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 AX25 Appropriate AX.25 support is enabled. 10 CLK Common clock infrastructure is enabled. 11 CMA Contiguous Memory Area support is enabled. 12 DRM Direct Rendering Management support is enabled. 13 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 14 EARLY Parameter processed too early to be embedded in initrd. 15 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 16 EFI EFI Partitioning (GPT) is enabled 17 EVM Extended Verification Module 18 FB The frame buffer device is enabled. 19 FTRACE Function tracing enabled. 20 GCOV GCOV profiling is enabled. 21 HIBERNATION HIBERNATION is enabled. 22 HW Appropriate hardware is enabled. 23 HYPER_V HYPERV support is enabled. 24 IMA Integrity measurement architecture is enabled. 25 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 26 IPV6 IPv6 support is enabled. 27 ISAPNP ISA PnP code is enabled. 28 ISDN Appropriate ISDN support is enabled. 29 ISOL CPU Isolation is enabled. 30 JOY Appropriate joystick support is enabled. 31 KGDB Kernel debugger support is enabled. 32 KVM Kernel Virtual Machine support is enabled. 33 LIBATA Libata driver is enabled 34 LOONGARCH LoongArch architecture is enabled. 35 LOOP Loopback device support is enabled. 36 LP Printer support is enabled. 37 M68k M68k architecture is enabled. 38 These options have more detailed description inside of 39 Documentation/arch/m68k/kernel-options.rst. 40 MDA MDA console support is enabled. 41 MIPS MIPS architecture is enabled. 42 MOUSE Appropriate mouse support is enabled. 43 MSI Message Signaled Interrupts (PCI). 44 MTD MTD (Memory Technology Device) support is enabled. 45 NET Appropriate network support is enabled. 46 NFS Appropriate NFS support is enabled. 47 NUMA NUMA support is enabled. 48 OF Devicetree is enabled. 49 PARISC The PA-RISC architecture is enabled. 50 PCI PCI bus support is enabled. 51 PCIE PCI Express support is enabled. 52 PCMCIA The PCMCIA subsystem is enabled. 53 PNP Plug & Play support is enabled. 54 PPC PowerPC architecture is enabled. 55 PPT Parallel port support is enabled. 56 PS2 Appropriate PS/2 support is enabled. 57 PV_OPS A paravirtualized kernel is enabled. 58 RAM RAM disk support is enabled. 59 RDT Intel Resource Director Technology. 60 RISCV RISCV architecture is enabled. 61 S390 S390 architecture is enabled. 62 SCSI Appropriate SCSI support is enabled. 63 A lot of drivers have their options described inside 64 the Documentation/scsi/ sub-directory. 65 SDW SoundWire support is enabled. 66 SECURITY Different security models are enabled. 67 SELINUX SELinux support is enabled. 68 SERIAL Serial support is enabled. 69 SH SuperH architecture is enabled. 70 SMP The kernel is an SMP kernel. 71 SPARC Sparc architecture is enabled. 72 SUSPEND System suspend states are enabled. 73 SWSUSP Software suspend (hibernation) is enabled. 74 TPM TPM drivers are enabled. 75 UMS USB Mass Storage support is enabled. 76 USB USB support is enabled. 77 USBHID USB Human Interface Device support is enabled. 78 V4L Video For Linux support is enabled. 79 VGA The VGA console has been enabled. 80 VMMIO Driver for memory mapped virtio devices is enabled. 81 VT Virtual terminal support is enabled. 82 WDT Watchdog support is enabled. 83 X86-32 X86-32, aka i386 architecture is enabled. 84 X86-64 X86-64 architecture is enabled. 85 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 86 X86_UV SGI UV support is enabled. 87 XEN Xen support is enabled 88 XTENSA xtensa architecture is enabled. 89 90In addition, the following text indicates that the option 91 92 BOOT Is a boot loader parameter. 93 BUGS= Relates to possible processor bugs on the said processor. 94 KNL Is a kernel start-up parameter. 95 96 97Kernel parameters 98 99 accept_memory= [MM] 100 Format: { eager | lazy } 101 default: lazy 102 By default, unaccepted memory is accepted lazily to 103 avoid prolonged boot times. The lazy option will add 104 some runtime overhead until all memory is eventually 105 accepted. In most cases the overhead is negligible. 106 For some workloads or for debugging purposes 107 accept_memory=eager can be used to accept all memory 108 at once during boot. 109 110 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 111 Advanced Configuration and Power Interface 112 Format: { force | on | off | strict | noirq | rsdt | 113 copy_dsdt | nospcr } 114 force -- enable ACPI if default was off 115 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 116 off -- disable ACPI if default was on 117 noirq -- do not use ACPI for IRQ routing 118 strict -- Be less tolerant of platforms that are not 119 strictly ACPI specification compliant. 120 rsdt -- prefer RSDT over (default) XSDT 121 copy_dsdt -- copy DSDT to memory 122 nocmcff -- Disable firmware first mode for corrected 123 errors. This disables parsing the HEST CMC error 124 source to check if firmware has set the FF flag. This 125 may result in duplicate corrected error reports. 126 nospcr -- disable console in ACPI SPCR table as 127 default _serial_ console on ARM64 128 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 129 "acpi=nospcr" are available 130 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 131 are available 132 133 See also Documentation/power/runtime_pm.rst, pci=noacpi 134 135 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 136 Format: <int> 137 2: use 2nd APIC table, if available 138 1,0: use 1st APIC table 139 default: 0 140 141 acpi_backlight= [HW,ACPI] 142 { vendor | video | native | none } 143 If set to vendor, prefer vendor-specific driver 144 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 145 of the ACPI video.ko driver. 146 If set to video, use the ACPI video.ko driver. 147 If set to native, use the device's native backlight mode. 148 If set to none, disable the ACPI backlight interface. 149 150 acpi_force_32bit_fadt_addr [ACPI,EARLY] 151 force FADT to use 32 bit addresses rather than the 152 64 bit X_* addresses. Some firmware have broken 64 153 bit addresses for force ACPI ignore these and use 154 the older legacy 32 bit addresses. 155 156 acpica_no_return_repair [HW, ACPI] 157 Disable AML predefined validation mechanism 158 This mechanism can repair the evaluation result to make 159 the return objects more ACPI specification compliant. 160 This option is useful for developers to identify the 161 root cause of an AML interpreter issue when the issue 162 has something to do with the repair mechanism. 163 164 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 165 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 166 Format: <int> 167 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 168 debug output. Bits in debug_layer correspond to a 169 _COMPONENT in an ACPI source file, e.g., 170 #define _COMPONENT ACPI_EVENTS 171 Bits in debug_level correspond to a level in 172 ACPI_DEBUG_PRINT statements, e.g., 173 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 174 The debug_level mask defaults to "info". See 175 Documentation/firmware-guide/acpi/debug.rst for more information about 176 debug layers and levels. 177 178 Enable processor driver info messages: 179 acpi.debug_layer=0x20000000 180 Enable AML "Debug" output, i.e., stores to the Debug 181 object while interpreting AML: 182 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 183 Enable all messages related to ACPI hardware: 184 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 185 186 Some values produce so much output that the system is 187 unusable. The "log_buf_len" parameter may be useful 188 if you need to capture more output. 189 190 acpi_enforce_resources= [ACPI] 191 { strict | lax | no } 192 Check for resource conflicts between native drivers 193 and ACPI OperationRegions (SystemIO and SystemMemory 194 only). IO ports and memory declared in ACPI might be 195 used by the ACPI subsystem in arbitrary AML code and 196 can interfere with legacy drivers. 197 strict (default): access to resources claimed by ACPI 198 is denied; legacy drivers trying to access reserved 199 resources will fail to bind to device using them. 200 lax: access to resources claimed by ACPI is allowed; 201 legacy drivers trying to access reserved resources 202 will bind successfully but a warning message is logged. 203 no: ACPI OperationRegions are not marked as reserved, 204 no further checks are performed. 205 206 acpi_force_table_verification [HW,ACPI,EARLY] 207 Enable table checksum verification during early stage. 208 By default, this is disabled due to x86 early mapping 209 size limitation. 210 211 acpi_irq_balance [HW,ACPI] 212 ACPI will balance active IRQs 213 default in APIC mode 214 215 acpi_irq_nobalance [HW,ACPI] 216 ACPI will not move active IRQs (default) 217 default in PIC mode 218 219 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 220 Format: <irq>,<irq>... 221 222 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 223 use by PCI 224 Format: <irq>,<irq>... 225 226 acpi_mask_gpe= [HW,ACPI] 227 Due to the existence of _Lxx/_Exx, some GPEs triggered 228 by unsupported hardware/firmware features can result in 229 GPE floodings that cannot be automatically disabled by 230 the GPE dispatcher. 231 This facility can be used to prevent such uncontrolled 232 GPE floodings. 233 Format: <byte> or <bitmap-list> 234 235 acpi_no_auto_serialize [HW,ACPI] 236 Disable auto-serialization of AML methods 237 AML control methods that contain the opcodes to create 238 named objects will be marked as "Serialized" by the 239 auto-serialization feature. 240 This feature is enabled by default. 241 This option allows to turn off the feature. 242 243 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 244 kernels. 245 246 acpi_no_static_ssdt [HW,ACPI,EARLY] 247 Disable installation of static SSDTs at early boot time 248 By default, SSDTs contained in the RSDT/XSDT will be 249 installed automatically and they will appear under 250 /sys/firmware/acpi/tables. 251 This option turns off this feature. 252 Note that specifying this option does not affect 253 dynamic table installation which will install SSDT 254 tables to /sys/firmware/acpi/tables/dynamic. 255 256 acpi_no_watchdog [HW,ACPI,WDT] 257 Ignore the ACPI-based watchdog interface (WDAT) and let 258 a native driver control the watchdog device instead. 259 260 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 261 Pass the RSDP address to the kernel, mostly used 262 on machines running EFI runtime service to boot the 263 second kernel for kdump. 264 265 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 266 Format: To spoof as Windows 98: ="Microsoft Windows" 267 268 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 269 of 2 which is mandated by ACPI 6) as the supported ACPI 270 specification revision (when using this switch, it may 271 be necessary to carry out a cold reboot _twice_ in a 272 row to make it take effect on the platform firmware). 273 274 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 275 acpi_osi="string1" # add string1 276 acpi_osi="!string2" # remove string2 277 acpi_osi=!* # remove all strings 278 acpi_osi=! # disable all built-in OS vendor 279 strings 280 acpi_osi=!! # enable all built-in OS vendor 281 strings 282 acpi_osi= # disable all strings 283 284 'acpi_osi=!' can be used in combination with single or 285 multiple 'acpi_osi="string1"' to support specific OS 286 vendor string(s). Note that such command can only 287 affect the default state of the OS vendor strings, thus 288 it cannot affect the default state of the feature group 289 strings and the current state of the OS vendor strings, 290 specifying it multiple times through kernel command line 291 is meaningless. This command is useful when one do not 292 care about the state of the feature group strings which 293 should be controlled by the OSPM. 294 Examples: 295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 297 can make '_OSI("Windows 2000")' TRUE. 298 299 'acpi_osi=' cannot be used in combination with other 300 'acpi_osi=' command lines, the _OSI method will not 301 exist in the ACPI namespace. NOTE that such command can 302 only affect the _OSI support state, thus specifying it 303 multiple times through kernel command line is also 304 meaningless. 305 Examples: 306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 307 FALSE. 308 309 'acpi_osi=!*' can be used in combination with single or 310 multiple 'acpi_osi="string1"' to support specific 311 string(s). Note that such command can affect the 312 current state of both the OS vendor strings and the 313 feature group strings, thus specifying it multiple times 314 through kernel command line is meaningful. But it may 315 still not able to affect the final state of a string if 316 there are quirks related to this string. This command 317 is useful when one want to control the state of the 318 feature group strings to debug BIOS issues related to 319 the OSPM features. 320 Examples: 321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 322 '_OSI("Module Device")' FALSE. 323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 324 '_OSI("Module Device")' TRUE. 325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 326 equivalent to 327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 328 and 329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 330 they all will make '_OSI("Windows 2000")' TRUE. 331 332 acpi_pm_good [X86] 333 Override the pmtimer bug detection: force the kernel 334 to assume that this machine's pmtimer latches its value 335 and always returns good values. 336 337 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 338 Format: { level | edge | high | low } 339 340 acpi_skip_timer_override [HW,ACPI,EARLY] 341 Recognize and ignore IRQ0/pin2 Interrupt Override. 342 For broken nForce2 BIOS resulting in XT-PIC timer. 343 344 acpi_sleep= [HW,ACPI] Sleep options 345 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 346 s4_nohwsig, old_ordering, nonvs, 347 sci_force_enable, nobl } 348 See Documentation/power/video.rst for information on 349 s3_bios and s3_mode. 350 s3_beep is for debugging; it makes the PC's speaker beep 351 as soon as the kernel's real-mode entry point is called. 352 s4_hwsig causes the kernel to check the ACPI hardware 353 signature during resume from hibernation, and gracefully 354 refuse to resume if it has changed. This complies with 355 the ACPI specification but not with reality, since 356 Windows does not do this and many laptops do change it 357 on docking. So the default behaviour is to allow resume 358 and simply warn when the signature changes, unless the 359 s4_hwsig option is enabled. 360 s4_nohwsig prevents ACPI hardware signature from being 361 used (or even warned about) during resume. 362 old_ordering causes the ACPI 1.0 ordering of the _PTS 363 control method, with respect to putting devices into 364 low power states, to be enforced (the ACPI 2.0 ordering 365 of _PTS is used by default). 366 nonvs prevents the kernel from saving/restoring the 367 ACPI NVS memory during suspend/hibernation and resume. 368 sci_force_enable causes the kernel to set SCI_EN directly 369 on resume from S1/S3 (which is against the ACPI spec, 370 but some broken systems don't work without it). 371 nobl causes the internal blacklist of systems known to 372 behave incorrectly in some ways with respect to system 373 suspend and resume to be ignored (use wisely). 374 375 acpi_use_timer_override [HW,ACPI,EARLY] 376 Use timer override. For some broken Nvidia NF5 boards 377 that require a timer override, but don't have HPET 378 379 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 380 kernel's map of available physical RAM. 381 382 agp= [AGP] 383 { off | try_unsupported } 384 off: disable AGP support 385 try_unsupported: try to drive unsupported chipsets 386 (may crash computer or cause data corruption) 387 388 ALSA [HW,ALSA] 389 See Documentation/sound/alsa-configuration.rst 390 391 alignment= [KNL,ARM] 392 Allow the default userspace alignment fault handler 393 behaviour to be specified. Bit 0 enables warnings, 394 bit 1 enables fixups, and bit 2 sends a segfault. 395 396 align_va_addr= [X86-64] 397 Align virtual addresses by clearing slice [14:12] when 398 allocating a VMA at process creation time. This option 399 gives you up to 3% performance improvement on AMD F15h 400 machines (where it is enabled by default) for a 401 CPU-intensive style benchmark, and it can vary highly in 402 a microbenchmark depending on workload and compiler. 403 404 32: only for 32-bit processes 405 64: only for 64-bit processes 406 on: enable for both 32- and 64-bit processes 407 off: disable for both 32- and 64-bit processes 408 409 alloc_snapshot [FTRACE] 410 Allocate the ftrace snapshot buffer on boot up when the 411 main buffer is allocated. This is handy if debugging 412 and you need to use tracing_snapshot() on boot up, and 413 do not want to use tracing_snapshot_alloc() as it needs 414 to be done where GFP_KERNEL allocations are allowed. 415 416 allow_mismatched_32bit_el0 [ARM64,EARLY] 417 Allow execve() of 32-bit applications and setting of the 418 PER_LINUX32 personality on systems where only a strict 419 subset of the CPUs support 32-bit EL0. When this 420 parameter is present, the set of CPUs supporting 32-bit 421 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 422 and hot-unplug operations may be restricted. 423 424 See Documentation/arch/arm64/asymmetric-32bit.rst for more 425 information. 426 427 amd_iommu= [HW,X86-64] 428 Pass parameters to the AMD IOMMU driver in the system. 429 Possible values are: 430 fullflush - Deprecated, equivalent to iommu.strict=1 431 off - do not initialize any AMD IOMMU found in 432 the system 433 force_isolation - Force device isolation for all 434 devices. The IOMMU driver is not 435 allowed anymore to lift isolation 436 requirements as needed. This option 437 does not override iommu=pt 438 force_enable - Force enable the IOMMU on platforms known 439 to be buggy with IOMMU enabled. Use this 440 option with care. 441 pgtbl_v1 - Use v1 page table for DMA-API (Default). 442 pgtbl_v2 - Use v2 page table for DMA-API. 443 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 444 nohugepages - Limit page-sizes used for v1 page-tables 445 to 4 KiB. 446 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 447 to 4KiB/2Mib/1GiB. 448 449 450 amd_iommu_dump= [HW,X86-64] 451 Enable AMD IOMMU driver option to dump the ACPI table 452 for AMD IOMMU. With this option enabled, AMD IOMMU 453 driver will print ACPI tables for AMD IOMMU during 454 IOMMU initialization. 455 456 amd_iommu_intr= [HW,X86-64] 457 Specifies one of the following AMD IOMMU interrupt 458 remapping modes: 459 legacy - Use legacy interrupt remapping mode. 460 vapic - Use virtual APIC mode, which allows IOMMU 461 to inject interrupts directly into guest. 462 This mode requires kvm-amd.avic=1. 463 (Default when IOMMU HW support is present.) 464 465 amd_pstate= [X86,EARLY] 466 disable 467 Do not enable amd_pstate as the default 468 scaling driver for the supported processors 469 passive 470 Use amd_pstate with passive mode as a scaling driver. 471 In this mode autonomous selection is disabled. 472 Driver requests a desired performance level and platform 473 tries to match the same performance level if it is 474 satisfied by guaranteed performance level. 475 active 476 Use amd_pstate_epp driver instance as the scaling driver, 477 driver provides a hint to the hardware if software wants 478 to bias toward performance (0x0) or energy efficiency (0xff) 479 to the CPPC firmware. then CPPC power algorithm will 480 calculate the runtime workload and adjust the realtime cores 481 frequency. 482 guided 483 Activate guided autonomous mode. Driver requests minimum and 484 maximum performance level and the platform autonomously 485 selects a performance level in this range and appropriate 486 to the current workload. 487 488 amd_prefcore= 489 [X86] 490 disable 491 Disable amd-pstate preferred core. 492 493 amijoy.map= [HW,JOY] Amiga joystick support 494 Map of devices attached to JOY0DAT and JOY1DAT 495 Format: <a>,<b> 496 See also Documentation/input/joydev/joystick.rst 497 498 analog.map= [HW,JOY] Analog joystick and gamepad support 499 Specifies type or capabilities of an analog joystick 500 connected to one of 16 gameports 501 Format: <type1>,<type2>,..<type16> 502 503 apc= [HW,SPARC] 504 Power management functions (SPARCstation-4/5 + deriv.) 505 Format: noidle 506 Disable APC CPU standby support. SPARCstation-Fox does 507 not play well with APC CPU idle - disable it if you have 508 APC and your system crashes randomly. 509 510 apic [APIC,X86-64] Use IO-APIC. Default. 511 512 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 513 Change the output verbosity while booting 514 Format: { quiet (default) | verbose | debug } 515 Change the amount of debugging information output 516 when initialising the APIC and IO-APIC components. 517 518 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 519 Format: { bsp (default) | all | none } 520 bsp: External NMI is delivered only to CPU 0 521 all: External NMIs are broadcast to all CPUs as a 522 backup of CPU 0 523 none: External NMI is masked for all CPUs. This is 524 useful so that a dump capture kernel won't be 525 shot down by NMI 526 527 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 528 apicmaintimer. Useful when your PIT timer is totally 529 broken. 530 531 autoconf= [IPV6] 532 See Documentation/networking/ipv6.rst. 533 534 apm= [APM] Advanced Power Management 535 See header of arch/x86/kernel/apm_32.c. 536 537 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 538 Format: { "0" | "1" } 539 See security/apparmor/Kconfig help text 540 0 -- disable. 541 1 -- enable. 542 Default value is set via kernel config option. 543 544 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 545 Format: <io>,<irq>,<nodeID> 546 547 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 548 32 bit applications. 549 550 arm64.nobti [ARM64] Unconditionally disable Branch Target 551 Identification support 552 553 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 554 support 555 556 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 557 Set instructions support 558 559 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 560 Monitoring support 561 562 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 563 support 564 565 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 566 support 567 568 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 569 Extension support 570 571 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 572 Extension support 573 574 ataflop= [HW,M68k] 575 576 atarimouse= [HW,MOUSE] Atari Mouse 577 578 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 579 EzKey and similar keyboards 580 581 atkbd.reset= [HW] Reset keyboard during initialization 582 583 atkbd.set= [HW] Select keyboard code set 584 Format: <int> (2 = AT (default), 3 = PS/2) 585 586 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 587 keyboards 588 589 atkbd.softraw= [HW] Choose between synthetic and real raw mode 590 Format: <bool> (0 = real, 1 = synthetic (default)) 591 592 atkbd.softrepeat= [HW] 593 Use software keyboard repeat 594 595 audit= [KNL] Enable the audit sub-system 596 Format: { "0" | "1" | "off" | "on" } 597 0 | off - kernel audit is disabled and can not be 598 enabled until the next reboot 599 unset - kernel audit is initialized but disabled and 600 will be fully enabled by the userspace auditd. 601 1 | on - kernel audit is initialized and partially 602 enabled, storing at most audit_backlog_limit 603 messages in RAM until it is fully enabled by the 604 userspace auditd. 605 Default: unset 606 607 audit_backlog_limit= [KNL] Set the audit queue size limit. 608 Format: <int> (must be >=0) 609 Default: 64 610 611 bau= [X86_UV] Enable the BAU on SGI UV. The default 612 behavior is to disable the BAU (i.e. bau=0). 613 Format: { "0" | "1" } 614 0 - Disable the BAU. 615 1 - Enable the BAU. 616 unset - Disable the BAU. 617 618 baycom_epp= [HW,AX25] 619 Format: <io>,<mode> 620 621 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 622 Format: <io>,<mode> 623 See header of drivers/net/hamradio/baycom_par.c. 624 625 baycom_ser_fdx= [HW,AX25] 626 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 627 Format: <io>,<irq>,<mode>[,<baud>] 628 See header of drivers/net/hamradio/baycom_ser_fdx.c. 629 630 baycom_ser_hdx= [HW,AX25] 631 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 632 Format: <io>,<irq>,<mode> 633 See header of drivers/net/hamradio/baycom_ser_hdx.c. 634 635 bdev_allow_write_mounted= 636 Format: <bool> 637 Control the ability to open a mounted block device 638 for writing, i.e., allow / disallow writes that bypass 639 the FS. This was implemented as a means to prevent 640 fuzzers from crashing the kernel by overwriting the 641 metadata underneath a mounted FS without its awareness. 642 This also prevents destructive formatting of mounted 643 filesystems by naive storage tooling that don't use 644 O_EXCL. Default is Y and can be changed through the 645 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 646 647 bert_disable [ACPI] 648 Disable BERT OS support on buggy BIOSes. 649 650 bgrt_disable [ACPI,X86,EARLY] 651 Disable BGRT to avoid flickering OEM logo. 652 653 blkdevparts= Manual partition parsing of block device(s) for 654 embedded devices based on command line input. 655 See Documentation/block/cmdline-partition.rst 656 657 boot_delay= [KNL,EARLY] 658 Milliseconds to delay each printk during boot. 659 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 660 and you may also have to specify "lpj=". Boot_delay 661 values larger than 10 seconds (10000) are assumed 662 erroneous and ignored. 663 Format: integer 664 665 bootconfig [KNL,EARLY] 666 Extended command line options can be added to an initrd 667 and this will cause the kernel to look for it. 668 669 See Documentation/admin-guide/bootconfig.rst 670 671 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 672 bttv.radio= Most important insmod options are available as 673 kernel args too. 674 bttv.pll= See Documentation/admin-guide/media/bttv.rst 675 bttv.tuner= 676 677 bulk_remove=off [PPC] This parameter disables the use of the pSeries 678 firmware feature for flushing multiple hpte entries 679 at a time. 680 681 c101= [NET] Moxa C101 synchronous serial card 682 683 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 684 Sometimes CPU hardware bugs make them report the cache 685 size incorrectly. The kernel will attempt work arounds 686 to fix known problems, but for some CPUs it is not 687 possible to determine what the correct size should be. 688 This option provides an override for these situations. 689 690 carrier_timeout= 691 [NET] Specifies amount of time (in seconds) that 692 the kernel should wait for a network carrier. By default 693 it waits 120 seconds. 694 695 ca_keys= [KEYS] This parameter identifies a specific key(s) on 696 the system trusted keyring to be used for certificate 697 trust validation. 698 format: { id:<keyid> | builtin } 699 700 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 701 algorithm. Accepted values range from 0 to 7 702 inclusive. See arch/mips/include/asm/pgtable-bits.h 703 for platform specific values (SB1, Loongson3 and 704 others). 705 706 ccw_timeout_log [S390] 707 See Documentation/arch/s390/common_io.rst for details. 708 709 cfi= [X86-64] Set Control Flow Integrity checking features 710 when CONFIG_FINEIBT is enabled. 711 Format: feature[,feature...] 712 Default: auto 713 714 auto: Use FineIBT if IBT available, otherwise kCFI. 715 Under FineIBT, enable "paranoid" mode when 716 FRED is not available. 717 off: Turn off CFI checking. 718 kcfi: Use kCFI (disable FineIBT). 719 fineibt: Use FineIBT (even if IBT not available). 720 norand: Do not re-randomize CFI hashes. 721 paranoid: Add caller hash checking under FineIBT. 722 bhi: Enable register poisoning to stop speculation 723 across FineIBT. (Disabled by default.) 724 warn: Do not enforce CFI checking: warn only. 725 debug: Report CFI initialization details. 726 727 cgroup_disable= [KNL] Disable a particular controller or optional feature 728 Format: {name of the controller(s) or feature(s) to disable} 729 The effects of cgroup_disable=foo are: 730 - foo isn't auto-mounted if you mount all cgroups in 731 a single hierarchy 732 - foo isn't visible as an individually mountable 733 subsystem 734 - if foo is an optional feature then the feature is 735 disabled and corresponding cgroup files are not 736 created 737 {Currently only "memory" controller deal with this and 738 cut the overhead, others just disable the usage. So 739 only cgroup_disable=memory is actually worthy} 740 Specifying "pressure" disables per-cgroup pressure 741 stall information accounting feature 742 743 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 744 Format: { { controller | "all" | "named" } 745 [,{ controller | "all" | "named" }...] } 746 Like cgroup_disable, but only applies to cgroup v1; 747 the blacklisted controllers remain available in cgroup2. 748 "all" blacklists all controllers and "named" disables 749 named mounts. Specifying both "all" and "named" disables 750 all v1 hierarchies. 751 752 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 753 Format: { "true" | "false" } 754 /proc/cgroups lists only v1 controllers by default. 755 This compatibility option enables listing also v2 756 controllers (whose v1 code is not compiled!), so that 757 semi-legacy software can check this file to decide 758 about usage of v2 (sic) controllers. 759 760 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 761 Format: { "true" | "false" } 762 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 763 764 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 765 Format: <string> 766 nosocket -- Disable socket memory accounting. 767 nokmem -- Disable kernel memory accounting. 768 nobpf -- Disable BPF memory accounting. 769 770 check_pages= [MM,EARLY] Enable sanity checking of pages after 771 allocations / before freeing. This adds checks to catch 772 double-frees, use-after-frees, and other sources of 773 page corruption by inspecting page internals (flags, 774 mapcount/refcount, memcg_data, etc.). 775 Format: { "0" | "1" } 776 Default: 0 (1 if CONFIG_DEBUG_VM is set) 777 778 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 779 Format: { "0" | "1" } 780 See security/selinux/Kconfig help text. 781 0 -- check protection applied by kernel (includes 782 any implied execute protection). 783 1 -- check protection requested by application. 784 Default value is set via a kernel config option. 785 Value can be changed at runtime via 786 /sys/fs/selinux/checkreqprot. 787 Setting checkreqprot to 1 is deprecated. 788 789 cio_ignore= [S390] 790 See Documentation/arch/s390/common_io.rst for details. 791 792 clearcpuid=X[,X...] [X86] 793 Disable CPUID feature X for the kernel. See 794 arch/x86/include/asm/cpufeatures.h for the valid bit 795 numbers X. Note the Linux-specific bits are not necessarily 796 stable over kernel options, but the vendor-specific 797 ones should be. 798 X can also be a string as appearing in the flags: line 799 in /proc/cpuinfo which does not have the above 800 instability issue. However, not all features have names 801 in /proc/cpuinfo. 802 Note that using this option will taint your kernel. 803 Also note that user programs calling CPUID directly 804 or using the feature without checking anything 805 will still see it. This just prevents it from 806 being used by the kernel or shown in /proc/cpuinfo. 807 Also note the kernel might malfunction if you disable 808 some critical bits. 809 810 clk_ignore_unused 811 [CLK] 812 Prevents the clock framework from automatically gating 813 clocks that have not been explicitly enabled by a Linux 814 device driver but are enabled in hardware at reset or 815 by the bootloader/firmware. Note that this does not 816 force such clocks to be always-on nor does it reserve 817 those clocks in any way. This parameter is useful for 818 debug and development, but should not be needed on a 819 platform with proper driver support. For more 820 information, see Documentation/driver-api/clk.rst. 821 822 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 823 [Deprecated] 824 Forces specified clocksource (if available) to be used 825 when calculating gettimeofday(). If specified 826 clocksource is not available, it defaults to PIT. 827 Format: { pit | tsc | cyclone | pmtmr } 828 829 clocksource= Override the default clocksource 830 Format: <string> 831 Override the default clocksource and use the clocksource 832 with the name specified. 833 Some clocksource names to choose from, depending on 834 the platform: 835 [all] jiffies (this is the base, fallback clocksource) 836 [ACPI] acpi_pm 837 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 838 pxa_timer,timer3,32k_counter,timer0_1 839 [X86-32] pit,hpet,tsc; 840 scx200_hrt on Geode; cyclone on IBM x440 841 [MIPS] MIPS 842 [PARISC] cr16 843 [S390] tod 844 [SH] SuperH 845 [SPARC64] tick 846 [X86-64] hpet,tsc 847 848 clocksource.arm_arch_timer.evtstrm= 849 [ARM,ARM64,EARLY] 850 Format: <bool> 851 Enable/disable the eventstream feature of the ARM 852 architected timer so that code using WFE-based polling 853 loops can be debugged more effectively on production 854 systems. 855 856 clocksource.verify_n_cpus= [KNL] 857 Limit the number of CPUs checked for clocksources 858 marked with CLOCK_SOURCE_VERIFY_PERCPU that 859 are marked unstable due to excessive skew. 860 A negative value says to check all CPUs, while 861 zero says not to check any. Values larger than 862 nr_cpu_ids are silently truncated to nr_cpu_ids. 863 The actual CPUs are chosen randomly, with 864 no replacement if the same CPU is chosen twice. 865 866 clocksource-wdtest.holdoff= [KNL] 867 Set the time in seconds that the clocksource 868 watchdog test waits before commencing its tests. 869 Defaults to zero when built as a module and to 870 10 seconds when built into the kernel. 871 872 cma=nn[MG]@[start[MG][-end[MG]]] 873 [KNL,CMA,EARLY] 874 Sets the size of kernel global memory area for 875 contiguous memory allocations and optionally the 876 placement constraint by the physical address range of 877 memory allocations. A value of 0 disables CMA 878 altogether. For more information, see 879 kernel/dma/contiguous.c 880 881 cma_pernuma=nn[MG] 882 [KNL,CMA,EARLY] 883 Sets the size of kernel per-numa memory area for 884 contiguous memory allocations. A value of 0 disables 885 per-numa CMA altogether. And If this option is not 886 specified, the default value is 0. 887 With per-numa CMA enabled, DMA users on node nid will 888 first try to allocate buffer from the pernuma area 889 which is located in node nid, if the allocation fails, 890 they will fallback to the global default memory area. 891 892 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 893 [KNL,CMA,EARLY] 894 Sets the size of kernel numa memory area for 895 contiguous memory allocations. It will reserve CMA 896 area for the specified node. 897 898 With numa CMA enabled, DMA users on node nid will 899 first try to allocate buffer from the numa area 900 which is located in node nid, if the allocation fails, 901 they will fallback to the global default memory area. 902 903 cmo_free_hint= [PPC] Format: { yes | no } 904 Specify whether pages are marked as being inactive 905 when they are freed. This is used in CMO environments 906 to determine OS memory pressure for page stealing by 907 a hypervisor. 908 Default: yes 909 910 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 911 Sets the size of memory pool for coherent, atomic dma 912 allocations, by default set to 256K. 913 914 com20020= [HW,NET] ARCnet - COM20020 chipset 915 Format: 916 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 917 918 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 919 Format: <io>[,<irq>] 920 921 com90xx= [HW,NET] 922 ARCnet - COM90xx chipset (memory-mapped buffers) 923 Format: <io>[,<irq>[,<memstart>]] 924 925 condev= [HW,S390] console device 926 conmode= 927 928 con3215_drop= [S390,EARLY] 3215 console drop mode. 929 Format: y|n|Y|N|1|0 930 When set to true, drop data on the 3215 console when 931 the console buffer is full. In this case the 932 operator using a 3270 terminal emulator (for example 933 x3270) does not have to enter the clear key for the 934 console output to advance and the kernel to continue. 935 This leads to a much faster boot time when a 3270 936 terminal emulator is active. If no 3270 terminal 937 emulator is used, this parameter has no effect. 938 939 console= [KNL] Output console device and options. 940 941 tty<n> Use the virtual console device <n>. 942 943 ttyS<n>[,options] 944 ttyUSB0[,options] 945 Use the specified serial port. The options are of 946 the form "bbbbpnf", where "bbbb" is the baud rate, 947 "p" is parity ("n", "o", or "e"), "n" is number of 948 bits, and "f" is flow control ("r" for RTS or 949 omit it). Default is "9600n8". 950 951 See Documentation/admin-guide/serial-console.rst for more 952 information. See 953 Documentation/networking/netconsole.rst for an 954 alternative. 955 956 <DEVNAME>:<n>.<n>[,options] 957 Use the specified serial port on the serial core bus. 958 The addressing uses DEVNAME of the physical serial port 959 device, followed by the serial core controller instance, 960 and the serial port instance. The options are the same 961 as documented for the ttyS addressing above. 962 963 The mapping of the serial ports to the tty instances 964 can be viewed with: 965 966 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 967 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 968 969 In the above example, the console can be addressed with 970 console=00:04:0.0. Note that a console addressed this 971 way will only get added when the related device driver 972 is ready. The use of an earlycon parameter in addition to 973 the console may be desired for console output early on. 974 975 uart[8250],io,<addr>[,options] 976 uart[8250],mmio,<addr>[,options] 977 uart[8250],mmio16,<addr>[,options] 978 uart[8250],mmio32,<addr>[,options] 979 uart[8250],0x<addr>[,options] 980 Start an early, polled-mode console on the 8250/16550 981 UART at the specified I/O port or MMIO address, 982 switching to the matching ttyS device later. 983 MMIO inter-register address stride is either 8-bit 984 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 985 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 986 to be equivalent to 'mmio'. 'options' are specified in 987 the same format described for ttyS above; if unspecified, 988 the h/w is not re-initialized. 989 990 hvc<n> Use the hypervisor console device <n>. This is for 991 both Xen and PowerPC hypervisors. 992 993 { null | "" } 994 Use to disable console output, i.e., to have kernel 995 console messages discarded. 996 This must be the only console= parameter used on the 997 kernel command line. 998 999 If the device connected to the port is not a TTY but a braille 1000 device, prepend "brl," before the device type, for instance 1001 console=brl,ttyS0 1002 For now, only VisioBraille is supported. 1003 1004 console_msg_format= 1005 [KNL] Change console messages format 1006 default 1007 By default we print messages on consoles in 1008 "[time stamp] text\n" format (time stamp may not be 1009 printed, depending on CONFIG_PRINTK_TIME or 1010 `printk_time' param). 1011 syslog 1012 Switch to syslog format: "<%u>[time stamp] text\n" 1013 IOW, each message will have a facility and loglevel 1014 prefix. The format is similar to one used by syslog() 1015 syscall, or to executing "dmesg -S --raw" or to reading 1016 from /proc/kmsg. 1017 1018 consoleblank= [KNL] The console blank (screen saver) timeout in 1019 seconds. A value of 0 disables the blank timer. 1020 Defaults to 0. 1021 1022 coredump_filter= 1023 [KNL] Change the default value for 1024 /proc/<pid>/coredump_filter. 1025 See also Documentation/filesystems/proc.rst. 1026 1027 coresight_cpu_debug.enable 1028 [ARM,ARM64] 1029 Format: <bool> 1030 Enable/disable the CPU sampling based debugging. 1031 0: default value, disable debugging 1032 1: enable debugging at boot time 1033 1034 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1035 Format: 1036 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1037 1038 cpuidle.off=1 [CPU_IDLE] 1039 disable the cpuidle sub-system 1040 1041 cpuidle.governor= 1042 [CPU_IDLE] Name of the cpuidle governor to use. 1043 1044 cpufreq.off=1 [CPU_FREQ] 1045 disable the cpufreq sub-system 1046 1047 cpufreq.default_governor= 1048 [CPU_FREQ] Name of the default cpufreq governor or 1049 policy to use. This governor must be registered in the 1050 kernel before the cpufreq driver probes. 1051 1052 cpu_init_udelay=N 1053 [X86,EARLY] Delay for N microsec between assert and de-assert 1054 of APIC INIT to start processors. This delay occurs 1055 on every CPU online, such as boot, and resume from suspend. 