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 cfi= [X86-64] Set Control Flow Integrity checking features 612 when CONFIG_FINEIBT is enabled. 613 Format: feature[,feature...] 614 Default: auto 615 616 auto: Use FineIBT if IBT available, otherwise kCFI. 617 Under FineIBT, enable "paranoid" mode when 618 FRED is not available. 619 off: Turn off CFI checking. 620 kcfi: Use kCFI (disable FineIBT). 621 fineibt: Use FineIBT (even if IBT not available). 622 norand: Do not re-randomize CFI hashes. 623 paranoid: Add caller hash checking under FineIBT. 624 bhi: Enable register poisoning to stop speculation 625 across FineIBT. (Disabled by default.) 626 warn: Do not enforce CFI checking: warn only. 627 debug: Report CFI initialization details. 628 629 cgroup_disable= [KNL] Disable a particular controller or optional feature 630 Format: {name of the controller(s) or feature(s) to disable} 631 The effects of cgroup_disable=foo are: 632 - foo isn't auto-mounted if you mount all cgroups in 633 a single hierarchy 634 - foo isn't visible as an individually mountable 635 subsystem 636 - if foo is an optional feature then the feature is 637 disabled and corresponding cgroup files are not 638 created 639 {Currently only "memory" controller deal with this and 640 cut the overhead, others just disable the usage. So 641 only cgroup_disable=memory is actually worthy} 642 Specifying "pressure" disables per-cgroup pressure 643 stall information accounting feature 644 645 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 646 Format: { { controller | "all" | "named" } 647 [,{ controller | "all" | "named" }...] } 648 Like cgroup_disable, but only applies to cgroup v1; 649 the blacklisted controllers remain available in cgroup2. 650 "all" blacklists all controllers and "named" disables 651 named mounts. Specifying both "all" and "named" disables 652 all v1 hierarchies. 653 654 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 655 Format: { "true" | "false" } 656 /proc/cgroups lists only v1 controllers by default. 657 This compatibility option enables listing also v2 658 controllers (whose v1 code is not compiled!), so that 659 semi-legacy software can check this file to decide 660 about usage of v2 (sic) controllers. 661 662 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 663 Format: { "true" | "false" } 664 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 665 666 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 667 Format: <string> 668 nosocket -- Disable socket memory accounting. 669 nokmem -- Disable kernel memory accounting. 670 nobpf -- Disable BPF memory accounting. 671 672 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 673 Format: { "0" | "1" } 674 See security/selinux/Kconfig help text. 675 0 -- check protection applied by kernel (includes 676 any implied execute protection). 677 1 -- check protection requested by application. 678 Default value is set via a kernel config option. 679 Value can be changed at runtime via 680 /sys/fs/selinux/checkreqprot. 681 Setting checkreqprot to 1 is deprecated. 682 683 cio_ignore= [S390] 684 See Documentation/arch/s390/common_io.rst for details. 685 686 clearcpuid=X[,X...] [X86] 687 Disable CPUID feature X for the kernel. See 688 arch/x86/include/asm/cpufeatures.h for the valid bit 689 numbers X. Note the Linux-specific bits are not necessarily 690 stable over kernel options, but the vendor-specific 691 ones should be. 692 X can also be a string as appearing in the flags: line 693 in /proc/cpuinfo which does not have the above 694 instability issue. However, not all features have names 695 in /proc/cpuinfo. 696 Note that using this option will taint your kernel. 697 Also note that user programs calling CPUID directly 698 or using the feature without checking anything 699 will still see it. This just prevents it from 700 being used by the kernel or shown in /proc/cpuinfo. 701 Also note the kernel might malfunction if you disable 702 some critical bits. 703 704 clk_ignore_unused 705 [CLK] 706 Prevents the clock framework from automatically gating 707 clocks that have not been explicitly enabled by a Linux 708 device driver but are enabled in hardware at reset or 709 by the bootloader/firmware. Note that this does not 710 force such clocks to be always-on nor does it reserve 711 those clocks in any way. This parameter is useful for 712 debug and development, but should not be needed on a 713 platform with proper driver support. For more 714 information, see Documentation/driver-api/clk.rst. 715 716 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 717 [Deprecated] 718 Forces specified clocksource (if available) to be used 719 when calculating gettimeofday(). If specified 720 clocksource is not available, it defaults to PIT. 721 Format: { pit | tsc | cyclone | pmtmr } 722 723 clocksource= Override the default clocksource 724 Format: <string> 725 Override the default clocksource and use the clocksource 726 with the name specified. 727 Some clocksource names to choose from, depending on 728 the platform: 729 [all] jiffies (this is the base, fallback clocksource) 730 [ACPI] acpi_pm 731 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 732 pxa_timer,timer3,32k_counter,timer0_1 733 [X86-32] pit,hpet,tsc; 734 scx200_hrt on Geode; cyclone on IBM x440 735 [MIPS] MIPS 736 [PARISC] cr16 737 [S390] tod 738 [SH] SuperH 739 [SPARC64] tick 740 [X86-64] hpet,tsc 741 742 clocksource.arm_arch_timer.evtstrm= 743 [ARM,ARM64,EARLY] 744 Format: <bool> 745 Enable/disable the eventstream feature of the ARM 746 architected timer so that code using WFE-based polling 747 loops can be debugged more effectively on production 748 systems. 749 750 clocksource.verify_n_cpus= [KNL] 751 Limit the number of CPUs checked for clocksources 752 marked with CLOCK_SOURCE_VERIFY_PERCPU that 753 are marked unstable due to excessive skew. 754 A negative value says to check all CPUs, while 755 zero says not to check any. Values larger than 756 nr_cpu_ids are silently truncated to nr_cpu_ids. 757 The actual CPUs are chosen randomly, with 758 no replacement if the same CPU is chosen twice. 759 760 clocksource-wdtest.holdoff= [KNL] 761 Set the time in seconds that the clocksource 762 watchdog test waits before commencing its tests. 763 Defaults to zero when built as a module and to 764 10 seconds when built into the kernel. 765 766 cma=nn[MG]@[start[MG][-end[MG]]] 767 [KNL,CMA,EARLY] 768 Sets the size of kernel global memory area for 769 contiguous memory allocations and optionally the 770 placement constraint by the physical address range of 771 memory allocations. A value of 0 disables CMA 772 altogether. For more information, see 773 kernel/dma/contiguous.c 774 775 cma_pernuma=nn[MG] 776 [KNL,CMA,EARLY] 777 Sets the size of kernel per-numa memory area for 778 contiguous memory allocations. A value of 0 disables 779 per-numa CMA altogether. And If this option is not 780 specified, the default value is 0. 781 With per-numa CMA enabled, DMA users on node nid will 782 first try to allocate buffer from the pernuma area 783 which is located in node nid, if the allocation fails, 784 they will fallback to the global default memory area. 785 786 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 787 [KNL,CMA,EARLY] 788 Sets the size of kernel numa memory area for 789 contiguous memory allocations. It will reserve CMA 790 area for the specified node. 791 792 With numa CMA enabled, DMA users on node nid will 793 first try to allocate buffer from the numa area 794 which is located in node nid, if the allocation fails, 795 they will fallback to the global default memory area. 796 797 cmo_free_hint= [PPC] Format: { yes | no } 798 Specify whether pages are marked as being inactive 799 when they are freed. This is used in CMO environments 800 to determine OS memory pressure for page stealing by 801 a hypervisor. 802 Default: yes 803 804 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 805 Sets the size of memory pool for coherent, atomic dma 806 allocations, by default set to 256K. 807 808 com20020= [HW,NET] ARCnet - COM20020 chipset 809 Format: 810 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 811 812 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 813 Format: <io>[,<irq>] 814 815 com90xx= [HW,NET] 816 ARCnet - COM90xx chipset (memory-mapped buffers) 817 Format: <io>[,<irq>[,<memstart>]] 818 819 condev= [HW,S390] console device 820 conmode= 821 822 con3215_drop= [S390,EARLY] 3215 console drop mode. 823 Format: y|n|Y|N|1|0 824 When set to true, drop data on the 3215 console when 825 the console buffer is full. In this case the 826 operator using a 3270 terminal emulator (for example 827 x3270) does not have to enter the clear key for the 828 console output to advance and the kernel to continue. 829 This leads to a much faster boot time when a 3270 830 terminal emulator is active. If no 3270 terminal 831 emulator is used, this parameter has no effect. 832 833 console= [KNL] Output console device and options. 834 835 tty<n> Use the virtual console device <n>. 836 837 ttyS<n>[,options] 838 ttyUSB0[,options] 839 Use the specified serial port. The options are of 840 the form "bbbbpnf", where "bbbb" is the baud rate, 841 "p" is parity ("n", "o", or "e"), "n" is number of 842 bits, and "f" is flow control ("r" for RTS or 843 omit it). Default is "9600n8". 844 845 See Documentation/admin-guide/serial-console.rst for more 846 information. See 847 Documentation/networking/netconsole.rst for an 848 alternative. 849 850 <DEVNAME>:<n>.<n>[,options] 851 Use the specified serial port on the serial core bus. 852 The addressing uses DEVNAME of the physical serial port 853 device, followed by the serial core controller instance, 854 and the serial port instance. The options are the same 855 as documented for the ttyS addressing above. 856 857 The mapping of the serial ports to the tty instances 858 can be viewed with: 859 860 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 861 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 862 863 In the above example, the console can be addressed with 864 console=00:04:0.0. Note that a console addressed this 865 way will only get added when the related device driver 866 is ready. The use of an earlycon parameter in addition to 867 the console may be desired for console output early on. 868 869 uart[8250],io,<addr>[,options] 870 uart[8250],mmio,<addr>[,options] 871 uart[8250],mmio16,<addr>[,options] 872 uart[8250],mmio32,<addr>[,options] 873 uart[8250],0x<addr>[,options] 874 Start an early, polled-mode console on the 8250/16550 875 UART at the specified I/O port or MMIO address, 876 switching to the matching ttyS device later. 877 MMIO inter-register address stride is either 8-bit 878 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 879 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 880 to be equivalent to 'mmio'. 'options' are specified in 881 the same format described for ttyS above; if unspecified, 882 the h/w is not re-initialized. 883 884 hvc<n> Use the hypervisor console device <n>. This is for 885 both Xen and PowerPC hypervisors. 886 887 { null | "" } 888 Use to disable console output, i.e., to have kernel 889 console messages discarded. 890 This must be the only console= parameter used on the 891 kernel command line. 892 893 If the device connected to the port is not a TTY but a braille 894 device, prepend "brl," before the device type, for instance 895 console=brl,ttyS0 896 For now, only VisioBraille is supported. 897 898 console_msg_format= 899 [KNL] Change console messages format 900 default 901 By default we print messages on consoles in 902 "[time stamp] text\n" format (time stamp may not be 903 printed, depending on CONFIG_PRINTK_TIME or 904 `printk_time' param). 905 syslog 906 Switch to syslog format: "<%u>[time stamp] text\n" 907 IOW, each message will have a facility and loglevel 908 prefix. The format is similar to one used by syslog() 909 syscall, or to executing "dmesg -S --raw" or to reading 910 from /proc/kmsg. 911 912 consoleblank= [KNL] The console blank (screen saver) timeout in 913 seconds. A value of 0 disables the blank timer. 914 Defaults to 0. 915 916 coredump_filter= 917 [KNL] Change the default value for 918 /proc/<pid>/coredump_filter. 919 See also Documentation/filesystems/proc.rst. 920 921 coresight_cpu_debug.enable 922 [ARM,ARM64] 923 Format: <bool> 924 Enable/disable the CPU sampling based debugging. 925 0: default value, disable debugging 926 1: enable debugging at boot time 927 928 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 929 Format: 930 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 931 932 cpuidle.off=1 [CPU_IDLE] 933 disable the cpuidle sub-system 934 935 cpuidle.governor= 936 [CPU_IDLE] Name of the cpuidle governor to use. 937 938 cpufreq.off=1 [CPU_FREQ] 939 disable the cpufreq sub-system 940 941 cpufreq.default_governor= 942 [CPU_FREQ] Name of the default cpufreq governor or 943 policy to use. This governor must be registered in the 944 kernel before the cpufreq driver probes. 945 946 cpu_init_udelay=N 947 [X86,EARLY] Delay for N microsec between assert and de-assert 948 of APIC INIT to start processors. This delay occurs 949 on every CPU online, such as boot, and resume from suspend. 950 Default: 10000 951 952 cpuhp.parallel= 953 [SMP] Enable/disable parallel bringup of secondary CPUs 954 Format: <bool> 955 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 956 the parameter has no effect. 957 958 crash_kexec_post_notifiers 959 Only jump to kdump kernel after running the panic 960 notifiers and dumping kmsg. This option increases 961 the risks of a kdump failure, since some panic 962 notifiers can make the crashed kernel more unstable. 963 In configurations where kdump may not be reliable, 964 running the panic notifiers could allow collecting 965 more data on dmesg, like stack traces from other CPUS 966 or extra data dumped by panic_print. Note that some 967 configurations enable this option unconditionally, 968 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 969 970 crashkernel=size[KMG][@offset[KMG]] 971 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 972 upon panic. This parameter reserves the physical 973 memory region [offset, offset + size] for that kernel 974 image. If '@offset' is omitted, then a suitable offset 975 is selected automatically. 976 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 977 under 4G first, and fall back to reserve region above 978 4G when '@offset' hasn't been specified. 979 See Documentation/admin-guide/kdump/kdump.rst for further details. 980 981 crashkernel=range1:size1[,range2:size2,...][@offset] 982 [KNL] Same as above, but depends on the memory 983 in the running system. The syntax of range is 984 start-[end] where start and end are both 985 a memory unit (amount[KMG]). See also 986 Documentation/admin-guide/kdump/kdump.rst for an example. 987 988 crashkernel=size[KMG],high 989 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 990 above 4G. 991 Allow kernel to allocate physical memory region from top, 992 so could be above 4G if system have more than 4G ram 993 installed. Otherwise memory region will be allocated 994 below 4G, if available. 995 It will be ignored if crashkernel=X is specified. 996 crashkernel=size[KMG],low 997 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 998 When crashkernel=X,high is passed, kernel could allocate 999 physical memory region above 4G, that cause second kernel 1000 crash on system that require some amount of low memory, 1001 e.g. swiotlb requires at least 64M+32K low memory, also 1002 enough extra low memory is needed to make sure DMA buffers 1003 for 32-bit devices won't run out. Kernel would try to allocate 1004 default size of memory below 4G automatically. The default 1005 size is platform dependent. 1006 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1007 --> arm64: 128MiB 1008 --> riscv: 128MiB 1009 --> loongarch: 128MiB 1010 This one lets the user specify own low range under 4G 1011 for second kernel instead. 1012 0: to disable low allocation. 1013 It will be ignored when crashkernel=X,high is not used 1014 or memory reserved is below 4G. 1015 crashkernel=size[KMG],cma 1016 [KNL, X86] Reserve additional crash kernel memory from 1017 CMA. This reservation is usable by the first system's 1018 userspace memory and kernel movable allocations (memory 1019 balloon, zswap). Pages allocated from this memory range 1020 will not be included in the vmcore so this should not 1021 be used if dumping of userspace memory is intended and 1022 it has to be expected that some movable kernel pages 1023 may be missing from the dump. 1024 1025 A standard crashkernel reservation, as described above, 1026 is still needed to hold the crash kernel and initrd. 1027 1028 This option increases the risk of a kdump failure: DMA 1029 transfers configured by the first kernel may end up 1030 corrupting the second kernel's memory. 1031 1032 This reservation method is intended for systems that 1033 can't afford to sacrifice enough memory for standard 1034 crashkernel reservation and where less reliable and 1035 possibly incomplete kdump is preferable to no kdump at 1036 all. 1037 1038 cryptomgr.notests 1039 [KNL] Disable crypto self-tests 1040 1041 cs89x0_dma= [HW,NET] 1042 Format: <dma> 1043 1044 cs89x0_media= [HW,NET] 1045 Format: { rj45 | aui | bnc } 1046 1047 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1048 function call handling. When switched on, 1049 additional debug data is printed to the console 1050 in case a hanging CPU is detected, and that 1051 CPU is pinged again in order to try to resolve 1052 the hang situation. The default value of this 1053 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1054 Kconfig option. 1055 1056 dasd= [HW,NET] 1057 See header of drivers/s390/block/dasd_devmap.c. 1058 1059 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1060 (one device per port) 1061 Format: <port#>,<type> 1062 See also Documentation/input/devices/joystick-parport.rst 1063 1064 debug [KNL,EARLY] Enable kernel debugging (events log level). 1065 1066 debug_boot_weak_hash 1067 [KNL,EARLY] Enable printing [hashed] pointers early in the 1068 boot sequence. If enabled, we use a weak hash instead 1069 of siphash to hash pointers. Use this option if you are 1070 seeing instances of '(___ptrval___)') and need to see a 1071 value (hashed pointer) instead. Cryptographically 1072 insecure, please do not use on production kernels. 1073 1074 debug_locks_verbose= 1075 [KNL] verbose locking self-tests 1076 Format: <int> 1077 Print debugging info while doing the locking API 1078 self-tests. 1079 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1080 (no extra messages), setting it to -1 (all bits set) 1081 will print _a_lot_ more information - normally only 1082 useful to lockdep developers. 1083 1084 debug_objects [KNL,EARLY] Enable object debugging 1085 1086 debug_guardpage_minorder= 1087 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1088 parameter allows control of the order of pages that will 1089 be intentionally kept free (and hence protected) by the 1090 buddy allocator. Bigger value increase the probability 1091 of catching random memory corruption, but reduce the 1092 amount of memory for normal system use. The maximum 1093 possible value is MAX_PAGE_ORDER/2. Setting this 1094 parameter to 1 or 2 should be enough to identify most 1095 random memory corruption problems caused by bugs in 1096 kernel or driver code when a CPU writes to (or reads 1097 from) a random memory location. Note that there exists 1098 a class of memory corruptions problems caused by buggy 1099 H/W or F/W or by drivers badly programming DMA 1100 (basically when memory is written at bus level and the 1101 CPU MMU is bypassed) which are not detectable by 1102 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1103 help tracking down these problems. 1104 1105 debug_pagealloc= 1106 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1107 enables the feature at boot time. By default, it is 1108 disabled and the system will work mostly the same as a 1109 kernel built without CONFIG_DEBUG_PAGEALLOC. 1110 Note: to get most of debug_pagealloc error reports, it's 1111 useful to also enable the page_owner functionality. 1112 on: enable the feature 1113 1114 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1115 userspace and debugfs internal clients. 1116 Format: { on, no-mount, off } 1117 on: All functions are enabled. 1118 no-mount: 1119 Filesystem is not registered but kernel clients can 1120 access APIs and a crashkernel can be used to read 1121 its content. There is nothing to mount. 1122 off: Filesystem is not registered and clients 1123 get a -EPERM as result when trying to register files 1124 or directories within debugfs. 1125 This is equivalent of the runtime functionality if 1126 debugfs was not enabled in the kernel at all. 1127 Default value is set in build-time with a kernel configuration. 1128 1129 debugpat [X86] Enable PAT debugging 1130 1131 default_hugepagesz= 1132 [HW] The size of the default HugeTLB page. This is 1133 the size represented by the legacy /proc/ hugepages 1134 APIs. In addition, this is the default hugetlb size 1135 used for shmget(), mmap() and mounting hugetlbfs 1136 filesystems. If not specified, defaults to the 1137 architecture's default huge page size. Huge page 1138 sizes are architecture dependent. See also 1139 Documentation/admin-guide/mm/hugetlbpage.rst. 1140 Format: size[KMG] 1141 1142 deferred_probe_timeout= 1143 [KNL] Debugging option to set a timeout in seconds for 1144 deferred probe to give up waiting on dependencies to 1145 probe. Only specific dependencies (subsystems or 1146 drivers) that have opted in will be ignored. A timeout 1147 of 0 will timeout at the end of initcalls. If the time 1148 out hasn't expired, it'll be restarted by each 1149 successful driver registration. This option will also 1150 dump out devices still on the deferred probe list after 1151 retrying. 1152 1153 delayacct [KNL] Enable per-task delay accounting 1154 1155 dell_smm_hwmon.ignore_dmi= 1156 [HW] Continue probing hardware even if DMI data 1157 indicates that the driver is running on unsupported 1158 hardware. 1159 1160 dell_smm_hwmon.force= 1161 [HW] Activate driver even if SMM BIOS signature does 1162 not match list of supported models and enable otherwise 1163 blacklisted features. 1164 1165 dell_smm_hwmon.power_status= 1166 [HW] Report power status in /proc/i8k 1167 (disabled by default). 1168 1169 dell_smm_hwmon.restricted= 1170 [HW] Allow controlling fans only if SYS_ADMIN 1171 capability is set. 1172 1173 dell_smm_hwmon.fan_mult= 1174 [HW] Factor to multiply fan speed with. 1175 1176 dell_smm_hwmon.fan_max= 1177 [HW] Maximum configurable fan speed. 1178 1179 dfltcc= [HW,S390] 1180 Format: { on | off | def_only | inf_only | always } 1181 on: s390 zlib hardware support for compression on 1182 level 1 and decompression (default) 1183 off: No s390 zlib hardware support 1184 def_only: s390 zlib hardware support for deflate 1185 only (compression on level 1) 1186 inf_only: s390 zlib hardware support for inflate 1187 only (decompression) 1188 always: Same as 'on' but ignores the selected compression 1189 level always using hardware support (used for debugging) 1190 1191 dhash_entries= [KNL] 1192 Set number of hash buckets for dentry cache. 1193 1194 disable_1tb_segments [PPC,EARLY] 1195 Disables the use of 1TB hash page table segments. This 1196 causes the kernel to fall back to 256MB segments which 1197 can be useful when debugging issues that require an SLB 1198 miss to occur. 1199 1200 disable= [IPV6] 1201 See Documentation/networking/ipv6.rst. 1202 1203 disable_radix [PPC,EARLY] 1204 Disable RADIX MMU mode on POWER9 1205 1206 disable_tlbie [PPC] 1207 Disable TLBIE instruction. Currently does not work 1208 with KVM, with HASH MMU, or with coherent accelerators. 1209 1210 disable_ddw [PPC/PSERIES,EARLY] 1211 Disable Dynamic DMA Window support. Use this 1212 to workaround buggy firmware. 1213 1214 disable_ipv6= [IPV6] 1215 See Documentation/networking/ipv6.rst. 1216 1217 disable_mtrr_cleanup [X86,EARLY] 1218 The kernel tries to adjust MTRR layout from continuous 1219 to discrete, to make X server driver able to add WB 1220 entry later. This parameter disables that. 1221 1222 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1223 By default the kernel will trim any uncacheable 1224 memory out of your available memory pool based on 1225 MTRR settings. This parameter disables that behavior, 1226 possibly causing your machine to run very slowly. 1227 1228 disable_timer_pin_1 [X86,EARLY] 1229 Disable PIN 1 of APIC timer 1230 Can be useful to work around chipset bugs. 1231 1232 dis_ucode_ldr [X86] Disable the microcode loader. 1233 1234 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1235 this option disables the debugging code at boot. 1236 1237 dma_debug_entries=<number> 1238 This option allows to tune the number of preallocated 1239 entries for DMA-API debugging code. One entry is 1240 required per DMA-API allocation. Use this if the 1241 DMA-API debugging code disables itself because the 1242 architectural default is too low. 1243 1244 dma_debug_driver=<driver_name> 1245 With this option the DMA-API debugging driver 1246 filter feature can be enabled at boot time. Just 1247 pass the driver to filter for as the parameter. 1248 The filter can be disabled or changed to another 1249 driver later using sysfs. 1250 1251 reg_file_data_sampling= 1252 [X86] Controls mitigation for Register File Data 1253 Sampling (RFDS) vulnerability. RFDS is a CPU 1254 vulnerability which may allow userspace to infer 1255 kernel data values previously stored in floating point 1256 registers, vector registers, or integer registers. 1257 RFDS only affects Intel Atom processors. 1258 1259 on: Turns ON the mitigation. 1260 off: Turns OFF the mitigation. 1261 1262 This parameter overrides the compile time default set 1263 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1264 disabled when other VERW based mitigations (like MDS) 1265 are enabled. In order to disable RFDS mitigation all 1266 VERW based mitigations need to be disabled. 1267 1268 For details see: 1269 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1270 1271 driver_async_probe= [KNL] 1272 List of driver names to be probed asynchronously. * 1273 matches with all driver names. If * is specified, the 1274 rest of the listed driver names are those that will NOT 1275 match the *. 1276 Format: <driver_name1>,<driver_name2>... 1277 1278 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1279 Broken monitors, graphic adapters, KVMs and EDIDless 1280 panels may send no or incorrect EDID data sets. 1281 This parameter allows to specify an EDID data sets 1282 in the /lib/firmware directory that are used instead. 1283 An EDID data set will only be used for a particular 1284 connector, if its name and a colon are prepended to 1285 the EDID name. Each connector may use a unique EDID 1286 data set by separating the files with a comma. An EDID 1287 data set with no connector name will be used for 1288 any connectors not explicitly specified. 1289 1290 dscc4.setup= [NET] 1291 1292 dt_cpu_ftrs= [PPC,EARLY] 1293 Format: {"off" | "known"} 1294 Control how the dt_cpu_ftrs device-tree binding is 1295 used for CPU feature discovery and setup (if it 1296 exists). 1297 off: Do not use it, fall back to legacy cpu table. 1298 known: Do not pass through unknown features to guests 1299 or userspace, only those that the kernel is aware of. 1300 1301 dump_apple_properties [X86] 1302 Dump name and content of EFI device properties on 1303 x86 Macs. Useful for driver authors to determine 1304 what data is available or for reverse-engineering. 1305 1306 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1307 <module>.dyndbg[="val"] 1308 Enable debug messages at boot time. See 1309 Documentation/admin-guide/dynamic-debug-howto.rst 1310 for details. 1311 1312 early_ioremap_debug [KNL,EARLY] 1313 Enable debug messages in early_ioremap support. This 1314 is useful for tracking down temporary early mappings 1315 which are not unmapped. 1316 1317 earlycon= [KNL,EARLY] Output early console device and options. 1318 1319 When used with no options, the early console is 1320 determined by stdout-path property in device tree's 1321 chosen node or the ACPI SPCR table if supported by 1322 the platform. 1323 1324 cdns,<addr>[,options] 1325 Start an early, polled-mode console on a Cadence 1326 (xuartps) serial port at the specified address. Only 1327 supported option is baud rate. If baud rate is not 1328 specified, the serial port must already be setup and 1329 configured. 1330 1331 uart[8250],io,<addr>[,options[,uartclk]] 1332 uart[8250],mmio,<addr>[,options[,uartclk]] 1333 uart[8250],mmio32,<addr>[,options[,uartclk]] 1334 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1335 uart[8250],0x<addr>[,options] 1336 Start an early, polled-mode console on the 8250/16550 1337 UART at the specified I/O port or MMIO address. 1338 MMIO inter-register address stride is either 8-bit 1339 (mmio) or 32-bit (mmio32 or mmio32be). 1340 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1341 to be equivalent to 'mmio'. 'options' are specified 1342 in the same format described for "console=ttyS<n>"; if 1343 unspecified, the h/w is not initialized. 'uartclk' is 1344 the uart clock frequency; if unspecified, it is set 1345 to 'BASE_BAUD' * 16. 1346 1347 pl011,<addr> 1348 pl011,mmio32,<addr> 1349 Start an early, polled-mode console on a pl011 serial 1350 port at the specified address. The pl011 serial port 1351 must already be setup and configured. Options are not 1352 yet supported. If 'mmio32' is specified, then only 1353 the driver will use only 32-bit accessors to read/write 1354 the device registers. 1355 1356 liteuart,<addr> 1357 Start an early console on a litex serial port at the 1358 specified address. The serial port must already be 1359 setup and configured. Options are not yet supported. 1360 1361 meson,<addr> 1362 Start an early, polled-mode console on a meson serial 1363 port at the specified address. The serial port must 1364 already be setup and configured. Options are not yet 1365 supported. 1366 1367 msm_serial,<addr> 1368 Start an early, polled-mode console on an msm serial 1369 port at the specified address. The serial port 1370 must already be setup and configured. Options are not 1371 yet supported. 1372 1373 msm_serial_dm,<addr> 1374 Start an early, polled-mode console on an msm serial 1375 dm port at the specified address. The serial port 1376 must already be setup and configured. Options are not 1377 yet supported. 1378 1379 owl,<addr> 1380 Start an early, polled-mode console on a serial port 1381 of an Actions Semi SoC, such as S500 or S900, at the 1382 specified address. The serial port must already be 1383 setup and configured. Options are not yet supported. 1384 1385 rda,<addr> 1386 Start an early, polled-mode console on a serial port 1387 of an RDA Micro SoC, such as RDA8810PL, at the 1388 specified address. The serial port must already be 1389 setup and configured. Options are not yet supported. 1390 1391 sbi 1392 Use RISC-V SBI (Supervisor Binary Interface) for early 1393 console. 1394 1395 smh Use ARM semihosting calls for early console. 1396 1397 s3c2410,<addr> 1398 s3c2412,<addr> 1399 s3c2440,<addr> 1400 s3c6400,<addr> 1401 s5pv210,<addr> 1402 exynos4210,<addr> 1403 Use early console provided by serial driver available 1404 on Samsung SoCs, requires selecting proper type and 1405 a correct base address of the selected UART port. The 1406 serial port must already be setup and configured. 1407 Options are not yet supported. 1408 1409 lantiq,<addr> 1410 Start an early, polled-mode console on a lantiq serial 1411 (lqasc) port at the specified address. The serial port 1412 must already be setup and configured. Options are not 1413 yet supported. 1414 1415 lpuart,<addr> 1416 lpuart32,<addr> 1417 Use early console provided by Freescale LP UART driver 1418 found on Freescale Vybrid and QorIQ LS1021A processors. 1419 A valid base address must be provided, and the serial 1420 port must already be setup and configured. 1421 1422 ec_imx21,<addr> 1423 ec_imx6q,<addr> 1424 Start an early, polled-mode, output-only console on the 1425 Freescale i.MX UART at the specified address. The UART 1426 must already be setup and configured. 1427 1428 ar3700_uart,<addr> 1429 Start an early, polled-mode console on the 1430 Armada 3700 serial port at the specified 1431 address. The serial port must already be setup 1432 and configured. Options are not yet supported. 1433 1434 qcom_geni,<addr> 1435 Start an early, polled-mode console on a Qualcomm 1436 Generic Interface (GENI) based serial port at the 1437 specified address. The serial port must already be 1438 setup and configured. Options are not yet supported. 1439 1440 efifb,[options] 1441 Start an early, unaccelerated console on the EFI 1442 memory mapped framebuffer (if available). On cache 1443 coherent non-x86 systems that use system memory for 1444 the framebuffer, pass the 'ram' option so that it is 1445 mapped with the correct attributes. 1446 1447 linflex,<addr> 1448 Use early console provided by Freescale LINFlexD UART 1449 serial driver for NXP S32V234 SoCs. A valid base 1450 address must be provided, and the serial port must 1451 already be setup and configured. 1452 1453 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1454 earlyprintk=vga 1455 earlyprintk=sclp 1456 earlyprintk=xen 1457 earlyprintk=serial[,ttySn[,baudrate]] 1458 earlyprintk=serial[,0x...[,baudrate]] 1459 earlyprintk=ttySn[,baudrate] 1460 earlyprintk=dbgp[debugController#] 1461 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1462 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1463 earlyprintk=xdbc[xhciController#] 1464 earlyprintk=bios 1465 1466 earlyprintk is useful when the kernel crashes before 1467 the normal console is initialized. It is not enabled by 1468 default because it has some cosmetic problems. 1469 1470 Use "nocfg" to skip UART configuration, assume 1471 BIOS/firmware has configured UART correctly. 1472 1473 Append ",keep" to not disable it when the real console 1474 takes over. 1475 1476 Only one of vga, serial, or usb debug port can 1477 be used at a time. 1478 1479 Currently only ttyS0 and ttyS1 may be specified by 1480 name. Other I/O ports may be explicitly specified 1481 on some architectures (x86 and arm at least) by 1482 replacing ttySn with an I/O port address, like this: 1483 earlyprintk=serial,0x1008,115200 1484 You can find the port for a given device in 1485 /proc/tty/driver/serial: 1486 2: uart:ST16650V2 port:00001008 irq:18 ... 1487 1488 Interaction with the standard serial driver is not 1489 very good. 1490 1491 The VGA output is eventually overwritten by 1492 the real console. 1493 1494 The xen option can only be used in Xen domains. 1495 1496 The sclp output can only be used on s390. 1497 1498 The bios output can only be used on SuperH. 1499 1500 The optional "force" to "pciserial" enables use of a 1501 PCI device even when its classcode is not of the 1502 UART class. 1503 1504 edac_report= [HW,EDAC] Control how to report EDAC event 1505 Format: {"on" | "off" | "force"} 1506 on: enable EDAC to report H/W event. May be overridden 1507 by other higher priority error reporting module. 1508 off: disable H/W event reporting through EDAC. 1509 force: enforce the use of EDAC to report H/W event. 1510 default: on. 1511 1512 edd= [EDD] 1513 Format: {"off" | "on" | "skip[mbr]"} 1514 1515 efi= [EFI,EARLY] 1516 Format: { "debug", "disable_early_pci_dma", 1517 "nochunk", "noruntime", "nosoftreserve", 1518 "novamap", "no_disable_early_pci_dma" } 1519 debug: enable misc debug output. 1520 disable_early_pci_dma: disable the busmaster bit on all 1521 PCI bridges while in the EFI boot stub. 1522 nochunk: disable reading files in "chunks" in the EFI 1523 boot stub, as chunking can cause problems with some 1524 firmware implementations. 1525 noruntime : disable EFI runtime services support 1526 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1527 attribute may cause the kernel to reserve the 1528 memory range for a memory mapping driver to 1529 claim. Specify efi=nosoftreserve to disable this 1530 reservation and treat the memory by its base type 1531 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1532 novamap: do not call SetVirtualAddressMap(). 1533 no_disable_early_pci_dma: Leave the busmaster bit set 1534 on all PCI bridges while in the EFI boot stub 1535 1536 efi_no_storage_paranoia [EFI,X86,EARLY] 1537 Using this parameter you can use more than 50% of 1538 your efi variable storage. Use this parameter only if 1539 you are really sure that your UEFI does sane gc and 1540 fulfills the spec otherwise your board may brick. 1541 1542 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1543 that is to be dynamically loaded by Linux. If there are 1544 multiple variables with the same name but with different 1545 vendor GUIDs, all of them will be loaded. See 1546 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1547 1548 1549 eisa_irq_edge= [PARISC,HW] 1550 See header of drivers/parisc/eisa.c. 1551 1552 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1553 Format: ekgdboc=kbd 1554 1555 This is designed to be used in conjunction with 1556 the boot argument: earlyprintk=vga 1557 1558 This parameter works in place of the kgdboc parameter 1559 but can only be used if the backing tty is available 1560 very early in the boot process. For early debugging 1561 via a serial port see kgdboc_earlycon instead. 