on the console. It may be useful to only include the 7259 printing of events during boot up, as user space may 7260 make the system inoperable. 7261 7262 This command line option will stop the printing of events 7263 to console at the late_initcall_sync() time frame. 7264 7265 trace_buf_size=nn[KMG] 7266 [FTRACE] will set tracing buffer size on each cpu. 7267 7268 trace_clock= [FTRACE] Set the clock used for tracing events 7269 at boot up. 7270 local - Use the per CPU time stamp counter 7271 (converted into nanoseconds). Fast, but 7272 depending on the architecture, may not be 7273 in sync between CPUs. 7274 global - Event time stamps are synchronize across 7275 CPUs. May be slower than the local clock, 7276 but better for some race conditions. 7277 counter - Simple counting of events (1, 2, ..) 7278 note, some counts may be skipped due to the 7279 infrastructure grabbing the clock more than 7280 once per event. 7281 uptime - Use jiffies as the time stamp. 7282 perf - Use the same clock that perf uses. 7283 mono - Use ktime_get_mono_fast_ns() for time stamps. 7284 mono_raw - Use ktime_get_raw_fast_ns() for time 7285 stamps. 7286 boot - Use ktime_get_boot_fast_ns() for time stamps. 7287 Architectures may add more clocks. See 7288 Documentation/trace/ftrace.rst for more details. 7289 7290 trace_event=[event-list] 7291 [FTRACE] Set and start specified trace events in order 7292 to facilitate early boot debugging. The event-list is a 7293 comma-separated list of trace events to enable. See 7294 also Documentation/trace/events.rst 7295 7296 To enable modules, use :mod: keyword: 7297 7298 trace_event=:mod:<module> 7299 7300 The value before :mod: will only enable specific events 7301 that are part of the module. See the above mentioned 7302 document for more information. 7303 7304 trace_instance=[instance-info] 7305 [FTRACE] Create a ring buffer instance early in boot up. 7306 This will be listed in: 7307 7308 /sys/kernel/tracing/instances 7309 7310 Events can be enabled at the time the instance is created 7311 via: 7312 7313 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7314 7315 Note, the "<system*>:" portion is optional if the event is 7316 unique. 7317 7318 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7319 7320 will enable the "sched_switch" event (note, the "sched:" is optional, and 7321 the same thing would happen if it was left off). The irq_handler_entry 7322 event, and all events under the "initcall" system. 7323 7324 Flags can be added to the instance to modify its behavior when it is 7325 created. The flags are separated by '^'. 7326 7327 The available flags are: 7328 7329 traceoff - Have the tracing instance tracing disabled after it is created. 7330 traceprintk - Have trace_printk() write into this trace instance 7331 (note, "printk" and "trace_printk" can also be used) 7332 7333 trace_instance=foo^traceoff^traceprintk,sched,irq 7334 7335 The flags must come before the defined events. 7336 7337 If memory has been reserved (see memmap for x86), the instance 7338 can use that memory: 7339 7340 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7341 7342 The above will create a "boot_map" instance that uses the physical 7343 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7344 instance will be split up accordingly. 7345 7346 Alternatively, the memory can be reserved by the reserve_mem option: 7347 7348 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7349 7350 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7351 and place the ring buffer in this memory. Note that due to KASLR, the 7352 memory may not be the same location each time, which will not preserve 7353 the buffer content. 7354 7355 Also note that the layout of the ring buffer data may change between 7356 kernel versions where the validator will fail and reset the ring buffer 7357 if the layout is not the same as the previous kernel. 7358 7359 If the ring buffer is used for persistent bootups and has events enabled, 7360 it is recommend to disable tracing so that events from a previous boot do not 7361 mix with events of the current boot (unless you are debugging a random crash 7362 at boot up). 7363 7364 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7365 7366 Note, saving the trace buffer across reboots does require that the system 7367 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7368 can force a memory reset on boot which will clear any trace that was stored. 7369 This is just one of many ways that can clear memory. Make sure your system 7370 keeps the content of memory across reboots before relying on this option. 7371 7372 NB: Both the mapped address and size must be page aligned for the architecture. 