1 ACPI ACPI support is enabled. 2 AGP AGP (Accelerated Graphics Port) is enabled. 3 ALSA ALSA sound support is enabled. 4 APIC APIC support is enabled. 5 APM Advanced Power Management support is enabled. 6 APPARMOR AppArmor support is enabled. 7 ARM ARM architecture is enabled. 8 ARM64 ARM64 architecture is enabled. 9 CLK Common clock infrastructure is enabled. 10 CMA Contiguous Memory Area support is enabled. 11 DRM Direct Rendering Management support is enabled. 12 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 13 EARLY Parameter processed too early to be embedded in initrd. 14 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 15 EFI EFI Partitioning (GPT) is enabled 16 EVM Extended Verification Module 17 FB The frame buffer device is enabled. 18 FTRACE Function tracing enabled. 19 GCOV GCOV profiling is enabled. 20 HIBERNATION HIBERNATION is enabled. 21 HW Appropriate hardware is enabled. 22 HYPER_V HYPERV support is enabled. 23 IMA Integrity measurement architecture is enabled. 24 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 25 IPV6 IPv6 support is enabled. 26 ISAPNP ISA PnP code is enabled. 27 ISOL CPU Isolation is enabled. 28 JOY Appropriate joystick support is enabled. 29 KGDB Kernel debugger support is enabled. 30 KVM Kernel Virtual Machine support is enabled. 31 LIBATA Libata driver is enabled 32 LOONGARCH LoongArch architecture is enabled. 33 LOOP Loopback device support is enabled. 34 LP Printer support is enabled. 35 M68k M68k architecture is enabled. 36 These options have more detailed description inside of 37 Documentation/arch/m68k/kernel-options.rst. 38 MDA MDA console support is enabled. 39 MIPS MIPS architecture is enabled. 40 MOUSE Appropriate mouse support is enabled. 41 MSI Message Signaled Interrupts (PCI). 42 MTD MTD (Memory Technology Device) support is enabled. 43 NET Appropriate network support is enabled. 44 NFS Appropriate NFS support is enabled. 45 NUMA NUMA support is enabled. 46 OF Devicetree is enabled. 47 PARISC The PA-RISC architecture is enabled. 48 PCI PCI bus support is enabled. 49 PCIE PCI Express support is enabled. 50 PCMCIA The PCMCIA subsystem is enabled. 51 PNP Plug & Play support is enabled. 52 PPC PowerPC architecture is enabled. 53 PPT Parallel port support is enabled. 54 PS2 Appropriate PS/2 support is enabled. 55 PV_OPS A paravirtualized kernel is enabled. 56 RAM RAM disk support is enabled. 57 RDT Intel Resource Director Technology. 58 RISCV RISCV architecture is enabled. 59 S390 S390 architecture is enabled. 60 SCSI Appropriate SCSI support is enabled. 61 A lot of drivers have their options described inside 62 the Documentation/scsi/ sub-directory. 63 SDW SoundWire support is enabled. 64 SECURITY Different security models are enabled. 65 SELINUX SELinux support is enabled. 66 SERIAL Serial support is enabled. 67 SH SuperH architecture is enabled. 68 SMP The kernel is an SMP kernel. 69 SPARC Sparc architecture is enabled. 70 SUSPEND System suspend states are enabled. 71 SWSUSP Software suspend (hibernation) is enabled. 72 TPM TPM drivers are enabled. 73 UMS USB Mass Storage support is enabled. 74 USB USB support is enabled. 75 NVME NVMe support is enabled 76 USBHID USB Human Interface Device support is enabled. 77 V4L Video For Linux support is enabled. 78 VGA The VGA console has been enabled. 79 VMMIO Driver for memory mapped virtio devices is enabled. 80 VT Virtual terminal support is enabled. 81 WDT Watchdog support is enabled. 82 X86-32 X86-32, aka i386 architecture is enabled. 83 X86-64 X86-64 architecture is enabled. 84 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 85 X86_UV SGI UV support is enabled. 86 XEN Xen support is enabled 87 XTENSA xtensa architecture is enabled. 88 89In addition, the following text indicates that the option 90 91 BOOT Is a boot loader parameter. 92 BUGS= Relates to possible processor bugs on the said processor. 93 KNL Is a kernel start-up parameter. 94 95 96Kernel parameters 97 98 accept_memory= [MM] 99 Format: { eager | lazy } 100 default: lazy 101 By default, unaccepted memory is accepted lazily to 102 avoid prolonged boot times. The lazy option will add 103 some runtime overhead until all memory is eventually 104 accepted. In most cases the overhead is negligible. 105 For some workloads or for debugging purposes 106 accept_memory=eager can be used to accept all memory 107 at once during boot. 108 109 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 110 Advanced Configuration and Power Interface 111 Format: { force | on | off | strict | noirq | rsdt | 112 copy_dsdt | nospcr } 113 force -- enable ACPI if default was off 114 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 115 off -- disable ACPI if default was on 116 noirq -- do not use ACPI for IRQ routing 117 strict -- Be less tolerant of platforms that are not 118 strictly ACPI specification compliant. 119 rsdt -- prefer RSDT over (default) XSDT 120 copy_dsdt -- copy DSDT to memory 121 nocmcff -- Disable firmware first mode for corrected 122 errors. This disables parsing the HEST CMC error 123 source to check if firmware has set the FF flag. This 124 may result in duplicate corrected error reports. 125 nospcr -- disable console in ACPI SPCR table as 126 default _serial_ console on ARM64 127 spcr -- enable console in ACPI SPCR table as 128 default _serial_ console on x86 129 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 130 "acpi=nospcr" are available 131 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 132 are available 133 134 See also Documentation/power/runtime_pm.rst, pci=noacpi 135 136 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 137 Format: <int> 138 2: use 2nd APIC table, if available 139 1,0: use 1st APIC table 140 default: 0 141 142 acpi_backlight= [HW,ACPI] 143 { vendor | video | native | none } 144 If set to vendor, prefer vendor-specific driver 145 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 146 of the ACPI video.ko driver. 147 If set to video, use the ACPI video.ko driver. 148 If set to native, use the device's native backlight mode. 149 If set to none, disable the ACPI backlight interface. 150 151 acpi_force_32bit_fadt_addr [ACPI,EARLY] 152 force FADT to use 32 bit addresses rather than the 153 64 bit X_* addresses. Some firmware have broken 64 154 bit addresses for force ACPI ignore these and use 155 the older legacy 32 bit addresses. 156 157 acpica_no_return_repair [HW, ACPI] 158 Disable AML predefined validation mechanism 159 This mechanism can repair the evaluation result to make 160 the return objects more ACPI specification compliant. 161 This option is useful for developers to identify the 162 root cause of an AML interpreter issue when the issue 163 has something to do with the repair mechanism. 164 165 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 166 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 167 Format: <int> 168 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 169 debug output. Bits in debug_layer correspond to a 170 _COMPONENT in an ACPI source file, e.g., 171 #define _COMPONENT ACPI_EVENTS 172 Bits in debug_level correspond to a level in 173 ACPI_DEBUG_PRINT statements, e.g., 174 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 175 The debug_level mask defaults to "info". See 176 Documentation/firmware-guide/acpi/debug.rst for more information about 177 debug layers and levels. 178 179 Enable processor driver info messages: 180 acpi.debug_layer=0x20000000 181 Enable AML "Debug" output, i.e., stores to the Debug 182 object while interpreting AML: 183 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 184 Enable all messages related to ACPI hardware: 185 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 186 187 Some values produce so much output that the system is 188 unusable. The "log_buf_len" parameter may be useful 189 if you need to capture more output. 190 191 acpi.poweroff_on_fatal= [ACPI] 192 {0 | 1} 193 Causes the system to poweroff when the ACPI bytecode signals 194 a fatal error. The default value of this setting is 1. 195 Overriding this value should only be done for diagnosing 196 ACPI firmware problems, as the system might behave erratically 197 after having encountered a fatal ACPI error. 198 199 acpi_enforce_resources= [ACPI] 200 { strict | lax | no } 201 Check for resource conflicts between native drivers 202 and ACPI OperationRegions (SystemIO and SystemMemory 203 only). IO ports and memory declared in ACPI might be 204 used by the ACPI subsystem in arbitrary AML code and 205 can interfere with legacy drivers. 206 strict (default): access to resources claimed by ACPI 207 is denied; legacy drivers trying to access reserved 208 resources will fail to bind to device using them. 209 lax: access to resources claimed by ACPI is allowed; 210 legacy drivers trying to access reserved resources 211 will bind successfully but a warning message is logged. 212 no: ACPI OperationRegions are not marked as reserved, 213 no further checks are performed. 214 215 acpi_force_table_verification [HW,ACPI,EARLY] 216 Enable table checksum verification during early stage. 217 By default, this is disabled due to x86 early mapping 218 size limitation. 219 220 acpi_irq_balance [HW,ACPI] 221 ACPI will balance active IRQs 222 default in APIC mode 223 224 acpi_irq_nobalance [HW,ACPI] 225 ACPI will not move active IRQs (default) 226 default in PIC mode 227 228 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 229 Format: <irq>,<irq>... 230 231 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 232 use by PCI 233 Format: <irq>,<irq>... 234 235 acpi_mask_gpe= [HW,ACPI] 236 Due to the existence of _Lxx/_Exx, some GPEs triggered 237 by unsupported hardware/firmware features can result in 238 GPE floodings that cannot be automatically disabled by 239 the GPE dispatcher. 240 This facility can be used to prevent such uncontrolled 241 GPE floodings. 242 Format: <byte> or <bitmap-list> 243 244 acpi_no_auto_serialize [HW,ACPI] 245 Disable auto-serialization of AML methods 246 AML control methods that contain the opcodes to create 247 named objects will be marked as "Serialized" by the 248 auto-serialization feature. 249 This feature is enabled by default. 250 This option allows to turn off the feature. 251 252 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 253 kernels. 254 255 acpi_no_static_ssdt [HW,ACPI,EARLY] 256 Disable installation of static SSDTs at early boot time 257 By default, SSDTs contained in the RSDT/XSDT will be 258 installed automatically and they will appear under 259 /sys/firmware/acpi/tables. 260 This option turns off this feature. 261 Note that specifying this option does not affect 262 dynamic table installation which will install SSDT 263 tables to /sys/firmware/acpi/tables/dynamic. 264 265 acpi_no_watchdog [HW,ACPI,WDT] 266 Ignore the ACPI-based watchdog interface (WDAT) and let 267 a native driver control the watchdog device instead. 268 269 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 270 Pass the RSDP address to the kernel, mostly used 271 on machines running EFI runtime service to boot the 272 second kernel for kdump. 273 274 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 275 Format: To spoof as Windows 98: ="Microsoft Windows" 276 277 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 278 of 2 which is mandated by ACPI 6) as the supported ACPI 279 specification revision (when using this switch, it may 280 be necessary to carry out a cold reboot _twice_ in a 281 row to make it take effect on the platform firmware). 282 283 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 284 acpi_osi="string1" # add string1 285 acpi_osi="!string2" # remove string2 286 acpi_osi=!* # remove all strings 287 acpi_osi=! # disable all built-in OS vendor 288 strings 289 acpi_osi=!! # enable all built-in OS vendor 290 strings 291 acpi_osi= # disable all strings 292 293 'acpi_osi=!' can be used in combination with single or 294 multiple 'acpi_osi="string1"' to support specific OS 295 vendor string(s). Note that such command can only 296 affect the default state of the OS vendor strings, thus 297 it cannot affect the default state of the feature group 298 strings and the current state of the OS vendor strings, 299 specifying it multiple times through kernel command line 300 is meaningless. This command is useful when one do not 301 care about the state of the feature group strings which 302 should be controlled by the OSPM. 303 Examples: 304 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 305 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 306 can make '_OSI("Windows 2000")' TRUE. 307 308 'acpi_osi=' cannot be used in combination with other 309 'acpi_osi=' command lines, the _OSI method will not 310 exist in the ACPI namespace. NOTE that such command can 311 only affect the _OSI support state, thus specifying it 312 multiple times through kernel command line is also 313 meaningless. 314 Examples: 315 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 316 FALSE. 317 318 'acpi_osi=!*' can be used in combination with single or 319 multiple 'acpi_osi="string1"' to support specific 320 string(s). Note that such command can affect the 321 current state of both the OS vendor strings and the 322 feature group strings, thus specifying it multiple times 323 through kernel command line is meaningful. But it may 324 still not able to affect the final state of a string if 325 there are quirks related to this string. This command 326 is useful when one want to control the state of the 327 feature group strings to debug BIOS issues related to 328 the OSPM features. 329 Examples: 330 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 331 '_OSI("Module Device")' FALSE. 332 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 333 '_OSI("Module Device")' TRUE. 334 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 335 equivalent to 336 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 337 and 338 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 339 they all will make '_OSI("Windows 2000")' TRUE. 340 341 acpi_pm_good [X86] 342 Override the pmtimer bug detection: force the kernel 343 to assume that this machine's pmtimer latches its value 344 and always returns good values. 345 346 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 347 Format: { level | edge | high | low } 348 349 acpi_skip_timer_override [HW,ACPI,EARLY] 350 Recognize and ignore IRQ0/pin2 Interrupt Override. 351 For broken nForce2 BIOS resulting in XT-PIC timer. 352 353 acpi_sleep= [HW,ACPI] Sleep options 354 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 355 s4_nohwsig, old_ordering, nonvs, 356 sci_force_enable, nobl } 357 See Documentation/power/video.rst for information on 358 s3_bios and s3_mode. 359 s3_beep is for debugging; it makes the PC's speaker beep 360 as soon as the kernel's real-mode entry point is called. 361 s4_hwsig causes the kernel to check the ACPI hardware 362 signature during resume from hibernation, and gracefully 363 refuse to resume if it has changed. This complies with 364 the ACPI specification but not with reality, since 365 Windows does not do this and many laptops do change it 366 on docking. So the default behaviour is to allow resume 367 and simply warn when the signature changes, unless the 368 s4_hwsig option is enabled. 369 s4_nohwsig prevents ACPI hardware signature from being 370 used (or even warned about) during resume. 371 old_ordering causes the ACPI 1.0 ordering of the _PTS 372 control method, with respect to putting devices into 373 low power states, to be enforced (the ACPI 2.0 ordering 374 of _PTS is used by default). 375 nonvs prevents the kernel from saving/restoring the 376 ACPI NVS memory during suspend/hibernation and resume. 377 sci_force_enable causes the kernel to set SCI_EN directly 378 on resume from S1/S3 (which is against the ACPI spec, 379 but some broken systems don't work without it). 380 nobl causes the internal blacklist of systems known to 381 behave incorrectly in some ways with respect to system 382 suspend and resume to be ignored (use wisely). 383 384 acpi_use_timer_override [HW,ACPI,EARLY] 385 Use timer override. For some broken Nvidia NF5 boards 386 that require a timer override, but don't have HPET 387 388 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 389 kernel's map of available physical RAM. 390 391 agp= [AGP] 392 { off | try_unsupported } 393 off: disable AGP support 394 try_unsupported: try to drive unsupported chipsets 395 (may crash computer or cause data corruption) 396 397 ALSA [HW,ALSA] 398 See Documentation/sound/alsa-configuration.rst 399 400 alignment= [KNL,ARM] 401 Allow the default userspace alignment fault handler 402 behaviour to be specified. Bit 0 enables warnings, 403 bit 1 enables fixups, and bit 2 sends a segfault. 404 405 align_va_addr= [X86-64] 406 Align virtual addresses by clearing slice [14:12] when 407 allocating a VMA at process creation time. This option 408 gives you up to 3% performance improvement on AMD F15h 409 machines (where it is enabled by default) for a 410 CPU-intensive style benchmark, and it can vary highly in 411 a microbenchmark depending on workload and compiler. 412 413 32: only for 32-bit processes 414 64: only for 64-bit processes 415 on: enable for both 32- and 64-bit processes 416 off: disable for both 32- and 64-bit processes 417 418 alloc_snapshot [FTRACE] 419 Allocate the ftrace snapshot buffer on boot up when the 420 main buffer is allocated. This is handy if debugging 421 and you need to use tracing_snapshot() on boot up, and 422 do not want to use tracing_snapshot_alloc() as it needs 423 to be done where GFP_KERNEL allocations are allowed. 424 425 allow_mismatched_32bit_el0 [ARM64,EARLY] 426 Allow execve() of 32-bit applications and setting of the 427 PER_LINUX32 personality on systems where only a strict 428 subset of the CPUs support 32-bit EL0. When this 429 parameter is present, the set of CPUs supporting 32-bit 430 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 431 and hot-unplug operations may be restricted. 432 433 See Documentation/arch/arm64/asymmetric-32bit.rst for more 434 information. 435 436 amd_iommu= [HW,X86-64] 437 Pass parameters to the AMD IOMMU driver in the system. 438 Possible values are: 439 fullflush - Deprecated, equivalent to iommu.strict=1 440 off - do not initialize any AMD IOMMU found in 441 the system 442 force_isolation - Force device isolation for all 443 devices. The IOMMU driver is not 444 allowed anymore to lift isolation 445 requirements as needed. This option 446 does not override iommu=pt 447 force_enable - Force enable the IOMMU on platforms known 448 to be buggy with IOMMU enabled. Use this 449 option with care. 450 pgtbl_v1 - Use v1 page table for DMA-API (Default). 451 pgtbl_v2 - Use v2 page table for DMA-API. 452 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 453 nohugepages - Limit page-sizes used for v1 page-tables 454 to 4 KiB. 455 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 456 to 4KiB/2Mib/1GiB. 457 458 459 amd_iommu_dump= [HW,X86-64] 460 Enable AMD IOMMU driver option to dump the ACPI table 461 for AMD IOMMU. With this option enabled, AMD IOMMU 462 driver will print ACPI tables for AMD IOMMU during 463 IOMMU initialization. 464 465 amd_iommu_intr= [HW,X86-64] 466 Specifies one of the following AMD IOMMU interrupt 467 remapping modes: 468 legacy - Use legacy interrupt remapping mode. 469 vapic - Use virtual APIC mode, which allows IOMMU 470 to inject interrupts directly into guest. 471 This mode requires kvm-amd.avic=1. 472 (Default when IOMMU HW support is present.) 473 474 amd_pstate= [X86,EARLY] 475 disable 476 Do not enable amd_pstate as the default 477 scaling driver for the supported processors 478 passive 479 Use amd_pstate with passive mode as a scaling driver. 480 In this mode autonomous selection is disabled. 481 Driver requests a desired performance level and platform 482 tries to match the same performance level if it is 483 satisfied by guaranteed performance level. 484 active 485 Use amd_pstate_epp driver instance as the scaling driver, 486 driver provides a hint to the hardware if software wants 487 to bias toward performance (0x0) or energy efficiency (0xff) 488 to the CPPC firmware. then CPPC power algorithm will 489 calculate the runtime workload and adjust the realtime cores 490 frequency. 491 guided 492 Activate guided autonomous mode. Driver requests minimum and 493 maximum performance level and the platform autonomously 494 selects a performance level in this range and appropriate 495 to the current workload. 496 497 amd_prefcore= 498 [X86] 499 disable 500 Disable amd-pstate preferred core. 501 502 amd_dynamic_epp= 503 [X86] 504 disable 505 Disable amd-pstate dynamic EPP. 506 enable 507 Enable amd-pstate dynamic EPP. 508 509 amijoy.map= [HW,JOY] Amiga joystick support 510 Map of devices attached to JOY0DAT and JOY1DAT 511 Format: <a>,<b> 512 See also Documentation/input/joydev/joystick.rst 513 514 analog.map= [HW,JOY] Analog joystick and gamepad support 515 Specifies type or capabilities of an analog joystick 516 connected to one of 16 gameports 517 Format: <type1>,<type2>,..<type16> 518 519 apc= [HW,SPARC] 520 Power management functions (SPARCstation-4/5 + deriv.) 521 Format: noidle 522 Disable APC CPU standby support. SPARCstation-Fox does 523 not play well with APC CPU idle - disable it if you have 524 APC and your system crashes randomly. 525 526 apic [APIC,X86-64] Use IO-APIC. Default. 527 528 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 529 Change the output verbosity while booting 530 Format: { quiet (default) | verbose | debug } 531 Change the amount of debugging information output 532 when initialising the APIC and IO-APIC components. 533 534 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 535 Format: { bsp (default) | all | none } 536 bsp: External NMI is delivered only to CPU 0 537 all: External NMIs are broadcast to all CPUs as a 538 backup of CPU 0 539 none: External NMI is masked for all CPUs. This is 540 useful so that a dump capture kernel won't be 541 shot down by NMI 542 543 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 544 apicmaintimer. Useful when your PIT timer is totally 545 broken. 546 547 autoconf= [IPV6] 548 See Documentation/networking/ipv6.rst. 549 550 apm= [APM] Advanced Power Management 551 See header of arch/x86/kernel/apm_32.c. 552 553 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 554 Format: { "0" | "1" } 555 See security/apparmor/Kconfig help text 556 0 -- disable. 557 1 -- enable. 558 Default value is set via kernel config option. 559 560 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 561 Format: <io>,<irq>,<nodeID> 562 563 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 564 32 bit applications. 565 566 arm64.nobti [ARM64] Unconditionally disable Branch Target 567 Identification support 568 569 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 570 support 571 572 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 573 Set instructions support 574 575 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 576 Monitoring support 577 578 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 579 support 580 581 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 582 support 583 584 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 585 Extension support 586 587 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 588 Extension support 589 590 ataflop= [HW,M68k] 591 592 atarimouse= [HW,MOUSE] Atari Mouse 593 594 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 595 EzKey and similar keyboards 596 597 atkbd.reset= [HW] Reset keyboard during initialization 598 599 atkbd.set= [HW] Select keyboard code set 600 Format: <int> (2 = AT (default), 3 = PS/2) 601 602 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 603 keyboards 604 605 atkbd.softraw= [HW] Choose between synthetic and real raw mode 606 Format: <bool> (0 = real, 1 = synthetic (default)) 607 608 atkbd.softrepeat= [HW] 609 Use software keyboard repeat 610 611 audit= [KNL] Enable the audit sub-system 612 Format: { "0" | "1" | "off" | "on" } 613 0 | off - kernel audit is disabled and can not be 614 enabled until the next reboot 615 unset - kernel audit is initialized but disabled and 616 will be fully enabled by the userspace auditd. 617 1 | on - kernel audit is initialized and partially 618 enabled, storing at most audit_backlog_limit 619 messages in RAM until it is fully enabled by the 620 userspace auditd. 621 Default: unset 622 623 audit_backlog_limit= [KNL] Set the audit queue size limit. 624 Format: <int> (must be >=0) 625 Default: 64 626 627 bau= [X86_UV] Enable the BAU on SGI UV. The default 628 behavior is to disable the BAU (i.e. bau=0). 629 Format: { "0" | "1" } 630 0 - Disable the BAU. 631 1 - Enable the BAU. 632 unset - Disable the BAU. 633 634 bdev_allow_write_mounted= 635 Format: <bool> 636 Control the ability to open a mounted block device 637 for writing, i.e., allow / disallow writes that bypass 638 the FS. This was implemented as a means to prevent 639 fuzzers from crashing the kernel by overwriting the 640 metadata underneath a mounted FS without its awareness. 641 This also prevents destructive formatting of mounted 642 filesystems by naive storage tooling that don't use 643 O_EXCL. Default is Y and can be changed through the 644 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 645 646 bert_disable [ACPI] 647 Disable BERT OS support on buggy BIOSes. 648 649 bgrt_disable [ACPI,X86,EARLY] 650 Disable BGRT to avoid flickering OEM logo. 651 652 blkdevparts= Manual partition parsing of block device(s) for 653 embedded devices based on command line input. 654 See Documentation/block/cmdline-partition.rst 655 656 boot_delay= [KNL,EARLY] 657 Milliseconds to delay each printk during boot. 658 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 659 and you may also have to specify "lpj=". Boot_delay 660 values larger than 10 seconds (10000) are assumed 661 erroneous and ignored. 662 Format: integer 663 664 bootconfig [KNL,EARLY] 665 Extended command line options can be added to an initrd 666 and this will cause the kernel to look for it. 667 668 See Documentation/admin-guide/bootconfig.rst 669 670 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 671 bttv.radio= Most important insmod options are available as 672 kernel args too. 673 bttv.pll= See Documentation/admin-guide/media/bttv.rst 674 bttv.tuner= 675 676 bulk_remove=off [PPC] This parameter disables the use of the pSeries 677 firmware feature for flushing multiple hpte entries 678 at a time. 679 680 c101= [NET] Moxa C101 synchronous serial card 681 682 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 683 Sometimes CPU hardware bugs make them report the cache 684 size incorrectly. The kernel will attempt work arounds 685 to fix known problems, but for some CPUs it is not 686 possible to determine what the correct size should be. 687 This option provides an override for these situations. 688 689 carrier_timeout= 690 [NET] Specifies amount of time (in seconds) that 691 the kernel should wait for a network carrier. By default 692 it waits 120 seconds. 693 694 ca_keys= [KEYS] This parameter identifies a specific key(s) on 695 the system trusted keyring to be used for certificate 696 trust validation. 697 format: { id:<keyid> | builtin } 698 699 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 700 algorithm. Accepted values range from 0 to 7 701 inclusive. See arch/mips/include/asm/pgtable-bits.h 702 for platform specific values (SB1, Loongson3 and 703 others). 704 705 ccw_timeout_log [S390] 706 See Documentation/arch/s390/common_io.rst for details. 707 708 cfi= [X86-64] Set Control Flow Integrity checking features 709 when CONFIG_FINEIBT is enabled. 710 Format: feature[,feature...] 711 Default: auto 712 713 auto: Use FineIBT if IBT available, otherwise kCFI. 714 Under FineIBT, enable "paranoid" mode when 715 FRED is not available. 716 off: Turn off CFI checking. 717 kcfi: Use kCFI (disable FineIBT). 718 fineibt: Use FineIBT (even if IBT not available). 719 norand: Do not re-randomize CFI hashes. 720 paranoid: Add caller hash checking under FineIBT. 721 bhi: Enable register poisoning to stop speculation 722 across FineIBT. (Disabled by default.) 723 warn: Do not enforce CFI checking: warn only. 724 debug: Report CFI initialization details. 725 726 cgroup_disable= [KNL] Disable a particular controller or optional feature 727 Format: {name of the controller(s) or feature(s) to disable} 728 The effects of cgroup_disable=foo are: 729 - foo isn't auto-mounted if you mount all cgroups in 730 a single hierarchy 731 - foo isn't visible as an individually mountable 732 subsystem 733 - if foo is an optional feature then the feature is 734 disabled and corresponding cgroup files are not 735 created 736 {Currently only "memory" controller deal with this and 737 cut the overhead, others just disable the usage. So 738 only cgroup_disable=memory is actually worthy} 739 Specifying "pressure" disables per-cgroup pressure 740 stall information accounting feature 741 742 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 743 Format: { { controller | "all" | "named" } 744 [,{ controller | "all" | "named" }...] } 745 Like cgroup_disable, but only applies to cgroup v1; 746 the blacklisted controllers remain available in cgroup2. 747 "all" blacklists all controllers and "named" disables 748 named mounts. Specifying both "all" and "named" disables 749 all v1 hierarchies. 750 751 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 752 Format: { "true" | "false" } 753 /proc/cgroups lists only v1 controllers by default. 754 This compatibility option enables listing also v2 755 controllers (whose v1 code is not compiled!), so that 756 semi-legacy software can check this file to decide 757 about usage of v2 (sic) controllers. 758 759 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 760 Format: { "true" | "false" } 761 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 762 763 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 764 Format: <string> 765 nosocket -- Disable socket memory accounting. 766 nokmem -- Disable kernel memory accounting. 767 nobpf -- Disable BPF memory accounting. 768 769 check_pages= [MM,EARLY] Enable sanity checking of pages after 770 allocations / before freeing. This adds checks to catch 771 double-frees, use-after-frees, and other sources of 772 page corruption by inspecting page internals (flags, 773 mapcount/refcount, memcg_data, etc.). 774 Format: { "0" | "1" } 775 Default: 0 (1 if CONFIG_DEBUG_VM is set) 776 777 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 778 Format: { "0" | "1" } 779 See security/selinux/Kconfig help text. 780 0 -- check protection applied by kernel (includes 781 any implied execute protection). 782 1 -- check protection requested by application. 783 Default value is set via a kernel config option. 784 Value can be changed at runtime via 785 /sys/fs/selinux/checkreqprot. 786 Setting checkreqprot to 1 is deprecated. 787 788 cio_ignore= [S390] 789 See Documentation/arch/s390/common_io.rst for details. 790 791 clearcpuid=X[,X...] [X86] 792 Disable CPUID feature X for the kernel. See 793 arch/x86/include/asm/cpufeatures.h for the valid bit 794 numbers X. Note the Linux-specific bits are not necessarily 795 stable over kernel options, but the vendor-specific 796 ones should be. 797 X can also be a string as appearing in the flags: line 798 in /proc/cpuinfo which does not have the above 799 instability issue. However, not all features have names 800 in /proc/cpuinfo. 801 Note that using this option will taint your kernel. 802 Also note that user programs calling CPUID directly 803 or using the feature without checking anything 804 will still see it. This just prevents it from 805 being used by the kernel or shown in /proc/cpuinfo. 806 Also note the kernel might malfunction if you disable 807 some critical bits. 808 809 clk_ignore_unused 810 [CLK] 811 Prevents the clock framework from automatically gating 812 clocks that have not been explicitly enabled by a Linux 813 device driver but are enabled in hardware at reset or 814 by the bootloader/firmware. Note that this does not 815 force such clocks to be always-on nor does it reserve 816 those clocks in any way. This parameter is useful for 817 debug and development, but should not be needed on a 818 platform with proper driver support. For more 819 information, see Documentation/driver-api/clk.rst. 820 821 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 822 [Deprecated] 823 Forces specified clocksource (if available) to be used 824 when calculating gettimeofday(). If specified 825 clocksource is not available, it defaults to PIT. 826 Format: { pit | tsc | cyclone | pmtmr } 827 828 clocksource= Override the default clocksource 829 Format: <string> 830 Override the default clocksource and use the clocksource 831 with the name specified. 832 Some clocksource names to choose from, depending on 833 the platform: 834 [all] jiffies (this is the base, fallback clocksource) 835 [ACPI] acpi_pm 836 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 837 pxa_timer,timer3,32k_counter,timer0_1 838 [X86-32] pit,hpet,tsc; 839 scx200_hrt on Geode; cyclone on IBM x440 840 [MIPS] MIPS 841 [PARISC] cr16 842 [S390] tod 843 [SH] SuperH 844 [SPARC64] tick 845 [X86-64] hpet,tsc 846 847 clocksource.arm_arch_timer.evtstrm= 848 [ARM,ARM64,EARLY] 849 Format: <bool> 850 Enable/disable the eventstream feature of the ARM 851 architected timer so that code using WFE-based polling 852 loops can be debugged more effectively on production 853 systems. 854 855 clocksource.verify_n_cpus= [KNL] 856 Limit the number of CPUs checked for clocksources 857 marked with CLOCK_SOURCE_VERIFY_PERCPU that 858 are marked unstable due to excessive skew. 859 A negative value says to check all CPUs, while 860 zero says not to check any. Values larger than 861 nr_cpu_ids are silently truncated to nr_cpu_ids. 862 The actual CPUs are chosen randomly, with 863 no replacement if the same CPU is chosen twice. 864 865 clocksource-wdtest.holdoff= [KNL] 866 Set the time in seconds that the clocksource 867 watchdog test waits before commencing its tests. 868 Defaults to zero when built as a module and to 869 10 seconds when built into the kernel. 870 871 cma=nn[MG]@[start[MG][-end[MG]]] 872 [KNL,CMA,EARLY] 873 Sets the size of kernel global memory area for 874 contiguous memory allocations and optionally the 875 placement constraint by the physical address range of 876 memory allocations. A value of 0 disables CMA 877 altogether. For more information, see 878 kernel/dma/contiguous.c 879 880 cma_pernuma=nn[MG] 881 [KNL,CMA,EARLY] 882 Sets the size of kernel per-numa memory area for 883 contiguous memory allocations. A value of 0 disables 884 per-numa CMA altogether. And If this option is not 885 specified, the default value is 0. 886 With per-numa CMA enabled, DMA users on node nid will 887 first try to allocate buffer from the pernuma area 888 which is located in node nid, if the allocation fails, 889 they will fallback to the global default memory area. 890 891 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 892 [KNL,CMA,EARLY] 893 Sets the size of kernel numa memory area for 894 contiguous memory allocations. It will reserve CMA 895 area for the specified node. 896 897 With numa CMA enabled, DMA users on node nid will 898 first try to allocate buffer from the numa area 899 which is located in node nid, if the allocation fails, 900 they will fallback to the global default memory area. 901 902 cmo_free_hint= [PPC] Format: { yes | no } 903 Specify whether pages are marked as being inactive 904 when they are freed. This is used in CMO environments 905 to determine OS memory pressure for page stealing by 906 a hypervisor. 907 Default: yes 908 909 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 910 Sets the size of memory pool for coherent, atomic dma 911 allocations, by default set to 256K. 912 913 com20020= [HW,NET] ARCnet - COM20020 chipset 914 Format: 915 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 916 917 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 918 Format: <io>[,<irq>] 919 920 com90xx= [HW,NET] 921 ARCnet - COM90xx chipset (memory-mapped buffers) 922 Format: <io>[,<irq>[,<memstart>]] 923 924 condev= [HW,S390] console device 925 conmode= 926 927 con3215_drop= [S390,EARLY] 3215 console drop mode. 928 Format: y|n|Y|N|1|0 929 When set to true, drop data on the 3215 console when 930 the console buffer is full. In this case the 931 operator using a 3270 terminal emulator (for example 932 x3270) does not have to enter the clear key for the 933 console output to advance and the kernel to continue. 934 This leads to a much faster boot time when a 3270 935 terminal emulator is active. If no 3270 terminal 936 emulator is used, this parameter has no effect. 937 938 console= [KNL] Output console device and options. 939 940 tty<n> Use the virtual console device <n>. 941 942 ttyS<n>[,options] 943 ttyUSB0[,options] 944 Use the specified serial port. The options are of 945 the form "bbbbpnf", where "bbbb" is the baud rate, 946 "p" is parity ("n", "o", or "e"), "n" is number of 947 bits, and "f" is flow control ("r" for RTS or 948 omit it). Default is "9600n8". 949 950 See Documentation/admin-guide/serial-console.rst for more 951 information. See 952 Documentation/networking/netconsole.rst for an 953 alternative. 954 955 <DEVNAME>:<n>.<n>[,options] 956 Use the specified serial port on the serial core bus. 957 The addressing uses DEVNAME of the physical serial port 958 device, followed by the serial core controller instance, 959 and the serial port instance. The options are the same 960 as documented for the ttyS addressing above. 961 962 The mapping of the serial ports to the tty instances 963 can be viewed with: 964 965 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 966 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 967 968 In the above example, the console can be addressed with 969 console=00:04:0.0. Note that a console addressed this 970 way will only get added when the related device driver 971 is ready. The use of an earlycon parameter in addition to 972 the console may be desired for console output early on. 973 974 uart[8250],io,<addr>[,options] 975 uart[8250],mmio,<addr>[,options] 976 uart[8250],mmio16,<addr>[,options] 977 uart[8250],mmio32,<addr>[,options] 978 uart[8250],0x<addr>[,options] 979 Start an early, polled-mode console on the 8250/16550 980 UART at the specified I/O port or MMIO address, 981 switching to the matching ttyS device later. 982 MMIO inter-register address stride is either 8-bit 983 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 984 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 985 to be equivalent to 'mmio'. 'options' are specified in 986 the same format described for ttyS above; if unspecified, 987 the h/w is not re-initialized. 988 989 hvc<n> Use the hypervisor console device <n>. This is for 990 both Xen and PowerPC hypervisors. 991 992 { null | "" } 993 Use to disable console output, i.e., to have kernel 994 console messages discarded. 995 This must be the only console= parameter used on the 996 kernel command line. 997 998 If the device connected to the port is not a TTY but a braille 999 device, prepend "brl," before the device type, for instance 1000 console=brl,ttyS0 1001 For now, only VisioBraille is supported. 1002 1003 console_msg_format= 1004 [KNL] Change console messages format 1005 default 1006 By default we print messages on consoles in 1007 "[time stamp] text\n" format (time stamp may not be 1008 printed, depending on CONFIG_PRINTK_TIME or 1009 `printk_time' param). 1010 syslog 1011 Switch to syslog format: "<%u>[time stamp] text\n" 1012 IOW, each message will have a facility and loglevel 1013 prefix. The format is similar to one used by syslog() 1014 syscall, or to executing "dmesg -S --raw" or to reading 1015 from /proc/kmsg. 1016 1017 consoleblank= [KNL] The console blank (screen saver) timeout in 1018 seconds. A value of 0 disables the blank timer. 1019 Defaults to 0. 1020 1021 coredump_filter= 1022 [KNL] Change the default value for 1023 /proc/<pid>/coredump_filter. 1024 See also Documentation/filesystems/proc.rst. 1025 1026 coresight_cpu_debug.enable 1027 [ARM,ARM64] 1028 Format: <bool> 1029 Enable/disable the CPU sampling based debugging. 1030 0: default value, disable debugging 1031 1: enable debugging at boot time 1032 1033 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1034 Format: 1035 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1036 1037 cpuidle.off=1 [CPU_IDLE] 1038 disable the cpuidle sub-system 1039 1040 cpuidle.governor= 1041 [CPU_IDLE] Name of the cpuidle governor to use. 1042 1043 cpufreq.off=1 [CPU_FREQ] 1044 disable the cpufreq sub-system 1045 1046 cpufreq.default_governor= 1047 [CPU_FREQ] Name of the default cpufreq governor or 1048 policy to use. This governor must be registered in the 1049 kernel before the cpufreq driver probes. 1050 1051 cpu_init_udelay=N 1052 [X86,EARLY] Delay for N microsec between assert and de-assert 1053 of APIC INIT to start processors. This delay occurs 1054 on every CPU online, such as boot, and resume from suspend. 1055 Default: 10000 1056 1057 cpuhp.parallel= 1058 [SMP] Enable/disable parallel bringup of secondary CPUs 1059 Format: <bool> 1060 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1061 the parameter has no effect. 1062 1063 crash_kexec_post_notifiers 1064 Only jump to kdump kernel after running the panic 1065 notifiers and dumping kmsg. This option increases 1066 the risks of a kdump failure, since some panic 1067 notifiers can make the crashed kernel more unstable. 