1562 1563 elanfreq= [X86-32] 1564 See comment before function elanfreq_setup() in 1565 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1566 1567 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1568 Specifies physical address of start of kernel core 1569 image elf header and optionally the size. Generally 1570 kexec loader will pass this option to capture kernel. 1571 See Documentation/admin-guide/kdump/kdump.rst for details. 1572 1573 enable_mtrr_cleanup [X86,EARLY] 1574 The kernel tries to adjust MTRR layout from continuous 1575 to discrete, to make X server driver able to add WB 1576 entry later. This parameter enables that. 1577 1578 enable_timer_pin_1 [X86] 1579 Enable PIN 1 of APIC timer 1580 Can be useful to work around chipset bugs 1581 (in particular on some ATI chipsets). 1582 The kernel tries to set a reasonable default. 1583 1584 enforcing= [SELINUX] Set initial enforcing status. 1585 Format: {"0" | "1"} 1586 See security/selinux/Kconfig help text. 1587 0 -- permissive (log only, no denials). 1588 1 -- enforcing (deny and log). 1589 Default value is 0. 1590 Value can be changed at runtime via 1591 /sys/fs/selinux/enforce. 1592 1593 erst_disable [ACPI] 1594 Disable Error Record Serialization Table (ERST) 1595 support. 1596 1597 ether= [HW,NET] Ethernet cards parameters 1598 This option is obsoleted by the "netdev=" option, which 1599 has equivalent usage. See its documentation for details. 1600 1601 evm= [EVM] 1602 Format: { "fix" } 1603 Permit 'security.evm' to be updated regardless of 1604 current integrity status. 1605 1606 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1607 stages so cover more early boot allocations. 1608 Please note that as side effect some optimizations 1609 might be disabled to achieve that (e.g. parallelized 1610 memory initialization is disabled) so the boot process 1611 might take longer, especially on systems with a lot of 1612 memory. Available with CONFIG_PAGE_EXTENSION=y. 1613 1614 failslab= 1615 fail_usercopy= 1616 fail_page_alloc= 1617 fail_skb_realloc= 1618 fail_make_request=[KNL] 1619 General fault injection mechanism. 1620 Format: <interval>,<probability>,<space>,<times> 1621 See also Documentation/fault-injection/. 1622 1623 fb_tunnels= [NET] 1624 Format: { initns | none } 1625 See Documentation/admin-guide/sysctl/net.rst for 1626 fb_tunnels_only_for_init_ns 1627 1628 floppy= [HW] 1629 See Documentation/admin-guide/blockdev/floppy.rst. 1630 1631 forcepae [X86-32] 1632 Forcefully enable Physical Address Extension (PAE). 1633 Many Pentium M systems disable PAE but may have a 1634 functionally usable PAE implementation. 1635 Warning: use of this parameter will taint the kernel 1636 and may cause unknown problems. 1637 1638 fred= [X86-64] 1639 Enable/disable Flexible Return and Event Delivery. 1640 Format: { on | off } 1641 on: enable FRED when it's present. 1642 off: disable FRED, the default setting. 1643 1644 ftrace=[tracer] 1645 [FTRACE] will set and start the specified tracer 1646 as early as possible in order to facilitate early 1647 boot debugging. 1648 1649 ftrace_boot_snapshot 1650 [FTRACE] On boot up, a snapshot will be taken of the 1651 ftrace ring buffer that can be read at: 1652 /sys/kernel/tracing/snapshot. 1653 This is useful if you need tracing information from kernel 1654 boot up that is likely to be overridden by user space 1655 start up functionality. 1656 1657 Optionally, the snapshot can also be defined for a tracing 1658 instance that was created by the trace_instance= command 1659 line parameter. 1660 1661 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1662 1663 The above will cause the "foo" tracing instance to trigger 1664 a snapshot at the end of boot up. 1665 1666 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1667 ,<instance>=2(orig_cpu)] 1668 [FTRACE] will dump the trace buffers on oops. 1669 If no parameter is passed, ftrace will dump global 1670 buffers of all CPUs, if you pass 2 or orig_cpu, it 1671 will dump only the buffer of the CPU that triggered 1672 the oops, or the specific instance will be dumped if 1673 its name is passed. Multiple instance dump is also 1674 supported, and instances are separated by commas. Each 1675 instance supports only dump on CPU that triggered the 1676 oops by passing 2 or orig_cpu to it. 1677 1678 ftrace_dump_on_oops=foo=orig_cpu 1679 1680 The above will dump only the buffer of "foo" instance 1681 on CPU that triggered the oops. 1682 1683 ftrace_dump_on_oops,foo,bar=orig_cpu 1684 1685 The above will dump global buffer on all CPUs, the 1686 buffer of "foo" instance on all CPUs and the buffer 1687 of "bar" instance on CPU that triggered the oops. 1688 1689 ftrace_filter=[function-list] 1690 [FTRACE] Limit the functions traced by the function 1691 tracer at boot up. function-list is a comma-separated 1692 list of functions. This list can be changed at run 1693 time by the set_ftrace_filter file in the debugfs 1694 tracing directory. 1695 1696 ftrace_notrace=[function-list] 1697 [FTRACE] Do not trace the functions specified in 1698 function-list. This list can be changed at run time 1699 by the set_ftrace_notrace file in the debugfs 1700 tracing directory. 1701 1702 ftrace_graph_filter=[function-list] 1703 [FTRACE] Limit the top level callers functions traced 1704 by the function graph tracer at boot up. 1705 function-list is a comma-separated list of functions 1706 that can be changed at run time by the 1707 set_graph_function file in the debugfs tracing directory. 1708 1709 ftrace_graph_notrace=[function-list] 1710 [FTRACE] Do not trace from the functions specified in 1711 function-list. This list is a comma-separated list of 1712 functions that can be changed at run time by the 1713 set_graph_notrace file in the debugfs tracing directory. 1714 1715 ftrace_graph_max_depth=<uint> 1716 [FTRACE] Used with the function graph tracer. This is 1717 the max depth it will trace into a function. This value 1718 can be changed at run time by the max_graph_depth file 1719 in the tracefs tracing directory. default: 0 (no limit) 1720 1721 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1722 devices by scanning the firmware to infer the 1723 consumer/supplier relationships. This feature is 1724 especially useful when drivers are loaded as modules as 1725 it ensures proper ordering of tasks like device probing 1726 (suppliers first, then consumers), supplier boot state 1727 clean up (only after all consumers have probed), 1728 suspend/resume & runtime PM (consumers first, then 1729 suppliers). 1730 Format: { off | permissive | on | rpm } 1731 off -- Don't create device links from firmware info. 1732 permissive -- Create device links from firmware info 1733 but use it only for ordering boot state clean 1734 up (sync_state() calls). 1735 on -- Create device links from firmware info and use it 1736 to enforce probe and suspend/resume ordering. 1737 rpm -- Like "on", but also use to order runtime PM. 1738 1739 fw_devlink.strict=<bool> 1740 [KNL,EARLY] Treat all inferred dependencies as mandatory 1741 dependencies. This only applies for fw_devlink=on|rpm. 1742 Format: <bool> 1743 1744 fw_devlink.sync_state = 1745 [KNL,EARLY] When all devices that could probe have finished 1746 probing, this parameter controls what to do with 1747 devices that haven't yet received their sync_state() 1748 calls. 1749 Format: { strict | timeout } 1750 strict -- Default. Continue waiting on consumers to 1751 probe successfully. 1752 timeout -- Give up waiting on consumers and call 1753 sync_state() on any devices that haven't yet 1754 received their sync_state() calls after 1755 deferred_probe_timeout has expired or by 1756 late_initcall() if !CONFIG_MODULES. 1757 1758 gamecon.map[2|3]= 1759 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1760 support via parallel port (up to 5 devices per port) 1761 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1762 See also Documentation/input/devices/joystick-parport.rst 1763 1764 gamma= [HW,DRM] 1765 1766 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1767 Format: off | on 1768 default: on 1769 1770 gather_data_sampling= 1771 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1772 mitigation. 1773 1774 Gather Data Sampling is a hardware vulnerability which 1775 allows unprivileged speculative access to data which was 1776 previously stored in vector registers. 1777 1778 This issue is mitigated by default in updated microcode. 1779 The mitigation may have a performance impact but can be 1780 disabled. On systems without the microcode mitigation 1781 disabling AVX serves as a mitigation. 1782 1783 force: Disable AVX to mitigate systems without 1784 microcode mitigation. No effect if the microcode 1785 mitigation is present. Known to cause crashes in 1786 userspace with buggy AVX enumeration. 1787 1788 off: Disable GDS mitigation. 1789 1790 gbpages [X86] Use GB pages for kernel direct mappings. 1791 1792 gcov_persist= [GCOV] When non-zero (default), profiling data for 1793 kernel modules is saved and remains accessible via 1794 debugfs, even when the module is unloaded/reloaded. 1795 When zero, profiling data is discarded and associated 1796 debugfs files are removed at module unload time. 1797 1798 goldfish [X86] Enable the goldfish android emulator platform. 1799 Don't use this when you are not running on the 1800 android emulator 1801 1802 gpio-mockup.gpio_mockup_ranges 1803 [HW] Sets the ranges of gpiochip of for this device. 1804 Format: <start1>,<end1>,<start2>,<end2>... 1805 gpio-mockup.gpio_mockup_named_lines 1806 [HW] Let the driver know GPIO lines should be named. 1807 1808 gpt [EFI] Forces disk with valid GPT signature but 1809 invalid Protective MBR to be treated as GPT. If the 1810 primary GPT is corrupted, it enables the backup/alternate 1811 GPT to be used instead. 1812 1813 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1814 the "Enable 0" bit of the configuration register. 1815 Format: 0 | 1 1816 Default: 0 1817 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1818 the "Enable 0" bit of the configuration register. 1819 Format: 0 | 1 1820 Default: 0 1821 grcan.select= [HW] Select which physical interface to use. 1822 Format: 0 | 1 1823 Default: 0 1824 grcan.txsize= [HW] Sets the size of the tx buffer. 1825 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1826 Default: 1024 1827 grcan.rxsize= [HW] Sets the size of the rx buffer. 1828 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1829 Default: 1024 1830 1831 hardened_usercopy= 1832 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1833 hardening is enabled for this boot. Hardened 1834 usercopy checking is used to protect the kernel 1835 from reading or writing beyond known memory 1836 allocation boundaries as a proactive defense 1837 against bounds-checking flaws in the kernel's 1838 copy_to_user()/copy_from_user() interface. 1839 The default is determined by 1840 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1841 on Perform hardened usercopy checks. 1842 off Disable hardened usercopy checks. 1843 1844 hardlockup_all_cpu_backtrace= 1845 [KNL] Should the hard-lockup detector generate 1846 backtraces on all cpus. 1847 Format: 0 | 1 1848 1849 hash_pointers= 1850 [KNL,EARLY] 1851 By default, when pointers are printed to the console 1852 or buffers via the %p format string, that pointer is 1853 "hashed", i.e. obscured by hashing the pointer value. 1854 This is a security feature that hides actual kernel 1855 addresses from unprivileged users, but it also makes 1856 debugging the kernel more difficult since unequal 1857 pointers can no longer be compared. The choices are: 1858 Format: { auto | always | never } 1859 Default: auto 1860 1861 auto - Hash pointers unless slab_debug is enabled. 1862 always - Always hash pointers (even if slab_debug is 1863 enabled). 1864 never - Never hash pointers. This option should only 1865 be specified when debugging the kernel. Do 1866 not use on production kernels. The boot 1867 param "no_hash_pointers" is an alias for 1868 this mode. 1869 1870 hashdist= [KNL,NUMA] Large hashes allocated during boot 1871 are distributed across NUMA nodes. Defaults on 1872 for 64-bit NUMA, off otherwise. 1873 Format: 0 | 1 (for off | on) 1874 1875 hd= [EIDE] (E)IDE hard drive subsystem geometry 1876 Format: <cyl>,<head>,<sect> 1877 1878 hest_disable [ACPI] 1879 Disable Hardware Error Source Table (HEST) support; 1880 corresponding firmware-first mode error processing 1881 logic will be disabled. 1882 1883 hibernate= [HIBERNATION] 1884 noresume Don't check if there's a hibernation image 1885 present during boot. 1886 nocompress Don't compress/decompress hibernation images. 1887 no Disable hibernation and resume. 1888 protect_image Turn on image protection during restoration 1889 (that will set all pages holding image data 1890 during restoration read-only). 1891 1892 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1893 used with hibernation. 1894 Format: { lzo | lz4 } 1895 Default: lzo 1896 1897 lzo: Select LZO compression algorithm to 1898 compress/decompress hibernation image. 1899 1900 lz4: Select LZ4 compression algorithm to 1901 compress/decompress hibernation image. 1902 1903 hibernate.pm_test_delay= 1904 [HIBERNATION] 1905 Sets the number of seconds to remain in a hibernation test 1906 mode before resuming the system (see 1907 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 1908 is set. Default value is 5. 1909 1910 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 1911 size of <nn>. This works even on boxes that have no 1912 highmem otherwise. This also works to reduce highmem 1913 size on bigger boxes. 1914 1915 highres= [KNL] Enable/disable high resolution timer mode. 1916 Valid parameters: "on", "off" 1917 Default: "on" 1918 1919 hlt [BUGS=ARM,SH] 1920 1921 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 1922 Format: <string> 1923 This allows setting the system's hostname during early 1924 startup. This sets the name returned by gethostname. 1925 Using this parameter to set the hostname makes it 1926 possible to ensure the hostname is correctly set before 1927 any userspace processes run, avoiding the possibility 1928 that a process may call gethostname before the hostname 1929 has been explicitly set, resulting in the calling 1930 process getting an incorrect result. The string must 1931 not exceed the maximum allowed hostname length (usually 1932 64 characters) and will be truncated otherwise. 1933 1934 hpet= [X86-32,HPET] option to control HPET usage 1935 Format: { enable (default) | disable | force | 1936 verbose } 1937 disable: disable HPET and use PIT instead 1938 force: allow force enabled of undocumented chips (ICH4, 1939 VIA, nVidia) 1940 verbose: show contents of HPET registers during setup 1941 1942 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1943 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1944 1945 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 1946 If this follows hugepagesz (below), it specifies 1947 the number of pages of hugepagesz to be allocated. 1948 If this is the first HugeTLB parameter on the command 1949 line, it specifies the number of pages to allocate for 1950 the default huge page size. If using node format, the 1951 number of pages to allocate per-node can be specified. 1952 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1953 Format: <integer> or (node format) 1954 <node>:<integer>[,<node>:<integer>] 1955 1956 hugepagesz= 1957 [HW,EARLY] The size of the HugeTLB pages. This is 1958 used in conjunction with hugepages (above) to 1959 allocate huge pages of a specific size at boot. The 1960 pair hugepagesz=X hugepages=Y can be specified once 1961 for each supported huge page size. Huge page sizes 1962 are architecture dependent. See also 1963 Documentation/admin-guide/mm/hugetlbpage.rst. 1964 Format: size[KMG] 1965 1966 hugepage_alloc_threads= 1967 [HW] The number of threads that should be used to 1968 allocate hugepages during boot. This option can be 1969 used to improve system bootup time when allocating 1970 a large amount of huge pages. 1971 The default value is 25% of the available hardware threads. 1972 1973 Note that this parameter only applies to non-gigantic huge pages. 1974 1975 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 1976 of gigantic hugepages. Or using node format, the size 1977 of a CMA area per node can be specified. 1978 Format: nn[KMGTPE] or (node format) 1979 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1980 1981 Reserve a CMA area of given size and allocate gigantic 1982 hugepages using the CMA allocator. If enabled, the 1983 boot-time allocation of gigantic hugepages is skipped. 1984 1985 hugetlb_cma_only= 1986 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 1987 try to allocate from the CMA areas. 1988 1989 This option does nothing if hugetlb_cma= is not also 1990 specified. 1991 1992 hugetlb_free_vmemmap= 1993 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 1994 enabled. 1995 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 1996 Allows heavy hugetlb users to free up some more 1997 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1998 Format: { on | off (default) } 1999 2000 on: enable HVO 2001 off: disable HVO 2002 2003 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2004 the default is on. 2005 2006 Note that the vmemmap pages may be allocated from the added 2007 memory block itself when memory_hotplug.memmap_on_memory is 2008 enabled, those vmemmap pages cannot be optimized even if this 2009 feature is enabled. Other vmemmap pages not allocated from 2010 the added memory block itself do not be affected. 2011 2012 hung_task_panic= 2013 [KNL] Should the hung task detector generate panics. 2014 Format: 0 | 1 2015 2016 A value of 1 instructs the kernel to panic when a 2017 hung task is detected. The default value is controlled 2018 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 2019 option. The value selected by this boot parameter can 2020 be changed later by the kernel.hung_task_panic sysctl. 2021 2022 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2023 terminal devices. Valid values: 0..8 2024 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2025 If specified, z/VM IUCV HVC accepts connections 2026 from listed z/VM user IDs only. 2027 2028 hv_nopvspin [X86,HYPER_V,EARLY] 2029 Disables the paravirt spinlock optimizations 2030 which allow the hypervisor to 'idle' the guest 2031 on lock contention. 2032 2033 hw_protection= [HW] 2034 Format: reboot | shutdown 2035 2036 Hardware protection action taken on critical events like 2037 overtemperature or imminent voltage loss. 2038 2039 i2c_bus= [HW] Override the default board specific I2C bus speed 2040 or register an additional I2C bus that is not 2041 registered from board initialization code. 2042 Format: 2043 <bus_id>,<clkrate> 2044 2045 i2c_touchscreen_props= [HW,ACPI,X86] 2046 Set device-properties for ACPI-enumerated I2C-attached 2047 touchscreen, to e.g. fix coordinates of upside-down 2048 mounted touchscreens. If you need this option please 2049 submit a drivers/platform/x86/touchscreen_dmi.c patch 2050 adding a DMI quirk for this. 2051 2052 Format: 2053 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2054 Where <val> is one of: 2055 Omit "=<val>" entirely Set a boolean device-property 2056 Unsigned number Set a u32 device-property 2057 Anything else Set a string device-property 2058 2059 Examples (split over multiple lines): 2060 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2061 touchscreen-inverted-y 2062 2063 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2064 touchscreen-size-y=1080:touchscreen-inverted-y: 2065 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2066 2067 i8042.debug [HW] Toggle i8042 debug mode 2068 i8042.unmask_kbd_data 2069 [HW] Enable printing of interrupt data from the KBD port 2070 (disabled by default, and as a pre-condition 2071 requires that i8042.debug=1 be enabled) 2072 i8042.direct [HW] Put keyboard port into non-translated mode 2073 i8042.dumbkbd [HW] Pretend that controller can only read data from 2074 keyboard and cannot control its state 2075 (Don't attempt to blink the leds) 2076 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2077 i8042.nokbd [HW] Don't check/create keyboard port 2078 i8042.noloop [HW] Disable the AUX Loopback command while probing 2079 for the AUX port 2080 i8042.nomux [HW] Don't check presence of an active multiplexing 2081 controller 2082 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2083 controllers 2084 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2085 i8042.reset [HW] Reset the controller during init, cleanup and 2086 suspend-to-ram transitions, only during s2r 2087 transitions, or never reset 2088 Format: { 1 | Y | y | 0 | N | n } 2089 1, Y, y: always reset controller 2090 0, N, n: don't ever reset controller 2091 Default: only on s2r transitions on x86; most other 2092 architectures force reset to be always executed 2093 i8042.unlock [HW] Unlock (ignore) the keylock 2094 i8042.kbdreset [HW] Reset device connected to KBD port 2095 i8042.probe_defer 2096 [HW] Allow deferred probing upon i8042 probe errors 2097 2098 i810= [HW,DRM] 2099 2100 i915.invert_brightness= 2101 [DRM] Invert the sense of the variable that is used to 2102 set the brightness of the panel backlight. Normally a 2103 brightness value of 0 indicates backlight switched off, 2104 and the maximum of the brightness value sets the backlight 2105 to maximum brightness. If this parameter is set to 0 2106 (default) and the machine requires it, or this parameter 2107 is set to 1, a brightness value of 0 sets the backlight 2108 to maximum brightness, and the maximum of the brightness 2109 value switches the backlight off. 2110 -1 -- never invert brightness 2111 0 -- machine default 2112 1 -- force brightness inversion 2113 2114 ia32_emulation= [X86-64] 2115 Format: <bool> 2116 When true, allows loading 32-bit programs and executing 32-bit 2117 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2118 boot time. When false, unconditionally disables IA32 emulation. 2119 2120 icn= [HW,ISDN] 2121 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2122 2123 2124 idle= [X86,EARLY] 2125 Format: idle=poll, idle=halt, idle=nomwait 2126 2127 idle=poll: Don't do power saving in the idle loop 2128 using HLT, but poll for rescheduling event. This will 2129 make the CPUs eat a lot more power, but may be useful 2130 to get slightly better performance in multiprocessor 2131 benchmarks. It also makes some profiling using 2132 performance counters more accurate. Please note that 2133 on systems with MONITOR/MWAIT support (like Intel 2134 EM64T CPUs) this option has no performance advantage 2135 over the normal idle loop. It may also interact badly 2136 with hyperthreading. 2137 2138 idle=halt: Halt is forced to be used for CPU idle. 2139 In such case C2/C3 won't be used again. 2140 2141 idle=nomwait: Disable mwait for CPU C-states 2142 2143 idxd.sva= [HW] 2144 Format: <bool> 2145 Allow force disabling of Shared Virtual Memory (SVA) 2146 support for the idxd driver. By default it is set to 2147 true (1). 2148 2149 idxd.tc_override= [HW] 2150 Format: <bool> 2151 Allow override of default traffic class configuration 2152 for the device. By default it is set to false (0). 2153 2154 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2155 Format: { strict | legacy | 2008 | relaxed | emulated } 2156 Default: strict 2157 2158 Choose which programs will be accepted for execution 2159 based on the IEEE 754 NaN encoding(s) supported by 2160 the FPU and the NaN encoding requested with the value 2161 of an ELF file header flag individually set by each 2162 binary. Hardware implementations are permitted to 2163 support either or both of the legacy and the 2008 NaN 2164 encoding mode. 2165 2166 Available settings are as follows: 2167 strict accept binaries that request a NaN encoding 2168 supported by the FPU 2169 legacy only accept legacy-NaN binaries, if supported 2170 by the FPU 2171 2008 only accept 2008-NaN binaries, if supported 2172 by the FPU 2173 relaxed accept any binaries regardless of whether 2174 supported by the FPU 2175 emulated accept any binaries but enable FPU emulator 2176 if binary mode is unsupported by the FPU. 2177 2178 The FPU emulator is always able to support both NaN 2179 encodings, so if no FPU hardware is present or it has 2180 been disabled with 'nofpu', then the settings of 2181 'legacy' and '2008' strap the emulator accordingly, 2182 'relaxed' straps the emulator for both legacy-NaN and 2183 2008-NaN, whereas 'strict' enables legacy-NaN only on 2184 legacy processors and both NaN encodings on MIPS32 or 2185 MIPS64 CPUs. 2186 2187 The setting for ABS.fmt/NEG.fmt instruction execution 2188 mode generally follows that for the NaN encoding, 2189 except where unsupported by hardware. 2190 2191 ignore_loglevel [KNL,EARLY] 2192 Ignore loglevel setting - this will print /all/ 2193 kernel messages to the console. Useful for debugging. 2194 We also add it as printk module parameter, so users 2195 could change it dynamically, usually by 2196 /sys/module/printk/parameters/ignore_loglevel. 2197 2198 ignore_rlimit_data 2199 Ignore RLIMIT_DATA setting for data mappings, 2200 print warning at first misuse. Can be changed via 2201 /sys/module/kernel/parameters/ignore_rlimit_data. 2202 2203 ihash_entries= [KNL] 2204 Set number of hash buckets for inode cache. 2205 2206 ima_appraise= [IMA] appraise integrity measurements 2207 Format: { "off" | "enforce" | "fix" | "log" } 2208 default: "enforce" 2209 2210 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2211 The builtin appraise policy appraises all files 2212 owned by uid=0. 2213 2214 ima_canonical_fmt [IMA] 2215 Use the canonical format for the binary runtime 2216 measurements, instead of host native format. 2217 2218 ima_hash= [IMA] 2219 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2220 | sha512 | ... } 2221 default: "sha1" 2222 2223 The list of supported hash algorithms is defined 2224 in crypto/hash_info.h. 2225 2226 ima_policy= [IMA] 2227 The builtin policies to load during IMA setup. 2228 Format: "tcb | appraise_tcb | secure_boot | 2229 fail_securely | critical_data" 2230 2231 The "tcb" policy measures all programs exec'd, files 2232 mmap'd for exec, and all files opened with the read 2233 mode bit set by either the effective uid (euid=0) or 2234 uid=0. 2235 2236 The "appraise_tcb" policy appraises the integrity of 2237 all files owned by root. 2238 2239 The "secure_boot" policy appraises the integrity 2240 of files (eg. kexec kernel image, kernel modules, 2241 firmware, policy, etc) based on file signatures. 2242 2243 The "fail_securely" policy forces file signature 2244 verification failure also on privileged mounted 2245 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2246 flag. 2247 2248 The "critical_data" policy measures kernel integrity 2249 critical data. 2250 2251 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2252 Load a policy which meets the needs of the Trusted 2253 Computing Base. This means IMA will measure all 2254 programs exec'd, files mmap'd for exec, and all files 2255 opened for read by uid=0. 2256 2257 ima_template= [IMA] 2258 Select one of defined IMA measurements template formats. 2259 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2260 "ima-sigv2" } 2261 Default: "ima-ng" 2262 2263 ima_template_fmt= 2264 [IMA] Define a custom template format. 2265 Format: { "field1|...|fieldN" } 2266 2267 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2268 Format: <min_file_size> 2269 Set the minimal file size for using asynchronous hash. 2270 If left unspecified, ahash usage is disabled. 2271 2272 ahash performance varies for different data sizes on 2273 different crypto accelerators. This option can be used 2274 to achieve the best performance for a particular HW. 2275 2276 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2277 Format: <bufsize> 2278 Set hashing buffer size. Default: 4k. 2279 2280 ahash performance varies for different chunk sizes on 2281 different crypto accelerators. This option can be used 2282 to achieve best performance for particular HW. 2283 2284 ima= [IMA] Enable or disable IMA 2285 Format: { "off" | "on" } 2286 Default: "on" 2287 Note that disabling IMA is limited to kdump kernel. 2288 2289 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2290 Target Selection(ITS) bug in Intel CPUs. Updated 2291 microcode is also required for a fix in IBPB. 2292 2293 on: Enable mitigation (default). 2294 off: Disable mitigation. 2295 force: Force the ITS bug and deploy default 2296 mitigation. 2297 vmexit: Only deploy mitigation if CPU is affected by 2298 guest/host isolation part of ITS. 2299 stuff: Deploy RSB-fill mitigation when retpoline is 2300 also deployed. Otherwise, deploy the default 2301 mitigation. 2302 2303 For details see: 2304 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2305 2306 init= [KNL] 2307 Format: <full_path> 2308 Run specified binary instead of /sbin/init as init 2309 process. 2310 2311 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2312 for working out where the kernel is dying during 2313 startup. 2314 2315 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2316 initcall functions. Useful for debugging built-in 2317 modules and initcalls. 2318 2319 initramfs_async= [KNL] 2320 Format: <bool> 2321 Default: 1 2322 This parameter controls whether the initramfs 2323 image is unpacked asynchronously, concurrently 2324 with devices being probed and 2325 initialized. This should normally just work, 2326 but as a debugging aid, one can get the 2327 historical behaviour of the initramfs 2328 unpacking being completed before device_ and 2329 late_ initcalls. 2330 2331 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2332 2333 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2334 load the initrd. If an initrd is compiled in or 2335 specified in the bootparams, it takes priority over this 2336 setting. 2337 Format: ss[KMG],nn[KMG] 2338 Default is 0, 0 2339 2340 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2341 zeroes. 2342 Format: 0 | 1 2343 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2344 2345 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2346 Format: 0 | 1 2347 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2348 2349 init_pkru= [X86] Specify the default memory protection keys rights 2350 register contents for all processes. 0x55555554 by 2351 default (disallow access to all but pkey 0). Can 2352 override in debugfs after boot. 2353 2354 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2355 Format: <irq> 2356 2357 int_pln_enable [X86] Enable power limit notification interrupt 2358 2359 integrity_audit=[IMA] 2360 Format: { "0" | "1" } 2361 0 -- basic integrity auditing messages. (Default) 2362 1 -- additional integrity auditing messages. 2363 2364 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2365 on 2366 Enable intel iommu driver. 2367 off 2368 Disable intel iommu driver. 2369 igfx_off [Default Off] 2370 By default, gfx is mapped as normal device. If a gfx 2371 device has a dedicated DMAR unit, the DMAR unit is 2372 bypassed by not enabling DMAR with this option. In 2373 this case, gfx device will use physical address for 2374 DMA. 2375 strict [Default Off] 2376 Deprecated, equivalent to iommu.strict=1. 2377 sp_off [Default Off] 2378 By default, super page will be supported if Intel IOMMU 2379 has the capability. With this option, super page will 2380 not be supported. 2381 sm_on 2382 Enable the Intel IOMMU scalable mode if the hardware 2383 advertises that it has support for the scalable mode 2384 translation. 2385 sm_off 2386 Disallow use of the Intel IOMMU scalable mode. 2387 tboot_noforce [Default Off] 2388 Do not force the Intel IOMMU enabled under tboot. 2389 By default, tboot will force Intel IOMMU on, which 2390 could harm performance of some high-throughput 2391 devices like 40GBit network cards, even if identity 2392 mapping is enabled. 2393 Note that using this option lowers the security 2394 provided by tboot because it makes the system 2395 vulnerable to DMA attacks. 2396 2397 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2398 0 disables intel_idle and fall back on acpi_idle. 2399 1 to 9 specify maximum depth of C-state. 2400 2401 intel_pstate= [X86,EARLY] 2402 disable 2403 Do not enable intel_pstate as the default 2404 scaling driver for the supported processors 2405 active 2406 Use intel_pstate driver to bypass the scaling 2407 governors layer of cpufreq and provides it own 2408 algorithms for p-state selection. There are two 2409 P-state selection algorithms provided by 2410 intel_pstate in the active mode: powersave and 2411 performance. The way they both operate depends 2412 on whether or not the hardware managed P-states 2413 (HWP) feature has been enabled in the processor 2414 and possibly on the processor model. 2415 passive 2416 Use intel_pstate as a scaling driver, but configure it 2417 to work with generic cpufreq governors (instead of 2418 enabling its internal governor). This mode cannot be 2419 used along with the hardware-managed P-states (HWP) 2420 feature. 2421 force 2422 Enable intel_pstate on systems that prohibit it by default 2423 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2424 instead of acpi-cpufreq may disable platform features, such 2425 as thermal controls and power capping, that rely on ACPI 2426 P-States information being indicated to OSPM and therefore 2427 should be used with caution. This option does not work with 2428 processors that aren't supported by the intel_pstate driver 2429 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2430 no_hwp 2431 Do not enable hardware P state control (HWP) 2432 if available. 2433 hwp_only 2434 Only load intel_pstate on systems which support 2435 hardware P state control (HWP) if available. 2436 support_acpi_ppc 2437 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2438 Description Table, specifies preferred power management 2439 profile as "Enterprise Server" or "Performance Server", 2440 then this feature is turned on by default. 2441 per_cpu_perf_limits 2442 Allow per-logical-CPU P-State performance control limits using 2443 cpufreq sysfs interface 2444 no_cas 2445 Do not enable capacity-aware scheduling (CAS) on 2446 hybrid systems 2447 2448 intremap= [X86-64,Intel-IOMMU,EARLY] 2449 on enable Interrupt Remapping (default) 2450 off disable Interrupt Remapping 2451 nosid disable Source ID checking 2452 no_x2apic_optout 2453 BIOS x2APIC opt-out request will be ignored 2454 nopost disable Interrupt Posting 2455 posted_msi 2456 enable MSIs delivered as posted interrupts 2457 2458 iomem= Disable strict checking of access to MMIO memory 2459 strict regions from userspace. 2460 relaxed 2461 2462 iommu= [X86,EARLY] 2463 2464 off 2465 Don't initialize and use any kind of IOMMU. 2466 2467 force 2468 Force the use of the hardware IOMMU even when 2469 it is not actually needed (e.g. because < 3 GB 2470 memory). 2471 2472 noforce 2473 Don't force hardware IOMMU usage when it is not 2474 needed. (default). 2475 2476 biomerge 2477 panic 2478 nopanic 2479 merge 2480 nomerge 2481 2482 soft 2483 Use software bounce buffering (SWIOTLB) (default for 2484 Intel machines). This can be used to prevent the usage 2485 of an available hardware IOMMU. 2486 2487 [X86] 2488 pt 2489 [X86] 2490 nopt 2491 [PPC/POWERNV] 2492 nobypass 2493 Disable IOMMU bypass, using IOMMU for PCI devices. 2494 2495 [X86] 2496 AMD Gart HW IOMMU-specific options: 2497 2498 <size> 2499 Set the size of the remapping area in bytes. 2500 2501 allowed 2502 Overwrite iommu off workarounds for specific chipsets 2503 2504 fullflush 2505 Flush IOMMU on each allocation (default). 2506 2507 nofullflush 2508 Don't use IOMMU fullflush. 2509 2510 memaper[=<order>] 2511 Allocate an own aperture over RAM with size 2512 32MB<<order. (default: order=1, i.e. 64MB) 2513 2514 merge 2515 Do scatter-gather (SG) merging. Implies "force" 2516 (experimental). 2517 2518 nomerge 2519 Don't do scatter-gather (SG) merging. 2520 2521 noaperture 2522 Ask the IOMMU not to touch the aperture for AGP. 2523 2524 noagp 2525 Don't initialize the AGP driver and use full aperture. 2526 2527 panic 2528 Always panic when IOMMU overflows. 2529 2530 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2531 Format: { "0" | "1" } 2532 0 - Try to allocate a 32-bit DMA address first, before 2533 falling back to the full range if needed. 2534 1 - Allocate directly from the full usable range, 2535 forcing Dual Address Cycle for PCI cards supporting 2536 greater than 32-bit addressing. 2537 2538 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2539 Format: { "0" | "1" } 2540 0 - Lazy mode. 2541 Request that DMA unmap operations use deferred 2542 invalidation of hardware TLBs, for increased 2543 throughput at the cost of reduced device isolation. 2544 Will fall back to strict mode if not supported by 2545 the relevant IOMMU driver. 2546 1 - Strict mode. 2547 DMA unmap operations invalidate IOMMU hardware TLBs 2548 synchronously. 