7373 7374 See also Documentation/trace/debugging.rst 7375 7376 7377 trace_options=[option-list] 7378 [FTRACE] Enable or disable tracer options at boot. 7379 The option-list is a comma delimited list of options 7380 that can be enabled or disabled just as if you were 7381 to echo the option name into 7382 7383 /sys/kernel/tracing/trace_options 7384 7385 For example, to enable stacktrace option (to dump the 7386 stack trace of each event), add to the command line: 7387 7388 trace_options=stacktrace 7389 7390 See also Documentation/trace/ftrace.rst "trace options" 7391 section. 7392 7393 trace_trigger=[trigger-list] 7394 [FTRACE] Add a event trigger on specific events. 7395 Set a trigger on top of a specific event, with an optional 7396 filter. 7397 7398 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7399 Where more than one trigger may be specified that are comma deliminated. 7400 7401 For example: 7402 7403 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7404 7405 The above will enable the "stacktrace" trigger on the "sched_switch" 7406 event but only trigger it if the "prev_state" of the "sched_switch" 7407 event is "2" (TASK_UNINTERUPTIBLE). 7408 7409 See also "Event triggers" in Documentation/trace/events.rst 7410 7411 7412 traceoff_after_boot 7413 [FTRACE] Sometimes tracing is used to debug issues 7414 during the boot process. Since the trace buffer has a 7415 limited amount of storage, it may be prudent to 7416 disable tracing after the boot is finished, otherwise 7417 the critical information may be overwritten. With this 7418 option, the main tracing buffer will be turned off at 7419 the end of the boot process. 7420 7421 traceoff_on_warning 7422 [FTRACE] enable this option to disable tracing when a 7423 warning is hit. This turns off "tracing_on". Tracing can 7424 be enabled again by echoing '1' into the "tracing_on" 7425 file located in /sys/kernel/tracing/ 7426 7427 This option is useful, as it disables the trace before 7428 the WARNING dump is called, which prevents the trace to 7429 be filled with content caused by the warning output. 7430 7431 This option can also be set at run time via the sysctl 7432 option: kernel/traceoff_on_warning 7433 7434 transparent_hugepage= 7435 [KNL] 7436 Format: [always|madvise|never] 7437 Can be used to control the default behavior of the system 7438 with respect to transparent hugepages. 7439 See Documentation/admin-guide/mm/transhuge.rst 7440 for more details. 7441 7442 transparent_hugepage_shmem= [KNL] 7443 Format: [always|within_size|advise|never|deny|force] 7444 Can be used to control the hugepage allocation policy for 7445 the internal shmem mount. 7446 See Documentation/admin-guide/mm/transhuge.rst 7447 for more details. 7448 7449 transparent_hugepage_tmpfs= [KNL] 7450 Format: [always|within_size|advise|never] 7451 Can be used to control the default hugepage allocation policy 7452 for the tmpfs mount. 7453 See Documentation/admin-guide/mm/transhuge.rst 7454 for more details. 7455 7456 trusted.source= [KEYS] 7457 Format: <string> 7458 This parameter identifies the trust source as a backend 7459 for trusted keys implementation. Supported trust 7460 sources: 7461 - "tpm" 7462 - "tee" 7463 - "caam" 7464 - "dcp" 7465 If not specified then it defaults to iterating through 7466 the trust source list starting with TPM and assigns the 7467 first trust source as a backend which is initialized 7468 successfully during iteration. 7469 7470 trusted.rng= [KEYS] 7471 Format: <string> 7472 The RNG used to generate key material for trusted keys. 7473 Can be one of: 7474 - "kernel" 7475 - the same value as trusted.source: "tpm" or "tee" 7476 - "default" 7477 If not specified, "default" is used. In this case, 7478 the RNG's choice is left to each individual trust source. 7479 7480 trusted.dcp_use_otp_key 7481 This is intended to be used in combination with 7482 trusted.source=dcp and will select the DCP OTP key 7483 instead of the DCP UNIQUE key blob encryption. 7484 7485 trusted.dcp_skip_zk_test 7486 This is intended to be used in combination with 7487 trusted.source=dcp and will disable the check if the 7488 blob key is all zeros. This is helpful for situations where 7489 having this key zero'ed is acceptable. E.g. in testing 7490 scenarios. 7491 7492 tsc= Disable clocksource stability checks for TSC. 7493 Format: <string> 7494 [x86] reliable: mark tsc clocksource as reliable, this 7495 disables clocksource verification at runtime, as well 7496 as the stability checks done at bootup. Used to enable 7497 high-resolution timer mode on older hardware, and in 7498 virtualized environment. 