1068 In configurations where kdump may not be reliable, 1069 running the panic notifiers could allow collecting 1070 more data on dmesg, like stack traces from other CPUS 1071 or extra data dumped by panic_print. Note that some 1072 configurations enable this option unconditionally, 1073 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1074 1075 crashkernel=size[KMG][@offset[KMG]] 1076 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1077 upon panic. This parameter reserves the physical 1078 memory region [offset, offset + size] for that kernel 1079 image. If '@offset' is omitted, then a suitable offset 1080 is selected automatically. 1081 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1082 under 4G first, and fall back to reserve region above 1083 4G when '@offset' hasn't been specified. 1084 See Documentation/admin-guide/kdump/kdump.rst for further details. 1085 1086 crashkernel=range1:size1[,range2:size2,...][@offset] 1087 [KNL] Same as above, but depends on the memory 1088 in the running system. The syntax of range is 1089 start-[end] where start and end are both 1090 a memory unit (amount[KMG]). See also 1091 Documentation/admin-guide/kdump/kdump.rst for an example. 1092 1093 crashkernel=size[KMG],high 1094 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1095 above 4G. 1096 Allow kernel to allocate physical memory region from top, 1097 so could be above 4G if system have more than 4G ram 1098 installed. Otherwise memory region will be allocated 1099 below 4G, if available. 1100 It will be ignored if crashkernel=X is specified. 1101 crashkernel=size[KMG],low 1102 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1103 When crashkernel=X,high is passed, kernel could allocate 1104 physical memory region above 4G, that cause second kernel 1105 crash on system that require some amount of low memory, 1106 e.g. swiotlb requires at least 64M+32K low memory, also 1107 enough extra low memory is needed to make sure DMA buffers 1108 for 32-bit devices won't run out. Kernel would try to allocate 1109 default size of memory below 4G automatically. The default 1110 size is platform dependent. 1111 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1112 --> arm64: 128MiB 1113 --> riscv: 128MiB 1114 --> loongarch: 128MiB 1115 This one lets the user specify own low range under 4G 1116 for second kernel instead. 1117 0: to disable low allocation. 1118 It will be ignored when crashkernel=X,high is not used 1119 or memory reserved is below 4G. 1120 crashkernel=size[KMG],cma 1121 [KNL, X86, ppc] Reserve additional crash kernel memory from 1122 CMA. This reservation is usable by the first system's 1123 userspace memory and kernel movable allocations (memory 1124 balloon, zswap). Pages allocated from this memory range 1125 will not be included in the vmcore so this should not 1126 be used if dumping of userspace memory is intended and 1127 it has to be expected that some movable kernel pages 1128 may be missing from the dump. 1129 1130 A standard crashkernel reservation, as described above, 1131 is still needed to hold the crash kernel and initrd. 1132 1133 This option increases the risk of a kdump failure: DMA 1134 transfers configured by the first kernel may end up 1135 corrupting the second kernel's memory. 1136 1137 This reservation method is intended for systems that 1138 can't afford to sacrifice enough memory for standard 1139 crashkernel reservation and where less reliable and 1140 possibly incomplete kdump is preferable to no kdump at 1141 all. 1142 1143 cryptomgr.notests 1144 [KNL] Disable crypto self-tests 1145 1146 cs89x0_dma= [HW,NET] 1147 Format: <dma> 1148 1149 cs89x0_media= [HW,NET] 1150 Format: { rj45 | aui | bnc } 1151 1152 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1153 function call handling. When switched on, 1154 additional debug data is printed to the console 1155 in case a hanging CPU is detected, and that 1156 CPU is pinged again in order to try to resolve 1157 the hang situation. The default value of this 1158 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1159 Kconfig option. 1160 1161 dasd= [HW,NET] 1162 See header of drivers/s390/block/dasd_devmap.c. 1163 1164 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1165 (one device per port) 1166 Format: <port#>,<type> 1167 See also Documentation/input/devices/joystick-parport.rst 1168 1169 debug [KNL,EARLY] Enable kernel debugging (events log level). 1170 1171 debug_boot_weak_hash 1172 [KNL,EARLY] Enable printing [hashed] pointers early in the 1173 boot sequence. If enabled, we use a weak hash instead 1174 of siphash to hash pointers. Use this option if you are 1175 seeing instances of '(___ptrval___)') and need to see a 1176 value (hashed pointer) instead. Cryptographically 1177 insecure, please do not use on production kernels. 1178 1179 debug_locks_verbose= 1180 [KNL] verbose locking self-tests 1181 Format: <int> 1182 Print debugging info while doing the locking API 1183 self-tests. 1184 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1185 (no extra messages), setting it to -1 (all bits set) 1186 will print _a_lot_ more information - normally only 1187 useful to lockdep developers. 1188 1189 debug_objects [KNL,EARLY] Enable object debugging 1190 1191 debug_guardpage_minorder= 1192 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1193 parameter allows control of the order of pages that will 1194 be intentionally kept free (and hence protected) by the 1195 buddy allocator. Bigger value increase the probability 1196 of catching random memory corruption, but reduce the 1197 amount of memory for normal system use. The maximum 1198 possible value is MAX_PAGE_ORDER/2. Setting this 1199 parameter to 1 or 2 should be enough to identify most 1200 random memory corruption problems caused by bugs in 1201 kernel or driver code when a CPU writes to (or reads 1202 from) a random memory location. Note that there exists 1203 a class of memory corruptions problems caused by buggy 1204 H/W or F/W or by drivers badly programming DMA 1205 (basically when memory is written at bus level and the 1206 CPU MMU is bypassed) which are not detectable by 1207 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1208 help tracking down these problems. 1209 1210 debug_pagealloc= 1211 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1212 enables the feature at boot time. By default, it is 1213 disabled and the system will work mostly the same as a 1214 kernel built without CONFIG_DEBUG_PAGEALLOC. 1215 Note: to get most of debug_pagealloc error reports, it's 1216 useful to also enable the page_owner functionality. 1217 on: enable the feature 1218 1219 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1220 userspace and debugfs internal clients. 1221 Format: { on, off } 1222 on: All functions are enabled. 1223 off: Filesystem is not registered and clients 1224 get a -EPERM as result when trying to register files 1225 or directories within debugfs. 1226 This is equivalent of the runtime functionality if 1227 debugfs was not enabled in the kernel at all. 1228 Default value is set in build-time with a kernel configuration. 1229 1230 debugpat [X86] Enable PAT debugging 1231 1232 default_hugepagesz= 1233 [HW] The size of the default HugeTLB page. This is 1234 the size represented by the legacy /proc/ hugepages 1235 APIs. In addition, this is the default hugetlb size 1236 used for shmget(), mmap() and mounting hugetlbfs 1237 filesystems. If not specified, defaults to the 1238 architecture's default huge page size. Huge page 1239 sizes are architecture dependent. See also 1240 Documentation/admin-guide/mm/hugetlbpage.rst. 1241 Format: size[KMG] 1242 1243 deferred_probe_timeout= 1244 [KNL] Debugging option to set a timeout in seconds for 1245 deferred probe to give up waiting on dependencies to 1246 probe. Only specific dependencies (subsystems or 1247 drivers) that have opted in will be ignored. A timeout 1248 of 0 will timeout at the end of initcalls. If the time 1249 out hasn't expired, it'll be restarted by each 1250 successful driver registration. This option will also 1251 dump out devices still on the deferred probe list after 1252 retrying. 1253 1254 delayacct [KNL] Enable per-task delay accounting 1255 1256 dell_smm_hwmon.ignore_dmi= 1257 [HW] Continue probing hardware even if DMI data 1258 indicates that the driver is running on unsupported 1259 hardware. 1260 1261 dell_smm_hwmon.force= 1262 [HW] Activate driver even if SMM BIOS signature does 1263 not match list of supported models and enable otherwise 1264 blacklisted features. 1265 1266 dell_smm_hwmon.power_status= 1267 [HW] Report power status in /proc/i8k 1268 (disabled by default). 1269 1270 dell_smm_hwmon.restricted= 1271 [HW] Allow controlling fans only if SYS_ADMIN 1272 capability is set. 1273 1274 dell_smm_hwmon.fan_mult= 1275 [HW] Factor to multiply fan speed with. 1276 1277 dell_smm_hwmon.fan_max= 1278 [HW] Maximum configurable fan speed. 1279 1280 dfltcc= [HW,S390] 1281 Format: { on | off | def_only | inf_only | always } 1282 on: s390 zlib hardware support for compression on 1283 level 1 and decompression (default) 1284 off: No s390 zlib hardware support 1285 def_only: s390 zlib hardware support for deflate 1286 only (compression on level 1) 1287 inf_only: s390 zlib hardware support for inflate 1288 only (decompression) 1289 always: Same as 'on' but ignores the selected compression 1290 level always using hardware support (used for debugging) 1291 1292 dhash_entries= [KNL] 1293 Set number of hash buckets for dentry cache. 1294 1295 disable_1tb_segments [PPC,EARLY] 1296 Disables the use of 1TB hash page table segments. This 1297 causes the kernel to fall back to 256MB segments which 1298 can be useful when debugging issues that require an SLB 1299 miss to occur. 1300 1301 disable= [IPV6] 1302 See Documentation/networking/ipv6.rst. 1303 1304 disable_radix [PPC,EARLY] 1305 Disable RADIX MMU mode on POWER9 1306 1307 disable_tlbie [PPC] 1308 Disable TLBIE instruction. Currently does not work 1309 with KVM, with HASH MMU, or with coherent accelerators. 1310 1311 disable_ddw [PPC/PSERIES,EARLY] 1312 Disable Dynamic DMA Window support. Use this 1313 to workaround buggy firmware. 1314 1315 disable_ipv6= [IPV6] 1316 See Documentation/networking/ipv6.rst. 1317 1318 disable_mtrr_cleanup [X86,EARLY] 1319 The kernel tries to adjust MTRR layout from continuous 1320 to discrete, to make X server driver able to add WB 1321 entry later. This parameter disables that. 1322 1323 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1324 By default the kernel will trim any uncacheable 1325 memory out of your available memory pool based on 1326 MTRR settings. This parameter disables that behavior, 1327 possibly causing your machine to run very slowly. 1328 1329 disable_timer_pin_1 [X86,EARLY] 1330 Disable PIN 1 of APIC timer 1331 Can be useful to work around chipset bugs. 1332 1333 dis_ucode_ldr [X86] Disable the microcode loader. 1334 1335 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1336 this option disables the debugging code at boot. 1337 1338 dma_debug_entries=<number> 1339 This option allows to tune the number of preallocated 1340 entries for DMA-API debugging code. One entry is 1341 required per DMA-API allocation. Use this if the 1342 DMA-API debugging code disables itself because the 1343 architectural default is too low. 1344 1345 dma_debug_driver=<driver_name> 1346 With this option the DMA-API debugging driver 1347 filter feature can be enabled at boot time. Just 1348 pass the driver to filter for as the parameter. 1349 The filter can be disabled or changed to another 1350 driver later using sysfs. 1351 1352 reg_file_data_sampling= 1353 [X86] Controls mitigation for Register File Data 1354 Sampling (RFDS) vulnerability. RFDS is a CPU 1355 vulnerability which may allow userspace to infer 1356 kernel data values previously stored in floating point 1357 registers, vector registers, or integer registers. 1358 RFDS only affects Intel Atom processors. 1359 1360 on: Turns ON the mitigation. 1361 off: Turns OFF the mitigation. 1362 1363 This parameter overrides the compile time default set 1364 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1365 disabled when other VERW based mitigations (like MDS) 1366 are enabled. In order to disable RFDS mitigation all 1367 VERW based mitigations need to be disabled. 1368 1369 For details see: 1370 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1371 1372 dm_verity.keyring_unsealed= 1373 [KNL] When set to 1, leave the dm-verity keyring 1374 unsealed after initialization so userspace can 1375 provision keys. Once the keyring is restricted 1376 it becomes active and is searched during signature 1377 verification. 1378 1379 driver_async_probe= [KNL] 1380 List of driver names to be probed asynchronously. * 1381 matches with all driver names. If * is specified, the 1382 rest of the listed driver names are those that will NOT 1383 match the *. 1384 Format: <driver_name1>,<driver_name2>... 1385 1386 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1387 Broken monitors, graphic adapters, KVMs and EDIDless 1388 panels may send no or incorrect EDID data sets. 1389 This parameter allows to specify an EDID data sets 1390 in the /lib/firmware directory that are used instead. 1391 An EDID data set will only be used for a particular 1392 connector, if its name and a colon are prepended to 1393 the EDID name. Each connector may use a unique EDID 1394 data set by separating the files with a comma. An EDID 1395 data set with no connector name will be used for 1396 any connectors not explicitly specified. 1397 1398 dscc4.setup= [NET] 1399 1400 dt_cpu_ftrs= [PPC,EARLY] 1401 Format: {"off" | "known"} 1402 Control how the dt_cpu_ftrs device-tree binding is 1403 used for CPU feature discovery and setup (if it 1404 exists). 1405 off: Do not use it, fall back to legacy cpu table. 1406 known: Do not pass through unknown features to guests 1407 or userspace, only those that the kernel is aware of. 1408 1409 dump_apple_properties [X86] 1410 Dump name and content of EFI device properties on 1411 x86 Macs. Useful for driver authors to determine 1412 what data is available or for reverse-engineering. 1413 1414 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1415 <module>.dyndbg[="val"] 1416 Enable debug messages at boot time. See 1417 Documentation/admin-guide/dynamic-debug-howto.rst 1418 for details. 1419 1420 early_ioremap_debug [KNL,EARLY] 1421 Enable debug messages in early_ioremap support. This 1422 is useful for tracking down temporary early mappings 1423 which are not unmapped. 1424 1425 earlycon= [KNL,EARLY] Output early console device and options. 1426 1427 When used with no options, the early console is 1428 determined by stdout-path property in device tree's 1429 chosen node or the ACPI SPCR table if supported by 1430 the platform. 1431 1432 cdns,<addr>[,options] 1433 Start an early, polled-mode console on a Cadence 1434 (xuartps) serial port at the specified address. Only 1435 supported option is baud rate. If baud rate is not 1436 specified, the serial port must already be setup and 1437 configured. 1438 1439 uart[8250],io,<addr>[,options[,uartclk]] 1440 uart[8250],mmio,<addr>[,options[,uartclk]] 1441 uart[8250],mmio32,<addr>[,options[,uartclk]] 1442 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1443 uart[8250],0x<addr>[,options] 1444 Start an early, polled-mode console on the 8250/16550 1445 UART at the specified I/O port or MMIO address. 1446 MMIO inter-register address stride is either 8-bit 1447 (mmio) or 32-bit (mmio32 or mmio32be). 1448 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1449 to be equivalent to 'mmio'. 'options' are specified 1450 in the same format described for "console=ttyS<n>"; if 1451 unspecified, the h/w is not initialized. 'uartclk' is 1452 the uart clock frequency; if unspecified, it is set 1453 to 'BASE_BAUD' * 16. 1454 1455 pl011,<addr> 1456 pl011,mmio32,<addr> 1457 Start an early, polled-mode console on a pl011 serial 1458 port at the specified address. The pl011 serial port 1459 must already be setup and configured. Options are not 1460 yet supported. If 'mmio32' is specified, then only 1461 the driver will use only 32-bit accessors to read/write 1462 the device registers. 1463 1464 liteuart,<addr> 1465 Start an early console on a litex serial port at the 1466 specified address. The serial port must already be 1467 setup and configured. Options are not yet supported. 1468 1469 meson,<addr> 1470 Start an early, polled-mode console on a meson serial 1471 port at the specified address. The serial port must 1472 already be setup and configured. Options are not yet 1473 supported. 1474 1475 msm_serial,<addr> 1476 Start an early, polled-mode console on an msm serial 1477 port at the specified address. The serial port 1478 must already be setup and configured. Options are not 1479 yet supported. 1480 1481 msm_serial_dm,<addr> 1482 Start an early, polled-mode console on an msm serial 1483 dm port at the specified address. The serial port 1484 must already be setup and configured. Options are not 1485 yet supported. 1486 1487 owl,<addr> 1488 Start an early, polled-mode console on a serial port 1489 of an Actions Semi SoC, such as S500 or S900, at the 1490 specified address. The serial port must already be 1491 setup and configured. Options are not yet supported. 1492 1493 rda,<addr> 1494 Start an early, polled-mode console on a serial port 1495 of an RDA Micro SoC, such as RDA8810PL, at the 1496 specified address. The serial port must already be 1497 setup and configured. Options are not yet supported. 1498 1499 sbi 1500 Use RISC-V SBI (Supervisor Binary Interface) for early 1501 console. 1502 1503 smh Use ARM semihosting calls for early console. 1504 1505 s3c2410,<addr> 1506 s3c2412,<addr> 1507 s3c2440,<addr> 1508 s3c6400,<addr> 1509 s5pv210,<addr> 1510 exynos4210,<addr> 1511 Use early console provided by serial driver available 1512 on Samsung SoCs, requires selecting proper type and 1513 a correct base address of the selected UART port. The 1514 serial port must already be setup and configured. 1515 Options are not yet supported. 1516 1517 lantiq,<addr> 1518 Start an early, polled-mode console on a lantiq serial 1519 (lqasc) port at the specified address. The serial port 1520 must already be setup and configured. Options are not 1521 yet supported. 1522 1523 lpuart,<addr> 1524 lpuart32,<addr> 1525 Use early console provided by Freescale LP UART driver 1526 found on Freescale Vybrid and QorIQ LS1021A processors. 1527 A valid base address must be provided, and the serial 1528 port must already be setup and configured. 1529 1530 ec_imx21,<addr> 1531 ec_imx6q,<addr> 1532 Start an early, polled-mode, output-only console on the 1533 Freescale i.MX UART at the specified address. The UART 1534 must already be setup and configured. 1535 1536 ar3700_uart,<addr> 1537 Start an early, polled-mode console on the 1538 Armada 3700 serial port at the specified 1539 address. The serial port must already be setup 1540 and configured. Options are not yet supported. 1541 1542 qcom_geni,<addr> 1543 Start an early, polled-mode console on a Qualcomm 1544 Generic Interface (GENI) based serial port at the 1545 specified address. The serial port must already be 1546 setup and configured. Options are not yet supported. 1547 1548 efifb,[options] 1549 Start an early, unaccelerated console on the EFI 1550 memory mapped framebuffer (if available). On cache 1551 coherent non-x86 systems that use system memory for 1552 the framebuffer, pass the 'ram' option so that it is 1553 mapped with the correct attributes. 1554 1555 linflex,<addr> 1556 Use early console provided by Freescale LINFlexD UART 1557 serial driver for NXP S32V234 SoCs. A valid base 1558 address must be provided, and the serial port must 1559 already be setup and configured. 1560 1561 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1562 earlyprintk=vga 1563 earlyprintk=sclp 1564 earlyprintk=xen 1565 earlyprintk=serial[,ttySn[,baudrate]] 1566 earlyprintk=serial[,0x...[,baudrate]] 1567 earlyprintk=ttySn[,baudrate] 1568 earlyprintk=dbgp[debugController#] 1569 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1570 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1571 earlyprintk=xdbc[xhciController#] 1572 earlyprintk=bios 1573 1574 earlyprintk is useful when the kernel crashes before 1575 the normal console is initialized. It is not enabled by 1576 default because it has some cosmetic problems. 1577 1578 Use "nocfg" to skip UART configuration, assume 1579 BIOS/firmware has configured UART correctly. 1580 1581 Append ",keep" to not disable it when the real console 1582 takes over. 1583 1584 Only one of vga, serial, or usb debug port can 1585 be used at a time. 1586 1587 Currently only ttyS0 and ttyS1 may be specified by 1588 name. Other I/O ports may be explicitly specified 1589 on some architectures (x86 and arm at least) by 1590 replacing ttySn with an I/O port address, like this: 1591 earlyprintk=serial,0x1008,115200 1592 You can find the port for a given device in 1593 /proc/tty/driver/serial: 1594 2: uart:ST16650V2 port:00001008 irq:18 ... 1595 1596 Interaction with the standard serial driver is not 1597 very good. 1598 1599 The VGA output is eventually overwritten by 1600 the real console. 1601 1602 The xen option can only be used in Xen domains. 1603 1604 The sclp output can only be used on s390. 1605 1606 The bios output can only be used on SuperH. 1607 1608 The optional "force" to "pciserial" enables use of a 1609 PCI device even when its classcode is not of the 1610 UART class. 1611 1612 edac_report= [HW,EDAC] Control how to report EDAC event 1613 Format: {"on" | "off" | "force"} 1614 on: enable EDAC to report H/W event. May be overridden 1615 by other higher priority error reporting module. 1616 off: disable H/W event reporting through EDAC. 1617 force: enforce the use of EDAC to report H/W event. 1618 default: on. 1619 1620 edd= [EDD] 1621 Format: {"off" | "on" | "skip[mbr]"} 1622 1623 efi= [EFI,EARLY] 1624 Format: { "debug", "disable_early_pci_dma", 1625 "nochunk", "noruntime", "nosoftreserve", 1626 "novamap", "no_disable_early_pci_dma" } 1627 debug: enable misc debug output. 1628 disable_early_pci_dma: disable the busmaster bit on all 1629 PCI bridges while in the EFI boot stub. 1630 nochunk: disable reading files in "chunks" in the EFI 1631 boot stub, as chunking can cause problems with some 1632 firmware implementations. 1633 noruntime : disable EFI runtime services support 1634 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1635 attribute may cause the kernel to reserve the 1636 memory range for a memory mapping driver to 1637 claim. Specify efi=nosoftreserve to disable this 1638 reservation and treat the memory by its base type 1639 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1640 novamap: do not call SetVirtualAddressMap(). 1641 no_disable_early_pci_dma: Leave the busmaster bit set 1642 on all PCI bridges while in the EFI boot stub 1643 1644 efi_no_storage_paranoia [EFI,X86,EARLY] 1645 Using this parameter you can use more than 50% of 1646 your efi variable storage. Use this parameter only if 1647 you are really sure that your UEFI does sane gc and 1648 fulfills the spec otherwise your board may brick. 1649 1650 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1651 that is to be dynamically loaded by Linux. If there are 1652 multiple variables with the same name but with different 1653 vendor GUIDs, all of them will be loaded. See 1654 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1655 1656 1657 eisa_irq_edge= [PARISC,HW] 1658 See header of drivers/parisc/eisa.c. 1659 1660 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1661 Format: ekgdboc=kbd 1662 1663 This is designed to be used in conjunction with 1664 the boot argument: earlyprintk=vga 1665 1666 This parameter works in place of the kgdboc parameter 1667 but can only be used if the backing tty is available 1668 very early in the boot process. For early debugging 1669 via a serial port see kgdboc_earlycon instead. 1670 1671 elanfreq= [X86-32] 1672 See comment before function elanfreq_setup() in 1673 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1674 1675 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1676 Specifies physical address of start of kernel core 1677 image elf header and optionally the size. Generally 1678 kexec loader will pass this option to capture kernel. 1679 See Documentation/admin-guide/kdump/kdump.rst for details. 1680 1681 enable_mtrr_cleanup [X86,EARLY] 1682 The kernel tries to adjust MTRR layout from continuous 1683 to discrete, to make X server driver able to add WB 1684 entry later. This parameter enables that. 1685 1686 enable_timer_pin_1 [X86] 1687 Enable PIN 1 of APIC timer 1688 Can be useful to work around chipset bugs 1689 (in particular on some ATI chipsets). 1690 The kernel tries to set a reasonable default. 1691 1692 enforcing= [SELINUX] Set initial enforcing status. 1693 Format: {"0" | "1"} 1694 See security/selinux/Kconfig help text. 1695 0 -- permissive (log only, no denials). 1696 1 -- enforcing (deny and log). 1697 Default value is 0. 1698 Value can be changed at runtime via 1699 /sys/fs/selinux/enforce. 1700 1701 erst_disable [ACPI] 1702 Disable Error Record Serialization Table (ERST) 1703 support. 1704 1705 ether= [HW,NET] Ethernet cards parameters 1706 This option is obsoleted by the "netdev=" option, which 1707 has equivalent usage. See its documentation for details. 1708 1709 evm= [EVM] 1710 Format: { "fix" } 1711 Permit 'security.evm' to be updated regardless of 1712 current integrity status. 1713 1714 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1715 stages so cover more early boot allocations. 1716 Please note that as side effect some optimizations 1717 might be disabled to achieve that (e.g. parallelized 1718 memory initialization is disabled) so the boot process 1719 might take longer, especially on systems with a lot of 1720 memory. Available with CONFIG_PAGE_EXTENSION=y. 1721 1722 failslab= 1723 fail_usercopy= 1724 fail_page_alloc= 1725 fail_skb_realloc= 1726 fail_make_request=[KNL] 1727 General fault injection mechanism. 1728 Format: <interval>,<probability>,<space>,<times> 1729 See also Documentation/fault-injection/. 1730 1731 fb_tunnels= [NET] 1732 Format: { initns | none } 1733 See Documentation/admin-guide/sysctl/net.rst for 1734 fb_tunnels_only_for_init_ns 1735 1736 floppy= [HW] 1737 See Documentation/admin-guide/blockdev/floppy.rst. 1738 1739 forcepae [X86-32] 1740 Forcefully enable Physical Address Extension (PAE). 1741 Many Pentium M systems disable PAE but may have a 1742 functionally usable PAE implementation. 1743 Warning: use of this parameter will taint the kernel 1744 and may cause unknown problems. 1745 1746 fred= [X86-64] 1747 Enable/disable Flexible Return and Event Delivery. 1748 Format: { on | off } 1749 on: enable FRED when it's present, the default setting. 1750 off: disable FRED. 1751 1752 ftrace=[tracer] 1753 [FTRACE] will set and start the specified tracer 1754 as early as possible in order to facilitate early 1755 boot debugging. 1756 1757 ftrace_boot_snapshot 1758 [FTRACE] On boot up, a snapshot will be taken of the 1759 ftrace ring buffer that can be read at: 1760 /sys/kernel/tracing/snapshot. 1761 This is useful if you need tracing information from kernel 1762 boot up that is likely to be overridden by user space 1763 start up functionality. 1764 1765 Optionally, the snapshot can also be defined for a tracing 1766 instance that was created by the trace_instance= command 1767 line parameter. 1768 1769 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1770 1771 The above will cause the "foo" tracing instance to trigger 1772 a snapshot at the end of boot up. 1773 1774 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1775 ,<instance>=2(orig_cpu)] 1776 [FTRACE] will dump the trace buffers on oops. 1777 If no parameter is passed, ftrace will dump global 1778 buffers of all CPUs, if you pass 2 or orig_cpu, it 1779 will dump only the buffer of the CPU that triggered 1780 the oops, or the specific instance will be dumped if 1781 its name is passed. Multiple instance dump is also 1782 supported, and instances are separated by commas. Each 1783 instance supports only dump on CPU that triggered the 1784 oops by passing 2 or orig_cpu to it. 1785 1786 ftrace_dump_on_oops=foo=orig_cpu 1787 1788 The above will dump only the buffer of "foo" instance 1789 on CPU that triggered the oops. 1790 1791 ftrace_dump_on_oops,foo,bar=orig_cpu 1792 1793 The above will dump global buffer on all CPUs, the 1794 buffer of "foo" instance on all CPUs and the buffer 1795 of "bar" instance on CPU that triggered the oops. 1796 1797 ftrace_filter=[function-list] 1798 [FTRACE] Limit the functions traced by the function 1799 tracer at boot up. function-list is a comma-separated 1800 list of functions. This list can be changed at run 1801 time by the set_ftrace_filter file in the debugfs 1802 tracing directory. 1803 1804 ftrace_notrace=[function-list] 1805 [FTRACE] Do not trace the functions specified in 1806 function-list. This list can be changed at run time 1807 by the set_ftrace_notrace file in the debugfs 1808 tracing directory. 1809 1810 ftrace_graph_filter=[function-list] 1811 [FTRACE] Limit the top level callers functions traced 1812 by the function graph tracer at boot up. 1813 function-list is a comma-separated list of functions 1814 that can be changed at run time by the 1815 set_graph_function file in the debugfs tracing directory. 1816 1817 ftrace_graph_notrace=[function-list] 1818 [FTRACE] Do not trace from the functions specified in 1819 function-list. This list is a comma-separated list of 1820 functions that can be changed at run time by the 1821 set_graph_notrace file in the debugfs tracing directory. 1822 1823 ftrace_graph_max_depth=<uint> 1824 [FTRACE] Used with the function graph tracer. This is 1825 the max depth it will trace into a function. This value 1826 can be changed at run time by the max_graph_depth file 1827 in the tracefs tracing directory. default: 0 (no limit) 1828 1829 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1830 devices by scanning the firmware to infer the 1831 consumer/supplier relationships. This feature is 1832 especially useful when drivers are loaded as modules as 1833 it ensures proper ordering of tasks like device probing 1834 (suppliers first, then consumers), supplier boot state 1835 clean up (only after all consumers have probed), 1836 suspend/resume & runtime PM (consumers first, then 1837 suppliers). 1838 Format: { off | permissive | on | rpm } 1839 off -- Don't create device links from firmware info. 1840 permissive -- Create device links from firmware info 1841 but use it only for ordering boot state clean 1842 up (sync_state() calls). 1843 on -- Create device links from firmware info and use it 1844 to enforce probe and suspend/resume ordering. 1845 rpm -- Like "on", but also use to order runtime PM. 1846 1847 fw_devlink.strict=<bool> 1848 [KNL,EARLY] Treat all inferred dependencies as mandatory 1849 dependencies. This only applies for fw_devlink=on|rpm. 1850 Format: <bool> 1851 1852 fw_devlink.sync_state = 1853 [KNL,EARLY] When all devices that could probe have finished 1854 probing, this parameter controls what to do with 1855 devices that haven't yet received their sync_state() 1856 calls. 1857 Format: { strict | timeout } 1858 strict -- Default. Continue waiting on consumers to 1859 probe successfully. 1860 timeout -- Give up waiting on consumers and call 1861 sync_state() on any devices that haven't yet 1862 received their sync_state() calls after 1863 deferred_probe_timeout has expired or by 1864 late_initcall() if !CONFIG_MODULES. 1865 1866 gamecon.map[2|3]= 1867 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1868 support via parallel port (up to 5 devices per port) 1869 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1870 See also Documentation/input/devices/joystick-parport.rst 1871 1872 gamma= [HW,DRM] 1873 1874 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1875 Format: off | on 1876 default: on 1877 1878 gather_data_sampling= 1879 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1880 mitigation. 1881 1882 Gather Data Sampling is a hardware vulnerability which 1883 allows unprivileged speculative access to data which was 1884 previously stored in vector registers. 1885 1886 This issue is mitigated by default in updated microcode. 1887 The mitigation may have a performance impact but can be 1888 disabled. On systems without the microcode mitigation 1889 disabling AVX serves as a mitigation. 1890 1891 force: Disable AVX to mitigate systems without 1892 microcode mitigation. No effect if the microcode 1893 mitigation is present. Known to cause crashes in 1894 userspace with buggy AVX enumeration. 1895 1896 off: Disable GDS mitigation. 1897 1898 gbpages [X86] Use GB pages for kernel direct mappings. 1899 1900 gcov_persist= [GCOV] When non-zero (default), profiling data for 1901 kernel modules is saved and remains accessible via 1902 debugfs, even when the module is unloaded/reloaded. 1903 When zero, profiling data is discarded and associated 1904 debugfs files are removed at module unload time. 1905 1906 goldfish [X86] Enable the goldfish android emulator platform. 1907 Don't use this when you are not running on the 1908 android emulator 1909 1910 gpio-mockup.gpio_mockup_ranges 1911 [HW] Sets the ranges of gpiochip of for this device. 1912 Format: <start1>,<end1>,<start2>,<end2>... 1913 gpio-mockup.gpio_mockup_named_lines 1914 [HW] Let the driver know GPIO lines should be named. 1915 1916 gpt [EFI] Forces disk with valid GPT signature but 1917 invalid Protective MBR to be treated as GPT. If the 1918 primary GPT is corrupted, it enables the backup/alternate 1919 GPT to be used instead. 1920 1921 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1922 the "Enable 0" bit of the configuration register. 1923 Format: 0 | 1 1924 Default: 0 1925 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1926 the "Enable 0" bit of the configuration register. 1927 Format: 0 | 1 1928 Default: 0 1929 grcan.select= [HW] Select which physical interface to use. 1930 Format: 0 | 1 1931 Default: 0 1932 grcan.txsize= [HW] Sets the size of the tx buffer. 1933 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1934 Default: 1024 1935 grcan.rxsize= [HW] Sets the size of the rx buffer. 1936 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1937 Default: 1024 1938 1939 hardened_usercopy= 1940 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1941 hardening is enabled for this boot. Hardened 1942 usercopy checking is used to protect the kernel 1943 from reading or writing beyond known memory 1944 allocation boundaries as a proactive defense 1945 against bounds-checking flaws in the kernel's 1946 copy_to_user()/copy_from_user() interface. 1947 The default is determined by 1948 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1949 on Perform hardened usercopy checks. 1950 off Disable hardened usercopy checks. 1951 1952 hardlockup_all_cpu_backtrace= 1953 [KNL] Should the hard-lockup detector generate 1954 backtraces on all cpus. 1955 Format: 0 | 1 1956 1957 hash_pointers= 1958 [KNL,EARLY] 1959 By default, when pointers are printed to the console 1960 or buffers via the %p format string, that pointer is 1961 "hashed", i.e. obscured by hashing the pointer value. 1962 This is a security feature that hides actual kernel 1963 addresses from unprivileged users, but it also makes 1964 debugging the kernel more difficult since unequal 1965 pointers can no longer be compared. The choices are: 1966 Format: { auto | always | never } 1967 Default: auto 1968 1969 auto - Hash pointers unless slab_debug is enabled. 1970 always - Always hash pointers (even if slab_debug is 1971 enabled). 1972 never - Never hash pointers. This option should only 1973 be specified when debugging the kernel. Do 1974 not use on production kernels. The boot 1975 param "no_hash_pointers" is an alias for 1976 this mode. 1977 1978 For controlling hashing dynamically at runtime, 1979 use the "kernel.kptr_restrict" sysctl instead. 1980 1981 hashdist= [KNL,NUMA] Large hashes allocated during boot 1982 are distributed across NUMA nodes. Defaults on 1983 for 64-bit NUMA, off otherwise. 1984 Format: 0 | 1 (for off | on) 1985 1986 hd= [EIDE] (E)IDE hard drive subsystem geometry 1987 Format: <cyl>,<head>,<sect> 1988 1989 hest_disable [ACPI] 1990 Disable Hardware Error Source Table (HEST) support; 1991 corresponding firmware-first mode error processing 1992 logic will be disabled. 1993 1994 hibernate= [HIBERNATION] 1995 noresume Don't check if there's a hibernation image 1996 present during boot. 1997 nocompress Don't compress/decompress hibernation images. 1998 no Disable hibernation and resume. 1999 protect_image Turn on image protection during restoration 2000 (that will set all pages holding image data 2001 during restoration read-only). 2002 2003 hibernate.compressor= [HIBERNATION] Compression algorithm to be 2004 used with hibernation. 2005 Format: { lzo | lz4 } 2006 Default: lzo 2007 2008 lzo: Select LZO compression algorithm to 2009 compress/decompress hibernation image. 2010 2011 lz4: Select LZ4 compression algorithm to 2012 compress/decompress hibernation image. 2013 2014 hibernate.pm_test_delay= 2015 [HIBERNATION] 2016 Sets the number of seconds to remain in a hibernation test 2017 mode before resuming the system (see 2018 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 2019 is set. Default value is 5. 2020 2021 hibernate_compression_threads= 2022 [HIBERNATION] 2023 Set the number of threads used for compressing or decompressing 2024 hibernation images. 2025 2026 Format: <integer> 2027 Default: 3 2028 Minimum: 1 2029 Example: hibernate_compression_threads=4 2030 2031 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2032 size of <nn>. This works even on boxes that have no 2033 highmem otherwise. This also works to reduce highmem 2034 size on bigger boxes. 2035 2036 highres= [KNL] Enable/disable high resolution timer mode. 2037 Valid parameters: "on", "off" 2038 Default: "on" 2039 2040 hlt [BUGS=ARM,SH] 2041 2042 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2043 Format: <string> 2044 This allows setting the system's hostname during early 2045 startup. This sets the name returned by gethostname. 2046 Using this parameter to set the hostname makes it 2047 possible to ensure the hostname is correctly set before 2048 any userspace processes run, avoiding the possibility 2049 that a process may call gethostname before the hostname 2050 has been explicitly set, resulting in the calling 2051 process getting an incorrect result. The string must 2052 not exceed the maximum allowed hostname length (usually 2053 64 characters) and will be truncated otherwise. 2054 2055 hpet= [X86-32,HPET] option to control HPET usage 2056 Format: { enable (default) | disable | force | 2057 verbose } 2058 disable: disable HPET and use PIT instead 2059 force: allow force enabled of undocumented chips (ICH4, 2060 VIA, nVidia) 2061 verbose: show contents of HPET registers during setup 2062 2063 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2064 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2065 2066 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2067 If this follows hugepagesz (below), it specifies 2068 the number of pages of hugepagesz to be allocated. 2069 If this is the first HugeTLB parameter on the command 2070 line, it specifies the number of pages to allocate for 2071 the default huge page size. If using node format, the 2072 number of pages to allocate per-node can be specified. 2073 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2074 Format: <integer> or (node format) 2075 <node>:<integer>[,<node>:<integer>] 2076 2077 hugepagesz= 2078 [HW,EARLY] The size of the HugeTLB pages. This is 2079 used in conjunction with hugepages (above) to 2080 allocate huge pages of a specific size at boot. The 2081 pair hugepagesz=X hugepages=Y can be specified once 2082 for each supported huge page size. Huge page sizes 2083 are architecture dependent. See also 2084 Documentation/admin-guide/mm/hugetlbpage.rst. 2085 Format: size[KMG] 2086 2087 hugepage_alloc_threads= 2088 [HW] The number of threads that should be used to 2089 allocate hugepages during boot. This option can be 2090 used to improve system bootup time when allocating 2091 a large amount of huge pages. 2092 The default value is 25% of the available hardware threads. 2093 2094 Note that this parameter only applies to non-gigantic huge pages. 2095 2096 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2097 of gigantic hugepages. Or using node format, the size 2098 of a CMA area per node can be specified. 2099 Format: nn[KMGTPE] or (node format) 2100 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2101 2102 Reserve a CMA area of given size and allocate gigantic 2103 hugepages using the CMA allocator. If enabled, the 2104 boot-time allocation of gigantic hugepages is skipped. 2105 2106 hugetlb_cma_only= 2107 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2108 try to allocate from the CMA areas. 2109 2110 This option does nothing if hugetlb_cma= is not also 2111 specified. 2112 2113 hugetlb_free_vmemmap= 2114 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2115 enabled. 