2549 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2550 Note: on x86, strict mode specified via one of the 2551 legacy driver-specific options takes precedence. 2552 2553 iommu.passthrough= 2554 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2555 Format: { "0" | "1" } 2556 0 - Use IOMMU translation for DMA. 2557 1 - Bypass the IOMMU for DMA. 2558 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2559 2560 io7= [HW] IO7 for Marvel-based Alpha systems 2561 See comment before marvel_specify_io7 in 2562 arch/alpha/kernel/core_marvel.c. 2563 2564 io_delay= [X86,EARLY] I/O delay method 2565 0x80 2566 Standard port 0x80 based delay 2567 0xed 2568 Alternate port 0xed based delay (needed on some systems) 2569 udelay 2570 Simple two microseconds delay 2571 none 2572 No delay 2573 2574 ip= [IP_PNP] 2575 See Documentation/admin-guide/nfs/nfsroot.rst. 2576 2577 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2578 IPC identifiers from 32,768 to 16,777,216. 2579 2580 ipe.enforce= [IPE] 2581 Format: <bool> 2582 Determine whether IPE starts in permissive (0) or 2583 enforce (1) mode. The default is enforce. 2584 2585 ipe.success_audit= 2586 [IPE] 2587 Format: <bool> 2588 Start IPE with success auditing enabled, emitting 2589 an audit event when a binary is allowed. The default 2590 is 0. 2591 2592 irqaffinity= [SMP] Set the default irq affinity mask 2593 The argument is a cpu list, as described above. 2594 2595 irqchip.gicv2_force_probe= 2596 [ARM,ARM64,EARLY] 2597 Format: <bool> 2598 Force the kernel to look for the second 4kB page 2599 of a GICv2 controller even if the memory range 2600 exposed by the device tree is too small. 2601 2602 irqchip.gicv3_nolpi= 2603 [ARM,ARM64,EARLY] 2604 Force the kernel to ignore the availability of 2605 LPIs (and by consequence ITSs). Intended for system 2606 that use the kernel as a bootloader, and thus want 2607 to let secondary kernels in charge of setting up 2608 LPIs. 2609 2610 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2611 Enables support for pseudo-NMIs in the kernel. This 2612 requires the kernel to be built with 2613 CONFIG_ARM64_PSEUDO_NMI. 2614 2615 irqchip.riscv_imsic_noipi 2616 [RISC-V,EARLY] 2617 Force the kernel to not use IMSIC software injected MSIs 2618 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2619 and thus want to reduce MMIO traps when triggering IPIs 2620 to multiple harts. 2621 2622 irqfixup [HW] 2623 When an interrupt is not handled search all handlers 2624 for it. Intended to get systems with badly broken 2625 firmware running. 2626 2627 irqhandler.duration_warn_us= [KNL] 2628 Warn if an IRQ handler exceeds the specified duration 2629 threshold in microseconds. Useful for identifying 2630 long-running IRQs in the system. 2631 2632 irqpoll [HW] 2633 When an interrupt is not handled search all handlers 2634 for it. Also check all handlers each timer 2635 interrupt. Intended to get systems with badly broken 2636 firmware running. 2637 2638 isapnp= [ISAPNP] 2639 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2640 2641 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2642 [Deprecated - use cpusets instead] 2643 Format: [flag-list,]<cpu-list> 2644 2645 Specify one or more CPUs to isolate from disturbances 2646 specified in the flag list (default: domain): 2647 2648 nohz 2649 Disable the tick when a single task runs as well as 2650 disabling other kernel noises like having RCU callbacks 2651 offloaded. This is equivalent to the nohz_full parameter. 2652 2653 A residual 1Hz tick is offloaded to workqueues, which you 2654 need to affine to housekeeping through the global 2655 workqueue's affinity configured via the 2656 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2657 by using the 'domain' flag described below. 2658 2659 NOTE: by default the global workqueue runs on all CPUs, 2660 so to protect individual CPUs the 'cpumask' file has to 2661 be configured manually after bootup. 2662 2663 domain 2664 Isolate from the general SMP balancing and scheduling 2665 algorithms. Note that performing domain isolation this way 2666 is irreversible: it's not possible to bring back a CPU to 2667 the domains once isolated through isolcpus. It's strongly 2668 advised to use cpusets instead to disable scheduler load 2669 balancing through the "cpuset.sched_load_balance" file. 2670 It offers a much more flexible interface where CPUs can 2671 move in and out of an isolated set anytime. 2672 2673 You can move a process onto or off an "isolated" CPU via 2674 the CPU affinity syscalls or cpuset. 2675 <cpu number> begins at 0 and the maximum value is 2676 "number of CPUs in system - 1". 2677 2678 managed_irq 2679 2680 Isolate from being targeted by managed interrupts 2681 which have an interrupt mask containing isolated 2682 CPUs. The affinity of managed interrupts is 2683 handled by the kernel and cannot be changed via 2684 the /proc/irq/* interfaces. 2685 2686 This isolation is best effort and only effective 2687 if the automatically assigned interrupt mask of a 2688 device queue contains isolated and housekeeping 2689 CPUs. If housekeeping CPUs are online then such 2690 interrupts are directed to the housekeeping CPU 2691 so that IO submitted on the housekeeping CPU 2692 cannot disturb the isolated CPU. 2693 2694 If a queue's affinity mask contains only isolated 2695 CPUs then this parameter has no effect on the 2696 interrupt routing decision, though interrupts are 2697 only delivered when tasks running on those 2698 isolated CPUs submit IO. IO submitted on 2699 housekeeping CPUs has no influence on those 2700 queues. 2701 2702 The format of <cpu-list> is described above. 2703 2704 iucv= [HW,NET] 2705 2706 ivrs_ioapic [HW,X86-64] 2707 Provide an override to the IOAPIC-ID<->DEVICE-ID 2708 mapping provided in the IVRS ACPI table. 2709 By default, PCI segment is 0, and can be omitted. 2710 2711 For example, to map IOAPIC-ID decimal 10 to 2712 PCI segment 0x1 and PCI device 00:14.0, 2713 write the parameter as: 2714 ivrs_ioapic=10@0001:00:14.0 2715 2716 Deprecated formats: 2717 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2718 write the parameter as: 2719 ivrs_ioapic[10]=00:14.0 2720 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2721 PCI device 00:14.0 write the parameter as: 2722 ivrs_ioapic[10]=0001:00:14.0 2723 2724 ivrs_hpet [HW,X86-64] 2725 Provide an override to the HPET-ID<->DEVICE-ID 2726 mapping provided in the IVRS ACPI table. 2727 By default, PCI segment is 0, and can be omitted. 2728 2729 For example, to map HPET-ID decimal 10 to 2730 PCI segment 0x1 and PCI device 00:14.0, 2731 write the parameter as: 2732 ivrs_hpet=10@0001:00:14.0 2733 2734 Deprecated formats: 2735 * To map HPET-ID decimal 0 to PCI device 00:14.0 2736 write the parameter as: 2737 ivrs_hpet[0]=00:14.0 2738 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2739 PCI device 00:14.0 write the parameter as: 2740 ivrs_ioapic[10]=0001:00:14.0 2741 2742 ivrs_acpihid [HW,X86-64] 2743 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2744 mapping provided in the IVRS ACPI table. 2745 By default, PCI segment is 0, and can be omitted. 2746 2747 For example, to map UART-HID:UID AMD0020:0 to 2748 PCI segment 0x1 and PCI device ID 00:14.5, 2749 write the parameter as: 2750 ivrs_acpihid=AMD0020:0@0001:00:14.5 2751 2752 Deprecated formats: 2753 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2754 PCI device ID 00:14.5, write the parameter as: 2755 ivrs_acpihid[00:14.5]=AMD0020:0 2756 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2757 PCI device ID 00:14.5, write the parameter as: 2758 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2759 2760 js= [HW,JOY] Analog joystick 2761 See Documentation/input/joydev/joystick.rst. 2762 2763 kasan_multi_shot 2764 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2765 report on every invalid memory access. Without this 2766 parameter KASAN will print report only for the first 2767 invalid access. 2768 2769 keep_bootcon [KNL,EARLY] 2770 Do not unregister boot console at start. This is only 2771 useful for debugging when something happens in the window 2772 between unregistering the boot console and initializing 2773 the real console. 2774 2775 keepinitrd [HW,ARM] See retain_initrd. 2776 2777 kernelcore= [KNL,X86,PPC,EARLY] 2778 Format: nn[KMGTPE] | nn% | "mirror" 2779 This parameter specifies the amount of memory usable by 2780 the kernel for non-movable allocations. The requested 2781 amount is spread evenly throughout all nodes in the 2782 system as ZONE_NORMAL. The remaining memory is used for 2783 movable memory in its own zone, ZONE_MOVABLE. In the 2784 event, a node is too small to have both ZONE_NORMAL and 2785 ZONE_MOVABLE, kernelcore memory will take priority and 2786 other nodes will have a larger ZONE_MOVABLE. 2787 2788 ZONE_MOVABLE is used for the allocation of pages that 2789 may be reclaimed or moved by the page migration 2790 subsystem. Note that allocations like PTEs-from-HighMem 2791 still use the HighMem zone if it exists, and the Normal 2792 zone if it does not. 2793 2794 It is possible to specify the exact amount of memory in 2795 the form of "nn[KMGTPE]", a percentage of total system 2796 memory in the form of "nn%", or "mirror". If "mirror" 2797 option is specified, mirrored (reliable) memory is used 2798 for non-movable allocations and remaining memory is used 2799 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2800 are exclusive, so you cannot specify multiple forms. 2801 2802 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2803 Format: <Controller#>[,poll interval] 2804 The controller # is the number of the ehci usb debug 2805 port as it is probed via PCI. The poll interval is 2806 optional and is the number seconds in between 2807 each poll cycle to the debug port in case you need 2808 the functionality for interrupting the kernel with 2809 gdb or control-c on the dbgp connection. When 2810 not using this parameter you use sysrq-g to break into 2811 the kernel debugger. 2812 2813 kgdboc= [KGDB,HW] kgdb over consoles. 2814 Requires a tty driver that supports console polling, 2815 or a supported polling keyboard driver (non-usb). 2816 Serial only format: <serial_device>[,baud] 2817 keyboard only format: kbd 2818 keyboard and serial format: kbd,<serial_device>[,baud] 2819 Optional Kernel mode setting: 2820 kms, kbd format: kms,kbd 2821 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2822 2823 kgdboc_earlycon= [KGDB,HW,EARLY] 2824 If the boot console provides the ability to read 2825 characters and can work in polling mode, you can use 2826 this parameter to tell kgdb to use it as a backend 2827 until the normal console is registered. Intended to 2828 be used together with the kgdboc parameter which 2829 specifies the normal console to transition to. 2830 2831 The name of the early console should be specified 2832 as the value of this parameter. Note that the name of 2833 the early console might be different than the tty 2834 name passed to kgdboc. It's OK to leave the value 2835 blank and the first boot console that implements 2836 read() will be picked. 2837 2838 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 2839 kernel debugger at the earliest opportunity. 2840 2841 kho= [KEXEC,EARLY] 2842 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 2843 Enables or disables Kexec HandOver. 2844 "0" | "off" | "n" - kexec handover is disabled 2845 "1" | "on" | "y" - kexec handover is enabled 2846 2847 kho_scratch= [KEXEC,EARLY] 2848 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 2849 Defines the size of the KHO scratch region. The KHO 2850 scratch regions are physically contiguous memory 2851 ranges that can only be used for non-kernel 2852 allocations. That way, even when memory is heavily 2853 fragmented with handed over memory, the kexeced 2854 kernel will always have enough contiguous ranges to 2855 bootstrap itself. 2856 2857 It is possible to specify the exact amount of 2858 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 2859 where the first parameter defines the size of a low 2860 memory scratch area, the second parameter defines 2861 the size of a global scratch area and the third 2862 parameter defines the size of additional per-node 2863 scratch areas. The form "nn%" defines scale factor 2864 (in percents) of memory that was used during boot. 2865 2866 kmac= [MIPS] Korina ethernet MAC address. 2867 Configure the RouterBoard 532 series on-chip 2868 Ethernet adapter MAC address. 2869 2870 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 2871 Valid arguments: on, off 2872 Default: on 2873 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2874 the default is off. 2875 2876 kprobe_event=[probe-list] 2877 [FTRACE] Add kprobe events and enable at boot time. 2878 The probe-list is a semicolon delimited list of probe 2879 definitions. Each definition is same as kprobe_events 2880 interface, but the parameters are comma delimited. 2881 For example, to add a kprobe event on vfs_read with 2882 arg1 and arg2, add to the command line; 2883 2884 kprobe_event=p,vfs_read,$arg1,$arg2 2885 2886 See also Documentation/trace/kprobetrace.rst "Kernel 2887 Boot Parameter" section. 2888 2889 kpti= [ARM64,EARLY] Control page table isolation of 2890 user and kernel address spaces. 2891 Default: enabled on cores which need mitigation. 2892 0: force disabled 2893 1: force enabled 2894 2895 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 2896 CONFIG_KUNIT to be set to be fully enabled. The 2897 default value can be overridden via 2898 KUNIT_DEFAULT_ENABLED. 2899 Default is 1 (enabled) 2900 2901 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2902 Default is 0 (don't ignore, but inject #GP) 2903 2904 kvm.eager_page_split= 2905 [KVM,X86] Controls whether or not KVM will try to 2906 proactively split all huge pages during dirty logging. 2907 Eager page splitting reduces interruptions to vCPU 2908 execution by eliminating the write-protection faults 2909 and MMU lock contention that would otherwise be 2910 required to split huge pages lazily. 2911 2912 VM workloads that rarely perform writes or that write 2913 only to a small region of VM memory may benefit from 2914 disabling eager page splitting to allow huge pages to 2915 still be used for reads. 2916 2917 The behavior of eager page splitting depends on whether 2918 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2919 disabled, all huge pages in a memslot will be eagerly 2920 split when dirty logging is enabled on that memslot. If 2921 enabled, eager page splitting will be performed during 2922 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2923 cleared. 2924 2925 Eager page splitting is only supported when kvm.tdp_mmu=Y. 2926 2927 Default is Y (on). 2928 2929 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 2930 If enabled, KVM will enable virtualization in hardware 2931 when KVM is loaded, and disable virtualization when KVM 2932 is unloaded (if KVM is built as a module). 2933 2934 If disabled, KVM will dynamically enable and disable 2935 virtualization on-demand when creating and destroying 2936 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 2937 number of VMs. 2938 2939 Enabling virtualization at module load avoids potential 2940 latency for creation of the 0=>1 VM, as KVM serializes 2941 virtualization enabling across all online CPUs. The 2942 "cost" of enabling virtualization when KVM is loaded, 2943 is that doing so may interfere with using out-of-tree 2944 hypervisors that want to "own" virtualization hardware. 2945 2946 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2947 Default is false (don't support). 2948 2949 kvm.nx_huge_pages= 2950 [KVM] Controls the software workaround for the 2951 X86_BUG_ITLB_MULTIHIT bug. 2952 force : Always deploy workaround. 2953 off : Never deploy workaround. 2954 auto : Deploy workaround based on the presence of 2955 X86_BUG_ITLB_MULTIHIT. 2956 2957 Default is 'auto'. 2958 2959 If the software workaround is enabled for the host, 2960 guests do need not to enable it for nested guests. 2961 2962 kvm.nx_huge_pages_recovery_ratio= 2963 [KVM] Controls how many 4KiB pages are periodically zapped 2964 back to huge pages. 0 disables the recovery, otherwise if 2965 the value is N KVM will zap 1/Nth of the 4KiB pages every 2966 period (see below). The default is 60. 2967 2968 kvm.nx_huge_pages_recovery_period_ms= 2969 [KVM] Controls the time period at which KVM zaps 4KiB pages 2970 back to huge pages. If the value is a non-zero N, KVM will 2971 zap a portion (see ratio above) of the pages every N msecs. 2972 If the value is 0 (the default), KVM will pick a period based 2973 on the ratio, such that a page is zapped after 1 hour on average. 2974 2975 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 2976 KVM/SVM. Default is 1 (enabled). 2977 2978 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 2979 a.k.a. Two-Dimensional Page Tables. Default is 1 2980 (enabled). Disable by KVM if hardware lacks support 2981 for NPT. 2982 2983 kvm-amd.ciphertext_hiding_asids= 2984 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 2985 to SNP private memory from reading ciphertext. Instead, 2986 reads will see constant default values (0xff). 2987 2988 If ciphertext hiding is enabled, the joint SEV-ES and 2989 SEV-SNP ASID space is partitioned into separate SEV-ES 2990 and SEV-SNP ASID ranges, with the SEV-SNP range being 2991 [1..max_snp_asid] and the SEV-ES range being 2992 (max_snp_asid..min_sev_asid), where min_sev_asid is 2993 enumerated by CPUID.0x.8000_001F[EDX]. 2994 2995 A non-zero value enables SEV-SNP ciphertext hiding and 2996 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 2997 KVM caps the number of SEV-SNP ASIDs at the maximum 2998 possible value, e.g. specifying -1u will assign all 2999 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3000 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3001 max_snp_asid == min_sev_asid-1, will effectively make 3002 SEV-ES unusable. 3003 3004 kvm-arm.mode= 3005 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3006 operation. 3007 3008 none: Forcefully disable KVM. 3009 3010 nvhe: Standard nVHE-based mode, without support for 3011 protected guests. 3012 3013 protected: Mode with support for guests whose state is 3014 kept private from the host, using VHE or 3015 nVHE depending on HW support. 3016 3017 nested: VHE-based mode with support for nested 3018 virtualization. Requires at least ARMv8.4 3019 hardware (with FEAT_NV2). 3020 3021 Defaults to VHE/nVHE based on hardware support. Setting 3022 mode to "protected" will disable kexec and hibernation 3023 for the host. To force nVHE on VHE hardware, add 3024 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3025 command-line. 3026 "nested" is experimental and should be used with 3027 extreme caution. 3028 3029 kvm-arm.vgic_v3_group0_trap= 3030 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3031 system registers 3032 3033 kvm-arm.vgic_v3_group1_trap= 3034 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3035 system registers 3036 3037 kvm-arm.vgic_v3_common_trap= 3038 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3039 system registers 3040 3041 kvm-arm.vgic_v4_enable= 3042 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3043 injection of LPIs. 3044 3045 kvm-arm.wfe_trap_policy= 3046 [KVM,ARM] Control when to set WFE instruction trap for 3047 KVM VMs. Traps are allowed but not guaranteed by the 3048 CPU architecture. 3049 3050 trap: set WFE instruction trap 3051 3052 notrap: clear WFE instruction trap 3053 3054 kvm-arm.wfi_trap_policy= 3055 [KVM,ARM] Control when to set WFI instruction trap for 3056 KVM VMs. Traps are allowed but not guaranteed by the 3057 CPU architecture. 3058 3059 trap: set WFI instruction trap 3060 3061 notrap: clear WFI instruction trap 3062 3063 kvm_cma_resv_ratio=n [PPC,EARLY] 3064 Reserves given percentage from system memory area for 3065 contiguous memory allocation for KVM hash pagetable 3066 allocation. 3067 By default it reserves 5% of total system memory. 3068 Format: <integer> 3069 Default: 5 3070 3071 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3072 a.k.a. Two-Dimensional Page Tables. Default is 1 3073 (enabled). Disable by KVM if hardware lacks support 3074 for EPT. 3075 3076 kvm-intel.emulate_invalid_guest_state= 3077 [KVM,Intel] Control whether to emulate invalid guest 3078 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3079 as guest state is never invalid for unrestricted 3080 guests. This param doesn't apply to nested guests (L2), 3081 as KVM never emulates invalid L2 guest state. 3082 Default is 1 (enabled). 3083 3084 kvm-intel.flexpriority= 3085 [KVM,Intel] Control KVM's use of FlexPriority feature 3086 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3087 hardware lacks support for it. 3088 3089 kvm-intel.nested= 3090 [KVM,Intel] Control nested virtualization feature in 3091 KVM/VMX. Default is 1 (enabled). 3092 3093 kvm-intel.unrestricted_guest= 3094 [KVM,Intel] Control KVM's use of unrestricted guest 3095 feature (virtualized real and unpaged mode). Default 3096 is 1 (enabled). Disable by KVM if EPT is disabled or 3097 hardware lacks support for it. 3098 3099 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3100 CVE-2018-3620. 3101 3102 Valid arguments: never, cond, always 3103 3104 always: L1D cache flush on every VMENTER. 3105 cond: Flush L1D on VMENTER only when the code between 3106 VMEXIT and VMENTER can leak host memory. 3107 never: Disables the mitigation 3108 3109 Default is cond (do L1 cache flush in specific instances) 3110 3111 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3112 Identification feature (tagged TLBs). Default is 1 3113 (enabled). Disable by KVM if hardware lacks support 3114 for it. 3115 3116 l1d_flush= [X86,INTEL,EARLY] 3117 Control mitigation for L1D based snooping vulnerability. 3118 3119 Certain CPUs are vulnerable to an exploit against CPU 3120 internal buffers which can forward information to a 3121 disclosure gadget under certain conditions. 3122 3123 In vulnerable processors, the speculatively 3124 forwarded data can be used in a cache side channel 3125 attack, to access data to which the attacker does 3126 not have direct access. 3127 3128 This parameter controls the mitigation. The 3129 options are: 3130 3131 on - enable the interface for the mitigation 3132 3133 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3134 affected CPUs 3135 3136 The kernel PTE inversion protection is unconditionally 3137 enabled and cannot be disabled. 3138 3139 full 3140 Provides all available mitigations for the 3141 L1TF vulnerability. Disables SMT and 3142 enables all mitigations in the 3143 hypervisors, i.e. unconditional L1D flush. 3144 3145 SMT control and L1D flush control via the 3146 sysfs interface is still possible after 3147 boot. Hypervisors will issue a warning 3148 when the first VM is started in a 3149 potentially insecure configuration, 3150 i.e. SMT enabled or L1D flush disabled. 3151 3152 full,force 3153 Same as 'full', but disables SMT and L1D 3154 flush runtime control. Implies the 3155 'nosmt=force' command line option. 3156 (i.e. sysfs control of SMT is disabled.) 3157 3158 flush 3159 Leaves SMT enabled and enables the default 3160 hypervisor mitigation, i.e. conditional 3161 L1D flush. 3162 3163 SMT control and L1D flush control via the 3164 sysfs interface is still possible after 3165 boot. Hypervisors will issue a warning 3166 when the first VM is started in a 3167 potentially insecure configuration, 3168 i.e. SMT enabled or L1D flush disabled. 3169 3170 flush,nosmt 3171 3172 Disables SMT and enables the default 3173 hypervisor mitigation. 3174 3175 SMT control and L1D flush control via the 3176 sysfs interface is still possible after 3177 boot. Hypervisors will issue a warning 3178 when the first VM is started in a 3179 potentially insecure configuration, 3180 i.e. SMT enabled or L1D flush disabled. 3181 3182 flush,nowarn 3183 Same as 'flush', but hypervisors will not 3184 warn when a VM is started in a potentially 3185 insecure configuration. 3186 3187 off 3188 Disables hypervisor mitigations and doesn't 3189 emit any warnings. 3190 It also drops the swap size and available 3191 RAM limit restriction on both hypervisor and 3192 bare metal. 3193 3194 Default is 'flush'. 3195 3196 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3197 3198 l2cr= [PPC] 3199 3200 l3cr= [PPC] 3201 3202 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3203 disabled it. 3204 3205 lapic= [X86,APIC] Do not use TSC deadline 3206 value for LAPIC timer one-shot implementation. Default 3207 back to the programmable timer unit in the LAPIC. 3208 Format: notscdeadline 3209 3210 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3211 in C2 power state. 3212 3213 libata.dma= [LIBATA] DMA control 3214 libata.dma=0 Disable all PATA and SATA DMA 3215 libata.dma=1 PATA and SATA Disk DMA only 3216 libata.dma=2 ATAPI (CDROM) DMA only 3217 libata.dma=4 Compact Flash DMA only 3218 Combinations also work, so libata.dma=3 enables DMA 3219 for disks and CDROMs, but not CFs. 3220 3221 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3222 libata.ignore_hpa=0 keep BIOS limits (default) 3223 libata.ignore_hpa=1 ignore limits, using full disk 3224 3225 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3226 when set. 3227 Format: <int> 3228 3229 libata.force= [LIBATA] Force configurations. The format is a comma- 3230 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3231 PORT and DEVICE are decimal numbers matching port, link 3232 or device. Basically, it matches the ATA ID string 3233 printed on console by libata. If the whole ID part is 3234 omitted, the last PORT and DEVICE values are used. If 3235 ID hasn't been specified yet, the configuration applies 3236 to all ports, links and devices. 3237 3238 If only DEVICE is omitted, the parameter applies to 3239 the port and all links and devices behind it. DEVICE 3240 number of 0 either selects the first device or the 3241 first fan-out link behind PMP device. It does not 3242 select the host link. DEVICE number of 15 selects the 3243 host link and device attached to it. 3244 3245 The VAL specifies the configuration to force. As long 3246 as there is no ambiguity, shortcut notation is allowed. 3247 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3248 The following configurations can be forced. 3249 3250 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3251 Any ID with matching PORT is used. 3252 3253 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3254 3255 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3256 udma[/][16,25,33,44,66,100,133] notation is also 3257 allowed. 3258 3259 * nohrst, nosrst, norst: suppress hard, soft and both 3260 resets. 3261 3262 * rstonce: only attempt one reset during hot-unplug 3263 link recovery. 3264 3265 * [no]dbdelay: Enable or disable the extra 200ms delay 3266 before debouncing a link PHY and device presence 3267 detection. 3268 3269 * [no]ncq: Turn on or off NCQ. 3270 3271 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3272 3273 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3274 3275 * [no]trim: Enable or disable (unqueued) TRIM. 3276 3277 * trim_zero: Indicate that TRIM command zeroes data. 3278 3279 * max_trim_128m: Set 128M maximum trim size limit. 3280 3281 * [no]dma: Turn on or off DMA transfers. 3282 3283 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3284 3285 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3286 commands that are not a multiple of 16 bytes. 3287 3288 * [no]dmalog: Enable or disable the use of the 3289 READ LOG DMA EXT command to access logs. 3290 3291 * [no]iddevlog: Enable or disable access to the 3292 identify device data log. 3293 3294 * [no]logdir: Enable or disable access to the general 3295 purpose log directory. 3296 3297 * max_sec_128: Set transfer size limit to 128 sectors. 3298 3299 * max_sec_1024: Set or clear transfer size limit to 3300 1024 sectors. 3301 3302 * max_sec_lba48: Set or clear transfer size limit to 3303 65535 sectors. 3304 3305 * external: Mark port as external (hotplug-capable). 3306 3307 * [no]lpm: Enable or disable link power management. 3308 3309 * [no]setxfer: Indicate if transfer speed mode setting 3310 should be skipped. 3311 3312 * [no]fua: Disable or enable FUA (Force Unit Access) 3313 support for devices supporting this feature. 3314 3315 * dump_id: Dump IDENTIFY data. 3316 3317 * disable: Disable this device. 3318 3319 If there are multiple matching configurations changing 3320 the same attribute, the last one is used. 3321 3322 load_ramdisk= [RAM] [Deprecated] 3323 3324 lockd.nlm_grace_period=P [NFS] Assign grace period. 3325 Format: <integer> 3326 3327 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3328 Format: <integer> 3329 3330 lockd.nlm_timeout=T [NFS] Assign timeout value. 3331 Format: <integer> 3332 3333 lockd.nlm_udpport=M [NFS] Assign UDP port. 3334 Format: <integer> 3335 3336 lockdown= [SECURITY,EARLY] 3337 { integrity | confidentiality } 3338 Enable the kernel lockdown feature. If set to 3339 integrity, kernel features that allow userland to 3340 modify the running kernel are disabled. If set to 3341 confidentiality, kernel features that allow userland 3342 to extract confidential information from the kernel 3343 are also disabled. 3344 3345 locktorture.acq_writer_lim= [KNL] 3346 Set the time limit in jiffies for a lock 3347 acquisition. Acquisitions exceeding this limit 3348 will result in a splat once they do complete. 3349 3350 locktorture.bind_readers= [KNL] 3351 Specify the list of CPUs to which the readers are 3352 to be bound. 3353 3354 locktorture.bind_writers= [KNL] 3355 Specify the list of CPUs to which the writers are 3356 to be bound. 3357 3358 locktorture.call_rcu_chains= [KNL] 3359 Specify the number of self-propagating call_rcu() 3360 chains to set up. These are used to ensure that 3361 there is a high probability of an RCU grace period 3362 in progress at any given time. Defaults to 0, 3363 which disables these call_rcu() chains. 3364 3365 locktorture.long_hold= [KNL] 3366 Specify the duration in milliseconds for the 3367 occasional long-duration lock hold time. Defaults 3368 to 100 milliseconds. Select 0 to disable. 3369 3370 locktorture.nested_locks= [KNL] 3371 Specify the maximum lock nesting depth that 3372 locktorture is to exercise, up to a limit of 8 3373 (MAX_NESTED_LOCKS). Specify zero to disable. 3374 Note that this parameter is ineffective on types 3375 of locks that do not support nested acquisition. 3376 3377 locktorture.nreaders_stress= [KNL] 3378 Set the number of locking read-acquisition kthreads. 3379 Defaults to being automatically set based on the 3380 number of online CPUs. 3381 3382 locktorture.nwriters_stress= [KNL] 3383 Set the number of locking write-acquisition kthreads. 3384 3385 locktorture.onoff_holdoff= [KNL] 3386 Set time (s) after boot for CPU-hotplug testing. 3387 3388 locktorture.onoff_interval= [KNL] 3389 Set time (s) between CPU-hotplug operations, or 3390 zero to disable CPU-hotplug testing. 3391 3392 locktorture.rt_boost= [KNL] 3393 Do periodic testing of real-time lock priority 3394 boosting. Select 0 to disable, 1 to boost 3395 only rt_mutex, and 2 to boost unconditionally. 3396 Defaults to 2, which might seem to be an 3397 odd choice, but which should be harmless for 3398 non-real-time spinlocks, due to their disabling 3399 of preemption. Note that non-realtime mutexes 3400 disable boosting. 3401 3402 locktorture.rt_boost_factor= [KNL] 3403 Number that determines how often and for how 3404 long priority boosting is exercised. This is 3405 scaled down by the number of writers, so that the 3406 number of boosts per unit time remains roughly 3407 constant as the number of writers increases. 3408 On the other hand, the duration of each boost 3409 increases with the number of writers. 3410 3411 locktorture.shuffle_interval= [KNL] 3412 Set task-shuffle interval (jiffies). Shuffling 3413 tasks allows some CPUs to go into dyntick-idle 3414 mode during the locktorture test. 3415 3416 locktorture.shutdown_secs= [KNL] 3417 Set time (s) after boot system shutdown. This 3418 is useful for hands-off automated testing. 3419 3420 locktorture.stat_interval= [KNL] 3421 Time (s) between statistics printk()s. 3422 3423 locktorture.stutter= [KNL] 3424 Time (s) to stutter testing, for example, 3425 specifying five seconds causes the test to run for 3426 five seconds, wait for five seconds, and so on. 3427 This tests the locking primitive's ability to 3428 transition abruptly to and from idle. 3429 3430 locktorture.torture_type= [KNL] 3431 Specify the locking implementation to test. 3432 3433 locktorture.verbose= [KNL] 3434 Enable additional printk() statements. 3435 3436 locktorture.writer_fifo= [KNL] 3437 Run the write-side locktorture kthreads at 3438 sched_set_fifo() real-time priority. 3439 3440 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3441 Format: <irq> 3442 3443 loglevel= [KNL,EARLY] 3444 All Kernel Messages with a loglevel smaller than the 3445 console loglevel will be printed to the console. It can 3446 also be changed with klogd or other programs. The 3447 loglevels are defined as follows: 3448 3449 0 (KERN_EMERG) system is unusable 3450 1 (KERN_ALERT) action must be taken immediately 3451 2 (KERN_CRIT) critical conditions 3452 3 (KERN_ERR) error conditions 3453 4 (KERN_WARNING) warning conditions 3454 5 (KERN_NOTICE) normal but significant condition 3455 6 (KERN_INFO) informational 3456 7 (KERN_DEBUG) debug-level messages 3457 3458 log_buf_len=n[KMG] [KNL,EARLY] 3459 Sets the size of the printk ring buffer, in bytes. 3460 n must be a power of two and greater than the 3461 minimal size. The minimal size is defined by 3462 LOG_BUF_SHIFT kernel config parameter. There 3463 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3464 parameter that allows to increase the default size 3465 depending on the number of CPUs. See init/Kconfig 3466 for more details. 3467 3468 logo.nologo [FB] Disables display of the built-in Linux logo. 3469 This may be used to provide more screen space for 3470 kernel log messages and is useful when debugging 3471 kernel boot problems. 3472 3473 lp=0 [LP] Specify parallel ports to use, e.g, 3474 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3475 lp=reset first parallel port). 'lp=0' disables the 3476 lp=auto printer driver. 'lp=reset' (which can be 3477 specified in addition to the ports) causes 3478 attached printers to be reset. Using 3479 lp=port1,port2,... specifies the parallel ports 3480 to associate lp devices with, starting with 3481 lp0. A port specification may be 'none' to skip 3482 that lp device, or a parport name such as 3483 'parport0'. Specifying 'lp=auto' instead of a 3484 port specification list means that device IDs 3485 from each port should be examined, to see if 3486 an IEEE 1284-compliant printer is attached; if 3487 so, the driver will manage that printer. 3488 See also header of drivers/char/lp.c. 3489 3490 lpj=n [KNL] 3491 Sets loops_per_jiffy to given constant, thus avoiding 3492 time-consuming boot-time autodetection (up to 250 ms per 3493 CPU). 0 enables autodetection (default). To determine 3494 the correct value for your kernel, boot with normal 3495 autodetection and see what value is printed. Note that 3496 on SMP systems the preset will be applied to all CPUs, 3497 which is likely to cause problems if your CPUs need 3498 significantly divergent settings. An incorrect value 3499 will cause delays in the kernel to be wrong, leading to 3500 unpredictable I/O errors and other breakage. Although 3501 unlikely, in the extreme case this might damage your 3502 hardware. 3503 3504 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3505 3506 lsm=lsm1,...,lsmN 3507 [SECURITY] Choose order of LSM initialization. This 3508 overrides CONFIG_LSM, and the "security=" parameter. 3509 3510 machtype= [Loongson] Share the same kernel image file between 3511 different yeeloong laptops. 3512 Example: machtype=lemote-yeeloong-2f-7inch 3513 3514 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3515 will bring up during bootup. maxcpus=n : n >= 0 limits 3516 the kernel to bring up 'n' processors. Surely after 3517 bootup you can bring up the other plugged cpu by executing 3518 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3519 only takes effect during system bootup. 3520 While n=0 is a special case, it is equivalent to "nosmp", 3521 which also disables the IO APIC. 3522 3523 max_loop= [LOOP] The number of loop block devices that get 3524 (loop.max_loop) unconditionally pre-created at init time. The default 3525 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3526 of statically allocating a predefined number, loop 3527 devices can be requested on-demand with the 3528 /dev/loop-control interface. 3529 3530 mce= [X86-{32,64}] 3531 3532 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3533 3534 off 3535 disable machine check 3536 3537 no_cmci 3538 disable CMCI(Corrected Machine Check Interrupt) that 3539 Intel processor supports. Usually this disablement is 3540 not recommended, but it might be handy if your 3541 hardware is misbehaving. 3542 3543 Note that you'll get more problems without CMCI than 3544 with due to the shared banks, i.e. you might get 3545 duplicated error logs. 3546 3547 dont_log_ce 3548 don't make logs for corrected errors. All events 3549 reported as corrected are silently cleared by OS. This 3550 option will be useful if you have no interest in any 3551 of corrected errors. 