1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_PCI_COMPONENT 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [ARM,X86,KNL] 595 Sets the size of kernel global memory area for 596 contiguous memory allocations and optionally the 597 placement constraint by the physical address range of 598 memory allocations. A value of 0 disables CMA 599 altogether. For more information, see 600 include/linux/dma-contiguous.h 601 602 cmo_free_hint= [PPC] Format: { yes | no } 603 Specify whether pages are marked as being inactive 604 when they are freed. This is used in CMO environments 605 to determine OS memory pressure for page stealing by 606 a hypervisor. 607 Default: yes 608 609 coherent_pool=nn[KMG] [ARM,KNL] 610 Sets the size of memory pool for coherent, atomic dma 611 allocations, by default set to 256K. 612 613 com20020= [HW,NET] ARCnet - COM20020 chipset 614 Format: 615 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 616 617 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 618 Format: <io>[,<irq>] 619 620 com90xx= [HW,NET] 621 ARCnet - COM90xx chipset (memory-mapped buffers) 622 Format: <io>[,<irq>[,<memstart>]] 623 624 condev= [HW,S390] console device 625 conmode= 626 627 console= [KNL] Output console device and options. 628 629 tty<n> Use the virtual console device <n>. 630 631 ttyS<n>[,options] 632 ttyUSB0[,options] 633 Use the specified serial port. The options are of 634 the form "bbbbpnf", where "bbbb" is the baud rate, 635 "p" is parity ("n", "o", or "e"), "n" is number of 636 bits, and "f" is flow control ("r" for RTS or 637 omit it). Default is "9600n8". 638 639 See Documentation/admin-guide/serial-console.rst for more 640 information. See 641 Documentation/networking/netconsole.rst for an 642 alternative. 643 644 uart[8250],io,<addr>[,options] 645 uart[8250],mmio,<addr>[,options] 646 uart[8250],mmio16,<addr>[,options] 647 uart[8250],mmio32,<addr>[,options] 648 uart[8250],0x<addr>[,options] 649 Start an early, polled-mode console on the 8250/16550 650 UART at the specified I/O port or MMIO address, 651 switching to the matching ttyS device later. 652 MMIO inter-register address stride is either 8-bit 653 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 654 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 655 to be equivalent to 'mmio'. 'options' are specified in 656 the same format described for ttyS above; if unspecified, 657 the h/w is not re-initialized. 658 659 hvc<n> Use the hypervisor console device <n>. This is for 660 both Xen and PowerPC hypervisors. 661 662 If the device connected to the port is not a TTY but a braille 663 device, prepend "brl," before the device type, for instance 664 console=brl,ttyS0 665 For now, only VisioBraille is supported. 666 667 console_msg_format= 668 [KNL] Change console messages format 669 default 670 By default we print messages on consoles in 671 "[time stamp] text\n" format (time stamp may not be 672 printed, depending on CONFIG_PRINTK_TIME or 673 `printk_time' param). 674 syslog 675 Switch to syslog format: "<%u>[time stamp] text\n" 676 IOW, each message will have a facility and loglevel 677 prefix. The format is similar to one used by syslog() 678 syscall, or to executing "dmesg -S --raw" or to reading 679 from /proc/kmsg. 680 681 consoleblank= [KNL] The console blank (screen saver) timeout in 682 seconds. A value of 0 disables the blank timer. 683 Defaults to 0. 684 685 coredump_filter= 686 [KNL] Change the default value for 687 /proc/<pid>/coredump_filter. 688 See also Documentation/filesystems/proc.rst. 689 690 coresight_cpu_debug.enable 691 [ARM,ARM64] 692 Format: <bool> 693 Enable/disable the CPU sampling based debugging. 694 0: default value, disable debugging 695 1: enable debugging at boot time 696 697 cpuidle.off=1 [CPU_IDLE] 698 disable the cpuidle sub-system 699 700 cpuidle.governor= 701 [CPU_IDLE] Name of the cpuidle governor to use. 702 703 cpufreq.off=1 [CPU_FREQ] 704 disable the cpufreq sub-system 705 706 cpufreq.default_governor= 707 [CPU_FREQ] Name of the default cpufreq governor or 708 policy to use. This governor must be registered in the 709 kernel before the cpufreq driver probes. 710 711 cpu_init_udelay=N 712 [X86] Delay for N microsec between assert and de-assert 713 of APIC INIT to start processors. This delay occurs 714 on every CPU online, such as boot, and resume from suspend. 715 Default: 10000 716 717 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 718 Format: 719 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 720 721 crashkernel=size[KMG][@offset[KMG]] 722 [KNL] Using kexec, Linux can switch to a 'crash kernel' 723 upon panic. This parameter reserves the physical 724 memory region [offset, offset + size] for that kernel 725 image. If '@offset' is omitted, then a suitable offset 726 is selected automatically. 727 [KNL, X86-64] Select a region under 4G first, and 728 fall back to reserve region above 4G when '@offset' 729 hasn't been specified. 730 See Documentation/admin-guide/kdump/kdump.rst for further details. 731 732 crashkernel=range1:size1[,range2:size2,...][@offset] 733 [KNL] Same as above, but depends on the memory 734 in the running system. The syntax of range is 735 start-[end] where start and end are both 736 a memory unit (amount[KMG]). See also 737 Documentation/admin-guide/kdump/kdump.rst for an example. 738 739 crashkernel=size[KMG],high 740 [KNL, X86-64] range could be above 4G. Allow kernel 741 to allocate physical memory region from top, so could 742 be above 4G if system have more than 4G ram installed. 743 Otherwise memory region will be allocated below 4G, if 744 available. 745 It will be ignored if crashkernel=X is specified. 746 crashkernel=size[KMG],low 747 [KNL, X86-64] range under 4G. When crashkernel=X,high 748 is passed, kernel could allocate physical memory region 749 above 4G, that cause second kernel crash on system 750 that require some amount of low memory, e.g. swiotlb 751 requires at least 64M+32K low memory, also enough extra 752 low memory is needed to make sure DMA buffers for 32-bit 753 devices won't run out. Kernel would try to allocate at 754 at least 256M below 4G automatically. 755 This one let user to specify own low range under 4G 756 for second kernel instead. 757 0: to disable low allocation. 758 It will be ignored when crashkernel=X,high is not used 759 or memory reserved is below 4G. 760 761 cryptomgr.notests 762 [KNL] Disable crypto self-tests 763 764 cs89x0_dma= [HW,NET] 765 Format: <dma> 766 767 cs89x0_media= [HW,NET] 768 Format: { rj45 | aui | bnc } 769 770 dasd= [HW,NET] 771 See header of drivers/s390/block/dasd_devmap.c. 772 773 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 774 (one device per port) 775 Format: <port#>,<type> 776 See also Documentation/input/devices/joystick-parport.rst 777 778 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 779 time. See 780 Documentation/admin-guide/dynamic-debug-howto.rst for 781 details. Deprecated, see dyndbg. 782 783 debug [KNL] Enable kernel debugging (events log level). 784 785 debug_boot_weak_hash 786 [KNL] Enable printing [hashed] pointers early in the 787 boot sequence. If enabled, we use a weak hash instead 788 of siphash to hash pointers. Use this option if you are 789 seeing instances of '(___ptrval___)') and need to see a 790 value (hashed pointer) instead. Cryptographically 791 insecure, please do not use on production kernels. 792 793 debug_locks_verbose= 794 [KNL] verbose self-tests 795 Format=<0|1> 796 Print debugging info while doing the locking API 797 self-tests. 798 We default to 0 (no extra messages), setting it to 799 1 will print _a lot_ more information - normally 800 only useful to kernel developers. 801 802 debug_objects [KNL] Enable object debugging 803 804 no_debug_objects 805 [KNL] Disable object debugging 806 807 debug_guardpage_minorder= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 809 parameter allows control of the order of pages that will 810 be intentionally kept free (and hence protected) by the 811 buddy allocator. Bigger value increase the probability 812 of catching random memory corruption, but reduce the 813 amount of memory for normal system use. The maximum 814 possible value is MAX_ORDER/2. Setting this parameter 815 to 1 or 2 should be enough to identify most random 816 memory corruption problems caused by bugs in kernel or 817 driver code when a CPU writes to (or reads from) a 818 random memory location. Note that there exists a class 819 of memory corruptions problems caused by buggy H/W or 820 F/W or by drivers badly programing DMA (basically when 821 memory is written at bus level and the CPU MMU is 822 bypassed) which are not detectable by 823 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 824 tracking down these problems. 825 826 debug_pagealloc= 827 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 828 enables the feature at boot time. By default, it is 829 disabled and the system will work mostly the same as a 830 kernel built without CONFIG_DEBUG_PAGEALLOC. 831 Note: to get most of debug_pagealloc error reports, it's 832 useful to also enable the page_owner functionality. 833 on: enable the feature 834 835 debugfs= [KNL] This parameter enables what is exposed to userspace 836 and debugfs internal clients. 837 Format: { on, no-mount, off } 838 on: All functions are enabled. 839 no-mount: 840 Filesystem is not registered but kernel clients can 841 access APIs and a crashkernel can be used to read 842 its content. There is nothing to mount. 843 off: Filesystem is not registered and clients 844 get a -EPERM as result when trying to register files 845 or directories within debugfs. 846 This is equivalent of the runtime functionality if 847 debugfs was not enabled in the kernel at all. 848 Default value is set in build-time with a kernel configuration. 849 850 debugpat [X86] Enable PAT debugging 851 852 decnet.addr= [HW,NET] 853 Format: <area>[,<node>] 854 See also Documentation/networking/decnet.rst. 855 856 default_hugepagesz= 857 [HW] The size of the default HugeTLB page. This is 858 the size represented by the legacy /proc/ hugepages 859 APIs. In addition, this is the default hugetlb size 860 used for shmget(), mmap() and mounting hugetlbfs 861 filesystems. If not specified, defaults to the 862 architecture's default huge page size. Huge page 863 sizes are architecture dependent. See also 864 Documentation/admin-guide/mm/hugetlbpage.rst. 865 Format: size[KMG] 866 867 deferred_probe_timeout= 868 [KNL] Debugging option to set a timeout in seconds for 869 deferred probe to give up waiting on dependencies to 870 probe. Only specific dependencies (subsystems or 871 drivers) that have opted in will be ignored. A timeout of 0 872 will timeout at the end of initcalls. This option will also 873 dump out devices still on the deferred probe list after 874 retrying. 875 876 dfltcc= [HW,S390] 877 Format: { on | off | def_only | inf_only | always } 878 on: s390 zlib hardware support for compression on 879 level 1 and decompression (default) 880 off: No s390 zlib hardware support 881 def_only: s390 zlib hardware support for deflate 882 only (compression on level 1) 883 inf_only: s390 zlib hardware support for inflate 884 only (decompression) 885 always: Same as 'on' but ignores the selected compression 886 level always using hardware support (used for debugging) 887 888 dhash_entries= [KNL] 889 Set number of hash buckets for dentry cache. 890 891 disable_1tb_segments [PPC] 892 Disables the use of 1TB hash page table segments. This 893 causes the kernel to fall back to 256MB segments which 894 can be useful when debugging issues that require an SLB 895 miss to occur. 896 897 stress_slb [PPC] 898 Limits the number of kernel SLB entries, and flushes 899 them frequently to increase the rate of SLB faults 900 on kernel addresses. 901 902 disable= [IPV6] 903 See Documentation/networking/ipv6.rst. 904 905 hardened_usercopy= 906 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 907 hardening is enabled for this boot. Hardened 908 usercopy checking is used to protect the kernel 909 from reading or writing beyond known memory 910 allocation boundaries as a proactive defense 911 against bounds-checking flaws in the kernel's 912 copy_to_user()/copy_from_user() interface. 913 on Perform hardened usercopy checks (default). 914 off Disable hardened usercopy checks. 915 916 disable_radix [PPC] 917 Disable RADIX MMU mode on POWER9 918 919 radix_hcall_invalidate=on [PPC/PSERIES] 920 Disable RADIX GTSE feature and use hcall for TLB 921 invalidate. 922 923 disable_tlbie [PPC] 924 Disable TLBIE instruction. Currently does not work 925 with KVM, with HASH MMU, or with coherent accelerators. 926 927 disable_cpu_apicid= [X86,APIC,SMP] 928 Format: <int> 929 The number of initial APIC ID for the 930 corresponding CPU to be disabled at boot, 931 mostly used for the kdump 2nd kernel to 932 disable BSP to wake up multiple CPUs without 933 causing system reset or hang due to sending 934 INIT from AP to BSP. 935 936 perf_v4_pmi= [X86,INTEL] 937 Format: <bool> 938 Disable Intel PMU counter freezing feature. 939 The feature only exists starting from 940 Arch Perfmon v4 (Skylake and newer). 941 942 disable_ddw [PPC/PSERIES] 943 Disable Dynamic DMA Window support. Use this if 944 to workaround buggy firmware. 945 946 disable_ipv6= [IPV6] 947 See Documentation/networking/ipv6.rst. 948 949 disable_mtrr_cleanup [X86] 950 The kernel tries to adjust MTRR layout from continuous 951 to discrete, to make X server driver able to add WB 952 entry later. This parameter disables that. 953 954 disable_mtrr_trim [X86, Intel and AMD only] 955 By default the kernel will trim any uncacheable 956 memory out of your available memory pool based on 957 MTRR settings. This parameter disables that behavior, 958 possibly causing your machine to run very slowly. 959 960 disable_timer_pin_1 [X86] 961 Disable PIN 1 of APIC timer 962 Can be useful to work around chipset bugs. 963 964 dis_ucode_ldr [X86] Disable the microcode loader. 965 966 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 967 this option disables the debugging code at boot. 968 969 dma_debug_entries=<number> 970 This option allows to tune the number of preallocated 971 entries for DMA-API debugging code. One entry is 972 required per DMA-API allocation. Use this if the 973 DMA-API debugging code disables itself because the 974 architectural default is too low. 975 976 dma_debug_driver=<driver_name> 977 With this option the DMA-API debugging driver 978 filter feature can be enabled at boot time. Just 979 pass the driver to filter for as the parameter. 980 The filter can be disabled or changed to another 981 driver later using sysfs. 982 983 driver_async_probe= [KNL] 984 List of driver names to be probed asynchronously. 985 Format: <driver_name1>,<driver_name2>... 986 987 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 988 Broken monitors, graphic adapters, KVMs and EDIDless 989 panels may send no or incorrect EDID data sets. 990 This parameter allows to specify an EDID data sets 991 in the /lib/firmware directory that are used instead. 992 Generic built-in EDID data sets are used, if one of 993 edid/1024x768.bin, edid/1280x1024.bin, 994 edid/1680x1050.bin, or edid/1920x1080.bin is given 995 and no file with the same name exists. Details and 996 instructions how to build your own EDID data are 997 available in Documentation/admin-guide/edid.rst. An EDID 998 data set will only be used for a particular connector, 999 if its name and a colon are prepended to the EDID 1000 name. Each connector may use a unique EDID data 1001 set by separating the files with a comma. An EDID 1002 data set with no connector name will be used for 1003 any connectors not explicitly specified. 1004 1005 dscc4.setup= [NET] 1006 1007 dt_cpu_ftrs= [PPC] 1008 Format: {"off" | "known"} 1009 Control how the dt_cpu_ftrs device-tree binding is 1010 used for CPU feature discovery and setup (if it 1011 exists). 1012 off: Do not use it, fall back to legacy cpu table. 1013 known: Do not pass through unknown features to guests 1014 or userspace, only those that the kernel is aware of. 1015 1016 dump_apple_properties [X86] 1017 Dump name and content of EFI device properties on 1018 x86 Macs. Useful for driver authors to determine 1019 what data is available or for reverse-engineering. 1020 1021 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1022 module.dyndbg[="val"] 1023 Enable debug messages at boot time. See 1024 Documentation/admin-guide/dynamic-debug-howto.rst 1025 for details. 1026 1027 nopku [X86] Disable Memory Protection Keys CPU feature found 1028 in some Intel CPUs. 1029 1030 module.async_probe [KNL] 1031 Enable asynchronous probe on this module. 1032 1033 early_ioremap_debug [KNL] 1034 Enable debug messages in early_ioremap support. This 1035 is useful for tracking down temporary early mappings 1036 which are not unmapped. 1037 1038 earlycon= [KNL] Output early console device and options. 1039 1040 When used with no options, the early console is 1041 determined by stdout-path property in device tree's 1042 chosen node or the ACPI SPCR table if supported by 1043 the platform. 1044 1045 cdns,<addr>[,options] 1046 Start an early, polled-mode console on a Cadence 1047 (xuartps) serial port at the specified address. Only 1048 supported option is baud rate. If baud rate is not 1049 specified, the serial port must already be setup and 1050 configured. 1051 1052 uart[8250],io,<addr>[,options] 1053 uart[8250],mmio,<addr>[,options] 1054 uart[8250],mmio32,<addr>[,options] 1055 uart[8250],mmio32be,<addr>[,options] 1056 uart[8250],0x<addr>[,options] 1057 Start an early, polled-mode console on the 8250/16550 1058 UART at the specified I/O port or MMIO address. 1059 MMIO inter-register address stride is either 8-bit 1060 (mmio) or 32-bit (mmio32 or mmio32be). 1061 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1062 to be equivalent to 'mmio'. 'options' are specified 1063 in the same format described for "console=ttyS<n>"; if 1064 unspecified, the h/w is not initialized. 1065 1066 pl011,<addr> 1067 pl011,mmio32,<addr> 1068 Start an early, polled-mode console on a pl011 serial 1069 port at the specified address. The pl011 serial port 1070 must already be setup and configured. Options are not 1071 yet supported. If 'mmio32' is specified, then only 1072 the driver will use only 32-bit accessors to read/write 1073 the device registers. 1074 1075 meson,<addr> 1076 Start an early, polled-mode console on a meson serial 1077 port at the specified address. The serial port must 1078 already be setup and configured. Options are not yet 1079 supported. 1080 1081 msm_serial,<addr> 1082 Start an early, polled-mode console on an msm serial 1083 port at the specified address. The serial port 1084 must already be setup and configured. Options are not 1085 yet supported. 1086 1087 msm_serial_dm,<addr> 1088 Start an early, polled-mode console on an msm serial 1089 dm port at the specified address. The serial port 1090 must already be setup and configured. Options are not 1091 yet supported. 1092 1093 owl,<addr> 1094 Start an early, polled-mode console on a serial port 1095 of an Actions Semi SoC, such as S500 or S900, at the 1096 specified address. The serial port must already be 1097 setup and configured. Options are not yet supported. 1098 1099 rda,<addr> 1100 Start an early, polled-mode console on a serial port 1101 of an RDA Micro SoC, such as RDA8810PL, at the 1102 specified address. The serial port must already be 1103 setup and configured. Options are not yet supported. 1104 1105 sbi 1106 Use RISC-V SBI (Supervisor Binary Interface) for early 1107 console. 1108 1109 smh Use ARM semihosting calls for early console. 1110 1111 s3c2410,<addr> 1112 s3c2412,<addr> 1113 s3c2440,<addr> 1114 s3c6400,<addr> 1115 s5pv210,<addr> 1116 exynos4210,<addr> 1117 Use early console provided by serial driver available 1118 on Samsung SoCs, requires selecting proper type and 1119 a correct base address of the selected UART port. The 1120 serial port must already be setup and configured. 1121 Options are not yet supported. 1122 1123 lantiq,<addr> 1124 Start an early, polled-mode console on a lantiq serial 1125 (lqasc) port at the specified address. The serial port 1126 must already be setup and configured. Options are not 1127 yet supported. 1128 1129 lpuart,<addr> 1130 lpuart32,<addr> 1131 Use early console provided by Freescale LP UART driver 1132 found on Freescale Vybrid and QorIQ LS1021A processors. 1133 A valid base address must be provided, and the serial 1134 port must already be setup and configured. 1135 1136 ec_imx21,<addr> 1137 ec_imx6q,<addr> 1138 Start an early, polled-mode, output-only console on the 1139 Freescale i.MX UART at the specified address. The UART 1140 must already be setup and configured. 1141 1142 ar3700_uart,<addr> 1143 Start an early, polled-mode console on the 1144 Armada 3700 serial port at the specified 1145 address. The serial port must already be setup 1146 and configured. Options are not yet supported. 1147 1148 qcom_geni,<addr> 1149 Start an early, polled-mode console on a Qualcomm 1150 Generic Interface (GENI) based serial port at the 1151 specified address. The serial port must already be 1152 setup and configured. Options are not yet supported. 1153 1154 efifb,[options] 1155 Start an early, unaccelerated console on the EFI 1156 memory mapped framebuffer (if available). On cache 1157 coherent non-x86 systems that use system memory for 1158 the framebuffer, pass the 'ram' option so that it is 1159 mapped with the correct attributes. 1160 1161 linflex,<addr> 1162 Use early console provided by Freescale LINFlexD UART 1163 serial driver for NXP S32V234 SoCs. A valid base 1164 address must be provided, and the serial port must 1165 already be setup and configured. 1166 1167 earlyprintk= [X86,SH,ARM,M68k,S390] 1168 earlyprintk=vga 1169 earlyprintk=sclp 1170 earlyprintk=xen 1171 earlyprintk=serial[,ttySn[,baudrate]] 1172 earlyprintk=serial[,0x...[,baudrate]] 1173 earlyprintk=ttySn[,baudrate] 1174 earlyprintk=dbgp[debugController#] 1175 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1176 earlyprintk=xdbc[xhciController#] 1177 1178 earlyprintk is useful when the kernel crashes before 1179 the normal console is initialized. It is not enabled by 1180 default because it has some cosmetic problems. 1181 1182 Append ",keep" to not disable it when the real console 1183 takes over. 1184 1185 Only one of vga, efi, serial, or usb debug port can 1186 be used at a time. 1187 1188 Currently only ttyS0 and ttyS1 may be specified by 1189 name. Other I/O ports may be explicitly specified 1190 on some architectures (x86 and arm at least) by 1191 replacing ttySn with an I/O port address, like this: 1192 earlyprintk=serial,0x1008,115200 1193 You can find the port for a given device in 1194 /proc/tty/driver/serial: 1195 2: uart:ST16650V2 port:00001008 irq:18 ... 1196 1197 Interaction with the standard serial driver is not 1198 very good. 1199 1200 The VGA and EFI output is eventually overwritten by 1201 the real console. 1202 1203 The xen output can only be used by Xen PV guests. 1204 1205 The sclp output can only be used on s390. 1206 1207 The optional "force" to "pciserial" enables use of a 1208 PCI device even when its classcode is not of the 1209 UART class. 1210 1211 edac_report= [HW,EDAC] Control how to report EDAC event 1212 Format: {"on" | "off" | "force"} 1213 on: enable EDAC to report H/W event. May be overridden 1214 by other higher priority error reporting module. 1215 off: disable H/W event reporting through EDAC. 1216 force: enforce the use of EDAC to report H/W event. 1217 default: on. 1218 1219 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1220 ekgdboc=kbd 1221 1222 This is designed to be used in conjunction with 1223 the boot argument: earlyprintk=vga 1224 1225 This parameter works in place of the kgdboc parameter 1226 but can only be used if the backing tty is available 1227 very early in the boot process. For early debugging 1228 via a serial port see kgdboc_earlycon instead. 1229 1230 edd= [EDD] 1231 Format: {"off" | "on" | "skip[mbr]"} 1232 1233 efi= [EFI] 1234 Format: { "debug", "disable_early_pci_dma", 1235 "nochunk", "noruntime", "nosoftreserve", 1236 "novamap", "no_disable_early_pci_dma", 1237 "old_map" } 1238 debug: enable misc debug output. 1239 disable_early_pci_dma: disable the busmaster bit on all 1240 PCI bridges while in the EFI boot stub. 1241 nochunk: disable reading files in "chunks" in the EFI 1242 boot stub, as chunking can cause problems with some 1243 firmware implementations. 1244 noruntime : disable EFI runtime services support 1245 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1246 attribute may cause the kernel to reserve the 1247 memory range for a memory mapping driver to 1248 claim. Specify efi=nosoftreserve to disable this 1249 reservation and treat the memory by its base type 1250 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1251 novamap: do not call SetVirtualAddressMap(). 