2116 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2117 Allows heavy hugetlb users to free up some more 2118 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2119 Format: { on | off (default) } 2120 2121 on: enable HVO 2122 off: disable HVO 2123 2124 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2125 the default is on. 2126 2127 Note that the vmemmap pages may be allocated from the added 2128 memory block itself when memory_hotplug.memmap_on_memory is 2129 enabled, those vmemmap pages cannot be optimized even if this 2130 feature is enabled. Other vmemmap pages not allocated from 2131 the added memory block itself do not be affected. 2132 2133 hung_task_panic= 2134 [KNL] Number of hung tasks to trigger kernel panic. 2135 Format: <int> 2136 2137 When set to a non-zero value, a kernel panic will be triggered if 2138 the number of detected hung tasks reaches this value. 2139 2140 0: don't panic 2141 1: panic immediately on first hung task 2142 N: panic after N hung tasks are detected in a single scan 2143 2144 The default value is controlled by the 2145 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2146 selected by this boot parameter can be changed later by the 2147 kernel.hung_task_panic sysctl. 2148 2149 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2150 terminal devices. Valid values: 0..8 2151 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2152 If specified, z/VM IUCV HVC accepts connections 2153 from listed z/VM user IDs only. 2154 2155 hv_nopvspin [X86,HYPER_V,EARLY] 2156 Disables the paravirt spinlock optimizations 2157 which allow the hypervisor to 'idle' the guest 2158 on lock contention. 2159 2160 hw_protection= [HW] 2161 Format: reboot | shutdown 2162 2163 Hardware protection action taken on critical events like 2164 overtemperature or imminent voltage loss. 2165 2166 i2c_bus= [HW] Override the default board specific I2C bus speed 2167 or register an additional I2C bus that is not 2168 registered from board initialization code. 2169 Format: 2170 <bus_id>,<clkrate> 2171 2172 i2c_touchscreen_props= [HW,ACPI,X86] 2173 Set device-properties for ACPI-enumerated I2C-attached 2174 touchscreen, to e.g. fix coordinates of upside-down 2175 mounted touchscreens. If you need this option please 2176 submit a drivers/platform/x86/touchscreen_dmi.c patch 2177 adding a DMI quirk for this. 2178 2179 Format: 2180 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2181 Where <val> is one of: 2182 Omit "=<val>" entirely Set a boolean device-property 2183 Unsigned number Set a u32 device-property 2184 Anything else Set a string device-property 2185 2186 Examples (split over multiple lines): 2187 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2188 touchscreen-inverted-y 2189 2190 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2191 touchscreen-size-y=1080:touchscreen-inverted-y: 2192 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2193 2194 i8042.debug [HW] Toggle i8042 debug mode 2195 i8042.unmask_kbd_data 2196 [HW] Enable printing of interrupt data from the KBD port 2197 (disabled by default, and as a pre-condition 2198 requires that i8042.debug=1 be enabled) 2199 i8042.direct [HW] Put keyboard port into non-translated mode 2200 i8042.dumbkbd [HW] Pretend that controller can only read data from 2201 keyboard and cannot control its state 2202 (Don't attempt to blink the leds) 2203 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2204 i8042.nokbd [HW] Don't check/create keyboard port 2205 i8042.noloop [HW] Disable the AUX Loopback command while probing 2206 for the AUX port 2207 i8042.nomux [HW] Don't check presence of an active multiplexing 2208 controller 2209 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2210 controllers 2211 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2212 i8042.reset [HW] Reset the controller during init, cleanup and 2213 suspend-to-ram transitions, only during s2r 2214 transitions, or never reset 2215 Format: { 1 | Y | y | 0 | N | n } 2216 1, Y, y: always reset controller 2217 0, N, n: don't ever reset controller 2218 Default: only on s2r transitions on x86; most other 2219 architectures force reset to be always executed 2220 i8042.unlock [HW] Unlock (ignore) the keylock 2221 i8042.kbdreset [HW] Reset device connected to KBD port 2222 i8042.probe_defer 2223 [HW] Allow deferred probing upon i8042 probe errors 2224 2225 i810= [HW,DRM] 2226 2227 i915.invert_brightness= 2228 [DRM] Invert the sense of the variable that is used to 2229 set the brightness of the panel backlight. Normally a 2230 brightness value of 0 indicates backlight switched off, 2231 and the maximum of the brightness value sets the backlight 2232 to maximum brightness. If this parameter is set to 0 2233 (default) and the machine requires it, or this parameter 2234 is set to 1, a brightness value of 0 sets the backlight 2235 to maximum brightness, and the maximum of the brightness 2236 value switches the backlight off. 2237 -1 -- never invert brightness 2238 0 -- machine default 2239 1 -- force brightness inversion 2240 2241 ia32_emulation= [X86-64] 2242 Format: <bool> 2243 When true, allows loading 32-bit programs and executing 32-bit 2244 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2245 boot time. When false, unconditionally disables IA32 emulation. 2246 2247 2248 idle= [X86,EARLY] 2249 Format: idle=poll, idle=halt, idle=nomwait 2250 2251 idle=poll: Don't do power saving in the idle loop 2252 using HLT, but poll for rescheduling event. This will 2253 make the CPUs eat a lot more power, but may be useful 2254 to get slightly better performance in multiprocessor 2255 benchmarks. It also makes some profiling using 2256 performance counters more accurate. Please note that 2257 on systems with MONITOR/MWAIT support (like Intel 2258 EM64T CPUs) this option has no performance advantage 2259 over the normal idle loop. It may also interact badly 2260 with hyperthreading. 2261 2262 idle=halt: Halt is forced to be used for CPU idle. 2263 In such case C2/C3 won't be used again. 2264 2265 idle=nomwait: Disable mwait for CPU C-states 2266 2267 idxd.sva= [HW] 2268 Format: <bool> 2269 Allow force disabling of Shared Virtual Memory (SVA) 2270 support for the idxd driver. By default it is set to 2271 true (1). 2272 2273 idxd.tc_override= [HW] 2274 Format: <bool> 2275 Allow override of default traffic class configuration 2276 for the device. By default it is set to false (0). 2277 2278 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2279 Format: { strict | legacy | 2008 | relaxed | emulated } 2280 Default: strict 2281 2282 Choose which programs will be accepted for execution 2283 based on the IEEE 754 NaN encoding(s) supported by 2284 the FPU and the NaN encoding requested with the value 2285 of an ELF file header flag individually set by each 2286 binary. Hardware implementations are permitted to 2287 support either or both of the legacy and the 2008 NaN 2288 encoding mode. 2289 2290 Available settings are as follows: 2291 strict accept binaries that request a NaN encoding 2292 supported by the FPU 2293 legacy only accept legacy-NaN binaries, if supported 2294 by the FPU 2295 2008 only accept 2008-NaN binaries, if supported 2296 by the FPU 2297 relaxed accept any binaries regardless of whether 2298 supported by the FPU 2299 emulated accept any binaries but enable FPU emulator 2300 if binary mode is unsupported by the FPU. 2301 2302 The FPU emulator is always able to support both NaN 2303 encodings, so if no FPU hardware is present or it has 2304 been disabled with 'nofpu', then the settings of 2305 'legacy' and '2008' strap the emulator accordingly, 2306 'relaxed' straps the emulator for both legacy-NaN and 2307 2008-NaN, whereas 'strict' enables legacy-NaN only on 2308 legacy processors and both NaN encodings on MIPS32 or 2309 MIPS64 CPUs. 2310 2311 The setting for ABS.fmt/NEG.fmt instruction execution 2312 mode generally follows that for the NaN encoding, 2313 except where unsupported by hardware. 2314 2315 ignore_loglevel [KNL,EARLY] 2316 Ignore loglevel setting - this will print /all/ 2317 kernel messages to the console. Useful for debugging. 2318 We also add it as printk module parameter, so users 2319 could change it dynamically, usually by 2320 /sys/module/printk/parameters/ignore_loglevel. 2321 2322 ignore_rlimit_data 2323 Ignore RLIMIT_DATA setting for data mappings, 2324 print warning at first misuse. Can be changed via 2325 /sys/module/kernel/parameters/ignore_rlimit_data. 2326 2327 ihash_entries= [KNL] 2328 Set number of hash buckets for inode cache. 2329 2330 ima_appraise= [IMA] appraise integrity measurements 2331 Format: { "off" | "enforce" | "fix" | "log" } 2332 default: "enforce" 2333 2334 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2335 The builtin appraise policy appraises all files 2336 owned by uid=0. 2337 2338 ima_canonical_fmt [IMA] 2339 Use the canonical format for the binary runtime 2340 measurements, instead of host native format. 2341 2342 ima_hash= [IMA] 2343 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2344 | sha512 | ... } 2345 default: "sha1" 2346 2347 The list of supported hash algorithms is defined 2348 in crypto/hash_info.h. 2349 2350 ima_policy= [IMA] 2351 The builtin policies to load during IMA setup. 2352 Format: "tcb | appraise_tcb | secure_boot | 2353 fail_securely | critical_data" 2354 2355 The "tcb" policy measures all programs exec'd, files 2356 mmap'd for exec, and all files opened with the read 2357 mode bit set by either the effective uid (euid=0) or 2358 uid=0. 2359 2360 The "appraise_tcb" policy appraises the integrity of 2361 all files owned by root. 2362 2363 The "secure_boot" policy appraises the integrity 2364 of files (eg. kexec kernel image, kernel modules, 2365 firmware, policy, etc) based on file signatures. 2366 2367 The "fail_securely" policy forces file signature 2368 verification failure also on privileged mounted 2369 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2370 flag. 2371 2372 The "critical_data" policy measures kernel integrity 2373 critical data. 2374 2375 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2376 Load a policy which meets the needs of the Trusted 2377 Computing Base. This means IMA will measure all 2378 programs exec'd, files mmap'd for exec, and all files 2379 opened for read by uid=0. 2380 2381 ima_template= [IMA] 2382 Select one of defined IMA measurements template formats. 2383 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2384 "ima-sigv2" } 2385 Default: "ima-ng" 2386 2387 ima_template_fmt= 2388 [IMA] Define a custom template format. 2389 Format: { "field1|...|fieldN" } 2390 2391 ima= [IMA] Enable or disable IMA 2392 Format: { "off" | "on" } 2393 Default: "on" 2394 Note that disabling IMA is limited to kdump kernel. 2395 2396 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2397 Target Selection(ITS) bug in Intel CPUs. Updated 2398 microcode is also required for a fix in IBPB. 2399 2400 on: Enable mitigation (default). 2401 off: Disable mitigation. 2402 force: Force the ITS bug and deploy default 2403 mitigation. 2404 vmexit: Only deploy mitigation if CPU is affected by 2405 guest/host isolation part of ITS. 2406 stuff: Deploy RSB-fill mitigation when retpoline is 2407 also deployed. Otherwise, deploy the default 2408 mitigation. 2409 2410 For details see: 2411 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2412 2413 init= [KNL] 2414 Format: <full_path> 2415 Run specified binary instead of /sbin/init as init 2416 process. 2417 2418 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2419 for working out where the kernel is dying during 2420 startup. 2421 2422 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2423 initcall functions. Useful for debugging built-in 2424 modules and initcalls. 2425 2426 initramfs_async= [KNL] 2427 Format: <bool> 2428 Default: 1 2429 This parameter controls whether the initramfs 2430 image is unpacked asynchronously, concurrently 2431 with devices being probed and 2432 initialized. This should normally just work, 2433 but as a debugging aid, one can get the 2434 historical behaviour of the initramfs 2435 unpacking being completed before device_ and 2436 late_ initcalls. 2437 2438 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2439 2440 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2441 load the initrd. If an initrd is compiled in or 2442 specified in the bootparams, it takes priority over this 2443 setting. 2444 Format: ss[KMG],nn[KMG] 2445 Default is 0, 0 2446 2447 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2448 zeroes. 2449 Format: 0 | 1 2450 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2451 2452 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2453 Format: 0 | 1 2454 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2455 2456 init_pkru= [X86] Specify the default memory protection keys rights 2457 register contents for all processes. 0x55555554 by 2458 default (disallow access to all but pkey 0). Can 2459 override in debugfs after boot. 2460 2461 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2462 Format: <irq> 2463 2464 int_pln_enable [X86] Enable power limit notification interrupt 2465 2466 integrity_audit=[IMA] 2467 Format: { "0" | "1" } 2468 0 -- basic integrity auditing messages. (Default) 2469 1 -- additional integrity auditing messages. 2470 2471 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2472 on 2473 Enable intel iommu driver. 2474 off 2475 Disable intel iommu driver. 2476 igfx_off [Default Off] 2477 By default, gfx is mapped as normal device. If a gfx 2478 device has a dedicated DMAR unit, the DMAR unit is 2479 bypassed by not enabling DMAR with this option. In 2480 this case, gfx device will use physical address for 2481 DMA. 2482 strict [Default Off] 2483 Deprecated, equivalent to iommu.strict=1. 2484 sp_off [Default Off] 2485 By default, super page will be supported if Intel IOMMU 2486 has the capability. With this option, super page will 2487 not be supported. 2488 sm_on 2489 Enable the Intel IOMMU scalable mode if the hardware 2490 advertises that it has support for the scalable mode 2491 translation. 2492 sm_off 2493 Disallow use of the Intel IOMMU scalable mode. 2494 tboot_noforce [Default Off] 2495 Do not force the Intel IOMMU enabled under tboot. 2496 By default, tboot will force Intel IOMMU on, which 2497 could harm performance of some high-throughput 2498 devices like 40GBit network cards, even if identity 2499 mapping is enabled. 2500 Note that using this option lowers the security 2501 provided by tboot because it makes the system 2502 vulnerable to DMA attacks. 2503 2504 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2505 0 disables intel_idle and fall back on acpi_idle. 2506 1 to 9 specify maximum depth of C-state. 2507 2508 intel_pstate= [X86,EARLY] 2509 disable 2510 Do not enable intel_pstate as the default 2511 scaling driver for the supported processors 2512 active 2513 Use intel_pstate driver to bypass the scaling 2514 governors layer of cpufreq and provides it own 2515 algorithms for p-state selection. There are two 2516 P-state selection algorithms provided by 2517 intel_pstate in the active mode: powersave and 2518 performance. The way they both operate depends 2519 on whether or not the hardware managed P-states 2520 (HWP) feature has been enabled in the processor 2521 and possibly on the processor model. 2522 passive 2523 Use intel_pstate as a scaling driver, but configure it 2524 to work with generic cpufreq governors (instead of 2525 enabling its internal governor). This mode cannot be 2526 used along with the hardware-managed P-states (HWP) 2527 feature. 2528 force 2529 Enable intel_pstate on systems that prohibit it by default 2530 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2531 instead of acpi-cpufreq may disable platform features, such 2532 as thermal controls and power capping, that rely on ACPI 2533 P-States information being indicated to OSPM and therefore 2534 should be used with caution. This option does not work with 2535 processors that aren't supported by the intel_pstate driver 2536 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2537 no_hwp 2538 Do not enable hardware P state control (HWP) 2539 if available. 2540 hwp_only 2541 Only load intel_pstate on systems which support 2542 hardware P state control (HWP) if available. 2543 support_acpi_ppc 2544 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2545 Description Table, specifies preferred power management 2546 profile as "Enterprise Server" or "Performance Server", 2547 then this feature is turned on by default. 2548 per_cpu_perf_limits 2549 Allow per-logical-CPU P-State performance control limits using 2550 cpufreq sysfs interface 2551 no_cas 2552 Do not enable capacity-aware scheduling (CAS) on 2553 hybrid systems 2554 2555 intremap= [X86-64,Intel-IOMMU,EARLY] 2556 on enable Interrupt Remapping (default) 2557 off disable Interrupt Remapping 2558 nosid disable Source ID checking 2559 no_x2apic_optout 2560 BIOS x2APIC opt-out request will be ignored 2561 nopost disable Interrupt Posting 2562 posted_msi 2563 enable MSIs delivered as posted interrupts 2564 2565 iomem= Disable strict checking of access to MMIO memory 2566 strict regions from userspace. 2567 relaxed 2568 2569 iommu= [X86,EARLY] 2570 2571 off 2572 Don't initialize and use any kind of IOMMU. 2573 2574 force 2575 Force the use of the hardware IOMMU even when 2576 it is not actually needed (e.g. because < 3 GB 2577 memory). 2578 2579 noforce 2580 Don't force hardware IOMMU usage when it is not 2581 needed. (default). 2582 2583 merge 2584 Do scatter-gather (SG) merging. Implies "force" 2585 (experimental). 2586 2587 nomerge 2588 Don't do scatter-gather (SG) merging. 2589 2590 biomerge 2591 Do scatter-gather (SG) merging. Implies "force" 2592 (experimental). [same as "merge"] 2593 2594 panic 2595 Always panic when IOMMU overflows. 2596 2597 nopanic 2598 Don't panic on IOMMU overflows. 2599 2600 pt 2601 Use passththrough mode by default 2602 (Equivalent to iommu.passthrough=1) 2603 2604 nopt 2605 Use translated mode for DMA by default 2606 (Equivalent to iommu.passthrough=0) 2607 2608 soft 2609 Use software bounce buffering (SWIOTLB) (default for 2610 Intel machines). This can be used to prevent the usage 2611 of an available hardware IOMMU. 2612 2613 usedac 2614 Use the DAC on VIA PCI bridge 2615 (default: disable the VIA PCI bridge DAC) 2616 2617 AMD Gart HW IOMMU-specific options: (CONFIG_GART_IOMMU) 2618 2619 <size> 2620 Set the size of the remapping area in bytes. 2621 2622 allowed 2623 Overwrite iommu off workarounds for specific chipsets 2624 2625 force 2626 Overwrite iommu off workarounds for specific chipsets 2627 2628 fullflush 2629 Flush IOMMU on each allocation (default). 2630 2631 nofullflush 2632 Don't use IOMMU fullflush. 2633 2634 memaper[=<order>] 2635 Allocate an own aperture over RAM with size 2636 32MB<<order. (default: order=1, i.e. 64MB) 2637 2638 noaperture 2639 Ask the IOMMU not to touch the aperture for AGP. 2640 2641 noagp 2642 Don't initialize the AGP driver and use full aperture. 2643 2644 iommu= [PPC/POWERNV] 2645 2646 nobypass 2647 Disable IOMMU bypass, using IOMMU for PCI devices. 2648 2649 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2650 Format: { "0" | "1" } 2651 0 - Try to allocate a 32-bit DMA address first, before 2652 falling back to the full range if needed. 2653 1 - Allocate directly from the full usable range, 2654 forcing Dual Address Cycle for PCI cards supporting 2655 greater than 32-bit addressing. 2656 2657 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2658 Format: { "0" | "1" } 2659 0 - Lazy mode. 2660 Request that DMA unmap operations use deferred 2661 invalidation of hardware TLBs, for increased 2662 throughput at the cost of reduced device isolation. 2663 Will fall back to strict mode if not supported by 2664 the relevant IOMMU driver. 2665 1 - Strict mode. 2666 DMA unmap operations invalidate IOMMU hardware TLBs 2667 synchronously. 2668 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2669 Note: on x86, strict mode specified via one of the 2670 legacy driver-specific options takes precedence. 2671 2672 iommu.passthrough= 2673 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2674 Format: { "0" | "1" } 2675 0 - Use IOMMU translation for DMA. 2676 1 - Bypass the IOMMU for DMA. 2677 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2678 2679 iommu.debug_pagealloc= 2680 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2681 parameter enables the feature at boot time. By default, it 2682 is disabled and the system behaves the same way as a kernel 2683 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2684 Format: { "0" | "1" } 2685 0 - Sanitizer disabled. 2686 1 - Sanitizer enabled, expect runtime overhead. 2687 2688 io7= [HW] IO7 for Marvel-based Alpha systems 2689 See comment before marvel_specify_io7 in 2690 arch/alpha/kernel/core_marvel.c. 2691 2692 io_delay= [X86,EARLY] I/O delay method 2693 0x80 2694 Standard port 0x80 based delay 2695 0xed 2696 Alternate port 0xed based delay (needed on some systems) 2697 udelay 2698 Simple two microseconds delay 2699 none 2700 No delay 2701 2702 ip= [IP_PNP] 2703 See Documentation/admin-guide/nfs/nfsroot.rst. 2704 2705 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2706 IPC identifiers from 32,768 to 16,777,216. 2707 2708 ipe.enforce= [IPE] 2709 Format: <bool> 2710 Determine whether IPE starts in permissive (0) or 2711 enforce (1) mode. The default is enforce. 2712 2713 ipe.success_audit= 2714 [IPE] 2715 Format: <bool> 2716 Start IPE with success auditing enabled, emitting 2717 an audit event when a binary is allowed. The default 2718 is 0. 2719 2720 irqaffinity= [SMP] Set the default irq affinity mask 2721 The argument is a cpu list, as described above. 2722 2723 irqchip.gicv2_force_probe= 2724 [ARM,ARM64,EARLY] 2725 Format: <bool> 2726 Force the kernel to look for the second 4kB page 2727 of a GICv2 controller even if the memory range 2728 exposed by the device tree is too small. 2729 2730 irqchip.gicv3_nolpi= 2731 [ARM,ARM64,EARLY] 2732 Force the kernel to ignore the availability of 2733 LPIs (and by consequence ITSs). Intended for system 2734 that use the kernel as a bootloader, and thus want 2735 to let secondary kernels in charge of setting up 2736 LPIs. 2737 2738 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2739 Enables support for pseudo-NMIs in the kernel. This 2740 requires the kernel to be built with 2741 CONFIG_ARM64_PSEUDO_NMI. 2742 2743 irqchip.riscv_imsic_noipi 2744 [RISC-V,EARLY] 2745 Force the kernel to not use IMSIC software injected MSIs 2746 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2747 and thus want to reduce MMIO traps when triggering IPIs 2748 to multiple harts. 2749 2750 irqfixup [HW] 2751 When an interrupt is not handled search all handlers 2752 for it. Intended to get systems with badly broken 2753 firmware running. 2754 2755 irqhandler.duration_warn_us= [KNL] 2756 Warn if an IRQ handler exceeds the specified duration 2757 threshold in microseconds. Useful for identifying 2758 long-running IRQs in the system. 2759 2760 irqpoll [HW] 2761 When an interrupt is not handled search all handlers 2762 for it. Also check all handlers each timer 2763 interrupt. Intended to get systems with badly broken 2764 firmware running. 2765 2766 isapnp= [ISAPNP] 2767 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2768 2769 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2770 Format: [flag-list,]<cpu-list> 2771 2772 Specify one or more CPUs to isolate from disturbances 2773 specified in the flag list (default: domain): 2774 2775 nohz 2776 Disable the tick when a single task runs as well as 2777 disabling other kernel noises like having RCU callbacks 2778 offloaded. This is equivalent to the nohz_full parameter. 2779 2780 A residual 1Hz tick is offloaded to workqueues, which you 2781 need to affine to housekeeping through the global 2782 workqueue's affinity configured via the 2783 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2784 by using the 'domain' flag described below. 2785 2786 NOTE: by default the global workqueue runs on all CPUs, 2787 so to protect individual CPUs the 'cpumask' file has to 2788 be configured manually after bootup. 2789 2790 domain 2791 Isolate from the general SMP balancing and scheduling 2792 algorithms. Note that performing domain isolation this way 2793 is irreversible: it's not possible to bring back a CPU to 2794 the domains once isolated through this boot time 2795 configuration. Use cpusets for a dynamic configuration 2796 which can be altered at runtime. For details see 2797 Documentation/admin-guide/cpu-isolation.rst. 2798 2799 You can move a process onto or off an "isolated" CPU via 2800 the CPU affinity syscalls or cpuset. 2801 <cpu number> begins at 0 and the maximum value is 2802 "number of CPUs in system - 1". 2803 2804 managed_irq 2805 2806 Isolate from being targeted by managed interrupts 2807 which have an interrupt mask containing isolated 2808 CPUs. The affinity of managed interrupts is 2809 handled by the kernel and cannot be changed via 2810 the /proc/irq/* interfaces. 2811 2812 This isolation is best effort and only effective 2813 if the automatically assigned interrupt mask of a 2814 device queue contains isolated and housekeeping 2815 CPUs. If housekeeping CPUs are online then such 2816 interrupts are directed to the housekeeping CPU 2817 so that IO submitted on the housekeeping CPU 2818 cannot disturb the isolated CPU. 2819 2820 If a queue's affinity mask contains only isolated 2821 CPUs then this parameter has no effect on the 2822 interrupt routing decision, though interrupts are 2823 only delivered when tasks running on those 2824 isolated CPUs submit IO. IO submitted on 2825 housekeeping CPUs has no influence on those 2826 queues. 2827 2828 The format of <cpu-list> is described above. 2829 2830 iucv= [HW,NET] 2831 2832 ivrs_ioapic [HW,X86-64] 2833 Provide an override to the IOAPIC-ID<->DEVICE-ID 2834 mapping provided in the IVRS ACPI table. 2835 By default, PCI segment is 0, and can be omitted. 2836 2837 For example, to map IOAPIC-ID decimal 10 to 2838 PCI segment 0x1 and PCI device 00:14.0, 2839 write the parameter as: 2840 ivrs_ioapic=10@0001:00:14.0 2841 2842 Deprecated formats: 2843 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2844 write the parameter as: 2845 ivrs_ioapic[10]=00:14.0 2846 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2847 PCI device 00:14.0 write the parameter as: 2848 ivrs_ioapic[10]=0001:00:14.0 2849 2850 ivrs_hpet [HW,X86-64] 2851 Provide an override to the HPET-ID<->DEVICE-ID 2852 mapping provided in the IVRS ACPI table. 2853 By default, PCI segment is 0, and can be omitted. 2854 2855 For example, to map HPET-ID decimal 10 to 2856 PCI segment 0x1 and PCI device 00:14.0, 2857 write the parameter as: 2858 ivrs_hpet=10@0001:00:14.0 2859 2860 Deprecated formats: 2861 * To map HPET-ID decimal 0 to PCI device 00:14.0 2862 write the parameter as: 2863 ivrs_hpet[0]=00:14.0 2864 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2865 PCI device 00:14.0 write the parameter as: 2866 ivrs_ioapic[10]=0001:00:14.0 2867 2868 ivrs_acpihid [HW,X86-64] 2869 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2870 mapping provided in the IVRS ACPI table. 2871 By default, PCI segment is 0, and can be omitted. 2872 2873 For example, to map UART-HID:UID AMD0020:0 to 2874 PCI segment 0x1 and PCI device ID 00:14.5, 2875 write the parameter as: 2876 ivrs_acpihid=AMD0020:0@0001:00:14.5 2877 2878 Deprecated formats: 2879 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2880 PCI device ID 00:14.5, write the parameter as: 2881 ivrs_acpihid[00:14.5]=AMD0020:0 2882 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2883 PCI device ID 00:14.5, write the parameter as: 2884 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2885 2886 js= [HW,JOY] Analog joystick 2887 See Documentation/input/joydev/joystick.rst. 2888 2889 kasan_multi_shot 2890 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2891 report on every invalid memory access. Without this 2892 parameter KASAN will print report only for the first 2893 invalid access. 2894 2895 keep_bootcon [KNL,EARLY] 2896 Do not unregister boot console at start. This is only 2897 useful for debugging when something happens in the window 2898 between unregistering the boot console and initializing 2899 the real console. 2900 2901 keepinitrd [HW,ARM] See retain_initrd. 2902 2903 kernelcore= [KNL,X86,PPC,EARLY] 2904 Format: nn[KMGTPE] | nn% | "mirror" 2905 This parameter specifies the amount of memory usable by 2906 the kernel for non-movable allocations. The requested 2907 amount is spread evenly throughout all nodes in the 2908 system as ZONE_NORMAL. The remaining memory is used for 2909 movable memory in its own zone, ZONE_MOVABLE. In the 2910 event, a node is too small to have both ZONE_NORMAL and 2911 ZONE_MOVABLE, kernelcore memory will take priority and 2912 other nodes will have a larger ZONE_MOVABLE. 2913 2914 ZONE_MOVABLE is used for the allocation of pages that 2915 may be reclaimed or moved by the page migration 2916 subsystem. Note that allocations like PTEs-from-HighMem 2917 still use the HighMem zone if it exists, and the Normal 2918 zone if it does not. 2919 2920 It is possible to specify the exact amount of memory in 2921 the form of "nn[KMGTPE]", a percentage of total system 2922 memory in the form of "nn%", or "mirror". If "mirror" 2923 option is specified, mirrored (reliable) memory is used 2924 for non-movable allocations and remaining memory is used 2925 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2926 are exclusive, so you cannot specify multiple forms. 2927 2928 kfence.burst= [MM,KFENCE] The number of additional successive 2929 allocations to be attempted through KFENCE for each 2930 sample interval. 2931 Format: <unsigned integer> 2932 Default: 0 2933 2934 kfence.check_on_panic= 2935 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2936 canaries on panic. 2937 Format: <bool> 2938 Default: false 2939 2940 kfence.deferrable= 2941 [MM,KFENCE] Whether to use a deferrable timer to trigger 2942 allocations. This avoids forcing CPU wake-ups if the 2943 system is idle, at the risk of a less predictable 2944 sample interval. 2945 Format: <bool> 2946 Default: CONFIG_KFENCE_DEFERRABLE 2947 2948 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE 2949 error is detected. 2950 report - print the error report and continue (default). 2951 oops - print the error report and oops. 2952 panic - print the error report and panic. 2953 2954 kfence.sample_interval= 2955 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2956 Format: <unsigned integer> 2957 0 - Disable KFENCE. 2958 >0 - Enabled KFENCE with given sample interval. 2959 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2960 2961 kfence.skip_covered_thresh= 2962 [MM,KFENCE] If pool utilization reaches this threshold 2963 (pool usage%), KFENCE limits currently covered 2964 allocations of the same source from further filling 2965 up the pool. 2966 Format: <unsigned integer> 2967 Default: 75 2968 2969 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2970 Format: <Controller#>[,poll interval] 2971 The controller # is the number of the ehci usb debug 2972 port as it is probed via PCI. The poll interval is 2973 optional and is the number seconds in between 2974 each poll cycle to the debug port in case you need 2975 the functionality for interrupting the kernel with 2976 gdb or control-c on the dbgp connection. When 2977 not using this parameter you use sysrq-g to break into 2978 the kernel debugger. 2979 2980 kgdboc= [KGDB,HW] kgdb over consoles. 2981 Requires a tty driver that supports console polling, 2982 or a supported polling keyboard driver (non-usb). 2983 Serial only format: <serial_device>[,baud] 2984 keyboard only format: kbd 2985 keyboard and serial format: kbd,<serial_device>[,baud] 2986 Optional Kernel mode setting: 2987 kms, kbd format: kms,kbd 2988 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2989 2990 kgdboc_earlycon= [KGDB,HW,EARLY] 2991 If the boot console provides the ability to read 2992 characters and can work in polling mode, you can use 2993 this parameter to tell kgdb to use it as a backend 2994 until the normal console is registered. Intended to 2995 be used together with the kgdboc parameter which 2996 specifies the normal console to transition to. 2997 2998 The name of the early console should be specified 2999 as the value of this parameter. Note that the name of 3000 the early console might be different than the tty 3001 name passed to kgdboc. It's OK to leave the value 3002 blank and the first boot console that implements 3003 read() will be picked. 3004 3005 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 3006 kernel debugger at the earliest opportunity. 3007 3008 kho= [KEXEC,EARLY] 3009 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3010 Enables or disables Kexec HandOver. 3011 "0" | "off" | "n" - kexec handover is disabled 3012 "1" | "on" | "y" - kexec handover is enabled 3013 3014 kho_scratch= [KEXEC,EARLY] 3015 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3016 Defines the size of the KHO scratch region. The KHO 3017 scratch regions are physically contiguous memory 3018 ranges that can only be used for non-kernel 3019 allocations. That way, even when memory is heavily 3020 fragmented with handed over memory, the kexeced 3021 kernel will always have enough contiguous ranges to 3022 bootstrap itself. 3023 3024 It is possible to specify the exact amount of 3025 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3026 where the first parameter defines the size of a low 3027 memory scratch area, the second parameter defines 3028 the size of a global scratch area and the third 3029 parameter defines the size of additional per-node 3030 scratch areas. The form "nn%" defines scale factor 3031 (in percents) of memory that was used during boot. 3032 3033 kmac= [MIPS] Korina ethernet MAC address. 3034 Configure the RouterBoard 532 series on-chip 3035 Ethernet adapter MAC address. 3036 3037 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3038 Valid arguments: on, off 3039 Default: on 3040 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3041 the default is off. 3042 3043 kprobe_event=[probe-list] 3044 [FTRACE] Add kprobe events and enable at boot time. 3045 The probe-list is a semicolon delimited list of probe 3046 definitions. Each definition is same as kprobe_events 3047 interface, but the parameters are comma delimited. 3048 For example, to add a kprobe event on vfs_read with 3049 arg1 and arg2, add to the command line; 3050 3051 kprobe_event=p,vfs_read,$arg1,$arg2 3052 3053 See also Documentation/trace/kprobetrace.rst "Kernel 3054 Boot Parameter" section. 3055 3056 kpti= [ARM64,EARLY] Control page table isolation of 3057 user and kernel address spaces. 3058 Default: enabled on cores which need mitigation. 3059 0: force disabled 3060 1: force enabled 3061 3062 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3063 CONFIG_KUNIT to be set to be fully enabled. The 3064 default value can be overridden via 3065 KUNIT_DEFAULT_ENABLED. 3066 Default is 1 (enabled) 3067 3068 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3069 Default is 0 (don't ignore, but inject #GP) 3070 3071 kvm.eager_page_split= 3072 [KVM,X86] Controls whether or not KVM will try to 3073 proactively split all huge pages during dirty logging. 3074 Eager page splitting reduces interruptions to vCPU 3075 execution by eliminating the write-protection faults 3076 and MMU lock contention that would otherwise be 3077 required to split huge pages lazily. 3078 3079 VM workloads that rarely perform writes or that write 3080 only to a small region of VM memory may benefit from 3081 disabling eager page splitting to allow huge pages to 3082 still be used for reads. 3083 3084 The behavior of eager page splitting depends on whether 3085 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3086 disabled, all huge pages in a memslot will be eagerly 3087 split when dirty logging is enabled on that memslot. If 3088 enabled, eager page splitting will be performed during 3089 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3090 cleared. 3091 3092 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3093 3094 Default is Y (on). 3095 3096 kvm.enable_pmu=[KVM,X86] 3097 If enabled, KVM will virtualize PMU functionality based 3098 on the virtual CPU model defined by userspace. This 3099 can be overridden on a per-VM basis via 3100 KVM_CAP_PMU_CAPABILITY. 3101 3102 If disabled, KVM will not virtualize PMU functionality, 3103 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3104 a virtual CPU model that contains PMU assets. 3105 3106 Note, KVM's vPMU support implicitly requires running 3107 with an in-kernel local APIC, e.g. to deliver PMIs to 3108 the guest. Running without an in-kernel local APIC is 3109 not supported, though KVM will allow such a combination 3110 (with severely degraded functionality). 3111 3112 See also enable_mediated_pmu. 3113 3114 Default is Y (on). 3115 3116 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3117 If enabled, KVM will enable virtualization in hardware 3118 when KVM is loaded, and disable virtualization when KVM 3119 is unloaded (if KVM is built as a module). 3120 3121 If disabled, KVM will dynamically enable and disable 3122 virtualization on-demand when creating and destroying 3123 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3124 number of VMs. 3125 3126 Enabling virtualization at module load avoids potential 3127 latency for creation of the 0=>1 VM, as KVM serializes 3128 virtualization enabling across all online CPUs. The 3129 "cost" of enabling virtualization when KVM is loaded, 3130 is that doing so may interfere with using out-of-tree 3131 hypervisors that want to "own" virtualization hardware. 3132 3133 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3134 Default is false (don't support). 3135 3136 kvm.nx_huge_pages= 3137 [KVM] Controls the software workaround for the 3138 X86_BUG_ITLB_MULTIHIT bug. 3139 force : Always deploy workaround. 3140 off : Never deploy workaround. 3141 auto : Deploy workaround based on the presence of 3142 X86_BUG_ITLB_MULTIHIT. 3143 3144 Default is 'auto'. 3145 3146 If the software workaround is enabled for the host, 3147 guests do need not to enable it for nested guests. 3148 3149 kvm.nx_huge_pages_recovery_ratio= 3150 [KVM] Controls how many 4KiB pages are periodically zapped 3151 back to huge pages. 0 disables the recovery, otherwise if 3152 the value is N KVM will zap 1/Nth of the 4KiB pages every 3153 period (see below). The default is 60. 3154 3155 kvm.nx_huge_pages_recovery_period_ms= 3156 [KVM] Controls the time period at which KVM zaps 4KiB pages 3157 back to huge pages. If the value is a non-zero N, KVM will 3158 zap a portion (see ratio above) of the pages every N msecs. 3159 If the value is 0 (the default), KVM will pick a period based 3160 on the ratio, such that a page is zapped after 1 hour on average. 3161 3162 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3163 If enabled, KVM will provide a mediated virtual PMU, 3164 instead of the default perf-based virtual PMU (if 3165 kvm.enable_pmu is true and PMU is enumerated via the 3166 virtual CPU model). 3167 3168 With a perf-based vPMU, KVM operates as a user of perf, 3169 i.e. emulates guest PMU counters using perf events. 3170 KVM-created perf events are managed by perf as regular 3171 (guest-only) events, e.g. are scheduled in/out, contend 3172 for hardware resources, etc. Using a perf-based vPMU 3173 allows guest and host usage of the PMU to co-exist, but 3174 incurs non-trivial overhead and can result in silently 3175 dropped guest events (due to resource contention). 3176 3177 With a mediated vPMU, hardware PMU state is context 3178 switched around the world switch to/from the guest. 3179 KVM mediates which events the guest can utilize, but 3180 gives the guest direct access to all other PMU assets 3181 when possible (KVM may intercept some accesses if the 3182 virtual CPU model provides a subset of hardware PMU 3183 functionality). Using a mediated vPMU significantly 3184 reduces PMU virtualization overhead and eliminates lost 3185 guest events, but is mutually exclusive with using perf 3186 to profile KVM guests and adds latency to most VM-Exits 3187 (to context switch PMU state). 3188 3189 Default is N (off). 3190 3191 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3192 KVM/SVM. Default is 1 (enabled). 3193 3194 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3195 a.k.a. Two-Dimensional Page Tables. Default is 1 3196 (enabled). Disable by KVM if hardware lacks support 3197 for NPT. 3198 3199 kvm-amd.ciphertext_hiding_asids= 3200 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3201 to SNP private memory from reading ciphertext. Instead, 3202 reads will see constant default values (0xff). 3203 3204 If ciphertext hiding is enabled, the joint SEV-ES and 3205 SEV-SNP ASID space is partitioned into separate SEV-ES 3206 and SEV-SNP ASID ranges, with the SEV-SNP range being 3207 [1..max_snp_asid] and the SEV-ES range being 3208 (max_snp_asid..min_sev_asid), where min_sev_asid is 3209 enumerated by CPUID.0x.8000_001F[EDX]. 3210 3211 A non-zero value enables SEV-SNP ciphertext hiding and 3212 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3213 KVM caps the number of SEV-SNP ASIDs at the maximum 3214 possible value, e.g. specifying -1u will assign all 3215 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3216 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3217 max_snp_asid == min_sev_asid-1, will effectively make 3218 SEV-ES unusable. 3219 3220 kvm-arm.mode= 3221 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3222 operation. 3223 3224 none: Forcefully disable KVM. 3225 3226 nvhe: Standard nVHE-based mode, without support for 3227 protected guests. 