7499 [x86] noirqtime: Do not use TSC to do irq accounting. 7500 Used to run time disable IRQ_TIME_ACCOUNTING on any 7501 platforms where RDTSC is slow and this accounting 7502 can add overhead. 7503 [x86] unstable: mark the TSC clocksource as unstable, this 7504 marks the TSC unconditionally unstable at bootup and 7505 avoids any further wobbles once the TSC watchdog notices. 7506 [x86] nowatchdog: disable clocksource watchdog. Used 7507 in situations with strict latency requirements (where 7508 interruptions from clocksource watchdog are not 7509 acceptable). 7510 [x86] recalibrate: force recalibration against a HW timer 7511 (HPET or PM timer) on systems whose TSC frequency was 7512 obtained from HW or FW using either an MSR or CPUID(0x15). 7513 Warn if the difference is more than 500 ppm. 7514 [x86] watchdog: Use TSC as the watchdog clocksource with 7515 which to check other HW timers (HPET or PM timer), but 7516 only on systems where TSC has been deemed trustworthy. 7517 This will be suppressed by an earlier tsc=nowatchdog and 7518 can be overridden by a later tsc=nowatchdog. A console 7519 message will flag any such suppression or overriding. 7520 7521 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7522 value instead. Useful when the early TSC frequency discovery 7523 procedure is not reliable, such as on overclocked systems 7524 with CPUID.16h support and partial CPUID.15h support. 7525 Format: <unsigned int> 7526 7527 tsx= [X86] Control Transactional Synchronization 7528 Extensions (TSX) feature in Intel processors that 7529 support TSX control. 7530 7531 This parameter controls the TSX feature. The options are: 7532 7533 on - Enable TSX on the system. Although there are 7534 mitigations for all known security vulnerabilities, 7535 TSX has been known to be an accelerator for 7536 several previous speculation-related CVEs, and 7537 so there may be unknown security risks associated 7538 with leaving it enabled. 7539 7540 off - Disable TSX on the system. (Note that this 7541 option takes effect only on newer CPUs which are 7542 not vulnerable to MDS, i.e., have 7543 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7544 the new IA32_TSX_CTRL MSR through a microcode 7545 update. This new MSR allows for the reliable 7546 deactivation of the TSX functionality.) 7547 7548 auto - Disable TSX if X86_BUG_TAA is present, 7549 otherwise enable TSX on the system. 7550 7551 Not specifying this option is equivalent to tsx=off. 7552 7553 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7554 for more details. 7555 7556 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7557 Abort (TAA) vulnerability. 7558 7559 Similar to Micro-architectural Data Sampling (MDS) 7560 certain CPUs that support Transactional 7561 Synchronization Extensions (TSX) are vulnerable to an 7562 exploit against CPU internal buffers which can forward 7563 information to a disclosure gadget under certain 7564 conditions. 7565 7566 In vulnerable processors, the speculatively forwarded 7567 data can be used in a cache side channel attack, to 7568 access data to which the attacker does not have direct 7569 access. 7570 7571 This parameter controls the TAA mitigation. The 7572 options are: 7573 7574 full - Enable TAA mitigation on vulnerable CPUs 7575 if TSX is enabled. 7576 7577 full,nosmt - Enable TAA mitigation and disable SMT on 7578 vulnerable CPUs. If TSX is disabled, SMT 7579 is not disabled because CPU is not 7580 vulnerable to cross-thread TAA attacks. 7581 off - Unconditionally disable TAA mitigation 7582 7583 On MDS-affected machines, tsx_async_abort=off can be 7584 prevented by an active MDS mitigation as both vulnerabilities 7585 are mitigated with the same mechanism so in order to disable 7586 this mitigation, you need to specify mds=off too. 7587 7588 Not specifying this option is equivalent to 7589 tsx_async_abort=full. On CPUs which are MDS affected 7590 and deploy MDS mitigation, TAA mitigation is not 7591 required and doesn't provide any additional 7592 mitigation. 7593 7594 For details see: 7595 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7596 7597 turbografx.map[2|3]= [HW,JOY] 7598 TurboGraFX parallel port interface 7599 Format: 7600 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 7601 See also Documentation/input/devices/joystick-parport.rst 7602 7603 udbg-immortal [PPC] When debugging early kernel crashes that 7604 happen after console_init() and before a proper 7605 console driver takes over, this boot options might 7606 help "seeing" what's going on. 7607 7608 uhash_entries= [KNL,NET] 7609 Set number of hash buckets for UDP/UDP-Lite connections 7610 7611 uhci-hcd.ignore_oc= 7612 [USB] Ignore overcurrent events (default N). 