1056 Default: 10000 1057 1058 cpuhp.parallel= 1059 [SMP] Enable/disable parallel bringup of secondary CPUs 1060 Format: <bool> 1061 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1062 the parameter has no effect. 1063 1064 crash_kexec_post_notifiers 1065 Only jump to kdump kernel after running the panic 1066 notifiers and dumping kmsg. This option increases 1067 the risks of a kdump failure, since some panic 1068 notifiers can make the crashed kernel more unstable. 1069 In configurations where kdump may not be reliable, 1070 running the panic notifiers could allow collecting 1071 more data on dmesg, like stack traces from other CPUS 1072 or extra data dumped by panic_print. Note that some 1073 configurations enable this option unconditionally, 1074 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1075 1076 crashkernel=size[KMG][@offset[KMG]] 1077 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1078 upon panic. This parameter reserves the physical 1079 memory region [offset, offset + size] for that kernel 1080 image. If '@offset' is omitted, then a suitable offset 1081 is selected automatically. 1082 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1083 under 4G first, and fall back to reserve region above 1084 4G when '@offset' hasn't been specified. 1085 See Documentation/admin-guide/kdump/kdump.rst for further details. 1086 1087 crashkernel=range1:size1[,range2:size2,...][@offset] 1088 [KNL] Same as above, but depends on the memory 1089 in the running system. The syntax of range is 1090 start-[end] where start and end are both 1091 a memory unit (amount[KMG]). See also 1092 Documentation/admin-guide/kdump/kdump.rst for an example. 1093 1094 crashkernel=size[KMG],high 1095 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1096 above 4G. 1097 Allow kernel to allocate physical memory region from top, 1098 so could be above 4G if system have more than 4G ram 1099 installed. Otherwise memory region will be allocated 1100 below 4G, if available. 1101 It will be ignored if crashkernel=X is specified. 1102 crashkernel=size[KMG],low 1103 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1104 When crashkernel=X,high is passed, kernel could allocate 1105 physical memory region above 4G, that cause second kernel 1106 crash on system that require some amount of low memory, 1107 e.g. swiotlb requires at least 64M+32K low memory, also 1108 enough extra low memory is needed to make sure DMA buffers 1109 for 32-bit devices won't run out. Kernel would try to allocate 1110 default size of memory below 4G automatically. The default 1111 size is platform dependent. 1112 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1113 --> arm64: 128MiB 1114 --> riscv: 128MiB 1115 --> loongarch: 128MiB 1116 This one lets the user specify own low range under 4G 1117 for second kernel instead. 1118 0: to disable low allocation. 1119 It will be ignored when crashkernel=X,high is not used 1120 or memory reserved is below 4G. 1121 crashkernel=size[KMG],cma 1122 [KNL, X86, ppc] Reserve additional crash kernel memory from 1123 CMA. This reservation is usable by the first system's 1124 userspace memory and kernel movable allocations (memory 1125 balloon, zswap). Pages allocated from this memory range 1126 will not be included in the vmcore so this should not 1127 be used if dumping of userspace memory is intended and 1128 it has to be expected that some movable kernel pages 1129 may be missing from the dump. 1130 1131 A standard crashkernel reservation, as described above, 1132 is still needed to hold the crash kernel and initrd. 1133 1134 This option increases the risk of a kdump failure: DMA 1135 transfers configured by the first kernel may end up 1136 corrupting the second kernel's memory. 1137 1138 This reservation method is intended for systems that 1139 can't afford to sacrifice enough memory for standard 1140 crashkernel reservation and where less reliable and 1141 possibly incomplete kdump is preferable to no kdump at 1142 all. 1143 1144 cryptomgr.notests 1145 [KNL] Disable crypto self-tests 1146 1147 cs89x0_dma= [HW,NET] 1148 Format: <dma> 1149 1150 cs89x0_media= [HW,NET] 1151 Format: { rj45 | aui | bnc } 1152 1153 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1154 function call handling. When switched on, 1155 additional debug data is printed to the console 1156 in case a hanging CPU is detected, and that 1157 CPU is pinged again in order to try to resolve 1158 the hang situation. The default value of this 1159 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1160 Kconfig option. 1161 1162 dasd= [HW,NET] 1163 See header of drivers/s390/block/dasd_devmap.c. 1164 1165 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1166 (one device per port) 1167 Format: <port#>,<type> 1168 See also Documentation/input/devices/joystick-parport.rst 1169 1170 debug [KNL,EARLY] Enable kernel debugging (events log level). 1171 1172 debug_boot_weak_hash 1173 [KNL,EARLY] Enable printing [hashed] pointers early in the 1174 boot sequence. If enabled, we use a weak hash instead 1175 of siphash to hash pointers. Use this option if you are 1176 seeing instances of '(___ptrval___)') and need to see a 1177 value (hashed pointer) instead. Cryptographically 1178 insecure, please do not use on production kernels. 1179 1180 debug_locks_verbose= 1181 [KNL] verbose locking self-tests 1182 Format: <int> 1183 Print debugging info while doing the locking API 1184 self-tests. 1185 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1186 (no extra messages), setting it to -1 (all bits set) 1187 will print _a_lot_ more information - normally only 1188 useful to lockdep developers. 1189 1190 debug_objects [KNL,EARLY] Enable object debugging 1191 1192 debug_guardpage_minorder= 1193 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1194 parameter allows control of the order of pages that will 1195 be intentionally kept free (and hence protected) by the 1196 buddy allocator. Bigger value increase the probability 1197 of catching random memory corruption, but reduce the 1198 amount of memory for normal system use. The maximum 1199 possible value is MAX_PAGE_ORDER/2. Setting this 1200 parameter to 1 or 2 should be enough to identify most 1201 random memory corruption problems caused by bugs in 1202 kernel or driver code when a CPU writes to (or reads 1203 from) a random memory location. Note that there exists 1204 a class of memory corruptions problems caused by buggy 1205 H/W or F/W or by drivers badly programming DMA 1206 (basically when memory is written at bus level and the 1207 CPU MMU is bypassed) which are not detectable by 1208 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1209 help tracking down these problems. 1210 1211 debug_pagealloc= 1212 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1213 enables the feature at boot time. By default, it is 1214 disabled and the system will work mostly the same as a 1215 kernel built without CONFIG_DEBUG_PAGEALLOC. 1216 Note: to get most of debug_pagealloc error reports, it's 1217 useful to also enable the page_owner functionality. 1218 on: enable the feature 1219 1220 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1221 userspace and debugfs internal clients. 1222 Format: { on, off } 1223 on: All functions are enabled. 1224 off: Filesystem is not registered and clients 1225 get a -EPERM as result when trying to register files 1226 or directories within debugfs. 1227 This is equivalent of the runtime functionality if 1228 debugfs was not enabled in the kernel at all. 1229 Default value is set in build-time with a kernel configuration. 1230 1231 debugpat [X86] Enable PAT debugging 1232 1233 default_hugepagesz= 1234 [HW] The size of the default HugeTLB page. This is 1235 the size represented by the legacy /proc/ hugepages 1236 APIs. In addition, this is the default hugetlb size 1237 used for shmget(), mmap() and mounting hugetlbfs 1238 filesystems. If not specified, defaults to the 1239 architecture's default huge page size. Huge page 1240 sizes are architecture dependent. See also 1241 Documentation/admin-guide/mm/hugetlbpage.rst. 1242 Format: size[KMG] 1243 1244 deferred_probe_timeout= 1245 [KNL] Debugging option to set a timeout in seconds for 1246 deferred probe to give up waiting on dependencies to 1247 probe. Only specific dependencies (subsystems or 1248 drivers) that have opted in will be ignored. A timeout 1249 of 0 will timeout at the end of initcalls. If the time 1250 out hasn't expired, it'll be restarted by each 1251 successful driver registration. This option will also 1252 dump out devices still on the deferred probe list after 1253 retrying. 1254 1255 delayacct [KNL] Enable per-task delay accounting 1256 1257 dell_smm_hwmon.ignore_dmi= 1258 [HW] Continue probing hardware even if DMI data 1259 indicates that the driver is running on unsupported 1260 hardware. 1261 1262 dell_smm_hwmon.force= 1263 [HW] Activate driver even if SMM BIOS signature does 1264 not match list of supported models and enable otherwise 1265 blacklisted features. 1266 1267 dell_smm_hwmon.power_status= 1268 [HW] Report power status in /proc/i8k 1269 (disabled by default). 1270 1271 dell_smm_hwmon.restricted= 1272 [HW] Allow controlling fans only if SYS_ADMIN 1273 capability is set. 1274 1275 dell_smm_hwmon.fan_mult= 1276 [HW] Factor to multiply fan speed with. 1277 1278 dell_smm_hwmon.fan_max= 1279 [HW] Maximum configurable fan speed. 1280 1281 dfltcc= [HW,S390] 1282 Format: { on | off | def_only | inf_only | always } 1283 on: s390 zlib hardware support for compression on 1284 level 1 and decompression (default) 1285 off: No s390 zlib hardware support 1286 def_only: s390 zlib hardware support for deflate 1287 only (compression on level 1) 1288 inf_only: s390 zlib hardware support for inflate 1289 only (decompression) 1290 always: Same as 'on' but ignores the selected compression 1291 level always using hardware support (used for debugging) 1292 1293 dhash_entries= [KNL] 1294 Set number of hash buckets for dentry cache. 1295 1296 disable_1tb_segments [PPC,EARLY] 1297 Disables the use of 1TB hash page table segments. This 1298 causes the kernel to fall back to 256MB segments which 1299 can be useful when debugging issues that require an SLB 1300 miss to occur. 1301 1302 disable= [IPV6] 1303 See Documentation/networking/ipv6.rst. 1304 1305 disable_radix [PPC,EARLY] 1306 Disable RADIX MMU mode on POWER9 1307 1308 disable_tlbie [PPC] 1309 Disable TLBIE instruction. Currently does not work 1310 with KVM, with HASH MMU, or with coherent accelerators. 1311 1312 disable_ddw [PPC/PSERIES,EARLY] 1313 Disable Dynamic DMA Window support. Use this 1314 to workaround buggy firmware. 1315 1316 disable_ipv6= [IPV6] 1317 See Documentation/networking/ipv6.rst. 1318 1319 disable_mtrr_cleanup [X86,EARLY] 1320 The kernel tries to adjust MTRR layout from continuous 1321 to discrete, to make X server driver able to add WB 1322 entry later. This parameter disables that. 1323 1324 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1325 By default the kernel will trim any uncacheable 1326 memory out of your available memory pool based on 1327 MTRR settings. This parameter disables that behavior, 1328 possibly causing your machine to run very slowly. 1329 1330 disable_timer_pin_1 [X86,EARLY] 1331 Disable PIN 1 of APIC timer 1332 Can be useful to work around chipset bugs. 1333 1334 dis_ucode_ldr [X86] Disable the microcode loader. 1335 1336 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1337 this option disables the debugging code at boot. 1338 1339 dma_debug_entries=<number> 1340 This option allows to tune the number of preallocated 1341 entries for DMA-API debugging code. One entry is 1342 required per DMA-API allocation. Use this if the 1343 DMA-API debugging code disables itself because the 1344 architectural default is too low. 1345 1346 dma_debug_driver=<driver_name> 1347 With this option the DMA-API debugging driver 1348 filter feature can be enabled at boot time. Just 1349 pass the driver to filter for as the parameter. 1350 The filter can be disabled or changed to another 1351 driver later using sysfs. 1352 1353 reg_file_data_sampling= 1354 [X86] Controls mitigation for Register File Data 1355 Sampling (RFDS) vulnerability. RFDS is a CPU 1356 vulnerability which may allow userspace to infer 1357 kernel data values previously stored in floating point 1358 registers, vector registers, or integer registers. 1359 RFDS only affects Intel Atom processors. 1360 1361 on: Turns ON the mitigation. 1362 off: Turns OFF the mitigation. 1363 1364 This parameter overrides the compile time default set 1365 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1366 disabled when other VERW based mitigations (like MDS) 1367 are enabled. In order to disable RFDS mitigation all 1368 VERW based mitigations need to be disabled. 1369 1370 For details see: 1371 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1372 1373 driver_async_probe= [KNL] 1374 List of driver names to be probed asynchronously. * 1375 matches with all driver names. If * is specified, the 1376 rest of the listed driver names are those that will NOT 1377 match the *. 1378 Format: <driver_name1>,<driver_name2>... 1379 1380 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1381 Broken monitors, graphic adapters, KVMs and EDIDless 1382 panels may send no or incorrect EDID data sets. 1383 This parameter allows to specify an EDID data sets 1384 in the /lib/firmware directory that are used instead. 1385 An EDID data set will only be used for a particular 1386 connector, if its name and a colon are prepended to 1387 the EDID name. Each connector may use a unique EDID 1388 data set by separating the files with a comma. An EDID 1389 data set with no connector name will be used for 1390 any connectors not explicitly specified. 1391 1392 dscc4.setup= [NET] 1393 1394 dt_cpu_ftrs= [PPC,EARLY] 1395 Format: {"off" | "known"} 1396 Control how the dt_cpu_ftrs device-tree binding is 1397 used for CPU feature discovery and setup (if it 1398 exists). 1399 off: Do not use it, fall back to legacy cpu table. 1400 known: Do not pass through unknown features to guests 1401 or userspace, only those that the kernel is aware of. 1402 1403 dump_apple_properties [X86] 1404 Dump name and content of EFI device properties on 1405 x86 Macs. Useful for driver authors to determine 1406 what data is available or for reverse-engineering. 1407 1408 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1409 <module>.dyndbg[="val"] 1410 Enable debug messages at boot time. See 1411 Documentation/admin-guide/dynamic-debug-howto.rst 1412 for details. 1413 1414 early_ioremap_debug [KNL,EARLY] 1415 Enable debug messages in early_ioremap support. This 1416 is useful for tracking down temporary early mappings 1417 which are not unmapped. 1418 1419 earlycon= [KNL,EARLY] Output early console device and options. 1420 1421 When used with no options, the early console is 1422 determined by stdout-path property in device tree's 1423 chosen node or the ACPI SPCR table if supported by 1424 the platform. 1425 1426 cdns,<addr>[,options] 1427 Start an early, polled-mode console on a Cadence 1428 (xuartps) serial port at the specified address. Only 1429 supported option is baud rate. If baud rate is not 1430 specified, the serial port must already be setup and 1431 configured. 1432 1433 uart[8250],io,<addr>[,options[,uartclk]] 1434 uart[8250],mmio,<addr>[,options[,uartclk]] 1435 uart[8250],mmio32,<addr>[,options[,uartclk]] 1436 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1437 uart[8250],0x<addr>[,options] 1438 Start an early, polled-mode console on the 8250/16550 1439 UART at the specified I/O port or MMIO address. 1440 MMIO inter-register address stride is either 8-bit 1441 (mmio) or 32-bit (mmio32 or mmio32be). 1442 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1443 to be equivalent to 'mmio'. 'options' are specified 1444 in the same format described for "console=ttyS<n>"; if 1445 unspecified, the h/w is not initialized. 'uartclk' is 1446 the uart clock frequency; if unspecified, it is set 1447 to 'BASE_BAUD' * 16. 1448 1449 pl011,<addr> 1450 pl011,mmio32,<addr> 1451 Start an early, polled-mode console on a pl011 serial 1452 port at the specified address. The pl011 serial port 1453 must already be setup and configured. Options are not 1454 yet supported. If 'mmio32' is specified, then only 1455 the driver will use only 32-bit accessors to read/write 1456 the device registers. 1457 1458 liteuart,<addr> 1459 Start an early console on a litex serial port at the 1460 specified address. The serial port must already be 1461 setup and configured. Options are not yet supported. 1462 1463 meson,<addr> 1464 Start an early, polled-mode console on a meson serial 1465 port at the specified address. The serial port must 1466 already be setup and configured. Options are not yet 1467 supported. 1468 1469 msm_serial,<addr> 1470 Start an early, polled-mode console on an msm serial 1471 port at the specified address. The serial port 1472 must already be setup and configured. Options are not 1473 yet supported. 1474 1475 msm_serial_dm,<addr> 1476 Start an early, polled-mode console on an msm serial 1477 dm port at the specified address. The serial port 1478 must already be setup and configured. Options are not 1479 yet supported. 1480 1481 owl,<addr> 1482 Start an early, polled-mode console on a serial port 1483 of an Actions Semi SoC, such as S500 or S900, at the 1484 specified address. The serial port must already be 1485 setup and configured. Options are not yet supported. 1486 1487 rda,<addr> 1488 Start an early, polled-mode console on a serial port 1489 of an RDA Micro SoC, such as RDA8810PL, at the 1490 specified address. The serial port must already be 1491 setup and configured. Options are not yet supported. 1492 1493 sbi 1494 Use RISC-V SBI (Supervisor Binary Interface) for early 1495 console. 1496 1497 smh Use ARM semihosting calls for early console. 1498 1499 s3c2410,<addr> 1500 s3c2412,<addr> 1501 s3c2440,<addr> 1502 s3c6400,<addr> 1503 s5pv210,<addr> 1504 exynos4210,<addr> 1505 Use early console provided by serial driver available 1506 on Samsung SoCs, requires selecting proper type and 1507 a correct base address of the selected UART port. The 1508 serial port must already be setup and configured. 1509 Options are not yet supported. 1510 1511 lantiq,<addr> 1512 Start an early, polled-mode console on a lantiq serial 1513 (lqasc) port at the specified address. The serial port 1514 must already be setup and configured. Options are not 1515 yet supported. 1516 1517 lpuart,<addr> 1518 lpuart32,<addr> 1519 Use early console provided by Freescale LP UART driver 1520 found on Freescale Vybrid and QorIQ LS1021A processors. 1521 A valid base address must be provided, and the serial 1522 port must already be setup and configured. 1523 1524 ec_imx21,<addr> 1525 ec_imx6q,<addr> 1526 Start an early, polled-mode, output-only console on the 1527 Freescale i.MX UART at the specified address. The UART 1528 must already be setup and configured. 1529 1530 ar3700_uart,<addr> 1531 Start an early, polled-mode console on the 1532 Armada 3700 serial port at the specified 1533 address. The serial port must already be setup 1534 and configured. Options are not yet supported. 1535 1536 qcom_geni,<addr> 1537 Start an early, polled-mode console on a Qualcomm 1538 Generic Interface (GENI) based serial port at the 1539 specified address. The serial port must already be 1540 setup and configured. Options are not yet supported. 1541 1542 efifb,[options] 1543 Start an early, unaccelerated console on the EFI 1544 memory mapped framebuffer (if available). On cache 1545 coherent non-x86 systems that use system memory for 1546 the framebuffer, pass the 'ram' option so that it is 1547 mapped with the correct attributes. 1548 1549 linflex,<addr> 1550 Use early console provided by Freescale LINFlexD UART 1551 serial driver for NXP S32V234 SoCs. A valid base 1552 address must be provided, and the serial port must 1553 already be setup and configured. 1554 1555 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1556 earlyprintk=vga 1557 earlyprintk=sclp 1558 earlyprintk=xen 1559 earlyprintk=serial[,ttySn[,baudrate]] 1560 earlyprintk=serial[,0x...[,baudrate]] 1561 earlyprintk=ttySn[,baudrate] 1562 earlyprintk=dbgp[debugController#] 1563 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1564 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1565 earlyprintk=xdbc[xhciController#] 1566 earlyprintk=bios 1567 1568 earlyprintk is useful when the kernel crashes before 1569 the normal console is initialized. It is not enabled by 1570 default because it has some cosmetic problems. 1571 1572 Use "nocfg" to skip UART configuration, assume 1573 BIOS/firmware has configured UART correctly. 1574 1575 Append ",keep" to not disable it when the real console 1576 takes over. 1577 1578 Only one of vga, serial, or usb debug port can 1579 be used at a time. 1580 1581 Currently only ttyS0 and ttyS1 may be specified by 1582 name. Other I/O ports may be explicitly specified 1583 on some architectures (x86 and arm at least) by 1584 replacing ttySn with an I/O port address, like this: 1585 earlyprintk=serial,0x1008,115200 1586 You can find the port for a given device in 1587 /proc/tty/driver/serial: 1588 2: uart:ST16650V2 port:00001008 irq:18 ... 1589 1590 Interaction with the standard serial driver is not 1591 very good. 1592 1593 The VGA output is eventually overwritten by 1594 the real console. 1595 1596 The xen option can only be used in Xen domains. 1597 1598 The sclp output can only be used on s390. 1599 1600 The bios output can only be used on SuperH. 1601 1602 The optional "force" to "pciserial" enables use of a 1603 PCI device even when its classcode is not of the 1604 UART class. 1605 1606 edac_report= [HW,EDAC] Control how to report EDAC event 1607 Format: {"on" | "off" | "force"} 1608 on: enable EDAC to report H/W event. May be overridden 1609 by other higher priority error reporting module. 1610 off: disable H/W event reporting through EDAC. 1611 force: enforce the use of EDAC to report H/W event. 1612 default: on. 1613 1614 edd= [EDD] 1615 Format: {"off" | "on" | "skip[mbr]"} 1616 1617 efi= [EFI,EARLY] 1618 Format: { "debug", "disable_early_pci_dma", 1619 "nochunk", "noruntime", "nosoftreserve", 1620 "novamap", "no_disable_early_pci_dma" } 1621 debug: enable misc debug output. 1622 disable_early_pci_dma: disable the busmaster bit on all 1623 PCI bridges while in the EFI boot stub. 1624 nochunk: disable reading files in "chunks" in the EFI 1625 boot stub, as chunking can cause problems with some 1626 firmware implementations. 1627 noruntime : disable EFI runtime services support 1628 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1629 attribute may cause the kernel to reserve the 1630 memory range for a memory mapping driver to 1631 claim. Specify efi=nosoftreserve to disable this 1632 reservation and treat the memory by its base type 1633 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1634 novamap: do not call SetVirtualAddressMap(). 1635 no_disable_early_pci_dma: Leave the busmaster bit set 1636 on all PCI bridges while in the EFI boot stub 1637 1638 efi_no_storage_paranoia [EFI,X86,EARLY] 1639 Using this parameter you can use more than 50% of 1640 your efi variable storage. Use this parameter only if 1641 you are really sure that your UEFI does sane gc and 1642 fulfills the spec otherwise your board may brick. 1643 1644 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1645 that is to be dynamically loaded by Linux. If there are 1646 multiple variables with the same name but with different 1647 vendor GUIDs, all of them will be loaded. See 1648 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1649 1650 1651 eisa_irq_edge= [PARISC,HW] 1652 See header of drivers/parisc/eisa.c. 1653 1654 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1655 Format: ekgdboc=kbd 1656 1657 This is designed to be used in conjunction with 1658 the boot argument: earlyprintk=vga 1659 1660 This parameter works in place of the kgdboc parameter 1661 but can only be used if the backing tty is available 1662 very early in the boot process. For early debugging 1663 via a serial port see kgdboc_earlycon instead. 1664 1665 elanfreq= [X86-32] 1666 See comment before function elanfreq_setup() in 1667 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1668 1669 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1670 Specifies physical address of start of kernel core 1671 image elf header and optionally the size. Generally 1672 kexec loader will pass this option to capture kernel. 1673 See Documentation/admin-guide/kdump/kdump.rst for details. 1674 1675 enable_mtrr_cleanup [X86,EARLY] 1676 The kernel tries to adjust MTRR layout from continuous 1677 to discrete, to make X server driver able to add WB 1678 entry later. This parameter enables that. 1679 1680 enable_timer_pin_1 [X86] 1681 Enable PIN 1 of APIC timer 1682 Can be useful to work around chipset bugs 1683 (in particular on some ATI chipsets). 1684 The kernel tries to set a reasonable default. 1685 1686 enforcing= [SELINUX] Set initial enforcing status. 1687 Format: {"0" | "1"} 1688 See security/selinux/Kconfig help text. 1689 0 -- permissive (log only, no denials). 1690 1 -- enforcing (deny and log). 1691 Default value is 0. 1692 Value can be changed at runtime via 1693 /sys/fs/selinux/enforce. 1694 1695 erst_disable [ACPI] 1696 Disable Error Record Serialization Table (ERST) 1697 support. 1698 1699 ether= [HW,NET] Ethernet cards parameters 1700 This option is obsoleted by the "netdev=" option, which 1701 has equivalent usage. See its documentation for details. 1702 1703 evm= [EVM] 1704 Format: { "fix" } 1705 Permit 'security.evm' to be updated regardless of 1706 current integrity status. 1707 1708 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1709 stages so cover more early boot allocations. 1710 Please note that as side effect some optimizations 1711 might be disabled to achieve that (e.g. parallelized 1712 memory initialization is disabled) so the boot process 1713 might take longer, especially on systems with a lot of 1714 memory. Available with CONFIG_PAGE_EXTENSION=y. 1715 1716 failslab= 1717 fail_usercopy= 1718 fail_page_alloc= 1719 fail_skb_realloc= 1720 fail_make_request=[KNL] 1721 General fault injection mechanism. 1722 Format: <interval>,<probability>,<space>,<times> 1723 See also Documentation/fault-injection/. 1724 1725 fb_tunnels= [NET] 1726 Format: { initns | none } 1727 See Documentation/admin-guide/sysctl/net.rst for 1728 fb_tunnels_only_for_init_ns 1729 1730 floppy= [HW] 1731 See Documentation/admin-guide/blockdev/floppy.rst. 1732 1733 forcepae [X86-32] 1734 Forcefully enable Physical Address Extension (PAE). 1735 Many Pentium M systems disable PAE but may have a 1736 functionally usable PAE implementation. 1737 Warning: use of this parameter will taint the kernel 1738 and may cause unknown problems. 1739 1740 fred= [X86-64] 1741 Enable/disable Flexible Return and Event Delivery. 1742 Format: { on | off } 1743 on: enable FRED when it's present. 1744 off: disable FRED, the default setting. 1745 1746 ftrace=[tracer] 1747 [FTRACE] will set and start the specified tracer 1748 as early as possible in order to facilitate early 1749 boot debugging. 1750 1751 ftrace_boot_snapshot 1752 [FTRACE] On boot up, a snapshot will be taken of the 1753 ftrace ring buffer that can be read at: 1754 /sys/kernel/tracing/snapshot. 1755 This is useful if you need tracing information from kernel 1756 boot up that is likely to be overridden by user space 1757 start up functionality. 1758 1759 Optionally, the snapshot can also be defined for a tracing 1760 instance that was created by the trace_instance= command 1761 line parameter. 1762 1763 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1764 1765 The above will cause the "foo" tracing instance to trigger 1766 a snapshot at the end of boot up. 1767 1768 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1769 ,<instance>=2(orig_cpu)] 1770 [FTRACE] will dump the trace buffers on oops. 1771 If no parameter is passed, ftrace will dump global 1772 buffers of all CPUs, if you pass 2 or orig_cpu, it 1773 will dump only the buffer of the CPU that triggered 1774 the oops, or the specific instance will be dumped if 1775 its name is passed. Multiple instance dump is also 1776 supported, and instances are separated by commas. Each 1777 instance supports only dump on CPU that triggered the 1778 oops by passing 2 or orig_cpu to it. 1779 1780 ftrace_dump_on_oops=foo=orig_cpu 1781 1782 The above will dump only the buffer of "foo" instance 1783 on CPU that triggered the oops. 1784 1785 ftrace_dump_on_oops,foo,bar=orig_cpu 1786 1787 The above will dump global buffer on all CPUs, the 1788 buffer of "foo" instance on all CPUs and the buffer 1789 of "bar" instance on CPU that triggered the oops. 1790 1791 ftrace_filter=[function-list] 1792 [FTRACE] Limit the functions traced by the function 1793 tracer at boot up. function-list is a comma-separated 1794 list of functions. This list can be changed at run 1795 time by the set_ftrace_filter file in the debugfs 1796 tracing directory. 1797 1798 ftrace_notrace=[function-list] 1799 [FTRACE] Do not trace the functions specified in 1800 function-list. This list can be changed at run time 1801 by the set_ftrace_notrace file in the debugfs 1802 tracing directory. 1803 1804 ftrace_graph_filter=[function-list] 1805 [FTRACE] Limit the top level callers functions traced 1806 by the function graph tracer at boot up. 1807 function-list is a comma-separated list of functions 1808 that can be changed at run time by the 1809 set_graph_function file in the debugfs tracing directory. 1810 1811 ftrace_graph_notrace=[function-list] 1812 [FTRACE] Do not trace from the functions specified in 1813 function-list. This list is a comma-separated list of 1814 functions that can be changed at run time by the 1815 set_graph_notrace file in the debugfs tracing directory. 1816 1817 ftrace_graph_max_depth=<uint> 1818 [FTRACE] Used with the function graph tracer. This is 1819 the max depth it will trace into a function. This value 1820 can be changed at run time by the max_graph_depth file 1821 in the tracefs tracing directory. default: 0 (no limit) 1822 1823 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1824 devices by scanning the firmware to infer the 1825 consumer/supplier relationships. This feature is 1826 especially useful when drivers are loaded as modules as 1827 it ensures proper ordering of tasks like device probing 1828 (suppliers first, then consumers), supplier boot state 1829 clean up (only after all consumers have probed), 1830 suspend/resume & runtime PM (consumers first, then 1831 suppliers). 1832 Format: { off | permissive | on | rpm } 1833 off -- Don't create device links from firmware info. 1834 permissive -- Create device links from firmware info 1835 but use it only for ordering boot state clean 1836 up (sync_state() calls). 1837 on -- Create device links from firmware info and use it 1838 to enforce probe and suspend/resume ordering. 1839 rpm -- Like "on", but also use to order runtime PM. 1840 1841 fw_devlink.strict=<bool> 1842 [KNL,EARLY] Treat all inferred dependencies as mandatory 1843 dependencies. This only applies for fw_devlink=on|rpm. 1844 Format: <bool> 1845 1846 fw_devlink.sync_state = 1847 [KNL,EARLY] When all devices that could probe have finished 1848 probing, this parameter controls what to do with 1849 devices that haven't yet received their sync_state() 1850 calls. 1851 Format: { strict | timeout } 1852 strict -- Default. Continue waiting on consumers to 1853 probe successfully. 1854 timeout -- Give up waiting on consumers and call 1855 sync_state() on any devices that haven't yet 1856 received their sync_state() calls after 1857 deferred_probe_timeout has expired or by 1858 late_initcall() if !CONFIG_MODULES. 1859 1860 gamecon.map[2|3]= 1861 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1862 support via parallel port (up to 5 devices per port) 1863 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1864 See also Documentation/input/devices/joystick-parport.rst 1865 1866 gamma= [HW,DRM] 1867 1868 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1869 Format: off | on 1870 default: on 1871 1872 gather_data_sampling= 1873 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1874 mitigation. 1875 1876 Gather Data Sampling is a hardware vulnerability which 1877 allows unprivileged speculative access to data which was 1878 previously stored in vector registers. 1879 1880 This issue is mitigated by default in updated microcode. 1881 The mitigation may have a performance impact but can be 1882 disabled. On systems without the microcode mitigation 1883 disabling AVX serves as a mitigation. 1884 1885 force: Disable AVX to mitigate systems without 1886 microcode mitigation. No effect if the microcode 1887 mitigation is present. Known to cause crashes in 1888 userspace with buggy AVX enumeration. 1889 1890 off: Disable GDS mitigation. 1891 1892 gbpages [X86] Use GB pages for kernel direct mappings. 1893 1894 gcov_persist= [GCOV] When non-zero (default), profiling data for 1895 kernel modules is saved and remains accessible via 1896 debugfs, even when the module is unloaded/reloaded. 1897 When zero, profiling data is discarded and associated 1898 debugfs files are removed at module unload time. 1899 1900 goldfish [X86] Enable the goldfish android emulator platform. 1901 Don't use this when you are not running on the 1902 android emulator 1903 1904 gpio-mockup.gpio_mockup_ranges 1905 [HW] Sets the ranges of gpiochip of for this device. 1906 Format: <start1>,<end1>,<start2>,<end2>... 1907 gpio-mockup.gpio_mockup_named_lines 1908 [HW] Let the driver know GPIO lines should be named. 1909 1910 gpt [EFI] Forces disk with valid GPT signature but 1911 invalid Protective MBR to be treated as GPT. If the 1912 primary GPT is corrupted, it enables the backup/alternate 1913 GPT to be used instead. 1914 1915 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1916 the "Enable 0" bit of the configuration register. 1917 Format: 0 | 1 1918 Default: 0 1919 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1920 the "Enable 0" bit of the configuration register. 1921 Format: 0 | 1 1922 Default: 0 1923 grcan.select= [HW] Select which physical interface to use. 1924 Format: 0 | 1 1925 Default: 0 1926 grcan.txsize= [HW] Sets the size of the tx buffer. 1927 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1928 Default: 1024 1929 grcan.rxsize= [HW] Sets the size of the rx buffer. 1930 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1931 Default: 1024 1932 1933 hardened_usercopy= 1934 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1935 hardening is enabled for this boot. Hardened 1936 usercopy checking is used to protect the kernel 1937 from reading or writing beyond known memory 1938 allocation boundaries as a proactive defense 1939 against bounds-checking flaws in the kernel's 1940 copy_to_user()/copy_from_user() interface. 1941 The default is determined by 1942 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1943 on Perform hardened usercopy checks. 1944 off Disable hardened usercopy checks. 1945 1946 hardlockup_all_cpu_backtrace= 1947 [KNL] Should the hard-lockup detector generate 1948 backtraces on all cpus. 1949 Format: 0 | 1 1950 1951 hash_pointers= 1952 [KNL,EARLY] 1953 By default, when pointers are printed to the console 1954 or buffers via the %p format string, that pointer is 1955 "hashed", i.e. obscured by hashing the pointer value. 1956 This is a security feature that hides actual kernel 1957 addresses from unprivileged users, but it also makes 1958 debugging the kernel more difficult since unequal 1959 pointers can no longer be compared. The choices are: 1960 Format: { auto | always | never } 1961 Default: auto 1962 1963 auto - Hash pointers unless slab_debug is enabled. 1964 always - Always hash pointers (even if slab_debug is 1965 enabled). 1966 never - Never hash pointers. This option should only 1967 be specified when debugging the kernel. Do 1968 not use on production kernels. The boot 1969 param "no_hash_pointers" is an alias for 1970 this mode. 1971 1972 For controlling hashing dynamically at runtime, 1973 use the "kernel.kptr_restrict" sysctl instead. 1974 1975 hashdist= [KNL,NUMA] Large hashes allocated during boot 1976 are distributed across NUMA nodes. Defaults on 1977 for 64-bit NUMA, off otherwise. 1978 Format: 0 | 1 (for off | on) 1979 1980 hd= [EIDE] (E)IDE hard drive subsystem geometry 1981 Format: <cyl>,<head>,<sect> 1982 1983 hest_disable [ACPI] 1984 Disable Hardware Error Source Table (HEST) support; 1985 corresponding firmware-first mode error processing 1986 logic will be disabled. 1987 1988 hibernate= [HIBERNATION] 1989 noresume Don't check if there's a hibernation image 1990 present during boot. 1991 nocompress Don't compress/decompress hibernation images. 1992 no Disable hibernation and resume. 1993 protect_image Turn on image protection during restoration 1994 (that will set all pages holding image data 1995 during restoration read-only). 1996 1997 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1998 used with hibernation. 1999 Format: { lzo | lz4 } 2000 Default: lzo 2001 2002 lzo: Select LZO compression algorithm to 2003 compress/decompress hibernation image. 2004 2005 lz4: Select LZ4 compression algorithm to 2006 compress/decompress hibernation image. 2007 2008 hibernate.pm_test_delay= 2009 [HIBERNATION] 2010 Sets the number of seconds to remain in a hibernation test 2011 mode before resuming the system (see 2012 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 2013 is set. Default value is 5. 2014 2015 hibernate_compression_threads= 2016 [HIBERNATION] 2017 Set the number of threads used for compressing or decompressing 2018 hibernation images. 2019 2020 Format: <integer> 2021 Default: 3 2022 Minimum: 1 2023 Example: hibernate_compression_threads=4 2024 2025 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2026 size of <nn>. This works even on boxes that have no 2027 highmem otherwise. This also works to reduce highmem 2028 size on bigger boxes. 2029 2030 highres= [KNL] Enable/disable high resolution timer mode. 2031 Valid parameters: "on", "off" 2032 Default: "on" 2033 2034 hlt [BUGS=ARM,SH] 2035 2036 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2037 Format: <string> 2038 This allows setting the system's hostname during early 2039 startup. This sets the name returned by gethostname. 2040 Using this parameter to set the hostname makes it 2041 possible to ensure the hostname is correctly set before 2042 any userspace processes run, avoiding the possibility 2043 that a process may call gethostname before the hostname 2044 has been explicitly set, resulting in the calling 2045 process getting an incorrect result. The string must 2046 not exceed the maximum allowed hostname length (usually 2047 64 characters) and will be truncated otherwise. 2048 2049 hpet= [X86-32,HPET] option to control HPET usage 2050 Format: { enable (default) | disable | force | 2051 verbose } 2052 disable: disable HPET and use PIT instead 2053 force: allow force enabled of undocumented chips (ICH4, 2054 VIA, nVidia) 2055 verbose: show contents of HPET registers during setup 2056 2057 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2058 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2059 2060 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2061 If this follows hugepagesz (below), it specifies 2062 the number of pages of hugepagesz to be allocated. 2063 If this is the first HugeTLB parameter on the command 2064 line, it specifies the number of pages to allocate for 2065 the default huge page size. If using node format, the 2066 number of pages to allocate per-node can be specified. 2067 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2068 Format: <integer> or (node format) 2069 <node>:<integer>[,<node>:<integer>] 2070 2071 hugepagesz= 2072 [HW,EARLY] The size of the HugeTLB pages. This is 2073 used in conjunction with hugepages (above) to 2074 allocate huge pages of a specific size at boot. The 2075 pair hugepagesz=X hugepages=Y can be specified once 2076 for each supported huge page size. Huge page sizes 2077 are architecture dependent. See also 2078 Documentation/admin-guide/mm/hugetlbpage.rst. 2079 Format: size[KMG] 2080 2081 hugepage_alloc_threads= 2082 [HW] The number of threads that should be used to 2083 allocate hugepages during boot. This option can be 2084 used to improve system bootup time when allocating 2085 a large amount of huge pages. 2086 The default value is 25% of the available hardware threads. 2087 2088 Note that this parameter only applies to non-gigantic huge pages. 2089 2090 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2091 of gigantic hugepages. Or using node format, the size 2092 of a CMA area per node can be specified. 