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[,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 [KNL,CMA] 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 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 debug: enable misc debug output. 1238 disable_early_pci_dma: disable the busmaster bit on all 1239 PCI bridges while in the EFI boot stub. 1240 nochunk: disable reading files in "chunks" in the EFI 1241 boot stub, as chunking can cause problems with some 1242 firmware implementations. 1243 noruntime : disable EFI runtime services support 1244 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1245 attribute may cause the kernel to reserve the 1246 memory range for a memory mapping driver to 1247 claim. Specify efi=nosoftreserve to disable this 1248 reservation and treat the memory by its base type 1249 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1250 novamap: do not call SetVirtualAddressMap(). 1251 no_disable_early_pci_dma: Leave the busmaster bit set 1252 on all PCI bridges while in the EFI boot stub 1253 1254 efi_no_storage_paranoia [EFI; X86] 1255 Using this parameter you can use more than 50% of 1256 your efi variable storage. Use this parameter only if 1257 you are really sure that your UEFI does sane gc and 1258 fulfills the spec otherwise your board may brick. 1259 1260 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1261 Add arbitrary attribute to specific memory range by 1262 updating original EFI memory map. 1263 Region of memory which aa attribute is added to is 1264 from ss to ss+nn. 1265 1266 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1267 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1268 attribute is added to range 0x100000000-0x180000000 and 1269 0x10a0000000-0x1120000000. 1270 1271 If efi_fake_mem=8G@9G:0x40000 is specified, the 1272 EFI_MEMORY_SP(0x40000) attribute is added to 1273 range 0x240000000-0x43fffffff. 1274 1275 Using this parameter you can do debugging of EFI memmap 1276 related features. For example, you can do debugging of 1277 Address Range Mirroring feature even if your box 1278 doesn't support it, or mark specific memory as 1279 "soft reserved". 1280 1281 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1282 that is to be dynamically loaded by Linux. If there are 1283 multiple variables with the same name but with different 1284 vendor GUIDs, all of them will be loaded. See 1285 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1286 1287 1288 eisa_irq_edge= [PARISC,HW] 1289 See header of drivers/parisc/eisa.c. 1290 1291 elanfreq= [X86-32] 1292 See comment before function elanfreq_setup() in 1293 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1294 1295 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1296 Specifies physical address of start of kernel core 1297 image elf header and optionally the size. Generally 1298 kexec loader will pass this option to capture kernel. 1299 See Documentation/admin-guide/kdump/kdump.rst for details. 1300 1301 enable_mtrr_cleanup [X86] 1302 The kernel tries to adjust MTRR layout from continuous 1303 to discrete, to make X server driver able to add WB 1304 entry later. This parameter enables that. 1305 1306 enable_timer_pin_1 [X86] 1307 Enable PIN 1 of APIC timer 1308 Can be useful to work around chipset bugs 1309 (in particular on some ATI chipsets). 1310 The kernel tries to set a reasonable default. 1311 1312 enforcing [SELINUX] Set initial enforcing status. 1313 Format: {"0" | "1"} 1314 See security/selinux/Kconfig help text. 1315 0 -- permissive (log only, no denials). 1316 1 -- enforcing (deny and log). 1317 Default value is 0. 1318 Value can be changed at runtime via 1319 /sys/fs/selinux/enforce. 1320 1321 erst_disable [ACPI] 1322 Disable Error Record Serialization Table (ERST) 1323 support. 1324 1325 ether= [HW,NET] Ethernet cards parameters 1326 This option is obsoleted by the "netdev=" option, which 1327 has equivalent usage. See its documentation for details. 1328 1329 evm= [EVM] 1330 Format: { "fix" } 1331 Permit 'security.evm' to be updated regardless of 1332 current integrity status. 1333 1334 failslab= 1335 fail_page_alloc= 1336 fail_make_request=[KNL] 1337 General fault injection mechanism. 1338 Format: <interval>,<probability>,<space>,<times> 1339 See also Documentation/fault-injection/. 1340 1341 floppy= [HW] 1342 See Documentation/admin-guide/blockdev/floppy.rst. 1343 1344 force_pal_cache_flush 1345 [IA-64] Avoid check_sal_cache_flush which may hang on 1346 buggy SAL_CACHE_FLUSH implementations. Using this 1347 parameter will force ia64_sal_cache_flush to call 1348 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1349 1350 forcepae [X86-32] 1351 Forcefully enable Physical Address Extension (PAE). 1352 Many Pentium M systems disable PAE but may have a 1353 functionally usable PAE implementation. 1354 Warning: use of this parameter will taint the kernel 1355 and may cause unknown problems. 1356 1357 ftrace=[tracer] 1358 [FTRACE] will set and start the specified tracer 1359 as early as possible in order to facilitate early 1360 boot debugging. 1361 1362 ftrace_dump_on_oops[=orig_cpu] 1363 [FTRACE] will dump the trace buffers on oops. 1364 If no parameter is passed, ftrace will dump 1365 buffers of all CPUs, but if you pass orig_cpu, it will 1366 dump only the buffer of the CPU that triggered the 1367 oops. 1368 1369 ftrace_filter=[function-list] 1370 [FTRACE] Limit the functions traced by the function 1371 tracer at boot up. function-list is a comma separated 1372 list of functions. This list can be changed at run 1373 time by the set_ftrace_filter file in the debugfs 1374 tracing directory. 1375 1376 ftrace_notrace=[function-list] 1377 [FTRACE] Do not trace the functions specified in 1378 function-list. This list can be changed at run time 1379 by the set_ftrace_notrace file in the debugfs 1380 tracing directory. 1381 1382 ftrace_graph_filter=[function-list] 1383 [FTRACE] Limit the top level callers functions traced 1384 by the function graph tracer at boot up. 1385 function-list is a comma separated list of functions 1386 that can be changed at run time by the 1387 set_graph_function file in the debugfs tracing directory. 1388 1389 ftrace_graph_notrace=[function-list] 1390 [FTRACE] Do not trace from the functions specified in 1391 function-list. This list is a comma separated list of 1392 functions that can be changed at run time by the 1393 set_graph_notrace file in the debugfs tracing directory. 1394 1395 ftrace_graph_max_depth=<uint> 1396 [FTRACE] Used with the function graph tracer. This is 1397 the max depth it will trace into a function. This value 1398 can be changed at run time by the max_graph_depth file 1399 in the tracefs tracing directory. default: 0 (no limit) 1400 1401 fw_devlink= [KNL] Create device links between consumer and supplier 1402 devices by scanning the firmware to infer the 1403 consumer/supplier relationships. This feature is 1404 especially useful when drivers are loaded as modules as 1405 it ensures proper ordering of tasks like device probing 1406 (suppliers first, then consumers), supplier boot state 1407 clean up (only after all consumers have probed), 1408 suspend/resume & runtime PM (consumers first, then 1409 suppliers). 1410 Format: { off | permissive | on | rpm } 1411 off -- Don't create device links from firmware info. 1412 permissive -- Create device links from firmware info 1413 but use it only for ordering boot state clean 1414 up (sync_state() calls). 1415 on -- Create device links from firmware info and use it 1416 to enforce probe and suspend/resume ordering. 1417 rpm -- Like "on", but also use to order runtime PM. 1418 1419 gamecon.map[2|3]= 1420 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1421 support via parallel port (up to 5 devices per port) 1422 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1423 See also Documentation/input/devices/joystick-parport.rst 1424 1425 gamma= [HW,DRM] 1426 1427 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1428 Format: off | on 1429 default: on 1430 1431 gcov_persist= [GCOV] When non-zero (default), profiling data for 1432 kernel modules is saved and remains accessible via 1433 debugfs, even when the module is unloaded/reloaded. 1434 When zero, profiling data is discarded and associated 1435 debugfs files are removed at module unload time. 1436 1437 goldfish [X86] Enable the goldfish android emulator platform. 1438 Don't use this when you are not running on the 1439 android emulator 1440 1441 gpt [EFI] Forces disk with valid GPT signature but 1442 invalid Protective MBR to be treated as GPT. If the 1443 primary GPT is corrupted, it enables the backup/alternate 1444 GPT to be used instead. 1445 1446 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1447 the "Enable 0" bit of the configuration register. 1448 Format: 0 | 1 1449 Default: 0 1450 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1451 the "Enable 0" bit of the configuration register. 1452 Format: 0 | 1 1453 Default: 0 1454 grcan.select= [HW] Select which physical interface to use. 1455 Format: 0 | 1 1456 Default: 0 1457 grcan.txsize= [HW] Sets the size of the tx buffer. 1458 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1459 Default: 1024 1460 grcan.rxsize= [HW] Sets the size of the rx buffer. 1461 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1462 Default: 1024 1463 1464 gpio-mockup.gpio_mockup_ranges 1465 [HW] Sets the ranges of gpiochip of for this device. 1466 Format: <start1>,<end1>,<start2>,<end2>... 1467 1468 hardlockup_all_cpu_backtrace= 1469 [KNL] Should the hard-lockup detector generate 1470 backtraces on all cpus. 1471 Format: 0 | 1 1472 1473 hashdist= [KNL,NUMA] Large hashes allocated during boot 1474 are distributed across NUMA nodes. Defaults on 1475 for 64-bit NUMA, off otherwise. 1476 Format: 0 | 1 (for off | on) 1477 1478 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1479 1480 hd= [EIDE] (E)IDE hard drive subsystem geometry 1481 Format: <cyl>,<head>,<sect> 1482 1483 hest_disable [ACPI] 1484 Disable Hardware Error Source Table (HEST) support; 1485 corresponding firmware-first mode error processing 1486 logic will be disabled. 1487 1488 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1489 size of <nn>. This works even on boxes that have no 1490 highmem otherwise. This also works to reduce highmem 1491 size on bigger boxes. 1492 1493 highres= [KNL] Enable/disable high resolution timer mode. 1494 Valid parameters: "on", "off" 1495 Default: "on" 1496 1497 hlt [BUGS=ARM,SH] 1498 1499 hpet= [X86-32,HPET] option to control HPET usage 1500 Format: { enable (default) | disable | force | 1501 verbose } 1502 disable: disable HPET and use PIT instead 1503 force: allow force enabled of undocumented chips (ICH4, 1504 VIA, nVidia) 1505 verbose: show contents of HPET registers during setup 1506 1507 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1508 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1509 1510 hugetlb_cma= [HW] The size of a cma area used for allocation 1511 of gigantic hugepages. 1512 Format: nn[KMGTPE] 1513 1514 Reserve a cma area of given size and allocate gigantic 1515 hugepages using the cma allocator. If enabled, the 1516 boot-time allocation of gigantic hugepages is skipped. 1517 1518 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1519 If this follows hugepagesz (below), it specifies 1520 the number of pages of hugepagesz to be allocated. 1521 If this is the first HugeTLB parameter on the command 1522 line, it specifies the number of pages to allocate for 1523 the default huge page size. See also 1524 Documentation/admin-guide/mm/hugetlbpage.rst. 1525 Format: <integer> 1526 1527 hugepagesz= 1528 [HW] The size of the HugeTLB pages. This is used in 1529 conjunction with hugepages (above) to allocate huge 1530 pages of a specific size at boot. The pair 1531 hugepagesz=X hugepages=Y can be specified once for 1532 each supported huge page size. Huge page sizes are 1533 architecture dependent. See also 1534 Documentation/admin-guide/mm/hugetlbpage.rst. 1535 Format: size[KMG] 1536 1537 hung_task_panic= 1538 [KNL] Should the hung task detector generate panics. 1539 Format: 0 | 1 1540 1541 A value of 1 instructs the kernel to panic when a 1542 hung task is detected. The default value is controlled 1543 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1544 option. The value selected by this boot parameter can 1545 be changed later by the kernel.hung_task_panic sysctl. 1546 1547 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1548 terminal devices. Valid values: 0..8 1549 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1550 If specified, z/VM IUCV HVC accepts connections 1551 from listed z/VM user IDs only. 1552 1553 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1554 which allow the hypervisor to 'idle' the 1555 guest on lock contention. 1556 1557 keep_bootcon [KNL] 1558 Do not unregister boot console at start. This is only 1559 useful for debugging when something happens in the window 1560 between unregistering the boot console and initializing 1561 the real console. 1562 1563 i2c_bus= [HW] Override the default board specific I2C bus speed 1564 or register an additional I2C bus that is not 1565 registered from board initialization code. 1566 Format: 1567 <bus_id>,<clkrate> 1568 1569 i8042.debug [HW] Toggle i8042 debug mode 1570 i8042.unmask_kbd_data 1571 [HW] Enable printing of interrupt data from the KBD port 1572 (disabled by default, and as a pre-condition 1573 requires that i8042.debug=1 be enabled) 1574 i8042.direct [HW] Put keyboard port into non-translated mode 1575 i8042.dumbkbd [HW] Pretend that controller can only read data from 1576 keyboard and cannot control its state 1577 (Don't attempt to blink the leds) 1578 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1579 i8042.nokbd [HW] Don't check/create keyboard port 1580 i8042.noloop [HW] Disable the AUX Loopback command while probing 1581 for the AUX port 1582 i8042.nomux [HW] Don't check presence of an active multiplexing 1583 controller 1584 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1585 controllers 1586 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1587 i8042.reset [HW] Reset the controller during init, cleanup and 1588 suspend-to-ram transitions, only during s2r 1589 transitions, or never reset 1590 Format: { 1 | Y | y | 0 | N | n } 1591 1, Y, y: always reset controller 1592 0, N, n: don't ever reset controller 1593 Default: only on s2r transitions on x86; most other 1594 architectures force reset to be always executed 1595 i8042.unlock [HW] Unlock (ignore) the keylock 1596 i8042.kbdreset [HW] Reset device connected to KBD port 1597 1598 i810= [HW,DRM] 1599 1600 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1601 indicates that the driver is running on unsupported 1602 hardware. 1603 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1604 does not match list of supported models. 1605 i8k.power_status 1606 [HW] Report power status in /proc/i8k 1607 (disabled by default) 1608 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1609 capability is set. 1610 1611 i915.invert_brightness= 1612 [DRM] Invert the sense of the variable that is used to 1613 set the brightness of the panel backlight. Normally a 1614 brightness value of 0 indicates backlight switched off, 1615 and the maximum of the brightness value sets the backlight 1616 to maximum brightness. If this parameter is set to 0 1617 (default) and the machine requires it, or this parameter 1618 is set to 1, a brightness value of 0 sets the backlight 1619 to maximum brightness, and the maximum of the brightness 1620 value switches the backlight off. 1621 -1 -- never invert brightness 1622 0 -- machine default 1623 1 -- force brightness inversion 1624 1625 icn= [HW,ISDN] 1626 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1627 1628 ide-core.nodma= [HW] (E)IDE subsystem 1629 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1630 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1631 .cdrom .chs .ignore_cable are additional options 1632 See Documentation/ide/ide.rst. 1633 1634 ide-generic.probe-mask= [HW] (E)IDE subsystem 1635 Format: <int> 1636 Probe mask for legacy ISA IDE ports. Depending on 1637 platform up to 6 ports are supported, enabled by 1638 setting corresponding bits in the mask to 1. The 1639 default value is 0x0, which has a special meaning. 1640 On systems that have PCI, it triggers scanning the 1641 PCI bus for the first and the second port, which 1642 are then probed. On systems without PCI the value 1643 of 0x0 enables probing the two first ports as if it 1644 was 0x3. 1645 1646 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1647 Claim all unknown PCI IDE storage controllers. 1648 1649 idle= [X86] 1650 Format: idle=poll, idle=halt, idle=nomwait 1651 Poll forces a polling idle loop that can slightly 1652 improve the performance of waking up a idle CPU, but 1653 will use a lot of power and make the system run hot. 1654 Not recommended. 1655 idle=halt: Halt is forced to be used for CPU idle. 1656 In such case C2/C3 won't be used again. 1657 idle=nomwait: Disable mwait for CPU C-states 1658 1659 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1660 Format: { strict | legacy | 2008 | relaxed } 1661 Default: strict 1662 1663 Choose which programs will be accepted for execution 1664 based on the IEEE 754 NaN encoding(s) supported by 1665 the FPU and the NaN encoding requested with the value 1666 of an ELF file header flag individually set by each 1667 binary. Hardware implementations are permitted to 1668 support either or both of the legacy and the 2008 NaN 1669 encoding mode. 1670 1671 Available settings are as follows: 1672 strict accept binaries that request a NaN encoding 1673 supported by the FPU 1674 legacy only accept legacy-NaN binaries, if supported 1675 by the FPU 1676 2008 only accept 2008-NaN binaries, if supported 1677 by the FPU 1678 relaxed accept any binaries regardless of whether 1679 supported by the FPU 1680 1681 The FPU emulator is always able to support both NaN 1682 encodings, so if no FPU hardware is present or it has 1683 been disabled with 'nofpu', then the settings of 1684 'legacy' and '2008' strap the emulator accordingly, 1685 'relaxed' straps the emulator for both legacy-NaN and 1686 2008-NaN, whereas 'strict' enables legacy-NaN only on 1687 legacy processors and both NaN encodings on MIPS32 or 1688 MIPS64 CPUs. 1689 1690 The setting for ABS.fmt/NEG.fmt instruction execution 1691 mode generally follows that for the NaN encoding, 1692 except where unsupported by hardware. 1693 1694 ignore_loglevel [KNL] 1695 Ignore loglevel setting - this will print /all/ 1696 kernel messages to the console. Useful for debugging. 1697 We also add it as printk module parameter, so users 1698 could change it dynamically, usually by 1699 /sys/module/printk/parameters/ignore_loglevel. 1700 1701 ignore_rlimit_data 1702 Ignore RLIMIT_DATA setting for data mappings, 1703 print warning at first misuse. Can be changed via 1704 /sys/module/kernel/parameters/ignore_rlimit_data. 1705 1706 ihash_entries= [KNL] 1707 Set number of hash buckets for inode cache. 1708 1709 ima_appraise= [IMA] appraise integrity measurements 1710 Format: { "off" | "enforce" | "fix" | "log" } 1711 default: "enforce" 1712 1713 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1714 The builtin appraise policy appraises all files 1715 owned by uid=0. 1716 1717 ima_canonical_fmt [IMA] 1718 Use the canonical format for the binary runtime 1719 measurements, instead of host native format. 1720 1721 ima_hash= [IMA] 1722 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1723 | sha512 | ... } 1724 default: "sha1" 1725 1726 The list of supported hash algorithms is defined 1727 in crypto/hash_info.h. 1728 1729 ima_policy= [IMA] 1730 The builtin policies to load during IMA setup. 1731 Format: "tcb | appraise_tcb | secure_boot | 1732 fail_securely" 1733 1734 The "tcb" policy measures all programs exec'd, files 1735 mmap'd for exec, and all files opened with the read 1736 mode bit set by either the effective uid (euid=0) or 1737 uid=0. 1738 1739 The "appraise_tcb" policy appraises the integrity of 1740 all files owned by root. 1741 1742 The "secure_boot" policy appraises the integrity 1743 of files (eg. kexec kernel image, kernel modules, 1744 firmware, policy, etc) based on file signatures. 1745 1746 The "fail_securely" policy forces file signature 1747 verification failure also on privileged mounted 1748 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1749 flag. 1750 1751 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1752 Load a policy which meets the needs of the Trusted 1753 Computing Base. This means IMA will measure all 1754 programs exec'd, files mmap'd for exec, and all files 1755 opened for read by uid=0. 1756 1757 ima_template= [IMA] 1758 Select one of defined IMA measurements template formats. 1759 Formats: { "ima" | "ima-ng" | "ima-sig" } 1760 Default: "ima-ng" 1761 1762 ima_template_fmt= 1763 [IMA] Define a custom template format. 1764 Format: { "field1|...|fieldN" } 1765 1766 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1767 Format: <min_file_size> 1768 Set the minimal file size for using asynchronous hash. 1769 If left unspecified, ahash usage is disabled. 1770 1771 ahash performance varies for different data sizes on 1772 different crypto accelerators. This option can be used 1773 to achieve the best performance for a particular HW. 1774 1775 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1776 Format: <bufsize> 1777 Set hashing buffer size. Default: 4k. 1778 1779 ahash performance varies for different chunk sizes on 1780 different crypto accelerators. This option can be used 1781 to achieve best performance for particular HW. 1782 1783 init= [KNL] 1784 Format: <full_path> 1785 Run specified binary instead of /sbin/init as init 1786 process. 