1252 no_disable_early_pci_dma: Leave the busmaster bit set 1253 on all PCI bridges while in the EFI boot stub 1254 old_map [X86-64]: switch to the old ioremap-based EFI 1255 runtime services mapping. [Needs CONFIG_X86_UV=y] 1256 1257 efi_no_storage_paranoia [EFI; X86] 1258 Using this parameter you can use more than 50% of 1259 your efi variable storage. Use this parameter only if 1260 you are really sure that your UEFI does sane gc and 1261 fulfills the spec otherwise your board may brick. 1262 1263 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1264 Add arbitrary attribute to specific memory range by 1265 updating original EFI memory map. 1266 Region of memory which aa attribute is added to is 1267 from ss to ss+nn. 1268 1269 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1270 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1271 attribute is added to range 0x100000000-0x180000000 and 1272 0x10a0000000-0x1120000000. 1273 1274 If efi_fake_mem=8G@9G:0x40000 is specified, the 1275 EFI_MEMORY_SP(0x40000) attribute is added to 1276 range 0x240000000-0x43fffffff. 1277 1278 Using this parameter you can do debugging of EFI memmap 1279 related features. For example, you can do debugging of 1280 Address Range Mirroring feature even if your box 1281 doesn't support it, or mark specific memory as 1282 "soft reserved". 1283 1284 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1285 that is to be dynamically loaded by Linux. If there are 1286 multiple variables with the same name but with different 1287 vendor GUIDs, all of them will be loaded. See 1288 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1289 1290 1291 eisa_irq_edge= [PARISC,HW] 1292 See header of drivers/parisc/eisa.c. 1293 1294 elanfreq= [X86-32] 1295 See comment before function elanfreq_setup() in 1296 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1297 1298 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1299 Specifies physical address of start of kernel core 1300 image elf header and optionally the size. Generally 1301 kexec loader will pass this option to capture kernel. 1302 See Documentation/admin-guide/kdump/kdump.rst for details. 1303 1304 enable_mtrr_cleanup [X86] 1305 The kernel tries to adjust MTRR layout from continuous 1306 to discrete, to make X server driver able to add WB 1307 entry later. This parameter enables that. 1308 1309 enable_timer_pin_1 [X86] 1310 Enable PIN 1 of APIC timer 1311 Can be useful to work around chipset bugs 1312 (in particular on some ATI chipsets). 1313 The kernel tries to set a reasonable default. 1314 1315 enforcing [SELINUX] Set initial enforcing status. 1316 Format: {"0" | "1"} 1317 See security/selinux/Kconfig help text. 1318 0 -- permissive (log only, no denials). 1319 1 -- enforcing (deny and log). 1320 Default value is 0. 1321 Value can be changed at runtime via 1322 /sys/fs/selinux/enforce. 1323 1324 erst_disable [ACPI] 1325 Disable Error Record Serialization Table (ERST) 1326 support. 1327 1328 ether= [HW,NET] Ethernet cards parameters 1329 This option is obsoleted by the "netdev=" option, which 1330 has equivalent usage. See its documentation for details. 1331 1332 evm= [EVM] 1333 Format: { "fix" } 1334 Permit 'security.evm' to be updated regardless of 1335 current integrity status. 1336 1337 failslab= 1338 fail_page_alloc= 1339 fail_make_request=[KNL] 1340 General fault injection mechanism. 1341 Format: <interval>,<probability>,<space>,<times> 1342 See also Documentation/fault-injection/. 1343 1344 floppy= [HW] 1345 See Documentation/admin-guide/blockdev/floppy.rst. 1346 1347 force_pal_cache_flush 1348 [IA-64] Avoid check_sal_cache_flush which may hang on 1349 buggy SAL_CACHE_FLUSH implementations. Using this 1350 parameter will force ia64_sal_cache_flush to call 1351 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1352 1353 forcepae [X86-32] 1354 Forcefully enable Physical Address Extension (PAE). 1355 Many Pentium M systems disable PAE but may have a 1356 functionally usable PAE implementation. 1357 Warning: use of this parameter will taint the kernel 1358 and may cause unknown problems. 1359 1360 ftrace=[tracer] 1361 [FTRACE] will set and start the specified tracer 1362 as early as possible in order to facilitate early 1363 boot debugging. 1364 1365 ftrace_dump_on_oops[=orig_cpu] 1366 [FTRACE] will dump the trace buffers on oops. 1367 If no parameter is passed, ftrace will dump 1368 buffers of all CPUs, but if you pass orig_cpu, it will 1369 dump only the buffer of the CPU that triggered the 1370 oops. 1371 1372 ftrace_filter=[function-list] 1373 [FTRACE] Limit the functions traced by the function 1374 tracer at boot up. function-list is a comma separated 1375 list of functions. This list can be changed at run 1376 time by the set_ftrace_filter file in the debugfs 1377 tracing directory. 1378 1379 ftrace_notrace=[function-list] 1380 [FTRACE] Do not trace the functions specified in 1381 function-list. This list can be changed at run time 1382 by the set_ftrace_notrace file in the debugfs 1383 tracing directory. 1384 1385 ftrace_graph_filter=[function-list] 1386 [FTRACE] Limit the top level callers functions traced 1387 by the function graph tracer at boot up. 1388 function-list is a comma separated list of functions 1389 that can be changed at run time by the 1390 set_graph_function file in the debugfs tracing directory. 1391 1392 ftrace_graph_notrace=[function-list] 1393 [FTRACE] Do not trace from the functions specified in 1394 function-list. This list is a comma separated list of 1395 functions that can be changed at run time by the 1396 set_graph_notrace file in the debugfs tracing directory. 1397 1398 ftrace_graph_max_depth=<uint> 1399 [FTRACE] Used with the function graph tracer. This is 1400 the max depth it will trace into a function. This value 1401 can be changed at run time by the max_graph_depth file 1402 in the tracefs tracing directory. default: 0 (no limit) 1403 1404 fw_devlink= [KNL] Create device links between consumer and supplier 1405 devices by scanning the firmware to infer the 1406 consumer/supplier relationships. This feature is 1407 especially useful when drivers are loaded as modules as 1408 it ensures proper ordering of tasks like device probing 1409 (suppliers first, then consumers), supplier boot state 1410 clean up (only after all consumers have probed), 1411 suspend/resume & runtime PM (consumers first, then 1412 suppliers). 1413 Format: { off | permissive | on | rpm } 1414 off -- Don't create device links from firmware info. 1415 permissive -- Create device links from firmware info 1416 but use it only for ordering boot state clean 1417 up (sync_state() calls). 1418 on -- Create device links from firmware info and use it 1419 to enforce probe and suspend/resume ordering. 1420 rpm -- Like "on", but also use to order runtime PM. 1421 1422 gamecon.map[2|3]= 1423 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1424 support via parallel port (up to 5 devices per port) 1425 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1426 See also Documentation/input/devices/joystick-parport.rst 1427 1428 gamma= [HW,DRM] 1429 1430 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1431 Format: off | on 1432 default: on 1433 1434 gcov_persist= [GCOV] When non-zero (default), profiling data for 1435 kernel modules is saved and remains accessible via 1436 debugfs, even when the module is unloaded/reloaded. 1437 When zero, profiling data is discarded and associated 1438 debugfs files are removed at module unload time. 1439 1440 goldfish [X86] Enable the goldfish android emulator platform. 1441 Don't use this when you are not running on the 1442 android emulator 1443 1444 gpt [EFI] Forces disk with valid GPT signature but 1445 invalid Protective MBR to be treated as GPT. If the 1446 primary GPT is corrupted, it enables the backup/alternate 1447 GPT to be used instead. 1448 1449 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1450 the "Enable 0" bit of the configuration register. 1451 Format: 0 | 1 1452 Default: 0 1453 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1454 the "Enable 0" bit of the configuration register. 1455 Format: 0 | 1 1456 Default: 0 1457 grcan.select= [HW] Select which physical interface to use. 1458 Format: 0 | 1 1459 Default: 0 1460 grcan.txsize= [HW] Sets the size of the tx buffer. 1461 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1462 Default: 1024 1463 grcan.rxsize= [HW] Sets the size of the rx buffer. 1464 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1465 Default: 1024 1466 1467 gpio-mockup.gpio_mockup_ranges 1468 [HW] Sets the ranges of gpiochip of for this device. 1469 Format: <start1>,<end1>,<start2>,<end2>... 1470 1471 hardlockup_all_cpu_backtrace= 1472 [KNL] Should the hard-lockup detector generate 1473 backtraces on all cpus. 1474 Format: 0 | 1 1475 1476 hashdist= [KNL,NUMA] Large hashes allocated during boot 1477 are distributed across NUMA nodes. Defaults on 1478 for 64-bit NUMA, off otherwise. 1479 Format: 0 | 1 (for off | on) 1480 1481 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1482 1483 hd= [EIDE] (E)IDE hard drive subsystem geometry 1484 Format: <cyl>,<head>,<sect> 1485 1486 hest_disable [ACPI] 1487 Disable Hardware Error Source Table (HEST) support; 1488 corresponding firmware-first mode error processing 1489 logic will be disabled. 1490 1491 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1492 size of <nn>. This works even on boxes that have no 1493 highmem otherwise. This also works to reduce highmem 1494 size on bigger boxes. 1495 1496 highres= [KNL] Enable/disable high resolution timer mode. 1497 Valid parameters: "on", "off" 1498 Default: "on" 1499 1500 hlt [BUGS=ARM,SH] 1501 1502 hpet= [X86-32,HPET] option to control HPET usage 1503 Format: { enable (default) | disable | force | 1504 verbose } 1505 disable: disable HPET and use PIT instead 1506 force: allow force enabled of undocumented chips (ICH4, 1507 VIA, nVidia) 1508 verbose: show contents of HPET registers during setup 1509 1510 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1511 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1512 1513 hugetlb_cma= [HW] The size of a cma area used for allocation 1514 of gigantic hugepages. 1515 Format: nn[KMGTPE] 1516 1517 Reserve a cma area of given size and allocate gigantic 1518 hugepages using the cma allocator. If enabled, the 1519 boot-time allocation of gigantic hugepages is skipped. 1520 1521 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1522 If this follows hugepagesz (below), it specifies 1523 the number of pages of hugepagesz to be allocated. 1524 If this is the first HugeTLB parameter on the command 1525 line, it specifies the number of pages to allocate for 1526 the default huge page size. See also 1527 Documentation/admin-guide/mm/hugetlbpage.rst. 1528 Format: <integer> 1529 1530 hugepagesz= 1531 [HW] The size of the HugeTLB pages. This is used in 1532 conjunction with hugepages (above) to allocate huge 1533 pages of a specific size at boot. The pair 1534 hugepagesz=X hugepages=Y can be specified once for 1535 each supported huge page size. Huge page sizes are 1536 architecture dependent. See also 1537 Documentation/admin-guide/mm/hugetlbpage.rst. 1538 Format: size[KMG] 1539 1540 hung_task_panic= 1541 [KNL] Should the hung task detector generate panics. 1542 Format: 0 | 1 1543 1544 A value of 1 instructs the kernel to panic when a 1545 hung task is detected. The default value is controlled 1546 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1547 option. The value selected by this boot parameter can 1548 be changed later by the kernel.hung_task_panic sysctl. 1549 1550 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1551 terminal devices. Valid values: 0..8 1552 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1553 If specified, z/VM IUCV HVC accepts connections 1554 from listed z/VM user IDs only. 1555 1556 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1557 which allow the hypervisor to 'idle' the 1558 guest on lock contention. 1559 1560 keep_bootcon [KNL] 1561 Do not unregister boot console at start. This is only 1562 useful for debugging when something happens in the window 1563 between unregistering the boot console and initializing 1564 the real console. 1565 1566 i2c_bus= [HW] Override the default board specific I2C bus speed 1567 or register an additional I2C bus that is not 1568 registered from board initialization code. 1569 Format: 1570 <bus_id>,<clkrate> 1571 1572 i8042.debug [HW] Toggle i8042 debug mode 1573 i8042.unmask_kbd_data 1574 [HW] Enable printing of interrupt data from the KBD port 1575 (disabled by default, and as a pre-condition 1576 requires that i8042.debug=1 be enabled) 1577 i8042.direct [HW] Put keyboard port into non-translated mode 1578 i8042.dumbkbd [HW] Pretend that controller can only read data from 1579 keyboard and cannot control its state 1580 (Don't attempt to blink the leds) 1581 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1582 i8042.nokbd [HW] Don't check/create keyboard port 1583 i8042.noloop [HW] Disable the AUX Loopback command while probing 1584 for the AUX port 1585 i8042.nomux [HW] Don't check presence of an active multiplexing 1586 controller 1587 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1588 controllers 1589 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1590 i8042.reset [HW] Reset the controller during init, cleanup and 1591 suspend-to-ram transitions, only during s2r 1592 transitions, or never reset 1593 Format: { 1 | Y | y | 0 | N | n } 1594 1, Y, y: always reset controller 1595 0, N, n: don't ever reset controller 1596 Default: only on s2r transitions on x86; most other 1597 architectures force reset to be always executed 1598 i8042.unlock [HW] Unlock (ignore) the keylock 1599 i8042.kbdreset [HW] Reset device connected to KBD port 1600 1601 i810= [HW,DRM] 1602 1603 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1604 indicates that the driver is running on unsupported 1605 hardware. 1606 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1607 does not match list of supported models. 1608 i8k.power_status 1609 [HW] Report power status in /proc/i8k 1610 (disabled by default) 1611 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1612 capability is set. 1613 1614 i915.invert_brightness= 1615 [DRM] Invert the sense of the variable that is used to 1616 set the brightness of the panel backlight. Normally a 1617 brightness value of 0 indicates backlight switched off, 1618 and the maximum of the brightness value sets the backlight 1619 to maximum brightness. If this parameter is set to 0 1620 (default) and the machine requires it, or this parameter 1621 is set to 1, a brightness value of 0 sets the backlight 1622 to maximum brightness, and the maximum of the brightness 1623 value switches the backlight off. 1624 -1 -- never invert brightness 1625 0 -- machine default 1626 1 -- force brightness inversion 1627 1628 icn= [HW,ISDN] 1629 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1630 1631 ide-core.nodma= [HW] (E)IDE subsystem 1632 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1633 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1634 .cdrom .chs .ignore_cable are additional options 1635 See Documentation/ide/ide.rst. 1636 1637 ide-generic.probe-mask= [HW] (E)IDE subsystem 1638 Format: <int> 1639 Probe mask for legacy ISA IDE ports. Depending on 1640 platform up to 6 ports are supported, enabled by 1641 setting corresponding bits in the mask to 1. The 1642 default value is 0x0, which has a special meaning. 1643 On systems that have PCI, it triggers scanning the 1644 PCI bus for the first and the second port, which 1645 are then probed. On systems without PCI the value 1646 of 0x0 enables probing the two first ports as if it 1647 was 0x3. 1648 1649 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1650 Claim all unknown PCI IDE storage controllers. 1651 1652 idle= [X86] 1653 Format: idle=poll, idle=halt, idle=nomwait 1654 Poll forces a polling idle loop that can slightly 1655 improve the performance of waking up a idle CPU, but 1656 will use a lot of power and make the system run hot. 1657 Not recommended. 1658 idle=halt: Halt is forced to be used for CPU idle. 1659 In such case C2/C3 won't be used again. 1660 idle=nomwait: Disable mwait for CPU C-states 1661 1662 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1663 Format: { strict | legacy | 2008 | relaxed } 1664 Default: strict 1665 1666 Choose which programs will be accepted for execution 1667 based on the IEEE 754 NaN encoding(s) supported by 1668 the FPU and the NaN encoding requested with the value 1669 of an ELF file header flag individually set by each 1670 binary. Hardware implementations are permitted to 1671 support either or both of the legacy and the 2008 NaN 1672 encoding mode. 1673 1674 Available settings are as follows: 1675 strict accept binaries that request a NaN encoding 1676 supported by the FPU 1677 legacy only accept legacy-NaN binaries, if supported 1678 by the FPU 1679 2008 only accept 2008-NaN binaries, if supported 1680 by the FPU 1681 relaxed accept any binaries regardless of whether 1682 supported by the FPU 1683 1684 The FPU emulator is always able to support both NaN 1685 encodings, so if no FPU hardware is present or it has 1686 been disabled with 'nofpu', then the settings of 1687 'legacy' and '2008' strap the emulator accordingly, 1688 'relaxed' straps the emulator for both legacy-NaN and 1689 2008-NaN, whereas 'strict' enables legacy-NaN only on 1690 legacy processors and both NaN encodings on MIPS32 or 1691 MIPS64 CPUs. 1692 1693 The setting for ABS.fmt/NEG.fmt instruction execution 1694 mode generally follows that for the NaN encoding, 1695 except where unsupported by hardware. 1696 1697 ignore_loglevel [KNL] 1698 Ignore loglevel setting - this will print /all/ 1699 kernel messages to the console. Useful for debugging. 1700 We also add it as printk module parameter, so users 1701 could change it dynamically, usually by 1702 /sys/module/printk/parameters/ignore_loglevel. 1703 1704 ignore_rlimit_data 1705 Ignore RLIMIT_DATA setting for data mappings, 1706 print warning at first misuse. Can be changed via 1707 /sys/module/kernel/parameters/ignore_rlimit_data. 1708 1709 ihash_entries= [KNL] 1710 Set number of hash buckets for inode cache. 1711 1712 ima_appraise= [IMA] appraise integrity measurements 1713 Format: { "off" | "enforce" | "fix" | "log" } 1714 default: "enforce" 1715 1716 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1717 The builtin appraise policy appraises all files 1718 owned by uid=0. 1719 1720 ima_canonical_fmt [IMA] 1721 Use the canonical format for the binary runtime 1722 measurements, instead of host native format. 1723 1724 ima_hash= [IMA] 1725 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1726 | sha512 | ... } 1727 default: "sha1" 1728 1729 The list of supported hash algorithms is defined 1730 in crypto/hash_info.h. 1731 1732 ima_policy= [IMA] 1733 The builtin policies to load during IMA setup. 1734 Format: "tcb | appraise_tcb | secure_boot | 1735 fail_securely" 1736 1737 The "tcb" policy measures all programs exec'd, files 1738 mmap'd for exec, and all files opened with the read 1739 mode bit set by either the effective uid (euid=0) or 1740 uid=0. 1741 1742 The "appraise_tcb" policy appraises the integrity of 1743 all files owned by root. 1744 1745 The "secure_boot" policy appraises the integrity 1746 of files (eg. kexec kernel image, kernel modules, 1747 firmware, policy, etc) based on file signatures. 1748 1749 The "fail_securely" policy forces file signature 1750 verification failure also on privileged mounted 1751 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1752 flag. 1753 1754 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1755 Load a policy which meets the needs of the Trusted 1756 Computing Base. This means IMA will measure all 1757 programs exec'd, files mmap'd for exec, and all files 1758 opened for read by uid=0. 1759 1760 ima_template= [IMA] 1761 Select one of defined IMA measurements template formats. 1762 Formats: { "ima" | "ima-ng" | "ima-sig" } 1763 Default: "ima-ng" 1764 1765 ima_template_fmt= 1766 [IMA] Define a custom template format. 1767 Format: { "field1|...|fieldN" } 1768 1769 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1770 Format: <min_file_size> 1771 Set the minimal file size for using asynchronous hash. 1772 If left unspecified, ahash usage is disabled. 1773 1774 ahash performance varies for different data sizes on 1775 different crypto accelerators. This option can be used 1776 to achieve the best performance for a particular HW. 1777 1778 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1779 Format: <bufsize> 1780 Set hashing buffer size. Default: 4k. 1781 1782 ahash performance varies for different chunk sizes on 1783 different crypto accelerators. This option can be used 1784 to achieve best performance for particular HW. 1785 1786 init= [KNL] 1787 Format: <full_path> 1788 Run specified binary instead of /sbin/init as init 1789 process. 1790 1791 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1792 for working out where the kernel is dying during 1793 startup. 1794 1795 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1796 initcall functions. Useful for debugging built-in 1797 modules and initcalls. 1798 1799 initrd= [BOOT] Specify the location of the initial ramdisk 1800 1801 initrdmem= [KNL] Specify a physical address and size from which to 1802 load the initrd. If an initrd is compiled in or 1803 specified in the bootparams, it takes priority over this 1804 setting. 1805 Format: ss[KMG],nn[KMG] 1806 Default is 0, 0 1807 1808 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1809 zeroes. 1810 Format: 0 | 1 1811 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1812 1813 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1814 Format: 0 | 1 1815 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1816 1817 init_pkru= [X86] Specify the default memory protection keys rights 1818 register contents for all processes. 0x55555554 by 1819 default (disallow access to all but pkey 0). Can 1820 override in debugfs after boot. 1821 1822 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1823 Format: <irq> 1824 1825 int_pln_enable [X86] Enable power limit notification interrupt 1826 1827 integrity_audit=[IMA] 1828 Format: { "0" | "1" } 1829 0 -- basic integrity auditing messages. (Default) 1830 1 -- additional integrity auditing messages. 1831 1832 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1833 on 1834 Enable intel iommu driver. 1835 off 1836 Disable intel iommu driver. 1837 igfx_off [Default Off] 1838 By default, gfx is mapped as normal device. If a gfx 1839 device has a dedicated DMAR unit, the DMAR unit is 1840 bypassed by not enabling DMAR with this option. In 1841 this case, gfx device will use physical address for 1842 DMA. 1843 forcedac [X86-64] 1844 With this option iommu will not optimize to look 1845 for io virtual address below 32-bit forcing dual 1846 address cycle on pci bus for cards supporting greater 1847 than 32-bit addressing. The default is to look 1848 for translation below 32-bit and if not available 1849 then look in the higher range. 1850 strict [Default Off] 1851 With this option on every unmap_single operation will 1852 result in a hardware IOTLB flush operation as opposed 1853 to batching them for performance. 1854 sp_off [Default Off] 1855 By default, super page will be supported if Intel IOMMU 1856 has the capability. With this option, super page will 1857 not be supported. 1858 sm_on [Default Off] 1859 By default, scalable mode will be disabled even if the 1860 hardware advertises that it has support for the scalable 1861 mode translation. With this option set, scalable mode 1862 will be used on hardware which claims to support it. 1863 tboot_noforce [Default Off] 1864 Do not force the Intel IOMMU enabled under tboot. 1865 By default, tboot will force Intel IOMMU on, which 1866 could harm performance of some high-throughput 1867 devices like 40GBit network cards, even if identity 1868 mapping is enabled. 1869 Note that using this option lowers the security 1870 provided by tboot because it makes the system 1871 vulnerable to DMA attacks. 1872 nobounce [Default off] 1873 Disable bounce buffer for untrusted devices such as 1874 the Thunderbolt devices. This will treat the untrusted 1875 devices as the trusted ones, hence might expose security 1876 risks of DMA attacks. 1877 1878 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1879 0 disables intel_idle and fall back on acpi_idle. 1880 1 to 9 specify maximum depth of C-state. 