3228 3229 protected: Mode with support for guests whose state is 3230 kept private from the host, using VHE or 3231 nVHE depending on HW support. 3232 3233 nested: VHE-based mode with support for nested 3234 virtualization. Requires at least ARMv8.4 3235 hardware (with FEAT_NV2). 3236 3237 Defaults to VHE/nVHE based on hardware support. Setting 3238 mode to "protected" will disable kexec and hibernation 3239 for the host. To force nVHE on VHE hardware, add 3240 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3241 command-line. 3242 "nested" and "protected" are experimental and should be 3243 used with extreme caution. 3244 3245 kvm-arm.vgic_v3_group0_trap= 3246 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3247 system registers 3248 3249 kvm-arm.vgic_v3_group1_trap= 3250 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3251 system registers 3252 3253 kvm-arm.vgic_v3_common_trap= 3254 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3255 system registers 3256 3257 kvm-arm.vgic_v4_enable= 3258 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3259 injection of LPIs. 3260 3261 kvm-arm.wfe_trap_policy= 3262 [KVM,ARM] Control when to set WFE instruction trap for 3263 KVM VMs. Traps are allowed but not guaranteed by the 3264 CPU architecture. 3265 3266 trap: set WFE instruction trap 3267 3268 notrap: clear WFE instruction trap 3269 3270 kvm-arm.wfi_trap_policy= 3271 [KVM,ARM] Control when to set WFI instruction trap for 3272 KVM VMs. Traps are allowed but not guaranteed by the 3273 CPU architecture. 3274 3275 trap: set WFI instruction trap 3276 3277 notrap: clear WFI instruction trap 3278 3279 kvm_cma_resv_ratio=n [PPC,EARLY] 3280 Reserves given percentage from system memory area for 3281 contiguous memory allocation for KVM hash pagetable 3282 allocation. 3283 By default it reserves 5% of total system memory. 3284 Format: <integer> 3285 Default: 5 3286 3287 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3288 a.k.a. Two-Dimensional Page Tables. Default is 1 3289 (enabled). Disable by KVM if hardware lacks support 3290 for EPT. 3291 3292 kvm-intel.emulate_invalid_guest_state= 3293 [KVM,Intel] Control whether to emulate invalid guest 3294 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3295 as guest state is never invalid for unrestricted 3296 guests. This param doesn't apply to nested guests (L2), 3297 as KVM never emulates invalid L2 guest state. 3298 Default is 1 (enabled). 3299 3300 kvm-intel.flexpriority= 3301 [KVM,Intel] Control KVM's use of FlexPriority feature 3302 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3303 hardware lacks support for it. 3304 3305 kvm-intel.nested= 3306 [KVM,Intel] Control nested virtualization feature in 3307 KVM/VMX. Default is 1 (enabled). 3308 3309 kvm-intel.unrestricted_guest= 3310 [KVM,Intel] Control KVM's use of unrestricted guest 3311 feature (virtualized real and unpaged mode). Default 3312 is 1 (enabled). Disable by KVM if EPT is disabled or 3313 hardware lacks support for it. 3314 3315 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3316 CVE-2018-3620. 3317 3318 Valid arguments: never, cond, always 3319 3320 always: L1D cache flush on every VMENTER. 3321 cond: Flush L1D on VMENTER only when the code between 3322 VMEXIT and VMENTER can leak host memory. 3323 never: Disables the mitigation 3324 3325 Default is cond (do L1 cache flush in specific instances) 3326 3327 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3328 Identification feature (tagged TLBs). Default is 1 3329 (enabled). Disable by KVM if hardware lacks support 3330 for it. 3331 3332 l1d_flush= [X86,INTEL,EARLY] 3333 Control mitigation for L1D based snooping vulnerability. 3334 3335 Certain CPUs are vulnerable to an exploit against CPU 3336 internal buffers which can forward information to a 3337 disclosure gadget under certain conditions. 3338 3339 In vulnerable processors, the speculatively 3340 forwarded data can be used in a cache side channel 3341 attack, to access data to which the attacker does 3342 not have direct access. 3343 3344 This parameter controls the mitigation. The 3345 options are: 3346 3347 on - enable the interface for the mitigation 3348 3349 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3350 affected CPUs 3351 3352 The kernel PTE inversion protection is unconditionally 3353 enabled and cannot be disabled. 3354 3355 full 3356 Provides all available mitigations for the 3357 L1TF vulnerability. Disables SMT and 3358 enables all mitigations in the 3359 hypervisors, i.e. unconditional L1D flush. 3360 3361 SMT control and L1D flush control via the 3362 sysfs interface is still possible after 3363 boot. Hypervisors will issue a warning 3364 when the first VM is started in a 3365 potentially insecure configuration, 3366 i.e. SMT enabled or L1D flush disabled. 3367 3368 full,force 3369 Same as 'full', but disables SMT and L1D 3370 flush runtime control. Implies the 3371 'nosmt=force' command line option. 3372 (i.e. sysfs control of SMT is disabled.) 3373 3374 flush 3375 Leaves SMT enabled and enables the default 3376 hypervisor mitigation, i.e. conditional 3377 L1D flush. 3378 3379 SMT control and L1D flush control via the 3380 sysfs interface is still possible after 3381 boot. Hypervisors will issue a warning 3382 when the first VM is started in a 3383 potentially insecure configuration, 3384 i.e. SMT enabled or L1D flush disabled. 3385 3386 flush,nosmt 3387 3388 Disables SMT and enables the default 3389 hypervisor mitigation. 3390 3391 SMT control and L1D flush control via the 3392 sysfs interface is still possible after 3393 boot. Hypervisors will issue a warning 3394 when the first VM is started in a 3395 potentially insecure configuration, 3396 i.e. SMT enabled or L1D flush disabled. 3397 3398 flush,nowarn 3399 Same as 'flush', but hypervisors will not 3400 warn when a VM is started in a potentially 3401 insecure configuration. 3402 3403 off 3404 Disables hypervisor mitigations and doesn't 3405 emit any warnings. 3406 It also drops the swap size and available 3407 RAM limit restriction on both hypervisor and 3408 bare metal. 3409 3410 Default is 'flush'. 3411 3412 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3413 3414 l2cr= [PPC] 3415 3416 l3cr= [PPC] 3417 3418 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3419 disabled it. 3420 3421 lapic= [X86,APIC] Do not use TSC deadline 3422 value for LAPIC timer one-shot implementation. Default 3423 back to the programmable timer unit in the LAPIC. 3424 Format: notscdeadline 3425 3426 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3427 in C2 power state. 3428 3429 libata.dma= [LIBATA] DMA control 3430 libata.dma=0 Disable all PATA and SATA DMA 3431 libata.dma=1 PATA and SATA Disk DMA only 3432 libata.dma=2 ATAPI (CDROM) DMA only 3433 libata.dma=4 Compact Flash DMA only 3434 Combinations also work, so libata.dma=3 enables DMA 3435 for disks and CDROMs, but not CFs. 3436 3437 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3438 libata.ignore_hpa=0 keep BIOS limits (default) 3439 libata.ignore_hpa=1 ignore limits, using full disk 3440 3441 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3442 when set. 3443 Format: <int> 3444 3445 libata.force= [LIBATA] Force configurations. The format is a comma- 3446 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3447 PORT and DEVICE are decimal numbers matching port, link 3448 or device. Basically, it matches the ATA ID string 3449 printed on console by libata. If the whole ID part is 3450 omitted, the last PORT and DEVICE values are used. If 3451 ID hasn't been specified yet, the configuration applies 3452 to all ports, links and devices. 3453 3454 If only DEVICE is omitted, the parameter applies to 3455 the port and all links and devices behind it. DEVICE 3456 number of 0 either selects the first device or the 3457 first fan-out link behind PMP device. It does not 3458 select the host link. DEVICE number of 15 selects the 3459 host link and device attached to it. 3460 3461 The VAL specifies the configuration to force. As long 3462 as there is no ambiguity, shortcut notation is allowed. 3463 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3464 The following configurations can be forced. 3465 3466 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3467 Any ID with matching PORT is used. 3468 3469 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3470 3471 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3472 udma[/][16,25,33,44,66,100,133] notation is also 3473 allowed. 3474 3475 * nohrst, nosrst, norst: suppress hard, soft and both 3476 resets. 3477 3478 * rstonce: only attempt one reset during hot-unplug 3479 link recovery. 3480 3481 * [no]dbdelay: Enable or disable the extra 200ms delay 3482 before debouncing a link PHY and device presence 3483 detection. 3484 3485 * [no]ncq: Turn on or off NCQ. 3486 3487 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3488 3489 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3490 3491 * [no]trim: Enable or disable (unqueued) TRIM. 3492 3493 * trim_zero: Indicate that TRIM command zeroes data. 3494 3495 * max_trim_128m: Set 128M maximum trim size limit. 3496 3497 * [no]dma: Turn on or off DMA transfers. 3498 3499 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3500 3501 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3502 commands that are not a multiple of 16 bytes. 3503 3504 * [no]dmalog: Enable or disable the use of the 3505 READ LOG DMA EXT command to access logs. 3506 3507 * [no]iddevlog: Enable or disable access to the 3508 identify device data log. 3509 3510 * [no]logdir: Enable or disable access to the general 3511 purpose log directory. 3512 3513 * max_sec=<sectors>: Set the transfer size limit, in 3514 number of 512-byte sectors, to the value specified in 3515 <sectors>. The value specified in <sectors> has to be 3516 a non-zero positive integer. 3517 3518 * max_sec_128: Set transfer size limit to 128 sectors. 3519 3520 * max_sec_1024: Set or clear transfer size limit to 3521 1024 sectors. 3522 3523 * max_sec_lba48: Set or clear transfer size limit to 3524 65535 sectors. 3525 3526 * external: Mark port as external (hotplug-capable). 3527 3528 * [no]lpm: Enable or disable link power management. 3529 3530 * [no]setxfer: Indicate if transfer speed mode setting 3531 should be skipped. 3532 3533 * [no]fua: Disable or enable FUA (Force Unit Access) 3534 support for devices supporting this feature. 3535 3536 * dump_id: Dump IDENTIFY data. 3537 3538 * disable: Disable this device. 3539 3540 If there are multiple matching configurations changing 3541 the same attribute, the last one is used. 3542 3543 liveupdate= [KNL,EARLY] 3544 Format: <bool> 3545 Enable Live Update Orchestrator (LUO). 3546 Default: off. 3547 3548 lockd.nlm_grace_period=P [NFS] Assign grace period. 3549 Format: <integer> 3550 3551 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3552 Format: <integer> 3553 3554 lockd.nlm_timeout=T [NFS] Assign timeout value. 3555 Format: <integer> 3556 3557 lockd.nlm_udpport=M [NFS] Assign UDP port. 3558 Format: <integer> 3559 3560 lockdown= [SECURITY,EARLY] 3561 { integrity | confidentiality } 3562 Enable the kernel lockdown feature. If set to 3563 integrity, kernel features that allow userland to 3564 modify the running kernel are disabled. If set to 3565 confidentiality, kernel features that allow userland 3566 to extract confidential information from the kernel 3567 are also disabled. 3568 3569 locktorture.acq_writer_lim= [KNL] 3570 Set the time limit in jiffies for a lock 3571 acquisition. Acquisitions exceeding this limit 3572 will result in a splat once they do complete. 3573 3574 locktorture.bind_readers= [KNL] 3575 Specify the list of CPUs to which the readers are 3576 to be bound. 3577 3578 locktorture.bind_writers= [KNL] 3579 Specify the list of CPUs to which the writers are 3580 to be bound. 3581 3582 locktorture.call_rcu_chains= [KNL] 3583 Specify the number of self-propagating call_rcu() 3584 chains to set up. These are used to ensure that 3585 there is a high probability of an RCU grace period 3586 in progress at any given time. Defaults to 0, 3587 which disables these call_rcu() chains. 3588 3589 locktorture.long_hold= [KNL] 3590 Specify the duration in milliseconds for the 3591 occasional long-duration lock hold time. Defaults 3592 to 100 milliseconds. Select 0 to disable. 3593 3594 locktorture.nested_locks= [KNL] 3595 Specify the maximum lock nesting depth that 3596 locktorture is to exercise, up to a limit of 8 3597 (MAX_NESTED_LOCKS). Specify zero to disable. 3598 Note that this parameter is ineffective on types 3599 of locks that do not support nested acquisition. 3600 3601 locktorture.nreaders_stress= [KNL] 3602 Set the number of locking read-acquisition kthreads. 3603 Defaults to being automatically set based on the 3604 number of online CPUs. 3605 3606 locktorture.nwriters_stress= [KNL] 3607 Set the number of locking write-acquisition kthreads. 3608 3609 locktorture.onoff_holdoff= [KNL] 3610 Set time (s) after boot for CPU-hotplug testing. 3611 3612 locktorture.onoff_interval= [KNL] 3613 Set time (s) between CPU-hotplug operations, or 3614 zero to disable CPU-hotplug testing. 3615 3616 locktorture.rt_boost= [KNL] 3617 Do periodic testing of real-time lock priority 3618 boosting. Select 0 to disable, 1 to boost 3619 only rt_mutex, and 2 to boost unconditionally. 3620 Defaults to 2, which might seem to be an 3621 odd choice, but which should be harmless for 3622 non-real-time spinlocks, due to their disabling 3623 of preemption. Note that non-realtime mutexes 3624 disable boosting. 3625 3626 locktorture.rt_boost_factor= [KNL] 3627 Number that determines how often and for how 3628 long priority boosting is exercised. This is 3629 scaled down by the number of writers, so that the 3630 number of boosts per unit time remains roughly 3631 constant as the number of writers increases. 3632 On the other hand, the duration of each boost 3633 increases with the number of writers. 3634 3635 locktorture.shuffle_interval= [KNL] 3636 Set task-shuffle interval (jiffies). Shuffling 3637 tasks allows some CPUs to go into dyntick-idle 3638 mode during the locktorture test. 3639 3640 locktorture.shutdown_secs= [KNL] 3641 Set time (s) after boot system shutdown. This 3642 is useful for hands-off automated testing. 3643 3644 locktorture.stat_interval= [KNL] 3645 Time (s) between statistics printk()s. 3646 3647 locktorture.stutter= [KNL] 3648 Time (s) to stutter testing, for example, 3649 specifying five seconds causes the test to run for 3650 five seconds, wait for five seconds, and so on. 3651 This tests the locking primitive's ability to 3652 transition abruptly to and from idle. 3653 3654 locktorture.torture_type= [KNL] 3655 Specify the locking implementation to test. 3656 3657 locktorture.verbose= [KNL] 3658 Enable additional printk() statements. 3659 3660 locktorture.writer_fifo= [KNL] 3661 Run the write-side locktorture kthreads at 3662 sched_set_fifo() real-time priority. 3663 3664 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3665 Format: <irq> 3666 3667 loglevel= [KNL,EARLY] 3668 All Kernel Messages with a loglevel smaller than the 3669 console loglevel will be printed to the console. It can 3670 also be changed with klogd or other programs. The 3671 loglevels are defined as follows: 3672 3673 0 (KERN_EMERG) system is unusable 3674 1 (KERN_ALERT) action must be taken immediately 3675 2 (KERN_CRIT) critical conditions 3676 3 (KERN_ERR) error conditions 3677 4 (KERN_WARNING) warning conditions 3678 5 (KERN_NOTICE) normal but significant condition 3679 6 (KERN_INFO) informational 3680 7 (KERN_DEBUG) debug-level messages 3681 3682 log_buf_len=n[KMG] [KNL,EARLY] 3683 Sets the size of the printk ring buffer, in bytes. 3684 n must be a power of two and greater than the 3685 minimal size. The minimal size is defined by 3686 LOG_BUF_SHIFT kernel config parameter. There 3687 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3688 parameter that allows to increase the default size 3689 depending on the number of CPUs. See init/Kconfig 3690 for more details. 3691 3692 logo.nologo [FB] Disables display of the built-in Linux logo. 3693 This may be used to provide more screen space for 3694 kernel log messages and is useful when debugging 3695 kernel boot problems. 3696 3697 lp=0 [LP] Specify parallel ports to use, e.g, 3698 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3699 lp=reset first parallel port). 'lp=0' disables the 3700 lp=auto printer driver. 'lp=reset' (which can be 3701 specified in addition to the ports) causes 3702 attached printers to be reset. Using 3703 lp=port1,port2,... specifies the parallel ports 3704 to associate lp devices with, starting with 3705 lp0. A port specification may be 'none' to skip 3706 that lp device, or a parport name such as 3707 'parport0'. Specifying 'lp=auto' instead of a 3708 port specification list means that device IDs 3709 from each port should be examined, to see if 3710 an IEEE 1284-compliant printer is attached; if 3711 so, the driver will manage that printer. 3712 See also header of drivers/char/lp.c. 3713 3714 lpj=n [KNL] 3715 Sets loops_per_jiffy to given constant, thus avoiding 3716 time-consuming boot-time autodetection (up to 250 ms per 3717 CPU). 0 enables autodetection (default). To determine 3718 the correct value for your kernel, boot with normal 3719 autodetection and see what value is printed. Note that 3720 on SMP systems the preset will be applied to all CPUs, 3721 which is likely to cause problems if your CPUs need 3722 significantly divergent settings. An incorrect value 3723 will cause delays in the kernel to be wrong, leading to 3724 unpredictable I/O errors and other breakage. Although 3725 unlikely, in the extreme case this might damage your 3726 hardware. 3727 3728 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3729 3730 lsm=lsm1,...,lsmN 3731 [SECURITY] Choose order of LSM initialization. This 3732 overrides CONFIG_LSM, and the "security=" parameter. 3733 3734 machtype= [Loongson] Share the same kernel image file between 3735 different yeeloong laptops. 3736 Example: machtype=lemote-yeeloong-2f-7inch 3737 3738 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3739 will bring up during bootup. maxcpus=n : n >= 0 limits 3740 the kernel to bring up 'n' processors. Surely after 3741 bootup you can bring up the other plugged cpu by executing 3742 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3743 only takes effect during system bootup. 3744 While n=0 is a special case, it is equivalent to "nosmp", 3745 which also disables the IO APIC. 3746 3747 max_loop= [LOOP] The number of loop block devices that get 3748 (loop.max_loop) unconditionally pre-created at init time. The default 3749 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3750 of statically allocating a predefined number, loop 3751 devices can be requested on-demand with the 3752 /dev/loop-control interface. 3753 3754 mce= [X86-{32,64}] 3755 3756 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3757 3758 off 3759 disable machine check 3760 3761 no_cmci 3762 disable CMCI(Corrected Machine Check Interrupt) that 3763 Intel processor supports. Usually this disablement is 3764 not recommended, but it might be handy if your 3765 hardware is misbehaving. 3766 3767 Note that you'll get more problems without CMCI than 3768 with due to the shared banks, i.e. you might get 3769 duplicated error logs. 3770 3771 dont_log_ce 3772 don't make logs for corrected errors. All events 3773 reported as corrected are silently cleared by OS. This 3774 option will be useful if you have no interest in any 3775 of corrected errors. 3776 3777 ignore_ce 3778 disable features for corrected errors, e.g. 3779 polling timer and CMCI. All events reported as 3780 corrected are not cleared by OS and remained in its 3781 error banks. 3782 3783 Usually this disablement is not recommended, however 3784 if there is an agent checking/clearing corrected 3785 errors (e.g. BIOS or hardware monitoring 3786 applications), conflicting with OS's error handling, 3787 and you cannot deactivate the agent, then this option 3788 will be a help. 3789 3790 no_lmce 3791 do not opt-in to Local MCE delivery. Use legacy method 3792 to broadcast MCEs. 3793 3794 bootlog 3795 enable logging of machine checks left over from 3796 booting. Disabled by default on AMD Fam10h and older 3797 because some BIOS leave bogus ones. 3798 3799 If your BIOS doesn't do that it's a good idea to 3800 enable though to make sure you log even machine check 3801 events that result in a reboot. On Intel systems it is 3802 enabled by default. 3803 3804 nobootlog 3805 disable boot machine check logging. 3806 3807 monarchtimeout (number) 3808 sets the time in us to wait for other CPUs on machine 3809 checks. 0 to disable. 3810 3811 bios_cmci_threshold 3812 don't overwrite the bios-set CMCI threshold. This boot 3813 option prevents Linux from overwriting the CMCI 3814 threshold set by the bios. Without this option, Linux 3815 always sets the CMCI threshold to 1. Enabling this may 3816 make memory predictive failure analysis less effective 3817 if the bios sets thresholds for memory errors since we 3818 will not see details for all errors. 3819 3820 recovery 3821 force-enable recoverable machine check code paths 3822 3823 Everything else is in sysfs now. 3824 3825 3826 md= [HW] RAID subsystems devices and level 3827 See Documentation/admin-guide/md.rst. 3828 3829 mdacon= [MDA] 3830 Format: <first>,<last> 3831 Specifies range of consoles to be captured by the MDA. 3832 3833 mds= [X86,INTEL,EARLY] 3834 Control mitigation for the Micro-architectural Data 3835 Sampling (MDS) vulnerability. 3836 3837 Certain CPUs are vulnerable to an exploit against CPU 3838 internal buffers which can forward information to a 3839 disclosure gadget under certain conditions. 3840 3841 In vulnerable processors, the speculatively 3842 forwarded data can be used in a cache side channel 3843 attack, to access data to which the attacker does 3844 not have direct access. 3845 3846 This parameter controls the MDS mitigation. The 3847 options are: 3848 3849 full - Enable MDS mitigation on vulnerable CPUs 3850 full,nosmt - Enable MDS mitigation and disable 3851 SMT on vulnerable CPUs 3852 off - Unconditionally disable MDS mitigation 3853 3854 On TAA-affected machines, mds=off can be prevented by 3855 an active TAA mitigation as both vulnerabilities are 3856 mitigated with the same mechanism so in order to disable 3857 this mitigation, you need to specify tsx_async_abort=off 3858 too. 3859 3860 Not specifying this option is equivalent to 3861 mds=full. 3862 3863 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3864 3865 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3866 Must be specified, otherwise memory size will be 0. 3867 3868 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3869 of memory Amount of memory to be used in cases 3870 as follows: 3871 3872 1 for test; 3873 2 when the kernel is not able to see the whole system memory; 3874 3 memory that lies after 'mem=' boundary is excluded from 3875 the hypervisor, then assigned to KVM guests. 3876 4 to limit the memory available for kdump kernel. 3877 3878 [ARC,MICROBLAZE] - the limit applies only to low memory, 3879 high memory is not affected. 3880 3881 [ARM64] - only limits memory covered by the linear 3882 mapping. The NOMAP regions are not affected. 3883 3884 [X86] Work as limiting max address. Use together 3885 with memmap= to avoid physical address space collisions. 3886 Without memmap= PCI devices could be placed at addresses 3887 belonging to unused RAM. 3888 3889 Note that this only takes effects during boot time since 3890 in above case 3, memory may need be hot added after boot 3891 if system memory of hypervisor is not sufficient. 3892 3893 mem=nn[KMG]@ss[KMG] 3894 [ARM,MIPS,EARLY] - override the memory layout 3895 reported by firmware. 3896 Define a memory region of size nn[KMG] starting at 3897 ss[KMG]. 3898 Multiple different regions can be specified with 3899 multiple mem= parameters on the command line. 3900 3901 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3902 memory. 3903 3904 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3905 3906 memchunk=nn[KMG] 3907 [KNL,SH] Allow user to override the default size for 3908 per-device physically contiguous DMA buffers. 3909 3910 memhp_default_state=online/offline/online_kernel/online_movable 3911 [KNL] Set the initial state for the memory hotplug 3912 onlining policy. If not specified, the default value is 3913 set according to the 3914 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3915 options. 3916 See Documentation/admin-guide/mm/memory-hotplug.rst. 3917 3918 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3919 E820 memory map, as specified by the user. 3920 Such memmap=exactmap lines can be constructed based on 3921 BIOS output or other requirements. See the memmap=nn@ss 3922 option description. 3923 3924 memmap=nn[KMG]@ss[KMG] 3925 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3926 Region of memory to be used is from ss to ss+nn. 3927 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3928 which limits max address to nn[KMG]. 3929 Multiple different regions can be specified, 3930 comma delimited. 3931 Example: 3932 memmap=100M@2G,100M#3G,1G!1024G 3933 3934 memmap=nn[KMG]#ss[KMG] 3935 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3936 Region of memory to be marked is from ss to ss+nn. 3937 3938 memmap=nn[KMG]$ss[KMG] 3939 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3940 Region of memory to be reserved is from ss to ss+nn. 3941 Example: Exclude memory from 0x18690000-0x1869ffff 3942 memmap=64K$0x18690000 3943 or 3944 memmap=0x10000$0x18690000 3945 Some bootloaders may need an escape character before '$', 3946 like Grub2, otherwise '$' and the following number 3947 will be eaten. 3948 3949 memmap=nn[KMG]!ss[KMG,EARLY] 3950 [KNL,X86] Mark specific memory as protected. 3951 Region of memory to be used, from ss to ss+nn. 3952 The memory region may be marked as e820 type 12 (0xc) 3953 and is NVDIMM or ADR memory. 3954 3955 memmap=<size>%<offset>-<oldtype>+<newtype> 3956 [KNL,ACPI,EARLY] Convert memory within the specified region 3957 from <oldtype> to <newtype>. If "-<oldtype>" is left 3958 out, the whole region will be marked as <newtype>, 3959 even if previously unavailable. If "+<newtype>" is left 3960 out, matching memory will be removed. Types are 3961 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3962 3 = ACPI, 12 = PRAM. 3963 3964 memory_corruption_check=0/1 [X86,EARLY] 3965 Some BIOSes seem to corrupt the first 64k of 3966 memory when doing things like suspend/resume. 3967 Setting this option will scan the memory 3968 looking for corruption. Enabling this will 3969 both detect corruption and prevent the kernel 3970 from using the memory being corrupted. 3971 However, it's intended as a diagnostic tool; if 3972 repeatable BIOS-originated corruption always 3973 affects the same memory, you can use memmap= 3974 to prevent the kernel from using that memory. 3975 3976 memory_corruption_check_size=size [X86,EARLY] 3977 By default it checks for corruption in the low 3978 64k, making this memory unavailable for normal 3979 use. Use this parameter to scan for 3980 corruption in more or less memory. 3981 3982 memory_corruption_check_period=seconds [X86,EARLY] 3983 By default it checks for corruption every 60 3984 seconds. Use this parameter to check at some 3985 other rate. 0 disables periodic checking. 3986 3987 memory_hotplug.memmap_on_memory 3988 [KNL,X86,ARM] Boolean flag to enable this feature. 3989 Format: {on | off (default)} 3990 When enabled, runtime hotplugged memory will 3991 allocate its internal metadata (struct pages, 3992 those vmemmap pages cannot be optimized even 3993 if hugetlb_free_vmemmap is enabled) from the 3994 hotadded memory which will allow to hotadd a 3995 lot of memory without requiring additional 3996 memory to do so. 3997 This feature is disabled by default because it 3998 has some implication on large (e.g. GB) 3999 allocations in some configurations (e.g. small 4000 memory blocks). 4001 The state of the flag can be read in 4002 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4003 Note that even when enabled, there are a few cases where 4004 the feature is not effective. 4005 4006 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4007 Format: <integer> 4008 default : 0 <disable> 4009 Specifies the number of memtest passes to be 4010 performed. Each pass selects another test 4011 pattern from a given set of patterns. Memtest 4012 fills the memory with this pattern, validates 4013 memory contents and reserves bad memory 4014 regions that are detected. 4015 4016 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4017 Valid arguments: on, off 4018 Default: off 4019 mem_encrypt=on: Activate SME 4020 mem_encrypt=off: Do not activate SME 4021 4022 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4023 for details on when memory encryption can be activated. 4024 4025 mem_sleep_default= [SUSPEND] Default system suspend mode: 4026 s2idle - Suspend-To-Idle 4027 shallow - Power-On Suspend or equivalent (if supported) 4028 deep - Suspend-To-RAM or equivalent (if supported) 4029 See Documentation/admin-guide/pm/sleep-states.rst. 4030 4031 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4032 the BIOS has incorrectly applied a workaround. TinyBIOS 4033 version 0.98 is known to be affected, 0.99 fixes the 4034 problem by letting the user disable the workaround. 4035 4036 mga= [HW,DRM] 4037 4038 microcode= [X86] Control the behavior of the microcode loader. 4039 Available options, comma separated: 4040 4041 base_rev=X - with <X> with format: <u32> 4042 Set the base microcode revision of each thread when in 4043 debug mode. 4044 4045 dis_ucode_ldr: disable the microcode loader 4046 4047 force_minrev: 4048 Enable or disable the microcode minimal revision 4049 enforcement for the runtime microcode loader. 4050 4051 mini2440= [ARM,HW,KNL] 4052 Format:[0..2][b][c][t] 4053 Default: "0tb" 4054 MINI2440 configuration specification: 4055 0 - The attached screen is the 3.5" TFT 4056 1 - The attached screen is the 7" TFT 4057 2 - The VGA Shield is attached (1024x768) 4058 Leaving out the screen size parameter will not load 4059 the TFT driver, and the framebuffer will be left 4060 unconfigured. 4061 b - Enable backlight. The TFT backlight pin will be 4062 linked to the kernel VESA blanking code and a GPIO 4063 LED. This parameter is not necessary when using the 4064 VGA shield. 4065 c - Enable the s3c camera interface. 4066 t - Reserved for enabling touchscreen support. The 4067 touchscreen support is not enabled in the mainstream 4068 kernel as of 2.6.30, a preliminary port can be found 4069 in the "bleeding edge" mini2440 support kernel at 4070 https://repo.or.cz/w/linux-2.6/mini2440.git 4071 4072 mitigations= 4073 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4074 CPU vulnerabilities. This is a set of curated, 4075 arch-independent options, each of which is an 4076 aggregation of existing arch-specific options. 4077 4078 Note, "mitigations" is supported if and only if the 4079 kernel was built with CPU_MITIGATIONS=y. 4080 4081 off 4082 Disable all optional CPU mitigations. This 4083 improves system performance, but it may also 4084 expose users to several CPU vulnerabilities. 4085 Equivalent to: if nokaslr then kpti=0 [ARM64] 4086 gather_data_sampling=off [X86] 4087 indirect_target_selection=off [X86] 4088 kvm.nx_huge_pages=off [X86] 4089 l1tf=off [X86] 4090 mds=off [X86] 4091 mmio_stale_data=off [X86] 4092 no_entry_flush [PPC] 4093 no_uaccess_flush [PPC] 4094 nobp=0 [S390] 4095 nopti [X86,PPC] 4096 nospectre_bhb [ARM64] 4097 nospectre_v1 [X86,PPC] 4098 nospectre_v2 [X86,PPC,S390,ARM64] 4099 reg_file_data_sampling=off [X86] 4100 retbleed=off [X86] 4101 spec_rstack_overflow=off [X86] 4102 spec_store_bypass_disable=off [X86,PPC] 4103 spectre_bhi=off [X86] 4104 spectre_v2_user=off [X86] 4105 srbds=off [X86,INTEL] 4106 ssbd=force-off [ARM64] 4107 tsa=off [X86,AMD] 4108 tsx_async_abort=off [X86] 4109 vmscape=off [X86] 4110 4111 Exceptions: 4112 This does not have any effect on 4113 kvm.nx_huge_pages when 4114 kvm.nx_huge_pages=force. 4115 4116 auto (default) 4117 Mitigate all CPU vulnerabilities, but leave SMT 4118 enabled, even if it's vulnerable. This is for 4119 users who don't want to be surprised by SMT 4120 getting disabled across kernel upgrades, or who 4121 have other ways of avoiding SMT-based attacks. 4122 Equivalent to: (default behavior) 4123 4124 auto,nosmt 4125 Mitigate all CPU vulnerabilities, disabling SMT 4126 if needed. This is for users who always want to 4127 be fully mitigated, even if it means losing SMT. 4128 Equivalent to: l1tf=flush,nosmt [X86] 4129 mds=full,nosmt [X86] 4130 tsx_async_abort=full,nosmt [X86] 4131 mmio_stale_data=full,nosmt [X86] 4132 retbleed=auto,nosmt [X86] 4133 4134 [X86] After one of the above options, additionally 4135 supports attack-vector based controls as documented in 4136 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4137 4138 mminit_loglevel= 4139 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4140 parameter allows control of the logging verbosity for 4141 the additional memory initialisation checks. A value 4142 of 0 disables mminit logging and a level of 4 will 4143 log everything. Information is printed at KERN_DEBUG 4144 so loglevel=8 may also need to be specified. 4145 4146 mmio_stale_data= 4147 [X86,INTEL,EARLY] Control mitigation for the Processor 4148 MMIO Stale Data vulnerabilities. 4149 4150 Processor MMIO Stale Data is a class of 4151 vulnerabilities that may expose data after an MMIO 4152 operation. Exposed data could originate or end in 4153 the same CPU buffers as affected by MDS and TAA. 4154 Therefore, similar to MDS and TAA, the mitigation 4155 is to clear the affected CPU buffers. 4156 4157 This parameter controls the mitigation. The 4158 options are: 4159 4160 full - Enable mitigation on vulnerable CPUs 4161 4162 full,nosmt - Enable mitigation and disable SMT on 4163 vulnerable CPUs. 4164 4165 off - Unconditionally disable mitigation 4166 4167 On MDS or TAA affected machines, 4168 mmio_stale_data=off can be prevented by an active 4169 MDS or TAA mitigation as these vulnerabilities are 4170 mitigated with the same mechanism so in order to 4171 disable this mitigation, you need to specify 4172 mds=off and tsx_async_abort=off too. 4173 4174 Not specifying this option is equivalent to 4175 mmio_stale_data=full. 4176 4177 For details see: 4178 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4179 4180 <module>.async_probe[=<bool>] [KNL] 4181 If no <bool> value is specified or if the value 4182 specified is not a valid <bool>, enable asynchronous 4183 probe on this module. Otherwise, enable/disable 4184 asynchronous probe on this module as indicated by the 4185 <bool> value. See also: module.async_probe 4186 4187 module.async_probe=<bool> 4188 [KNL] When set to true, modules will use async probing 4189 by default. To enable/disable async probing for a 4190 specific module, use the module specific control that 4191 is documented under <module>.async_probe. When both 4192 module.async_probe and <module>.async_probe are 4193 specified, <module>.async_probe takes precedence for 4194 the specific module. 4195 4196 module.enable_dups_trace 4197 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4198 this means that duplicate request_module() calls will 4199 trigger a WARN_ON() instead of a pr_warn(). Note that 4200 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4201 will always be issued and this option does nothing. 4202 module.sig_enforce 4203 [KNL] When CONFIG_MODULE_SIG is set, this means that 4204 modules without (valid) signatures will fail to load. 4205 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4206 is always true, so this option does nothing. 4207 4208 module_blacklist= [KNL] Do not load a comma-separated list of 4209 modules. Useful for debugging problem modules. 4210 4211 mousedev.tap_time= 4212 [MOUSE] Maximum time between finger touching and 4213 leaving touchpad surface for touch to be considered 4214 a tap and be reported as a left button click (for 4215 touchpads working in absolute mode only). 4216 Format: <msecs> 4217 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4218 reporting absolute coordinates, such as tablets 4219 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4220 reporting absolute coordinates, such as tablets 4221 4222 movablecore= [KNL,X86,PPC,EARLY] 4223 Format: nn[KMGTPE] | nn% 4224 This parameter is the complement to kernelcore=, it 4225 specifies the amount of memory used for migratable 4226 allocations. If both kernelcore and movablecore is 4227 specified, then kernelcore will be at *least* the 4228 specified value but may be more. If movablecore on its 4229 own is specified, the administrator must be careful 4230 that the amount of memory usable for all allocations 4231 is not too small. 4232 4233 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4234 NUMA nodes to be movable. This means that the memory 4235 of such nodes will be usable only for movable 4236 allocations which rules out almost all kernel 4237 allocations. Use with caution! 4238 4239 MTD_Partition= [MTD] 4240 Format: <name>,<region-number>,<size>,<offset> 4241 4242 MTD_Region= [MTD] Format: 4243 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4244 4245 mtdparts= [MTD] 4246 See drivers/mtd/parsers/cmdlinepart.c 4247 4248 mtouchusb.raw_coordinates= 4249 [HW] Make the MicroTouch USB driver use raw coordinates 4250 ('y', default) or cooked coordinates ('n') 4251 4252 mtrr=debug [X86,EARLY] 4253 Enable printing debug information related to MTRR 4254 registers at boot time. 4255 4256 mtrr_chunk_size=nn[KMG,X86,EARLY] 4257 used for mtrr cleanup. It is largest continuous chunk 4258 that could hold holes aka. UC entries. 4259 4260 mtrr_gran_size=nn[KMG,X86,EARLY] 4261 Used for mtrr cleanup. It is granularity of mtrr block. 4262 Default is 1. 4263 Large value could prevent small alignment from 4264 using up MTRRs. 4265 4266 mtrr_spare_reg_nr=n [X86,EARLY] 4267 Format: <integer> 4268 Range: 0,7 : spare reg number 4269 Default : 1 4270 Used for mtrr cleanup. It is spare mtrr entries number. 4271 Set to 2 or more if your graphical card needs more. 4272 4273 multitce=off [PPC] This parameter disables the use of the pSeries 4274 firmware feature for updating multiple TCE entries 4275 at a time. 4276 4277 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4278 4279 netdev= [NET] Network devices parameters 4280 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4281 Note that mem_start is often overloaded to mean 4282 something different and driver-specific. 4283 This usage is only documented in each driver source 4284 file if at all. 4285 4286 netpoll.carrier_timeout= 4287 [NET] Specifies amount of time (in seconds) that 4288 netpoll should wait for a carrier. By default netpoll 4289 waits 4 seconds. 4290 4291 nf_conntrack.acct= 4292 [NETFILTER] Enable connection tracking flow accounting 4293 0 to disable accounting 4294 1 to enable accounting 4295 Default value is 0. 4296 4297 nfs.cache_getent= 4298 [NFS] sets the pathname to the program which is used 4299 to update the NFS client cache entries. 4300 4301 nfs.cache_getent_timeout= 4302 [NFS] sets the timeout after which an attempt to 4303 update a cache entry is deemed to have failed. 4304 4305 nfs.callback_nr_threads= 4306 [NFSv4] set the total number of threads that the 4307 NFS client will assign to service NFSv4 callback 4308 requests. 4309 4310 nfs.callback_tcpport= 4311 [NFS] set the TCP port on which the NFSv4 callback 4312 channel should listen. 4313 4314 nfs.delay_retrans= 4315 [NFS] specifies the number of times the NFSv4 client 4316 retries the request before returning an EAGAIN error, 4317 after a reply of NFS4ERR_DELAY from the server. 4318 Only applies if the softerr mount option is enabled, 4319 and the specified value is >= 0. 4320 4321 nfs.enable_ino64= 4322 [NFS] enable 64-bit inode numbers. 4323 If zero, the NFS client will fake up a 32-bit inode 4324 number for the readdir() and stat() syscalls instead 4325 of returning the full 64-bit number. 4326 The default is to return 64-bit inode numbers. 4327 4328 nfs.idmap_cache_timeout= 4329 [NFS] set the maximum lifetime for idmapper cache 4330 entries. 4331 4332 nfs.max_session_cb_slots= 4333 [NFSv4.1] Sets the maximum number of session 4334 slots the client will assign to the callback 4335 channel. This determines the maximum number of 4336 callbacks the client will process in parallel for 4337 a particular server. 4338 4339 nfs.max_session_slots= 4340 [NFSv4.1] Sets the maximum number of session slots 4341 the client will attempt to negotiate with the server. 4342 This limits the number of simultaneous RPC requests 4343 that the client can send to the NFSv4.1 server. 4344 Note that there is little point in setting this 4345 value higher than the max_tcp_slot_table_limit. 4346 4347 nfs.nfs4_disable_idmapping= 4348 [NFSv4] When set to the default of '1', this option 4349 ensures that both the RPC level authentication 4350 scheme and the NFS level operations agree to use 4351 numeric uids/gids if the mount is using the 4352 'sec=sys' security flavour. In effect it is 4353 disabling idmapping, which can make migration from 4354 legacy NFSv2/v3 systems to NFSv4 easier. 4355 Servers that do not support this mode of operation 4356 will be autodetected by the client, and it will fall 4357 back to using the idmapper. 4358 To turn off this behaviour, set the value to '0'. 