7613 Some badly-designed motherboards generate lots of 7614 bogus events, for ports that aren't wired to 7615 anything. Set this parameter to avoid log spamming. 7616 Note that genuine overcurrent events won't be 7617 reported either. 7618 7619 unaligned_scalar_speed= 7620 [RISCV] 7621 Format: {slow | fast | unsupported} 7622 Allow skipping scalar unaligned access speed tests. This 7623 is useful for testing alternative code paths and to skip 7624 the tests in environments where they run too slowly. All 7625 CPUs must have the same scalar unaligned access speed. 7626 7627 unaligned_vector_speed= 7628 [RISCV] 7629 Format: {slow | fast | unsupported} 7630 Allow skipping vector unaligned access speed tests. This 7631 is useful for testing alternative code paths and to skip 7632 the tests in environments where they run too slowly. All 7633 CPUs must have the same vector unaligned access speed. 7634 7635 unknown_nmi_panic 7636 [X86] Cause panic on unknown NMI. 7637 7638 unwind_debug [X86-64,EARLY] 7639 Enable unwinder debug output. This can be 7640 useful for debugging certain unwinder error 7641 conditions, including corrupt stacks and 7642 bad/missing unwinder metadata. 7643 7644 usbcore.authorized_default= 7645 [USB] Default USB device authorization: 7646 (default -1 = authorized (same as 1), 7647 0 = not authorized, 1 = authorized, 2 = authorized 7648 if device connected to internal port) 7649 7650 usbcore.autosuspend= 7651 [USB] The autosuspend time delay (in seconds) used 7652 for newly-detected USB devices (default 2). This 7653 is the time required before an idle device will be 7654 autosuspended. Devices for which the delay is set 7655 to a negative value won't be autosuspended at all. 7656 7657 usbcore.usbfs_snoop= 7658 [USB] Set to log all usbfs traffic (default 0 = off). 7659 7660 usbcore.usbfs_snoop_max= 7661 [USB] Maximum number of bytes to snoop in each URB 7662 (default = 65536). 7663 7664 usbcore.blinkenlights= 7665 [USB] Set to cycle leds on hubs (default 0 = off). 7666 7667 usbcore.old_scheme_first= 7668 [USB] Start with the old device initialization 7669 scheme (default 0 = off). 7670 7671 usbcore.usbfs_memory_mb= 7672 [USB] Memory limit (in MB) for buffers allocated by 7673 usbfs (default = 16, 0 = max = 2047). 7674 7675 usbcore.use_both_schemes= 7676 [USB] Try the other device initialization scheme 7677 if the first one fails (default 1 = enabled). 7678 7679 usbcore.initial_descriptor_timeout= 7680 [USB] Specifies timeout for the initial 64-byte 7681 USB_REQ_GET_DESCRIPTOR request in milliseconds 7682 (default 5000 = 5.0 seconds). 7683 7684 usbcore.nousb [USB] Disable the USB subsystem 7685 7686 usbcore.quirks= 7687 [USB] A list of quirk entries to augment the built-in 7688 usb core quirk list. List entries are separated by 7689 commas. Each entry has the form 7690 VendorID:ProductID:Flags. The IDs are 4-digit hex 7691 numbers and Flags is a set of letters. Each letter 7692 will change the built-in quirk; setting it if it is 7693 clear and clearing it if it is set. The letters have 7694 the following meanings: 7695 a = USB_QUIRK_STRING_FETCH_255 (string 7696 descriptors must not be fetched using 7697 a 255-byte read); 7698 b = USB_QUIRK_RESET_RESUME (device can't resume 7699 correctly so reset it instead); 7700 c = USB_QUIRK_NO_SET_INTF (device can't handle 7701 Set-Interface requests); 7702 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 7703 handle its Configuration or Interface 7704 strings); 7705 e = USB_QUIRK_RESET (device can't be reset 7706 (e.g morph devices), don't use reset); 7707 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 7708 more interface descriptions than the 7709 bNumInterfaces count, and can't handle 7710 talking to these interfaces); 7711 g = USB_QUIRK_DELAY_INIT (device needs a pause 7712 during initialization, after we read 7713 the device descriptor); 7714 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 7715 high speed and super speed interrupt 7716 endpoints, the USB 2.0 and USB 3.0 spec 7717 require the interval in microframes (1 7718 microframe = 125 microseconds) to be 7719 calculated as interval = 2 ^ 7720 (bInterval-1). 