1881 1882 intel_pstate= [X86] 1883 disable 1884 Do not enable intel_pstate as the default 1885 scaling driver for the supported processors 1886 passive 1887 Use intel_pstate as a scaling driver, but configure it 1888 to work with generic cpufreq governors (instead of 1889 enabling its internal governor). This mode cannot be 1890 used along with the hardware-managed P-states (HWP) 1891 feature. 1892 force 1893 Enable intel_pstate on systems that prohibit it by default 1894 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1895 instead of acpi-cpufreq may disable platform features, such 1896 as thermal controls and power capping, that rely on ACPI 1897 P-States information being indicated to OSPM and therefore 1898 should be used with caution. This option does not work with 1899 processors that aren't supported by the intel_pstate driver 1900 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1901 no_hwp 1902 Do not enable hardware P state control (HWP) 1903 if available. 1904 hwp_only 1905 Only load intel_pstate on systems which support 1906 hardware P state control (HWP) if available. 1907 support_acpi_ppc 1908 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1909 Description Table, specifies preferred power management 1910 profile as "Enterprise Server" or "Performance Server", 1911 then this feature is turned on by default. 1912 per_cpu_perf_limits 1913 Allow per-logical-CPU P-State performance control limits using 1914 cpufreq sysfs interface 1915 1916 intremap= [X86-64, Intel-IOMMU] 1917 on enable Interrupt Remapping (default) 1918 off disable Interrupt Remapping 1919 nosid disable Source ID checking 1920 no_x2apic_optout 1921 BIOS x2APIC opt-out request will be ignored 1922 nopost disable Interrupt Posting 1923 1924 iomem= Disable strict checking of access to MMIO memory 1925 strict regions from userspace. 1926 relaxed 1927 1928 iommu= [X86] 1929 off 1930 force 1931 noforce 1932 biomerge 1933 panic 1934 nopanic 1935 merge 1936 nomerge 1937 soft 1938 pt [X86] 1939 nopt [X86] 1940 nobypass [PPC/POWERNV] 1941 Disable IOMMU bypass, using IOMMU for PCI devices. 1942 1943 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1944 Format: { "0" | "1" } 1945 0 - Lazy mode. 1946 Request that DMA unmap operations use deferred 1947 invalidation of hardware TLBs, for increased 1948 throughput at the cost of reduced device isolation. 1949 Will fall back to strict mode if not supported by 1950 the relevant IOMMU driver. 1951 1 - Strict mode (default). 1952 DMA unmap operations invalidate IOMMU hardware TLBs 1953 synchronously. 1954 1955 iommu.passthrough= 1956 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1957 Format: { "0" | "1" } 1958 0 - Use IOMMU translation for DMA. 1959 1 - Bypass the IOMMU for DMA. 1960 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1961 1962 io7= [HW] IO7 for Marvel based alpha systems 1963 See comment before marvel_specify_io7 in 1964 arch/alpha/kernel/core_marvel.c. 1965 1966 io_delay= [X86] I/O delay method 1967 0x80 1968 Standard port 0x80 based delay 1969 0xed 1970 Alternate port 0xed based delay (needed on some systems) 1971 udelay 1972 Simple two microseconds delay 1973 none 1974 No delay 1975 1976 ip= [IP_PNP] 1977 See Documentation/admin-guide/nfs/nfsroot.rst. 1978 1979 ipcmni_extend [KNL] Extend the maximum number of unique System V 1980 IPC identifiers from 32,768 to 16,777,216. 1981 1982 irqaffinity= [SMP] Set the default irq affinity mask 1983 The argument is a cpu list, as described above. 1984 1985 irqchip.gicv2_force_probe= 1986 [ARM, ARM64] 1987 Format: <bool> 1988 Force the kernel to look for the second 4kB page 1989 of a GICv2 controller even if the memory range 1990 exposed by the device tree is too small. 1991 1992 irqchip.gicv3_nolpi= 1993 [ARM, ARM64] 1994 Force the kernel to ignore the availability of 1995 LPIs (and by consequence ITSs). Intended for system 1996 that use the kernel as a bootloader, and thus want 1997 to let secondary kernels in charge of setting up 1998 LPIs. 1999 2000 irqchip.gicv3_pseudo_nmi= [ARM64] 2001 Enables support for pseudo-NMIs in the kernel. This 2002 requires the kernel to be built with 2003 CONFIG_ARM64_PSEUDO_NMI. 2004 2005 irqfixup [HW] 2006 When an interrupt is not handled search all handlers 2007 for it. Intended to get systems with badly broken 2008 firmware running. 2009 2010 irqpoll [HW] 2011 When an interrupt is not handled search all handlers 2012 for it. Also check all handlers each timer 2013 interrupt. Intended to get systems with badly broken 2014 firmware running. 2015 2016 isapnp= [ISAPNP] 2017 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2018 2019 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2020 [Deprecated - use cpusets instead] 2021 Format: [flag-list,]<cpu-list> 2022 2023 Specify one or more CPUs to isolate from disturbances 2024 specified in the flag list (default: domain): 2025 2026 nohz 2027 Disable the tick when a single task runs. 2028 2029 A residual 1Hz tick is offloaded to workqueues, which you 2030 need to affine to housekeeping through the global 2031 workqueue's affinity configured via the 2032 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2033 by using the 'domain' flag described below. 2034 2035 NOTE: by default the global workqueue runs on all CPUs, 2036 so to protect individual CPUs the 'cpumask' file has to 2037 be configured manually after bootup. 2038 2039 domain 2040 Isolate from the general SMP balancing and scheduling 2041 algorithms. Note that performing domain isolation this way 2042 is irreversible: it's not possible to bring back a CPU to 2043 the domains once isolated through isolcpus. It's strongly 2044 advised to use cpusets instead to disable scheduler load 2045 balancing through the "cpuset.sched_load_balance" file. 2046 It offers a much more flexible interface where CPUs can 2047 move in and out of an isolated set anytime. 2048 2049 You can move a process onto or off an "isolated" CPU via 2050 the CPU affinity syscalls or cpuset. 2051 <cpu number> begins at 0 and the maximum value is 2052 "number of CPUs in system - 1". 2053 2054 managed_irq 2055 2056 Isolate from being targeted by managed interrupts 2057 which have an interrupt mask containing isolated 2058 CPUs. The affinity of managed interrupts is 2059 handled by the kernel and cannot be changed via 2060 the /proc/irq/* interfaces. 2061 2062 This isolation is best effort and only effective 2063 if the automatically assigned interrupt mask of a 2064 device queue contains isolated and housekeeping 2065 CPUs. If housekeeping CPUs are online then such 2066 interrupts are directed to the housekeeping CPU 2067 so that IO submitted on the housekeeping CPU 2068 cannot disturb the isolated CPU. 2069 2070 If a queue's affinity mask contains only isolated 2071 CPUs then this parameter has no effect on the 2072 interrupt routing decision, though interrupts are 2073 only delivered when tasks running on those 2074 isolated CPUs submit IO. IO submitted on 2075 housekeeping CPUs has no influence on those 2076 queues. 2077 2078 The format of <cpu-list> is described above. 2079 2080 iucv= [HW,NET] 2081 2082 ivrs_ioapic [HW,X86-64] 2083 Provide an override to the IOAPIC-ID<->DEVICE-ID 2084 mapping provided in the IVRS ACPI table. For 2085 example, to map IOAPIC-ID decimal 10 to 2086 PCI device 00:14.0 write the parameter as: 2087 ivrs_ioapic[10]=00:14.0 2088 2089 ivrs_hpet [HW,X86-64] 2090 Provide an override to the HPET-ID<->DEVICE-ID 2091 mapping provided in the IVRS ACPI table. For 2092 example, to map HPET-ID decimal 0 to 2093 PCI device 00:14.0 write the parameter as: 2094 ivrs_hpet[0]=00:14.0 2095 2096 ivrs_acpihid [HW,X86-64] 2097 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2098 mapping provided in the IVRS ACPI table. For 2099 example, to map UART-HID:UID AMD0020:0 to 2100 PCI device 00:14.5 write the parameter as: 2101 ivrs_acpihid[00:14.5]=AMD0020:0 2102 2103 js= [HW,JOY] Analog joystick 2104 See Documentation/input/joydev/joystick.rst. 2105 2106 nokaslr [KNL] 2107 When CONFIG_RANDOMIZE_BASE is set, this disables 2108 kernel and module base offset ASLR (Address Space 2109 Layout Randomization). 2110 2111 kasan_multi_shot 2112 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2113 report on every invalid memory access. Without this 2114 parameter KASAN will print report only for the first 2115 invalid access. 2116 2117 keepinitrd [HW,ARM] 2118 2119 kernelcore= [KNL,X86,IA-64,PPC] 2120 Format: nn[KMGTPE] | nn% | "mirror" 2121 This parameter specifies the amount of memory usable by 2122 the kernel for non-movable allocations. The requested 2123 amount is spread evenly throughout all nodes in the 2124 system as ZONE_NORMAL. The remaining memory is used for 2125 movable memory in its own zone, ZONE_MOVABLE. In the 2126 event, a node is too small to have both ZONE_NORMAL and 2127 ZONE_MOVABLE, kernelcore memory will take priority and 2128 other nodes will have a larger ZONE_MOVABLE. 2129 2130 ZONE_MOVABLE is used for the allocation of pages that 2131 may be reclaimed or moved by the page migration 2132 subsystem. Note that allocations like PTEs-from-HighMem 2133 still use the HighMem zone if it exists, and the Normal 2134 zone if it does not. 2135 2136 It is possible to specify the exact amount of memory in 2137 the form of "nn[KMGTPE]", a percentage of total system 2138 memory in the form of "nn%", or "mirror". If "mirror" 2139 option is specified, mirrored (reliable) memory is used 2140 for non-movable allocations and remaining memory is used 2141 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2142 are exclusive, so you cannot specify multiple forms. 2143 2144 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2145 Format: <Controller#>[,poll interval] 2146 The controller # is the number of the ehci usb debug 2147 port as it is probed via PCI. The poll interval is 2148 optional and is the number seconds in between 2149 each poll cycle to the debug port in case you need 2150 the functionality for interrupting the kernel with 2151 gdb or control-c on the dbgp connection. When 2152 not using this parameter you use sysrq-g to break into 2153 the kernel debugger. 2154 2155 kgdboc= [KGDB,HW] kgdb over consoles. 2156 Requires a tty driver that supports console polling, 2157 or a supported polling keyboard driver (non-usb). 2158 Serial only format: <serial_device>[,baud] 2159 keyboard only format: kbd 2160 keyboard and serial format: kbd,<serial_device>[,baud] 2161 Optional Kernel mode setting: 2162 kms, kbd format: kms,kbd 2163 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2164 2165 kgdboc_earlycon= [KGDB,HW] 2166 If the boot console provides the ability to read 2167 characters and can work in polling mode, you can use 2168 this parameter to tell kgdb to use it as a backend 2169 until the normal console is registered. Intended to 2170 be used together with the kgdboc parameter which 2171 specifies the normal console to transition to. 2172 2173 The name of the early console should be specified 2174 as the value of this parameter. Note that the name of 2175 the early console might be different than the tty 2176 name passed to kgdboc. It's OK to leave the value 2177 blank and the first boot console that implements 2178 read() will be picked. 2179 2180 kgdbwait [KGDB] Stop kernel execution and enter the 2181 kernel debugger at the earliest opportunity. 2182 2183 kmac= [MIPS] korina ethernet MAC address. 2184 Configure the RouterBoard 532 series on-chip 2185 Ethernet adapter MAC address. 2186 2187 kmemleak= [KNL] Boot-time kmemleak enable/disable 2188 Valid arguments: on, off 2189 Default: on 2190 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2191 the default is off. 2192 2193 kprobe_event=[probe-list] 2194 [FTRACE] Add kprobe events and enable at boot time. 2195 The probe-list is a semicolon delimited list of probe 2196 definitions. Each definition is same as kprobe_events 2197 interface, but the parameters are comma delimited. 2198 For example, to add a kprobe event on vfs_read with 2199 arg1 and arg2, add to the command line; 2200 2201 kprobe_event=p,vfs_read,$arg1,$arg2 2202 2203 See also Documentation/trace/kprobetrace.rst "Kernel 2204 Boot Parameter" section. 2205 2206 kpti= [ARM64] Control page table isolation of user 2207 and kernel address spaces. 2208 Default: enabled on cores which need mitigation. 2209 0: force disabled 2210 1: force enabled 2211 2212 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2213 Default is 0 (don't ignore, but inject #GP) 2214 2215 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2216 Default is false (don't support). 2217 2218 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2219 KVM MMU at runtime. 2220 Default is 0 (off) 2221 2222 kvm.nx_huge_pages= 2223 [KVM] Controls the software workaround for the 2224 X86_BUG_ITLB_MULTIHIT bug. 2225 force : Always deploy workaround. 2226 off : Never deploy workaround. 2227 auto : Deploy workaround based on the presence of 2228 X86_BUG_ITLB_MULTIHIT. 2229 2230 Default is 'auto'. 2231 2232 If the software workaround is enabled for the host, 2233 guests do need not to enable it for nested guests. 2234 2235 kvm.nx_huge_pages_recovery_ratio= 2236 [KVM] Controls how many 4KiB pages are periodically zapped 2237 back to huge pages. 0 disables the recovery, otherwise if 2238 the value is N KVM will zap 1/Nth of the 4KiB pages every 2239 minute. The default is 60. 2240 2241 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2242 Default is 1 (enabled) 2243 2244 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2245 for all guests. 2246 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2247 2248 kvm-arm.vgic_v3_group0_trap= 2249 [KVM,ARM] Trap guest accesses to GICv3 group-0 2250 system registers 2251 2252 kvm-arm.vgic_v3_group1_trap= 2253 [KVM,ARM] Trap guest accesses to GICv3 group-1 2254 system registers 2255 2256 kvm-arm.vgic_v3_common_trap= 2257 [KVM,ARM] Trap guest accesses to GICv3 common 2258 system registers 2259 2260 kvm-arm.vgic_v4_enable= 2261 [KVM,ARM] Allow use of GICv4 for direct injection of 2262 LPIs. 2263 2264 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2265 (virtualized MMU) support on capable Intel chips. 2266 Default is 1 (enabled) 2267 2268 kvm-intel.emulate_invalid_guest_state= 2269 [KVM,Intel] Enable emulation of invalid guest states 2270 Default is 0 (disabled) 2271 2272 kvm-intel.flexpriority= 2273 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2274 Default is 1 (enabled) 2275 2276 kvm-intel.nested= 2277 [KVM,Intel] Enable VMX nesting (nVMX). 2278 Default is 0 (disabled) 2279 2280 kvm-intel.unrestricted_guest= 2281 [KVM,Intel] Disable unrestricted guest feature 2282 (virtualized real and unpaged mode) on capable 2283 Intel chips. Default is 1 (enabled) 2284 2285 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2286 CVE-2018-3620. 2287 2288 Valid arguments: never, cond, always 2289 2290 always: L1D cache flush on every VMENTER. 2291 cond: Flush L1D on VMENTER only when the code between 2292 VMEXIT and VMENTER can leak host memory. 2293 never: Disables the mitigation 2294 2295 Default is cond (do L1 cache flush in specific instances) 2296 2297 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2298 feature (tagged TLBs) on capable Intel chips. 2299 Default is 1 (enabled) 2300 2301 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2302 affected CPUs 2303 2304 The kernel PTE inversion protection is unconditionally 2305 enabled and cannot be disabled. 2306 2307 full 2308 Provides all available mitigations for the 2309 L1TF vulnerability. Disables SMT and 2310 enables all mitigations in the 2311 hypervisors, i.e. unconditional L1D flush. 2312 2313 SMT control and L1D flush control via the 2314 sysfs interface is still possible after 2315 boot. Hypervisors will issue a warning 2316 when the first VM is started in a 2317 potentially insecure configuration, 2318 i.e. SMT enabled or L1D flush disabled. 2319 2320 full,force 2321 Same as 'full', but disables SMT and L1D 2322 flush runtime control. Implies the 2323 'nosmt=force' command line option. 2324 (i.e. sysfs control of SMT is disabled.) 2325 2326 flush 2327 Leaves SMT enabled and enables the default 2328 hypervisor mitigation, i.e. conditional 2329 L1D flush. 2330 2331 SMT control and L1D flush control via the 2332 sysfs interface is still possible after 2333 boot. Hypervisors will issue a warning 2334 when the first VM is started in a 2335 potentially insecure configuration, 2336 i.e. SMT enabled or L1D flush disabled. 2337 2338 flush,nosmt 2339 2340 Disables SMT and enables the default 2341 hypervisor mitigation. 2342 2343 SMT control and L1D flush control via the 2344 sysfs interface is still possible after 2345 boot. Hypervisors will issue a warning 2346 when the first VM is started in a 2347 potentially insecure configuration, 2348 i.e. SMT enabled or L1D flush disabled. 2349 2350 flush,nowarn 2351 Same as 'flush', but hypervisors will not 2352 warn when a VM is started in a potentially 2353 insecure configuration. 2354 2355 off 2356 Disables hypervisor mitigations and doesn't 2357 emit any warnings. 2358 It also drops the swap size and available 2359 RAM limit restriction on both hypervisor and 2360 bare metal. 2361 2362 Default is 'flush'. 2363 2364 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2365 2366 l2cr= [PPC] 2367 2368 l3cr= [PPC] 2369 2370 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2371 disabled it. 2372 2373 lapic= [X86,APIC] "notscdeadline" Do not use TSC deadline 2374 value for LAPIC timer one-shot implementation. Default 2375 back to the programmable timer unit in the LAPIC. 2376 2377 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2378 in C2 power state. 2379 2380 libata.dma= [LIBATA] DMA control 2381 libata.dma=0 Disable all PATA and SATA DMA 2382 libata.dma=1 PATA and SATA Disk DMA only 2383 libata.dma=2 ATAPI (CDROM) DMA only 2384 libata.dma=4 Compact Flash DMA only 2385 Combinations also work, so libata.dma=3 enables DMA 2386 for disks and CDROMs, but not CFs. 2387 2388 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2389 libata.ignore_hpa=0 keep BIOS limits (default) 2390 libata.ignore_hpa=1 ignore limits, using full disk 2391 2392 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2393 when set. 2394 Format: <int> 2395 2396 libata.force= [LIBATA] Force configurations. The format is comma 2397 separated list of "[ID:]VAL" where ID is 2398 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2399 matching port, link or device. Basically, it matches 2400 the ATA ID string printed on console by libata. If 2401 the whole ID part is omitted, the last PORT and DEVICE 2402 values are used. If ID hasn't been specified yet, the 2403 configuration applies to all ports, links and devices. 2404 2405 If only DEVICE is omitted, the parameter applies to 2406 the port and all links and devices behind it. DEVICE 2407 number of 0 either selects the first device or the 2408 first fan-out link behind PMP device. It does not 2409 select the host link. DEVICE number of 15 selects the 2410 host link and device attached to it. 2411 2412 The VAL specifies the configuration to force. As long 2413 as there's no ambiguity shortcut notation is allowed. 2414 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2415 The following configurations can be forced. 2416 2417 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2418 Any ID with matching PORT is used. 2419 2420 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2421 2422 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2423 udma[/][16,25,33,44,66,100,133] notation is also 2424 allowed. 2425 2426 * [no]ncq: Turn on or off NCQ. 2427 2428 * [no]ncqtrim: Turn off queued DSM TRIM. 2429 2430 * nohrst, nosrst, norst: suppress hard, soft 2431 and both resets. 2432 2433 * rstonce: only attempt one reset during 2434 hot-unplug link recovery 2435 2436 * dump_id: dump IDENTIFY data. 2437 2438 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2439 2440 * disable: Disable this device. 2441 2442 If there are multiple matching configurations changing 2443 the same attribute, the last one is used. 2444 2445 memblock=debug [KNL] Enable memblock debug messages. 2446 2447 load_ramdisk= [RAM] List of ramdisks to load from floppy 2448 See Documentation/admin-guide/blockdev/ramdisk.rst. 2449 2450 lockd.nlm_grace_period=P [NFS] Assign grace period. 2451 Format: <integer> 2452 2453 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2454 Format: <integer> 2455 2456 lockd.nlm_timeout=T [NFS] Assign timeout value. 2457 Format: <integer> 2458 2459 lockd.nlm_udpport=M [NFS] Assign UDP port. 2460 Format: <integer> 2461 2462 lockdown= [SECURITY] 2463 { integrity | confidentiality } 2464 Enable the kernel lockdown feature. If set to 2465 integrity, kernel features that allow userland to 2466 modify the running kernel are disabled. If set to 2467 confidentiality, kernel features that allow userland 2468 to extract confidential information from the kernel 2469 are also disabled. 2470 2471 locktorture.nreaders_stress= [KNL] 2472 Set the number of locking read-acquisition kthreads. 2473 Defaults to being automatically set based on the 2474 number of online CPUs. 2475 2476 locktorture.nwriters_stress= [KNL] 2477 Set the number of locking write-acquisition kthreads. 2478 2479 locktorture.onoff_holdoff= [KNL] 2480 Set time (s) after boot for CPU-hotplug testing. 2481 2482 locktorture.onoff_interval= [KNL] 2483 Set time (s) between CPU-hotplug operations, or 2484 zero to disable CPU-hotplug testing. 2485 2486 locktorture.shuffle_interval= [KNL] 2487 Set task-shuffle interval (jiffies). Shuffling 2488 tasks allows some CPUs to go into dyntick-idle 2489 mode during the locktorture test. 2490 2491 locktorture.shutdown_secs= [KNL] 2492 Set time (s) after boot system shutdown. This 2493 is useful for hands-off automated testing. 2494 2495 locktorture.stat_interval= [KNL] 2496 Time (s) between statistics printk()s. 2497 2498 locktorture.stutter= [KNL] 2499 Time (s) to stutter testing, for example, 2500 specifying five seconds causes the test to run for 2501 five seconds, wait for five seconds, and so on. 2502 This tests the locking primitive's ability to 2503 transition abruptly to and from idle. 2504 2505 locktorture.torture_type= [KNL] 2506 Specify the locking implementation to test. 2507 2508 locktorture.verbose= [KNL] 2509 Enable additional printk() statements. 2510 2511 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2512 Format: <irq> 2513 2514 loglevel= All Kernel Messages with a loglevel smaller than the 2515 console loglevel will be printed to the console. It can 2516 also be changed with klogd or other programs. The 2517 loglevels are defined as follows: 2518 2519 0 (KERN_EMERG) system is unusable 2520 1 (KERN_ALERT) action must be taken immediately 2521 2 (KERN_CRIT) critical conditions 2522 3 (KERN_ERR) error conditions 2523 4 (KERN_WARNING) warning conditions 2524 5 (KERN_NOTICE) normal but significant condition 2525 6 (KERN_INFO) informational 2526 7 (KERN_DEBUG) debug-level messages 2527 2528 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2529 in bytes. n must be a power of two and greater 2530 than the minimal size. The minimal size is defined 2531 by LOG_BUF_SHIFT kernel config parameter. There is 2532 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2533 that allows to increase the default size depending on 2534 the number of CPUs. See init/Kconfig for more details. 2535 2536 logo.nologo [FB] Disables display of the built-in Linux logo. 2537 This may be used to provide more screen space for 2538 kernel log messages and is useful when debugging 2539 kernel boot problems. 2540 2541 lp=0 [LP] Specify parallel ports to use, e.g, 2542 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2543 lp=reset first parallel port). 'lp=0' disables the 2544 lp=auto printer driver. 'lp=reset' (which can be 2545 specified in addition to the ports) causes 2546 attached printers to be reset. Using 2547 lp=port1,port2,... specifies the parallel ports 2548 to associate lp devices with, starting with 2549 lp0. A port specification may be 'none' to skip 2550 that lp device, or a parport name such as 2551 'parport0'. Specifying 'lp=auto' instead of a 2552 port specification list means that device IDs 2553 from each port should be examined, to see if 2554 an IEEE 1284-compliant printer is attached; if 2555 so, the driver will manage that printer. 2556 See also header of drivers/char/lp.c. 2557 2558 lpj=n [KNL] 2559 Sets loops_per_jiffy to given constant, thus avoiding 2560 time-consuming boot-time autodetection (up to 250 ms per 2561 CPU). 0 enables autodetection (default). To determine 2562 the correct value for your kernel, boot with normal 2563 autodetection and see what value is printed. Note that 2564 on SMP systems the preset will be applied to all CPUs, 2565 which is likely to cause problems if your CPUs need 2566 significantly divergent settings. An incorrect value 2567 will cause delays in the kernel to be wrong, leading to 2568 unpredictable I/O errors and other breakage. Although 2569 unlikely, in the extreme case this might damage your 2570 hardware. 