3552 3553 ignore_ce 3554 disable features for corrected errors, e.g. 3555 polling timer and CMCI. All events reported as 3556 corrected are not cleared by OS and remained in its 3557 error banks. 3558 3559 Usually this disablement is not recommended, however 3560 if there is an agent checking/clearing corrected 3561 errors (e.g. BIOS or hardware monitoring 3562 applications), conflicting with OS's error handling, 3563 and you cannot deactivate the agent, then this option 3564 will be a help. 3565 3566 no_lmce 3567 do not opt-in to Local MCE delivery. Use legacy method 3568 to broadcast MCEs. 3569 3570 bootlog 3571 enable logging of machine checks left over from 3572 booting. Disabled by default on AMD Fam10h and older 3573 because some BIOS leave bogus ones. 3574 3575 If your BIOS doesn't do that it's a good idea to 3576 enable though to make sure you log even machine check 3577 events that result in a reboot. On Intel systems it is 3578 enabled by default. 3579 3580 nobootlog 3581 disable boot machine check logging. 3582 3583 monarchtimeout (number) 3584 sets the time in us to wait for other CPUs on machine 3585 checks. 0 to disable. 3586 3587 bios_cmci_threshold 3588 don't overwrite the bios-set CMCI threshold. This boot 3589 option prevents Linux from overwriting the CMCI 3590 threshold set by the bios. Without this option, Linux 3591 always sets the CMCI threshold to 1. Enabling this may 3592 make memory predictive failure analysis less effective 3593 if the bios sets thresholds for memory errors since we 3594 will not see details for all errors. 3595 3596 recovery 3597 force-enable recoverable machine check code paths 3598 3599 Everything else is in sysfs now. 3600 3601 3602 md= [HW] RAID subsystems devices and level 3603 See Documentation/admin-guide/md.rst. 3604 3605 mdacon= [MDA] 3606 Format: <first>,<last> 3607 Specifies range of consoles to be captured by the MDA. 3608 3609 mds= [X86,INTEL,EARLY] 3610 Control mitigation for the Micro-architectural Data 3611 Sampling (MDS) vulnerability. 3612 3613 Certain CPUs are vulnerable to an exploit against CPU 3614 internal buffers which can forward information to a 3615 disclosure gadget under certain conditions. 3616 3617 In vulnerable processors, the speculatively 3618 forwarded data can be used in a cache side channel 3619 attack, to access data to which the attacker does 3620 not have direct access. 3621 3622 This parameter controls the MDS mitigation. The 3623 options are: 3624 3625 full - Enable MDS mitigation on vulnerable CPUs 3626 full,nosmt - Enable MDS mitigation and disable 3627 SMT on vulnerable CPUs 3628 off - Unconditionally disable MDS mitigation 3629 3630 On TAA-affected machines, mds=off can be prevented by 3631 an active TAA mitigation as both vulnerabilities are 3632 mitigated with the same mechanism so in order to disable 3633 this mitigation, you need to specify tsx_async_abort=off 3634 too. 3635 3636 Not specifying this option is equivalent to 3637 mds=full. 3638 3639 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3640 3641 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3642 Must be specified, otherwise memory size will be 0. 3643 3644 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3645 of memory Amount of memory to be used in cases 3646 as follows: 3647 3648 1 for test; 3649 2 when the kernel is not able to see the whole system memory; 3650 3 memory that lies after 'mem=' boundary is excluded from 3651 the hypervisor, then assigned to KVM guests. 3652 4 to limit the memory available for kdump kernel. 3653 3654 [ARC,MICROBLAZE] - the limit applies only to low memory, 3655 high memory is not affected. 3656 3657 [ARM64] - only limits memory covered by the linear 3658 mapping. The NOMAP regions are not affected. 3659 3660 [X86] Work as limiting max address. Use together 3661 with memmap= to avoid physical address space collisions. 3662 Without memmap= PCI devices could be placed at addresses 3663 belonging to unused RAM. 3664 3665 Note that this only takes effects during boot time since 3666 in above case 3, memory may need be hot added after boot 3667 if system memory of hypervisor is not sufficient. 3668 3669 mem=nn[KMG]@ss[KMG] 3670 [ARM,MIPS,EARLY] - override the memory layout 3671 reported by firmware. 3672 Define a memory region of size nn[KMG] starting at 3673 ss[KMG]. 3674 Multiple different regions can be specified with 3675 multiple mem= parameters on the command line. 3676 3677 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3678 memory. 3679 3680 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3681 3682 memchunk=nn[KMG] 3683 [KNL,SH] Allow user to override the default size for 3684 per-device physically contiguous DMA buffers. 3685 3686 memhp_default_state=online/offline/online_kernel/online_movable 3687 [KNL] Set the initial state for the memory hotplug 3688 onlining policy. If not specified, the default value is 3689 set according to the 3690 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3691 options. 3692 See Documentation/admin-guide/mm/memory-hotplug.rst. 3693 3694 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3695 E820 memory map, as specified by the user. 3696 Such memmap=exactmap lines can be constructed based on 3697 BIOS output or other requirements. See the memmap=nn@ss 3698 option description. 3699 3700 memmap=nn[KMG]@ss[KMG] 3701 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3702 Region of memory to be used is from ss to ss+nn. 3703 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3704 which limits max address to nn[KMG]. 3705 Multiple different regions can be specified, 3706 comma delimited. 3707 Example: 3708 memmap=100M@2G,100M#3G,1G!1024G 3709 3710 memmap=nn[KMG]#ss[KMG] 3711 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3712 Region of memory to be marked is from ss to ss+nn. 3713 3714 memmap=nn[KMG]$ss[KMG] 3715 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3716 Region of memory to be reserved is from ss to ss+nn. 3717 Example: Exclude memory from 0x18690000-0x1869ffff 3718 memmap=64K$0x18690000 3719 or 3720 memmap=0x10000$0x18690000 3721 Some bootloaders may need an escape character before '$', 3722 like Grub2, otherwise '$' and the following number 3723 will be eaten. 3724 3725 memmap=nn[KMG]!ss[KMG,EARLY] 3726 [KNL,X86] Mark specific memory as protected. 3727 Region of memory to be used, from ss to ss+nn. 3728 The memory region may be marked as e820 type 12 (0xc) 3729 and is NVDIMM or ADR memory. 3730 3731 memmap=<size>%<offset>-<oldtype>+<newtype> 3732 [KNL,ACPI,EARLY] Convert memory within the specified region 3733 from <oldtype> to <newtype>. If "-<oldtype>" is left 3734 out, the whole region will be marked as <newtype>, 3735 even if previously unavailable. If "+<newtype>" is left 3736 out, matching memory will be removed. Types are 3737 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3738 3 = ACPI, 12 = PRAM. 3739 3740 memory_corruption_check=0/1 [X86,EARLY] 3741 Some BIOSes seem to corrupt the first 64k of 3742 memory when doing things like suspend/resume. 3743 Setting this option will scan the memory 3744 looking for corruption. Enabling this will 3745 both detect corruption and prevent the kernel 3746 from using the memory being corrupted. 3747 However, it's intended as a diagnostic tool; if 3748 repeatable BIOS-originated corruption always 3749 affects the same memory, you can use memmap= 3750 to prevent the kernel from using that memory. 3751 3752 memory_corruption_check_size=size [X86,EARLY] 3753 By default it checks for corruption in the low 3754 64k, making this memory unavailable for normal 3755 use. Use this parameter to scan for 3756 corruption in more or less memory. 3757 3758 memory_corruption_check_period=seconds [X86,EARLY] 3759 By default it checks for corruption every 60 3760 seconds. Use this parameter to check at some 3761 other rate. 0 disables periodic checking. 3762 3763 memory_hotplug.memmap_on_memory 3764 [KNL,X86,ARM] Boolean flag to enable this feature. 3765 Format: {on | off (default)} 3766 When enabled, runtime hotplugged memory will 3767 allocate its internal metadata (struct pages, 3768 those vmemmap pages cannot be optimized even 3769 if hugetlb_free_vmemmap is enabled) from the 3770 hotadded memory which will allow to hotadd a 3771 lot of memory without requiring additional 3772 memory to do so. 3773 This feature is disabled by default because it 3774 has some implication on large (e.g. GB) 3775 allocations in some configurations (e.g. small 3776 memory blocks). 3777 The state of the flag can be read in 3778 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3779 Note that even when enabled, there are a few cases where 3780 the feature is not effective. 3781 3782 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 3783 Format: <integer> 3784 default : 0 <disable> 3785 Specifies the number of memtest passes to be 3786 performed. Each pass selects another test 3787 pattern from a given set of patterns. Memtest 3788 fills the memory with this pattern, validates 3789 memory contents and reserves bad memory 3790 regions that are detected. 3791 3792 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3793 Valid arguments: on, off 3794 Default: off 3795 mem_encrypt=on: Activate SME 3796 mem_encrypt=off: Do not activate SME 3797 3798 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3799 for details on when memory encryption can be activated. 3800 3801 mem_sleep_default= [SUSPEND] Default system suspend mode: 3802 s2idle - Suspend-To-Idle 3803 shallow - Power-On Suspend or equivalent (if supported) 3804 deep - Suspend-To-RAM or equivalent (if supported) 3805 See Documentation/admin-guide/pm/sleep-states.rst. 3806 3807 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3808 the BIOS has incorrectly applied a workaround. TinyBIOS 3809 version 0.98 is known to be affected, 0.99 fixes the 3810 problem by letting the user disable the workaround. 3811 3812 mga= [HW,DRM] 3813 3814 microcode= [X86] Control the behavior of the microcode loader. 3815 Available options, comma separated: 3816 3817 base_rev=X - with <X> with format: <u32> 3818 Set the base microcode revision of each thread when in 3819 debug mode. 3820 3821 dis_ucode_ldr: disable the microcode loader 3822 3823 force_minrev: 3824 Enable or disable the microcode minimal revision 3825 enforcement for the runtime microcode loader. 3826 3827 mini2440= [ARM,HW,KNL] 3828 Format:[0..2][b][c][t] 3829 Default: "0tb" 3830 MINI2440 configuration specification: 3831 0 - The attached screen is the 3.5" TFT 3832 1 - The attached screen is the 7" TFT 3833 2 - The VGA Shield is attached (1024x768) 3834 Leaving out the screen size parameter will not load 3835 the TFT driver, and the framebuffer will be left 3836 unconfigured. 3837 b - Enable backlight. The TFT backlight pin will be 3838 linked to the kernel VESA blanking code and a GPIO 3839 LED. This parameter is not necessary when using the 3840 VGA shield. 3841 c - Enable the s3c camera interface. 3842 t - Reserved for enabling touchscreen support. The 3843 touchscreen support is not enabled in the mainstream 3844 kernel as of 2.6.30, a preliminary port can be found 3845 in the "bleeding edge" mini2440 support kernel at 3846 https://repo.or.cz/w/linux-2.6/mini2440.git 3847 3848 mitigations= 3849 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 3850 CPU vulnerabilities. This is a set of curated, 3851 arch-independent options, each of which is an 3852 aggregation of existing arch-specific options. 3853 3854 Note, "mitigations" is supported if and only if the 3855 kernel was built with CPU_MITIGATIONS=y. 3856 3857 off 3858 Disable all optional CPU mitigations. This 3859 improves system performance, but it may also 3860 expose users to several CPU vulnerabilities. 3861 Equivalent to: if nokaslr then kpti=0 [ARM64] 3862 gather_data_sampling=off [X86] 3863 indirect_target_selection=off [X86] 3864 kvm.nx_huge_pages=off [X86] 3865 l1tf=off [X86] 3866 mds=off [X86] 3867 mmio_stale_data=off [X86] 3868 no_entry_flush [PPC] 3869 no_uaccess_flush [PPC] 3870 nobp=0 [S390] 3871 nopti [X86,PPC] 3872 nospectre_bhb [ARM64] 3873 nospectre_v1 [X86,PPC] 3874 nospectre_v2 [X86,PPC,S390,ARM64] 3875 reg_file_data_sampling=off [X86] 3876 retbleed=off [X86] 3877 spec_rstack_overflow=off [X86] 3878 spec_store_bypass_disable=off [X86,PPC] 3879 spectre_bhi=off [X86] 3880 spectre_v2_user=off [X86] 3881 srbds=off [X86,INTEL] 3882 ssbd=force-off [ARM64] 3883 tsx_async_abort=off [X86] 3884 vmscape=off [X86] 3885 3886 Exceptions: 3887 This does not have any effect on 3888 kvm.nx_huge_pages when 3889 kvm.nx_huge_pages=force. 3890 3891 auto (default) 3892 Mitigate all CPU vulnerabilities, but leave SMT 3893 enabled, even if it's vulnerable. This is for 3894 users who don't want to be surprised by SMT 3895 getting disabled across kernel upgrades, or who 3896 have other ways of avoiding SMT-based attacks. 3897 Equivalent to: (default behavior) 3898 3899 auto,nosmt 3900 Mitigate all CPU vulnerabilities, disabling SMT 3901 if needed. This is for users who always want to 3902 be fully mitigated, even if it means losing SMT. 3903 Equivalent to: l1tf=flush,nosmt [X86] 3904 mds=full,nosmt [X86] 3905 tsx_async_abort=full,nosmt [X86] 3906 mmio_stale_data=full,nosmt [X86] 3907 retbleed=auto,nosmt [X86] 3908 3909 [X86] After one of the above options, additionally 3910 supports attack-vector based controls as documented in 3911 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 3912 3913 mminit_loglevel= 3914 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 3915 parameter allows control of the logging verbosity for 3916 the additional memory initialisation checks. A value 3917 of 0 disables mminit logging and a level of 4 will 3918 log everything. Information is printed at KERN_DEBUG 3919 so loglevel=8 may also need to be specified. 3920 3921 mmio_stale_data= 3922 [X86,INTEL,EARLY] Control mitigation for the Processor 3923 MMIO Stale Data vulnerabilities. 3924 3925 Processor MMIO Stale Data is a class of 3926 vulnerabilities that may expose data after an MMIO 3927 operation. Exposed data could originate or end in 3928 the same CPU buffers as affected by MDS and TAA. 3929 Therefore, similar to MDS and TAA, the mitigation 3930 is to clear the affected CPU buffers. 3931 3932 This parameter controls the mitigation. The 3933 options are: 3934 3935 full - Enable mitigation on vulnerable CPUs 3936 3937 full,nosmt - Enable mitigation and disable SMT on 3938 vulnerable CPUs. 3939 3940 off - Unconditionally disable mitigation 3941 3942 On MDS or TAA affected machines, 3943 mmio_stale_data=off can be prevented by an active 3944 MDS or TAA mitigation as these vulnerabilities are 3945 mitigated with the same mechanism so in order to 3946 disable this mitigation, you need to specify 3947 mds=off and tsx_async_abort=off too. 3948 3949 Not specifying this option is equivalent to 3950 mmio_stale_data=full. 3951 3952 For details see: 3953 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 3954 3955 <module>.async_probe[=<bool>] [KNL] 3956 If no <bool> value is specified or if the value 3957 specified is not a valid <bool>, enable asynchronous 3958 probe on this module. Otherwise, enable/disable 3959 asynchronous probe on this module as indicated by the 3960 <bool> value. See also: module.async_probe 3961 3962 module.async_probe=<bool> 3963 [KNL] When set to true, modules will use async probing 3964 by default. To enable/disable async probing for a 3965 specific module, use the module specific control that 3966 is documented under <module>.async_probe. When both 3967 module.async_probe and <module>.async_probe are 3968 specified, <module>.async_probe takes precedence for 3969 the specific module. 3970 3971 module.enable_dups_trace 3972 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 3973 this means that duplicate request_module() calls will 3974 trigger a WARN_ON() instead of a pr_warn(). Note that 3975 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 3976 will always be issued and this option does nothing. 3977 module.sig_enforce 3978 [KNL] When CONFIG_MODULE_SIG is set, this means that 3979 modules without (valid) signatures will fail to load. 3980 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3981 is always true, so this option does nothing. 3982 3983 module_blacklist= [KNL] Do not load a comma-separated list of 3984 modules. Useful for debugging problem modules. 3985 3986 mousedev.tap_time= 3987 [MOUSE] Maximum time between finger touching and 3988 leaving touchpad surface for touch to be considered 3989 a tap and be reported as a left button click (for 3990 touchpads working in absolute mode only). 3991 Format: <msecs> 3992 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3993 reporting absolute coordinates, such as tablets 3994 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3995 reporting absolute coordinates, such as tablets 3996 3997 movablecore= [KNL,X86,PPC,EARLY] 3998 Format: nn[KMGTPE] | nn% 3999 This parameter is the complement to kernelcore=, it 4000 specifies the amount of memory used for migratable 4001 allocations. If both kernelcore and movablecore is 4002 specified, then kernelcore will be at *least* the 4003 specified value but may be more. If movablecore on its 4004 own is specified, the administrator must be careful 4005 that the amount of memory usable for all allocations 4006 is not too small. 4007 4008 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4009 NUMA nodes to be movable. This means that the memory 4010 of such nodes will be usable only for movable 4011 allocations which rules out almost all kernel 4012 allocations. Use with caution! 4013 4014 MTD_Partition= [MTD] 4015 Format: <name>,<region-number>,<size>,<offset> 4016 4017 MTD_Region= [MTD] Format: 4018 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4019 4020 mtdparts= [MTD] 4021 See drivers/mtd/parsers/cmdlinepart.c 4022 4023 mtouchusb.raw_coordinates= 4024 [HW] Make the MicroTouch USB driver use raw coordinates 4025 ('y', default) or cooked coordinates ('n') 4026 4027 mtrr=debug [X86,EARLY] 4028 Enable printing debug information related to MTRR 4029 registers at boot time. 4030 4031 mtrr_chunk_size=nn[KMG,X86,EARLY] 4032 used for mtrr cleanup. It is largest continuous chunk 4033 that could hold holes aka. UC entries. 4034 4035 mtrr_gran_size=nn[KMG,X86,EARLY] 4036 Used for mtrr cleanup. It is granularity of mtrr block. 4037 Default is 1. 4038 Large value could prevent small alignment from 4039 using up MTRRs. 4040 4041 mtrr_spare_reg_nr=n [X86,EARLY] 4042 Format: <integer> 4043 Range: 0,7 : spare reg number 4044 Default : 1 4045 Used for mtrr cleanup. It is spare mtrr entries number. 4046 Set to 2 or more if your graphical card needs more. 4047 4048 multitce=off [PPC] This parameter disables the use of the pSeries 4049 firmware feature for updating multiple TCE entries 4050 at a time. 4051 4052 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4053 4054 netdev= [NET] Network devices parameters 4055 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4056 Note that mem_start is often overloaded to mean 4057 something different and driver-specific. 4058 This usage is only documented in each driver source 4059 file if at all. 4060 4061 netpoll.carrier_timeout= 4062 [NET] Specifies amount of time (in seconds) that 4063 netpoll should wait for a carrier. By default netpoll 4064 waits 4 seconds. 4065 4066 nf_conntrack.acct= 4067 [NETFILTER] Enable connection tracking flow accounting 4068 0 to disable accounting 4069 1 to enable accounting 4070 Default value is 0. 4071 4072 nfs.cache_getent= 4073 [NFS] sets the pathname to the program which is used 4074 to update the NFS client cache entries. 4075 4076 nfs.cache_getent_timeout= 4077 [NFS] sets the timeout after which an attempt to 4078 update a cache entry is deemed to have failed. 4079 4080 nfs.callback_nr_threads= 4081 [NFSv4] set the total number of threads that the 4082 NFS client will assign to service NFSv4 callback 4083 requests. 4084 4085 nfs.callback_tcpport= 4086 [NFS] set the TCP port on which the NFSv4 callback 4087 channel should listen. 4088 4089 nfs.delay_retrans= 4090 [NFS] specifies the number of times the NFSv4 client 4091 retries the request before returning an EAGAIN error, 4092 after a reply of NFS4ERR_DELAY from the server. 4093 Only applies if the softerr mount option is enabled, 4094 and the specified value is >= 0. 4095 4096 nfs.enable_ino64= 4097 [NFS] enable 64-bit inode numbers. 4098 If zero, the NFS client will fake up a 32-bit inode 4099 number for the readdir() and stat() syscalls instead 4100 of returning the full 64-bit number. 4101 The default is to return 64-bit inode numbers. 4102 4103 nfs.idmap_cache_timeout= 4104 [NFS] set the maximum lifetime for idmapper cache 4105 entries. 4106 4107 nfs.max_session_cb_slots= 4108 [NFSv4.1] Sets the maximum number of session 4109 slots the client will assign to the callback 4110 channel. This determines the maximum number of 4111 callbacks the client will process in parallel for 4112 a particular server. 4113 4114 nfs.max_session_slots= 4115 [NFSv4.1] Sets the maximum number of session slots 4116 the client will attempt to negotiate with the server. 4117 This limits the number of simultaneous RPC requests 4118 that the client can send to the NFSv4.1 server. 4119 Note that there is little point in setting this 4120 value higher than the max_tcp_slot_table_limit. 4121 4122 nfs.nfs4_disable_idmapping= 4123 [NFSv4] When set to the default of '1', this option 4124 ensures that both the RPC level authentication 4125 scheme and the NFS level operations agree to use 4126 numeric uids/gids if the mount is using the 4127 'sec=sys' security flavour. In effect it is 4128 disabling idmapping, which can make migration from 4129 legacy NFSv2/v3 systems to NFSv4 easier. 4130 Servers that do not support this mode of operation 4131 will be autodetected by the client, and it will fall 4132 back to using the idmapper. 4133 To turn off this behaviour, set the value to '0'. 4134 4135 nfs.nfs4_unique_id= 4136 [NFS4] Specify an additional fixed unique ident- 4137 ification string that NFSv4 clients can insert into 4138 their nfs_client_id4 string. This is typically a 4139 UUID that is generated at system install time. 4140 4141 nfs.recover_lost_locks= 4142 [NFSv4] Attempt to recover locks that were lost due 4143 to a lease timeout on the server. Please note that 4144 doing this risks data corruption, since there are 4145 no guarantees that the file will remain unchanged 4146 after the locks are lost. 4147 If you want to enable the kernel legacy behaviour of 4148 attempting to recover these locks, then set this 4149 parameter to '1'. 4150 The default parameter value of '0' causes the kernel 4151 not to attempt recovery of lost locks. 4152 4153 nfs.send_implementation_id= 4154 [NFSv4.1] Send client implementation identification 4155 information in exchange_id requests. 4156 If zero, no implementation identification information 4157 will be sent. 4158 The default is to send the implementation identification 4159 information. 4160 4161 nfs4.layoutstats_timer= 4162 [NFSv4.2] Change the rate at which the kernel sends 4163 layoutstats to the pNFS metadata server. 4164 4165 Setting this to value to 0 causes the kernel to use 4166 whatever value is the default set by the layout 4167 driver. A non-zero value sets the minimum interval 4168 in seconds between layoutstats transmissions. 4169 4170 nfsd.inter_copy_offload_enable= 4171 [NFSv4.2] When set to 1, the server will support 4172 server-to-server copies for which this server is 4173 the destination of the copy. 4174 4175 nfsd.nfs4_disable_idmapping= 4176 [NFSv4] When set to the default of '1', the NFSv4 4177 server will return only numeric uids and gids to 4178 clients using auth_sys, and will accept numeric uids 4179 and gids from such clients. This is intended to ease 4180 migration from NFSv2/v3. 4181 4182 nfsd.nfsd4_ssc_umount_timeout= 4183 [NFSv4.2] When used as the destination of a 4184 server-to-server copy, knfsd temporarily mounts 4185 the source server. It caches the mount in case 4186 it will be needed again, and discards it if not 4187 used for the number of milliseconds specified by 4188 this parameter. 4189 4190 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4191 See Documentation/admin-guide/nfs/nfsroot.rst. 4192 4193 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4194 See Documentation/admin-guide/nfs/nfsroot.rst. 4195 4196 nfsrootdebug [NFS] enable nfsroot debugging messages. 4197 See Documentation/admin-guide/nfs/nfsroot.rst. 4198 4199 nmi_backtrace.backtrace_idle [KNL] 4200 Dump stacks even of idle CPUs in response to an 4201 NMI stack-backtrace request. 4202 4203 nmi_debug= [KNL,SH] Specify one or more actions to take 4204 when a NMI is triggered. 4205 Format: [state][,regs][,debounce][,die] 4206 4207 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4208 Format: [panic,][nopanic,][rNNN,][num] 4209 Valid num: 0 or 1 4210 0 - turn hardlockup detector in nmi_watchdog off 4211 1 - turn hardlockup detector in nmi_watchdog on 4212 rNNN - configure the watchdog with raw perf event 0xNNN 4213 4214 When panic is specified, panic when an NMI watchdog 4215 timeout occurs (or 'nopanic' to not panic on an NMI 4216 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4217 To disable both hard and soft lockup detectors, 4218 please see 'nowatchdog'. 4219 This is useful when you use a panic=... timeout and 4220 need the box quickly up again. 4221 4222 These settings can be accessed at runtime via 4223 the nmi_watchdog and hardlockup_panic sysctls. 4224 4225 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4226 emulation library even if a 387 maths coprocessor 4227 is present. 4228 4229 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4230 Forces kernel to use 3-level paging instead. 4231 4232 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4233 kernel to use 4-level paging instead. 4234 4235 noalign [KNL,ARM] 4236 4237 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4238 IOAPICs that may be present in the system. 4239 4240 noapictimer [APIC,X86] Don't set up the APIC timer 4241 4242 noautogroup Disable scheduler automatic task group creation. 4243 4244 nocache [ARM,EARLY] 4245 4246 no_console_suspend 4247 [HW] Never suspend the console 4248 Disable suspending of consoles during suspend and 4249 hibernate operations. Once disabled, debugging 4250 messages can reach various consoles while the rest 4251 of the system is being put to sleep (ie, while 4252 debugging driver suspend/resume hooks). This may 4253 not work reliably with all consoles, but is known 4254 to work with serial and VGA consoles. 4255 To facilitate more flexible debugging, we also add 4256 console_suspend, a printk module parameter to control 4257 it. Users could use console_suspend (usually 4258 /sys/module/printk/parameters/console_suspend) to 4259 turn on/off it dynamically. 4260 4261 no_debug_objects 4262 [KNL,EARLY] Disable object debugging 4263 4264 nodsp [SH] Disable hardware DSP at boot time. 4265 4266 noefi [EFI,EARLY] Disable EFI runtime services support. 4267 4268 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4269 4270 noexec32 [X86-64] 4271 This affects only 32-bit executables. 4272 noexec32=on: enable non-executable mappings (default) 4273 read doesn't imply executable mappings 4274 noexec32=off: disable non-executable mappings 4275 read implies executable mappings 4276 4277 no_file_caps Tells the kernel not to honor file capabilities. The 4278 only way then for a file to be executed with privilege 4279 is to be setuid root or executed by root. 4280 4281 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4282 4283 nofsgsbase [X86] Disables FSGSBASE instructions. 4284 4285 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4286 register save and restore. The kernel will only save 4287 legacy floating-point registers on task switch. 4288 4289 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4290 4291 no_hash_pointers 4292 [KNL,EARLY] 4293 Alias for "hash_pointers=never". 4294 4295 nohibernate [HIBERNATION] Disable hibernation and resume. 4296 4297 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4298 busy wait in do_idle() and not use the arch_cpu_idle() 4299 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4300 to be effective. This is useful on platforms where the 4301 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4302 correctly or when doing power measurements to evaluate 4303 the impact of the sleep instructions. This is also 4304 useful when using JTAG debugger. 4305 4306 nohpet [X86] Don't use the HPET timer. 4307 4308 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4309 4310 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4311 4312 nohz= [KNL] Boottime enable/disable dynamic ticks 4313 Valid arguments: on, off 4314 Default: on 4315 4316 nohz_full= [KNL,BOOT,SMP,ISOL] 4317 The argument is a cpu list, as described above. 4318 In kernels built with CONFIG_NO_HZ_FULL=y, set 4319 the specified list of CPUs whose tick will be stopped 4320 whenever possible. The boot CPU will be forced outside 4321 the range to maintain the timekeeping. Any CPUs 4322 in this list will have their RCU callbacks offloaded, 4323 just as if they had also been called out in the 4324 rcu_nocbs= boot parameter. 4325 4326 Note that this argument takes precedence over 4327 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4328 4329 noinitrd [RAM] Tells the kernel not to load any configured 4330 initial RAM disk. 4331 4332 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4333 remapping. 4334 [Deprecated - use intremap=off] 4335 4336 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4337 4338 noiotrap [SH] Disables trapped I/O port accesses. 4339 4340 noirqdebug [X86-32] Disables the code which attempts to detect and 4341 disable unhandled interrupt sources. 4342 4343 noisapnp [ISAPNP] Disables ISA PnP code. 4344 4345 nokaslr [KNL,EARLY] 4346 When CONFIG_RANDOMIZE_BASE is set, this disables 4347 kernel and module base offset ASLR (Address Space 4348 Layout Randomization). 4349 4350 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4351 fault handling. 4352 4353 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4354 4355 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4356 4357 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4358 4359 nomce [X86-32] Disable Machine Check Exception 4360 4361 nomfgpt [X86-32] Disable Multi-Function General Purpose 4362 Timer usage (for AMD Geode machines). 4363 4364 nomodeset Disable kernel modesetting. Most systems' firmware 4365 sets up a display mode and provides framebuffer memory 4366 for output. With nomodeset, DRM and fbdev drivers will 4367 not load if they could possibly displace the pre- 4368 initialized output. Only the system framebuffer will 4369 be available for use. The respective drivers will not 4370 perform display-mode changes or accelerated rendering. 4371 4372 Useful as error fallback, or for testing and debugging. 4373 4374 nomodule Disable module load 4375 4376 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4377 shutdown the other cpus. Instead use the REBOOT_VECTOR 4378 irq. 4379 4380 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4381 pagetables) support. 4382 4383 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4384 4385 nopku [X86] Disable Memory Protection Keys CPU feature found 4386 in some Intel CPUs. 4387 4388 nopti [X86-64,EARLY] 4389 Equivalent to pti=off 4390 4391 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4392 Disables the PV optimizations forcing the guest to run 4393 as generic guest with no PV drivers. Currently support 4394 XEN HVM, KVM, HYPER_V and VMWARE guest. 4395 4396 nopvspin [X86,XEN,KVM,EARLY] 4397 Disables the qspinlock slow path using PV optimizations 4398 which allow the hypervisor to 'idle' the guest on lock 4399 contention. 4400 4401 norandmaps Don't use address space randomization. Equivalent to 4402 echo 0 > /proc/sys/kernel/randomize_va_space 4403 4404 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4405 with UP alternatives 4406 4407 noresume [SWSUSP] Disables resume and restores original swap 4408 space. 4409 4410 no-scroll [VGA] Disables scrollback. 4411 This is required for the Braillex ib80-piezo Braille 4412 reader made by F.H. Papenmeier (Germany). 4413 4414 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4415 4416 nosmap [PPC,EARLY] 4417 Disable SMAP (Supervisor Mode Access Prevention) 4418 even if it is supported by processor. 4419 4420 nosmep [PPC64s,EARLY] 4421 Disable SMEP (Supervisor Mode Execution Prevention) 4422 even if it is supported by processor. 4423 4424 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4425 and disable the IO APIC. legacy for "maxcpus=0". 4426 4427 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4428 Equivalent to smt=1. 4429 4430 [KNL,X86,PPC,S390] Disable symmetric multithreading (SMT). 4431 nosmt=force: Force disable SMT, cannot be undone 4432 via the sysfs control file. 4433 4434 nosoftlockup [KNL] Disable the soft-lockup detector. 4435 4436 nospec_store_bypass_disable 4437 [HW,EARLY] Disable all mitigations for the Speculative 4438 Store Bypass vulnerability 4439 4440 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4441 history injection) vulnerability. System may allow data leaks 4442 with this option. 4443 4444 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4445 (bounds check bypass). With this option data leaks are 4446 possible in the system. 4447 4448 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4449 for the Spectre variant 2 (indirect branch 4450 prediction) vulnerability. System may allow data 4451 leaks with this option. 4452 4453 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4454 Disable paravirtualized steal time accounting. steal time 4455 is computed, but won't influence scheduler behaviour 4456 4457 nosync [HW,M68K] Disables sync negotiation for all devices. 4458 4459 no_timer_check [X86,APIC] Disables the code which tests for broken 4460 timer IRQ sources, i.e., the IO-APIC timer. This can 4461 work around problems with incorrect timer 4462 initialization on some boards. 4463 4464 no_uaccess_flush 4465 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4466 4467 novmcoredd [KNL,KDUMP] 4468 Disable device dump. Device dump allows drivers to 4469 append dump data to vmcore so you can collect driver 4470 specified debug info. Drivers can append the data 4471 without any limit and this data is stored in memory, 4472 so this may cause significant memory stress. Disabling 4473 device dump can help save memory but the driver debug 4474 data will be no longer available. This parameter 4475 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4476 is set. 4477 4478 no-vmw-sched-clock 4479 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4480 scheduler clock and use the default one. 4481 4482 nowatchdog [KNL] Disable both lockup detectors, i.e. 4483 soft-lockup and NMI watchdog (hard-lockup). 4484 4485 nowb [ARM,EARLY] 4486 4487 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4488 4489 NOTE: this parameter will be ignored on systems with the 4490 LEGACY_XAPIC_DISABLED bit set in the 4491 IA32_XAPIC_DISABLE_STATUS MSR. 4492 4493 noxsave [BUGS=X86] Disables x86 extended register state save 4494 and restore using xsave. The kernel will fallback to 4495 enabling legacy floating-point and sse state. 4496 4497 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4498 register states. The kernel will fall back to use 4499 xsave to save the states. By using this parameter, 4500 performance of saving the states is degraded because 4501 xsave doesn't support modified optimization while 4502 xsaveopt supports it on xsaveopt enabled systems. 4503 4504 noxsaves [X86] Disables xsaves and xrstors used in saving and 4505 restoring x86 extended register state in compacted 4506 form of xsave area. The kernel will fall back to use 4507 xsaveopt and xrstor to save and restore the states 4508 in standard form of xsave area. By using this 4509 parameter, xsave area per process might occupy more 4510 memory on xsaves enabled systems. 4511 4512 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4513 could support. nr_cpus=n : n >= 1 limits the kernel to 4514 support 'n' processors. It could be larger than the 4515 number of already plugged CPU during bootup, later in 4516 runtime you can physically add extra cpu until it reaches 4517 n. So during boot up some boot time memory for per-cpu 4518 variables need be pre-allocated for later physical cpu 4519 hot plugging. 4520 4521 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4522 4523 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4524 Disable NUMA, Only set up a single NUMA node 4525 spanning all memory. 4526 4527 numa=fake=<size>[MG] 4528 [KNL, ARM64, RISCV, X86, EARLY] 4529 If given as a memory unit, fills all system RAM with 4530 nodes of size interleaved over physical nodes. 4531 4532 numa=fake=<N> 4533 [KNL, ARM64, RISCV, X86, EARLY] 4534 If given as an integer, fills all system RAM with N 4535 fake nodes interleaved over physical nodes. 