1787 1788 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1789 for working out where the kernel is dying during 1790 startup. 1791 1792 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1793 initcall functions. Useful for debugging built-in 1794 modules and initcalls. 1795 1796 initrd= [BOOT] Specify the location of the initial ramdisk 1797 1798 initrdmem= [KNL] Specify a physical address and size from which to 1799 load the initrd. If an initrd is compiled in or 1800 specified in the bootparams, it takes priority over this 1801 setting. 1802 Format: ss[KMG],nn[KMG] 1803 Default is 0, 0 1804 1805 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1806 zeroes. 1807 Format: 0 | 1 1808 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1809 1810 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1811 Format: 0 | 1 1812 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1813 1814 init_pkru= [X86] Specify the default memory protection keys rights 1815 register contents for all processes. 0x55555554 by 1816 default (disallow access to all but pkey 0). Can 1817 override in debugfs after boot. 1818 1819 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1820 Format: <irq> 1821 1822 int_pln_enable [X86] Enable power limit notification interrupt 1823 1824 integrity_audit=[IMA] 1825 Format: { "0" | "1" } 1826 0 -- basic integrity auditing messages. (Default) 1827 1 -- additional integrity auditing messages. 1828 1829 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1830 on 1831 Enable intel iommu driver. 1832 off 1833 Disable intel iommu driver. 1834 igfx_off [Default Off] 1835 By default, gfx is mapped as normal device. If a gfx 1836 device has a dedicated DMAR unit, the DMAR unit is 1837 bypassed by not enabling DMAR with this option. In 1838 this case, gfx device will use physical address for 1839 DMA. 1840 forcedac [X86-64] 1841 With this option iommu will not optimize to look 1842 for io virtual address below 32-bit forcing dual 1843 address cycle on pci bus for cards supporting greater 1844 than 32-bit addressing. The default is to look 1845 for translation below 32-bit and if not available 1846 then look in the higher range. 1847 strict [Default Off] 1848 With this option on every unmap_single operation will 1849 result in a hardware IOTLB flush operation as opposed 1850 to batching them for performance. 1851 sp_off [Default Off] 1852 By default, super page will be supported if Intel IOMMU 1853 has the capability. With this option, super page will 1854 not be supported. 1855 sm_on [Default Off] 1856 By default, scalable mode will be disabled even if the 1857 hardware advertises that it has support for the scalable 1858 mode translation. With this option set, scalable mode 1859 will be used on hardware which claims to support it. 1860 tboot_noforce [Default Off] 1861 Do not force the Intel IOMMU enabled under tboot. 1862 By default, tboot will force Intel IOMMU on, which 1863 could harm performance of some high-throughput 1864 devices like 40GBit network cards, even if identity 1865 mapping is enabled. 1866 Note that using this option lowers the security 1867 provided by tboot because it makes the system 1868 vulnerable to DMA attacks. 1869 nobounce [Default off] 1870 Disable bounce buffer for untrusted devices such as 1871 the Thunderbolt devices. This will treat the untrusted 1872 devices as the trusted ones, hence might expose security 1873 risks of DMA attacks. 1874 1875 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1876 0 disables intel_idle and fall back on acpi_idle. 1877 1 to 9 specify maximum depth of C-state. 1878 1879 intel_pstate= [X86] 1880 disable 1881 Do not enable intel_pstate as the default 1882 scaling driver for the supported processors 1883 passive 1884 Use intel_pstate as a scaling driver, but configure it 1885 to work with generic cpufreq governors (instead of 1886 enabling its internal governor). This mode cannot be 1887 used along with the hardware-managed P-states (HWP) 1888 feature. 1889 force 1890 Enable intel_pstate on systems that prohibit it by default 1891 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1892 instead of acpi-cpufreq may disable platform features, such 1893 as thermal controls and power capping, that rely on ACPI 1894 P-States information being indicated to OSPM and therefore 1895 should be used with caution. This option does not work with 1896 processors that aren't supported by the intel_pstate driver 1897 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1898 no_hwp 1899 Do not enable hardware P state control (HWP) 1900 if available. 1901 hwp_only 1902 Only load intel_pstate on systems which support 1903 hardware P state control (HWP) if available. 1904 support_acpi_ppc 1905 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1906 Description Table, specifies preferred power management 1907 profile as "Enterprise Server" or "Performance Server", 1908 then this feature is turned on by default. 1909 per_cpu_perf_limits 1910 Allow per-logical-CPU P-State performance control limits using 1911 cpufreq sysfs interface 1912 1913 intremap= [X86-64, Intel-IOMMU] 1914 on enable Interrupt Remapping (default) 1915 off disable Interrupt Remapping 1916 nosid disable Source ID checking 1917 no_x2apic_optout 1918 BIOS x2APIC opt-out request will be ignored 1919 nopost disable Interrupt Posting 1920 1921 iomem= Disable strict checking of access to MMIO memory 1922 strict regions from userspace. 1923 relaxed 1924 1925 iommu= [X86] 1926 off 1927 force 1928 noforce 1929 biomerge 1930 panic 1931 nopanic 1932 merge 1933 nomerge 1934 soft 1935 pt [X86] 1936 nopt [X86] 1937 nobypass [PPC/POWERNV] 1938 Disable IOMMU bypass, using IOMMU for PCI devices. 1939 1940 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1941 Format: { "0" | "1" } 1942 0 - Lazy mode. 1943 Request that DMA unmap operations use deferred 1944 invalidation of hardware TLBs, for increased 1945 throughput at the cost of reduced device isolation. 1946 Will fall back to strict mode if not supported by 1947 the relevant IOMMU driver. 1948 1 - Strict mode (default). 1949 DMA unmap operations invalidate IOMMU hardware TLBs 1950 synchronously. 1951 1952 iommu.passthrough= 1953 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1954 Format: { "0" | "1" } 1955 0 - Use IOMMU translation for DMA. 1956 1 - Bypass the IOMMU for DMA. 1957 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1958 1959 io7= [HW] IO7 for Marvel-based Alpha systems 1960 See comment before marvel_specify_io7 in 1961 arch/alpha/kernel/core_marvel.c. 1962 1963 io_delay= [X86] I/O delay method 1964 0x80 1965 Standard port 0x80 based delay 1966 0xed 1967 Alternate port 0xed based delay (needed on some systems) 1968 udelay 1969 Simple two microseconds delay 1970 none 1971 No delay 1972 1973 ip= [IP_PNP] 1974 See Documentation/admin-guide/nfs/nfsroot.rst. 1975 1976 ipcmni_extend [KNL] Extend the maximum number of unique System V 1977 IPC identifiers from 32,768 to 16,777,216. 1978 1979 irqaffinity= [SMP] Set the default irq affinity mask 1980 The argument is a cpu list, as described above. 1981 1982 irqchip.gicv2_force_probe= 1983 [ARM, ARM64] 1984 Format: <bool> 1985 Force the kernel to look for the second 4kB page 1986 of a GICv2 controller even if the memory range 1987 exposed by the device tree is too small. 1988 1989 irqchip.gicv3_nolpi= 1990 [ARM, ARM64] 1991 Force the kernel to ignore the availability of 1992 LPIs (and by consequence ITSs). Intended for system 1993 that use the kernel as a bootloader, and thus want 1994 to let secondary kernels in charge of setting up 1995 LPIs. 1996 1997 irqchip.gicv3_pseudo_nmi= [ARM64] 1998 Enables support for pseudo-NMIs in the kernel. This 1999 requires the kernel to be built with 2000 CONFIG_ARM64_PSEUDO_NMI. 2001 2002 irqfixup [HW] 2003 When an interrupt is not handled search all handlers 2004 for it. Intended to get systems with badly broken 2005 firmware running. 2006 2007 irqpoll [HW] 2008 When an interrupt is not handled search all handlers 2009 for it. Also check all handlers each timer 2010 interrupt. Intended to get systems with badly broken 2011 firmware running. 2012 2013 isapnp= [ISAPNP] 2014 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2015 2016 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2017 [Deprecated - use cpusets instead] 2018 Format: [flag-list,]<cpu-list> 2019 2020 Specify one or more CPUs to isolate from disturbances 2021 specified in the flag list (default: domain): 2022 2023 nohz 2024 Disable the tick when a single task runs. 2025 2026 A residual 1Hz tick is offloaded to workqueues, which you 2027 need to affine to housekeeping through the global 2028 workqueue's affinity configured via the 2029 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2030 by using the 'domain' flag described below. 2031 2032 NOTE: by default the global workqueue runs on all CPUs, 2033 so to protect individual CPUs the 'cpumask' file has to 2034 be configured manually after bootup. 2035 2036 domain 2037 Isolate from the general SMP balancing and scheduling 2038 algorithms. Note that performing domain isolation this way 2039 is irreversible: it's not possible to bring back a CPU to 2040 the domains once isolated through isolcpus. It's strongly 2041 advised to use cpusets instead to disable scheduler load 2042 balancing through the "cpuset.sched_load_balance" file. 2043 It offers a much more flexible interface where CPUs can 2044 move in and out of an isolated set anytime. 2045 2046 You can move a process onto or off an "isolated" CPU via 2047 the CPU affinity syscalls or cpuset. 2048 <cpu number> begins at 0 and the maximum value is 2049 "number of CPUs in system - 1". 2050 2051 managed_irq 2052 2053 Isolate from being targeted by managed interrupts 2054 which have an interrupt mask containing isolated 2055 CPUs. The affinity of managed interrupts is 2056 handled by the kernel and cannot be changed via 2057 the /proc/irq/* interfaces. 2058 2059 This isolation is best effort and only effective 2060 if the automatically assigned interrupt mask of a 2061 device queue contains isolated and housekeeping 2062 CPUs. If housekeeping CPUs are online then such 2063 interrupts are directed to the housekeeping CPU 2064 so that IO submitted on the housekeeping CPU 2065 cannot disturb the isolated CPU. 2066 2067 If a queue's affinity mask contains only isolated 2068 CPUs then this parameter has no effect on the 2069 interrupt routing decision, though interrupts are 2070 only delivered when tasks running on those 2071 isolated CPUs submit IO. IO submitted on 2072 housekeeping CPUs has no influence on those 2073 queues. 2074 2075 The format of <cpu-list> is described above. 2076 2077 iucv= [HW,NET] 2078 2079 ivrs_ioapic [HW,X86-64] 2080 Provide an override to the IOAPIC-ID<->DEVICE-ID 2081 mapping provided in the IVRS ACPI table. For 2082 example, to map IOAPIC-ID decimal 10 to 2083 PCI device 00:14.0 write the parameter as: 2084 ivrs_ioapic[10]=00:14.0 2085 2086 ivrs_hpet [HW,X86-64] 2087 Provide an override to the HPET-ID<->DEVICE-ID 2088 mapping provided in the IVRS ACPI table. For 2089 example, to map HPET-ID decimal 0 to 2090 PCI device 00:14.0 write the parameter as: 2091 ivrs_hpet[0]=00:14.0 2092 2093 ivrs_acpihid [HW,X86-64] 2094 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2095 mapping provided in the IVRS ACPI table. For 2096 example, to map UART-HID:UID AMD0020:0 to 2097 PCI device 00:14.5 write the parameter as: 2098 ivrs_acpihid[00:14.5]=AMD0020:0 2099 2100 js= [HW,JOY] Analog joystick 2101 See Documentation/input/joydev/joystick.rst. 2102 2103 nokaslr [KNL] 2104 When CONFIG_RANDOMIZE_BASE is set, this disables 2105 kernel and module base offset ASLR (Address Space 2106 Layout Randomization). 2107 2108 kasan_multi_shot 2109 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2110 report on every invalid memory access. Without this 2111 parameter KASAN will print report only for the first 2112 invalid access. 2113 2114 keepinitrd [HW,ARM] 2115 2116 kernelcore= [KNL,X86,IA-64,PPC] 2117 Format: nn[KMGTPE] | nn% | "mirror" 2118 This parameter specifies the amount of memory usable by 2119 the kernel for non-movable allocations. The requested 2120 amount is spread evenly throughout all nodes in the 2121 system as ZONE_NORMAL. The remaining memory is used for 2122 movable memory in its own zone, ZONE_MOVABLE. In the 2123 event, a node is too small to have both ZONE_NORMAL and 2124 ZONE_MOVABLE, kernelcore memory will take priority and 2125 other nodes will have a larger ZONE_MOVABLE. 2126 2127 ZONE_MOVABLE is used for the allocation of pages that 2128 may be reclaimed or moved by the page migration 2129 subsystem. Note that allocations like PTEs-from-HighMem 2130 still use the HighMem zone if it exists, and the Normal 2131 zone if it does not. 2132 2133 It is possible to specify the exact amount of memory in 2134 the form of "nn[KMGTPE]", a percentage of total system 2135 memory in the form of "nn%", or "mirror". If "mirror" 2136 option is specified, mirrored (reliable) memory is used 2137 for non-movable allocations and remaining memory is used 2138 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2139 are exclusive, so you cannot specify multiple forms. 2140 2141 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2142 Format: <Controller#>[,poll interval] 2143 The controller # is the number of the ehci usb debug 2144 port as it is probed via PCI. The poll interval is 2145 optional and is the number seconds in between 2146 each poll cycle to the debug port in case you need 2147 the functionality for interrupting the kernel with 2148 gdb or control-c on the dbgp connection. When 2149 not using this parameter you use sysrq-g to break into 2150 the kernel debugger. 2151 2152 kgdboc= [KGDB,HW] kgdb over consoles. 2153 Requires a tty driver that supports console polling, 2154 or a supported polling keyboard driver (non-usb). 2155 Serial only format: <serial_device>[,baud] 2156 keyboard only format: kbd 2157 keyboard and serial format: kbd,<serial_device>[,baud] 2158 Optional Kernel mode setting: 2159 kms, kbd format: kms,kbd 2160 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2161 2162 kgdboc_earlycon= [KGDB,HW] 2163 If the boot console provides the ability to read 2164 characters and can work in polling mode, you can use 2165 this parameter to tell kgdb to use it as a backend 2166 until the normal console is registered. Intended to 2167 be used together with the kgdboc parameter which 2168 specifies the normal console to transition to. 2169 2170 The name of the early console should be specified 2171 as the value of this parameter. Note that the name of 2172 the early console might be different than the tty 2173 name passed to kgdboc. It's OK to leave the value 2174 blank and the first boot console that implements 2175 read() will be picked. 2176 2177 kgdbwait [KGDB] Stop kernel execution and enter the 2178 kernel debugger at the earliest opportunity. 2179 2180 kmac= [MIPS] Korina ethernet MAC address. 2181 Configure the RouterBoard 532 series on-chip 2182 Ethernet adapter MAC address. 2183 2184 kmemleak= [KNL] Boot-time kmemleak enable/disable 2185 Valid arguments: on, off 2186 Default: on 2187 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2188 the default is off. 2189 2190 kprobe_event=[probe-list] 2191 [FTRACE] Add kprobe events and enable at boot time. 2192 The probe-list is a semicolon delimited list of probe 2193 definitions. Each definition is same as kprobe_events 2194 interface, but the parameters are comma delimited. 2195 For example, to add a kprobe event on vfs_read with 2196 arg1 and arg2, add to the command line; 2197 2198 kprobe_event=p,vfs_read,$arg1,$arg2 2199 2200 See also Documentation/trace/kprobetrace.rst "Kernel 2201 Boot Parameter" section. 2202 2203 kpti= [ARM64] Control page table isolation of user 2204 and kernel address spaces. 2205 Default: enabled on cores which need mitigation. 2206 0: force disabled 2207 1: force enabled 2208 2209 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2210 Default is 0 (don't ignore, but inject #GP) 2211 2212 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2213 Default is false (don't support). 2214 2215 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2216 KVM MMU at runtime. 2217 Default is 0 (off) 2218 2219 kvm.nx_huge_pages= 2220 [KVM] Controls the software workaround for the 2221 X86_BUG_ITLB_MULTIHIT bug. 2222 force : Always deploy workaround. 2223 off : Never deploy workaround. 2224 auto : Deploy workaround based on the presence of 2225 X86_BUG_ITLB_MULTIHIT. 2226 2227 Default is 'auto'. 2228 2229 If the software workaround is enabled for the host, 2230 guests do need not to enable it for nested guests. 2231 2232 kvm.nx_huge_pages_recovery_ratio= 2233 [KVM] Controls how many 4KiB pages are periodically zapped 2234 back to huge pages. 0 disables the recovery, otherwise if 2235 the value is N KVM will zap 1/Nth of the 4KiB pages every 2236 minute. The default is 60. 2237 2238 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2239 Default is 1 (enabled) 2240 2241 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2242 for all guests. 2243 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2244 2245 kvm-arm.vgic_v3_group0_trap= 2246 [KVM,ARM] Trap guest accesses to GICv3 group-0 2247 system registers 2248 2249 kvm-arm.vgic_v3_group1_trap= 2250 [KVM,ARM] Trap guest accesses to GICv3 group-1 2251 system registers 2252 2253 kvm-arm.vgic_v3_common_trap= 2254 [KVM,ARM] Trap guest accesses to GICv3 common 2255 system registers 2256 2257 kvm-arm.vgic_v4_enable= 2258 [KVM,ARM] Allow use of GICv4 for direct injection of 2259 LPIs. 2260 2261 kvm_cma_resv_ratio=n [PPC] 2262 Reserves given percentage from system memory area for 2263 contiguous memory allocation for KVM hash pagetable 2264 allocation. 2265 By default it reserves 5% of total system memory. 2266 Format: <integer> 2267 Default: 5 2268 2269 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2270 (virtualized MMU) support on capable Intel chips. 2271 Default is 1 (enabled) 2272 2273 kvm-intel.emulate_invalid_guest_state= 2274 [KVM,Intel] Enable emulation of invalid guest states 2275 Default is 0 (disabled) 2276 2277 kvm-intel.flexpriority= 2278 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2279 Default is 1 (enabled) 2280 2281 kvm-intel.nested= 2282 [KVM,Intel] Enable VMX nesting (nVMX). 2283 Default is 0 (disabled) 2284 2285 kvm-intel.unrestricted_guest= 2286 [KVM,Intel] Disable unrestricted guest feature 2287 (virtualized real and unpaged mode) on capable 2288 Intel chips. Default is 1 (enabled) 2289 2290 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2291 CVE-2018-3620. 2292 2293 Valid arguments: never, cond, always 2294 2295 always: L1D cache flush on every VMENTER. 2296 cond: Flush L1D on VMENTER only when the code between 2297 VMEXIT and VMENTER can leak host memory. 2298 never: Disables the mitigation 2299 2300 Default is cond (do L1 cache flush in specific instances) 2301 2302 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2303 feature (tagged TLBs) on capable Intel chips. 2304 Default is 1 (enabled) 2305 2306 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2307 affected CPUs 2308 2309 The kernel PTE inversion protection is unconditionally 2310 enabled and cannot be disabled. 2311 2312 full 2313 Provides all available mitigations for the 2314 L1TF vulnerability. Disables SMT and 2315 enables all mitigations in the 2316 hypervisors, i.e. unconditional L1D flush. 2317 2318 SMT control and L1D flush control via the 2319 sysfs interface is still possible after 2320 boot. Hypervisors will issue a warning 2321 when the first VM is started in a 2322 potentially insecure configuration, 2323 i.e. SMT enabled or L1D flush disabled. 2324 2325 full,force 2326 Same as 'full', but disables SMT and L1D 2327 flush runtime control. Implies the 2328 'nosmt=force' command line option. 2329 (i.e. sysfs control of SMT is disabled.) 2330 2331 flush 2332 Leaves SMT enabled and enables the default 2333 hypervisor mitigation, i.e. conditional 2334 L1D flush. 2335 2336 SMT control and L1D flush control via the 2337 sysfs interface is still possible after 2338 boot. Hypervisors will issue a warning 2339 when the first VM is started in a 2340 potentially insecure configuration, 2341 i.e. SMT enabled or L1D flush disabled. 2342 2343 flush,nosmt 2344 2345 Disables SMT and enables the default 2346 hypervisor mitigation. 2347 2348 SMT control and L1D flush control via the 2349 sysfs interface is still possible after 2350 boot. Hypervisors will issue a warning 2351 when the first VM is started in a 2352 potentially insecure configuration, 2353 i.e. SMT enabled or L1D flush disabled. 2354 2355 flush,nowarn 2356 Same as 'flush', but hypervisors will not 2357 warn when a VM is started in a potentially 2358 insecure configuration. 2359 2360 off 2361 Disables hypervisor mitigations and doesn't 2362 emit any warnings. 2363 It also drops the swap size and available 2364 RAM limit restriction on both hypervisor and 2365 bare metal. 2366 2367 Default is 'flush'. 2368 2369 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2370 2371 l2cr= [PPC] 2372 2373 l3cr= [PPC] 2374 2375 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2376 disabled it. 2377 2378 lapic= [X86,APIC] Do not use TSC deadline 2379 value for LAPIC timer one-shot implementation. Default 2380 back to the programmable timer unit in the LAPIC. 2381 Format: notscdeadline 2382 2383 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2384 in C2 power state. 