2571 2572 ltpc= [NET] 2573 Format: <io>,<irq>,<dma> 2574 2575 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2576 2577 lsm=lsm1,...,lsmN 2578 [SECURITY] Choose order of LSM initialization. This 2579 overrides CONFIG_LSM, and the "security=" parameter. 2580 2581 machvec= [IA-64] Force the use of a particular machine-vector 2582 (machvec) in a generic kernel. 2583 Example: machvec=hpzx1 2584 2585 machtype= [Loongson] Share the same kernel image file between different 2586 yeeloong laptop. 2587 Example: machtype=lemote-yeeloong-2f-7inch 2588 2589 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2590 than or equal to this physical address is ignored. 2591 2592 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2593 will bring up during bootup. maxcpus=n : n >= 0 limits 2594 the kernel to bring up 'n' processors. Surely after 2595 bootup you can bring up the other plugged cpu by executing 2596 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2597 only takes effect during system bootup. 2598 While n=0 is a special case, it is equivalent to "nosmp", 2599 which also disables the IO APIC. 2600 2601 max_loop= [LOOP] The number of loop block devices that get 2602 (loop.max_loop) unconditionally pre-created at init time. The default 2603 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2604 of statically allocating a predefined number, loop 2605 devices can be requested on-demand with the 2606 /dev/loop-control interface. 2607 2608 mce [X86-32] Machine Check Exception 2609 2610 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2611 2612 md= [HW] RAID subsystems devices and level 2613 See Documentation/admin-guide/md.rst. 2614 2615 mdacon= [MDA] 2616 Format: <first>,<last> 2617 Specifies range of consoles to be captured by the MDA. 2618 2619 mds= [X86,INTEL] 2620 Control mitigation for the Micro-architectural Data 2621 Sampling (MDS) vulnerability. 2622 2623 Certain CPUs are vulnerable to an exploit against CPU 2624 internal buffers which can forward information to a 2625 disclosure gadget under certain conditions. 2626 2627 In vulnerable processors, the speculatively 2628 forwarded data can be used in a cache side channel 2629 attack, to access data to which the attacker does 2630 not have direct access. 2631 2632 This parameter controls the MDS mitigation. The 2633 options are: 2634 2635 full - Enable MDS mitigation on vulnerable CPUs 2636 full,nosmt - Enable MDS mitigation and disable 2637 SMT on vulnerable CPUs 2638 off - Unconditionally disable MDS mitigation 2639 2640 On TAA-affected machines, mds=off can be prevented by 2641 an active TAA mitigation as both vulnerabilities are 2642 mitigated with the same mechanism so in order to disable 2643 this mitigation, you need to specify tsx_async_abort=off 2644 too. 2645 2646 Not specifying this option is equivalent to 2647 mds=full. 2648 2649 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2650 2651 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2652 Amount of memory to be used in cases as follows: 2653 2654 1 for test; 2655 2 when the kernel is not able to see the whole system memory; 2656 3 memory that lies after 'mem=' boundary is excluded from 2657 the hypervisor, then assigned to KVM guests. 2658 2659 [X86] Work as limiting max address. Use together 2660 with memmap= to avoid physical address space collisions. 2661 Without memmap= PCI devices could be placed at addresses 2662 belonging to unused RAM. 2663 2664 Note that this only takes effects during boot time since 2665 in above case 3, memory may need be hot added after boot 2666 if system memory of hypervisor is not sufficient. 2667 2668 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2669 memory. 2670 2671 memchunk=nn[KMG] 2672 [KNL,SH] Allow user to override the default size for 2673 per-device physically contiguous DMA buffers. 2674 2675 memhp_default_state=online/offline 2676 [KNL] Set the initial state for the memory hotplug 2677 onlining policy. If not specified, the default value is 2678 set according to the 2679 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2680 option. 2681 See Documentation/admin-guide/mm/memory-hotplug.rst. 2682 2683 memmap=exactmap [KNL,X86] Enable setting of an exact 2684 E820 memory map, as specified by the user. 2685 Such memmap=exactmap lines can be constructed based on 2686 BIOS output or other requirements. See the memmap=nn@ss 2687 option description. 2688 2689 memmap=nn[KMG]@ss[KMG] 2690 [KNL] Force usage of a specific region of memory. 2691 Region of memory to be used is from ss to ss+nn. 2692 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2693 which limits max address to nn[KMG]. 2694 Multiple different regions can be specified, 2695 comma delimited. 2696 Example: 2697 memmap=100M@2G,100M#3G,1G!1024G 2698 2699 memmap=nn[KMG]#ss[KMG] 2700 [KNL,ACPI] Mark specific memory as ACPI data. 2701 Region of memory to be marked is from ss to ss+nn. 2702 2703 memmap=nn[KMG]$ss[KMG] 2704 [KNL,ACPI] Mark specific memory as reserved. 2705 Region of memory to be reserved is from ss to ss+nn. 2706 Example: Exclude memory from 0x18690000-0x1869ffff 2707 memmap=64K$0x18690000 2708 or 2709 memmap=0x10000$0x18690000 2710 Some bootloaders may need an escape character before '$', 2711 like Grub2, otherwise '$' and the following number 2712 will be eaten. 2713 2714 memmap=nn[KMG]!ss[KMG] 2715 [KNL,X86] Mark specific memory as protected. 2716 Region of memory to be used, from ss to ss+nn. 2717 The memory region may be marked as e820 type 12 (0xc) 2718 and is NVDIMM or ADR memory. 2719 2720 memmap=<size>%<offset>-<oldtype>+<newtype> 2721 [KNL,ACPI] Convert memory within the specified region 2722 from <oldtype> to <newtype>. If "-<oldtype>" is left 2723 out, the whole region will be marked as <newtype>, 2724 even if previously unavailable. If "+<newtype>" is left 2725 out, matching memory will be removed. Types are 2726 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2727 3 = ACPI, 12 = PRAM. 2728 2729 memory_corruption_check=0/1 [X86] 2730 Some BIOSes seem to corrupt the first 64k of 2731 memory when doing things like suspend/resume. 2732 Setting this option will scan the memory 2733 looking for corruption. Enabling this will 2734 both detect corruption and prevent the kernel 2735 from using the memory being corrupted. 2736 However, its intended as a diagnostic tool; if 2737 repeatable BIOS-originated corruption always 2738 affects the same memory, you can use memmap= 2739 to prevent the kernel from using that memory. 2740 2741 memory_corruption_check_size=size [X86] 2742 By default it checks for corruption in the low 2743 64k, making this memory unavailable for normal 2744 use. Use this parameter to scan for 2745 corruption in more or less memory. 2746 2747 memory_corruption_check_period=seconds [X86] 2748 By default it checks for corruption every 60 2749 seconds. Use this parameter to check at some 2750 other rate. 0 disables periodic checking. 2751 2752 memtest= [KNL,X86,ARM,PPC] Enable memtest 2753 Format: <integer> 2754 default : 0 <disable> 2755 Specifies the number of memtest passes to be 2756 performed. Each pass selects another test 2757 pattern from a given set of patterns. Memtest 2758 fills the memory with this pattern, validates 2759 memory contents and reserves bad memory 2760 regions that are detected. 2761 2762 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2763 Valid arguments: on, off 2764 Default (depends on kernel configuration option): 2765 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2766 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2767 mem_encrypt=on: Activate SME 2768 mem_encrypt=off: Do not activate SME 2769 2770 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2771 for details on when memory encryption can be activated. 2772 2773 mem_sleep_default= [SUSPEND] Default system suspend mode: 2774 s2idle - Suspend-To-Idle 2775 shallow - Power-On Suspend or equivalent (if supported) 2776 deep - Suspend-To-RAM or equivalent (if supported) 2777 See Documentation/admin-guide/pm/sleep-states.rst. 2778 2779 meye.*= [HW] Set MotionEye Camera parameters 2780 See Documentation/admin-guide/media/meye.rst. 2781 2782 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2783 Multi-Function General Purpose Timers on AMD Geode 2784 platforms. 2785 2786 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2787 the BIOS has incorrectly applied a workaround. TinyBIOS 2788 version 0.98 is known to be affected, 0.99 fixes the 2789 problem by letting the user disable the workaround. 2790 2791 mga= [HW,DRM] 2792 2793 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2794 physical address is ignored. 2795 2796 mini2440= [ARM,HW,KNL] 2797 Format:[0..2][b][c][t] 2798 Default: "0tb" 2799 MINI2440 configuration specification: 2800 0 - The attached screen is the 3.5" TFT 2801 1 - The attached screen is the 7" TFT 2802 2 - The VGA Shield is attached (1024x768) 2803 Leaving out the screen size parameter will not load 2804 the TFT driver, and the framebuffer will be left 2805 unconfigured. 2806 b - Enable backlight. The TFT backlight pin will be 2807 linked to the kernel VESA blanking code and a GPIO 2808 LED. This parameter is not necessary when using the 2809 VGA shield. 2810 c - Enable the s3c camera interface. 2811 t - Reserved for enabling touchscreen support. The 2812 touchscreen support is not enabled in the mainstream 2813 kernel as of 2.6.30, a preliminary port can be found 2814 in the "bleeding edge" mini2440 support kernel at 2815 https://repo.or.cz/w/linux-2.6/mini2440.git 2816 2817 mitigations= 2818 [X86,PPC,S390,ARM64] Control optional mitigations for 2819 CPU vulnerabilities. This is a set of curated, 2820 arch-independent options, each of which is an 2821 aggregation of existing arch-specific options. 2822 2823 off 2824 Disable all optional CPU mitigations. This 2825 improves system performance, but it may also 2826 expose users to several CPU vulnerabilities. 2827 Equivalent to: nopti [X86,PPC] 2828 kpti=0 [ARM64] 2829 nospectre_v1 [X86,PPC] 2830 nobp=0 [S390] 2831 nospectre_v2 [X86,PPC,S390,ARM64] 2832 spectre_v2_user=off [X86] 2833 spec_store_bypass_disable=off [X86,PPC] 2834 ssbd=force-off [ARM64] 2835 l1tf=off [X86] 2836 mds=off [X86] 2837 tsx_async_abort=off [X86] 2838 kvm.nx_huge_pages=off [X86] 2839 2840 Exceptions: 2841 This does not have any effect on 2842 kvm.nx_huge_pages when 2843 kvm.nx_huge_pages=force. 2844 2845 auto (default) 2846 Mitigate all CPU vulnerabilities, but leave SMT 2847 enabled, even if it's vulnerable. This is for 2848 users who don't want to be surprised by SMT 2849 getting disabled across kernel upgrades, or who 2850 have other ways of avoiding SMT-based attacks. 2851 Equivalent to: (default behavior) 2852 2853 auto,nosmt 2854 Mitigate all CPU vulnerabilities, disabling SMT 2855 if needed. This is for users who always want to 2856 be fully mitigated, even if it means losing SMT. 2857 Equivalent to: l1tf=flush,nosmt [X86] 2858 mds=full,nosmt [X86] 2859 tsx_async_abort=full,nosmt [X86] 2860 2861 mminit_loglevel= 2862 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2863 parameter allows control of the logging verbosity for 2864 the additional memory initialisation checks. A value 2865 of 0 disables mminit logging and a level of 4 will 2866 log everything. Information is printed at KERN_DEBUG 2867 so loglevel=8 may also need to be specified. 2868 2869 module.sig_enforce 2870 [KNL] When CONFIG_MODULE_SIG is set, this means that 2871 modules without (valid) signatures will fail to load. 2872 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2873 is always true, so this option does nothing. 2874 2875 module_blacklist= [KNL] Do not load a comma-separated list of 2876 modules. Useful for debugging problem modules. 2877 2878 mousedev.tap_time= 2879 [MOUSE] Maximum time between finger touching and 2880 leaving touchpad surface for touch to be considered 2881 a tap and be reported as a left button click (for 2882 touchpads working in absolute mode only). 2883 Format: <msecs> 2884 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2885 reporting absolute coordinates, such as tablets 2886 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2887 reporting absolute coordinates, such as tablets 2888 2889 movablecore= [KNL,X86,IA-64,PPC] 2890 Format: nn[KMGTPE] | nn% 2891 This parameter is the complement to kernelcore=, it 2892 specifies the amount of memory used for migratable 2893 allocations. If both kernelcore and movablecore is 2894 specified, then kernelcore will be at *least* the 2895 specified value but may be more. If movablecore on its 2896 own is specified, the administrator must be careful 2897 that the amount of memory usable for all allocations 2898 is not too small. 2899 2900 movable_node [KNL] Boot-time switch to make hotplugable memory 2901 NUMA nodes to be movable. This means that the memory 2902 of such nodes will be usable only for movable 2903 allocations which rules out almost all kernel 2904 allocations. Use with caution! 2905 2906 MTD_Partition= [MTD] 2907 Format: <name>,<region-number>,<size>,<offset> 2908 2909 MTD_Region= [MTD] Format: 2910 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2911 2912 mtdparts= [MTD] 2913 See drivers/mtd/parsers/cmdlinepart.c 2914 2915 multitce=off [PPC] This parameter disables the use of the pSeries 2916 firmware feature for updating multiple TCE entries 2917 at a time. 2918 2919 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2920 2921 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2922 2923 boundary - index of last SLC block on Flex-OneNAND. 2924 The remaining blocks are configured as MLC blocks. 2925 lock - Configure if Flex-OneNAND boundary should be locked. 2926 Once locked, the boundary cannot be changed. 2927 1 indicates lock status, 0 indicates unlock status. 2928 2929 mtdset= [ARM] 2930 ARM/S3C2412 JIVE boot control 2931 2932 See arch/arm/mach-s3c2412/mach-jive.c 2933 2934 mtouchusb.raw_coordinates= 2935 [HW] Make the MicroTouch USB driver use raw coordinates 2936 ('y', default) or cooked coordinates ('n') 2937 2938 mtrr_chunk_size=nn[KMG] [X86] 2939 used for mtrr cleanup. It is largest continuous chunk 2940 that could hold holes aka. UC entries. 2941 2942 mtrr_gran_size=nn[KMG] [X86] 2943 Used for mtrr cleanup. It is granularity of mtrr block. 2944 Default is 1. 2945 Large value could prevent small alignment from 2946 using up MTRRs. 2947 2948 mtrr_spare_reg_nr=n [X86] 2949 Format: <integer> 2950 Range: 0,7 : spare reg number 2951 Default : 1 2952 Used for mtrr cleanup. It is spare mtrr entries number. 2953 Set to 2 or more if your graphical card needs more. 2954 2955 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2956 2957 netdev= [NET] Network devices parameters 2958 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2959 Note that mem_start is often overloaded to mean 2960 something different and driver-specific. 2961 This usage is only documented in each driver source 2962 file if at all. 2963 2964 nf_conntrack.acct= 2965 [NETFILTER] Enable connection tracking flow accounting 2966 0 to disable accounting 2967 1 to enable accounting 2968 Default value is 0. 2969 2970 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2971 See Documentation/admin-guide/nfs/nfsroot.rst. 2972 2973 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2974 See Documentation/admin-guide/nfs/nfsroot.rst. 2975 2976 nfsrootdebug [NFS] enable nfsroot debugging messages. 2977 See Documentation/admin-guide/nfs/nfsroot.rst. 2978 2979 nfs.callback_nr_threads= 2980 [NFSv4] set the total number of threads that the 2981 NFS client will assign to service NFSv4 callback 2982 requests. 2983 2984 nfs.callback_tcpport= 2985 [NFS] set the TCP port on which the NFSv4 callback 2986 channel should listen. 2987 2988 nfs.cache_getent= 2989 [NFS] sets the pathname to the program which is used 2990 to update the NFS client cache entries. 2991 2992 nfs.cache_getent_timeout= 2993 [NFS] sets the timeout after which an attempt to 2994 update a cache entry is deemed to have failed. 2995 2996 nfs.idmap_cache_timeout= 2997 [NFS] set the maximum lifetime for idmapper cache 2998 entries. 2999 3000 nfs.enable_ino64= 3001 [NFS] enable 64-bit inode numbers. 3002 If zero, the NFS client will fake up a 32-bit inode 3003 number for the readdir() and stat() syscalls instead 3004 of returning the full 64-bit number. 3005 The default is to return 64-bit inode numbers. 3006 3007 nfs.max_session_cb_slots= 3008 [NFSv4.1] Sets the maximum number of session 3009 slots the client will assign to the callback 3010 channel. This determines the maximum number of 3011 callbacks the client will process in parallel for 3012 a particular server. 3013 3014 nfs.max_session_slots= 3015 [NFSv4.1] Sets the maximum number of session slots 3016 the client will attempt to negotiate with the server. 3017 This limits the number of simultaneous RPC requests 3018 that the client can send to the NFSv4.1 server. 3019 Note that there is little point in setting this 3020 value higher than the max_tcp_slot_table_limit. 3021 3022 nfs.nfs4_disable_idmapping= 3023 [NFSv4] When set to the default of '1', this option 3024 ensures that both the RPC level authentication 3025 scheme and the NFS level operations agree to use 3026 numeric uids/gids if the mount is using the 3027 'sec=sys' security flavour. In effect it is 3028 disabling idmapping, which can make migration from 3029 legacy NFSv2/v3 systems to NFSv4 easier. 3030 Servers that do not support this mode of operation 3031 will be autodetected by the client, and it will fall 3032 back to using the idmapper. 3033 To turn off this behaviour, set the value to '0'. 3034 nfs.nfs4_unique_id= 3035 [NFS4] Specify an additional fixed unique ident- 3036 ification string that NFSv4 clients can insert into 3037 their nfs_client_id4 string. This is typically a 3038 UUID that is generated at system install time. 3039 3040 nfs.send_implementation_id = 3041 [NFSv4.1] Send client implementation identification 3042 information in exchange_id requests. 3043 If zero, no implementation identification information 3044 will be sent. 3045 The default is to send the implementation identification 3046 information. 3047 3048 nfs.recover_lost_locks = 3049 [NFSv4] Attempt to recover locks that were lost due 3050 to a lease timeout on the server. Please note that 3051 doing this risks data corruption, since there are 3052 no guarantees that the file will remain unchanged 3053 after the locks are lost. 3054 If you want to enable the kernel legacy behaviour of 3055 attempting to recover these locks, then set this 3056 parameter to '1'. 3057 The default parameter value of '0' causes the kernel 3058 not to attempt recovery of lost locks. 3059 3060 nfs4.layoutstats_timer = 3061 [NFSv4.2] Change the rate at which the kernel sends 3062 layoutstats to the pNFS metadata server. 3063 3064 Setting this to value to 0 causes the kernel to use 3065 whatever value is the default set by the layout 3066 driver. A non-zero value sets the minimum interval 3067 in seconds between layoutstats transmissions. 3068 3069 nfsd.nfs4_disable_idmapping= 3070 [NFSv4] When set to the default of '1', the NFSv4 3071 server will return only numeric uids and gids to 3072 clients using auth_sys, and will accept numeric uids 3073 and gids from such clients. This is intended to ease 3074 migration from NFSv2/v3. 3075 3076 nmi_debug= [KNL,SH] Specify one or more actions to take 3077 when a NMI is triggered. 3078 Format: [state][,regs][,debounce][,die] 3079 3080 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3081 Format: [panic,][nopanic,][num] 3082 Valid num: 0 or 1 3083 0 - turn hardlockup detector in nmi_watchdog off 3084 1 - turn hardlockup detector in nmi_watchdog on 3085 When panic is specified, panic when an NMI watchdog 3086 timeout occurs (or 'nopanic' to not panic on an NMI 3087 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3088 To disable both hard and soft lockup detectors, 3089 please see 'nowatchdog'. 3090 This is useful when you use a panic=... timeout and 3091 need the box quickly up again. 3092 3093 These settings can be accessed at runtime via 3094 the nmi_watchdog and hardlockup_panic sysctls. 3095 3096 netpoll.carrier_timeout= 3097 [NET] Specifies amount of time (in seconds) that 3098 netpoll should wait for a carrier. By default netpoll 3099 waits 4 seconds. 3100 3101 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3102 emulation library even if a 387 maths coprocessor 3103 is present. 3104 3105 no5lvl [X86-64] Disable 5-level paging mode. Forces 3106 kernel to use 4-level paging instead. 3107 3108 nofsgsbase [X86] Disables FSGSBASE instructions. 3109 3110 no_console_suspend 3111 [HW] Never suspend the console 3112 Disable suspending of consoles during suspend and 3113 hibernate operations. Once disabled, debugging 3114 messages can reach various consoles while the rest 3115 of the system is being put to sleep (ie, while 3116 debugging driver suspend/resume hooks). This may 3117 not work reliably with all consoles, but is known 3118 to work with serial and VGA consoles. 3119 To facilitate more flexible debugging, we also add 3120 console_suspend, a printk module parameter to control 3121 it. Users could use console_suspend (usually 3122 /sys/module/printk/parameters/console_suspend) to 3123 turn on/off it dynamically. 3124 3125 novmcoredd [KNL,KDUMP] 3126 Disable device dump. Device dump allows drivers to 3127 append dump data to vmcore so you can collect driver 3128 specified debug info. Drivers can append the data 3129 without any limit and this data is stored in memory, 3130 so this may cause significant memory stress. Disabling 3131 device dump can help save memory but the driver debug 3132 data will be no longer available. This parameter 3133 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3134 is set. 3135 3136 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3137 caches in the slab allocator. Saves per-node memory, 3138 but will impact performance. 3139 3140 noalign [KNL,ARM] 3141 3142 noaltinstr [S390] Disables alternative instructions patching 3143 (CPU alternatives feature). 3144 3145 noapic [SMP,APIC] Tells the kernel to not make use of any 3146 IOAPICs that may be present in the system. 3147 3148 noautogroup Disable scheduler automatic task group creation. 3149 3150 nobats [PPC] Do not use BATs for mapping kernel lowmem 3151 on "Classic" PPC cores. 3152 3153 nocache [ARM] 3154 3155 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3156 3157 nodelayacct [KNL] Disable per-task delay accounting 3158 3159 nodsp [SH] Disable hardware DSP at boot time. 3160 3161 noefi Disable EFI runtime services support. 3162 3163 noexec [IA-64] 3164 3165 noexec [X86] 3166 On X86-32 available only on PAE configured kernels. 3167 noexec=on: enable non-executable mappings (default) 3168 noexec=off: disable non-executable mappings 3169 3170 nosmap [X86,PPC] 3171 Disable SMAP (Supervisor Mode Access Prevention) 3172 even if it is supported by processor. 3173 3174 nosmep [X86,PPC] 3175 Disable SMEP (Supervisor Mode Execution Prevention) 3176 even if it is supported by processor. 3177 3178 noexec32 [X86-64] 3179 This affects only 32-bit executables. 3180 noexec32=on: enable non-executable mappings (default) 3181 read doesn't imply executable mappings 3182 noexec32=off: disable non-executable mappings 3183 read implies executable mappings 3184 3185 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3186 3187 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3188 register save and restore. The kernel will only save 3189 legacy floating-point registers on task switch. 3190 3191 nohugeiomap [KNL,X86,PPC] Disable kernel huge I/O mappings. 3192 3193 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3194 Equivalent to smt=1. 3195 3196 [KNL,X86] Disable symmetric multithreading (SMT). 3197 nosmt=force: Force disable SMT, cannot be undone 3198 via the sysfs control file. 3199 3200 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3201 (bounds check bypass). With this option data leaks are 3202 possible in the system. 3203 3204 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3205 the Spectre variant 2 (indirect branch prediction) 3206 vulnerability. System may allow data leaks with this 3207 option. 3208 3209 nospec_store_bypass_disable 3210 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3211 3212 noxsave [BUGS=X86] Disables x86 extended register state save 3213 and restore using xsave. The kernel will fallback to 3214 enabling legacy floating-point and sse state. 3215 3216 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3217 register states. The kernel will fall back to use 3218 xsave to save the states. By using this parameter, 3219 performance of saving the states is degraded because 3220 xsave doesn't support modified optimization while 3221 xsaveopt supports it on xsaveopt enabled systems. 