4536 4537 numa=fake=<N>U 4538 [KNL, ARM64, RISCV, X86, EARLY] 4539 If given as an integer followed by 'U', it will 4540 divide each physical node into N emulated nodes. 4541 4542 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4543 4544 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4545 soft-reserved memory partitioning. 4546 4547 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4548 NUMA balancing. 4549 Allowed values are enable and disable 4550 4551 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4552 'node', 'default' can be specified 4553 This can be set from sysctl after boot. 4554 See Documentation/admin-guide/sysctl/vm.rst for details. 4555 4556 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4557 See Documentation/core-api/debugging-via-ohci1394.rst for more 4558 info. 4559 4560 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4561 Rather than timing out after 20 ms if an EC 4562 command is not properly ACKed, override the length 4563 of the timeout. We have interrupts disabled while 4564 waiting for the ACK, so if this is set too high 4565 interrupts *may* be lost! 4566 4567 omap_mux= [OMAP] Override bootloader pin multiplexing. 4568 Format: <mux_mode0.mode_name=value>... 4569 For example, to override I2C bus2: 4570 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4571 4572 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4573 4574 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4575 4576 boundary - index of last SLC block on Flex-OneNAND. 4577 The remaining blocks are configured as MLC blocks. 4578 lock - Configure if Flex-OneNAND boundary should be locked. 4579 Once locked, the boundary cannot be changed. 4580 1 indicates lock status, 0 indicates unlock status. 4581 4582 oops=panic [KNL,EARLY] 4583 Always panic on oopses. Default is to just kill the 4584 process, but there is a small probability of 4585 deadlocking the machine. 4586 This will also cause panics on machine check exceptions. 4587 Useful together with panic=30 to trigger a reboot. 4588 4589 page_alloc.shuffle= 4590 [KNL] Boolean flag to control whether the page allocator 4591 should randomize its free lists. This parameter can be 4592 used to enable/disable page randomization. The state of 4593 the flag can be read from sysfs at: 4594 /sys/module/page_alloc/parameters/shuffle. 4595 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4596 4597 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4598 Storage of the information about who allocated 4599 each page is disabled in default. With this switch, 4600 we can turn it on. 4601 on: enable the feature 4602 4603 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4604 poisoning on the buddy allocator, available with 4605 CONFIG_PAGE_POISONING=y. 4606 off: turn off poisoning (default) 4607 on: turn on poisoning 4608 4609 page_reporting.page_reporting_order= 4610 [KNL] Minimal page reporting order 4611 Format: <integer> 4612 Adjust the minimal page reporting order. The page 4613 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4614 4615 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4616 timeout > 0: seconds before rebooting 4617 timeout = 0: wait forever 4618 timeout < 0: reboot immediately 4619 Format: <timeout> 4620 4621 panic_on_taint= [KNL,EARLY] 4622 Bitmask for conditionally calling panic() in add_taint() 4623 Format: <hex>[,nousertaint] 4624 Hexadecimal bitmask representing the set of TAINT flags 4625 that will cause the kernel to panic when add_taint() is 4626 called with any of the flags in this set. 4627 The optional switch "nousertaint" can be utilized to 4628 prevent userspace forced crashes by writing to sysctl 4629 /proc/sys/kernel/tainted any flagset matching with the 4630 bitmask set on panic_on_taint. 4631 See Documentation/admin-guide/tainted-kernels.rst for 4632 extra details on the taint flags that users can pick 4633 to compose the bitmask to assign to panic_on_taint. 4634 4635 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4636 on a WARN(). 4637 4638 panic_print= Bitmask for printing system info when panic happens. 4639 User can chose combination of the following bits: 4640 bit 0: print all tasks info 4641 bit 1: print system memory info 4642 bit 2: print timer info 4643 bit 3: print locks info if CONFIG_LOCKDEP is on 4644 bit 4: print ftrace buffer 4645 bit 5: replay all kernel messages on consoles at the end of panic 4646 bit 6: print all CPUs backtrace (if available in the arch) 4647 bit 7: print only tasks in uninterruptible (blocked) state 4648 *Be aware* that this option may print a _lot_ of lines, 4649 so there are risks of losing older messages in the log. 4650 Use this option carefully, maybe worth to setup a 4651 bigger log buffer with "log_buf_len" along with this. 4652 4653 panic_sys_info= A comma separated list of extra information to be dumped 4654 on panic. 4655 Format: val[,val...] 4656 Where @val can be any of the following: 4657 4658 tasks: print all tasks info 4659 mem: print system memory info 4660 timers: print timers info 4661 locks: print locks info if CONFIG_LOCKDEP is on 4662 ftrace: print ftrace buffer 4663 all_bt: print all CPUs backtrace (if available in the arch) 4664 blocked_tasks: print only tasks in uninterruptible (blocked) state 4665 4666 This is a human readable alternative to the 'panic_print' option. 4667 4668 panic_console_replay 4669 When panic happens, replay all kernel messages on 4670 consoles at the end of panic. 4671 4672 parkbd.port= [HW] Parallel port number the keyboard adapter is 4673 connected to, default is 0. 4674 Format: <parport#> 4675 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4676 0 for XT, 1 for AT (default is AT). 4677 Format: <mode> 4678 4679 parport= [HW,PPT] Specify parallel ports. 0 disables. 4680 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4681 Use 'auto' to force the driver to use any 4682 IRQ/DMA settings detected (the default is to 4683 ignore detected IRQ/DMA settings because of 4684 possible conflicts). You can specify the base 4685 address, IRQ, and DMA settings; IRQ and DMA 4686 should be numbers, or 'auto' (for using detected 4687 settings on that particular port), or 'nofifo' 4688 (to avoid using a FIFO even if it is detected). 4689 Parallel ports are assigned in the order they 4690 are specified on the command line, starting 4691 with parport0. 4692 4693 parport_init_mode= [HW,PPT] 4694 Configure VIA parallel port to operate in 4695 a specific mode. This is necessary on Pegasos 4696 computer where firmware has no options for setting 4697 up parallel port mode and sets it to spp. 4698 Currently this function knows 686a and 8231 chips. 4699 Format: [spp|ps2|epp|ecp|ecpepp] 4700 4701 pata_legacy.all= [HW,LIBATA] 4702 Format: <int> 4703 Set to non-zero to probe primary and secondary ISA 4704 port ranges on PCI systems where no PCI PATA device 4705 has been found at either range. Disabled by default. 4706 4707 pata_legacy.autospeed= [HW,LIBATA] 4708 Format: <int> 4709 Set to non-zero if a chip is present that snoops speed 4710 changes. Disabled by default. 4711 4712 pata_legacy.ht6560a= [HW,LIBATA] 4713 Format: <int> 4714 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4715 the secondary channel, or both channels respectively. 4716 Disabled by default. 4717 4718 pata_legacy.ht6560b= [HW,LIBATA] 4719 Format: <int> 4720 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4721 the secondary channel, or both channels respectively. 4722 Disabled by default. 4723 4724 pata_legacy.iordy_mask= [HW,LIBATA] 4725 Format: <int> 4726 IORDY enable mask. Set individual bits to allow IORDY 4727 for the respective channel. Bit 0 is for the first 4728 legacy channel handled by this driver, bit 1 is for 4729 the second channel, and so on. The sequence will often 4730 correspond to the primary legacy channel, the secondary 4731 legacy channel, and so on, but the handling of a PCI 4732 bus and the use of other driver options may interfere 4733 with the sequence. By default IORDY is allowed across 4734 all channels. 4735 4736 pata_legacy.opti82c46x= [HW,LIBATA] 4737 Format: <int> 4738 Set to 1, 2, or 3 for Opti 82c611A on the primary 4739 channel, the secondary channel, or both channels 4740 respectively. Disabled by default. 4741 4742 pata_legacy.opti82c611a= [HW,LIBATA] 4743 Format: <int> 4744 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4745 channel, the secondary channel, or both channels 4746 respectively. Disabled by default. 4747 4748 pata_legacy.pio_mask= [HW,LIBATA] 4749 Format: <int> 4750 PIO mode mask for autospeed devices. Set individual 4751 bits to allow the use of the respective PIO modes. 4752 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4753 All modes allowed by default. 4754 4755 pata_legacy.probe_all= [HW,LIBATA] 4756 Format: <int> 4757 Set to non-zero to probe tertiary and further ISA 4758 port ranges on PCI systems. Disabled by default. 4759 4760 pata_legacy.probe_mask= [HW,LIBATA] 4761 Format: <int> 4762 Probe mask for legacy ISA PATA ports. Depending on 4763 platform configuration and the use of other driver 4764 options up to 6 legacy ports are supported: 0x1f0, 4765 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4766 of individual ports can be disabled by setting the 4767 corresponding bits in the mask to 1. Bit 0 is for 4768 the first port in the list above (0x1f0), and so on. 4769 By default all supported ports are probed. 4770 4771 pata_legacy.qdi= [HW,LIBATA] 4772 Format: <int> 4773 Set to non-zero to probe QDI controllers. By default 4774 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4775 4776 pata_legacy.winbond= [HW,LIBATA] 4777 Format: <int> 4778 Set to non-zero to probe Winbond controllers. Use 4779 the standard I/O port (0x130) if 1, otherwise the 4780 value given is the I/O port to use (typically 0x1b0). 4781 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4782 0 otherwise. 4783 4784 pata_platform.pio_mask= [HW,LIBATA] 4785 Format: <int> 4786 Supported PIO mode mask. Set individual bits to allow 4787 the use of the respective PIO modes. Bit 0 is for 4788 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4789 allowed by default. 4790 4791 pause_on_oops=<int> 4792 Halt all CPUs after the first oops has been printed for 4793 the specified number of seconds. This is to be used if 4794 your oopses keep scrolling off the screen. 4795 4796 pcbit= [HW,ISDN] 4797 4798 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 4799 4800 Some options herein operate on a specific device 4801 or a set of devices (<pci_dev>). These are 4802 specified in one of the following formats: 4803 4804 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4805 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4806 4807 Note: the first format specifies a PCI 4808 bus/device/function address which may change 4809 if new hardware is inserted, if motherboard 4810 firmware changes, or due to changes caused 4811 by other kernel parameters. If the 4812 domain is left unspecified, it is 4813 taken to be zero. Optionally, a path 4814 to a device through multiple device/function 4815 addresses can be specified after the base 4816 address (this is more robust against 4817 renumbering issues). The second format 4818 selects devices using IDs from the 4819 configuration space which may match multiple 4820 devices in the system. 4821 4822 earlydump dump PCI config space before the kernel 4823 changes anything 4824 off [X86] don't probe for the PCI bus 4825 bios [X86-32] force use of PCI BIOS, don't access 4826 the hardware directly. Use this if your machine 4827 has a non-standard PCI host bridge. 4828 nobios [X86-32] disallow use of PCI BIOS, only direct 4829 hardware access methods are allowed. Use this 4830 if you experience crashes upon bootup and you 4831 suspect they are caused by the BIOS. 4832 conf1 [X86] Force use of PCI Configuration Access 4833 Mechanism 1 (config address in IO port 0xCF8, 4834 data in IO port 0xCFC, both 32-bit). 4835 conf2 [X86] Force use of PCI Configuration Access 4836 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4837 the function, IO port 0xCFA, also 8-bit, sets 4838 bus number. The config space is then accessed 4839 through ports 0xC000-0xCFFF). 4840 See http://wiki.osdev.org/PCI for more info 4841 on the configuration access mechanisms. 4842 noaer [PCIE] If the PCIEAER kernel config parameter is 4843 enabled, this kernel boot option can be used to 4844 disable the use of PCIE advanced error reporting. 4845 nodomains [PCI] Disable support for multiple PCI 4846 root domains (aka PCI segments, in ACPI-speak). 4847 nommconf [X86] Disable use of MMCONFIG for PCI 4848 Configuration 4849 check_enable_amd_mmconf [X86] check for and enable 4850 properly configured MMIO access to PCI 4851 config space on AMD family 10h CPU 4852 nomsi [MSI] If the PCI_MSI kernel config parameter is 4853 enabled, this kernel boot option can be used to 4854 disable the use of MSI interrupts system-wide. 4855 noioapicquirk [APIC] Disable all boot interrupt quirks. 4856 Safety option to keep boot IRQs enabled. This 4857 should never be necessary. 4858 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4859 primary IO-APIC for bridges that cannot disable 4860 boot IRQs. This fixes a source of spurious IRQs 4861 when the system masks IRQs. 4862 noioapicreroute [APIC] Disable workaround that uses the 4863 boot IRQ equivalent of an IRQ that connects to 4864 a chipset where boot IRQs cannot be disabled. 4865 The opposite of ioapicreroute. 4866 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4867 routing table. These calls are known to be buggy 4868 on several machines and they hang the machine 4869 when used, but on other computers it's the only 4870 way to get the interrupt routing table. Try 4871 this option if the kernel is unable to allocate 4872 IRQs or discover secondary PCI buses on your 4873 motherboard. 4874 rom [X86] Assign address space to expansion ROMs. 4875 Use with caution as certain devices share 4876 address decoders between ROMs and other 4877 resources. 4878 norom [X86] Do not assign address space to 4879 expansion ROMs that do not already have 4880 BIOS assigned address ranges. 4881 nobar [X86] Do not assign address space to the 4882 BARs that weren't assigned by the BIOS. 4883 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4884 assigned automatically to PCI devices. You can 4885 make the kernel exclude IRQs of your ISA cards 4886 this way. 4887 pirqaddr=0xAAAAA [X86] Specify the physical address 4888 of the PIRQ table (normally generated 4889 by the BIOS) if it is outside the 4890 F0000h-100000h range. 4891 lastbus=N [X86] Scan all buses thru bus #N. Can be 4892 useful if the kernel is unable to find your 4893 secondary buses and you want to tell it 4894 explicitly which ones they are. 4895 assign-busses [X86] Always assign all PCI bus 4896 numbers ourselves, overriding 4897 whatever the firmware may have done. 4898 usepirqmask [X86] Honor the possible IRQ mask stored 4899 in the BIOS $PIR table. This is needed on 4900 some systems with broken BIOSes, notably 4901 some HP Pavilion N5400 and Omnibook XE3 4902 notebooks. This will have no effect if ACPI 4903 IRQ routing is enabled. 4904 noacpi [X86] Do not use ACPI for IRQ routing 4905 or for PCI scanning. 4906 use_crs [X86] Use PCI host bridge window information 4907 from ACPI. On BIOSes from 2008 or later, this 4908 is enabled by default. If you need to use this, 4909 please report a bug. 4910 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4911 If you need to use this, please report a bug. 4912 use_e820 [X86] Use E820 reservations to exclude parts of 4913 PCI host bridge windows. This is a workaround 4914 for BIOS defects in host bridge _CRS methods. 4915 If you need to use this, please report a bug to 4916 <linux-pci@vger.kernel.org>. 4917 no_e820 [X86] Ignore E820 reservations for PCI host 4918 bridge windows. This is the default on modern 4919 hardware. If you need to use this, please report 4920 a bug to <linux-pci@vger.kernel.org>. 4921 routeirq Do IRQ routing for all PCI devices. 4922 This is normally done in pci_enable_device(), 4923 so this option is a temporary workaround 4924 for broken drivers that don't call it. 4925 skip_isa_align [X86] do not align io start addr, so can 4926 handle more pci cards 4927 noearly [X86] Don't do any early type 1 scanning. 4928 This might help on some broken boards which 4929 machine check when some devices' config space 4930 is read. But various workarounds are disabled 4931 and some IOMMU drivers will not work. 4932 bfsort Sort PCI devices into breadth-first order. 4933 This sorting is done to get a device 4934 order compatible with older (<= 2.4) kernels. 4935 nobfsort Don't sort PCI devices into breadth-first order. 4936 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4937 tuning and use the BIOS-configured MPS defaults. 4938 pcie_bus_safe Set every device's MPS to the largest value 4939 supported by all devices below the root complex. 4940 pcie_bus_perf Set device MPS to the largest allowable MPS 4941 based on its parent bus. Also set MRRS (Max 4942 Read Request Size) to the largest supported 4943 value (no larger than the MPS that the device 4944 or bus can support) for best performance. 4945 pcie_bus_peer2peer Set every device's MPS to 128B, which 4946 every device is guaranteed to support. This 4947 configuration allows peer-to-peer DMA between 4948 any pair of devices, possibly at the cost of 4949 reduced performance. This also guarantees 4950 that hot-added devices will work. 4951 cbiosize=nn[KMG] The fixed amount of bus space which is 4952 reserved for the CardBus bridge's IO window. 4953 The default value is 256 bytes. 4954 cbmemsize=nn[KMG] The fixed amount of bus space which is 4955 reserved for the CardBus bridge's memory 4956 window. The default value is 64 megabytes. 4957 resource_alignment= 4958 Format: 4959 [<order of align>@]<pci_dev>[; ...] 4960 Specifies alignment and device to reassign 4961 aligned memory resources. How to 4962 specify the device is described above. 4963 If <order of align> is not specified, 4964 PAGE_SIZE is used as alignment. 4965 A PCI-PCI bridge can be specified if resource 4966 windows need to be expanded. 4967 To specify the alignment for several 4968 instances of a device, the PCI vendor, 4969 device, subvendor, and subdevice may be 4970 specified, e.g., 12@pci:8086:9c22:103c:198f 4971 for 4096-byte alignment. 4972 ecrc= Enable/disable PCIe ECRC (transaction layer 4973 end-to-end CRC checking). Only effective if 4974 OS has native AER control (either granted by 4975 ACPI _OSC or forced via "pcie_ports=native") 4976 bios: Use BIOS/firmware settings. This is the 4977 the default. 4978 off: Turn ECRC off 4979 on: Turn ECRC on. 4980 hpiosize=nn[KMG] The fixed amount of bus space which is 4981 reserved for hotplug bridge's IO window. 4982 Default size is 256 bytes. 4983 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4984 reserved for hotplug bridge's MMIO window. 4985 Default size is 2 megabytes. 4986 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4987 reserved for hotplug bridge's MMIO_PREF window. 4988 Default size is 2 megabytes. 4989 hpmemsize=nn[KMG] The fixed amount of bus space which is 4990 reserved for hotplug bridge's MMIO and 4991 MMIO_PREF window. 4992 Default size is 2 megabytes. 4993 hpbussize=nn The minimum amount of additional bus numbers 4994 reserved for buses below a hotplug bridge. 4995 Default is 1. 4996 realloc= Enable/disable reallocating PCI bridge resources 4997 if allocations done by BIOS are too small to 4998 accommodate resources required by all child 4999 devices. 5000 off: Turn realloc off 5001 on: Turn realloc on 5002 realloc same as realloc=on 5003 noari do not use PCIe ARI. 5004 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5005 do not use PCIe ATS (and IOMMU device IOTLB). 5006 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5007 only look for one device below a PCIe downstream 5008 port. 5009 big_root_window Try to add a big 64bit memory window to the PCIe 5010 root complex on AMD CPUs. Some GFX hardware 5011 can resize a BAR to allow access to all VRAM. 5012 Adding the window is slightly risky (it may 5013 conflict with unreported devices), so this 5014 taints the kernel. 5015 disable_acs_redir=<pci_dev>[; ...] 5016 Specify one or more PCI devices (in the format 5017 specified above) separated by semicolons. 5018 Each device specified will have the PCI ACS 5019 redirect capabilities forced off which will 5020 allow P2P traffic between devices through 5021 bridges without forcing it upstream. Note: 5022 this removes isolation between devices and 5023 may put more devices in an IOMMU group. 5024 config_acs= 5025 Format: 5026 <ACS flags>@<pci_dev>[; ...] 5027 Specify one or more PCI devices (in the format 5028 specified above) optionally prepended with flags 5029 and separated by semicolons. The respective 5030 capabilities will be enabled, disabled or 5031 unchanged based on what is specified in 5032 flags. 5033 5034 ACS Flags is defined as follows: 5035 bit-0 : ACS Source Validation 5036 bit-1 : ACS Translation Blocking 5037 bit-2 : ACS P2P Request Redirect 5038 bit-3 : ACS P2P Completion Redirect 5039 bit-4 : ACS Upstream Forwarding 5040 bit-5 : ACS P2P Egress Control 5041 bit-6 : ACS Direct Translated P2P 5042 Each bit can be marked as: 5043 '0' – force disabled 5044 '1' – force enabled 5045 'x' – unchanged 5046 For example, 5047 pci=config_acs=10x@pci:0:0 5048 would configure all devices that support 5049 ACS to enable P2P Request Redirect, disable 5050 Translation Blocking, and leave Source 5051 Validation unchanged from whatever power-up 5052 or firmware set it to. 5053 5054 Note: this may remove isolation between devices 5055 and may put more devices in an IOMMU group. 5056 force_floating [S390] Force usage of floating interrupts. 5057 nomio [S390] Do not use MIO instructions. 5058 norid [S390] ignore the RID field and force use of 5059 one PCI domain per PCI function 5060 notph [PCIE] If the PCIE_TPH kernel config parameter 5061 is enabled, this kernel boot option can be used 5062 to disable PCIe TLP Processing Hints support 5063 system-wide. 5064 5065 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5066 Management. 5067 off Don't touch ASPM configuration at all. Leave any 5068 configuration done by firmware unchanged. 5069 force Enable ASPM even on devices that claim not to support it. 5070 WARNING: Forcing ASPM on may cause system lockups. 5071 5072 pcie_ports= [PCIE] PCIe port services handling: 5073 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5074 even if the platform doesn't give the OS permission to 5075 use them. This may cause conflicts if the platform 5076 also tries to use these services. 5077 dpc-native Use native PCIe service for DPC only. May 5078 cause conflicts if firmware uses AER or DPC. 5079 compat Disable native PCIe services (PME, AER, DPC, PCIe 5080 hotplug). 5081 5082 pcie_port_pm= [PCIE] PCIe port power management handling: 5083 off Disable power management of all PCIe ports 5084 force Forcibly enable power management of all PCIe ports 5085 5086 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5087 nomsi Do not use MSI for native PCIe PME signaling (this makes 5088 all PCIe root ports use INTx for all services). 5089 5090 pcmv= [HW,PCMCIA] BadgePAD 4 5091 5092 pd_ignore_unused 5093 [PM] 5094 Keep all power-domains already enabled by bootloader on, 5095 even if no driver has claimed them. This is useful 5096 for debug and development, but should not be 5097 needed on a platform with proper driver support. 5098 5099 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5100 boot time. 5101 Format: { 0 | 1 } 5102 See arch/parisc/kernel/pdc_chassis.c 5103 5104 percpu_alloc= [MM,EARLY] 5105 Select which percpu first chunk allocator to use. 5106 Currently supported values are "embed" and "page". 5107 Archs may support subset or none of the selections. 5108 See comments in mm/percpu.c for details on each 5109 allocator. This parameter is primarily for debugging 5110 and performance comparison. 5111 5112 pirq= [SMP,APIC] Manual mp-table setup 5113 See Documentation/arch/x86/i386/IO-APIC.rst. 5114 5115 plip= [PPT,NET] Parallel port network link 5116 Format: { parport<nr> | timid | 0 } 5117 See also Documentation/admin-guide/parport.rst. 5118 5119 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5120 Override pmtimer IOPort with a hex value. 5121 e.g. pmtmr=0x508 5122 5123 pmu_override= [PPC] Override the PMU. 5124 This option takes over the PMU facility, so it is no 5125 longer usable by perf. Setting this option starts the 5126 PMU counters by setting MMCR0 to 0 (the FC bit is 5127 cleared). If a number is given, then MMCR1 is set to 5128 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5129 remains 0. 5130 5131 pm_async= [PM] 5132 Format: off 5133 This parameter sets the initial value of the 5134 /sys/power/pm_async sysfs knob at boot time. 5135 If set to "off", disables asynchronous suspend and 5136 resume of devices during system-wide power transitions. 5137 This can be useful on platforms where device 5138 dependencies are not well-defined, or for debugging 5139 power management issues. Asynchronous operations are 5140 enabled by default. 5141 5142 5143 pm_debug_messages [SUSPEND,KNL] 5144 Enable suspend/resume debug messages during boot up. 5145 5146 pnp.debug=1 [PNP] 5147 Enable PNP debug messages (depends on the 5148 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5149 via /sys/module/pnp/parameters/debug. We always show 5150 current resource usage; turning this on also shows 5151 possible settings and some assignment information. 5152 5153 pnpacpi= [ACPI] 5154 { off } 5155 5156 pnpbios= [ISAPNP] 5157 { on | off | curr | res | no-curr | no-res } 5158 5159 pnp_reserve_irq= 5160 [ISAPNP] Exclude IRQs for the autoconfiguration 5161 5162 pnp_reserve_dma= 5163 [ISAPNP] Exclude DMAs for the autoconfiguration 5164 5165 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5166 Ranges are in pairs (I/O port base and size). 5167 5168 pnp_reserve_mem= 5169 [ISAPNP] Exclude memory regions for the 5170 autoconfiguration. 5171 Ranges are in pairs (memory base and size). 5172 5173 ports= [IP_VS_FTP] IPVS ftp helper module 5174 Default is 21. 5175 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5176 may be specified. 5177 Format: <port>,<port>.... 5178 5179 possible_cpus= [SMP,S390,X86] 5180 Format: <unsigned int> 5181 Set the number of possible CPUs, overriding the 5182 regular discovery mechanisms (such as ACPI/FW, etc). 5183 5184 powersave=off [PPC] This option disables power saving features. 5185 It specifically disables cpuidle and sets the 5186 platform machine description specific power_save 5187 function to NULL. On Idle the CPU just reduces 5188 execution priority. 5189 5190 ppc_strict_facility_enable 5191 [PPC,ENABLE] This option catches any kernel floating point, 5192 Altivec, VSX and SPE outside of regions specifically 5193 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5194 There is some performance impact when enabling this. 5195 5196 ppc_tm= [PPC,EARLY] 5197 Format: {"off"} 5198 Disable Hardware Transactional Memory 5199 5200 preempt= [KNL] 5201 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5202 none - Limited to cond_resched() calls 5203 voluntary - Limited to cond_resched() and might_sleep() calls 5204 full - Any section that isn't explicitly preempt disabled 5205 can be preempted anytime. Tasks will also yield 5206 contended spinlocks (if the critical section isn't 5207 explicitly preempt disabled beyond the lock itself). 5208 lazy - Scheduler controlled. Similar to full but instead 5209 of preempting the task immediately, the task gets 5210 one HZ tick time to yield itself before the 5211 preemption will be forced. One preemption is when the 5212 task returns to user space. 5213 5214 print-fatal-signals= 5215 [KNL] debug: print fatal signals 5216 5217 If enabled, warn about various signal handling 5218 related application anomalies: too many signals, 5219 too many POSIX.1 timers, fatal signals causing a 5220 coredump - etc. 5221 5222 If you hit the warning due to signal overflow, 5223 you might want to try "ulimit -i unlimited". 5224 5225 default: off. 5226 5227 printk.always_kmsg_dump= 5228 Trigger kmsg_dump for cases other than kernel oops or 5229 panics 5230 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5231 default: disabled 5232 5233 printk.console_no_auto_verbose= 5234 Disable console loglevel raise on oops, panic 5235 or lockdep-detected issues (only if lock debug is on). 5236 With an exception to setups with low baudrate on 5237 serial console, keeping this 0 is a good choice 5238 in order to provide more debug information. 5239 Format: <bool> 5240 default: 0 (auto_verbose is enabled) 5241 5242 printk.debug_non_panic_cpus= 5243 Allows storing messages from non-panic CPUs into 5244 the printk log buffer during panic(). They are 5245 flushed to consoles by the panic-CPU on 5246 a best-effort basis. 5247 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5248 Default: disabled 5249 5250 printk.devkmsg={on,off,ratelimit} 5251 Control writing to /dev/kmsg. 5252 on - unlimited logging to /dev/kmsg from userspace 5253 off - logging to /dev/kmsg disabled 5254 ratelimit - ratelimit the logging 5255 Default: ratelimit 5256 5257 printk.time= Show timing data prefixed to each printk message line 5258 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5259 5260 proc_mem.force_override= [KNL] 5261 Format: {always | ptrace | never} 5262 Traditionally /proc/pid/mem allows memory permissions to be 5263 overridden without restrictions. This option may be set to 5264 restrict that. Can be one of: 5265 - 'always': traditional behavior always allows mem overrides. 5266 - 'ptrace': only allow mem overrides for active ptracers. 5267 - 'never': never allow mem overrides. 5268 If not specified, default is the CONFIG_PROC_MEM_* choice. 5269 5270 processor.max_cstate= [HW,ACPI] 5271 Limit processor to maximum C-state 5272 max_cstate=9 overrides any DMI blacklist limit. 5273 5274 processor.nocst [HW,ACPI] 5275 Ignore the _CST method to determine C-states, 5276 instead using the legacy FADT method 5277 5278 profile= [KNL] Enable kernel profiling via /proc/profile 5279 Format: [<profiletype>,]<number> 5280 Param: <profiletype>: "schedule" or "kvm" 5281 [defaults to kernel profiling] 5282 Param: "schedule" - profile schedule points. 5283 Param: "kvm" - profile VM exits. 5284 Param: <number> - step/bucket size as a power of 2 for 5285 statistical time based profiling. 5286 5287 prompt_ramdisk= [RAM] [Deprecated] 5288 5289 prot_virt= [S390] enable hosting protected virtual machines 5290 isolated from the hypervisor (if hardware supports 5291 that). If enabled, the default kernel base address 5292 might be overridden even when Kernel Address Space 5293 Layout Randomization is disabled. 5294 Format: <bool> 5295 5296 psi= [KNL] Enable or disable pressure stall information 5297 tracking. 5298 Format: <bool> 5299 5300 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5301 probe for; one of (bare|imps|exps|lifebook|any). 5302 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5303 per second. 5304 psmouse.resetafter= [HW,MOUSE] 5305 Try to reset the device after so many bad packets 5306 (0 = never). 5307 psmouse.resolution= 5308 [HW,MOUSE] Set desired mouse resolution, in dpi. 5309 psmouse.smartscroll= 5310 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5311 0 = disabled, 1 = enabled (default). 5312 5313 pstore.backend= Specify the name of the pstore backend to use 5314 5315 pti= [X86-64] Control Page Table Isolation of user and 5316 kernel address spaces. Disabling this feature 5317 removes hardening, but improves performance of 5318 system calls and interrupts. 5319 5320 on - unconditionally enable 5321 off - unconditionally disable 5322 auto - kernel detects whether your CPU model is 5323 vulnerable to issues that PTI mitigates 5324 5325 Not specifying this option is equivalent to pti=auto. 5326 5327 pty.legacy_count= 5328 [KNL] Number of legacy pty's. Overwrites compiled-in 5329 default number. 5330 5331 quiet [KNL,EARLY] Disable most log messages 5332 5333 r128= [HW,DRM] 5334 5335 radix_hcall_invalidate=on [PPC/PSERIES] 5336 Disable RADIX GTSE feature and use hcall for TLB 5337 invalidate. 5338 5339 raid= [HW,RAID] 5340 See Documentation/admin-guide/md.rst. 5341 5342 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5343 See Documentation/admin-guide/blockdev/ramdisk.rst. 5344 5345 ramdisk_start= [RAM] RAM disk image start address 5346 5347 random.trust_cpu=off 5348 [KNL,EARLY] Disable trusting the use of the CPU's 5349 random number generator (if available) to 5350 initialize the kernel's RNG. 5351 5352 random.trust_bootloader=off 5353 [KNL,EARLY] Disable trusting the use of the a seed 5354 passed by the bootloader (if available) to 5355 initialize the kernel's RNG. 5356 5357 randomize_kstack_offset= 5358 [KNL,EARLY] Enable or disable kernel stack offset 5359 randomization, which provides roughly 5 bits of 5360 entropy, frustrating memory corruption attacks 5361 that depend on stack address determinism or 5362 cross-syscall address exposures. This is only 5363 available on architectures that have defined 5364 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5365 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5366 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5367 5368 ras=option[,option,...] [KNL] RAS-specific options 5369 5370 cec_disable [X86] 5371 Disable the Correctable Errors Collector, 5372 see CONFIG_RAS_CEC help text. 5373 5374 rcu_nocbs[=cpu-list] 5375 [KNL] The optional argument is a cpu list, 5376 as described above. 5377 5378 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5379 enable the no-callback CPU mode, which prevents 5380 such CPUs' callbacks from being invoked in 5381 softirq context. Invocation of such CPUs' RCU 5382 callbacks will instead be offloaded to "rcuox/N" 5383 kthreads created for that purpose, where "x" is 5384 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5385 for the kthreads that mediate grace periods; and 5386 "N" is the CPU number. This reduces OS jitter on 5387 the offloaded CPUs, which can be useful for HPC 5388 and real-time workloads. It can also improve 5389 energy efficiency for asymmetric multiprocessors. 5390 5391 If a cpulist is passed as an argument, the specified 5392 list of CPUs is set to no-callback mode from boot. 5393 5394 Otherwise, if the '=' sign and the cpulist 5395 arguments are omitted, no CPU will be set to 5396 no-callback mode from boot but the mode may be 5397 toggled at runtime via cpusets. 5398 5399 Note that this argument takes precedence over 5400 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5401 5402 rcu_nocb_poll [KNL] 5403 Rather than requiring that offloaded CPUs 5404 (specified by rcu_nocbs= above) explicitly 5405 awaken the corresponding "rcuoN" kthreads, 5406 make these kthreads poll for callbacks. 5407 This improves the real-time response for the 5408 offloaded CPUs by relieving them of the need to 5409 wake up the corresponding kthread, but degrades 5410 energy efficiency by requiring that the kthreads 5411 periodically wake up to do the polling. 5412 5413 rcutree.blimit= [KNL] 5414 Set maximum number of finished RCU callbacks to 5415 process in one batch. 5416 5417 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5418 Do only a one-line RCU CPU stall warning when 5419 there is an ongoing too-long CSD-lock wait. 5420 5421 rcutree.do_rcu_barrier= [KNL] 5422 Request a call to rcu_barrier(). This is 5423 throttled so that userspace tests can safely 5424 hammer on the sysfs variable if they so choose. 5425 If triggered before the RCU grace-period machinery 5426 is fully active, this will error out with EAGAIN. 5427 5428 rcutree.dump_tree= [KNL] 5429 Dump the structure of the rcu_node combining tree 5430 out at early boot. This is used for diagnostic 5431 purposes, to verify correct tree setup. 5432 5433 rcutree.gp_cleanup_delay= [KNL] 5434 Set the number of jiffies to delay each step of 5435 RCU grace-period cleanup. 5436 5437 rcutree.gp_init_delay= [KNL] 5438 Set the number of jiffies to delay each step of 5439 RCU grace-period initialization. 5440 5441 rcutree.gp_preinit_delay= [KNL] 5442 Set the number of jiffies to delay each step of 5443 RCU grace-period pre-initialization, that is, 5444 the propagation of recent CPU-hotplug changes up 5445 the rcu_node combining tree. 5446 5447 rcutree.jiffies_till_first_fqs= [KNL] 5448 Set delay from grace-period initialization to 5449 first attempt to force quiescent states. 5450 Units are jiffies, minimum value is zero, 5451 and maximum value is HZ. 5452 5453 rcutree.jiffies_till_next_fqs= [KNL] 5454 Set delay between subsequent attempts to force 5455 quiescent states. Units are jiffies, minimum 5456 value is one, and maximum value is HZ. 5457 5458 rcutree.jiffies_till_sched_qs= [KNL] 5459 Set required age in jiffies for a 5460 given grace period before RCU starts 5461 soliciting quiescent-state help from 5462 rcu_note_context_switch() and cond_resched(). 5463 If not specified, the kernel will calculate 5464 a value based on the most recent settings 5465 of rcutree.jiffies_till_first_fqs 5466 and rcutree.jiffies_till_next_fqs. 5467 This calculated value may be viewed in 5468 rcutree.jiffies_to_sched_qs. Any attempt to set 5469 rcutree.jiffies_to_sched_qs will be cheerfully 5470 overwritten. 