2385 2386 libata.dma= [LIBATA] DMA control 2387 libata.dma=0 Disable all PATA and SATA DMA 2388 libata.dma=1 PATA and SATA Disk DMA only 2389 libata.dma=2 ATAPI (CDROM) DMA only 2390 libata.dma=4 Compact Flash DMA only 2391 Combinations also work, so libata.dma=3 enables DMA 2392 for disks and CDROMs, but not CFs. 2393 2394 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2395 libata.ignore_hpa=0 keep BIOS limits (default) 2396 libata.ignore_hpa=1 ignore limits, using full disk 2397 2398 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2399 when set. 2400 Format: <int> 2401 2402 libata.force= [LIBATA] Force configurations. The format is comma 2403 separated list of "[ID:]VAL" where ID is 2404 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2405 matching port, link or device. Basically, it matches 2406 the ATA ID string printed on console by libata. If 2407 the whole ID part is omitted, the last PORT and DEVICE 2408 values are used. If ID hasn't been specified yet, the 2409 configuration applies to all ports, links and devices. 2410 2411 If only DEVICE is omitted, the parameter applies to 2412 the port and all links and devices behind it. DEVICE 2413 number of 0 either selects the first device or the 2414 first fan-out link behind PMP device. It does not 2415 select the host link. DEVICE number of 15 selects the 2416 host link and device attached to it. 2417 2418 The VAL specifies the configuration to force. As long 2419 as there's no ambiguity shortcut notation is allowed. 2420 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2421 The following configurations can be forced. 2422 2423 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2424 Any ID with matching PORT is used. 2425 2426 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2427 2428 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2429 udma[/][16,25,33,44,66,100,133] notation is also 2430 allowed. 2431 2432 * [no]ncq: Turn on or off NCQ. 2433 2434 * [no]ncqtrim: Turn off queued DSM TRIM. 2435 2436 * nohrst, nosrst, norst: suppress hard, soft 2437 and both resets. 2438 2439 * rstonce: only attempt one reset during 2440 hot-unplug link recovery 2441 2442 * dump_id: dump IDENTIFY data. 2443 2444 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2445 2446 * disable: Disable this device. 2447 2448 If there are multiple matching configurations changing 2449 the same attribute, the last one is used. 2450 2451 memblock=debug [KNL] Enable memblock debug messages. 2452 2453 load_ramdisk= [RAM] [Deprecated] 2454 2455 lockd.nlm_grace_period=P [NFS] Assign grace period. 2456 Format: <integer> 2457 2458 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2459 Format: <integer> 2460 2461 lockd.nlm_timeout=T [NFS] Assign timeout value. 2462 Format: <integer> 2463 2464 lockd.nlm_udpport=M [NFS] Assign UDP port. 2465 Format: <integer> 2466 2467 lockdown= [SECURITY] 2468 { integrity | confidentiality } 2469 Enable the kernel lockdown feature. If set to 2470 integrity, kernel features that allow userland to 2471 modify the running kernel are disabled. If set to 2472 confidentiality, kernel features that allow userland 2473 to extract confidential information from the kernel 2474 are also disabled. 2475 2476 locktorture.nreaders_stress= [KNL] 2477 Set the number of locking read-acquisition kthreads. 2478 Defaults to being automatically set based on the 2479 number of online CPUs. 2480 2481 locktorture.nwriters_stress= [KNL] 2482 Set the number of locking write-acquisition kthreads. 2483 2484 locktorture.onoff_holdoff= [KNL] 2485 Set time (s) after boot for CPU-hotplug testing. 2486 2487 locktorture.onoff_interval= [KNL] 2488 Set time (s) between CPU-hotplug operations, or 2489 zero to disable CPU-hotplug testing. 2490 2491 locktorture.shuffle_interval= [KNL] 2492 Set task-shuffle interval (jiffies). Shuffling 2493 tasks allows some CPUs to go into dyntick-idle 2494 mode during the locktorture test. 2495 2496 locktorture.shutdown_secs= [KNL] 2497 Set time (s) after boot system shutdown. This 2498 is useful for hands-off automated testing. 2499 2500 locktorture.stat_interval= [KNL] 2501 Time (s) between statistics printk()s. 2502 2503 locktorture.stutter= [KNL] 2504 Time (s) to stutter testing, for example, 2505 specifying five seconds causes the test to run for 2506 five seconds, wait for five seconds, and so on. 2507 This tests the locking primitive's ability to 2508 transition abruptly to and from idle. 2509 2510 locktorture.torture_type= [KNL] 2511 Specify the locking implementation to test. 2512 2513 locktorture.verbose= [KNL] 2514 Enable additional printk() statements. 2515 2516 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2517 Format: <irq> 2518 2519 loglevel= All Kernel Messages with a loglevel smaller than the 2520 console loglevel will be printed to the console. It can 2521 also be changed with klogd or other programs. The 2522 loglevels are defined as follows: 2523 2524 0 (KERN_EMERG) system is unusable 2525 1 (KERN_ALERT) action must be taken immediately 2526 2 (KERN_CRIT) critical conditions 2527 3 (KERN_ERR) error conditions 2528 4 (KERN_WARNING) warning conditions 2529 5 (KERN_NOTICE) normal but significant condition 2530 6 (KERN_INFO) informational 2531 7 (KERN_DEBUG) debug-level messages 2532 2533 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2534 in bytes. n must be a power of two and greater 2535 than the minimal size. The minimal size is defined 2536 by LOG_BUF_SHIFT kernel config parameter. There is 2537 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2538 that allows to increase the default size depending on 2539 the number of CPUs. See init/Kconfig for more details. 2540 2541 logo.nologo [FB] Disables display of the built-in Linux logo. 2542 This may be used to provide more screen space for 2543 kernel log messages and is useful when debugging 2544 kernel boot problems. 2545 2546 lp=0 [LP] Specify parallel ports to use, e.g, 2547 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2548 lp=reset first parallel port). 'lp=0' disables the 2549 lp=auto printer driver. 'lp=reset' (which can be 2550 specified in addition to the ports) causes 2551 attached printers to be reset. Using 2552 lp=port1,port2,... specifies the parallel ports 2553 to associate lp devices with, starting with 2554 lp0. A port specification may be 'none' to skip 2555 that lp device, or a parport name such as 2556 'parport0'. Specifying 'lp=auto' instead of a 2557 port specification list means that device IDs 2558 from each port should be examined, to see if 2559 an IEEE 1284-compliant printer is attached; if 2560 so, the driver will manage that printer. 2561 See also header of drivers/char/lp.c. 2562 2563 lpj=n [KNL] 2564 Sets loops_per_jiffy to given constant, thus avoiding 2565 time-consuming boot-time autodetection (up to 250 ms per 2566 CPU). 0 enables autodetection (default). To determine 2567 the correct value for your kernel, boot with normal 2568 autodetection and see what value is printed. Note that 2569 on SMP systems the preset will be applied to all CPUs, 2570 which is likely to cause problems if your CPUs need 2571 significantly divergent settings. An incorrect value 2572 will cause delays in the kernel to be wrong, leading to 2573 unpredictable I/O errors and other breakage. Although 2574 unlikely, in the extreme case this might damage your 2575 hardware. 2576 2577 ltpc= [NET] 2578 Format: <io>,<irq>,<dma> 2579 2580 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2581 2582 lsm=lsm1,...,lsmN 2583 [SECURITY] Choose order of LSM initialization. This 2584 overrides CONFIG_LSM, and the "security=" parameter. 2585 2586 machvec= [IA-64] Force the use of a particular machine-vector 2587 (machvec) in a generic kernel. 2588 Example: machvec=hpzx1 2589 2590 machtype= [Loongson] Share the same kernel image file between 2591 different yeeloong laptops. 2592 Example: machtype=lemote-yeeloong-2f-7inch 2593 2594 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2595 than or equal to this physical address is ignored. 2596 2597 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2598 will bring up during bootup. maxcpus=n : n >= 0 limits 2599 the kernel to bring up 'n' processors. Surely after 2600 bootup you can bring up the other plugged cpu by executing 2601 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2602 only takes effect during system bootup. 2603 While n=0 is a special case, it is equivalent to "nosmp", 2604 which also disables the IO APIC. 2605 2606 max_loop= [LOOP] The number of loop block devices that get 2607 (loop.max_loop) unconditionally pre-created at init time. The default 2608 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2609 of statically allocating a predefined number, loop 2610 devices can be requested on-demand with the 2611 /dev/loop-control interface. 2612 2613 mce [X86-32] Machine Check Exception 2614 2615 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2616 2617 md= [HW] RAID subsystems devices and level 2618 See Documentation/admin-guide/md.rst. 2619 2620 mdacon= [MDA] 2621 Format: <first>,<last> 2622 Specifies range of consoles to be captured by the MDA. 2623 2624 mds= [X86,INTEL] 2625 Control mitigation for the Micro-architectural Data 2626 Sampling (MDS) vulnerability. 2627 2628 Certain CPUs are vulnerable to an exploit against CPU 2629 internal buffers which can forward information to a 2630 disclosure gadget under certain conditions. 2631 2632 In vulnerable processors, the speculatively 2633 forwarded data can be used in a cache side channel 2634 attack, to access data to which the attacker does 2635 not have direct access. 2636 2637 This parameter controls the MDS mitigation. The 2638 options are: 2639 2640 full - Enable MDS mitigation on vulnerable CPUs 2641 full,nosmt - Enable MDS mitigation and disable 2642 SMT on vulnerable CPUs 2643 off - Unconditionally disable MDS mitigation 2644 2645 On TAA-affected machines, mds=off can be prevented by 2646 an active TAA mitigation as both vulnerabilities are 2647 mitigated with the same mechanism so in order to disable 2648 this mitigation, you need to specify tsx_async_abort=off 2649 too. 2650 2651 Not specifying this option is equivalent to 2652 mds=full. 2653 2654 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2655 2656 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2657 Amount of memory to be used in cases as follows: 2658 2659 1 for test; 2660 2 when the kernel is not able to see the whole system memory; 2661 3 memory that lies after 'mem=' boundary is excluded from 2662 the hypervisor, then assigned to KVM guests. 2663 2664 [X86] Work as limiting max address. Use together 2665 with memmap= to avoid physical address space collisions. 2666 Without memmap= PCI devices could be placed at addresses 2667 belonging to unused RAM. 2668 2669 Note that this only takes effects during boot time since 2670 in above case 3, memory may need be hot added after boot 2671 if system memory of hypervisor is not sufficient. 2672 2673 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2674 memory. 2675 2676 memchunk=nn[KMG] 2677 [KNL,SH] Allow user to override the default size for 2678 per-device physically contiguous DMA buffers. 2679 2680 memhp_default_state=online/offline 2681 [KNL] Set the initial state for the memory hotplug 2682 onlining policy. If not specified, the default value is 2683 set according to the 2684 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2685 option. 2686 See Documentation/admin-guide/mm/memory-hotplug.rst. 2687 2688 memmap=exactmap [KNL,X86] Enable setting of an exact 2689 E820 memory map, as specified by the user. 2690 Such memmap=exactmap lines can be constructed based on 2691 BIOS output or other requirements. See the memmap=nn@ss 2692 option description. 2693 2694 memmap=nn[KMG]@ss[KMG] 2695 [KNL] Force usage of a specific region of memory. 2696 Region of memory to be used is from ss to ss+nn. 2697 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2698 which limits max address to nn[KMG]. 2699 Multiple different regions can be specified, 2700 comma delimited. 2701 Example: 2702 memmap=100M@2G,100M#3G,1G!1024G 2703 2704 memmap=nn[KMG]#ss[KMG] 2705 [KNL,ACPI] Mark specific memory as ACPI data. 2706 Region of memory to be marked is from ss to ss+nn. 2707 2708 memmap=nn[KMG]$ss[KMG] 2709 [KNL,ACPI] Mark specific memory as reserved. 2710 Region of memory to be reserved is from ss to ss+nn. 2711 Example: Exclude memory from 0x18690000-0x1869ffff 2712 memmap=64K$0x18690000 2713 or 2714 memmap=0x10000$0x18690000 2715 Some bootloaders may need an escape character before '$', 2716 like Grub2, otherwise '$' and the following number 2717 will be eaten. 2718 2719 memmap=nn[KMG]!ss[KMG] 2720 [KNL,X86] Mark specific memory as protected. 2721 Region of memory to be used, from ss to ss+nn. 2722 The memory region may be marked as e820 type 12 (0xc) 2723 and is NVDIMM or ADR memory. 2724 2725 memmap=<size>%<offset>-<oldtype>+<newtype> 2726 [KNL,ACPI] Convert memory within the specified region 2727 from <oldtype> to <newtype>. If "-<oldtype>" is left 2728 out, the whole region will be marked as <newtype>, 2729 even if previously unavailable. If "+<newtype>" is left 2730 out, matching memory will be removed. Types are 2731 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2732 3 = ACPI, 12 = PRAM. 2733 2734 memory_corruption_check=0/1 [X86] 2735 Some BIOSes seem to corrupt the first 64k of 2736 memory when doing things like suspend/resume. 2737 Setting this option will scan the memory 2738 looking for corruption. Enabling this will 2739 both detect corruption and prevent the kernel 2740 from using the memory being corrupted. 2741 However, its intended as a diagnostic tool; if 2742 repeatable BIOS-originated corruption always 2743 affects the same memory, you can use memmap= 2744 to prevent the kernel from using that memory. 2745 2746 memory_corruption_check_size=size [X86] 2747 By default it checks for corruption in the low 2748 64k, making this memory unavailable for normal 2749 use. Use this parameter to scan for 2750 corruption in more or less memory. 2751 2752 memory_corruption_check_period=seconds [X86] 2753 By default it checks for corruption every 60 2754 seconds. Use this parameter to check at some 2755 other rate. 0 disables periodic checking. 2756 2757 memtest= [KNL,X86,ARM,PPC] Enable memtest 2758 Format: <integer> 2759 default : 0 <disable> 2760 Specifies the number of memtest passes to be 2761 performed. Each pass selects another test 2762 pattern from a given set of patterns. Memtest 2763 fills the memory with this pattern, validates 2764 memory contents and reserves bad memory 2765 regions that are detected. 2766 2767 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2768 Valid arguments: on, off 2769 Default (depends on kernel configuration option): 2770 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2771 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2772 mem_encrypt=on: Activate SME 2773 mem_encrypt=off: Do not activate SME 2774 2775 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2776 for details on when memory encryption can be activated. 2777 2778 mem_sleep_default= [SUSPEND] Default system suspend mode: 2779 s2idle - Suspend-To-Idle 2780 shallow - Power-On Suspend or equivalent (if supported) 2781 deep - Suspend-To-RAM or equivalent (if supported) 2782 See Documentation/admin-guide/pm/sleep-states.rst. 2783 2784 meye.*= [HW] Set MotionEye Camera parameters 2785 See Documentation/admin-guide/media/meye.rst. 2786 2787 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2788 Multi-Function General Purpose Timers on AMD Geode 2789 platforms. 2790 2791 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2792 the BIOS has incorrectly applied a workaround. TinyBIOS 2793 version 0.98 is known to be affected, 0.99 fixes the 2794 problem by letting the user disable the workaround. 2795 2796 mga= [HW,DRM] 2797 2798 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2799 physical address is ignored. 2800 2801 mini2440= [ARM,HW,KNL] 2802 Format:[0..2][b][c][t] 2803 Default: "0tb" 2804 MINI2440 configuration specification: 2805 0 - The attached screen is the 3.5" TFT 2806 1 - The attached screen is the 7" TFT 2807 2 - The VGA Shield is attached (1024x768) 2808 Leaving out the screen size parameter will not load 2809 the TFT driver, and the framebuffer will be left 2810 unconfigured. 2811 b - Enable backlight. The TFT backlight pin will be 2812 linked to the kernel VESA blanking code and a GPIO 2813 LED. This parameter is not necessary when using the 2814 VGA shield. 2815 c - Enable the s3c camera interface. 2816 t - Reserved for enabling touchscreen support. The 2817 touchscreen support is not enabled in the mainstream 2818 kernel as of 2.6.30, a preliminary port can be found 2819 in the "bleeding edge" mini2440 support kernel at 2820 https://repo.or.cz/w/linux-2.6/mini2440.git 2821 2822 mitigations= 2823 [X86,PPC,S390,ARM64] Control optional mitigations for 2824 CPU vulnerabilities. This is a set of curated, 2825 arch-independent options, each of which is an 2826 aggregation of existing arch-specific options. 2827 2828 off 2829 Disable all optional CPU mitigations. This 2830 improves system performance, but it may also 2831 expose users to several CPU vulnerabilities. 2832 Equivalent to: nopti [X86,PPC] 2833 kpti=0 [ARM64] 2834 nospectre_v1 [X86,PPC] 2835 nobp=0 [S390] 2836 nospectre_v2 [X86,PPC,S390,ARM64] 2837 spectre_v2_user=off [X86] 2838 spec_store_bypass_disable=off [X86,PPC] 2839 ssbd=force-off [ARM64] 2840 l1tf=off [X86] 2841 mds=off [X86] 2842 tsx_async_abort=off [X86] 2843 kvm.nx_huge_pages=off [X86] 2844 2845 Exceptions: 2846 This does not have any effect on 2847 kvm.nx_huge_pages when 2848 kvm.nx_huge_pages=force. 2849 2850 auto (default) 2851 Mitigate all CPU vulnerabilities, but leave SMT 2852 enabled, even if it's vulnerable. This is for 2853 users who don't want to be surprised by SMT 2854 getting disabled across kernel upgrades, or who 2855 have other ways of avoiding SMT-based attacks. 2856 Equivalent to: (default behavior) 2857 2858 auto,nosmt 2859 Mitigate all CPU vulnerabilities, disabling SMT 2860 if needed. This is for users who always want to 2861 be fully mitigated, even if it means losing SMT. 2862 Equivalent to: l1tf=flush,nosmt [X86] 2863 mds=full,nosmt [X86] 2864 tsx_async_abort=full,nosmt [X86] 2865 2866 mminit_loglevel= 2867 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2868 parameter allows control of the logging verbosity for 2869 the additional memory initialisation checks. A value 2870 of 0 disables mminit logging and a level of 4 will 2871 log everything. Information is printed at KERN_DEBUG 2872 so loglevel=8 may also need to be specified. 2873 2874 module.sig_enforce 2875 [KNL] When CONFIG_MODULE_SIG is set, this means that 2876 modules without (valid) signatures will fail to load. 2877 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2878 is always true, so this option does nothing. 2879 2880 module_blacklist= [KNL] Do not load a comma-separated list of 2881 modules. Useful for debugging problem modules. 2882 2883 mousedev.tap_time= 2884 [MOUSE] Maximum time between finger touching and 2885 leaving touchpad surface for touch to be considered 2886 a tap and be reported as a left button click (for 2887 touchpads working in absolute mode only). 2888 Format: <msecs> 2889 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2890 reporting absolute coordinates, such as tablets 2891 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2892 reporting absolute coordinates, such as tablets 2893 2894 movablecore= [KNL,X86,IA-64,PPC] 2895 Format: nn[KMGTPE] | nn% 2896 This parameter is the complement to kernelcore=, it 2897 specifies the amount of memory used for migratable 2898 allocations. If both kernelcore and movablecore is 2899 specified, then kernelcore will be at *least* the 2900 specified value but may be more. If movablecore on its 2901 own is specified, the administrator must be careful 2902 that the amount of memory usable for all allocations 2903 is not too small. 2904 2905 movable_node [KNL] Boot-time switch to make hotplugable memory 2906 NUMA nodes to be movable. This means that the memory 2907 of such nodes will be usable only for movable 2908 allocations which rules out almost all kernel 2909 allocations. Use with caution! 2910 2911 MTD_Partition= [MTD] 2912 Format: <name>,<region-number>,<size>,<offset> 2913 2914 MTD_Region= [MTD] Format: 2915 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2916 2917 mtdparts= [MTD] 2918 See drivers/mtd/parsers/cmdlinepart.c 2919 2920 multitce=off [PPC] This parameter disables the use of the pSeries 2921 firmware feature for updating multiple TCE entries 2922 at a time. 2923 2924 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2925 2926 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2927 2928 boundary - index of last SLC block on Flex-OneNAND. 2929 The remaining blocks are configured as MLC blocks. 2930 lock - Configure if Flex-OneNAND boundary should be locked. 2931 Once locked, the boundary cannot be changed. 2932 1 indicates lock status, 0 indicates unlock status. 2933 2934 mtdset= [ARM] 2935 ARM/S3C2412 JIVE boot control 2936 2937 See arch/arm/mach-s3c2412/mach-jive.c 2938 2939 mtouchusb.raw_coordinates= 2940 [HW] Make the MicroTouch USB driver use raw coordinates 2941 ('y', default) or cooked coordinates ('n') 2942 2943 mtrr_chunk_size=nn[KMG] [X86] 2944 used for mtrr cleanup. It is largest continuous chunk 2945 that could hold holes aka. UC entries. 2946 2947 mtrr_gran_size=nn[KMG] [X86] 2948 Used for mtrr cleanup. It is granularity of mtrr block. 2949 Default is 1. 2950 Large value could prevent small alignment from 2951 using up MTRRs. 2952 2953 mtrr_spare_reg_nr=n [X86] 2954 Format: <integer> 2955 Range: 0,7 : spare reg number 2956 Default : 1 2957 Used for mtrr cleanup. It is spare mtrr entries number. 2958 Set to 2 or more if your graphical card needs more. 2959 2960 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2961 2962 netdev= [NET] Network devices parameters 2963 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2964 Note that mem_start is often overloaded to mean 2965 something different and driver-specific. 