4359 4360 nfs.nfs4_unique_id= 4361 [NFS4] Specify an additional fixed unique ident- 4362 ification string that NFSv4 clients can insert into 4363 their nfs_client_id4 string. This is typically a 4364 UUID that is generated at system install time. 4365 4366 nfs.recover_lost_locks= 4367 [NFSv4] Attempt to recover locks that were lost due 4368 to a lease timeout on the server. Please note that 4369 doing this risks data corruption, since there are 4370 no guarantees that the file will remain unchanged 4371 after the locks are lost. 4372 If you want to enable the kernel legacy behaviour of 4373 attempting to recover these locks, then set this 4374 parameter to '1'. 4375 The default parameter value of '0' causes the kernel 4376 not to attempt recovery of lost locks. 4377 4378 nfs.send_implementation_id= 4379 [NFSv4.1] Send client implementation identification 4380 information in exchange_id requests. 4381 If zero, no implementation identification information 4382 will be sent. 4383 The default is to send the implementation identification 4384 information. 4385 4386 nfs4.layoutstats_timer= 4387 [NFSv4.2] Change the rate at which the kernel sends 4388 layoutstats to the pNFS metadata server. 4389 4390 Setting this to value to 0 causes the kernel to use 4391 whatever value is the default set by the layout 4392 driver. A non-zero value sets the minimum interval 4393 in seconds between layoutstats transmissions. 4394 4395 nfsd.inter_copy_offload_enable= 4396 [NFSv4.2] When set to 1, the server will support 4397 server-to-server copies for which this server is 4398 the destination of the copy. 4399 4400 nfsd.nfs4_disable_idmapping= 4401 [NFSv4] When set to the default of '1', the NFSv4 4402 server will return only numeric uids and gids to 4403 clients using auth_sys, and will accept numeric uids 4404 and gids from such clients. This is intended to ease 4405 migration from NFSv2/v3. 4406 4407 nfsd.nfsd4_ssc_umount_timeout= 4408 [NFSv4.2] When used as the destination of a 4409 server-to-server copy, knfsd temporarily mounts 4410 the source server. It caches the mount in case 4411 it will be needed again, and discards it if not 4412 used for the number of milliseconds specified by 4413 this parameter. 4414 4415 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4416 See Documentation/admin-guide/nfs/nfsroot.rst. 4417 4418 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4419 See Documentation/admin-guide/nfs/nfsroot.rst. 4420 4421 nfsrootdebug [NFS] enable nfsroot debugging messages. 4422 See Documentation/admin-guide/nfs/nfsroot.rst. 4423 4424 nmi_backtrace.backtrace_idle [KNL] 4425 Dump stacks even of idle CPUs in response to an 4426 NMI stack-backtrace request. 4427 4428 nmi_debug= [KNL,SH] Specify one or more actions to take 4429 when a NMI is triggered. 4430 Format: [state][,regs][,debounce][,die] 4431 4432 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4433 Format: [panic,][nopanic,][rNNN,][num] 4434 Valid num: 0 or 1 4435 0 - turn hardlockup detector in nmi_watchdog off 4436 1 - turn hardlockup detector in nmi_watchdog on 4437 rNNN - configure the watchdog with raw perf event 0xNNN 4438 4439 When panic is specified, panic when an NMI watchdog 4440 timeout occurs (or 'nopanic' to not panic on an NMI 4441 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4442 To disable both hard and soft lockup detectors, 4443 please see 'nowatchdog'. 4444 This is useful when you use a panic=... timeout and 4445 need the box quickly up again. 4446 4447 These settings can be accessed at runtime via 4448 the nmi_watchdog and hardlockup_panic sysctls. 4449 4450 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4451 emulation library even if a 387 maths coprocessor 4452 is present. 4453 4454 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4455 Forces kernel to use 3-level paging instead. 4456 4457 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4458 kernel to use 4-level paging instead. 4459 4460 noalign [KNL,ARM] 4461 4462 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4463 IOAPICs that may be present in the system. 4464 4465 noapictimer [APIC,X86] Don't set up the APIC timer 4466 4467 noautogroup Disable scheduler automatic task group creation. 4468 4469 nocache [ARM,EARLY] 4470 4471 no_console_suspend 4472 [HW] Never suspend the console 4473 Disable suspending of consoles during suspend and 4474 hibernate operations. Once disabled, debugging 4475 messages can reach various consoles while the rest 4476 of the system is being put to sleep (ie, while 4477 debugging driver suspend/resume hooks). This may 4478 not work reliably with all consoles, but is known 4479 to work with serial and VGA consoles. 4480 To facilitate more flexible debugging, we also add 4481 console_suspend, a printk module parameter to control 4482 it. Users could use console_suspend (usually 4483 /sys/module/printk/parameters/console_suspend) to 4484 turn on/off it dynamically. 4485 4486 no_debug_objects 4487 [KNL,EARLY] Disable object debugging 4488 4489 nodsp [SH] Disable hardware DSP at boot time. 4490 4491 noefi [EFI,EARLY] Disable EFI runtime services support. 4492 4493 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4494 4495 noexec32 [X86-64] 4496 This affects only 32-bit executables. 4497 noexec32=on: enable non-executable mappings (default) 4498 read doesn't imply executable mappings 4499 noexec32=off: disable non-executable mappings 4500 read implies executable mappings 4501 4502 no_file_caps Tells the kernel not to honor file capabilities. The 4503 only way then for a file to be executed with privilege 4504 is to be setuid root or executed by root. 4505 4506 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4507 4508 nofsgsbase [X86] Disables FSGSBASE instructions. 4509 4510 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4511 register save and restore. The kernel will only save 4512 legacy floating-point registers on task switch. 4513 4514 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4515 4516 no_hash_pointers 4517 [KNL,EARLY] 4518 Alias for "hash_pointers=never". 4519 4520 nohibernate [HIBERNATION] Disable hibernation and resume. 4521 4522 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4523 busy wait in do_idle() and not use the arch_cpu_idle() 4524 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4525 to be effective. This is useful on platforms where the 4526 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4527 correctly or when doing power measurements to evaluate 4528 the impact of the sleep instructions. This is also 4529 useful when using JTAG debugger. 4530 4531 nohpet [X86] Don't use the HPET timer. 4532 4533 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4534 4535 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4536 4537 nohz= [KNL] Boottime enable/disable dynamic ticks 4538 Valid arguments: on, off 4539 Default: on 4540 4541 nohz_full= [KNL,BOOT,SMP,ISOL] 4542 The argument is a cpu list, as described above. 4543 In kernels built with CONFIG_NO_HZ_FULL=y, set 4544 the specified list of CPUs whose tick will be stopped 4545 whenever possible. The boot CPU will be forced outside 4546 the range to maintain the timekeeping. Any CPUs 4547 in this list will have their RCU callbacks offloaded, 4548 just as if they had also been called out in the 4549 rcu_nocbs= boot parameter. 4550 4551 Note that this argument takes precedence over 4552 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4553 4554 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4555 initial RAM disk. Currently this parameter applies to 4556 initrd only, not to initramfs. But it applies to both 4557 in EFI mode. 4558 4559 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4560 remapping. 4561 [Deprecated - use intremap=off] 4562 4563 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4564 4565 noiotrap [SH] Disables trapped I/O port accesses. 4566 4567 noirqdebug [X86-32] Disables the code which attempts to detect and 4568 disable unhandled interrupt sources. 4569 4570 noisapnp [ISAPNP] Disables ISA PnP code. 4571 4572 nokaslr [KNL,EARLY] 4573 When CONFIG_RANDOMIZE_BASE is set, this disables 4574 kernel and module base offset ASLR (Address Space 4575 Layout Randomization). 4576 4577 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4578 fault handling. 4579 4580 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4581 4582 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4583 4584 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4585 4586 nomce [X86-32] Disable Machine Check Exception 4587 4588 nomfgpt [X86-32] Disable Multi-Function General Purpose 4589 Timer usage (for AMD Geode machines). 4590 4591 nomodeset Disable kernel modesetting. Most systems' firmware 4592 sets up a display mode and provides framebuffer memory 4593 for output. With nomodeset, DRM and fbdev drivers will 4594 not load if they could possibly displace the pre- 4595 initialized output. Only the system framebuffer will 4596 be available for use. The respective drivers will not 4597 perform display-mode changes or accelerated rendering. 4598 4599 Useful as error fallback, or for testing and debugging. 4600 4601 nomodule Disable module load 4602 4603 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4604 shutdown the other cpus. Instead use the REBOOT_VECTOR 4605 irq. 4606 4607 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4608 pagetables) support. 4609 4610 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4611 4612 nopku [X86] Disable Memory Protection Keys CPU feature found 4613 in some Intel CPUs. 4614 4615 nopti [X86-64,EARLY] 4616 Equivalent to pti=off 4617 4618 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4619 Disables the PV optimizations forcing the guest to run 4620 as generic guest with no PV drivers. Currently support 4621 XEN HVM, KVM, HYPER_V and VMWARE guest. 4622 4623 nopvspin [X86,XEN,KVM,EARLY] 4624 Disables the qspinlock slow path using PV optimizations 4625 which allow the hypervisor to 'idle' the guest on lock 4626 contention. 4627 4628 norandmaps Don't use address space randomization. Equivalent to 4629 echo 0 > /proc/sys/kernel/randomize_va_space 4630 4631 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4632 with UP alternatives 4633 4634 noresume [SWSUSP] Disables resume and restores original swap 4635 space. 4636 4637 no-scroll [VGA] Disables scrollback. 4638 This is required for the Braillex ib80-piezo Braille 4639 reader made by F.H. Papenmeier (Germany). 4640 4641 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4642 4643 nosmap [PPC,EARLY] 4644 Disable SMAP (Supervisor Mode Access Prevention) 4645 even if it is supported by processor. 4646 4647 nosmep [PPC64s,EARLY] 4648 Disable SMEP (Supervisor Mode Execution Prevention) 4649 even if it is supported by processor. 4650 4651 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4652 and disable the IO APIC. legacy for "maxcpus=0". 4653 4654 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4655 Equivalent to smt=1. 4656 4657 [KNL,LOONGARCH,X86,ARM64,PPC,S390] Disable symmetric multithreading (SMT). 4658 nosmt=force: Force disable SMT, cannot be undone 4659 via the sysfs control file. 4660 4661 nosoftlockup [KNL] Disable the soft-lockup detector. 4662 4663 nospec_store_bypass_disable 4664 [HW,EARLY] Disable all mitigations for the Speculative 4665 Store Bypass vulnerability 4666 4667 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4668 history injection) vulnerability. System may allow data leaks 4669 with this option. 4670 4671 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4672 (bounds check bypass). With this option data leaks are 4673 possible in the system. 4674 4675 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4676 for the Spectre variant 2 (indirect branch 4677 prediction) vulnerability. System may allow data 4678 leaks with this option. 4679 4680 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4681 Disable paravirtualized steal time accounting. steal time 4682 is computed, but won't influence scheduler behaviour 4683 4684 nosync [HW,M68K] Disables sync negotiation for all devices. 4685 4686 no_timer_check [X86,APIC] Disables the code which tests for broken 4687 timer IRQ sources, i.e., the IO-APIC timer. This can 4688 work around problems with incorrect timer 4689 initialization on some boards. 4690 4691 no_uaccess_flush 4692 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4693 4694 novmcoredd [KNL,KDUMP] 4695 Disable device dump. Device dump allows drivers to 4696 append dump data to vmcore so you can collect driver 4697 specified debug info. Drivers can append the data 4698 without any limit and this data is stored in memory, 4699 so this may cause significant memory stress. Disabling 4700 device dump can help save memory but the driver debug 4701 data will be no longer available. This parameter 4702 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4703 is set. 4704 4705 no-vmw-sched-clock 4706 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4707 scheduler clock and use the default one. 4708 4709 nowatchdog [KNL] Disable both lockup detectors, i.e. 4710 soft-lockup and NMI watchdog (hard-lockup). 4711 4712 nowb [ARM,EARLY] 4713 4714 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4715 4716 NOTE: this parameter will be ignored on systems with the 4717 LEGACY_XAPIC_DISABLED bit set in the 4718 IA32_XAPIC_DISABLE_STATUS MSR. 4719 4720 noxsave [BUGS=X86] Disables x86 extended register state save 4721 and restore using xsave. The kernel will fallback to 4722 enabling legacy floating-point and sse state. 4723 4724 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4725 register states. The kernel will fall back to use 4726 xsave to save the states. By using this parameter, 4727 performance of saving the states is degraded because 4728 xsave doesn't support modified optimization while 4729 xsaveopt supports it on xsaveopt enabled systems. 4730 4731 noxsaves [X86] Disables xsaves and xrstors used in saving and 4732 restoring x86 extended register state in compacted 4733 form of xsave area. The kernel will fall back to use 4734 xsaveopt and xrstor to save and restore the states 4735 in standard form of xsave area. By using this 4736 parameter, xsave area per process might occupy more 4737 memory on xsaves enabled systems. 4738 4739 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4740 could support. nr_cpus=n : n >= 1 limits the kernel to 4741 support 'n' processors. It could be larger than the 4742 number of already plugged CPU during bootup, later in 4743 runtime you can physically add extra cpu until it reaches 4744 n. So during boot up some boot time memory for per-cpu 4745 variables need be pre-allocated for later physical cpu 4746 hot plugging. 4747 4748 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4749 4750 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4751 Disable NUMA, Only set up a single NUMA node 4752 spanning all memory. 4753 4754 numa=fake=<size>[MG] 4755 [KNL, ARM64, RISCV, X86, EARLY] 4756 If given as a memory unit, fills all system RAM with 4757 nodes of size interleaved over physical nodes. 4758 4759 numa=fake=<N> 4760 [KNL, ARM64, RISCV, X86, EARLY] 4761 If given as an integer, fills all system RAM with N 4762 fake nodes interleaved over physical nodes. 4763 4764 numa=fake=<N>U 4765 [KNL, ARM64, RISCV, X86, EARLY] 4766 If given as an integer followed by 'U', it will 4767 divide each physical node into N emulated nodes. 4768 4769 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4770 4771 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4772 soft-reserved memory partitioning. 4773 4774 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4775 NUMA balancing. 4776 Allowed values are enable and disable 4777 4778 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4779 'node', 'default' can be specified 4780 This can be set from sysctl after boot. 4781 See Documentation/admin-guide/sysctl/vm.rst for details. 4782 4783 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4784 nvme quirk list. List entries are separated by a 4785 '-' character. 4786 Each entry has the form VendorID:ProductID:quirk_names. 4787 The IDs are 4-digits hex numbers and quirk_names is a 4788 list of quirk names separated by commas. A quirk name 4789 can be prefixed by '^', meaning that the specified 4790 quirk must be disabled. 4791 4792 Example: 4793 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4794 4795 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4796 See Documentation/core-api/debugging-via-ohci1394.rst for more 4797 info. 4798 4799 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4800 Rather than timing out after 20 ms if an EC 4801 command is not properly ACKed, override the length 4802 of the timeout. We have interrupts disabled while 4803 waiting for the ACK, so if this is set too high 4804 interrupts *may* be lost! 4805 4806 omap_mux= [OMAP] Override bootloader pin multiplexing. 4807 Format: <mux_mode0.mode_name=value>... 4808 For example, to override I2C bus2: 4809 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4810 4811 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4812 4813 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4814 4815 boundary - index of last SLC block on Flex-OneNAND. 4816 The remaining blocks are configured as MLC blocks. 4817 lock - Configure if Flex-OneNAND boundary should be locked. 4818 Once locked, the boundary cannot be changed. 4819 1 indicates lock status, 0 indicates unlock status. 4820 4821 oops=panic [KNL,EARLY] 4822 Always panic on oopses. Default is to just kill the 4823 process, but there is a small probability of 4824 deadlocking the machine. 4825 This will also cause panics on machine check exceptions. 4826 Useful together with panic=30 to trigger a reboot. 4827 4828 page_alloc.shuffle= 4829 [KNL] Boolean flag to control whether the page allocator 4830 should randomize its free lists. This parameter can be 4831 used to enable/disable page randomization. The state of 4832 the flag can be read from sysfs at: 4833 /sys/module/page_alloc/parameters/shuffle. 4834 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4835 4836 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4837 Storage of the information about who allocated 4838 each page is disabled in default. With this switch, 4839 we can turn it on. 4840 on: enable the feature 4841 4842 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4843 poisoning on the buddy allocator, available with 4844 CONFIG_PAGE_POISONING=y. 4845 off: turn off poisoning (default) 4846 on: turn on poisoning 4847 4848 page_reporting.page_reporting_order= 4849 [KNL] Minimal page reporting order 4850 Format: <integer> 4851 Adjust the minimal page reporting order. The page 4852 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4853 4854 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4855 timeout > 0: seconds before rebooting 4856 timeout = 0: wait forever 4857 timeout < 0: reboot immediately 4858 Format: <timeout> 4859 4860 panic_on_taint= [KNL,EARLY] 4861 Bitmask for conditionally calling panic() in add_taint() 4862 Format: <hex>[,nousertaint] 4863 Hexadecimal bitmask representing the set of TAINT flags 4864 that will cause the kernel to panic when add_taint() is 4865 called with any of the flags in this set. 4866 The optional switch "nousertaint" can be utilized to 4867 prevent userspace forced crashes by writing to sysctl 4868 /proc/sys/kernel/tainted any flagset matching with the 4869 bitmask set on panic_on_taint. 4870 See Documentation/admin-guide/tainted-kernels.rst for 4871 extra details on the taint flags that users can pick 4872 to compose the bitmask to assign to panic_on_taint. 4873 4874 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4875 on a WARN(). 4876 4877 panic_force_cpu= 4878 [KNL,SMP] Force panic handling to execute on a specific CPU. 4879 Format: <cpu number> 4880 Some platforms require panic handling to occur on a 4881 specific CPU for the crash kernel to function correctly. 4882 This can be due to firmware limitations, interrupt routing 4883 constraints, or platform-specific requirements where only 4884 a particular CPU can safely enter the crash kernel. 4885 When set, panic() will redirect execution to the specified 4886 CPU before proceeding with the normal panic and kexec flow. 4887 If the target CPU is offline or unavailable, panic proceeds 4888 on the current CPU. 4889 This option should only be used for systems with the above 4890 constraints as it might cause the panic operation to be less reliable. 4891 4892 panic_print= Bitmask for printing system info when panic happens. 4893 User can chose combination of the following bits: 4894 bit 0: print all tasks info 4895 bit 1: print system memory info 4896 bit 2: print timer info 4897 bit 3: print locks info if CONFIG_LOCKDEP is on 4898 bit 4: print ftrace buffer 4899 bit 5: replay all kernel messages on consoles at the end of panic 4900 bit 6: print all CPUs backtrace (if available in the arch) 4901 bit 7: print only tasks in uninterruptible (blocked) state 4902 *Be aware* that this option may print a _lot_ of lines, 4903 so there are risks of losing older messages in the log. 4904 Use this option carefully, maybe worth to setup a 4905 bigger log buffer with "log_buf_len" along with this. 4906 4907 panic_sys_info= A comma separated list of extra information to be dumped 4908 on panic. 4909 Format: val[,val...] 4910 Where @val can be any of the following: 4911 4912 tasks: print all tasks info 4913 mem: print system memory info 4914 timers: print timers info 4915 locks: print locks info if CONFIG_LOCKDEP is on 4916 ftrace: print ftrace buffer 4917 all_bt: print all CPUs backtrace (if available in the arch) 4918 blocked_tasks: print only tasks in uninterruptible (blocked) state 4919 4920 This is a human readable alternative to the 'panic_print' option. 4921 4922 panic_console_replay 4923 When panic happens, replay all kernel messages on 4924 consoles at the end of panic. 4925 4926 parkbd.port= [HW] Parallel port number the keyboard adapter is 4927 connected to, default is 0. 4928 Format: <parport#> 4929 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4930 0 for XT, 1 for AT (default is AT). 4931 Format: <mode> 4932 4933 parport= [HW,PPT] Specify parallel ports. 0 disables. 4934 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4935 Use 'auto' to force the driver to use any 4936 IRQ/DMA settings detected (the default is to 4937 ignore detected IRQ/DMA settings because of 4938 possible conflicts). You can specify the base 4939 address, IRQ, and DMA settings; IRQ and DMA 4940 should be numbers, or 'auto' (for using detected 4941 settings on that particular port), or 'nofifo' 4942 (to avoid using a FIFO even if it is detected). 4943 Parallel ports are assigned in the order they 4944 are specified on the command line, starting 4945 with parport0. 4946 4947 parport_init_mode= [HW,PPT] 4948 Configure VIA parallel port to operate in 4949 a specific mode. This is necessary on Pegasos 4950 computer where firmware has no options for setting 4951 up parallel port mode and sets it to spp. 4952 Currently this function knows 686a and 8231 chips. 4953 Format: [spp|ps2|epp|ecp|ecpepp] 4954 4955 pata_legacy.all= [HW,LIBATA] 4956 Format: <int> 4957 Set to non-zero to probe primary and secondary ISA 4958 port ranges on PCI systems where no PCI PATA device 4959 has been found at either range. Disabled by default. 4960 4961 pata_legacy.autospeed= [HW,LIBATA] 4962 Format: <int> 4963 Set to non-zero if a chip is present that snoops speed 4964 changes. Disabled by default. 4965 4966 pata_legacy.ht6560a= [HW,LIBATA] 4967 Format: <int> 4968 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4969 the secondary channel, or both channels respectively. 4970 Disabled by default. 4971 4972 pata_legacy.ht6560b= [HW,LIBATA] 4973 Format: <int> 4974 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4975 the secondary channel, or both channels respectively. 4976 Disabled by default. 4977 4978 pata_legacy.iordy_mask= [HW,LIBATA] 4979 Format: <int> 4980 IORDY enable mask. Set individual bits to allow IORDY 4981 for the respective channel. Bit 0 is for the first 4982 legacy channel handled by this driver, bit 1 is for 4983 the second channel, and so on. The sequence will often 4984 correspond to the primary legacy channel, the secondary 4985 legacy channel, and so on, but the handling of a PCI 4986 bus and the use of other driver options may interfere 4987 with the sequence. By default IORDY is allowed across 4988 all channels. 4989 4990 pata_legacy.opti82c46x= [HW,LIBATA] 4991 Format: <int> 4992 Set to 1, 2, or 3 for Opti 82c611A on the primary 4993 channel, the secondary channel, or both channels 4994 respectively. Disabled by default. 4995 4996 pata_legacy.opti82c611a= [HW,LIBATA] 4997 Format: <int> 4998 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4999 channel, the secondary channel, or both channels 5000 respectively. Disabled by default. 5001 5002 pata_legacy.pio_mask= [HW,LIBATA] 5003 Format: <int> 5004 PIO mode mask for autospeed devices. Set individual 5005 bits to allow the use of the respective PIO modes. 5006 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 5007 All modes allowed by default. 5008 5009 pata_legacy.probe_all= [HW,LIBATA] 5010 Format: <int> 5011 Set to non-zero to probe tertiary and further ISA 5012 port ranges on PCI systems. Disabled by default. 5013 5014 pata_legacy.probe_mask= [HW,LIBATA] 5015 Format: <int> 5016 Probe mask for legacy ISA PATA ports. Depending on 5017 platform configuration and the use of other driver 5018 options up to 6 legacy ports are supported: 0x1f0, 5019 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5020 of individual ports can be disabled by setting the 5021 corresponding bits in the mask to 1. Bit 0 is for 5022 the first port in the list above (0x1f0), and so on. 5023 By default all supported ports are probed. 5024 5025 pata_legacy.qdi= [HW,LIBATA] 5026 Format: <int> 5027 Set to non-zero to probe QDI controllers. By default 5028 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5029 5030 pata_legacy.winbond= [HW,LIBATA] 5031 Format: <int> 5032 Set to non-zero to probe Winbond controllers. Use 5033 the standard I/O port (0x130) if 1, otherwise the 5034 value given is the I/O port to use (typically 0x1b0). 5035 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5036 0 otherwise. 5037 5038 pata_platform.pio_mask= [HW,LIBATA] 5039 Format: <int> 5040 Supported PIO mode mask. Set individual bits to allow 5041 the use of the respective PIO modes. Bit 0 is for 5042 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5043 allowed by default. 5044 5045 pause_on_oops=<int> 5046 Halt all CPUs after the first oops has been printed for 5047 the specified number of seconds. This is to be used if 5048 your oopses keep scrolling off the screen. 5049 5050 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5051 5052 Some options herein operate on a specific device 5053 or a set of devices (<pci_dev>). These are 5054 specified in one of the following formats: 5055 5056 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5057 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5058 5059 Note: the first format specifies a PCI 5060 bus/device/function address which may change 5061 if new hardware is inserted, if motherboard 5062 firmware changes, or due to changes caused 5063 by other kernel parameters. If the 5064 domain is left unspecified, it is 5065 taken to be zero. Optionally, a path 5066 to a device through multiple device/function 5067 addresses can be specified after the base 5068 address (this is more robust against 5069 renumbering issues). The second format 5070 selects devices using IDs from the 5071 configuration space which may match multiple 5072 devices in the system. 5073 5074 earlydump dump PCI config space before the kernel 5075 changes anything 5076 off [X86] don't probe for the PCI bus 5077 bios [X86-32] force use of PCI BIOS, don't access 5078 the hardware directly. Use this if your machine 5079 has a non-standard PCI host bridge. 5080 nobios [X86-32] disallow use of PCI BIOS, only direct 5081 hardware access methods are allowed. Use this 5082 if you experience crashes upon bootup and you 5083 suspect they are caused by the BIOS. 5084 conf1 [X86] Force use of PCI Configuration Access 5085 Mechanism 1 (config address in IO port 0xCF8, 5086 data in IO port 0xCFC, both 32-bit). 5087 conf2 [X86] Force use of PCI Configuration Access 5088 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5089 the function, IO port 0xCFA, also 8-bit, sets 5090 bus number. The config space is then accessed 5091 through ports 0xC000-0xCFFF). 5092 See http://wiki.osdev.org/PCI for more info 5093 on the configuration access mechanisms. 5094 noaer [PCIE] If the PCIEAER kernel config parameter is 5095 enabled, this kernel boot option can be used to 5096 disable the use of PCIE advanced error reporting. 5097 nodomains [PCI] Disable support for multiple PCI 5098 root domains (aka PCI segments, in ACPI-speak). 5099 nommconf [X86] Disable use of MMCONFIG for PCI 5100 Configuration 5101 check_enable_amd_mmconf [X86] check for and enable 5102 properly configured MMIO access to PCI 5103 config space on AMD family 10h CPU 5104 nomsi [MSI] If the PCI_MSI kernel config parameter is 5105 enabled, this kernel boot option can be used to 5106 disable the use of MSI interrupts system-wide. 5107 noioapicquirk [APIC] Disable all boot interrupt quirks. 5108 Safety option to keep boot IRQs enabled. This 5109 should never be necessary. 5110 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5111 primary IO-APIC for bridges that cannot disable 5112 boot IRQs. This fixes a source of spurious IRQs 5113 when the system masks IRQs. 5114 noioapicreroute [APIC] Disable workaround that uses the 5115 boot IRQ equivalent of an IRQ that connects to 5116 a chipset where boot IRQs cannot be disabled. 5117 The opposite of ioapicreroute. 5118 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5119 routing table. These calls are known to be buggy 5120 on several machines and they hang the machine 5121 when used, but on other computers it's the only 5122 way to get the interrupt routing table. Try 5123 this option if the kernel is unable to allocate 5124 IRQs or discover secondary PCI buses on your 5125 motherboard. 5126 rom [X86] Assign address space to expansion ROMs. 5127 Use with caution as certain devices share 5128 address decoders between ROMs and other 5129 resources. 5130 norom [X86] Do not assign address space to 5131 expansion ROMs that do not already have 5132 BIOS assigned address ranges. 5133 nobar [X86] Do not assign address space to the 5134 BARs that weren't assigned by the BIOS. 5135 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5136 assigned automatically to PCI devices. You can 5137 make the kernel exclude IRQs of your ISA cards 5138 this way. 5139 pirqaddr=0xAAAAA [X86] Specify the physical address 5140 of the PIRQ table (normally generated 5141 by the BIOS) if it is outside the 5142 F0000h-100000h range. 5143 lastbus=N [X86] Scan all buses thru bus #N. Can be 5144 useful if the kernel is unable to find your 5145 secondary buses and you want to tell it 5146 explicitly which ones they are. 5147 assign-busses [X86] Always assign all PCI bus 5148 numbers ourselves, overriding 5149 whatever the firmware may have done. 5150 usepirqmask [X86] Honor the possible IRQ mask stored 5151 in the BIOS $PIR table. This is needed on 5152 some systems with broken BIOSes, notably 5153 some HP Pavilion N5400 and Omnibook XE3 5154 notebooks. This will have no effect if ACPI 5155 IRQ routing is enabled. 5156 noacpi [X86] Do not use ACPI for IRQ routing 5157 or for PCI scanning. 5158 use_crs [X86] Use PCI host bridge window information 5159 from ACPI. On BIOSes from 2008 or later, this 5160 is enabled by default. If you need to use this, 5161 please report a bug. 5162 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5163 If you need to use this, please report a bug. 5164 use_e820 [X86] Use E820 reservations to exclude parts of 5165 PCI host bridge windows. This is a workaround 5166 for BIOS defects in host bridge _CRS methods. 5167 If you need to use this, please report a bug to 5168 <linux-pci@vger.kernel.org>. 5169 no_e820 [X86] Ignore E820 reservations for PCI host 5170 bridge windows. This is the default on modern 5171 hardware. If you need to use this, please report 5172 a bug to <linux-pci@vger.kernel.org>. 5173 routeirq Do IRQ routing for all PCI devices. 5174 This is normally done in pci_enable_device(), 5175 so this option is a temporary workaround 5176 for broken drivers that don't call it. 5177 skip_isa_align [X86] do not align io start addr, so can 5178 handle more pci cards 5179 noearly [X86] Don't do any early type 1 scanning. 5180 This might help on some broken boards which 5181 machine check when some devices' config space 5182 is read. But various workarounds are disabled 5183 and some IOMMU drivers will not work. 5184 bfsort Sort PCI devices into breadth-first order. 5185 This sorting is done to get a device 5186 order compatible with older (<= 2.4) kernels. 5187 nobfsort Don't sort PCI devices into breadth-first order. 5188 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5189 tuning and use the BIOS-configured MPS defaults. 5190 pcie_bus_safe Set every device's MPS to the largest value 5191 supported by all devices below the root complex. 5192 pcie_bus_perf Set device MPS to the largest allowable MPS 5193 based on its parent bus. Also set MRRS (Max 5194 Read Request Size) to the largest supported 5195 value (no larger than the MPS that the device 5196 or bus can support) for best performance. 5197 pcie_bus_peer2peer Set every device's MPS to 128B, which 5198 every device is guaranteed to support. This 5199 configuration allows peer-to-peer DMA between 5200 any pair of devices, possibly at the cost of 5201 reduced performance. This also guarantees 5202 that hot-added devices will work. 5203 cbiosize=nn[KMG] The fixed amount of bus space which is 5204 reserved for the CardBus bridge's IO window. 5205 The default value is 256 bytes. 5206 cbmemsize=nn[KMG] The fixed amount of bus space which is 5207 reserved for the CardBus bridge's memory 5208 window. The default value is 64 megabytes. 5209 resource_alignment= 5210 Format: 5211 [<order of align>@]<pci_dev>[; ...] 5212 Specifies alignment and device to reassign 5213 aligned memory resources. How to 5214 specify the device is described above. 5215 If <order of align> is not specified, 5216 PAGE_SIZE is used as alignment. 5217 A PCI-PCI bridge can be specified if resource 5218 windows need to be expanded. 5219 To specify the alignment for several 5220 instances of a device, the PCI vendor, 5221 device, subvendor, and subdevice may be 5222 specified, e.g., 12@pci:8086:9c22:103c:198f 5223 for 4096-byte alignment. 5224 ecrc= Enable/disable PCIe ECRC (transaction layer 5225 end-to-end CRC checking). Only effective if 5226 OS has native AER control (either granted by 5227 ACPI _OSC or forced via "pcie_ports=native") 5228 bios: Use BIOS/firmware settings. This is the 5229 the default. 5230 off: Turn ECRC off 5231 on: Turn ECRC on. 5232 hpiosize=nn[KMG] The fixed amount of bus space which is 5233 reserved for hotplug bridge's IO window. 5234 Default size is 256 bytes. 5235 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5236 reserved for hotplug bridge's MMIO window. 5237 Default size is 2 megabytes. 5238 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5239 reserved for hotplug bridge's MMIO_PREF window. 5240 Default size is 2 megabytes. 5241 hpmemsize=nn[KMG] The fixed amount of bus space which is 5242 reserved for hotplug bridge's MMIO and 5243 MMIO_PREF window. 5244 Default size is 2 megabytes. 5245 hpbussize=nn The minimum amount of additional bus numbers 5246 reserved for buses below a hotplug bridge. 5247 Default is 1. 5248 realloc= Enable/disable reallocating PCI bridge resources 5249 if allocations done by BIOS are too small to 5250 accommodate resources required by all child 5251 devices. 5252 off: Turn realloc off 5253 on: Turn realloc on 5254 realloc same as realloc=on 5255 noari do not use PCIe ARI. 5256 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5257 do not use PCIe ATS (and IOMMU device IOTLB). 5258 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5259 only look for one device below a PCIe downstream 5260 port. 5261 big_root_window Try to add a big 64bit memory window to the PCIe 5262 root complex on AMD CPUs. Some GFX hardware 5263 can resize a BAR to allow access to all VRAM. 5264 Adding the window is slightly risky (it may 5265 conflict with unreported devices), so this 5266 taints the kernel. 5267 disable_acs_redir=<pci_dev>[; ...] 5268 Specify one or more PCI devices (in the format 5269 specified above) separated by semicolons. 5270 Each device specified will have the PCI ACS 5271 redirect capabilities forced off which will 5272 allow P2P traffic between devices through 5273 bridges without forcing it upstream. Note: 5274 this removes isolation between devices and 5275 may put more devices in an IOMMU group. 5276 config_acs= 5277 Format: 5278 <ACS flags>@<pci_dev>[; ...] 5279 Specify one or more PCI devices (in the format 5280 specified above) optionally prepended with flags 5281 and separated by semicolons. The respective 5282 capabilities will be enabled, disabled or 5283 unchanged based on what is specified in 5284 flags. 5285 5286 ACS Flags is defined as follows: 5287 bit-0 : ACS Source Validation 5288 bit-1 : ACS Translation Blocking 5289 bit-2 : ACS P2P Request Redirect 5290 bit-3 : ACS P2P Completion Redirect 5291 bit-4 : ACS Upstream Forwarding 5292 bit-5 : ACS P2P Egress Control 5293 bit-6 : ACS Direct Translated P2P 5294 Each bit can be marked as: 5295 '0' – force disabled 5296 '1' – force enabled 5297 'x' – unchanged 5298 For example, 5299 pci=config_acs=10x@pci:0:0 5300 would configure all devices that support 5301 ACS to enable P2P Request Redirect, disable 5302 Translation Blocking, and leave Source 5303 Validation unchanged from whatever power-up 5304 or firmware set it to. 5305 5306 Note: this may remove isolation between devices 5307 and may put more devices in an IOMMU group. 5308 force_floating [S390] Force usage of floating interrupts. 5309 nomio [S390] Do not use MIO instructions. 5310 norid [S390] ignore the RID field and force use of 5311 one PCI domain per PCI function 5312 notph [PCIE] If the PCIE_TPH kernel config parameter 5313 is enabled, this kernel boot option can be used 5314 to disable PCIe TLP Processing Hints support 5315 system-wide. 5316 5317 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5318 Management. 5319 off Don't touch ASPM configuration at all. Leave any 5320 configuration done by firmware unchanged. 5321 force Enable ASPM even on devices that claim not to support it. 5322 WARNING: Forcing ASPM on may cause system lockups. 5323 5324 pcie_ports= [PCIE] PCIe port services handling: 5325 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5326 even if the platform doesn't give the OS permission to 5327 use them. This may cause conflicts if the platform 5328 also tries to use these services. 5329 dpc-native Use native PCIe service for DPC only. May 5330 cause conflicts if firmware uses AER or DPC. 5331 compat Disable native PCIe services (PME, AER, DPC, PCIe 5332 hotplug). 5333 5334 pcie_port_pm= [PCIE] PCIe port power management handling: 5335 off Disable power management of all PCIe ports 5336 force Forcibly enable power management of all PCIe ports 5337 5338 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5339 nomsi Do not use MSI for native PCIe PME signaling (this makes 5340 all PCIe root ports use INTx for all services). 5341 5342 pcmv= [HW,PCMCIA] BadgePAD 4 5343 5344 pd_ignore_unused 5345 [PM] 5346 Keep all power-domains already enabled by bootloader on, 5347 even if no driver has claimed them. This is useful 5348 for debug and development, but should not be 5349 needed on a platform with proper driver support. 5350 5351 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5352 boot time. 5353 Format: { 0 | 1 } 5354 See arch/parisc/kernel/pdc_chassis.c 5355 5356 percpu_alloc= [MM,EARLY] 5357 Select which percpu first chunk allocator to use. 5358 Currently supported values are "embed" and "page". 5359 Archs may support subset or none of the selections. 5360 See comments in mm/percpu.c for details on each 5361 allocator. This parameter is primarily for debugging 5362 and performance comparison. 5363 5364 pirq= [SMP,APIC] Manual mp-table setup 5365 See Documentation/arch/x86/i386/IO-APIC.rst. 5366 5367 plip= [PPT,NET] Parallel port network link 5368 Format: { parport<nr> | timid | 0 } 5369 See also Documentation/admin-guide/parport.rst. 5370 5371 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5372 Override pmtimer IOPort with a hex value. 5373 e.g. pmtmr=0x508 5374 5375 pmu_override= [PPC] Override the PMU. 5376 This option takes over the PMU facility, so it is no 5377 longer usable by perf. Setting this option starts the 5378 PMU counters by setting MMCR0 to 0 (the FC bit is 5379 cleared). If a number is given, then MMCR1 is set to 5380 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5381 remains 0. 5382 5383 pm_async= [PM] 5384 Format: off 5385 This parameter sets the initial value of the 5386 /sys/power/pm_async sysfs knob at boot time. 5387 If set to "off", disables asynchronous suspend and 5388 resume of devices during system-wide power transitions. 5389 This can be useful on platforms where device 5390 dependencies are not well-defined, or for debugging 5391 power management issues. Asynchronous operations are 5392 enabled by default. 