3222 3223 noxsaves [X86] Disables xsaves and xrstors used in saving and 3224 restoring x86 extended register state in compacted 3225 form of xsave area. The kernel will fall back to use 3226 xsaveopt and xrstor to save and restore the states 3227 in standard form of xsave area. By using this 3228 parameter, xsave area per process might occupy more 3229 memory on xsaves enabled systems. 3230 3231 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3232 wfi(ARM) instruction doesn't work correctly and not to 3233 use it. This is also useful when using JTAG debugger. 3234 3235 no_file_caps Tells the kernel not to honor file capabilities. The 3236 only way then for a file to be executed with privilege 3237 is to be setuid root or executed by root. 3238 3239 nohalt [IA-64] Tells the kernel not to use the power saving 3240 function PAL_HALT_LIGHT when idle. This increases 3241 power-consumption. On the positive side, it reduces 3242 interrupt wake-up latency, which may improve performance 3243 in certain environments such as networked servers or 3244 real-time systems. 3245 3246 nohibernate [HIBERNATION] Disable hibernation and resume. 3247 3248 nohz= [KNL] Boottime enable/disable dynamic ticks 3249 Valid arguments: on, off 3250 Default: on 3251 3252 nohz_full= [KNL,BOOT,SMP,ISOL] 3253 The argument is a cpu list, as described above. 3254 In kernels built with CONFIG_NO_HZ_FULL=y, set 3255 the specified list of CPUs whose tick will be stopped 3256 whenever possible. The boot CPU will be forced outside 3257 the range to maintain the timekeeping. Any CPUs 3258 in this list will have their RCU callbacks offloaded, 3259 just as if they had also been called out in the 3260 rcu_nocbs= boot parameter. 3261 3262 noiotrap [SH] Disables trapped I/O port accesses. 3263 3264 noirqdebug [X86-32] Disables the code which attempts to detect and 3265 disable unhandled interrupt sources. 3266 3267 no_timer_check [X86,APIC] Disables the code which tests for 3268 broken timer IRQ sources. 3269 3270 noisapnp [ISAPNP] Disables ISA PnP code. 3271 3272 noinitrd [RAM] Tells the kernel not to load any configured 3273 initial RAM disk. 3274 3275 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3276 remapping. 3277 [Deprecated - use intremap=off] 3278 3279 nointroute [IA-64] 3280 3281 noinvpcid [X86] Disable the INVPCID cpu feature. 3282 3283 nojitter [IA-64] Disables jitter checking for ITC timers. 3284 3285 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3286 3287 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3288 fault handling. 3289 3290 no-vmw-sched-clock 3291 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3292 clock and use the default one. 3293 3294 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3295 accounting. steal time is computed, but won't 3296 influence scheduler behaviour 3297 3298 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3299 3300 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3301 3302 noltlbs [PPC] Do not use large page/tlb entries for kernel 3303 lowmem mapping on PPC40x and PPC8xx 3304 3305 nomca [IA-64] Disable machine check abort handling 3306 3307 nomce [X86-32] Disable Machine Check Exception 3308 3309 nomfgpt [X86-32] Disable Multi-Function General Purpose 3310 Timer usage (for AMD Geode machines). 3311 3312 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3313 shutdown the other cpus. Instead use the REBOOT_VECTOR 3314 irq. 3315 3316 nomodule Disable module load 3317 3318 nopat [X86] Disable PAT (page attribute table extension of 3319 pagetables) support. 3320 3321 nopcid [X86-64] Disable the PCID cpu feature. 3322 3323 norandmaps Don't use address space randomization. Equivalent to 3324 echo 0 > /proc/sys/kernel/randomize_va_space 3325 3326 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3327 with UP alternatives 3328 3329 nordrand [X86] Disable kernel use of the RDRAND and 3330 RDSEED instructions even if they are supported 3331 by the processor. RDRAND and RDSEED are still 3332 available to user space applications. 3333 3334 noresume [SWSUSP] Disables resume and restores original swap 3335 space. 3336 3337 no-scroll [VGA] Disables scrollback. 3338 This is required for the Braillex ib80-piezo Braille 3339 reader made by F.H. Papenmeier (Germany). 3340 3341 nosbagart [IA-64] 3342 3343 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3344 3345 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3346 and disable the IO APIC. legacy for "maxcpus=0". 3347 3348 nosoftlockup [KNL] Disable the soft-lockup detector. 3349 3350 nosync [HW,M68K] Disables sync negotiation for all devices. 3351 3352 nowatchdog [KNL] Disable both lockup detectors, i.e. 3353 soft-lockup and NMI watchdog (hard-lockup). 3354 3355 nowb [ARM] 3356 3357 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3358 3359 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3360 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3361 Some features depend on CPU0. Known dependencies are: 3362 1. Resume from suspend/hibernate depends on CPU0. 3363 Suspend/hibernate will fail if CPU0 is offline and you 3364 need to online CPU0 before suspend/hibernate. 3365 2. PIC interrupts also depend on CPU0. CPU0 can't be 3366 removed if a PIC interrupt is detected. 3367 It's said poweroff/reboot may depend on CPU0 on some 3368 machines although I haven't seen such issues so far 3369 after CPU0 is offline on a few tested machines. 3370 If the dependencies are under your control, you can 3371 turn on cpu0_hotplug. 3372 3373 nps_mtm_hs_ctr= [KNL,ARC] 3374 This parameter sets the maximum duration, in 3375 cycles, each HW thread of the CTOP can run 3376 without interruptions, before HW switches it. 3377 The actual maximum duration is 16 times this 3378 parameter's value. 3379 Format: integer between 1 and 255 3380 Default: 255 3381 3382 nptcg= [IA-64] Override max number of concurrent global TLB 3383 purges which is reported from either PAL_VM_SUMMARY or 3384 SAL PALO. 3385 3386 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3387 could support. nr_cpus=n : n >= 1 limits the kernel to 3388 support 'n' processors. It could be larger than the 3389 number of already plugged CPU during bootup, later in 3390 runtime you can physically add extra cpu until it reaches 3391 n. So during boot up some boot time memory for per-cpu 3392 variables need be pre-allocated for later physical cpu 3393 hot plugging. 3394 3395 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3396 3397 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3398 Allowed values are enable and disable 3399 3400 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3401 'node', 'default' can be specified 3402 This can be set from sysctl after boot. 3403 See Documentation/admin-guide/sysctl/vm.rst for details. 3404 3405 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3406 See Documentation/core-api/debugging-via-ohci1394.rst for more 3407 info. 3408 3409 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3410 Rather than timing out after 20 ms if an EC 3411 command is not properly ACKed, override the length 3412 of the timeout. We have interrupts disabled while 3413 waiting for the ACK, so if this is set too high 3414 interrupts *may* be lost! 3415 3416 omap_mux= [OMAP] Override bootloader pin multiplexing. 3417 Format: <mux_mode0.mode_name=value>... 3418 For example, to override I2C bus2: 3419 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3420 3421 oprofile.timer= [HW] 3422 Use timer interrupt instead of performance counters 3423 3424 oprofile.cpu_type= Force an oprofile cpu type 3425 This might be useful if you have an older oprofile 3426 userland or if you want common events. 3427 Format: { arch_perfmon } 3428 arch_perfmon: [X86] Force use of architectural 3429 perfmon on Intel CPUs instead of the 3430 CPU specific event set. 3431 timer: [X86] Force use of architectural NMI 3432 timer mode (see also oprofile.timer 3433 for generic hr timer mode) 3434 3435 oops=panic Always panic on oopses. Default is to just kill the 3436 process, but there is a small probability of 3437 deadlocking the machine. 3438 This will also cause panics on machine check exceptions. 3439 Useful together with panic=30 to trigger a reboot. 3440 3441 page_alloc.shuffle= 3442 [KNL] Boolean flag to control whether the page allocator 3443 should randomize its free lists. The randomization may 3444 be automatically enabled if the kernel detects it is 3445 running on a platform with a direct-mapped memory-side 3446 cache, and this parameter can be used to 3447 override/disable that behavior. The state of the flag 3448 can be read from sysfs at: 3449 /sys/module/page_alloc/parameters/shuffle. 3450 3451 page_owner= [KNL] Boot-time page_owner enabling option. 3452 Storage of the information about who allocated 3453 each page is disabled in default. With this switch, 3454 we can turn it on. 3455 on: enable the feature 3456 3457 page_poison= [KNL] Boot-time parameter changing the state of 3458 poisoning on the buddy allocator, available with 3459 CONFIG_PAGE_POISONING=y. 3460 off: turn off poisoning (default) 3461 on: turn on poisoning 3462 3463 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3464 timeout > 0: seconds before rebooting 3465 timeout = 0: wait forever 3466 timeout < 0: reboot immediately 3467 Format: <timeout> 3468 3469 panic_print= Bitmask for printing system info when panic happens. 3470 User can chose combination of the following bits: 3471 bit 0: print all tasks info 3472 bit 1: print system memory info 3473 bit 2: print timer info 3474 bit 3: print locks info if CONFIG_LOCKDEP is on 3475 bit 4: print ftrace buffer 3476 bit 5: print all printk messages in buffer 3477 3478 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3479 Format: <hex>[,nousertaint] 3480 Hexadecimal bitmask representing the set of TAINT flags 3481 that will cause the kernel to panic when add_taint() is 3482 called with any of the flags in this set. 3483 The optional switch "nousertaint" can be utilized to 3484 prevent userspace forced crashes by writing to sysctl 3485 /proc/sys/kernel/tainted any flagset matching with the 3486 bitmask set on panic_on_taint. 3487 See Documentation/admin-guide/tainted-kernels.rst for 3488 extra details on the taint flags that users can pick 3489 to compose the bitmask to assign to panic_on_taint. 3490 3491 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3492 on a WARN(). 3493 3494 crash_kexec_post_notifiers 3495 Run kdump after running panic-notifiers and dumping 3496 kmsg. This only for the users who doubt kdump always 3497 succeeds in any situation. 3498 Note that this also increases risks of kdump failure, 3499 because some panic notifiers can make the crashed 3500 kernel more unstable. 3501 3502 parkbd.port= [HW] Parallel port number the keyboard adapter is 3503 connected to, default is 0. 3504 Format: <parport#> 3505 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3506 0 for XT, 1 for AT (default is AT). 3507 Format: <mode> 3508 3509 parport= [HW,PPT] Specify parallel ports. 0 disables. 3510 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3511 Use 'auto' to force the driver to use any 3512 IRQ/DMA settings detected (the default is to 3513 ignore detected IRQ/DMA settings because of 3514 possible conflicts). You can specify the base 3515 address, IRQ, and DMA settings; IRQ and DMA 3516 should be numbers, or 'auto' (for using detected 3517 settings on that particular port), or 'nofifo' 3518 (to avoid using a FIFO even if it is detected). 3519 Parallel ports are assigned in the order they 3520 are specified on the command line, starting 3521 with parport0. 3522 3523 parport_init_mode= [HW,PPT] 3524 Configure VIA parallel port to operate in 3525 a specific mode. This is necessary on Pegasos 3526 computer where firmware has no options for setting 3527 up parallel port mode and sets it to spp. 3528 Currently this function knows 686a and 8231 chips. 3529 Format: [spp|ps2|epp|ecp|ecpepp] 3530 3531 pause_on_oops= 3532 Halt all CPUs after the first oops has been printed for 3533 the specified number of seconds. This is to be used if 3534 your oopses keep scrolling off the screen. 3535 3536 pcbit= [HW,ISDN] 3537 3538 pcd. [PARIDE] 3539 See header of drivers/block/paride/pcd.c. 3540 See also Documentation/admin-guide/blockdev/paride.rst. 3541 3542 pci=option[,option...] [PCI] various PCI subsystem options. 3543 3544 Some options herein operate on a specific device 3545 or a set of devices (<pci_dev>). These are 3546 specified in one of the following formats: 3547 3548 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3549 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3550 3551 Note: the first format specifies a PCI 3552 bus/device/function address which may change 3553 if new hardware is inserted, if motherboard 3554 firmware changes, or due to changes caused 3555 by other kernel parameters. If the 3556 domain is left unspecified, it is 3557 taken to be zero. Optionally, a path 3558 to a device through multiple device/function 3559 addresses can be specified after the base 3560 address (this is more robust against 3561 renumbering issues). The second format 3562 selects devices using IDs from the 3563 configuration space which may match multiple 3564 devices in the system. 3565 3566 earlydump dump PCI config space before the kernel 3567 changes anything 3568 off [X86] don't probe for the PCI bus 3569 bios [X86-32] force use of PCI BIOS, don't access 3570 the hardware directly. Use this if your machine 3571 has a non-standard PCI host bridge. 3572 nobios [X86-32] disallow use of PCI BIOS, only direct 3573 hardware access methods are allowed. Use this 3574 if you experience crashes upon bootup and you 3575 suspect they are caused by the BIOS. 3576 conf1 [X86] Force use of PCI Configuration Access 3577 Mechanism 1 (config address in IO port 0xCF8, 3578 data in IO port 0xCFC, both 32-bit). 3579 conf2 [X86] Force use of PCI Configuration Access 3580 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3581 the function, IO port 0xCFA, also 8-bit, sets 3582 bus number. The config space is then accessed 3583 through ports 0xC000-0xCFFF). 3584 See http://wiki.osdev.org/PCI for more info 3585 on the configuration access mechanisms. 3586 noaer [PCIE] If the PCIEAER kernel config parameter is 3587 enabled, this kernel boot option can be used to 3588 disable the use of PCIE advanced error reporting. 3589 nodomains [PCI] Disable support for multiple PCI 3590 root domains (aka PCI segments, in ACPI-speak). 3591 nommconf [X86] Disable use of MMCONFIG for PCI 3592 Configuration 3593 check_enable_amd_mmconf [X86] check for and enable 3594 properly configured MMIO access to PCI 3595 config space on AMD family 10h CPU 3596 nomsi [MSI] If the PCI_MSI kernel config parameter is 3597 enabled, this kernel boot option can be used to 3598 disable the use of MSI interrupts system-wide. 3599 noioapicquirk [APIC] Disable all boot interrupt quirks. 3600 Safety option to keep boot IRQs enabled. This 3601 should never be necessary. 3602 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3603 primary IO-APIC for bridges that cannot disable 3604 boot IRQs. This fixes a source of spurious IRQs 3605 when the system masks IRQs. 3606 noioapicreroute [APIC] Disable workaround that uses the 3607 boot IRQ equivalent of an IRQ that connects to 3608 a chipset where boot IRQs cannot be disabled. 3609 The opposite of ioapicreroute. 3610 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3611 routing table. These calls are known to be buggy 3612 on several machines and they hang the machine 3613 when used, but on other computers it's the only 3614 way to get the interrupt routing table. Try 3615 this option if the kernel is unable to allocate 3616 IRQs or discover secondary PCI buses on your 3617 motherboard. 3618 rom [X86] Assign address space to expansion ROMs. 3619 Use with caution as certain devices share 3620 address decoders between ROMs and other 3621 resources. 3622 norom [X86] Do not assign address space to 3623 expansion ROMs that do not already have 3624 BIOS assigned address ranges. 3625 nobar [X86] Do not assign address space to the 3626 BARs that weren't assigned by the BIOS. 3627 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3628 assigned automatically to PCI devices. You can 3629 make the kernel exclude IRQs of your ISA cards 3630 this way. 3631 pirqaddr=0xAAAAA [X86] Specify the physical address 3632 of the PIRQ table (normally generated 3633 by the BIOS) if it is outside the 3634 F0000h-100000h range. 3635 lastbus=N [X86] Scan all buses thru bus #N. Can be 3636 useful if the kernel is unable to find your 3637 secondary buses and you want to tell it 3638 explicitly which ones they are. 3639 assign-busses [X86] Always assign all PCI bus 3640 numbers ourselves, overriding 3641 whatever the firmware may have done. 3642 usepirqmask [X86] Honor the possible IRQ mask stored 3643 in the BIOS $PIR table. This is needed on 3644 some systems with broken BIOSes, notably 3645 some HP Pavilion N5400 and Omnibook XE3 3646 notebooks. This will have no effect if ACPI 3647 IRQ routing is enabled. 3648 noacpi [X86] Do not use ACPI for IRQ routing 3649 or for PCI scanning. 3650 use_crs [X86] Use PCI host bridge window information 3651 from ACPI. On BIOSes from 2008 or later, this 3652 is enabled by default. If you need to use this, 3653 please report a bug. 3654 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3655 If you need to use this, please report a bug. 3656 routeirq Do IRQ routing for all PCI devices. 3657 This is normally done in pci_enable_device(), 3658 so this option is a temporary workaround 3659 for broken drivers that don't call it. 3660 skip_isa_align [X86] do not align io start addr, so can 3661 handle more pci cards 3662 noearly [X86] Don't do any early type 1 scanning. 3663 This might help on some broken boards which 3664 machine check when some devices' config space 3665 is read. But various workarounds are disabled 3666 and some IOMMU drivers will not work. 3667 bfsort Sort PCI devices into breadth-first order. 3668 This sorting is done to get a device 3669 order compatible with older (<= 2.4) kernels. 3670 nobfsort Don't sort PCI devices into breadth-first order. 3671 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3672 tuning and use the BIOS-configured MPS defaults. 3673 pcie_bus_safe Set every device's MPS to the largest value 3674 supported by all devices below the root complex. 3675 pcie_bus_perf Set device MPS to the largest allowable MPS 3676 based on its parent bus. Also set MRRS (Max 3677 Read Request Size) to the largest supported 3678 value (no larger than the MPS that the device 3679 or bus can support) for best performance. 3680 pcie_bus_peer2peer Set every device's MPS to 128B, which 3681 every device is guaranteed to support. This 3682 configuration allows peer-to-peer DMA between 3683 any pair of devices, possibly at the cost of 3684 reduced performance. This also guarantees 3685 that hot-added devices will work. 3686 cbiosize=nn[KMG] The fixed amount of bus space which is 3687 reserved for the CardBus bridge's IO window. 3688 The default value is 256 bytes. 3689 cbmemsize=nn[KMG] The fixed amount of bus space which is 3690 reserved for the CardBus bridge's memory 3691 window. The default value is 64 megabytes. 3692 resource_alignment= 3693 Format: 3694 [<order of align>@]<pci_dev>[; ...] 3695 Specifies alignment and device to reassign 3696 aligned memory resources. How to 3697 specify the device is described above. 3698 If <order of align> is not specified, 3699 PAGE_SIZE is used as alignment. 3700 A PCI-PCI bridge can be specified if resource 3701 windows need to be expanded. 3702 To specify the alignment for several 3703 instances of a device, the PCI vendor, 3704 device, subvendor, and subdevice may be 3705 specified, e.g., 12@pci:8086:9c22:103c:198f 3706 for 4096-byte alignment. 3707 ecrc= Enable/disable PCIe ECRC (transaction layer 3708 end-to-end CRC checking). 3709 bios: Use BIOS/firmware settings. This is the 3710 the default. 3711 off: Turn ECRC off 3712 on: Turn ECRC on. 3713 hpiosize=nn[KMG] The fixed amount of bus space which is 3714 reserved for hotplug bridge's IO window. 3715 Default size is 256 bytes. 3716 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3717 reserved for hotplug bridge's MMIO window. 3718 Default size is 2 megabytes. 3719 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3720 reserved for hotplug bridge's MMIO_PREF window. 3721 Default size is 2 megabytes. 3722 hpmemsize=nn[KMG] The fixed amount of bus space which is 3723 reserved for hotplug bridge's MMIO and 3724 MMIO_PREF window. 3725 Default size is 2 megabytes. 3726 hpbussize=nn The minimum amount of additional bus numbers 3727 reserved for buses below a hotplug bridge. 3728 Default is 1. 3729 realloc= Enable/disable reallocating PCI bridge resources 3730 if allocations done by BIOS are too small to 3731 accommodate resources required by all child 3732 devices. 3733 off: Turn realloc off 3734 on: Turn realloc on 3735 realloc same as realloc=on 3736 noari do not use PCIe ARI. 3737 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3738 do not use PCIe ATS (and IOMMU device IOTLB). 3739 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3740 only look for one device below a PCIe downstream 3741 port. 3742 big_root_window Try to add a big 64bit memory window to the PCIe 3743 root complex on AMD CPUs. Some GFX hardware 3744 can resize a BAR to allow access to all VRAM. 3745 Adding the window is slightly risky (it may 3746 conflict with unreported devices), so this 3747 taints the kernel. 3748 disable_acs_redir=<pci_dev>[; ...] 3749 Specify one or more PCI devices (in the format 3750 specified above) separated by semicolons. 3751 Each device specified will have the PCI ACS 3752 redirect capabilities forced off which will 3753 allow P2P traffic between devices through 3754 bridges without forcing it upstream. Note: 3755 this removes isolation between devices and 3756 may put more devices in an IOMMU group. 3757 force_floating [S390] Force usage of floating interrupts. 3758 nomio [S390] Do not use MIO instructions. 3759 norid [S390] ignore the RID field and force use of 3760 one PCI domain per PCI function 3761 3762 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3763 Management. 3764 off Disable ASPM. 3765 force Enable ASPM even on devices that claim not to support it. 3766 WARNING: Forcing ASPM on may cause system lockups. 3767 3768 pcie_ports= [PCIE] PCIe port services handling: 3769 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3770 even if the platform doesn't give the OS permission to 3771 use them. This may cause conflicts if the platform 3772 also tries to use these services. 3773 dpc-native Use native PCIe service for DPC only. May 3774 cause conflicts if firmware uses AER or DPC. 3775 compat Disable native PCIe services (PME, AER, DPC, PCIe 3776 hotplug). 3777 3778 pcie_port_pm= [PCIE] PCIe port power management handling: 3779 off Disable power management of all PCIe ports 3780 force Forcibly enable power management of all PCIe ports 3781 3782 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3783 nomsi Do not use MSI for native PCIe PME signaling (this makes 3784 all PCIe root ports use INTx for all services). 3785 3786 pcmv= [HW,PCMCIA] BadgePAD 4 3787 3788 pd_ignore_unused 3789 [PM] 3790 Keep all power-domains already enabled by bootloader on, 3791 even if no driver has claimed them. This is useful 3792 for debug and development, but should not be 3793 needed on a platform with proper driver support. 3794 3795 pd. [PARIDE] 3796 See Documentation/admin-guide/blockdev/paride.rst. 3797 3798 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3799 boot time. 3800 Format: { 0 | 1 } 3801 See arch/parisc/kernel/pdc_chassis.c 3802 3803 percpu_alloc= Select which percpu first chunk allocator to use. 3804 Currently supported values are "embed" and "page". 3805 Archs may support subset or none of the selections. 3806 See comments in mm/percpu.c for details on each 3807 allocator. This parameter is primarily for debugging 3808 and performance comparison. 3809 3810 pf. [PARIDE] 3811 See Documentation/admin-guide/blockdev/paride.rst. 3812 3813 pg. [PARIDE] 3814 See Documentation/admin-guide/blockdev/paride.rst. 3815 3816 pirq= [SMP,APIC] Manual mp-table setup 3817 See Documentation/x86/i386/IO-APIC.rst. 3818 3819 plip= [PPT,NET] Parallel port network link 3820 Format: { parport<nr> | timid | 0 } 3821 See also Documentation/admin-guide/parport.rst. 3822 3823 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3824 Override pmtimer IOPort with a hex value. 3825 e.g. pmtmr=0x508 3826 3827 pm_debug_messages [SUSPEND,KNL] 3828 Enable suspend/resume debug messages during boot up. 3829 3830 pnp.debug=1 [PNP] 3831 Enable PNP debug messages (depends on the 3832 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3833 via /sys/module/pnp/parameters/debug. We always show 3834 current resource usage; turning this on also shows 3835 possible settings and some assignment information. 