2093 Format: nn[KMGTPE] or (node format) 2094 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2095 2096 Reserve a CMA area of given size and allocate gigantic 2097 hugepages using the CMA allocator. If enabled, the 2098 boot-time allocation of gigantic hugepages is skipped. 2099 2100 hugetlb_cma_only= 2101 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2102 try to allocate from the CMA areas. 2103 2104 This option does nothing if hugetlb_cma= is not also 2105 specified. 2106 2107 hugetlb_free_vmemmap= 2108 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2109 enabled. 2110 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2111 Allows heavy hugetlb users to free up some more 2112 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2113 Format: { on | off (default) } 2114 2115 on: enable HVO 2116 off: disable HVO 2117 2118 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2119 the default is on. 2120 2121 Note that the vmemmap pages may be allocated from the added 2122 memory block itself when memory_hotplug.memmap_on_memory is 2123 enabled, those vmemmap pages cannot be optimized even if this 2124 feature is enabled. Other vmemmap pages not allocated from 2125 the added memory block itself do not be affected. 2126 2127 hung_task_panic= 2128 [KNL] Number of hung tasks to trigger kernel panic. 2129 Format: <int> 2130 2131 When set to a non-zero value, a kernel panic will be triggered if 2132 the number of detected hung tasks reaches this value. 2133 2134 0: don't panic 2135 1: panic immediately on first hung task 2136 N: panic after N hung tasks are detected in a single scan 2137 2138 The default value is controlled by the 2139 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2140 selected by this boot parameter can be changed later by the 2141 kernel.hung_task_panic sysctl. 2142 2143 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2144 terminal devices. Valid values: 0..8 2145 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2146 If specified, z/VM IUCV HVC accepts connections 2147 from listed z/VM user IDs only. 2148 2149 hv_nopvspin [X86,HYPER_V,EARLY] 2150 Disables the paravirt spinlock optimizations 2151 which allow the hypervisor to 'idle' the guest 2152 on lock contention. 2153 2154 hw_protection= [HW] 2155 Format: reboot | shutdown 2156 2157 Hardware protection action taken on critical events like 2158 overtemperature or imminent voltage loss. 2159 2160 i2c_bus= [HW] Override the default board specific I2C bus speed 2161 or register an additional I2C bus that is not 2162 registered from board initialization code. 2163 Format: 2164 <bus_id>,<clkrate> 2165 2166 i2c_touchscreen_props= [HW,ACPI,X86] 2167 Set device-properties for ACPI-enumerated I2C-attached 2168 touchscreen, to e.g. fix coordinates of upside-down 2169 mounted touchscreens. If you need this option please 2170 submit a drivers/platform/x86/touchscreen_dmi.c patch 2171 adding a DMI quirk for this. 2172 2173 Format: 2174 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2175 Where <val> is one of: 2176 Omit "=<val>" entirely Set a boolean device-property 2177 Unsigned number Set a u32 device-property 2178 Anything else Set a string device-property 2179 2180 Examples (split over multiple lines): 2181 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2182 touchscreen-inverted-y 2183 2184 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2185 touchscreen-size-y=1080:touchscreen-inverted-y: 2186 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2187 2188 i8042.debug [HW] Toggle i8042 debug mode 2189 i8042.unmask_kbd_data 2190 [HW] Enable printing of interrupt data from the KBD port 2191 (disabled by default, and as a pre-condition 2192 requires that i8042.debug=1 be enabled) 2193 i8042.direct [HW] Put keyboard port into non-translated mode 2194 i8042.dumbkbd [HW] Pretend that controller can only read data from 2195 keyboard and cannot control its state 2196 (Don't attempt to blink the leds) 2197 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2198 i8042.nokbd [HW] Don't check/create keyboard port 2199 i8042.noloop [HW] Disable the AUX Loopback command while probing 2200 for the AUX port 2201 i8042.nomux [HW] Don't check presence of an active multiplexing 2202 controller 2203 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2204 controllers 2205 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2206 i8042.reset [HW] Reset the controller during init, cleanup and 2207 suspend-to-ram transitions, only during s2r 2208 transitions, or never reset 2209 Format: { 1 | Y | y | 0 | N | n } 2210 1, Y, y: always reset controller 2211 0, N, n: don't ever reset controller 2212 Default: only on s2r transitions on x86; most other 2213 architectures force reset to be always executed 2214 i8042.unlock [HW] Unlock (ignore) the keylock 2215 i8042.kbdreset [HW] Reset device connected to KBD port 2216 i8042.probe_defer 2217 [HW] Allow deferred probing upon i8042 probe errors 2218 2219 i810= [HW,DRM] 2220 2221 i915.invert_brightness= 2222 [DRM] Invert the sense of the variable that is used to 2223 set the brightness of the panel backlight. Normally a 2224 brightness value of 0 indicates backlight switched off, 2225 and the maximum of the brightness value sets the backlight 2226 to maximum brightness. If this parameter is set to 0 2227 (default) and the machine requires it, or this parameter 2228 is set to 1, a brightness value of 0 sets the backlight 2229 to maximum brightness, and the maximum of the brightness 2230 value switches the backlight off. 2231 -1 -- never invert brightness 2232 0 -- machine default 2233 1 -- force brightness inversion 2234 2235 ia32_emulation= [X86-64] 2236 Format: <bool> 2237 When true, allows loading 32-bit programs and executing 32-bit 2238 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2239 boot time. When false, unconditionally disables IA32 emulation. 2240 2241 icn= [HW,ISDN] 2242 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2243 2244 2245 idle= [X86,EARLY] 2246 Format: idle=poll, idle=halt, idle=nomwait 2247 2248 idle=poll: Don't do power saving in the idle loop 2249 using HLT, but poll for rescheduling event. This will 2250 make the CPUs eat a lot more power, but may be useful 2251 to get slightly better performance in multiprocessor 2252 benchmarks. It also makes some profiling using 2253 performance counters more accurate. Please note that 2254 on systems with MONITOR/MWAIT support (like Intel 2255 EM64T CPUs) this option has no performance advantage 2256 over the normal idle loop. It may also interact badly 2257 with hyperthreading. 2258 2259 idle=halt: Halt is forced to be used for CPU idle. 2260 In such case C2/C3 won't be used again. 2261 2262 idle=nomwait: Disable mwait for CPU C-states 2263 2264 idxd.sva= [HW] 2265 Format: <bool> 2266 Allow force disabling of Shared Virtual Memory (SVA) 2267 support for the idxd driver. By default it is set to 2268 true (1). 2269 2270 idxd.tc_override= [HW] 2271 Format: <bool> 2272 Allow override of default traffic class configuration 2273 for the device. By default it is set to false (0). 2274 2275 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2276 Format: { strict | legacy | 2008 | relaxed | emulated } 2277 Default: strict 2278 2279 Choose which programs will be accepted for execution 2280 based on the IEEE 754 NaN encoding(s) supported by 2281 the FPU and the NaN encoding requested with the value 2282 of an ELF file header flag individually set by each 2283 binary. Hardware implementations are permitted to 2284 support either or both of the legacy and the 2008 NaN 2285 encoding mode. 2286 2287 Available settings are as follows: 2288 strict accept binaries that request a NaN encoding 2289 supported by the FPU 2290 legacy only accept legacy-NaN binaries, if supported 2291 by the FPU 2292 2008 only accept 2008-NaN binaries, if supported 2293 by the FPU 2294 relaxed accept any binaries regardless of whether 2295 supported by the FPU 2296 emulated accept any binaries but enable FPU emulator 2297 if binary mode is unsupported by the FPU. 2298 2299 The FPU emulator is always able to support both NaN 2300 encodings, so if no FPU hardware is present or it has 2301 been disabled with 'nofpu', then the settings of 2302 'legacy' and '2008' strap the emulator accordingly, 2303 'relaxed' straps the emulator for both legacy-NaN and 2304 2008-NaN, whereas 'strict' enables legacy-NaN only on 2305 legacy processors and both NaN encodings on MIPS32 or 2306 MIPS64 CPUs. 2307 2308 The setting for ABS.fmt/NEG.fmt instruction execution 2309 mode generally follows that for the NaN encoding, 2310 except where unsupported by hardware. 2311 2312 ignore_loglevel [KNL,EARLY] 2313 Ignore loglevel setting - this will print /all/ 2314 kernel messages to the console. Useful for debugging. 2315 We also add it as printk module parameter, so users 2316 could change it dynamically, usually by 2317 /sys/module/printk/parameters/ignore_loglevel. 2318 2319 ignore_rlimit_data 2320 Ignore RLIMIT_DATA setting for data mappings, 2321 print warning at first misuse. Can be changed via 2322 /sys/module/kernel/parameters/ignore_rlimit_data. 2323 2324 ihash_entries= [KNL] 2325 Set number of hash buckets for inode cache. 2326 2327 ima_appraise= [IMA] appraise integrity measurements 2328 Format: { "off" | "enforce" | "fix" | "log" } 2329 default: "enforce" 2330 2331 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2332 The builtin appraise policy appraises all files 2333 owned by uid=0. 2334 2335 ima_canonical_fmt [IMA] 2336 Use the canonical format for the binary runtime 2337 measurements, instead of host native format. 2338 2339 ima_hash= [IMA] 2340 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2341 | sha512 | ... } 2342 default: "sha1" 2343 2344 The list of supported hash algorithms is defined 2345 in crypto/hash_info.h. 2346 2347 ima_policy= [IMA] 2348 The builtin policies to load during IMA setup. 2349 Format: "tcb | appraise_tcb | secure_boot | 2350 fail_securely | critical_data" 2351 2352 The "tcb" policy measures all programs exec'd, files 2353 mmap'd for exec, and all files opened with the read 2354 mode bit set by either the effective uid (euid=0) or 2355 uid=0. 2356 2357 The "appraise_tcb" policy appraises the integrity of 2358 all files owned by root. 2359 2360 The "secure_boot" policy appraises the integrity 2361 of files (eg. kexec kernel image, kernel modules, 2362 firmware, policy, etc) based on file signatures. 2363 2364 The "fail_securely" policy forces file signature 2365 verification failure also on privileged mounted 2366 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2367 flag. 2368 2369 The "critical_data" policy measures kernel integrity 2370 critical data. 2371 2372 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2373 Load a policy which meets the needs of the Trusted 2374 Computing Base. This means IMA will measure all 2375 programs exec'd, files mmap'd for exec, and all files 2376 opened for read by uid=0. 2377 2378 ima_template= [IMA] 2379 Select one of defined IMA measurements template formats. 2380 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2381 "ima-sigv2" } 2382 Default: "ima-ng" 2383 2384 ima_template_fmt= 2385 [IMA] Define a custom template format. 2386 Format: { "field1|...|fieldN" } 2387 2388 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2389 Format: <min_file_size> 2390 Set the minimal file size for using asynchronous hash. 2391 If left unspecified, ahash usage is disabled. 2392 2393 ahash performance varies for different data sizes on 2394 different crypto accelerators. This option can be used 2395 to achieve the best performance for a particular HW. 2396 2397 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2398 Format: <bufsize> 2399 Set hashing buffer size. Default: 4k. 2400 2401 ahash performance varies for different chunk sizes on 2402 different crypto accelerators. This option can be used 2403 to achieve best performance for particular HW. 2404 2405 ima= [IMA] Enable or disable IMA 2406 Format: { "off" | "on" } 2407 Default: "on" 2408 Note that disabling IMA is limited to kdump kernel. 2409 2410 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2411 Target Selection(ITS) bug in Intel CPUs. Updated 2412 microcode is also required for a fix in IBPB. 2413 2414 on: Enable mitigation (default). 2415 off: Disable mitigation. 2416 force: Force the ITS bug and deploy default 2417 mitigation. 2418 vmexit: Only deploy mitigation if CPU is affected by 2419 guest/host isolation part of ITS. 2420 stuff: Deploy RSB-fill mitigation when retpoline is 2421 also deployed. Otherwise, deploy the default 2422 mitigation. 2423 2424 For details see: 2425 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2426 2427 init= [KNL] 2428 Format: <full_path> 2429 Run specified binary instead of /sbin/init as init 2430 process. 2431 2432 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2433 for working out where the kernel is dying during 2434 startup. 2435 2436 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2437 initcall functions. Useful for debugging built-in 2438 modules and initcalls. 2439 2440 initramfs_async= [KNL] 2441 Format: <bool> 2442 Default: 1 2443 This parameter controls whether the initramfs 2444 image is unpacked asynchronously, concurrently 2445 with devices being probed and 2446 initialized. This should normally just work, 2447 but as a debugging aid, one can get the 2448 historical behaviour of the initramfs 2449 unpacking being completed before device_ and 2450 late_ initcalls. 2451 2452 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2453 2454 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2455 load the initrd. If an initrd is compiled in or 2456 specified in the bootparams, it takes priority over this 2457 setting. 2458 Format: ss[KMG],nn[KMG] 2459 Default is 0, 0 2460 2461 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2462 zeroes. 2463 Format: 0 | 1 2464 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2465 2466 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2467 Format: 0 | 1 2468 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2469 2470 init_pkru= [X86] Specify the default memory protection keys rights 2471 register contents for all processes. 0x55555554 by 2472 default (disallow access to all but pkey 0). Can 2473 override in debugfs after boot. 2474 2475 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2476 Format: <irq> 2477 2478 int_pln_enable [X86] Enable power limit notification interrupt 2479 2480 integrity_audit=[IMA] 2481 Format: { "0" | "1" } 2482 0 -- basic integrity auditing messages. (Default) 2483 1 -- additional integrity auditing messages. 2484 2485 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2486 on 2487 Enable intel iommu driver. 2488 off 2489 Disable intel iommu driver. 2490 igfx_off [Default Off] 2491 By default, gfx is mapped as normal device. If a gfx 2492 device has a dedicated DMAR unit, the DMAR unit is 2493 bypassed by not enabling DMAR with this option. In 2494 this case, gfx device will use physical address for 2495 DMA. 2496 strict [Default Off] 2497 Deprecated, equivalent to iommu.strict=1. 2498 sp_off [Default Off] 2499 By default, super page will be supported if Intel IOMMU 2500 has the capability. With this option, super page will 2501 not be supported. 2502 sm_on 2503 Enable the Intel IOMMU scalable mode if the hardware 2504 advertises that it has support for the scalable mode 2505 translation. 2506 sm_off 2507 Disallow use of the Intel IOMMU scalable mode. 2508 tboot_noforce [Default Off] 2509 Do not force the Intel IOMMU enabled under tboot. 2510 By default, tboot will force Intel IOMMU on, which 2511 could harm performance of some high-throughput 2512 devices like 40GBit network cards, even if identity 2513 mapping is enabled. 2514 Note that using this option lowers the security 2515 provided by tboot because it makes the system 2516 vulnerable to DMA attacks. 2517 2518 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2519 0 disables intel_idle and fall back on acpi_idle. 2520 1 to 9 specify maximum depth of C-state. 2521 2522 intel_pstate= [X86,EARLY] 2523 disable 2524 Do not enable intel_pstate as the default 2525 scaling driver for the supported processors 2526 active 2527 Use intel_pstate driver to bypass the scaling 2528 governors layer of cpufreq and provides it own 2529 algorithms for p-state selection. There are two 2530 P-state selection algorithms provided by 2531 intel_pstate in the active mode: powersave and 2532 performance. The way they both operate depends 2533 on whether or not the hardware managed P-states 2534 (HWP) feature has been enabled in the processor 2535 and possibly on the processor model. 2536 passive 2537 Use intel_pstate as a scaling driver, but configure it 2538 to work with generic cpufreq governors (instead of 2539 enabling its internal governor). This mode cannot be 2540 used along with the hardware-managed P-states (HWP) 2541 feature. 2542 force 2543 Enable intel_pstate on systems that prohibit it by default 2544 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2545 instead of acpi-cpufreq may disable platform features, such 2546 as thermal controls and power capping, that rely on ACPI 2547 P-States information being indicated to OSPM and therefore 2548 should be used with caution. This option does not work with 2549 processors that aren't supported by the intel_pstate driver 2550 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2551 no_hwp 2552 Do not enable hardware P state control (HWP) 2553 if available. 2554 hwp_only 2555 Only load intel_pstate on systems which support 2556 hardware P state control (HWP) if available. 2557 support_acpi_ppc 2558 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2559 Description Table, specifies preferred power management 2560 profile as "Enterprise Server" or "Performance Server", 2561 then this feature is turned on by default. 2562 per_cpu_perf_limits 2563 Allow per-logical-CPU P-State performance control limits using 2564 cpufreq sysfs interface 2565 no_cas 2566 Do not enable capacity-aware scheduling (CAS) on 2567 hybrid systems 2568 2569 intremap= [X86-64,Intel-IOMMU,EARLY] 2570 on enable Interrupt Remapping (default) 2571 off disable Interrupt Remapping 2572 nosid disable Source ID checking 2573 no_x2apic_optout 2574 BIOS x2APIC opt-out request will be ignored 2575 nopost disable Interrupt Posting 2576 posted_msi 2577 enable MSIs delivered as posted interrupts 2578 2579 iomem= Disable strict checking of access to MMIO memory 2580 strict regions from userspace. 2581 relaxed 2582 2583 iommu= [X86,EARLY] 2584 2585 off 2586 Don't initialize and use any kind of IOMMU. 2587 2588 force 2589 Force the use of the hardware IOMMU even when 2590 it is not actually needed (e.g. because < 3 GB 2591 memory). 2592 2593 noforce 2594 Don't force hardware IOMMU usage when it is not 2595 needed. (default). 2596 2597 biomerge 2598 panic 2599 nopanic 2600 merge 2601 nomerge 2602 2603 soft 2604 Use software bounce buffering (SWIOTLB) (default for 2605 Intel machines). This can be used to prevent the usage 2606 of an available hardware IOMMU. 2607 2608 [X86] 2609 pt 2610 [X86] 2611 nopt 2612 [PPC/POWERNV] 2613 nobypass 2614 Disable IOMMU bypass, using IOMMU for PCI devices. 2615 2616 [X86] 2617 AMD Gart HW IOMMU-specific options: 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 fullflush 2626 Flush IOMMU on each allocation (default). 2627 2628 nofullflush 2629 Don't use IOMMU fullflush. 2630 2631 memaper[=<order>] 2632 Allocate an own aperture over RAM with size 2633 32MB<<order. (default: order=1, i.e. 64MB) 2634 2635 merge 2636 Do scatter-gather (SG) merging. Implies "force" 2637 (experimental). 2638 2639 nomerge 2640 Don't do scatter-gather (SG) merging. 2641 2642 noaperture 2643 Ask the IOMMU not to touch the aperture for AGP. 2644 2645 noagp 2646 Don't initialize the AGP driver and use full aperture. 2647 2648 panic 2649 Always panic when IOMMU overflows. 2650 2651 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2652 Format: { "0" | "1" } 2653 0 - Try to allocate a 32-bit DMA address first, before 2654 falling back to the full range if needed. 2655 1 - Allocate directly from the full usable range, 2656 forcing Dual Address Cycle for PCI cards supporting 2657 greater than 32-bit addressing. 2658 2659 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2660 Format: { "0" | "1" } 2661 0 - Lazy mode. 2662 Request that DMA unmap operations use deferred 2663 invalidation of hardware TLBs, for increased 2664 throughput at the cost of reduced device isolation. 2665 Will fall back to strict mode if not supported by 2666 the relevant IOMMU driver. 2667 1 - Strict mode. 2668 DMA unmap operations invalidate IOMMU hardware TLBs 2669 synchronously. 2670 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2671 Note: on x86, strict mode specified via one of the 2672 legacy driver-specific options takes precedence. 2673 2674 iommu.passthrough= 2675 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2676 Format: { "0" | "1" } 2677 0 - Use IOMMU translation for DMA. 2678 1 - Bypass the IOMMU for DMA. 2679 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2680 2681 io7= [HW] IO7 for Marvel-based Alpha systems 2682 See comment before marvel_specify_io7 in 2683 arch/alpha/kernel/core_marvel.c. 2684 2685 io_delay= [X86,EARLY] I/O delay method 2686 0x80 2687 Standard port 0x80 based delay 2688 0xed 2689 Alternate port 0xed based delay (needed on some systems) 2690 udelay 2691 Simple two microseconds delay 2692 none 2693 No delay 2694 2695 ip= [IP_PNP] 2696 See Documentation/admin-guide/nfs/nfsroot.rst. 2697 2698 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2699 IPC identifiers from 32,768 to 16,777,216. 2700 2701 ipe.enforce= [IPE] 2702 Format: <bool> 2703 Determine whether IPE starts in permissive (0) or 2704 enforce (1) mode. The default is enforce. 2705 2706 ipe.success_audit= 2707 [IPE] 2708 Format: <bool> 2709 Start IPE with success auditing enabled, emitting 2710 an audit event when a binary is allowed. The default 2711 is 0. 2712 2713 irqaffinity= [SMP] Set the default irq affinity mask 2714 The argument is a cpu list, as described above. 2715 2716 irqchip.gicv2_force_probe= 2717 [ARM,ARM64,EARLY] 2718 Format: <bool> 2719 Force the kernel to look for the second 4kB page 2720 of a GICv2 controller even if the memory range 2721 exposed by the device tree is too small. 2722 2723 irqchip.gicv3_nolpi= 2724 [ARM,ARM64,EARLY] 2725 Force the kernel to ignore the availability of 2726 LPIs (and by consequence ITSs). Intended for system 2727 that use the kernel as a bootloader, and thus want 2728 to let secondary kernels in charge of setting up 2729 LPIs. 2730 2731 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2732 Enables support for pseudo-NMIs in the kernel. This 2733 requires the kernel to be built with 2734 CONFIG_ARM64_PSEUDO_NMI. 2735 2736 irqchip.riscv_imsic_noipi 2737 [RISC-V,EARLY] 2738 Force the kernel to not use IMSIC software injected MSIs 2739 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2740 and thus want to reduce MMIO traps when triggering IPIs 2741 to multiple harts. 2742 2743 irqfixup [HW] 2744 When an interrupt is not handled search all handlers 2745 for it. Intended to get systems with badly broken 2746 firmware running. 2747 2748 irqhandler.duration_warn_us= [KNL] 2749 Warn if an IRQ handler exceeds the specified duration 2750 threshold in microseconds. Useful for identifying 2751 long-running IRQs in the system. 2752 2753 irqpoll [HW] 2754 When an interrupt is not handled search all handlers 2755 for it. Also check all handlers each timer 2756 interrupt. Intended to get systems with badly broken 2757 firmware running. 2758 2759 isapnp= [ISAPNP] 2760 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2761 2762 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2763 [Deprecated - use cpusets instead] 2764 Format: [flag-list,]<cpu-list> 2765 2766 Specify one or more CPUs to isolate from disturbances 2767 specified in the flag list (default: domain): 2768 2769 nohz 2770 Disable the tick when a single task runs as well as 2771 disabling other kernel noises like having RCU callbacks 2772 offloaded. This is equivalent to the nohz_full parameter. 2773 2774 A residual 1Hz tick is offloaded to workqueues, which you 2775 need to affine to housekeeping through the global 2776 workqueue's affinity configured via the 2777 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2778 by using the 'domain' flag described below. 2779 2780 NOTE: by default the global workqueue runs on all CPUs, 2781 so to protect individual CPUs the 'cpumask' file has to 2782 be configured manually after bootup. 2783 2784 domain 2785 Isolate from the general SMP balancing and scheduling 2786 algorithms. Note that performing domain isolation this way 2787 is irreversible: it's not possible to bring back a CPU to 2788 the domains once isolated through isolcpus. It's strongly 2789 advised to use cpusets instead to disable scheduler load 2790 balancing through the "cpuset.sched_load_balance" file. 2791 It offers a much more flexible interface where CPUs can 2792 move in and out of an isolated set anytime. 2793 2794 You can move a process onto or off an "isolated" CPU via 2795 the CPU affinity syscalls or cpuset. 2796 <cpu number> begins at 0 and the maximum value is 2797 "number of CPUs in system - 1". 2798 2799 managed_irq 2800 2801 Isolate from being targeted by managed interrupts 2802 which have an interrupt mask containing isolated 2803 CPUs. The affinity of managed interrupts is 2804 handled by the kernel and cannot be changed via 2805 the /proc/irq/* interfaces. 2806 2807 This isolation is best effort and only effective 2808 if the automatically assigned interrupt mask of a 2809 device queue contains isolated and housekeeping 2810 CPUs. If housekeeping CPUs are online then such 2811 interrupts are directed to the housekeeping CPU 2812 so that IO submitted on the housekeeping CPU 2813 cannot disturb the isolated CPU. 2814 2815 If a queue's affinity mask contains only isolated 2816 CPUs then this parameter has no effect on the 2817 interrupt routing decision, though interrupts are 2818 only delivered when tasks running on those 2819 isolated CPUs submit IO. IO submitted on 2820 housekeeping CPUs has no influence on those 2821 queues. 2822 2823 The format of <cpu-list> is described above. 2824 2825 iucv= [HW,NET] 2826 2827 ivrs_ioapic [HW,X86-64] 2828 Provide an override to the IOAPIC-ID<->DEVICE-ID 2829 mapping provided in the IVRS ACPI table. 2830 By default, PCI segment is 0, and can be omitted. 2831 2832 For example, to map IOAPIC-ID decimal 10 to 2833 PCI segment 0x1 and PCI device 00:14.0, 2834 write the parameter as: 2835 ivrs_ioapic=10@0001:00:14.0 2836 2837 Deprecated formats: 2838 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2839 write the parameter as: 2840 ivrs_ioapic[10]=00:14.0 2841 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2842 PCI device 00:14.0 write the parameter as: 2843 ivrs_ioapic[10]=0001:00:14.0 2844 2845 ivrs_hpet [HW,X86-64] 2846 Provide an override to the HPET-ID<->DEVICE-ID 2847 mapping provided in the IVRS ACPI table. 2848 By default, PCI segment is 0, and can be omitted. 2849 2850 For example, to map HPET-ID decimal 10 to 2851 PCI segment 0x1 and PCI device 00:14.0, 2852 write the parameter as: 2853 ivrs_hpet=10@0001:00:14.0 2854 2855 Deprecated formats: 2856 * To map HPET-ID decimal 0 to PCI device 00:14.0 2857 write the parameter as: 2858 ivrs_hpet[0]=00:14.0 2859 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2860 PCI device 00:14.0 write the parameter as: 2861 ivrs_ioapic[10]=0001:00:14.0 2862 2863 ivrs_acpihid [HW,X86-64] 2864 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2865 mapping provided in the IVRS ACPI table. 2866 By default, PCI segment is 0, and can be omitted. 2867 2868 For example, to map UART-HID:UID AMD0020:0 to 2869 PCI segment 0x1 and PCI device ID 00:14.5, 2870 write the parameter as: 2871 ivrs_acpihid=AMD0020:0@0001:00:14.5 2872 2873 Deprecated formats: 2874 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2875 PCI device ID 00:14.5, write the parameter as: 2876 ivrs_acpihid[00:14.5]=AMD0020:0 2877 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2878 PCI device ID 00:14.5, write the parameter as: 2879 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2880 2881 js= [HW,JOY] Analog joystick 2882 See Documentation/input/joydev/joystick.rst. 2883 2884 kasan_multi_shot 2885 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2886 report on every invalid memory access. Without this 2887 parameter KASAN will print report only for the first 2888 invalid access. 2889 2890 keep_bootcon [KNL,EARLY] 2891 Do not unregister boot console at start. This is only 2892 useful for debugging when something happens in the window 2893 between unregistering the boot console and initializing 2894 the real console. 2895 2896 keepinitrd [HW,ARM] See retain_initrd. 2897 2898 kernelcore= [KNL,X86,PPC,EARLY] 2899 Format: nn[KMGTPE] | nn% | "mirror" 2900 This parameter specifies the amount of memory usable by 2901 the kernel for non-movable allocations. The requested 2902 amount is spread evenly throughout all nodes in the 2903 system as ZONE_NORMAL. The remaining memory is used for 2904 movable memory in its own zone, ZONE_MOVABLE. In the 2905 event, a node is too small to have both ZONE_NORMAL and 2906 ZONE_MOVABLE, kernelcore memory will take priority and 2907 other nodes will have a larger ZONE_MOVABLE. 2908 2909 ZONE_MOVABLE is used for the allocation of pages that 2910 may be reclaimed or moved by the page migration 2911 subsystem. Note that allocations like PTEs-from-HighMem 2912 still use the HighMem zone if it exists, and the Normal 2913 zone if it does not. 2914 2915 It is possible to specify the exact amount of memory in 2916 the form of "nn[KMGTPE]", a percentage of total system 2917 memory in the form of "nn%", or "mirror". If "mirror" 2918 option is specified, mirrored (reliable) memory is used 2919 for non-movable allocations and remaining memory is used 2920 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2921 are exclusive, so you cannot specify multiple forms. 2922 2923 kfence.burst= [MM,KFENCE] The number of additional successive 2924 allocations to be attempted through KFENCE for each 2925 sample interval. 2926 Format: <unsigned integer> 2927 Default: 0 2928 2929 kfence.check_on_panic= 2930 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2931 canaries on panic. 2932 Format: <bool> 2933 Default: false 2934 2935 kfence.deferrable= 2936 [MM,KFENCE] Whether to use a deferrable timer to trigger 2937 allocations. This avoids forcing CPU wake-ups if the 2938 system is idle, at the risk of a less predictable 2939 sample interval. 2940 Format: <bool> 2941 Default: CONFIG_KFENCE_DEFERRABLE 2942 2943 kfence.sample_interval= 2944 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2945 Format: <unsigned integer> 2946 0 - Disable KFENCE. 2947 >0 - Enabled KFENCE with given sample interval. 2948 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2949 2950 kfence.skip_covered_thresh= 2951 [MM,KFENCE] If pool utilization reaches this threshold 2952 (pool usage%), KFENCE limits currently covered 2953 allocations of the same source from further filling 2954 up the pool. 2955 Format: <unsigned integer> 2956 Default: 75 2957 2958 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2959 Format: <Controller#>[,poll interval] 2960 The controller # is the number of the ehci usb debug 2961 port as it is probed via PCI. The poll interval is 2962 optional and is the number seconds in between 2963 each poll cycle to the debug port in case you need 2964 the functionality for interrupting the kernel with 2965 gdb or control-c on the dbgp connection. When 2966 not using this parameter you use sysrq-g to break into 2967 the kernel debugger. 2968 2969 kgdboc= [KGDB,HW] kgdb over consoles. 2970 Requires a tty driver that supports console polling, 2971 or a supported polling keyboard driver (non-usb). 2972 Serial only format: <serial_device>[,baud] 2973 keyboard only format: kbd 2974 keyboard and serial format: kbd,<serial_device>[,baud] 2975 Optional Kernel mode setting: 2976 kms, kbd format: kms,kbd 2977 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2978 2979 kgdboc_earlycon= [KGDB,HW,EARLY] 2980 If the boot console provides the ability to read 2981 characters and can work in polling mode, you can use 2982 this parameter to tell kgdb to use it as a backend 2983 until the normal console is registered. Intended to 2984 be used together with the kgdboc parameter which 2985 specifies the normal console to transition to. 2986 2987 The name of the early console should be specified 2988 as the value of this parameter. Note that the name of 2989 the early console might be different than the tty 2990 name passed to kgdboc. It's OK to leave the value 2991 blank and the first boot console that implements 2992 read() will be picked. 2993 2994 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 2995 kernel debugger at the earliest opportunity. 2996 2997 kho= [KEXEC,EARLY] 2998 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 2999 Enables or disables Kexec HandOver. 3000 "0" | "off" | "n" - kexec handover is disabled 3001 "1" | "on" | "y" - kexec handover is enabled 3002 3003 kho_scratch= [KEXEC,EARLY] 3004 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3005 Defines the size of the KHO scratch region. The KHO 3006 scratch regions are physically contiguous memory 3007 ranges that can only be used for non-kernel 3008 allocations. That way, even when memory is heavily 3009 fragmented with handed over memory, the kexeced 3010 kernel will always have enough contiguous ranges to 3011 bootstrap itself. 3012 3013 It is possible to specify the exact amount of 3014 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3015 where the first parameter defines the size of a low 3016 memory scratch area, the second parameter defines 3017 the size of a global scratch area and the third 3018 parameter defines the size of additional per-node 3019 scratch areas. The form "nn%" defines scale factor 3020 (in percents) of memory that was used during boot. 3021 3022 kmac= [MIPS] Korina ethernet MAC address. 3023 Configure the RouterBoard 532 series on-chip 3024 Ethernet adapter MAC address. 3025 3026 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3027 Valid arguments: on, off 3028 Default: on 3029 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3030 the default is off. 3031 3032 kprobe_event=[probe-list] 3033 [FTRACE] Add kprobe events and enable at boot time. 3034 The probe-list is a semicolon delimited list of probe 3035 definitions. Each definition is same as kprobe_events 3036 interface, but the parameters are comma delimited. 3037 For example, to add a kprobe event on vfs_read with 3038 arg1 and arg2, add to the command line; 3039 3040 kprobe_event=p,vfs_read,$arg1,$arg2 3041 3042 See also Documentation/trace/kprobetrace.rst "Kernel 3043 Boot Parameter" section. 3044 3045 kpti= [ARM64,EARLY] Control page table isolation of 3046 user and kernel address spaces. 3047 Default: enabled on cores which need mitigation. 3048 0: force disabled 3049 1: force enabled 3050 3051 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3052 CONFIG_KUNIT to be set to be fully enabled. The 3053 default value can be overridden via 3054 KUNIT_DEFAULT_ENABLED. 3055 Default is 1 (enabled) 3056 3057 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3058 Default is 0 (don't ignore, but inject #GP) 3059 3060 kvm.eager_page_split= 3061 [KVM,X86] Controls whether or not KVM will try to 3062 proactively split all huge pages during dirty logging. 3063 Eager page splitting reduces interruptions to vCPU 3064 execution by eliminating the write-protection faults 3065 and MMU lock contention that would otherwise be 3066 required to split huge pages lazily. 3067 3068 VM workloads that rarely perform writes or that write 3069 only to a small region of VM memory may benefit from 3070 disabling eager page splitting to allow huge pages to 3071 still be used for reads. 3072 3073 The behavior of eager page splitting depends on whether 3074 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3075 disabled, all huge pages in a memslot will be eagerly 3076 split when dirty logging is enabled on that memslot. If 3077 enabled, eager page splitting will be performed during 3078 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3079 cleared. 3080 3081 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3082 3083 Default is Y (on). 3084 3085 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3086 If enabled, KVM will enable virtualization in hardware 3087 when KVM is loaded, and disable virtualization when KVM 3088 is unloaded (if KVM is built as a module). 3089 3090 If disabled, KVM will dynamically enable and disable 3091 virtualization on-demand when creating and destroying 3092 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3093 number of VMs. 3094 3095 Enabling virtualization at module load avoids potential 3096 latency for creation of the 0=>1 VM, as KVM serializes 3097 virtualization enabling across all online CPUs. The 3098 "cost" of enabling virtualization when KVM is loaded, 3099 is that doing so may interfere with using out-of-tree 3100 hypervisors that want to "own" virtualization hardware. 3101 3102 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3103 Default is false (don't support). 3104 3105 kvm.nx_huge_pages= 3106 [KVM] Controls the software workaround for the 3107 X86_BUG_ITLB_MULTIHIT bug. 3108 force : Always deploy workaround. 3109 off : Never deploy workaround. 3110 auto : Deploy workaround based on the presence of 3111 X86_BUG_ITLB_MULTIHIT. 3112 3113 Default is 'auto'. 3114 3115 If the software workaround is enabled for the host, 3116 guests do need not to enable it for nested guests. 3117 3118 kvm.nx_huge_pages_recovery_ratio= 3119 [KVM] Controls how many 4KiB pages are periodically zapped 3120 back to huge pages. 0 disables the recovery, otherwise if 3121 the value is N KVM will zap 1/Nth of the 4KiB pages every 3122 period (see below). The default is 60. 3123 3124 kvm.nx_huge_pages_recovery_period_ms= 3125 [KVM] Controls the time period at which KVM zaps 4KiB pages 3126 back to huge pages. If the value is a non-zero N, KVM will 3127 zap a portion (see ratio above) of the pages every N msecs. 3128 If the value is 0 (the default), KVM will pick a period based 3129 on the ratio, such that a page is zapped after 1 hour on average. 3130 3131 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3132 KVM/SVM. Default is 1 (enabled). 3133 3134 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3135 a.k.a. Two-Dimensional Page Tables. Default is 1 3136 (enabled). Disable by KVM if hardware lacks support 3137 for NPT. 3138 3139 kvm-amd.ciphertext_hiding_asids= 3140 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3141 to SNP private memory from reading ciphertext. Instead, 3142 reads will see constant default values (0xff). 3143 3144 If ciphertext hiding is enabled, the joint SEV-ES and 3145 SEV-SNP ASID space is partitioned into separate SEV-ES 3146 and SEV-SNP ASID ranges, with the SEV-SNP range being 3147 [1..max_snp_asid] and the SEV-ES range being 3148 (max_snp_asid..min_sev_asid), where min_sev_asid is 3149 enumerated by CPUID.0x.8000_001F[EDX]. 3150 3151 A non-zero value enables SEV-SNP ciphertext hiding and 3152 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3153 KVM caps the number of SEV-SNP ASIDs at the maximum 3154 possible value, e.g. specifying -1u will assign all 3155 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3156 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3157 max_snp_asid == min_sev_asid-1, will effectively make 3158 SEV-ES unusable. 3159 3160 kvm-arm.mode= 3161 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3162 operation. 3163 3164 none: Forcefully disable KVM. 3165 3166 nvhe: Standard nVHE-based mode, without support for 3167 protected guests. 3168 3169 protected: Mode with support for guests whose state is 3170 kept private from the host, using VHE or 3171 nVHE depending on HW support. 3172 3173 nested: VHE-based mode with support for nested 3174 virtualization. Requires at least ARMv8.4 3175 hardware (with FEAT_NV2). 3176 3177 Defaults to VHE/nVHE based on hardware support. Setting 3178 mode to "protected" will disable kexec and hibernation 3179 for the host. To force nVHE on VHE hardware, add 3180 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3181 command-line. 3182 "nested" is experimental and should be used with 3183 extreme caution. 3184 3185 kvm-arm.vgic_v3_group0_trap= 3186 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3187 system registers 3188 3189 kvm-arm.vgic_v3_group1_trap= 3190 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3191 system registers 3192 3193 kvm-arm.vgic_v3_common_trap= 3194 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3195 system registers 3196 3197 kvm-arm.vgic_v4_enable= 3198 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3199 injection of LPIs. 3200 3201 kvm-arm.wfe_trap_policy= 3202 [KVM,ARM] Control when to set WFE instruction trap for 3203 KVM VMs. Traps are allowed but not guaranteed by the 3204 CPU architecture. 