7721 Devices with this quirk report their 7722 bInterval as the result of this 7723 calculation instead of the exponent 7724 variable used in the calculation); 7725 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 7726 handle device_qualifier descriptor 7727 requests); 7728 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 7729 generates spurious wakeup, ignore 7730 remote wakeup capability); 7731 k = USB_QUIRK_NO_LPM (device can't handle Link 7732 Power Management); 7733 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 7734 (Device reports its bInterval as linear 7735 frames instead of the USB 2.0 7736 calculation); 7737 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 7738 to be disconnected before suspend to 7739 prevent spurious wakeup); 7740 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 7741 pause after every control message); 7742 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 7743 delay after resetting its port); 7744 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 7745 (Reduce timeout of the SET_ADDRESS 7746 request from 5000 ms to 500 ms); 7747 Example: quirks=0781:5580:bk,0a5c:5834:gij 7748 7749 usbhid.mousepoll= 7750 [USBHID] The interval which mice are to be polled at. 7751 7752 usbhid.jspoll= 7753 [USBHID] The interval which joysticks are to be polled at. 7754 7755 usbhid.kbpoll= 7756 [USBHID] The interval which keyboards are to be polled at. 7757 7758 usb-storage.delay_use= 7759 [UMS] The delay in seconds before a new device is 7760 scanned for Logical Units (default 1). 7761 Optionally the delay in milliseconds if the value has 7762 suffix with "ms". 7763 Example: delay_use=2567ms 7764 7765 usb-storage.quirks= 7766 [UMS] A list of quirks entries to supplement or 7767 override the built-in unusual_devs list. List 7768 entries are separated by commas. Each entry has 7769 the form VID:PID:Flags where VID and PID are Vendor 7770 and Product ID values (4-digit hex numbers) and 7771 Flags is a set of characters, each corresponding 7772 to a common usb-storage quirk flag as follows: 7773 a = SANE_SENSE (collect more than 18 bytes 7774 of sense data, not on uas); 7775 b = BAD_SENSE (don't collect more than 18 7776 bytes of sense data, not on uas); 7777 c = FIX_CAPACITY (decrease the reported 7778 device capacity by one sector); 7779 d = NO_READ_DISC_INFO (don't use 7780 READ_DISC_INFO command, not on uas); 7781 e = NO_READ_CAPACITY_16 (don't use 7782 READ_CAPACITY_16 command); 7783 f = NO_REPORT_OPCODES (don't use report opcodes 7784 command, uas only); 7785 g = MAX_SECTORS_240 (don't transfer more than 7786 240 sectors at a time, uas only); 7787 h = CAPACITY_HEURISTICS (decrease the 7788 reported device capacity by one 7789 sector if the number is odd); 7790 i = IGNORE_DEVICE (don't bind to this 7791 device); 7792 j = NO_REPORT_LUNS (don't use report luns 7793 command, uas only); 7794 k = NO_SAME (do not use WRITE_SAME, uas only) 7795 l = NOT_LOCKABLE (don't try to lock and 7796 unlock ejectable media, not on uas); 7797 m = MAX_SECTORS_64 (don't transfer more 7798 than 64 sectors = 32 KB at a time, 7799 not on uas); 7800 n = INITIAL_READ10 (force a retry of the 7801 initial READ(10) command, not on uas); 7802 o = CAPACITY_OK (accept the capacity 7803 reported by the device, not on uas); 7804 p = WRITE_CACHE (the device cache is ON 7805 by default, not on uas); 7806 r = IGNORE_RESIDUE (the device reports 7807 bogus residue values, not on uas); 7808 s = SINGLE_LUN (the device has only one 7809 Logical Unit); 7810 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 7811 commands, uas only); 7812 u = IGNORE_UAS (don't bind to the uas driver); 7813 w = NO_WP_DETECT (don't test whether the 7814 medium is write-protected). 7815 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 7816 even if the device claims no cache, 7817 not on uas) 7818 Example: quirks=0419:aaf5:rl,0421:0433:rc 7819 7820 user_debug= [KNL,ARM] 7821 Format: <int> 7822 See arch/arm/Kconfig.debug help text. 7823 1 - undefined instruction events 7824 2 - system calls 7825 4 - invalid data aborts 7826 8 - SIGSEGV faults 7827 16 - SIGBUS faults 7828 Example: user_debug=31 7829 7830 vdso= [X86,SH,SPARC] 7831 On X86_32, this is an alias for vdso32=. Otherwise: 7832 7833 vdso=1: enable VDSO (the default) 7834 vdso=0: disable VDSO mapping 7835 7836 vdso32= [X86] Control the 32-bit vDSO 7837 vdso32=1: enable 32-bit VDSO 7838 vdso32=0 or vdso32=2: disable 32-bit VDSO 7839 7840 See the help text for CONFIG_COMPAT_VDSO for more 7841 details. If CONFIG_COMPAT_VDSO is set, the default is 7842 vdso32=0; otherwise, the default is vdso32=1. 7843 7844 For compatibility with older kernels, vdso32=2 is an 7845 alias for vdso32=0. 7846 7847 Try vdso32=0 if you encounter an error that says: 7848 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 7849 7850 video= [FB,EARLY] Frame buffer configuration 7851 See Documentation/fb/modedb.rst. 7852 7853 video.brightness_switch_enabled= [ACPI] 7854 Format: [0|1] 7855 If set to 1, on receiving an ACPI notify event 7856 generated by hotkey, video driver will adjust brightness 7857 level and then send out the event to user space through 7858 the allocated input device. If set to 0, video driver 7859 will only send out the event without touching backlight 7860 brightness level. 