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.txt. 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/media/v4l-drivers/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [ARM,X86,KNL] 595 Sets the size of kernel global memory area for 596 contiguous memory allocations and optionally the 597 placement constraint by the physical address range of 598 memory allocations. A value of 0 disables CMA 599 altogether. For more information, see 600 include/linux/dma-contiguous.h 601 602 cmo_free_hint= [PPC] Format: { yes | no } 603 Specify whether pages are marked as being inactive 604 when they are freed. This is used in CMO environments 605 to determine OS memory pressure for page stealing by 606 a hypervisor. 607 Default: yes 608 609 coherent_pool=nn[KMG] [ARM,KNL] 610 Sets the size of memory pool for coherent, atomic dma 611 allocations, by default set to 256K. 612 613 com20020= [HW,NET] ARCnet - COM20020 chipset 614 Format: 615 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 616 617 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 618 Format: <io>[,<irq>] 619 620 com90xx= [HW,NET] 621 ARCnet - COM90xx chipset (memory-mapped buffers) 622 Format: <io>[,<irq>[,<memstart>]] 623 624 condev= [HW,S390] console device 625 conmode= 626 627 console= [KNL] Output console device and options. 628 629 tty<n> Use the virtual console device <n>. 630 631 ttyS<n>[,options] 632 ttyUSB0[,options] 633 Use the specified serial port. The options are of 634 the form "bbbbpnf", where "bbbb" is the baud rate, 635 "p" is parity ("n", "o", or "e"), "n" is number of 636 bits, and "f" is flow control ("r" for RTS or 637 omit it). Default is "9600n8". 638 639 See Documentation/admin-guide/serial-console.rst for more 640 information. See 641 Documentation/networking/netconsole.txt 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 cpu_init_udelay=N 707 [X86] Delay for N microsec between assert and de-assert 708 of APIC INIT to start processors. This delay occurs 709 on every CPU online, such as boot, and resume from suspend. 710 Default: 10000 711 712 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 713 Format: 714 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 715 716 crashkernel=size[KMG][@offset[KMG]] 717 [KNL] Using kexec, Linux can switch to a 'crash kernel' 718 upon panic. This parameter reserves the physical 719 memory region [offset, offset + size] for that kernel 720 image. If '@offset' is omitted, then a suitable offset 721 is selected automatically. 722 [KNL, x86_64] select a region under 4G first, and 723 fall back to reserve region above 4G when '@offset' 724 hasn't been specified. 725 See Documentation/admin-guide/kdump/kdump.rst for further details. 726 727 crashkernel=range1:size1[,range2:size2,...][@offset] 728 [KNL] Same as above, but depends on the memory 729 in the running system. The syntax of range is 730 start-[end] where start and end are both 731 a memory unit (amount[KMG]). See also 732 Documentation/admin-guide/kdump/kdump.rst for an example. 733 734 crashkernel=size[KMG],high 735 [KNL, x86_64] range could be above 4G. Allow kernel 736 to allocate physical memory region from top, so could 737 be above 4G if system have more than 4G ram installed. 738 Otherwise memory region will be allocated below 4G, if 739 available. 740 It will be ignored if crashkernel=X is specified. 741 crashkernel=size[KMG],low 742 [KNL, x86_64] range under 4G. When crashkernel=X,high 743 is passed, kernel could allocate physical memory region 744 above 4G, that cause second kernel crash on system 745 that require some amount of low memory, e.g. swiotlb 746 requires at least 64M+32K low memory, also enough extra 747 low memory is needed to make sure DMA buffers for 32-bit 748 devices won't run out. Kernel would try to allocate at 749 at least 256M below 4G automatically. 750 This one let user to specify own low range under 4G 751 for second kernel instead. 752 0: to disable low allocation. 753 It will be ignored when crashkernel=X,high is not used 754 or memory reserved is below 4G. 755 756 cryptomgr.notests 757 [KNL] Disable crypto self-tests 758 759 cs89x0_dma= [HW,NET] 760 Format: <dma> 761 762 cs89x0_media= [HW,NET] 763 Format: { rj45 | aui | bnc } 764 765 dasd= [HW,NET] 766 See header of drivers/s390/block/dasd_devmap.c. 767 768 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 769 (one device per port) 770 Format: <port#>,<type> 771 See also Documentation/input/devices/joystick-parport.rst 772 773 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 774 time. See 775 Documentation/admin-guide/dynamic-debug-howto.rst for 776 details. Deprecated, see dyndbg. 777 778 debug [KNL] Enable kernel debugging (events log level). 779 780 debug_boot_weak_hash 781 [KNL] Enable printing [hashed] pointers early in the 782 boot sequence. If enabled, we use a weak hash instead 783 of siphash to hash pointers. Use this option if you are 784 seeing instances of '(___ptrval___)') and need to see a 785 value (hashed pointer) instead. Cryptographically 786 insecure, please do not use on production kernels. 787 788 debug_locks_verbose= 789 [KNL] verbose self-tests 790 Format=<0|1> 791 Print debugging info while doing the locking API 792 self-tests. 793 We default to 0 (no extra messages), setting it to 794 1 will print _a lot_ more information - normally 795 only useful to kernel developers. 796 797 debug_objects [KNL] Enable object debugging 798 799 no_debug_objects 800 [KNL] Disable object debugging 801 802 debug_guardpage_minorder= 803 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 804 parameter allows control of the order of pages that will 805 be intentionally kept free (and hence protected) by the 806 buddy allocator. Bigger value increase the probability 807 of catching random memory corruption, but reduce the 808 amount of memory for normal system use. The maximum 809 possible value is MAX_ORDER/2. Setting this parameter 810 to 1 or 2 should be enough to identify most random 811 memory corruption problems caused by bugs in kernel or 812 driver code when a CPU writes to (or reads from) a 813 random memory location. Note that there exists a class 814 of memory corruptions problems caused by buggy H/W or 815 F/W or by drivers badly programing DMA (basically when 816 memory is written at bus level and the CPU MMU is 817 bypassed) which are not detectable by 818 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 819 tracking down these problems. 820 821 debug_pagealloc= 822 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 823 enables the feature at boot time. By default, it is 824 disabled and the system will work mostly the same as a 825 kernel built without CONFIG_DEBUG_PAGEALLOC. 826 Note: to get most of debug_pagealloc error reports, it's 827 useful to also enable the page_owner functionality. 828 on: enable the feature 829 830 debugpat [X86] Enable PAT debugging 831 832 decnet.addr= [HW,NET] 833 Format: <area>[,<node>] 834 See also Documentation/networking/decnet.txt. 835 836 default_hugepagesz= 837 [same as hugepagesz=] The size of the default 838 HugeTLB page size. This is the size represented by 839 the legacy /proc/ hugepages APIs, used for SHM, and 840 default size when mounting hugetlbfs filesystems. 841 Defaults to the default architecture's huge page size 842 if not specified. 843 844 deferred_probe_timeout= 845 [KNL] Debugging option to set a timeout in seconds for 846 deferred probe to give up waiting on dependencies to 847 probe. Only specific dependencies (subsystems or 848 drivers) that have opted in will be ignored. A timeout of 0 849 will timeout at the end of initcalls. This option will also 850 dump out devices still on the deferred probe list after 851 retrying. 852 853 dfltcc= [HW,S390] 854 Format: { on | off | def_only | inf_only | always } 855 on: s390 zlib hardware support for compression on 856 level 1 and decompression (default) 857 off: No s390 zlib hardware support 858 def_only: s390 zlib hardware support for deflate 859 only (compression on level 1) 860 inf_only: s390 zlib hardware support for inflate 861 only (decompression) 862 always: Same as 'on' but ignores the selected compression 863 level always using hardware support (used for debugging) 864 865 dhash_entries= [KNL] 866 Set number of hash buckets for dentry cache. 867 868 disable_1tb_segments [PPC] 869 Disables the use of 1TB hash page table segments. This 870 causes the kernel to fall back to 256MB segments which 871 can be useful when debugging issues that require an SLB 872 miss to occur. 873 874 disable= [IPV6] 875 See Documentation/networking/ipv6.txt. 876 877 hardened_usercopy= 878 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 879 hardening is enabled for this boot. Hardened 880 usercopy checking is used to protect the kernel 881 from reading or writing beyond known memory 882 allocation boundaries as a proactive defense 883 against bounds-checking flaws in the kernel's 884 copy_to_user()/copy_from_user() interface. 885 on Perform hardened usercopy checks (default). 886 off Disable hardened usercopy checks. 887 888 disable_radix [PPC] 889 Disable RADIX MMU mode on POWER9 890 891 disable_tlbie [PPC] 892 Disable TLBIE instruction. Currently does not work 893 with KVM, with HASH MMU, or with coherent accelerators. 894 895 disable_cpu_apicid= [X86,APIC,SMP] 896 Format: <int> 897 The number of initial APIC ID for the 898 corresponding CPU to be disabled at boot, 899 mostly used for the kdump 2nd kernel to 900 disable BSP to wake up multiple CPUs without 901 causing system reset or hang due to sending 902 INIT from AP to BSP. 903 904 perf_v4_pmi= [X86,INTEL] 905 Format: <bool> 906 Disable Intel PMU counter freezing feature. 907 The feature only exists starting from 908 Arch Perfmon v4 (Skylake and newer). 909 910 disable_ddw [PPC/PSERIES] 911 Disable Dynamic DMA Window support. Use this if 912 to workaround buggy firmware. 913 914 disable_ipv6= [IPV6] 915 See Documentation/networking/ipv6.txt. 916 917 disable_mtrr_cleanup [X86] 918 The kernel tries to adjust MTRR layout from continuous 919 to discrete, to make X server driver able to add WB 920 entry later. This parameter disables that. 921 922 disable_mtrr_trim [X86, Intel and AMD only] 923 By default the kernel will trim any uncacheable 924 memory out of your available memory pool based on 925 MTRR settings. This parameter disables that behavior, 926 possibly causing your machine to run very slowly. 927 928 disable_timer_pin_1 [X86] 929 Disable PIN 1 of APIC timer 930 Can be useful to work around chipset bugs. 931 932 dis_ucode_ldr [X86] Disable the microcode loader. 933 934 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 935 this option disables the debugging code at boot. 936 937 dma_debug_entries=<number> 938 This option allows to tune the number of preallocated 939 entries for DMA-API debugging code. One entry is 940 required per DMA-API allocation. Use this if the 941 DMA-API debugging code disables itself because the 942 architectural default is too low. 943 944 dma_debug_driver=<driver_name> 945 With this option the DMA-API debugging driver 946 filter feature can be enabled at boot time. Just 947 pass the driver to filter for as the parameter. 948 The filter can be disabled or changed to another 949 driver later using sysfs. 950 951 driver_async_probe= [KNL] 952 List of driver names to be probed asynchronously. 953 Format: <driver_name1>,<driver_name2>... 954 955 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 956 Broken monitors, graphic adapters, KVMs and EDIDless 957 panels may send no or incorrect EDID data sets. 958 This parameter allows to specify an EDID data sets 959 in the /lib/firmware directory that are used instead. 960 Generic built-in EDID data sets are used, if one of 961 edid/1024x768.bin, edid/1280x1024.bin, 962 edid/1680x1050.bin, or edid/1920x1080.bin is given 963 and no file with the same name exists. Details and 964 instructions how to build your own EDID data are 965 available in Documentation/admin-guide/edid.rst. An EDID 966 data set will only be used for a particular connector, 967 if its name and a colon are prepended to the EDID 968 name. Each connector may use a unique EDID data 969 set by separating the files with a comma. An EDID 970 data set with no connector name will be used for 971 any connectors not explicitly specified. 972 973 dscc4.setup= [NET] 974 975 dt_cpu_ftrs= [PPC] 976 Format: {"off" | "known"} 977 Control how the dt_cpu_ftrs device-tree binding is 978 used for CPU feature discovery and setup (if it 979 exists). 980 off: Do not use it, fall back to legacy cpu table. 981 known: Do not pass through unknown features to guests 982 or userspace, only those that the kernel is aware of. 983 984 dump_apple_properties [X86] 985 Dump name and content of EFI device properties on 986 x86 Macs. Useful for driver authors to determine 987 what data is available or for reverse-engineering. 988 989 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 990 module.dyndbg[="val"] 991 Enable debug messages at boot time. See 992 Documentation/admin-guide/dynamic-debug-howto.rst 993 for details. 994 995 nopku [X86] Disable Memory Protection Keys CPU feature found 996 in some Intel CPUs. 997 998 module.async_probe [KNL] 999 Enable asynchronous probe on this module. 1000 1001 early_ioremap_debug [KNL] 1002 Enable debug messages in early_ioremap support. This 1003 is useful for tracking down temporary early mappings 1004 which are not unmapped. 1005 1006 earlycon= [KNL] Output early console device and options. 1007 1008 When used with no options, the early console is 1009 determined by stdout-path property in device tree's 1010 chosen node or the ACPI SPCR table if supported by 1011 the platform. 1012 1013 cdns,<addr>[,options] 1014 Start an early, polled-mode console on a Cadence 1015 (xuartps) serial port at the specified address. Only 1016 supported option is baud rate. If baud rate is not 1017 specified, the serial port must already be setup and 1018 configured. 1019 1020 uart[8250],io,<addr>[,options] 1021 uart[8250],mmio,<addr>[,options] 1022 uart[8250],mmio32,<addr>[,options] 1023 uart[8250],mmio32be,<addr>[,options] 1024 uart[8250],0x<addr>[,options] 1025 Start an early, polled-mode console on the 8250/16550 1026 UART at the specified I/O port or MMIO address. 1027 MMIO inter-register address stride is either 8-bit 1028 (mmio) or 32-bit (mmio32 or mmio32be). 1029 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1030 to be equivalent to 'mmio'. 'options' are specified 1031 in the same format described for "console=ttyS<n>"; if 1032 unspecified, the h/w is not initialized. 1033 1034 pl011,<addr> 1035 pl011,mmio32,<addr> 1036 Start an early, polled-mode console on a pl011 serial 1037 port at the specified address. The pl011 serial port 1038 must already be setup and configured. Options are not 1039 yet supported. If 'mmio32' is specified, then only 1040 the driver will use only 32-bit accessors to read/write 1041 the device registers. 1042 1043 meson,<addr> 1044 Start an early, polled-mode console on a meson serial 1045 port at the specified address. The serial port must 1046 already be setup and configured. Options are not yet 1047 supported. 1048 1049 msm_serial,<addr> 1050 Start an early, polled-mode console on an msm serial 1051 port at the specified address. The serial port 1052 must already be setup and configured. Options are not 1053 yet supported. 1054 1055 msm_serial_dm,<addr> 1056 Start an early, polled-mode console on an msm serial 1057 dm port at the specified address. The serial port 1058 must already be setup and configured. Options are not 1059 yet supported. 1060 1061 owl,<addr> 1062 Start an early, polled-mode console on a serial port 1063 of an Actions Semi SoC, such as S500 or S900, at the 1064 specified address. The serial port must already be 1065 setup and configured. Options are not yet supported. 1066 1067 rda,<addr> 1068 Start an early, polled-mode console on a serial port 1069 of an RDA Micro SoC, such as RDA8810PL, at the 1070 specified address. The serial port must already be 1071 setup and configured. Options are not yet supported. 1072 1073 sbi 1074 Use RISC-V SBI (Supervisor Binary Interface) for early 1075 console. 1076 1077 smh Use ARM semihosting calls for early console. 1078 1079 s3c2410,<addr> 1080 s3c2412,<addr> 1081 s3c2440,<addr> 1082 s3c6400,<addr> 1083 s5pv210,<addr> 1084 exynos4210,<addr> 1085 Use early console provided by serial driver available 1086 on Samsung SoCs, requires selecting proper type and 1087 a correct base address of the selected UART port. The 1088 serial port must already be setup and configured. 1089 Options are not yet supported. 1090 1091 lantiq,<addr> 1092 Start an early, polled-mode console on a lantiq serial 1093 (lqasc) port at the specified address. The serial port 1094 must already be setup and configured. Options are not 1095 yet supported. 1096 1097 lpuart,<addr> 1098 lpuart32,<addr> 1099 Use early console provided by Freescale LP UART driver 1100 found on Freescale Vybrid and QorIQ LS1021A processors. 1101 A valid base address must be provided, and the serial 1102 port must already be setup and configured. 1103 1104 ec_imx21,<addr> 1105 ec_imx6q,<addr> 1106 Start an early, polled-mode, output-only console on the 1107 Freescale i.MX UART at the specified address. The UART 1108 must already be setup and configured. 1109 1110 ar3700_uart,<addr> 1111 Start an early, polled-mode console on the 1112 Armada 3700 serial port at the specified 1113 address. The serial port must already be setup 1114 and configured. Options are not yet supported. 1115 1116 qcom_geni,<addr> 1117 Start an early, polled-mode console on a Qualcomm 1118 Generic Interface (GENI) based serial port at the 1119 specified address. The serial port must already be 1120 setup and configured. Options are not yet supported. 1121 1122 efifb,[options] 1123 Start an early, unaccelerated console on the EFI 1124 memory mapped framebuffer (if available). On cache 1125 coherent non-x86 systems that use system memory for 1126 the framebuffer, pass the 'ram' option so that it is 1127 mapped with the correct attributes. 1128 1129 linflex,<addr> 1130 Use early console provided by Freescale LINFlexD UART 1131 serial driver for NXP S32V234 SoCs. A valid base 1132 address must be provided, and the serial port must 1133 already be setup and configured. 1134 1135 earlyprintk= [X86,SH,ARM,M68k,S390] 1136 earlyprintk=vga 1137 earlyprintk=sclp 1138 earlyprintk=xen 1139 earlyprintk=serial[,ttySn[,baudrate]] 1140 earlyprintk=serial[,0x...[,baudrate]] 1141 earlyprintk=ttySn[,baudrate] 1142 earlyprintk=dbgp[debugController#] 1143 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1144 earlyprintk=xdbc[xhciController#] 1145 1146 earlyprintk is useful when the kernel crashes before 1147 the normal console is initialized. It is not enabled by 1148 default because it has some cosmetic problems. 1149 1150 Append ",keep" to not disable it when the real console 1151 takes over. 1152 1153 Only one of vga, efi, serial, or usb debug port can 1154 be used at a time. 1155 1156 Currently only ttyS0 and ttyS1 may be specified by 1157 name. Other I/O ports may be explicitly specified 1158 on some architectures (x86 and arm at least) by 1159 replacing ttySn with an I/O port address, like this: 1160 earlyprintk=serial,0x1008,115200 1161 You can find the port for a given device in 1162 /proc/tty/driver/serial: 1163 2: uart:ST16650V2 port:00001008 irq:18 ... 1164 1165 Interaction with the standard serial driver is not 1166 very good. 1167 1168 The VGA and EFI output is eventually overwritten by 1169 the real console. 1170 1171 The xen output can only be used by Xen PV guests. 1172 1173 The sclp output can only be used on s390. 1174 1175 The optional "force" to "pciserial" enables use of a 1176 PCI device even when its classcode is not of the 1177 UART class. 1178 1179 edac_report= [HW,EDAC] Control how to report EDAC event 1180 Format: {"on" | "off" | "force"} 1181 on: enable EDAC to report H/W event. May be overridden 1182 by other higher priority error reporting module. 1183 off: disable H/W event reporting through EDAC. 1184 force: enforce the use of EDAC to report H/W event. 