5393 5394 5395 pm_debug_messages [SUSPEND,KNL] 5396 Enable suspend/resume debug messages during boot up. 5397 5398 pnp.debug=1 [PNP] 5399 Enable PNP debug messages (depends on the 5400 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5401 via /sys/module/pnp/parameters/debug. We always show 5402 current resource usage; turning this on also shows 5403 possible settings and some assignment information. 5404 5405 pnpacpi= [ACPI] 5406 { off } 5407 5408 pnpbios= [ISAPNP] 5409 { on | off | curr | res | no-curr | no-res } 5410 5411 pnp_reserve_irq= 5412 [ISAPNP] Exclude IRQs for the autoconfiguration 5413 5414 pnp_reserve_dma= 5415 [ISAPNP] Exclude DMAs for the autoconfiguration 5416 5417 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5418 Ranges are in pairs (I/O port base and size). 5419 5420 pnp_reserve_mem= 5421 [ISAPNP] Exclude memory regions for the 5422 autoconfiguration. 5423 Ranges are in pairs (memory base and size). 5424 5425 ports= [IP_VS_FTP] IPVS ftp helper module 5426 Default is 21. 5427 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5428 may be specified. 5429 Format: <port>,<port>.... 5430 5431 possible_cpus= [SMP,S390,X86] 5432 Format: <unsigned int> 5433 Set the number of possible CPUs, overriding the 5434 regular discovery mechanisms (such as ACPI/FW, etc). 5435 5436 powersave=off [PPC] This option disables power saving features. 5437 It specifically disables cpuidle and sets the 5438 platform machine description specific power_save 5439 function to NULL. On Idle the CPU just reduces 5440 execution priority. 5441 5442 ppc_strict_facility_enable 5443 [PPC,ENABLE] This option catches any kernel floating point, 5444 Altivec, VSX and SPE outside of regions specifically 5445 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5446 There is some performance impact when enabling this. 5447 5448 ppc_tm= [PPC,EARLY] 5449 Format: {"off"} 5450 Disable Hardware Transactional Memory 5451 5452 preempt= [KNL] 5453 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5454 none - Limited to cond_resched() calls 5455 voluntary - Limited to cond_resched() and might_sleep() calls 5456 full - Any section that isn't explicitly preempt disabled 5457 can be preempted anytime. Tasks will also yield 5458 contended spinlocks (if the critical section isn't 5459 explicitly preempt disabled beyond the lock itself). 5460 lazy - Scheduler controlled. Similar to full but instead 5461 of preempting the task immediately, the task gets 5462 one HZ tick time to yield itself before the 5463 preemption will be forced. One preemption is when the 5464 task returns to user space. 5465 5466 print-fatal-signals= 5467 [KNL] debug: print fatal signals 5468 5469 If enabled, warn about various signal handling 5470 related application anomalies: too many signals, 5471 too many POSIX.1 timers, fatal signals causing a 5472 coredump - etc. 5473 5474 If you hit the warning due to signal overflow, 5475 you might want to try "ulimit -i unlimited". 5476 5477 default: off. 5478 5479 printk.always_kmsg_dump= 5480 Trigger kmsg_dump for cases other than kernel oops or 5481 panics 5482 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5483 default: disabled 5484 5485 printk.console_no_auto_verbose= 5486 Disable console loglevel raise on oops, panic 5487 or lockdep-detected issues (only if lock debug is on). 5488 With an exception to setups with low baudrate on 5489 serial console, keeping this 0 is a good choice 5490 in order to provide more debug information. 5491 Format: <bool> 5492 default: 0 (auto_verbose is enabled) 5493 5494 printk.debug_non_panic_cpus= 5495 Allows storing messages from non-panic CPUs into 5496 the printk log buffer during panic(). They are 5497 flushed to consoles by the panic-CPU on 5498 a best-effort basis. 5499 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5500 Default: disabled 5501 5502 printk.devkmsg={on,off,ratelimit} 5503 Control writing to /dev/kmsg. 5504 on - unlimited logging to /dev/kmsg from userspace 5505 off - logging to /dev/kmsg disabled 5506 ratelimit - ratelimit the logging 5507 Default: ratelimit 5508 5509 printk.time= Show timing data prefixed to each printk message line 5510 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5511 5512 proc_mem.force_override= [KNL] 5513 Format: {always | ptrace | never} 5514 Traditionally /proc/pid/mem allows memory permissions to be 5515 overridden without restrictions. This option may be set to 5516 restrict that. Can be one of: 5517 - 'always': traditional behavior always allows mem overrides. 5518 - 'ptrace': only allow mem overrides for active ptracers. 5519 - 'never': never allow mem overrides. 5520 If not specified, default is the CONFIG_PROC_MEM_* choice. 5521 5522 processor.max_cstate= [HW,ACPI] 5523 Limit processor to maximum C-state 5524 max_cstate=9 overrides any DMI blacklist limit. 5525 5526 processor.nocst [HW,ACPI] 5527 Ignore the _CST method to determine C-states, 5528 instead using the legacy FADT method 5529 5530 profile= [KNL] Enable kernel profiling via /proc/profile 5531 Format: [<profiletype>,]<number> 5532 Param: <profiletype>: "schedule" or "kvm" 5533 [defaults to kernel profiling] 5534 Param: "schedule" - profile schedule points. 5535 Param: "kvm" - profile VM exits. 5536 Param: <number> - step/bucket size as a power of 2 for 5537 statistical time based profiling. 5538 5539 prot_virt= [S390] enable hosting protected virtual machines 5540 isolated from the hypervisor (if hardware supports 5541 that). If enabled, the default kernel base address 5542 might be overridden even when Kernel Address Space 5543 Layout Randomization is disabled. 5544 Format: <bool> 5545 5546 psi= [KNL] Enable or disable pressure stall information 5547 tracking. 5548 Format: <bool> 5549 5550 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5551 probe for; one of (bare|imps|exps|lifebook|any). 5552 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5553 per second. 5554 psmouse.resetafter= [HW,MOUSE] 5555 Try to reset the device after so many bad packets 5556 (0 = never). 5557 psmouse.resolution= 5558 [HW,MOUSE] Set desired mouse resolution, in dpi. 5559 psmouse.smartscroll= 5560 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5561 0 = disabled, 1 = enabled (default). 5562 5563 pstore.backend= Specify the name of the pstore backend to use 5564 5565 pti= [X86-64] Control Page Table Isolation of user and 5566 kernel address spaces. Disabling this feature 5567 removes hardening, but improves performance of 5568 system calls and interrupts. 5569 5570 on - unconditionally enable 5571 off - unconditionally disable 5572 auto - kernel detects whether your CPU model is 5573 vulnerable to issues that PTI mitigates 5574 5575 Not specifying this option is equivalent to pti=auto. 5576 5577 pty.legacy_count= 5578 [KNL] Number of legacy pty's. Overwrites compiled-in 5579 default number. 5580 5581 quiet [KNL,EARLY] Disable most log messages 5582 5583 r128= [HW,DRM] 5584 5585 radix_hcall_invalidate=on [PPC/PSERIES] 5586 Disable RADIX GTSE feature and use hcall for TLB 5587 invalidate. 5588 5589 raid= [HW,RAID] 5590 See Documentation/admin-guide/md.rst. 5591 5592 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5593 See Documentation/admin-guide/blockdev/ramdisk.rst. 5594 5595 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5596 5597 random.trust_cpu=off 5598 [KNL,EARLY] Disable trusting the use of the CPU's 5599 random number generator (if available) to 5600 initialize the kernel's RNG. 5601 5602 random.trust_bootloader=off 5603 [KNL,EARLY] Disable trusting the use of the a seed 5604 passed by the bootloader (if available) to 5605 initialize the kernel's RNG. 5606 5607 randomize_kstack_offset= 5608 [KNL,EARLY] Enable or disable kernel stack offset 5609 randomization, which provides roughly 5 bits of 5610 entropy, frustrating memory corruption attacks 5611 that depend on stack address determinism or 5612 cross-syscall address exposures. This is only 5613 available on architectures that have defined 5614 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5615 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5616 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5617 5618 ras=option[,option,...] [KNL] RAS-specific options 5619 5620 cec_disable [X86] 5621 Disable the Correctable Errors Collector, 5622 see CONFIG_RAS_CEC help text. 5623 5624 rcu_nocbs[=cpu-list] 5625 [KNL] The optional argument is a cpu list, 5626 as described above. 5627 5628 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5629 enable the no-callback CPU mode, which prevents 5630 such CPUs' callbacks from being invoked in 5631 softirq context. Invocation of such CPUs' RCU 5632 callbacks will instead be offloaded to "rcuox/N" 5633 kthreads created for that purpose, where "x" is 5634 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5635 for the kthreads that mediate grace periods; and 5636 "N" is the CPU number. This reduces OS jitter on 5637 the offloaded CPUs, which can be useful for HPC 5638 and real-time workloads. It can also improve 5639 energy efficiency for asymmetric multiprocessors. 5640 5641 If a cpulist is passed as an argument, the specified 5642 list of CPUs is set to no-callback mode from boot. 5643 5644 Otherwise, if the '=' sign and the cpulist 5645 arguments are omitted, no CPU will be set to 5646 no-callback mode from boot but the mode may be 5647 toggled at runtime via cpusets. 5648 5649 Note that this argument takes precedence over 5650 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5651 5652 rcu_nocb_poll [KNL] 5653 Rather than requiring that offloaded CPUs 5654 (specified by rcu_nocbs= above) explicitly 5655 awaken the corresponding "rcuoN" kthreads, 5656 make these kthreads poll for callbacks. 5657 This improves the real-time response for the 5658 offloaded CPUs by relieving them of the need to 5659 wake up the corresponding kthread, but degrades 5660 energy efficiency by requiring that the kthreads 5661 periodically wake up to do the polling. 5662 5663 rcutree.blimit= [KNL] 5664 Set maximum number of finished RCU callbacks to 5665 process in one batch. 5666 5667 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5668 Do only a one-line RCU CPU stall warning when 5669 there is an ongoing too-long CSD-lock wait. 5670 5671 rcutree.do_rcu_barrier= [KNL] 5672 Request a call to rcu_barrier(). This is 5673 throttled so that userspace tests can safely 5674 hammer on the sysfs variable if they so choose. 5675 If triggered before the RCU grace-period machinery 5676 is fully active, this will error out with EAGAIN. 5677 5678 rcutree.dump_tree= [KNL] 5679 Dump the structure of the rcu_node combining tree 5680 out at early boot. This is used for diagnostic 5681 purposes, to verify correct tree setup. 5682 5683 rcutree.gp_cleanup_delay= [KNL] 5684 Set the number of jiffies to delay each step of 5685 RCU grace-period cleanup. 5686 5687 rcutree.gp_init_delay= [KNL] 5688 Set the number of jiffies to delay each step of 5689 RCU grace-period initialization. 5690 5691 rcutree.gp_preinit_delay= [KNL] 5692 Set the number of jiffies to delay each step of 5693 RCU grace-period pre-initialization, that is, 5694 the propagation of recent CPU-hotplug changes up 5695 the rcu_node combining tree. 5696 5697 rcutree.jiffies_till_first_fqs= [KNL] 5698 Set delay from grace-period initialization to 5699 first attempt to force quiescent states. 5700 Units are jiffies, minimum value is zero, 5701 and maximum value is HZ. 5702 5703 rcutree.jiffies_till_next_fqs= [KNL] 5704 Set delay between subsequent attempts to force 5705 quiescent states. Units are jiffies, minimum 5706 value is one, and maximum value is HZ. 5707 5708 rcutree.jiffies_till_sched_qs= [KNL] 5709 Set required age in jiffies for a 5710 given grace period before RCU starts 5711 soliciting quiescent-state help from 5712 rcu_note_context_switch() and cond_resched(). 5713 If not specified, the kernel will calculate 5714 a value based on the most recent settings 5715 of rcutree.jiffies_till_first_fqs 5716 and rcutree.jiffies_till_next_fqs. 5717 This calculated value may be viewed in 5718 rcutree.jiffies_to_sched_qs. Any attempt to set 5719 rcutree.jiffies_to_sched_qs will be cheerfully 5720 overwritten. 5721 5722 rcutree.kthread_prio= [KNL,BOOT] 5723 Set the SCHED_FIFO priority of the RCU per-CPU 5724 kthreads (rcuc/N). This value is also used for 5725 the priority of the RCU boost threads (rcub/N) 5726 and for the RCU grace-period kthreads (rcu_bh, 5727 rcu_preempt, and rcu_sched). If RCU_BOOST is 5728 set, valid values are 1-99 and the default is 1 5729 (the least-favored priority). Otherwise, when 5730 RCU_BOOST is not set, valid values are 0-99 and 5731 the default is zero (non-realtime operation). 5732 When RCU_NOCB_CPU is set, also adjust the 5733 priority of NOCB callback kthreads. 5734 5735 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5736 On callback-offloaded (rcu_nocbs) CPUs, 5737 RCU reduces the lock contention that would 5738 otherwise be caused by callback floods through 5739 use of the ->nocb_bypass list. However, in the 5740 common non-flooded case, RCU queues directly to 5741 the main ->cblist in order to avoid the extra 5742 overhead of the ->nocb_bypass list and its lock. 5743 But if there are too many callbacks queued during 5744 a single jiffy, RCU pre-queues the callbacks into 5745 the ->nocb_bypass queue. The definition of "too 5746 many" is supplied by this kernel boot parameter. 5747 5748 rcutree.nohz_full_patience_delay= [KNL] 5749 On callback-offloaded (rcu_nocbs) CPUs, avoid 5750 disturbing RCU unless the grace period has 5751 reached the specified age in milliseconds. 5752 Defaults to zero. Large values will be capped 5753 at five seconds. All values will be rounded down 5754 to the nearest value representable by jiffies. 5755 5756 rcutree.qhimark= [KNL] 5757 Set threshold of queued RCU callbacks beyond which 5758 batch limiting is disabled. 5759 5760 rcutree.qlowmark= [KNL] 5761 Set threshold of queued RCU callbacks below which 5762 batch limiting is re-enabled. 5763 5764 rcutree.qovld= [KNL] 5765 Set threshold of queued RCU callbacks beyond which 5766 RCU's force-quiescent-state scan will aggressively 5767 enlist help from cond_resched() and sched IPIs to 5768 help CPUs more quickly reach quiescent states. 5769 Set to less than zero to make this be set based 5770 on rcutree.qhimark at boot time and to zero to 5771 disable more aggressive help enlistment. 5772 5773 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5774 Set the page-cache refill delay (in milliseconds) 5775 in response to low-memory conditions. The range 5776 of permitted values is in the range 0:100000. 5777 5778 rcutree.rcu_divisor= [KNL] 5779 Set the shift-right count to use to compute 5780 the callback-invocation batch limit bl from 5781 the number of callbacks queued on this CPU. 5782 The result will be bounded below by the value of 5783 the rcutree.blimit kernel parameter. Every bl 5784 callbacks, the softirq handler will exit in 5785 order to allow the CPU to do other work. 5786 5787 Please note that this callback-invocation batch 5788 limit applies only to non-offloaded callback 5789 invocation. Offloaded callbacks are instead 5790 invoked in the context of an rcuoc kthread, which 5791 scheduler will preempt as it does any other task. 5792 5793 rcutree.rcu_fanout_exact= [KNL] 5794 Disable autobalancing of the rcu_node combining 5795 tree. This is used by rcutorture, and might 5796 possibly be useful for architectures having high 5797 cache-to-cache transfer latencies. 5798 5799 rcutree.rcu_fanout_leaf= [KNL] 5800 Change the number of CPUs assigned to each 5801 leaf rcu_node structure. Useful for very 5802 large systems, which will choose the value 64, 5803 and for NUMA systems with large remote-access 5804 latencies, which will choose a value aligned 5805 with the appropriate hardware boundaries. 5806 5807 rcutree.rcu_min_cached_objs= [KNL] 5808 Minimum number of objects which are cached and 5809 maintained per one CPU. Object size is equal 5810 to PAGE_SIZE. The cache allows to reduce the 5811 pressure to page allocator, also it makes the 5812 whole algorithm to behave better in low memory 5813 condition. 5814 5815 rcutree.rcu_nocb_gp_stride= [KNL] 5816 Set the number of NOCB callback kthreads in 5817 each group, which defaults to the square root 5818 of the number of CPUs. Larger numbers reduce 5819 the wakeup overhead on the global grace-period 5820 kthread, but increases that same overhead on 5821 each group's NOCB grace-period kthread. 5822 5823 rcutree.rcu_kick_kthreads= [KNL] 5824 Cause the grace-period kthread to get an extra 5825 wake_up() if it sleeps three times longer than 5826 it should at force-quiescent-state time. 5827 This wake_up() will be accompanied by a 5828 WARN_ONCE() splat and an ftrace_dump(). 5829 5830 rcutree.rcu_resched_ns= [KNL] 5831 Limit the time spend invoking a batch of RCU 5832 callbacks to the specified number of nanoseconds. 5833 By default, this limit is checked only once 5834 every 32 callbacks in order to limit the pain 5835 inflicted by local_clock() overhead. 5836 5837 rcutree.rcu_unlock_delay= [KNL] 5838 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5839 this specifies an rcu_read_unlock()-time delay 5840 in microseconds. This defaults to zero. 5841 Larger delays increase the probability of 5842 catching RCU pointer leaks, that is, buggy use 5843 of RCU-protected pointers after the relevant 5844 rcu_read_unlock() has completed. 5845 5846 rcutree.sysrq_rcu= [KNL] 5847 Commandeer a sysrq key to dump out Tree RCU's 5848 rcu_node tree with an eye towards determining 5849 why a new grace period has not yet started. 5850 5851 rcutree.use_softirq= [KNL] 5852 If set to zero, move all RCU_SOFTIRQ processing to 5853 per-CPU rcuc kthreads. Defaults to a non-zero 5854 value, meaning that RCU_SOFTIRQ is used by default. 5855 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5856 5857 But note that CONFIG_PREEMPT_RT=y kernels disable 5858 this kernel boot parameter, forcibly setting it 5859 to zero. 5860 5861 rcutree.enable_rcu_lazy= [KNL] 5862 To save power, batch RCU callbacks and flush after 5863 delay, memory pressure or callback list growing too 5864 big. 5865 5866 rcutree.rcu_normal_wake_from_gp= [KNL] 5867 Reduces a latency of synchronize_rcu() call. This approach 5868 maintains its own track of synchronize_rcu() callers, so it 5869 does not interact with regular callbacks because it does not 5870 use a call_rcu[_hurry]() path. Please note, this is for a 5871 normal grace period. 5872 5873 How to enable it: 5874 5875 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5876 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5877 5878 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5879 disabled by the boot parameter passing 0. 5880 5881 rcuscale.gp_async= [KNL] 5882 Measure performance of asynchronous 5883 grace-period primitives such as call_rcu(). 5884 5885 rcuscale.gp_async_max= [KNL] 5886 Specify the maximum number of outstanding 5887 callbacks per writer thread. When a writer 5888 thread exceeds this limit, it invokes the 5889 corresponding flavor of rcu_barrier() to allow 5890 previously posted callbacks to drain. 5891 5892 rcuscale.gp_exp= [KNL] 5893 Measure performance of expedited synchronous 5894 grace-period primitives. 5895 5896 rcuscale.holdoff= [KNL] 5897 Set test-start holdoff period. The purpose of 5898 this parameter is to delay the start of the 5899 test until boot completes in order to avoid 5900 interference. 5901 5902 rcuscale.kfree_by_call_rcu= [KNL] 5903 In kernels built with CONFIG_RCU_LAZY=y, test 5904 call_rcu() instead of kfree_rcu(). 5905 5906 rcuscale.kfree_mult= [KNL] 5907 Instead of allocating an object of size kfree_obj, 5908 allocate one of kfree_mult * sizeof(kfree_obj). 5909 Defaults to 1. 5910 5911 rcuscale.kfree_rcu_test= [KNL] 5912 Set to measure performance of kfree_rcu() flooding. 5913 5914 rcuscale.kfree_rcu_test_double= [KNL] 5915 Test the double-argument variant of kfree_rcu(). 5916 If this parameter has the same value as 5917 rcuscale.kfree_rcu_test_single, both the single- 5918 and double-argument variants are tested. 5919 5920 rcuscale.kfree_rcu_test_single= [KNL] 5921 Test the single-argument variant of kfree_rcu(). 5922 If this parameter has the same value as 5923 rcuscale.kfree_rcu_test_double, both the single- 5924 and double-argument variants are tested. 5925 5926 rcuscale.kfree_nthreads= [KNL] 5927 The number of threads running loops of kfree_rcu(). 5928 5929 rcuscale.kfree_alloc_num= [KNL] 5930 Number of allocations and frees done in an iteration. 5931 5932 rcuscale.kfree_loops= [KNL] 5933 Number of loops doing rcuscale.kfree_alloc_num number 5934 of allocations and frees. 5935 5936 rcuscale.minruntime= [KNL] 5937 Set the minimum test run time in seconds. This 5938 does not affect the data-collection interval, 5939 but instead allows better measurement of things 5940 like CPU consumption. 5941 5942 rcuscale.nreaders= [KNL] 5943 Set number of RCU readers. The value -1 selects 5944 N, where N is the number of CPUs. A value 5945 "n" less than -1 selects N-n+1, where N is again 5946 the number of CPUs. For example, -2 selects N 5947 (the number of CPUs), -3 selects N+1, and so on. 5948 A value of "n" less than or equal to -N selects 5949 a single reader. 5950 5951 rcuscale.nwriters= [KNL] 5952 Set number of RCU writers. The values operate 5953 the same as for rcuscale.nreaders. 5954 N, where N is the number of CPUs 5955 5956 rcuscale.scale_type= [KNL] 5957 Specify the RCU implementation to test. 5958 5959 rcuscale.shutdown= [KNL] 5960 Shut the system down after performance tests 5961 complete. This is useful for hands-off automated 5962 testing. 5963 5964 rcuscale.verbose= [KNL] 5965 Enable additional printk() statements. 5966 5967 rcuscale.writer_holdoff= [KNL] 5968 Write-side holdoff between grace periods, 5969 in microseconds. The default of zero says 5970 no holdoff. 5971 5972 rcuscale.writer_holdoff_jiffies= [KNL] 5973 Additional write-side holdoff between grace 5974 periods, but in jiffies. The default of zero 5975 says no holdoff. 5976 5977 rcutorture.fqs_duration= [KNL] 5978 Set duration of force_quiescent_state bursts 5979 in microseconds. 5980 5981 rcutorture.fqs_holdoff= [KNL] 5982 Set holdoff time within force_quiescent_state bursts 5983 in microseconds. 5984 5985 rcutorture.fqs_stutter= [KNL] 5986 Set wait time between force_quiescent_state bursts 5987 in seconds. 5988 5989 rcutorture.fwd_progress= [KNL] 5990 Specifies the number of kthreads to be used 5991 for RCU grace-period forward-progress testing 5992 for the types of RCU supporting this notion. 5993 Defaults to 1 kthread, values less than zero or 5994 greater than the number of CPUs cause the number 5995 of CPUs to be used. 5996 5997 rcutorture.fwd_progress_div= [KNL] 5998 Specify the fraction of a CPU-stall-warning 5999 period to do tight-loop forward-progress testing. 6000 6001 rcutorture.fwd_progress_holdoff= [KNL] 6002 Number of seconds to wait between successive 6003 forward-progress tests. 6004 6005 rcutorture.fwd_progress_need_resched= [KNL] 6006 Enclose cond_resched() calls within checks for 6007 need_resched() during tight-loop forward-progress 6008 testing. 6009 6010 rcutorture.gp_cond= [KNL] 6011 Use conditional/asynchronous update-side 6012 normal-grace-period primitives, if available. 6013 6014 rcutorture.gp_cond_exp= [KNL] 6015 Use conditional/asynchronous update-side 6016 expedited-grace-period primitives, if available. 6017 6018 rcutorture.gp_cond_full= [KNL] 6019 Use conditional/asynchronous update-side 6020 normal-grace-period primitives that also take 6021 concurrent expedited grace periods into account, 6022 if available. 6023 6024 rcutorture.gp_cond_exp_full= [KNL] 6025 Use conditional/asynchronous update-side 6026 expedited-grace-period primitives that also take 6027 concurrent normal grace periods into account, 6028 if available. 6029 6030 rcutorture.gp_cond_wi= [KNL] 6031 Nominal wait interval for normal conditional 6032 grace periods (specified by rcutorture's 6033 gp_cond and gp_cond_full module parameters), 6034 in microseconds. The actual wait interval will 6035 be randomly selected to nanosecond granularity up 6036 to this wait interval. Defaults to 16 jiffies, 6037 for example, 16,000 microseconds on a system 6038 with HZ=1000. 6039 6040 rcutorture.gp_cond_wi_exp= [KNL] 6041 Nominal wait interval for expedited conditional 6042 grace periods (specified by rcutorture's 6043 gp_cond_exp and gp_cond_exp_full module 6044 parameters), in microseconds. The actual wait 6045 interval will be randomly selected to nanosecond 6046 granularity up to this wait interval. Defaults to 6047 128 microseconds. 6048 6049 rcutorture.gp_exp= [KNL] 6050 Use expedited update-side primitives, if available. 6051 6052 rcutorture.gp_normal= [KNL] 6053 Use normal (non-expedited) asynchronous 6054 update-side primitives, if available. 6055 6056 rcutorture.gp_poll= [KNL] 6057 Use polled update-side normal-grace-period 6058 primitives, if available. 6059 6060 rcutorture.gp_poll_exp= [KNL] 6061 Use polled update-side expedited-grace-period 6062 primitives, if available. 6063 6064 rcutorture.gp_poll_full= [KNL] 6065 Use polled update-side normal-grace-period 6066 primitives that also take concurrent expedited 6067 grace periods into account, if available. 6068 6069 rcutorture.gp_poll_exp_full= [KNL] 6070 Use polled update-side expedited-grace-period 6071 primitives that also take concurrent normal 6072 grace periods into account, if available. 6073 6074 rcutorture.gp_poll_wi= [KNL] 6075 Nominal wait interval for normal conditional 6076 grace periods (specified by rcutorture's 6077 gp_poll and gp_poll_full module parameters), 6078 in microseconds. The actual wait interval will 6079 be randomly selected to nanosecond granularity up 6080 to this wait interval. Defaults to 16 jiffies, 6081 for example, 16,000 microseconds on a system 6082 with HZ=1000. 6083 6084 rcutorture.gp_poll_wi_exp= [KNL] 6085 Nominal wait interval for expedited conditional 6086 grace periods (specified by rcutorture's 6087 gp_poll_exp and gp_poll_exp_full module 6088 parameters), in microseconds. The actual wait 6089 interval will be randomly selected to nanosecond 6090 granularity up to this wait interval. Defaults to 6091 128 microseconds. 6092 6093 rcutorture.gp_sync= [KNL] 6094 Use normal (non-expedited) synchronous 6095 update-side primitives, if available. If all 6096 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6097 rcutorture.gp_normal=, and rcutorture.gp_sync= 6098 are zero, rcutorture acts as if is interpreted 6099 they are all non-zero. 6100 6101 rcutorture.gpwrap_lag= [KNL] 6102 Enable grace-period wrap lag testing. Setting 6103 to false prevents the gpwrap lag test from 6104 running. Default is true. 6105 6106 rcutorture.gpwrap_lag_gps= [KNL] 6107 Set the value for grace-period wrap lag during 6108 active lag testing periods. This controls how many 6109 grace periods differences we tolerate between 6110 rdp and rnp's gp_seq before setting overflow flag. 6111 The default is always set to 8. 6112 6113 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6114 Set the total cycle duration for gpwrap lag 6115 testing in minutes. This is the total time for 6116 one complete cycle of active and inactive 6117 testing periods. Default is 30 minutes. 6118 6119 rcutorture.gpwrap_lag_active_mins= [KNL] 6120 Set the duration for which gpwrap lag is active 6121 within each cycle, in minutes. During this time, 6122 the grace-period wrap lag will be set to the 6123 value specified by gpwrap_lag_gps. Default is 6124 5 minutes. 6125 6126 rcutorture.irqreader= [KNL] 6127 Run RCU readers from irq handlers, or, more 6128 accurately, from a timer handler. Not all RCU 6129 flavors take kindly to this sort of thing. 6130 6131 rcutorture.leakpointer= [KNL] 6132 Leak an RCU-protected pointer out of the reader. 6133 This can of course result in splats, and is 6134 intended to test the ability of things like 6135 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6136 such leaks. 6137 6138 rcutorture.n_barrier_cbs= [KNL] 6139 Set callbacks/threads for rcu_barrier() testing. 6140 6141 rcutorture.nfakewriters= [KNL] 6142 Set number of concurrent RCU writers. These just 6143 stress RCU, they don't participate in the actual 6144 test, hence the "fake". 6145 6146 rcutorture.nocbs_nthreads= [KNL] 6147 Set number of RCU callback-offload togglers. 6148 Zero (the default) disables toggling. 6149 6150 rcutorture.nocbs_toggle= [KNL] 6151 Set the delay in milliseconds between successive 6152 callback-offload toggling attempts. 6153 6154 rcutorture.nreaders= [KNL] 6155 Set number of RCU readers. The value -1 selects 6156 N-1, where N is the number of CPUs. A value 6157 "n" less than -1 selects N-n-2, where N is again 6158 the number of CPUs. For example, -2 selects N 6159 (the number of CPUs), -3 selects N+1, and so on. 6160 6161 rcutorture.object_debug= [KNL] 6162 Enable debug-object double-call_rcu() testing. 6163 6164 rcutorture.onoff_holdoff= [KNL] 6165 Set time (s) after boot for CPU-hotplug testing. 6166 6167 rcutorture.onoff_interval= [KNL] 6168 Set time (jiffies) between CPU-hotplug operations, 6169 or zero to disable CPU-hotplug testing. 6170 6171 rcutorture.preempt_duration= [KNL] 6172 Set duration (in milliseconds) of preemptions 6173 by a high-priority FIFO real-time task. Set to 6174 zero (the default) to disable. The CPUs to 6175 preempt are selected randomly from the set that 6176 are online at a given point in time. Races with 6177 CPUs going offline are ignored, with that attempt 6178 at preemption skipped. 6179 6180 rcutorture.preempt_interval= [KNL] 6181 Set interval (in milliseconds, defaulting to one 6182 second) between preemptions by a high-priority 6183 FIFO real-time task. This delay is mediated 6184 by an hrtimer and is further fuzzed to avoid 6185 inadvertent synchronizations. 6186 6187 rcutorture.read_exit_burst= [KNL] 6188 The number of times in a given read-then-exit 6189 episode that a set of read-then-exit kthreads 6190 is spawned. 6191 6192 rcutorture.read_exit_delay= [KNL] 6193 The delay, in seconds, between successive 6194 read-then-exit testing episodes. 6195 6196 rcutorture.reader_flavor= [KNL] 6197 A bit mask indicating which readers to use. 6198 If there is more than one bit set, the readers 6199 are entered from low-order bit up, and are 6200 exited in the opposite order. For SRCU, the 6201 0x1 bit is normal readers, 0x2 NMI-safe readers, 6202 and 0x4 light-weight readers. 6203 6204 rcutorture.shuffle_interval= [KNL] 6205 Set task-shuffle interval (s). Shuffling tasks 6206 allows some CPUs to go into dyntick-idle mode 6207 during the rcutorture test. 6208 6209 rcutorture.shutdown_secs= [KNL] 6210 Set time (s) after boot system shutdown. This 6211 is useful for hands-off automated testing. 6212 6213 rcutorture.stall_cpu= [KNL] 6214 Duration of CPU stall (s) to test RCU CPU stall 6215 warnings, zero to disable. 6216 6217 rcutorture.stall_cpu_block= [KNL] 6218 Sleep while stalling if set. This will result 6219 in warnings from preemptible RCU in addition to 6220 any other stall-related activity. Note that 6221 in kernels built with CONFIG_PREEMPTION=n and 6222 CONFIG_PREEMPT_COUNT=y, this parameter will 6223 cause the CPU to pass through a quiescent state. 6224 Given CONFIG_PREEMPTION=n, this will suppress 6225 RCU CPU stall warnings, but will instead result 6226 in scheduling-while-atomic splats. 6227 6228 Use of this module parameter results in splats. 6229 6230 6231 rcutorture.stall_cpu_holdoff= [KNL] 6232 Time to wait (s) after boot before inducing stall. 6233 6234 rcutorture.stall_cpu_irqsoff= [KNL] 6235 Disable interrupts while stalling if set, but only 6236 on the first stall in the set. 6237 6238 rcutorture.stall_cpu_repeat= [KNL] 6239 Number of times to repeat the stall sequence, 6240 so that rcutorture.stall_cpu_repeat=3 will result 6241 in four stall sequences. 6242 6243 rcutorture.stall_gp_kthread= [KNL] 6244 Duration (s) of forced sleep within RCU 6245 grace-period kthread to test RCU CPU stall 6246 warnings, zero to disable. If both stall_cpu 6247 and stall_gp_kthread are specified, the 6248 kthread is starved first, then the CPU. 6249 6250 rcutorture.stat_interval= [KNL] 6251 Time (s) between statistics printk()s. 6252 6253 rcutorture.stutter= [KNL] 6254 Time (s) to stutter testing, for example, specifying 6255 five seconds causes the test to run for five seconds, 6256 wait for five seconds, and so on. This tests RCU's 6257 ability to transition abruptly to and from idle. 6258 6259 rcutorture.test_boost= [KNL] 6260 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6261 "Maybe" means test if the RCU implementation 6262 under test support RCU priority boosting. 6263 6264 rcutorture.test_boost_duration= [KNL] 6265 Duration (s) of each individual boost test. 6266 6267 rcutorture.test_boost_holdoff= [KNL] 6268 Holdoff time (s) from start of test to the start 6269 of RCU priority-boost testing. Defaults to zero, 6270 that is, no holdoff. 6271 6272 rcutorture.test_boost_interval= [KNL] 6273 Interval (s) between each boost test. 6274 6275 rcutorture.test_no_idle_hz= [KNL] 6276 Test RCU's dyntick-idle handling. See also the 6277 rcutorture.shuffle_interval parameter. 6278 6279 rcutorture.torture_type= [KNL] 6280 Specify the RCU implementation to test. 6281 6282 rcutorture.verbose= [KNL] 6283 Enable additional printk() statements. 6284 6285 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6286 Dump ftrace buffer after reporting RCU CPU 6287 stall warning. 6288 6289 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6290 Provide RCU CPU stall notifiers, but see the 6291 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6292 option's help text. TL;DR: You almost certainly 6293 do not want rcupdate.rcu_cpu_stall_notifiers. 6294 6295 rcupdate.rcu_cpu_stall_suppress= [KNL] 6296 Suppress RCU CPU stall warning messages. 6297 6298 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6299 Suppress RCU CPU stall warning messages and 6300 rcutorture writer stall warnings that occur 6301 during early boot, that is, during the time 6302 before the init task is spawned. 6303 6304 rcupdate.rcu_cpu_stall_timeout= [KNL] 6305 Set timeout for RCU CPU stall warning messages. 6306 The value is in seconds and the maximum allowed 6307 value is 300 seconds. 6308 6309 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6310 Set timeout for expedited RCU CPU stall warning 6311 messages. The value is in milliseconds 6312 and the maximum allowed value is 21000 6313 milliseconds. Please note that this value is 6314 adjusted to an arch timer tick resolution. 6315 Setting this to zero causes the value from 6316 rcupdate.rcu_cpu_stall_timeout to be used (after 6317 conversion from seconds to milliseconds). 6318 6319 rcupdate.rcu_cpu_stall_cputime= [KNL] 6320 Provide statistics on the cputime and count of 6321 interrupts and tasks during the sampling period. For 6322 multiple continuous RCU stalls, all sampling periods 6323 begin at half of the first RCU stall timeout. 6324 6325 rcupdate.rcu_exp_stall_task_details= [KNL] 6326 Print stack dumps of any tasks blocking the 6327 current expedited RCU grace period during an 6328 expedited RCU CPU stall warning. 6329 6330 rcupdate.rcu_expedited= [KNL] 6331 Use expedited grace-period primitives, for 6332 example, synchronize_rcu_expedited() instead 6333 of synchronize_rcu(). This reduces latency, 6334 but can increase CPU utilization, degrade 6335 real-time latency, and degrade energy efficiency. 6336 No effect on CONFIG_TINY_RCU kernels. 6337 6338 rcupdate.rcu_normal= [KNL] 6339 Use only normal grace-period primitives, 6340 for example, synchronize_rcu() instead of 6341 synchronize_rcu_expedited(). This improves 6342 real-time latency, CPU utilization, and 6343 energy efficiency, but can expose users to 6344 increased grace-period latency. This parameter 6345 overrides rcupdate.rcu_expedited. No effect on 6346 CONFIG_TINY_RCU kernels. 6347 6348 rcupdate.rcu_normal_after_boot= [KNL] 6349 Once boot has completed (that is, after 6350 rcu_end_inkernel_boot() has been invoked), use 6351 only normal grace-period primitives. No effect 6352 on CONFIG_TINY_RCU kernels. 6353 6354 But note that CONFIG_PREEMPT_RT=y kernels enables 6355 this kernel boot parameter, forcibly setting 6356 it to the value one, that is, converting any 6357 post-boot attempt at an expedited RCU grace 6358 period to instead use normal non-expedited 6359 grace-period processing. 6360 6361 rcupdate.rcu_task_collapse_lim= [KNL] 6362 Set the maximum number of callbacks present 6363 at the beginning of a grace period that allows 6364 the RCU Tasks flavors to collapse back to using 6365 a single callback queue. This switching only 6366 occurs when rcupdate.rcu_task_enqueue_lim is 6367 set to the default value of -1. 6368 6369 rcupdate.rcu_task_contend_lim= [KNL] 6370 Set the minimum number of callback-queuing-time 6371 lock-contention events per jiffy required to 6372 cause the RCU Tasks flavors to switch to per-CPU 6373 callback queuing. This switching only occurs 6374 when rcupdate.rcu_task_enqueue_lim is set to 6375 the default value of -1. 6376 6377 rcupdate.rcu_task_enqueue_lim= [KNL] 6378 Set the number of callback queues to use for the 6379 RCU Tasks family of RCU flavors. The default 6380 of -1 allows this to be automatically (and 6381 dynamically) adjusted. This parameter is intended 6382 for use in testing. 6383 6384 rcupdate.rcu_task_lazy_lim= [KNL] 6385 Number of callbacks on a given CPU that will 6386 cancel laziness on that CPU. Use -1 to disable 6387 cancellation of laziness, but be advised that 6388 doing so increases the danger of OOM due to 6389 callback flooding. 6390 6391 rcupdate.rcu_task_stall_info= [KNL] 6392 Set initial timeout in jiffies for RCU task stall 6393 informational messages, which give some indication 6394 of the problem for those not patient enough to 6395 wait for ten minutes. Informational messages are 6396 only printed prior to the stall-warning message 6397 for a given grace period. Disable with a value 6398 less than or equal to zero. Defaults to ten 6399 seconds. A change in value does not take effect 6400 until the beginning of the next grace period. 6401 6402 rcupdate.rcu_task_stall_info_mult= [KNL] 6403 Multiplier for time interval between successive 6404 RCU task stall informational messages for a given 6405 RCU tasks grace period. This value is clamped 6406 to one through ten, inclusive. It defaults to 6407 the value three, so that the first informational 6408 message is printed 10 seconds into the grace 6409 period, the second at 40 seconds, the third at 6410 160 seconds, and then the stall warning at 600 6411 seconds would prevent a fourth at 640 seconds. 6412 6413 rcupdate.rcu_task_stall_timeout= [KNL] 6414 Set timeout in jiffies for RCU task stall 6415 warning messages. Disable with a value less 6416 than or equal to zero. Defaults to ten minutes. 6417 A change in value does not take effect until 6418 the beginning of the next grace period. 6419 6420 rcupdate.rcu_tasks_lazy_ms= [KNL] 6421 Set timeout in milliseconds RCU Tasks asynchronous 6422 callback batching for call_rcu_tasks(). 6423 A negative value will take the default. A value 6424 of zero will disable batching. Batching is 6425 always disabled for synchronize_rcu_tasks(). 6426 6427 rcupdate.rcu_self_test= [KNL] 6428 Run the RCU early boot self tests 6429 6430 rdinit= [KNL] 6431 Format: <full_path> 6432 Run specified binary instead of /init from the ramdisk, 6433 used for early userspace startup. See initrd. 6434 6435 rdrand= [X86,EARLY] 6436 force - Override the decision by the kernel to hide the 6437 advertisement of RDRAND support (this affects 6438 certain AMD processors because of buggy BIOS 6439 support, specifically around the suspend/resume 6440 path). 6441 6442 rdt= [HW,X86,RDT] 6443 Turn on/off individual RDT features. List is: 6444 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6445 mba, smba, bmec, abmc, sdciae, energy[:guid], 6446 perf[:guid]. 6447 E.g. to turn on cmt and turn off mba use: 6448 rdt=cmt,!mba 6449 To turn off all energy telemetry monitoring and ensure that 6450 perf telemetry monitoring associated with guid 0x12345 6451 is enabled use: 6452 rdt=!energy,perf:0x12345 6453 6454 reboot= [KNL] 6455 Format (x86 or x86_64): 6456 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6457 [[,]s[mp]#### \ 6458 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6459 [[,]f[orce] 6460 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6461 (prefix with 'panic_' to set mode for panic 6462 reboot only), 6463 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6464 reboot_force is either force or not specified, 6465 reboot_cpu is s[mp]#### with #### being the processor 6466 to be used for rebooting. 6467 6468 acpi 6469 Use the ACPI RESET_REG in the FADT. If ACPI is not 6470 configured or the ACPI reset does not work, the reboot 6471 path attempts the reset using the keyboard controller. 6472 6473 bios 6474 Use the CPU reboot vector for warm reset 6475 6476 cold 6477 Set the cold reboot flag 6478 6479 default 6480 There are some built-in platform specific "quirks" 6481 - you may see: "reboot: <name> series board detected. 6482 Selecting <type> for reboots." In the case where you 6483 think the quirk is in error (e.g. you have newer BIOS, 6484 or newer board) using this option will ignore the 6485 built-in quirk table, and use the generic default 6486 reboot actions. 