3836 3837 pnpacpi= [ACPI] 3838 { off } 3839 3840 pnpbios= [ISAPNP] 3841 { on | off | curr | res | no-curr | no-res } 3842 3843 pnp_reserve_irq= 3844 [ISAPNP] Exclude IRQs for the autoconfiguration 3845 3846 pnp_reserve_dma= 3847 [ISAPNP] Exclude DMAs for the autoconfiguration 3848 3849 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3850 Ranges are in pairs (I/O port base and size). 3851 3852 pnp_reserve_mem= 3853 [ISAPNP] Exclude memory regions for the 3854 autoconfiguration. 3855 Ranges are in pairs (memory base and size). 3856 3857 ports= [IP_VS_FTP] IPVS ftp helper module 3858 Default is 21. 3859 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3860 may be specified. 3861 Format: <port>,<port>.... 3862 3863 powersave=off [PPC] This option disables power saving features. 3864 It specifically disables cpuidle and sets the 3865 platform machine description specific power_save 3866 function to NULL. On Idle the CPU just reduces 3867 execution priority. 3868 3869 ppc_strict_facility_enable 3870 [PPC] This option catches any kernel floating point, 3871 Altivec, VSX and SPE outside of regions specifically 3872 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3873 There is some performance impact when enabling this. 3874 3875 ppc_tm= [PPC] 3876 Format: {"off"} 3877 Disable Hardware Transactional Memory 3878 3879 print-fatal-signals= 3880 [KNL] debug: print fatal signals 3881 3882 If enabled, warn about various signal handling 3883 related application anomalies: too many signals, 3884 too many POSIX.1 timers, fatal signals causing a 3885 coredump - etc. 3886 3887 If you hit the warning due to signal overflow, 3888 you might want to try "ulimit -i unlimited". 3889 3890 default: off. 3891 3892 printk.always_kmsg_dump= 3893 Trigger kmsg_dump for cases other than kernel oops or 3894 panics 3895 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3896 default: disabled 3897 3898 printk.devkmsg={on,off,ratelimit} 3899 Control writing to /dev/kmsg. 3900 on - unlimited logging to /dev/kmsg from userspace 3901 off - logging to /dev/kmsg disabled 3902 ratelimit - ratelimit the logging 3903 Default: ratelimit 3904 3905 printk.time= Show timing data prefixed to each printk message line 3906 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3907 3908 processor.max_cstate= [HW,ACPI] 3909 Limit processor to maximum C-state 3910 max_cstate=9 overrides any DMI blacklist limit. 3911 3912 processor.nocst [HW,ACPI] 3913 Ignore the _CST method to determine C-states, 3914 instead using the legacy FADT method 3915 3916 profile= [KNL] Enable kernel profiling via /proc/profile 3917 Format: [<profiletype>,]<number> 3918 Param: <profiletype>: "schedule", "sleep", or "kvm" 3919 [defaults to kernel profiling] 3920 Param: "schedule" - profile schedule points. 3921 Param: "sleep" - profile D-state sleeping (millisecs). 3922 Requires CONFIG_SCHEDSTATS 3923 Param: "kvm" - profile VM exits. 3924 Param: <number> - step/bucket size as a power of 2 for 3925 statistical time based profiling. 3926 3927 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3928 before loading. 3929 See Documentation/admin-guide/blockdev/ramdisk.rst. 3930 3931 prot_virt= [S390] enable hosting protected virtual machines 3932 isolated from the hypervisor (if hardware supports 3933 that). 3934 Format: <bool> 3935 3936 psi= [KNL] Enable or disable pressure stall information 3937 tracking. 3938 Format: <bool> 3939 3940 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3941 probe for; one of (bare|imps|exps|lifebook|any). 3942 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3943 per second. 3944 psmouse.resetafter= [HW,MOUSE] 3945 Try to reset the device after so many bad packets 3946 (0 = never). 3947 psmouse.resolution= 3948 [HW,MOUSE] Set desired mouse resolution, in dpi. 3949 psmouse.smartscroll= 3950 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3951 0 = disabled, 1 = enabled (default). 3952 3953 pstore.backend= Specify the name of the pstore backend to use 3954 3955 pt. [PARIDE] 3956 See Documentation/admin-guide/blockdev/paride.rst. 3957 3958 pti= [X86-64] Control Page Table Isolation of user and 3959 kernel address spaces. Disabling this feature 3960 removes hardening, but improves performance of 3961 system calls and interrupts. 3962 3963 on - unconditionally enable 3964 off - unconditionally disable 3965 auto - kernel detects whether your CPU model is 3966 vulnerable to issues that PTI mitigates 3967 3968 Not specifying this option is equivalent to pti=auto. 3969 3970 nopti [X86-64] 3971 Equivalent to pti=off 3972 3973 pty.legacy_count= 3974 [KNL] Number of legacy pty's. Overwrites compiled-in 3975 default number. 3976 3977 quiet [KNL] Disable most log messages 3978 3979 r128= [HW,DRM] 3980 3981 raid= [HW,RAID] 3982 See Documentation/admin-guide/md.rst. 3983 3984 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3985 See Documentation/admin-guide/blockdev/ramdisk.rst. 3986 3987 random.trust_cpu={on,off} 3988 [KNL] Enable or disable trusting the use of the 3989 CPU's random number generator (if available) to 3990 fully seed the kernel's CRNG. Default is controlled 3991 by CONFIG_RANDOM_TRUST_CPU. 3992 3993 ras=option[,option,...] [KNL] RAS-specific options 3994 3995 cec_disable [X86] 3996 Disable the Correctable Errors Collector, 3997 see CONFIG_RAS_CEC help text. 3998 3999 rcu_nocbs= [KNL] 4000 The argument is a cpu list, as described above, 4001 except that the string "all" can be used to 4002 specify every CPU on the system. 4003 4004 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4005 the specified list of CPUs to be no-callback CPUs. 4006 Invocation of these CPUs' RCU callbacks will be 4007 offloaded to "rcuox/N" kthreads created for that 4008 purpose, where "x" is "p" for RCU-preempt, and 4009 "s" for RCU-sched, and "N" is the CPU number. 4010 This reduces OS jitter on the offloaded CPUs, 4011 which can be useful for HPC and real-time 4012 workloads. It can also improve energy efficiency 4013 for asymmetric multiprocessors. 4014 4015 rcu_nocb_poll [KNL] 4016 Rather than requiring that offloaded CPUs 4017 (specified by rcu_nocbs= above) explicitly 4018 awaken the corresponding "rcuoN" kthreads, 4019 make these kthreads poll for callbacks. 4020 This improves the real-time response for the 4021 offloaded CPUs by relieving them of the need to 4022 wake up the corresponding kthread, but degrades 4023 energy efficiency by requiring that the kthreads 4024 periodically wake up to do the polling. 4025 4026 rcutree.blimit= [KNL] 4027 Set maximum number of finished RCU callbacks to 4028 process in one batch. 4029 4030 rcutree.dump_tree= [KNL] 4031 Dump the structure of the rcu_node combining tree 4032 out at early boot. This is used for diagnostic 4033 purposes, to verify correct tree setup. 4034 4035 rcutree.gp_cleanup_delay= [KNL] 4036 Set the number of jiffies to delay each step of 4037 RCU grace-period cleanup. 4038 4039 rcutree.gp_init_delay= [KNL] 4040 Set the number of jiffies to delay each step of 4041 RCU grace-period initialization. 4042 4043 rcutree.gp_preinit_delay= [KNL] 4044 Set the number of jiffies to delay each step of 4045 RCU grace-period pre-initialization, that is, 4046 the propagation of recent CPU-hotplug changes up 4047 the rcu_node combining tree. 4048 4049 rcutree.use_softirq= [KNL] 4050 If set to zero, move all RCU_SOFTIRQ processing to 4051 per-CPU rcuc kthreads. Defaults to a non-zero 4052 value, meaning that RCU_SOFTIRQ is used by default. 4053 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4054 4055 rcutree.rcu_fanout_exact= [KNL] 4056 Disable autobalancing of the rcu_node combining 4057 tree. This is used by rcutorture, and might 4058 possibly be useful for architectures having high 4059 cache-to-cache transfer latencies. 4060 4061 rcutree.rcu_fanout_leaf= [KNL] 4062 Change the number of CPUs assigned to each 4063 leaf rcu_node structure. Useful for very 4064 large systems, which will choose the value 64, 4065 and for NUMA systems with large remote-access 4066 latencies, which will choose a value aligned 4067 with the appropriate hardware boundaries. 4068 4069 rcutree.rcu_min_cached_objs= [KNL] 4070 Minimum number of objects which are cached and 4071 maintained per one CPU. Object size is equal 4072 to PAGE_SIZE. The cache allows to reduce the 4073 pressure to page allocator, also it makes the 4074 whole algorithm to behave better in low memory 4075 condition. 4076 4077 rcutree.jiffies_till_first_fqs= [KNL] 4078 Set delay from grace-period initialization to 4079 first attempt to force quiescent states. 4080 Units are jiffies, minimum value is zero, 4081 and maximum value is HZ. 4082 4083 rcutree.jiffies_till_next_fqs= [KNL] 4084 Set delay between subsequent attempts to force 4085 quiescent states. Units are jiffies, minimum 4086 value is one, and maximum value is HZ. 4087 4088 rcutree.jiffies_till_sched_qs= [KNL] 4089 Set required age in jiffies for a 4090 given grace period before RCU starts 4091 soliciting quiescent-state help from 4092 rcu_note_context_switch() and cond_resched(). 4093 If not specified, the kernel will calculate 4094 a value based on the most recent settings 4095 of rcutree.jiffies_till_first_fqs 4096 and rcutree.jiffies_till_next_fqs. 4097 This calculated value may be viewed in 4098 rcutree.jiffies_to_sched_qs. Any attempt to set 4099 rcutree.jiffies_to_sched_qs will be cheerfully 4100 overwritten. 4101 4102 rcutree.kthread_prio= [KNL,BOOT] 4103 Set the SCHED_FIFO priority of the RCU per-CPU 4104 kthreads (rcuc/N). This value is also used for 4105 the priority of the RCU boost threads (rcub/N) 4106 and for the RCU grace-period kthreads (rcu_bh, 4107 rcu_preempt, and rcu_sched). If RCU_BOOST is 4108 set, valid values are 1-99 and the default is 1 4109 (the least-favored priority). Otherwise, when 4110 RCU_BOOST is not set, valid values are 0-99 and 4111 the default is zero (non-realtime operation). 4112 4113 rcutree.rcu_nocb_gp_stride= [KNL] 4114 Set the number of NOCB callback kthreads in 4115 each group, which defaults to the square root 4116 of the number of CPUs. Larger numbers reduce 4117 the wakeup overhead on the global grace-period 4118 kthread, but increases that same overhead on 4119 each group's NOCB grace-period kthread. 4120 4121 rcutree.qhimark= [KNL] 4122 Set threshold of queued RCU callbacks beyond which 4123 batch limiting is disabled. 4124 4125 rcutree.qlowmark= [KNL] 4126 Set threshold of queued RCU callbacks below which 4127 batch limiting is re-enabled. 4128 4129 rcutree.qovld= [KNL] 4130 Set threshold of queued RCU callbacks beyond which 4131 RCU's force-quiescent-state scan will aggressively 4132 enlist help from cond_resched() and sched IPIs to 4133 help CPUs more quickly reach quiescent states. 4134 Set to less than zero to make this be set based 4135 on rcutree.qhimark at boot time and to zero to 4136 disable more aggressive help enlistment. 4137 4138 rcutree.rcu_idle_gp_delay= [KNL] 4139 Set wakeup interval for idle CPUs that have 4140 RCU callbacks (RCU_FAST_NO_HZ=y). 4141 4142 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4143 Set wakeup interval for idle CPUs that have 4144 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4145 Lazy RCU callbacks are those which RCU can 4146 prove do nothing more than free memory. 4147 4148 rcutree.rcu_kick_kthreads= [KNL] 4149 Cause the grace-period kthread to get an extra 4150 wake_up() if it sleeps three times longer than 4151 it should at force-quiescent-state time. 4152 This wake_up() will be accompanied by a 4153 WARN_ONCE() splat and an ftrace_dump(). 4154 4155 rcutree.sysrq_rcu= [KNL] 4156 Commandeer a sysrq key to dump out Tree RCU's 4157 rcu_node tree with an eye towards determining 4158 why a new grace period has not yet started. 4159 4160 rcuperf.gp_async= [KNL] 4161 Measure performance of asynchronous 4162 grace-period primitives such as call_rcu(). 4163 4164 rcuperf.gp_async_max= [KNL] 4165 Specify the maximum number of outstanding 4166 callbacks per writer thread. When a writer 4167 thread exceeds this limit, it invokes the 4168 corresponding flavor of rcu_barrier() to allow 4169 previously posted callbacks to drain. 4170 4171 rcuperf.gp_exp= [KNL] 4172 Measure performance of expedited synchronous 4173 grace-period primitives. 4174 4175 rcuperf.holdoff= [KNL] 4176 Set test-start holdoff period. The purpose of 4177 this parameter is to delay the start of the 4178 test until boot completes in order to avoid 4179 interference. 4180 4181 rcuperf.kfree_rcu_test= [KNL] 4182 Set to measure performance of kfree_rcu() flooding. 4183 4184 rcuperf.kfree_nthreads= [KNL] 4185 The number of threads running loops of kfree_rcu(). 4186 4187 rcuperf.kfree_alloc_num= [KNL] 4188 Number of allocations and frees done in an iteration. 4189 4190 rcuperf.kfree_loops= [KNL] 4191 Number of loops doing rcuperf.kfree_alloc_num number 4192 of allocations and frees. 4193 4194 rcuperf.nreaders= [KNL] 4195 Set number of RCU readers. The value -1 selects 4196 N, where N is the number of CPUs. A value 4197 "n" less than -1 selects N-n+1, where N is again 4198 the number of CPUs. For example, -2 selects N 4199 (the number of CPUs), -3 selects N+1, and so on. 4200 A value of "n" less than or equal to -N selects 4201 a single reader. 4202 4203 rcuperf.nwriters= [KNL] 4204 Set number of RCU writers. The values operate 4205 the same as for rcuperf.nreaders. 4206 N, where N is the number of CPUs 4207 4208 rcuperf.perf_type= [KNL] 4209 Specify the RCU implementation to test. 4210 4211 rcuperf.shutdown= [KNL] 4212 Shut the system down after performance tests 4213 complete. This is useful for hands-off automated 4214 testing. 4215 4216 rcuperf.verbose= [KNL] 4217 Enable additional printk() statements. 4218 4219 rcuperf.writer_holdoff= [KNL] 4220 Write-side holdoff between grace periods, 4221 in microseconds. The default of zero says 4222 no holdoff. 4223 4224 rcutorture.fqs_duration= [KNL] 4225 Set duration of force_quiescent_state bursts 4226 in microseconds. 4227 4228 rcutorture.fqs_holdoff= [KNL] 4229 Set holdoff time within force_quiescent_state bursts 4230 in microseconds. 4231 4232 rcutorture.fqs_stutter= [KNL] 4233 Set wait time between force_quiescent_state bursts 4234 in seconds. 4235 4236 rcutorture.fwd_progress= [KNL] 4237 Enable RCU grace-period forward-progress testing 4238 for the types of RCU supporting this notion. 4239 4240 rcutorture.fwd_progress_div= [KNL] 4241 Specify the fraction of a CPU-stall-warning 4242 period to do tight-loop forward-progress testing. 4243 4244 rcutorture.fwd_progress_holdoff= [KNL] 4245 Number of seconds to wait between successive 4246 forward-progress tests. 4247 4248 rcutorture.fwd_progress_need_resched= [KNL] 4249 Enclose cond_resched() calls within checks for 4250 need_resched() during tight-loop forward-progress 4251 testing. 4252 4253 rcutorture.gp_cond= [KNL] 4254 Use conditional/asynchronous update-side 4255 primitives, if available. 4256 4257 rcutorture.gp_exp= [KNL] 4258 Use expedited update-side primitives, if available. 4259 4260 rcutorture.gp_normal= [KNL] 4261 Use normal (non-expedited) asynchronous 4262 update-side primitives, if available. 4263 4264 rcutorture.gp_sync= [KNL] 4265 Use normal (non-expedited) synchronous 4266 update-side primitives, if available. If all 4267 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4268 rcutorture.gp_normal=, and rcutorture.gp_sync= 4269 are zero, rcutorture acts as if is interpreted 4270 they are all non-zero. 4271 4272 rcutorture.n_barrier_cbs= [KNL] 4273 Set callbacks/threads for rcu_barrier() testing. 4274 4275 rcutorture.nfakewriters= [KNL] 4276 Set number of concurrent RCU writers. These just 4277 stress RCU, they don't participate in the actual 4278 test, hence the "fake". 4279 4280 rcutorture.nreaders= [KNL] 4281 Set number of RCU readers. The value -1 selects 4282 N-1, where N is the number of CPUs. A value 4283 "n" less than -1 selects N-n-2, where N is again 4284 the number of CPUs. For example, -2 selects N 4285 (the number of CPUs), -3 selects N+1, and so on. 4286 4287 rcutorture.object_debug= [KNL] 4288 Enable debug-object double-call_rcu() testing. 4289 4290 rcutorture.onoff_holdoff= [KNL] 4291 Set time (s) after boot for CPU-hotplug testing. 4292 4293 rcutorture.onoff_interval= [KNL] 4294 Set time (jiffies) between CPU-hotplug operations, 4295 or zero to disable CPU-hotplug testing. 4296 4297 rcutorture.read_exit= [KNL] 4298 Set the number of read-then-exit kthreads used 4299 to test the interaction of RCU updaters and 4300 task-exit processing. 4301 4302 rcutorture.read_exit_burst= [KNL] 4303 The number of times in a given read-then-exit 4304 episode that a set of read-then-exit kthreads 4305 is spawned. 4306 4307 rcutorture.read_exit_delay= [KNL] 4308 The delay, in seconds, between successive 4309 read-then-exit testing episodes. 4310 4311 rcutorture.shuffle_interval= [KNL] 4312 Set task-shuffle interval (s). Shuffling tasks 4313 allows some CPUs to go into dyntick-idle mode 4314 during the rcutorture test. 4315 4316 rcutorture.shutdown_secs= [KNL] 4317 Set time (s) after boot system shutdown. This 4318 is useful for hands-off automated testing. 4319 4320 rcutorture.stall_cpu= [KNL] 4321 Duration of CPU stall (s) to test RCU CPU stall 4322 warnings, zero to disable. 4323 4324 rcutorture.stall_cpu_block= [KNL] 4325 Sleep while stalling if set. This will result 4326 in warnings from preemptible RCU in addition 4327 to any other stall-related activity. 4328 4329 rcutorture.stall_cpu_holdoff= [KNL] 4330 Time to wait (s) after boot before inducing stall. 4331 4332 rcutorture.stall_cpu_irqsoff= [KNL] 4333 Disable interrupts while stalling if set. 4334 4335 rcutorture.stall_gp_kthread= [KNL] 4336 Duration (s) of forced sleep within RCU 4337 grace-period kthread to test RCU CPU stall 4338 warnings, zero to disable. If both stall_cpu 4339 and stall_gp_kthread are specified, the 4340 kthread is starved first, then the CPU. 4341 4342 rcutorture.stat_interval= [KNL] 4343 Time (s) between statistics printk()s. 4344 4345 rcutorture.stutter= [KNL] 4346 Time (s) to stutter testing, for example, specifying 4347 five seconds causes the test to run for five seconds, 4348 wait for five seconds, and so on. This tests RCU's 4349 ability to transition abruptly to and from idle. 4350 4351 rcutorture.test_boost= [KNL] 4352 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4353 "Maybe" means test if the RCU implementation 4354 under test support RCU priority boosting. 4355 4356 rcutorture.test_boost_duration= [KNL] 4357 Duration (s) of each individual boost test. 4358 4359 rcutorture.test_boost_interval= [KNL] 4360 Interval (s) between each boost test. 4361 4362 rcutorture.test_no_idle_hz= [KNL] 4363 Test RCU's dyntick-idle handling. See also the 4364 rcutorture.shuffle_interval parameter. 4365 4366 rcutorture.torture_type= [KNL] 4367 Specify the RCU implementation to test. 4368 4369 rcutorture.verbose= [KNL] 4370 Enable additional printk() statements. 4371 4372 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4373 Dump ftrace buffer after reporting RCU CPU 4374 stall warning. 4375 4376 rcupdate.rcu_cpu_stall_suppress= [KNL] 4377 Suppress RCU CPU stall warning messages. 4378 4379 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4380 Suppress RCU CPU stall warning messages and 4381 rcutorture writer stall warnings that occur 4382 during early boot, that is, during the time 4383 before the init task is spawned. 4384 4385 rcupdate.rcu_cpu_stall_timeout= [KNL] 4386 Set timeout for RCU CPU stall warning messages. 4387 4388 rcupdate.rcu_expedited= [KNL] 4389 Use expedited grace-period primitives, for 4390 example, synchronize_rcu_expedited() instead 4391 of synchronize_rcu(). This reduces latency, 4392 but can increase CPU utilization, degrade 4393 real-time latency, and degrade energy efficiency. 4394 No effect on CONFIG_TINY_RCU kernels. 4395 4396 rcupdate.rcu_normal= [KNL] 4397 Use only normal grace-period primitives, 4398 for example, synchronize_rcu() instead of 4399 synchronize_rcu_expedited(). This improves 4400 real-time latency, CPU utilization, and 4401 energy efficiency, but can expose users to 4402 increased grace-period latency. This parameter 4403 overrides rcupdate.rcu_expedited. No effect on 4404 CONFIG_TINY_RCU kernels. 4405 4406 rcupdate.rcu_normal_after_boot= [KNL] 4407 Once boot has completed (that is, after 4408 rcu_end_inkernel_boot() has been invoked), use 4409 only normal grace-period primitives. No effect 4410 on CONFIG_TINY_RCU kernels. 4411 4412 rcupdate.rcu_task_ipi_delay= [KNL] 4413 Set time in jiffies during which RCU tasks will 4414 avoid sending IPIs, starting with the beginning 4415 of a given grace period. Setting a large 4416 number avoids disturbing real-time workloads, 4417 but lengthens grace periods. 4418 4419 rcupdate.rcu_task_stall_timeout= [KNL] 4420 Set timeout in jiffies for RCU task stall warning 4421 messages. Disable with a value less than or equal 4422 to zero. 4423 4424 rcupdate.rcu_self_test= [KNL] 4425 Run the RCU early boot self tests 4426 4427 rdinit= [KNL] 4428 Format: <full_path> 4429 Run specified binary instead of /init from the ramdisk, 4430 used for early userspace startup. See initrd. 4431 4432 rdrand= [X86] 4433 force - Override the decision by the kernel to hide the 4434 advertisement of RDRAND support (this affects 4435 certain AMD processors because of buggy BIOS 4436 support, specifically around the suspend/resume 4437 path). 4438 4439 rdt= [HW,X86,RDT] 4440 Turn on/off individual RDT features. List is: 4441 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4442 mba. 4443 E.g. to turn on cmt and turn off mba use: 4444 rdt=cmt,!mba 4445 4446 reboot= [KNL] 4447 Format (x86 or x86_64): 4448 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4449 [[,]s[mp]#### \ 4450 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4451 [[,]f[orce] 4452 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4453 (prefix with 'panic_' to set mode for panic 4454 reboot only), 4455 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4456 reboot_force is either force or not specified, 4457 reboot_cpu is s[mp]#### with #### being the processor 4458 to be used for rebooting. 4459 4460 refscale.holdoff= [KNL] 4461 Set test-start holdoff period. The purpose of 4462 this parameter is to delay the start of the 4463 test until boot completes in order to avoid 4464 interference. 4465 4466 refscale.loops= [KNL] 4467 Set the number of loops over the synchronization 4468 primitive under test. Increasing this number 4469 reduces noise due to loop start/end overhead, 4470 but the default has already reduced the per-pass 4471 noise to a handful of picoseconds on ca. 2020 4472 x86 laptops. 4473 4474 refscale.nreaders= [KNL] 4475 Set number of readers. The default value of -1 4476 selects N, where N is roughly 75% of the number 4477 of CPUs. A value of zero is an interesting choice. 4478 4479 refscale.nruns= [KNL] 4480 Set number of runs, each of which is dumped onto 4481 the console log. 4482 4483 refscale.readdelay= [KNL] 4484 Set the read-side critical-section duration, 4485 measured in microseconds. 4486 4487 refscale.scale_type= [KNL] 4488 Specify the read-protection implementation to test. 4489 4490 refscale.shutdown= [KNL] 4491 Shut down the system at the end of the performance 4492 test. This defaults to 1 (shut it down) when 4493 rcuperf is built into the kernel and to 0 (leave 4494 it running) when rcuperf is built as a module. 4495 4496 refscale.verbose= [KNL] 4497 Enable additional printk() statements. 4498 4499 relax_domain_level= 4500 [KNL, SMP] Set scheduler's default relax_domain_level. 4501 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4502 4503 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4504 Format: <base1>,<size1>[,<base2>,<size2>,...] 4505 Reserve I/O ports or memory so the kernel won't use 4506 them. If <base> is less than 0x10000, the region 4507 is assumed to be I/O ports; otherwise it is memory. 4508 4509 reservetop= [X86-32] 4510 Format: nn[KMG] 4511 Reserves a hole at the top of the kernel virtual 4512 address space. 4513 4514 reservelow= [X86] 4515 Format: nn[K] 4516 Set the amount of memory to reserve for BIOS at 4517 the bottom of the address space. 4518 4519 reset_devices [KNL] Force drivers to reset the underlying device 4520 during initialization. 4521 4522 resume= [SWSUSP] 4523 Specify the partition device for software suspend 4524 Format: 4525 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4526 4527 resume_offset= [SWSUSP] 4528 Specify the offset from the beginning of the partition 4529 given by "resume=" at which the swap header is located, 4530 in <PAGE_SIZE> units (needed only for swap files). 4531 See Documentation/power/swsusp-and-swap-files.rst 4532 4533 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4534 read the resume files 4535 4536 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4537 Useful for devices that are detected asynchronously 4538 (e.g. USB and MMC devices). 