1185 default: on. 1186 1187 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1188 ekgdboc=kbd 1189 1190 This is designed to be used in conjunction with 1191 the boot argument: earlyprintk=vga 1192 1193 edd= [EDD] 1194 Format: {"off" | "on" | "skip[mbr]"} 1195 1196 efi= [EFI] 1197 Format: { "old_map", "nochunk", "noruntime", "debug", 1198 "nosoftreserve", "disable_early_pci_dma", 1199 "no_disable_early_pci_dma" } 1200 old_map [X86-64]: switch to the old ioremap-based EFI 1201 runtime services mapping. [Needs CONFIG_X86_UV=y] 1202 nochunk: disable reading files in "chunks" in the EFI 1203 boot stub, as chunking can cause problems with some 1204 firmware implementations. 1205 noruntime : disable EFI runtime services support 1206 debug: enable misc debug output 1207 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1208 attribute may cause the kernel to reserve the 1209 memory range for a memory mapping driver to 1210 claim. Specify efi=nosoftreserve to disable this 1211 reservation and treat the memory by its base type 1212 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1213 disable_early_pci_dma: Disable the busmaster bit on all 1214 PCI bridges while in the EFI boot stub 1215 no_disable_early_pci_dma: Leave the busmaster bit set 1216 on all PCI bridges while in the EFI boot stub 1217 1218 efi_no_storage_paranoia [EFI; X86] 1219 Using this parameter you can use more than 50% of 1220 your efi variable storage. Use this parameter only if 1221 you are really sure that your UEFI does sane gc and 1222 fulfills the spec otherwise your board may brick. 1223 1224 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1225 Add arbitrary attribute to specific memory range by 1226 updating original EFI memory map. 1227 Region of memory which aa attribute is added to is 1228 from ss to ss+nn. 1229 1230 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1231 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1232 attribute is added to range 0x100000000-0x180000000 and 1233 0x10a0000000-0x1120000000. 1234 1235 If efi_fake_mem=8G@9G:0x40000 is specified, the 1236 EFI_MEMORY_SP(0x40000) attribute is added to 1237 range 0x240000000-0x43fffffff. 1238 1239 Using this parameter you can do debugging of EFI memmap 1240 related features. For example, you can do debugging of 1241 Address Range Mirroring feature even if your box 1242 doesn't support it, or mark specific memory as 1243 "soft reserved". 1244 1245 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1246 that is to be dynamically loaded by Linux. If there are 1247 multiple variables with the same name but with different 1248 vendor GUIDs, all of them will be loaded. See 1249 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1250 1251 1252 eisa_irq_edge= [PARISC,HW] 1253 See header of drivers/parisc/eisa.c. 1254 1255 elanfreq= [X86-32] 1256 See comment before function elanfreq_setup() in 1257 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1258 1259 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1260 Specifies physical address of start of kernel core 1261 image elf header and optionally the size. Generally 1262 kexec loader will pass this option to capture kernel. 1263 See Documentation/admin-guide/kdump/kdump.rst for details. 1264 1265 enable_mtrr_cleanup [X86] 1266 The kernel tries to adjust MTRR layout from continuous 1267 to discrete, to make X server driver able to add WB 1268 entry later. This parameter enables that. 1269 1270 enable_timer_pin_1 [X86] 1271 Enable PIN 1 of APIC timer 1272 Can be useful to work around chipset bugs 1273 (in particular on some ATI chipsets). 1274 The kernel tries to set a reasonable default. 1275 1276 enforcing [SELINUX] Set initial enforcing status. 1277 Format: {"0" | "1"} 1278 See security/selinux/Kconfig help text. 1279 0 -- permissive (log only, no denials). 1280 1 -- enforcing (deny and log). 1281 Default value is 0. 1282 Value can be changed at runtime via 1283 /sys/fs/selinux/enforce. 1284 1285 erst_disable [ACPI] 1286 Disable Error Record Serialization Table (ERST) 1287 support. 1288 1289 ether= [HW,NET] Ethernet cards parameters 1290 This option is obsoleted by the "netdev=" option, which 1291 has equivalent usage. See its documentation for details. 1292 1293 evm= [EVM] 1294 Format: { "fix" } 1295 Permit 'security.evm' to be updated regardless of 1296 current integrity status. 1297 1298 failslab= 1299 fail_page_alloc= 1300 fail_make_request=[KNL] 1301 General fault injection mechanism. 1302 Format: <interval>,<probability>,<space>,<times> 1303 See also Documentation/fault-injection/. 1304 1305 floppy= [HW] 1306 See Documentation/admin-guide/blockdev/floppy.rst. 1307 1308 force_pal_cache_flush 1309 [IA-64] Avoid check_sal_cache_flush which may hang on 1310 buggy SAL_CACHE_FLUSH implementations. Using this 1311 parameter will force ia64_sal_cache_flush to call 1312 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1313 1314 forcepae [X86-32] 1315 Forcefully enable Physical Address Extension (PAE). 1316 Many Pentium M systems disable PAE but may have a 1317 functionally usable PAE implementation. 1318 Warning: use of this parameter will taint the kernel 1319 and may cause unknown problems. 1320 1321 ftrace=[tracer] 1322 [FTRACE] will set and start the specified tracer 1323 as early as possible in order to facilitate early 1324 boot debugging. 1325 1326 ftrace_dump_on_oops[=orig_cpu] 1327 [FTRACE] will dump the trace buffers on oops. 1328 If no parameter is passed, ftrace will dump 1329 buffers of all CPUs, but if you pass orig_cpu, it will 1330 dump only the buffer of the CPU that triggered the 1331 oops. 1332 1333 ftrace_filter=[function-list] 1334 [FTRACE] Limit the functions traced by the function 1335 tracer at boot up. function-list is a comma separated 1336 list of functions. This list can be changed at run 1337 time by the set_ftrace_filter file in the debugfs 1338 tracing directory. 1339 1340 ftrace_notrace=[function-list] 1341 [FTRACE] Do not trace the functions specified in 1342 function-list. This list can be changed at run time 1343 by the set_ftrace_notrace file in the debugfs 1344 tracing directory. 1345 1346 ftrace_graph_filter=[function-list] 1347 [FTRACE] Limit the top level callers functions traced 1348 by the function graph tracer at boot up. 1349 function-list is a comma separated list of functions 1350 that can be changed at run time by the 1351 set_graph_function file in the debugfs tracing directory. 1352 1353 ftrace_graph_notrace=[function-list] 1354 [FTRACE] Do not trace from the functions specified in 1355 function-list. This list is a comma separated list of 1356 functions that can be changed at run time by the 1357 set_graph_notrace file in the debugfs tracing directory. 1358 1359 ftrace_graph_max_depth=<uint> 1360 [FTRACE] Used with the function graph tracer. This is 1361 the max depth it will trace into a function. This value 1362 can be changed at run time by the max_graph_depth file 1363 in the tracefs tracing directory. default: 0 (no limit) 1364 1365 fw_devlink= [KNL] Create device links between consumer and supplier 1366 devices by scanning the firmware to infer the 1367 consumer/supplier relationships. This feature is 1368 especially useful when drivers are loaded as modules as 1369 it ensures proper ordering of tasks like device probing 1370 (suppliers first, then consumers), supplier boot state 1371 clean up (only after all consumers have probed), 1372 suspend/resume & runtime PM (consumers first, then 1373 suppliers). 1374 Format: { off | permissive | on | rpm } 1375 off -- Don't create device links from firmware info. 1376 permissive -- Create device links from firmware info 1377 but use it only for ordering boot state clean 1378 up (sync_state() calls). 1379 on -- Create device links from firmware info and use it 1380 to enforce probe and suspend/resume ordering. 1381 rpm -- Like "on", but also use to order runtime PM. 1382 1383 gamecon.map[2|3]= 1384 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1385 support via parallel port (up to 5 devices per port) 1386 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1387 See also Documentation/input/devices/joystick-parport.rst 1388 1389 gamma= [HW,DRM] 1390 1391 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1392 Format: off | on 1393 default: on 1394 1395 gcov_persist= [GCOV] When non-zero (default), profiling data for 1396 kernel modules is saved and remains accessible via 1397 debugfs, even when the module is unloaded/reloaded. 1398 When zero, profiling data is discarded and associated 1399 debugfs files are removed at module unload time. 1400 1401 goldfish [X86] Enable the goldfish android emulator platform. 1402 Don't use this when you are not running on the 1403 android emulator 1404 1405 gpt [EFI] Forces disk with valid GPT signature but 1406 invalid Protective MBR to be treated as GPT. If the 1407 primary GPT is corrupted, it enables the backup/alternate 1408 GPT to be used instead. 1409 1410 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1411 the "Enable 0" bit of the configuration register. 1412 Format: 0 | 1 1413 Default: 0 1414 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1415 the "Enable 0" bit of the configuration register. 1416 Format: 0 | 1 1417 Default: 0 1418 grcan.select= [HW] Select which physical interface to use. 1419 Format: 0 | 1 1420 Default: 0 1421 grcan.txsize= [HW] Sets the size of the tx buffer. 1422 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1423 Default: 1024 1424 grcan.rxsize= [HW] Sets the size of the rx buffer. 1425 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1426 Default: 1024 1427 1428 gpio-mockup.gpio_mockup_ranges 1429 [HW] Sets the ranges of gpiochip of for this device. 1430 Format: <start1>,<end1>,<start2>,<end2>... 1431 1432 hardlockup_all_cpu_backtrace= 1433 [KNL] Should the hard-lockup detector generate 1434 backtraces on all cpus. 1435 Format: <integer> 1436 1437 hashdist= [KNL,NUMA] Large hashes allocated during boot 1438 are distributed across NUMA nodes. Defaults on 1439 for 64-bit NUMA, off otherwise. 1440 Format: 0 | 1 (for off | on) 1441 1442 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1443 1444 hd= [EIDE] (E)IDE hard drive subsystem geometry 1445 Format: <cyl>,<head>,<sect> 1446 1447 hest_disable [ACPI] 1448 Disable Hardware Error Source Table (HEST) support; 1449 corresponding firmware-first mode error processing 1450 logic will be disabled. 1451 1452 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1453 size of <nn>. This works even on boxes that have no 1454 highmem otherwise. This also works to reduce highmem 1455 size on bigger boxes. 1456 1457 highres= [KNL] Enable/disable high resolution timer mode. 1458 Valid parameters: "on", "off" 1459 Default: "on" 1460 1461 hlt [BUGS=ARM,SH] 1462 1463 hpet= [X86-32,HPET] option to control HPET usage 1464 Format: { enable (default) | disable | force | 1465 verbose } 1466 disable: disable HPET and use PIT instead 1467 force: allow force enabled of undocumented chips (ICH4, 1468 VIA, nVidia) 1469 verbose: show contents of HPET registers during setup 1470 1471 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1472 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1473 1474 hugetlb_cma= [HW] The size of a cma area used for allocation 1475 of gigantic hugepages. 1476 Format: nn[KMGTPE] 1477 1478 Reserve a cma area of given size and allocate gigantic 1479 hugepages using the cma allocator. If enabled, the 1480 boot-time allocation of gigantic hugepages is skipped. 1481 1482 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1483 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1484 On x86-64 and powerpc, this option can be specified 1485 multiple times interleaved with hugepages= to reserve 1486 huge pages of different sizes. Valid pages sizes on 1487 x86-64 are 2M (when the CPU supports "pse") and 1G 1488 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1489 1490 hung_task_panic= 1491 [KNL] Should the hung task detector generate panics. 1492 Format: <integer> 1493 1494 A nonzero value instructs the kernel to panic when a 1495 hung task is detected. The default value is controlled 1496 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1497 option. The value selected by this boot parameter can 1498 be changed later by the kernel.hung_task_panic sysctl. 1499 1500 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1501 terminal devices. Valid values: 0..8 1502 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1503 If specified, z/VM IUCV HVC accepts connections 1504 from listed z/VM user IDs only. 1505 1506 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1507 which allow the hypervisor to 'idle' the 1508 guest on lock contention. 1509 1510 keep_bootcon [KNL] 1511 Do not unregister boot console at start. This is only 1512 useful for debugging when something happens in the window 1513 between unregistering the boot console and initializing 1514 the real console. 1515 1516 i2c_bus= [HW] Override the default board specific I2C bus speed 1517 or register an additional I2C bus that is not 1518 registered from board initialization code. 1519 Format: 1520 <bus_id>,<clkrate> 1521 1522 i8042.debug [HW] Toggle i8042 debug mode 1523 i8042.unmask_kbd_data 1524 [HW] Enable printing of interrupt data from the KBD port 1525 (disabled by default, and as a pre-condition 1526 requires that i8042.debug=1 be enabled) 1527 i8042.direct [HW] Put keyboard port into non-translated mode 1528 i8042.dumbkbd [HW] Pretend that controller can only read data from 1529 keyboard and cannot control its state 1530 (Don't attempt to blink the leds) 1531 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1532 i8042.nokbd [HW] Don't check/create keyboard port 1533 i8042.noloop [HW] Disable the AUX Loopback command while probing 1534 for the AUX port 1535 i8042.nomux [HW] Don't check presence of an active multiplexing 1536 controller 1537 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1538 controllers 1539 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1540 i8042.reset [HW] Reset the controller during init, cleanup and 1541 suspend-to-ram transitions, only during s2r 1542 transitions, or never reset 1543 Format: { 1 | Y | y | 0 | N | n } 1544 1, Y, y: always reset controller 1545 0, N, n: don't ever reset controller 1546 Default: only on s2r transitions on x86; most other 1547 architectures force reset to be always executed 1548 i8042.unlock [HW] Unlock (ignore) the keylock 1549 i8042.kbdreset [HW] Reset device connected to KBD port 1550 1551 i810= [HW,DRM] 1552 1553 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1554 indicates that the driver is running on unsupported 1555 hardware. 1556 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1557 does not match list of supported models. 1558 i8k.power_status 1559 [HW] Report power status in /proc/i8k 1560 (disabled by default) 1561 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1562 capability is set. 1563 1564 i915.invert_brightness= 1565 [DRM] Invert the sense of the variable that is used to 1566 set the brightness of the panel backlight. Normally a 1567 brightness value of 0 indicates backlight switched off, 1568 and the maximum of the brightness value sets the backlight 1569 to maximum brightness. If this parameter is set to 0 1570 (default) and the machine requires it, or this parameter 1571 is set to 1, a brightness value of 0 sets the backlight 1572 to maximum brightness, and the maximum of the brightness 1573 value switches the backlight off. 1574 -1 -- never invert brightness 1575 0 -- machine default 1576 1 -- force brightness inversion 1577 1578 icn= [HW,ISDN] 1579 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1580 1581 ide-core.nodma= [HW] (E)IDE subsystem 1582 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1583 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1584 .cdrom .chs .ignore_cable are additional options 1585 See Documentation/ide/ide.rst. 1586 1587 ide-generic.probe-mask= [HW] (E)IDE subsystem 1588 Format: <int> 1589 Probe mask for legacy ISA IDE ports. Depending on 1590 platform up to 6 ports are supported, enabled by 1591 setting corresponding bits in the mask to 1. The 1592 default value is 0x0, which has a special meaning. 1593 On systems that have PCI, it triggers scanning the 1594 PCI bus for the first and the second port, which 1595 are then probed. On systems without PCI the value 1596 of 0x0 enables probing the two first ports as if it 1597 was 0x3. 1598 1599 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1600 Claim all unknown PCI IDE storage controllers. 1601 1602 idle= [X86] 1603 Format: idle=poll, idle=halt, idle=nomwait 1604 Poll forces a polling idle loop that can slightly 1605 improve the performance of waking up a idle CPU, but 1606 will use a lot of power and make the system run hot. 1607 Not recommended. 1608 idle=halt: Halt is forced to be used for CPU idle. 1609 In such case C2/C3 won't be used again. 1610 idle=nomwait: Disable mwait for CPU C-states 1611 1612 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1613 Format: { strict | legacy | 2008 | relaxed } 1614 Default: strict 1615 1616 Choose which programs will be accepted for execution 1617 based on the IEEE 754 NaN encoding(s) supported by 1618 the FPU and the NaN encoding requested with the value 1619 of an ELF file header flag individually set by each 1620 binary. Hardware implementations are permitted to 1621 support either or both of the legacy and the 2008 NaN 1622 encoding mode. 1623 1624 Available settings are as follows: 1625 strict accept binaries that request a NaN encoding 1626 supported by the FPU 1627 legacy only accept legacy-NaN binaries, if supported 1628 by the FPU 1629 2008 only accept 2008-NaN binaries, if supported 1630 by the FPU 1631 relaxed accept any binaries regardless of whether 1632 supported by the FPU 1633 1634 The FPU emulator is always able to support both NaN 1635 encodings, so if no FPU hardware is present or it has 1636 been disabled with 'nofpu', then the settings of 1637 'legacy' and '2008' strap the emulator accordingly, 1638 'relaxed' straps the emulator for both legacy-NaN and 1639 2008-NaN, whereas 'strict' enables legacy-NaN only on 1640 legacy processors and both NaN encodings on MIPS32 or 1641 MIPS64 CPUs. 1642 1643 The setting for ABS.fmt/NEG.fmt instruction execution 1644 mode generally follows that for the NaN encoding, 1645 except where unsupported by hardware. 1646 1647 ignore_loglevel [KNL] 1648 Ignore loglevel setting - this will print /all/ 1649 kernel messages to the console. Useful for debugging. 1650 We also add it as printk module parameter, so users 1651 could change it dynamically, usually by 1652 /sys/module/printk/parameters/ignore_loglevel. 1653 1654 ignore_rlimit_data 1655 Ignore RLIMIT_DATA setting for data mappings, 1656 print warning at first misuse. Can be changed via 1657 /sys/module/kernel/parameters/ignore_rlimit_data. 1658 1659 ihash_entries= [KNL] 1660 Set number of hash buckets for inode cache. 1661 1662 ima_appraise= [IMA] appraise integrity measurements 1663 Format: { "off" | "enforce" | "fix" | "log" } 1664 default: "enforce" 1665 1666 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1667 The builtin appraise policy appraises all files 1668 owned by uid=0. 1669 1670 ima_canonical_fmt [IMA] 1671 Use the canonical format for the binary runtime 1672 measurements, instead of host native format. 1673 1674 ima_hash= [IMA] 1675 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1676 | sha512 | ... } 1677 default: "sha1" 1678 1679 The list of supported hash algorithms is defined 1680 in crypto/hash_info.h. 1681 1682 ima_policy= [IMA] 1683 The builtin policies to load during IMA setup. 1684 Format: "tcb | appraise_tcb | secure_boot | 1685 fail_securely" 1686 1687 The "tcb" policy measures all programs exec'd, files 1688 mmap'd for exec, and all files opened with the read 1689 mode bit set by either the effective uid (euid=0) or 1690 uid=0. 1691 1692 The "appraise_tcb" policy appraises the integrity of 1693 all files owned by root. 1694 1695 The "secure_boot" policy appraises the integrity 1696 of files (eg. kexec kernel image, kernel modules, 1697 firmware, policy, etc) based on file signatures. 1698 1699 The "fail_securely" policy forces file signature 1700 verification failure also on privileged mounted 1701 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1702 flag. 1703 1704 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1705 Load a policy which meets the needs of the Trusted 1706 Computing Base. This means IMA will measure all 1707 programs exec'd, files mmap'd for exec, and all files 1708 opened for read by uid=0. 1709 1710 ima_template= [IMA] 1711 Select one of defined IMA measurements template formats. 