7861 default: 1 7862 7863 virtio_mmio.device= 7864 [VMMIO] Memory mapped virtio (platform) device. 7865 7866 <size>@<baseaddr>:<irq>[:<id>] 7867 where: 7868 <size> := size (can use standard suffixes 7869 like K, M and G) 7870 <baseaddr> := physical base address 7871 <irq> := interrupt number (as passed to 7872 request_irq()) 7873 <id> := (optional) platform device id 7874 example: 7875 virtio_mmio.device=1K@0x100b0000:48:7 7876 7877 Can be used multiple times for multiple devices. 7878 7879 vga= [BOOT,X86-32] Select a particular video mode 7880 See Documentation/arch/x86/boot.rst and 7881 Documentation/admin-guide/svga.rst. 7882 Use vga=ask for menu. 7883 This is actually a boot loader parameter; the value is 7884 passed to the kernel using a special protocol. 7885 7886 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 7887 May slow down system boot speed, especially when 7888 enabled on systems with a large amount of memory. 7889 All options are enabled by default, and this 7890 interface is meant to allow for selectively 7891 enabling or disabling specific virtual memory 7892 debugging features. 7893 7894 Available options are: 7895 P Enable page structure init time poisoning 7896 - Disable all of the above options 7897 7898 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 7899 exact size of <nn>. This can be used to increase 7900 the minimum size (128MB on x86, arm32 platforms). 7901 It can also be used to decrease the size and leave more room 7902 for directly mapped kernel RAM. Note that this parameter does 7903 not exist on many other platforms (including arm64, alpha, 7904 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 7905 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 7906 7907 vmcp_cma=nn[MG] [KNL,S390,EARLY] 7908 Sets the memory size reserved for contiguous memory 7909 allocations for the vmcp device driver. 7910 7911 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 7912 Format: <command> 7913 7914 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 7915 Format: <command> 7916 7917 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 7918 Format: <command> 7919 7920 vsyscall= [X86-64,EARLY] 7921 Controls the behavior of vsyscalls (i.e. calls to 7922 fixed addresses of 0xffffffffff600x00 from legacy 7923 code). Most statically-linked binaries and older 7924 versions of glibc use these calls. Because these 7925 functions are at fixed addresses, they make nice 7926 targets for exploits that can control RIP. 7927 7928 emulate Vsyscalls turn into traps and are emulated 7929 reasonably safely. The vsyscall page is 7930 readable. 7931 7932 xonly [default] Vsyscalls turn into traps and are 7933 emulated reasonably safely. The vsyscall 7934 page is not readable. 7935 7936 none Vsyscalls don't work at all. This makes 7937 them quite hard to use for exploits but 7938 might break your system. 7939 7940 vt.color= [VT] Default text color. 7941 Format: 0xYX, X = foreground, Y = background. 7942 Default: 0x07 = light gray on black. 7943 7944 vt.cur_default= [VT] Default cursor shape. 7945 Format: 0xCCBBAA, where AA, BB, and CC are the same as 7946 the parameters of the <Esc>[?A;B;Cc escape sequence; 7947 see vga-softcursor.rst. Default: 2 = underline. 7948 7949 vt.default_blu= [VT] 7950 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 7951 Change the default blue palette of the console. 7952 This is a 16-member array composed of values 7953 ranging from 0-255. 7954 7955 vt.default_grn= [VT] 7956 Format: <green0>,<green1>,<green2>,...,<green15> 7957 Change the default green palette of the console. 7958 This is a 16-member array composed of values 7959 ranging from 0-255. 7960 7961 vt.default_red= [VT] 7962 Format: <red0>,<red1>,<red2>,...,<red15> 7963 Change the default red palette of the console. 7964 This is a 16-member array composed of values 7965 ranging from 0-255. 7966 7967 vt.default_utf8= 7968 [VT] 7969 Format=<0|1> 7970 Set system-wide default UTF-8 mode for all tty's. 7971 Default is 1, i.e. UTF-8 mode is enabled for all 7972 newly opened terminals. 7973 7974 vt.global_cursor_default= 7975 [VT] 7976 Format=<-1|0|1> 7977 Set system-wide default for whether a cursor 7978 is shown on new VTs. Default is -1, 7979 i.e. cursors will be created by default unless 7980 overridden by individual drivers. 0 will hide 7981 cursors, 1 will display them. 7982 7983 vt.italic= [VT] Default color for italic text; 0-15. 7984 Default: 2 = green. 