6487 6488 efi 6489 Use efi reset_system runtime service. If EFI is not 6490 configured or the EFI reset does not work, the reboot 6491 path attempts the reset using the keyboard controller. 6492 6493 force 6494 Don't stop other CPUs on reboot. This can make reboot 6495 more reliable in some cases. 6496 6497 kbd 6498 Use the keyboard controller. cold reset (default) 6499 6500 pci 6501 Use a write to the PCI config space register 0xcf9 to 6502 trigger reboot. 6503 6504 triple 6505 Force a triple fault (init) 6506 6507 warm 6508 Don't set the cold reboot flag 6509 6510 Using warm reset will be much faster especially on big 6511 memory systems because the BIOS will not go through 6512 the memory check. Disadvantage is that not all 6513 hardware will be completely reinitialized on reboot so 6514 there may be boot problems on some systems. 6515 6516 6517 refscale.holdoff= [KNL] 6518 Set test-start holdoff period. The purpose of 6519 this parameter is to delay the start of the 6520 test until boot completes in order to avoid 6521 interference. 6522 6523 refscale.lookup_instances= [KNL] 6524 Number of data elements to use for the forms of 6525 SLAB_TYPESAFE_BY_RCU testing. A negative number 6526 is negated and multiplied by nr_cpu_ids, while 6527 zero specifies nr_cpu_ids. 6528 6529 refscale.loops= [KNL] 6530 Set the number of loops over the synchronization 6531 primitive under test. Increasing this number 6532 reduces noise due to loop start/end overhead, 6533 but the default has already reduced the per-pass 6534 noise to a handful of picoseconds on ca. 2020 6535 x86 laptops. 6536 6537 refscale.nreaders= [KNL] 6538 Set number of readers. The default value of -1 6539 selects N, where N is roughly 75% of the number 6540 of CPUs. A value of zero is an interesting choice. 6541 6542 refscale.nruns= [KNL] 6543 Set number of runs, each of which is dumped onto 6544 the console log. 6545 6546 refscale.readdelay= [KNL] 6547 Set the read-side critical-section duration, 6548 measured in microseconds. 6549 6550 refscale.scale_type= [KNL] 6551 Specify the read-protection implementation to test. 6552 6553 refscale.shutdown= [KNL] 6554 Shut down the system at the end of the performance 6555 test. This defaults to 1 (shut it down) when 6556 refscale is built into the kernel and to 0 (leave 6557 it running) when refscale is built as a module. 6558 6559 refscale.verbose= [KNL] 6560 Enable additional printk() statements. 6561 6562 refscale.verbose_batched= [KNL] 6563 Batch the additional printk() statements. If zero 6564 (the default) or negative, print everything. Otherwise, 6565 print every Nth verbose statement, where N is the value 6566 specified. 6567 6568 regulator_ignore_unused 6569 [REGULATOR] 6570 Prevents regulator framework from disabling regulators 6571 that are unused, due no driver claiming them. This may 6572 be useful for debug and development, but should not be 6573 needed on a platform with proper driver support. 6574 6575 relax_domain_level= 6576 [KNL, SMP] Set scheduler's default relax_domain_level. 6577 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6578 6579 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6580 Format: <base1>,<size1>[,<base2>,<size2>,...] 6581 Reserve I/O ports or memory so the kernel won't use 6582 them. If <base> is less than 0x10000, the region 6583 is assumed to be I/O ports; otherwise it is memory. 6584 6585 reserve_mem= [RAM] 6586 Format: nn[KMG]:<align>:<label> 6587 Reserve physical memory and label it with a name that 6588 other subsystems can use to access it. This is typically 6589 used for systems that do not wipe the RAM, and this command 6590 line will try to reserve the same physical memory on 6591 soft reboots. Note, it is not guaranteed to be the same 6592 location. For example, if anything about the system changes 6593 or if booting a different kernel. It can also fail if KASLR 6594 places the kernel at the location of where the RAM reservation 6595 was from a previous boot, the new reservation will be at a 6596 different location. 6597 Any subsystem using this feature must add a way to verify 6598 that the contents of the physical memory is from a previous 6599 boot, as there may be cases where the memory will not be 6600 located at the same location. 6601 6602 The format is size:align:label for example, to request 6603 12 megabytes of 4096 alignment for ramoops: 6604 6605 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6606 6607 reservetop= [X86-32,EARLY] 6608 Format: nn[KMG] 6609 Reserves a hole at the top of the kernel virtual 6610 address space. 6611 6612 reset_devices [KNL] Force drivers to reset the underlying device 6613 during initialization. 6614 6615 resume= [SWSUSP] 6616 Specify the partition device for software suspend 6617 Format: 6618 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6619 6620 resume_offset= [SWSUSP] 6621 Specify the offset from the beginning of the partition 6622 given by "resume=" at which the swap header is located, 6623 in <PAGE_SIZE> units (needed only for swap files). 6624 See Documentation/power/swsusp-and-swap-files.rst 6625 6626 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6627 read the resume files 6628 6629 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6630 Useful for devices that are detected asynchronously 6631 (e.g. USB and MMC devices). 6632 6633 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6634 be accessible via /sys/firmware/initrd. 6635 6636 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6637 Speculative Code Execution with Return Instructions) 6638 vulnerability. 6639 6640 AMD-based UNRET and IBPB mitigations alone do not stop 6641 sibling threads from influencing the predictions of other 6642 sibling threads. For that reason, STIBP is used on pro- 6643 cessors that support it, and mitigate SMT on processors 6644 that don't. 6645 6646 off - no mitigation 6647 auto - automatically select a mitigation 6648 auto,nosmt - automatically select a mitigation, 6649 disabling SMT if necessary for 6650 the full mitigation (only on Zen1 6651 and older without STIBP). 6652 ibpb - On AMD, mitigate short speculation 6653 windows on basic block boundaries too. 6654 Safe, highest perf impact. It also 6655 enables STIBP if present. Not suitable 6656 on Intel. 6657 ibpb,nosmt - Like "ibpb" above but will disable SMT 6658 when STIBP is not available. This is 6659 the alternative for systems which do not 6660 have STIBP. 6661 unret - Force enable untrained return thunks, 6662 only effective on AMD f15h-f17h based 6663 systems. 6664 unret,nosmt - Like unret, but will disable SMT when STIBP 6665 is not available. This is the alternative for 6666 systems which do not have STIBP. 6667 6668 Selecting 'auto' will choose a mitigation method at run 6669 time according to the CPU. 6670 6671 Not specifying this option is equivalent to retbleed=auto. 6672 6673 rfkill.default_state= 6674 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6675 etc. communication is blocked by default. 6676 1 Unblocked. 6677 6678 rfkill.master_switch_mode= 6679 0 The "airplane mode" button does nothing. 6680 1 The "airplane mode" button toggles between everything 6681 blocked and the previous configuration. 6682 2 The "airplane mode" button toggles between everything 6683 blocked and everything unblocked. 6684 6685 ring3mwait=disable 6686 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6687 CPUs. 6688 6689 riscv_isa_fallback [RISCV,EARLY] 6690 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6691 falling back to detecting extension support by parsing 6692 "riscv,isa" property on devicetree systems when the 6693 replacement properties are not found. See the Kconfig 6694 entry for RISCV_ISA_FALLBACK. 6695 6696 riscv_nousercfi= 6697 all Disable user CFI ABI to userspace even if cpu extension 6698 are available. 6699 bcfi Disable user backward CFI ABI to userspace even if 6700 the shadow stack extension is available. 6701 fcfi Disable user forward CFI ABI to userspace even if the 6702 landing pad extension is available. 6703 6704 ro [KNL] Mount root device read-only on boot 6705 6706 rodata= [KNL,EARLY] 6707 on Mark read-only kernel memory as read-only (default). 6708 off Leave read-only kernel memory writable for debugging. 6709 noalias Mark read-only kernel memory as read-only but retain 6710 writable aliases in the direct map for regions outside 6711 of the kernel image. [arm64] 6712 6713 rockchip.usb_uart 6714 [EARLY] 6715 Enable the uart passthrough on the designated usb port 6716 on Rockchip SoCs. When active, the signals of the 6717 debug-uart get routed to the D+ and D- pins of the usb 6718 port and the regular usb controller gets disabled. 6719 6720 root= [KNL] Root filesystem 6721 Usually this is a block device specifier of some kind, 6722 see the early_lookup_bdev comment in 6723 block/early-lookup.c for details. 6724 Alternatively this can be "ram" for the legacy initial 6725 ramdisk, "nfs" and "cifs" for root on a network file 6726 system, or "mtd" and "ubi" for mounting from raw flash. 6727 6728 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6729 mount the root filesystem 6730 6731 rootflags= [KNL] Set root filesystem mount option string 6732 6733 rseq_slice_ext= [KNL] RSEQ based time slice extension 6734 Format: boolean 6735 Control enablement of RSEQ based time slice extension. 6736 Default is 'on'. 6737 6738 initramfs_options= [KNL] 6739 Specify mount options for the initramfs mount. 6740 6741 rootfstype= [KNL] Set root filesystem type 6742 6743 rootwait [KNL] Wait (indefinitely) for root device to show up. 6744 Useful for devices that are detected asynchronously 6745 (e.g. USB and MMC devices). 6746 6747 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6748 to show up before attempting to mount the root 6749 filesystem. 6750 6751 rproc_mem=nn[KMG][@address] 6752 [KNL,ARM,CMA] Remoteproc physical memory block. 6753 Memory area to be used by remote processor image, 6754 managed by CMA. 6755 6756 rseq_debug= [KNL] Enable or disable restartable sequence 6757 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6758 Format: <bool> 6759 6760 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6761 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6762 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6763 Format: <bool> 6764 6765 rw [KNL] Mount root device read-write on boot 6766 6767 S [KNL] Run init in single mode 6768 6769 s390_iommu= [HW,S390] 6770 Set s390 IOTLB flushing mode 6771 strict 6772 With strict flushing every unmap operation will result 6773 in an IOTLB flush. Default is lazy flushing before 6774 reuse, which is faster. Deprecated, equivalent to 6775 iommu.strict=1. 6776 6777 s390_iommu_aperture= [KNL,S390] 6778 Specifies the size of the per device DMA address space 6779 accessible through the DMA and IOMMU APIs as a decimal 6780 factor of the size of main memory. 6781 The default is 1 meaning that one can concurrently use 6782 as many DMA addresses as physical memory is installed, 6783 if supported by hardware, and thus map all of memory 6784 once. With a value of 2 one can map all of memory twice 6785 and so on. As a special case a factor of 0 imposes no 6786 restrictions other than those given by hardware at the 6787 cost of significant additional memory use for tables. 6788 6789 6790 sched_proxy_exec= [KNL] 6791 Enables or disables "proxy execution" style 6792 solution to mutex-based priority inversion. 6793 Format: <bool> 6794 6795 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6796 6797 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6798 Allowed values are enable and disable. This feature 6799 incurs a small amount of overhead in the scheduler 6800 but is useful for debugging and performance tuning. 6801 6802 sched_thermal_decay_shift= 6803 [Deprecated] 6804 [KNL, SMP] Set a decay shift for scheduler thermal 6805 pressure signal. Thermal pressure signal follows the 6806 default decay period of other scheduler pelt 6807 signals(usually 32 ms but configurable). Setting 6808 sched_thermal_decay_shift will left shift the decay 6809 period for the thermal pressure signal by the shift 6810 value. 6811 i.e. with the default pelt decay period of 32 ms 6812 sched_thermal_decay_shift thermal pressure decay pr 6813 1 64 ms 6814 2 128 ms 6815 and so on. 6816 Format: integer between 0 and 10 6817 Default is 0. 6818 6819 scftorture.holdoff= [KNL] 6820 Number of seconds to hold off before starting 6821 test. Defaults to zero for module insertion and 6822 to 10 seconds for built-in smp_call_function() 6823 tests. 6824 6825 scftorture.longwait= [KNL] 6826 Request ridiculously long waits randomly selected 6827 up to the chosen limit in seconds. Zero (the 6828 default) disables this feature. Please note 6829 that requesting even small non-zero numbers of 6830 seconds can result in RCU CPU stall warnings, 6831 softlockup complaints, and so on. 6832 6833 scftorture.nthreads= [KNL] 6834 Number of kthreads to spawn to invoke the 6835 smp_call_function() family of functions. 6836 The default of -1 specifies a number of kthreads 6837 equal to the number of CPUs. 6838 6839 scftorture.onoff_holdoff= [KNL] 6840 Number seconds to wait after the start of the 6841 test before initiating CPU-hotplug operations. 6842 6843 scftorture.onoff_interval= [KNL] 6844 Number seconds to wait between successive 6845 CPU-hotplug operations. Specifying zero (which 6846 is the default) disables CPU-hotplug operations. 6847 6848 scftorture.shutdown_secs= [KNL] 6849 The number of seconds following the start of the 6850 test after which to shut down the system. The 6851 default of zero avoids shutting down the system. 6852 Non-zero values are useful for automated tests. 6853 6854 scftorture.stat_interval= [KNL] 6855 The number of seconds between outputting the 6856 current test statistics to the console. A value 6857 of zero disables statistics output. 6858 6859 scftorture.stutter_cpus= [KNL] 6860 The number of jiffies to wait between each change 6861 to the set of CPUs under test. 6862 6863 scftorture.use_cpus_read_lock= [KNL] 6864 Use use_cpus_read_lock() instead of the default 6865 preempt_disable() to disable CPU hotplug 6866 while invoking one of the smp_call_function*() 6867 functions. 6868 6869 scftorture.verbose= [KNL] 6870 Enable additional printk() statements. 6871 6872 scftorture.weight_single= [KNL] 6873 The probability weighting to use for the 6874 smp_call_function_single() function with a zero 6875 "wait" parameter. A value of -1 selects the 6876 default if all other weights are -1. However, 6877 if at least one weight has some other value, a 6878 value of -1 will instead select a weight of zero. 6879 6880 scftorture.weight_single_wait= [KNL] 6881 The probability weighting to use for the 6882 smp_call_function_single() function with a 6883 non-zero "wait" parameter. See weight_single. 6884 6885 scftorture.weight_many= [KNL] 6886 The probability weighting to use for the 6887 smp_call_function_many() function with a zero 6888 "wait" parameter. See weight_single. 6889 Note well that setting a high probability for 6890 this weighting can place serious IPI load 6891 on the system. 6892 6893 scftorture.weight_many_wait= [KNL] 6894 The probability weighting to use for the 6895 smp_call_function_many() function with a 6896 non-zero "wait" parameter. See weight_single 6897 and weight_many. 6898 6899 scftorture.weight_all= [KNL] 6900 The probability weighting to use for the 6901 smp_call_function_all() function with a zero 6902 "wait" parameter. See weight_single and 6903 weight_many. 6904 6905 scftorture.weight_all_wait= [KNL] 6906 The probability weighting to use for the 6907 smp_call_function_all() function with a 6908 non-zero "wait" parameter. See weight_single 6909 and weight_many. 6910 6911 sdw_mclk_divider=[SDW] 6912 Specify the MCLK divider for Intel SoundWire buses in 6913 case the BIOS does not provide the clock rate properly. 6914 6915 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6916 xtime_lock contention on larger systems, and/or RCU lock 6917 contention on all systems with CONFIG_MAXSMP set. 6918 Format: { "0" | "1" } 6919 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6920 1 -- enable. 6921 Note: increases power consumption, thus should only be 6922 enabled if running jitter sensitive (HPC/RT) workloads. 6923 6924 security= [SECURITY] Choose a legacy "major" security module to 6925 enable at boot. This has been deprecated by the 6926 "lsm=" parameter. 6927 6928 selinux= [SELINUX] Disable or enable SELinux at boot time. 6929 Format: { "0" | "1" } 6930 See security/selinux/Kconfig help text. 6931 0 -- disable. 6932 1 -- enable. 6933 Default value is 1. 6934 6935 serialnumber [BUGS=X86-32] 6936 6937 sev=option[,option...] [X86-64] 6938 6939 debug 6940 Enable debug messages. 6941 6942 nosnp 6943 Do not enable SEV-SNP (applies to host/hypervisor 6944 only). Setting 'nosnp' avoids the RMP check overhead 6945 in memory accesses when users do not want to run 6946 SEV-SNP guests. 6947 6948 shapers= [NET] 6949 Maximal number of shapers. 6950 6951 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6952 Limit apic dumping. The parameter defines the maximal 6953 number of local apics being dumped. Also it is possible 6954 to set it to "all" by meaning -- no limit here. 6955 Format: { 1 (default) | 2 | ... | all }. 6956 The parameter valid if only apic=debug or 6957 apic=verbose is specified. 6958 Example: apic=debug show_lapic=all 6959 6960 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6961 Enabling slab_debug allows one to determine the 6962 culprit if slab objects become corrupted. Enabling 6963 slab_debug can create guard zones around objects and 6964 may poison objects when not in use. Also tracks the 6965 last alloc / free. For more information see 6966 Documentation/admin-guide/mm/slab.rst. 6967 (slub_debug legacy name also accepted for now) 6968 6969 Using this option implies the "no_hash_pointers" 6970 option which can be undone by adding the 6971 "hash_pointers=always" option. 6972 6973 slab_max_order= [MM] 6974 Determines the maximum allowed order for slabs. 6975 A high setting may cause OOMs due to memory 6976 fragmentation. For more information see 6977 Documentation/admin-guide/mm/slab.rst. 6978 (slub_max_order legacy name also accepted for now) 6979 6980 slab_merge [MM] 6981 Enable merging of slabs with similar size when the 6982 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6983 (slub_merge legacy name also accepted for now) 6984 6985 slab_min_objects= [MM] 6986 The minimum number of objects per slab. SLUB will 6987 increase the slab order up to slab_max_order to 6988 generate a sufficiently large slab able to contain 6989 the number of objects indicated. The higher the number 6990 of objects the smaller the overhead of tracking slabs 6991 and the less frequently locks need to be acquired. 6992 For more information see 6993 Documentation/admin-guide/mm/slab.rst. 6994 (slub_min_objects legacy name also accepted for now) 6995 6996 slab_min_order= [MM] 6997 Determines the minimum page order for slabs. Must be 6998 lower or equal to slab_max_order. For more information see 6999 Documentation/admin-guide/mm/slab.rst. 7000 (slub_min_order legacy name also accepted for now) 7001 7002 slab_nomerge [MM] 7003 Disable merging of slabs with similar size. May be 7004 necessary if there is some reason to distinguish 7005 allocs to different slabs, especially in hardened 7006 environments where the risk of heap overflows and 7007 layout control by attackers can usually be 7008 frustrated by disabling merging. This will reduce 7009 most of the exposure of a heap attack to a single 7010 cache (risks via metadata attacks are mostly 7011 unchanged). Debug options disable merging on their 7012 own. 7013 For more information see 7014 Documentation/admin-guide/mm/slab.rst. 7015 (slub_nomerge legacy name also accepted for now) 7016 7017 slab_strict_numa [MM] 7018 Support memory policies on a per object level 7019 in the slab allocator. The default is for memory 7020 policies to be applied at the folio level when 7021 a new folio is needed or a partial folio is 7022 retrieved from the lists. Increases overhead 7023 in the slab fastpaths but gains more accurate 7024 NUMA kernel object placement which helps with slow 7025 interconnects in NUMA systems. 7026 7027 slram= [HW,MTD] 7028 7029 smart2= [HW] 7030 Format: <io1>[,<io2>[,...,<io8>]] 7031 7032 smp.csd_lock_timeout= [KNL] 7033 Specify the period of time in milliseconds 7034 that smp_call_function() and friends will wait 7035 for a CPU to release the CSD lock. This is 7036 useful when diagnosing bugs involving CPUs 7037 disabling interrupts for extended periods 7038 of time. Defaults to 5,000 milliseconds, and 7039 setting a value of zero disables this feature. 7040 This feature may be more efficiently disabled 7041 using the csdlock_debug- kernel parameter. 7042 7043 smp.panic_on_ipistall= [KNL] 7044 If a csd_lock_timeout extends for more than 7045 the specified number of milliseconds, panic the 7046 system. By default, let CSD-lock acquisition 7047 take as long as they take. Specifying 300,000 7048 for this value provides a 5-minute timeout. 7049 7050 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 7051 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 7052 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 7053 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 7054 smsc-ircc2.ircc_irq= [HW] IRQ line 7055 smsc-ircc2.ircc_dma= [HW] DMA channel 7056 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 7057 0: Toshiba Satellite 1800 (GP data pin select) 7058 1: Fast pin select (default) 7059 2: ATC IRMode 7060 7061 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7062 (logical CPUs) to use per physical CPU on systems 7063 capable of symmetric multithreading (SMT). Will 7064 be capped to the actual hardware limit. 7065 Format: <integer> 7066 Default: -1 (no limit) 7067 7068 softlockup_panic= 7069 [KNL] Should the soft-lockup detector generate panics. 7070 Format: <int> 7071 7072 A value of non-zero instructs the soft-lockup detector 7073 to panic the machine when a soft-lockup duration exceeds 7074 N thresholds. It is also controlled by the kernel.softlockup_panic 7075 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7076 respective build-time switch to that functionality. 7077 7078 softlockup_all_cpu_backtrace= 7079 [KNL] Should the soft-lockup detector generate 7080 backtraces on all cpus. 7081 Format: 0 | 1 7082 7083 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7084 See Documentation/admin-guide/laptops/sonypi.rst 7085 7086 spectre_bhi= [X86] Control mitigation of Branch History Injection 7087 (BHI) vulnerability. This setting affects the 7088 deployment of the HW BHI control and the SW BHB 7089 clearing sequence. 7090 7091 on - (default) Enable the HW or SW mitigation as 7092 needed. This protects the kernel from 7093 both syscalls and VMs. 7094 vmexit - On systems which don't have the HW mitigation 7095 available, enable the SW mitigation on vmexit 7096 ONLY. On such systems, the host kernel is 7097 protected from VM-originated BHI attacks, but 7098 may still be vulnerable to syscall attacks. 7099 off - Disable the mitigation. 7100 7101 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7102 (indirect branch speculation) vulnerability. 7103 The default operation protects the kernel from 7104 user space attacks. 7105 7106 on - unconditionally enable, implies 7107 spectre_v2_user=on 7108 off - unconditionally disable, implies 7109 spectre_v2_user=off 7110 auto - kernel detects whether your CPU model is 7111 vulnerable 7112 7113 Selecting 'on' will, and 'auto' may, choose a 7114 mitigation method at run time according to the 7115 CPU, the available microcode, the setting of the 7116 CONFIG_MITIGATION_RETPOLINE configuration option, 7117 and the compiler with which the kernel was built. 7118 7119 Selecting 'on' will also enable the mitigation 7120 against user space to user space task attacks. 7121 Selecting specific mitigation does not force enable 7122 user mitigations. 7123 7124 Selecting 'off' will disable both the kernel and 7125 the user space protections. 7126 7127 Specific mitigations can also be selected manually: 7128 7129 retpoline - replace indirect branches 7130 retpoline,generic - Retpolines 7131 retpoline,lfence - LFENCE; indirect branch 7132 retpoline,amd - alias for retpoline,lfence 7133 eibrs - Enhanced/Auto IBRS 7134 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7135 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7136 ibrs - use IBRS to protect kernel 7137 7138 Not specifying this option is equivalent to 7139 spectre_v2=auto. 7140 7141 spectre_v2_user= 7142 [X86] Control mitigation of Spectre variant 2 7143 (indirect branch speculation) vulnerability between 7144 user space tasks 7145 7146 on - Unconditionally enable mitigations. Is 7147 enforced by spectre_v2=on 7148 7149 off - Unconditionally disable mitigations. Is 7150 enforced by spectre_v2=off 7151 7152 prctl - Indirect branch speculation is enabled, 7153 but mitigation can be enabled via prctl 7154 per thread. The mitigation control state 7155 is inherited on fork. 7156 7157 prctl,ibpb 7158 - Like "prctl" above, but only STIBP is 7159 controlled per thread. IBPB is issued 7160 always when switching between different user 7161 space processes. 7162 7163 seccomp 7164 - Same as "prctl" above, but all seccomp 7165 threads will enable the mitigation unless 7166 they explicitly opt out. 7167 7168 seccomp,ibpb 7169 - Like "seccomp" above, but only STIBP is 7170 controlled per thread. IBPB is issued 7171 always when switching between different 7172 user space processes. 7173 7174 auto - Kernel selects the mitigation depending on 7175 the available CPU features and vulnerability. 7176 7177 Default mitigation: "prctl" 7178 7179 Not specifying this option is equivalent to 7180 spectre_v2_user=auto. 7181 7182 spec_rstack_overflow= 7183 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7184 7185 off - Disable mitigation 7186 microcode - Enable microcode mitigation only 7187 safe-ret - Enable sw-only safe RET mitigation (default) 7188 ibpb - Enable mitigation by issuing IBPB on 7189 kernel entry 7190 ibpb-vmexit - Issue IBPB only on VMEXIT 7191 (cloud-specific mitigation) 7192 7193 spec_store_bypass_disable= 7194 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7195 (Speculative Store Bypass vulnerability) 7196 7197 Certain CPUs are vulnerable to an exploit against a 7198 a common industry wide performance optimization known 7199 as "Speculative Store Bypass" in which recent stores 7200 to the same memory location may not be observed by 7201 later loads during speculative execution. The idea 7202 is that such stores are unlikely and that they can 7203 be detected prior to instruction retirement at the 7204 end of a particular speculation execution window. 7205 7206 In vulnerable processors, the speculatively forwarded 7207 store can be used in a cache side channel attack, for 7208 example to read memory to which the attacker does not 7209 directly have access (e.g. inside sandboxed code). 7210 7211 This parameter controls whether the Speculative Store 7212 Bypass optimization is used. 7213 7214 On x86 the options are: 7215 7216 on - Unconditionally disable Speculative Store Bypass 7217 off - Unconditionally enable Speculative Store Bypass 7218 auto - Kernel detects whether the CPU model contains an 7219 implementation of Speculative Store Bypass and 7220 picks the most appropriate mitigation. If the 7221 CPU is not vulnerable, "off" is selected. If the 7222 CPU is vulnerable the default mitigation is 7223 architecture and Kconfig dependent. See below. 7224 prctl - Control Speculative Store Bypass per thread 7225 via prctl. Speculative Store Bypass is enabled 7226 for a process by default. The state of the control 7227 is inherited on fork. 7228 seccomp - Same as "prctl" above, but all seccomp threads 7229 will disable SSB unless they explicitly opt out. 7230 7231 Default mitigations: 7232 X86: "prctl" 7233 7234 On powerpc the options are: 7235 7236 on,auto - On Power8 and Power9 insert a store-forwarding 7237 barrier on kernel entry and exit. On Power7 7238 perform a software flush on kernel entry and 7239 exit. 7240 off - No action. 7241 7242 Not specifying this option is equivalent to 7243 spec_store_bypass_disable=auto. 7244 7245 split_lock_detect= 7246 [X86] Enable split lock detection or bus lock detection 7247 7248 When enabled (and if hardware support is present), atomic 7249 instructions that access data across cache line 7250 boundaries will result in an alignment check exception 7251 for split lock detection or a debug exception for 7252 bus lock detection. 7253 7254 off - not enabled 7255 7256 warn - the kernel will emit rate-limited warnings 7257 about applications triggering the #AC 7258 exception or the #DB exception. This mode is 7259 the default on CPUs that support split lock 7260 detection or bus lock detection. Default 7261 behavior is by #AC if both features are 7262 enabled in hardware. 7263 7264 fatal - the kernel will send SIGBUS to applications 7265 that trigger the #AC exception or the #DB 7266 exception. Default behavior is by #AC if 7267 both features are enabled in hardware. 7268 7269 ratelimit:N - 7270 Set system wide rate limit to N bus locks 7271 per second for bus lock detection. 7272 0 < N <= 1000. 7273 7274 N/A for split lock detection. 7275 7276 7277 If an #AC exception is hit in the kernel or in 7278 firmware (i.e. not while executing in user mode) 7279 the kernel will oops in either "warn" or "fatal" 7280 mode. 7281 7282 #DB exception for bus lock is triggered only when 7283 CPL > 0. 7284 7285 srbds= [X86,INTEL,EARLY] 7286 Control the Special Register Buffer Data Sampling 7287 (SRBDS) mitigation. 7288 7289 Certain CPUs are vulnerable to an MDS-like 7290 exploit which can leak bits from the random 7291 number generator. 7292 7293 By default, this issue is mitigated by 7294 microcode. However, the microcode fix can cause 7295 the RDRAND and RDSEED instructions to become 7296 much slower. Among other effects, this will 7297 result in reduced throughput from /dev/urandom. 7298 7299 The microcode mitigation can be disabled with 7300 the following option: 7301 7302 off: Disable mitigation and remove 7303 performance impact to RDRAND and RDSEED 7304 7305 srcutree.big_cpu_lim [KNL] 7306 Specifies the number of CPUs constituting a 7307 large system, such that srcu_struct structures 7308 should immediately allocate an srcu_node array. 7309 This kernel-boot parameter defaults to 128, 7310 but takes effect only when the low-order four 7311 bits of srcutree.convert_to_big is equal to 3 7312 (decide at boot). 7313 7314 srcutree.convert_to_big [KNL] 7315 Specifies under what conditions an SRCU tree 7316 srcu_struct structure will be converted to big 7317 form, that is, with an rcu_node tree: 7318 7319 0: Never. 7320 1: At init_srcu_struct() time. 7321 2: When rcutorture decides to. 7322 3: Decide at boot time (default). 7323 0x1X: Above plus if high contention. 7324 7325 Either way, the srcu_node tree will be sized based 7326 on the actual runtime number of CPUs (nr_cpu_ids) 7327 instead of the compile-time CONFIG_NR_CPUS. 7328 7329 srcutree.counter_wrap_check [KNL] 7330 Specifies how frequently to check for 7331 grace-period sequence counter wrap for the 7332 srcu_data structure's ->srcu_gp_seq_needed field. 7333 The greater the number of bits set in this kernel 7334 parameter, the less frequently counter wrap will 7335 be checked for. Note that the bottom two bits 7336 are ignored. 7337 7338 srcutree.exp_holdoff [KNL] 7339 Specifies how many nanoseconds must elapse 7340 since the end of the last SRCU grace period for 7341 a given srcu_struct until the next normal SRCU 7342 grace period will be considered for automatic 7343 expediting. Set to zero to disable automatic 7344 expediting. 7345 7346 srcutree.srcu_max_nodelay [KNL] 7347 Specifies the number of no-delay instances 7348 per jiffy for which the SRCU grace period 7349 worker thread will be rescheduled with zero 7350 delay. Beyond this limit, worker thread will 7351 be rescheduled with a sleep delay of one jiffy. 7352 7353 srcutree.srcu_max_nodelay_phase [KNL] 7354 Specifies the per-grace-period phase, number of 7355 non-sleeping polls of readers. Beyond this limit, 7356 grace period worker thread will be rescheduled 7357 with a sleep delay of one jiffy, between each 7358 rescan of the readers, for a grace period phase. 7359 7360 srcutree.srcu_retry_check_delay [KNL] 7361 Specifies number of microseconds of non-sleeping 7362 delay between each non-sleeping poll of readers. 7363 7364 srcutree.small_contention_lim [KNL] 7365 Specifies the number of update-side contention 7366 events per jiffy will be tolerated before 7367 initiating a conversion of an srcu_struct 7368 structure to big form. Note that the value of 7369 srcutree.convert_to_big must have the 0x10 bit 7370 set for contention-based conversions to occur. 7371 7372 ssbd= [ARM64,HW,EARLY] 7373 Speculative Store Bypass Disable control 7374 7375 On CPUs that are vulnerable to the Speculative 7376 Store Bypass vulnerability and offer a 7377 firmware based mitigation, this parameter 7378 indicates how the mitigation should be used: 7379 7380 force-on: Unconditionally enable mitigation for 7381 for both kernel and userspace 7382 force-off: Unconditionally disable mitigation for 7383 for both kernel and userspace 7384 kernel: Always enable mitigation in the 7385 kernel, and offer a prctl interface 7386 to allow userspace to register its 7387 interest in being mitigated too. 7388 7389 stack_guard_gap= [MM] 7390 override the default stack gap protection. The value 7391 is in page units and it defines how many pages prior 7392 to (for stacks growing down) resp. after (for stacks 7393 growing up) the main stack are reserved for no other 7394 mapping. Default value is 256 pages. 7395 7396 stack_depot_disable= [KNL,EARLY] 7397 Setting this to true through kernel command line will 7398 disable the stack depot thereby saving the static memory 7399 consumed by the stack hash table. By default this is set 7400 to false. 7401 7402 stack_depot_max_pools= [KNL,EARLY] 7403 Specify the maximum number of pools to use for storing 7404 stack traces. Pools are allocated on-demand up to this 7405 limit. Default value is 8191 pools. 7406 7407 stacktrace [FTRACE] 7408 Enable the stack tracer on boot up. 7409 7410 stacktrace_filter=[function-list] 7411 [FTRACE] Limit the functions that the stack tracer 7412 will trace at boot up. function-list is a comma-separated 7413 list of functions. This list can be changed at run 7414 time by the stack_trace_filter file in the debugfs 7415 tracing directory. Note, this enables stack tracing 7416 and the stacktrace above is not needed. 7417 7418 sti= [PARISC,HW] 7419 Format: <num> 7420 Set the STI (builtin display/keyboard on the HP-PARISC 7421 machines) console (graphic card) which should be used 7422 as the initial boot-console. 7423 See also comment in drivers/video/sticore.c. 7424 7425 sti_font= [HW] 7426 See comment in drivers/video/sticore.c. 7427 7428 stifb= [HW] 7429 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7430 7431 strict_sas_size= 7432 [X86] 7433 Format: <bool> 7434 Enable or disable strict sigaltstack size checks 7435 against the required signal frame size which 7436 depends on the supported FPU features. This can 7437 be used to filter out binaries which have 7438 not yet been made aware of AT_MINSIGSTKSZ. 7439 7440 stress_hpt [PPC,EARLY] 7441 Limits the number of kernel HPT entries in the hash 7442 page table to increase the rate of hash page table 7443 faults on kernel addresses. 7444 7445 stress_slb [PPC,EARLY] 7446 Limits the number of kernel SLB entries, and flushes 7447 them frequently to increase the rate of SLB faults 7448 on kernel addresses. 7449 7450 no_slb_preload [PPC,EARLY] 7451 Disables slb preloading for userspace. 7452 7453 sunrpc.min_resvport= 7454 sunrpc.max_resvport= 7455 [NFS,SUNRPC] 7456 SunRPC servers often require that client requests 7457 originate from a privileged port (i.e. a port in the 7458 range 0 < portnr < 1024). 7459 An administrator who wishes to reserve some of these 7460 ports for other uses may adjust the range that the 7461 kernel's sunrpc client considers to be privileged 7462 using these two parameters to set the minimum and 7463 maximum port values. 7464 7465 sunrpc.svc_rpc_per_connection_limit= 7466 [NFS,SUNRPC] 7467 Limit the number of requests that the server will 7468 process in parallel from a single connection. 7469 The default value is 0 (no limit). 7470 7471 sunrpc.pool_mode= 7472 [NFS] 7473 Control how the NFS server code allocates CPUs to 7474 service thread pools. Depending on how many NICs 7475 you have and where their interrupts are bound, this 7476 option will affect which CPUs will do NFS serving. 7477 Note: this parameter cannot be changed while the 7478 NFS server is running. 7479 7480 auto the server chooses an appropriate mode 7481 automatically using heuristics 7482 global a single global pool contains all CPUs 7483 percpu one pool for each CPU 7484 pernode one pool for each NUMA node (equivalent 7485 to global on non-NUMA machines) 7486 7487 sunrpc.tcp_slot_table_entries= 7488 sunrpc.udp_slot_table_entries= 7489 [NFS,SUNRPC] 7490 Sets the upper limit on the number of simultaneous 7491 RPC calls that can be sent from the client to a 7492 server. Increasing these values may allow you to 7493 improve throughput, but will also increase the 7494 amount of memory reserved for use by the client. 7495 7496 suspend.pm_test_delay= 7497 [SUSPEND] 7498 Sets the number of seconds to remain in a suspend test 7499 mode before resuming the system (see 7500 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7501 is set. Default value is 5. 7502 7503 svm= [PPC] 7504 Format: { on | off | y | n | 1 | 0 } 7505 This parameter controls use of the Protected 7506 Execution Facility on pSeries. 7507 7508 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7509 Format: { <int> [,<int>] | force | noforce } 7510 <int> -- Number of I/O TLB slabs 7511 <int> -- Second integer after comma. Number of swiotlb 7512 areas with their own lock. Will be rounded up 7513 to a power of 2. 7514 force -- force using of bounce buffers even if they 7515 wouldn't be automatically used by the kernel 7516 noforce -- Never use bounce buffers (for debugging) 7517 7518 switches= [HW,M68k,EARLY] 7519 7520 sysctl.*= [KNL] 7521 Set a sysctl parameter, right before loading the init 7522 process, as if the value was written to the respective 7523 /proc/sys/... file. Both '.' and '/' are recognized as 7524 separators. Unrecognized parameters and invalid values 7525 are reported in the kernel log. Sysctls registered 7526 later by a loaded module cannot be set this way. 7527 Example: sysctl.vm.swappiness=40 7528 7529 sysrq_always_enabled 7530 [KNL] 7531 Ignore sysrq setting - this boot parameter will 7532 neutralize any effect of /proc/sys/kernel/sysrq. 7533 Useful for debugging. 7534 7535 tcpmhash_entries= [KNL,NET] 7536 Set the number of tcp_metrics_hash slots. 7537 Default value is 8192 or 16384 depending on total 7538 ram pages. This is used to specify the TCP metrics 7539 cache size. See Documentation/networking/ip-sysctl.rst 7540 "tcp_no_metrics_save" section for more details. 7541 7542 tdfx= [HW,DRM] 7543 7544 test_suspend= [SUSPEND] 7545 Format: { "mem" | "standby" | "freeze" }[,N] 7546 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7547 standby suspend) or "freeze" (for suspend type freeze) 7548 as the system sleep state during system startup with 7549 the optional capability to repeat N number of times. 7550 The system is woken from this state using a 7551 wakeup-capable RTC alarm. 7552 7553 thash_entries= [KNL,NET] 7554 Set number of hash buckets for TCP connection 7555 7556 thermal.act= [HW,ACPI] 7557 -1: disable all active trip points in all thermal zones 7558 <degrees C>: override all lowest active trip points 7559 7560 thermal.crt= [HW,ACPI] 7561 -1: disable all critical trip points in all thermal zones 7562 <degrees C>: override all critical trip points 7563 7564 thermal.off= [HW,ACPI] 7565 1: disable ACPI thermal control 7566 7567 thermal.psv= [HW,ACPI] 7568 -1: disable all passive trip points 7569 <degrees C>: override all passive trip points to this 7570 value 7571 7572 thermal.tzp= [HW,ACPI] 7573 Specify global default ACPI thermal zone polling rate 7574 <deci-seconds>: poll all this frequency 7575 0: no polling (default) 7576 7577 thp_anon= [KNL] 7578 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7579 state is one of "always", "madvise", "never" or "inherit". 7580 Control the default behavior of the system with respect 7581 to anonymous transparent hugepages. 7582 Can be used multiple times for multiple anon THP sizes. 7583 See Documentation/admin-guide/mm/transhuge.rst for more 7584 details. 7585 7586 threadirqs [KNL,EARLY] 7587 Force threading of all interrupt handlers except those 7588 marked explicitly IRQF_NO_THREAD. 7589 7590 thp_shmem= [KNL] 7591 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7592 Control the default policy of each hugepage size for the 7593 internal shmem mount. <policy> is one of policies available 7594 for the shmem mount ("always", "inherit", "never", "within_size", 7595 and "advise"). 7596 It can be used multiple times for multiple shmem THP sizes. 7597 See Documentation/admin-guide/mm/transhuge.rst for more 7598 details. 7599 7600 topology= [S390,EARLY] 7601 Format: {off | on} 7602 Specify if the kernel should make use of the cpu 7603 topology information if the hardware supports this. 7604 The scheduler will make use of this information and 7605 e.g. base its process migration decisions on it. 7606 Default is on. 7607 7608 torture.disable_onoff_at_boot= [KNL] 7609 Prevent the CPU-hotplug component of torturing 7610 until after init has spawned. 