1712 Formats: { "ima" | "ima-ng" | "ima-sig" } 1713 Default: "ima-ng" 1714 1715 ima_template_fmt= 1716 [IMA] Define a custom template format. 1717 Format: { "field1|...|fieldN" } 1718 1719 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1720 Format: <min_file_size> 1721 Set the minimal file size for using asynchronous hash. 1722 If left unspecified, ahash usage is disabled. 1723 1724 ahash performance varies for different data sizes on 1725 different crypto accelerators. This option can be used 1726 to achieve the best performance for a particular HW. 1727 1728 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1729 Format: <bufsize> 1730 Set hashing buffer size. Default: 4k. 1731 1732 ahash performance varies for different chunk sizes on 1733 different crypto accelerators. This option can be used 1734 to achieve best performance for particular HW. 1735 1736 init= [KNL] 1737 Format: <full_path> 1738 Run specified binary instead of /sbin/init as init 1739 process. 1740 1741 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1742 for working out where the kernel is dying during 1743 startup. 1744 1745 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1746 initcall functions. Useful for debugging built-in 1747 modules and initcalls. 1748 1749 initrd= [BOOT] Specify the location of the initial ramdisk 1750 1751 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1752 zeroes. 1753 Format: 0 | 1 1754 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1755 1756 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1757 Format: 0 | 1 1758 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1759 1760 init_pkru= [x86] Specify the default memory protection keys rights 1761 register contents for all processes. 0x55555554 by 1762 default (disallow access to all but pkey 0). Can 1763 override in debugfs after boot. 1764 1765 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1766 Format: <irq> 1767 1768 int_pln_enable [x86] Enable power limit notification interrupt 1769 1770 integrity_audit=[IMA] 1771 Format: { "0" | "1" } 1772 0 -- basic integrity auditing messages. (Default) 1773 1 -- additional integrity auditing messages. 1774 1775 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1776 on 1777 Enable intel iommu driver. 1778 off 1779 Disable intel iommu driver. 1780 igfx_off [Default Off] 1781 By default, gfx is mapped as normal device. If a gfx 1782 device has a dedicated DMAR unit, the DMAR unit is 1783 bypassed by not enabling DMAR with this option. In 1784 this case, gfx device will use physical address for 1785 DMA. 1786 forcedac [x86_64] 1787 With this option iommu will not optimize to look 1788 for io virtual address below 32-bit forcing dual 1789 address cycle on pci bus for cards supporting greater 1790 than 32-bit addressing. The default is to look 1791 for translation below 32-bit and if not available 1792 then look in the higher range. 1793 strict [Default Off] 1794 With this option on every unmap_single operation will 1795 result in a hardware IOTLB flush operation as opposed 1796 to batching them for performance. 1797 sp_off [Default Off] 1798 By default, super page will be supported if Intel IOMMU 1799 has the capability. With this option, super page will 1800 not be supported. 1801 sm_on [Default Off] 1802 By default, scalable mode will be disabled even if the 1803 hardware advertises that it has support for the scalable 1804 mode translation. With this option set, scalable mode 1805 will be used on hardware which claims to support it. 1806 tboot_noforce [Default Off] 1807 Do not force the Intel IOMMU enabled under tboot. 1808 By default, tboot will force Intel IOMMU on, which 1809 could harm performance of some high-throughput 1810 devices like 40GBit network cards, even if identity 1811 mapping is enabled. 1812 Note that using this option lowers the security 1813 provided by tboot because it makes the system 1814 vulnerable to DMA attacks. 1815 nobounce [Default off] 1816 Disable bounce buffer for untrusted devices such as 1817 the Thunderbolt devices. This will treat the untrusted 1818 devices as the trusted ones, hence might expose security 1819 risks of DMA attacks. 1820 1821 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1822 0 disables intel_idle and fall back on acpi_idle. 1823 1 to 9 specify maximum depth of C-state. 1824 1825 intel_pstate= [X86] 1826 disable 1827 Do not enable intel_pstate as the default 1828 scaling driver for the supported processors 1829 passive 1830 Use intel_pstate as a scaling driver, but configure it 1831 to work with generic cpufreq governors (instead of 1832 enabling its internal governor). This mode cannot be 1833 used along with the hardware-managed P-states (HWP) 1834 feature. 1835 force 1836 Enable intel_pstate on systems that prohibit it by default 1837 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1838 instead of acpi-cpufreq may disable platform features, such 1839 as thermal controls and power capping, that rely on ACPI 1840 P-States information being indicated to OSPM and therefore 1841 should be used with caution. This option does not work with 1842 processors that aren't supported by the intel_pstate driver 1843 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1844 no_hwp 1845 Do not enable hardware P state control (HWP) 1846 if available. 1847 hwp_only 1848 Only load intel_pstate on systems which support 1849 hardware P state control (HWP) if available. 1850 support_acpi_ppc 1851 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1852 Description Table, specifies preferred power management 1853 profile as "Enterprise Server" or "Performance Server", 1854 then this feature is turned on by default. 1855 per_cpu_perf_limits 1856 Allow per-logical-CPU P-State performance control limits using 1857 cpufreq sysfs interface 1858 1859 intremap= [X86-64, Intel-IOMMU] 1860 on enable Interrupt Remapping (default) 1861 off disable Interrupt Remapping 1862 nosid disable Source ID checking 1863 no_x2apic_optout 1864 BIOS x2APIC opt-out request will be ignored 1865 nopost disable Interrupt Posting 1866 1867 iomem= Disable strict checking of access to MMIO memory 1868 strict regions from userspace. 1869 relaxed 1870 1871 iommu= [x86] 1872 off 1873 force 1874 noforce 1875 biomerge 1876 panic 1877 nopanic 1878 merge 1879 nomerge 1880 soft 1881 pt [x86] 1882 nopt [x86] 1883 nobypass [PPC/POWERNV] 1884 Disable IOMMU bypass, using IOMMU for PCI devices. 1885 1886 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1887 Format: { "0" | "1" } 1888 0 - Lazy mode. 1889 Request that DMA unmap operations use deferred 1890 invalidation of hardware TLBs, for increased 1891 throughput at the cost of reduced device isolation. 1892 Will fall back to strict mode if not supported by 1893 the relevant IOMMU driver. 1894 1 - Strict mode (default). 1895 DMA unmap operations invalidate IOMMU hardware TLBs 1896 synchronously. 1897 1898 iommu.passthrough= 1899 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1900 Format: { "0" | "1" } 1901 0 - Use IOMMU translation for DMA. 1902 1 - Bypass the IOMMU for DMA. 1903 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1904 1905 io7= [HW] IO7 for Marvel based alpha systems 1906 See comment before marvel_specify_io7 in 1907 arch/alpha/kernel/core_marvel.c. 1908 1909 io_delay= [X86] I/O delay method 1910 0x80 1911 Standard port 0x80 based delay 1912 0xed 1913 Alternate port 0xed based delay (needed on some systems) 1914 udelay 1915 Simple two microseconds delay 1916 none 1917 No delay 1918 1919 ip= [IP_PNP] 1920 See Documentation/admin-guide/nfs/nfsroot.rst. 1921 1922 ipcmni_extend [KNL] Extend the maximum number of unique System V 1923 IPC identifiers from 32,768 to 16,777,216. 1924 1925 irqaffinity= [SMP] Set the default irq affinity mask 1926 The argument is a cpu list, as described above. 1927 1928 irqchip.gicv2_force_probe= 1929 [ARM, ARM64] 1930 Format: <bool> 1931 Force the kernel to look for the second 4kB page 1932 of a GICv2 controller even if the memory range 1933 exposed by the device tree is too small. 1934 1935 irqchip.gicv3_nolpi= 1936 [ARM, ARM64] 1937 Force the kernel to ignore the availability of 1938 LPIs (and by consequence ITSs). Intended for system 1939 that use the kernel as a bootloader, and thus want 1940 to let secondary kernels in charge of setting up 1941 LPIs. 1942 1943 irqchip.gicv3_pseudo_nmi= [ARM64] 1944 Enables support for pseudo-NMIs in the kernel. This 1945 requires the kernel to be built with 1946 CONFIG_ARM64_PSEUDO_NMI. 1947 1948 irqfixup [HW] 1949 When an interrupt is not handled search all handlers 1950 for it. Intended to get systems with badly broken 1951 firmware running. 1952 1953 irqpoll [HW] 1954 When an interrupt is not handled search all handlers 1955 for it. Also check all handlers each timer 1956 interrupt. Intended to get systems with badly broken 1957 firmware running. 1958 1959 isapnp= [ISAPNP] 1960 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1961 1962 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1963 [Deprecated - use cpusets instead] 1964 Format: [flag-list,]<cpu-list> 1965 1966 Specify one or more CPUs to isolate from disturbances 1967 specified in the flag list (default: domain): 1968 1969 nohz 1970 Disable the tick when a single task runs. 1971 1972 A residual 1Hz tick is offloaded to workqueues, which you 1973 need to affine to housekeeping through the global 1974 workqueue's affinity configured via the 1975 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1976 by using the 'domain' flag described below. 1977 1978 NOTE: by default the global workqueue runs on all CPUs, 1979 so to protect individual CPUs the 'cpumask' file has to 1980 be configured manually after bootup. 1981 1982 domain 1983 Isolate from the general SMP balancing and scheduling 1984 algorithms. Note that performing domain isolation this way 1985 is irreversible: it's not possible to bring back a CPU to 1986 the domains once isolated through isolcpus. It's strongly 1987 advised to use cpusets instead to disable scheduler load 1988 balancing through the "cpuset.sched_load_balance" file. 1989 It offers a much more flexible interface where CPUs can 1990 move in and out of an isolated set anytime. 1991 1992 You can move a process onto or off an "isolated" CPU via 1993 the CPU affinity syscalls or cpuset. 1994 <cpu number> begins at 0 and the maximum value is 1995 "number of CPUs in system - 1". 1996 1997 managed_irq 1998 1999 Isolate from being targeted by managed interrupts 2000 which have an interrupt mask containing isolated 2001 CPUs. The affinity of managed interrupts is 2002 handled by the kernel and cannot be changed via 2003 the /proc/irq/* interfaces. 2004 2005 This isolation is best effort and only effective 2006 if the automatically assigned interrupt mask of a 2007 device queue contains isolated and housekeeping 2008 CPUs. If housekeeping CPUs are online then such 2009 interrupts are directed to the housekeeping CPU 2010 so that IO submitted on the housekeeping CPU 2011 cannot disturb the isolated CPU. 2012 2013 If a queue's affinity mask contains only isolated 2014 CPUs then this parameter has no effect on the 2015 interrupt routing decision, though interrupts are 2016 only delivered when tasks running on those 2017 isolated CPUs submit IO. IO submitted on 2018 housekeeping CPUs has no influence on those 2019 queues. 2020 2021 The format of <cpu-list> is described above. 2022 2023 iucv= [HW,NET] 2024 2025 ivrs_ioapic [HW,X86_64] 2026 Provide an override to the IOAPIC-ID<->DEVICE-ID 2027 mapping provided in the IVRS ACPI table. For 2028 example, to map IOAPIC-ID decimal 10 to 2029 PCI device 00:14.0 write the parameter as: 2030 ivrs_ioapic[10]=00:14.0 2031 2032 ivrs_hpet [HW,X86_64] 2033 Provide an override to the HPET-ID<->DEVICE-ID 2034 mapping provided in the IVRS ACPI table. For 2035 example, to map HPET-ID decimal 0 to 2036 PCI device 00:14.0 write the parameter as: 2037 ivrs_hpet[0]=00:14.0 2038 2039 ivrs_acpihid [HW,X86_64] 2040 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2041 mapping provided in the IVRS ACPI table. For 2042 example, to map UART-HID:UID AMD0020:0 to 2043 PCI device 00:14.5 write the parameter as: 2044 ivrs_acpihid[00:14.5]=AMD0020:0 2045 2046 js= [HW,JOY] Analog joystick 2047 See Documentation/input/joydev/joystick.rst. 2048 2049 nokaslr [KNL] 2050 When CONFIG_RANDOMIZE_BASE is set, this disables 2051 kernel and module base offset ASLR (Address Space 2052 Layout Randomization). 2053 2054 kasan_multi_shot 2055 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2056 report on every invalid memory access. Without this 2057 parameter KASAN will print report only for the first 2058 invalid access. 2059 2060 keepinitrd [HW,ARM] 2061 2062 kernelcore= [KNL,X86,IA-64,PPC] 2063 Format: nn[KMGTPE] | nn% | "mirror" 2064 This parameter specifies the amount of memory usable by 2065 the kernel for non-movable allocations. The requested 2066 amount is spread evenly throughout all nodes in the 2067 system as ZONE_NORMAL. The remaining memory is used for 2068 movable memory in its own zone, ZONE_MOVABLE. In the 2069 event, a node is too small to have both ZONE_NORMAL and 2070 ZONE_MOVABLE, kernelcore memory will take priority and 2071 other nodes will have a larger ZONE_MOVABLE. 2072 2073 ZONE_MOVABLE is used for the allocation of pages that 2074 may be reclaimed or moved by the page migration 2075 subsystem. Note that allocations like PTEs-from-HighMem 2076 still use the HighMem zone if it exists, and the Normal 2077 zone if it does not. 2078 2079 It is possible to specify the exact amount of memory in 2080 the form of "nn[KMGTPE]", a percentage of total system 2081 memory in the form of "nn%", or "mirror". If "mirror" 2082 option is specified, mirrored (reliable) memory is used 2083 for non-movable allocations and remaining memory is used 2084 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2085 are exclusive, so you cannot specify multiple forms. 2086 2087 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2088 Format: <Controller#>[,poll interval] 2089 The controller # is the number of the ehci usb debug 2090 port as it is probed via PCI. The poll interval is 2091 optional and is the number seconds in between 2092 each poll cycle to the debug port in case you need 2093 the functionality for interrupting the kernel with 2094 gdb or control-c on the dbgp connection. When 2095 not using this parameter you use sysrq-g to break into 2096 the kernel debugger. 2097 2098 kgdboc= [KGDB,HW] kgdb over consoles. 2099 Requires a tty driver that supports console polling, 2100 or a supported polling keyboard driver (non-usb). 2101 Serial only format: <serial_device>[,baud] 2102 keyboard only format: kbd 2103 keyboard and serial format: kbd,<serial_device>[,baud] 2104 Optional Kernel mode setting: 2105 kms, kbd format: kms,kbd 2106 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2107 2108 kgdbwait [KGDB] Stop kernel execution and enter the 2109 kernel debugger at the earliest opportunity. 2110 2111 kmac= [MIPS] korina ethernet MAC address. 2112 Configure the RouterBoard 532 series on-chip 2113 Ethernet adapter MAC address. 2114 2115 kmemleak= [KNL] Boot-time kmemleak enable/disable 2116 Valid arguments: on, off 2117 Default: on 2118 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2119 the default is off. 2120 2121 kprobe_event=[probe-list] 2122 [FTRACE] Add kprobe events and enable at boot time. 2123 The probe-list is a semicolon delimited list of probe 2124 definitions. Each definition is same as kprobe_events 2125 interface, but the parameters are comma delimited. 2126 For example, to add a kprobe event on vfs_read with 2127 arg1 and arg2, add to the command line; 2128 2129 kprobe_event=p,vfs_read,$arg1,$arg2 2130 2131 See also Documentation/trace/kprobetrace.rst "Kernel 2132 Boot Parameter" section. 2133 2134 kpti= [ARM64] Control page table isolation of user 2135 and kernel address spaces. 2136 Default: enabled on cores which need mitigation. 2137 0: force disabled 2138 1: force enabled 2139 2140 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2141 Default is 0 (don't ignore, but inject #GP) 2142 2143 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2144 Default is false (don't support). 2145 2146 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2147 KVM MMU at runtime. 2148 Default is 0 (off) 2149 2150 kvm.nx_huge_pages= 2151 [KVM] Controls the software workaround for the 2152 X86_BUG_ITLB_MULTIHIT bug. 2153 force : Always deploy workaround. 2154 off : Never deploy workaround. 2155 auto : Deploy workaround based on the presence of 2156 X86_BUG_ITLB_MULTIHIT. 2157 2158 Default is 'auto'. 2159 2160 If the software workaround is enabled for the host, 2161 guests do need not to enable it for nested guests. 2162 2163 kvm.nx_huge_pages_recovery_ratio= 2164 [KVM] Controls how many 4KiB pages are periodically zapped 2165 back to huge pages. 0 disables the recovery, otherwise if 2166 the value is N KVM will zap 1/Nth of the 4KiB pages every 2167 minute. The default is 60. 2168 2169 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2170 Default is 1 (enabled) 2171 2172 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2173 for all guests. 2174 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2175 2176 kvm-arm.vgic_v3_group0_trap= 2177 [KVM,ARM] Trap guest accesses to GICv3 group-0 2178 system registers 2179 2180 kvm-arm.vgic_v3_group1_trap= 2181 [KVM,ARM] Trap guest accesses to GICv3 group-1 2182 system registers 2183 2184 kvm-arm.vgic_v3_common_trap= 2185 [KVM,ARM] Trap guest accesses to GICv3 common 2186 system registers 2187 2188 kvm-arm.vgic_v4_enable= 2189 [KVM,ARM] Allow use of GICv4 for direct injection of 2190 LPIs. 2191 2192 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2193 (virtualized MMU) support on capable Intel chips. 2194 Default is 1 (enabled) 2195 2196 kvm-intel.emulate_invalid_guest_state= 2197 [KVM,Intel] Enable emulation of invalid guest states 2198 Default is 0 (disabled) 2199 2200 kvm-intel.flexpriority= 2201 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2202 Default is 1 (enabled) 2203 2204 kvm-intel.nested= 2205 [KVM,Intel] Enable VMX nesting (nVMX). 2206 Default is 0 (disabled) 2207 2208 kvm-intel.unrestricted_guest= 2209 [KVM,Intel] Disable unrestricted guest feature 2210 (virtualized real and unpaged mode) on capable 2211 Intel chips. Default is 1 (enabled) 2212 2213 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2214 CVE-2018-3620. 2215 2216 Valid arguments: never, cond, always 2217 2218 always: L1D cache flush on every VMENTER. 2219 cond: Flush L1D on VMENTER only when the code between 2220 VMEXIT and VMENTER can leak host memory. 2221 never: Disables the mitigation 2222 2223 Default is cond (do L1 cache flush in specific instances) 2224 2225 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2226 feature (tagged TLBs) on capable Intel chips. 2227 Default is 1 (enabled) 2228 2229 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2230 affected CPUs 2231 2232 The kernel PTE inversion protection is unconditionally 2233 enabled and cannot be disabled. 2234 2235 full 2236 Provides all available mitigations for the 2237 L1TF vulnerability. Disables SMT and 2238 enables all mitigations in the 2239 hypervisors, i.e. unconditional L1D flush. 2240 2241 SMT control and L1D flush control via the 2242 sysfs interface is still possible after 2243 boot. Hypervisors will issue a warning 2244 when the first VM is started in a 2245 potentially insecure configuration, 2246 i.e. SMT enabled or L1D flush disabled. 2247 2248 full,force 2249 Same as 'full', but disables SMT and L1D 2250 flush runtime control. Implies the 2251 'nosmt=force' command line option. 2252 (i.e. sysfs control of SMT is disabled.) 2253 2254 flush 2255 Leaves SMT enabled and enables the default 2256 hypervisor mitigation, i.e. conditional 2257 L1D flush. 2258 2259 SMT control and L1D flush control via the 2260 sysfs interface is still possible after 2261 boot. Hypervisors will issue a warning 2262 when the first VM is started in a 2263 potentially insecure configuration, 2264 i.e. SMT enabled or L1D flush disabled. 2265 2266 flush,nosmt 2267 2268 Disables SMT and enables the default 2269 hypervisor mitigation. 2270 2271 SMT control and L1D flush control via the 2272 sysfs interface is still possible after 2273 boot. Hypervisors will issue a warning 2274 when the first VM is started in a 2275 potentially insecure configuration, 2276 i.e. SMT enabled or L1D flush disabled. 