4539 4540 hibernate= [HIBERNATION] 4541 noresume Don't check if there's a hibernation image 4542 present during boot. 4543 nocompress Don't compress/decompress hibernation images. 4544 no Disable hibernation and resume. 4545 protect_image Turn on image protection during restoration 4546 (that will set all pages holding image data 4547 during restoration read-only). 4548 4549 retain_initrd [RAM] Keep initrd memory after extraction 4550 4551 rfkill.default_state= 4552 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4553 etc. communication is blocked by default. 4554 1 Unblocked. 4555 4556 rfkill.master_switch_mode= 4557 0 The "airplane mode" button does nothing. 4558 1 The "airplane mode" button toggles between everything 4559 blocked and the previous configuration. 4560 2 The "airplane mode" button toggles between everything 4561 blocked and everything unblocked. 4562 4563 rhash_entries= [KNL,NET] 4564 Set number of hash buckets for route cache 4565 4566 ring3mwait=disable 4567 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4568 CPUs. 4569 4570 ro [KNL] Mount root device read-only on boot 4571 4572 rodata= [KNL] 4573 on Mark read-only kernel memory as read-only (default). 4574 off Leave read-only kernel memory writable for debugging. 4575 4576 rockchip.usb_uart 4577 Enable the uart passthrough on the designated usb port 4578 on Rockchip SoCs. When active, the signals of the 4579 debug-uart get routed to the D+ and D- pins of the usb 4580 port and the regular usb controller gets disabled. 4581 4582 root= [KNL] Root filesystem 4583 See name_to_dev_t comment in init/do_mounts.c. 4584 4585 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4586 mount the root filesystem 4587 4588 rootflags= [KNL] Set root filesystem mount option string 4589 4590 rootfstype= [KNL] Set root filesystem type 4591 4592 rootwait [KNL] Wait (indefinitely) for root device to show up. 4593 Useful for devices that are detected asynchronously 4594 (e.g. USB and MMC devices). 4595 4596 rproc_mem=nn[KMG][@address] 4597 [KNL,ARM,CMA] Remoteproc physical memory block. 4598 Memory area to be used by remote processor image, 4599 managed by CMA. 4600 4601 rw [KNL] Mount root device read-write on boot 4602 4603 S [KNL] Run init in single mode 4604 4605 s390_iommu= [HW,S390] 4606 Set s390 IOTLB flushing mode 4607 strict 4608 With strict flushing every unmap operation will result in 4609 an IOTLB flush. Default is lazy flushing before reuse, 4610 which is faster. 4611 4612 sa1100ir [NET] 4613 See drivers/net/irda/sa1100_ir.c. 4614 4615 sbni= [NET] Granch SBNI12 leased line adapter 4616 4617 sched_debug [KNL] Enables verbose scheduler debug messages. 4618 4619 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4620 Allowed values are enable and disable. This feature 4621 incurs a small amount of overhead in the scheduler 4622 but is useful for debugging and performance tuning. 4623 4624 sched_thermal_decay_shift= 4625 [KNL, SMP] Set a decay shift for scheduler thermal 4626 pressure signal. Thermal pressure signal follows the 4627 default decay period of other scheduler pelt 4628 signals(usually 32 ms but configurable). Setting 4629 sched_thermal_decay_shift will left shift the decay 4630 period for the thermal pressure signal by the shift 4631 value. 4632 i.e. with the default pelt decay period of 32 ms 4633 sched_thermal_decay_shift thermal pressure decay pr 4634 1 64 ms 4635 2 128 ms 4636 and so on. 4637 Format: integer between 0 and 10 4638 Default is 0. 4639 4640 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4641 xtime_lock contention on larger systems, and/or RCU lock 4642 contention on all systems with CONFIG_MAXSMP set. 4643 Format: { "0" | "1" } 4644 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4645 1 -- enable. 4646 Note: increases power consumption, thus should only be 4647 enabled if running jitter sensitive (HPC/RT) workloads. 4648 4649 security= [SECURITY] Choose a legacy "major" security module to 4650 enable at boot. This has been deprecated by the 4651 "lsm=" parameter. 4652 4653 selinux= [SELINUX] Disable or enable SELinux at boot time. 4654 Format: { "0" | "1" } 4655 See security/selinux/Kconfig help text. 4656 0 -- disable. 4657 1 -- enable. 4658 Default value is 1. 4659 4660 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4661 Format: { "0" | "1" } 4662 See security/apparmor/Kconfig help text 4663 0 -- disable. 4664 1 -- enable. 4665 Default value is set via kernel config option. 4666 4667 serialnumber [BUGS=X86-32] 4668 4669 shapers= [NET] 4670 Maximal number of shapers. 4671 4672 simeth= [IA-64] 4673 simscsi= 4674 4675 slram= [HW,MTD] 4676 4677 slab_nomerge [MM] 4678 Disable merging of slabs with similar size. May be 4679 necessary if there is some reason to distinguish 4680 allocs to different slabs, especially in hardened 4681 environments where the risk of heap overflows and 4682 layout control by attackers can usually be 4683 frustrated by disabling merging. This will reduce 4684 most of the exposure of a heap attack to a single 4685 cache (risks via metadata attacks are mostly 4686 unchanged). Debug options disable merging on their 4687 own. 4688 For more information see Documentation/vm/slub.rst. 4689 4690 slab_max_order= [MM, SLAB] 4691 Determines the maximum allowed order for slabs. 4692 A high setting may cause OOMs due to memory 4693 fragmentation. Defaults to 1 for systems with 4694 more than 32MB of RAM, 0 otherwise. 4695 4696 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4697 Enabling slub_debug allows one to determine the 4698 culprit if slab objects become corrupted. Enabling 4699 slub_debug can create guard zones around objects and 4700 may poison objects when not in use. Also tracks the 4701 last alloc / free. For more information see 4702 Documentation/vm/slub.rst. 4703 4704 slub_memcg_sysfs= [MM, SLUB] 4705 Determines whether to enable sysfs directories for 4706 memory cgroup sub-caches. 1 to enable, 0 to disable. 4707 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4708 Enabling this can lead to a very high number of debug 4709 directories and files being created under 4710 /sys/kernel/slub. 4711 4712 slub_max_order= [MM, SLUB] 4713 Determines the maximum allowed order for slabs. 4714 A high setting may cause OOMs due to memory 4715 fragmentation. For more information see 4716 Documentation/vm/slub.rst. 4717 4718 slub_min_objects= [MM, SLUB] 4719 The minimum number of objects per slab. SLUB will 4720 increase the slab order up to slub_max_order to 4721 generate a sufficiently large slab able to contain 4722 the number of objects indicated. The higher the number 4723 of objects the smaller the overhead of tracking slabs 4724 and the less frequently locks need to be acquired. 4725 For more information see Documentation/vm/slub.rst. 4726 4727 slub_min_order= [MM, SLUB] 4728 Determines the minimum page order for slabs. Must be 4729 lower than slub_max_order. 4730 For more information see Documentation/vm/slub.rst. 4731 4732 slub_nomerge [MM, SLUB] 4733 Same with slab_nomerge. This is supported for legacy. 4734 See slab_nomerge for more information. 4735 4736 smart2= [HW] 4737 Format: <io1>[,<io2>[,...,<io8>]] 4738 4739 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4740 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4741 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4742 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4743 smsc-ircc2.ircc_irq= [HW] IRQ line 4744 smsc-ircc2.ircc_dma= [HW] DMA channel 4745 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4746 0: Toshiba Satellite 1800 (GP data pin select) 4747 1: Fast pin select (default) 4748 2: ATC IRMode 4749 4750 smt [KNL,S390] Set the maximum number of threads (logical 4751 CPUs) to use per physical CPU on systems capable of 4752 symmetric multithreading (SMT). Will be capped to the 4753 actual hardware limit. 4754 Format: <integer> 4755 Default: -1 (no limit) 4756 4757 softlockup_panic= 4758 [KNL] Should the soft-lockup detector generate panics. 4759 Format: 0 | 1 4760 4761 A value of 1 instructs the soft-lockup detector 4762 to panic the machine when a soft-lockup occurs. It is 4763 also controlled by the kernel.softlockup_panic sysctl 4764 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4765 respective build-time switch to that functionality. 4766 4767 softlockup_all_cpu_backtrace= 4768 [KNL] Should the soft-lockup detector generate 4769 backtraces on all cpus. 4770 Format: 0 | 1 4771 4772 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4773 See Documentation/admin-guide/laptops/sonypi.rst 4774 4775 spectre_v2= [X86] Control mitigation of Spectre variant 2 4776 (indirect branch speculation) vulnerability. 4777 The default operation protects the kernel from 4778 user space attacks. 4779 4780 on - unconditionally enable, implies 4781 spectre_v2_user=on 4782 off - unconditionally disable, implies 4783 spectre_v2_user=off 4784 auto - kernel detects whether your CPU model is 4785 vulnerable 4786 4787 Selecting 'on' will, and 'auto' may, choose a 4788 mitigation method at run time according to the 4789 CPU, the available microcode, the setting of the 4790 CONFIG_RETPOLINE configuration option, and the 4791 compiler with which the kernel was built. 4792 4793 Selecting 'on' will also enable the mitigation 4794 against user space to user space task attacks. 4795 4796 Selecting 'off' will disable both the kernel and 4797 the user space protections. 4798 4799 Specific mitigations can also be selected manually: 4800 4801 retpoline - replace indirect branches 4802 retpoline,generic - google's original retpoline 4803 retpoline,amd - AMD-specific minimal thunk 4804 4805 Not specifying this option is equivalent to 4806 spectre_v2=auto. 4807 4808 spectre_v2_user= 4809 [X86] Control mitigation of Spectre variant 2 4810 (indirect branch speculation) vulnerability between 4811 user space tasks 4812 4813 on - Unconditionally enable mitigations. Is 4814 enforced by spectre_v2=on 4815 4816 off - Unconditionally disable mitigations. Is 4817 enforced by spectre_v2=off 4818 4819 prctl - Indirect branch speculation is enabled, 4820 but mitigation can be enabled via prctl 4821 per thread. The mitigation control state 4822 is inherited on fork. 4823 4824 prctl,ibpb 4825 - Like "prctl" above, but only STIBP is 4826 controlled per thread. IBPB is issued 4827 always when switching between different user 4828 space processes. 4829 4830 seccomp 4831 - Same as "prctl" above, but all seccomp 4832 threads will enable the mitigation unless 4833 they explicitly opt out. 4834 4835 seccomp,ibpb 4836 - Like "seccomp" above, but only STIBP is 4837 controlled per thread. IBPB is issued 4838 always when switching between different 4839 user space processes. 4840 4841 auto - Kernel selects the mitigation depending on 4842 the available CPU features and vulnerability. 4843 4844 Default mitigation: 4845 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4846 4847 Not specifying this option is equivalent to 4848 spectre_v2_user=auto. 4849 4850 spec_store_bypass_disable= 4851 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4852 (Speculative Store Bypass vulnerability) 4853 4854 Certain CPUs are vulnerable to an exploit against a 4855 a common industry wide performance optimization known 4856 as "Speculative Store Bypass" in which recent stores 4857 to the same memory location may not be observed by 4858 later loads during speculative execution. The idea 4859 is that such stores are unlikely and that they can 4860 be detected prior to instruction retirement at the 4861 end of a particular speculation execution window. 4862 4863 In vulnerable processors, the speculatively forwarded 4864 store can be used in a cache side channel attack, for 4865 example to read memory to which the attacker does not 4866 directly have access (e.g. inside sandboxed code). 4867 4868 This parameter controls whether the Speculative Store 4869 Bypass optimization is used. 4870 4871 On x86 the options are: 4872 4873 on - Unconditionally disable Speculative Store Bypass 4874 off - Unconditionally enable Speculative Store Bypass 4875 auto - Kernel detects whether the CPU model contains an 4876 implementation of Speculative Store Bypass and 4877 picks the most appropriate mitigation. If the 4878 CPU is not vulnerable, "off" is selected. If the 4879 CPU is vulnerable the default mitigation is 4880 architecture and Kconfig dependent. See below. 4881 prctl - Control Speculative Store Bypass per thread 4882 via prctl. Speculative Store Bypass is enabled 4883 for a process by default. The state of the control 4884 is inherited on fork. 4885 seccomp - Same as "prctl" above, but all seccomp threads 4886 will disable SSB unless they explicitly opt out. 4887 4888 Default mitigations: 4889 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4890 4891 On powerpc the options are: 4892 4893 on,auto - On Power8 and Power9 insert a store-forwarding 4894 barrier on kernel entry and exit. On Power7 4895 perform a software flush on kernel entry and 4896 exit. 4897 off - No action. 4898 4899 Not specifying this option is equivalent to 4900 spec_store_bypass_disable=auto. 4901 4902 spia_io_base= [HW,MTD] 4903 spia_fio_base= 4904 spia_pedr= 4905 spia_peddr= 4906 4907 split_lock_detect= 4908 [X86] Enable split lock detection 4909 4910 When enabled (and if hardware support is present), atomic 4911 instructions that access data across cache line 4912 boundaries will result in an alignment check exception. 4913 4914 off - not enabled 4915 4916 warn - the kernel will emit rate limited warnings 4917 about applications triggering the #AC 4918 exception. This mode is the default on CPUs 4919 that supports split lock detection. 4920 4921 fatal - the kernel will send SIGBUS to applications 4922 that trigger the #AC exception. 4923 4924 If an #AC exception is hit in the kernel or in 4925 firmware (i.e. not while executing in user mode) 4926 the kernel will oops in either "warn" or "fatal" 4927 mode. 4928 4929 srbds= [X86,INTEL] 4930 Control the Special Register Buffer Data Sampling 4931 (SRBDS) mitigation. 4932 4933 Certain CPUs are vulnerable to an MDS-like 4934 exploit which can leak bits from the random 4935 number generator. 4936 4937 By default, this issue is mitigated by 4938 microcode. However, the microcode fix can cause 4939 the RDRAND and RDSEED instructions to become 4940 much slower. Among other effects, this will 4941 result in reduced throughput from /dev/urandom. 4942 4943 The microcode mitigation can be disabled with 4944 the following option: 4945 4946 off: Disable mitigation and remove 4947 performance impact to RDRAND and RDSEED 4948 4949 srcutree.counter_wrap_check [KNL] 4950 Specifies how frequently to check for 4951 grace-period sequence counter wrap for the 4952 srcu_data structure's ->srcu_gp_seq_needed field. 4953 The greater the number of bits set in this kernel 4954 parameter, the less frequently counter wrap will 4955 be checked for. Note that the bottom two bits 4956 are ignored. 4957 4958 srcutree.exp_holdoff [KNL] 4959 Specifies how many nanoseconds must elapse 4960 since the end of the last SRCU grace period for 4961 a given srcu_struct until the next normal SRCU 4962 grace period will be considered for automatic 4963 expediting. Set to zero to disable automatic 4964 expediting. 4965 4966 ssbd= [ARM64,HW] 4967 Speculative Store Bypass Disable control 4968 4969 On CPUs that are vulnerable to the Speculative 4970 Store Bypass vulnerability and offer a 4971 firmware based mitigation, this parameter 4972 indicates how the mitigation should be used: 4973 4974 force-on: Unconditionally enable mitigation for 4975 for both kernel and userspace 4976 force-off: Unconditionally disable mitigation for 4977 for both kernel and userspace 4978 kernel: Always enable mitigation in the 4979 kernel, and offer a prctl interface 4980 to allow userspace to register its 4981 interest in being mitigated too. 4982 4983 stack_guard_gap= [MM] 4984 override the default stack gap protection. The value 4985 is in page units and it defines how many pages prior 4986 to (for stacks growing down) resp. after (for stacks 4987 growing up) the main stack are reserved for no other 4988 mapping. Default value is 256 pages. 4989 4990 stacktrace [FTRACE] 4991 Enabled the stack tracer on boot up. 4992 4993 stacktrace_filter=[function-list] 4994 [FTRACE] Limit the functions that the stack tracer 4995 will trace at boot up. function-list is a comma separated 4996 list of functions. This list can be changed at run 4997 time by the stack_trace_filter file in the debugfs 4998 tracing directory. Note, this enables stack tracing 4999 and the stacktrace above is not needed. 5000 5001 sti= [PARISC,HW] 5002 Format: <num> 5003 Set the STI (builtin display/keyboard on the HP-PARISC 5004 machines) console (graphic card) which should be used 5005 as the initial boot-console. 5006 See also comment in drivers/video/console/sticore.c. 5007 5008 sti_font= [HW] 5009 See comment in drivers/video/console/sticore.c. 5010 5011 stifb= [HW] 5012 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5013 5014 sunrpc.min_resvport= 5015 sunrpc.max_resvport= 5016 [NFS,SUNRPC] 5017 SunRPC servers often require that client requests 5018 originate from a privileged port (i.e. a port in the 5019 range 0 < portnr < 1024). 5020 An administrator who wishes to reserve some of these 5021 ports for other uses may adjust the range that the 5022 kernel's sunrpc client considers to be privileged 5023 using these two parameters to set the minimum and 5024 maximum port values. 5025 5026 sunrpc.svc_rpc_per_connection_limit= 5027 [NFS,SUNRPC] 5028 Limit the number of requests that the server will 5029 process in parallel from a single connection. 5030 The default value is 0 (no limit). 5031 5032 sunrpc.pool_mode= 5033 [NFS] 5034 Control how the NFS server code allocates CPUs to 5035 service thread pools. Depending on how many NICs 5036 you have and where their interrupts are bound, this 5037 option will affect which CPUs will do NFS serving. 5038 Note: this parameter cannot be changed while the 5039 NFS server is running. 5040 5041 auto the server chooses an appropriate mode 5042 automatically using heuristics 5043 global a single global pool contains all CPUs 5044 percpu one pool for each CPU 5045 pernode one pool for each NUMA node (equivalent 5046 to global on non-NUMA machines) 5047 5048 sunrpc.tcp_slot_table_entries= 5049 sunrpc.udp_slot_table_entries= 5050 [NFS,SUNRPC] 5051 Sets the upper limit on the number of simultaneous 5052 RPC calls that can be sent from the client to a 5053 server. Increasing these values may allow you to 5054 improve throughput, but will also increase the 5055 amount of memory reserved for use by the client. 5056 5057 suspend.pm_test_delay= 5058 [SUSPEND] 5059 Sets the number of seconds to remain in a suspend test 5060 mode before resuming the system (see 5061 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5062 is set. Default value is 5. 5063 5064 svm= [PPC] 5065 Format: { on | off | y | n | 1 | 0 } 5066 This parameter controls use of the Protected 5067 Execution Facility on pSeries. 5068 5069 swapaccount=[0|1] 5070 [KNL] Enable accounting of swap in memory resource 5071 controller if no parameter or 1 is given or disable 5072 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5073 5074 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5075 Format: { <int> | force | noforce } 5076 <int> -- Number of I/O TLB slabs 5077 force -- force using of bounce buffers even if they 5078 wouldn't be automatically used by the kernel 5079 noforce -- Never use bounce buffers (for debugging) 5080 5081 switches= [HW,M68k] 5082 5083 sysctl.*= [KNL] 5084 Set a sysctl parameter, right before loading the init 5085 process, as if the value was written to the respective 5086 /proc/sys/... file. Both '.' and '/' are recognized as 5087 separators. Unrecognized parameters and invalid values 5088 are reported in the kernel log. Sysctls registered 5089 later by a loaded module cannot be set this way. 5090 Example: sysctl.vm.swappiness=40 5091 5092 sysfs.deprecated=0|1 [KNL] 5093 Enable/disable old style sysfs layout for old udev 5094 on older distributions. When this option is enabled 5095 very new udev will not work anymore. When this option 5096 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5097 in older udev will not work anymore. 5098 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5099 the kernel configuration. 5100 5101 sysrq_always_enabled 5102 [KNL] 5103 Ignore sysrq setting - this boot parameter will 5104 neutralize any effect of /proc/sys/kernel/sysrq. 5105 Useful for debugging. 5106 5107 tcpmhash_entries= [KNL,NET] 5108 Set the number of tcp_metrics_hash slots. 5109 Default value is 8192 or 16384 depending on total 5110 ram pages. This is used to specify the TCP metrics 5111 cache size. See Documentation/networking/ip-sysctl.rst 5112 "tcp_no_metrics_save" section for more details. 5113 5114 tdfx= [HW,DRM] 5115 5116 test_suspend= [SUSPEND][,N] 5117 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5118 standby suspend) or "freeze" (for suspend type freeze) 5119 as the system sleep state during system startup with 5120 the optional capability to repeat N number of times. 5121 The system is woken from this state using a 5122 wakeup-capable RTC alarm. 5123 5124 thash_entries= [KNL,NET] 5125 Set number of hash buckets for TCP connection 5126 5127 thermal.act= [HW,ACPI] 5128 -1: disable all active trip points in all thermal zones 5129 <degrees C>: override all lowest active trip points 5130 5131 thermal.crt= [HW,ACPI] 5132 -1: disable all critical trip points in all thermal zones 5133 <degrees C>: override all critical trip points 5134 5135 thermal.nocrt= [HW,ACPI] 5136 Set to disable actions on ACPI thermal zone 5137 critical and hot trip points. 5138 5139 thermal.off= [HW,ACPI] 5140 1: disable ACPI thermal control 5141 5142 thermal.psv= [HW,ACPI] 5143 -1: disable all passive trip points 5144 <degrees C>: override all passive trip points to this 5145 value 5146 5147 thermal.tzp= [HW,ACPI] 5148 Specify global default ACPI thermal zone polling rate 5149 <deci-seconds>: poll all this frequency 5150 0: no polling (default) 5151 5152 threadirqs [KNL] 5153 Force threading of all interrupt handlers except those 5154 marked explicitly IRQF_NO_THREAD. 5155 5156 topology= [S390] 5157 Format: {off | on} 5158 Specify if the kernel should make use of the cpu 5159 topology information if the hardware supports this. 5160 The scheduler will make use of this information and 5161 e.g. base its process migration decisions on it. 5162 Default is on. 5163 5164 topology_updates= [KNL, PPC, NUMA] 5165 Format: {off} 5166 Specify if the kernel should ignore (off) 5167 topology updates sent by the hypervisor to this 5168 LPAR. 5169 5170 torture.disable_onoff_at_boot= [KNL] 5171 Prevent the CPU-hotplug component of torturing 5172 until after init has spawned. 5173 5174 torture.ftrace_dump_at_shutdown= [KNL] 5175 Dump the ftrace buffer at torture-test shutdown, 5176 even if there were no errors. This can be a 5177 very costly operation when many torture tests 5178 are running concurrently, especially on systems 5179 with rotating-rust storage. 5180 5181 tp720= [HW,PS2] 5182 5183 tpm_suspend_pcr=[HW,TPM] 5184 Format: integer pcr id 5185 Specify that at suspend time, the tpm driver 5186 should extend the specified pcr with zeros, 5187 as a workaround for some chips which fail to 5188 flush the last written pcr on TPM_SaveState. 5189 This will guarantee that all the other pcrs 5190 are saved. 5191 5192 trace_buf_size=nn[KMG] 5193 [FTRACE] will set tracing buffer size on each cpu. 5194 5195 trace_event=[event-list] 5196 [FTRACE] Set and start specified trace events in order 5197 to facilitate early boot debugging. The event-list is a 5198 comma separated list of trace events to enable. See 5199 also Documentation/trace/events.rst 5200 5201 trace_options=[option-list] 5202 [FTRACE] Enable or disable tracer options at boot. 5203 The option-list is a comma delimited list of options 5204 that can be enabled or disabled just as if you were 5205 to echo the option name into 5206 5207 /sys/kernel/debug/tracing/trace_options 5208 5209 For example, to enable stacktrace option (to dump the 5210 stack trace of each event), add to the command line: 5211 5212 trace_options=stacktrace 5213 5214 See also Documentation/trace/ftrace.rst "trace options" 5215 section. 5216 5217 tp_printk[FTRACE] 5218 Have the tracepoints sent to printk as well as the 5219 tracing ring buffer. This is useful for early boot up 5220 where the system hangs or reboots and does not give the 5221 option for reading the tracing buffer or performing a 5222 ftrace_dump_on_oops. 5223 5224 To turn off having tracepoints sent to printk, 5225 echo 0 > /proc/sys/kernel/tracepoint_printk 5226 Note, echoing 1 into this file without the 5227 tracepoint_printk kernel cmdline option has no effect. 