3205 3206 trap: set WFE instruction trap 3207 3208 notrap: clear WFE instruction trap 3209 3210 kvm-arm.wfi_trap_policy= 3211 [KVM,ARM] Control when to set WFI instruction trap for 3212 KVM VMs. Traps are allowed but not guaranteed by the 3213 CPU architecture. 3214 3215 trap: set WFI instruction trap 3216 3217 notrap: clear WFI instruction trap 3218 3219 kvm_cma_resv_ratio=n [PPC,EARLY] 3220 Reserves given percentage from system memory area for 3221 contiguous memory allocation for KVM hash pagetable 3222 allocation. 3223 By default it reserves 5% of total system memory. 3224 Format: <integer> 3225 Default: 5 3226 3227 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3228 a.k.a. Two-Dimensional Page Tables. Default is 1 3229 (enabled). Disable by KVM if hardware lacks support 3230 for EPT. 3231 3232 kvm-intel.emulate_invalid_guest_state= 3233 [KVM,Intel] Control whether to emulate invalid guest 3234 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3235 as guest state is never invalid for unrestricted 3236 guests. This param doesn't apply to nested guests (L2), 3237 as KVM never emulates invalid L2 guest state. 3238 Default is 1 (enabled). 3239 3240 kvm-intel.flexpriority= 3241 [KVM,Intel] Control KVM's use of FlexPriority feature 3242 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3243 hardware lacks support for it. 3244 3245 kvm-intel.nested= 3246 [KVM,Intel] Control nested virtualization feature in 3247 KVM/VMX. Default is 1 (enabled). 3248 3249 kvm-intel.unrestricted_guest= 3250 [KVM,Intel] Control KVM's use of unrestricted guest 3251 feature (virtualized real and unpaged mode). Default 3252 is 1 (enabled). Disable by KVM if EPT is disabled or 3253 hardware lacks support for it. 3254 3255 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3256 CVE-2018-3620. 3257 3258 Valid arguments: never, cond, always 3259 3260 always: L1D cache flush on every VMENTER. 3261 cond: Flush L1D on VMENTER only when the code between 3262 VMEXIT and VMENTER can leak host memory. 3263 never: Disables the mitigation 3264 3265 Default is cond (do L1 cache flush in specific instances) 3266 3267 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3268 Identification feature (tagged TLBs). Default is 1 3269 (enabled). Disable by KVM if hardware lacks support 3270 for it. 3271 3272 l1d_flush= [X86,INTEL,EARLY] 3273 Control mitigation for L1D based snooping vulnerability. 3274 3275 Certain CPUs are vulnerable to an exploit against CPU 3276 internal buffers which can forward information to a 3277 disclosure gadget under certain conditions. 3278 3279 In vulnerable processors, the speculatively 3280 forwarded data can be used in a cache side channel 3281 attack, to access data to which the attacker does 3282 not have direct access. 3283 3284 This parameter controls the mitigation. The 3285 options are: 3286 3287 on - enable the interface for the mitigation 3288 3289 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3290 affected CPUs 3291 3292 The kernel PTE inversion protection is unconditionally 3293 enabled and cannot be disabled. 3294 3295 full 3296 Provides all available mitigations for the 3297 L1TF vulnerability. Disables SMT and 3298 enables all mitigations in the 3299 hypervisors, i.e. unconditional L1D flush. 3300 3301 SMT control and L1D flush control via the 3302 sysfs interface is still possible after 3303 boot. Hypervisors will issue a warning 3304 when the first VM is started in a 3305 potentially insecure configuration, 3306 i.e. SMT enabled or L1D flush disabled. 3307 3308 full,force 3309 Same as 'full', but disables SMT and L1D 3310 flush runtime control. Implies the 3311 'nosmt=force' command line option. 3312 (i.e. sysfs control of SMT is disabled.) 3313 3314 flush 3315 Leaves SMT enabled and enables the default 3316 hypervisor mitigation, i.e. conditional 3317 L1D flush. 3318 3319 SMT control and L1D flush control via the 3320 sysfs interface is still possible after 3321 boot. Hypervisors will issue a warning 3322 when the first VM is started in a 3323 potentially insecure configuration, 3324 i.e. SMT enabled or L1D flush disabled. 3325 3326 flush,nosmt 3327 3328 Disables SMT and enables the default 3329 hypervisor mitigation. 3330 3331 SMT control and L1D flush control via the 3332 sysfs interface is still possible after 3333 boot. Hypervisors will issue a warning 3334 when the first VM is started in a 3335 potentially insecure configuration, 3336 i.e. SMT enabled or L1D flush disabled. 3337 3338 flush,nowarn 3339 Same as 'flush', but hypervisors will not 3340 warn when a VM is started in a potentially 3341 insecure configuration. 3342 3343 off 3344 Disables hypervisor mitigations and doesn't 3345 emit any warnings. 3346 It also drops the swap size and available 3347 RAM limit restriction on both hypervisor and 3348 bare metal. 3349 3350 Default is 'flush'. 3351 3352 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3353 3354 l2cr= [PPC] 3355 3356 l3cr= [PPC] 3357 3358 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3359 disabled it. 3360 3361 lapic= [X86,APIC] Do not use TSC deadline 3362 value for LAPIC timer one-shot implementation. Default 3363 back to the programmable timer unit in the LAPIC. 3364 Format: notscdeadline 3365 3366 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3367 in C2 power state. 3368 3369 libata.dma= [LIBATA] DMA control 3370 libata.dma=0 Disable all PATA and SATA DMA 3371 libata.dma=1 PATA and SATA Disk DMA only 3372 libata.dma=2 ATAPI (CDROM) DMA only 3373 libata.dma=4 Compact Flash DMA only 3374 Combinations also work, so libata.dma=3 enables DMA 3375 for disks and CDROMs, but not CFs. 3376 3377 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3378 libata.ignore_hpa=0 keep BIOS limits (default) 3379 libata.ignore_hpa=1 ignore limits, using full disk 3380 3381 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3382 when set. 3383 Format: <int> 3384 3385 libata.force= [LIBATA] Force configurations. The format is a comma- 3386 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3387 PORT and DEVICE are decimal numbers matching port, link 3388 or device. Basically, it matches the ATA ID string 3389 printed on console by libata. If the whole ID part is 3390 omitted, the last PORT and DEVICE values are used. If 3391 ID hasn't been specified yet, the configuration applies 3392 to all ports, links and devices. 3393 3394 If only DEVICE is omitted, the parameter applies to 3395 the port and all links and devices behind it. DEVICE 3396 number of 0 either selects the first device or the 3397 first fan-out link behind PMP device. It does not 3398 select the host link. DEVICE number of 15 selects the 3399 host link and device attached to it. 3400 3401 The VAL specifies the configuration to force. As long 3402 as there is no ambiguity, shortcut notation is allowed. 3403 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3404 The following configurations can be forced. 3405 3406 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3407 Any ID with matching PORT is used. 3408 3409 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3410 3411 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3412 udma[/][16,25,33,44,66,100,133] notation is also 3413 allowed. 3414 3415 * nohrst, nosrst, norst: suppress hard, soft and both 3416 resets. 3417 3418 * rstonce: only attempt one reset during hot-unplug 3419 link recovery. 3420 3421 * [no]dbdelay: Enable or disable the extra 200ms delay 3422 before debouncing a link PHY and device presence 3423 detection. 3424 3425 * [no]ncq: Turn on or off NCQ. 3426 3427 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3428 3429 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3430 3431 * [no]trim: Enable or disable (unqueued) TRIM. 3432 3433 * trim_zero: Indicate that TRIM command zeroes data. 3434 3435 * max_trim_128m: Set 128M maximum trim size limit. 3436 3437 * [no]dma: Turn on or off DMA transfers. 3438 3439 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3440 3441 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3442 commands that are not a multiple of 16 bytes. 3443 3444 * [no]dmalog: Enable or disable the use of the 3445 READ LOG DMA EXT command to access logs. 3446 3447 * [no]iddevlog: Enable or disable access to the 3448 identify device data log. 3449 3450 * [no]logdir: Enable or disable access to the general 3451 purpose log directory. 3452 3453 * max_sec_128: Set transfer size limit to 128 sectors. 3454 3455 * max_sec_1024: Set or clear transfer size limit to 3456 1024 sectors. 3457 3458 * max_sec_lba48: Set or clear transfer size limit to 3459 65535 sectors. 3460 3461 * external: Mark port as external (hotplug-capable). 3462 3463 * [no]lpm: Enable or disable link power management. 3464 3465 * [no]setxfer: Indicate if transfer speed mode setting 3466 should be skipped. 3467 3468 * [no]fua: Disable or enable FUA (Force Unit Access) 3469 support for devices supporting this feature. 3470 3471 * dump_id: Dump IDENTIFY data. 3472 3473 * disable: Disable this device. 3474 3475 If there are multiple matching configurations changing 3476 the same attribute, the last one is used. 3477 3478 liveupdate= [KNL,EARLY] 3479 Format: <bool> 3480 Enable Live Update Orchestrator (LUO). 3481 Default: off. 3482 3483 lockd.nlm_grace_period=P [NFS] Assign grace period. 3484 Format: <integer> 3485 3486 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3487 Format: <integer> 3488 3489 lockd.nlm_timeout=T [NFS] Assign timeout value. 3490 Format: <integer> 3491 3492 lockd.nlm_udpport=M [NFS] Assign UDP port. 3493 Format: <integer> 3494 3495 lockdown= [SECURITY,EARLY] 3496 { integrity | confidentiality } 3497 Enable the kernel lockdown feature. If set to 3498 integrity, kernel features that allow userland to 3499 modify the running kernel are disabled. If set to 3500 confidentiality, kernel features that allow userland 3501 to extract confidential information from the kernel 3502 are also disabled. 3503 3504 locktorture.acq_writer_lim= [KNL] 3505 Set the time limit in jiffies for a lock 3506 acquisition. Acquisitions exceeding this limit 3507 will result in a splat once they do complete. 3508 3509 locktorture.bind_readers= [KNL] 3510 Specify the list of CPUs to which the readers are 3511 to be bound. 3512 3513 locktorture.bind_writers= [KNL] 3514 Specify the list of CPUs to which the writers are 3515 to be bound. 3516 3517 locktorture.call_rcu_chains= [KNL] 3518 Specify the number of self-propagating call_rcu() 3519 chains to set up. These are used to ensure that 3520 there is a high probability of an RCU grace period 3521 in progress at any given time. Defaults to 0, 3522 which disables these call_rcu() chains. 3523 3524 locktorture.long_hold= [KNL] 3525 Specify the duration in milliseconds for the 3526 occasional long-duration lock hold time. Defaults 3527 to 100 milliseconds. Select 0 to disable. 3528 3529 locktorture.nested_locks= [KNL] 3530 Specify the maximum lock nesting depth that 3531 locktorture is to exercise, up to a limit of 8 3532 (MAX_NESTED_LOCKS). Specify zero to disable. 3533 Note that this parameter is ineffective on types 3534 of locks that do not support nested acquisition. 3535 3536 locktorture.nreaders_stress= [KNL] 3537 Set the number of locking read-acquisition kthreads. 3538 Defaults to being automatically set based on the 3539 number of online CPUs. 3540 3541 locktorture.nwriters_stress= [KNL] 3542 Set the number of locking write-acquisition kthreads. 3543 3544 locktorture.onoff_holdoff= [KNL] 3545 Set time (s) after boot for CPU-hotplug testing. 3546 3547 locktorture.onoff_interval= [KNL] 3548 Set time (s) between CPU-hotplug operations, or 3549 zero to disable CPU-hotplug testing. 3550 3551 locktorture.rt_boost= [KNL] 3552 Do periodic testing of real-time lock priority 3553 boosting. Select 0 to disable, 1 to boost 3554 only rt_mutex, and 2 to boost unconditionally. 3555 Defaults to 2, which might seem to be an 3556 odd choice, but which should be harmless for 3557 non-real-time spinlocks, due to their disabling 3558 of preemption. Note that non-realtime mutexes 3559 disable boosting. 3560 3561 locktorture.rt_boost_factor= [KNL] 3562 Number that determines how often and for how 3563 long priority boosting is exercised. This is 3564 scaled down by the number of writers, so that the 3565 number of boosts per unit time remains roughly 3566 constant as the number of writers increases. 3567 On the other hand, the duration of each boost 3568 increases with the number of writers. 3569 3570 locktorture.shuffle_interval= [KNL] 3571 Set task-shuffle interval (jiffies). Shuffling 3572 tasks allows some CPUs to go into dyntick-idle 3573 mode during the locktorture test. 3574 3575 locktorture.shutdown_secs= [KNL] 3576 Set time (s) after boot system shutdown. This 3577 is useful for hands-off automated testing. 3578 3579 locktorture.stat_interval= [KNL] 3580 Time (s) between statistics printk()s. 3581 3582 locktorture.stutter= [KNL] 3583 Time (s) to stutter testing, for example, 3584 specifying five seconds causes the test to run for 3585 five seconds, wait for five seconds, and so on. 3586 This tests the locking primitive's ability to 3587 transition abruptly to and from idle. 3588 3589 locktorture.torture_type= [KNL] 3590 Specify the locking implementation to test. 3591 3592 locktorture.verbose= [KNL] 3593 Enable additional printk() statements. 3594 3595 locktorture.writer_fifo= [KNL] 3596 Run the write-side locktorture kthreads at 3597 sched_set_fifo() real-time priority. 3598 3599 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3600 Format: <irq> 3601 3602 loglevel= [KNL,EARLY] 3603 All Kernel Messages with a loglevel smaller than the 3604 console loglevel will be printed to the console. It can 3605 also be changed with klogd or other programs. The 3606 loglevels are defined as follows: 3607 3608 0 (KERN_EMERG) system is unusable 3609 1 (KERN_ALERT) action must be taken immediately 3610 2 (KERN_CRIT) critical conditions 3611 3 (KERN_ERR) error conditions 3612 4 (KERN_WARNING) warning conditions 3613 5 (KERN_NOTICE) normal but significant condition 3614 6 (KERN_INFO) informational 3615 7 (KERN_DEBUG) debug-level messages 3616 3617 log_buf_len=n[KMG] [KNL,EARLY] 3618 Sets the size of the printk ring buffer, in bytes. 3619 n must be a power of two and greater than the 3620 minimal size. The minimal size is defined by 3621 LOG_BUF_SHIFT kernel config parameter. There 3622 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3623 parameter that allows to increase the default size 3624 depending on the number of CPUs. See init/Kconfig 3625 for more details. 3626 3627 logo.nologo [FB] Disables display of the built-in Linux logo. 3628 This may be used to provide more screen space for 3629 kernel log messages and is useful when debugging 3630 kernel boot problems. 3631 3632 lp=0 [LP] Specify parallel ports to use, e.g, 3633 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3634 lp=reset first parallel port). 'lp=0' disables the 3635 lp=auto printer driver. 'lp=reset' (which can be 3636 specified in addition to the ports) causes 3637 attached printers to be reset. Using 3638 lp=port1,port2,... specifies the parallel ports 3639 to associate lp devices with, starting with 3640 lp0. A port specification may be 'none' to skip 3641 that lp device, or a parport name such as 3642 'parport0'. Specifying 'lp=auto' instead of a 3643 port specification list means that device IDs 3644 from each port should be examined, to see if 3645 an IEEE 1284-compliant printer is attached; if 3646 so, the driver will manage that printer. 3647 See also header of drivers/char/lp.c. 3648 3649 lpj=n [KNL] 3650 Sets loops_per_jiffy to given constant, thus avoiding 3651 time-consuming boot-time autodetection (up to 250 ms per 3652 CPU). 0 enables autodetection (default). To determine 3653 the correct value for your kernel, boot with normal 3654 autodetection and see what value is printed. Note that 3655 on SMP systems the preset will be applied to all CPUs, 3656 which is likely to cause problems if your CPUs need 3657 significantly divergent settings. An incorrect value 3658 will cause delays in the kernel to be wrong, leading to 3659 unpredictable I/O errors and other breakage. Although 3660 unlikely, in the extreme case this might damage your 3661 hardware. 3662 3663 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3664 3665 lsm=lsm1,...,lsmN 3666 [SECURITY] Choose order of LSM initialization. This 3667 overrides CONFIG_LSM, and the "security=" parameter. 3668 3669 machtype= [Loongson] Share the same kernel image file between 3670 different yeeloong laptops. 3671 Example: machtype=lemote-yeeloong-2f-7inch 3672 3673 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3674 will bring up during bootup. maxcpus=n : n >= 0 limits 3675 the kernel to bring up 'n' processors. Surely after 3676 bootup you can bring up the other plugged cpu by executing 3677 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3678 only takes effect during system bootup. 3679 While n=0 is a special case, it is equivalent to "nosmp", 3680 which also disables the IO APIC. 3681 3682 max_loop= [LOOP] The number of loop block devices that get 3683 (loop.max_loop) unconditionally pre-created at init time. The default 3684 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3685 of statically allocating a predefined number, loop 3686 devices can be requested on-demand with the 3687 /dev/loop-control interface. 3688 3689 mce= [X86-{32,64}] 3690 3691 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3692 3693 off 3694 disable machine check 3695 3696 no_cmci 3697 disable CMCI(Corrected Machine Check Interrupt) that 3698 Intel processor supports. Usually this disablement is 3699 not recommended, but it might be handy if your 3700 hardware is misbehaving. 3701 3702 Note that you'll get more problems without CMCI than 3703 with due to the shared banks, i.e. you might get 3704 duplicated error logs. 3705 3706 dont_log_ce 3707 don't make logs for corrected errors. All events 3708 reported as corrected are silently cleared by OS. This 3709 option will be useful if you have no interest in any 3710 of corrected errors. 3711 3712 ignore_ce 3713 disable features for corrected errors, e.g. 3714 polling timer and CMCI. All events reported as 3715 corrected are not cleared by OS and remained in its 3716 error banks. 3717 3718 Usually this disablement is not recommended, however 3719 if there is an agent checking/clearing corrected 3720 errors (e.g. BIOS or hardware monitoring 3721 applications), conflicting with OS's error handling, 3722 and you cannot deactivate the agent, then this option 3723 will be a help. 3724 3725 no_lmce 3726 do not opt-in to Local MCE delivery. Use legacy method 3727 to broadcast MCEs. 3728 3729 bootlog 3730 enable logging of machine checks left over from 3731 booting. Disabled by default on AMD Fam10h and older 3732 because some BIOS leave bogus ones. 3733 3734 If your BIOS doesn't do that it's a good idea to 3735 enable though to make sure you log even machine check 3736 events that result in a reboot. On Intel systems it is 3737 enabled by default. 3738 3739 nobootlog 3740 disable boot machine check logging. 3741 3742 monarchtimeout (number) 3743 sets the time in us to wait for other CPUs on machine 3744 checks. 0 to disable. 3745 3746 bios_cmci_threshold 3747 don't overwrite the bios-set CMCI threshold. This boot 3748 option prevents Linux from overwriting the CMCI 3749 threshold set by the bios. Without this option, Linux 3750 always sets the CMCI threshold to 1. Enabling this may 3751 make memory predictive failure analysis less effective 3752 if the bios sets thresholds for memory errors since we 3753 will not see details for all errors. 3754 3755 recovery 3756 force-enable recoverable machine check code paths 3757 3758 Everything else is in sysfs now. 3759 3760 3761 md= [HW] RAID subsystems devices and level 3762 See Documentation/admin-guide/md.rst. 3763 3764 mdacon= [MDA] 3765 Format: <first>,<last> 3766 Specifies range of consoles to be captured by the MDA. 3767 3768 mds= [X86,INTEL,EARLY] 3769 Control mitigation for the Micro-architectural Data 3770 Sampling (MDS) vulnerability. 3771 3772 Certain CPUs are vulnerable to an exploit against CPU 3773 internal buffers which can forward information to a 3774 disclosure gadget under certain conditions. 3775 3776 In vulnerable processors, the speculatively 3777 forwarded data can be used in a cache side channel 3778 attack, to access data to which the attacker does 3779 not have direct access. 3780 3781 This parameter controls the MDS mitigation. The 3782 options are: 3783 3784 full - Enable MDS mitigation on vulnerable CPUs 3785 full,nosmt - Enable MDS mitigation and disable 3786 SMT on vulnerable CPUs 3787 off - Unconditionally disable MDS mitigation 3788 3789 On TAA-affected machines, mds=off can be prevented by 3790 an active TAA mitigation as both vulnerabilities are 3791 mitigated with the same mechanism so in order to disable 3792 this mitigation, you need to specify tsx_async_abort=off 3793 too. 3794 3795 Not specifying this option is equivalent to 3796 mds=full. 3797 3798 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3799 3800 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3801 Must be specified, otherwise memory size will be 0. 3802 3803 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3804 of memory Amount of memory to be used in cases 3805 as follows: 3806 3807 1 for test; 3808 2 when the kernel is not able to see the whole system memory; 3809 3 memory that lies after 'mem=' boundary is excluded from 3810 the hypervisor, then assigned to KVM guests. 3811 4 to limit the memory available for kdump kernel. 3812 3813 [ARC,MICROBLAZE] - the limit applies only to low memory, 3814 high memory is not affected. 3815 3816 [ARM64] - only limits memory covered by the linear 3817 mapping. The NOMAP regions are not affected. 3818 3819 [X86] Work as limiting max address. Use together 3820 with memmap= to avoid physical address space collisions. 3821 Without memmap= PCI devices could be placed at addresses 3822 belonging to unused RAM. 3823 3824 Note that this only takes effects during boot time since 3825 in above case 3, memory may need be hot added after boot 3826 if system memory of hypervisor is not sufficient. 3827 3828 mem=nn[KMG]@ss[KMG] 3829 [ARM,MIPS,EARLY] - override the memory layout 3830 reported by firmware. 3831 Define a memory region of size nn[KMG] starting at 3832 ss[KMG]. 3833 Multiple different regions can be specified with 3834 multiple mem= parameters on the command line. 3835 3836 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3837 memory. 3838 3839 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3840 3841 memchunk=nn[KMG] 3842 [KNL,SH] Allow user to override the default size for 3843 per-device physically contiguous DMA buffers. 3844 3845 memhp_default_state=online/offline/online_kernel/online_movable 3846 [KNL] Set the initial state for the memory hotplug 3847 onlining policy. If not specified, the default value is 3848 set according to the 3849 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3850 options. 3851 See Documentation/admin-guide/mm/memory-hotplug.rst. 3852 3853 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3854 E820 memory map, as specified by the user. 3855 Such memmap=exactmap lines can be constructed based on 3856 BIOS output or other requirements. See the memmap=nn@ss 3857 option description. 3858 3859 memmap=nn[KMG]@ss[KMG] 3860 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3861 Region of memory to be used is from ss to ss+nn. 3862 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3863 which limits max address to nn[KMG]. 3864 Multiple different regions can be specified, 3865 comma delimited. 3866 Example: 3867 memmap=100M@2G,100M#3G,1G!1024G 3868 3869 memmap=nn[KMG]#ss[KMG] 3870 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3871 Region of memory to be marked is from ss to ss+nn. 3872 3873 memmap=nn[KMG]$ss[KMG] 3874 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3875 Region of memory to be reserved is from ss to ss+nn. 3876 Example: Exclude memory from 0x18690000-0x1869ffff 3877 memmap=64K$0x18690000 3878 or 3879 memmap=0x10000$0x18690000 3880 Some bootloaders may need an escape character before '$', 3881 like Grub2, otherwise '$' and the following number 3882 will be eaten. 3883 3884 memmap=nn[KMG]!ss[KMG,EARLY] 3885 [KNL,X86] Mark specific memory as protected. 3886 Region of memory to be used, from ss to ss+nn. 3887 The memory region may be marked as e820 type 12 (0xc) 3888 and is NVDIMM or ADR memory. 3889 3890 memmap=<size>%<offset>-<oldtype>+<newtype> 3891 [KNL,ACPI,EARLY] Convert memory within the specified region 3892 from <oldtype> to <newtype>. If "-<oldtype>" is left 3893 out, the whole region will be marked as <newtype>, 3894 even if previously unavailable. If "+<newtype>" is left 3895 out, matching memory will be removed. Types are 3896 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3897 3 = ACPI, 12 = PRAM. 3898 3899 memory_corruption_check=0/1 [X86,EARLY] 3900 Some BIOSes seem to corrupt the first 64k of 3901 memory when doing things like suspend/resume. 3902 Setting this option will scan the memory 3903 looking for corruption. Enabling this will 3904 both detect corruption and prevent the kernel 3905 from using the memory being corrupted. 3906 However, it's intended as a diagnostic tool; if 3907 repeatable BIOS-originated corruption always 3908 affects the same memory, you can use memmap= 3909 to prevent the kernel from using that memory. 3910 3911 memory_corruption_check_size=size [X86,EARLY] 3912 By default it checks for corruption in the low 3913 64k, making this memory unavailable for normal 3914 use. Use this parameter to scan for 3915 corruption in more or less memory. 3916 3917 memory_corruption_check_period=seconds [X86,EARLY] 3918 By default it checks for corruption every 60 3919 seconds. Use this parameter to check at some 3920 other rate. 0 disables periodic checking. 3921 3922 memory_hotplug.memmap_on_memory 3923 [KNL,X86,ARM] Boolean flag to enable this feature. 3924 Format: {on | off (default)} 3925 When enabled, runtime hotplugged memory will 3926 allocate its internal metadata (struct pages, 3927 those vmemmap pages cannot be optimized even 3928 if hugetlb_free_vmemmap is enabled) from the 3929 hotadded memory which will allow to hotadd a 3930 lot of memory without requiring additional 3931 memory to do so. 3932 This feature is disabled by default because it 3933 has some implication on large (e.g. GB) 3934 allocations in some configurations (e.g. small 3935 memory blocks). 3936 The state of the flag can be read in 3937 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3938 Note that even when enabled, there are a few cases where 3939 the feature is not effective. 3940 3941 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 3942 Format: <integer> 3943 default : 0 <disable> 3944 Specifies the number of memtest passes to be 3945 performed. Each pass selects another test 3946 pattern from a given set of patterns. Memtest 3947 fills the memory with this pattern, validates 3948 memory contents and reserves bad memory 3949 regions that are detected. 3950 3951 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3952 Valid arguments: on, off 3953 Default: off 3954 mem_encrypt=on: Activate SME 3955 mem_encrypt=off: Do not activate SME 3956 3957 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3958 for details on when memory encryption can be activated. 3959 3960 mem_sleep_default= [SUSPEND] Default system suspend mode: 3961 s2idle - Suspend-To-Idle 3962 shallow - Power-On Suspend or equivalent (if supported) 3963 deep - Suspend-To-RAM or equivalent (if supported) 3964 See Documentation/admin-guide/pm/sleep-states.rst. 3965 3966 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3967 the BIOS has incorrectly applied a workaround. TinyBIOS 3968 version 0.98 is known to be affected, 0.99 fixes the 3969 problem by letting the user disable the workaround. 3970 3971 mga= [HW,DRM] 3972 3973 microcode= [X86] Control the behavior of the microcode loader. 3974 Available options, comma separated: 3975 3976 base_rev=X - with <X> with format: <u32> 3977 Set the base microcode revision of each thread when in 3978 debug mode. 3979 3980 dis_ucode_ldr: disable the microcode loader 3981 3982 force_minrev: 3983 Enable or disable the microcode minimal revision 3984 enforcement for the runtime microcode loader. 3985 3986 mini2440= [ARM,HW,KNL] 3987 Format:[0..2][b][c][t] 3988 Default: "0tb" 3989 MINI2440 configuration specification: 3990 0 - The attached screen is the 3.5" TFT 3991 1 - The attached screen is the 7" TFT 3992 2 - The VGA Shield is attached (1024x768) 3993 Leaving out the screen size parameter will not load 3994 the TFT driver, and the framebuffer will be left 3995 unconfigured. 3996 b - Enable backlight. The TFT backlight pin will be 3997 linked to the kernel VESA blanking code and a GPIO 3998 LED. This parameter is not necessary when using the 3999 VGA shield. 4000 c - Enable the s3c camera interface. 4001 t - Reserved for enabling touchscreen support. The 4002 touchscreen support is not enabled in the mainstream 4003 kernel as of 2.6.30, a preliminary port can be found 4004 in the "bleeding edge" mini2440 support kernel at 4005 https://repo.or.cz/w/linux-2.6/mini2440.git 4006 4007 mitigations= 4008 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4009 CPU vulnerabilities. This is a set of curated, 4010 arch-independent options, each of which is an 4011 aggregation of existing arch-specific options. 4012 4013 Note, "mitigations" is supported if and only if the 4014 kernel was built with CPU_MITIGATIONS=y. 4015 4016 off 4017 Disable all optional CPU mitigations. This 4018 improves system performance, but it may also 4019 expose users to several CPU vulnerabilities. 4020 Equivalent to: if nokaslr then kpti=0 [ARM64] 4021 gather_data_sampling=off [X86] 4022 indirect_target_selection=off [X86] 4023 kvm.nx_huge_pages=off [X86] 4024 l1tf=off [X86] 4025 mds=off [X86] 4026 mmio_stale_data=off [X86] 4027 no_entry_flush [PPC] 4028 no_uaccess_flush [PPC] 4029 nobp=0 [S390] 4030 nopti [X86,PPC] 4031 nospectre_bhb [ARM64] 4032 nospectre_v1 [X86,PPC] 4033 nospectre_v2 [X86,PPC,S390,ARM64] 4034 reg_file_data_sampling=off [X86] 4035 retbleed=off [X86] 4036 spec_rstack_overflow=off [X86] 4037 spec_store_bypass_disable=off [X86,PPC] 4038 spectre_bhi=off [X86] 4039 spectre_v2_user=off [X86] 4040 srbds=off [X86,INTEL] 4041 ssbd=force-off [ARM64] 4042 tsa=off [X86,AMD] 4043 tsx_async_abort=off [X86] 4044 vmscape=off [X86] 4045 4046 Exceptions: 4047 This does not have any effect on 4048 kvm.nx_huge_pages when 4049 kvm.nx_huge_pages=force. 4050 4051 auto (default) 4052 Mitigate all CPU vulnerabilities, but leave SMT 4053 enabled, even if it's vulnerable. This is for 4054 users who don't want to be surprised by SMT 4055 getting disabled across kernel upgrades, or who 4056 have other ways of avoiding SMT-based attacks. 4057 Equivalent to: (default behavior) 4058 4059 auto,nosmt 4060 Mitigate all CPU vulnerabilities, disabling SMT 4061 if needed. This is for users who always want to 4062 be fully mitigated, even if it means losing SMT. 4063 Equivalent to: l1tf=flush,nosmt [X86] 4064 mds=full,nosmt [X86] 4065 tsx_async_abort=full,nosmt [X86] 4066 mmio_stale_data=full,nosmt [X86] 4067 retbleed=auto,nosmt [X86] 4068 4069 [X86] After one of the above options, additionally 4070 supports attack-vector based controls as documented in 4071 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4072 4073 mminit_loglevel= 4074 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4075 parameter allows control of the logging verbosity for 4076 the additional memory initialisation checks. A value 4077 of 0 disables mminit logging and a level of 4 will 4078 log everything. Information is printed at KERN_DEBUG 4079 so loglevel=8 may also need to be specified. 4080 4081 mmio_stale_data= 4082 [X86,INTEL,EARLY] Control mitigation for the Processor 4083 MMIO Stale Data vulnerabilities. 4084 4085 Processor MMIO Stale Data is a class of 4086 vulnerabilities that may expose data after an MMIO 4087 operation. Exposed data could originate or end in 4088 the same CPU buffers as affected by MDS and TAA. 4089 Therefore, similar to MDS and TAA, the mitigation 4090 is to clear the affected CPU buffers. 4091 4092 This parameter controls the mitigation. The 4093 options are: 4094 4095 full - Enable mitigation on vulnerable CPUs 4096 4097 full,nosmt - Enable mitigation and disable SMT on 4098 vulnerable CPUs. 4099 4100 off - Unconditionally disable mitigation 4101 4102 On MDS or TAA affected machines, 4103 mmio_stale_data=off can be prevented by an active 4104 MDS or TAA mitigation as these vulnerabilities are 4105 mitigated with the same mechanism so in order to 4106 disable this mitigation, you need to specify 4107 mds=off and tsx_async_abort=off too. 4108 4109 Not specifying this option is equivalent to 4110 mmio_stale_data=full. 4111 4112 For details see: 4113 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4114 4115 <module>.async_probe[=<bool>] [KNL] 4116 If no <bool> value is specified or if the value 4117 specified is not a valid <bool>, enable asynchronous 4118 probe on this module. Otherwise, enable/disable 4119 asynchronous probe on this module as indicated by the 4120 <bool> value. See also: module.async_probe 4121 4122 module.async_probe=<bool> 4123 [KNL] When set to true, modules will use async probing 4124 by default. To enable/disable async probing for a 4125 specific module, use the module specific control that 4126 is documented under <module>.async_probe. When both 4127 module.async_probe and <module>.async_probe are 4128 specified, <module>.async_probe takes precedence for 4129 the specific module. 4130 4131 module.enable_dups_trace 4132 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4133 this means that duplicate request_module() calls will 4134 trigger a WARN_ON() instead of a pr_warn(). Note that 4135 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4136 will always be issued and this option does nothing. 4137 module.sig_enforce 4138 [KNL] When CONFIG_MODULE_SIG is set, this means that 4139 modules without (valid) signatures will fail to load. 4140 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4141 is always true, so this option does nothing. 4142 4143 module_blacklist= [KNL] Do not load a comma-separated list of 4144 modules. Useful for debugging problem modules. 4145 4146 mousedev.tap_time= 4147 [MOUSE] Maximum time between finger touching and 4148 leaving touchpad surface for touch to be considered 4149 a tap and be reported as a left button click (for 4150 touchpads working in absolute mode only). 4151 Format: <msecs> 4152 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4153 reporting absolute coordinates, such as tablets 4154 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4155 reporting absolute coordinates, such as tablets 4156 4157 movablecore= [KNL,X86,PPC,EARLY] 4158 Format: nn[KMGTPE] | nn% 4159 This parameter is the complement to kernelcore=, it 4160 specifies the amount of memory used for migratable 4161 allocations. If both kernelcore and movablecore is 4162 specified, then kernelcore will be at *least* the 4163 specified value but may be more. If movablecore on its 4164 own is specified, the administrator must be careful 4165 that the amount of memory usable for all allocations 4166 is not too small. 4167 4168 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4169 NUMA nodes to be movable. This means that the memory 4170 of such nodes will be usable only for movable 4171 allocations which rules out almost all kernel 4172 allocations. Use with caution! 4173 4174 MTD_Partition= [MTD] 4175 Format: <name>,<region-number>,<size>,<offset> 4176 4177 MTD_Region= [MTD] Format: 4178 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4179 4180 mtdparts= [MTD] 4181 See drivers/mtd/parsers/cmdlinepart.c 4182 4183 mtouchusb.raw_coordinates= 4184 [HW] Make the MicroTouch USB driver use raw coordinates 4185 ('y', default) or cooked coordinates ('n') 4186 4187 mtrr=debug [X86,EARLY] 4188 Enable printing debug information related to MTRR 4189 registers at boot time. 4190 4191 mtrr_chunk_size=nn[KMG,X86,EARLY] 4192 used for mtrr cleanup. It is largest continuous chunk 4193 that could hold holes aka. UC entries. 4194 4195 mtrr_gran_size=nn[KMG,X86,EARLY] 4196 Used for mtrr cleanup. It is granularity of mtrr block. 4197 Default is 1. 4198 Large value could prevent small alignment from 4199 using up MTRRs. 4200 4201 mtrr_spare_reg_nr=n [X86,EARLY] 4202 Format: <integer> 4203 Range: 0,7 : spare reg number 4204 Default : 1 4205 Used for mtrr cleanup. It is spare mtrr entries number. 4206 Set to 2 or more if your graphical card needs more. 4207 4208 multitce=off [PPC] This parameter disables the use of the pSeries 4209 firmware feature for updating multiple TCE entries 4210 at a time. 4211 4212 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4213 4214 netdev= [NET] Network devices parameters 4215 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4216 Note that mem_start is often overloaded to mean 4217 something different and driver-specific. 4218 This usage is only documented in each driver source 4219 file if at all. 4220 4221 netpoll.carrier_timeout= 4222 [NET] Specifies amount of time (in seconds) that 4223 netpoll should wait for a carrier. By default netpoll 4224 waits 4 seconds. 4225 4226 nf_conntrack.acct= 4227 [NETFILTER] Enable connection tracking flow accounting 4228 0 to disable accounting 4229 1 to enable accounting 4230 Default value is 0. 4231 4232 nfs.cache_getent= 4233 [NFS] sets the pathname to the program which is used 4234 to update the NFS client cache entries. 4235 4236 nfs.cache_getent_timeout= 4237 [NFS] sets the timeout after which an attempt to 4238 update a cache entry is deemed to have failed. 4239 4240 nfs.callback_nr_threads= 4241 [NFSv4] set the total number of threads that the 4242 NFS client will assign to service NFSv4 callback 4243 requests. 4244 4245 nfs.callback_tcpport= 4246 [NFS] set the TCP port on which the NFSv4 callback 4247 channel should listen. 4248 4249 nfs.delay_retrans= 4250 [NFS] specifies the number of times the NFSv4 client 4251 retries the request before returning an EAGAIN error, 4252 after a reply of NFS4ERR_DELAY from the server. 4253 Only applies if the softerr mount option is enabled, 4254 and the specified value is >= 0. 4255 4256 nfs.enable_ino64= 4257 [NFS] enable 64-bit inode numbers. 4258 If zero, the NFS client will fake up a 32-bit inode 4259 number for the readdir() and stat() syscalls instead 4260 of returning the full 64-bit number. 4261 The default is to return 64-bit inode numbers. 4262 4263 nfs.idmap_cache_timeout= 4264 [NFS] set the maximum lifetime for idmapper cache 4265 entries. 4266 4267 nfs.max_session_cb_slots= 4268 [NFSv4.1] Sets the maximum number of session 4269 slots the client will assign to the callback 4270 channel. This determines the maximum number of 4271 callbacks the client will process in parallel for 4272 a particular server. 4273 4274 nfs.max_session_slots= 4275 [NFSv4.1] Sets the maximum number of session slots 4276 the client will attempt to negotiate with the server. 4277 This limits the number of simultaneous RPC requests 4278 that the client can send to the NFSv4.1 server. 4279 Note that there is little point in setting this 4280 value higher than the max_tcp_slot_table_limit. 4281 4282 nfs.nfs4_disable_idmapping= 4283 [NFSv4] When set to the default of '1', this option 4284 ensures that both the RPC level authentication 4285 scheme and the NFS level operations agree to use 4286 numeric uids/gids if the mount is using the 4287 'sec=sys' security flavour. In effect it is 4288 disabling idmapping, which can make migration from 4289 legacy NFSv2/v3 systems to NFSv4 easier. 4290 Servers that do not support this mode of operation 4291 will be autodetected by the client, and it will fall 4292 back to using the idmapper. 4293 To turn off this behaviour, set the value to '0'. 4294 4295 nfs.nfs4_unique_id= 4296 [NFS4] Specify an additional fixed unique ident- 4297 ification string that NFSv4 clients can insert into 4298 their nfs_client_id4 string. This is typically a 4299 UUID that is generated at system install time. 4300 4301 nfs.recover_lost_locks= 4302 [NFSv4] Attempt to recover locks that were lost due 4303 to a lease timeout on the server. Please note that 4304 doing this risks data corruption, since there are 4305 no guarantees that the file will remain unchanged 4306 after the locks are lost. 4307 If you want to enable the kernel legacy behaviour of 4308 attempting to recover these locks, then set this 4309 parameter to '1'. 