2277 2278 flush,nowarn 2279 Same as 'flush', but hypervisors will not 2280 warn when a VM is started in a potentially 2281 insecure configuration. 2282 2283 off 2284 Disables hypervisor mitigations and doesn't 2285 emit any warnings. 2286 It also drops the swap size and available 2287 RAM limit restriction on both hypervisor and 2288 bare metal. 2289 2290 Default is 'flush'. 2291 2292 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2293 2294 l2cr= [PPC] 2295 2296 l3cr= [PPC] 2297 2298 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2299 disabled it. 2300 2301 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2302 value for LAPIC timer one-shot implementation. Default 2303 back to the programmable timer unit in the LAPIC. 2304 2305 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2306 in C2 power state. 2307 2308 libata.dma= [LIBATA] DMA control 2309 libata.dma=0 Disable all PATA and SATA DMA 2310 libata.dma=1 PATA and SATA Disk DMA only 2311 libata.dma=2 ATAPI (CDROM) DMA only 2312 libata.dma=4 Compact Flash DMA only 2313 Combinations also work, so libata.dma=3 enables DMA 2314 for disks and CDROMs, but not CFs. 2315 2316 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2317 libata.ignore_hpa=0 keep BIOS limits (default) 2318 libata.ignore_hpa=1 ignore limits, using full disk 2319 2320 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2321 when set. 2322 Format: <int> 2323 2324 libata.force= [LIBATA] Force configurations. The format is comma 2325 separated list of "[ID:]VAL" where ID is 2326 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2327 matching port, link or device. Basically, it matches 2328 the ATA ID string printed on console by libata. If 2329 the whole ID part is omitted, the last PORT and DEVICE 2330 values are used. If ID hasn't been specified yet, the 2331 configuration applies to all ports, links and devices. 2332 2333 If only DEVICE is omitted, the parameter applies to 2334 the port and all links and devices behind it. DEVICE 2335 number of 0 either selects the first device or the 2336 first fan-out link behind PMP device. It does not 2337 select the host link. DEVICE number of 15 selects the 2338 host link and device attached to it. 2339 2340 The VAL specifies the configuration to force. As long 2341 as there's no ambiguity shortcut notation is allowed. 2342 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2343 The following configurations can be forced. 2344 2345 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2346 Any ID with matching PORT is used. 2347 2348 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2349 2350 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2351 udma[/][16,25,33,44,66,100,133] notation is also 2352 allowed. 2353 2354 * [no]ncq: Turn on or off NCQ. 2355 2356 * [no]ncqtrim: Turn off queued DSM TRIM. 2357 2358 * nohrst, nosrst, norst: suppress hard, soft 2359 and both resets. 2360 2361 * rstonce: only attempt one reset during 2362 hot-unplug link recovery 2363 2364 * dump_id: dump IDENTIFY data. 2365 2366 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2367 2368 * disable: Disable this device. 2369 2370 If there are multiple matching configurations changing 2371 the same attribute, the last one is used. 2372 2373 memblock=debug [KNL] Enable memblock debug messages. 2374 2375 load_ramdisk= [RAM] List of ramdisks to load from floppy 2376 See Documentation/admin-guide/blockdev/ramdisk.rst. 2377 2378 lockd.nlm_grace_period=P [NFS] Assign grace period. 2379 Format: <integer> 2380 2381 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2382 Format: <integer> 2383 2384 lockd.nlm_timeout=T [NFS] Assign timeout value. 2385 Format: <integer> 2386 2387 lockd.nlm_udpport=M [NFS] Assign UDP port. 2388 Format: <integer> 2389 2390 lockdown= [SECURITY] 2391 { integrity | confidentiality } 2392 Enable the kernel lockdown feature. If set to 2393 integrity, kernel features that allow userland to 2394 modify the running kernel are disabled. If set to 2395 confidentiality, kernel features that allow userland 2396 to extract confidential information from the kernel 2397 are also disabled. 2398 2399 locktorture.nreaders_stress= [KNL] 2400 Set the number of locking read-acquisition kthreads. 2401 Defaults to being automatically set based on the 2402 number of online CPUs. 2403 2404 locktorture.nwriters_stress= [KNL] 2405 Set the number of locking write-acquisition kthreads. 2406 2407 locktorture.onoff_holdoff= [KNL] 2408 Set time (s) after boot for CPU-hotplug testing. 2409 2410 locktorture.onoff_interval= [KNL] 2411 Set time (s) between CPU-hotplug operations, or 2412 zero to disable CPU-hotplug testing. 2413 2414 locktorture.shuffle_interval= [KNL] 2415 Set task-shuffle interval (jiffies). Shuffling 2416 tasks allows some CPUs to go into dyntick-idle 2417 mode during the locktorture test. 2418 2419 locktorture.shutdown_secs= [KNL] 2420 Set time (s) after boot system shutdown. This 2421 is useful for hands-off automated testing. 2422 2423 locktorture.stat_interval= [KNL] 2424 Time (s) between statistics printk()s. 2425 2426 locktorture.stutter= [KNL] 2427 Time (s) to stutter testing, for example, 2428 specifying five seconds causes the test to run for 2429 five seconds, wait for five seconds, and so on. 2430 This tests the locking primitive's ability to 2431 transition abruptly to and from idle. 2432 2433 locktorture.torture_type= [KNL] 2434 Specify the locking implementation to test. 2435 2436 locktorture.verbose= [KNL] 2437 Enable additional printk() statements. 2438 2439 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2440 Format: <irq> 2441 2442 loglevel= All Kernel Messages with a loglevel smaller than the 2443 console loglevel will be printed to the console. It can 2444 also be changed with klogd or other programs. The 2445 loglevels are defined as follows: 2446 2447 0 (KERN_EMERG) system is unusable 2448 1 (KERN_ALERT) action must be taken immediately 2449 2 (KERN_CRIT) critical conditions 2450 3 (KERN_ERR) error conditions 2451 4 (KERN_WARNING) warning conditions 2452 5 (KERN_NOTICE) normal but significant condition 2453 6 (KERN_INFO) informational 2454 7 (KERN_DEBUG) debug-level messages 2455 2456 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2457 in bytes. n must be a power of two and greater 2458 than the minimal size. The minimal size is defined 2459 by LOG_BUF_SHIFT kernel config parameter. There is 2460 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2461 that allows to increase the default size depending on 2462 the number of CPUs. See init/Kconfig for more details. 2463 2464 logo.nologo [FB] Disables display of the built-in Linux logo. 2465 This may be used to provide more screen space for 2466 kernel log messages and is useful when debugging 2467 kernel boot problems. 2468 2469 lp=0 [LP] Specify parallel ports to use, e.g, 2470 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2471 lp=reset first parallel port). 'lp=0' disables the 2472 lp=auto printer driver. 'lp=reset' (which can be 2473 specified in addition to the ports) causes 2474 attached printers to be reset. Using 2475 lp=port1,port2,... specifies the parallel ports 2476 to associate lp devices with, starting with 2477 lp0. A port specification may be 'none' to skip 2478 that lp device, or a parport name such as 2479 'parport0'. Specifying 'lp=auto' instead of a 2480 port specification list means that device IDs 2481 from each port should be examined, to see if 2482 an IEEE 1284-compliant printer is attached; if 2483 so, the driver will manage that printer. 2484 See also header of drivers/char/lp.c. 2485 2486 lpj=n [KNL] 2487 Sets loops_per_jiffy to given constant, thus avoiding 2488 time-consuming boot-time autodetection (up to 250 ms per 2489 CPU). 0 enables autodetection (default). To determine 2490 the correct value for your kernel, boot with normal 2491 autodetection and see what value is printed. Note that 2492 on SMP systems the preset will be applied to all CPUs, 2493 which is likely to cause problems if your CPUs need 2494 significantly divergent settings. An incorrect value 2495 will cause delays in the kernel to be wrong, leading to 2496 unpredictable I/O errors and other breakage. Although 2497 unlikely, in the extreme case this might damage your 2498 hardware. 2499 2500 ltpc= [NET] 2501 Format: <io>,<irq>,<dma> 2502 2503 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2504 2505 lsm=lsm1,...,lsmN 2506 [SECURITY] Choose order of LSM initialization. This 2507 overrides CONFIG_LSM, and the "security=" parameter. 2508 2509 machvec= [IA-64] Force the use of a particular machine-vector 2510 (machvec) in a generic kernel. 2511 Example: machvec=hpzx1 2512 2513 machtype= [Loongson] Share the same kernel image file between different 2514 yeeloong laptop. 2515 Example: machtype=lemote-yeeloong-2f-7inch 2516 2517 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2518 than or equal to this physical address is ignored. 2519 2520 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2521 will bring up during bootup. maxcpus=n : n >= 0 limits 2522 the kernel to bring up 'n' processors. Surely after 2523 bootup you can bring up the other plugged cpu by executing 2524 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2525 only takes effect during system bootup. 2526 While n=0 is a special case, it is equivalent to "nosmp", 2527 which also disables the IO APIC. 2528 2529 max_loop= [LOOP] The number of loop block devices that get 2530 (loop.max_loop) unconditionally pre-created at init time. The default 2531 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2532 of statically allocating a predefined number, loop 2533 devices can be requested on-demand with the 2534 /dev/loop-control interface. 2535 2536 mce [X86-32] Machine Check Exception 2537 2538 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2539 2540 md= [HW] RAID subsystems devices and level 2541 See Documentation/admin-guide/md.rst. 2542 2543 mdacon= [MDA] 2544 Format: <first>,<last> 2545 Specifies range of consoles to be captured by the MDA. 2546 2547 mds= [X86,INTEL] 2548 Control mitigation for the Micro-architectural Data 2549 Sampling (MDS) vulnerability. 2550 2551 Certain CPUs are vulnerable to an exploit against CPU 2552 internal buffers which can forward information to a 2553 disclosure gadget under certain conditions. 2554 2555 In vulnerable processors, the speculatively 2556 forwarded data can be used in a cache side channel 2557 attack, to access data to which the attacker does 2558 not have direct access. 2559 2560 This parameter controls the MDS mitigation. The 2561 options are: 2562 2563 full - Enable MDS mitigation on vulnerable CPUs 2564 full,nosmt - Enable MDS mitigation and disable 2565 SMT on vulnerable CPUs 2566 off - Unconditionally disable MDS mitigation 2567 2568 On TAA-affected machines, mds=off can be prevented by 2569 an active TAA mitigation as both vulnerabilities are 2570 mitigated with the same mechanism so in order to disable 2571 this mitigation, you need to specify tsx_async_abort=off 2572 too. 2573 2574 Not specifying this option is equivalent to 2575 mds=full. 2576 2577 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2578 2579 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2580 Amount of memory to be used in cases as follows: 2581 2582 1 for test; 2583 2 when the kernel is not able to see the whole system memory; 2584 3 memory that lies after 'mem=' boundary is excluded from 2585 the hypervisor, then assigned to KVM guests. 2586 2587 [X86] Work as limiting max address. Use together 2588 with memmap= to avoid physical address space collisions. 2589 Without memmap= PCI devices could be placed at addresses 2590 belonging to unused RAM. 2591 2592 Note that this only takes effects during boot time since 2593 in above case 3, memory may need be hot added after boot 2594 if system memory of hypervisor is not sufficient. 2595 2596 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2597 memory. 2598 2599 memchunk=nn[KMG] 2600 [KNL,SH] Allow user to override the default size for 2601 per-device physically contiguous DMA buffers. 2602 2603 memhp_default_state=online/offline 2604 [KNL] Set the initial state for the memory hotplug 2605 onlining policy. If not specified, the default value is 2606 set according to the 2607 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2608 option. 2609 See Documentation/admin-guide/mm/memory-hotplug.rst. 2610 2611 memmap=exactmap [KNL,X86] Enable setting of an exact 2612 E820 memory map, as specified by the user. 2613 Such memmap=exactmap lines can be constructed based on 2614 BIOS output or other requirements. See the memmap=nn@ss 2615 option description. 2616 2617 memmap=nn[KMG]@ss[KMG] 2618 [KNL] Force usage of a specific region of memory. 2619 Region of memory to be used is from ss to ss+nn. 2620 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2621 which limits max address to nn[KMG]. 2622 Multiple different regions can be specified, 2623 comma delimited. 2624 Example: 2625 memmap=100M@2G,100M#3G,1G!1024G 2626 2627 memmap=nn[KMG]#ss[KMG] 2628 [KNL,ACPI] Mark specific memory as ACPI data. 2629 Region of memory to be marked is from ss to ss+nn. 2630 2631 memmap=nn[KMG]$ss[KMG] 2632 [KNL,ACPI] Mark specific memory as reserved. 2633 Region of memory to be reserved is from ss to ss+nn. 2634 Example: Exclude memory from 0x18690000-0x1869ffff 2635 memmap=64K$0x18690000 2636 or 2637 memmap=0x10000$0x18690000 2638 Some bootloaders may need an escape character before '$', 2639 like Grub2, otherwise '$' and the following number 2640 will be eaten. 2641 2642 memmap=nn[KMG]!ss[KMG] 2643 [KNL,X86] Mark specific memory as protected. 2644 Region of memory to be used, from ss to ss+nn. 2645 The memory region may be marked as e820 type 12 (0xc) 2646 and is NVDIMM or ADR memory. 2647 2648 memmap=<size>%<offset>-<oldtype>+<newtype> 2649 [KNL,ACPI] Convert memory within the specified region 2650 from <oldtype> to <newtype>. If "-<oldtype>" is left 2651 out, the whole region will be marked as <newtype>, 2652 even if previously unavailable. If "+<newtype>" is left 2653 out, matching memory will be removed. Types are 2654 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2655 3 = ACPI, 12 = PRAM. 2656 2657 memory_corruption_check=0/1 [X86] 2658 Some BIOSes seem to corrupt the first 64k of 2659 memory when doing things like suspend/resume. 2660 Setting this option will scan the memory 2661 looking for corruption. Enabling this will 2662 both detect corruption and prevent the kernel 2663 from using the memory being corrupted. 2664 However, its intended as a diagnostic tool; if 2665 repeatable BIOS-originated corruption always 2666 affects the same memory, you can use memmap= 2667 to prevent the kernel from using that memory. 2668 2669 memory_corruption_check_size=size [X86] 2670 By default it checks for corruption in the low 2671 64k, making this memory unavailable for normal 2672 use. Use this parameter to scan for 2673 corruption in more or less memory. 2674 2675 memory_corruption_check_period=seconds [X86] 2676 By default it checks for corruption every 60 2677 seconds. Use this parameter to check at some 2678 other rate. 0 disables periodic checking. 2679 2680 memtest= [KNL,X86,ARM,PPC] Enable memtest 2681 Format: <integer> 2682 default : 0 <disable> 2683 Specifies the number of memtest passes to be 2684 performed. Each pass selects another test 2685 pattern from a given set of patterns. Memtest 2686 fills the memory with this pattern, validates 2687 memory contents and reserves bad memory 2688 regions that are detected. 2689 2690 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2691 Valid arguments: on, off 2692 Default (depends on kernel configuration option): 2693 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2694 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2695 mem_encrypt=on: Activate SME 2696 mem_encrypt=off: Do not activate SME 2697 2698 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2699 for details on when memory encryption can be activated. 2700 2701 mem_sleep_default= [SUSPEND] Default system suspend mode: 2702 s2idle - Suspend-To-Idle 2703 shallow - Power-On Suspend or equivalent (if supported) 2704 deep - Suspend-To-RAM or equivalent (if supported) 2705 See Documentation/admin-guide/pm/sleep-states.rst. 2706 2707 meye.*= [HW] Set MotionEye Camera parameters 2708 See Documentation/media/v4l-drivers/meye.rst. 2709 2710 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2711 Multi-Function General Purpose Timers on AMD Geode 2712 platforms. 2713 2714 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2715 the BIOS has incorrectly applied a workaround. TinyBIOS 2716 version 0.98 is known to be affected, 0.99 fixes the 2717 problem by letting the user disable the workaround. 2718 2719 mga= [HW,DRM] 2720 2721 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2722 physical address is ignored. 2723 2724 mini2440= [ARM,HW,KNL] 2725 Format:[0..2][b][c][t] 2726 Default: "0tb" 2727 MINI2440 configuration specification: 2728 0 - The attached screen is the 3.5" TFT 2729 1 - The attached screen is the 7" TFT 2730 2 - The VGA Shield is attached (1024x768) 2731 Leaving out the screen size parameter will not load 2732 the TFT driver, and the framebuffer will be left 2733 unconfigured. 2734 b - Enable backlight. The TFT backlight pin will be 2735 linked to the kernel VESA blanking code and a GPIO 2736 LED. This parameter is not necessary when using the 2737 VGA shield. 2738 c - Enable the s3c camera interface. 2739 t - Reserved for enabling touchscreen support. The 2740 touchscreen support is not enabled in the mainstream 2741 kernel as of 2.6.30, a preliminary port can be found 2742 in the "bleeding edge" mini2440 support kernel at 2743 http://repo.or.cz/w/linux-2.6/mini2440.git 2744 2745 mitigations= 2746 [X86,PPC,S390,ARM64] Control optional mitigations for 2747 CPU vulnerabilities. This is a set of curated, 2748 arch-independent options, each of which is an 2749 aggregation of existing arch-specific options. 2750 2751 off 2752 Disable all optional CPU mitigations. This 2753 improves system performance, but it may also 2754 expose users to several CPU vulnerabilities. 2755 Equivalent to: nopti [X86,PPC] 2756 kpti=0 [ARM64] 2757 nospectre_v1 [X86,PPC] 2758 nobp=0 [S390] 2759 nospectre_v2 [X86,PPC,S390,ARM64] 2760 spectre_v2_user=off [X86] 2761 spec_store_bypass_disable=off [X86,PPC] 2762 ssbd=force-off [ARM64] 2763 l1tf=off [X86] 2764 mds=off [X86] 2765 tsx_async_abort=off [X86] 2766 kvm.nx_huge_pages=off [X86] 2767 2768 Exceptions: 2769 This does not have any effect on 2770 kvm.nx_huge_pages when 2771 kvm.nx_huge_pages=force. 2772 2773 auto (default) 2774 Mitigate all CPU vulnerabilities, but leave SMT 2775 enabled, even if it's vulnerable. This is for 2776 users who don't want to be surprised by SMT 2777 getting disabled across kernel upgrades, or who 2778 have other ways of avoiding SMT-based attacks. 2779 Equivalent to: (default behavior) 2780 2781 auto,nosmt 2782 Mitigate all CPU vulnerabilities, disabling SMT 2783 if needed. This is for users who always want to 2784 be fully mitigated, even if it means losing SMT. 2785 Equivalent to: l1tf=flush,nosmt [X86] 2786 mds=full,nosmt [X86] 2787 tsx_async_abort=full,nosmt [X86] 2788 2789 mminit_loglevel= 2790 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2791 parameter allows control of the logging verbosity for 2792 the additional memory initialisation checks. A value 2793 of 0 disables mminit logging and a level of 4 will 2794 log everything. Information is printed at KERN_DEBUG 2795 so loglevel=8 may also need to be specified. 2796 2797 module.sig_enforce 2798 [KNL] When CONFIG_MODULE_SIG is set, this means that 2799 modules without (valid) signatures will fail to load. 2800 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2801 is always true, so this option does nothing. 2802 2803 module_blacklist= [KNL] Do not load a comma-separated list of 2804 modules. Useful for debugging problem modules. 2805 2806 mousedev.tap_time= 2807 [MOUSE] Maximum time between finger touching and 2808 leaving touchpad surface for touch to be considered 2809 a tap and be reported as a left button click (for 2810 touchpads working in absolute mode only). 