2966 This usage is only documented in each driver source 2967 file if at all. 2968 2969 nf_conntrack.acct= 2970 [NETFILTER] Enable connection tracking flow accounting 2971 0 to disable accounting 2972 1 to enable accounting 2973 Default value is 0. 2974 2975 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2976 See Documentation/admin-guide/nfs/nfsroot.rst. 2977 2978 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2979 See Documentation/admin-guide/nfs/nfsroot.rst. 2980 2981 nfsrootdebug [NFS] enable nfsroot debugging messages. 2982 See Documentation/admin-guide/nfs/nfsroot.rst. 2983 2984 nfs.callback_nr_threads= 2985 [NFSv4] set the total number of threads that the 2986 NFS client will assign to service NFSv4 callback 2987 requests. 2988 2989 nfs.callback_tcpport= 2990 [NFS] set the TCP port on which the NFSv4 callback 2991 channel should listen. 2992 2993 nfs.cache_getent= 2994 [NFS] sets the pathname to the program which is used 2995 to update the NFS client cache entries. 2996 2997 nfs.cache_getent_timeout= 2998 [NFS] sets the timeout after which an attempt to 2999 update a cache entry is deemed to have failed. 3000 3001 nfs.idmap_cache_timeout= 3002 [NFS] set the maximum lifetime for idmapper cache 3003 entries. 3004 3005 nfs.enable_ino64= 3006 [NFS] enable 64-bit inode numbers. 3007 If zero, the NFS client will fake up a 32-bit inode 3008 number for the readdir() and stat() syscalls instead 3009 of returning the full 64-bit number. 3010 The default is to return 64-bit inode numbers. 3011 3012 nfs.max_session_cb_slots= 3013 [NFSv4.1] Sets the maximum number of session 3014 slots the client will assign to the callback 3015 channel. This determines the maximum number of 3016 callbacks the client will process in parallel for 3017 a particular server. 3018 3019 nfs.max_session_slots= 3020 [NFSv4.1] Sets the maximum number of session slots 3021 the client will attempt to negotiate with the server. 3022 This limits the number of simultaneous RPC requests 3023 that the client can send to the NFSv4.1 server. 3024 Note that there is little point in setting this 3025 value higher than the max_tcp_slot_table_limit. 3026 3027 nfs.nfs4_disable_idmapping= 3028 [NFSv4] When set to the default of '1', this option 3029 ensures that both the RPC level authentication 3030 scheme and the NFS level operations agree to use 3031 numeric uids/gids if the mount is using the 3032 'sec=sys' security flavour. In effect it is 3033 disabling idmapping, which can make migration from 3034 legacy NFSv2/v3 systems to NFSv4 easier. 3035 Servers that do not support this mode of operation 3036 will be autodetected by the client, and it will fall 3037 back to using the idmapper. 3038 To turn off this behaviour, set the value to '0'. 3039 nfs.nfs4_unique_id= 3040 [NFS4] Specify an additional fixed unique ident- 3041 ification string that NFSv4 clients can insert into 3042 their nfs_client_id4 string. This is typically a 3043 UUID that is generated at system install time. 3044 3045 nfs.send_implementation_id = 3046 [NFSv4.1] Send client implementation identification 3047 information in exchange_id requests. 3048 If zero, no implementation identification information 3049 will be sent. 3050 The default is to send the implementation identification 3051 information. 3052 3053 nfs.recover_lost_locks = 3054 [NFSv4] Attempt to recover locks that were lost due 3055 to a lease timeout on the server. Please note that 3056 doing this risks data corruption, since there are 3057 no guarantees that the file will remain unchanged 3058 after the locks are lost. 3059 If you want to enable the kernel legacy behaviour of 3060 attempting to recover these locks, then set this 3061 parameter to '1'. 3062 The default parameter value of '0' causes the kernel 3063 not to attempt recovery of lost locks. 3064 3065 nfs4.layoutstats_timer = 3066 [NFSv4.2] Change the rate at which the kernel sends 3067 layoutstats to the pNFS metadata server. 3068 3069 Setting this to value to 0 causes the kernel to use 3070 whatever value is the default set by the layout 3071 driver. A non-zero value sets the minimum interval 3072 in seconds between layoutstats transmissions. 3073 3074 nfsd.nfs4_disable_idmapping= 3075 [NFSv4] When set to the default of '1', the NFSv4 3076 server will return only numeric uids and gids to 3077 clients using auth_sys, and will accept numeric uids 3078 and gids from such clients. This is intended to ease 3079 migration from NFSv2/v3. 3080 3081 nmi_debug= [KNL,SH] Specify one or more actions to take 3082 when a NMI is triggered. 3083 Format: [state][,regs][,debounce][,die] 3084 3085 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3086 Format: [panic,][nopanic,][num] 3087 Valid num: 0 or 1 3088 0 - turn hardlockup detector in nmi_watchdog off 3089 1 - turn hardlockup detector in nmi_watchdog on 3090 When panic is specified, panic when an NMI watchdog 3091 timeout occurs (or 'nopanic' to not panic on an NMI 3092 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3093 To disable both hard and soft lockup detectors, 3094 please see 'nowatchdog'. 3095 This is useful when you use a panic=... timeout and 3096 need the box quickly up again. 3097 3098 These settings can be accessed at runtime via 3099 the nmi_watchdog and hardlockup_panic sysctls. 3100 3101 netpoll.carrier_timeout= 3102 [NET] Specifies amount of time (in seconds) that 3103 netpoll should wait for a carrier. By default netpoll 3104 waits 4 seconds. 3105 3106 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3107 emulation library even if a 387 maths coprocessor 3108 is present. 3109 3110 no5lvl [X86-64] Disable 5-level paging mode. Forces 3111 kernel to use 4-level paging instead. 3112 3113 nofsgsbase [X86] Disables FSGSBASE instructions. 3114 3115 no_console_suspend 3116 [HW] Never suspend the console 3117 Disable suspending of consoles during suspend and 3118 hibernate operations. Once disabled, debugging 3119 messages can reach various consoles while the rest 3120 of the system is being put to sleep (ie, while 3121 debugging driver suspend/resume hooks). This may 3122 not work reliably with all consoles, but is known 3123 to work with serial and VGA consoles. 3124 To facilitate more flexible debugging, we also add 3125 console_suspend, a printk module parameter to control 3126 it. Users could use console_suspend (usually 3127 /sys/module/printk/parameters/console_suspend) to 3128 turn on/off it dynamically. 3129 3130 novmcoredd [KNL,KDUMP] 3131 Disable device dump. Device dump allows drivers to 3132 append dump data to vmcore so you can collect driver 3133 specified debug info. Drivers can append the data 3134 without any limit and this data is stored in memory, 3135 so this may cause significant memory stress. Disabling 3136 device dump can help save memory but the driver debug 3137 data will be no longer available. This parameter 3138 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3139 is set. 3140 3141 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3142 caches in the slab allocator. Saves per-node memory, 3143 but will impact performance. 3144 3145 noalign [KNL,ARM] 3146 3147 noaltinstr [S390] Disables alternative instructions patching 3148 (CPU alternatives feature). 3149 3150 noapic [SMP,APIC] Tells the kernel to not make use of any 3151 IOAPICs that may be present in the system. 3152 3153 noautogroup Disable scheduler automatic task group creation. 3154 3155 nobats [PPC] Do not use BATs for mapping kernel lowmem 3156 on "Classic" PPC cores. 3157 3158 nocache [ARM] 3159 3160 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3161 3162 nodelayacct [KNL] Disable per-task delay accounting 3163 3164 nodsp [SH] Disable hardware DSP at boot time. 3165 3166 noefi Disable EFI runtime services support. 3167 3168 noexec [IA-64] 3169 3170 noexec [X86] 3171 On X86-32 available only on PAE configured kernels. 3172 noexec=on: enable non-executable mappings (default) 3173 noexec=off: disable non-executable mappings 3174 3175 nosmap [X86,PPC] 3176 Disable SMAP (Supervisor Mode Access Prevention) 3177 even if it is supported by processor. 3178 3179 nosmep [X86,PPC] 3180 Disable SMEP (Supervisor Mode Execution Prevention) 3181 even if it is supported by processor. 3182 3183 noexec32 [X86-64] 3184 This affects only 32-bit executables. 3185 noexec32=on: enable non-executable mappings (default) 3186 read doesn't imply executable mappings 3187 noexec32=off: disable non-executable mappings 3188 read implies executable mappings 3189 3190 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3191 3192 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3193 register save and restore. The kernel will only save 3194 legacy floating-point registers on task switch. 3195 3196 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3197 3198 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3199 Equivalent to smt=1. 3200 3201 [KNL,X86] Disable symmetric multithreading (SMT). 3202 nosmt=force: Force disable SMT, cannot be undone 3203 via the sysfs control file. 3204 3205 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3206 (bounds check bypass). With this option data leaks are 3207 possible in the system. 3208 3209 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3210 the Spectre variant 2 (indirect branch prediction) 3211 vulnerability. System may allow data leaks with this 3212 option. 3213 3214 nospec_store_bypass_disable 3215 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3216 3217 noxsave [BUGS=X86] Disables x86 extended register state save 3218 and restore using xsave. The kernel will fallback to 3219 enabling legacy floating-point and sse state. 3220 3221 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3222 register states. The kernel will fall back to use 3223 xsave to save the states. By using this parameter, 3224 performance of saving the states is degraded because 3225 xsave doesn't support modified optimization while 3226 xsaveopt supports it on xsaveopt enabled systems. 3227 3228 noxsaves [X86] Disables xsaves and xrstors used in saving and 3229 restoring x86 extended register state in compacted 3230 form of xsave area. The kernel will fall back to use 3231 xsaveopt and xrstor to save and restore the states 3232 in standard form of xsave area. By using this 3233 parameter, xsave area per process might occupy more 3234 memory on xsaves enabled systems. 3235 3236 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3237 wfi(ARM) instruction doesn't work correctly and not to 3238 use it. This is also useful when using JTAG debugger. 3239 3240 no_file_caps Tells the kernel not to honor file capabilities. The 3241 only way then for a file to be executed with privilege 3242 is to be setuid root or executed by root. 3243 3244 nohalt [IA-64] Tells the kernel not to use the power saving 3245 function PAL_HALT_LIGHT when idle. This increases 3246 power-consumption. On the positive side, it reduces 3247 interrupt wake-up latency, which may improve performance 3248 in certain environments such as networked servers or 3249 real-time systems. 3250 3251 nohibernate [HIBERNATION] Disable hibernation and resume. 3252 3253 nohz= [KNL] Boottime enable/disable dynamic ticks 3254 Valid arguments: on, off 3255 Default: on 3256 3257 nohz_full= [KNL,BOOT,SMP,ISOL] 3258 The argument is a cpu list, as described above. 3259 In kernels built with CONFIG_NO_HZ_FULL=y, set 3260 the specified list of CPUs whose tick will be stopped 3261 whenever possible. The boot CPU will be forced outside 3262 the range to maintain the timekeeping. Any CPUs 3263 in this list will have their RCU callbacks offloaded, 3264 just as if they had also been called out in the 3265 rcu_nocbs= boot parameter. 3266 3267 noiotrap [SH] Disables trapped I/O port accesses. 3268 3269 noirqdebug [X86-32] Disables the code which attempts to detect and 3270 disable unhandled interrupt sources. 3271 3272 no_timer_check [X86,APIC] Disables the code which tests for 3273 broken timer IRQ sources. 3274 3275 noisapnp [ISAPNP] Disables ISA PnP code. 3276 3277 noinitrd [RAM] Tells the kernel not to load any configured 3278 initial RAM disk. 3279 3280 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3281 remapping. 3282 [Deprecated - use intremap=off] 3283 3284 nointroute [IA-64] 3285 3286 noinvpcid [X86] Disable the INVPCID cpu feature. 3287 3288 nojitter [IA-64] Disables jitter checking for ITC timers. 3289 3290 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3291 3292 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3293 fault handling. 3294 3295 no-vmw-sched-clock 3296 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3297 clock and use the default one. 3298 3299 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3300 accounting. steal time is computed, but won't 3301 influence scheduler behaviour 3302 3303 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3304 3305 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3306 3307 noltlbs [PPC] Do not use large page/tlb entries for kernel 3308 lowmem mapping on PPC40x and PPC8xx 3309 3310 nomca [IA-64] Disable machine check abort handling 3311 3312 nomce [X86-32] Disable Machine Check Exception 3313 3314 nomfgpt [X86-32] Disable Multi-Function General Purpose 3315 Timer usage (for AMD Geode machines). 3316 3317 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3318 shutdown the other cpus. Instead use the REBOOT_VECTOR 3319 irq. 3320 3321 nomodule Disable module load 3322 3323 nopat [X86] Disable PAT (page attribute table extension of 3324 pagetables) support. 3325 3326 nopcid [X86-64] Disable the PCID cpu feature. 3327 3328 norandmaps Don't use address space randomization. Equivalent to 3329 echo 0 > /proc/sys/kernel/randomize_va_space 3330 3331 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3332 with UP alternatives 3333 3334 nordrand [X86] Disable kernel use of the RDRAND and 3335 RDSEED instructions even if they are supported 3336 by the processor. RDRAND and RDSEED are still 3337 available to user space applications. 3338 3339 noresume [SWSUSP] Disables resume and restores original swap 3340 space. 3341 3342 no-scroll [VGA] Disables scrollback. 3343 This is required for the Braillex ib80-piezo Braille 3344 reader made by F.H. Papenmeier (Germany). 3345 3346 nosbagart [IA-64] 3347 3348 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3349 3350 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3351 and disable the IO APIC. legacy for "maxcpus=0". 3352 3353 nosoftlockup [KNL] Disable the soft-lockup detector. 3354 3355 nosync [HW,M68K] Disables sync negotiation for all devices. 3356 3357 nowatchdog [KNL] Disable both lockup detectors, i.e. 3358 soft-lockup and NMI watchdog (hard-lockup). 3359 3360 nowb [ARM] 3361 3362 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3363 3364 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3365 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3366 Some features depend on CPU0. Known dependencies are: 3367 1. Resume from suspend/hibernate depends on CPU0. 3368 Suspend/hibernate will fail if CPU0 is offline and you 3369 need to online CPU0 before suspend/hibernate. 3370 2. PIC interrupts also depend on CPU0. CPU0 can't be 3371 removed if a PIC interrupt is detected. 3372 It's said poweroff/reboot may depend on CPU0 on some 3373 machines although I haven't seen such issues so far 3374 after CPU0 is offline on a few tested machines. 3375 If the dependencies are under your control, you can 3376 turn on cpu0_hotplug. 3377 3378 nps_mtm_hs_ctr= [KNL,ARC] 3379 This parameter sets the maximum duration, in 3380 cycles, each HW thread of the CTOP can run 3381 without interruptions, before HW switches it. 3382 The actual maximum duration is 16 times this 3383 parameter's value. 3384 Format: integer between 1 and 255 3385 Default: 255 3386 3387 nptcg= [IA-64] Override max number of concurrent global TLB 3388 purges which is reported from either PAL_VM_SUMMARY or 3389 SAL PALO. 3390 3391 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3392 could support. nr_cpus=n : n >= 1 limits the kernel to 3393 support 'n' processors. It could be larger than the 3394 number of already plugged CPU during bootup, later in 3395 runtime you can physically add extra cpu until it reaches 3396 n. So during boot up some boot time memory for per-cpu 3397 variables need be pre-allocated for later physical cpu 3398 hot plugging. 3399 3400 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3401 3402 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3403 Allowed values are enable and disable 3404 3405 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3406 'node', 'default' can be specified 3407 This can be set from sysctl after boot. 3408 See Documentation/admin-guide/sysctl/vm.rst for details. 3409 3410 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3411 See Documentation/core-api/debugging-via-ohci1394.rst for more 3412 info. 3413 3414 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3415 Rather than timing out after 20 ms if an EC 3416 command is not properly ACKed, override the length 3417 of the timeout. We have interrupts disabled while 3418 waiting for the ACK, so if this is set too high 3419 interrupts *may* be lost! 3420 3421 omap_mux= [OMAP] Override bootloader pin multiplexing. 3422 Format: <mux_mode0.mode_name=value>... 3423 For example, to override I2C bus2: 3424 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3425 3426 oprofile.timer= [HW] 3427 Use timer interrupt instead of performance counters 3428 3429 oprofile.cpu_type= Force an oprofile cpu type 3430 This might be useful if you have an older oprofile 3431 userland or if you want common events. 3432 Format: { arch_perfmon } 3433 arch_perfmon: [X86] Force use of architectural 3434 perfmon on Intel CPUs instead of the 3435 CPU specific event set. 3436 timer: [X86] Force use of architectural NMI 3437 timer mode (see also oprofile.timer 3438 for generic hr timer mode) 3439 3440 oops=panic Always panic on oopses. Default is to just kill the 3441 process, but there is a small probability of 3442 deadlocking the machine. 3443 This will also cause panics on machine check exceptions. 3444 Useful together with panic=30 to trigger a reboot. 3445 3446 page_alloc.shuffle= 3447 [KNL] Boolean flag to control whether the page allocator 3448 should randomize its free lists. The randomization may 3449 be automatically enabled if the kernel detects it is 3450 running on a platform with a direct-mapped memory-side 3451 cache, and this parameter can be used to 3452 override/disable that behavior. The state of the flag 3453 can be read from sysfs at: 3454 /sys/module/page_alloc/parameters/shuffle. 3455 3456 page_owner= [KNL] Boot-time page_owner enabling option. 3457 Storage of the information about who allocated 3458 each page is disabled in default. With this switch, 3459 we can turn it on. 3460 on: enable the feature 3461 3462 page_poison= [KNL] Boot-time parameter changing the state of 3463 poisoning on the buddy allocator, available with 3464 CONFIG_PAGE_POISONING=y. 3465 off: turn off poisoning (default) 3466 on: turn on poisoning 3467 3468 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3469 timeout > 0: seconds before rebooting 3470 timeout = 0: wait forever 3471 timeout < 0: reboot immediately 3472 Format: <timeout> 3473 3474 panic_print= Bitmask for printing system info when panic happens. 3475 User can chose combination of the following bits: 3476 bit 0: print all tasks info 3477 bit 1: print system memory info 3478 bit 2: print timer info 3479 bit 3: print locks info if CONFIG_LOCKDEP is on 3480 bit 4: print ftrace buffer 3481 bit 5: print all printk messages in buffer 3482 3483 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3484 Format: <hex>[,nousertaint] 3485 Hexadecimal bitmask representing the set of TAINT flags 3486 that will cause the kernel to panic when add_taint() is 3487 called with any of the flags in this set. 3488 The optional switch "nousertaint" can be utilized to 3489 prevent userspace forced crashes by writing to sysctl 3490 /proc/sys/kernel/tainted any flagset matching with the 3491 bitmask set on panic_on_taint. 3492 See Documentation/admin-guide/tainted-kernels.rst for 3493 extra details on the taint flags that users can pick 3494 to compose the bitmask to assign to panic_on_taint. 3495 3496 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3497 on a WARN(). 3498 3499 crash_kexec_post_notifiers 3500 Run kdump after running panic-notifiers and dumping 3501 kmsg. This only for the users who doubt kdump always 3502 succeeds in any situation. 3503 Note that this also increases risks of kdump failure, 3504 because some panic notifiers can make the crashed 3505 kernel more unstable. 3506 3507 parkbd.port= [HW] Parallel port number the keyboard adapter is 3508 connected to, default is 0. 3509 Format: <parport#> 3510 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3511 0 for XT, 1 for AT (default is AT). 3512 Format: <mode> 3513 3514 parport= [HW,PPT] Specify parallel ports. 0 disables. 3515 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3516 Use 'auto' to force the driver to use any 3517 IRQ/DMA settings detected (the default is to 3518 ignore detected IRQ/DMA settings because of 3519 possible conflicts). You can specify the base 3520 address, IRQ, and DMA settings; IRQ and DMA 3521 should be numbers, or 'auto' (for using detected 3522 settings on that particular port), or 'nofifo' 3523 (to avoid using a FIFO even if it is detected). 3524 Parallel ports are assigned in the order they 3525 are specified on the command line, starting 3526 with parport0. 3527 3528 parport_init_mode= [HW,PPT] 3529 Configure VIA parallel port to operate in 3530 a specific mode. This is necessary on Pegasos 3531 computer where firmware has no options for setting 3532 up parallel port mode and sets it to spp. 3533 Currently this function knows 686a and 8231 chips. 