4310 The default parameter value of '0' causes the kernel 4311 not to attempt recovery of lost locks. 4312 4313 nfs.send_implementation_id= 4314 [NFSv4.1] Send client implementation identification 4315 information in exchange_id requests. 4316 If zero, no implementation identification information 4317 will be sent. 4318 The default is to send the implementation identification 4319 information. 4320 4321 nfs4.layoutstats_timer= 4322 [NFSv4.2] Change the rate at which the kernel sends 4323 layoutstats to the pNFS metadata server. 4324 4325 Setting this to value to 0 causes the kernel to use 4326 whatever value is the default set by the layout 4327 driver. A non-zero value sets the minimum interval 4328 in seconds between layoutstats transmissions. 4329 4330 nfsd.inter_copy_offload_enable= 4331 [NFSv4.2] When set to 1, the server will support 4332 server-to-server copies for which this server is 4333 the destination of the copy. 4334 4335 nfsd.nfs4_disable_idmapping= 4336 [NFSv4] When set to the default of '1', the NFSv4 4337 server will return only numeric uids and gids to 4338 clients using auth_sys, and will accept numeric uids 4339 and gids from such clients. This is intended to ease 4340 migration from NFSv2/v3. 4341 4342 nfsd.nfsd4_ssc_umount_timeout= 4343 [NFSv4.2] When used as the destination of a 4344 server-to-server copy, knfsd temporarily mounts 4345 the source server. It caches the mount in case 4346 it will be needed again, and discards it if not 4347 used for the number of milliseconds specified by 4348 this parameter. 4349 4350 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4351 See Documentation/admin-guide/nfs/nfsroot.rst. 4352 4353 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4354 See Documentation/admin-guide/nfs/nfsroot.rst. 4355 4356 nfsrootdebug [NFS] enable nfsroot debugging messages. 4357 See Documentation/admin-guide/nfs/nfsroot.rst. 4358 4359 nmi_backtrace.backtrace_idle [KNL] 4360 Dump stacks even of idle CPUs in response to an 4361 NMI stack-backtrace request. 4362 4363 nmi_debug= [KNL,SH] Specify one or more actions to take 4364 when a NMI is triggered. 4365 Format: [state][,regs][,debounce][,die] 4366 4367 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4368 Format: [panic,][nopanic,][rNNN,][num] 4369 Valid num: 0 or 1 4370 0 - turn hardlockup detector in nmi_watchdog off 4371 1 - turn hardlockup detector in nmi_watchdog on 4372 rNNN - configure the watchdog with raw perf event 0xNNN 4373 4374 When panic is specified, panic when an NMI watchdog 4375 timeout occurs (or 'nopanic' to not panic on an NMI 4376 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4377 To disable both hard and soft lockup detectors, 4378 please see 'nowatchdog'. 4379 This is useful when you use a panic=... timeout and 4380 need the box quickly up again. 4381 4382 These settings can be accessed at runtime via 4383 the nmi_watchdog and hardlockup_panic sysctls. 4384 4385 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4386 emulation library even if a 387 maths coprocessor 4387 is present. 4388 4389 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4390 Forces kernel to use 3-level paging instead. 4391 4392 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4393 kernel to use 4-level paging instead. 4394 4395 noalign [KNL,ARM] 4396 4397 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4398 IOAPICs that may be present in the system. 4399 4400 noapictimer [APIC,X86] Don't set up the APIC timer 4401 4402 noautogroup Disable scheduler automatic task group creation. 4403 4404 nocache [ARM,EARLY] 4405 4406 no_console_suspend 4407 [HW] Never suspend the console 4408 Disable suspending of consoles during suspend and 4409 hibernate operations. Once disabled, debugging 4410 messages can reach various consoles while the rest 4411 of the system is being put to sleep (ie, while 4412 debugging driver suspend/resume hooks). This may 4413 not work reliably with all consoles, but is known 4414 to work with serial and VGA consoles. 4415 To facilitate more flexible debugging, we also add 4416 console_suspend, a printk module parameter to control 4417 it. Users could use console_suspend (usually 4418 /sys/module/printk/parameters/console_suspend) to 4419 turn on/off it dynamically. 4420 4421 no_debug_objects 4422 [KNL,EARLY] Disable object debugging 4423 4424 nodsp [SH] Disable hardware DSP at boot time. 4425 4426 noefi [EFI,EARLY] Disable EFI runtime services support. 4427 4428 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4429 4430 noexec32 [X86-64] 4431 This affects only 32-bit executables. 4432 noexec32=on: enable non-executable mappings (default) 4433 read doesn't imply executable mappings 4434 noexec32=off: disable non-executable mappings 4435 read implies executable mappings 4436 4437 no_file_caps Tells the kernel not to honor file capabilities. The 4438 only way then for a file to be executed with privilege 4439 is to be setuid root or executed by root. 4440 4441 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4442 4443 nofsgsbase [X86] Disables FSGSBASE instructions. 4444 4445 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4446 register save and restore. The kernel will only save 4447 legacy floating-point registers on task switch. 4448 4449 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4450 4451 no_hash_pointers 4452 [KNL,EARLY] 4453 Alias for "hash_pointers=never". 4454 4455 nohibernate [HIBERNATION] Disable hibernation and resume. 4456 4457 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4458 busy wait in do_idle() and not use the arch_cpu_idle() 4459 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4460 to be effective. This is useful on platforms where the 4461 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4462 correctly or when doing power measurements to evaluate 4463 the impact of the sleep instructions. This is also 4464 useful when using JTAG debugger. 4465 4466 nohpet [X86] Don't use the HPET timer. 4467 4468 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4469 4470 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4471 4472 nohz= [KNL] Boottime enable/disable dynamic ticks 4473 Valid arguments: on, off 4474 Default: on 4475 4476 nohz_full= [KNL,BOOT,SMP,ISOL] 4477 The argument is a cpu list, as described above. 4478 In kernels built with CONFIG_NO_HZ_FULL=y, set 4479 the specified list of CPUs whose tick will be stopped 4480 whenever possible. The boot CPU will be forced outside 4481 the range to maintain the timekeeping. Any CPUs 4482 in this list will have their RCU callbacks offloaded, 4483 just as if they had also been called out in the 4484 rcu_nocbs= boot parameter. 4485 4486 Note that this argument takes precedence over 4487 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4488 4489 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4490 initial RAM disk. Currently this parameter applies to 4491 initrd only, not to initramfs. But it applies to both 4492 in EFI mode. 4493 4494 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4495 remapping. 4496 [Deprecated - use intremap=off] 4497 4498 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4499 4500 noiotrap [SH] Disables trapped I/O port accesses. 4501 4502 noirqdebug [X86-32] Disables the code which attempts to detect and 4503 disable unhandled interrupt sources. 4504 4505 noisapnp [ISAPNP] Disables ISA PnP code. 4506 4507 nokaslr [KNL,EARLY] 4508 When CONFIG_RANDOMIZE_BASE is set, this disables 4509 kernel and module base offset ASLR (Address Space 4510 Layout Randomization). 4511 4512 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4513 fault handling. 4514 4515 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4516 4517 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4518 4519 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4520 4521 nomce [X86-32] Disable Machine Check Exception 4522 4523 nomfgpt [X86-32] Disable Multi-Function General Purpose 4524 Timer usage (for AMD Geode machines). 4525 4526 nomodeset Disable kernel modesetting. Most systems' firmware 4527 sets up a display mode and provides framebuffer memory 4528 for output. With nomodeset, DRM and fbdev drivers will 4529 not load if they could possibly displace the pre- 4530 initialized output. Only the system framebuffer will 4531 be available for use. The respective drivers will not 4532 perform display-mode changes or accelerated rendering. 4533 4534 Useful as error fallback, or for testing and debugging. 4535 4536 nomodule Disable module load 4537 4538 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4539 shutdown the other cpus. Instead use the REBOOT_VECTOR 4540 irq. 4541 4542 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4543 pagetables) support. 4544 4545 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4546 4547 nopku [X86] Disable Memory Protection Keys CPU feature found 4548 in some Intel CPUs. 4549 4550 nopti [X86-64,EARLY] 4551 Equivalent to pti=off 4552 4553 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4554 Disables the PV optimizations forcing the guest to run 4555 as generic guest with no PV drivers. Currently support 4556 XEN HVM, KVM, HYPER_V and VMWARE guest. 4557 4558 nopvspin [X86,XEN,KVM,EARLY] 4559 Disables the qspinlock slow path using PV optimizations 4560 which allow the hypervisor to 'idle' the guest on lock 4561 contention. 4562 4563 norandmaps Don't use address space randomization. Equivalent to 4564 echo 0 > /proc/sys/kernel/randomize_va_space 4565 4566 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4567 with UP alternatives 4568 4569 noresume [SWSUSP] Disables resume and restores original swap 4570 space. 4571 4572 no-scroll [VGA] Disables scrollback. 4573 This is required for the Braillex ib80-piezo Braille 4574 reader made by F.H. Papenmeier (Germany). 4575 4576 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4577 4578 nosmap [PPC,EARLY] 4579 Disable SMAP (Supervisor Mode Access Prevention) 4580 even if it is supported by processor. 4581 4582 nosmep [PPC64s,EARLY] 4583 Disable SMEP (Supervisor Mode Execution Prevention) 4584 even if it is supported by processor. 4585 4586 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4587 and disable the IO APIC. legacy for "maxcpus=0". 4588 4589 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4590 Equivalent to smt=1. 4591 4592 [KNL,X86,PPC,S390] Disable symmetric multithreading (SMT). 4593 nosmt=force: Force disable SMT, cannot be undone 4594 via the sysfs control file. 4595 4596 nosoftlockup [KNL] Disable the soft-lockup detector. 4597 4598 nospec_store_bypass_disable 4599 [HW,EARLY] Disable all mitigations for the Speculative 4600 Store Bypass vulnerability 4601 4602 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4603 history injection) vulnerability. System may allow data leaks 4604 with this option. 4605 4606 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4607 (bounds check bypass). With this option data leaks are 4608 possible in the system. 4609 4610 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4611 for the Spectre variant 2 (indirect branch 4612 prediction) vulnerability. System may allow data 4613 leaks with this option. 4614 4615 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4616 Disable paravirtualized steal time accounting. steal time 4617 is computed, but won't influence scheduler behaviour 4618 4619 nosync [HW,M68K] Disables sync negotiation for all devices. 4620 4621 no_timer_check [X86,APIC] Disables the code which tests for broken 4622 timer IRQ sources, i.e., the IO-APIC timer. This can 4623 work around problems with incorrect timer 4624 initialization on some boards. 4625 4626 no_uaccess_flush 4627 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4628 4629 novmcoredd [KNL,KDUMP] 4630 Disable device dump. Device dump allows drivers to 4631 append dump data to vmcore so you can collect driver 4632 specified debug info. Drivers can append the data 4633 without any limit and this data is stored in memory, 4634 so this may cause significant memory stress. Disabling 4635 device dump can help save memory but the driver debug 4636 data will be no longer available. This parameter 4637 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4638 is set. 4639 4640 no-vmw-sched-clock 4641 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4642 scheduler clock and use the default one. 4643 4644 nowatchdog [KNL] Disable both lockup detectors, i.e. 4645 soft-lockup and NMI watchdog (hard-lockup). 4646 4647 nowb [ARM,EARLY] 4648 4649 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4650 4651 NOTE: this parameter will be ignored on systems with the 4652 LEGACY_XAPIC_DISABLED bit set in the 4653 IA32_XAPIC_DISABLE_STATUS MSR. 4654 4655 noxsave [BUGS=X86] Disables x86 extended register state save 4656 and restore using xsave. The kernel will fallback to 4657 enabling legacy floating-point and sse state. 4658 4659 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4660 register states. The kernel will fall back to use 4661 xsave to save the states. By using this parameter, 4662 performance of saving the states is degraded because 4663 xsave doesn't support modified optimization while 4664 xsaveopt supports it on xsaveopt enabled systems. 4665 4666 noxsaves [X86] Disables xsaves and xrstors used in saving and 4667 restoring x86 extended register state in compacted 4668 form of xsave area. The kernel will fall back to use 4669 xsaveopt and xrstor to save and restore the states 4670 in standard form of xsave area. By using this 4671 parameter, xsave area per process might occupy more 4672 memory on xsaves enabled systems. 4673 4674 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4675 could support. nr_cpus=n : n >= 1 limits the kernel to 4676 support 'n' processors. It could be larger than the 4677 number of already plugged CPU during bootup, later in 4678 runtime you can physically add extra cpu until it reaches 4679 n. So during boot up some boot time memory for per-cpu 4680 variables need be pre-allocated for later physical cpu 4681 hot plugging. 4682 4683 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4684 4685 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4686 Disable NUMA, Only set up a single NUMA node 4687 spanning all memory. 4688 4689 numa=fake=<size>[MG] 4690 [KNL, ARM64, RISCV, X86, EARLY] 4691 If given as a memory unit, fills all system RAM with 4692 nodes of size interleaved over physical nodes. 4693 4694 numa=fake=<N> 4695 [KNL, ARM64, RISCV, X86, EARLY] 4696 If given as an integer, fills all system RAM with N 4697 fake nodes interleaved over physical nodes. 4698 4699 numa=fake=<N>U 4700 [KNL, ARM64, RISCV, X86, EARLY] 4701 If given as an integer followed by 'U', it will 4702 divide each physical node into N emulated nodes. 4703 4704 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4705 4706 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4707 soft-reserved memory partitioning. 4708 4709 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4710 NUMA balancing. 4711 Allowed values are enable and disable 4712 4713 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4714 'node', 'default' can be specified 4715 This can be set from sysctl after boot. 4716 See Documentation/admin-guide/sysctl/vm.rst for details. 4717 4718 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4719 See Documentation/core-api/debugging-via-ohci1394.rst for more 4720 info. 4721 4722 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4723 Rather than timing out after 20 ms if an EC 4724 command is not properly ACKed, override the length 4725 of the timeout. We have interrupts disabled while 4726 waiting for the ACK, so if this is set too high 4727 interrupts *may* be lost! 4728 4729 omap_mux= [OMAP] Override bootloader pin multiplexing. 4730 Format: <mux_mode0.mode_name=value>... 4731 For example, to override I2C bus2: 4732 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4733 4734 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4735 4736 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4737 4738 boundary - index of last SLC block on Flex-OneNAND. 4739 The remaining blocks are configured as MLC blocks. 4740 lock - Configure if Flex-OneNAND boundary should be locked. 4741 Once locked, the boundary cannot be changed. 4742 1 indicates lock status, 0 indicates unlock status. 4743 4744 oops=panic [KNL,EARLY] 4745 Always panic on oopses. Default is to just kill the 4746 process, but there is a small probability of 4747 deadlocking the machine. 4748 This will also cause panics on machine check exceptions. 4749 Useful together with panic=30 to trigger a reboot. 4750 4751 page_alloc.shuffle= 4752 [KNL] Boolean flag to control whether the page allocator 4753 should randomize its free lists. This parameter can be 4754 used to enable/disable page randomization. The state of 4755 the flag can be read from sysfs at: 4756 /sys/module/page_alloc/parameters/shuffle. 4757 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4758 4759 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4760 Storage of the information about who allocated 4761 each page is disabled in default. With this switch, 4762 we can turn it on. 4763 on: enable the feature 4764 4765 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4766 poisoning on the buddy allocator, available with 4767 CONFIG_PAGE_POISONING=y. 4768 off: turn off poisoning (default) 4769 on: turn on poisoning 4770 4771 page_reporting.page_reporting_order= 4772 [KNL] Minimal page reporting order 4773 Format: <integer> 4774 Adjust the minimal page reporting order. The page 4775 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4776 4777 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4778 timeout > 0: seconds before rebooting 4779 timeout = 0: wait forever 4780 timeout < 0: reboot immediately 4781 Format: <timeout> 4782 4783 panic_on_taint= [KNL,EARLY] 4784 Bitmask for conditionally calling panic() in add_taint() 4785 Format: <hex>[,nousertaint] 4786 Hexadecimal bitmask representing the set of TAINT flags 4787 that will cause the kernel to panic when add_taint() is 4788 called with any of the flags in this set. 4789 The optional switch "nousertaint" can be utilized to 4790 prevent userspace forced crashes by writing to sysctl 4791 /proc/sys/kernel/tainted any flagset matching with the 4792 bitmask set on panic_on_taint. 4793 See Documentation/admin-guide/tainted-kernels.rst for 4794 extra details on the taint flags that users can pick 4795 to compose the bitmask to assign to panic_on_taint. 4796 4797 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4798 on a WARN(). 4799 4800 panic_print= Bitmask for printing system info when panic happens. 4801 User can chose combination of the following bits: 4802 bit 0: print all tasks info 4803 bit 1: print system memory info 4804 bit 2: print timer info 4805 bit 3: print locks info if CONFIG_LOCKDEP is on 4806 bit 4: print ftrace buffer 4807 bit 5: replay all kernel messages on consoles at the end of panic 4808 bit 6: print all CPUs backtrace (if available in the arch) 4809 bit 7: print only tasks in uninterruptible (blocked) state 4810 *Be aware* that this option may print a _lot_ of lines, 4811 so there are risks of losing older messages in the log. 4812 Use this option carefully, maybe worth to setup a 4813 bigger log buffer with "log_buf_len" along with this. 4814 4815 panic_sys_info= A comma separated list of extra information to be dumped 4816 on panic. 4817 Format: val[,val...] 4818 Where @val can be any of the following: 4819 4820 tasks: print all tasks info 4821 mem: print system memory info 4822 timers: print timers info 4823 locks: print locks info if CONFIG_LOCKDEP is on 4824 ftrace: print ftrace buffer 4825 all_bt: print all CPUs backtrace (if available in the arch) 4826 blocked_tasks: print only tasks in uninterruptible (blocked) state 4827 4828 This is a human readable alternative to the 'panic_print' option. 4829 4830 panic_console_replay 4831 When panic happens, replay all kernel messages on 4832 consoles at the end of panic. 4833 4834 parkbd.port= [HW] Parallel port number the keyboard adapter is 4835 connected to, default is 0. 4836 Format: <parport#> 4837 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4838 0 for XT, 1 for AT (default is AT). 4839 Format: <mode> 4840 4841 parport= [HW,PPT] Specify parallel ports. 0 disables. 4842 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4843 Use 'auto' to force the driver to use any 4844 IRQ/DMA settings detected (the default is to 4845 ignore detected IRQ/DMA settings because of 4846 possible conflicts). You can specify the base 4847 address, IRQ, and DMA settings; IRQ and DMA 4848 should be numbers, or 'auto' (for using detected 4849 settings on that particular port), or 'nofifo' 4850 (to avoid using a FIFO even if it is detected). 4851 Parallel ports are assigned in the order they 4852 are specified on the command line, starting 4853 with parport0. 4854 4855 parport_init_mode= [HW,PPT] 4856 Configure VIA parallel port to operate in 4857 a specific mode. This is necessary on Pegasos 4858 computer where firmware has no options for setting 4859 up parallel port mode and sets it to spp. 4860 Currently this function knows 686a and 8231 chips. 4861 Format: [spp|ps2|epp|ecp|ecpepp] 4862 4863 pata_legacy.all= [HW,LIBATA] 4864 Format: <int> 4865 Set to non-zero to probe primary and secondary ISA 4866 port ranges on PCI systems where no PCI PATA device 4867 has been found at either range. Disabled by default. 4868 4869 pata_legacy.autospeed= [HW,LIBATA] 4870 Format: <int> 4871 Set to non-zero if a chip is present that snoops speed 4872 changes. Disabled by default. 4873 4874 pata_legacy.ht6560a= [HW,LIBATA] 4875 Format: <int> 4876 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4877 the secondary channel, or both channels respectively. 4878 Disabled by default. 4879 4880 pata_legacy.ht6560b= [HW,LIBATA] 4881 Format: <int> 4882 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4883 the secondary channel, or both channels respectively. 4884 Disabled by default. 4885 4886 pata_legacy.iordy_mask= [HW,LIBATA] 4887 Format: <int> 4888 IORDY enable mask. Set individual bits to allow IORDY 4889 for the respective channel. Bit 0 is for the first 4890 legacy channel handled by this driver, bit 1 is for 4891 the second channel, and so on. The sequence will often 4892 correspond to the primary legacy channel, the secondary 4893 legacy channel, and so on, but the handling of a PCI 4894 bus and the use of other driver options may interfere 4895 with the sequence. By default IORDY is allowed across 4896 all channels. 4897 4898 pata_legacy.opti82c46x= [HW,LIBATA] 4899 Format: <int> 4900 Set to 1, 2, or 3 for Opti 82c611A on the primary 4901 channel, the secondary channel, or both channels 4902 respectively. Disabled by default. 4903 4904 pata_legacy.opti82c611a= [HW,LIBATA] 4905 Format: <int> 4906 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4907 channel, the secondary channel, or both channels 4908 respectively. Disabled by default. 4909 4910 pata_legacy.pio_mask= [HW,LIBATA] 4911 Format: <int> 4912 PIO mode mask for autospeed devices. Set individual 4913 bits to allow the use of the respective PIO modes. 4914 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4915 All modes allowed by default. 4916 4917 pata_legacy.probe_all= [HW,LIBATA] 4918 Format: <int> 4919 Set to non-zero to probe tertiary and further ISA 4920 port ranges on PCI systems. Disabled by default. 4921 4922 pata_legacy.probe_mask= [HW,LIBATA] 4923 Format: <int> 4924 Probe mask for legacy ISA PATA ports. Depending on 4925 platform configuration and the use of other driver 4926 options up to 6 legacy ports are supported: 0x1f0, 4927 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4928 of individual ports can be disabled by setting the 4929 corresponding bits in the mask to 1. Bit 0 is for 4930 the first port in the list above (0x1f0), and so on. 4931 By default all supported ports are probed. 4932 4933 pata_legacy.qdi= [HW,LIBATA] 4934 Format: <int> 4935 Set to non-zero to probe QDI controllers. By default 4936 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4937 4938 pata_legacy.winbond= [HW,LIBATA] 4939 Format: <int> 4940 Set to non-zero to probe Winbond controllers. Use 4941 the standard I/O port (0x130) if 1, otherwise the 4942 value given is the I/O port to use (typically 0x1b0). 4943 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4944 0 otherwise. 4945 4946 pata_platform.pio_mask= [HW,LIBATA] 4947 Format: <int> 4948 Supported PIO mode mask. Set individual bits to allow 4949 the use of the respective PIO modes. Bit 0 is for 4950 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4951 allowed by default. 4952 4953 pause_on_oops=<int> 4954 Halt all CPUs after the first oops has been printed for 4955 the specified number of seconds. This is to be used if 4956 your oopses keep scrolling off the screen. 4957 4958 pcbit= [HW,ISDN] 4959 4960 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 4961 4962 Some options herein operate on a specific device 4963 or a set of devices (<pci_dev>). These are 4964 specified in one of the following formats: 4965 4966 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4967 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4968 4969 Note: the first format specifies a PCI 4970 bus/device/function address which may change 4971 if new hardware is inserted, if motherboard 4972 firmware changes, or due to changes caused 4973 by other kernel parameters. If the 4974 domain is left unspecified, it is 4975 taken to be zero. Optionally, a path 4976 to a device through multiple device/function 4977 addresses can be specified after the base 4978 address (this is more robust against 4979 renumbering issues). The second format 4980 selects devices using IDs from the 4981 configuration space which may match multiple 4982 devices in the system. 4983 4984 earlydump dump PCI config space before the kernel 4985 changes anything 4986 off [X86] don't probe for the PCI bus 4987 bios [X86-32] force use of PCI BIOS, don't access 4988 the hardware directly. Use this if your machine 4989 has a non-standard PCI host bridge. 4990 nobios [X86-32] disallow use of PCI BIOS, only direct 4991 hardware access methods are allowed. Use this 4992 if you experience crashes upon bootup and you 4993 suspect they are caused by the BIOS. 4994 conf1 [X86] Force use of PCI Configuration Access 4995 Mechanism 1 (config address in IO port 0xCF8, 4996 data in IO port 0xCFC, both 32-bit). 4997 conf2 [X86] Force use of PCI Configuration Access 4998 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4999 the function, IO port 0xCFA, also 8-bit, sets 5000 bus number. The config space is then accessed 5001 through ports 0xC000-0xCFFF). 5002 See http://wiki.osdev.org/PCI for more info 5003 on the configuration access mechanisms. 5004 noaer [PCIE] If the PCIEAER kernel config parameter is 5005 enabled, this kernel boot option can be used to 5006 disable the use of PCIE advanced error reporting. 5007 nodomains [PCI] Disable support for multiple PCI 5008 root domains (aka PCI segments, in ACPI-speak). 5009 nommconf [X86] Disable use of MMCONFIG for PCI 5010 Configuration 5011 check_enable_amd_mmconf [X86] check for and enable 5012 properly configured MMIO access to PCI 5013 config space on AMD family 10h CPU 5014 nomsi [MSI] If the PCI_MSI kernel config parameter is 5015 enabled, this kernel boot option can be used to 5016 disable the use of MSI interrupts system-wide. 5017 noioapicquirk [APIC] Disable all boot interrupt quirks. 5018 Safety option to keep boot IRQs enabled. This 5019 should never be necessary. 5020 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5021 primary IO-APIC for bridges that cannot disable 5022 boot IRQs. This fixes a source of spurious IRQs 5023 when the system masks IRQs. 5024 noioapicreroute [APIC] Disable workaround that uses the 5025 boot IRQ equivalent of an IRQ that connects to 5026 a chipset where boot IRQs cannot be disabled. 5027 The opposite of ioapicreroute. 5028 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5029 routing table. These calls are known to be buggy 5030 on several machines and they hang the machine 5031 when used, but on other computers it's the only 5032 way to get the interrupt routing table. Try 5033 this option if the kernel is unable to allocate 5034 IRQs or discover secondary PCI buses on your 5035 motherboard. 5036 rom [X86] Assign address space to expansion ROMs. 5037 Use with caution as certain devices share 5038 address decoders between ROMs and other 5039 resources. 5040 norom [X86] Do not assign address space to 5041 expansion ROMs that do not already have 5042 BIOS assigned address ranges. 5043 nobar [X86] Do not assign address space to the 5044 BARs that weren't assigned by the BIOS. 5045 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5046 assigned automatically to PCI devices. You can 5047 make the kernel exclude IRQs of your ISA cards 5048 this way. 5049 pirqaddr=0xAAAAA [X86] Specify the physical address 5050 of the PIRQ table (normally generated 5051 by the BIOS) if it is outside the 5052 F0000h-100000h range. 5053 lastbus=N [X86] Scan all buses thru bus #N. Can be 5054 useful if the kernel is unable to find your 5055 secondary buses and you want to tell it 5056 explicitly which ones they are. 5057 assign-busses [X86] Always assign all PCI bus 5058 numbers ourselves, overriding 5059 whatever the firmware may have done. 5060 usepirqmask [X86] Honor the possible IRQ mask stored 5061 in the BIOS $PIR table. This is needed on 5062 some systems with broken BIOSes, notably 5063 some HP Pavilion N5400 and Omnibook XE3 5064 notebooks. This will have no effect if ACPI 5065 IRQ routing is enabled. 5066 noacpi [X86] Do not use ACPI for IRQ routing 5067 or for PCI scanning. 5068 use_crs [X86] Use PCI host bridge window information 5069 from ACPI. On BIOSes from 2008 or later, this 5070 is enabled by default. If you need to use this, 5071 please report a bug. 5072 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5073 If you need to use this, please report a bug. 5074 use_e820 [X86] Use E820 reservations to exclude parts of 5075 PCI host bridge windows. This is a workaround 5076 for BIOS defects in host bridge _CRS methods. 5077 If you need to use this, please report a bug to 5078 <linux-pci@vger.kernel.org>. 5079 no_e820 [X86] Ignore E820 reservations for PCI host 5080 bridge windows. This is the default on modern 5081 hardware. If you need to use this, please report 5082 a bug to <linux-pci@vger.kernel.org>. 5083 routeirq Do IRQ routing for all PCI devices. 5084 This is normally done in pci_enable_device(), 5085 so this option is a temporary workaround 5086 for broken drivers that don't call it. 5087 skip_isa_align [X86] do not align io start addr, so can 5088 handle more pci cards 5089 noearly [X86] Don't do any early type 1 scanning. 5090 This might help on some broken boards which 5091 machine check when some devices' config space 5092 is read. But various workarounds are disabled 5093 and some IOMMU drivers will not work. 5094 bfsort Sort PCI devices into breadth-first order. 5095 This sorting is done to get a device 5096 order compatible with older (<= 2.4) kernels. 5097 nobfsort Don't sort PCI devices into breadth-first order. 5098 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5099 tuning and use the BIOS-configured MPS defaults. 5100 pcie_bus_safe Set every device's MPS to the largest value 5101 supported by all devices below the root complex. 5102 pcie_bus_perf Set device MPS to the largest allowable MPS 5103 based on its parent bus. Also set MRRS (Max 5104 Read Request Size) to the largest supported 5105 value (no larger than the MPS that the device 5106 or bus can support) for best performance. 5107 pcie_bus_peer2peer Set every device's MPS to 128B, which 5108 every device is guaranteed to support. This 5109 configuration allows peer-to-peer DMA between 5110 any pair of devices, possibly at the cost of 5111 reduced performance. This also guarantees 5112 that hot-added devices will work. 5113 cbiosize=nn[KMG] The fixed amount of bus space which is 5114 reserved for the CardBus bridge's IO window. 5115 The default value is 256 bytes. 5116 cbmemsize=nn[KMG] The fixed amount of bus space which is 5117 reserved for the CardBus bridge's memory 5118 window. The default value is 64 megabytes. 5119 resource_alignment= 5120 Format: 5121 [<order of align>@]<pci_dev>[; ...] 5122 Specifies alignment and device to reassign 5123 aligned memory resources. How to 5124 specify the device is described above. 5125 If <order of align> is not specified, 5126 PAGE_SIZE is used as alignment. 5127 A PCI-PCI bridge can be specified if resource 5128 windows need to be expanded. 5129 To specify the alignment for several 5130 instances of a device, the PCI vendor, 5131 device, subvendor, and subdevice may be 5132 specified, e.g., 12@pci:8086:9c22:103c:198f 5133 for 4096-byte alignment. 5134 ecrc= Enable/disable PCIe ECRC (transaction layer 5135 end-to-end CRC checking). Only effective if 5136 OS has native AER control (either granted by 5137 ACPI _OSC or forced via "pcie_ports=native") 5138 bios: Use BIOS/firmware settings. This is the 5139 the default. 5140 off: Turn ECRC off 5141 on: Turn ECRC on. 5142 hpiosize=nn[KMG] The fixed amount of bus space which is 5143 reserved for hotplug bridge's IO window. 5144 Default size is 256 bytes. 5145 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5146 reserved for hotplug bridge's MMIO window. 5147 Default size is 2 megabytes. 5148 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5149 reserved for hotplug bridge's MMIO_PREF window. 5150 Default size is 2 megabytes. 5151 hpmemsize=nn[KMG] The fixed amount of bus space which is 5152 reserved for hotplug bridge's MMIO and 5153 MMIO_PREF window. 5154 Default size is 2 megabytes. 5155 hpbussize=nn The minimum amount of additional bus numbers 5156 reserved for buses below a hotplug bridge. 5157 Default is 1. 5158 realloc= Enable/disable reallocating PCI bridge resources 5159 if allocations done by BIOS are too small to 5160 accommodate resources required by all child 5161 devices. 5162 off: Turn realloc off 5163 on: Turn realloc on 5164 realloc same as realloc=on 5165 noari do not use PCIe ARI. 5166 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5167 do not use PCIe ATS (and IOMMU device IOTLB). 5168 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5169 only look for one device below a PCIe downstream 5170 port. 5171 big_root_window Try to add a big 64bit memory window to the PCIe 5172 root complex on AMD CPUs. Some GFX hardware 5173 can resize a BAR to allow access to all VRAM. 5174 Adding the window is slightly risky (it may 5175 conflict with unreported devices), so this 5176 taints the kernel. 5177 disable_acs_redir=<pci_dev>[; ...] 5178 Specify one or more PCI devices (in the format 5179 specified above) separated by semicolons. 5180 Each device specified will have the PCI ACS 5181 redirect capabilities forced off which will 5182 allow P2P traffic between devices through 5183 bridges without forcing it upstream. Note: 5184 this removes isolation between devices and 5185 may put more devices in an IOMMU group. 5186 config_acs= 5187 Format: 5188 <ACS flags>@<pci_dev>[; ...] 5189 Specify one or more PCI devices (in the format 5190 specified above) optionally prepended with flags 5191 and separated by semicolons. The respective 5192 capabilities will be enabled, disabled or 5193 unchanged based on what is specified in 5194 flags. 5195 5196 ACS Flags is defined as follows: 5197 bit-0 : ACS Source Validation 5198 bit-1 : ACS Translation Blocking 5199 bit-2 : ACS P2P Request Redirect 5200 bit-3 : ACS P2P Completion Redirect 5201 bit-4 : ACS Upstream Forwarding 5202 bit-5 : ACS P2P Egress Control 5203 bit-6 : ACS Direct Translated P2P 5204 Each bit can be marked as: 5205 '0' – force disabled 5206 '1' – force enabled 5207 'x' – unchanged 5208 For example, 5209 pci=config_acs=10x@pci:0:0 5210 would configure all devices that support 5211 ACS to enable P2P Request Redirect, disable 5212 Translation Blocking, and leave Source 5213 Validation unchanged from whatever power-up 5214 or firmware set it to. 5215 5216 Note: this may remove isolation between devices 5217 and may put more devices in an IOMMU group. 5218 force_floating [S390] Force usage of floating interrupts. 5219 nomio [S390] Do not use MIO instructions. 5220 norid [S390] ignore the RID field and force use of 5221 one PCI domain per PCI function 5222 notph [PCIE] If the PCIE_TPH kernel config parameter 5223 is enabled, this kernel boot option can be used 5224 to disable PCIe TLP Processing Hints support 5225 system-wide. 5226 5227 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5228 Management. 5229 off Don't touch ASPM configuration at all. Leave any 5230 configuration done by firmware unchanged. 5231 force Enable ASPM even on devices that claim not to support it. 5232 WARNING: Forcing ASPM on may cause system lockups. 5233 5234 pcie_ports= [PCIE] PCIe port services handling: 5235 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5236 even if the platform doesn't give the OS permission to 5237 use them. This may cause conflicts if the platform 5238 also tries to use these services. 5239 dpc-native Use native PCIe service for DPC only. May 5240 cause conflicts if firmware uses AER or DPC. 5241 compat Disable native PCIe services (PME, AER, DPC, PCIe 5242 hotplug). 5243 5244 pcie_port_pm= [PCIE] PCIe port power management handling: 5245 off Disable power management of all PCIe ports 5246 force Forcibly enable power management of all PCIe ports 5247 5248 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5249 nomsi Do not use MSI for native PCIe PME signaling (this makes 5250 all PCIe root ports use INTx for all services). 5251 5252 pcmv= [HW,PCMCIA] BadgePAD 4 5253 5254 pd_ignore_unused 5255 [PM] 5256 Keep all power-domains already enabled by bootloader on, 5257 even if no driver has claimed them. This is useful 5258 for debug and development, but should not be 5259 needed on a platform with proper driver support. 5260 5261 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5262 boot time. 5263 Format: { 0 | 1 } 5264 See arch/parisc/kernel/pdc_chassis.c 5265 5266 percpu_alloc= [MM,EARLY] 5267 Select which percpu first chunk allocator to use. 5268 Currently supported values are "embed" and "page". 5269 Archs may support subset or none of the selections. 5270 See comments in mm/percpu.c for details on each 5271 allocator. This parameter is primarily for debugging 5272 and performance comparison. 5273 5274 pirq= [SMP,APIC] Manual mp-table setup 5275 See Documentation/arch/x86/i386/IO-APIC.rst. 5276 5277 plip= [PPT,NET] Parallel port network link 5278 Format: { parport<nr> | timid | 0 } 5279 See also Documentation/admin-guide/parport.rst. 5280 5281 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5282 Override pmtimer IOPort with a hex value. 5283 e.g. pmtmr=0x508 5284 5285 pmu_override= [PPC] Override the PMU. 5286 This option takes over the PMU facility, so it is no 5287 longer usable by perf. Setting this option starts the 5288 PMU counters by setting MMCR0 to 0 (the FC bit is 5289 cleared). If a number is given, then MMCR1 is set to 5290 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5291 remains 0. 5292 5293 pm_async= [PM] 5294 Format: off 5295 This parameter sets the initial value of the 5296 /sys/power/pm_async sysfs knob at boot time. 5297 If set to "off", disables asynchronous suspend and 5298 resume of devices during system-wide power transitions. 5299 This can be useful on platforms where device 5300 dependencies are not well-defined, or for debugging 5301 power management issues. Asynchronous operations are 5302 enabled by default. 5303 5304 5305 pm_debug_messages [SUSPEND,KNL] 5306 Enable suspend/resume debug messages during boot up. 5307 5308 pnp.debug=1 [PNP] 5309 Enable PNP debug messages (depends on the 5310 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5311 via /sys/module/pnp/parameters/debug. We always show 5312 current resource usage; turning this on also shows 5313 possible settings and some assignment information. 5314 5315 pnpacpi= [ACPI] 5316 { off } 5317 5318 pnpbios= [ISAPNP] 5319 { on | off | curr | res | no-curr | no-res } 5320 5321 pnp_reserve_irq= 5322 [ISAPNP] Exclude IRQs for the autoconfiguration 5323 5324 pnp_reserve_dma= 5325 [ISAPNP] Exclude DMAs for the autoconfiguration 5326 5327 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5328 Ranges are in pairs (I/O port base and size). 5329 5330 pnp_reserve_mem= 5331 [ISAPNP] Exclude memory regions for the 5332 autoconfiguration. 5333 Ranges are in pairs (memory base and size). 5334 5335 ports= [IP_VS_FTP] IPVS ftp helper module 5336 Default is 21. 5337 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5338 may be specified. 