7985 7986 vt.underline= [VT] Default color for underlined text; 0-15. 7987 Default: 3 = cyan. 7988 7989 watchdog timers [HW,WDT] For information on watchdog timers, 7990 see Documentation/watchdog/watchdog-parameters.rst 7991 or other driver-specific files in the 7992 Documentation/watchdog/ directory. 7993 7994 watchdog_thresh= 7995 [KNL] 7996 Set the hard lockup detector stall duration 7997 threshold in seconds. The soft lockup detector 7998 threshold is set to twice the value. A value of 0 7999 disables both lockup detectors. Default is 10 8000 seconds. 8001 8002 workqueue.unbound_cpus= 8003 [KNL,SMP] Specify to constrain one or some CPUs 8004 to use in unbound workqueues. 8005 Format: <cpu-list> 8006 By default, all online CPUs are available for 8007 unbound workqueues. 8008 8009 workqueue.watchdog_thresh= 8010 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8011 warn stall conditions and dump internal state to 8012 help debugging. 0 disables workqueue stall 8013 detection; otherwise, it's the stall threshold 8014 duration in seconds. The default value is 30 and 8015 it can be updated at runtime by writing to the 8016 corresponding sysfs file. 8017 8018 workqueue.panic_on_stall=<uint> 8019 Panic when workqueue stall is detected by 8020 CONFIG_WQ_WATCHDOG. It sets the number times of the 8021 stall to trigger panic. 8022 8023 The default is 0, which disables the panic on stall. 8024 8025 workqueue.cpu_intensive_thresh_us= 8026 Per-cpu work items which run for longer than this 8027 threshold are automatically considered CPU intensive 8028 and excluded from concurrency management to prevent 8029 them from noticeably delaying other per-cpu work 8030 items. Default is 10000 (10ms). 8031 8032 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8033 will report the work functions which violate this 8034 threshold repeatedly. They are likely good 8035 candidates for using WQ_UNBOUND workqueues instead. 8036 8037 workqueue.cpu_intensive_warning_thresh=<uint> 8038 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8039 will report the work functions which violate the 8040 intensive_threshold_us repeatedly. In order to prevent 8041 spurious warnings, start printing only after a work 8042 function has violated this threshold number of times. 8043 8044 The default is 4 times. 0 disables the warning. 8045 8046 workqueue.power_efficient 8047 Per-cpu workqueues are generally preferred because 8048 they show better performance thanks to cache 8049 locality; unfortunately, per-cpu workqueues tend to 8050 be more power hungry than unbound workqueues. 8051 8052 Enabling this makes the per-cpu workqueues which 8053 were observed to contribute significantly to power 8054 consumption unbound, leading to measurably lower 8055 power usage at the cost of small performance 8056 overhead. 8057 8058 The default value of this parameter is determined by 8059 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8060 8061 workqueue.default_affinity_scope= 8062 Select the default affinity scope to use for unbound 8063 workqueues. Can be one of "cpu", "smt", "cache", 8064 "numa" and "system". Default is "cache". For more 8065 information, see the Affinity Scopes section in 8066 Documentation/core-api/workqueue.rst. 8067 8068 This can be changed after boot by writing to the 8069 matching /sys/module/workqueue/parameters file. All 8070 workqueues with the "default" affinity scope will be 8071 updated accordingly. 8072 8073 workqueue.debug_force_rr_cpu 8074 Workqueue used to implicitly guarantee that work 8075 items queued without explicit CPU specified are put 8076 on the local CPU. This guarantee is no longer true 8077 and while local CPU is still preferred work items 8078 may be put on foreign CPUs. This debug option 8079 forces round-robin CPU selection to flush out 8080 usages which depend on the now broken guarantee. 8081 When enabled, memory and cache locality will be 8082 impacted. 8083 8084 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8085 Type) of ioremap_wc(). 8086 8087 on - Enable writecombine, use WUC for ioremap_wc() 8088 off - Disable writecombine, use SUC for ioremap_wc() 8089 8090 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8091 default x2apic cluster mode on platforms 8092 supporting x2apic. 8093 8094 xen_512gb_limit [KNL,X86-64,XEN] 8095 Restricts the kernel running paravirtualized under Xen 8096 to use only up to 512 GB of RAM. The reason to do so is 8097 crash analysis tools and Xen tools for doing domain 8098 save/restore/migration must be enabled to handle larger 8099 domains. 