2811 Format: <msecs> 2812 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2813 reporting absolute coordinates, such as tablets 2814 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2815 reporting absolute coordinates, such as tablets 2816 2817 movablecore= [KNL,X86,IA-64,PPC] 2818 Format: nn[KMGTPE] | nn% 2819 This parameter is the complement to kernelcore=, it 2820 specifies the amount of memory used for migratable 2821 allocations. If both kernelcore and movablecore is 2822 specified, then kernelcore will be at *least* the 2823 specified value but may be more. If movablecore on its 2824 own is specified, the administrator must be careful 2825 that the amount of memory usable for all allocations 2826 is not too small. 2827 2828 movable_node [KNL] Boot-time switch to make hotplugable memory 2829 NUMA nodes to be movable. This means that the memory 2830 of such nodes will be usable only for movable 2831 allocations which rules out almost all kernel 2832 allocations. Use with caution! 2833 2834 MTD_Partition= [MTD] 2835 Format: <name>,<region-number>,<size>,<offset> 2836 2837 MTD_Region= [MTD] Format: 2838 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2839 2840 mtdparts= [MTD] 2841 See drivers/mtd/parsers/cmdlinepart.c 2842 2843 multitce=off [PPC] This parameter disables the use of the pSeries 2844 firmware feature for updating multiple TCE entries 2845 at a time. 2846 2847 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2848 2849 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2850 2851 boundary - index of last SLC block on Flex-OneNAND. 2852 The remaining blocks are configured as MLC blocks. 2853 lock - Configure if Flex-OneNAND boundary should be locked. 2854 Once locked, the boundary cannot be changed. 2855 1 indicates lock status, 0 indicates unlock status. 2856 2857 mtdset= [ARM] 2858 ARM/S3C2412 JIVE boot control 2859 2860 See arch/arm/mach-s3c2412/mach-jive.c 2861 2862 mtouchusb.raw_coordinates= 2863 [HW] Make the MicroTouch USB driver use raw coordinates 2864 ('y', default) or cooked coordinates ('n') 2865 2866 mtrr_chunk_size=nn[KMG] [X86] 2867 used for mtrr cleanup. It is largest continuous chunk 2868 that could hold holes aka. UC entries. 2869 2870 mtrr_gran_size=nn[KMG] [X86] 2871 Used for mtrr cleanup. It is granularity of mtrr block. 2872 Default is 1. 2873 Large value could prevent small alignment from 2874 using up MTRRs. 2875 2876 mtrr_spare_reg_nr=n [X86] 2877 Format: <integer> 2878 Range: 0,7 : spare reg number 2879 Default : 1 2880 Used for mtrr cleanup. It is spare mtrr entries number. 2881 Set to 2 or more if your graphical card needs more. 2882 2883 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2884 2885 netdev= [NET] Network devices parameters 2886 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2887 Note that mem_start is often overloaded to mean 2888 something different and driver-specific. 2889 This usage is only documented in each driver source 2890 file if at all. 2891 2892 nf_conntrack.acct= 2893 [NETFILTER] Enable connection tracking flow accounting 2894 0 to disable accounting 2895 1 to enable accounting 2896 Default value is 0. 2897 2898 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2899 See Documentation/admin-guide/nfs/nfsroot.rst. 2900 2901 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2902 See Documentation/admin-guide/nfs/nfsroot.rst. 2903 2904 nfsrootdebug [NFS] enable nfsroot debugging messages. 2905 See Documentation/admin-guide/nfs/nfsroot.rst. 2906 2907 nfs.callback_nr_threads= 2908 [NFSv4] set the total number of threads that the 2909 NFS client will assign to service NFSv4 callback 2910 requests. 2911 2912 nfs.callback_tcpport= 2913 [NFS] set the TCP port on which the NFSv4 callback 2914 channel should listen. 2915 2916 nfs.cache_getent= 2917 [NFS] sets the pathname to the program which is used 2918 to update the NFS client cache entries. 2919 2920 nfs.cache_getent_timeout= 2921 [NFS] sets the timeout after which an attempt to 2922 update a cache entry is deemed to have failed. 2923 2924 nfs.idmap_cache_timeout= 2925 [NFS] set the maximum lifetime for idmapper cache 2926 entries. 2927 2928 nfs.enable_ino64= 2929 [NFS] enable 64-bit inode numbers. 2930 If zero, the NFS client will fake up a 32-bit inode 2931 number for the readdir() and stat() syscalls instead 2932 of returning the full 64-bit number. 2933 The default is to return 64-bit inode numbers. 2934 2935 nfs.max_session_cb_slots= 2936 [NFSv4.1] Sets the maximum number of session 2937 slots the client will assign to the callback 2938 channel. This determines the maximum number of 2939 callbacks the client will process in parallel for 2940 a particular server. 2941 2942 nfs.max_session_slots= 2943 [NFSv4.1] Sets the maximum number of session slots 2944 the client will attempt to negotiate with the server. 2945 This limits the number of simultaneous RPC requests 2946 that the client can send to the NFSv4.1 server. 2947 Note that there is little point in setting this 2948 value higher than the max_tcp_slot_table_limit. 2949 2950 nfs.nfs4_disable_idmapping= 2951 [NFSv4] When set to the default of '1', this option 2952 ensures that both the RPC level authentication 2953 scheme and the NFS level operations agree to use 2954 numeric uids/gids if the mount is using the 2955 'sec=sys' security flavour. In effect it is 2956 disabling idmapping, which can make migration from 2957 legacy NFSv2/v3 systems to NFSv4 easier. 2958 Servers that do not support this mode of operation 2959 will be autodetected by the client, and it will fall 2960 back to using the idmapper. 2961 To turn off this behaviour, set the value to '0'. 2962 nfs.nfs4_unique_id= 2963 [NFS4] Specify an additional fixed unique ident- 2964 ification string that NFSv4 clients can insert into 2965 their nfs_client_id4 string. This is typically a 2966 UUID that is generated at system install time. 2967 2968 nfs.send_implementation_id = 2969 [NFSv4.1] Send client implementation identification 2970 information in exchange_id requests. 2971 If zero, no implementation identification information 2972 will be sent. 2973 The default is to send the implementation identification 2974 information. 2975 2976 nfs.recover_lost_locks = 2977 [NFSv4] Attempt to recover locks that were lost due 2978 to a lease timeout on the server. Please note that 2979 doing this risks data corruption, since there are 2980 no guarantees that the file will remain unchanged 2981 after the locks are lost. 2982 If you want to enable the kernel legacy behaviour of 2983 attempting to recover these locks, then set this 2984 parameter to '1'. 2985 The default parameter value of '0' causes the kernel 2986 not to attempt recovery of lost locks. 2987 2988 nfs4.layoutstats_timer = 2989 [NFSv4.2] Change the rate at which the kernel sends 2990 layoutstats to the pNFS metadata server. 2991 2992 Setting this to value to 0 causes the kernel to use 2993 whatever value is the default set by the layout 2994 driver. A non-zero value sets the minimum interval 2995 in seconds between layoutstats transmissions. 2996 2997 nfsd.nfs4_disable_idmapping= 2998 [NFSv4] When set to the default of '1', the NFSv4 2999 server will return only numeric uids and gids to 3000 clients using auth_sys, and will accept numeric uids 3001 and gids from such clients. This is intended to ease 3002 migration from NFSv2/v3. 3003 3004 nmi_debug= [KNL,SH] Specify one or more actions to take 3005 when a NMI is triggered. 3006 Format: [state][,regs][,debounce][,die] 3007 3008 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3009 Format: [panic,][nopanic,][num] 3010 Valid num: 0 or 1 3011 0 - turn hardlockup detector in nmi_watchdog off 3012 1 - turn hardlockup detector in nmi_watchdog on 3013 When panic is specified, panic when an NMI watchdog 3014 timeout occurs (or 'nopanic' to not panic on an NMI 3015 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3016 To disable both hard and soft lockup detectors, 3017 please see 'nowatchdog'. 3018 This is useful when you use a panic=... timeout and 3019 need the box quickly up again. 3020 3021 These settings can be accessed at runtime via 3022 the nmi_watchdog and hardlockup_panic sysctls. 3023 3024 netpoll.carrier_timeout= 3025 [NET] Specifies amount of time (in seconds) that 3026 netpoll should wait for a carrier. By default netpoll 3027 waits 4 seconds. 3028 3029 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3030 emulation library even if a 387 maths coprocessor 3031 is present. 3032 3033 no5lvl [X86-64] Disable 5-level paging mode. Forces 3034 kernel to use 4-level paging instead. 3035 3036 no_console_suspend 3037 [HW] Never suspend the console 3038 Disable suspending of consoles during suspend and 3039 hibernate operations. Once disabled, debugging 3040 messages can reach various consoles while the rest 3041 of the system is being put to sleep (ie, while 3042 debugging driver suspend/resume hooks). This may 3043 not work reliably with all consoles, but is known 3044 to work with serial and VGA consoles. 3045 To facilitate more flexible debugging, we also add 3046 console_suspend, a printk module parameter to control 3047 it. Users could use console_suspend (usually 3048 /sys/module/printk/parameters/console_suspend) to 3049 turn on/off it dynamically. 3050 3051 novmcoredd [KNL,KDUMP] 3052 Disable device dump. Device dump allows drivers to 3053 append dump data to vmcore so you can collect driver 3054 specified debug info. Drivers can append the data 3055 without any limit and this data is stored in memory, 3056 so this may cause significant memory stress. Disabling 3057 device dump can help save memory but the driver debug 3058 data will be no longer available. This parameter 3059 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3060 is set. 3061 3062 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3063 caches in the slab allocator. Saves per-node memory, 3064 but will impact performance. 3065 3066 noalign [KNL,ARM] 3067 3068 noaltinstr [S390] Disables alternative instructions patching 3069 (CPU alternatives feature). 3070 3071 noapic [SMP,APIC] Tells the kernel to not make use of any 3072 IOAPICs that may be present in the system. 3073 3074 noautogroup Disable scheduler automatic task group creation. 3075 3076 nobats [PPC] Do not use BATs for mapping kernel lowmem 3077 on "Classic" PPC cores. 3078 3079 nocache [ARM] 3080 3081 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3082 3083 nodelayacct [KNL] Disable per-task delay accounting 3084 3085 nodsp [SH] Disable hardware DSP at boot time. 3086 3087 noefi Disable EFI runtime services support. 3088 3089 noexec [IA-64] 3090 3091 noexec [X86] 3092 On X86-32 available only on PAE configured kernels. 3093 noexec=on: enable non-executable mappings (default) 3094 noexec=off: disable non-executable mappings 3095 3096 nosmap [X86,PPC] 3097 Disable SMAP (Supervisor Mode Access Prevention) 3098 even if it is supported by processor. 3099 3100 nosmep [X86,PPC] 3101 Disable SMEP (Supervisor Mode Execution Prevention) 3102 even if it is supported by processor. 3103 3104 noexec32 [X86-64] 3105 This affects only 32-bit executables. 3106 noexec32=on: enable non-executable mappings (default) 3107 read doesn't imply executable mappings 3108 noexec32=off: disable non-executable mappings 3109 read implies executable mappings 3110 3111 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3112 3113 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3114 register save and restore. The kernel will only save 3115 legacy floating-point registers on task switch. 3116 3117 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3118 3119 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3120 Equivalent to smt=1. 3121 3122 [KNL,x86] Disable symmetric multithreading (SMT). 3123 nosmt=force: Force disable SMT, cannot be undone 3124 via the sysfs control file. 3125 3126 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3127 (bounds check bypass). With this option data leaks are 3128 possible in the system. 3129 3130 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3131 the Spectre variant 2 (indirect branch prediction) 3132 vulnerability. System may allow data leaks with this 3133 option. 3134 3135 nospec_store_bypass_disable 3136 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3137 3138 noxsave [BUGS=X86] Disables x86 extended register state save 3139 and restore using xsave. The kernel will fallback to 3140 enabling legacy floating-point and sse state. 3141 3142 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3143 register states. The kernel will fall back to use 3144 xsave to save the states. By using this parameter, 3145 performance of saving the states is degraded because 3146 xsave doesn't support modified optimization while 3147 xsaveopt supports it on xsaveopt enabled systems. 3148 3149 noxsaves [X86] Disables xsaves and xrstors used in saving and 3150 restoring x86 extended register state in compacted 3151 form of xsave area. The kernel will fall back to use 3152 xsaveopt and xrstor to save and restore the states 3153 in standard form of xsave area. By using this 3154 parameter, xsave area per process might occupy more 3155 memory on xsaves enabled systems. 3156 3157 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3158 wfi(ARM) instruction doesn't work correctly and not to 3159 use it. This is also useful when using JTAG debugger. 3160 3161 no_file_caps Tells the kernel not to honor file capabilities. The 3162 only way then for a file to be executed with privilege 3163 is to be setuid root or executed by root. 3164 3165 nohalt [IA-64] Tells the kernel not to use the power saving 3166 function PAL_HALT_LIGHT when idle. This increases 3167 power-consumption. On the positive side, it reduces 3168 interrupt wake-up latency, which may improve performance 3169 in certain environments such as networked servers or 3170 real-time systems. 3171 3172 nohibernate [HIBERNATION] Disable hibernation and resume. 3173 3174 nohz= [KNL] Boottime enable/disable dynamic ticks 3175 Valid arguments: on, off 3176 Default: on 3177 3178 nohz_full= [KNL,BOOT,SMP,ISOL] 3179 The argument is a cpu list, as described above. 3180 In kernels built with CONFIG_NO_HZ_FULL=y, set 3181 the specified list of CPUs whose tick will be stopped 3182 whenever possible. The boot CPU will be forced outside 3183 the range to maintain the timekeeping. Any CPUs 3184 in this list will have their RCU callbacks offloaded, 3185 just as if they had also been called out in the 3186 rcu_nocbs= boot parameter. 3187 3188 noiotrap [SH] Disables trapped I/O port accesses. 3189 3190 noirqdebug [X86-32] Disables the code which attempts to detect and 3191 disable unhandled interrupt sources. 3192 3193 no_timer_check [X86,APIC] Disables the code which tests for 3194 broken timer IRQ sources. 3195 3196 noisapnp [ISAPNP] Disables ISA PnP code. 3197 3198 noinitrd [RAM] Tells the kernel not to load any configured 3199 initial RAM disk. 3200 3201 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3202 remapping. 3203 [Deprecated - use intremap=off] 3204 3205 nointroute [IA-64] 3206 3207 noinvpcid [X86] Disable the INVPCID cpu feature. 3208 3209 nojitter [IA-64] Disables jitter checking for ITC timers. 3210 3211 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3212 3213 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3214 fault handling. 3215 3216 no-vmw-sched-clock 3217 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3218 clock and use the default one. 3219 3220 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3221 accounting. steal time is computed, but won't 3222 influence scheduler behaviour 3223 3224 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3225 3226 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3227 3228 noltlbs [PPC] Do not use large page/tlb entries for kernel 3229 lowmem mapping on PPC40x and PPC8xx 3230 3231 nomca [IA-64] Disable machine check abort handling 3232 3233 nomce [X86-32] Disable Machine Check Exception 3234 3235 nomfgpt [X86-32] Disable Multi-Function General Purpose 3236 Timer usage (for AMD Geode machines). 3237 3238 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3239 shutdown the other cpus. Instead use the REBOOT_VECTOR 3240 irq. 3241 3242 nomodule Disable module load 3243 3244 nopat [X86] Disable PAT (page attribute table extension of 3245 pagetables) support. 3246 3247 nopcid [X86-64] Disable the PCID cpu feature. 3248 3249 norandmaps Don't use address space randomization. Equivalent to 3250 echo 0 > /proc/sys/kernel/randomize_va_space 3251 3252 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3253 with UP alternatives 3254 3255 nordrand [X86] Disable kernel use of the RDRAND and 3256 RDSEED instructions even if they are supported 3257 by the processor. RDRAND and RDSEED are still 3258 available to user space applications. 3259 3260 noresume [SWSUSP] Disables resume and restores original swap 3261 space. 3262 3263 no-scroll [VGA] Disables scrollback. 3264 This is required for the Braillex ib80-piezo Braille 3265 reader made by F.H. Papenmeier (Germany). 3266 3267 nosbagart [IA-64] 3268 3269 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3270 3271 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3272 and disable the IO APIC. legacy for "maxcpus=0". 3273 3274 nosoftlockup [KNL] Disable the soft-lockup detector. 3275 3276 nosync [HW,M68K] Disables sync negotiation for all devices. 3277 3278 nowatchdog [KNL] Disable both lockup detectors, i.e. 3279 soft-lockup and NMI watchdog (hard-lockup). 3280 3281 nowb [ARM] 3282 3283 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3284 3285 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3286 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3287 Some features depend on CPU0. Known dependencies are: 3288 1. Resume from suspend/hibernate depends on CPU0. 3289 Suspend/hibernate will fail if CPU0 is offline and you 3290 need to online CPU0 before suspend/hibernate. 3291 2. PIC interrupts also depend on CPU0. CPU0 can't be 3292 removed if a PIC interrupt is detected. 3293 It's said poweroff/reboot may depend on CPU0 on some 3294 machines although I haven't seen such issues so far 3295 after CPU0 is offline on a few tested machines. 3296 If the dependencies are under your control, you can 3297 turn on cpu0_hotplug. 3298 3299 nps_mtm_hs_ctr= [KNL,ARC] 3300 This parameter sets the maximum duration, in 3301 cycles, each HW thread of the CTOP can run 3302 without interruptions, before HW switches it. 3303 The actual maximum duration is 16 times this 3304 parameter's value. 3305 Format: integer between 1 and 255 3306 Default: 255 3307 3308 nptcg= [IA-64] Override max number of concurrent global TLB 3309 purges which is reported from either PAL_VM_SUMMARY or 3310 SAL PALO. 3311 3312 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3313 could support. nr_cpus=n : n >= 1 limits the kernel to 3314 support 'n' processors. It could be larger than the 3315 number of already plugged CPU during bootup, later in 3316 runtime you can physically add extra cpu until it reaches 3317 n. So during boot up some boot time memory for per-cpu 3318 variables need be pre-allocated for later physical cpu 3319 hot plugging. 3320 3321 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3322 3323 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3324 Allowed values are enable and disable 3325 3326 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3327 'node', 'default' can be specified 3328 This can be set from sysctl after boot. 3329 See Documentation/admin-guide/sysctl/vm.rst for details. 3330 3331 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3332 See Documentation/debugging-via-ohci1394.txt for more 3333 info. 3334 3335 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3336 Rather than timing out after 20 ms if an EC 3337 command is not properly ACKed, override the length 3338 of the timeout. We have interrupts disabled while 3339 waiting for the ACK, so if this is set too high 3340 interrupts *may* be lost! 3341 3342 omap_mux= [OMAP] Override bootloader pin multiplexing. 3343 Format: <mux_mode0.mode_name=value>... 3344 For example, to override I2C bus2: 3345 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3346 3347 oprofile.timer= [HW] 3348 Use timer interrupt instead of performance counters 3349 3350 oprofile.cpu_type= Force an oprofile cpu type 3351 This might be useful if you have an older oprofile 3352 userland or if you want common events. 