3534 Format: [spp|ps2|epp|ecp|ecpepp] 3535 3536 pause_on_oops= 3537 Halt all CPUs after the first oops has been printed for 3538 the specified number of seconds. This is to be used if 3539 your oopses keep scrolling off the screen. 3540 3541 pcbit= [HW,ISDN] 3542 3543 pcd. [PARIDE] 3544 See header of drivers/block/paride/pcd.c. 3545 See also Documentation/admin-guide/blockdev/paride.rst. 3546 3547 pci=option[,option...] [PCI] various PCI subsystem options. 3548 3549 Some options herein operate on a specific device 3550 or a set of devices (<pci_dev>). These are 3551 specified in one of the following formats: 3552 3553 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3554 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3555 3556 Note: the first format specifies a PCI 3557 bus/device/function address which may change 3558 if new hardware is inserted, if motherboard 3559 firmware changes, or due to changes caused 3560 by other kernel parameters. If the 3561 domain is left unspecified, it is 3562 taken to be zero. Optionally, a path 3563 to a device through multiple device/function 3564 addresses can be specified after the base 3565 address (this is more robust against 3566 renumbering issues). The second format 3567 selects devices using IDs from the 3568 configuration space which may match multiple 3569 devices in the system. 3570 3571 earlydump dump PCI config space before the kernel 3572 changes anything 3573 off [X86] don't probe for the PCI bus 3574 bios [X86-32] force use of PCI BIOS, don't access 3575 the hardware directly. Use this if your machine 3576 has a non-standard PCI host bridge. 3577 nobios [X86-32] disallow use of PCI BIOS, only direct 3578 hardware access methods are allowed. Use this 3579 if you experience crashes upon bootup and you 3580 suspect they are caused by the BIOS. 3581 conf1 [X86] Force use of PCI Configuration Access 3582 Mechanism 1 (config address in IO port 0xCF8, 3583 data in IO port 0xCFC, both 32-bit). 3584 conf2 [X86] Force use of PCI Configuration Access 3585 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3586 the function, IO port 0xCFA, also 8-bit, sets 3587 bus number. The config space is then accessed 3588 through ports 0xC000-0xCFFF). 3589 See http://wiki.osdev.org/PCI for more info 3590 on the configuration access mechanisms. 3591 noaer [PCIE] If the PCIEAER kernel config parameter is 3592 enabled, this kernel boot option can be used to 3593 disable the use of PCIE advanced error reporting. 3594 nodomains [PCI] Disable support for multiple PCI 3595 root domains (aka PCI segments, in ACPI-speak). 3596 nommconf [X86] Disable use of MMCONFIG for PCI 3597 Configuration 3598 check_enable_amd_mmconf [X86] check for and enable 3599 properly configured MMIO access to PCI 3600 config space on AMD family 10h CPU 3601 nomsi [MSI] If the PCI_MSI kernel config parameter is 3602 enabled, this kernel boot option can be used to 3603 disable the use of MSI interrupts system-wide. 3604 noioapicquirk [APIC] Disable all boot interrupt quirks. 3605 Safety option to keep boot IRQs enabled. This 3606 should never be necessary. 3607 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3608 primary IO-APIC for bridges that cannot disable 3609 boot IRQs. This fixes a source of spurious IRQs 3610 when the system masks IRQs. 3611 noioapicreroute [APIC] Disable workaround that uses the 3612 boot IRQ equivalent of an IRQ that connects to 3613 a chipset where boot IRQs cannot be disabled. 3614 The opposite of ioapicreroute. 3615 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3616 routing table. These calls are known to be buggy 3617 on several machines and they hang the machine 3618 when used, but on other computers it's the only 3619 way to get the interrupt routing table. Try 3620 this option if the kernel is unable to allocate 3621 IRQs or discover secondary PCI buses on your 3622 motherboard. 3623 rom [X86] Assign address space to expansion ROMs. 3624 Use with caution as certain devices share 3625 address decoders between ROMs and other 3626 resources. 3627 norom [X86] Do not assign address space to 3628 expansion ROMs that do not already have 3629 BIOS assigned address ranges. 3630 nobar [X86] Do not assign address space to the 3631 BARs that weren't assigned by the BIOS. 3632 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3633 assigned automatically to PCI devices. You can 3634 make the kernel exclude IRQs of your ISA cards 3635 this way. 3636 pirqaddr=0xAAAAA [X86] Specify the physical address 3637 of the PIRQ table (normally generated 3638 by the BIOS) if it is outside the 3639 F0000h-100000h range. 3640 lastbus=N [X86] Scan all buses thru bus #N. Can be 3641 useful if the kernel is unable to find your 3642 secondary buses and you want to tell it 3643 explicitly which ones they are. 3644 assign-busses [X86] Always assign all PCI bus 3645 numbers ourselves, overriding 3646 whatever the firmware may have done. 3647 usepirqmask [X86] Honor the possible IRQ mask stored 3648 in the BIOS $PIR table. This is needed on 3649 some systems with broken BIOSes, notably 3650 some HP Pavilion N5400 and Omnibook XE3 3651 notebooks. This will have no effect if ACPI 3652 IRQ routing is enabled. 3653 noacpi [X86] Do not use ACPI for IRQ routing 3654 or for PCI scanning. 3655 use_crs [X86] Use PCI host bridge window information 3656 from ACPI. On BIOSes from 2008 or later, this 3657 is enabled by default. If you need to use this, 3658 please report a bug. 3659 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3660 If you need to use this, please report a bug. 3661 routeirq Do IRQ routing for all PCI devices. 3662 This is normally done in pci_enable_device(), 3663 so this option is a temporary workaround 3664 for broken drivers that don't call it. 3665 skip_isa_align [X86] do not align io start addr, so can 3666 handle more pci cards 3667 noearly [X86] Don't do any early type 1 scanning. 3668 This might help on some broken boards which 3669 machine check when some devices' config space 3670 is read. But various workarounds are disabled 3671 and some IOMMU drivers will not work. 3672 bfsort Sort PCI devices into breadth-first order. 3673 This sorting is done to get a device 3674 order compatible with older (<= 2.4) kernels. 3675 nobfsort Don't sort PCI devices into breadth-first order. 3676 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3677 tuning and use the BIOS-configured MPS defaults. 3678 pcie_bus_safe Set every device's MPS to the largest value 3679 supported by all devices below the root complex. 3680 pcie_bus_perf Set device MPS to the largest allowable MPS 3681 based on its parent bus. Also set MRRS (Max 3682 Read Request Size) to the largest supported 3683 value (no larger than the MPS that the device 3684 or bus can support) for best performance. 3685 pcie_bus_peer2peer Set every device's MPS to 128B, which 3686 every device is guaranteed to support. This 3687 configuration allows peer-to-peer DMA between 3688 any pair of devices, possibly at the cost of 3689 reduced performance. This also guarantees 3690 that hot-added devices will work. 3691 cbiosize=nn[KMG] The fixed amount of bus space which is 3692 reserved for the CardBus bridge's IO window. 3693 The default value is 256 bytes. 3694 cbmemsize=nn[KMG] The fixed amount of bus space which is 3695 reserved for the CardBus bridge's memory 3696 window. The default value is 64 megabytes. 3697 resource_alignment= 3698 Format: 3699 [<order of align>@]<pci_dev>[; ...] 3700 Specifies alignment and device to reassign 3701 aligned memory resources. How to 3702 specify the device is described above. 3703 If <order of align> is not specified, 3704 PAGE_SIZE is used as alignment. 3705 A PCI-PCI bridge can be specified if resource 3706 windows need to be expanded. 3707 To specify the alignment for several 3708 instances of a device, the PCI vendor, 3709 device, subvendor, and subdevice may be 3710 specified, e.g., 12@pci:8086:9c22:103c:198f 3711 for 4096-byte alignment. 3712 ecrc= Enable/disable PCIe ECRC (transaction layer 3713 end-to-end CRC checking). 3714 bios: Use BIOS/firmware settings. This is the 3715 the default. 3716 off: Turn ECRC off 3717 on: Turn ECRC on. 3718 hpiosize=nn[KMG] The fixed amount of bus space which is 3719 reserved for hotplug bridge's IO window. 3720 Default size is 256 bytes. 3721 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3722 reserved for hotplug bridge's MMIO window. 3723 Default size is 2 megabytes. 3724 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3725 reserved for hotplug bridge's MMIO_PREF window. 3726 Default size is 2 megabytes. 3727 hpmemsize=nn[KMG] The fixed amount of bus space which is 3728 reserved for hotplug bridge's MMIO and 3729 MMIO_PREF window. 3730 Default size is 2 megabytes. 3731 hpbussize=nn The minimum amount of additional bus numbers 3732 reserved for buses below a hotplug bridge. 3733 Default is 1. 3734 realloc= Enable/disable reallocating PCI bridge resources 3735 if allocations done by BIOS are too small to 3736 accommodate resources required by all child 3737 devices. 3738 off: Turn realloc off 3739 on: Turn realloc on 3740 realloc same as realloc=on 3741 noari do not use PCIe ARI. 3742 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3743 do not use PCIe ATS (and IOMMU device IOTLB). 3744 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3745 only look for one device below a PCIe downstream 3746 port. 3747 big_root_window Try to add a big 64bit memory window to the PCIe 3748 root complex on AMD CPUs. Some GFX hardware 3749 can resize a BAR to allow access to all VRAM. 3750 Adding the window is slightly risky (it may 3751 conflict with unreported devices), so this 3752 taints the kernel. 3753 disable_acs_redir=<pci_dev>[; ...] 3754 Specify one or more PCI devices (in the format 3755 specified above) separated by semicolons. 3756 Each device specified will have the PCI ACS 3757 redirect capabilities forced off which will 3758 allow P2P traffic between devices through 3759 bridges without forcing it upstream. Note: 3760 this removes isolation between devices and 3761 may put more devices in an IOMMU group. 3762 force_floating [S390] Force usage of floating interrupts. 3763 nomio [S390] Do not use MIO instructions. 3764 norid [S390] ignore the RID field and force use of 3765 one PCI domain per PCI function 3766 3767 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3768 Management. 3769 off Disable ASPM. 3770 force Enable ASPM even on devices that claim not to support it. 3771 WARNING: Forcing ASPM on may cause system lockups. 3772 3773 pcie_ports= [PCIE] PCIe port services handling: 3774 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3775 even if the platform doesn't give the OS permission to 3776 use them. This may cause conflicts if the platform 3777 also tries to use these services. 3778 dpc-native Use native PCIe service for DPC only. May 3779 cause conflicts if firmware uses AER or DPC. 3780 compat Disable native PCIe services (PME, AER, DPC, PCIe 3781 hotplug). 3782 3783 pcie_port_pm= [PCIE] PCIe port power management handling: 3784 off Disable power management of all PCIe ports 3785 force Forcibly enable power management of all PCIe ports 3786 3787 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3788 nomsi Do not use MSI for native PCIe PME signaling (this makes 3789 all PCIe root ports use INTx for all services). 3790 3791 pcmv= [HW,PCMCIA] BadgePAD 4 3792 3793 pd_ignore_unused 3794 [PM] 3795 Keep all power-domains already enabled by bootloader on, 3796 even if no driver has claimed them. This is useful 3797 for debug and development, but should not be 3798 needed on a platform with proper driver support. 3799 3800 pd. [PARIDE] 3801 See Documentation/admin-guide/blockdev/paride.rst. 3802 3803 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3804 boot time. 3805 Format: { 0 | 1 } 3806 See arch/parisc/kernel/pdc_chassis.c 3807 3808 percpu_alloc= Select which percpu first chunk allocator to use. 3809 Currently supported values are "embed" and "page". 3810 Archs may support subset or none of the selections. 3811 See comments in mm/percpu.c for details on each 3812 allocator. This parameter is primarily for debugging 3813 and performance comparison. 3814 3815 pf. [PARIDE] 3816 See Documentation/admin-guide/blockdev/paride.rst. 3817 3818 pg. [PARIDE] 3819 See Documentation/admin-guide/blockdev/paride.rst. 3820 3821 pirq= [SMP,APIC] Manual mp-table setup 3822 See Documentation/x86/i386/IO-APIC.rst. 3823 3824 plip= [PPT,NET] Parallel port network link 3825 Format: { parport<nr> | timid | 0 } 3826 See also Documentation/admin-guide/parport.rst. 3827 3828 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3829 Override pmtimer IOPort with a hex value. 3830 e.g. pmtmr=0x508 3831 3832 pm_debug_messages [SUSPEND,KNL] 3833 Enable suspend/resume debug messages during boot up. 3834 3835 pnp.debug=1 [PNP] 3836 Enable PNP debug messages (depends on the 3837 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3838 via /sys/module/pnp/parameters/debug. We always show 3839 current resource usage; turning this on also shows 3840 possible settings and some assignment information. 3841 3842 pnpacpi= [ACPI] 3843 { off } 3844 3845 pnpbios= [ISAPNP] 3846 { on | off | curr | res | no-curr | no-res } 3847 3848 pnp_reserve_irq= 3849 [ISAPNP] Exclude IRQs for the autoconfiguration 3850 3851 pnp_reserve_dma= 3852 [ISAPNP] Exclude DMAs for the autoconfiguration 3853 3854 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3855 Ranges are in pairs (I/O port base and size). 3856 3857 pnp_reserve_mem= 3858 [ISAPNP] Exclude memory regions for the 3859 autoconfiguration. 3860 Ranges are in pairs (memory base and size). 3861 3862 ports= [IP_VS_FTP] IPVS ftp helper module 3863 Default is 21. 3864 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3865 may be specified. 3866 Format: <port>,<port>.... 3867 3868 powersave=off [PPC] This option disables power saving features. 3869 It specifically disables cpuidle and sets the 3870 platform machine description specific power_save 3871 function to NULL. On Idle the CPU just reduces 3872 execution priority. 3873 3874 ppc_strict_facility_enable 3875 [PPC] This option catches any kernel floating point, 3876 Altivec, VSX and SPE outside of regions specifically 3877 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3878 There is some performance impact when enabling this. 3879 3880 ppc_tm= [PPC] 3881 Format: {"off"} 3882 Disable Hardware Transactional Memory 3883 3884 print-fatal-signals= 3885 [KNL] debug: print fatal signals 3886 3887 If enabled, warn about various signal handling 3888 related application anomalies: too many signals, 3889 too many POSIX.1 timers, fatal signals causing a 3890 coredump - etc. 3891 3892 If you hit the warning due to signal overflow, 3893 you might want to try "ulimit -i unlimited". 3894 3895 default: off. 3896 3897 printk.always_kmsg_dump= 3898 Trigger kmsg_dump for cases other than kernel oops or 3899 panics 3900 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3901 default: disabled 3902 3903 printk.devkmsg={on,off,ratelimit} 3904 Control writing to /dev/kmsg. 3905 on - unlimited logging to /dev/kmsg from userspace 3906 off - logging to /dev/kmsg disabled 3907 ratelimit - ratelimit the logging 3908 Default: ratelimit 3909 3910 printk.time= Show timing data prefixed to each printk message line 3911 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3912 3913 processor.max_cstate= [HW,ACPI] 3914 Limit processor to maximum C-state 3915 max_cstate=9 overrides any DMI blacklist limit. 3916 3917 processor.nocst [HW,ACPI] 3918 Ignore the _CST method to determine C-states, 3919 instead using the legacy FADT method 3920 3921 profile= [KNL] Enable kernel profiling via /proc/profile 3922 Format: [<profiletype>,]<number> 3923 Param: <profiletype>: "schedule", "sleep", or "kvm" 3924 [defaults to kernel profiling] 3925 Param: "schedule" - profile schedule points. 3926 Param: "sleep" - profile D-state sleeping (millisecs). 3927 Requires CONFIG_SCHEDSTATS 3928 Param: "kvm" - profile VM exits. 3929 Param: <number> - step/bucket size as a power of 2 for 3930 statistical time based profiling. 3931 3932 prompt_ramdisk= [RAM] [Deprecated] 3933 3934 prot_virt= [S390] enable hosting protected virtual machines 3935 isolated from the hypervisor (if hardware supports 3936 that). 3937 Format: <bool> 3938 3939 psi= [KNL] Enable or disable pressure stall information 3940 tracking. 3941 Format: <bool> 3942 3943 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3944 probe for; one of (bare|imps|exps|lifebook|any). 3945 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3946 per second. 3947 psmouse.resetafter= [HW,MOUSE] 3948 Try to reset the device after so many bad packets 3949 (0 = never). 3950 psmouse.resolution= 3951 [HW,MOUSE] Set desired mouse resolution, in dpi. 3952 psmouse.smartscroll= 3953 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3954 0 = disabled, 1 = enabled (default). 3955 3956 pstore.backend= Specify the name of the pstore backend to use 3957 3958 pt. [PARIDE] 3959 See Documentation/admin-guide/blockdev/paride.rst. 3960 3961 pti= [X86-64] Control Page Table Isolation of user and 3962 kernel address spaces. Disabling this feature 3963 removes hardening, but improves performance of 3964 system calls and interrupts. 3965 3966 on - unconditionally enable 3967 off - unconditionally disable 3968 auto - kernel detects whether your CPU model is 3969 vulnerable to issues that PTI mitigates 3970 3971 Not specifying this option is equivalent to pti=auto. 3972 3973 nopti [X86-64] 3974 Equivalent to pti=off 3975 3976 pty.legacy_count= 3977 [KNL] Number of legacy pty's. Overwrites compiled-in 3978 default number. 3979 3980 quiet [KNL] Disable most log messages 3981 3982 r128= [HW,DRM] 3983 3984 raid= [HW,RAID] 3985 See Documentation/admin-guide/md.rst. 3986 3987 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3988 See Documentation/admin-guide/blockdev/ramdisk.rst. 3989 3990 ramdisk_start= [RAM] RAM disk image start address 3991 3992 random.trust_cpu={on,off} 3993 [KNL] Enable or disable trusting the use of the 3994 CPU's random number generator (if available) to 3995 fully seed the kernel's CRNG. Default is controlled 3996 by CONFIG_RANDOM_TRUST_CPU. 3997 3998 ras=option[,option,...] [KNL] RAS-specific options 3999 4000 cec_disable [X86] 4001 Disable the Correctable Errors Collector, 4002 see CONFIG_RAS_CEC help text. 4003 4004 rcu_nocbs= [KNL] 4005 The argument is a cpu list, as described above, 4006 except that the string "all" can be used to 4007 specify every CPU on the system. 4008 4009 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4010 the specified list of CPUs to be no-callback CPUs. 4011 Invocation of these CPUs' RCU callbacks will be 4012 offloaded to "rcuox/N" kthreads created for that 4013 purpose, where "x" is "p" for RCU-preempt, and 4014 "s" for RCU-sched, and "N" is the CPU number. 4015 This reduces OS jitter on the offloaded CPUs, 4016 which can be useful for HPC and real-time 4017 workloads. It can also improve energy efficiency 4018 for asymmetric multiprocessors. 4019 4020 rcu_nocb_poll [KNL] 4021 Rather than requiring that offloaded CPUs 4022 (specified by rcu_nocbs= above) explicitly 4023 awaken the corresponding "rcuoN" kthreads, 4024 make these kthreads poll for callbacks. 4025 This improves the real-time response for the 4026 offloaded CPUs by relieving them of the need to 4027 wake up the corresponding kthread, but degrades 4028 energy efficiency by requiring that the kthreads 4029 periodically wake up to do the polling. 4030 4031 rcutree.blimit= [KNL] 4032 Set maximum number of finished RCU callbacks to 4033 process in one batch. 4034 4035 rcutree.dump_tree= [KNL] 4036 Dump the structure of the rcu_node combining tree 4037 out at early boot. This is used for diagnostic 4038 purposes, to verify correct tree setup. 4039 4040 rcutree.gp_cleanup_delay= [KNL] 4041 Set the number of jiffies to delay each step of 4042 RCU grace-period cleanup. 4043 4044 rcutree.gp_init_delay= [KNL] 4045 Set the number of jiffies to delay each step of 4046 RCU grace-period initialization. 4047 4048 rcutree.gp_preinit_delay= [KNL] 4049 Set the number of jiffies to delay each step of 4050 RCU grace-period pre-initialization, that is, 4051 the propagation of recent CPU-hotplug changes up 4052 the rcu_node combining tree. 4053 4054 rcutree.use_softirq= [KNL] 4055 If set to zero, move all RCU_SOFTIRQ processing to 4056 per-CPU rcuc kthreads. Defaults to a non-zero 4057 value, meaning that RCU_SOFTIRQ is used by default. 4058 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4059 4060 rcutree.rcu_fanout_exact= [KNL] 4061 Disable autobalancing of the rcu_node combining 4062 tree. This is used by rcutorture, and might 4063 possibly be useful for architectures having high 4064 cache-to-cache transfer latencies. 4065 4066 rcutree.rcu_fanout_leaf= [KNL] 4067 Change the number of CPUs assigned to each 4068 leaf rcu_node structure. Useful for very 4069 large systems, which will choose the value 64, 4070 and for NUMA systems with large remote-access 4071 latencies, which will choose a value aligned 4072 with the appropriate hardware boundaries. 4073 4074 rcutree.rcu_min_cached_objs= [KNL] 4075 Minimum number of objects which are cached and 4076 maintained per one CPU. Object size is equal 4077 to PAGE_SIZE. The cache allows to reduce the 4078 pressure to page allocator, also it makes the 4079 whole algorithm to behave better in low memory 4080 condition. 4081 4082 rcutree.jiffies_till_first_fqs= [KNL] 4083 Set delay from grace-period initialization to 4084 first attempt to force quiescent states. 4085 Units are jiffies, minimum value is zero, 4086 and maximum value is HZ. 4087 4088 rcutree.jiffies_till_next_fqs= [KNL] 4089 Set delay between subsequent attempts to force 4090 quiescent states. Units are jiffies, minimum 4091 value is one, and maximum value is HZ. 4092 4093 rcutree.jiffies_till_sched_qs= [KNL] 4094 Set required age in jiffies for a 4095 given grace period before RCU starts 4096 soliciting quiescent-state help from 4097 rcu_note_context_switch() and cond_resched(). 