5471 5472 rcutree.kthread_prio= [KNL,BOOT] 5473 Set the SCHED_FIFO priority of the RCU per-CPU 5474 kthreads (rcuc/N). This value is also used for 5475 the priority of the RCU boost threads (rcub/N) 5476 and for the RCU grace-period kthreads (rcu_bh, 5477 rcu_preempt, and rcu_sched). If RCU_BOOST is 5478 set, valid values are 1-99 and the default is 1 5479 (the least-favored priority). Otherwise, when 5480 RCU_BOOST is not set, valid values are 0-99 and 5481 the default is zero (non-realtime operation). 5482 When RCU_NOCB_CPU is set, also adjust the 5483 priority of NOCB callback kthreads. 5484 5485 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5486 On callback-offloaded (rcu_nocbs) CPUs, 5487 RCU reduces the lock contention that would 5488 otherwise be caused by callback floods through 5489 use of the ->nocb_bypass list. However, in the 5490 common non-flooded case, RCU queues directly to 5491 the main ->cblist in order to avoid the extra 5492 overhead of the ->nocb_bypass list and its lock. 5493 But if there are too many callbacks queued during 5494 a single jiffy, RCU pre-queues the callbacks into 5495 the ->nocb_bypass queue. The definition of "too 5496 many" is supplied by this kernel boot parameter. 5497 5498 rcutree.nohz_full_patience_delay= [KNL] 5499 On callback-offloaded (rcu_nocbs) CPUs, avoid 5500 disturbing RCU unless the grace period has 5501 reached the specified age in milliseconds. 5502 Defaults to zero. Large values will be capped 5503 at five seconds. All values will be rounded down 5504 to the nearest value representable by jiffies. 5505 5506 rcutree.qhimark= [KNL] 5507 Set threshold of queued RCU callbacks beyond which 5508 batch limiting is disabled. 5509 5510 rcutree.qlowmark= [KNL] 5511 Set threshold of queued RCU callbacks below which 5512 batch limiting is re-enabled. 5513 5514 rcutree.qovld= [KNL] 5515 Set threshold of queued RCU callbacks beyond which 5516 RCU's force-quiescent-state scan will aggressively 5517 enlist help from cond_resched() and sched IPIs to 5518 help CPUs more quickly reach quiescent states. 5519 Set to less than zero to make this be set based 5520 on rcutree.qhimark at boot time and to zero to 5521 disable more aggressive help enlistment. 5522 5523 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5524 Set the page-cache refill delay (in milliseconds) 5525 in response to low-memory conditions. The range 5526 of permitted values is in the range 0:100000. 5527 5528 rcutree.rcu_divisor= [KNL] 5529 Set the shift-right count to use to compute 5530 the callback-invocation batch limit bl from 5531 the number of callbacks queued on this CPU. 5532 The result will be bounded below by the value of 5533 the rcutree.blimit kernel parameter. Every bl 5534 callbacks, the softirq handler will exit in 5535 order to allow the CPU to do other work. 5536 5537 Please note that this callback-invocation batch 5538 limit applies only to non-offloaded callback 5539 invocation. Offloaded callbacks are instead 5540 invoked in the context of an rcuoc kthread, which 5541 scheduler will preempt as it does any other task. 5542 5543 rcutree.rcu_fanout_exact= [KNL] 5544 Disable autobalancing of the rcu_node combining 5545 tree. This is used by rcutorture, and might 5546 possibly be useful for architectures having high 5547 cache-to-cache transfer latencies. 5548 5549 rcutree.rcu_fanout_leaf= [KNL] 5550 Change the number of CPUs assigned to each 5551 leaf rcu_node structure. Useful for very 5552 large systems, which will choose the value 64, 5553 and for NUMA systems with large remote-access 5554 latencies, which will choose a value aligned 5555 with the appropriate hardware boundaries. 5556 5557 rcutree.rcu_min_cached_objs= [KNL] 5558 Minimum number of objects which are cached and 5559 maintained per one CPU. Object size is equal 5560 to PAGE_SIZE. The cache allows to reduce the 5561 pressure to page allocator, also it makes the 5562 whole algorithm to behave better in low memory 5563 condition. 5564 5565 rcutree.rcu_nocb_gp_stride= [KNL] 5566 Set the number of NOCB callback kthreads in 5567 each group, which defaults to the square root 5568 of the number of CPUs. Larger numbers reduce 5569 the wakeup overhead on the global grace-period 5570 kthread, but increases that same overhead on 5571 each group's NOCB grace-period kthread. 5572 5573 rcutree.rcu_kick_kthreads= [KNL] 5574 Cause the grace-period kthread to get an extra 5575 wake_up() if it sleeps three times longer than 5576 it should at force-quiescent-state time. 5577 This wake_up() will be accompanied by a 5578 WARN_ONCE() splat and an ftrace_dump(). 5579 5580 rcutree.rcu_resched_ns= [KNL] 5581 Limit the time spend invoking a batch of RCU 5582 callbacks to the specified number of nanoseconds. 5583 By default, this limit is checked only once 5584 every 32 callbacks in order to limit the pain 5585 inflicted by local_clock() overhead. 5586 5587 rcutree.rcu_unlock_delay= [KNL] 5588 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5589 this specifies an rcu_read_unlock()-time delay 5590 in microseconds. This defaults to zero. 5591 Larger delays increase the probability of 5592 catching RCU pointer leaks, that is, buggy use 5593 of RCU-protected pointers after the relevant 5594 rcu_read_unlock() has completed. 5595 5596 rcutree.sysrq_rcu= [KNL] 5597 Commandeer a sysrq key to dump out Tree RCU's 5598 rcu_node tree with an eye towards determining 5599 why a new grace period has not yet started. 5600 5601 rcutree.use_softirq= [KNL] 5602 If set to zero, move all RCU_SOFTIRQ processing to 5603 per-CPU rcuc kthreads. Defaults to a non-zero 5604 value, meaning that RCU_SOFTIRQ is used by default. 5605 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5606 5607 But note that CONFIG_PREEMPT_RT=y kernels disable 5608 this kernel boot parameter, forcibly setting it 5609 to zero. 5610 5611 rcutree.enable_rcu_lazy= [KNL] 5612 To save power, batch RCU callbacks and flush after 5613 delay, memory pressure or callback list growing too 5614 big. 5615 5616 rcutree.rcu_normal_wake_from_gp= [KNL] 5617 Reduces a latency of synchronize_rcu() call. This approach 5618 maintains its own track of synchronize_rcu() callers, so it 5619 does not interact with regular callbacks because it does not 5620 use a call_rcu[_hurry]() path. Please note, this is for a 5621 normal grace period. 5622 5623 How to enable it: 5624 5625 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5626 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5627 5628 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5629 disabled by the boot parameter passing 0. 5630 5631 rcuscale.gp_async= [KNL] 5632 Measure performance of asynchronous 5633 grace-period primitives such as call_rcu(). 5634 5635 rcuscale.gp_async_max= [KNL] 5636 Specify the maximum number of outstanding 5637 callbacks per writer thread. When a writer 5638 thread exceeds this limit, it invokes the 5639 corresponding flavor of rcu_barrier() to allow 5640 previously posted callbacks to drain. 5641 5642 rcuscale.gp_exp= [KNL] 5643 Measure performance of expedited synchronous 5644 grace-period primitives. 5645 5646 rcuscale.holdoff= [KNL] 5647 Set test-start holdoff period. The purpose of 5648 this parameter is to delay the start of the 5649 test until boot completes in order to avoid 5650 interference. 5651 5652 rcuscale.kfree_by_call_rcu= [KNL] 5653 In kernels built with CONFIG_RCU_LAZY=y, test 5654 call_rcu() instead of kfree_rcu(). 5655 5656 rcuscale.kfree_mult= [KNL] 5657 Instead of allocating an object of size kfree_obj, 5658 allocate one of kfree_mult * sizeof(kfree_obj). 5659 Defaults to 1. 5660 5661 rcuscale.kfree_rcu_test= [KNL] 5662 Set to measure performance of kfree_rcu() flooding. 5663 5664 rcuscale.kfree_rcu_test_double= [KNL] 5665 Test the double-argument variant of kfree_rcu(). 5666 If this parameter has the same value as 5667 rcuscale.kfree_rcu_test_single, both the single- 5668 and double-argument variants are tested. 5669 5670 rcuscale.kfree_rcu_test_single= [KNL] 5671 Test the single-argument variant of kfree_rcu(). 5672 If this parameter has the same value as 5673 rcuscale.kfree_rcu_test_double, both the single- 5674 and double-argument variants are tested. 5675 5676 rcuscale.kfree_nthreads= [KNL] 5677 The number of threads running loops of kfree_rcu(). 5678 5679 rcuscale.kfree_alloc_num= [KNL] 5680 Number of allocations and frees done in an iteration. 5681 5682 rcuscale.kfree_loops= [KNL] 5683 Number of loops doing rcuscale.kfree_alloc_num number 5684 of allocations and frees. 5685 5686 rcuscale.minruntime= [KNL] 5687 Set the minimum test run time in seconds. This 5688 does not affect the data-collection interval, 5689 but instead allows better measurement of things 5690 like CPU consumption. 5691 5692 rcuscale.nreaders= [KNL] 5693 Set number of RCU readers. The value -1 selects 5694 N, where N is the number of CPUs. A value 5695 "n" less than -1 selects N-n+1, where N is again 5696 the number of CPUs. For example, -2 selects N 5697 (the number of CPUs), -3 selects N+1, and so on. 5698 A value of "n" less than or equal to -N selects 5699 a single reader. 5700 5701 rcuscale.nwriters= [KNL] 5702 Set number of RCU writers. The values operate 5703 the same as for rcuscale.nreaders. 5704 N, where N is the number of CPUs 5705 5706 rcuscale.scale_type= [KNL] 5707 Specify the RCU implementation to test. 5708 5709 rcuscale.shutdown= [KNL] 5710 Shut the system down after performance tests 5711 complete. This is useful for hands-off automated 5712 testing. 5713 5714 rcuscale.verbose= [KNL] 5715 Enable additional printk() statements. 5716 5717 rcuscale.writer_holdoff= [KNL] 5718 Write-side holdoff between grace periods, 5719 in microseconds. The default of zero says 5720 no holdoff. 5721 5722 rcuscale.writer_holdoff_jiffies= [KNL] 5723 Additional write-side holdoff between grace 5724 periods, but in jiffies. The default of zero 5725 says no holdoff. 5726 5727 rcutorture.fqs_duration= [KNL] 5728 Set duration of force_quiescent_state bursts 5729 in microseconds. 5730 5731 rcutorture.fqs_holdoff= [KNL] 5732 Set holdoff time within force_quiescent_state bursts 5733 in microseconds. 5734 5735 rcutorture.fqs_stutter= [KNL] 5736 Set wait time between force_quiescent_state bursts 5737 in seconds. 5738 5739 rcutorture.fwd_progress= [KNL] 5740 Specifies the number of kthreads to be used 5741 for RCU grace-period forward-progress testing 5742 for the types of RCU supporting this notion. 5743 Defaults to 1 kthread, values less than zero or 5744 greater than the number of CPUs cause the number 5745 of CPUs to be used. 5746 5747 rcutorture.fwd_progress_div= [KNL] 5748 Specify the fraction of a CPU-stall-warning 5749 period to do tight-loop forward-progress testing. 5750 5751 rcutorture.fwd_progress_holdoff= [KNL] 5752 Number of seconds to wait between successive 5753 forward-progress tests. 5754 5755 rcutorture.fwd_progress_need_resched= [KNL] 5756 Enclose cond_resched() calls within checks for 5757 need_resched() during tight-loop forward-progress 5758 testing. 5759 5760 rcutorture.gp_cond= [KNL] 5761 Use conditional/asynchronous update-side 5762 normal-grace-period primitives, if available. 5763 5764 rcutorture.gp_cond_exp= [KNL] 5765 Use conditional/asynchronous update-side 5766 expedited-grace-period primitives, if available. 5767 5768 rcutorture.gp_cond_full= [KNL] 5769 Use conditional/asynchronous update-side 5770 normal-grace-period primitives that also take 5771 concurrent expedited grace periods into account, 5772 if available. 5773 5774 rcutorture.gp_cond_exp_full= [KNL] 5775 Use conditional/asynchronous update-side 5776 expedited-grace-period primitives that also take 5777 concurrent normal grace periods into account, 5778 if available. 5779 5780 rcutorture.gp_cond_wi= [KNL] 5781 Nominal wait interval for normal conditional 5782 grace periods (specified by rcutorture's 5783 gp_cond and gp_cond_full module parameters), 5784 in microseconds. The actual wait interval will 5785 be randomly selected to nanosecond granularity up 5786 to this wait interval. Defaults to 16 jiffies, 5787 for example, 16,000 microseconds on a system 5788 with HZ=1000. 5789 5790 rcutorture.gp_cond_wi_exp= [KNL] 5791 Nominal wait interval for expedited conditional 5792 grace periods (specified by rcutorture's 5793 gp_cond_exp and gp_cond_exp_full module 5794 parameters), in microseconds. The actual wait 5795 interval will be randomly selected to nanosecond 5796 granularity up to this wait interval. Defaults to 5797 128 microseconds. 5798 5799 rcutorture.gp_exp= [KNL] 5800 Use expedited update-side primitives, if available. 5801 5802 rcutorture.gp_normal= [KNL] 5803 Use normal (non-expedited) asynchronous 5804 update-side primitives, if available. 5805 5806 rcutorture.gp_poll= [KNL] 5807 Use polled update-side normal-grace-period 5808 primitives, if available. 5809 5810 rcutorture.gp_poll_exp= [KNL] 5811 Use polled update-side expedited-grace-period 5812 primitives, if available. 5813 5814 rcutorture.gp_poll_full= [KNL] 5815 Use polled update-side normal-grace-period 5816 primitives that also take concurrent expedited 5817 grace periods into account, if available. 5818 5819 rcutorture.gp_poll_exp_full= [KNL] 5820 Use polled update-side expedited-grace-period 5821 primitives that also take concurrent normal 5822 grace periods into account, if available. 5823 5824 rcutorture.gp_poll_wi= [KNL] 5825 Nominal wait interval for normal conditional 5826 grace periods (specified by rcutorture's 5827 gp_poll and gp_poll_full module parameters), 5828 in microseconds. The actual wait interval will 5829 be randomly selected to nanosecond granularity up 5830 to this wait interval. Defaults to 16 jiffies, 5831 for example, 16,000 microseconds on a system 5832 with HZ=1000. 5833 5834 rcutorture.gp_poll_wi_exp= [KNL] 5835 Nominal wait interval for expedited conditional 5836 grace periods (specified by rcutorture's 5837 gp_poll_exp and gp_poll_exp_full module 5838 parameters), in microseconds. The actual wait 5839 interval will be randomly selected to nanosecond 5840 granularity up to this wait interval. Defaults to 5841 128 microseconds. 5842 5843 rcutorture.gp_sync= [KNL] 5844 Use normal (non-expedited) synchronous 5845 update-side primitives, if available. If all 5846 of rcutorture.gp_cond=, rcutorture.gp_exp=, 5847 rcutorture.gp_normal=, and rcutorture.gp_sync= 5848 are zero, rcutorture acts as if is interpreted 5849 they are all non-zero. 5850 5851 rcutorture.gpwrap_lag= [KNL] 5852 Enable grace-period wrap lag testing. Setting 5853 to false prevents the gpwrap lag test from 5854 running. Default is true. 5855 5856 rcutorture.gpwrap_lag_gps= [KNL] 5857 Set the value for grace-period wrap lag during 5858 active lag testing periods. This controls how many 5859 grace periods differences we tolerate between 5860 rdp and rnp's gp_seq before setting overflow flag. 5861 The default is always set to 8. 5862 5863 rcutorture.gpwrap_lag_cycle_mins= [KNL] 5864 Set the total cycle duration for gpwrap lag 5865 testing in minutes. This is the total time for 5866 one complete cycle of active and inactive 5867 testing periods. Default is 30 minutes. 5868 5869 rcutorture.gpwrap_lag_active_mins= [KNL] 5870 Set the duration for which gpwrap lag is active 5871 within each cycle, in minutes. During this time, 5872 the grace-period wrap lag will be set to the 5873 value specified by gpwrap_lag_gps. Default is 5874 5 minutes. 5875 5876 rcutorture.irqreader= [KNL] 5877 Run RCU readers from irq handlers, or, more 5878 accurately, from a timer handler. Not all RCU 5879 flavors take kindly to this sort of thing. 5880 5881 rcutorture.leakpointer= [KNL] 5882 Leak an RCU-protected pointer out of the reader. 5883 This can of course result in splats, and is 5884 intended to test the ability of things like 5885 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 5886 such leaks. 5887 5888 rcutorture.n_barrier_cbs= [KNL] 5889 Set callbacks/threads for rcu_barrier() testing. 5890 5891 rcutorture.nfakewriters= [KNL] 5892 Set number of concurrent RCU writers. These just 5893 stress RCU, they don't participate in the actual 5894 test, hence the "fake". 5895 5896 rcutorture.nocbs_nthreads= [KNL] 5897 Set number of RCU callback-offload togglers. 5898 Zero (the default) disables toggling. 5899 5900 rcutorture.nocbs_toggle= [KNL] 5901 Set the delay in milliseconds between successive 5902 callback-offload toggling attempts. 5903 5904 rcutorture.nreaders= [KNL] 5905 Set number of RCU readers. The value -1 selects 5906 N-1, where N is the number of CPUs. A value 5907 "n" less than -1 selects N-n-2, where N is again 5908 the number of CPUs. For example, -2 selects N 5909 (the number of CPUs), -3 selects N+1, and so on. 5910 5911 rcutorture.object_debug= [KNL] 5912 Enable debug-object double-call_rcu() testing. 5913 5914 rcutorture.onoff_holdoff= [KNL] 5915 Set time (s) after boot for CPU-hotplug testing. 5916 5917 rcutorture.onoff_interval= [KNL] 5918 Set time (jiffies) between CPU-hotplug operations, 5919 or zero to disable CPU-hotplug testing. 5920 5921 rcutorture.preempt_duration= [KNL] 5922 Set duration (in milliseconds) of preemptions 5923 by a high-priority FIFO real-time task. Set to 5924 zero (the default) to disable. The CPUs to 5925 preempt are selected randomly from the set that 5926 are online at a given point in time. Races with 5927 CPUs going offline are ignored, with that attempt 5928 at preemption skipped. 5929 5930 rcutorture.preempt_interval= [KNL] 5931 Set interval (in milliseconds, defaulting to one 5932 second) between preemptions by a high-priority 5933 FIFO real-time task. This delay is mediated 5934 by an hrtimer and is further fuzzed to avoid 5935 inadvertent synchronizations. 5936 5937 rcutorture.read_exit_burst= [KNL] 5938 The number of times in a given read-then-exit 5939 episode that a set of read-then-exit kthreads 5940 is spawned. 5941 5942 rcutorture.read_exit_delay= [KNL] 5943 The delay, in seconds, between successive 5944 read-then-exit testing episodes. 5945 5946 rcutorture.reader_flavor= [KNL] 5947 A bit mask indicating which readers to use. 5948 If there is more than one bit set, the readers 5949 are entered from low-order bit up, and are 5950 exited in the opposite order. For SRCU, the 5951 0x1 bit is normal readers, 0x2 NMI-safe readers, 5952 and 0x4 light-weight readers. 5953 5954 rcutorture.shuffle_interval= [KNL] 5955 Set task-shuffle interval (s). Shuffling tasks 5956 allows some CPUs to go into dyntick-idle mode 5957 during the rcutorture test. 5958 5959 rcutorture.shutdown_secs= [KNL] 5960 Set time (s) after boot system shutdown. This 5961 is useful for hands-off automated testing. 5962 5963 rcutorture.stall_cpu= [KNL] 5964 Duration of CPU stall (s) to test RCU CPU stall 5965 warnings, zero to disable. 5966 5967 rcutorture.stall_cpu_block= [KNL] 5968 Sleep while stalling if set. This will result 5969 in warnings from preemptible RCU in addition to 5970 any other stall-related activity. Note that 5971 in kernels built with CONFIG_PREEMPTION=n and 5972 CONFIG_PREEMPT_COUNT=y, this parameter will 5973 cause the CPU to pass through a quiescent state. 5974 Given CONFIG_PREEMPTION=n, this will suppress 5975 RCU CPU stall warnings, but will instead result 5976 in scheduling-while-atomic splats. 5977 5978 Use of this module parameter results in splats. 5979 5980 5981 rcutorture.stall_cpu_holdoff= [KNL] 5982 Time to wait (s) after boot before inducing stall. 5983 5984 rcutorture.stall_cpu_irqsoff= [KNL] 5985 Disable interrupts while stalling if set, but only 5986 on the first stall in the set. 5987 5988 rcutorture.stall_cpu_repeat= [KNL] 5989 Number of times to repeat the stall sequence, 5990 so that rcutorture.stall_cpu_repeat=3 will result 5991 in four stall sequences. 5992 5993 rcutorture.stall_gp_kthread= [KNL] 5994 Duration (s) of forced sleep within RCU 5995 grace-period kthread to test RCU CPU stall 5996 warnings, zero to disable. If both stall_cpu 5997 and stall_gp_kthread are specified, the 5998 kthread is starved first, then the CPU. 5999 6000 rcutorture.stat_interval= [KNL] 6001 Time (s) between statistics printk()s. 6002 6003 rcutorture.stutter= [KNL] 6004 Time (s) to stutter testing, for example, specifying 6005 five seconds causes the test to run for five seconds, 6006 wait for five seconds, and so on. This tests RCU's 6007 ability to transition abruptly to and from idle. 6008 6009 rcutorture.test_boost= [KNL] 6010 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6011 "Maybe" means test if the RCU implementation 6012 under test support RCU priority boosting. 6013 6014 rcutorture.test_boost_duration= [KNL] 6015 Duration (s) of each individual boost test. 6016 6017 rcutorture.test_boost_holdoff= [KNL] 6018 Holdoff time (s) from start of test to the start 6019 of RCU priority-boost testing. Defaults to zero, 6020 that is, no holdoff. 6021 6022 rcutorture.test_boost_interval= [KNL] 6023 Interval (s) between each boost test. 6024 6025 rcutorture.test_no_idle_hz= [KNL] 6026 Test RCU's dyntick-idle handling. See also the 6027 rcutorture.shuffle_interval parameter. 6028 6029 rcutorture.torture_type= [KNL] 6030 Specify the RCU implementation to test. 6031 6032 rcutorture.verbose= [KNL] 6033 Enable additional printk() statements. 6034 6035 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6036 Dump ftrace buffer after reporting RCU CPU 6037 stall warning. 6038 6039 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6040 Provide RCU CPU stall notifiers, but see the 6041 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6042 option's help text. TL;DR: You almost certainly 6043 do not want rcupdate.rcu_cpu_stall_notifiers. 6044 6045 rcupdate.rcu_cpu_stall_suppress= [KNL] 6046 Suppress RCU CPU stall warning messages. 6047 6048 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6049 Suppress RCU CPU stall warning messages and 6050 rcutorture writer stall warnings that occur 6051 during early boot, that is, during the time 6052 before the init task is spawned. 6053 6054 rcupdate.rcu_cpu_stall_timeout= [KNL] 6055 Set timeout for RCU CPU stall warning messages. 6056 The value is in seconds and the maximum allowed 6057 value is 300 seconds. 6058 6059 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6060 Set timeout for expedited RCU CPU stall warning 6061 messages. The value is in milliseconds 6062 and the maximum allowed value is 21000 6063 milliseconds. Please note that this value is 6064 adjusted to an arch timer tick resolution. 6065 Setting this to zero causes the value from 6066 rcupdate.rcu_cpu_stall_timeout to be used (after 6067 conversion from seconds to milliseconds). 6068 6069 rcupdate.rcu_cpu_stall_cputime= [KNL] 6070 Provide statistics on the cputime and count of 6071 interrupts and tasks during the sampling period. For 6072 multiple continuous RCU stalls, all sampling periods 6073 begin at half of the first RCU stall timeout. 6074 6075 rcupdate.rcu_exp_stall_task_details= [KNL] 6076 Print stack dumps of any tasks blocking the 6077 current expedited RCU grace period during an 6078 expedited RCU CPU stall warning. 6079 6080 rcupdate.rcu_expedited= [KNL] 6081 Use expedited grace-period primitives, for 6082 example, synchronize_rcu_expedited() instead 6083 of synchronize_rcu(). This reduces latency, 6084 but can increase CPU utilization, degrade 6085 real-time latency, and degrade energy efficiency. 6086 No effect on CONFIG_TINY_RCU kernels. 6087 6088 rcupdate.rcu_normal= [KNL] 6089 Use only normal grace-period primitives, 6090 for example, synchronize_rcu() instead of 6091 synchronize_rcu_expedited(). This improves 6092 real-time latency, CPU utilization, and 6093 energy efficiency, but can expose users to 6094 increased grace-period latency. This parameter 6095 overrides rcupdate.rcu_expedited. No effect on 6096 CONFIG_TINY_RCU kernels. 6097 6098 rcupdate.rcu_normal_after_boot= [KNL] 6099 Once boot has completed (that is, after 6100 rcu_end_inkernel_boot() has been invoked), use 6101 only normal grace-period primitives. No effect 6102 on CONFIG_TINY_RCU kernels. 6103 6104 But note that CONFIG_PREEMPT_RT=y kernels enables 6105 this kernel boot parameter, forcibly setting 6106 it to the value one, that is, converting any 6107 post-boot attempt at an expedited RCU grace 6108 period to instead use normal non-expedited 6109 grace-period processing. 6110 6111 rcupdate.rcu_task_collapse_lim= [KNL] 6112 Set the maximum number of callbacks present 6113 at the beginning of a grace period that allows 6114 the RCU Tasks flavors to collapse back to using 6115 a single callback queue. This switching only 6116 occurs when rcupdate.rcu_task_enqueue_lim is 6117 set to the default value of -1. 6118 6119 rcupdate.rcu_task_contend_lim= [KNL] 6120 Set the minimum number of callback-queuing-time 6121 lock-contention events per jiffy required to 6122 cause the RCU Tasks flavors to switch to per-CPU 6123 callback queuing. This switching only occurs 6124 when rcupdate.rcu_task_enqueue_lim is set to 6125 the default value of -1. 6126 6127 rcupdate.rcu_task_enqueue_lim= [KNL] 6128 Set the number of callback queues to use for the 6129 RCU Tasks family of RCU flavors. The default 6130 of -1 allows this to be automatically (and 6131 dynamically) adjusted. This parameter is intended 6132 for use in testing. 6133 6134 rcupdate.rcu_task_ipi_delay= [KNL] 6135 Set time in jiffies during which RCU tasks will 6136 avoid sending IPIs, starting with the beginning 6137 of a given grace period. Setting a large 6138 number avoids disturbing real-time workloads, 6139 but lengthens grace periods. 6140 6141 rcupdate.rcu_task_lazy_lim= [KNL] 6142 Number of callbacks on a given CPU that will 6143 cancel laziness on that CPU. Use -1 to disable 6144 cancellation of laziness, but be advised that 6145 doing so increases the danger of OOM due to 6146 callback flooding. 6147 6148 rcupdate.rcu_task_stall_info= [KNL] 6149 Set initial timeout in jiffies for RCU task stall 6150 informational messages, which give some indication 6151 of the problem for those not patient enough to 6152 wait for ten minutes. Informational messages are 6153 only printed prior to the stall-warning message 6154 for a given grace period. Disable with a value 6155 less than or equal to zero. Defaults to ten 6156 seconds. A change in value does not take effect 6157 until the beginning of the next grace period. 6158 6159 rcupdate.rcu_task_stall_info_mult= [KNL] 6160 Multiplier for time interval between successive 6161 RCU task stall informational messages for a given 6162 RCU tasks grace period. This value is clamped 6163 to one through ten, inclusive. It defaults to 6164 the value three, so that the first informational 6165 message is printed 10 seconds into the grace 6166 period, the second at 40 seconds, the third at 6167 160 seconds, and then the stall warning at 600 6168 seconds would prevent a fourth at 640 seconds. 6169 6170 rcupdate.rcu_task_stall_timeout= [KNL] 6171 Set timeout in jiffies for RCU task stall 6172 warning messages. Disable with a value less 6173 than or equal to zero. Defaults to ten minutes. 6174 A change in value does not take effect until 6175 the beginning of the next grace period. 6176 6177 rcupdate.rcu_tasks_lazy_ms= [KNL] 6178 Set timeout in milliseconds RCU Tasks asynchronous 6179 callback batching for call_rcu_tasks(). 6180 A negative value will take the default. A value 6181 of zero will disable batching. Batching is 6182 always disabled for synchronize_rcu_tasks(). 6183 6184 rcupdate.rcu_tasks_trace_lazy_ms= [KNL] 6185 Set timeout in milliseconds RCU Tasks 6186 Trace asynchronous callback batching for 6187 call_rcu_tasks_trace(). A negative value 6188 will take the default. A value of zero will 6189 disable batching. Batching is always disabled 6190 for synchronize_rcu_tasks_trace(). 6191 6192 rcupdate.rcu_self_test= [KNL] 6193 Run the RCU early boot self tests 6194 6195 rdinit= [KNL] 6196 Format: <full_path> 6197 Run specified binary instead of /init from the ramdisk, 6198 used for early userspace startup. See initrd. 6199 6200 rdrand= [X86,EARLY] 6201 force - Override the decision by the kernel to hide the 6202 advertisement of RDRAND support (this affects 6203 certain AMD processors because of buggy BIOS 6204 support, specifically around the suspend/resume 6205 path). 6206 6207 rdt= [HW,X86,RDT] 6208 Turn on/off individual RDT features. List is: 6209 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6210 mba, smba, bmec, abmc. 6211 E.g. to turn on cmt and turn off mba use: 6212 rdt=cmt,!mba 6213 6214 reboot= [KNL] 6215 Format (x86 or x86_64): 6216 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6217 [[,]s[mp]#### \ 6218 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6219 [[,]f[orce] 6220 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6221 (prefix with 'panic_' to set mode for panic 6222 reboot only), 6223 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6224 reboot_force is either force or not specified, 6225 reboot_cpu is s[mp]#### with #### being the processor 6226 to be used for rebooting. 6227 6228 acpi 6229 Use the ACPI RESET_REG in the FADT. If ACPI is not 6230 configured or the ACPI reset does not work, the reboot 6231 path attempts the reset using the keyboard controller. 6232 6233 bios 6234 Use the CPU reboot vector for warm reset 6235 6236 cold 6237 Set the cold reboot flag 6238 6239 default 6240 There are some built-in platform specific "quirks" 6241 - you may see: "reboot: <name> series board detected. 6242 Selecting <type> for reboots." In the case where you 6243 think the quirk is in error (e.g. you have newer BIOS, 6244 or newer board) using this option will ignore the 6245 built-in quirk table, and use the generic default 6246 reboot actions. 6247 6248 efi 6249 Use efi reset_system runtime service. If EFI is not 6250 configured or the EFI reset does not work, the reboot 6251 path attempts the reset using the keyboard controller. 6252 6253 force 6254 Don't stop other CPUs on reboot. This can make reboot 6255 more reliable in some cases. 6256 6257 kbd 6258 Use the keyboard controller. cold reset (default) 6259 6260 pci 6261 Use a write to the PCI config space register 0xcf9 to 6262 trigger reboot. 6263 6264 triple 6265 Force a triple fault (init) 6266 6267 warm 6268 Don't set the cold reboot flag 6269 6270 Using warm reset will be much faster especially on big 6271 memory systems because the BIOS will not go through 6272 the memory check. Disadvantage is that not all 6273 hardware will be completely reinitialized on reboot so 6274 there may be boot problems on some systems. 6275 6276 6277 refscale.holdoff= [KNL] 6278 Set test-start holdoff period. The purpose of 6279 this parameter is to delay the start of the 6280 test until boot completes in order to avoid 6281 interference. 6282 6283 refscale.lookup_instances= [KNL] 6284 Number of data elements to use for the forms of 6285 SLAB_TYPESAFE_BY_RCU testing. A negative number 6286 is negated and multiplied by nr_cpu_ids, while 6287 zero specifies nr_cpu_ids. 6288 6289 refscale.loops= [KNL] 6290 Set the number of loops over the synchronization 6291 primitive under test. Increasing this number 6292 reduces noise due to loop start/end overhead, 6293 but the default has already reduced the per-pass 6294 noise to a handful of picoseconds on ca. 2020 6295 x86 laptops. 6296 6297 refscale.nreaders= [KNL] 6298 Set number of readers. The default value of -1 6299 selects N, where N is roughly 75% of the number 6300 of CPUs. A value of zero is an interesting choice. 6301 6302 refscale.nruns= [KNL] 6303 Set number of runs, each of which is dumped onto 6304 the console log. 6305 6306 refscale.readdelay= [KNL] 6307 Set the read-side critical-section duration, 6308 measured in microseconds. 6309 6310 refscale.scale_type= [KNL] 6311 Specify the read-protection implementation to test. 6312 6313 refscale.shutdown= [KNL] 6314 Shut down the system at the end of the performance 6315 test. This defaults to 1 (shut it down) when 6316 refscale is built into the kernel and to 0 (leave 6317 it running) when refscale is built as a module. 6318 6319 refscale.verbose= [KNL] 6320 Enable additional printk() statements. 6321 6322 refscale.verbose_batched= [KNL] 6323 Batch the additional printk() statements. If zero 6324 (the default) or negative, print everything. Otherwise, 6325 print every Nth verbose statement, where N is the value 6326 specified. 6327 6328 regulator_ignore_unused 6329 [REGULATOR] 6330 Prevents regulator framework from disabling regulators 6331 that are unused, due no driver claiming them. This may 6332 be useful for debug and development, but should not be 6333 needed on a platform with proper driver support. 6334 6335 relax_domain_level= 6336 [KNL, SMP] Set scheduler's default relax_domain_level. 6337 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6338 6339 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6340 Format: <base1>,<size1>[,<base2>,<size2>,...] 6341 Reserve I/O ports or memory so the kernel won't use 6342 them. If <base> is less than 0x10000, the region 6343 is assumed to be I/O ports; otherwise it is memory. 6344 6345 reserve_mem= [RAM] 6346 Format: nn[KMG]:<align>:<label> 6347 Reserve physical memory and label it with a name that 6348 other subsystems can use to access it. This is typically 6349 used for systems that do not wipe the RAM, and this command 6350 line will try to reserve the same physical memory on 6351 soft reboots. Note, it is not guaranteed to be the same 6352 location. For example, if anything about the system changes 6353 or if booting a different kernel. It can also fail if KASLR 6354 places the kernel at the location of where the RAM reservation 6355 was from a previous boot, the new reservation will be at a 6356 different location. 6357 Any subsystem using this feature must add a way to verify 6358 that the contents of the physical memory is from a previous 6359 boot, as there may be cases where the memory will not be 6360 located at the same location. 6361 6362 The format is size:align:label for example, to request 6363 12 megabytes of 4096 alignment for ramoops: 6364 6365 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6366 6367 reservetop= [X86-32,EARLY] 6368 Format: nn[KMG] 6369 Reserves a hole at the top of the kernel virtual 6370 address space. 6371 6372 reset_devices [KNL] Force drivers to reset the underlying device 6373 during initialization. 6374 6375 resume= [SWSUSP] 6376 Specify the partition device for software suspend 6377 Format: 6378 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6379 6380 resume_offset= [SWSUSP] 6381 Specify the offset from the beginning of the partition 6382 given by "resume=" at which the swap header is located, 6383 in <PAGE_SIZE> units (needed only for swap files). 6384 See Documentation/power/swsusp-and-swap-files.rst 6385 6386 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6387 read the resume files 6388 6389 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6390 Useful for devices that are detected asynchronously 6391 (e.g. USB and MMC devices). 6392 6393 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6394 be accessible via /sys/firmware/initrd. 6395 6396 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6397 Speculative Code Execution with Return Instructions) 6398 vulnerability. 6399 6400 AMD-based UNRET and IBPB mitigations alone do not stop 6401 sibling threads from influencing the predictions of other 6402 sibling threads. For that reason, STIBP is used on pro- 6403 cessors that support it, and mitigate SMT on processors 6404 that don't. 6405 6406 off - no mitigation 6407 auto - automatically select a migitation 6408 auto,nosmt - automatically select a mitigation, 6409 disabling SMT if necessary for 6410 the full mitigation (only on Zen1 6411 and older without STIBP). 6412 ibpb - On AMD, mitigate short speculation 6413 windows on basic block boundaries too. 6414 Safe, highest perf impact. It also 6415 enables STIBP if present. Not suitable 6416 on Intel. 6417 ibpb,nosmt - Like "ibpb" above but will disable SMT 6418 when STIBP is not available. This is 6419 the alternative for systems which do not 6420 have STIBP. 6421 unret - Force enable untrained return thunks, 6422 only effective on AMD f15h-f17h based 6423 systems. 6424 unret,nosmt - Like unret, but will disable SMT when STIBP 6425 is not available. This is the alternative for 6426 systems which do not have STIBP. 6427 6428 Selecting 'auto' will choose a mitigation method at run 6429 time according to the CPU. 6430 6431 Not specifying this option is equivalent to retbleed=auto. 6432 6433 rfkill.default_state= 6434 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6435 etc. communication is blocked by default. 6436 1 Unblocked. 6437 6438 rfkill.master_switch_mode= 6439 0 The "airplane mode" button does nothing. 6440 1 The "airplane mode" button toggles between everything 6441 blocked and the previous configuration. 6442 2 The "airplane mode" button toggles between everything 6443 blocked and everything unblocked. 6444 6445 ring3mwait=disable 6446 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6447 CPUs. 6448 6449 riscv_isa_fallback [RISCV,EARLY] 6450 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6451 falling back to detecting extension support by parsing 6452 "riscv,isa" property on devicetree systems when the 6453 replacement properties are not found. See the Kconfig 6454 entry for RISCV_ISA_FALLBACK. 