3353 Format: { arch_perfmon } 3354 arch_perfmon: [X86] Force use of architectural 3355 perfmon on Intel CPUs instead of the 3356 CPU specific event set. 3357 timer: [X86] Force use of architectural NMI 3358 timer mode (see also oprofile.timer 3359 for generic hr timer mode) 3360 3361 oops=panic Always panic on oopses. Default is to just kill the 3362 process, but there is a small probability of 3363 deadlocking the machine. 3364 This will also cause panics on machine check exceptions. 3365 Useful together with panic=30 to trigger a reboot. 3366 3367 page_alloc.shuffle= 3368 [KNL] Boolean flag to control whether the page allocator 3369 should randomize its free lists. The randomization may 3370 be automatically enabled if the kernel detects it is 3371 running on a platform with a direct-mapped memory-side 3372 cache, and this parameter can be used to 3373 override/disable that behavior. The state of the flag 3374 can be read from sysfs at: 3375 /sys/module/page_alloc/parameters/shuffle. 3376 3377 page_owner= [KNL] Boot-time page_owner enabling option. 3378 Storage of the information about who allocated 3379 each page is disabled in default. With this switch, 3380 we can turn it on. 3381 on: enable the feature 3382 3383 page_poison= [KNL] Boot-time parameter changing the state of 3384 poisoning on the buddy allocator, available with 3385 CONFIG_PAGE_POISONING=y. 3386 off: turn off poisoning (default) 3387 on: turn on poisoning 3388 3389 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3390 timeout > 0: seconds before rebooting 3391 timeout = 0: wait forever 3392 timeout < 0: reboot immediately 3393 Format: <timeout> 3394 3395 panic_print= Bitmask for printing system info when panic happens. 3396 User can chose combination of the following bits: 3397 bit 0: print all tasks info 3398 bit 1: print system memory info 3399 bit 2: print timer info 3400 bit 3: print locks info if CONFIG_LOCKDEP is on 3401 bit 4: print ftrace buffer 3402 bit 5: print all printk messages in buffer 3403 3404 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3405 on a WARN(). 3406 3407 crash_kexec_post_notifiers 3408 Run kdump after running panic-notifiers and dumping 3409 kmsg. This only for the users who doubt kdump always 3410 succeeds in any situation. 3411 Note that this also increases risks of kdump failure, 3412 because some panic notifiers can make the crashed 3413 kernel more unstable. 3414 3415 parkbd.port= [HW] Parallel port number the keyboard adapter is 3416 connected to, default is 0. 3417 Format: <parport#> 3418 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3419 0 for XT, 1 for AT (default is AT). 3420 Format: <mode> 3421 3422 parport= [HW,PPT] Specify parallel ports. 0 disables. 3423 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3424 Use 'auto' to force the driver to use any 3425 IRQ/DMA settings detected (the default is to 3426 ignore detected IRQ/DMA settings because of 3427 possible conflicts). You can specify the base 3428 address, IRQ, and DMA settings; IRQ and DMA 3429 should be numbers, or 'auto' (for using detected 3430 settings on that particular port), or 'nofifo' 3431 (to avoid using a FIFO even if it is detected). 3432 Parallel ports are assigned in the order they 3433 are specified on the command line, starting 3434 with parport0. 3435 3436 parport_init_mode= [HW,PPT] 3437 Configure VIA parallel port to operate in 3438 a specific mode. This is necessary on Pegasos 3439 computer where firmware has no options for setting 3440 up parallel port mode and sets it to spp. 3441 Currently this function knows 686a and 8231 chips. 3442 Format: [spp|ps2|epp|ecp|ecpepp] 3443 3444 pause_on_oops= 3445 Halt all CPUs after the first oops has been printed for 3446 the specified number of seconds. This is to be used if 3447 your oopses keep scrolling off the screen. 3448 3449 pcbit= [HW,ISDN] 3450 3451 pcd. [PARIDE] 3452 See header of drivers/block/paride/pcd.c. 3453 See also Documentation/admin-guide/blockdev/paride.rst. 3454 3455 pci=option[,option...] [PCI] various PCI subsystem options. 3456 3457 Some options herein operate on a specific device 3458 or a set of devices (<pci_dev>). These are 3459 specified in one of the following formats: 3460 3461 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3462 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3463 3464 Note: the first format specifies a PCI 3465 bus/device/function address which may change 3466 if new hardware is inserted, if motherboard 3467 firmware changes, or due to changes caused 3468 by other kernel parameters. If the 3469 domain is left unspecified, it is 3470 taken to be zero. Optionally, a path 3471 to a device through multiple device/function 3472 addresses can be specified after the base 3473 address (this is more robust against 3474 renumbering issues). The second format 3475 selects devices using IDs from the 3476 configuration space which may match multiple 3477 devices in the system. 3478 3479 earlydump dump PCI config space before the kernel 3480 changes anything 3481 off [X86] don't probe for the PCI bus 3482 bios [X86-32] force use of PCI BIOS, don't access 3483 the hardware directly. Use this if your machine 3484 has a non-standard PCI host bridge. 3485 nobios [X86-32] disallow use of PCI BIOS, only direct 3486 hardware access methods are allowed. Use this 3487 if you experience crashes upon bootup and you 3488 suspect they are caused by the BIOS. 3489 conf1 [X86] Force use of PCI Configuration Access 3490 Mechanism 1 (config address in IO port 0xCF8, 3491 data in IO port 0xCFC, both 32-bit). 3492 conf2 [X86] Force use of PCI Configuration Access 3493 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3494 the function, IO port 0xCFA, also 8-bit, sets 3495 bus number. The config space is then accessed 3496 through ports 0xC000-0xCFFF). 3497 See http://wiki.osdev.org/PCI for more info 3498 on the configuration access mechanisms. 3499 noaer [PCIE] If the PCIEAER kernel config parameter is 3500 enabled, this kernel boot option can be used to 3501 disable the use of PCIE advanced error reporting. 3502 nodomains [PCI] Disable support for multiple PCI 3503 root domains (aka PCI segments, in ACPI-speak). 3504 nommconf [X86] Disable use of MMCONFIG for PCI 3505 Configuration 3506 check_enable_amd_mmconf [X86] check for and enable 3507 properly configured MMIO access to PCI 3508 config space on AMD family 10h CPU 3509 nomsi [MSI] If the PCI_MSI kernel config parameter is 3510 enabled, this kernel boot option can be used to 3511 disable the use of MSI interrupts system-wide. 3512 noioapicquirk [APIC] Disable all boot interrupt quirks. 3513 Safety option to keep boot IRQs enabled. This 3514 should never be necessary. 3515 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3516 primary IO-APIC for bridges that cannot disable 3517 boot IRQs. This fixes a source of spurious IRQs 3518 when the system masks IRQs. 3519 noioapicreroute [APIC] Disable workaround that uses the 3520 boot IRQ equivalent of an IRQ that connects to 3521 a chipset where boot IRQs cannot be disabled. 3522 The opposite of ioapicreroute. 3523 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3524 routing table. These calls are known to be buggy 3525 on several machines and they hang the machine 3526 when used, but on other computers it's the only 3527 way to get the interrupt routing table. Try 3528 this option if the kernel is unable to allocate 3529 IRQs or discover secondary PCI buses on your 3530 motherboard. 3531 rom [X86] Assign address space to expansion ROMs. 3532 Use with caution as certain devices share 3533 address decoders between ROMs and other 3534 resources. 3535 norom [X86] Do not assign address space to 3536 expansion ROMs that do not already have 3537 BIOS assigned address ranges. 3538 nobar [X86] Do not assign address space to the 3539 BARs that weren't assigned by the BIOS. 3540 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3541 assigned automatically to PCI devices. You can 3542 make the kernel exclude IRQs of your ISA cards 3543 this way. 3544 pirqaddr=0xAAAAA [X86] Specify the physical address 3545 of the PIRQ table (normally generated 3546 by the BIOS) if it is outside the 3547 F0000h-100000h range. 3548 lastbus=N [X86] Scan all buses thru bus #N. Can be 3549 useful if the kernel is unable to find your 3550 secondary buses and you want to tell it 3551 explicitly which ones they are. 3552 assign-busses [X86] Always assign all PCI bus 3553 numbers ourselves, overriding 3554 whatever the firmware may have done. 3555 usepirqmask [X86] Honor the possible IRQ mask stored 3556 in the BIOS $PIR table. This is needed on 3557 some systems with broken BIOSes, notably 3558 some HP Pavilion N5400 and Omnibook XE3 3559 notebooks. This will have no effect if ACPI 3560 IRQ routing is enabled. 3561 noacpi [X86] Do not use ACPI for IRQ routing 3562 or for PCI scanning. 3563 use_crs [X86] Use PCI host bridge window information 3564 from ACPI. On BIOSes from 2008 or later, this 3565 is enabled by default. If you need to use this, 3566 please report a bug. 3567 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3568 If you need to use this, please report a bug. 3569 routeirq Do IRQ routing for all PCI devices. 3570 This is normally done in pci_enable_device(), 3571 so this option is a temporary workaround 3572 for broken drivers that don't call it. 3573 skip_isa_align [X86] do not align io start addr, so can 3574 handle more pci cards 3575 noearly [X86] Don't do any early type 1 scanning. 3576 This might help on some broken boards which 3577 machine check when some devices' config space 3578 is read. But various workarounds are disabled 3579 and some IOMMU drivers will not work. 3580 bfsort Sort PCI devices into breadth-first order. 3581 This sorting is done to get a device 3582 order compatible with older (<= 2.4) kernels. 3583 nobfsort Don't sort PCI devices into breadth-first order. 3584 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3585 tuning and use the BIOS-configured MPS defaults. 3586 pcie_bus_safe Set every device's MPS to the largest value 3587 supported by all devices below the root complex. 3588 pcie_bus_perf Set device MPS to the largest allowable MPS 3589 based on its parent bus. Also set MRRS (Max 3590 Read Request Size) to the largest supported 3591 value (no larger than the MPS that the device 3592 or bus can support) for best performance. 3593 pcie_bus_peer2peer Set every device's MPS to 128B, which 3594 every device is guaranteed to support. This 3595 configuration allows peer-to-peer DMA between 3596 any pair of devices, possibly at the cost of 3597 reduced performance. This also guarantees 3598 that hot-added devices will work. 3599 cbiosize=nn[KMG] The fixed amount of bus space which is 3600 reserved for the CardBus bridge's IO window. 3601 The default value is 256 bytes. 3602 cbmemsize=nn[KMG] The fixed amount of bus space which is 3603 reserved for the CardBus bridge's memory 3604 window. The default value is 64 megabytes. 3605 resource_alignment= 3606 Format: 3607 [<order of align>@]<pci_dev>[; ...] 3608 Specifies alignment and device to reassign 3609 aligned memory resources. How to 3610 specify the device is described above. 3611 If <order of align> is not specified, 3612 PAGE_SIZE is used as alignment. 3613 A PCI-PCI bridge can be specified if resource 3614 windows need to be expanded. 3615 To specify the alignment for several 3616 instances of a device, the PCI vendor, 3617 device, subvendor, and subdevice may be 3618 specified, e.g., 12@pci:8086:9c22:103c:198f 3619 for 4096-byte alignment. 3620 ecrc= Enable/disable PCIe ECRC (transaction layer 3621 end-to-end CRC checking). 3622 bios: Use BIOS/firmware settings. This is the 3623 the default. 3624 off: Turn ECRC off 3625 on: Turn ECRC on. 3626 hpiosize=nn[KMG] The fixed amount of bus space which is 3627 reserved for hotplug bridge's IO window. 3628 Default size is 256 bytes. 3629 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3630 reserved for hotplug bridge's MMIO window. 3631 Default size is 2 megabytes. 3632 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3633 reserved for hotplug bridge's MMIO_PREF window. 3634 Default size is 2 megabytes. 3635 hpmemsize=nn[KMG] The fixed amount of bus space which is 3636 reserved for hotplug bridge's MMIO and 3637 MMIO_PREF window. 3638 Default size is 2 megabytes. 3639 hpbussize=nn The minimum amount of additional bus numbers 3640 reserved for buses below a hotplug bridge. 3641 Default is 1. 3642 realloc= Enable/disable reallocating PCI bridge resources 3643 if allocations done by BIOS are too small to 3644 accommodate resources required by all child 3645 devices. 3646 off: Turn realloc off 3647 on: Turn realloc on 3648 realloc same as realloc=on 3649 noari do not use PCIe ARI. 3650 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3651 do not use PCIe ATS (and IOMMU device IOTLB). 3652 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3653 only look for one device below a PCIe downstream 3654 port. 3655 big_root_window Try to add a big 64bit memory window to the PCIe 3656 root complex on AMD CPUs. Some GFX hardware 3657 can resize a BAR to allow access to all VRAM. 3658 Adding the window is slightly risky (it may 3659 conflict with unreported devices), so this 3660 taints the kernel. 3661 disable_acs_redir=<pci_dev>[; ...] 3662 Specify one or more PCI devices (in the format 3663 specified above) separated by semicolons. 3664 Each device specified will have the PCI ACS 3665 redirect capabilities forced off which will 3666 allow P2P traffic between devices through 3667 bridges without forcing it upstream. Note: 3668 this removes isolation between devices and 3669 may put more devices in an IOMMU group. 3670 force_floating [S390] Force usage of floating interrupts. 3671 nomio [S390] Do not use MIO instructions. 3672 3673 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3674 Management. 3675 off Disable ASPM. 3676 force Enable ASPM even on devices that claim not to support it. 3677 WARNING: Forcing ASPM on may cause system lockups. 3678 3679 pcie_ports= [PCIE] PCIe port services handling: 3680 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3681 even if the platform doesn't give the OS permission to 3682 use them. This may cause conflicts if the platform 3683 also tries to use these services. 3684 dpc-native Use native PCIe service for DPC only. May 3685 cause conflicts if firmware uses AER or DPC. 3686 compat Disable native PCIe services (PME, AER, DPC, PCIe 3687 hotplug). 3688 3689 pcie_port_pm= [PCIE] PCIe port power management handling: 3690 off Disable power management of all PCIe ports 3691 force Forcibly enable power management of all PCIe ports 3692 3693 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3694 nomsi Do not use MSI for native PCIe PME signaling (this makes 3695 all PCIe root ports use INTx for all services). 3696 3697 pcmv= [HW,PCMCIA] BadgePAD 4 3698 3699 pd_ignore_unused 3700 [PM] 3701 Keep all power-domains already enabled by bootloader on, 3702 even if no driver has claimed them. This is useful 3703 for debug and development, but should not be 3704 needed on a platform with proper driver support. 3705 3706 pd. [PARIDE] 3707 See Documentation/admin-guide/blockdev/paride.rst. 3708 3709 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3710 boot time. 3711 Format: { 0 | 1 } 3712 See arch/parisc/kernel/pdc_chassis.c 3713 3714 percpu_alloc= Select which percpu first chunk allocator to use. 3715 Currently supported values are "embed" and "page". 3716 Archs may support subset or none of the selections. 3717 See comments in mm/percpu.c for details on each 3718 allocator. This parameter is primarily for debugging 3719 and performance comparison. 3720 3721 pf. [PARIDE] 3722 See Documentation/admin-guide/blockdev/paride.rst. 3723 3724 pg. [PARIDE] 3725 See Documentation/admin-guide/blockdev/paride.rst. 3726 3727 pirq= [SMP,APIC] Manual mp-table setup 3728 See Documentation/x86/i386/IO-APIC.rst. 3729 3730 plip= [PPT,NET] Parallel port network link 3731 Format: { parport<nr> | timid | 0 } 3732 See also Documentation/admin-guide/parport.rst. 3733 3734 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3735 Override pmtimer IOPort with a hex value. 3736 e.g. pmtmr=0x508 3737 3738 pm_debug_messages [SUSPEND,KNL] 3739 Enable suspend/resume debug messages during boot up. 3740 3741 pnp.debug=1 [PNP] 3742 Enable PNP debug messages (depends on the 3743 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3744 via /sys/module/pnp/parameters/debug. We always show 3745 current resource usage; turning this on also shows 3746 possible settings and some assignment information. 3747 3748 pnpacpi= [ACPI] 3749 { off } 3750 3751 pnpbios= [ISAPNP] 3752 { on | off | curr | res | no-curr | no-res } 3753 3754 pnp_reserve_irq= 3755 [ISAPNP] Exclude IRQs for the autoconfiguration 3756 3757 pnp_reserve_dma= 3758 [ISAPNP] Exclude DMAs for the autoconfiguration 3759 3760 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3761 Ranges are in pairs (I/O port base and size). 3762 3763 pnp_reserve_mem= 3764 [ISAPNP] Exclude memory regions for the 3765 autoconfiguration. 3766 Ranges are in pairs (memory base and size). 3767 3768 ports= [IP_VS_FTP] IPVS ftp helper module 3769 Default is 21. 3770 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3771 may be specified. 3772 Format: <port>,<port>.... 3773 3774 powersave=off [PPC] This option disables power saving features. 3775 It specifically disables cpuidle and sets the 3776 platform machine description specific power_save 3777 function to NULL. On Idle the CPU just reduces 3778 execution priority. 3779 3780 ppc_strict_facility_enable 3781 [PPC] This option catches any kernel floating point, 3782 Altivec, VSX and SPE outside of regions specifically 3783 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3784 There is some performance impact when enabling this. 3785 3786 ppc_tm= [PPC] 3787 Format: {"off"} 3788 Disable Hardware Transactional Memory 3789 3790 print-fatal-signals= 3791 [KNL] debug: print fatal signals 3792 3793 If enabled, warn about various signal handling 3794 related application anomalies: too many signals, 3795 too many POSIX.1 timers, fatal signals causing a 3796 coredump - etc. 3797 3798 If you hit the warning due to signal overflow, 3799 you might want to try "ulimit -i unlimited". 3800 3801 default: off. 3802 3803 printk.always_kmsg_dump= 3804 Trigger kmsg_dump for cases other than kernel oops or 3805 panics 3806 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3807 default: disabled 3808 3809 printk.devkmsg={on,off,ratelimit} 3810 Control writing to /dev/kmsg. 3811 on - unlimited logging to /dev/kmsg from userspace 3812 off - logging to /dev/kmsg disabled 3813 ratelimit - ratelimit the logging 3814 Default: ratelimit 3815 3816 printk.time= Show timing data prefixed to each printk message line 3817 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3818 3819 processor.max_cstate= [HW,ACPI] 3820 Limit processor to maximum C-state 3821 max_cstate=9 overrides any DMI blacklist limit. 3822 3823 processor.nocst [HW,ACPI] 3824 Ignore the _CST method to determine C-states, 3825 instead using the legacy FADT method 3826 3827 profile= [KNL] Enable kernel profiling via /proc/profile 3828 Format: [<profiletype>,]<number> 3829 Param: <profiletype>: "schedule", "sleep", or "kvm" 3830 [defaults to kernel profiling] 3831 Param: "schedule" - profile schedule points. 3832 Param: "sleep" - profile D-state sleeping (millisecs). 3833 Requires CONFIG_SCHEDSTATS 3834 Param: "kvm" - profile VM exits. 3835 Param: <number> - step/bucket size as a power of 2 for 3836 statistical time based profiling. 3837 3838 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3839 before loading. 3840 See Documentation/admin-guide/blockdev/ramdisk.rst. 3841 3842 prot_virt= [S390] enable hosting protected virtual machines 3843 isolated from the hypervisor (if hardware supports 3844 that). 3845 Format: <bool> 3846 3847 psi= [KNL] Enable or disable pressure stall information 3848 tracking. 3849 Format: <bool> 3850 3851 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3852 probe for; one of (bare|imps|exps|lifebook|any). 3853 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3854 per second. 3855 psmouse.resetafter= [HW,MOUSE] 3856 Try to reset the device after so many bad packets 3857 (0 = never). 3858 psmouse.resolution= 3859 [HW,MOUSE] Set desired mouse resolution, in dpi. 3860 psmouse.smartscroll= 3861 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3862 0 = disabled, 1 = enabled (default). 