7611 7612 torture.ftrace_dump_at_shutdown= [KNL] 7613 Dump the ftrace buffer at torture-test shutdown, 7614 even if there were no errors. This can be a 7615 very costly operation when many torture tests 7616 are running concurrently, especially on systems 7617 with rotating-rust storage. 7618 7619 torture.verbose_sleep_frequency= [KNL] 7620 Specifies how many verbose printk()s should be 7621 emitted between each sleep. The default of zero 7622 disables verbose-printk() sleeping. 7623 7624 torture.verbose_sleep_duration= [KNL] 7625 Duration of each verbose-printk() sleep in jiffies. 7626 7627 tpm.disable_pcr_integrity= [HW,TPM] 7628 Do not protect PCR registers from unintended physical 7629 access, or interposers in the bus by the means of 7630 having an integrity protected session wrapped around 7631 TPM2_PCR_Extend command. Consider this in a situation 7632 where TPM is heavily utilized by IMA, thus protection 7633 causing a major performance hit, and the space where 7634 machines are deployed is by other means guarded. 7635 7636 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7637 Maximum time in milliseconds to retry sending a message 7638 to the TPM service before giving up. This parameter controls 7639 how long the system will continue retrying when the TPM 7640 service is busy. 7641 Format: <unsigned int> 7642 Default: 2000 (2 seconds) 7643 7644 tpm_suspend_pcr=[HW,TPM] 7645 Format: integer pcr id 7646 Specify that at suspend time, the tpm driver 7647 should extend the specified pcr with zeros, 7648 as a workaround for some chips which fail to 7649 flush the last written pcr on TPM_SaveState. 7650 This will guarantee that all the other pcrs 7651 are saved. 7652 7653 tpm_tis.interrupts= [HW,TPM] 7654 Enable interrupts for the MMIO based physical layer 7655 for the FIFO interface. By default it is set to false 7656 (0). For more information about TPM hardware interfaces 7657 defined by Trusted Computing Group (TCG) see 7658 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7659 7660 tp_printk [FTRACE] 7661 Have the tracepoints sent to printk as well as the 7662 tracing ring buffer. This is useful for early boot up 7663 where the system hangs or reboots and does not give the 7664 option for reading the tracing buffer or performing a 7665 ftrace_dump_on_oops. 7666 7667 To turn off having tracepoints sent to printk, 7668 echo 0 > /proc/sys/kernel/tracepoint_printk 7669 Note, echoing 1 into this file without the 7670 tp_printk kernel cmdline option has no effect. 7671 7672 The tp_printk_stop_on_boot (see below) can also be used 7673 to stop the printing of events to console at 7674 late_initcall_sync. 7675 7676 ** CAUTION ** 7677 7678 Having tracepoints sent to printk() and activating high 7679 frequency tracepoints such as irq or sched, can cause 7680 the system to live lock. 7681 7682 tp_printk_stop_on_boot [FTRACE] 7683 When tp_printk (above) is set, it can cause a lot of noise 7684 on the console. It may be useful to only include the 7685 printing of events during boot up, as user space may 7686 make the system inoperable. 7687 7688 This command line option will stop the printing of events 7689 to console at the late_initcall_sync() time frame. 7690 7691 trace_buf_size=nn[KMG] 7692 [FTRACE] will set tracing buffer size on each cpu. 7693 7694 trace_clock= [FTRACE] Set the clock used for tracing events 7695 at boot up. 7696 local - Use the per CPU time stamp counter 7697 (converted into nanoseconds). Fast, but 7698 depending on the architecture, may not be 7699 in sync between CPUs. 7700 global - Event time stamps are synchronized across 7701 CPUs. May be slower than the local clock, 7702 but better for some race conditions. 7703 counter - Simple counting of events (1, 2, ..) 7704 note, some counts may be skipped due to the 7705 infrastructure grabbing the clock more than 7706 once per event. 7707 uptime - Use jiffies as the time stamp. 7708 perf - Use the same clock that perf uses. 7709 mono - Use ktime_get_mono_fast_ns() for time stamps. 7710 mono_raw - Use ktime_get_raw_fast_ns() for time 7711 stamps. 7712 boot - Use ktime_get_boot_fast_ns() for time stamps. 7713 Architectures may add more clocks. See 7714 Documentation/trace/ftrace.rst for more details. 7715 7716 trace_event=[event-list] 7717 [FTRACE] Set and start specified trace events in order 7718 to facilitate early boot debugging. The event-list is a 7719 comma-separated list of trace events to enable. See 7720 also Documentation/trace/events.rst 7721 7722 To enable modules, use :mod: keyword: 7723 7724 trace_event=:mod:<module> 7725 7726 The value before :mod: will only enable specific events 7727 that are part of the module. See the above mentioned 7728 document for more information. 7729 7730 trace_instance=[instance-info] 7731 [FTRACE] Create a ring buffer instance early in boot up. 7732 This will be listed in: 7733 7734 /sys/kernel/tracing/instances 7735 7736 Events can be enabled at the time the instance is created 7737 via: 7738 7739 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7740 7741 Note, the "<system*>:" portion is optional if the event is 7742 unique. 7743 7744 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7745 7746 will enable the "sched_switch" event (note, the "sched:" is optional, and 7747 the same thing would happen if it was left off). The irq_handler_entry 7748 event, and all events under the "initcall" system. 7749 7750 Flags can be added to the instance to modify its behavior when it is 7751 created. The flags are separated by '^'. 7752 7753 The available flags are: 7754 7755 traceoff - Have the tracing instance tracing disabled after it is created. 7756 traceprintk - Have trace_printk() write into this trace instance 7757 (note, "printk" and "trace_printk" can also be used) 7758 7759 trace_instance=foo^traceoff^traceprintk,sched,irq 7760 7761 The flags must come before the defined events. 7762 7763 If memory has been reserved (see memmap for x86), the instance 7764 can use that memory: 7765 7766 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7767 7768 The above will create a "boot_map" instance that uses the physical 7769 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7770 instance will be split up accordingly. 7771 7772 Alternatively, the memory can be reserved by the reserve_mem option: 7773 7774 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7775 7776 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7777 and place the ring buffer in this memory. Note that due to KASLR, the 7778 memory may not be the same location each time, which will not preserve 7779 the buffer content. 7780 7781 Also note that the layout of the ring buffer data may change between 7782 kernel versions where the validator will fail and reset the ring buffer 7783 if the layout is not the same as the previous kernel. 7784 7785 If the ring buffer is used for persistent bootups and has events enabled, 7786 it is recommend to disable tracing so that events from a previous boot do not 7787 mix with events of the current boot (unless you are debugging a random crash 7788 at boot up). 7789 7790 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7791 7792 Note, saving the trace buffer across reboots does require that the system 7793 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7794 can force a memory reset on boot which will clear any trace that was stored. 7795 This is just one of many ways that can clear memory. Make sure your system 7796 keeps the content of memory across reboots before relying on this option. 7797 7798 NB: Both the mapped address and size must be page aligned for the architecture. 7799 7800 See also Documentation/trace/debugging.rst 7801 7802 7803 trace_options=[option-list] 7804 [FTRACE] Enable or disable tracer options at boot. 7805 The option-list is a comma delimited list of options 7806 that can be enabled or disabled just as if you were 7807 to echo the option name into 7808 7809 /sys/kernel/tracing/trace_options 7810 7811 For example, to enable stacktrace option (to dump the 7812 stack trace of each event), add to the command line: 7813 7814 trace_options=stacktrace 7815 7816 See also Documentation/trace/ftrace.rst "trace options" 7817 section. 7818 7819 trace_trigger=[trigger-list] 7820 [FTRACE] Add an event trigger on specific events. 7821 Set a trigger on top of a specific event, with an optional 7822 filter. 7823 7824 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7825 Where more than one trigger may be specified that are comma delimited. 7826 7827 For example: 7828 7829 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7830 7831 The above will enable the "stacktrace" trigger on the "sched_switch" 7832 event but only trigger it if the "prev_state" of the "sched_switch" 7833 event is "2" (TASK_UNINTERRUPTIBLE). 7834 7835 See also "Event triggers" in Documentation/trace/events.rst 7836 7837 7838 traceoff_after_boot 7839 [FTRACE] Sometimes tracing is used to debug issues 7840 during the boot process. Since the trace buffer has a 7841 limited amount of storage, it may be prudent to 7842 disable tracing after the boot is finished, otherwise 7843 the critical information may be overwritten. With this 7844 option, the main tracing buffer will be turned off at 7845 the end of the boot process. 7846 7847 traceoff_on_warning 7848 [FTRACE] enable this option to disable tracing when a 7849 warning is hit. This turns off "tracing_on". Tracing can 7850 be enabled again by echoing '1' into the "tracing_on" 7851 file located in /sys/kernel/tracing/ 7852 7853 This option is useful, as it disables the trace before 7854 the WARNING dump is called, which prevents the trace to 7855 be filled with content caused by the warning output. 7856 7857 This option can also be set at run time via the sysctl 7858 option: kernel/traceoff_on_warning 7859 7860 transparent_hugepage= 7861 [KNL] 7862 Format: [always|madvise|never] 7863 Can be used to control the default behavior of the system 7864 with respect to transparent hugepages. 7865 See Documentation/admin-guide/mm/transhuge.rst 7866 for more details. 7867 7868 transparent_hugepage_shmem= [KNL] 7869 Format: [always|within_size|advise|never|deny|force] 7870 Can be used to control the hugepage allocation policy for 7871 the internal shmem mount. 7872 See Documentation/admin-guide/mm/transhuge.rst 7873 for more details. 7874 7875 transparent_hugepage_tmpfs= [KNL] 7876 Format: [always|within_size|advise|never] 7877 Can be used to control the default hugepage allocation policy 7878 for the tmpfs mount. 7879 See Documentation/admin-guide/mm/transhuge.rst 7880 for more details. 7881 7882 trusted.source= [KEYS] 7883 Format: <string> 7884 This parameter identifies the trust source as a backend 7885 for trusted keys implementation. Supported trust 7886 sources: 7887 - "tpm" 7888 - "tee" 7889 - "caam" 7890 - "dcp" 7891 - "pkwm" 7892 If not specified then it defaults to iterating through 7893 the trust source list starting with TPM and assigns the 7894 first trust source as a backend which is initialized 7895 successfully during iteration. 7896 7897 trusted.rng= [KEYS] 7898 Format: <string> 7899 The RNG used to generate key material for trusted keys. 7900 Can be one of: 7901 - "kernel" 7902 - the same value as trusted.source: "tpm" or "tee" 7903 - "default" 7904 If not specified, "default" is used. In this case, 7905 the RNG's choice is left to each individual trust source. 7906 7907 trusted.dcp_use_otp_key 7908 This is intended to be used in combination with 7909 trusted.source=dcp and will select the DCP OTP key 7910 instead of the DCP UNIQUE key blob encryption. 7911 7912 trusted.dcp_skip_zk_test 7913 This is intended to be used in combination with 7914 trusted.source=dcp and will disable the check if the 7915 blob key is all zeros. This is helpful for situations where 7916 having this key zero'ed is acceptable. E.g. in testing 7917 scenarios. 7918 7919 tsa= [X86] Control mitigation for Transient Scheduler 7920 Attacks on AMD CPUs. Search the following in your 7921 favourite search engine for more details: 7922 7923 "Technical guidance for mitigating transient scheduler 7924 attacks". 7925 7926 off - disable the mitigation 7927 on - enable the mitigation (default) 7928 user - mitigate only user/kernel transitions 7929 vm - mitigate only guest/host transitions 7930 7931 7932 tsc= Disable clocksource stability checks for TSC. 7933 Format: <string> 7934 [x86] reliable: mark tsc clocksource as reliable, this 7935 disables clocksource verification at runtime, as well 7936 as the stability checks done at bootup. Used to enable 7937 high-resolution timer mode on older hardware, and in 7938 virtualized environment. 7939 [x86] noirqtime: Do not use TSC to do irq accounting. 7940 Used to run time disable IRQ_TIME_ACCOUNTING on any 7941 platforms where RDTSC is slow and this accounting 7942 can add overhead. 7943 [x86] unstable: mark the TSC clocksource as unstable, this 7944 marks the TSC unconditionally unstable at bootup and 7945 avoids any further wobbles once the TSC watchdog notices. 7946 [x86] nowatchdog: disable clocksource watchdog. Used 7947 in situations with strict latency requirements (where 7948 interruptions from clocksource watchdog are not 7949 acceptable). 7950 [x86] recalibrate: force recalibration against a HW timer 7951 (HPET or PM timer) on systems whose TSC frequency was 7952 obtained from HW or FW using either an MSR or CPUID(0x15). 7953 Warn if the difference is more than 500 ppm. 7954 [x86] watchdog: Enforce the clocksource watchdog on TSC 7955 7956 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7957 value instead. Useful when the early TSC frequency discovery 7958 procedure is not reliable, such as on overclocked systems 7959 with CPUID.16h support and partial CPUID.15h support. 7960 Format: <unsigned int> 7961 7962 tsx= [X86] Control Transactional Synchronization 7963 Extensions (TSX) feature in Intel processors that 7964 support TSX control. 7965 7966 This parameter controls the TSX feature. The options are: 7967 7968 on - Enable TSX on the system. Although there are 7969 mitigations for all known security vulnerabilities, 7970 TSX has been known to be an accelerator for 7971 several previous speculation-related CVEs, and 7972 so there may be unknown security risks associated 7973 with leaving it enabled. 7974 7975 off - Disable TSX on the system. (Note that this 7976 option takes effect only on newer CPUs which are 7977 not vulnerable to MDS, i.e., have 7978 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7979 the new IA32_TSX_CTRL MSR through a microcode 7980 update. This new MSR allows for the reliable 7981 deactivation of the TSX functionality.) 7982 7983 auto - Disable TSX if X86_BUG_TAA is present, 7984 otherwise enable TSX on the system. 7985 7986 Not specifying this option is equivalent to tsx=off. 7987 7988 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7989 for more details. 7990 7991 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7992 Abort (TAA) vulnerability. 7993 7994 Similar to Micro-architectural Data Sampling (MDS) 7995 certain CPUs that support Transactional 7996 Synchronization Extensions (TSX) are vulnerable to an 7997 exploit against CPU internal buffers which can forward 7998 information to a disclosure gadget under certain 7999 conditions. 8000 8001 In vulnerable processors, the speculatively forwarded 8002 data can be used in a cache side channel attack, to 8003 access data to which the attacker does not have direct 8004 access. 8005 8006 This parameter controls the TAA mitigation. The 8007 options are: 8008 8009 full - Enable TAA mitigation on vulnerable CPUs 8010 if TSX is enabled. 8011 8012 full,nosmt - Enable TAA mitigation and disable SMT on 8013 vulnerable CPUs. If TSX is disabled, SMT 8014 is not disabled because CPU is not 8015 vulnerable to cross-thread TAA attacks. 8016 off - Unconditionally disable TAA mitigation 8017 8018 On MDS-affected machines, tsx_async_abort=off can be 8019 prevented by an active MDS mitigation as both vulnerabilities 8020 are mitigated with the same mechanism so in order to disable 8021 this mitigation, you need to specify mds=off too. 8022 8023 Not specifying this option is equivalent to 8024 tsx_async_abort=full. On CPUs which are MDS affected 8025 and deploy MDS mitigation, TAA mitigation is not 8026 required and doesn't provide any additional 8027 mitigation. 8028 8029 For details see: 8030 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8031 8032 turbografx.map[2|3]= [HW,JOY] 8033 TurboGraFX parallel port interface 8034 Format: 8035 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8036 See also Documentation/input/devices/joystick-parport.rst 8037 8038 udbg-immortal [PPC] When debugging early kernel crashes that 8039 happen after console_init() and before a proper 8040 console driver takes over, this boot options might 8041 help "seeing" what's going on. 8042 8043 uhash_entries= [KNL,NET] 8044 Set number of hash buckets for UDP/UDP-Lite connections 8045 8046 uhci-hcd.ignore_oc= 8047 [USB] Ignore overcurrent events (default N). 8048 Some badly-designed motherboards generate lots of 8049 bogus events, for ports that aren't wired to 8050 anything. Set this parameter to avoid log spamming. 8051 Note that genuine overcurrent events won't be 8052 reported either. 8053 8054 unaligned_scalar_speed= 8055 [RISCV] 8056 Format: {slow | fast | unsupported} 8057 Allow skipping scalar unaligned access speed tests. This 8058 is useful for testing alternative code paths and to skip 8059 the tests in environments where they run too slowly. All 8060 CPUs must have the same scalar unaligned access speed. 8061 8062 unaligned_vector_speed= 8063 [RISCV] 8064 Format: {slow | fast | unsupported} 8065 Allow skipping vector unaligned access speed tests. This 8066 is useful for testing alternative code paths and to skip 8067 the tests in environments where they run too slowly. All 8068 CPUs must have the same vector unaligned access speed. 8069 8070 unknown_nmi_panic 8071 [X86] Cause panic on unknown NMI. 8072 8073 unwind_debug [X86-64,EARLY] 8074 Enable unwinder debug output. This can be 8075 useful for debugging certain unwinder error 8076 conditions, including corrupt stacks and 8077 bad/missing unwinder metadata. 8078 8079 usbcore.authorized_default= 8080 [USB] Default USB device authorization: 8081 (default -1 = authorized (same as 1), 8082 0 = not authorized, 1 = authorized, 2 = authorized 8083 if device connected to internal port) 8084 8085 usbcore.autosuspend= 8086 [USB] The autosuspend time delay (in seconds) used 8087 for newly-detected USB devices (default 2). This 8088 is the time required before an idle device will be 8089 autosuspended. Devices for which the delay is set 8090 to a negative value won't be autosuspended at all. 8091 8092 usbcore.usbfs_snoop= 8093 [USB] Set to log all usbfs traffic (default 0 = off). 8094 8095 usbcore.usbfs_snoop_max= 8096 [USB] Maximum number of bytes to snoop in each URB 8097 (default = 65536). 8098 8099 usbcore.blinkenlights= 8100 [USB] Set to cycle leds on hubs (default 0 = off). 8101 8102 usbcore.old_scheme_first= 8103 [USB] Start with the old device initialization 8104 scheme (default 0 = off). 8105 8106 usbcore.usbfs_memory_mb= 8107 [USB] Memory limit (in MB) for buffers allocated by 8108 usbfs (default = 16, 0 = max = 2047). 8109 8110 usbcore.use_both_schemes= 8111 [USB] Try the other device initialization scheme 8112 if the first one fails (default 1 = enabled). 8113 8114 usbcore.initial_descriptor_timeout= 8115 [USB] Specifies timeout for the initial 64-byte 8116 USB_REQ_GET_DESCRIPTOR request in milliseconds 8117 (default 5000 = 5.0 seconds). 8118 8119 usbcore.nousb [USB] Disable the USB subsystem 8120 8121 usbcore.quirks= 8122 [USB] A list of quirk entries to augment the built-in 8123 usb core quirk list. List entries are separated by 8124 commas. Each entry has the form 8125 VendorID:ProductID:Flags. The IDs are 4-digit hex 8126 numbers and Flags is a set of letters. Each letter 8127 will change the built-in quirk; setting it if it is 8128 clear and clearing it if it is set. The letters have 8129 the following meanings: 8130 a = USB_QUIRK_STRING_FETCH_255 (string 8131 descriptors must not be fetched using 8132 a 255-byte read); 8133 b = USB_QUIRK_RESET_RESUME (device can't resume 8134 correctly so reset it instead); 8135 c = USB_QUIRK_NO_SET_INTF (device can't handle 8136 Set-Interface requests); 8137 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8138 handle its Configuration or Interface 8139 strings); 8140 e = USB_QUIRK_RESET (device can't be reset 8141 (e.g morph devices), don't use reset); 8142 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8143 more interface descriptions than the 8144 bNumInterfaces count, and can't handle 8145 talking to these interfaces); 8146 g = USB_QUIRK_DELAY_INIT (device needs a pause 8147 during initialization, after we read 8148 the device descriptor); 8149 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8150 high speed and super speed interrupt 8151 endpoints, the USB 2.0 and USB 3.0 spec 8152 require the interval in microframes (1 8153 microframe = 125 microseconds) to be 8154 calculated as interval = 2 ^ 8155 (bInterval-1). 8156 Devices with this quirk report their 8157 bInterval as the result of this 8158 calculation instead of the exponent 8159 variable used in the calculation); 8160 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8161 handle device_qualifier descriptor 8162 requests); 8163 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8164 generates spurious wakeup, ignore 8165 remote wakeup capability); 8166 k = USB_QUIRK_NO_LPM (device can't handle Link 8167 Power Management); 8168 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8169 (Device reports its bInterval as linear 8170 frames instead of the USB 2.0 8171 calculation); 8172 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8173 to be disconnected before suspend to 8174 prevent spurious wakeup); 8175 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8176 pause after every control message); 8177 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8178 delay after resetting its port); 8179 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8180 (Reduce timeout of the SET_ADDRESS 8181 request from 5000 ms to 500 ms); 8182 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8183 claims zero configurations, 8184 forcing to 1); 8185 Example: quirks=0781:5580:bk,0a5c:5834:gij 8186 8187 usbhid.mousepoll= 8188 [USBHID] The interval which mice are to be polled at. 8189 8190 usbhid.jspoll= 8191 [USBHID] The interval which joysticks are to be polled at. 8192 8193 usbhid.kbpoll= 8194 [USBHID] The interval which keyboards are to be polled at. 8195 8196 usb-storage.delay_use= 8197 [UMS] The delay in seconds before a new device is 8198 scanned for Logical Units (default 1). 8199 Optionally the delay in milliseconds if the value has 8200 suffix with "ms". 8201 Example: delay_use=2567ms 8202 8203 usb-storage.quirks= 8204 [UMS] A list of quirks entries to supplement or 8205 override the built-in unusual_devs list. List 8206 entries are separated by commas. Each entry has 8207 the form VID:PID:Flags where VID and PID are Vendor 8208 and Product ID values (4-digit hex numbers) and 8209 Flags is a set of characters, each corresponding 8210 to a common usb-storage quirk flag as follows: 8211 a = SANE_SENSE (collect more than 18 bytes 8212 of sense data, not on uas); 8213 b = BAD_SENSE (don't collect more than 18 8214 bytes of sense data, not on uas); 8215 c = FIX_CAPACITY (decrease the reported 8216 device capacity by one sector); 8217 d = NO_READ_DISC_INFO (don't use 8218 READ_DISC_INFO command, not on uas); 8219 e = NO_READ_CAPACITY_16 (don't use 8220 READ_CAPACITY_16 command); 8221 f = NO_REPORT_OPCODES (don't use report opcodes 8222 command, uas only); 8223 g = MAX_SECTORS_240 (don't transfer more than 8224 240 sectors at a time, uas only); 8225 h = CAPACITY_HEURISTICS (decrease the 8226 reported device capacity by one 8227 sector if the number is odd); 8228 i = IGNORE_DEVICE (don't bind to this 8229 device); 8230 j = NO_REPORT_LUNS (don't use report luns 8231 command, uas only); 8232 k = NO_SAME (do not use WRITE_SAME, uas only) 8233 l = NOT_LOCKABLE (don't try to lock and 8234 unlock ejectable media, not on uas); 8235 m = MAX_SECTORS_64 (don't transfer more 8236 than 64 sectors = 32 KB at a time, 8237 not on uas); 8238 n = INITIAL_READ10 (force a retry of the 8239 initial READ(10) command, not on uas); 8240 o = CAPACITY_OK (accept the capacity 8241 reported by the device, not on uas); 8242 p = WRITE_CACHE (the device cache is ON 8243 by default, not on uas); 8244 r = IGNORE_RESIDUE (the device reports 8245 bogus residue values, not on uas); 8246 s = SINGLE_LUN (the device has only one 8247 Logical Unit); 8248 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8249 commands, uas only); 8250 u = IGNORE_UAS (don't bind to the uas driver); 8251 w = NO_WP_DETECT (don't test whether the 8252 medium is write-protected). 8253 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8254 even if the device claims no cache, 8255 not on uas) 8256 Example: quirks=0419:aaf5:rl,0421:0433:rc 8257 8258 user_debug= [KNL,ARM] 8259 Format: <int> 8260 See arch/arm/Kconfig.debug help text. 8261 1 - undefined instruction events 8262 2 - system calls 8263 4 - invalid data aborts 8264 8 - SIGSEGV faults 8265 16 - SIGBUS faults 8266 Example: user_debug=31 8267 8268 vdso= [X86,SH,SPARC] 8269 On X86_32, this is an alias for vdso32=. Otherwise: 8270 8271 vdso=1: enable VDSO (the default) 8272 vdso=0: disable VDSO mapping 8273 8274 vdso32= [X86] Control the 32-bit vDSO 8275 vdso32=1: enable 32-bit VDSO 8276 vdso32=0 or vdso32=2: disable 32-bit VDSO 8277 8278 See the help text for CONFIG_COMPAT_VDSO for more 8279 details. If CONFIG_COMPAT_VDSO is set, the default is 8280 vdso32=0; otherwise, the default is vdso32=1. 8281 8282 For compatibility with older kernels, vdso32=2 is an 8283 alias for vdso32=0. 8284 8285 Try vdso32=0 if you encounter an error that says: 8286 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8287 8288 video= [FB,EARLY] Frame buffer configuration 8289 See Documentation/fb/modedb.rst. 8290 8291 video.brightness_switch_enabled= [ACPI] 8292 Format: [0|1] 8293 If set to 1, on receiving an ACPI notify event 8294 generated by hotkey, video driver will adjust brightness 8295 level and then send out the event to user space through 8296 the allocated input device. If set to 0, video driver 8297 will only send out the event without touching backlight 8298 brightness level. 8299 default: 1 8300 8301 virtio_mmio.device= 8302 [VMMIO] Memory mapped virtio (platform) device. 8303 8304 <size>@<baseaddr>:<irq>[:<id>] 8305 where: 8306 <size> := size (can use standard suffixes 8307 like K, M and G) 8308 <baseaddr> := physical base address 8309 <irq> := interrupt number (as passed to 8310 request_irq()) 8311 <id> := (optional) platform device id 8312 example: 8313 virtio_mmio.device=1K@0x100b0000:48:7 8314 8315 Can be used multiple times for multiple devices. 8316 8317 vga= [BOOT,X86-32] Select a particular video mode 8318 See Documentation/arch/x86/boot.rst and 8319 Documentation/admin-guide/svga.rst. 8320 Use vga=ask for menu. 8321 This is actually a boot loader parameter; the value is 8322 passed to the kernel using a special protocol. 8323 8324 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8325 May slow down system boot speed, especially when 8326 enabled on systems with a large amount of memory. 8327 All options are enabled by default, and this 8328 interface is meant to allow for selectively 8329 enabling or disabling specific virtual memory 8330 debugging features. 8331 8332 Available options are: 8333 P Enable page structure init time poisoning 8334 - Disable all of the above options 8335 8336 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8337 exact size of <nn>. This can be used to increase 8338 the minimum size (128MB on x86, arm32 platforms). 8339 It can also be used to decrease the size and leave more room 8340 for directly mapped kernel RAM. Note that this parameter does 8341 not exist on many other platforms (including arm64, alpha, 8342 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8343 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8344 8345 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8346 Sets the memory size reserved for contiguous memory 8347 allocations for the vmcp device driver. 8348 8349 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8350 Format: <command> 8351 8352 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8353 Format: <command> 8354 8355 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8356 Format: <command> 8357 8358 vmscape= [X86] Controls mitigation for VMscape attacks. 8359 VMscape attacks can leak information from a userspace 8360 hypervisor to a guest via speculative side-channels. 8361 8362 off - disable the mitigation 8363 ibpb - use Indirect Branch Prediction Barrier 8364 (IBPB) mitigation (default) 8365 force - force vulnerability detection even on 8366 unaffected processors 8367 8368 vsyscall= [X86-64,EARLY] 8369 Controls the behavior of vsyscalls (i.e. calls to 8370 fixed addresses of 0xffffffffff600x00 from legacy 8371 code). Most statically-linked binaries and older 8372 versions of glibc use these calls. Because these 8373 functions are at fixed addresses, they make nice 8374 targets for exploits that can control RIP. 8375 8376 emulate Vsyscalls turn into traps and are emulated 8377 reasonably safely. The vsyscall page is 8378 readable. This disables the Linear 8379 Address Space Separation (LASS) security 8380 feature and makes the system less secure. 8381 8382 xonly [default] Vsyscalls turn into traps and are 8383 emulated reasonably safely. The vsyscall 8384 page is not readable. 8385 8386 none Vsyscalls don't work at all. This makes 8387 them quite hard to use for exploits but 8388 might break your system. 8389 8390 vt.color= [VT] Default text color. 8391 Format: 0xYX, X = foreground, Y = background. 8392 Default: 0x07 = light gray on black. 8393 8394 vt.cur_default= [VT] Default cursor shape. 8395 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8396 the parameters of the <Esc>[?A;B;Cc escape sequence; 8397 see vga-softcursor.rst. Default: 2 = underline. 8398 8399 vt.default_blu= [VT] 8400 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8401 Change the default blue palette of the console. 8402 This is a 16-member array composed of values 8403 ranging from 0-255. 8404 8405 vt.default_grn= [VT] 8406 Format: <green0>,<green1>,<green2>,...,<green15> 8407 Change the default green palette of the console. 8408 This is a 16-member array composed of values 8409 ranging from 0-255. 8410 8411 vt.default_red= [VT] 8412 Format: <red0>,<red1>,<red2>,...,<red15> 8413 Change the default red palette of the console. 8414 This is a 16-member array composed of values 8415 ranging from 0-255. 8416 8417 vt.default_utf8= 8418 [VT] 8419 Format=<0|1> 8420 Set system-wide default UTF-8 mode for all tty's. 8421 Default is 1, i.e. UTF-8 mode is enabled for all 8422 newly opened terminals. 8423 8424 vt.global_cursor_default= 8425 [VT] 8426 Format=<-1|0|1> 8427 Set system-wide default for whether a cursor 8428 is shown on new VTs. Default is -1, 8429 i.e. cursors will be created by default unless 8430 overridden by individual drivers. 0 will hide 8431 cursors, 1 will display them. 8432 8433 vt.italic= [VT] Default color for italic text; 0-15. 8434 Default: 2 = green. 8435 8436 vt.underline= [VT] Default color for underlined text; 0-15. 8437 Default: 3 = cyan. 8438 8439 watchdog timers [HW,WDT] For information on watchdog timers, 8440 see Documentation/watchdog/watchdog-parameters.rst 8441 or other driver-specific files in the 8442 Documentation/watchdog/ directory. 8443 8444 watchdog_thresh= 8445 [KNL] 8446 Set the hard lockup detector stall duration 8447 threshold in seconds. The soft lockup detector 8448 threshold is set to twice the value. A value of 0 8449 disables both lockup detectors. Default is 10 8450 seconds. 8451 8452 workqueue.unbound_cpus= 8453 [KNL,SMP] Specify to constrain one or some CPUs 8454 to use in unbound workqueues. 8455 Format: <cpu-list> 8456 By default, all online CPUs are available for 8457 unbound workqueues. 8458 8459 workqueue.watchdog_thresh= 8460 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8461 warn stall conditions and dump internal state to 8462 help debugging. 0 disables workqueue stall 8463 detection; otherwise, it's the stall threshold 8464 duration in seconds. The default value is 30 and 8465 it can be updated at runtime by writing to the 8466 corresponding sysfs file. 8467 8468 workqueue.panic_on_stall=<uint> 8469 Panic when workqueue stall is detected by 8470 CONFIG_WQ_WATCHDOG. It sets the number times of the 8471 stall to trigger panic. 8472 8473 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8474 which is 0 (disabled) if not configured. 8475 8476 workqueue.panic_on_stall_time=<uint> 8477 Panic when a workqueue stall has been continuous for 8478 the specified number of seconds. Unlike panic_on_stall 8479 which counts accumulated stall events, this triggers 8480 based on the duration of a single continuous stall. 8481 8482 The default is 0, which disables the time-based panic. 8483 8484 workqueue.cpu_intensive_thresh_us= 8485 Per-cpu work items which run for longer than this 8486 threshold are automatically considered CPU intensive 8487 and excluded from concurrency management to prevent 8488 them from noticeably delaying other per-cpu work 8489 items. Default is 10000 (10ms). 8490 8491 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8492 will report the work functions which violate this 8493 threshold repeatedly. They are likely good 8494 candidates for using WQ_UNBOUND workqueues instead. 8495 8496 workqueue.cpu_intensive_warning_thresh=<uint> 8497 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8498 will report the work functions which violate the 8499 intensive_threshold_us repeatedly. In order to prevent 8500 spurious warnings, start printing only after a work 8501 function has violated this threshold number of times. 8502 8503 The default is 4 times. 0 disables the warning. 8504 8505 workqueue.power_efficient 8506 Per-cpu workqueues are generally preferred because 8507 they show better performance thanks to cache 8508 locality; unfortunately, per-cpu workqueues tend to 8509 be more power hungry than unbound workqueues. 8510 8511 Enabling this makes the per-cpu workqueues which 8512 were observed to contribute significantly to power 8513 consumption unbound, leading to measurably lower 8514 power usage at the cost of small performance 8515 overhead. 8516 8517 The default value of this parameter is determined by 8518 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8519 8520 workqueue.default_affinity_scope= 8521 Select the default affinity scope to use for unbound 8522 workqueues. Can be one of "cpu", "smt", "cache", 8523 "cache_shard", "numa" and "system". Default is 8524 "cache_shard". For more 8525 information, see the Affinity Scopes section in 8526 Documentation/core-api/workqueue.rst. 8527 8528 This can be changed after boot by writing to the 8529 matching /sys/module/workqueue/parameters file. All 8530 workqueues with the "default" affinity scope will be 8531 updated accordingly. 8532 8533 workqueue.debug_force_rr_cpu 8534 Workqueue used to implicitly guarantee that work 8535 items queued without explicit CPU specified are put 8536 on the local CPU. This guarantee is no longer true 8537 and while local CPU is still preferred work items 8538 may be put on foreign CPUs. This debug option 8539 forces round-robin CPU selection to flush out 8540 usages which depend on the now broken guarantee. 8541 When enabled, memory and cache locality will be 8542 impacted. 8543 8544 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8545 Type) of ioremap_wc(). 8546 8547 on - Enable writecombine, use WUC for ioremap_wc() 8548 off - Disable writecombine, use SUC for ioremap_wc() 8549 8550 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8551 default x2apic cluster mode on platforms 8552 supporting x2apic. 8553 8554 xen_512gb_limit [KNL,X86-64,XEN] 8555 Restricts the kernel running paravirtualized under Xen 8556 to use only up to 512 GB of RAM. The reason to do so is 8557 crash analysis tools and Xen tools for doing domain 8558 save/restore/migration must be enabled to handle larger 8559 domains. 8560 8561 xen_console_io [XEN,EARLY] 8562 Boolean option to enable/disable the usage of the Xen 8563 console_io hypercalls to read and write to the console. 8564 Mostly useful for debugging and development. 8565 8566 xen_emul_unplug= [HW,X86,XEN,EARLY] 8567 Unplug Xen emulated devices 8568 Format: [unplug0,][unplug1] 8569 ide-disks -- unplug primary master IDE devices 8570 aux-ide-disks -- unplug non-primary-master IDE devices 8571 nics -- unplug network devices 8572 all -- unplug all emulated devices (NICs and IDE disks) 8573 unnecessary -- unplugging emulated devices is 8574 unnecessary even if the host did not respond to 8575 the unplug protocol 8576 never -- do not unplug even if version check succeeds 8577 8578 xen_legacy_crash [X86,XEN,EARLY] 8579 Crash from Xen panic notifier, without executing late 8580 panic() code such as dumping handler. 8581 8582 xen_mc_debug [X86,XEN,EARLY] 8583 Enable multicall debugging when running as a Xen PV guest. 8584 Enabling this feature will reduce performance a little 8585 bit, so it should only be enabled for obtaining extended 8586 debug data in case of multicall errors. 8587 8588 xen_msr_safe= [X86,XEN,EARLY] 8589 Format: <bool> 8590 Select whether to always use non-faulting (safe) MSR 8591 access functions when running as Xen PV guest. The 8592 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8593 8594 xen_nopv [X86] 8595 Disables the PV optimizations forcing the HVM guest to 8596 run as generic HVM guest with no PV drivers. 8597 This option is obsoleted by the "nopv" option, which 8598 has equivalent effect for XEN platform. 8599 8600 xen_no_vector_callback 8601 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8602 event channel interrupts. 8603 8604 xen_scrub_pages= [XEN] 8605 Boolean option to control scrubbing pages before giving them back 8606 to Xen, for use by other domains. Can be also changed at runtime 8607 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8608 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8609 8610 xen_timer_slop= [X86-64,XEN,EARLY] 8611 Set the timer slop (in nanoseconds) for the virtual Xen 8612 timers (default is 100000). This adjusts the minimum 8613 delta of virtualized Xen timers, where lower values 8614 improve timer resolution at the expense of processing 8615 more timer interrupts. 8616 8617 xen.balloon_boot_timeout= [XEN] 8618 The time (in seconds) to wait before giving up to boot 8619 in case initial ballooning fails to free enough memory. 8620 Applies only when running as HVM or PVH guest and 8621 started with less memory configured than allowed at 8622 max. Default is 180. 8623 8624 xen.event_eoi_delay= [XEN] 8625 How long to delay EOI handling in case of event 8626 storms (jiffies). Default is 10. 8627 8628 xen.event_loop_timeout= [XEN] 8629 After which time (jiffies) the event handling loop 8630 should start to delay EOI handling. Default is 2. 8631 8632 xen.fifo_events= [XEN] 8633 Boolean parameter to disable using fifo event handling 8634 even if available. Normally fifo event handling is 8635 preferred over the 2-level event handling, as it is 8636 fairer and the number of possible event channels is 8637 much higher. Default is on (use fifo events). 8638 8639 xirc2ps_cs= [NET,PCMCIA] 8640 Format: 8641 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8642 8643 xive= [PPC] 8644 By default on POWER9 and above, the kernel will 8645 natively use the XIVE interrupt controller. This option 8646 allows the fallback firmware mode to be used: 8647 8648 off Fallback to firmware control of XIVE interrupt 8649 controller on both pseries and powernv 8650 platforms. Only useful on POWER9 and above. 8651 8652 xive.store-eoi=off [PPC] 8653 By default on POWER10 and above, the kernel will use 8654 stores for EOI handling when the XIVE interrupt mode 8655 is active. This option allows the XIVE driver to use 8656 loads instead, as on POWER9. 8657 8658 xhci-hcd.quirks [USB,KNL] 8659 A hex value specifying bitmask with supplemental xhci 8660 host controller quirks. Meaning of each bit can be 8661 consulted in header drivers/usb/host/xhci.h. 8662 8663 xmon [PPC,EARLY] 8664 Format: { early | on | rw | ro | off } 8665 Controls if xmon debugger is enabled. Default is off. 8666 Passing only "xmon" is equivalent to "xmon=early". 8667 early Call xmon as early as possible on boot; xmon 8668 debugger is called from setup_arch(). 8669 on xmon debugger hooks will be installed so xmon 8670 is only called on a kernel crash. Default mode, 8671 i.e. either "ro" or "rw" mode, is controlled 8672 with CONFIG_XMON_DEFAULT_RO_MODE. 8673 rw xmon debugger hooks will be installed so xmon 8674 is called only on a kernel crash, mode is write, 8675 meaning SPR registers, memory and, other data 8676 can be written using xmon commands. 8677 ro same as "rw" option above but SPR registers, 8678 memory, and other data can't be written using 8679 xmon commands. 8680 off xmon is disabled. 8681