6455 6456 ro [KNL] Mount root device read-only on boot 6457 6458 rodata= [KNL,EARLY] 6459 on Mark read-only kernel memory as read-only (default). 6460 off Leave read-only kernel memory writable for debugging. 6461 noalias Mark read-only kernel memory as read-only but retain 6462 writable aliases in the direct map for regions outside 6463 of the kernel image. [arm64] 6464 6465 rockchip.usb_uart 6466 [EARLY] 6467 Enable the uart passthrough on the designated usb port 6468 on Rockchip SoCs. When active, the signals of the 6469 debug-uart get routed to the D+ and D- pins of the usb 6470 port and the regular usb controller gets disabled. 6471 6472 root= [KNL] Root filesystem 6473 Usually this is a block device specifier of some kind, 6474 see the early_lookup_bdev comment in 6475 block/early-lookup.c for details. 6476 Alternatively this can be "ram" for the legacy initial 6477 ramdisk, "nfs" and "cifs" for root on a network file 6478 system, or "mtd" and "ubi" for mounting from raw flash. 6479 6480 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6481 mount the root filesystem 6482 6483 rootflags= [KNL] Set root filesystem mount option string 6484 6485 initramfs_options= [KNL] 6486 Specify mount options for for the initramfs mount. 6487 6488 rootfstype= [KNL] Set root filesystem type 6489 6490 rootwait [KNL] Wait (indefinitely) for root device to show up. 6491 Useful for devices that are detected asynchronously 6492 (e.g. USB and MMC devices). 6493 6494 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6495 to show up before attempting to mount the root 6496 filesystem. 6497 6498 rproc_mem=nn[KMG][@address] 6499 [KNL,ARM,CMA] Remoteproc physical memory block. 6500 Memory area to be used by remote processor image, 6501 managed by CMA. 6502 6503 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6504 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6505 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6506 Format: <bool> 6507 6508 rw [KNL] Mount root device read-write on boot 6509 6510 S [KNL] Run init in single mode 6511 6512 s390_iommu= [HW,S390] 6513 Set s390 IOTLB flushing mode 6514 strict 6515 With strict flushing every unmap operation will result 6516 in an IOTLB flush. Default is lazy flushing before 6517 reuse, which is faster. Deprecated, equivalent to 6518 iommu.strict=1. 6519 6520 s390_iommu_aperture= [KNL,S390] 6521 Specifies the size of the per device DMA address space 6522 accessible through the DMA and IOMMU APIs as a decimal 6523 factor of the size of main memory. 6524 The default is 1 meaning that one can concurrently use 6525 as many DMA addresses as physical memory is installed, 6526 if supported by hardware, and thus map all of memory 6527 once. With a value of 2 one can map all of memory twice 6528 and so on. As a special case a factor of 0 imposes no 6529 restrictions other than those given by hardware at the 6530 cost of significant additional memory use for tables. 6531 6532 sa1100ir [NET] 6533 See drivers/net/irda/sa1100_ir.c. 6534 6535 sched_proxy_exec= [KNL] 6536 Enables or disables "proxy execution" style 6537 solution to mutex-based priority inversion. 6538 Format: <bool> 6539 6540 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6541 6542 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6543 Allowed values are enable and disable. This feature 6544 incurs a small amount of overhead in the scheduler 6545 but is useful for debugging and performance tuning. 6546 6547 sched_thermal_decay_shift= 6548 [Deprecated] 6549 [KNL, SMP] Set a decay shift for scheduler thermal 6550 pressure signal. Thermal pressure signal follows the 6551 default decay period of other scheduler pelt 6552 signals(usually 32 ms but configurable). Setting 6553 sched_thermal_decay_shift will left shift the decay 6554 period for the thermal pressure signal by the shift 6555 value. 6556 i.e. with the default pelt decay period of 32 ms 6557 sched_thermal_decay_shift thermal pressure decay pr 6558 1 64 ms 6559 2 128 ms 6560 and so on. 6561 Format: integer between 0 and 10 6562 Default is 0. 6563 6564 scftorture.holdoff= [KNL] 6565 Number of seconds to hold off before starting 6566 test. Defaults to zero for module insertion and 6567 to 10 seconds for built-in smp_call_function() 6568 tests. 6569 6570 scftorture.longwait= [KNL] 6571 Request ridiculously long waits randomly selected 6572 up to the chosen limit in seconds. Zero (the 6573 default) disables this feature. Please note 6574 that requesting even small non-zero numbers of 6575 seconds can result in RCU CPU stall warnings, 6576 softlockup complaints, and so on. 6577 6578 scftorture.nthreads= [KNL] 6579 Number of kthreads to spawn to invoke the 6580 smp_call_function() family of functions. 6581 The default of -1 specifies a number of kthreads 6582 equal to the number of CPUs. 6583 6584 scftorture.onoff_holdoff= [KNL] 6585 Number seconds to wait after the start of the 6586 test before initiating CPU-hotplug operations. 6587 6588 scftorture.onoff_interval= [KNL] 6589 Number seconds to wait between successive 6590 CPU-hotplug operations. Specifying zero (which 6591 is the default) disables CPU-hotplug operations. 6592 6593 scftorture.shutdown_secs= [KNL] 6594 The number of seconds following the start of the 6595 test after which to shut down the system. The 6596 default of zero avoids shutting down the system. 6597 Non-zero values are useful for automated tests. 6598 6599 scftorture.stat_interval= [KNL] 6600 The number of seconds between outputting the 6601 current test statistics to the console. A value 6602 of zero disables statistics output. 6603 6604 scftorture.stutter_cpus= [KNL] 6605 The number of jiffies to wait between each change 6606 to the set of CPUs under test. 6607 6608 scftorture.use_cpus_read_lock= [KNL] 6609 Use use_cpus_read_lock() instead of the default 6610 preempt_disable() to disable CPU hotplug 6611 while invoking one of the smp_call_function*() 6612 functions. 6613 6614 scftorture.verbose= [KNL] 6615 Enable additional printk() statements. 6616 6617 scftorture.weight_single= [KNL] 6618 The probability weighting to use for the 6619 smp_call_function_single() function with a zero 6620 "wait" parameter. A value of -1 selects the 6621 default if all other weights are -1. However, 6622 if at least one weight has some other value, a 6623 value of -1 will instead select a weight of zero. 6624 6625 scftorture.weight_single_wait= [KNL] 6626 The probability weighting to use for the 6627 smp_call_function_single() function with a 6628 non-zero "wait" parameter. See weight_single. 6629 6630 scftorture.weight_many= [KNL] 6631 The probability weighting to use for the 6632 smp_call_function_many() function with a zero 6633 "wait" parameter. See weight_single. 6634 Note well that setting a high probability for 6635 this weighting can place serious IPI load 6636 on the system. 6637 6638 scftorture.weight_many_wait= [KNL] 6639 The probability weighting to use for the 6640 smp_call_function_many() function with a 6641 non-zero "wait" parameter. See weight_single 6642 and weight_many. 6643 6644 scftorture.weight_all= [KNL] 6645 The probability weighting to use for the 6646 smp_call_function_all() function with a zero 6647 "wait" parameter. See weight_single and 6648 weight_many. 6649 6650 scftorture.weight_all_wait= [KNL] 6651 The probability weighting to use for the 6652 smp_call_function_all() function with a 6653 non-zero "wait" parameter. See weight_single 6654 and weight_many. 6655 6656 sdw_mclk_divider=[SDW] 6657 Specify the MCLK divider for Intel SoundWire buses in 6658 case the BIOS does not provide the clock rate properly. 6659 6660 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6661 xtime_lock contention on larger systems, and/or RCU lock 6662 contention on all systems with CONFIG_MAXSMP set. 6663 Format: { "0" | "1" } 6664 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6665 1 -- enable. 6666 Note: increases power consumption, thus should only be 6667 enabled if running jitter sensitive (HPC/RT) workloads. 6668 6669 security= [SECURITY] Choose a legacy "major" security module to 6670 enable at boot. This has been deprecated by the 6671 "lsm=" parameter. 6672 6673 selinux= [SELINUX] Disable or enable SELinux at boot time. 6674 Format: { "0" | "1" } 6675 See security/selinux/Kconfig help text. 6676 0 -- disable. 6677 1 -- enable. 6678 Default value is 1. 6679 6680 serialnumber [BUGS=X86-32] 6681 6682 sev=option[,option...] [X86-64] 6683 6684 debug 6685 Enable debug messages. 6686 6687 nosnp 6688 Do not enable SEV-SNP (applies to host/hypervisor 6689 only). Setting 'nosnp' avoids the RMP check overhead 6690 in memory accesses when users do not want to run 6691 SEV-SNP guests. 6692 6693 shapers= [NET] 6694 Maximal number of shapers. 6695 6696 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6697 Limit apic dumping. The parameter defines the maximal 6698 number of local apics being dumped. Also it is possible 6699 to set it to "all" by meaning -- no limit here. 6700 Format: { 1 (default) | 2 | ... | all }. 6701 The parameter valid if only apic=debug or 6702 apic=verbose is specified. 6703 Example: apic=debug show_lapic=all 6704 6705 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6706 Enabling slab_debug allows one to determine the 6707 culprit if slab objects become corrupted. Enabling 6708 slab_debug can create guard zones around objects and 6709 may poison objects when not in use. Also tracks the 6710 last alloc / free. For more information see 6711 Documentation/admin-guide/mm/slab.rst. 6712 (slub_debug legacy name also accepted for now) 6713 6714 Using this option implies the "no_hash_pointers" 6715 option which can be undone by adding the 6716 "hash_pointers=always" option. 6717 6718 slab_max_order= [MM] 6719 Determines the maximum allowed order for slabs. 6720 A high setting may cause OOMs due to memory 6721 fragmentation. For more information see 6722 Documentation/admin-guide/mm/slab.rst. 6723 (slub_max_order legacy name also accepted for now) 6724 6725 slab_merge [MM] 6726 Enable merging of slabs with similar size when the 6727 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6728 (slub_merge legacy name also accepted for now) 6729 6730 slab_min_objects= [MM] 6731 The minimum number of objects per slab. SLUB will 6732 increase the slab order up to slab_max_order to 6733 generate a sufficiently large slab able to contain 6734 the number of objects indicated. The higher the number 6735 of objects the smaller the overhead of tracking slabs 6736 and the less frequently locks need to be acquired. 6737 For more information see 6738 Documentation/admin-guide/mm/slab.rst. 6739 (slub_min_objects legacy name also accepted for now) 6740 6741 slab_min_order= [MM] 6742 Determines the minimum page order for slabs. Must be 6743 lower or equal to slab_max_order. For more information see 6744 Documentation/admin-guide/mm/slab.rst. 6745 (slub_min_order legacy name also accepted for now) 6746 6747 slab_nomerge [MM] 6748 Disable merging of slabs with similar size. May be 6749 necessary if there is some reason to distinguish 6750 allocs to different slabs, especially in hardened 6751 environments where the risk of heap overflows and 6752 layout control by attackers can usually be 6753 frustrated by disabling merging. This will reduce 6754 most of the exposure of a heap attack to a single 6755 cache (risks via metadata attacks are mostly 6756 unchanged). Debug options disable merging on their 6757 own. 6758 For more information see 6759 Documentation/admin-guide/mm/slab.rst. 6760 (slub_nomerge legacy name also accepted for now) 6761 6762 slab_strict_numa [MM] 6763 Support memory policies on a per object level 6764 in the slab allocator. The default is for memory 6765 policies to be applied at the folio level when 6766 a new folio is needed or a partial folio is 6767 retrieved from the lists. Increases overhead 6768 in the slab fastpaths but gains more accurate 6769 NUMA kernel object placement which helps with slow 6770 interconnects in NUMA systems. 6771 6772 slram= [HW,MTD] 6773 6774 smart2= [HW] 6775 Format: <io1>[,<io2>[,...,<io8>]] 6776 6777 smp.csd_lock_timeout= [KNL] 6778 Specify the period of time in milliseconds 6779 that smp_call_function() and friends will wait 6780 for a CPU to release the CSD lock. This is 6781 useful when diagnosing bugs involving CPUs 6782 disabling interrupts for extended periods 6783 of time. Defaults to 5,000 milliseconds, and 6784 setting a value of zero disables this feature. 6785 This feature may be more efficiently disabled 6786 using the csdlock_debug- kernel parameter. 6787 6788 smp.panic_on_ipistall= [KNL] 6789 If a csd_lock_timeout extends for more than 6790 the specified number of milliseconds, panic the 6791 system. By default, let CSD-lock acquisition 6792 take as long as they take. Specifying 300,000 6793 for this value provides a 5-minute timeout. 6794 6795 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 6796 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 6797 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 6798 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 6799 smsc-ircc2.ircc_irq= [HW] IRQ line 6800 smsc-ircc2.ircc_dma= [HW] DMA channel 6801 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 6802 0: Toshiba Satellite 1800 (GP data pin select) 6803 1: Fast pin select (default) 6804 2: ATC IRMode 6805 6806 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 6807 (logical CPUs) to use per physical CPU on systems 6808 capable of symmetric multithreading (SMT). Will 6809 be capped to the actual hardware limit. 6810 Format: <integer> 6811 Default: -1 (no limit) 6812 6813 softlockup_panic= 6814 [KNL] Should the soft-lockup detector generate panics. 6815 Format: 0 | 1 6816 6817 A value of 1 instructs the soft-lockup detector 6818 to panic the machine when a soft-lockup occurs. It is 6819 also controlled by the kernel.softlockup_panic sysctl 6820 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 6821 respective build-time switch to that functionality. 6822 6823 softlockup_all_cpu_backtrace= 6824 [KNL] Should the soft-lockup detector generate 6825 backtraces on all cpus. 6826 Format: 0 | 1 6827 6828 sonypi.*= [HW] Sony Programmable I/O Control Device driver 6829 See Documentation/admin-guide/laptops/sonypi.rst 6830 6831 spectre_bhi= [X86] Control mitigation of Branch History Injection 6832 (BHI) vulnerability. This setting affects the 6833 deployment of the HW BHI control and the SW BHB 6834 clearing sequence. 6835 6836 on - (default) Enable the HW or SW mitigation as 6837 needed. This protects the kernel from 6838 both syscalls and VMs. 6839 vmexit - On systems which don't have the HW mitigation 6840 available, enable the SW mitigation on vmexit 6841 ONLY. On such systems, the host kernel is 6842 protected from VM-originated BHI attacks, but 6843 may still be vulnerable to syscall attacks. 6844 off - Disable the mitigation. 6845 6846 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 6847 (indirect branch speculation) vulnerability. 6848 The default operation protects the kernel from 6849 user space attacks. 6850 6851 on - unconditionally enable, implies 6852 spectre_v2_user=on 6853 off - unconditionally disable, implies 6854 spectre_v2_user=off 6855 auto - kernel detects whether your CPU model is 6856 vulnerable 6857 6858 Selecting 'on' will, and 'auto' may, choose a 6859 mitigation method at run time according to the 6860 CPU, the available microcode, the setting of the 6861 CONFIG_MITIGATION_RETPOLINE configuration option, 6862 and the compiler with which the kernel was built. 6863 6864 Selecting 'on' will also enable the mitigation 6865 against user space to user space task attacks. 6866 Selecting specific mitigation does not force enable 6867 user mitigations. 6868 6869 Selecting 'off' will disable both the kernel and 6870 the user space protections. 6871 6872 Specific mitigations can also be selected manually: 6873 6874 retpoline - replace indirect branches 6875 retpoline,generic - Retpolines 6876 retpoline,lfence - LFENCE; indirect branch 6877 retpoline,amd - alias for retpoline,lfence 6878 eibrs - Enhanced/Auto IBRS 6879 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 6880 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 6881 ibrs - use IBRS to protect kernel 6882 6883 Not specifying this option is equivalent to 6884 spectre_v2=auto. 6885 6886 spectre_v2_user= 6887 [X86] Control mitigation of Spectre variant 2 6888 (indirect branch speculation) vulnerability between 6889 user space tasks 6890 6891 on - Unconditionally enable mitigations. Is 6892 enforced by spectre_v2=on 6893 6894 off - Unconditionally disable mitigations. Is 6895 enforced by spectre_v2=off 6896 6897 prctl - Indirect branch speculation is enabled, 6898 but mitigation can be enabled via prctl 6899 per thread. The mitigation control state 6900 is inherited on fork. 6901 6902 prctl,ibpb 6903 - Like "prctl" above, but only STIBP is 6904 controlled per thread. IBPB is issued 6905 always when switching between different user 6906 space processes. 6907 6908 seccomp 6909 - Same as "prctl" above, but all seccomp 6910 threads will enable the mitigation unless 6911 they explicitly opt out. 6912 6913 seccomp,ibpb 6914 - Like "seccomp" above, but only STIBP is 6915 controlled per thread. IBPB is issued 6916 always when switching between different 6917 user space processes. 6918 6919 auto - Kernel selects the mitigation depending on 6920 the available CPU features and vulnerability. 6921 6922 Default mitigation: "prctl" 6923 6924 Not specifying this option is equivalent to 6925 spectre_v2_user=auto. 6926 6927 spec_rstack_overflow= 6928 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 6929 6930 off - Disable mitigation 6931 microcode - Enable microcode mitigation only 6932 safe-ret - Enable sw-only safe RET mitigation (default) 6933 ibpb - Enable mitigation by issuing IBPB on 6934 kernel entry 6935 ibpb-vmexit - Issue IBPB only on VMEXIT 6936 (cloud-specific mitigation) 6937 6938 spec_store_bypass_disable= 6939 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 6940 (Speculative Store Bypass vulnerability) 6941 6942 Certain CPUs are vulnerable to an exploit against a 6943 a common industry wide performance optimization known 6944 as "Speculative Store Bypass" in which recent stores 6945 to the same memory location may not be observed by 6946 later loads during speculative execution. The idea 6947 is that such stores are unlikely and that they can 6948 be detected prior to instruction retirement at the 6949 end of a particular speculation execution window. 6950 6951 In vulnerable processors, the speculatively forwarded 6952 store can be used in a cache side channel attack, for 6953 example to read memory to which the attacker does not 6954 directly have access (e.g. inside sandboxed code). 6955 6956 This parameter controls whether the Speculative Store 6957 Bypass optimization is used. 6958 6959 On x86 the options are: 6960 6961 on - Unconditionally disable Speculative Store Bypass 6962 off - Unconditionally enable Speculative Store Bypass 6963 auto - Kernel detects whether the CPU model contains an 6964 implementation of Speculative Store Bypass and 6965 picks the most appropriate mitigation. If the 6966 CPU is not vulnerable, "off" is selected. If the 6967 CPU is vulnerable the default mitigation is 6968 architecture and Kconfig dependent. See below. 6969 prctl - Control Speculative Store Bypass per thread 6970 via prctl. Speculative Store Bypass is enabled 6971 for a process by default. The state of the control 6972 is inherited on fork. 6973 seccomp - Same as "prctl" above, but all seccomp threads 6974 will disable SSB unless they explicitly opt out. 6975 6976 Default mitigations: 6977 X86: "prctl" 6978 6979 On powerpc the options are: 6980 6981 on,auto - On Power8 and Power9 insert a store-forwarding 6982 barrier on kernel entry and exit. On Power7 6983 perform a software flush on kernel entry and 6984 exit. 6985 off - No action. 6986 6987 Not specifying this option is equivalent to 6988 spec_store_bypass_disable=auto. 6989 6990 split_lock_detect= 6991 [X86] Enable split lock detection or bus lock detection 6992 6993 When enabled (and if hardware support is present), atomic 6994 instructions that access data across cache line 6995 boundaries will result in an alignment check exception 6996 for split lock detection or a debug exception for 6997 bus lock detection. 6998 6999 off - not enabled 7000 7001 warn - the kernel will emit rate-limited warnings 7002 about applications triggering the #AC 7003 exception or the #DB exception. This mode is 7004 the default on CPUs that support split lock 7005 detection or bus lock detection. Default 7006 behavior is by #AC if both features are 7007 enabled in hardware. 7008 7009 fatal - the kernel will send SIGBUS to applications 7010 that trigger the #AC exception or the #DB 7011 exception. Default behavior is by #AC if 7012 both features are enabled in hardware. 7013 7014 ratelimit:N - 7015 Set system wide rate limit to N bus locks 7016 per second for bus lock detection. 7017 0 < N <= 1000. 7018 7019 N/A for split lock detection. 7020 7021 7022 If an #AC exception is hit in the kernel or in 7023 firmware (i.e. not while executing in user mode) 7024 the kernel will oops in either "warn" or "fatal" 7025 mode. 7026 7027 #DB exception for bus lock is triggered only when 7028 CPL > 0. 7029 7030 srbds= [X86,INTEL,EARLY] 7031 Control the Special Register Buffer Data Sampling 7032 (SRBDS) mitigation. 7033 7034 Certain CPUs are vulnerable to an MDS-like 7035 exploit which can leak bits from the random 7036 number generator. 7037 7038 By default, this issue is mitigated by 7039 microcode. However, the microcode fix can cause 7040 the RDRAND and RDSEED instructions to become 7041 much slower. Among other effects, this will 7042 result in reduced throughput from /dev/urandom. 7043 7044 The microcode mitigation can be disabled with 7045 the following option: 7046 7047 off: Disable mitigation and remove 7048 performance impact to RDRAND and RDSEED 7049 7050 srcutree.big_cpu_lim [KNL] 7051 Specifies the number of CPUs constituting a 7052 large system, such that srcu_struct structures 7053 should immediately allocate an srcu_node array. 7054 This kernel-boot parameter defaults to 128, 7055 but takes effect only when the low-order four 7056 bits of srcutree.convert_to_big is equal to 3 7057 (decide at boot). 7058 7059 srcutree.convert_to_big [KNL] 7060 Specifies under what conditions an SRCU tree 7061 srcu_struct structure will be converted to big 7062 form, that is, with an rcu_node tree: 7063 7064 0: Never. 7065 1: At init_srcu_struct() time. 7066 2: When rcutorture decides to. 7067 3: Decide at boot time (default). 7068 0x1X: Above plus if high contention. 7069 7070 Either way, the srcu_node tree will be sized based 7071 on the actual runtime number of CPUs (nr_cpu_ids) 7072 instead of the compile-time CONFIG_NR_CPUS. 7073 7074 srcutree.counter_wrap_check [KNL] 7075 Specifies how frequently to check for 7076 grace-period sequence counter wrap for the 7077 srcu_data structure's ->srcu_gp_seq_needed field. 7078 The greater the number of bits set in this kernel 7079 parameter, the less frequently counter wrap will 7080 be checked for. Note that the bottom two bits 7081 are ignored. 7082 7083 srcutree.exp_holdoff [KNL] 7084 Specifies how many nanoseconds must elapse 7085 since the end of the last SRCU grace period for 7086 a given srcu_struct until the next normal SRCU 7087 grace period will be considered for automatic 7088 expediting. Set to zero to disable automatic 7089 expediting. 7090 7091 srcutree.srcu_max_nodelay [KNL] 7092 Specifies the number of no-delay instances 7093 per jiffy for which the SRCU grace period 7094 worker thread will be rescheduled with zero 7095 delay. Beyond this limit, worker thread will 7096 be rescheduled with a sleep delay of one jiffy. 7097 7098 srcutree.srcu_max_nodelay_phase [KNL] 7099 Specifies the per-grace-period phase, number of 7100 non-sleeping polls of readers. Beyond this limit, 7101 grace period worker thread will be rescheduled 7102 with a sleep delay of one jiffy, between each 7103 rescan of the readers, for a grace period phase. 7104 7105 srcutree.srcu_retry_check_delay [KNL] 7106 Specifies number of microseconds of non-sleeping 7107 delay between each non-sleeping poll of readers. 7108 7109 srcutree.small_contention_lim [KNL] 7110 Specifies the number of update-side contention 7111 events per jiffy will be tolerated before 7112 initiating a conversion of an srcu_struct 7113 structure to big form. Note that the value of 7114 srcutree.convert_to_big must have the 0x10 bit 7115 set for contention-based conversions to occur. 7116 7117 ssbd= [ARM64,HW,EARLY] 7118 Speculative Store Bypass Disable control 7119 7120 On CPUs that are vulnerable to the Speculative 7121 Store Bypass vulnerability and offer a 7122 firmware based mitigation, this parameter 7123 indicates how the mitigation should be used: 7124 7125 force-on: Unconditionally enable mitigation for 7126 for both kernel and userspace 7127 force-off: Unconditionally disable mitigation for 7128 for both kernel and userspace 7129 kernel: Always enable mitigation in the 7130 kernel, and offer a prctl interface 7131 to allow userspace to register its 7132 interest in being mitigated too. 7133 7134 stack_guard_gap= [MM] 7135 override the default stack gap protection. The value 7136 is in page units and it defines how many pages prior 7137 to (for stacks growing down) resp. after (for stacks 7138 growing up) the main stack are reserved for no other 7139 mapping. Default value is 256 pages. 7140 7141 stack_depot_disable= [KNL,EARLY] 7142 Setting this to true through kernel command line will 7143 disable the stack depot thereby saving the static memory 7144 consumed by the stack hash table. By default this is set 7145 to false. 7146 7147 stack_depot_max_pools= [KNL,EARLY] 7148 Specify the maximum number of pools to use for storing 7149 stack traces. Pools are allocated on-demand up to this 7150 limit. Default value is 8191 pools. 7151 7152 stacktrace [FTRACE] 7153 Enabled the stack tracer on boot up. 7154 7155 stacktrace_filter=[function-list] 7156 [FTRACE] Limit the functions that the stack tracer 7157 will trace at boot up. function-list is a comma-separated 7158 list of functions. This list can be changed at run 7159 time by the stack_trace_filter file in the debugfs 7160 tracing directory. Note, this enables stack tracing 7161 and the stacktrace above is not needed. 7162 7163 sti= [PARISC,HW] 7164 Format: <num> 7165 Set the STI (builtin display/keyboard on the HP-PARISC 7166 machines) console (graphic card) which should be used 7167 as the initial boot-console. 7168 See also comment in drivers/video/console/sticore.c. 7169 7170 sti_font= [HW] 7171 See comment in drivers/video/console/sticore.c. 7172 7173 stifb= [HW] 7174 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7175 7176 strict_sas_size= 7177 [X86] 7178 Format: <bool> 7179 Enable or disable strict sigaltstack size checks 7180 against the required signal frame size which 7181 depends on the supported FPU features. This can 7182 be used to filter out binaries which have 7183 not yet been made aware of AT_MINSIGSTKSZ. 7184 7185 stress_hpt [PPC,EARLY] 7186 Limits the number of kernel HPT entries in the hash 7187 page table to increase the rate of hash page table 7188 faults on kernel addresses. 7189 7190 stress_slb [PPC,EARLY] 7191 Limits the number of kernel SLB entries, and flushes 7192 them frequently to increase the rate of SLB faults 7193 on kernel addresses. 7194 7195 sunrpc.min_resvport= 7196 sunrpc.max_resvport= 7197 [NFS,SUNRPC] 7198 SunRPC servers often require that client requests 7199 originate from a privileged port (i.e. a port in the 7200 range 0 < portnr < 1024). 7201 An administrator who wishes to reserve some of these 7202 ports for other uses may adjust the range that the 7203 kernel's sunrpc client considers to be privileged 7204 using these two parameters to set the minimum and 7205 maximum port values. 7206 7207 sunrpc.svc_rpc_per_connection_limit= 7208 [NFS,SUNRPC] 7209 Limit the number of requests that the server will 7210 process in parallel from a single connection. 7211 The default value is 0 (no limit). 7212 7213 sunrpc.pool_mode= 7214 [NFS] 7215 Control how the NFS server code allocates CPUs to 7216 service thread pools. Depending on how many NICs 7217 you have and where their interrupts are bound, this 7218 option will affect which CPUs will do NFS serving. 7219 Note: this parameter cannot be changed while the 7220 NFS server is running. 7221 7222 auto the server chooses an appropriate mode 7223 automatically using heuristics 7224 global a single global pool contains all CPUs 7225 percpu one pool for each CPU 7226 pernode one pool for each NUMA node (equivalent 7227 to global on non-NUMA machines) 7228 7229 sunrpc.tcp_slot_table_entries= 7230 sunrpc.udp_slot_table_entries= 7231 [NFS,SUNRPC] 7232 Sets the upper limit on the number of simultaneous 7233 RPC calls that can be sent from the client to a 7234 server. Increasing these values may allow you to 7235 improve throughput, but will also increase the 7236 amount of memory reserved for use by the client. 7237 7238 suspend.pm_test_delay= 7239 [SUSPEND] 7240 Sets the number of seconds to remain in a suspend test 7241 mode before resuming the system (see 7242 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7243 is set. Default value is 5. 7244 7245 svm= [PPC] 7246 Format: { on | off | y | n | 1 | 0 } 7247 This parameter controls use of the Protected 7248 Execution Facility on pSeries. 7249 7250 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7251 Format: { <int> [,<int>] | force | noforce } 7252 <int> -- Number of I/O TLB slabs 7253 <int> -- Second integer after comma. Number of swiotlb 7254 areas with their own lock. Will be rounded up 7255 to a power of 2. 7256 force -- force using of bounce buffers even if they 7257 wouldn't be automatically used by the kernel 7258 noforce -- Never use bounce buffers (for debugging) 7259 7260 switches= [HW,M68k,EARLY] 7261 7262 sysctl.*= [KNL] 7263 Set a sysctl parameter, right before loading the init 7264 process, as if the value was written to the respective 7265 /proc/sys/... file. Both '.' and '/' are recognized as 7266 separators. Unrecognized parameters and invalid values 7267 are reported in the kernel log. Sysctls registered 7268 later by a loaded module cannot be set this way. 7269 Example: sysctl.vm.swappiness=40 7270 7271 sysrq_always_enabled 7272 [KNL] 7273 Ignore sysrq setting - this boot parameter will 7274 neutralize any effect of /proc/sys/kernel/sysrq. 7275 Useful for debugging. 7276 7277 tcpmhash_entries= [KNL,NET] 7278 Set the number of tcp_metrics_hash slots. 7279 Default value is 8192 or 16384 depending on total 7280 ram pages. This is used to specify the TCP metrics 7281 cache size. See Documentation/networking/ip-sysctl.rst 7282 "tcp_no_metrics_save" section for more details. 7283 7284 tdfx= [HW,DRM] 7285 7286 test_suspend= [SUSPEND] 7287 Format: { "mem" | "standby" | "freeze" }[,N] 7288 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7289 standby suspend) or "freeze" (for suspend type freeze) 7290 as the system sleep state during system startup with 7291 the optional capability to repeat N number of times. 7292 The system is woken from this state using a 7293 wakeup-capable RTC alarm. 7294 7295 thash_entries= [KNL,NET] 7296 Set number of hash buckets for TCP connection 7297 7298 thermal.act= [HW,ACPI] 7299 -1: disable all active trip points in all thermal zones 7300 <degrees C>: override all lowest active trip points 7301 7302 thermal.crt= [HW,ACPI] 7303 -1: disable all critical trip points in all thermal zones 7304 <degrees C>: override all critical trip points 7305 7306 thermal.off= [HW,ACPI] 7307 1: disable ACPI thermal control 7308 7309 thermal.psv= [HW,ACPI] 7310 -1: disable all passive trip points 7311 <degrees C>: override all passive trip points to this 7312 value 7313 7314 thermal.tzp= [HW,ACPI] 7315 Specify global default ACPI thermal zone polling rate 7316 <deci-seconds>: poll all this frequency 7317 0: no polling (default) 7318 7319 thp_anon= [KNL] 7320 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7321 state is one of "always", "madvise", "never" or "inherit". 7322 Control the default behavior of the system with respect 7323 to anonymous transparent hugepages. 7324 Can be used multiple times for multiple anon THP sizes. 7325 See Documentation/admin-guide/mm/transhuge.rst for more 7326 details. 7327 7328 threadirqs [KNL,EARLY] 7329 Force threading of all interrupt handlers except those 7330 marked explicitly IRQF_NO_THREAD. 7331 7332 thp_shmem= [KNL] 7333 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7334 Control the default policy of each hugepage size for the 7335 internal shmem mount. <policy> is one of policies available 7336 for the shmem mount ("always", "inherit", "never", "within_size", 7337 and "advise"). 7338 It can be used multiple times for multiple shmem THP sizes. 7339 See Documentation/admin-guide/mm/transhuge.rst for more 7340 details. 7341 7342 topology= [S390,EARLY] 7343 Format: {off | on} 7344 Specify if the kernel should make use of the cpu 7345 topology information if the hardware supports this. 7346 The scheduler will make use of this information and 7347 e.g. base its process migration decisions on it. 7348 Default is on. 7349 7350 torture.disable_onoff_at_boot= [KNL] 7351 Prevent the CPU-hotplug component of torturing 7352 until after init has spawned. 7353 7354 torture.ftrace_dump_at_shutdown= [KNL] 7355 Dump the ftrace buffer at torture-test shutdown, 7356 even if there were no errors. This can be a 7357 very costly operation when many torture tests 7358 are running concurrently, especially on systems 7359 with rotating-rust storage. 7360 7361 torture.verbose_sleep_frequency= [KNL] 7362 Specifies how many verbose printk()s should be 7363 emitted between each sleep. The default of zero 7364 disables verbose-printk() sleeping. 7365 7366 torture.verbose_sleep_duration= [KNL] 7367 Duration of each verbose-printk() sleep in jiffies. 7368 7369 tpm.disable_pcr_integrity= [HW,TPM] 7370 Do not protect PCR registers from unintended physical 7371 access, or interposers in the bus by the means of 7372 having an integrity protected session wrapped around 7373 TPM2_PCR_Extend command. Consider this in a situation 7374 where TPM is heavily utilized by IMA, thus protection 7375 causing a major performance hit, and the space where 7376 machines are deployed is by other means guarded. 7377 7378 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7379 Maximum time in milliseconds to retry sending a message 7380 to the TPM service before giving up. This parameter controls 7381 how long the system will continue retrying when the TPM 7382 service is busy. 7383 Format: <unsigned int> 7384 Default: 2000 (2 seconds) 7385 7386 tpm_suspend_pcr=[HW,TPM] 7387 Format: integer pcr id 7388 Specify that at suspend time, the tpm driver 7389 should extend the specified pcr with zeros, 7390 as a workaround for some chips which fail to 7391 flush the last written pcr on TPM_SaveState. 7392 This will guarantee that all the other pcrs 7393 are saved. 7394 7395 tpm_tis.interrupts= [HW,TPM] 7396 Enable interrupts for the MMIO based physical layer 7397 for the FIFO interface. By default it is set to false 7398 (0). For more information about TPM hardware interfaces 7399 defined by Trusted Computing Group (TCG) see 7400 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7401 7402 tp_printk [FTRACE] 7403 Have the tracepoints sent to printk as well as the 7404 tracing ring buffer. This is useful for early boot up 7405 where the system hangs or reboots and does not give the 7406 option for reading the tracing buffer or performing a 7407 ftrace_dump_on_oops. 7408 7409 To turn off having tracepoints sent to printk, 7410 echo 0 > /proc/sys/kernel/tracepoint_printk 7411 Note, echoing 1 into this file without the 7412 tp_printk kernel cmdline option has no effect. 7413 7414 The tp_printk_stop_on_boot (see below) can also be used 7415 to stop the printing of events to console at 7416 late_initcall_sync. 7417 7418 ** CAUTION ** 7419 7420 Having tracepoints sent to printk() and activating high 7421 frequency tracepoints such as irq or sched, can cause 7422 the system to live lock. 7423 7424 tp_printk_stop_on_boot [FTRACE] 7425 When tp_printk (above) is set, it can cause a lot of noise 7426 on the console. It may be useful to only include the 7427 printing of events during boot up, as user space may 7428 make the system inoperable. 7429 7430 This command line option will stop the printing of events 7431 to console at the late_initcall_sync() time frame. 7432 7433 trace_buf_size=nn[KMG] 7434 [FTRACE] will set tracing buffer size on each cpu. 7435 7436 trace_clock= [FTRACE] Set the clock used for tracing events 7437 at boot up. 7438 local - Use the per CPU time stamp counter 7439 (converted into nanoseconds). Fast, but 7440 depending on the architecture, may not be 7441 in sync between CPUs. 7442 global - Event time stamps are synchronized across 7443 CPUs. May be slower than the local clock, 7444 but better for some race conditions. 