5228 5229 ** CAUTION ** 5230 5231 Having tracepoints sent to printk() and activating high 5232 frequency tracepoints such as irq or sched, can cause 5233 the system to live lock. 5234 5235 traceoff_on_warning 5236 [FTRACE] enable this option to disable tracing when a 5237 warning is hit. This turns off "tracing_on". Tracing can 5238 be enabled again by echoing '1' into the "tracing_on" 5239 file located in /sys/kernel/debug/tracing/ 5240 5241 This option is useful, as it disables the trace before 5242 the WARNING dump is called, which prevents the trace to 5243 be filled with content caused by the warning output. 5244 5245 This option can also be set at run time via the sysctl 5246 option: kernel/traceoff_on_warning 5247 5248 transparent_hugepage= 5249 [KNL] 5250 Format: [always|madvise|never] 5251 Can be used to control the default behavior of the system 5252 with respect to transparent hugepages. 5253 See Documentation/admin-guide/mm/transhuge.rst 5254 for more details. 5255 5256 tsc= Disable clocksource stability checks for TSC. 5257 Format: <string> 5258 [x86] reliable: mark tsc clocksource as reliable, this 5259 disables clocksource verification at runtime, as well 5260 as the stability checks done at bootup. Used to enable 5261 high-resolution timer mode on older hardware, and in 5262 virtualized environment. 5263 [x86] noirqtime: Do not use TSC to do irq accounting. 5264 Used to run time disable IRQ_TIME_ACCOUNTING on any 5265 platforms where RDTSC is slow and this accounting 5266 can add overhead. 5267 [x86] unstable: mark the TSC clocksource as unstable, this 5268 marks the TSC unconditionally unstable at bootup and 5269 avoids any further wobbles once the TSC watchdog notices. 5270 [x86] nowatchdog: disable clocksource watchdog. Used 5271 in situations with strict latency requirements (where 5272 interruptions from clocksource watchdog are not 5273 acceptable). 5274 5275 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5276 value instead. Useful when the early TSC frequency discovery 5277 procedure is not reliable, such as on overclocked systems 5278 with CPUID.16h support and partial CPUID.15h support. 5279 Format: <unsigned int> 5280 5281 tsx= [X86] Control Transactional Synchronization 5282 Extensions (TSX) feature in Intel processors that 5283 support TSX control. 5284 5285 This parameter controls the TSX feature. The options are: 5286 5287 on - Enable TSX on the system. Although there are 5288 mitigations for all known security vulnerabilities, 5289 TSX has been known to be an accelerator for 5290 several previous speculation-related CVEs, and 5291 so there may be unknown security risks associated 5292 with leaving it enabled. 5293 5294 off - Disable TSX on the system. (Note that this 5295 option takes effect only on newer CPUs which are 5296 not vulnerable to MDS, i.e., have 5297 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5298 the new IA32_TSX_CTRL MSR through a microcode 5299 update. This new MSR allows for the reliable 5300 deactivation of the TSX functionality.) 5301 5302 auto - Disable TSX if X86_BUG_TAA is present, 5303 otherwise enable TSX on the system. 5304 5305 Not specifying this option is equivalent to tsx=off. 5306 5307 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5308 for more details. 5309 5310 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5311 Abort (TAA) vulnerability. 5312 5313 Similar to Micro-architectural Data Sampling (MDS) 5314 certain CPUs that support Transactional 5315 Synchronization Extensions (TSX) are vulnerable to an 5316 exploit against CPU internal buffers which can forward 5317 information to a disclosure gadget under certain 5318 conditions. 5319 5320 In vulnerable processors, the speculatively forwarded 5321 data can be used in a cache side channel attack, to 5322 access data to which the attacker does not have direct 5323 access. 5324 5325 This parameter controls the TAA mitigation. The 5326 options are: 5327 5328 full - Enable TAA mitigation on vulnerable CPUs 5329 if TSX is enabled. 5330 5331 full,nosmt - Enable TAA mitigation and disable SMT on 5332 vulnerable CPUs. If TSX is disabled, SMT 5333 is not disabled because CPU is not 5334 vulnerable to cross-thread TAA attacks. 5335 off - Unconditionally disable TAA mitigation 5336 5337 On MDS-affected machines, tsx_async_abort=off can be 5338 prevented by an active MDS mitigation as both vulnerabilities 5339 are mitigated with the same mechanism so in order to disable 5340 this mitigation, you need to specify mds=off too. 5341 5342 Not specifying this option is equivalent to 5343 tsx_async_abort=full. On CPUs which are MDS affected 5344 and deploy MDS mitigation, TAA mitigation is not 5345 required and doesn't provide any additional 5346 mitigation. 5347 5348 For details see: 5349 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5350 5351 turbografx.map[2|3]= [HW,JOY] 5352 TurboGraFX parallel port interface 5353 Format: 5354 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5355 See also Documentation/input/devices/joystick-parport.rst 5356 5357 udbg-immortal [PPC] When debugging early kernel crashes that 5358 happen after console_init() and before a proper 5359 console driver takes over, this boot options might 5360 help "seeing" what's going on. 5361 5362 uhash_entries= [KNL,NET] 5363 Set number of hash buckets for UDP/UDP-Lite connections 5364 5365 uhci-hcd.ignore_oc= 5366 [USB] Ignore overcurrent events (default N). 5367 Some badly-designed motherboards generate lots of 5368 bogus events, for ports that aren't wired to 5369 anything. Set this parameter to avoid log spamming. 5370 Note that genuine overcurrent events won't be 5371 reported either. 5372 5373 unknown_nmi_panic 5374 [X86] Cause panic on unknown NMI. 5375 5376 usbcore.authorized_default= 5377 [USB] Default USB device authorization: 5378 (default -1 = authorized except for wireless USB, 5379 0 = not authorized, 1 = authorized, 2 = authorized 5380 if device connected to internal port) 5381 5382 usbcore.autosuspend= 5383 [USB] The autosuspend time delay (in seconds) used 5384 for newly-detected USB devices (default 2). This 5385 is the time required before an idle device will be 5386 autosuspended. Devices for which the delay is set 5387 to a negative value won't be autosuspended at all. 5388 5389 usbcore.usbfs_snoop= 5390 [USB] Set to log all usbfs traffic (default 0 = off). 5391 5392 usbcore.usbfs_snoop_max= 5393 [USB] Maximum number of bytes to snoop in each URB 5394 (default = 65536). 5395 5396 usbcore.blinkenlights= 5397 [USB] Set to cycle leds on hubs (default 0 = off). 5398 5399 usbcore.old_scheme_first= 5400 [USB] Start with the old device initialization 5401 scheme (default 0 = off). 5402 5403 usbcore.usbfs_memory_mb= 5404 [USB] Memory limit (in MB) for buffers allocated by 5405 usbfs (default = 16, 0 = max = 2047). 5406 5407 usbcore.use_both_schemes= 5408 [USB] Try the other device initialization scheme 5409 if the first one fails (default 1 = enabled). 5410 5411 usbcore.initial_descriptor_timeout= 5412 [USB] Specifies timeout for the initial 64-byte 5413 USB_REQ_GET_DESCRIPTOR request in milliseconds 5414 (default 5000 = 5.0 seconds). 5415 5416 usbcore.nousb [USB] Disable the USB subsystem 5417 5418 usbcore.quirks= 5419 [USB] A list of quirk entries to augment the built-in 5420 usb core quirk list. List entries are separated by 5421 commas. Each entry has the form 5422 VendorID:ProductID:Flags. The IDs are 4-digit hex 5423 numbers and Flags is a set of letters. Each letter 5424 will change the built-in quirk; setting it if it is 5425 clear and clearing it if it is set. The letters have 5426 the following meanings: 5427 a = USB_QUIRK_STRING_FETCH_255 (string 5428 descriptors must not be fetched using 5429 a 255-byte read); 5430 b = USB_QUIRK_RESET_RESUME (device can't resume 5431 correctly so reset it instead); 5432 c = USB_QUIRK_NO_SET_INTF (device can't handle 5433 Set-Interface requests); 5434 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5435 handle its Configuration or Interface 5436 strings); 5437 e = USB_QUIRK_RESET (device can't be reset 5438 (e.g morph devices), don't use reset); 5439 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5440 more interface descriptions than the 5441 bNumInterfaces count, and can't handle 5442 talking to these interfaces); 5443 g = USB_QUIRK_DELAY_INIT (device needs a pause 5444 during initialization, after we read 5445 the device descriptor); 5446 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5447 high speed and super speed interrupt 5448 endpoints, the USB 2.0 and USB 3.0 spec 5449 require the interval in microframes (1 5450 microframe = 125 microseconds) to be 5451 calculated as interval = 2 ^ 5452 (bInterval-1). 5453 Devices with this quirk report their 5454 bInterval as the result of this 5455 calculation instead of the exponent 5456 variable used in the calculation); 5457 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5458 handle device_qualifier descriptor 5459 requests); 5460 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5461 generates spurious wakeup, ignore 5462 remote wakeup capability); 5463 k = USB_QUIRK_NO_LPM (device can't handle Link 5464 Power Management); 5465 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5466 (Device reports its bInterval as linear 5467 frames instead of the USB 2.0 5468 calculation); 5469 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5470 to be disconnected before suspend to 5471 prevent spurious wakeup); 5472 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5473 pause after every control message); 5474 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5475 delay after resetting its port); 5476 Example: quirks=0781:5580:bk,0a5c:5834:gij 5477 5478 usbhid.mousepoll= 5479 [USBHID] The interval which mice are to be polled at. 5480 5481 usbhid.jspoll= 5482 [USBHID] The interval which joysticks are to be polled at. 5483 5484 usbhid.kbpoll= 5485 [USBHID] The interval which keyboards are to be polled at. 5486 5487 usb-storage.delay_use= 5488 [UMS] The delay in seconds before a new device is 5489 scanned for Logical Units (default 1). 5490 5491 usb-storage.quirks= 5492 [UMS] A list of quirks entries to supplement or 5493 override the built-in unusual_devs list. List 5494 entries are separated by commas. Each entry has 5495 the form VID:PID:Flags where VID and PID are Vendor 5496 and Product ID values (4-digit hex numbers) and 5497 Flags is a set of characters, each corresponding 5498 to a common usb-storage quirk flag as follows: 5499 a = SANE_SENSE (collect more than 18 bytes 5500 of sense data, not on uas); 5501 b = BAD_SENSE (don't collect more than 18 5502 bytes of sense data, not on uas); 5503 c = FIX_CAPACITY (decrease the reported 5504 device capacity by one sector); 5505 d = NO_READ_DISC_INFO (don't use 5506 READ_DISC_INFO command, not on uas); 5507 e = NO_READ_CAPACITY_16 (don't use 5508 READ_CAPACITY_16 command); 5509 f = NO_REPORT_OPCODES (don't use report opcodes 5510 command, uas only); 5511 g = MAX_SECTORS_240 (don't transfer more than 5512 240 sectors at a time, uas only); 5513 h = CAPACITY_HEURISTICS (decrease the 5514 reported device capacity by one 5515 sector if the number is odd); 5516 i = IGNORE_DEVICE (don't bind to this 5517 device); 5518 j = NO_REPORT_LUNS (don't use report luns 5519 command, uas only); 5520 l = NOT_LOCKABLE (don't try to lock and 5521 unlock ejectable media, not on uas); 5522 m = MAX_SECTORS_64 (don't transfer more 5523 than 64 sectors = 32 KB at a time, 5524 not on uas); 5525 n = INITIAL_READ10 (force a retry of the 5526 initial READ(10) command, not on uas); 5527 o = CAPACITY_OK (accept the capacity 5528 reported by the device, not on uas); 5529 p = WRITE_CACHE (the device cache is ON 5530 by default, not on uas); 5531 r = IGNORE_RESIDUE (the device reports 5532 bogus residue values, not on uas); 5533 s = SINGLE_LUN (the device has only one 5534 Logical Unit); 5535 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5536 commands, uas only); 5537 u = IGNORE_UAS (don't bind to the uas driver); 5538 w = NO_WP_DETECT (don't test whether the 5539 medium is write-protected). 5540 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5541 even if the device claims no cache, 5542 not on uas) 5543 Example: quirks=0419:aaf5:rl,0421:0433:rc 5544 5545 user_debug= [KNL,ARM] 5546 Format: <int> 5547 See arch/arm/Kconfig.debug help text. 5548 1 - undefined instruction events 5549 2 - system calls 5550 4 - invalid data aborts 5551 8 - SIGSEGV faults 5552 16 - SIGBUS faults 5553 Example: user_debug=31 5554 5555 userpte= 5556 [X86] Flags controlling user PTE allocations. 5557 5558 nohigh = do not allocate PTE pages in 5559 HIGHMEM regardless of setting 5560 of CONFIG_HIGHPTE. 5561 5562 vdso= [X86,SH] 5563 On X86_32, this is an alias for vdso32=. Otherwise: 5564 5565 vdso=1: enable VDSO (the default) 5566 vdso=0: disable VDSO mapping 5567 5568 vdso32= [X86] Control the 32-bit vDSO 5569 vdso32=1: enable 32-bit VDSO 5570 vdso32=0 or vdso32=2: disable 32-bit VDSO 5571 5572 See the help text for CONFIG_COMPAT_VDSO for more 5573 details. If CONFIG_COMPAT_VDSO is set, the default is 5574 vdso32=0; otherwise, the default is vdso32=1. 5575 5576 For compatibility with older kernels, vdso32=2 is an 5577 alias for vdso32=0. 5578 5579 Try vdso32=0 if you encounter an error that says: 5580 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5581 5582 vector= [IA-64,SMP] 5583 vector=percpu: enable percpu vector domain 5584 5585 video= [FB] Frame buffer configuration 5586 See Documentation/fb/modedb.rst. 5587 5588 video.brightness_switch_enabled= [0,1] 5589 If set to 1, on receiving an ACPI notify event 5590 generated by hotkey, video driver will adjust brightness 5591 level and then send out the event to user space through 5592 the allocated input device; If set to 0, video driver 5593 will only send out the event without touching backlight 5594 brightness level. 5595 default: 1 5596 5597 virtio_mmio.device= 5598 [VMMIO] Memory mapped virtio (platform) device. 5599 5600 <size>@<baseaddr>:<irq>[:<id>] 5601 where: 5602 <size> := size (can use standard suffixes 5603 like K, M and G) 5604 <baseaddr> := physical base address 5605 <irq> := interrupt number (as passed to 5606 request_irq()) 5607 <id> := (optional) platform device id 5608 example: 5609 virtio_mmio.device=1K@0x100b0000:48:7 5610 5611 Can be used multiple times for multiple devices. 5612 5613 vga= [BOOT,X86-32] Select a particular video mode 5614 See Documentation/x86/boot.rst and 5615 Documentation/admin-guide/svga.rst. 5616 Use vga=ask for menu. 5617 This is actually a boot loader parameter; the value is 5618 passed to the kernel using a special protocol. 5619 5620 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5621 May slow down system boot speed, especially when 5622 enabled on systems with a large amount of memory. 5623 All options are enabled by default, and this 5624 interface is meant to allow for selectively 5625 enabling or disabling specific virtual memory 5626 debugging features. 5627 5628 Available options are: 5629 P Enable page structure init time poisoning 5630 - Disable all of the above options 5631 5632 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5633 size of <nn>. This can be used to increase the 5634 minimum size (128MB on x86). It can also be used to 5635 decrease the size and leave more room for directly 5636 mapped kernel RAM. 5637 5638 vmcp_cma=nn[MG] [KNL,S390] 5639 Sets the memory size reserved for contiguous memory 5640 allocations for the vmcp device driver. 5641 5642 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5643 Format: <command> 5644 5645 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5646 Format: <command> 5647 5648 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5649 Format: <command> 5650 5651 vsyscall= [X86-64] 5652 Controls the behavior of vsyscalls (i.e. calls to 5653 fixed addresses of 0xffffffffff600x00 from legacy 5654 code). Most statically-linked binaries and older 5655 versions of glibc use these calls. Because these 5656 functions are at fixed addresses, they make nice 5657 targets for exploits that can control RIP. 5658 5659 emulate [default] Vsyscalls turn into traps and are 5660 emulated reasonably safely. The vsyscall 5661 page is readable. 5662 5663 xonly Vsyscalls turn into traps and are 5664 emulated reasonably safely. The vsyscall 5665 page is not readable. 5666 5667 none Vsyscalls don't work at all. This makes 5668 them quite hard to use for exploits but 5669 might break your system. 5670 5671 vt.color= [VT] Default text color. 5672 Format: 0xYX, X = foreground, Y = background. 5673 Default: 0x07 = light gray on black. 5674 5675 vt.cur_default= [VT] Default cursor shape. 5676 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5677 the parameters of the <Esc>[?A;B;Cc escape sequence; 5678 see VGA-softcursor.txt. Default: 2 = underline. 5679 5680 vt.default_blu= [VT] 5681 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5682 Change the default blue palette of the console. 5683 This is a 16-member array composed of values 5684 ranging from 0-255. 5685 5686 vt.default_grn= [VT] 5687 Format: <green0>,<green1>,<green2>,...,<green15> 5688 Change the default green palette of the console. 5689 This is a 16-member array composed of values 5690 ranging from 0-255. 5691 5692 vt.default_red= [VT] 5693 Format: <red0>,<red1>,<red2>,...,<red15> 5694 Change the default red palette of the console. 5695 This is a 16-member array composed of values 5696 ranging from 0-255. 5697 5698 vt.default_utf8= 5699 [VT] 5700 Format=<0|1> 5701 Set system-wide default UTF-8 mode for all tty's. 5702 Default is 1, i.e. UTF-8 mode is enabled for all 5703 newly opened terminals. 5704 5705 vt.global_cursor_default= 5706 [VT] 5707 Format=<-1|0|1> 5708 Set system-wide default for whether a cursor 5709 is shown on new VTs. Default is -1, 5710 i.e. cursors will be created by default unless 5711 overridden by individual drivers. 0 will hide 5712 cursors, 1 will display them. 5713 5714 vt.italic= [VT] Default color for italic text; 0-15. 5715 Default: 2 = green. 5716 5717 vt.underline= [VT] Default color for underlined text; 0-15. 5718 Default: 3 = cyan. 5719 5720 watchdog timers [HW,WDT] For information on watchdog timers, 5721 see Documentation/watchdog/watchdog-parameters.rst 5722 or other driver-specific files in the 5723 Documentation/watchdog/ directory. 5724 5725 watchdog_thresh= 5726 [KNL] 5727 Set the hard lockup detector stall duration 5728 threshold in seconds. The soft lockup detector 5729 threshold is set to twice the value. A value of 0 5730 disables both lockup detectors. Default is 10 5731 seconds. 5732 5733 workqueue.watchdog_thresh= 5734 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5735 warn stall conditions and dump internal state to 5736 help debugging. 0 disables workqueue stall 5737 detection; otherwise, it's the stall threshold 5738 duration in seconds. The default value is 30 and 5739 it can be updated at runtime by writing to the 5740 corresponding sysfs file. 5741 5742 workqueue.disable_numa 5743 By default, all work items queued to unbound 5744 workqueues are affine to the NUMA nodes they're 5745 issued on, which results in better behavior in 5746 general. If NUMA affinity needs to be disabled for 5747 whatever reason, this option can be used. Note 5748 that this also can be controlled per-workqueue for 5749 workqueues visible under /sys/bus/workqueue/. 5750 5751 workqueue.power_efficient 5752 Per-cpu workqueues are generally preferred because 5753 they show better performance thanks to cache 5754 locality; unfortunately, per-cpu workqueues tend to 5755 be more power hungry than unbound workqueues. 5756 5757 Enabling this makes the per-cpu workqueues which 5758 were observed to contribute significantly to power 5759 consumption unbound, leading to measurably lower 5760 power usage at the cost of small performance 5761 overhead. 5762 5763 The default value of this parameter is determined by 5764 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5765 5766 workqueue.debug_force_rr_cpu 5767 Workqueue used to implicitly guarantee that work 5768 items queued without explicit CPU specified are put 5769 on the local CPU. This guarantee is no longer true 5770 and while local CPU is still preferred work items 5771 may be put on foreign CPUs. This debug option 5772 forces round-robin CPU selection to flush out 5773 usages which depend on the now broken guarantee. 5774 When enabled, memory and cache locality will be 5775 impacted. 5776 5777 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5778 default x2apic cluster mode on platforms 5779 supporting x2apic. 5780 5781 x86_intel_mid_timer= [X86-32,APBT] 5782 Choose timer option for x86 Intel MID platform. 5783 Two valid options are apbt timer only and lapic timer 5784 plus one apbt timer for broadcast timer. 5785 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5786 5787 xen_512gb_limit [KNL,X86-64,XEN] 5788 Restricts the kernel running paravirtualized under Xen 5789 to use only up to 512 GB of RAM. The reason to do so is 5790 crash analysis tools and Xen tools for doing domain 5791 save/restore/migration must be enabled to handle larger 5792 domains. 5793 5794 xen_emul_unplug= [HW,X86,XEN] 5795 Unplug Xen emulated devices 5796 Format: [unplug0,][unplug1] 5797 ide-disks -- unplug primary master IDE devices 5798 aux-ide-disks -- unplug non-primary-master IDE devices 5799 nics -- unplug network devices 5800 all -- unplug all emulated devices (NICs and IDE disks) 5801 unnecessary -- unplugging emulated devices is 5802 unnecessary even if the host did not respond to 5803 the unplug protocol 5804 never -- do not unplug even if version check succeeds 5805 5806 xen_legacy_crash [X86,XEN] 5807 Crash from Xen panic notifier, without executing late 5808 panic() code such as dumping handler. 5809 5810 xen_nopvspin [X86,XEN] 5811 Disables the qspinlock slowpath using Xen PV optimizations. 5812 This parameter is obsoleted by "nopvspin" parameter, which 5813 has equivalent effect for XEN platform. 5814 5815 xen_nopv [X86] 5816 Disables the PV optimizations forcing the HVM guest to 5817 run as generic HVM guest with no PV drivers. 5818 This option is obsoleted by the "nopv" option, which 5819 has equivalent effect for XEN platform. 5820 5821 xen_scrub_pages= [XEN] 5822 Boolean option to control scrubbing pages before giving them back 5823 to Xen, for use by other domains. Can be also changed at runtime 5824 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5825 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5826 5827 xen_timer_slop= [X86-64,XEN] 5828 Set the timer slop (in nanoseconds) for the virtual Xen 5829 timers (default is 100000). This adjusts the minimum 5830 delta of virtualized Xen timers, where lower values 5831 improve timer resolution at the expense of processing 5832 more timer interrupts. 5833 5834 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5835 Disables the PV optimizations forcing the guest to run 5836 as generic guest with no PV drivers. Currently support 5837 XEN HVM, KVM, HYPER_V and VMWARE guest. 5838 5839 nopvspin [X86,XEN,KVM] 5840 Disables the qspinlock slow path using PV optimizations 5841 which allow the hypervisor to 'idle' the guest on lock 5842 contention. 5843 5844 xirc2ps_cs= [NET,PCMCIA] 5845 Format: 5846 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5847 5848 xive= [PPC] 5849 By default on POWER9 and above, the kernel will 5850 natively use the XIVE interrupt controller. This option 5851 allows the fallback firmware mode to be used: 5852 5853 off Fallback to firmware control of XIVE interrupt 5854 controller on both pseries and powernv 5855 platforms. Only useful on POWER9 and above. 5856 5857 xhci-hcd.quirks [USB,KNL] 5858 A hex value specifying bitmask with supplemental xhci 5859 host controller quirks. Meaning of each bit can be 5860 consulted in header drivers/usb/host/xhci.h. 5861 5862 xmon [PPC] 5863 Format: { early | on | rw | ro | off } 5864 Controls if xmon debugger is enabled. Default is off. 5865 Passing only "xmon" is equivalent to "xmon=early". 5866 early Call xmon as early as possible on boot; xmon 5867 debugger is called from setup_arch(). 5868 on xmon debugger hooks will be installed so xmon 5869 is only called on a kernel crash. Default mode, 5870 i.e. either "ro" or "rw" mode, is controlled 5871 with CONFIG_XMON_DEFAULT_RO_MODE. 5872 rw xmon debugger hooks will be installed so xmon 5873 is called only on a kernel crash, mode is write, 5874 meaning SPR registers, memory and, other data 5875 can be written using xmon commands. 5876 ro same as "rw" option above but SPR registers, 5877 memory, and other data can't be written using 5878 xmon commands. 5879 off xmon is disabled. 5880