3863 3864 pstore.backend= Specify the name of the pstore backend to use 3865 3866 pt. [PARIDE] 3867 See Documentation/admin-guide/blockdev/paride.rst. 3868 3869 pti= [X86_64] Control Page Table Isolation of user and 3870 kernel address spaces. Disabling this feature 3871 removes hardening, but improves performance of 3872 system calls and interrupts. 3873 3874 on - unconditionally enable 3875 off - unconditionally disable 3876 auto - kernel detects whether your CPU model is 3877 vulnerable to issues that PTI mitigates 3878 3879 Not specifying this option is equivalent to pti=auto. 3880 3881 nopti [X86_64] 3882 Equivalent to pti=off 3883 3884 pty.legacy_count= 3885 [KNL] Number of legacy pty's. Overwrites compiled-in 3886 default number. 3887 3888 quiet [KNL] Disable most log messages 3889 3890 r128= [HW,DRM] 3891 3892 raid= [HW,RAID] 3893 See Documentation/admin-guide/md.rst. 3894 3895 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3896 See Documentation/admin-guide/blockdev/ramdisk.rst. 3897 3898 random.trust_cpu={on,off} 3899 [KNL] Enable or disable trusting the use of the 3900 CPU's random number generator (if available) to 3901 fully seed the kernel's CRNG. Default is controlled 3902 by CONFIG_RANDOM_TRUST_CPU. 3903 3904 ras=option[,option,...] [KNL] RAS-specific options 3905 3906 cec_disable [X86] 3907 Disable the Correctable Errors Collector, 3908 see CONFIG_RAS_CEC help text. 3909 3910 rcu_nocbs= [KNL] 3911 The argument is a cpu list, as described above, 3912 except that the string "all" can be used to 3913 specify every CPU on the system. 3914 3915 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3916 the specified list of CPUs to be no-callback CPUs. 3917 Invocation of these CPUs' RCU callbacks will be 3918 offloaded to "rcuox/N" kthreads created for that 3919 purpose, where "x" is "p" for RCU-preempt, and 3920 "s" for RCU-sched, and "N" is the CPU number. 3921 This reduces OS jitter on the offloaded CPUs, 3922 which can be useful for HPC and real-time 3923 workloads. It can also improve energy efficiency 3924 for asymmetric multiprocessors. 3925 3926 rcu_nocb_poll [KNL] 3927 Rather than requiring that offloaded CPUs 3928 (specified by rcu_nocbs= above) explicitly 3929 awaken the corresponding "rcuoN" kthreads, 3930 make these kthreads poll for callbacks. 3931 This improves the real-time response for the 3932 offloaded CPUs by relieving them of the need to 3933 wake up the corresponding kthread, but degrades 3934 energy efficiency by requiring that the kthreads 3935 periodically wake up to do the polling. 3936 3937 rcutree.blimit= [KNL] 3938 Set maximum number of finished RCU callbacks to 3939 process in one batch. 3940 3941 rcutree.dump_tree= [KNL] 3942 Dump the structure of the rcu_node combining tree 3943 out at early boot. This is used for diagnostic 3944 purposes, to verify correct tree setup. 3945 3946 rcutree.gp_cleanup_delay= [KNL] 3947 Set the number of jiffies to delay each step of 3948 RCU grace-period cleanup. 3949 3950 rcutree.gp_init_delay= [KNL] 3951 Set the number of jiffies to delay each step of 3952 RCU grace-period initialization. 3953 3954 rcutree.gp_preinit_delay= [KNL] 3955 Set the number of jiffies to delay each step of 3956 RCU grace-period pre-initialization, that is, 3957 the propagation of recent CPU-hotplug changes up 3958 the rcu_node combining tree. 3959 3960 rcutree.use_softirq= [KNL] 3961 If set to zero, move all RCU_SOFTIRQ processing to 3962 per-CPU rcuc kthreads. Defaults to a non-zero 3963 value, meaning that RCU_SOFTIRQ is used by default. 3964 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3965 3966 rcutree.rcu_fanout_exact= [KNL] 3967 Disable autobalancing of the rcu_node combining 3968 tree. This is used by rcutorture, and might 3969 possibly be useful for architectures having high 3970 cache-to-cache transfer latencies. 3971 3972 rcutree.rcu_fanout_leaf= [KNL] 3973 Change the number of CPUs assigned to each 3974 leaf rcu_node structure. Useful for very 3975 large systems, which will choose the value 64, 3976 and for NUMA systems with large remote-access 3977 latencies, which will choose a value aligned 3978 with the appropriate hardware boundaries. 3979 3980 rcutree.jiffies_till_first_fqs= [KNL] 3981 Set delay from grace-period initialization to 3982 first attempt to force quiescent states. 3983 Units are jiffies, minimum value is zero, 3984 and maximum value is HZ. 3985 3986 rcutree.jiffies_till_next_fqs= [KNL] 3987 Set delay between subsequent attempts to force 3988 quiescent states. Units are jiffies, minimum 3989 value is one, and maximum value is HZ. 3990 3991 rcutree.jiffies_till_sched_qs= [KNL] 3992 Set required age in jiffies for a 3993 given grace period before RCU starts 3994 soliciting quiescent-state help from 3995 rcu_note_context_switch() and cond_resched(). 3996 If not specified, the kernel will calculate 3997 a value based on the most recent settings 3998 of rcutree.jiffies_till_first_fqs 3999 and rcutree.jiffies_till_next_fqs. 4000 This calculated value may be viewed in 4001 rcutree.jiffies_to_sched_qs. Any attempt to set 4002 rcutree.jiffies_to_sched_qs will be cheerfully 4003 overwritten. 4004 4005 rcutree.kthread_prio= [KNL,BOOT] 4006 Set the SCHED_FIFO priority of the RCU per-CPU 4007 kthreads (rcuc/N). This value is also used for 4008 the priority of the RCU boost threads (rcub/N) 4009 and for the RCU grace-period kthreads (rcu_bh, 4010 rcu_preempt, and rcu_sched). If RCU_BOOST is 4011 set, valid values are 1-99 and the default is 1 4012 (the least-favored priority). Otherwise, when 4013 RCU_BOOST is not set, valid values are 0-99 and 4014 the default is zero (non-realtime operation). 4015 4016 rcutree.rcu_nocb_gp_stride= [KNL] 4017 Set the number of NOCB callback kthreads in 4018 each group, which defaults to the square root 4019 of the number of CPUs. Larger numbers reduce 4020 the wakeup overhead on the global grace-period 4021 kthread, but increases that same overhead on 4022 each group's NOCB grace-period kthread. 4023 4024 rcutree.qhimark= [KNL] 4025 Set threshold of queued RCU callbacks beyond which 4026 batch limiting is disabled. 4027 4028 rcutree.qlowmark= [KNL] 4029 Set threshold of queued RCU callbacks below which 4030 batch limiting is re-enabled. 4031 4032 rcutree.qovld= [KNL] 4033 Set threshold of queued RCU callbacks beyond which 4034 RCU's force-quiescent-state scan will aggressively 4035 enlist help from cond_resched() and sched IPIs to 4036 help CPUs more quickly reach quiescent states. 4037 Set to less than zero to make this be set based 4038 on rcutree.qhimark at boot time and to zero to 4039 disable more aggressive help enlistment. 4040 4041 rcutree.rcu_idle_gp_delay= [KNL] 4042 Set wakeup interval for idle CPUs that have 4043 RCU callbacks (RCU_FAST_NO_HZ=y). 4044 4045 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4046 Set wakeup interval for idle CPUs that have 4047 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4048 Lazy RCU callbacks are those which RCU can 4049 prove do nothing more than free memory. 4050 4051 rcutree.rcu_kick_kthreads= [KNL] 4052 Cause the grace-period kthread to get an extra 4053 wake_up() if it sleeps three times longer than 4054 it should at force-quiescent-state time. 4055 This wake_up() will be accompanied by a 4056 WARN_ONCE() splat and an ftrace_dump(). 4057 4058 rcutree.sysrq_rcu= [KNL] 4059 Commandeer a sysrq key to dump out Tree RCU's 4060 rcu_node tree with an eye towards determining 4061 why a new grace period has not yet started. 4062 4063 rcuperf.gp_async= [KNL] 4064 Measure performance of asynchronous 4065 grace-period primitives such as call_rcu(). 4066 4067 rcuperf.gp_async_max= [KNL] 4068 Specify the maximum number of outstanding 4069 callbacks per writer thread. When a writer 4070 thread exceeds this limit, it invokes the 4071 corresponding flavor of rcu_barrier() to allow 4072 previously posted callbacks to drain. 4073 4074 rcuperf.gp_exp= [KNL] 4075 Measure performance of expedited synchronous 4076 grace-period primitives. 4077 4078 rcuperf.holdoff= [KNL] 4079 Set test-start holdoff period. The purpose of 4080 this parameter is to delay the start of the 4081 test until boot completes in order to avoid 4082 interference. 4083 4084 rcuperf.kfree_rcu_test= [KNL] 4085 Set to measure performance of kfree_rcu() flooding. 4086 4087 rcuperf.kfree_nthreads= [KNL] 4088 The number of threads running loops of kfree_rcu(). 4089 4090 rcuperf.kfree_alloc_num= [KNL] 4091 Number of allocations and frees done in an iteration. 4092 4093 rcuperf.kfree_loops= [KNL] 4094 Number of loops doing rcuperf.kfree_alloc_num number 4095 of allocations and frees. 4096 4097 rcuperf.nreaders= [KNL] 4098 Set number of RCU readers. The value -1 selects 4099 N, where N is the number of CPUs. A value 4100 "n" less than -1 selects N-n+1, where N is again 4101 the number of CPUs. For example, -2 selects N 4102 (the number of CPUs), -3 selects N+1, and so on. 4103 A value of "n" less than or equal to -N selects 4104 a single reader. 4105 4106 rcuperf.nwriters= [KNL] 4107 Set number of RCU writers. The values operate 4108 the same as for rcuperf.nreaders. 4109 N, where N is the number of CPUs 4110 4111 rcuperf.perf_type= [KNL] 4112 Specify the RCU implementation to test. 4113 4114 rcuperf.shutdown= [KNL] 4115 Shut the system down after performance tests 4116 complete. This is useful for hands-off automated 4117 testing. 4118 4119 rcuperf.verbose= [KNL] 4120 Enable additional printk() statements. 4121 4122 rcuperf.writer_holdoff= [KNL] 4123 Write-side holdoff between grace periods, 4124 in microseconds. The default of zero says 4125 no holdoff. 4126 4127 rcutorture.fqs_duration= [KNL] 4128 Set duration of force_quiescent_state bursts 4129 in microseconds. 4130 4131 rcutorture.fqs_holdoff= [KNL] 4132 Set holdoff time within force_quiescent_state bursts 4133 in microseconds. 4134 4135 rcutorture.fqs_stutter= [KNL] 4136 Set wait time between force_quiescent_state bursts 4137 in seconds. 4138 4139 rcutorture.fwd_progress= [KNL] 4140 Enable RCU grace-period forward-progress testing 4141 for the types of RCU supporting this notion. 4142 4143 rcutorture.fwd_progress_div= [KNL] 4144 Specify the fraction of a CPU-stall-warning 4145 period to do tight-loop forward-progress testing. 4146 4147 rcutorture.fwd_progress_holdoff= [KNL] 4148 Number of seconds to wait between successive 4149 forward-progress tests. 4150 4151 rcutorture.fwd_progress_need_resched= [KNL] 4152 Enclose cond_resched() calls within checks for 4153 need_resched() during tight-loop forward-progress 4154 testing. 4155 4156 rcutorture.gp_cond= [KNL] 4157 Use conditional/asynchronous update-side 4158 primitives, if available. 4159 4160 rcutorture.gp_exp= [KNL] 4161 Use expedited update-side primitives, if available. 4162 4163 rcutorture.gp_normal= [KNL] 4164 Use normal (non-expedited) asynchronous 4165 update-side primitives, if available. 4166 4167 rcutorture.gp_sync= [KNL] 4168 Use normal (non-expedited) synchronous 4169 update-side primitives, if available. If all 4170 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4171 rcutorture.gp_normal=, and rcutorture.gp_sync= 4172 are zero, rcutorture acts as if is interpreted 4173 they are all non-zero. 4174 4175 rcutorture.n_barrier_cbs= [KNL] 4176 Set callbacks/threads for rcu_barrier() testing. 4177 4178 rcutorture.nfakewriters= [KNL] 4179 Set number of concurrent RCU writers. These just 4180 stress RCU, they don't participate in the actual 4181 test, hence the "fake". 4182 4183 rcutorture.nreaders= [KNL] 4184 Set number of RCU readers. The value -1 selects 4185 N-1, where N is the number of CPUs. A value 4186 "n" less than -1 selects N-n-2, where N is again 4187 the number of CPUs. For example, -2 selects N 4188 (the number of CPUs), -3 selects N+1, and so on. 4189 4190 rcutorture.object_debug= [KNL] 4191 Enable debug-object double-call_rcu() testing. 4192 4193 rcutorture.onoff_holdoff= [KNL] 4194 Set time (s) after boot for CPU-hotplug testing. 4195 4196 rcutorture.onoff_interval= [KNL] 4197 Set time (jiffies) between CPU-hotplug operations, 4198 or zero to disable CPU-hotplug testing. 4199 4200 rcutorture.shuffle_interval= [KNL] 4201 Set task-shuffle interval (s). Shuffling tasks 4202 allows some CPUs to go into dyntick-idle mode 4203 during the rcutorture test. 4204 4205 rcutorture.shutdown_secs= [KNL] 4206 Set time (s) after boot system shutdown. This 4207 is useful for hands-off automated testing. 4208 4209 rcutorture.stall_cpu= [KNL] 4210 Duration of CPU stall (s) to test RCU CPU stall 4211 warnings, zero to disable. 4212 4213 rcutorture.stall_cpu_holdoff= [KNL] 4214 Time to wait (s) after boot before inducing stall. 4215 4216 rcutorture.stall_cpu_irqsoff= [KNL] 4217 Disable interrupts while stalling if set. 4218 4219 rcutorture.stat_interval= [KNL] 4220 Time (s) between statistics printk()s. 4221 4222 rcutorture.stutter= [KNL] 4223 Time (s) to stutter testing, for example, specifying 4224 five seconds causes the test to run for five seconds, 4225 wait for five seconds, and so on. This tests RCU's 4226 ability to transition abruptly to and from idle. 4227 4228 rcutorture.test_boost= [KNL] 4229 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4230 "Maybe" means test if the RCU implementation 4231 under test support RCU priority boosting. 4232 4233 rcutorture.test_boost_duration= [KNL] 4234 Duration (s) of each individual boost test. 4235 4236 rcutorture.test_boost_interval= [KNL] 4237 Interval (s) between each boost test. 4238 4239 rcutorture.test_no_idle_hz= [KNL] 4240 Test RCU's dyntick-idle handling. See also the 4241 rcutorture.shuffle_interval parameter. 4242 4243 rcutorture.torture_type= [KNL] 4244 Specify the RCU implementation to test. 4245 4246 rcutorture.verbose= [KNL] 4247 Enable additional printk() statements. 4248 4249 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4250 Dump ftrace buffer after reporting RCU CPU 4251 stall warning. 4252 4253 rcupdate.rcu_cpu_stall_suppress= [KNL] 4254 Suppress RCU CPU stall warning messages. 4255 4256 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4257 Suppress RCU CPU stall warning messages and 4258 rcutorture writer stall warnings that occur 4259 during early boot, that is, during the time 4260 before the init task is spawned. 4261 4262 rcupdate.rcu_cpu_stall_timeout= [KNL] 4263 Set timeout for RCU CPU stall warning messages. 4264 4265 rcupdate.rcu_expedited= [KNL] 4266 Use expedited grace-period primitives, for 4267 example, synchronize_rcu_expedited() instead 4268 of synchronize_rcu(). This reduces latency, 4269 but can increase CPU utilization, degrade 4270 real-time latency, and degrade energy efficiency. 4271 No effect on CONFIG_TINY_RCU kernels. 4272 4273 rcupdate.rcu_normal= [KNL] 4274 Use only normal grace-period primitives, 4275 for example, synchronize_rcu() instead of 4276 synchronize_rcu_expedited(). This improves 4277 real-time latency, CPU utilization, and 4278 energy efficiency, but can expose users to 4279 increased grace-period latency. This parameter 4280 overrides rcupdate.rcu_expedited. No effect on 4281 CONFIG_TINY_RCU kernels. 4282 4283 rcupdate.rcu_normal_after_boot= [KNL] 4284 Once boot has completed (that is, after 4285 rcu_end_inkernel_boot() has been invoked), use 4286 only normal grace-period primitives. No effect 4287 on CONFIG_TINY_RCU kernels. 4288 4289 rcupdate.rcu_task_stall_timeout= [KNL] 4290 Set timeout in jiffies for RCU task stall warning 4291 messages. Disable with a value less than or equal 4292 to zero. 4293 4294 rcupdate.rcu_self_test= [KNL] 4295 Run the RCU early boot self tests 4296 4297 rdinit= [KNL] 4298 Format: <full_path> 4299 Run specified binary instead of /init from the ramdisk, 4300 used for early userspace startup. See initrd. 4301 4302 rdrand= [X86] 4303 force - Override the decision by the kernel to hide the 4304 advertisement of RDRAND support (this affects 4305 certain AMD processors because of buggy BIOS 4306 support, specifically around the suspend/resume 4307 path). 4308 4309 rdt= [HW,X86,RDT] 4310 Turn on/off individual RDT features. List is: 4311 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4312 mba. 4313 E.g. to turn on cmt and turn off mba use: 4314 rdt=cmt,!mba 4315 4316 reboot= [KNL] 4317 Format (x86 or x86_64): 4318 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4319 [[,]s[mp]#### \ 4320 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4321 [[,]f[orce] 4322 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4323 (prefix with 'panic_' to set mode for panic 4324 reboot only), 4325 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4326 reboot_force is either force or not specified, 4327 reboot_cpu is s[mp]#### with #### being the processor 4328 to be used for rebooting. 4329 4330 relax_domain_level= 4331 [KNL, SMP] Set scheduler's default relax_domain_level. 4332 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4333 4334 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4335 Format: <base1>,<size1>[,<base2>,<size2>,...] 4336 Reserve I/O ports or memory so the kernel won't use 4337 them. If <base> is less than 0x10000, the region 4338 is assumed to be I/O ports; otherwise it is memory. 4339 4340 reservetop= [X86-32] 4341 Format: nn[KMG] 4342 Reserves a hole at the top of the kernel virtual 4343 address space. 4344 4345 reservelow= [X86] 4346 Format: nn[K] 4347 Set the amount of memory to reserve for BIOS at 4348 the bottom of the address space. 4349 4350 reset_devices [KNL] Force drivers to reset the underlying device 4351 during initialization. 4352 4353 resume= [SWSUSP] 4354 Specify the partition device for software suspend 4355 Format: 4356 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4357 4358 resume_offset= [SWSUSP] 4359 Specify the offset from the beginning of the partition 4360 given by "resume=" at which the swap header is located, 4361 in <PAGE_SIZE> units (needed only for swap files). 4362 See Documentation/power/swsusp-and-swap-files.rst 4363 4364 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4365 read the resume files 4366 4367 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4368 Useful for devices that are detected asynchronously 4369 (e.g. USB and MMC devices). 4370 4371 hibernate= [HIBERNATION] 4372 noresume Don't check if there's a hibernation image 4373 present during boot. 4374 nocompress Don't compress/decompress hibernation images. 4375 no Disable hibernation and resume. 4376 protect_image Turn on image protection during restoration 4377 (that will set all pages holding image data 4378 during restoration read-only). 4379 4380 retain_initrd [RAM] Keep initrd memory after extraction 4381 4382 rfkill.default_state= 4383 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4384 etc. communication is blocked by default. 4385 1 Unblocked. 4386 4387 rfkill.master_switch_mode= 4388 0 The "airplane mode" button does nothing. 4389 1 The "airplane mode" button toggles between everything 4390 blocked and the previous configuration. 4391 2 The "airplane mode" button toggles between everything 4392 blocked and everything unblocked. 4393 4394 rhash_entries= [KNL,NET] 4395 Set number of hash buckets for route cache 4396 4397 ring3mwait=disable 4398 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4399 CPUs. 4400 4401 ro [KNL] Mount root device read-only on boot 4402 4403 rodata= [KNL] 4404 on Mark read-only kernel memory as read-only (default). 4405 off Leave read-only kernel memory writable for debugging. 4406 4407 rockchip.usb_uart 4408 Enable the uart passthrough on the designated usb port 4409 on Rockchip SoCs. When active, the signals of the 4410 debug-uart get routed to the D+ and D- pins of the usb 4411 port and the regular usb controller gets disabled. 4412 4413 root= [KNL] Root filesystem 4414 See name_to_dev_t comment in init/do_mounts.c. 4415 4416 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4417 mount the root filesystem 4418 4419 rootflags= [KNL] Set root filesystem mount option string 4420 4421 rootfstype= [KNL] Set root filesystem type 4422 4423 rootwait [KNL] Wait (indefinitely) for root device to show up. 4424 Useful for devices that are detected asynchronously 4425 (e.g. USB and MMC devices). 4426 4427 rproc_mem=nn[KMG][@address] 4428 [KNL,ARM,CMA] Remoteproc physical memory block. 4429 Memory area to be used by remote processor image, 4430 managed by CMA. 4431 4432 rw [KNL] Mount root device read-write on boot 4433 4434 S [KNL] Run init in single mode 4435 4436 s390_iommu= [HW,S390] 4437 Set s390 IOTLB flushing mode 4438 strict 4439 With strict flushing every unmap operation will result in 4440 an IOTLB flush. Default is lazy flushing before reuse, 4441 which is faster. 