4098 If not specified, the kernel will calculate 4099 a value based on the most recent settings 4100 of rcutree.jiffies_till_first_fqs 4101 and rcutree.jiffies_till_next_fqs. 4102 This calculated value may be viewed in 4103 rcutree.jiffies_to_sched_qs. Any attempt to set 4104 rcutree.jiffies_to_sched_qs will be cheerfully 4105 overwritten. 4106 4107 rcutree.kthread_prio= [KNL,BOOT] 4108 Set the SCHED_FIFO priority of the RCU per-CPU 4109 kthreads (rcuc/N). This value is also used for 4110 the priority of the RCU boost threads (rcub/N) 4111 and for the RCU grace-period kthreads (rcu_bh, 4112 rcu_preempt, and rcu_sched). If RCU_BOOST is 4113 set, valid values are 1-99 and the default is 1 4114 (the least-favored priority). Otherwise, when 4115 RCU_BOOST is not set, valid values are 0-99 and 4116 the default is zero (non-realtime operation). 4117 4118 rcutree.rcu_nocb_gp_stride= [KNL] 4119 Set the number of NOCB callback kthreads in 4120 each group, which defaults to the square root 4121 of the number of CPUs. Larger numbers reduce 4122 the wakeup overhead on the global grace-period 4123 kthread, but increases that same overhead on 4124 each group's NOCB grace-period kthread. 4125 4126 rcutree.qhimark= [KNL] 4127 Set threshold of queued RCU callbacks beyond which 4128 batch limiting is disabled. 4129 4130 rcutree.qlowmark= [KNL] 4131 Set threshold of queued RCU callbacks below which 4132 batch limiting is re-enabled. 4133 4134 rcutree.qovld= [KNL] 4135 Set threshold of queued RCU callbacks beyond which 4136 RCU's force-quiescent-state scan will aggressively 4137 enlist help from cond_resched() and sched IPIs to 4138 help CPUs more quickly reach quiescent states. 4139 Set to less than zero to make this be set based 4140 on rcutree.qhimark at boot time and to zero to 4141 disable more aggressive help enlistment. 4142 4143 rcutree.rcu_idle_gp_delay= [KNL] 4144 Set wakeup interval for idle CPUs that have 4145 RCU callbacks (RCU_FAST_NO_HZ=y). 4146 4147 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4148 Set wakeup interval for idle CPUs that have 4149 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4150 Lazy RCU callbacks are those which RCU can 4151 prove do nothing more than free memory. 4152 4153 rcutree.rcu_kick_kthreads= [KNL] 4154 Cause the grace-period kthread to get an extra 4155 wake_up() if it sleeps three times longer than 4156 it should at force-quiescent-state time. 4157 This wake_up() will be accompanied by a 4158 WARN_ONCE() splat and an ftrace_dump(). 4159 4160 rcutree.sysrq_rcu= [KNL] 4161 Commandeer a sysrq key to dump out Tree RCU's 4162 rcu_node tree with an eye towards determining 4163 why a new grace period has not yet started. 4164 4165 rcuperf.gp_async= [KNL] 4166 Measure performance of asynchronous 4167 grace-period primitives such as call_rcu(). 4168 4169 rcuperf.gp_async_max= [KNL] 4170 Specify the maximum number of outstanding 4171 callbacks per writer thread. When a writer 4172 thread exceeds this limit, it invokes the 4173 corresponding flavor of rcu_barrier() to allow 4174 previously posted callbacks to drain. 4175 4176 rcuperf.gp_exp= [KNL] 4177 Measure performance of expedited synchronous 4178 grace-period primitives. 4179 4180 rcuperf.holdoff= [KNL] 4181 Set test-start holdoff period. The purpose of 4182 this parameter is to delay the start of the 4183 test until boot completes in order to avoid 4184 interference. 4185 4186 rcuperf.kfree_rcu_test= [KNL] 4187 Set to measure performance of kfree_rcu() flooding. 4188 4189 rcuperf.kfree_nthreads= [KNL] 4190 The number of threads running loops of kfree_rcu(). 4191 4192 rcuperf.kfree_alloc_num= [KNL] 4193 Number of allocations and frees done in an iteration. 4194 4195 rcuperf.kfree_loops= [KNL] 4196 Number of loops doing rcuperf.kfree_alloc_num number 4197 of allocations and frees. 4198 4199 rcuperf.nreaders= [KNL] 4200 Set number of RCU readers. The value -1 selects 4201 N, where N is the number of CPUs. A value 4202 "n" less than -1 selects N-n+1, where N is again 4203 the number of CPUs. For example, -2 selects N 4204 (the number of CPUs), -3 selects N+1, and so on. 4205 A value of "n" less than or equal to -N selects 4206 a single reader. 4207 4208 rcuperf.nwriters= [KNL] 4209 Set number of RCU writers. The values operate 4210 the same as for rcuperf.nreaders. 4211 N, where N is the number of CPUs 4212 4213 rcuperf.perf_type= [KNL] 4214 Specify the RCU implementation to test. 4215 4216 rcuperf.shutdown= [KNL] 4217 Shut the system down after performance tests 4218 complete. This is useful for hands-off automated 4219 testing. 4220 4221 rcuperf.verbose= [KNL] 4222 Enable additional printk() statements. 4223 4224 rcuperf.writer_holdoff= [KNL] 4225 Write-side holdoff between grace periods, 4226 in microseconds. The default of zero says 4227 no holdoff. 4228 4229 rcutorture.fqs_duration= [KNL] 4230 Set duration of force_quiescent_state bursts 4231 in microseconds. 4232 4233 rcutorture.fqs_holdoff= [KNL] 4234 Set holdoff time within force_quiescent_state bursts 4235 in microseconds. 4236 4237 rcutorture.fqs_stutter= [KNL] 4238 Set wait time between force_quiescent_state bursts 4239 in seconds. 4240 4241 rcutorture.fwd_progress= [KNL] 4242 Enable RCU grace-period forward-progress testing 4243 for the types of RCU supporting this notion. 4244 4245 rcutorture.fwd_progress_div= [KNL] 4246 Specify the fraction of a CPU-stall-warning 4247 period to do tight-loop forward-progress testing. 4248 4249 rcutorture.fwd_progress_holdoff= [KNL] 4250 Number of seconds to wait between successive 4251 forward-progress tests. 4252 4253 rcutorture.fwd_progress_need_resched= [KNL] 4254 Enclose cond_resched() calls within checks for 4255 need_resched() during tight-loop forward-progress 4256 testing. 4257 4258 rcutorture.gp_cond= [KNL] 4259 Use conditional/asynchronous update-side 4260 primitives, if available. 4261 4262 rcutorture.gp_exp= [KNL] 4263 Use expedited update-side primitives, if available. 4264 4265 rcutorture.gp_normal= [KNL] 4266 Use normal (non-expedited) asynchronous 4267 update-side primitives, if available. 4268 4269 rcutorture.gp_sync= [KNL] 4270 Use normal (non-expedited) synchronous 4271 update-side primitives, if available. If all 4272 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4273 rcutorture.gp_normal=, and rcutorture.gp_sync= 4274 are zero, rcutorture acts as if is interpreted 4275 they are all non-zero. 4276 4277 rcutorture.n_barrier_cbs= [KNL] 4278 Set callbacks/threads for rcu_barrier() testing. 4279 4280 rcutorture.nfakewriters= [KNL] 4281 Set number of concurrent RCU writers. These just 4282 stress RCU, they don't participate in the actual 4283 test, hence the "fake". 4284 4285 rcutorture.nreaders= [KNL] 4286 Set number of RCU readers. The value -1 selects 4287 N-1, where N is the number of CPUs. A value 4288 "n" less than -1 selects N-n-2, where N is again 4289 the number of CPUs. For example, -2 selects N 4290 (the number of CPUs), -3 selects N+1, and so on. 4291 4292 rcutorture.object_debug= [KNL] 4293 Enable debug-object double-call_rcu() testing. 4294 4295 rcutorture.onoff_holdoff= [KNL] 4296 Set time (s) after boot for CPU-hotplug testing. 4297 4298 rcutorture.onoff_interval= [KNL] 4299 Set time (jiffies) between CPU-hotplug operations, 4300 or zero to disable CPU-hotplug testing. 4301 4302 rcutorture.read_exit= [KNL] 4303 Set the number of read-then-exit kthreads used 4304 to test the interaction of RCU updaters and 4305 task-exit processing. 4306 4307 rcutorture.read_exit_burst= [KNL] 4308 The number of times in a given read-then-exit 4309 episode that a set of read-then-exit kthreads 4310 is spawned. 4311 4312 rcutorture.read_exit_delay= [KNL] 4313 The delay, in seconds, between successive 4314 read-then-exit testing episodes. 4315 4316 rcutorture.shuffle_interval= [KNL] 4317 Set task-shuffle interval (s). Shuffling tasks 4318 allows some CPUs to go into dyntick-idle mode 4319 during the rcutorture test. 4320 4321 rcutorture.shutdown_secs= [KNL] 4322 Set time (s) after boot system shutdown. This 4323 is useful for hands-off automated testing. 4324 4325 rcutorture.stall_cpu= [KNL] 4326 Duration of CPU stall (s) to test RCU CPU stall 4327 warnings, zero to disable. 4328 4329 rcutorture.stall_cpu_block= [KNL] 4330 Sleep while stalling if set. This will result 4331 in warnings from preemptible RCU in addition 4332 to any other stall-related activity. 4333 4334 rcutorture.stall_cpu_holdoff= [KNL] 4335 Time to wait (s) after boot before inducing stall. 4336 4337 rcutorture.stall_cpu_irqsoff= [KNL] 4338 Disable interrupts while stalling if set. 4339 4340 rcutorture.stall_gp_kthread= [KNL] 4341 Duration (s) of forced sleep within RCU 4342 grace-period kthread to test RCU CPU stall 4343 warnings, zero to disable. If both stall_cpu 4344 and stall_gp_kthread are specified, the 4345 kthread is starved first, then the CPU. 4346 4347 rcutorture.stat_interval= [KNL] 4348 Time (s) between statistics printk()s. 4349 4350 rcutorture.stutter= [KNL] 4351 Time (s) to stutter testing, for example, specifying 4352 five seconds causes the test to run for five seconds, 4353 wait for five seconds, and so on. This tests RCU's 4354 ability to transition abruptly to and from idle. 4355 4356 rcutorture.test_boost= [KNL] 4357 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4358 "Maybe" means test if the RCU implementation 4359 under test support RCU priority boosting. 4360 4361 rcutorture.test_boost_duration= [KNL] 4362 Duration (s) of each individual boost test. 4363 4364 rcutorture.test_boost_interval= [KNL] 4365 Interval (s) between each boost test. 4366 4367 rcutorture.test_no_idle_hz= [KNL] 4368 Test RCU's dyntick-idle handling. See also the 4369 rcutorture.shuffle_interval parameter. 4370 4371 rcutorture.torture_type= [KNL] 4372 Specify the RCU implementation to test. 4373 4374 rcutorture.verbose= [KNL] 4375 Enable additional printk() statements. 4376 4377 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4378 Dump ftrace buffer after reporting RCU CPU 4379 stall warning. 4380 4381 rcupdate.rcu_cpu_stall_suppress= [KNL] 4382 Suppress RCU CPU stall warning messages. 4383 4384 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4385 Suppress RCU CPU stall warning messages and 4386 rcutorture writer stall warnings that occur 4387 during early boot, that is, during the time 4388 before the init task is spawned. 4389 4390 rcupdate.rcu_cpu_stall_timeout= [KNL] 4391 Set timeout for RCU CPU stall warning messages. 4392 4393 rcupdate.rcu_expedited= [KNL] 4394 Use expedited grace-period primitives, for 4395 example, synchronize_rcu_expedited() instead 4396 of synchronize_rcu(). This reduces latency, 4397 but can increase CPU utilization, degrade 4398 real-time latency, and degrade energy efficiency. 4399 No effect on CONFIG_TINY_RCU kernels. 4400 4401 rcupdate.rcu_normal= [KNL] 4402 Use only normal grace-period primitives, 4403 for example, synchronize_rcu() instead of 4404 synchronize_rcu_expedited(). This improves 4405 real-time latency, CPU utilization, and 4406 energy efficiency, but can expose users to 4407 increased grace-period latency. This parameter 4408 overrides rcupdate.rcu_expedited. No effect on 4409 CONFIG_TINY_RCU kernels. 4410 4411 rcupdate.rcu_normal_after_boot= [KNL] 4412 Once boot has completed (that is, after 4413 rcu_end_inkernel_boot() has been invoked), use 4414 only normal grace-period primitives. No effect 4415 on CONFIG_TINY_RCU kernels. 4416 4417 rcupdate.rcu_task_ipi_delay= [KNL] 4418 Set time in jiffies during which RCU tasks will 4419 avoid sending IPIs, starting with the beginning 4420 of a given grace period. Setting a large 4421 number avoids disturbing real-time workloads, 4422 but lengthens grace periods. 4423 4424 rcupdate.rcu_task_stall_timeout= [KNL] 4425 Set timeout in jiffies for RCU task stall warning 4426 messages. Disable with a value less than or equal 4427 to zero. 4428 4429 rcupdate.rcu_self_test= [KNL] 4430 Run the RCU early boot self tests 4431 4432 rdinit= [KNL] 4433 Format: <full_path> 4434 Run specified binary instead of /init from the ramdisk, 4435 used for early userspace startup. See initrd. 4436 4437 rdrand= [X86] 4438 force - Override the decision by the kernel to hide the 4439 advertisement of RDRAND support (this affects 4440 certain AMD processors because of buggy BIOS 4441 support, specifically around the suspend/resume 4442 path). 4443 4444 rdt= [HW,X86,RDT] 4445 Turn on/off individual RDT features. List is: 4446 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4447 mba. 4448 E.g. to turn on cmt and turn off mba use: 4449 rdt=cmt,!mba 4450 4451 reboot= [KNL] 4452 Format (x86 or x86_64): 4453 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4454 [[,]s[mp]#### \ 4455 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4456 [[,]f[orce] 4457 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4458 (prefix with 'panic_' to set mode for panic 4459 reboot only), 4460 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4461 reboot_force is either force or not specified, 4462 reboot_cpu is s[mp]#### with #### being the processor 4463 to be used for rebooting. 4464 4465 refscale.holdoff= [KNL] 4466 Set test-start holdoff period. The purpose of 4467 this parameter is to delay the start of the 4468 test until boot completes in order to avoid 4469 interference. 4470 4471 refscale.loops= [KNL] 4472 Set the number of loops over the synchronization 4473 primitive under test. Increasing this number 4474 reduces noise due to loop start/end overhead, 4475 but the default has already reduced the per-pass 4476 noise to a handful of picoseconds on ca. 2020 4477 x86 laptops. 4478 4479 refscale.nreaders= [KNL] 4480 Set number of readers. The default value of -1 4481 selects N, where N is roughly 75% of the number 4482 of CPUs. A value of zero is an interesting choice. 4483 4484 refscale.nruns= [KNL] 4485 Set number of runs, each of which is dumped onto 4486 the console log. 4487 4488 refscale.readdelay= [KNL] 4489 Set the read-side critical-section duration, 4490 measured in microseconds. 4491 4492 refscale.scale_type= [KNL] 4493 Specify the read-protection implementation to test. 4494 4495 refscale.shutdown= [KNL] 4496 Shut down the system at the end of the performance 4497 test. This defaults to 1 (shut it down) when 4498 rcuperf is built into the kernel and to 0 (leave 4499 it running) when rcuperf is built as a module. 4500 4501 refscale.verbose= [KNL] 4502 Enable additional printk() statements. 4503 4504 relax_domain_level= 4505 [KNL, SMP] Set scheduler's default relax_domain_level. 4506 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4507 4508 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4509 Format: <base1>,<size1>[,<base2>,<size2>,...] 4510 Reserve I/O ports or memory so the kernel won't use 4511 them. If <base> is less than 0x10000, the region 4512 is assumed to be I/O ports; otherwise it is memory. 4513 4514 reservetop= [X86-32] 4515 Format: nn[KMG] 4516 Reserves a hole at the top of the kernel virtual 4517 address space. 4518 4519 reservelow= [X86] 4520 Format: nn[K] 4521 Set the amount of memory to reserve for BIOS at 4522 the bottom of the address space. 4523 4524 reset_devices [KNL] Force drivers to reset the underlying device 4525 during initialization. 4526 4527 resume= [SWSUSP] 4528 Specify the partition device for software suspend 4529 Format: 4530 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4531 4532 resume_offset= [SWSUSP] 4533 Specify the offset from the beginning of the partition 4534 given by "resume=" at which the swap header is located, 4535 in <PAGE_SIZE> units (needed only for swap files). 4536 See Documentation/power/swsusp-and-swap-files.rst 4537 4538 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4539 read the resume files 4540 4541 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4542 Useful for devices that are detected asynchronously 4543 (e.g. USB and MMC devices). 4544 4545 hibernate= [HIBERNATION] 4546 noresume Don't check if there's a hibernation image 4547 present during boot. 4548 nocompress Don't compress/decompress hibernation images. 4549 no Disable hibernation and resume. 4550 protect_image Turn on image protection during restoration 4551 (that will set all pages holding image data 4552 during restoration read-only). 4553 4554 retain_initrd [RAM] Keep initrd memory after extraction 4555 4556 rfkill.default_state= 4557 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4558 etc. communication is blocked by default. 4559 1 Unblocked. 4560 4561 rfkill.master_switch_mode= 4562 0 The "airplane mode" button does nothing. 4563 1 The "airplane mode" button toggles between everything 4564 blocked and the previous configuration. 4565 2 The "airplane mode" button toggles between everything 4566 blocked and everything unblocked. 4567 4568 rhash_entries= [KNL,NET] 4569 Set number of hash buckets for route cache 4570 4571 ring3mwait=disable 4572 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4573 CPUs. 4574 4575 ro [KNL] Mount root device read-only on boot 4576 4577 rodata= [KNL] 4578 on Mark read-only kernel memory as read-only (default). 4579 off Leave read-only kernel memory writable for debugging. 4580 4581 rockchip.usb_uart 4582 Enable the uart passthrough on the designated usb port 4583 on Rockchip SoCs. When active, the signals of the 4584 debug-uart get routed to the D+ and D- pins of the usb 4585 port and the regular usb controller gets disabled. 4586 4587 root= [KNL] Root filesystem 4588 See name_to_dev_t comment in init/do_mounts.c. 4589 4590 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4591 mount the root filesystem 4592 4593 rootflags= [KNL] Set root filesystem mount option string 4594 4595 rootfstype= [KNL] Set root filesystem type 4596 4597 rootwait [KNL] Wait (indefinitely) for root device to show up. 4598 Useful for devices that are detected asynchronously 4599 (e.g. USB and MMC devices). 4600 4601 rproc_mem=nn[KMG][@address] 4602 [KNL,ARM,CMA] Remoteproc physical memory block. 4603 Memory area to be used by remote processor image, 4604 managed by CMA. 4605 4606 rw [KNL] Mount root device read-write on boot 4607 4608 S [KNL] Run init in single mode 4609 4610 s390_iommu= [HW,S390] 4611 Set s390 IOTLB flushing mode 4612 strict 4613 With strict flushing every unmap operation will result in 4614 an IOTLB flush. Default is lazy flushing before reuse, 4615 which is faster. 4616 4617 sa1100ir [NET] 4618 See drivers/net/irda/sa1100_ir.c. 4619 4620 sbni= [NET] Granch SBNI12 leased line adapter 4621 4622 sched_debug [KNL] Enables verbose scheduler debug messages. 4623 4624 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4625 Allowed values are enable and disable. This feature 4626 incurs a small amount of overhead in the scheduler 4627 but is useful for debugging and performance tuning. 4628 4629 sched_thermal_decay_shift= 4630 [KNL, SMP] Set a decay shift for scheduler thermal 4631 pressure signal. Thermal pressure signal follows the 4632 default decay period of other scheduler pelt 4633 signals(usually 32 ms but configurable). Setting 4634 sched_thermal_decay_shift will left shift the decay 4635 period for the thermal pressure signal by the shift 4636 value. 4637 i.e. with the default pelt decay period of 32 ms 4638 sched_thermal_decay_shift thermal pressure decay pr 4639 1 64 ms 4640 2 128 ms 4641 and so on. 4642 Format: integer between 0 and 10 4643 Default is 0. 4644 4645 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4646 xtime_lock contention on larger systems, and/or RCU lock 4647 contention on all systems with CONFIG_MAXSMP set. 4648 Format: { "0" | "1" } 4649 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4650 1 -- enable. 4651 Note: increases power consumption, thus should only be 4652 enabled if running jitter sensitive (HPC/RT) workloads. 4653 4654 security= [SECURITY] Choose a legacy "major" security module to 4655 enable at boot. This has been deprecated by the 4656 "lsm=" parameter. 4657 4658 selinux= [SELINUX] Disable or enable SELinux at boot time. 4659 Format: { "0" | "1" } 4660 See security/selinux/Kconfig help text. 4661 0 -- disable. 4662 1 -- enable. 4663 Default value is 1. 4664 4665 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4666 Format: { "0" | "1" } 4667 See security/apparmor/Kconfig help text 4668 0 -- disable. 4669 1 -- enable. 4670 Default value is set via kernel config option. 4671 4672 serialnumber [BUGS=X86-32] 4673 4674 shapers= [NET] 4675 Maximal number of shapers. 4676 4677 simeth= [IA-64] 4678 simscsi= 4679 4680 slram= [HW,MTD] 4681 4682 slab_nomerge [MM] 4683 Disable merging of slabs with similar size. May be 4684 necessary if there is some reason to distinguish 4685 allocs to different slabs, especially in hardened 4686 environments where the risk of heap overflows and 4687 layout control by attackers can usually be 4688 frustrated by disabling merging. This will reduce 4689 most of the exposure of a heap attack to a single 4690 cache (risks via metadata attacks are mostly 4691 unchanged). Debug options disable merging on their 4692 own. 4693 For more information see Documentation/vm/slub.rst. 4694 4695 slab_max_order= [MM, SLAB] 4696 Determines the maximum allowed order for slabs. 4697 A high setting may cause OOMs due to memory 4698 fragmentation. Defaults to 1 for systems with 4699 more than 32MB of RAM, 0 otherwise. 4700 4701 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4702 Enabling slub_debug allows one to determine the 4703 culprit if slab objects become corrupted. Enabling 4704 slub_debug can create guard zones around objects and 4705 may poison objects when not in use. Also tracks the 4706 last alloc / free. For more information see 4707 Documentation/vm/slub.rst. 4708 4709 slub_memcg_sysfs= [MM, SLUB] 4710 Determines whether to enable sysfs directories for 4711 memory cgroup sub-caches. 