8100 8101 xen_emul_unplug= [HW,X86,XEN,EARLY] 8102 Unplug Xen emulated devices 8103 Format: [unplug0,][unplug1] 8104 ide-disks -- unplug primary master IDE devices 8105 aux-ide-disks -- unplug non-primary-master IDE devices 8106 nics -- unplug network devices 8107 all -- unplug all emulated devices (NICs and IDE disks) 8108 unnecessary -- unplugging emulated devices is 8109 unnecessary even if the host did not respond to 8110 the unplug protocol 8111 never -- do not unplug even if version check succeeds 8112 8113 xen_legacy_crash [X86,XEN,EARLY] 8114 Crash from Xen panic notifier, without executing late 8115 panic() code such as dumping handler. 8116 8117 xen_mc_debug [X86,XEN,EARLY] 8118 Enable multicall debugging when running as a Xen PV guest. 8119 Enabling this feature will reduce performance a little 8120 bit, so it should only be enabled for obtaining extended 8121 debug data in case of multicall errors. 8122 8123 xen_msr_safe= [X86,XEN,EARLY] 8124 Format: <bool> 8125 Select whether to always use non-faulting (safe) MSR 8126 access functions when running as Xen PV guest. The 8127 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8128 8129 xen_nopv [X86] 8130 Disables the PV optimizations forcing the HVM guest to 8131 run as generic HVM guest with no PV drivers. 8132 This option is obsoleted by the "nopv" option, which 8133 has equivalent effect for XEN platform. 8134 8135 xen_no_vector_callback 8136 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8137 event channel interrupts. 8138 8139 xen_scrub_pages= [XEN] 8140 Boolean option to control scrubbing pages before giving them back 8141 to Xen, for use by other domains. Can be also changed at runtime 8142 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8143 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8144 8145 xen_timer_slop= [X86-64,XEN,EARLY] 8146 Set the timer slop (in nanoseconds) for the virtual Xen 8147 timers (default is 100000). This adjusts the minimum 8148 delta of virtualized Xen timers, where lower values 8149 improve timer resolution at the expense of processing 8150 more timer interrupts. 8151 8152 xen.balloon_boot_timeout= [XEN] 8153 The time (in seconds) to wait before giving up to boot 8154 in case initial ballooning fails to free enough memory. 8155 Applies only when running as HVM or PVH guest and 8156 started with less memory configured than allowed at 8157 max. Default is 180. 8158 8159 xen.event_eoi_delay= [XEN] 8160 How long to delay EOI handling in case of event 8161 storms (jiffies). Default is 10. 8162 8163 xen.event_loop_timeout= [XEN] 8164 After which time (jiffies) the event handling loop 8165 should start to delay EOI handling. Default is 2. 8166 8167 xen.fifo_events= [XEN] 8168 Boolean parameter to disable using fifo event handling 8169 even if available. Normally fifo event handling is 8170 preferred over the 2-level event handling, as it is 8171 fairer and the number of possible event channels is 8172 much higher. Default is on (use fifo events). 8173 8174 xirc2ps_cs= [NET,PCMCIA] 8175 Format: 8176 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8177 8178 xive= [PPC] 8179 By default on POWER9 and above, the kernel will 8180 natively use the XIVE interrupt controller. This option 8181 allows the fallback firmware mode to be used: 8182 8183 off Fallback to firmware control of XIVE interrupt 8184 controller on both pseries and powernv 8185 platforms. Only useful on POWER9 and above. 8186 8187 xive.store-eoi=off [PPC] 8188 By default on POWER10 and above, the kernel will use 8189 stores for EOI handling when the XIVE interrupt mode 8190 is active. This option allows the XIVE driver to use 8191 loads instead, as on POWER9. 8192 8193 xhci-hcd.quirks [USB,KNL] 8194 A hex value specifying bitmask with supplemental xhci 8195 host controller quirks. Meaning of each bit can be 8196 consulted in header drivers/usb/host/xhci.h. 8197 8198 xmon [PPC,EARLY] 8199 Format: { early | on | rw | ro | off } 8200 Controls if xmon debugger is enabled. Default is off. 8201 Passing only "xmon" is equivalent to "xmon=early". 8202 early Call xmon as early as possible on boot; xmon 8203 debugger is called from setup_arch(). 8204 on xmon debugger hooks will be installed so xmon 8205 is only called on a kernel crash. Default mode, 8206 i.e. either "ro" or "rw" mode, is controlled 8207 with CONFIG_XMON_DEFAULT_RO_MODE. 8208 rw xmon debugger hooks will be installed so xmon 8209 is called only on a kernel crash, mode is write, 8210 meaning SPR registers, memory and, other data 8211 can be written using xmon commands. 8212 ro same as "rw" option above but SPR registers, 8213 memory, and other data can't be written using 8214 xmon commands. 8215 off xmon is disabled. 8216