7445 counter - Simple counting of events (1, 2, ..) 7446 note, some counts may be skipped due to the 7447 infrastructure grabbing the clock more than 7448 once per event. 7449 uptime - Use jiffies as the time stamp. 7450 perf - Use the same clock that perf uses. 7451 mono - Use ktime_get_mono_fast_ns() for time stamps. 7452 mono_raw - Use ktime_get_raw_fast_ns() for time 7453 stamps. 7454 boot - Use ktime_get_boot_fast_ns() for time stamps. 7455 Architectures may add more clocks. See 7456 Documentation/trace/ftrace.rst for more details. 7457 7458 trace_event=[event-list] 7459 [FTRACE] Set and start specified trace events in order 7460 to facilitate early boot debugging. The event-list is a 7461 comma-separated list of trace events to enable. See 7462 also Documentation/trace/events.rst 7463 7464 To enable modules, use :mod: keyword: 7465 7466 trace_event=:mod:<module> 7467 7468 The value before :mod: will only enable specific events 7469 that are part of the module. See the above mentioned 7470 document for more information. 7471 7472 trace_instance=[instance-info] 7473 [FTRACE] Create a ring buffer instance early in boot up. 7474 This will be listed in: 7475 7476 /sys/kernel/tracing/instances 7477 7478 Events can be enabled at the time the instance is created 7479 via: 7480 7481 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7482 7483 Note, the "<system*>:" portion is optional if the event is 7484 unique. 7485 7486 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7487 7488 will enable the "sched_switch" event (note, the "sched:" is optional, and 7489 the same thing would happen if it was left off). The irq_handler_entry 7490 event, and all events under the "initcall" system. 7491 7492 Flags can be added to the instance to modify its behavior when it is 7493 created. The flags are separated by '^'. 7494 7495 The available flags are: 7496 7497 traceoff - Have the tracing instance tracing disabled after it is created. 7498 traceprintk - Have trace_printk() write into this trace instance 7499 (note, "printk" and "trace_printk" can also be used) 7500 7501 trace_instance=foo^traceoff^traceprintk,sched,irq 7502 7503 The flags must come before the defined events. 7504 7505 If memory has been reserved (see memmap for x86), the instance 7506 can use that memory: 7507 7508 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7509 7510 The above will create a "boot_map" instance that uses the physical 7511 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7512 instance will be split up accordingly. 7513 7514 Alternatively, the memory can be reserved by the reserve_mem option: 7515 7516 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7517 7518 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7519 and place the ring buffer in this memory. Note that due to KASLR, the 7520 memory may not be the same location each time, which will not preserve 7521 the buffer content. 7522 7523 Also note that the layout of the ring buffer data may change between 7524 kernel versions where the validator will fail and reset the ring buffer 7525 if the layout is not the same as the previous kernel. 7526 7527 If the ring buffer is used for persistent bootups and has events enabled, 7528 it is recommend to disable tracing so that events from a previous boot do not 7529 mix with events of the current boot (unless you are debugging a random crash 7530 at boot up). 7531 7532 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7533 7534 Note, saving the trace buffer across reboots does require that the system 7535 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7536 can force a memory reset on boot which will clear any trace that was stored. 7537 This is just one of many ways that can clear memory. Make sure your system 7538 keeps the content of memory across reboots before relying on this option. 7539 7540 NB: Both the mapped address and size must be page aligned for the architecture. 7541 7542 See also Documentation/trace/debugging.rst 7543 7544 7545 trace_options=[option-list] 7546 [FTRACE] Enable or disable tracer options at boot. 7547 The option-list is a comma delimited list of options 7548 that can be enabled or disabled just as if you were 7549 to echo the option name into 7550 7551 /sys/kernel/tracing/trace_options 7552 7553 For example, to enable stacktrace option (to dump the 7554 stack trace of each event), add to the command line: 7555 7556 trace_options=stacktrace 7557 7558 See also Documentation/trace/ftrace.rst "trace options" 7559 section. 7560 7561 trace_trigger=[trigger-list] 7562 [FTRACE] Add an event trigger on specific events. 7563 Set a trigger on top of a specific event, with an optional 7564 filter. 7565 7566 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7567 Where more than one trigger may be specified that are comma delimited. 7568 7569 For example: 7570 7571 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7572 7573 The above will enable the "stacktrace" trigger on the "sched_switch" 7574 event but only trigger it if the "prev_state" of the "sched_switch" 7575 event is "2" (TASK_UNINTERRUPTIBLE). 7576 7577 See also "Event triggers" in Documentation/trace/events.rst 7578 7579 7580 traceoff_after_boot 7581 [FTRACE] Sometimes tracing is used to debug issues 7582 during the boot process. Since the trace buffer has a 7583 limited amount of storage, it may be prudent to 7584 disable tracing after the boot is finished, otherwise 7585 the critical information may be overwritten. With this 7586 option, the main tracing buffer will be turned off at 7587 the end of the boot process. 7588 7589 traceoff_on_warning 7590 [FTRACE] enable this option to disable tracing when a 7591 warning is hit. This turns off "tracing_on". Tracing can 7592 be enabled again by echoing '1' into the "tracing_on" 7593 file located in /sys/kernel/tracing/ 7594 7595 This option is useful, as it disables the trace before 7596 the WARNING dump is called, which prevents the trace to 7597 be filled with content caused by the warning output. 7598 7599 This option can also be set at run time via the sysctl 7600 option: kernel/traceoff_on_warning 7601 7602 transparent_hugepage= 7603 [KNL] 7604 Format: [always|madvise|never] 7605 Can be used to control the default behavior of the system 7606 with respect to transparent hugepages. 7607 See Documentation/admin-guide/mm/transhuge.rst 7608 for more details. 7609 7610 transparent_hugepage_shmem= [KNL] 7611 Format: [always|within_size|advise|never|deny|force] 7612 Can be used to control the hugepage allocation policy for 7613 the internal shmem mount. 7614 See Documentation/admin-guide/mm/transhuge.rst 7615 for more details. 7616 7617 transparent_hugepage_tmpfs= [KNL] 7618 Format: [always|within_size|advise|never] 7619 Can be used to control the default hugepage allocation policy 7620 for the tmpfs mount. 7621 See Documentation/admin-guide/mm/transhuge.rst 7622 for more details. 7623 7624 trusted.source= [KEYS] 7625 Format: <string> 7626 This parameter identifies the trust source as a backend 7627 for trusted keys implementation. Supported trust 7628 sources: 7629 - "tpm" 7630 - "tee" 7631 - "caam" 7632 - "dcp" 7633 If not specified then it defaults to iterating through 7634 the trust source list starting with TPM and assigns the 7635 first trust source as a backend which is initialized 7636 successfully during iteration. 7637 7638 trusted.rng= [KEYS] 7639 Format: <string> 7640 The RNG used to generate key material for trusted keys. 7641 Can be one of: 7642 - "kernel" 7643 - the same value as trusted.source: "tpm" or "tee" 7644 - "default" 7645 If not specified, "default" is used. In this case, 7646 the RNG's choice is left to each individual trust source. 7647 7648 trusted.dcp_use_otp_key 7649 This is intended to be used in combination with 7650 trusted.source=dcp and will select the DCP OTP key 7651 instead of the DCP UNIQUE key blob encryption. 7652 7653 trusted.dcp_skip_zk_test 7654 This is intended to be used in combination with 7655 trusted.source=dcp and will disable the check if the 7656 blob key is all zeros. This is helpful for situations where 7657 having this key zero'ed is acceptable. E.g. in testing 7658 scenarios. 7659 7660 tsa= [X86] Control mitigation for Transient Scheduler 7661 Attacks on AMD CPUs. Search the following in your 7662 favourite search engine for more details: 7663 7664 "Technical guidance for mitigating transient scheduler 7665 attacks". 7666 7667 off - disable the mitigation 7668 on - enable the mitigation (default) 7669 user - mitigate only user/kernel transitions 7670 vm - mitigate only guest/host transitions 7671 7672 7673 tsc= Disable clocksource stability checks for TSC. 7674 Format: <string> 7675 [x86] reliable: mark tsc clocksource as reliable, this 7676 disables clocksource verification at runtime, as well 7677 as the stability checks done at bootup. Used to enable 7678 high-resolution timer mode on older hardware, and in 7679 virtualized environment. 7680 [x86] noirqtime: Do not use TSC to do irq accounting. 7681 Used to run time disable IRQ_TIME_ACCOUNTING on any 7682 platforms where RDTSC is slow and this accounting 7683 can add overhead. 7684 [x86] unstable: mark the TSC clocksource as unstable, this 7685 marks the TSC unconditionally unstable at bootup and 7686 avoids any further wobbles once the TSC watchdog notices. 7687 [x86] nowatchdog: disable clocksource watchdog. Used 7688 in situations with strict latency requirements (where 7689 interruptions from clocksource watchdog are not 7690 acceptable). 7691 [x86] recalibrate: force recalibration against a HW timer 7692 (HPET or PM timer) on systems whose TSC frequency was 7693 obtained from HW or FW using either an MSR or CPUID(0x15). 7694 Warn if the difference is more than 500 ppm. 7695 [x86] watchdog: Use TSC as the watchdog clocksource with 7696 which to check other HW timers (HPET or PM timer), but 7697 only on systems where TSC has been deemed trustworthy. 7698 This will be suppressed by an earlier tsc=nowatchdog and 7699 can be overridden by a later tsc=nowatchdog. A console 7700 message will flag any such suppression or overriding. 7701 7702 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7703 value instead. Useful when the early TSC frequency discovery 7704 procedure is not reliable, such as on overclocked systems 7705 with CPUID.16h support and partial CPUID.15h support. 7706 Format: <unsigned int> 7707 7708 tsx= [X86] Control Transactional Synchronization 7709 Extensions (TSX) feature in Intel processors that 7710 support TSX control. 7711 7712 This parameter controls the TSX feature. The options are: 7713 7714 on - Enable TSX on the system. Although there are 7715 mitigations for all known security vulnerabilities, 7716 TSX has been known to be an accelerator for 7717 several previous speculation-related CVEs, and 7718 so there may be unknown security risks associated 7719 with leaving it enabled. 7720 7721 off - Disable TSX on the system. (Note that this 7722 option takes effect only on newer CPUs which are 7723 not vulnerable to MDS, i.e., have 7724 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7725 the new IA32_TSX_CTRL MSR through a microcode 7726 update. This new MSR allows for the reliable 7727 deactivation of the TSX functionality.) 7728 7729 auto - Disable TSX if X86_BUG_TAA is present, 7730 otherwise enable TSX on the system. 7731 7732 Not specifying this option is equivalent to tsx=off. 7733 7734 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7735 for more details. 7736 7737 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7738 Abort (TAA) vulnerability. 7739 7740 Similar to Micro-architectural Data Sampling (MDS) 7741 certain CPUs that support Transactional 7742 Synchronization Extensions (TSX) are vulnerable to an 7743 exploit against CPU internal buffers which can forward 7744 information to a disclosure gadget under certain 7745 conditions. 7746 7747 In vulnerable processors, the speculatively forwarded 7748 data can be used in a cache side channel attack, to 7749 access data to which the attacker does not have direct 7750 access. 7751 7752 This parameter controls the TAA mitigation. The 7753 options are: 7754 7755 full - Enable TAA mitigation on vulnerable CPUs 7756 if TSX is enabled. 7757 7758 full,nosmt - Enable TAA mitigation and disable SMT on 7759 vulnerable CPUs. If TSX is disabled, SMT 7760 is not disabled because CPU is not 7761 vulnerable to cross-thread TAA attacks. 7762 off - Unconditionally disable TAA mitigation 7763 7764 On MDS-affected machines, tsx_async_abort=off can be 7765 prevented by an active MDS mitigation as both vulnerabilities 7766 are mitigated with the same mechanism so in order to disable 7767 this mitigation, you need to specify mds=off too. 7768 7769 Not specifying this option is equivalent to 7770 tsx_async_abort=full. On CPUs which are MDS affected 7771 and deploy MDS mitigation, TAA mitigation is not 7772 required and doesn't provide any additional 7773 mitigation. 7774 7775 For details see: 7776 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7777 7778 turbografx.map[2|3]= [HW,JOY] 7779 TurboGraFX parallel port interface 7780 Format: 7781 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 7782 See also Documentation/input/devices/joystick-parport.rst 7783 7784 udbg-immortal [PPC] When debugging early kernel crashes that 7785 happen after console_init() and before a proper 7786 console driver takes over, this boot options might 7787 help "seeing" what's going on. 7788 7789 uhash_entries= [KNL,NET] 7790 Set number of hash buckets for UDP/UDP-Lite connections 7791 7792 uhci-hcd.ignore_oc= 7793 [USB] Ignore overcurrent events (default N). 7794 Some badly-designed motherboards generate lots of 7795 bogus events, for ports that aren't wired to 7796 anything. Set this parameter to avoid log spamming. 7797 Note that genuine overcurrent events won't be 7798 reported either. 7799 7800 unaligned_scalar_speed= 7801 [RISCV] 7802 Format: {slow | fast | unsupported} 7803 Allow skipping scalar unaligned access speed tests. This 7804 is useful for testing alternative code paths and to skip 7805 the tests in environments where they run too slowly. All 7806 CPUs must have the same scalar unaligned access speed. 7807 7808 unaligned_vector_speed= 7809 [RISCV] 7810 Format: {slow | fast | unsupported} 7811 Allow skipping vector unaligned access speed tests. This 7812 is useful for testing alternative code paths and to skip 7813 the tests in environments where they run too slowly. All 7814 CPUs must have the same vector unaligned access speed. 7815 7816 unknown_nmi_panic 7817 [X86] Cause panic on unknown NMI. 7818 7819 unwind_debug [X86-64,EARLY] 7820 Enable unwinder debug output. This can be 7821 useful for debugging certain unwinder error 7822 conditions, including corrupt stacks and 7823 bad/missing unwinder metadata. 7824 7825 usbcore.authorized_default= 7826 [USB] Default USB device authorization: 7827 (default -1 = authorized (same as 1), 7828 0 = not authorized, 1 = authorized, 2 = authorized 7829 if device connected to internal port) 7830 7831 usbcore.autosuspend= 7832 [USB] The autosuspend time delay (in seconds) used 7833 for newly-detected USB devices (default 2). This 7834 is the time required before an idle device will be 7835 autosuspended. Devices for which the delay is set 7836 to a negative value won't be autosuspended at all. 7837 7838 usbcore.usbfs_snoop= 7839 [USB] Set to log all usbfs traffic (default 0 = off). 7840 7841 usbcore.usbfs_snoop_max= 7842 [USB] Maximum number of bytes to snoop in each URB 7843 (default = 65536). 7844 7845 usbcore.blinkenlights= 7846 [USB] Set to cycle leds on hubs (default 0 = off). 7847 7848 usbcore.old_scheme_first= 7849 [USB] Start with the old device initialization 7850 scheme (default 0 = off). 7851 7852 usbcore.usbfs_memory_mb= 7853 [USB] Memory limit (in MB) for buffers allocated by 7854 usbfs (default = 16, 0 = max = 2047). 7855 7856 usbcore.use_both_schemes= 7857 [USB] Try the other device initialization scheme 7858 if the first one fails (default 1 = enabled). 7859 7860 usbcore.initial_descriptor_timeout= 7861 [USB] Specifies timeout for the initial 64-byte 7862 USB_REQ_GET_DESCRIPTOR request in milliseconds 7863 (default 5000 = 5.0 seconds). 7864 7865 usbcore.nousb [USB] Disable the USB subsystem 7866 7867 usbcore.quirks= 7868 [USB] A list of quirk entries to augment the built-in 7869 usb core quirk list. List entries are separated by 7870 commas. Each entry has the form 7871 VendorID:ProductID:Flags. The IDs are 4-digit hex 7872 numbers and Flags is a set of letters. Each letter 7873 will change the built-in quirk; setting it if it is 7874 clear and clearing it if it is set. The letters have 7875 the following meanings: 7876 a = USB_QUIRK_STRING_FETCH_255 (string 7877 descriptors must not be fetched using 7878 a 255-byte read); 7879 b = USB_QUIRK_RESET_RESUME (device can't resume 7880 correctly so reset it instead); 7881 c = USB_QUIRK_NO_SET_INTF (device can't handle 7882 Set-Interface requests); 7883 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 7884 handle its Configuration or Interface 7885 strings); 7886 e = USB_QUIRK_RESET (device can't be reset 7887 (e.g morph devices), don't use reset); 7888 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 7889 more interface descriptions than the 7890 bNumInterfaces count, and can't handle 7891 talking to these interfaces); 7892 g = USB_QUIRK_DELAY_INIT (device needs a pause 7893 during initialization, after we read 7894 the device descriptor); 7895 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 7896 high speed and super speed interrupt 7897 endpoints, the USB 2.0 and USB 3.0 spec 7898 require the interval in microframes (1 7899 microframe = 125 microseconds) to be 7900 calculated as interval = 2 ^ 7901 (bInterval-1). 7902 Devices with this quirk report their 7903 bInterval as the result of this 7904 calculation instead of the exponent 7905 variable used in the calculation); 7906 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 7907 handle device_qualifier descriptor 7908 requests); 7909 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 7910 generates spurious wakeup, ignore 7911 remote wakeup capability); 7912 k = USB_QUIRK_NO_LPM (device can't handle Link 7913 Power Management); 7914 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 7915 (Device reports its bInterval as linear 7916 frames instead of the USB 2.0 7917 calculation); 7918 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 7919 to be disconnected before suspend to 7920 prevent spurious wakeup); 7921 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 7922 pause after every control message); 7923 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 7924 delay after resetting its port); 7925 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 7926 (Reduce timeout of the SET_ADDRESS 7927 request from 5000 ms to 500 ms); 7928 Example: quirks=0781:5580:bk,0a5c:5834:gij 7929 7930 usbhid.mousepoll= 7931 [USBHID] The interval which mice are to be polled at. 7932 7933 usbhid.jspoll= 7934 [USBHID] The interval which joysticks are to be polled at. 7935 7936 usbhid.kbpoll= 7937 [USBHID] The interval which keyboards are to be polled at. 7938 7939 usb-storage.delay_use= 7940 [UMS] The delay in seconds before a new device is 7941 scanned for Logical Units (default 1). 7942 Optionally the delay in milliseconds if the value has 7943 suffix with "ms". 7944 Example: delay_use=2567ms 7945 7946 usb-storage.quirks= 7947 [UMS] A list of quirks entries to supplement or 7948 override the built-in unusual_devs list. List 7949 entries are separated by commas. Each entry has 7950 the form VID:PID:Flags where VID and PID are Vendor 7951 and Product ID values (4-digit hex numbers) and 7952 Flags is a set of characters, each corresponding 7953 to a common usb-storage quirk flag as follows: 7954 a = SANE_SENSE (collect more than 18 bytes 7955 of sense data, not on uas); 7956 b = BAD_SENSE (don't collect more than 18 7957 bytes of sense data, not on uas); 7958 c = FIX_CAPACITY (decrease the reported 7959 device capacity by one sector); 7960 d = NO_READ_DISC_INFO (don't use 7961 READ_DISC_INFO command, not on uas); 7962 e = NO_READ_CAPACITY_16 (don't use 7963 READ_CAPACITY_16 command); 7964 f = NO_REPORT_OPCODES (don't use report opcodes 7965 command, uas only); 7966 g = MAX_SECTORS_240 (don't transfer more than 7967 240 sectors at a time, uas only); 7968 h = CAPACITY_HEURISTICS (decrease the 7969 reported device capacity by one 7970 sector if the number is odd); 7971 i = IGNORE_DEVICE (don't bind to this 7972 device); 7973 j = NO_REPORT_LUNS (don't use report luns 7974 command, uas only); 7975 k = NO_SAME (do not use WRITE_SAME, uas only) 7976 l = NOT_LOCKABLE (don't try to lock and 7977 unlock ejectable media, not on uas); 7978 m = MAX_SECTORS_64 (don't transfer more 7979 than 64 sectors = 32 KB at a time, 7980 not on uas); 7981 n = INITIAL_READ10 (force a retry of the 7982 initial READ(10) command, not on uas); 7983 o = CAPACITY_OK (accept the capacity 7984 reported by the device, not on uas); 7985 p = WRITE_CACHE (the device cache is ON 7986 by default, not on uas); 7987 r = IGNORE_RESIDUE (the device reports 7988 bogus residue values, not on uas); 7989 s = SINGLE_LUN (the device has only one 7990 Logical Unit); 7991 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 7992 commands, uas only); 7993 u = IGNORE_UAS (don't bind to the uas driver); 7994 w = NO_WP_DETECT (don't test whether the 7995 medium is write-protected). 7996 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 7997 even if the device claims no cache, 7998 not on uas) 7999 Example: quirks=0419:aaf5:rl,0421:0433:rc 8000 8001 user_debug= [KNL,ARM] 8002 Format: <int> 8003 See arch/arm/Kconfig.debug help text. 8004 1 - undefined instruction events 8005 2 - system calls 8006 4 - invalid data aborts 8007 8 - SIGSEGV faults 8008 16 - SIGBUS faults 8009 Example: user_debug=31 8010 8011 vdso= [X86,SH,SPARC] 8012 On X86_32, this is an alias for vdso32=. Otherwise: 8013 8014 vdso=1: enable VDSO (the default) 8015 vdso=0: disable VDSO mapping 8016 8017 vdso32= [X86] Control the 32-bit vDSO 8018 vdso32=1: enable 32-bit VDSO 8019 vdso32=0 or vdso32=2: disable 32-bit VDSO 8020 8021 See the help text for CONFIG_COMPAT_VDSO for more 8022 details. If CONFIG_COMPAT_VDSO is set, the default is 8023 vdso32=0; otherwise, the default is vdso32=1. 8024 8025 For compatibility with older kernels, vdso32=2 is an 8026 alias for vdso32=0. 8027 8028 Try vdso32=0 if you encounter an error that says: 8029 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8030 8031 video= [FB,EARLY] Frame buffer configuration 8032 See Documentation/fb/modedb.rst. 8033 8034 video.brightness_switch_enabled= [ACPI] 8035 Format: [0|1] 8036 If set to 1, on receiving an ACPI notify event 8037 generated by hotkey, video driver will adjust brightness 8038 level and then send out the event to user space through 8039 the allocated input device. If set to 0, video driver 8040 will only send out the event without touching backlight 8041 brightness level. 8042 default: 1 8043 8044 virtio_mmio.device= 8045 [VMMIO] Memory mapped virtio (platform) device. 8046 8047 <size>@<baseaddr>:<irq>[:<id>] 8048 where: 8049 <size> := size (can use standard suffixes 8050 like K, M and G) 8051 <baseaddr> := physical base address 8052 <irq> := interrupt number (as passed to 8053 request_irq()) 8054 <id> := (optional) platform device id 8055 example: 8056 virtio_mmio.device=1K@0x100b0000:48:7 8057 8058 Can be used multiple times for multiple devices. 8059 8060 vga= [BOOT,X86-32] Select a particular video mode 8061 See Documentation/arch/x86/boot.rst and 8062 Documentation/admin-guide/svga.rst. 8063 Use vga=ask for menu. 8064 This is actually a boot loader parameter; the value is 8065 passed to the kernel using a special protocol. 8066 8067 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8068 May slow down system boot speed, especially when 8069 enabled on systems with a large amount of memory. 8070 All options are enabled by default, and this 8071 interface is meant to allow for selectively 8072 enabling or disabling specific virtual memory 8073 debugging features. 8074 8075 Available options are: 8076 P Enable page structure init time poisoning 8077 - Disable all of the above options 8078 8079 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8080 exact size of <nn>. This can be used to increase 8081 the minimum size (128MB on x86, arm32 platforms). 8082 It can also be used to decrease the size and leave more room 8083 for directly mapped kernel RAM. Note that this parameter does 8084 not exist on many other platforms (including arm64, alpha, 8085 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8086 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8087 8088 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8089 Sets the memory size reserved for contiguous memory 8090 allocations for the vmcp device driver. 8091 8092 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8093 Format: <command> 8094 8095 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8096 Format: <command> 8097 8098 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8099 Format: <command> 8100 8101 vmscape= [X86] Controls mitigation for VMscape attacks. 8102 VMscape attacks can leak information from a userspace 8103 hypervisor to a guest via speculative side-channels. 8104 8105 off - disable the mitigation 8106 ibpb - use Indirect Branch Prediction Barrier 8107 (IBPB) mitigation (default) 8108 force - force vulnerability detection even on 8109 unaffected processors 8110 8111 vsyscall= [X86-64,EARLY] 8112 Controls the behavior of vsyscalls (i.e. calls to 8113 fixed addresses of 0xffffffffff600x00 from legacy 8114 code). Most statically-linked binaries and older 8115 versions of glibc use these calls. Because these 8116 functions are at fixed addresses, they make nice 8117 targets for exploits that can control RIP. 8118 8119 emulate Vsyscalls turn into traps and are emulated 8120 reasonably safely. The vsyscall page is 8121 readable. 8122 8123 xonly [default] Vsyscalls turn into traps and are 8124 emulated reasonably safely. The vsyscall 8125 page is not readable. 8126 8127 none Vsyscalls don't work at all. This makes 8128 them quite hard to use for exploits but 8129 might break your system. 8130 8131 vt.color= [VT] Default text color. 8132 Format: 0xYX, X = foreground, Y = background. 8133 Default: 0x07 = light gray on black. 8134 8135 vt.cur_default= [VT] Default cursor shape. 8136 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8137 the parameters of the <Esc>[?A;B;Cc escape sequence; 8138 see vga-softcursor.rst. Default: 2 = underline. 8139 8140 vt.default_blu= [VT] 8141 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8142 Change the default blue palette of the console. 8143 This is a 16-member array composed of values 8144 ranging from 0-255. 8145 8146 vt.default_grn= [VT] 8147 Format: <green0>,<green1>,<green2>,...,<green15> 8148 Change the default green palette of the console. 8149 This is a 16-member array composed of values 8150 ranging from 0-255. 8151 8152 vt.default_red= [VT] 8153 Format: <red0>,<red1>,<red2>,...,<red15> 8154 Change the default red palette of the console. 8155 This is a 16-member array composed of values 8156 ranging from 0-255. 8157 8158 vt.default_utf8= 8159 [VT] 8160 Format=<0|1> 8161 Set system-wide default UTF-8 mode for all tty's. 8162 Default is 1, i.e. UTF-8 mode is enabled for all 8163 newly opened terminals. 8164 8165 vt.global_cursor_default= 8166 [VT] 8167 Format=<-1|0|1> 8168 Set system-wide default for whether a cursor 8169 is shown on new VTs. Default is -1, 8170 i.e. cursors will be created by default unless 8171 overridden by individual drivers. 0 will hide 8172 cursors, 1 will display them. 8173 8174 vt.italic= [VT] Default color for italic text; 0-15. 8175 Default: 2 = green. 8176 8177 vt.underline= [VT] Default color for underlined text; 0-15. 8178 Default: 3 = cyan. 8179 8180 watchdog timers [HW,WDT] For information on watchdog timers, 8181 see Documentation/watchdog/watchdog-parameters.rst 8182 or other driver-specific files in the 8183 Documentation/watchdog/ directory. 8184 8185 watchdog_thresh= 8186 [KNL] 8187 Set the hard lockup detector stall duration 8188 threshold in seconds. The soft lockup detector 8189 threshold is set to twice the value. A value of 0 8190 disables both lockup detectors. Default is 10 8191 seconds. 8192 8193 workqueue.unbound_cpus= 8194 [KNL,SMP] Specify to constrain one or some CPUs 8195 to use in unbound workqueues. 8196 Format: <cpu-list> 8197 By default, all online CPUs are available for 8198 unbound workqueues. 8199 8200 workqueue.watchdog_thresh= 8201 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8202 warn stall conditions and dump internal state to 8203 help debugging. 0 disables workqueue stall 8204 detection; otherwise, it's the stall threshold 8205 duration in seconds. The default value is 30 and 8206 it can be updated at runtime by writing to the 8207 corresponding sysfs file. 8208 8209 workqueue.panic_on_stall=<uint> 8210 Panic when workqueue stall is detected by 8211 CONFIG_WQ_WATCHDOG. It sets the number times of the 8212 stall to trigger panic. 8213 8214 The default is 0, which disables the panic on stall. 8215 8216 workqueue.cpu_intensive_thresh_us= 8217 Per-cpu work items which run for longer than this 8218 threshold are automatically considered CPU intensive 8219 and excluded from concurrency management to prevent 8220 them from noticeably delaying other per-cpu work 8221 items. Default is 10000 (10ms). 8222 8223 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8224 will report the work functions which violate this 8225 threshold repeatedly. They are likely good 8226 candidates for using WQ_UNBOUND workqueues instead. 8227 8228 workqueue.cpu_intensive_warning_thresh=<uint> 8229 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8230 will report the work functions which violate the 8231 intensive_threshold_us repeatedly. In order to prevent 8232 spurious warnings, start printing only after a work 8233 function has violated this threshold number of times. 8234 8235 The default is 4 times. 0 disables the warning. 8236 8237 workqueue.power_efficient 8238 Per-cpu workqueues are generally preferred because 8239 they show better performance thanks to cache 8240 locality; unfortunately, per-cpu workqueues tend to 8241 be more power hungry than unbound workqueues. 8242 8243 Enabling this makes the per-cpu workqueues which 8244 were observed to contribute significantly to power 8245 consumption unbound, leading to measurably lower 8246 power usage at the cost of small performance 8247 overhead. 8248 8249 The default value of this parameter is determined by 8250 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8251 8252 workqueue.default_affinity_scope= 8253 Select the default affinity scope to use for unbound 8254 workqueues. Can be one of "cpu", "smt", "cache", 8255 "numa" and "system". Default is "cache". For more 8256 information, see the Affinity Scopes section in 8257 Documentation/core-api/workqueue.rst. 8258 8259 This can be changed after boot by writing to the 8260 matching /sys/module/workqueue/parameters file. All 8261 workqueues with the "default" affinity scope will be 8262 updated accordingly. 8263 8264 workqueue.debug_force_rr_cpu 8265 Workqueue used to implicitly guarantee that work 8266 items queued without explicit CPU specified are put 8267 on the local CPU. This guarantee is no longer true 8268 and while local CPU is still preferred work items 8269 may be put on foreign CPUs. This debug option 8270 forces round-robin CPU selection to flush out 8271 usages which depend on the now broken guarantee. 8272 When enabled, memory and cache locality will be 8273 impacted. 8274 8275 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8276 Type) of ioremap_wc(). 8277 8278 on - Enable writecombine, use WUC for ioremap_wc() 8279 off - Disable writecombine, use SUC for ioremap_wc() 8280 8281 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8282 default x2apic cluster mode on platforms 8283 supporting x2apic. 8284 8285 xen_512gb_limit [KNL,X86-64,XEN] 8286 Restricts the kernel running paravirtualized under Xen 8287 to use only up to 512 GB of RAM. The reason to do so is 8288 crash analysis tools and Xen tools for doing domain 8289 save/restore/migration must be enabled to handle larger 8290 domains. 8291 8292 xen_emul_unplug= [HW,X86,XEN,EARLY] 8293 Unplug Xen emulated devices 8294 Format: [unplug0,][unplug1] 8295 ide-disks -- unplug primary master IDE devices 8296 aux-ide-disks -- unplug non-primary-master IDE devices 8297 nics -- unplug network devices 8298 all -- unplug all emulated devices (NICs and IDE disks) 8299 unnecessary -- unplugging emulated devices is 8300 unnecessary even if the host did not respond to 8301 the unplug protocol 8302 never -- do not unplug even if version check succeeds 8303 8304 xen_legacy_crash [X86,XEN,EARLY] 8305 Crash from Xen panic notifier, without executing late 8306 panic() code such as dumping handler. 8307 8308 xen_mc_debug [X86,XEN,EARLY] 8309 Enable multicall debugging when running as a Xen PV guest. 8310 Enabling this feature will reduce performance a little 8311 bit, so it should only be enabled for obtaining extended 8312 debug data in case of multicall errors. 8313 8314 xen_msr_safe= [X86,XEN,EARLY] 8315 Format: <bool> 8316 Select whether to always use non-faulting (safe) MSR 8317 access functions when running as Xen PV guest. The 8318 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8319 8320 xen_nopv [X86] 8321 Disables the PV optimizations forcing the HVM guest to 8322 run as generic HVM guest with no PV drivers. 8323 This option is obsoleted by the "nopv" option, which 8324 has equivalent effect for XEN platform. 8325 8326 xen_no_vector_callback 8327 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8328 event channel interrupts. 8329 8330 xen_scrub_pages= [XEN] 8331 Boolean option to control scrubbing pages before giving them back 8332 to Xen, for use by other domains. Can be also changed at runtime 8333 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8334 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8335 8336 xen_timer_slop= [X86-64,XEN,EARLY] 8337 Set the timer slop (in nanoseconds) for the virtual Xen 8338 timers (default is 100000). This adjusts the minimum 8339 delta of virtualized Xen timers, where lower values 8340 improve timer resolution at the expense of processing 8341 more timer interrupts. 8342 8343 xen.balloon_boot_timeout= [XEN] 8344 The time (in seconds) to wait before giving up to boot 8345 in case initial ballooning fails to free enough memory. 8346 Applies only when running as HVM or PVH guest and 8347 started with less memory configured than allowed at 8348 max. Default is 180. 8349 8350 xen.event_eoi_delay= [XEN] 8351 How long to delay EOI handling in case of event 8352 storms (jiffies). Default is 10. 8353 8354 xen.event_loop_timeout= [XEN] 8355 After which time (jiffies) the event handling loop 8356 should start to delay EOI handling. Default is 2. 8357 8358 xen.fifo_events= [XEN] 8359 Boolean parameter to disable using fifo event handling 8360 even if available. Normally fifo event handling is 8361 preferred over the 2-level event handling, as it is 8362 fairer and the number of possible event channels is 8363 much higher. Default is on (use fifo events). 8364 8365 xirc2ps_cs= [NET,PCMCIA] 8366 Format: 8367 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8368 8369 xive= [PPC] 8370 By default on POWER9 and above, the kernel will 8371 natively use the XIVE interrupt controller. This option 8372 allows the fallback firmware mode to be used: 8373 8374 off Fallback to firmware control of XIVE interrupt 8375 controller on both pseries and powernv 8376 platforms. Only useful on POWER9 and above. 8377 8378 xive.store-eoi=off [PPC] 8379 By default on POWER10 and above, the kernel will use 8380 stores for EOI handling when the XIVE interrupt mode 8381 is active. This option allows the XIVE driver to use 8382 loads instead, as on POWER9. 8383 8384 xhci-hcd.quirks [USB,KNL] 8385 A hex value specifying bitmask with supplemental xhci 8386 host controller quirks. Meaning of each bit can be 8387 consulted in header drivers/usb/host/xhci.h. 8388 8389 xmon [PPC,EARLY] 8390 Format: { early | on | rw | ro | off } 8391 Controls if xmon debugger is enabled. Default is off. 8392 Passing only "xmon" is equivalent to "xmon=early". 8393 early Call xmon as early as possible on boot; xmon 8394 debugger is called from setup_arch(). 8395 on xmon debugger hooks will be installed so xmon 8396 is only called on a kernel crash. Default mode, 8397 i.e. either "ro" or "rw" mode, is controlled 8398 with CONFIG_XMON_DEFAULT_RO_MODE. 8399 rw xmon debugger hooks will be installed so xmon 8400 is called only on a kernel crash, mode is write, 8401 meaning SPR registers, memory and, other data 8402 can be written using xmon commands. 8403 ro same as "rw" option above but SPR registers, 8404 memory, and other data can't be written using 8405 xmon commands. 8406 off xmon is disabled. 8407