1 to enable, 0 to disable. 4712 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4713 Enabling this can lead to a very high number of debug 4714 directories and files being created under 4715 /sys/kernel/slub. 4716 4717 slub_max_order= [MM, SLUB] 4718 Determines the maximum allowed order for slabs. 4719 A high setting may cause OOMs due to memory 4720 fragmentation. For more information see 4721 Documentation/vm/slub.rst. 4722 4723 slub_min_objects= [MM, SLUB] 4724 The minimum number of objects per slab. SLUB will 4725 increase the slab order up to slub_max_order to 4726 generate a sufficiently large slab able to contain 4727 the number of objects indicated. The higher the number 4728 of objects the smaller the overhead of tracking slabs 4729 and the less frequently locks need to be acquired. 4730 For more information see Documentation/vm/slub.rst. 4731 4732 slub_min_order= [MM, SLUB] 4733 Determines the minimum page order for slabs. Must be 4734 lower than slub_max_order. 4735 For more information see Documentation/vm/slub.rst. 4736 4737 slub_nomerge [MM, SLUB] 4738 Same with slab_nomerge. This is supported for legacy. 4739 See slab_nomerge for more information. 4740 4741 smart2= [HW] 4742 Format: <io1>[,<io2>[,...,<io8>]] 4743 4744 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4745 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4746 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4747 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4748 smsc-ircc2.ircc_irq= [HW] IRQ line 4749 smsc-ircc2.ircc_dma= [HW] DMA channel 4750 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4751 0: Toshiba Satellite 1800 (GP data pin select) 4752 1: Fast pin select (default) 4753 2: ATC IRMode 4754 4755 smt [KNL,S390] Set the maximum number of threads (logical 4756 CPUs) to use per physical CPU on systems capable of 4757 symmetric multithreading (SMT). Will be capped to the 4758 actual hardware limit. 4759 Format: <integer> 4760 Default: -1 (no limit) 4761 4762 softlockup_panic= 4763 [KNL] Should the soft-lockup detector generate panics. 4764 Format: 0 | 1 4765 4766 A value of 1 instructs the soft-lockup detector 4767 to panic the machine when a soft-lockup occurs. It is 4768 also controlled by the kernel.softlockup_panic sysctl 4769 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4770 respective build-time switch to that functionality. 4771 4772 softlockup_all_cpu_backtrace= 4773 [KNL] Should the soft-lockup detector generate 4774 backtraces on all cpus. 4775 Format: 0 | 1 4776 4777 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4778 See Documentation/admin-guide/laptops/sonypi.rst 4779 4780 spectre_v2= [X86] Control mitigation of Spectre variant 2 4781 (indirect branch speculation) vulnerability. 4782 The default operation protects the kernel from 4783 user space attacks. 4784 4785 on - unconditionally enable, implies 4786 spectre_v2_user=on 4787 off - unconditionally disable, implies 4788 spectre_v2_user=off 4789 auto - kernel detects whether your CPU model is 4790 vulnerable 4791 4792 Selecting 'on' will, and 'auto' may, choose a 4793 mitigation method at run time according to the 4794 CPU, the available microcode, the setting of the 4795 CONFIG_RETPOLINE configuration option, and the 4796 compiler with which the kernel was built. 4797 4798 Selecting 'on' will also enable the mitigation 4799 against user space to user space task attacks. 4800 4801 Selecting 'off' will disable both the kernel and 4802 the user space protections. 4803 4804 Specific mitigations can also be selected manually: 4805 4806 retpoline - replace indirect branches 4807 retpoline,generic - google's original retpoline 4808 retpoline,amd - AMD-specific minimal thunk 4809 4810 Not specifying this option is equivalent to 4811 spectre_v2=auto. 4812 4813 spectre_v2_user= 4814 [X86] Control mitigation of Spectre variant 2 4815 (indirect branch speculation) vulnerability between 4816 user space tasks 4817 4818 on - Unconditionally enable mitigations. Is 4819 enforced by spectre_v2=on 4820 4821 off - Unconditionally disable mitigations. Is 4822 enforced by spectre_v2=off 4823 4824 prctl - Indirect branch speculation is enabled, 4825 but mitigation can be enabled via prctl 4826 per thread. The mitigation control state 4827 is inherited on fork. 4828 4829 prctl,ibpb 4830 - Like "prctl" above, but only STIBP is 4831 controlled per thread. IBPB is issued 4832 always when switching between different user 4833 space processes. 4834 4835 seccomp 4836 - Same as "prctl" above, but all seccomp 4837 threads will enable the mitigation unless 4838 they explicitly opt out. 4839 4840 seccomp,ibpb 4841 - Like "seccomp" above, but only STIBP is 4842 controlled per thread. IBPB is issued 4843 always when switching between different 4844 user space processes. 4845 4846 auto - Kernel selects the mitigation depending on 4847 the available CPU features and vulnerability. 4848 4849 Default mitigation: 4850 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4851 4852 Not specifying this option is equivalent to 4853 spectre_v2_user=auto. 4854 4855 spec_store_bypass_disable= 4856 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4857 (Speculative Store Bypass vulnerability) 4858 4859 Certain CPUs are vulnerable to an exploit against a 4860 a common industry wide performance optimization known 4861 as "Speculative Store Bypass" in which recent stores 4862 to the same memory location may not be observed by 4863 later loads during speculative execution. The idea 4864 is that such stores are unlikely and that they can 4865 be detected prior to instruction retirement at the 4866 end of a particular speculation execution window. 4867 4868 In vulnerable processors, the speculatively forwarded 4869 store can be used in a cache side channel attack, for 4870 example to read memory to which the attacker does not 4871 directly have access (e.g. inside sandboxed code). 4872 4873 This parameter controls whether the Speculative Store 4874 Bypass optimization is used. 4875 4876 On x86 the options are: 4877 4878 on - Unconditionally disable Speculative Store Bypass 4879 off - Unconditionally enable Speculative Store Bypass 4880 auto - Kernel detects whether the CPU model contains an 4881 implementation of Speculative Store Bypass and 4882 picks the most appropriate mitigation. If the 4883 CPU is not vulnerable, "off" is selected. If the 4884 CPU is vulnerable the default mitigation is 4885 architecture and Kconfig dependent. See below. 4886 prctl - Control Speculative Store Bypass per thread 4887 via prctl. Speculative Store Bypass is enabled 4888 for a process by default. The state of the control 4889 is inherited on fork. 4890 seccomp - Same as "prctl" above, but all seccomp threads 4891 will disable SSB unless they explicitly opt out. 4892 4893 Default mitigations: 4894 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4895 4896 On powerpc the options are: 4897 4898 on,auto - On Power8 and Power9 insert a store-forwarding 4899 barrier on kernel entry and exit. On Power7 4900 perform a software flush on kernel entry and 4901 exit. 4902 off - No action. 4903 4904 Not specifying this option is equivalent to 4905 spec_store_bypass_disable=auto. 4906 4907 spia_io_base= [HW,MTD] 4908 spia_fio_base= 4909 spia_pedr= 4910 spia_peddr= 4911 4912 split_lock_detect= 4913 [X86] Enable split lock detection 4914 4915 When enabled (and if hardware support is present), atomic 4916 instructions that access data across cache line 4917 boundaries will result in an alignment check exception. 4918 4919 off - not enabled 4920 4921 warn - the kernel will emit rate limited warnings 4922 about applications triggering the #AC 4923 exception. This mode is the default on CPUs 4924 that supports split lock detection. 4925 4926 fatal - the kernel will send SIGBUS to applications 4927 that trigger the #AC exception. 4928 4929 If an #AC exception is hit in the kernel or in 4930 firmware (i.e. not while executing in user mode) 4931 the kernel will oops in either "warn" or "fatal" 4932 mode. 4933 4934 srbds= [X86,INTEL] 4935 Control the Special Register Buffer Data Sampling 4936 (SRBDS) mitigation. 4937 4938 Certain CPUs are vulnerable to an MDS-like 4939 exploit which can leak bits from the random 4940 number generator. 4941 4942 By default, this issue is mitigated by 4943 microcode. However, the microcode fix can cause 4944 the RDRAND and RDSEED instructions to become 4945 much slower. Among other effects, this will 4946 result in reduced throughput from /dev/urandom. 4947 4948 The microcode mitigation can be disabled with 4949 the following option: 4950 4951 off: Disable mitigation and remove 4952 performance impact to RDRAND and RDSEED 4953 4954 srcutree.counter_wrap_check [KNL] 4955 Specifies how frequently to check for 4956 grace-period sequence counter wrap for the 4957 srcu_data structure's ->srcu_gp_seq_needed field. 4958 The greater the number of bits set in this kernel 4959 parameter, the less frequently counter wrap will 4960 be checked for. Note that the bottom two bits 4961 are ignored. 4962 4963 srcutree.exp_holdoff [KNL] 4964 Specifies how many nanoseconds must elapse 4965 since the end of the last SRCU grace period for 4966 a given srcu_struct until the next normal SRCU 4967 grace period will be considered for automatic 4968 expediting. Set to zero to disable automatic 4969 expediting. 4970 4971 ssbd= [ARM64,HW] 4972 Speculative Store Bypass Disable control 4973 4974 On CPUs that are vulnerable to the Speculative 4975 Store Bypass vulnerability and offer a 4976 firmware based mitigation, this parameter 4977 indicates how the mitigation should be used: 4978 4979 force-on: Unconditionally enable mitigation for 4980 for both kernel and userspace 4981 force-off: Unconditionally disable mitigation for 4982 for both kernel and userspace 4983 kernel: Always enable mitigation in the 4984 kernel, and offer a prctl interface 4985 to allow userspace to register its 4986 interest in being mitigated too. 4987 4988 stack_guard_gap= [MM] 4989 override the default stack gap protection. The value 4990 is in page units and it defines how many pages prior 4991 to (for stacks growing down) resp. after (for stacks 4992 growing up) the main stack are reserved for no other 4993 mapping. Default value is 256 pages. 4994 4995 stacktrace [FTRACE] 4996 Enabled the stack tracer on boot up. 4997 4998 stacktrace_filter=[function-list] 4999 [FTRACE] Limit the functions that the stack tracer 5000 will trace at boot up. function-list is a comma separated 5001 list of functions. This list can be changed at run 5002 time by the stack_trace_filter file in the debugfs 5003 tracing directory. Note, this enables stack tracing 5004 and the stacktrace above is not needed. 5005 5006 sti= [PARISC,HW] 5007 Format: <num> 5008 Set the STI (builtin display/keyboard on the HP-PARISC 5009 machines) console (graphic card) which should be used 5010 as the initial boot-console. 5011 See also comment in drivers/video/console/sticore.c. 5012 5013 sti_font= [HW] 5014 See comment in drivers/video/console/sticore.c. 5015 5016 stifb= [HW] 5017 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5018 5019 sunrpc.min_resvport= 5020 sunrpc.max_resvport= 5021 [NFS,SUNRPC] 5022 SunRPC servers often require that client requests 5023 originate from a privileged port (i.e. a port in the 5024 range 0 < portnr < 1024). 5025 An administrator who wishes to reserve some of these 5026 ports for other uses may adjust the range that the 5027 kernel's sunrpc client considers to be privileged 5028 using these two parameters to set the minimum and 5029 maximum port values. 5030 5031 sunrpc.svc_rpc_per_connection_limit= 5032 [NFS,SUNRPC] 5033 Limit the number of requests that the server will 5034 process in parallel from a single connection. 5035 The default value is 0 (no limit). 5036 5037 sunrpc.pool_mode= 5038 [NFS] 5039 Control how the NFS server code allocates CPUs to 5040 service thread pools. Depending on how many NICs 5041 you have and where their interrupts are bound, this 5042 option will affect which CPUs will do NFS serving. 5043 Note: this parameter cannot be changed while the 5044 NFS server is running. 5045 5046 auto the server chooses an appropriate mode 5047 automatically using heuristics 5048 global a single global pool contains all CPUs 5049 percpu one pool for each CPU 5050 pernode one pool for each NUMA node (equivalent 5051 to global on non-NUMA machines) 5052 5053 sunrpc.tcp_slot_table_entries= 5054 sunrpc.udp_slot_table_entries= 5055 [NFS,SUNRPC] 5056 Sets the upper limit on the number of simultaneous 5057 RPC calls that can be sent from the client to a 5058 server. Increasing these values may allow you to 5059 improve throughput, but will also increase the 5060 amount of memory reserved for use by the client. 5061 5062 suspend.pm_test_delay= 5063 [SUSPEND] 5064 Sets the number of seconds to remain in a suspend test 5065 mode before resuming the system (see 5066 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5067 is set. Default value is 5. 5068 5069 svm= [PPC] 5070 Format: { on | off | y | n | 1 | 0 } 5071 This parameter controls use of the Protected 5072 Execution Facility on pSeries. 5073 5074 swapaccount=[0|1] 5075 [KNL] Enable accounting of swap in memory resource 5076 controller if no parameter or 1 is given or disable 5077 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5078 5079 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5080 Format: { <int> | force | noforce } 5081 <int> -- Number of I/O TLB slabs 5082 force -- force using of bounce buffers even if they 5083 wouldn't be automatically used by the kernel 5084 noforce -- Never use bounce buffers (for debugging) 5085 5086 switches= [HW,M68k] 5087 5088 sysctl.*= [KNL] 5089 Set a sysctl parameter, right before loading the init 5090 process, as if the value was written to the respective 5091 /proc/sys/... file. Both '.' and '/' are recognized as 5092 separators. Unrecognized parameters and invalid values 5093 are reported in the kernel log. Sysctls registered 5094 later by a loaded module cannot be set this way. 5095 Example: sysctl.vm.swappiness=40 5096 5097 sysfs.deprecated=0|1 [KNL] 5098 Enable/disable old style sysfs layout for old udev 5099 on older distributions. When this option is enabled 5100 very new udev will not work anymore. When this option 5101 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5102 in older udev will not work anymore. 5103 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5104 the kernel configuration. 5105 5106 sysrq_always_enabled 5107 [KNL] 5108 Ignore sysrq setting - this boot parameter will 5109 neutralize any effect of /proc/sys/kernel/sysrq. 5110 Useful for debugging. 5111 5112 tcpmhash_entries= [KNL,NET] 5113 Set the number of tcp_metrics_hash slots. 5114 Default value is 8192 or 16384 depending on total 5115 ram pages. This is used to specify the TCP metrics 5116 cache size. See Documentation/networking/ip-sysctl.rst 5117 "tcp_no_metrics_save" section for more details. 5118 5119 tdfx= [HW,DRM] 5120 5121 test_suspend= [SUSPEND][,N] 5122 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5123 standby suspend) or "freeze" (for suspend type freeze) 5124 as the system sleep state during system startup with 5125 the optional capability to repeat N number of times. 5126 The system is woken from this state using a 5127 wakeup-capable RTC alarm. 5128 5129 thash_entries= [KNL,NET] 5130 Set number of hash buckets for TCP connection 5131 5132 thermal.act= [HW,ACPI] 5133 -1: disable all active trip points in all thermal zones 5134 <degrees C>: override all lowest active trip points 5135 5136 thermal.crt= [HW,ACPI] 5137 -1: disable all critical trip points in all thermal zones 5138 <degrees C>: override all critical trip points 5139 5140 thermal.nocrt= [HW,ACPI] 5141 Set to disable actions on ACPI thermal zone 5142 critical and hot trip points. 5143 5144 thermal.off= [HW,ACPI] 5145 1: disable ACPI thermal control 5146 5147 thermal.psv= [HW,ACPI] 5148 -1: disable all passive trip points 5149 <degrees C>: override all passive trip points to this 5150 value 5151 5152 thermal.tzp= [HW,ACPI] 5153 Specify global default ACPI thermal zone polling rate 5154 <deci-seconds>: poll all this frequency 5155 0: no polling (default) 5156 5157 threadirqs [KNL] 5158 Force threading of all interrupt handlers except those 5159 marked explicitly IRQF_NO_THREAD. 5160 5161 topology= [S390] 5162 Format: {off | on} 5163 Specify if the kernel should make use of the cpu 5164 topology information if the hardware supports this. 5165 The scheduler will make use of this information and 5166 e.g. base its process migration decisions on it. 5167 Default is on. 5168 5169 topology_updates= [KNL, PPC, NUMA] 5170 Format: {off} 5171 Specify if the kernel should ignore (off) 5172 topology updates sent by the hypervisor to this 5173 LPAR. 5174 5175 torture.disable_onoff_at_boot= [KNL] 5176 Prevent the CPU-hotplug component of torturing 5177 until after init has spawned. 5178 5179 torture.ftrace_dump_at_shutdown= [KNL] 5180 Dump the ftrace buffer at torture-test shutdown, 5181 even if there were no errors. This can be a 5182 very costly operation when many torture tests 5183 are running concurrently, especially on systems 5184 with rotating-rust storage. 5185 5186 tp720= [HW,PS2] 5187 5188 tpm_suspend_pcr=[HW,TPM] 5189 Format: integer pcr id 5190 Specify that at suspend time, the tpm driver 5191 should extend the specified pcr with zeros, 5192 as a workaround for some chips which fail to 5193 flush the last written pcr on TPM_SaveState. 5194 This will guarantee that all the other pcrs 5195 are saved. 5196 5197 trace_buf_size=nn[KMG] 5198 [FTRACE] will set tracing buffer size on each cpu. 5199 5200 trace_event=[event-list] 5201 [FTRACE] Set and start specified trace events in order 5202 to facilitate early boot debugging. The event-list is a 5203 comma separated list of trace events to enable. See 5204 also Documentation/trace/events.rst 5205 5206 trace_options=[option-list] 5207 [FTRACE] Enable or disable tracer options at boot. 5208 The option-list is a comma delimited list of options 5209 that can be enabled or disabled just as if you were 5210 to echo the option name into 5211 5212 /sys/kernel/debug/tracing/trace_options 5213 5214 For example, to enable stacktrace option (to dump the 5215 stack trace of each event), add to the command line: 5216 5217 trace_options=stacktrace 5218 5219 See also Documentation/trace/ftrace.rst "trace options" 5220 section. 5221 5222 tp_printk[FTRACE] 5223 Have the tracepoints sent to printk as well as the 5224 tracing ring buffer. This is useful for early boot up 5225 where the system hangs or reboots and does not give the 5226 option for reading the tracing buffer or performing a 5227 ftrace_dump_on_oops. 5228 5229 To turn off having tracepoints sent to printk, 5230 echo 0 > /proc/sys/kernel/tracepoint_printk 5231 Note, echoing 1 into this file without the 5232 tracepoint_printk kernel cmdline option has no effect. 5233 5234 ** CAUTION ** 5235 5236 Having tracepoints sent to printk() and activating high 5237 frequency tracepoints such as irq or sched, can cause 5238 the system to live lock. 5239 5240 traceoff_on_warning 5241 [FTRACE] enable this option to disable tracing when a 5242 warning is hit. This turns off "tracing_on". Tracing can 5243 be enabled again by echoing '1' into the "tracing_on" 5244 file located in /sys/kernel/debug/tracing/ 5245 5246 This option is useful, as it disables the trace before 5247 the WARNING dump is called, which prevents the trace to 5248 be filled with content caused by the warning output. 5249 5250 This option can also be set at run time via the sysctl 5251 option: kernel/traceoff_on_warning 5252 5253 transparent_hugepage= 5254 [KNL] 5255 Format: [always|madvise|never] 5256 Can be used to control the default behavior of the system 5257 with respect to transparent hugepages. 5258 See Documentation/admin-guide/mm/transhuge.rst 5259 for more details. 5260 5261 tsc= Disable clocksource stability checks for TSC. 5262 Format: <string> 5263 [x86] reliable: mark tsc clocksource as reliable, this 5264 disables clocksource verification at runtime, as well 5265 as the stability checks done at bootup. Used to enable 5266 high-resolution timer mode on older hardware, and in 5267 virtualized environment. 5268 [x86] noirqtime: Do not use TSC to do irq accounting. 5269 Used to run time disable IRQ_TIME_ACCOUNTING on any 5270 platforms where RDTSC is slow and this accounting 5271 can add overhead. 5272 [x86] unstable: mark the TSC clocksource as unstable, this 5273 marks the TSC unconditionally unstable at bootup and 5274 avoids any further wobbles once the TSC watchdog notices. 5275 [x86] nowatchdog: disable clocksource watchdog. Used 5276 in situations with strict latency requirements (where 5277 interruptions from clocksource watchdog are not 5278 acceptable). 5279 5280 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5281 value instead. Useful when the early TSC frequency discovery 5282 procedure is not reliable, such as on overclocked systems 5283 with CPUID.16h support and partial CPUID.15h support. 5284 Format: <unsigned int> 5285 5286 tsx= [X86] Control Transactional Synchronization 5287 Extensions (TSX) feature in Intel processors that 5288 support TSX control. 5289 5290 This parameter controls the TSX feature. The options are: 5291 5292 on - Enable TSX on the system. Although there are 5293 mitigations for all known security vulnerabilities, 5294 TSX has been known to be an accelerator for 5295 several previous speculation-related CVEs, and 5296 so there may be unknown security risks associated 5297 with leaving it enabled. 