5339 Format: <port>,<port>.... 5340 5341 possible_cpus= [SMP,S390,X86] 5342 Format: <unsigned int> 5343 Set the number of possible CPUs, overriding the 5344 regular discovery mechanisms (such as ACPI/FW, etc). 5345 5346 powersave=off [PPC] This option disables power saving features. 5347 It specifically disables cpuidle and sets the 5348 platform machine description specific power_save 5349 function to NULL. On Idle the CPU just reduces 5350 execution priority. 5351 5352 ppc_strict_facility_enable 5353 [PPC,ENABLE] This option catches any kernel floating point, 5354 Altivec, VSX and SPE outside of regions specifically 5355 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5356 There is some performance impact when enabling this. 5357 5358 ppc_tm= [PPC,EARLY] 5359 Format: {"off"} 5360 Disable Hardware Transactional Memory 5361 5362 preempt= [KNL] 5363 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5364 none - Limited to cond_resched() calls 5365 voluntary - Limited to cond_resched() and might_sleep() calls 5366 full - Any section that isn't explicitly preempt disabled 5367 can be preempted anytime. Tasks will also yield 5368 contended spinlocks (if the critical section isn't 5369 explicitly preempt disabled beyond the lock itself). 5370 lazy - Scheduler controlled. Similar to full but instead 5371 of preempting the task immediately, the task gets 5372 one HZ tick time to yield itself before the 5373 preemption will be forced. One preemption is when the 5374 task returns to user space. 5375 5376 print-fatal-signals= 5377 [KNL] debug: print fatal signals 5378 5379 If enabled, warn about various signal handling 5380 related application anomalies: too many signals, 5381 too many POSIX.1 timers, fatal signals causing a 5382 coredump - etc. 5383 5384 If you hit the warning due to signal overflow, 5385 you might want to try "ulimit -i unlimited". 5386 5387 default: off. 5388 5389 printk.always_kmsg_dump= 5390 Trigger kmsg_dump for cases other than kernel oops or 5391 panics 5392 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5393 default: disabled 5394 5395 printk.console_no_auto_verbose= 5396 Disable console loglevel raise on oops, panic 5397 or lockdep-detected issues (only if lock debug is on). 5398 With an exception to setups with low baudrate on 5399 serial console, keeping this 0 is a good choice 5400 in order to provide more debug information. 5401 Format: <bool> 5402 default: 0 (auto_verbose is enabled) 5403 5404 printk.debug_non_panic_cpus= 5405 Allows storing messages from non-panic CPUs into 5406 the printk log buffer during panic(). They are 5407 flushed to consoles by the panic-CPU on 5408 a best-effort basis. 5409 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5410 Default: disabled 5411 5412 printk.devkmsg={on,off,ratelimit} 5413 Control writing to /dev/kmsg. 5414 on - unlimited logging to /dev/kmsg from userspace 5415 off - logging to /dev/kmsg disabled 5416 ratelimit - ratelimit the logging 5417 Default: ratelimit 5418 5419 printk.time= Show timing data prefixed to each printk message line 5420 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5421 5422 proc_mem.force_override= [KNL] 5423 Format: {always | ptrace | never} 5424 Traditionally /proc/pid/mem allows memory permissions to be 5425 overridden without restrictions. This option may be set to 5426 restrict that. Can be one of: 5427 - 'always': traditional behavior always allows mem overrides. 5428 - 'ptrace': only allow mem overrides for active ptracers. 5429 - 'never': never allow mem overrides. 5430 If not specified, default is the CONFIG_PROC_MEM_* choice. 5431 5432 processor.max_cstate= [HW,ACPI] 5433 Limit processor to maximum C-state 5434 max_cstate=9 overrides any DMI blacklist limit. 5435 5436 processor.nocst [HW,ACPI] 5437 Ignore the _CST method to determine C-states, 5438 instead using the legacy FADT method 5439 5440 profile= [KNL] Enable kernel profiling via /proc/profile 5441 Format: [<profiletype>,]<number> 5442 Param: <profiletype>: "schedule" or "kvm" 5443 [defaults to kernel profiling] 5444 Param: "schedule" - profile schedule points. 5445 Param: "kvm" - profile VM exits. 5446 Param: <number> - step/bucket size as a power of 2 for 5447 statistical time based profiling. 5448 5449 prot_virt= [S390] enable hosting protected virtual machines 5450 isolated from the hypervisor (if hardware supports 5451 that). If enabled, the default kernel base address 5452 might be overridden even when Kernel Address Space 5453 Layout Randomization is disabled. 5454 Format: <bool> 5455 5456 psi= [KNL] Enable or disable pressure stall information 5457 tracking. 5458 Format: <bool> 5459 5460 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5461 probe for; one of (bare|imps|exps|lifebook|any). 5462 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5463 per second. 5464 psmouse.resetafter= [HW,MOUSE] 5465 Try to reset the device after so many bad packets 5466 (0 = never). 5467 psmouse.resolution= 5468 [HW,MOUSE] Set desired mouse resolution, in dpi. 5469 psmouse.smartscroll= 5470 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5471 0 = disabled, 1 = enabled (default). 5472 5473 pstore.backend= Specify the name of the pstore backend to use 5474 5475 pti= [X86-64] Control Page Table Isolation of user and 5476 kernel address spaces. Disabling this feature 5477 removes hardening, but improves performance of 5478 system calls and interrupts. 5479 5480 on - unconditionally enable 5481 off - unconditionally disable 5482 auto - kernel detects whether your CPU model is 5483 vulnerable to issues that PTI mitigates 5484 5485 Not specifying this option is equivalent to pti=auto. 5486 5487 pty.legacy_count= 5488 [KNL] Number of legacy pty's. Overwrites compiled-in 5489 default number. 5490 5491 quiet [KNL,EARLY] Disable most log messages 5492 5493 r128= [HW,DRM] 5494 5495 radix_hcall_invalidate=on [PPC/PSERIES] 5496 Disable RADIX GTSE feature and use hcall for TLB 5497 invalidate. 5498 5499 raid= [HW,RAID] 5500 See Documentation/admin-guide/md.rst. 5501 5502 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5503 See Documentation/admin-guide/blockdev/ramdisk.rst. 5504 5505 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5506 5507 random.trust_cpu=off 5508 [KNL,EARLY] Disable trusting the use of the CPU's 5509 random number generator (if available) to 5510 initialize the kernel's RNG. 5511 5512 random.trust_bootloader=off 5513 [KNL,EARLY] Disable trusting the use of the a seed 5514 passed by the bootloader (if available) to 5515 initialize the kernel's RNG. 5516 5517 randomize_kstack_offset= 5518 [KNL,EARLY] Enable or disable kernel stack offset 5519 randomization, which provides roughly 5 bits of 5520 entropy, frustrating memory corruption attacks 5521 that depend on stack address determinism or 5522 cross-syscall address exposures. This is only 5523 available on architectures that have defined 5524 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5525 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5526 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5527 5528 ras=option[,option,...] [KNL] RAS-specific options 5529 5530 cec_disable [X86] 5531 Disable the Correctable Errors Collector, 5532 see CONFIG_RAS_CEC help text. 5533 5534 rcu_nocbs[=cpu-list] 5535 [KNL] The optional argument is a cpu list, 5536 as described above. 5537 5538 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5539 enable the no-callback CPU mode, which prevents 5540 such CPUs' callbacks from being invoked in 5541 softirq context. Invocation of such CPUs' RCU 5542 callbacks will instead be offloaded to "rcuox/N" 5543 kthreads created for that purpose, where "x" is 5544 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5545 for the kthreads that mediate grace periods; and 5546 "N" is the CPU number. This reduces OS jitter on 5547 the offloaded CPUs, which can be useful for HPC 5548 and real-time workloads. It can also improve 5549 energy efficiency for asymmetric multiprocessors. 5550 5551 If a cpulist is passed as an argument, the specified 5552 list of CPUs is set to no-callback mode from boot. 5553 5554 Otherwise, if the '=' sign and the cpulist 5555 arguments are omitted, no CPU will be set to 5556 no-callback mode from boot but the mode may be 5557 toggled at runtime via cpusets. 5558 5559 Note that this argument takes precedence over 5560 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5561 5562 rcu_nocb_poll [KNL] 5563 Rather than requiring that offloaded CPUs 5564 (specified by rcu_nocbs= above) explicitly 5565 awaken the corresponding "rcuoN" kthreads, 5566 make these kthreads poll for callbacks. 5567 This improves the real-time response for the 5568 offloaded CPUs by relieving them of the need to 5569 wake up the corresponding kthread, but degrades 5570 energy efficiency by requiring that the kthreads 5571 periodically wake up to do the polling. 5572 5573 rcutree.blimit= [KNL] 5574 Set maximum number of finished RCU callbacks to 5575 process in one batch. 5576 5577 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5578 Do only a one-line RCU CPU stall warning when 5579 there is an ongoing too-long CSD-lock wait. 5580 5581 rcutree.do_rcu_barrier= [KNL] 5582 Request a call to rcu_barrier(). This is 5583 throttled so that userspace tests can safely 5584 hammer on the sysfs variable if they so choose. 5585 If triggered before the RCU grace-period machinery 5586 is fully active, this will error out with EAGAIN. 5587 5588 rcutree.dump_tree= [KNL] 5589 Dump the structure of the rcu_node combining tree 5590 out at early boot. This is used for diagnostic 5591 purposes, to verify correct tree setup. 5592 5593 rcutree.gp_cleanup_delay= [KNL] 5594 Set the number of jiffies to delay each step of 5595 RCU grace-period cleanup. 5596 5597 rcutree.gp_init_delay= [KNL] 5598 Set the number of jiffies to delay each step of 5599 RCU grace-period initialization. 5600 5601 rcutree.gp_preinit_delay= [KNL] 5602 Set the number of jiffies to delay each step of 5603 RCU grace-period pre-initialization, that is, 5604 the propagation of recent CPU-hotplug changes up 5605 the rcu_node combining tree. 5606 5607 rcutree.jiffies_till_first_fqs= [KNL] 5608 Set delay from grace-period initialization to 5609 first attempt to force quiescent states. 5610 Units are jiffies, minimum value is zero, 5611 and maximum value is HZ. 5612 5613 rcutree.jiffies_till_next_fqs= [KNL] 5614 Set delay between subsequent attempts to force 5615 quiescent states. Units are jiffies, minimum 5616 value is one, and maximum value is HZ. 5617 5618 rcutree.jiffies_till_sched_qs= [KNL] 5619 Set required age in jiffies for a 5620 given grace period before RCU starts 5621 soliciting quiescent-state help from 5622 rcu_note_context_switch() and cond_resched(). 5623 If not specified, the kernel will calculate 5624 a value based on the most recent settings 5625 of rcutree.jiffies_till_first_fqs 5626 and rcutree.jiffies_till_next_fqs. 5627 This calculated value may be viewed in 5628 rcutree.jiffies_to_sched_qs. Any attempt to set 5629 rcutree.jiffies_to_sched_qs will be cheerfully 5630 overwritten. 5631 5632 rcutree.kthread_prio= [KNL,BOOT] 5633 Set the SCHED_FIFO priority of the RCU per-CPU 5634 kthreads (rcuc/N). This value is also used for 5635 the priority of the RCU boost threads (rcub/N) 5636 and for the RCU grace-period kthreads (rcu_bh, 5637 rcu_preempt, and rcu_sched). If RCU_BOOST is 5638 set, valid values are 1-99 and the default is 1 5639 (the least-favored priority). Otherwise, when 5640 RCU_BOOST is not set, valid values are 0-99 and 5641 the default is zero (non-realtime operation). 5642 When RCU_NOCB_CPU is set, also adjust the 5643 priority of NOCB callback kthreads. 5644 5645 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5646 On callback-offloaded (rcu_nocbs) CPUs, 5647 RCU reduces the lock contention that would 5648 otherwise be caused by callback floods through 5649 use of the ->nocb_bypass list. However, in the 5650 common non-flooded case, RCU queues directly to 5651 the main ->cblist in order to avoid the extra 5652 overhead of the ->nocb_bypass list and its lock. 5653 But if there are too many callbacks queued during 5654 a single jiffy, RCU pre-queues the callbacks into 5655 the ->nocb_bypass queue. The definition of "too 5656 many" is supplied by this kernel boot parameter. 5657 5658 rcutree.nohz_full_patience_delay= [KNL] 5659 On callback-offloaded (rcu_nocbs) CPUs, avoid 5660 disturbing RCU unless the grace period has 5661 reached the specified age in milliseconds. 5662 Defaults to zero. Large values will be capped 5663 at five seconds. All values will be rounded down 5664 to the nearest value representable by jiffies. 5665 5666 rcutree.qhimark= [KNL] 5667 Set threshold of queued RCU callbacks beyond which 5668 batch limiting is disabled. 5669 5670 rcutree.qlowmark= [KNL] 5671 Set threshold of queued RCU callbacks below which 5672 batch limiting is re-enabled. 5673 5674 rcutree.qovld= [KNL] 5675 Set threshold of queued RCU callbacks beyond which 5676 RCU's force-quiescent-state scan will aggressively 5677 enlist help from cond_resched() and sched IPIs to 5678 help CPUs more quickly reach quiescent states. 5679 Set to less than zero to make this be set based 5680 on rcutree.qhimark at boot time and to zero to 5681 disable more aggressive help enlistment. 5682 5683 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5684 Set the page-cache refill delay (in milliseconds) 5685 in response to low-memory conditions. The range 5686 of permitted values is in the range 0:100000. 5687 5688 rcutree.rcu_divisor= [KNL] 5689 Set the shift-right count to use to compute 5690 the callback-invocation batch limit bl from 5691 the number of callbacks queued on this CPU. 5692 The result will be bounded below by the value of 5693 the rcutree.blimit kernel parameter. Every bl 5694 callbacks, the softirq handler will exit in 5695 order to allow the CPU to do other work. 5696 5697 Please note that this callback-invocation batch 5698 limit applies only to non-offloaded callback 5699 invocation. Offloaded callbacks are instead 5700 invoked in the context of an rcuoc kthread, which 5701 scheduler will preempt as it does any other task. 5702 5703 rcutree.rcu_fanout_exact= [KNL] 5704 Disable autobalancing of the rcu_node combining 5705 tree. This is used by rcutorture, and might 5706 possibly be useful for architectures having high 5707 cache-to-cache transfer latencies. 5708 5709 rcutree.rcu_fanout_leaf= [KNL] 5710 Change the number of CPUs assigned to each 5711 leaf rcu_node structure. Useful for very 5712 large systems, which will choose the value 64, 5713 and for NUMA systems with large remote-access 5714 latencies, which will choose a value aligned 5715 with the appropriate hardware boundaries. 5716 5717 rcutree.rcu_min_cached_objs= [KNL] 5718 Minimum number of objects which are cached and 5719 maintained per one CPU. Object size is equal 5720 to PAGE_SIZE. The cache allows to reduce the 5721 pressure to page allocator, also it makes the 5722 whole algorithm to behave better in low memory 5723 condition. 5724 5725 rcutree.rcu_nocb_gp_stride= [KNL] 5726 Set the number of NOCB callback kthreads in 5727 each group, which defaults to the square root 5728 of the number of CPUs. Larger numbers reduce 5729 the wakeup overhead on the global grace-period 5730 kthread, but increases that same overhead on 5731 each group's NOCB grace-period kthread. 5732 5733 rcutree.rcu_kick_kthreads= [KNL] 5734 Cause the grace-period kthread to get an extra 5735 wake_up() if it sleeps three times longer than 5736 it should at force-quiescent-state time. 5737 This wake_up() will be accompanied by a 5738 WARN_ONCE() splat and an ftrace_dump(). 5739 5740 rcutree.rcu_resched_ns= [KNL] 5741 Limit the time spend invoking a batch of RCU 5742 callbacks to the specified number of nanoseconds. 5743 By default, this limit is checked only once 5744 every 32 callbacks in order to limit the pain 5745 inflicted by local_clock() overhead. 5746 5747 rcutree.rcu_unlock_delay= [KNL] 5748 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5749 this specifies an rcu_read_unlock()-time delay 5750 in microseconds. This defaults to zero. 5751 Larger delays increase the probability of 5752 catching RCU pointer leaks, that is, buggy use 5753 of RCU-protected pointers after the relevant 5754 rcu_read_unlock() has completed. 5755 5756 rcutree.sysrq_rcu= [KNL] 5757 Commandeer a sysrq key to dump out Tree RCU's 5758 rcu_node tree with an eye towards determining 5759 why a new grace period has not yet started. 5760 5761 rcutree.use_softirq= [KNL] 5762 If set to zero, move all RCU_SOFTIRQ processing to 5763 per-CPU rcuc kthreads. Defaults to a non-zero 5764 value, meaning that RCU_SOFTIRQ is used by default. 5765 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5766 5767 But note that CONFIG_PREEMPT_RT=y kernels disable 5768 this kernel boot parameter, forcibly setting it 5769 to zero. 5770 5771 rcutree.enable_rcu_lazy= [KNL] 5772 To save power, batch RCU callbacks and flush after 5773 delay, memory pressure or callback list growing too 5774 big. 5775 5776 rcutree.rcu_normal_wake_from_gp= [KNL] 5777 Reduces a latency of synchronize_rcu() call. This approach 5778 maintains its own track of synchronize_rcu() callers, so it 5779 does not interact with regular callbacks because it does not 5780 use a call_rcu[_hurry]() path. Please note, this is for a 5781 normal grace period. 5782 5783 How to enable it: 5784 5785 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5786 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5787 5788 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5789 disabled by the boot parameter passing 0. 5790 5791 rcuscale.gp_async= [KNL] 5792 Measure performance of asynchronous 5793 grace-period primitives such as call_rcu(). 5794 5795 rcuscale.gp_async_max= [KNL] 5796 Specify the maximum number of outstanding 5797 callbacks per writer thread. When a writer 5798 thread exceeds this limit, it invokes the 5799 corresponding flavor of rcu_barrier() to allow 5800 previously posted callbacks to drain. 5801 5802 rcuscale.gp_exp= [KNL] 5803 Measure performance of expedited synchronous 5804 grace-period primitives. 5805 5806 rcuscale.holdoff= [KNL] 5807 Set test-start holdoff period. The purpose of 5808 this parameter is to delay the start of the 5809 test until boot completes in order to avoid 5810 interference. 5811 5812 rcuscale.kfree_by_call_rcu= [KNL] 5813 In kernels built with CONFIG_RCU_LAZY=y, test 5814 call_rcu() instead of kfree_rcu(). 5815 5816 rcuscale.kfree_mult= [KNL] 5817 Instead of allocating an object of size kfree_obj, 5818 allocate one of kfree_mult * sizeof(kfree_obj). 5819 Defaults to 1. 5820 5821 rcuscale.kfree_rcu_test= [KNL] 5822 Set to measure performance of kfree_rcu() flooding. 5823 5824 rcuscale.kfree_rcu_test_double= [KNL] 5825 Test the double-argument variant of kfree_rcu(). 5826 If this parameter has the same value as 5827 rcuscale.kfree_rcu_test_single, both the single- 5828 and double-argument variants are tested. 5829 5830 rcuscale.kfree_rcu_test_single= [KNL] 5831 Test the single-argument variant of kfree_rcu(). 5832 If this parameter has the same value as 5833 rcuscale.kfree_rcu_test_double, both the single- 5834 and double-argument variants are tested. 5835 5836 rcuscale.kfree_nthreads= [KNL] 5837 The number of threads running loops of kfree_rcu(). 5838 5839 rcuscale.kfree_alloc_num= [KNL] 5840 Number of allocations and frees done in an iteration. 5841 5842 rcuscale.kfree_loops= [KNL] 5843 Number of loops doing rcuscale.kfree_alloc_num number 5844 of allocations and frees. 5845 5846 rcuscale.minruntime= [KNL] 5847 Set the minimum test run time in seconds. This 5848 does not affect the data-collection interval, 5849 but instead allows better measurement of things 5850 like CPU consumption. 5851 5852 rcuscale.nreaders= [KNL] 5853 Set number of RCU readers. The value -1 selects 5854 N, where N is the number of CPUs. A value 5855 "n" less than -1 selects N-n+1, where N is again 5856 the number of CPUs. For example, -2 selects N 5857 (the number of CPUs), -3 selects N+1, and so on. 5858 A value of "n" less than or equal to -N selects 5859 a single reader. 5860 5861 rcuscale.nwriters= [KNL] 5862 Set number of RCU writers. The values operate 5863 the same as for rcuscale.nreaders. 5864 N, where N is the number of CPUs 5865 5866 rcuscale.scale_type= [KNL] 5867 Specify the RCU implementation to test. 5868 5869 rcuscale.shutdown= [KNL] 5870 Shut the system down after performance tests 5871 complete. This is useful for hands-off automated 5872 testing. 5873 5874 rcuscale.verbose= [KNL] 5875 Enable additional printk() statements. 5876 5877 rcuscale.writer_holdoff= [KNL] 5878 Write-side holdoff between grace periods, 5879 in microseconds. The default of zero says 5880 no holdoff. 5881 5882 rcuscale.writer_holdoff_jiffies= [KNL] 5883 Additional write-side holdoff between grace 5884 periods, but in jiffies. The default of zero 5885 says no holdoff. 5886 5887 rcutorture.fqs_duration= [KNL] 5888 Set duration of force_quiescent_state bursts 5889 in microseconds. 5890 5891 rcutorture.fqs_holdoff= [KNL] 5892 Set holdoff time within force_quiescent_state bursts 5893 in microseconds. 5894 5895 rcutorture.fqs_stutter= [KNL] 5896 Set wait time between force_quiescent_state bursts 5897 in seconds. 5898 5899 rcutorture.fwd_progress= [KNL] 5900 Specifies the number of kthreads to be used 5901 for RCU grace-period forward-progress testing 5902 for the types of RCU supporting this notion. 5903 Defaults to 1 kthread, values less than zero or 5904 greater than the number of CPUs cause the number 5905 of CPUs to be used. 5906 5907 rcutorture.fwd_progress_div= [KNL] 5908 Specify the fraction of a CPU-stall-warning 5909 period to do tight-loop forward-progress testing. 5910 5911 rcutorture.fwd_progress_holdoff= [KNL] 5912 Number of seconds to wait between successive 5913 forward-progress tests. 5914 5915 rcutorture.fwd_progress_need_resched= [KNL] 5916 Enclose cond_resched() calls within checks for 5917 need_resched() during tight-loop forward-progress 5918 testing. 5919 5920 rcutorture.gp_cond= [KNL] 5921 Use conditional/asynchronous update-side 5922 normal-grace-period primitives, if available. 5923 5924 rcutorture.gp_cond_exp= [KNL] 5925 Use conditional/asynchronous update-side 5926 expedited-grace-period primitives, if available. 5927 5928 rcutorture.gp_cond_full= [KNL] 5929 Use conditional/asynchronous update-side 5930 normal-grace-period primitives that also take 5931 concurrent expedited grace periods into account, 5932 if available. 5933 5934 rcutorture.gp_cond_exp_full= [KNL] 5935 Use conditional/asynchronous update-side 5936 expedited-grace-period primitives that also take 5937 concurrent normal grace periods into account, 5938 if available. 5939 5940 rcutorture.gp_cond_wi= [KNL] 5941 Nominal wait interval for normal conditional 5942 grace periods (specified by rcutorture's 5943 gp_cond and gp_cond_full module parameters), 5944 in microseconds. The actual wait interval will 5945 be randomly selected to nanosecond granularity up 5946 to this wait interval. Defaults to 16 jiffies, 5947 for example, 16,000 microseconds on a system 5948 with HZ=1000. 5949 5950 rcutorture.gp_cond_wi_exp= [KNL] 5951 Nominal wait interval for expedited conditional 5952 grace periods (specified by rcutorture's 5953 gp_cond_exp and gp_cond_exp_full module 5954 parameters), in microseconds. The actual wait 5955 interval will be randomly selected to nanosecond 5956 granularity up to this wait interval. Defaults to 5957 128 microseconds. 5958 5959 rcutorture.gp_exp= [KNL] 5960 Use expedited update-side primitives, if available. 5961 5962 rcutorture.gp_normal= [KNL] 5963 Use normal (non-expedited) asynchronous 5964 update-side primitives, if available. 5965 5966 rcutorture.gp_poll= [KNL] 5967 Use polled update-side normal-grace-period 5968 primitives, if available. 5969 5970 rcutorture.gp_poll_exp= [KNL] 5971 Use polled update-side expedited-grace-period 5972 primitives, if available. 5973 5974 rcutorture.gp_poll_full= [KNL] 5975 Use polled update-side normal-grace-period 5976 primitives that also take concurrent expedited 5977 grace periods into account, if available. 5978 5979 rcutorture.gp_poll_exp_full= [KNL] 5980 Use polled update-side expedited-grace-period 5981 primitives that also take concurrent normal 5982 grace periods into account, if available. 5983 5984 rcutorture.gp_poll_wi= [KNL] 5985 Nominal wait interval for normal conditional 5986 grace periods (specified by rcutorture's 5987 gp_poll and gp_poll_full module parameters), 5988 in microseconds. The actual wait interval will 5989 be randomly selected to nanosecond granularity up 5990 to this wait interval. Defaults to 16 jiffies, 5991 for example, 16,000 microseconds on a system 5992 with HZ=1000. 5993 5994 rcutorture.gp_poll_wi_exp= [KNL] 5995 Nominal wait interval for expedited conditional 5996 grace periods (specified by rcutorture's 5997 gp_poll_exp and gp_poll_exp_full module 5998 parameters), in microseconds. The actual wait 5999 interval will be randomly selected to nanosecond 6000 granularity up to this wait interval. Defaults to 6001 128 microseconds. 6002 6003 rcutorture.gp_sync= [KNL] 6004 Use normal (non-expedited) synchronous 6005 update-side primitives, if available. If all 6006 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6007 rcutorture.gp_normal=, and rcutorture.gp_sync= 6008 are zero, rcutorture acts as if is interpreted 6009 they are all non-zero. 6010 6011 rcutorture.gpwrap_lag= [KNL] 6012 Enable grace-period wrap lag testing. Setting 6013 to false prevents the gpwrap lag test from 6014 running. Default is true. 6015 6016 rcutorture.gpwrap_lag_gps= [KNL] 6017 Set the value for grace-period wrap lag during 6018 active lag testing periods. This controls how many 6019 grace periods differences we tolerate between 6020 rdp and rnp's gp_seq before setting overflow flag. 6021 The default is always set to 8. 6022 6023 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6024 Set the total cycle duration for gpwrap lag 6025 testing in minutes. This is the total time for 6026 one complete cycle of active and inactive 6027 testing periods. Default is 30 minutes. 6028 6029 rcutorture.gpwrap_lag_active_mins= [KNL] 6030 Set the duration for which gpwrap lag is active 6031 within each cycle, in minutes. During this time, 6032 the grace-period wrap lag will be set to the 6033 value specified by gpwrap_lag_gps. Default is 6034 5 minutes. 6035 6036 rcutorture.irqreader= [KNL] 6037 Run RCU readers from irq handlers, or, more 6038 accurately, from a timer handler. Not all RCU 6039 flavors take kindly to this sort of thing. 6040 6041 rcutorture.leakpointer= [KNL] 6042 Leak an RCU-protected pointer out of the reader. 6043 This can of course result in splats, and is 6044 intended to test the ability of things like 6045 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6046 such leaks. 6047 6048 rcutorture.n_barrier_cbs= [KNL] 6049 Set callbacks/threads for rcu_barrier() testing. 6050 6051 rcutorture.nfakewriters= [KNL] 6052 Set number of concurrent RCU writers. These just 6053 stress RCU, they don't participate in the actual 6054 test, hence the "fake". 6055 6056 rcutorture.nocbs_nthreads= [KNL] 6057 Set number of RCU callback-offload togglers. 6058 Zero (the default) disables toggling. 6059 6060 rcutorture.nocbs_toggle= [KNL] 6061 Set the delay in milliseconds between successive 6062 callback-offload toggling attempts. 6063 6064 rcutorture.nreaders= [KNL] 6065 Set number of RCU readers. The value -1 selects 6066 N-1, where N is the number of CPUs. A value 6067 "n" less than -1 selects N-n-2, where N is again 6068 the number of CPUs. For example, -2 selects N 6069 (the number of CPUs), -3 selects N+1, and so on. 6070 6071 rcutorture.object_debug= [KNL] 6072 Enable debug-object double-call_rcu() testing. 6073 6074 rcutorture.onoff_holdoff= [KNL] 6075 Set time (s) after boot for CPU-hotplug testing. 6076 6077 rcutorture.onoff_interval= [KNL] 6078 Set time (jiffies) between CPU-hotplug operations, 6079 or zero to disable CPU-hotplug testing. 6080 6081 rcutorture.preempt_duration= [KNL] 6082 Set duration (in milliseconds) of preemptions 6083 by a high-priority FIFO real-time task. Set to 6084 zero (the default) to disable. The CPUs to 6085 preempt are selected randomly from the set that 6086 are online at a given point in time. Races with 6087 CPUs going offline are ignored, with that attempt 6088 at preemption skipped. 6089 6090 rcutorture.preempt_interval= [KNL] 6091 Set interval (in milliseconds, defaulting to one 6092 second) between preemptions by a high-priority 6093 FIFO real-time task. This delay is mediated 6094 by an hrtimer and is further fuzzed to avoid 6095 inadvertent synchronizations. 6096 6097 rcutorture.read_exit_burst= [KNL] 6098 The number of times in a given read-then-exit 6099 episode that a set of read-then-exit kthreads 6100 is spawned. 6101 6102 rcutorture.read_exit_delay= [KNL] 6103 The delay, in seconds, between successive 6104 read-then-exit testing episodes. 6105 6106 rcutorture.reader_flavor= [KNL] 6107 A bit mask indicating which readers to use. 6108 If there is more than one bit set, the readers 6109 are entered from low-order bit up, and are 6110 exited in the opposite order. For SRCU, the 6111 0x1 bit is normal readers, 0x2 NMI-safe readers, 6112 and 0x4 light-weight readers. 6113 6114 rcutorture.shuffle_interval= [KNL] 6115 Set task-shuffle interval (s). Shuffling tasks 6116 allows some CPUs to go into dyntick-idle mode 6117 during the rcutorture test. 6118 6119 rcutorture.shutdown_secs= [KNL] 6120 Set time (s) after boot system shutdown. This 6121 is useful for hands-off automated testing. 6122 6123 rcutorture.stall_cpu= [KNL] 6124 Duration of CPU stall (s) to test RCU CPU stall 6125 warnings, zero to disable. 6126 6127 rcutorture.stall_cpu_block= [KNL] 6128 Sleep while stalling if set. This will result 6129 in warnings from preemptible RCU in addition to 6130 any other stall-related activity. Note that 6131 in kernels built with CONFIG_PREEMPTION=n and 6132 CONFIG_PREEMPT_COUNT=y, this parameter will 6133 cause the CPU to pass through a quiescent state. 6134 Given CONFIG_PREEMPTION=n, this will suppress 6135 RCU CPU stall warnings, but will instead result 6136 in scheduling-while-atomic splats. 6137 6138 Use of this module parameter results in splats. 6139 6140 6141 rcutorture.stall_cpu_holdoff= [KNL] 6142 Time to wait (s) after boot before inducing stall. 6143 6144 rcutorture.stall_cpu_irqsoff= [KNL] 6145 Disable interrupts while stalling if set, but only 6146 on the first stall in the set. 6147 6148 rcutorture.stall_cpu_repeat= [KNL] 6149 Number of times to repeat the stall sequence, 6150 so that rcutorture.stall_cpu_repeat=3 will result 6151 in four stall sequences. 6152 6153 rcutorture.stall_gp_kthread= [KNL] 6154 Duration (s) of forced sleep within RCU 6155 grace-period kthread to test RCU CPU stall 6156 warnings, zero to disable. If both stall_cpu 6157 and stall_gp_kthread are specified, the 6158 kthread is starved first, then the CPU. 6159 6160 rcutorture.stat_interval= [KNL] 6161 Time (s) between statistics printk()s. 6162 6163 rcutorture.stutter= [KNL] 6164 Time (s) to stutter testing, for example, specifying 6165 five seconds causes the test to run for five seconds, 6166 wait for five seconds, and so on. This tests RCU's 6167 ability to transition abruptly to and from idle. 6168 6169 rcutorture.test_boost= [KNL] 6170 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6171 "Maybe" means test if the RCU implementation 6172 under test support RCU priority boosting. 6173 6174 rcutorture.test_boost_duration= [KNL] 6175 Duration (s) of each individual boost test. 6176 6177 rcutorture.test_boost_holdoff= [KNL] 6178 Holdoff time (s) from start of test to the start 6179 of RCU priority-boost testing. Defaults to zero, 6180 that is, no holdoff. 6181 6182 rcutorture.test_boost_interval= [KNL] 6183 Interval (s) between each boost test. 6184 6185 rcutorture.test_no_idle_hz= [KNL] 6186 Test RCU's dyntick-idle handling. See also the 6187 rcutorture.shuffle_interval parameter. 6188 6189 rcutorture.torture_type= [KNL] 6190 Specify the RCU implementation to test. 6191 6192 rcutorture.verbose= [KNL] 6193 Enable additional printk() statements. 6194 6195 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6196 Dump ftrace buffer after reporting RCU CPU 6197 stall warning. 6198 6199 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6200 Provide RCU CPU stall notifiers, but see the 6201 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6202 option's help text. TL;DR: You almost certainly 6203 do not want rcupdate.rcu_cpu_stall_notifiers. 6204 6205 rcupdate.rcu_cpu_stall_suppress= [KNL] 6206 Suppress RCU CPU stall warning messages. 6207 6208 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6209 Suppress RCU CPU stall warning messages and 6210 rcutorture writer stall warnings that occur 6211 during early boot, that is, during the time 6212 before the init task is spawned. 6213 6214 rcupdate.rcu_cpu_stall_timeout= [KNL] 6215 Set timeout for RCU CPU stall warning messages. 6216 The value is in seconds and the maximum allowed 6217 value is 300 seconds. 6218 6219 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6220 Set timeout for expedited RCU CPU stall warning 6221 messages. The value is in milliseconds 6222 and the maximum allowed value is 21000 6223 milliseconds. Please note that this value is 6224 adjusted to an arch timer tick resolution. 6225 Setting this to zero causes the value from 6226 rcupdate.rcu_cpu_stall_timeout to be used (after 6227 conversion from seconds to milliseconds). 6228 6229 rcupdate.rcu_cpu_stall_cputime= [KNL] 6230 Provide statistics on the cputime and count of 6231 interrupts and tasks during the sampling period. For 6232 multiple continuous RCU stalls, all sampling periods 6233 begin at half of the first RCU stall timeout. 6234 6235 rcupdate.rcu_exp_stall_task_details= [KNL] 6236 Print stack dumps of any tasks blocking the 6237 current expedited RCU grace period during an 6238 expedited RCU CPU stall warning. 6239 6240 rcupdate.rcu_expedited= [KNL] 6241 Use expedited grace-period primitives, for 6242 example, synchronize_rcu_expedited() instead 6243 of synchronize_rcu(). This reduces latency, 6244 but can increase CPU utilization, degrade 6245 real-time latency, and degrade energy efficiency. 6246 No effect on CONFIG_TINY_RCU kernels. 6247 6248 rcupdate.rcu_normal= [KNL] 6249 Use only normal grace-period primitives, 6250 for example, synchronize_rcu() instead of 6251 synchronize_rcu_expedited(). This improves 6252 real-time latency, CPU utilization, and 6253 energy efficiency, but can expose users to 6254 increased grace-period latency. This parameter 6255 overrides rcupdate.rcu_expedited. No effect on 6256 CONFIG_TINY_RCU kernels. 6257 6258 rcupdate.rcu_normal_after_boot= [KNL] 6259 Once boot has completed (that is, after 6260 rcu_end_inkernel_boot() has been invoked), use 6261 only normal grace-period primitives. No effect 6262 on CONFIG_TINY_RCU kernels. 6263 6264 But note that CONFIG_PREEMPT_RT=y kernels enables 6265 this kernel boot parameter, forcibly setting 6266 it to the value one, that is, converting any 6267 post-boot attempt at an expedited RCU grace 6268 period to instead use normal non-expedited 6269 grace-period processing. 6270 6271 rcupdate.rcu_task_collapse_lim= [KNL] 6272 Set the maximum number of callbacks present 6273 at the beginning of a grace period that allows 6274 the RCU Tasks flavors to collapse back to using 6275 a single callback queue. This switching only 6276 occurs when rcupdate.rcu_task_enqueue_lim is 6277 set to the default value of -1. 6278 6279 rcupdate.rcu_task_contend_lim= [KNL] 6280 Set the minimum number of callback-queuing-time 6281 lock-contention events per jiffy required to 6282 cause the RCU Tasks flavors to switch to per-CPU 6283 callback queuing. This switching only occurs 6284 when rcupdate.rcu_task_enqueue_lim is set to 6285 the default value of -1. 6286 6287 rcupdate.rcu_task_enqueue_lim= [KNL] 6288 Set the number of callback queues to use for the 6289 RCU Tasks family of RCU flavors. The default 6290 of -1 allows this to be automatically (and 6291 dynamically) adjusted. This parameter is intended 6292 for use in testing. 6293 6294 rcupdate.rcu_task_lazy_lim= [KNL] 6295 Number of callbacks on a given CPU that will 6296 cancel laziness on that CPU. Use -1 to disable 6297 cancellation of laziness, but be advised that 6298 doing so increases the danger of OOM due to 6299 callback flooding. 6300 6301 rcupdate.rcu_task_stall_info= [KNL] 6302 Set initial timeout in jiffies for RCU task stall 6303 informational messages, which give some indication 6304 of the problem for those not patient enough to 6305 wait for ten minutes. Informational messages are 6306 only printed prior to the stall-warning message 6307 for a given grace period. Disable with a value 6308 less than or equal to zero. Defaults to ten 6309 seconds. A change in value does not take effect 6310 until the beginning of the next grace period. 6311 6312 rcupdate.rcu_task_stall_info_mult= [KNL] 6313 Multiplier for time interval between successive 6314 RCU task stall informational messages for a given 6315 RCU tasks grace period. This value is clamped 6316 to one through ten, inclusive. It defaults to 6317 the value three, so that the first informational 6318 message is printed 10 seconds into the grace 6319 period, the second at 40 seconds, the third at 6320 160 seconds, and then the stall warning at 600 6321 seconds would prevent a fourth at 640 seconds. 6322 6323 rcupdate.rcu_task_stall_timeout= [KNL] 6324 Set timeout in jiffies for RCU task stall 6325 warning messages. Disable with a value less 6326 than or equal to zero. Defaults to ten minutes. 6327 A change in value does not take effect until 6328 the beginning of the next grace period. 6329 6330 rcupdate.rcu_tasks_lazy_ms= [KNL] 6331 Set timeout in milliseconds RCU Tasks asynchronous 6332 callback batching for call_rcu_tasks(). 6333 A negative value will take the default. A value 6334 of zero will disable batching. Batching is 6335 always disabled for synchronize_rcu_tasks(). 6336 6337 rcupdate.rcu_self_test= [KNL] 6338 Run the RCU early boot self tests 6339 6340 rdinit= [KNL] 6341 Format: <full_path> 6342 Run specified binary instead of /init from the ramdisk, 6343 used for early userspace startup. See initrd. 6344 6345 rdrand= [X86,EARLY] 6346 force - Override the decision by the kernel to hide the 6347 advertisement of RDRAND support (this affects 6348 certain AMD processors because of buggy BIOS 6349 support, specifically around the suspend/resume 6350 path). 6351 6352 rdt= [HW,X86,RDT] 6353 Turn on/off individual RDT features. List is: 6354 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6355 mba, smba, bmec, abmc, sdciae. 6356 E.g. to turn on cmt and turn off mba use: 6357 rdt=cmt,!mba 6358 6359 reboot= [KNL] 6360 Format (x86 or x86_64): 6361 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6362 [[,]s[mp]#### \ 6363 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6364 [[,]f[orce] 6365 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6366 (prefix with 'panic_' to set mode for panic 6367 reboot only), 6368 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6369 reboot_force is either force or not specified, 6370 reboot_cpu is s[mp]#### with #### being the processor 6371 to be used for rebooting. 6372 6373 acpi 6374 Use the ACPI RESET_REG in the FADT. If ACPI is not 6375 configured or the ACPI reset does not work, the reboot 6376 path attempts the reset using the keyboard controller. 6377 6378 bios 6379 Use the CPU reboot vector for warm reset 6380 6381 cold 6382 Set the cold reboot flag 6383 6384 default 6385 There are some built-in platform specific "quirks" 6386 - you may see: "reboot: <name> series board detected. 6387 Selecting <type> for reboots." In the case where you 6388 think the quirk is in error (e.g. you have newer BIOS, 6389 or newer board) using this option will ignore the 6390 built-in quirk table, and use the generic default 6391 reboot actions. 6392 6393 efi 6394 Use efi reset_system runtime service. If EFI is not 6395 configured or the EFI reset does not work, the reboot 6396 path attempts the reset using the keyboard controller. 6397 6398 force 6399 Don't stop other CPUs on reboot. This can make reboot 6400 more reliable in some cases. 6401 6402 kbd 6403 Use the keyboard controller. cold reset (default) 6404 6405 pci 6406 Use a write to the PCI config space register 0xcf9 to 6407 trigger reboot. 6408 6409 triple 6410 Force a triple fault (init) 6411 6412 warm 6413 Don't set the cold reboot flag 6414 6415 Using warm reset will be much faster especially on big 6416 memory systems because the BIOS will not go through 6417 the memory check. Disadvantage is that not all 6418 hardware will be completely reinitialized on reboot so 6419 there may be boot problems on some systems. 