5298 5299 off - Disable TSX on the system. (Note that this 5300 option takes effect only on newer CPUs which are 5301 not vulnerable to MDS, i.e., have 5302 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5303 the new IA32_TSX_CTRL MSR through a microcode 5304 update. This new MSR allows for the reliable 5305 deactivation of the TSX functionality.) 5306 5307 auto - Disable TSX if X86_BUG_TAA is present, 5308 otherwise enable TSX on the system. 5309 5310 Not specifying this option is equivalent to tsx=off. 5311 5312 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5313 for more details. 5314 5315 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5316 Abort (TAA) vulnerability. 5317 5318 Similar to Micro-architectural Data Sampling (MDS) 5319 certain CPUs that support Transactional 5320 Synchronization Extensions (TSX) are vulnerable to an 5321 exploit against CPU internal buffers which can forward 5322 information to a disclosure gadget under certain 5323 conditions. 5324 5325 In vulnerable processors, the speculatively forwarded 5326 data can be used in a cache side channel attack, to 5327 access data to which the attacker does not have direct 5328 access. 5329 5330 This parameter controls the TAA mitigation. The 5331 options are: 5332 5333 full - Enable TAA mitigation on vulnerable CPUs 5334 if TSX is enabled. 5335 5336 full,nosmt - Enable TAA mitigation and disable SMT on 5337 vulnerable CPUs. If TSX is disabled, SMT 5338 is not disabled because CPU is not 5339 vulnerable to cross-thread TAA attacks. 5340 off - Unconditionally disable TAA mitigation 5341 5342 On MDS-affected machines, tsx_async_abort=off can be 5343 prevented by an active MDS mitigation as both vulnerabilities 5344 are mitigated with the same mechanism so in order to disable 5345 this mitigation, you need to specify mds=off too. 5346 5347 Not specifying this option is equivalent to 5348 tsx_async_abort=full. On CPUs which are MDS affected 5349 and deploy MDS mitigation, TAA mitigation is not 5350 required and doesn't provide any additional 5351 mitigation. 5352 5353 For details see: 5354 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5355 5356 turbografx.map[2|3]= [HW,JOY] 5357 TurboGraFX parallel port interface 5358 Format: 5359 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5360 See also Documentation/input/devices/joystick-parport.rst 5361 5362 udbg-immortal [PPC] When debugging early kernel crashes that 5363 happen after console_init() and before a proper 5364 console driver takes over, this boot options might 5365 help "seeing" what's going on. 5366 5367 uhash_entries= [KNL,NET] 5368 Set number of hash buckets for UDP/UDP-Lite connections 5369 5370 uhci-hcd.ignore_oc= 5371 [USB] Ignore overcurrent events (default N). 5372 Some badly-designed motherboards generate lots of 5373 bogus events, for ports that aren't wired to 5374 anything. Set this parameter to avoid log spamming. 5375 Note that genuine overcurrent events won't be 5376 reported either. 5377 5378 unknown_nmi_panic 5379 [X86] Cause panic on unknown NMI. 5380 5381 usbcore.authorized_default= 5382 [USB] Default USB device authorization: 5383 (default -1 = authorized except for wireless USB, 5384 0 = not authorized, 1 = authorized, 2 = authorized 5385 if device connected to internal port) 5386 5387 usbcore.autosuspend= 5388 [USB] The autosuspend time delay (in seconds) used 5389 for newly-detected USB devices (default 2). This 5390 is the time required before an idle device will be 5391 autosuspended. Devices for which the delay is set 5392 to a negative value won't be autosuspended at all. 5393 5394 usbcore.usbfs_snoop= 5395 [USB] Set to log all usbfs traffic (default 0 = off). 5396 5397 usbcore.usbfs_snoop_max= 5398 [USB] Maximum number of bytes to snoop in each URB 5399 (default = 65536). 5400 5401 usbcore.blinkenlights= 5402 [USB] Set to cycle leds on hubs (default 0 = off). 5403 5404 usbcore.old_scheme_first= 5405 [USB] Start with the old device initialization 5406 scheme (default 0 = off). 5407 5408 usbcore.usbfs_memory_mb= 5409 [USB] Memory limit (in MB) for buffers allocated by 5410 usbfs (default = 16, 0 = max = 2047). 5411 5412 usbcore.use_both_schemes= 5413 [USB] Try the other device initialization scheme 5414 if the first one fails (default 1 = enabled). 5415 5416 usbcore.initial_descriptor_timeout= 5417 [USB] Specifies timeout for the initial 64-byte 5418 USB_REQ_GET_DESCRIPTOR request in milliseconds 5419 (default 5000 = 5.0 seconds). 5420 5421 usbcore.nousb [USB] Disable the USB subsystem 5422 5423 usbcore.quirks= 5424 [USB] A list of quirk entries to augment the built-in 5425 usb core quirk list. List entries are separated by 5426 commas. Each entry has the form 5427 VendorID:ProductID:Flags. The IDs are 4-digit hex 5428 numbers and Flags is a set of letters. Each letter 5429 will change the built-in quirk; setting it if it is 5430 clear and clearing it if it is set. The letters have 5431 the following meanings: 5432 a = USB_QUIRK_STRING_FETCH_255 (string 5433 descriptors must not be fetched using 5434 a 255-byte read); 5435 b = USB_QUIRK_RESET_RESUME (device can't resume 5436 correctly so reset it instead); 5437 c = USB_QUIRK_NO_SET_INTF (device can't handle 5438 Set-Interface requests); 5439 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5440 handle its Configuration or Interface 5441 strings); 5442 e = USB_QUIRK_RESET (device can't be reset 5443 (e.g morph devices), don't use reset); 5444 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5445 more interface descriptions than the 5446 bNumInterfaces count, and can't handle 5447 talking to these interfaces); 5448 g = USB_QUIRK_DELAY_INIT (device needs a pause 5449 during initialization, after we read 5450 the device descriptor); 5451 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5452 high speed and super speed interrupt 5453 endpoints, the USB 2.0 and USB 3.0 spec 5454 require the interval in microframes (1 5455 microframe = 125 microseconds) to be 5456 calculated as interval = 2 ^ 5457 (bInterval-1). 5458 Devices with this quirk report their 5459 bInterval as the result of this 5460 calculation instead of the exponent 5461 variable used in the calculation); 5462 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5463 handle device_qualifier descriptor 5464 requests); 5465 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5466 generates spurious wakeup, ignore 5467 remote wakeup capability); 5468 k = USB_QUIRK_NO_LPM (device can't handle Link 5469 Power Management); 5470 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5471 (Device reports its bInterval as linear 5472 frames instead of the USB 2.0 5473 calculation); 5474 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5475 to be disconnected before suspend to 5476 prevent spurious wakeup); 5477 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5478 pause after every control message); 5479 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5480 delay after resetting its port); 5481 Example: quirks=0781:5580:bk,0a5c:5834:gij 5482 5483 usbhid.mousepoll= 5484 [USBHID] The interval which mice are to be polled at. 5485 5486 usbhid.jspoll= 5487 [USBHID] The interval which joysticks are to be polled at. 5488 5489 usbhid.kbpoll= 5490 [USBHID] The interval which keyboards are to be polled at. 5491 5492 usb-storage.delay_use= 5493 [UMS] The delay in seconds before a new device is 5494 scanned for Logical Units (default 1). 5495 5496 usb-storage.quirks= 5497 [UMS] A list of quirks entries to supplement or 5498 override the built-in unusual_devs list. List 5499 entries are separated by commas. Each entry has 5500 the form VID:PID:Flags where VID and PID are Vendor 5501 and Product ID values (4-digit hex numbers) and 5502 Flags is a set of characters, each corresponding 5503 to a common usb-storage quirk flag as follows: 5504 a = SANE_SENSE (collect more than 18 bytes 5505 of sense data, not on uas); 5506 b = BAD_SENSE (don't collect more than 18 5507 bytes of sense data, not on uas); 5508 c = FIX_CAPACITY (decrease the reported 5509 device capacity by one sector); 5510 d = NO_READ_DISC_INFO (don't use 5511 READ_DISC_INFO command, not on uas); 5512 e = NO_READ_CAPACITY_16 (don't use 5513 READ_CAPACITY_16 command); 5514 f = NO_REPORT_OPCODES (don't use report opcodes 5515 command, uas only); 5516 g = MAX_SECTORS_240 (don't transfer more than 5517 240 sectors at a time, uas only); 5518 h = CAPACITY_HEURISTICS (decrease the 5519 reported device capacity by one 5520 sector if the number is odd); 5521 i = IGNORE_DEVICE (don't bind to this 5522 device); 5523 j = NO_REPORT_LUNS (don't use report luns 5524 command, uas only); 5525 l = NOT_LOCKABLE (don't try to lock and 5526 unlock ejectable media, not on uas); 5527 m = MAX_SECTORS_64 (don't transfer more 5528 than 64 sectors = 32 KB at a time, 5529 not on uas); 5530 n = INITIAL_READ10 (force a retry of the 5531 initial READ(10) command, not on uas); 5532 o = CAPACITY_OK (accept the capacity 5533 reported by the device, not on uas); 5534 p = WRITE_CACHE (the device cache is ON 5535 by default, not on uas); 5536 r = IGNORE_RESIDUE (the device reports 5537 bogus residue values, not on uas); 5538 s = SINGLE_LUN (the device has only one 5539 Logical Unit); 5540 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5541 commands, uas only); 5542 u = IGNORE_UAS (don't bind to the uas driver); 5543 w = NO_WP_DETECT (don't test whether the 5544 medium is write-protected). 5545 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5546 even if the device claims no cache, 5547 not on uas) 5548 Example: quirks=0419:aaf5:rl,0421:0433:rc 5549 5550 user_debug= [KNL,ARM] 5551 Format: <int> 5552 See arch/arm/Kconfig.debug help text. 5553 1 - undefined instruction events 5554 2 - system calls 5555 4 - invalid data aborts 5556 8 - SIGSEGV faults 5557 16 - SIGBUS faults 5558 Example: user_debug=31 5559 5560 userpte= 5561 [X86] Flags controlling user PTE allocations. 5562 5563 nohigh = do not allocate PTE pages in 5564 HIGHMEM regardless of setting 5565 of CONFIG_HIGHPTE. 5566 5567 vdso= [X86,SH] 5568 On X86_32, this is an alias for vdso32=. Otherwise: 5569 5570 vdso=1: enable VDSO (the default) 5571 vdso=0: disable VDSO mapping 5572 5573 vdso32= [X86] Control the 32-bit vDSO 5574 vdso32=1: enable 32-bit VDSO 5575 vdso32=0 or vdso32=2: disable 32-bit VDSO 5576 5577 See the help text for CONFIG_COMPAT_VDSO for more 5578 details. If CONFIG_COMPAT_VDSO is set, the default is 5579 vdso32=0; otherwise, the default is vdso32=1. 5580 5581 For compatibility with older kernels, vdso32=2 is an 5582 alias for vdso32=0. 5583 5584 Try vdso32=0 if you encounter an error that says: 5585 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5586 5587 vector= [IA-64,SMP] 5588 vector=percpu: enable percpu vector domain 5589 5590 video= [FB] Frame buffer configuration 5591 See Documentation/fb/modedb.rst. 5592 5593 video.brightness_switch_enabled= [0,1] 5594 If set to 1, on receiving an ACPI notify event 5595 generated by hotkey, video driver will adjust brightness 5596 level and then send out the event to user space through 5597 the allocated input device; If set to 0, video driver 5598 will only send out the event without touching backlight 5599 brightness level. 5600 default: 1 5601 5602 virtio_mmio.device= 5603 [VMMIO] Memory mapped virtio (platform) device. 5604 5605 <size>@<baseaddr>:<irq>[:<id>] 5606 where: 5607 <size> := size (can use standard suffixes 5608 like K, M and G) 5609 <baseaddr> := physical base address 5610 <irq> := interrupt number (as passed to 5611 request_irq()) 5612 <id> := (optional) platform device id 5613 example: 5614 virtio_mmio.device=1K@0x100b0000:48:7 5615 5616 Can be used multiple times for multiple devices. 5617 5618 vga= [BOOT,X86-32] Select a particular video mode 5619 See Documentation/x86/boot.rst and 5620 Documentation/admin-guide/svga.rst. 5621 Use vga=ask for menu. 5622 This is actually a boot loader parameter; the value is 5623 passed to the kernel using a special protocol. 5624 5625 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5626 May slow down system boot speed, especially when 5627 enabled on systems with a large amount of memory. 5628 All options are enabled by default, and this 5629 interface is meant to allow for selectively 5630 enabling or disabling specific virtual memory 5631 debugging features. 5632 5633 Available options are: 5634 P Enable page structure init time poisoning 5635 - Disable all of the above options 5636 5637 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5638 size of <nn>. This can be used to increase the 5639 minimum size (128MB on x86). It can also be used to 5640 decrease the size and leave more room for directly 5641 mapped kernel RAM. 5642 5643 vmcp_cma=nn[MG] [KNL,S390] 5644 Sets the memory size reserved for contiguous memory 5645 allocations for the vmcp device driver. 5646 5647 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5648 Format: <command> 5649 5650 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5651 Format: <command> 5652 5653 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5654 Format: <command> 5655 5656 vsyscall= [X86-64] 5657 Controls the behavior of vsyscalls (i.e. calls to 5658 fixed addresses of 0xffffffffff600x00 from legacy 5659 code). Most statically-linked binaries and older 5660 versions of glibc use these calls. Because these 5661 functions are at fixed addresses, they make nice 5662 targets for exploits that can control RIP. 5663 5664 emulate [default] Vsyscalls turn into traps and are 5665 emulated reasonably safely. The vsyscall 5666 page is readable. 5667 5668 xonly Vsyscalls turn into traps and are 5669 emulated reasonably safely. The vsyscall 5670 page is not readable. 5671 5672 none Vsyscalls don't work at all. This makes 5673 them quite hard to use for exploits but 5674 might break your system. 5675 5676 vt.color= [VT] Default text color. 5677 Format: 0xYX, X = foreground, Y = background. 5678 Default: 0x07 = light gray on black. 5679 5680 vt.cur_default= [VT] Default cursor shape. 5681 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5682 the parameters of the <Esc>[?A;B;Cc escape sequence; 5683 see VGA-softcursor.txt. Default: 2 = underline. 5684 5685 vt.default_blu= [VT] 5686 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5687 Change the default blue palette of the console. 5688 This is a 16-member array composed of values 5689 ranging from 0-255. 5690 5691 vt.default_grn= [VT] 5692 Format: <green0>,<green1>,<green2>,...,<green15> 5693 Change the default green palette of the console. 5694 This is a 16-member array composed of values 5695 ranging from 0-255. 5696 5697 vt.default_red= [VT] 5698 Format: <red0>,<red1>,<red2>,...,<red15> 5699 Change the default red palette of the console. 5700 This is a 16-member array composed of values 5701 ranging from 0-255. 5702 5703 vt.default_utf8= 5704 [VT] 5705 Format=<0|1> 5706 Set system-wide default UTF-8 mode for all tty's. 5707 Default is 1, i.e. UTF-8 mode is enabled for all 5708 newly opened terminals. 5709 5710 vt.global_cursor_default= 5711 [VT] 5712 Format=<-1|0|1> 5713 Set system-wide default for whether a cursor 5714 is shown on new VTs. Default is -1, 5715 i.e. cursors will be created by default unless 5716 overridden by individual drivers. 0 will hide 5717 cursors, 1 will display them. 5718 5719 vt.italic= [VT] Default color for italic text; 0-15. 5720 Default: 2 = green. 5721 5722 vt.underline= [VT] Default color for underlined text; 0-15. 5723 Default: 3 = cyan. 5724 5725 watchdog timers [HW,WDT] For information on watchdog timers, 5726 see Documentation/watchdog/watchdog-parameters.rst 5727 or other driver-specific files in the 5728 Documentation/watchdog/ directory. 5729 5730 watchdog_thresh= 5731 [KNL] 5732 Set the hard lockup detector stall duration 5733 threshold in seconds. The soft lockup detector 5734 threshold is set to twice the value. A value of 0 5735 disables both lockup detectors. Default is 10 5736 seconds. 5737 5738 workqueue.watchdog_thresh= 5739 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5740 warn stall conditions and dump internal state to 5741 help debugging. 0 disables workqueue stall 5742 detection; otherwise, it's the stall threshold 5743 duration in seconds. The default value is 30 and 5744 it can be updated at runtime by writing to the 5745 corresponding sysfs file. 5746 5747 workqueue.disable_numa 5748 By default, all work items queued to unbound 5749 workqueues are affine to the NUMA nodes they're 5750 issued on, which results in better behavior in 5751 general. If NUMA affinity needs to be disabled for 5752 whatever reason, this option can be used. Note 5753 that this also can be controlled per-workqueue for 5754 workqueues visible under /sys/bus/workqueue/. 5755 5756 workqueue.power_efficient 5757 Per-cpu workqueues are generally preferred because 5758 they show better performance thanks to cache 5759 locality; unfortunately, per-cpu workqueues tend to 5760 be more power hungry than unbound workqueues. 5761 5762 Enabling this makes the per-cpu workqueues which 5763 were observed to contribute significantly to power 5764 consumption unbound, leading to measurably lower 5765 power usage at the cost of small performance 5766 overhead. 5767 5768 The default value of this parameter is determined by 5769 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5770 5771 workqueue.debug_force_rr_cpu 5772 Workqueue used to implicitly guarantee that work 5773 items queued without explicit CPU specified are put 5774 on the local CPU. This guarantee is no longer true 5775 and while local CPU is still preferred work items 5776 may be put on foreign CPUs. This debug option 5777 forces round-robin CPU selection to flush out 5778 usages which depend on the now broken guarantee. 5779 When enabled, memory and cache locality will be 5780 impacted. 5781 5782 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5783 default x2apic cluster mode on platforms 5784 supporting x2apic. 5785 5786 x86_intel_mid_timer= [X86-32,APBT] 5787 Choose timer option for x86 Intel MID platform. 5788 Two valid options are apbt timer only and lapic timer 5789 plus one apbt timer for broadcast timer. 5790 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5791 5792 xen_512gb_limit [KNL,X86-64,XEN] 5793 Restricts the kernel running paravirtualized under Xen 5794 to use only up to 512 GB of RAM. The reason to do so is 5795 crash analysis tools and Xen tools for doing domain 5796 save/restore/migration must be enabled to handle larger 5797 domains. 5798 5799 xen_emul_unplug= [HW,X86,XEN] 5800 Unplug Xen emulated devices 5801 Format: [unplug0,][unplug1] 5802 ide-disks -- unplug primary master IDE devices 5803 aux-ide-disks -- unplug non-primary-master IDE devices 5804 nics -- unplug network devices 5805 all -- unplug all emulated devices (NICs and IDE disks) 5806 unnecessary -- unplugging emulated devices is 5807 unnecessary even if the host did not respond to 5808 the unplug protocol 5809 never -- do not unplug even if version check succeeds 5810 5811 xen_legacy_crash [X86,XEN] 5812 Crash from Xen panic notifier, without executing late 5813 panic() code such as dumping handler. 5814 5815 xen_nopvspin [X86,XEN] 5816 Disables the qspinlock slowpath using Xen PV optimizations. 5817 This parameter is obsoleted by "nopvspin" parameter, which 5818 has equivalent effect for XEN platform. 5819 5820 xen_nopv [X86] 5821 Disables the PV optimizations forcing the HVM guest to 5822 run as generic HVM guest with no PV drivers. 5823 This option is obsoleted by the "nopv" option, which 5824 has equivalent effect for XEN platform. 5825 5826 xen_scrub_pages= [XEN] 5827 Boolean option to control scrubbing pages before giving them back 5828 to Xen, for use by other domains. Can be also changed at runtime 5829 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5830 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5831 5832 xen_timer_slop= [X86-64,XEN] 5833 Set the timer slop (in nanoseconds) for the virtual Xen 5834 timers (default is 100000). This adjusts the minimum 5835 delta of virtualized Xen timers, where lower values 5836 improve timer resolution at the expense of processing 5837 more timer interrupts. 5838 5839 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5840 Disables the PV optimizations forcing the guest to run 5841 as generic guest with no PV drivers. Currently support 5842 XEN HVM, KVM, HYPER_V and VMWARE guest. 5843 5844 nopvspin [X86,XEN,KVM] 5845 Disables the qspinlock slow path using PV optimizations 5846 which allow the hypervisor to 'idle' the guest on lock 5847 contention. 5848 5849 xirc2ps_cs= [NET,PCMCIA] 5850 Format: 5851 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5852 5853 xive= [PPC] 5854 By default on POWER9 and above, the kernel will 5855 natively use the XIVE interrupt controller. This option 5856 allows the fallback firmware mode to be used: 5857 5858 off Fallback to firmware control of XIVE interrupt 5859 controller on both pseries and powernv 5860 platforms. Only useful on POWER9 and above. 5861 5862 xhci-hcd.quirks [USB,KNL] 5863 A hex value specifying bitmask with supplemental xhci 5864 host controller quirks. Meaning of each bit can be 5865 consulted in header drivers/usb/host/xhci.h. 5866 5867 xmon [PPC] 5868 Format: { early | on | rw | ro | off } 5869 Controls if xmon debugger is enabled. Default is off. 5870 Passing only "xmon" is equivalent to "xmon=early". 5871 early Call xmon as early as possible on boot; xmon 5872 debugger is called from setup_arch(). 5873 on xmon debugger hooks will be installed so xmon 5874 is only called on a kernel crash. Default mode, 5875 i.e. either "ro" or "rw" mode, is controlled 5876 with CONFIG_XMON_DEFAULT_RO_MODE. 5877 rw xmon debugger hooks will be installed so xmon 5878 is called only on a kernel crash, mode is write, 5879 meaning SPR registers, memory and, other data 5880 can be written using xmon commands. 5881 ro same as "rw" option above but SPR registers, 5882 memory, and other data can't be written using 5883 xmon commands. 5884 off xmon is disabled. 5885