6420 6421 6422 refscale.holdoff= [KNL] 6423 Set test-start holdoff period. The purpose of 6424 this parameter is to delay the start of the 6425 test until boot completes in order to avoid 6426 interference. 6427 6428 refscale.lookup_instances= [KNL] 6429 Number of data elements to use for the forms of 6430 SLAB_TYPESAFE_BY_RCU testing. A negative number 6431 is negated and multiplied by nr_cpu_ids, while 6432 zero specifies nr_cpu_ids. 6433 6434 refscale.loops= [KNL] 6435 Set the number of loops over the synchronization 6436 primitive under test. Increasing this number 6437 reduces noise due to loop start/end overhead, 6438 but the default has already reduced the per-pass 6439 noise to a handful of picoseconds on ca. 2020 6440 x86 laptops. 6441 6442 refscale.nreaders= [KNL] 6443 Set number of readers. The default value of -1 6444 selects N, where N is roughly 75% of the number 6445 of CPUs. A value of zero is an interesting choice. 6446 6447 refscale.nruns= [KNL] 6448 Set number of runs, each of which is dumped onto 6449 the console log. 6450 6451 refscale.readdelay= [KNL] 6452 Set the read-side critical-section duration, 6453 measured in microseconds. 6454 6455 refscale.scale_type= [KNL] 6456 Specify the read-protection implementation to test. 6457 6458 refscale.shutdown= [KNL] 6459 Shut down the system at the end of the performance 6460 test. This defaults to 1 (shut it down) when 6461 refscale is built into the kernel and to 0 (leave 6462 it running) when refscale is built as a module. 6463 6464 refscale.verbose= [KNL] 6465 Enable additional printk() statements. 6466 6467 refscale.verbose_batched= [KNL] 6468 Batch the additional printk() statements. If zero 6469 (the default) or negative, print everything. Otherwise, 6470 print every Nth verbose statement, where N is the value 6471 specified. 6472 6473 regulator_ignore_unused 6474 [REGULATOR] 6475 Prevents regulator framework from disabling regulators 6476 that are unused, due no driver claiming them. This may 6477 be useful for debug and development, but should not be 6478 needed on a platform with proper driver support. 6479 6480 relax_domain_level= 6481 [KNL, SMP] Set scheduler's default relax_domain_level. 6482 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6483 6484 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6485 Format: <base1>,<size1>[,<base2>,<size2>,...] 6486 Reserve I/O ports or memory so the kernel won't use 6487 them. If <base> is less than 0x10000, the region 6488 is assumed to be I/O ports; otherwise it is memory. 6489 6490 reserve_mem= [RAM] 6491 Format: nn[KMG]:<align>:<label> 6492 Reserve physical memory and label it with a name that 6493 other subsystems can use to access it. This is typically 6494 used for systems that do not wipe the RAM, and this command 6495 line will try to reserve the same physical memory on 6496 soft reboots. Note, it is not guaranteed to be the same 6497 location. For example, if anything about the system changes 6498 or if booting a different kernel. It can also fail if KASLR 6499 places the kernel at the location of where the RAM reservation 6500 was from a previous boot, the new reservation will be at a 6501 different location. 6502 Any subsystem using this feature must add a way to verify 6503 that the contents of the physical memory is from a previous 6504 boot, as there may be cases where the memory will not be 6505 located at the same location. 6506 6507 The format is size:align:label for example, to request 6508 12 megabytes of 4096 alignment for ramoops: 6509 6510 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6511 6512 reservetop= [X86-32,EARLY] 6513 Format: nn[KMG] 6514 Reserves a hole at the top of the kernel virtual 6515 address space. 6516 6517 reset_devices [KNL] Force drivers to reset the underlying device 6518 during initialization. 6519 6520 resume= [SWSUSP] 6521 Specify the partition device for software suspend 6522 Format: 6523 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6524 6525 resume_offset= [SWSUSP] 6526 Specify the offset from the beginning of the partition 6527 given by "resume=" at which the swap header is located, 6528 in <PAGE_SIZE> units (needed only for swap files). 6529 See Documentation/power/swsusp-and-swap-files.rst 6530 6531 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6532 read the resume files 6533 6534 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6535 Useful for devices that are detected asynchronously 6536 (e.g. USB and MMC devices). 6537 6538 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6539 be accessible via /sys/firmware/initrd. 6540 6541 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6542 Speculative Code Execution with Return Instructions) 6543 vulnerability. 6544 6545 AMD-based UNRET and IBPB mitigations alone do not stop 6546 sibling threads from influencing the predictions of other 6547 sibling threads. For that reason, STIBP is used on pro- 6548 cessors that support it, and mitigate SMT on processors 6549 that don't. 6550 6551 off - no mitigation 6552 auto - automatically select a mitigation 6553 auto,nosmt - automatically select a mitigation, 6554 disabling SMT if necessary for 6555 the full mitigation (only on Zen1 6556 and older without STIBP). 6557 ibpb - On AMD, mitigate short speculation 6558 windows on basic block boundaries too. 6559 Safe, highest perf impact. It also 6560 enables STIBP if present. Not suitable 6561 on Intel. 6562 ibpb,nosmt - Like "ibpb" above but will disable SMT 6563 when STIBP is not available. This is 6564 the alternative for systems which do not 6565 have STIBP. 6566 unret - Force enable untrained return thunks, 6567 only effective on AMD f15h-f17h based 6568 systems. 6569 unret,nosmt - Like unret, but will disable SMT when STIBP 6570 is not available. This is the alternative for 6571 systems which do not have STIBP. 6572 6573 Selecting 'auto' will choose a mitigation method at run 6574 time according to the CPU. 6575 6576 Not specifying this option is equivalent to retbleed=auto. 6577 6578 rfkill.default_state= 6579 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6580 etc. communication is blocked by default. 6581 1 Unblocked. 6582 6583 rfkill.master_switch_mode= 6584 0 The "airplane mode" button does nothing. 6585 1 The "airplane mode" button toggles between everything 6586 blocked and the previous configuration. 6587 2 The "airplane mode" button toggles between everything 6588 blocked and everything unblocked. 6589 6590 ring3mwait=disable 6591 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6592 CPUs. 6593 6594 riscv_isa_fallback [RISCV,EARLY] 6595 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6596 falling back to detecting extension support by parsing 6597 "riscv,isa" property on devicetree systems when the 6598 replacement properties are not found. See the Kconfig 6599 entry for RISCV_ISA_FALLBACK. 6600 6601 ro [KNL] Mount root device read-only on boot 6602 6603 rodata= [KNL,EARLY] 6604 on Mark read-only kernel memory as read-only (default). 6605 off Leave read-only kernel memory writable for debugging. 6606 noalias Mark read-only kernel memory as read-only but retain 6607 writable aliases in the direct map for regions outside 6608 of the kernel image. [arm64] 6609 6610 rockchip.usb_uart 6611 [EARLY] 6612 Enable the uart passthrough on the designated usb port 6613 on Rockchip SoCs. When active, the signals of the 6614 debug-uart get routed to the D+ and D- pins of the usb 6615 port and the regular usb controller gets disabled. 6616 6617 root= [KNL] Root filesystem 6618 Usually this is a block device specifier of some kind, 6619 see the early_lookup_bdev comment in 6620 block/early-lookup.c for details. 6621 Alternatively this can be "ram" for the legacy initial 6622 ramdisk, "nfs" and "cifs" for root on a network file 6623 system, or "mtd" and "ubi" for mounting from raw flash. 6624 6625 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6626 mount the root filesystem 6627 6628 rootflags= [KNL] Set root filesystem mount option string 6629 6630 rseq_slice_ext= [KNL] RSEQ based time slice extension 6631 Format: boolean 6632 Control enablement of RSEQ based time slice extension. 6633 Default is 'on'. 6634 6635 initramfs_options= [KNL] 6636 Specify mount options for for the initramfs mount. 6637 6638 rootfstype= [KNL] Set root filesystem type 6639 6640 rootwait [KNL] Wait (indefinitely) for root device to show up. 6641 Useful for devices that are detected asynchronously 6642 (e.g. USB and MMC devices). 6643 6644 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6645 to show up before attempting to mount the root 6646 filesystem. 6647 6648 rproc_mem=nn[KMG][@address] 6649 [KNL,ARM,CMA] Remoteproc physical memory block. 6650 Memory area to be used by remote processor image, 6651 managed by CMA. 6652 6653 rseq_debug= [KNL] Enable or disable restartable sequence 6654 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6655 Format: <bool> 6656 6657 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6658 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6659 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6660 Format: <bool> 6661 6662 rw [KNL] Mount root device read-write on boot 6663 6664 S [KNL] Run init in single mode 6665 6666 s390_iommu= [HW,S390] 6667 Set s390 IOTLB flushing mode 6668 strict 6669 With strict flushing every unmap operation will result 6670 in an IOTLB flush. Default is lazy flushing before 6671 reuse, which is faster. Deprecated, equivalent to 6672 iommu.strict=1. 6673 6674 s390_iommu_aperture= [KNL,S390] 6675 Specifies the size of the per device DMA address space 6676 accessible through the DMA and IOMMU APIs as a decimal 6677 factor of the size of main memory. 6678 The default is 1 meaning that one can concurrently use 6679 as many DMA addresses as physical memory is installed, 6680 if supported by hardware, and thus map all of memory 6681 once. With a value of 2 one can map all of memory twice 6682 and so on. As a special case a factor of 0 imposes no 6683 restrictions other than those given by hardware at the 6684 cost of significant additional memory use for tables. 6685 6686 sa1100ir [NET] 6687 See drivers/net/irda/sa1100_ir.c. 6688 6689 sched_proxy_exec= [KNL] 6690 Enables or disables "proxy execution" style 6691 solution to mutex-based priority inversion. 6692 Format: <bool> 6693 6694 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6695 6696 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6697 Allowed values are enable and disable. This feature 6698 incurs a small amount of overhead in the scheduler 6699 but is useful for debugging and performance tuning. 6700 6701 sched_thermal_decay_shift= 6702 [Deprecated] 6703 [KNL, SMP] Set a decay shift for scheduler thermal 6704 pressure signal. Thermal pressure signal follows the 6705 default decay period of other scheduler pelt 6706 signals(usually 32 ms but configurable). Setting 6707 sched_thermal_decay_shift will left shift the decay 6708 period for the thermal pressure signal by the shift 6709 value. 6710 i.e. with the default pelt decay period of 32 ms 6711 sched_thermal_decay_shift thermal pressure decay pr 6712 1 64 ms 6713 2 128 ms 6714 and so on. 6715 Format: integer between 0 and 10 6716 Default is 0. 6717 6718 scftorture.holdoff= [KNL] 6719 Number of seconds to hold off before starting 6720 test. Defaults to zero for module insertion and 6721 to 10 seconds for built-in smp_call_function() 6722 tests. 6723 6724 scftorture.longwait= [KNL] 6725 Request ridiculously long waits randomly selected 6726 up to the chosen limit in seconds. Zero (the 6727 default) disables this feature. Please note 6728 that requesting even small non-zero numbers of 6729 seconds can result in RCU CPU stall warnings, 6730 softlockup complaints, and so on. 6731 6732 scftorture.nthreads= [KNL] 6733 Number of kthreads to spawn to invoke the 6734 smp_call_function() family of functions. 6735 The default of -1 specifies a number of kthreads 6736 equal to the number of CPUs. 6737 6738 scftorture.onoff_holdoff= [KNL] 6739 Number seconds to wait after the start of the 6740 test before initiating CPU-hotplug operations. 6741 6742 scftorture.onoff_interval= [KNL] 6743 Number seconds to wait between successive 6744 CPU-hotplug operations. Specifying zero (which 6745 is the default) disables CPU-hotplug operations. 6746 6747 scftorture.shutdown_secs= [KNL] 6748 The number of seconds following the start of the 6749 test after which to shut down the system. The 6750 default of zero avoids shutting down the system. 6751 Non-zero values are useful for automated tests. 6752 6753 scftorture.stat_interval= [KNL] 6754 The number of seconds between outputting the 6755 current test statistics to the console. A value 6756 of zero disables statistics output. 6757 6758 scftorture.stutter_cpus= [KNL] 6759 The number of jiffies to wait between each change 6760 to the set of CPUs under test. 6761 6762 scftorture.use_cpus_read_lock= [KNL] 6763 Use use_cpus_read_lock() instead of the default 6764 preempt_disable() to disable CPU hotplug 6765 while invoking one of the smp_call_function*() 6766 functions. 6767 6768 scftorture.verbose= [KNL] 6769 Enable additional printk() statements. 6770 6771 scftorture.weight_single= [KNL] 6772 The probability weighting to use for the 6773 smp_call_function_single() function with a zero 6774 "wait" parameter. A value of -1 selects the 6775 default if all other weights are -1. However, 6776 if at least one weight has some other value, a 6777 value of -1 will instead select a weight of zero. 6778 6779 scftorture.weight_single_wait= [KNL] 6780 The probability weighting to use for the 6781 smp_call_function_single() function with a 6782 non-zero "wait" parameter. See weight_single. 6783 6784 scftorture.weight_many= [KNL] 6785 The probability weighting to use for the 6786 smp_call_function_many() function with a zero 6787 "wait" parameter. See weight_single. 6788 Note well that setting a high probability for 6789 this weighting can place serious IPI load 6790 on the system. 6791 6792 scftorture.weight_many_wait= [KNL] 6793 The probability weighting to use for the 6794 smp_call_function_many() function with a 6795 non-zero "wait" parameter. See weight_single 6796 and weight_many. 6797 6798 scftorture.weight_all= [KNL] 6799 The probability weighting to use for the 6800 smp_call_function_all() function with a zero 6801 "wait" parameter. See weight_single and 6802 weight_many. 6803 6804 scftorture.weight_all_wait= [KNL] 6805 The probability weighting to use for the 6806 smp_call_function_all() function with a 6807 non-zero "wait" parameter. See weight_single 6808 and weight_many. 6809 6810 sdw_mclk_divider=[SDW] 6811 Specify the MCLK divider for Intel SoundWire buses in 6812 case the BIOS does not provide the clock rate properly. 6813 6814 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6815 xtime_lock contention on larger systems, and/or RCU lock 6816 contention on all systems with CONFIG_MAXSMP set. 6817 Format: { "0" | "1" } 6818 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6819 1 -- enable. 6820 Note: increases power consumption, thus should only be 6821 enabled if running jitter sensitive (HPC/RT) workloads. 6822 6823 security= [SECURITY] Choose a legacy "major" security module to 6824 enable at boot. This has been deprecated by the 6825 "lsm=" parameter. 6826 6827 selinux= [SELINUX] Disable or enable SELinux at boot time. 6828 Format: { "0" | "1" } 6829 See security/selinux/Kconfig help text. 6830 0 -- disable. 6831 1 -- enable. 6832 Default value is 1. 6833 6834 serialnumber [BUGS=X86-32] 6835 6836 sev=option[,option...] [X86-64] 6837 6838 debug 6839 Enable debug messages. 6840 6841 nosnp 6842 Do not enable SEV-SNP (applies to host/hypervisor 6843 only). Setting 'nosnp' avoids the RMP check overhead 6844 in memory accesses when users do not want to run 6845 SEV-SNP guests. 6846 6847 shapers= [NET] 6848 Maximal number of shapers. 6849 6850 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6851 Limit apic dumping. The parameter defines the maximal 6852 number of local apics being dumped. Also it is possible 6853 to set it to "all" by meaning -- no limit here. 6854 Format: { 1 (default) | 2 | ... | all }. 6855 The parameter valid if only apic=debug or 6856 apic=verbose is specified. 6857 Example: apic=debug show_lapic=all 6858 6859 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6860 Enabling slab_debug allows one to determine the 6861 culprit if slab objects become corrupted. Enabling 6862 slab_debug can create guard zones around objects and 6863 may poison objects when not in use. Also tracks the 6864 last alloc / free. For more information see 6865 Documentation/admin-guide/mm/slab.rst. 6866 (slub_debug legacy name also accepted for now) 6867 6868 Using this option implies the "no_hash_pointers" 6869 option which can be undone by adding the 6870 "hash_pointers=always" option. 6871 6872 slab_max_order= [MM] 6873 Determines the maximum allowed order for slabs. 6874 A high setting may cause OOMs due to memory 6875 fragmentation. For more information see 6876 Documentation/admin-guide/mm/slab.rst. 6877 (slub_max_order legacy name also accepted for now) 6878 6879 slab_merge [MM] 6880 Enable merging of slabs with similar size when the 6881 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6882 (slub_merge legacy name also accepted for now) 6883 6884 slab_min_objects= [MM] 6885 The minimum number of objects per slab. SLUB will 6886 increase the slab order up to slab_max_order to 6887 generate a sufficiently large slab able to contain 6888 the number of objects indicated. The higher the number 6889 of objects the smaller the overhead of tracking slabs 6890 and the less frequently locks need to be acquired. 6891 For more information see 6892 Documentation/admin-guide/mm/slab.rst. 6893 (slub_min_objects legacy name also accepted for now) 6894 6895 slab_min_order= [MM] 6896 Determines the minimum page order for slabs. Must be 6897 lower or equal to slab_max_order. For more information see 6898 Documentation/admin-guide/mm/slab.rst. 6899 (slub_min_order legacy name also accepted for now) 6900 6901 slab_nomerge [MM] 6902 Disable merging of slabs with similar size. May be 6903 necessary if there is some reason to distinguish 6904 allocs to different slabs, especially in hardened 6905 environments where the risk of heap overflows and 6906 layout control by attackers can usually be 6907 frustrated by disabling merging. This will reduce 6908 most of the exposure of a heap attack to a single 6909 cache (risks via metadata attacks are mostly 6910 unchanged). Debug options disable merging on their 6911 own. 6912 For more information see 6913 Documentation/admin-guide/mm/slab.rst. 6914 (slub_nomerge legacy name also accepted for now) 6915 6916 slab_strict_numa [MM] 6917 Support memory policies on a per object level 6918 in the slab allocator. The default is for memory 6919 policies to be applied at the folio level when 6920 a new folio is needed or a partial folio is 6921 retrieved from the lists. Increases overhead 6922 in the slab fastpaths but gains more accurate 6923 NUMA kernel object placement which helps with slow 6924 interconnects in NUMA systems. 6925 6926 slram= [HW,MTD] 6927 6928 smart2= [HW] 6929 Format: <io1>[,<io2>[,...,<io8>]] 6930 6931 smp.csd_lock_timeout= [KNL] 6932 Specify the period of time in milliseconds 6933 that smp_call_function() and friends will wait 6934 for a CPU to release the CSD lock. This is 6935 useful when diagnosing bugs involving CPUs 6936 disabling interrupts for extended periods 6937 of time. Defaults to 5,000 milliseconds, and 6938 setting a value of zero disables this feature. 6939 This feature may be more efficiently disabled 6940 using the csdlock_debug- kernel parameter. 6941 6942 smp.panic_on_ipistall= [KNL] 6943 If a csd_lock_timeout extends for more than 6944 the specified number of milliseconds, panic the 6945 system. By default, let CSD-lock acquisition 6946 take as long as they take. Specifying 300,000 6947 for this value provides a 5-minute timeout. 6948 6949 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 6950 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 6951 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 6952 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 6953 smsc-ircc2.ircc_irq= [HW] IRQ line 6954 smsc-ircc2.ircc_dma= [HW] DMA channel 6955 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 6956 0: Toshiba Satellite 1800 (GP data pin select) 6957 1: Fast pin select (default) 6958 2: ATC IRMode 6959 6960 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 6961 (logical CPUs) to use per physical CPU on systems 6962 capable of symmetric multithreading (SMT). Will 6963 be capped to the actual hardware limit. 6964 Format: <integer> 6965 Default: -1 (no limit) 6966 6967 softlockup_panic= 6968 [KNL] Should the soft-lockup detector generate panics. 6969 Format: 0 | 1 6970 6971 A value of 1 instructs the soft-lockup detector 6972 to panic the machine when a soft-lockup occurs. It is 6973 also controlled by the kernel.softlockup_panic sysctl 6974 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 6975 respective build-time switch to that functionality. 6976 6977 softlockup_all_cpu_backtrace= 6978 [KNL] Should the soft-lockup detector generate 6979 backtraces on all cpus. 6980 Format: 0 | 1 6981 6982 sonypi.*= [HW] Sony Programmable I/O Control Device driver 6983 See Documentation/admin-guide/laptops/sonypi.rst 6984 6985 spectre_bhi= [X86] Control mitigation of Branch History Injection 6986 (BHI) vulnerability. This setting affects the 6987 deployment of the HW BHI control and the SW BHB 6988 clearing sequence. 6989 6990 on - (default) Enable the HW or SW mitigation as 6991 needed. This protects the kernel from 6992 both syscalls and VMs. 6993 vmexit - On systems which don't have the HW mitigation 6994 available, enable the SW mitigation on vmexit 6995 ONLY. On such systems, the host kernel is 6996 protected from VM-originated BHI attacks, but 6997 may still be vulnerable to syscall attacks. 6998 off - Disable the mitigation. 6999 7000 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7001 (indirect branch speculation) vulnerability. 7002 The default operation protects the kernel from 7003 user space attacks. 7004 7005 on - unconditionally enable, implies 7006 spectre_v2_user=on 7007 off - unconditionally disable, implies 7008 spectre_v2_user=off 7009 auto - kernel detects whether your CPU model is 7010 vulnerable 7011 7012 Selecting 'on' will, and 'auto' may, choose a 7013 mitigation method at run time according to the 7014 CPU, the available microcode, the setting of the 7015 CONFIG_MITIGATION_RETPOLINE configuration option, 7016 and the compiler with which the kernel was built. 7017 7018 Selecting 'on' will also enable the mitigation 7019 against user space to user space task attacks. 7020 Selecting specific mitigation does not force enable 7021 user mitigations. 7022 7023 Selecting 'off' will disable both the kernel and 7024 the user space protections. 7025 7026 Specific mitigations can also be selected manually: 7027 7028 retpoline - replace indirect branches 7029 retpoline,generic - Retpolines 7030 retpoline,lfence - LFENCE; indirect branch 7031 retpoline,amd - alias for retpoline,lfence 7032 eibrs - Enhanced/Auto IBRS 7033 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7034 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7035 ibrs - use IBRS to protect kernel 7036 7037 Not specifying this option is equivalent to 7038 spectre_v2=auto. 7039 7040 spectre_v2_user= 7041 [X86] Control mitigation of Spectre variant 2 7042 (indirect branch speculation) vulnerability between 7043 user space tasks 7044 7045 on - Unconditionally enable mitigations. Is 7046 enforced by spectre_v2=on 7047 7048 off - Unconditionally disable mitigations. Is 7049 enforced by spectre_v2=off 7050 7051 prctl - Indirect branch speculation is enabled, 7052 but mitigation can be enabled via prctl 7053 per thread. The mitigation control state 7054 is inherited on fork. 7055 7056 prctl,ibpb 7057 - Like "prctl" above, but only STIBP is 7058 controlled per thread. IBPB is issued 7059 always when switching between different user 7060 space processes. 7061 7062 seccomp 7063 - Same as "prctl" above, but all seccomp 7064 threads will enable the mitigation unless 7065 they explicitly opt out. 7066 7067 seccomp,ibpb 7068 - Like "seccomp" above, but only STIBP is 7069 controlled per thread. IBPB is issued 7070 always when switching between different 7071 user space processes. 7072 7073 auto - Kernel selects the mitigation depending on 7074 the available CPU features and vulnerability. 7075 7076 Default mitigation: "prctl" 7077 7078 Not specifying this option is equivalent to 7079 spectre_v2_user=auto. 7080 7081 spec_rstack_overflow= 7082 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7083 7084 off - Disable mitigation 7085 microcode - Enable microcode mitigation only 7086 safe-ret - Enable sw-only safe RET mitigation (default) 7087 ibpb - Enable mitigation by issuing IBPB on 7088 kernel entry 7089 ibpb-vmexit - Issue IBPB only on VMEXIT 7090 (cloud-specific mitigation) 7091 7092 spec_store_bypass_disable= 7093 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7094 (Speculative Store Bypass vulnerability) 7095 7096 Certain CPUs are vulnerable to an exploit against a 7097 a common industry wide performance optimization known 7098 as "Speculative Store Bypass" in which recent stores 7099 to the same memory location may not be observed by 7100 later loads during speculative execution. The idea 7101 is that such stores are unlikely and that they can 7102 be detected prior to instruction retirement at the 7103 end of a particular speculation execution window. 7104 7105 In vulnerable processors, the speculatively forwarded 7106 store can be used in a cache side channel attack, for 7107 example to read memory to which the attacker does not 7108 directly have access (e.g. inside sandboxed code). 7109 7110 This parameter controls whether the Speculative Store 7111 Bypass optimization is used. 7112 7113 On x86 the options are: 7114 7115 on - Unconditionally disable Speculative Store Bypass 7116 off - Unconditionally enable Speculative Store Bypass 7117 auto - Kernel detects whether the CPU model contains an 7118 implementation of Speculative Store Bypass and 7119 picks the most appropriate mitigation. If the 7120 CPU is not vulnerable, "off" is selected. If the 7121 CPU is vulnerable the default mitigation is 7122 architecture and Kconfig dependent. See below. 7123 prctl - Control Speculative Store Bypass per thread 7124 via prctl. Speculative Store Bypass is enabled 7125 for a process by default. The state of the control 7126 is inherited on fork. 7127 seccomp - Same as "prctl" above, but all seccomp threads 7128 will disable SSB unless they explicitly opt out. 7129 7130 Default mitigations: 7131 X86: "prctl" 7132 7133 On powerpc the options are: 7134 7135 on,auto - On Power8 and Power9 insert a store-forwarding 7136 barrier on kernel entry and exit. On Power7 7137 perform a software flush on kernel entry and 7138 exit. 7139 off - No action. 7140 7141 Not specifying this option is equivalent to 7142 spec_store_bypass_disable=auto. 7143 7144 split_lock_detect= 7145 [X86] Enable split lock detection or bus lock detection 7146 7147 When enabled (and if hardware support is present), atomic 7148 instructions that access data across cache line 7149 boundaries will result in an alignment check exception 7150 for split lock detection or a debug exception for 7151 bus lock detection. 7152 7153 off - not enabled 7154 7155 warn - the kernel will emit rate-limited warnings 7156 about applications triggering the #AC 7157 exception or the #DB exception. This mode is 7158 the default on CPUs that support split lock 7159 detection or bus lock detection. Default 7160 behavior is by #AC if both features are 7161 enabled in hardware. 7162 7163 fatal - the kernel will send SIGBUS to applications 7164 that trigger the #AC exception or the #DB 7165 exception. Default behavior is by #AC if 7166 both features are enabled in hardware. 7167 7168 ratelimit:N - 7169 Set system wide rate limit to N bus locks 7170 per second for bus lock detection. 7171 0 < N <= 1000. 7172 7173 N/A for split lock detection. 7174 7175 7176 If an #AC exception is hit in the kernel or in 7177 firmware (i.e. not while executing in user mode) 7178 the kernel will oops in either "warn" or "fatal" 7179 mode. 7180 7181 #DB exception for bus lock is triggered only when 7182 CPL > 0. 7183 7184 srbds= [X86,INTEL,EARLY] 7185 Control the Special Register Buffer Data Sampling 7186 (SRBDS) mitigation. 7187 7188 Certain CPUs are vulnerable to an MDS-like 7189 exploit which can leak bits from the random 7190 number generator. 7191 7192 By default, this issue is mitigated by 7193 microcode. However, the microcode fix can cause 7194 the RDRAND and RDSEED instructions to become 7195 much slower. Among other effects, this will 7196 result in reduced throughput from /dev/urandom. 7197 7198 The microcode mitigation can be disabled with 7199 the following option: 7200 7201 off: Disable mitigation and remove 7202 performance impact to RDRAND and RDSEED 7203 7204 srcutree.big_cpu_lim [KNL] 7205 Specifies the number of CPUs constituting a 7206 large system, such that srcu_struct structures 7207 should immediately allocate an srcu_node array. 7208 This kernel-boot parameter defaults to 128, 7209 but takes effect only when the low-order four 7210 bits of srcutree.convert_to_big is equal to 3 7211 (decide at boot). 7212 7213 srcutree.convert_to_big [KNL] 7214 Specifies under what conditions an SRCU tree 7215 srcu_struct structure will be converted to big 7216 form, that is, with an rcu_node tree: 7217 7218 0: Never. 7219 1: At init_srcu_struct() time. 7220 2: When rcutorture decides to. 7221 3: Decide at boot time (default). 7222 0x1X: Above plus if high contention. 7223 7224 Either way, the srcu_node tree will be sized based 7225 on the actual runtime number of CPUs (nr_cpu_ids) 7226 instead of the compile-time CONFIG_NR_CPUS. 7227 7228 srcutree.counter_wrap_check [KNL] 7229 Specifies how frequently to check for 7230 grace-period sequence counter wrap for the 7231 srcu_data structure's ->srcu_gp_seq_needed field. 7232 The greater the number of bits set in this kernel 7233 parameter, the less frequently counter wrap will 7234 be checked for. Note that the bottom two bits 7235 are ignored. 7236 7237 srcutree.exp_holdoff [KNL] 7238 Specifies how many nanoseconds must elapse 7239 since the end of the last SRCU grace period for 7240 a given srcu_struct until the next normal SRCU 7241 grace period will be considered for automatic 7242 expediting. Set to zero to disable automatic 7243 expediting. 7244 7245 srcutree.srcu_max_nodelay [KNL] 7246 Specifies the number of no-delay instances 7247 per jiffy for which the SRCU grace period 7248 worker thread will be rescheduled with zero 7249 delay. Beyond this limit, worker thread will 7250 be rescheduled with a sleep delay of one jiffy. 7251 7252 srcutree.srcu_max_nodelay_phase [KNL] 7253 Specifies the per-grace-period phase, number of 7254 non-sleeping polls of readers. Beyond this limit, 7255 grace period worker thread will be rescheduled 7256 with a sleep delay of one jiffy, between each 7257 rescan of the readers, for a grace period phase. 7258 7259 srcutree.srcu_retry_check_delay [KNL] 7260 Specifies number of microseconds of non-sleeping 7261 delay between each non-sleeping poll of readers. 7262 7263 srcutree.small_contention_lim [KNL] 7264 Specifies the number of update-side contention 7265 events per jiffy will be tolerated before 7266 initiating a conversion of an srcu_struct 7267 structure to big form. Note that the value of 7268 srcutree.convert_to_big must have the 0x10 bit 7269 set for contention-based conversions to occur. 7270 7271 ssbd= [ARM64,HW,EARLY] 7272 Speculative Store Bypass Disable control 7273 7274 On CPUs that are vulnerable to the Speculative 7275 Store Bypass vulnerability and offer a 7276 firmware based mitigation, this parameter 7277 indicates how the mitigation should be used: 7278 7279 force-on: Unconditionally enable mitigation for 7280 for both kernel and userspace 7281 force-off: Unconditionally disable mitigation for 7282 for both kernel and userspace 7283 kernel: Always enable mitigation in the 7284 kernel, and offer a prctl interface 7285 to allow userspace to register its 7286 interest in being mitigated too. 7287 7288 stack_guard_gap= [MM] 7289 override the default stack gap protection. The value 7290 is in page units and it defines how many pages prior 7291 to (for stacks growing down) resp. after (for stacks 7292 growing up) the main stack are reserved for no other 7293 mapping. Default value is 256 pages. 7294 7295 stack_depot_disable= [KNL,EARLY] 7296 Setting this to true through kernel command line will 7297 disable the stack depot thereby saving the static memory 7298 consumed by the stack hash table. By default this is set 7299 to false. 7300 7301 stack_depot_max_pools= [KNL,EARLY] 7302 Specify the maximum number of pools to use for storing 7303 stack traces. Pools are allocated on-demand up to this 7304 limit. Default value is 8191 pools. 7305 7306 stacktrace [FTRACE] 7307 Enable the stack tracer on boot up. 7308 7309 stacktrace_filter=[function-list] 7310 [FTRACE] Limit the functions that the stack tracer 7311 will trace at boot up. function-list is a comma-separated 7312 list of functions. This list can be changed at run 7313 time by the stack_trace_filter file in the debugfs 7314 tracing directory. Note, this enables stack tracing 7315 and the stacktrace above is not needed. 7316 7317 sti= [PARISC,HW] 7318 Format: <num> 7319 Set the STI (builtin display/keyboard on the HP-PARISC 7320 machines) console (graphic card) which should be used 7321 as the initial boot-console. 7322 See also comment in drivers/video/console/sticore.c. 7323 7324 sti_font= [HW] 7325 See comment in drivers/video/console/sticore.c. 7326 7327 stifb= [HW] 7328 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7329 7330 strict_sas_size= 7331 [X86] 7332 Format: <bool> 7333 Enable or disable strict sigaltstack size checks 7334 against the required signal frame size which 7335 depends on the supported FPU features. This can 7336 be used to filter out binaries which have 7337 not yet been made aware of AT_MINSIGSTKSZ. 7338 7339 stress_hpt [PPC,EARLY] 7340 Limits the number of kernel HPT entries in the hash 7341 page table to increase the rate of hash page table 7342 faults on kernel addresses. 7343 7344 stress_slb [PPC,EARLY] 7345 Limits the number of kernel SLB entries, and flushes 7346 them frequently to increase the rate of SLB faults 7347 on kernel addresses. 7348 7349 no_slb_preload [PPC,EARLY] 7350 Disables slb preloading for userspace. 7351 7352 sunrpc.min_resvport= 7353 sunrpc.max_resvport= 7354 [NFS,SUNRPC] 7355 SunRPC servers often require that client requests 7356 originate from a privileged port (i.e. a port in the 7357 range 0 < portnr < 1024). 7358 An administrator who wishes to reserve some of these 7359 ports for other uses may adjust the range that the 7360 kernel's sunrpc client considers to be privileged 7361 using these two parameters to set the minimum and 7362 maximum port values. 7363 7364 sunrpc.svc_rpc_per_connection_limit= 7365 [NFS,SUNRPC] 7366 Limit the number of requests that the server will 7367 process in parallel from a single connection. 7368 The default value is 0 (no limit). 7369 7370 sunrpc.pool_mode= 7371 [NFS] 7372 Control how the NFS server code allocates CPUs to 7373 service thread pools. Depending on how many NICs 7374 you have and where their interrupts are bound, this 7375 option will affect which CPUs will do NFS serving. 7376 Note: this parameter cannot be changed while the 7377 NFS server is running. 7378 7379 auto the server chooses an appropriate mode 7380 automatically using heuristics 7381 global a single global pool contains all CPUs 7382 percpu one pool for each CPU 7383 pernode one pool for each NUMA node (equivalent 7384 to global on non-NUMA machines) 7385 7386 sunrpc.tcp_slot_table_entries= 7387 sunrpc.udp_slot_table_entries= 7388 [NFS,SUNRPC] 7389 Sets the upper limit on the number of simultaneous 7390 RPC calls that can be sent from the client to a 7391 server. Increasing these values may allow you to 7392 improve throughput, but will also increase the 7393 amount of memory reserved for use by the client. 7394 7395 suspend.pm_test_delay= 7396 [SUSPEND] 7397 Sets the number of seconds to remain in a suspend test 7398 mode before resuming the system (see 7399 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7400 is set. Default value is 5. 7401 7402 svm= [PPC] 7403 Format: { on | off | y | n | 1 | 0 } 7404 This parameter controls use of the Protected 7405 Execution Facility on pSeries. 7406 7407 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7408 Format: { <int> [,<int>] | force | noforce } 7409 <int> -- Number of I/O TLB slabs 7410 <int> -- Second integer after comma. Number of swiotlb 7411 areas with their own lock. Will be rounded up 7412 to a power of 2. 7413 force -- force using of bounce buffers even if they 7414 wouldn't be automatically used by the kernel 7415 noforce -- Never use bounce buffers (for debugging) 7416 7417 switches= [HW,M68k,EARLY] 7418 7419 sysctl.*= [KNL] 7420 Set a sysctl parameter, right before loading the init 7421 process, as if the value was written to the respective 7422 /proc/sys/... file. Both '.' and '/' are recognized as 7423 separators. Unrecognized parameters and invalid values 7424 are reported in the kernel log. Sysctls registered 7425 later by a loaded module cannot be set this way. 7426 Example: sysctl.vm.swappiness=40 7427 7428 sysrq_always_enabled 7429 [KNL] 7430 Ignore sysrq setting - this boot parameter will 7431 neutralize any effect of /proc/sys/kernel/sysrq. 7432 Useful for debugging. 7433 7434 tcpmhash_entries= [KNL,NET] 7435 Set the number of tcp_metrics_hash slots. 7436 Default value is 8192 or 16384 depending on total 7437 ram pages. This is used to specify the TCP metrics 7438 cache size. See Documentation/networking/ip-sysctl.rst 7439 "tcp_no_metrics_save" section for more details. 7440 7441 tdfx= [HW,DRM] 7442 7443 test_suspend= [SUSPEND] 7444 Format: { "mem" | "standby" | "freeze" }[,N] 7445 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7446 standby suspend) or "freeze" (for suspend type freeze) 7447 as the system sleep state during system startup with 7448 the optional capability to repeat N number of times. 7449 The system is woken from this state using a 7450 wakeup-capable RTC alarm. 7451 7452 thash_entries= [KNL,NET] 7453 Set number of hash buckets for TCP connection 7454 7455 thermal.act= [HW,ACPI] 7456 -1: disable all active trip points in all thermal zones 7457 <degrees C>: override all lowest active trip points 7458 7459 thermal.crt= [HW,ACPI] 7460 -1: disable all critical trip points in all thermal zones 7461 <degrees C>: override all critical trip points 7462 7463 thermal.off= [HW,ACPI] 7464 1: disable ACPI thermal control 7465 7466 thermal.psv= [HW,ACPI] 7467 -1: disable all passive trip points 7468 <degrees C>: override all passive trip points to this 7469 value 7470 7471 thermal.tzp= [HW,ACPI] 7472 Specify global default ACPI thermal zone polling rate 7473 <deci-seconds>: poll all this frequency 7474 0: no polling (default) 7475 7476 thp_anon= [KNL] 7477 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7478 state is one of "always", "madvise", "never" or "inherit". 7479 Control the default behavior of the system with respect 7480 to anonymous transparent hugepages. 7481 Can be used multiple times for multiple anon THP sizes. 7482 See Documentation/admin-guide/mm/transhuge.rst for more 7483 details. 7484 7485 threadirqs [KNL,EARLY] 7486 Force threading of all interrupt handlers except those 7487 marked explicitly IRQF_NO_THREAD. 7488 7489 thp_shmem= [KNL] 7490 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7491 Control the default policy of each hugepage size for the 7492 internal shmem mount. <policy> is one of policies available 7493 for the shmem mount ("always", "inherit", "never", "within_size", 7494 and "advise"). 7495 It can be used multiple times for multiple shmem THP sizes. 7496 See Documentation/admin-guide/mm/transhuge.rst for more 7497 details. 7498 7499 topology= [S390,EARLY] 7500 Format: {off | on} 7501 Specify if the kernel should make use of the cpu 7502 topology information if the hardware supports this. 7503 The scheduler will make use of this information and 7504 e.g. base its process migration decisions on it. 7505 Default is on. 7506 7507 torture.disable_onoff_at_boot= [KNL] 7508 Prevent the CPU-hotplug component of torturing 7509 until after init has spawned. 7510 7511 torture.ftrace_dump_at_shutdown= [KNL] 7512 Dump the ftrace buffer at torture-test shutdown, 7513 even if there were no errors. This can be a 7514 very costly operation when many torture tests 7515 are running concurrently, especially on systems 7516 with rotating-rust storage. 7517 7518 torture.verbose_sleep_frequency= [KNL] 7519 Specifies how many verbose printk()s should be 7520 emitted between each sleep. The default of zero 7521 disables verbose-printk() sleeping. 7522 7523 torture.verbose_sleep_duration= [KNL] 7524 Duration of each verbose-printk() sleep in jiffies. 7525 7526 tpm.disable_pcr_integrity= [HW,TPM] 7527 Do not protect PCR registers from unintended physical 7528 access, or interposers in the bus by the means of 7529 having an integrity protected session wrapped around 7530 TPM2_PCR_Extend command. Consider this in a situation 7531 where TPM is heavily utilized by IMA, thus protection 7532 causing a major performance hit, and the space where 7533 machines are deployed is by other means guarded. 7534 7535 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7536 Maximum time in milliseconds to retry sending a message 7537 to the TPM service before giving up. This parameter controls 7538 how long the system will continue retrying when the TPM 7539 service is busy. 7540 Format: <unsigned int> 7541 Default: 2000 (2 seconds) 7542 7543 tpm_suspend_pcr=[HW,TPM] 7544 Format: integer pcr id 7545 Specify that at suspend time, the tpm driver 7546 should extend the specified pcr with zeros, 7547 as a workaround for some chips which fail to 7548 flush the last written pcr on TPM_SaveState. 7549 This will guarantee that all the other pcrs 7550 are saved. 7551 7552 tpm_tis.interrupts= [HW,TPM] 7553 Enable interrupts for the MMIO based physical layer 7554 for the FIFO interface. By default it is set to false 7555 (0). For more information about TPM hardware interfaces 7556 defined by Trusted Computing Group (TCG) see 7557 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7558 7559 tp_printk [FTRACE] 7560 Have the tracepoints sent to printk as well as the 7561 tracing ring buffer. This is useful for early boot up 7562 where the system hangs or reboots and does not give the 7563 option for reading the tracing buffer or performing a 7564 ftrace_dump_on_oops. 7565 7566 To turn off having tracepoints sent to printk, 7567 echo 0 > /proc/sys/kernel/tracepoint_printk 7568 Note, echoing 1 into this file without the 7569 tp_printk kernel cmdline option has no effect. 7570 7571 The tp_printk_stop_on_boot (see below) can also be used 7572 to stop the printing of events to console at 7573 late_initcall_sync. 7574 7575 ** CAUTION ** 7576 7577 Having tracepoints sent to printk() and activating high 7578 frequency tracepoints such as irq or sched, can cause 7579 the system to live lock. 7580 7581 tp_printk_stop_on_boot [FTRACE] 7582 When tp_printk (above) is set, it can cause a lot of noise 7583 on the console. It may be useful to only include the 7584 printing of events during boot up, as user space may 7585 make the system inoperable. 7586 7587 This command line option will stop the printing of events 7588 to console at the late_initcall_sync() time frame. 7589 7590 trace_buf_size=nn[KMG] 7591 [FTRACE] will set tracing buffer size on each cpu. 7592 7593 trace_clock= [FTRACE] Set the clock used for tracing events 7594 at boot up. 7595 local - Use the per CPU time stamp counter 7596 (converted into nanoseconds). Fast, but 7597 depending on the architecture, may not be 7598 in sync between CPUs. 7599 global - Event time stamps are synchronized across 7600 CPUs. May be slower than the local clock, 7601 but better for some race conditions. 7602 counter - Simple counting of events (1, 2, ..) 7603 note, some counts may be skipped due to the 7604 infrastructure grabbing the clock more than 7605 once per event. 7606 uptime - Use jiffies as the time stamp. 7607 perf - Use the same clock that perf uses. 7608 mono - Use ktime_get_mono_fast_ns() for time stamps. 7609 mono_raw - Use ktime_get_raw_fast_ns() for time 7610 stamps. 7611 boot - Use ktime_get_boot_fast_ns() for time stamps. 7612 Architectures may add more clocks. See 7613 Documentation/trace/ftrace.rst for more details. 7614 7615 trace_event=[event-list] 7616 [FTRACE] Set and start specified trace events in order 7617 to facilitate early boot debugging. The event-list is a 7618 comma-separated list of trace events to enable. See 7619 also Documentation/trace/events.rst 7620 7621 To enable modules, use :mod: keyword: 7622 7623 trace_event=:mod:<module> 7624 7625 The value before :mod: will only enable specific events 7626 that are part of the module. See the above mentioned 7627 document for more information. 7628 7629 trace_instance=[instance-info] 7630 [FTRACE] Create a ring buffer instance early in boot up. 7631 This will be listed in: 7632 7633 /sys/kernel/tracing/instances 7634 7635 Events can be enabled at the time the instance is created 7636 via: 7637 7638 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7639 7640 Note, the "<system*>:" portion is optional if the event is 7641 unique. 7642 7643 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7644 7645 will enable the "sched_switch" event (note, the "sched:" is optional, and 7646 the same thing would happen if it was left off). The irq_handler_entry 7647 event, and all events under the "initcall" system. 7648 7649 Flags can be added to the instance to modify its behavior when it is 7650 created. The flags are separated by '^'. 7651 7652 The available flags are: 7653 7654 traceoff - Have the tracing instance tracing disabled after it is created. 7655 traceprintk - Have trace_printk() write into this trace instance 7656 (note, "printk" and "trace_printk" can also be used) 7657 7658 trace_instance=foo^traceoff^traceprintk,sched,irq 7659 7660 The flags must come before the defined events. 7661 7662 If memory has been reserved (see memmap for x86), the instance 7663 can use that memory: 7664 7665 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7666 7667 The above will create a "boot_map" instance that uses the physical 7668 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7669 instance will be split up accordingly. 7670 7671 Alternatively, the memory can be reserved by the reserve_mem option: 7672 7673 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7674 7675 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7676 and place the ring buffer in this memory. Note that due to KASLR, the 7677 memory may not be the same location each time, which will not preserve 7678 the buffer content. 7679 7680 Also note that the layout of the ring buffer data may change between 7681 kernel versions where the validator will fail and reset the ring buffer 7682 if the layout is not the same as the previous kernel. 7683 7684 If the ring buffer is used for persistent bootups and has events enabled, 7685 it is recommend to disable tracing so that events from a previous boot do not 7686 mix with events of the current boot (unless you are debugging a random crash 7687 at boot up). 7688 7689 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7690 7691 Note, saving the trace buffer across reboots does require that the system 7692 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7693 can force a memory reset on boot which will clear any trace that was stored. 7694 This is just one of many ways that can clear memory. Make sure your system 7695 keeps the content of memory across reboots before relying on this option. 7696 7697 NB: Both the mapped address and size must be page aligned for the architecture. 7698 7699 See also Documentation/trace/debugging.rst 7700 7701 7702 trace_options=[option-list] 7703 [FTRACE] Enable or disable tracer options at boot. 7704 The option-list is a comma delimited list of options 7705 that can be enabled or disabled just as if you were 7706 to echo the option name into 7707 7708 /sys/kernel/tracing/trace_options 7709 7710 For example, to enable stacktrace option (to dump the 7711 stack trace of each event), add to the command line: 7712 7713 trace_options=stacktrace 7714 7715 See also Documentation/trace/ftrace.rst "trace options" 7716 section. 7717 7718 trace_trigger=[trigger-list] 7719 [FTRACE] Add an event trigger on specific events. 7720 Set a trigger on top of a specific event, with an optional 7721 filter. 7722 7723 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7724 Where more than one trigger may be specified that are comma delimited. 7725 7726 For example: 7727 7728 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7729 7730 The above will enable the "stacktrace" trigger on the "sched_switch" 7731 event but only trigger it if the "prev_state" of the "sched_switch" 7732 event is "2" (TASK_UNINTERRUPTIBLE). 7733 7734 See also "Event triggers" in Documentation/trace/events.rst 7735 7736 7737 traceoff_after_boot 7738 [FTRACE] Sometimes tracing is used to debug issues 7739 during the boot process. Since the trace buffer has a 7740 limited amount of storage, it may be prudent to 7741 disable tracing after the boot is finished, otherwise 7742 the critical information may be overwritten. With this 7743 option, the main tracing buffer will be turned off at 7744 the end of the boot process. 7745 7746 traceoff_on_warning 7747 [FTRACE] enable this option to disable tracing when a 7748 warning is hit. This turns off "tracing_on". Tracing can 7749 be enabled again by echoing '1' into the "tracing_on" 7750 file located in /sys/kernel/tracing/ 7751 7752 This option is useful, as it disables the trace before 7753 the WARNING dump is called, which prevents the trace to 7754 be filled with content caused by the warning output. 7755 7756 This option can also be set at run time via the sysctl 7757 option: kernel/traceoff_on_warning 7758 7759 transparent_hugepage= 7760 [KNL] 7761 Format: [always|madvise|never] 7762 Can be used to control the default behavior of the system 7763 with respect to transparent hugepages. 7764 See Documentation/admin-guide/mm/transhuge.rst 7765 for more details. 7766 7767 transparent_hugepage_shmem= [KNL] 7768 Format: [always|within_size|advise|never|deny|force] 7769 Can be used to control the hugepage allocation policy for 7770 the internal shmem mount. 7771 See Documentation/admin-guide/mm/transhuge.rst 7772 for more details. 7773 7774 transparent_hugepage_tmpfs= [KNL] 7775 Format: [always|within_size|advise|never] 7776 Can be used to control the default hugepage allocation policy 7777 for the tmpfs mount. 7778 See Documentation/admin-guide/mm/transhuge.rst 7779 for more details. 7780 7781 trusted.source= [KEYS] 7782 Format: <string> 7783 This parameter identifies the trust source as a backend 7784 for trusted keys implementation. Supported trust 7785 sources: 7786 - "tpm" 7787 - "tee" 7788 - "caam" 7789 - "dcp" 7790 If not specified then it defaults to iterating through 7791 the trust source list starting with TPM and assigns the 7792 first trust source as a backend which is initialized 7793 successfully during iteration. 7794 7795 trusted.rng= [KEYS] 7796 Format: <string> 7797 The RNG used to generate key material for trusted keys. 7798 Can be one of: 7799 - "kernel" 7800 - the same value as trusted.source: "tpm" or "tee" 7801 - "default" 7802 If not specified, "default" is used. In this case, 7803 the RNG's choice is left to each individual trust source. 7804 7805 trusted.dcp_use_otp_key 7806 This is intended to be used in combination with 7807 trusted.source=dcp and will select the DCP OTP key 7808 instead of the DCP UNIQUE key blob encryption. 7809 7810 trusted.dcp_skip_zk_test 7811 This is intended to be used in combination with 7812 trusted.source=dcp and will disable the check if the 7813 blob key is all zeros. This is helpful for situations where 7814 having this key zero'ed is acceptable. E.g. in testing 7815 scenarios. 7816 7817 tsa= [X86] Control mitigation for Transient Scheduler 7818 Attacks on AMD CPUs. Search the following in your 7819 favourite search engine for more details: 7820 7821 "Technical guidance for mitigating transient scheduler 7822 attacks". 7823 7824 off - disable the mitigation 7825 on - enable the mitigation (default) 7826 user - mitigate only user/kernel transitions 7827 vm - mitigate only guest/host transitions 7828 7829 7830 tsc= Disable clocksource stability checks for TSC. 7831 Format: <string> 7832 [x86] reliable: mark tsc clocksource as reliable, this 7833 disables clocksource verification at runtime, as well 7834 as the stability checks done at bootup. Used to enable 7835 high-resolution timer mode on older hardware, and in 7836 virtualized environment. 7837 [x86] noirqtime: Do not use TSC to do irq accounting. 7838 Used to run time disable IRQ_TIME_ACCOUNTING on any 7839 platforms where RDTSC is slow and this accounting 7840 can add overhead. 7841 [x86] unstable: mark the TSC clocksource as unstable, this 7842 marks the TSC unconditionally unstable at bootup and 7843 avoids any further wobbles once the TSC watchdog notices. 7844 [x86] nowatchdog: disable clocksource watchdog. Used 7845 in situations with strict latency requirements (where 7846 interruptions from clocksource watchdog are not 7847 acceptable). 7848 [x86] recalibrate: force recalibration against a HW timer 7849 (HPET or PM timer) on systems whose TSC frequency was 7850 obtained from HW or FW using either an MSR or CPUID(0x15). 7851 Warn if the difference is more than 500 ppm. 7852 [x86] watchdog: Use TSC as the watchdog clocksource with 7853 which to check other HW timers (HPET or PM timer), but 7854 only on systems where TSC has been deemed trustworthy. 7855 This will be suppressed by an earlier tsc=nowatchdog and 7856 can be overridden by a later tsc=nowatchdog. A console 7857 message will flag any such suppression or overriding. 7858 7859 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7860 value instead. Useful when the early TSC frequency discovery 7861 procedure is not reliable, such as on overclocked systems 7862 with CPUID.16h support and partial CPUID.15h support. 7863 Format: <unsigned int> 7864 7865 tsx= [X86] Control Transactional Synchronization 7866 Extensions (TSX) feature in Intel processors that 7867 support TSX control. 7868 7869 This parameter controls the TSX feature. The options are: 7870 7871 on - Enable TSX on the system. Although there are 7872 mitigations for all known security vulnerabilities, 7873 TSX has been known to be an accelerator for 7874 several previous speculation-related CVEs, and 7875 so there may be unknown security risks associated 7876 with leaving it enabled. 7877 7878 off - Disable TSX on the system. (Note that this 7879 option takes effect only on newer CPUs which are 7880 not vulnerable to MDS, i.e., have 7881 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7882 the new IA32_TSX_CTRL MSR through a microcode 7883 update. This new MSR allows for the reliable 7884 deactivation of the TSX functionality.) 7885 7886 auto - Disable TSX if X86_BUG_TAA is present, 7887 otherwise enable TSX on the system. 7888 7889 Not specifying this option is equivalent to tsx=off. 7890 7891 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7892 for more details. 7893 7894 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7895 Abort (TAA) vulnerability. 7896 7897 Similar to Micro-architectural Data Sampling (MDS) 7898 certain CPUs that support Transactional 7899 Synchronization Extensions (TSX) are vulnerable to an 7900 exploit against CPU internal buffers which can forward 7901 information to a disclosure gadget under certain 7902 conditions. 7903 7904 In vulnerable processors, the speculatively forwarded 7905 data can be used in a cache side channel attack, to 7906 access data to which the attacker does not have direct 7907 access. 7908 7909 This parameter controls the TAA mitigation. The 7910 options are: 7911 7912 full - Enable TAA mitigation on vulnerable CPUs 7913 if TSX is enabled. 7914 7915 full,nosmt - Enable TAA mitigation and disable SMT on 7916 vulnerable CPUs. If TSX is disabled, SMT 7917 is not disabled because CPU is not 7918 vulnerable to cross-thread TAA attacks. 7919 off - Unconditionally disable TAA mitigation 7920 7921 On MDS-affected machines, tsx_async_abort=off can be 7922 prevented by an active MDS mitigation as both vulnerabilities 7923 are mitigated with the same mechanism so in order to disable 7924 this mitigation, you need to specify mds=off too. 7925 7926 Not specifying this option is equivalent to 7927 tsx_async_abort=full. On CPUs which are MDS affected 7928 and deploy MDS mitigation, TAA mitigation is not 7929 required and doesn't provide any additional 7930 mitigation. 7931 7932 For details see: 7933 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7934 7935 turbografx.map[2|3]= [HW,JOY] 7936 TurboGraFX parallel port interface 7937 Format: 7938 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 7939 See also Documentation/input/devices/joystick-parport.rst 7940 7941 udbg-immortal [PPC] When debugging early kernel crashes that 7942 happen after console_init() and before a proper 7943 console driver takes over, this boot options might 7944 help "seeing" what's going on. 7945 7946 uhash_entries= [KNL,NET] 7947 Set number of hash buckets for UDP/UDP-Lite connections 7948 7949 uhci-hcd.ignore_oc= 7950 [USB] Ignore overcurrent events (default N). 7951 Some badly-designed motherboards generate lots of 7952 bogus events, for ports that aren't wired to 7953 anything. Set this parameter to avoid log spamming. 7954 Note that genuine overcurrent events won't be 7955 reported either. 7956 7957 unaligned_scalar_speed= 7958 [RISCV] 7959 Format: {slow | fast | unsupported} 7960 Allow skipping scalar unaligned access speed tests. This 7961 is useful for testing alternative code paths and to skip 7962 the tests in environments where they run too slowly. All 7963 CPUs must have the same scalar unaligned access speed. 7964 7965 unaligned_vector_speed= 7966 [RISCV] 7967 Format: {slow | fast | unsupported} 7968 Allow skipping vector unaligned access speed tests. This 7969 is useful for testing alternative code paths and to skip 7970 the tests in environments where they run too slowly. All 7971 CPUs must have the same vector unaligned access speed. 7972 7973 unknown_nmi_panic 7974 [X86] Cause panic on unknown NMI. 7975 7976 unwind_debug [X86-64,EARLY] 7977 Enable unwinder debug output. This can be 7978 useful for debugging certain unwinder error 7979 conditions, including corrupt stacks and 7980 bad/missing unwinder metadata. 7981 7982 usbcore.authorized_default= 7983 [USB] Default USB device authorization: 7984 (default -1 = authorized (same as 1), 7985 0 = not authorized, 1 = authorized, 2 = authorized 7986 if device connected to internal port) 7987 7988 usbcore.autosuspend= 7989 [USB] The autosuspend time delay (in seconds) used 7990 for newly-detected USB devices (default 2). This 7991 is the time required before an idle device will be 7992 autosuspended. Devices for which the delay is set 7993 to a negative value won't be autosuspended at all. 7994 7995 usbcore.usbfs_snoop= 7996 [USB] Set to log all usbfs traffic (default 0 = off). 7997 7998 usbcore.usbfs_snoop_max= 7999 [USB] Maximum number of bytes to snoop in each URB 8000 (default = 65536). 8001 8002 usbcore.blinkenlights= 8003 [USB] Set to cycle leds on hubs (default 0 = off). 8004 8005 usbcore.old_scheme_first= 8006 [USB] Start with the old device initialization 8007 scheme (default 0 = off). 8008 8009 usbcore.usbfs_memory_mb= 8010 [USB] Memory limit (in MB) for buffers allocated by 8011 usbfs (default = 16, 0 = max = 2047). 8012 8013 usbcore.use_both_schemes= 8014 [USB] Try the other device initialization scheme 8015 if the first one fails (default 1 = enabled). 8016 8017 usbcore.initial_descriptor_timeout= 8018 [USB] Specifies timeout for the initial 64-byte 8019 USB_REQ_GET_DESCRIPTOR request in milliseconds 8020 (default 5000 = 5.0 seconds). 8021 8022 usbcore.nousb [USB] Disable the USB subsystem 8023 8024 usbcore.quirks= 8025 [USB] A list of quirk entries to augment the built-in 8026 usb core quirk list. List entries are separated by 8027 commas. Each entry has the form 8028 VendorID:ProductID:Flags. The IDs are 4-digit hex 8029 numbers and Flags is a set of letters. Each letter 8030 will change the built-in quirk; setting it if it is 8031 clear and clearing it if it is set. The letters have 8032 the following meanings: 8033 a = USB_QUIRK_STRING_FETCH_255 (string 8034 descriptors must not be fetched using 8035 a 255-byte read); 8036 b = USB_QUIRK_RESET_RESUME (device can't resume 8037 correctly so reset it instead); 8038 c = USB_QUIRK_NO_SET_INTF (device can't handle 8039 Set-Interface requests); 8040 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8041 handle its Configuration or Interface 8042 strings); 8043 e = USB_QUIRK_RESET (device can't be reset 8044 (e.g morph devices), don't use reset); 8045 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8046 more interface descriptions than the 8047 bNumInterfaces count, and can't handle 8048 talking to these interfaces); 8049 g = USB_QUIRK_DELAY_INIT (device needs a pause 8050 during initialization, after we read 8051 the device descriptor); 8052 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8053 high speed and super speed interrupt 8054 endpoints, the USB 2.0 and USB 3.0 spec 8055 require the interval in microframes (1 8056 microframe = 125 microseconds) to be 8057 calculated as interval = 2 ^ 8058 (bInterval-1). 8059 Devices with this quirk report their 8060 bInterval as the result of this 8061 calculation instead of the exponent 8062 variable used in the calculation); 8063 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8064 handle device_qualifier descriptor 8065 requests); 8066 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8067 generates spurious wakeup, ignore 8068 remote wakeup capability); 8069 k = USB_QUIRK_NO_LPM (device can't handle Link 8070 Power Management); 8071 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8072 (Device reports its bInterval as linear 8073 frames instead of the USB 2.0 8074 calculation); 8075 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8076 to be disconnected before suspend to 8077 prevent spurious wakeup); 8078 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8079 pause after every control message); 8080 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8081 delay after resetting its port); 8082 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8083 (Reduce timeout of the SET_ADDRESS 8084 request from 5000 ms to 500 ms); 8085 Example: quirks=0781:5580:bk,0a5c:5834:gij 8086 8087 usbhid.mousepoll= 8088 [USBHID] The interval which mice are to be polled at. 8089 8090 usbhid.jspoll= 8091 [USBHID] The interval which joysticks are to be polled at. 8092 8093 usbhid.kbpoll= 8094 [USBHID] The interval which keyboards are to be polled at. 8095 8096 usb-storage.delay_use= 8097 [UMS] The delay in seconds before a new device is 8098 scanned for Logical Units (default 1). 8099 Optionally the delay in milliseconds if the value has 8100 suffix with "ms". 8101 Example: delay_use=2567ms 8102 8103 usb-storage.quirks= 8104 [UMS] A list of quirks entries to supplement or 8105 override the built-in unusual_devs list. List 8106 entries are separated by commas. Each entry has 8107 the form VID:PID:Flags where VID and PID are Vendor 8108 and Product ID values (4-digit hex numbers) and 8109 Flags is a set of characters, each corresponding 8110 to a common usb-storage quirk flag as follows: 8111 a = SANE_SENSE (collect more than 18 bytes 8112 of sense data, not on uas); 8113 b = BAD_SENSE (don't collect more than 18 8114 bytes of sense data, not on uas); 8115 c = FIX_CAPACITY (decrease the reported 8116 device capacity by one sector); 8117 d = NO_READ_DISC_INFO (don't use 8118 READ_DISC_INFO command, not on uas); 8119 e = NO_READ_CAPACITY_16 (don't use 8120 READ_CAPACITY_16 command); 8121 f = NO_REPORT_OPCODES (don't use report opcodes 8122 command, uas only); 8123 g = MAX_SECTORS_240 (don't transfer more than 8124 240 sectors at a time, uas only); 8125 h = CAPACITY_HEURISTICS (decrease the 8126 reported device capacity by one 8127 sector if the number is odd); 8128 i = IGNORE_DEVICE (don't bind to this 8129 device); 8130 j = NO_REPORT_LUNS (don't use report luns 8131 command, uas only); 8132 k = NO_SAME (do not use WRITE_SAME, uas only) 8133 l = NOT_LOCKABLE (don't try to lock and 8134 unlock ejectable media, not on uas); 8135 m = MAX_SECTORS_64 (don't transfer more 8136 than 64 sectors = 32 KB at a time, 8137 not on uas); 8138 n = INITIAL_READ10 (force a retry of the 8139 initial READ(10) command, not on uas); 8140 o = CAPACITY_OK (accept the capacity 8141 reported by the device, not on uas); 8142 p = WRITE_CACHE (the device cache is ON 8143 by default, not on uas); 8144 r = IGNORE_RESIDUE (the device reports 8145 bogus residue values, not on uas); 8146 s = SINGLE_LUN (the device has only one 8147 Logical Unit); 8148 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8149 commands, uas only); 8150 u = IGNORE_UAS (don't bind to the uas driver); 8151 w = NO_WP_DETECT (don't test whether the 8152 medium is write-protected). 8153 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8154 even if the device claims no cache, 8155 not on uas) 8156 Example: quirks=0419:aaf5:rl,0421:0433:rc 8157 8158 user_debug= [KNL,ARM] 8159 Format: <int> 8160 See arch/arm/Kconfig.debug help text. 8161 1 - undefined instruction events 8162 2 - system calls 8163 4 - invalid data aborts 8164 8 - SIGSEGV faults 8165 16 - SIGBUS faults 8166 Example: user_debug=31 8167 8168 vdso= [X86,SH,SPARC] 8169 On X86_32, this is an alias for vdso32=. Otherwise: 8170 8171 vdso=1: enable VDSO (the default) 8172 vdso=0: disable VDSO mapping 8173 8174 vdso32= [X86] Control the 32-bit vDSO 8175 vdso32=1: enable 32-bit VDSO 8176 vdso32=0 or vdso32=2: disable 32-bit VDSO 8177 8178 See the help text for CONFIG_COMPAT_VDSO for more 8179 details. If CONFIG_COMPAT_VDSO is set, the default is 8180 vdso32=0; otherwise, the default is vdso32=1. 8181 8182 For compatibility with older kernels, vdso32=2 is an 8183 alias for vdso32=0. 8184 8185 Try vdso32=0 if you encounter an error that says: 8186 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8187 8188 video= [FB,EARLY] Frame buffer configuration 8189 See Documentation/fb/modedb.rst. 8190 8191 video.brightness_switch_enabled= [ACPI] 8192 Format: [0|1] 8193 If set to 1, on receiving an ACPI notify event 8194 generated by hotkey, video driver will adjust brightness 8195 level and then send out the event to user space through 8196 the allocated input device. If set to 0, video driver 8197 will only send out the event without touching backlight 8198 brightness level. 8199 default: 1 8200 8201 virtio_mmio.device= 8202 [VMMIO] Memory mapped virtio (platform) device. 8203 8204 <size>@<baseaddr>:<irq>[:<id>] 8205 where: 8206 <size> := size (can use standard suffixes 8207 like K, M and G) 8208 <baseaddr> := physical base address 8209 <irq> := interrupt number (as passed to 8210 request_irq()) 8211 <id> := (optional) platform device id 8212 example: 8213 virtio_mmio.device=1K@0x100b0000:48:7 8214 8215 Can be used multiple times for multiple devices. 8216 8217 vga= [BOOT,X86-32] Select a particular video mode 8218 See Documentation/arch/x86/boot.rst and 8219 Documentation/admin-guide/svga.rst. 8220 Use vga=ask for menu. 8221 This is actually a boot loader parameter; the value is 8222 passed to the kernel using a special protocol. 8223 8224 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8225 May slow down system boot speed, especially when 8226 enabled on systems with a large amount of memory. 8227 All options are enabled by default, and this 8228 interface is meant to allow for selectively 8229 enabling or disabling specific virtual memory 8230 debugging features. 8231 8232 Available options are: 8233 P Enable page structure init time poisoning 8234 - Disable all of the above options 8235 8236 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8237 exact size of <nn>. This can be used to increase 8238 the minimum size (128MB on x86, arm32 platforms). 8239 It can also be used to decrease the size and leave more room 8240 for directly mapped kernel RAM. Note that this parameter does 8241 not exist on many other platforms (including arm64, alpha, 8242 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8243 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8244 8245 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8246 Sets the memory size reserved for contiguous memory 8247 allocations for the vmcp device driver. 8248 8249 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8250 Format: <command> 8251 8252 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8253 Format: <command> 8254 8255 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8256 Format: <command> 8257 8258 vmscape= [X86] Controls mitigation for VMscape attacks. 8259 VMscape attacks can leak information from a userspace 8260 hypervisor to a guest via speculative side-channels. 8261 8262 off - disable the mitigation 8263 ibpb - use Indirect Branch Prediction Barrier 8264 (IBPB) mitigation (default) 8265 force - force vulnerability detection even on 8266 unaffected processors 8267 8268 vsyscall= [X86-64,EARLY] 8269 Controls the behavior of vsyscalls (i.e. calls to 8270 fixed addresses of 0xffffffffff600x00 from legacy 8271 code). Most statically-linked binaries and older 8272 versions of glibc use these calls. Because these 8273 functions are at fixed addresses, they make nice 8274 targets for exploits that can control RIP. 8275 8276 emulate Vsyscalls turn into traps and are emulated 8277 reasonably safely. The vsyscall page is 8278 readable. 8279 8280 xonly [default] Vsyscalls turn into traps and are 8281 emulated reasonably safely. The vsyscall 8282 page is not readable. 8283 8284 none Vsyscalls don't work at all. This makes 8285 them quite hard to use for exploits but 8286 might break your system. 8287 8288 vt.color= [VT] Default text color. 8289 Format: 0xYX, X = foreground, Y = background. 8290 Default: 0x07 = light gray on black. 8291 8292 vt.cur_default= [VT] Default cursor shape. 8293 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8294 the parameters of the <Esc>[?A;B;Cc escape sequence; 8295 see vga-softcursor.rst. Default: 2 = underline. 8296 8297 vt.default_blu= [VT] 8298 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8299 Change the default blue palette of the console. 8300 This is a 16-member array composed of values 8301 ranging from 0-255. 8302 8303 vt.default_grn= [VT] 8304 Format: <green0>,<green1>,<green2>,...,<green15> 8305 Change the default green palette of the console. 8306 This is a 16-member array composed of values 8307 ranging from 0-255. 8308 8309 vt.default_red= [VT] 8310 Format: <red0>,<red1>,<red2>,...,<red15> 8311 Change the default red palette of the console. 8312 This is a 16-member array composed of values 8313 ranging from 0-255. 8314 8315 vt.default_utf8= 8316 [VT] 8317 Format=<0|1> 8318 Set system-wide default UTF-8 mode for all tty's. 8319 Default is 1, i.e. UTF-8 mode is enabled for all 8320 newly opened terminals. 8321 8322 vt.global_cursor_default= 8323 [VT] 8324 Format=<-1|0|1> 8325 Set system-wide default for whether a cursor 8326 is shown on new VTs. Default is -1, 8327 i.e. cursors will be created by default unless 8328 overridden by individual drivers. 0 will hide 8329 cursors, 1 will display them. 8330 8331 vt.italic= [VT] Default color for italic text; 0-15. 8332 Default: 2 = green. 8333 8334 vt.underline= [VT] Default color for underlined text; 0-15. 8335 Default: 3 = cyan. 8336 8337 watchdog timers [HW,WDT] For information on watchdog timers, 8338 see Documentation/watchdog/watchdog-parameters.rst 8339 or other driver-specific files in the 8340 Documentation/watchdog/ directory. 8341 8342 watchdog_thresh= 8343 [KNL] 8344 Set the hard lockup detector stall duration 8345 threshold in seconds. The soft lockup detector 8346 threshold is set to twice the value. A value of 0 8347 disables both lockup detectors. Default is 10 8348 seconds. 8349 8350 workqueue.unbound_cpus= 8351 [KNL,SMP] Specify to constrain one or some CPUs 8352 to use in unbound workqueues. 8353 Format: <cpu-list> 8354 By default, all online CPUs are available for 8355 unbound workqueues. 8356 8357 workqueue.watchdog_thresh= 8358 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8359 warn stall conditions and dump internal state to 8360 help debugging. 0 disables workqueue stall 8361 detection; otherwise, it's the stall threshold 8362 duration in seconds. The default value is 30 and 8363 it can be updated at runtime by writing to the 8364 corresponding sysfs file. 8365 8366 workqueue.panic_on_stall=<uint> 8367 Panic when workqueue stall is detected by 8368 CONFIG_WQ_WATCHDOG. It sets the number times of the 8369 stall to trigger panic. 8370 8371 The default is 0, which disables the panic on stall. 8372 8373 workqueue.cpu_intensive_thresh_us= 8374 Per-cpu work items which run for longer than this 8375 threshold are automatically considered CPU intensive 8376 and excluded from concurrency management to prevent 8377 them from noticeably delaying other per-cpu work 8378 items. Default is 10000 (10ms). 8379 8380 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8381 will report the work functions which violate this 8382 threshold repeatedly. They are likely good 8383 candidates for using WQ_UNBOUND workqueues instead. 8384 8385 workqueue.cpu_intensive_warning_thresh=<uint> 8386 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8387 will report the work functions which violate the 8388 intensive_threshold_us repeatedly. In order to prevent 8389 spurious warnings, start printing only after a work 8390 function has violated this threshold number of times. 8391 8392 The default is 4 times. 0 disables the warning. 8393 8394 workqueue.power_efficient 8395 Per-cpu workqueues are generally preferred because 8396 they show better performance thanks to cache 8397 locality; unfortunately, per-cpu workqueues tend to 8398 be more power hungry than unbound workqueues. 8399 8400 Enabling this makes the per-cpu workqueues which 8401 were observed to contribute significantly to power 8402 consumption unbound, leading to measurably lower 8403 power usage at the cost of small performance 8404 overhead. 8405 8406 The default value of this parameter is determined by 8407 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8408 8409 workqueue.default_affinity_scope= 8410 Select the default affinity scope to use for unbound 8411 workqueues. Can be one of "cpu", "smt", "cache", 8412 "numa" and "system". Default is "cache". For more 8413 information, see the Affinity Scopes section in 8414 Documentation/core-api/workqueue.rst. 8415 8416 This can be changed after boot by writing to the 8417 matching /sys/module/workqueue/parameters file. All 8418 workqueues with the "default" affinity scope will be 8419 updated accordingly. 8420 8421 workqueue.debug_force_rr_cpu 8422 Workqueue used to implicitly guarantee that work 8423 items queued without explicit CPU specified are put 8424 on the local CPU. This guarantee is no longer true 8425 and while local CPU is still preferred work items 8426 may be put on foreign CPUs. This debug option 8427 forces round-robin CPU selection to flush out 8428 usages which depend on the now broken guarantee. 8429 When enabled, memory and cache locality will be 8430 impacted. 8431 8432 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8433 Type) of ioremap_wc(). 8434 8435 on - Enable writecombine, use WUC for ioremap_wc() 8436 off - Disable writecombine, use SUC for ioremap_wc() 8437 8438 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8439 default x2apic cluster mode on platforms 8440 supporting x2apic. 8441 8442 xen_512gb_limit [KNL,X86-64,XEN] 8443 Restricts the kernel running paravirtualized under Xen 8444 to use only up to 512 GB of RAM. The reason to do so is 8445 crash analysis tools and Xen tools for doing domain 8446 save/restore/migration must be enabled to handle larger 8447 domains. 8448 8449 xen_console_io [XEN,EARLY] 8450 Boolean option to enable/disable the usage of the Xen 8451 console_io hypercalls to read and write to the console. 8452 Mostly useful for debugging and development. 8453 8454 xen_emul_unplug= [HW,X86,XEN,EARLY] 8455 Unplug Xen emulated devices 8456 Format: [unplug0,][unplug1] 8457 ide-disks -- unplug primary master IDE devices 8458 aux-ide-disks -- unplug non-primary-master IDE devices 8459 nics -- unplug network devices 8460 all -- unplug all emulated devices (NICs and IDE disks) 8461 unnecessary -- unplugging emulated devices is 8462 unnecessary even if the host did not respond to 8463 the unplug protocol 8464 never -- do not unplug even if version check succeeds 8465 8466 xen_legacy_crash [X86,XEN,EARLY] 8467 Crash from Xen panic notifier, without executing late 8468 panic() code such as dumping handler. 8469 8470 xen_mc_debug [X86,XEN,EARLY] 8471 Enable multicall debugging when running as a Xen PV guest. 8472 Enabling this feature will reduce performance a little 8473 bit, so it should only be enabled for obtaining extended 8474 debug data in case of multicall errors. 8475 8476 xen_msr_safe= [X86,XEN,EARLY] 8477 Format: <bool> 8478 Select whether to always use non-faulting (safe) MSR 8479 access functions when running as Xen PV guest. The 8480 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8481 8482 xen_nopv [X86] 8483 Disables the PV optimizations forcing the HVM guest to 8484 run as generic HVM guest with no PV drivers. 8485 This option is obsoleted by the "nopv" option, which 8486 has equivalent effect for XEN platform. 8487 8488 xen_no_vector_callback 8489 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8490 event channel interrupts. 8491 8492 xen_scrub_pages= [XEN] 8493 Boolean option to control scrubbing pages before giving them back 8494 to Xen, for use by other domains. Can be also changed at runtime 8495 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8496 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8497 8498 xen_timer_slop= [X86-64,XEN,EARLY] 8499 Set the timer slop (in nanoseconds) for the virtual Xen 8500 timers (default is 100000). This adjusts the minimum 8501 delta of virtualized Xen timers, where lower values 8502 improve timer resolution at the expense of processing 8503 more timer interrupts. 8504 8505 xen.balloon_boot_timeout= [XEN] 8506 The time (in seconds) to wait before giving up to boot 8507 in case initial ballooning fails to free enough memory. 8508 Applies only when running as HVM or PVH guest and 8509 started with less memory configured than allowed at 8510 max. Default is 180. 8511 8512 xen.event_eoi_delay= [XEN] 8513 How long to delay EOI handling in case of event 8514 storms (jiffies). Default is 10. 8515 8516 xen.event_loop_timeout= [XEN] 8517 After which time (jiffies) the event handling loop 8518 should start to delay EOI handling. Default is 2. 8519 8520 xen.fifo_events= [XEN] 8521 Boolean parameter to disable using fifo event handling 8522 even if available. Normally fifo event handling is 8523 preferred over the 2-level event handling, as it is 8524 fairer and the number of possible event channels is 8525 much higher. Default is on (use fifo events). 8526 8527 xirc2ps_cs= [NET,PCMCIA] 8528 Format: 8529 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8530 8531 xive= [PPC] 8532 By default on POWER9 and above, the kernel will 8533 natively use the XIVE interrupt controller. This option 8534 allows the fallback firmware mode to be used: 8535 8536 off Fallback to firmware control of XIVE interrupt 8537 controller on both pseries and powernv 8538 platforms. Only useful on POWER9 and above. 8539 8540 xive.store-eoi=off [PPC] 8541 By default on POWER10 and above, the kernel will use 8542 stores for EOI handling when the XIVE interrupt mode 8543 is active. This option allows the XIVE driver to use 8544 loads instead, as on POWER9. 8545 8546 xhci-hcd.quirks [USB,KNL] 8547 A hex value specifying bitmask with supplemental xhci 8548 host controller quirks. Meaning of each bit can be 8549 consulted in header drivers/usb/host/xhci.h. 8550 8551 xmon [PPC,EARLY] 8552 Format: { early | on | rw | ro | off } 8553 Controls if xmon debugger is enabled. Default is off. 8554 Passing only "xmon" is equivalent to "xmon=early". 8555 early Call xmon as early as possible on boot; xmon 8556 debugger is called from setup_arch(). 8557 on xmon debugger hooks will be installed so xmon 8558 is only called on a kernel crash. Default mode, 8559 i.e. either "ro" or "rw" mode, is controlled 8560 with CONFIG_XMON_DEFAULT_RO_MODE. 8561 rw xmon debugger hooks will be installed so xmon 8562 is called only on a kernel crash, mode is write, 8563 meaning SPR registers, memory and, other data 8564 can be written using xmon commands. 8565 ro same as "rw" option above but SPR registers, 8566 memory, and other data can't be written using 8567 xmon commands. 8568 off xmon is disabled. 8569