4442 4443 sa1100ir [NET] 4444 See drivers/net/irda/sa1100_ir.c. 4445 4446 sbni= [NET] Granch SBNI12 leased line adapter 4447 4448 sched_debug [KNL] Enables verbose scheduler debug messages. 4449 4450 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4451 Allowed values are enable and disable. This feature 4452 incurs a small amount of overhead in the scheduler 4453 but is useful for debugging and performance tuning. 4454 4455 sched_thermal_decay_shift= 4456 [KNL, SMP] Set a decay shift for scheduler thermal 4457 pressure signal. Thermal pressure signal follows the 4458 default decay period of other scheduler pelt 4459 signals(usually 32 ms but configurable). Setting 4460 sched_thermal_decay_shift will left shift the decay 4461 period for the thermal pressure signal by the shift 4462 value. 4463 i.e. with the default pelt decay period of 32 ms 4464 sched_thermal_decay_shift thermal pressure decay pr 4465 1 64 ms 4466 2 128 ms 4467 and so on. 4468 Format: integer between 0 and 10 4469 Default is 0. 4470 4471 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4472 xtime_lock contention on larger systems, and/or RCU lock 4473 contention on all systems with CONFIG_MAXSMP set. 4474 Format: { "0" | "1" } 4475 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4476 1 -- enable. 4477 Note: increases power consumption, thus should only be 4478 enabled if running jitter sensitive (HPC/RT) workloads. 4479 4480 security= [SECURITY] Choose a legacy "major" security module to 4481 enable at boot. This has been deprecated by the 4482 "lsm=" parameter. 4483 4484 selinux= [SELINUX] Disable or enable SELinux at boot time. 4485 Format: { "0" | "1" } 4486 See security/selinux/Kconfig help text. 4487 0 -- disable. 4488 1 -- enable. 4489 Default value is 1. 4490 4491 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4492 Format: { "0" | "1" } 4493 See security/apparmor/Kconfig help text 4494 0 -- disable. 4495 1 -- enable. 4496 Default value is set via kernel config option. 4497 4498 serialnumber [BUGS=X86-32] 4499 4500 shapers= [NET] 4501 Maximal number of shapers. 4502 4503 simeth= [IA-64] 4504 simscsi= 4505 4506 slram= [HW,MTD] 4507 4508 slab_nomerge [MM] 4509 Disable merging of slabs with similar size. May be 4510 necessary if there is some reason to distinguish 4511 allocs to different slabs, especially in hardened 4512 environments where the risk of heap overflows and 4513 layout control by attackers can usually be 4514 frustrated by disabling merging. This will reduce 4515 most of the exposure of a heap attack to a single 4516 cache (risks via metadata attacks are mostly 4517 unchanged). Debug options disable merging on their 4518 own. 4519 For more information see Documentation/vm/slub.rst. 4520 4521 slab_max_order= [MM, SLAB] 4522 Determines the maximum allowed order for slabs. 4523 A high setting may cause OOMs due to memory 4524 fragmentation. Defaults to 1 for systems with 4525 more than 32MB of RAM, 0 otherwise. 4526 4527 slub_debug[=options[,slabs]] [MM, SLUB] 4528 Enabling slub_debug allows one to determine the 4529 culprit if slab objects become corrupted. Enabling 4530 slub_debug can create guard zones around objects and 4531 may poison objects when not in use. Also tracks the 4532 last alloc / free. For more information see 4533 Documentation/vm/slub.rst. 4534 4535 slub_memcg_sysfs= [MM, SLUB] 4536 Determines whether to enable sysfs directories for 4537 memory cgroup sub-caches. 1 to enable, 0 to disable. 4538 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4539 Enabling this can lead to a very high number of debug 4540 directories and files being created under 4541 /sys/kernel/slub. 4542 4543 slub_max_order= [MM, SLUB] 4544 Determines the maximum allowed order for slabs. 4545 A high setting may cause OOMs due to memory 4546 fragmentation. For more information see 4547 Documentation/vm/slub.rst. 4548 4549 slub_min_objects= [MM, SLUB] 4550 The minimum number of objects per slab. SLUB will 4551 increase the slab order up to slub_max_order to 4552 generate a sufficiently large slab able to contain 4553 the number of objects indicated. The higher the number 4554 of objects the smaller the overhead of tracking slabs 4555 and the less frequently locks need to be acquired. 4556 For more information see Documentation/vm/slub.rst. 4557 4558 slub_min_order= [MM, SLUB] 4559 Determines the minimum page order for slabs. Must be 4560 lower than slub_max_order. 4561 For more information see Documentation/vm/slub.rst. 4562 4563 slub_nomerge [MM, SLUB] 4564 Same with slab_nomerge. This is supported for legacy. 4565 See slab_nomerge for more information. 4566 4567 smart2= [HW] 4568 Format: <io1>[,<io2>[,...,<io8>]] 4569 4570 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4571 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4572 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4573 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4574 smsc-ircc2.ircc_irq= [HW] IRQ line 4575 smsc-ircc2.ircc_dma= [HW] DMA channel 4576 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4577 0: Toshiba Satellite 1800 (GP data pin select) 4578 1: Fast pin select (default) 4579 2: ATC IRMode 4580 4581 smt [KNL,S390] Set the maximum number of threads (logical 4582 CPUs) to use per physical CPU on systems capable of 4583 symmetric multithreading (SMT). Will be capped to the 4584 actual hardware limit. 4585 Format: <integer> 4586 Default: -1 (no limit) 4587 4588 softlockup_panic= 4589 [KNL] Should the soft-lockup detector generate panics. 4590 Format: <integer> 4591 4592 A nonzero value instructs the soft-lockup detector 4593 to panic the machine when a soft-lockup occurs. It is 4594 also controlled by the kernel.softlockup_panic sysctl 4595 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4596 respective build-time switch to that functionality. 4597 4598 softlockup_all_cpu_backtrace= 4599 [KNL] Should the soft-lockup detector generate 4600 backtraces on all cpus. 4601 Format: <integer> 4602 4603 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4604 See Documentation/admin-guide/laptops/sonypi.rst 4605 4606 spectre_v2= [X86] Control mitigation of Spectre variant 2 4607 (indirect branch speculation) vulnerability. 4608 The default operation protects the kernel from 4609 user space attacks. 4610 4611 on - unconditionally enable, implies 4612 spectre_v2_user=on 4613 off - unconditionally disable, implies 4614 spectre_v2_user=off 4615 auto - kernel detects whether your CPU model is 4616 vulnerable 4617 4618 Selecting 'on' will, and 'auto' may, choose a 4619 mitigation method at run time according to the 4620 CPU, the available microcode, the setting of the 4621 CONFIG_RETPOLINE configuration option, and the 4622 compiler with which the kernel was built. 4623 4624 Selecting 'on' will also enable the mitigation 4625 against user space to user space task attacks. 4626 4627 Selecting 'off' will disable both the kernel and 4628 the user space protections. 4629 4630 Specific mitigations can also be selected manually: 4631 4632 retpoline - replace indirect branches 4633 retpoline,generic - google's original retpoline 4634 retpoline,amd - AMD-specific minimal thunk 4635 4636 Not specifying this option is equivalent to 4637 spectre_v2=auto. 4638 4639 spectre_v2_user= 4640 [X86] Control mitigation of Spectre variant 2 4641 (indirect branch speculation) vulnerability between 4642 user space tasks 4643 4644 on - Unconditionally enable mitigations. Is 4645 enforced by spectre_v2=on 4646 4647 off - Unconditionally disable mitigations. Is 4648 enforced by spectre_v2=off 4649 4650 prctl - Indirect branch speculation is enabled, 4651 but mitigation can be enabled via prctl 4652 per thread. The mitigation control state 4653 is inherited on fork. 4654 4655 prctl,ibpb 4656 - Like "prctl" above, but only STIBP is 4657 controlled per thread. IBPB is issued 4658 always when switching between different user 4659 space processes. 4660 4661 seccomp 4662 - Same as "prctl" above, but all seccomp 4663 threads will enable the mitigation unless 4664 they explicitly opt out. 4665 4666 seccomp,ibpb 4667 - Like "seccomp" above, but only STIBP is 4668 controlled per thread. IBPB is issued 4669 always when switching between different 4670 user space processes. 4671 4672 auto - Kernel selects the mitigation depending on 4673 the available CPU features and vulnerability. 4674 4675 Default mitigation: 4676 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4677 4678 Not specifying this option is equivalent to 4679 spectre_v2_user=auto. 4680 4681 spec_store_bypass_disable= 4682 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4683 (Speculative Store Bypass vulnerability) 4684 4685 Certain CPUs are vulnerable to an exploit against a 4686 a common industry wide performance optimization known 4687 as "Speculative Store Bypass" in which recent stores 4688 to the same memory location may not be observed by 4689 later loads during speculative execution. The idea 4690 is that such stores are unlikely and that they can 4691 be detected prior to instruction retirement at the 4692 end of a particular speculation execution window. 4693 4694 In vulnerable processors, the speculatively forwarded 4695 store can be used in a cache side channel attack, for 4696 example to read memory to which the attacker does not 4697 directly have access (e.g. inside sandboxed code). 4698 4699 This parameter controls whether the Speculative Store 4700 Bypass optimization is used. 4701 4702 On x86 the options are: 4703 4704 on - Unconditionally disable Speculative Store Bypass 4705 off - Unconditionally enable Speculative Store Bypass 4706 auto - Kernel detects whether the CPU model contains an 4707 implementation of Speculative Store Bypass and 4708 picks the most appropriate mitigation. If the 4709 CPU is not vulnerable, "off" is selected. If the 4710 CPU is vulnerable the default mitigation is 4711 architecture and Kconfig dependent. See below. 4712 prctl - Control Speculative Store Bypass per thread 4713 via prctl. Speculative Store Bypass is enabled 4714 for a process by default. The state of the control 4715 is inherited on fork. 4716 seccomp - Same as "prctl" above, but all seccomp threads 4717 will disable SSB unless they explicitly opt out. 4718 4719 Default mitigations: 4720 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4721 4722 On powerpc the options are: 4723 4724 on,auto - On Power8 and Power9 insert a store-forwarding 4725 barrier on kernel entry and exit. On Power7 4726 perform a software flush on kernel entry and 4727 exit. 4728 off - No action. 4729 4730 Not specifying this option is equivalent to 4731 spec_store_bypass_disable=auto. 4732 4733 spia_io_base= [HW,MTD] 4734 spia_fio_base= 4735 spia_pedr= 4736 spia_peddr= 4737 4738 split_lock_detect= 4739 [X86] Enable split lock detection 4740 4741 When enabled (and if hardware support is present), atomic 4742 instructions that access data across cache line 4743 boundaries will result in an alignment check exception. 4744 4745 off - not enabled 4746 4747 warn - the kernel will emit rate limited warnings 4748 about applications triggering the #AC 4749 exception. This mode is the default on CPUs 4750 that supports split lock detection. 4751 4752 fatal - the kernel will send SIGBUS to applications 4753 that trigger the #AC exception. 4754 4755 If an #AC exception is hit in the kernel or in 4756 firmware (i.e. not while executing in user mode) 4757 the kernel will oops in either "warn" or "fatal" 4758 mode. 4759 4760 srcutree.counter_wrap_check [KNL] 4761 Specifies how frequently to check for 4762 grace-period sequence counter wrap for the 4763 srcu_data structure's ->srcu_gp_seq_needed field. 4764 The greater the number of bits set in this kernel 4765 parameter, the less frequently counter wrap will 4766 be checked for. Note that the bottom two bits 4767 are ignored. 4768 4769 srcutree.exp_holdoff [KNL] 4770 Specifies how many nanoseconds must elapse 4771 since the end of the last SRCU grace period for 4772 a given srcu_struct until the next normal SRCU 4773 grace period will be considered for automatic 4774 expediting. Set to zero to disable automatic 4775 expediting. 4776 4777 ssbd= [ARM64,HW] 4778 Speculative Store Bypass Disable control 4779 4780 On CPUs that are vulnerable to the Speculative 4781 Store Bypass vulnerability and offer a 4782 firmware based mitigation, this parameter 4783 indicates how the mitigation should be used: 4784 4785 force-on: Unconditionally enable mitigation for 4786 for both kernel and userspace 4787 force-off: Unconditionally disable mitigation for 4788 for both kernel and userspace 4789 kernel: Always enable mitigation in the 4790 kernel, and offer a prctl interface 4791 to allow userspace to register its 4792 interest in being mitigated too. 4793 4794 stack_guard_gap= [MM] 4795 override the default stack gap protection. The value 4796 is in page units and it defines how many pages prior 4797 to (for stacks growing down) resp. after (for stacks 4798 growing up) the main stack are reserved for no other 4799 mapping. Default value is 256 pages. 4800 4801 stacktrace [FTRACE] 4802 Enabled the stack tracer on boot up. 4803 4804 stacktrace_filter=[function-list] 4805 [FTRACE] Limit the functions that the stack tracer 4806 will trace at boot up. function-list is a comma separated 4807 list of functions. This list can be changed at run 4808 time by the stack_trace_filter file in the debugfs 4809 tracing directory. Note, this enables stack tracing 4810 and the stacktrace above is not needed. 4811 4812 sti= [PARISC,HW] 4813 Format: <num> 4814 Set the STI (builtin display/keyboard on the HP-PARISC 4815 machines) console (graphic card) which should be used 4816 as the initial boot-console. 4817 See also comment in drivers/video/console/sticore.c. 4818 4819 sti_font= [HW] 4820 See comment in drivers/video/console/sticore.c. 4821 4822 stifb= [HW] 4823 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4824 4825 sunrpc.min_resvport= 4826 sunrpc.max_resvport= 4827 [NFS,SUNRPC] 4828 SunRPC servers often require that client requests 4829 originate from a privileged port (i.e. a port in the 4830 range 0 < portnr < 1024). 4831 An administrator who wishes to reserve some of these 4832 ports for other uses may adjust the range that the 4833 kernel's sunrpc client considers to be privileged 4834 using these two parameters to set the minimum and 4835 maximum port values. 4836 4837 sunrpc.svc_rpc_per_connection_limit= 4838 [NFS,SUNRPC] 4839 Limit the number of requests that the server will 4840 process in parallel from a single connection. 4841 The default value is 0 (no limit). 4842 4843 sunrpc.pool_mode= 4844 [NFS] 4845 Control how the NFS server code allocates CPUs to 4846 service thread pools. Depending on how many NICs 4847 you have and where their interrupts are bound, this 4848 option will affect which CPUs will do NFS serving. 4849 Note: this parameter cannot be changed while the 4850 NFS server is running. 4851 4852 auto the server chooses an appropriate mode 4853 automatically using heuristics 4854 global a single global pool contains all CPUs 4855 percpu one pool for each CPU 4856 pernode one pool for each NUMA node (equivalent 4857 to global on non-NUMA machines) 4858 4859 sunrpc.tcp_slot_table_entries= 4860 sunrpc.udp_slot_table_entries= 4861 [NFS,SUNRPC] 4862 Sets the upper limit on the number of simultaneous 4863 RPC calls that can be sent from the client to a 4864 server. Increasing these values may allow you to 4865 improve throughput, but will also increase the 4866 amount of memory reserved for use by the client. 4867 4868 suspend.pm_test_delay= 4869 [SUSPEND] 4870 Sets the number of seconds to remain in a suspend test 4871 mode before resuming the system (see 4872 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4873 is set. Default value is 5. 4874 4875 svm= [PPC] 4876 Format: { on | off | y | n | 1 | 0 } 4877 This parameter controls use of the Protected 4878 Execution Facility on pSeries. 4879 4880 swapaccount=[0|1] 4881 [KNL] Enable accounting of swap in memory resource 4882 controller if no parameter or 1 is given or disable 4883 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4884 4885 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4886 Format: { <int> | force | noforce } 4887 <int> -- Number of I/O TLB slabs 4888 force -- force using of bounce buffers even if they 4889 wouldn't be automatically used by the kernel 4890 noforce -- Never use bounce buffers (for debugging) 4891 4892 switches= [HW,M68k] 4893 4894 sysfs.deprecated=0|1 [KNL] 4895 Enable/disable old style sysfs layout for old udev 4896 on older distributions. When this option is enabled 4897 very new udev will not work anymore. When this option 4898 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4899 in older udev will not work anymore. 4900 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4901 the kernel configuration. 4902 4903 sysrq_always_enabled 4904 [KNL] 4905 Ignore sysrq setting - this boot parameter will 4906 neutralize any effect of /proc/sys/kernel/sysrq. 4907 Useful for debugging. 4908 4909 tcpmhash_entries= [KNL,NET] 4910 Set the number of tcp_metrics_hash slots. 4911 Default value is 8192 or 16384 depending on total 4912 ram pages. This is used to specify the TCP metrics 4913 cache size. See Documentation/networking/ip-sysctl.txt 4914 "tcp_no_metrics_save" section for more details. 4915 4916 tdfx= [HW,DRM] 4917 4918 test_suspend= [SUSPEND][,N] 4919 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4920 standby suspend) or "freeze" (for suspend type freeze) 4921 as the system sleep state during system startup with 4922 the optional capability to repeat N number of times. 4923 The system is woken from this state using a 4924 wakeup-capable RTC alarm. 4925 4926 thash_entries= [KNL,NET] 4927 Set number of hash buckets for TCP connection 4928 4929 thermal.act= [HW,ACPI] 4930 -1: disable all active trip points in all thermal zones 4931 <degrees C>: override all lowest active trip points 4932 4933 thermal.crt= [HW,ACPI] 4934 -1: disable all critical trip points in all thermal zones 4935 <degrees C>: override all critical trip points 4936 4937 thermal.nocrt= [HW,ACPI] 4938 Set to disable actions on ACPI thermal zone 4939 critical and hot trip points. 4940 4941 thermal.off= [HW,ACPI] 4942 1: disable ACPI thermal control 4943 4944 thermal.psv= [HW,ACPI] 4945 -1: disable all passive trip points 4946 <degrees C>: override all passive trip points to this 4947 value 4948 4949 thermal.tzp= [HW,ACPI] 4950 Specify global default ACPI thermal zone polling rate 4951 <deci-seconds>: poll all this frequency 4952 0: no polling (default) 4953 4954 threadirqs [KNL] 4955 Force threading of all interrupt handlers except those 4956 marked explicitly IRQF_NO_THREAD. 4957 4958 topology= [S390] 4959 Format: {off | on} 4960 Specify if the kernel should make use of the cpu 4961 topology information if the hardware supports this. 4962 The scheduler will make use of this information and 4963 e.g. base its process migration decisions on it. 4964 Default is on. 4965 4966 topology_updates= [KNL, PPC, NUMA] 4967 Format: {off} 4968 Specify if the kernel should ignore (off) 4969 topology updates sent by the hypervisor to this 4970 LPAR. 4971 4972 torture.disable_onoff_at_boot= [KNL] 4973 Prevent the CPU-hotplug component of torturing 4974 until after init has spawned. 4975 4976 tp720= [HW,PS2] 4977 4978 tpm_suspend_pcr=[HW,TPM] 4979 Format: integer pcr id 4980 Specify that at suspend time, the tpm driver 4981 should extend the specified pcr with zeros, 4982 as a workaround for some chips which fail to 4983 flush the last written pcr on TPM_SaveState. 4984 This will guarantee that all the other pcrs 4985 are saved. 4986 4987 trace_buf_size=nn[KMG] 4988 [FTRACE] will set tracing buffer size on each cpu. 4989 4990 trace_event=[event-list] 4991 [FTRACE] Set and start specified trace events in order 4992 to facilitate early boot debugging. The event-list is a 4993 comma separated list of trace events to enable. See 4994 also Documentation/trace/events.rst 4995 4996 trace_options=[option-list] 4997 [FTRACE] Enable or disable tracer options at boot. 4998 The option-list is a comma delimited list of options 4999 that can be enabled or disabled just as if you were 5000 to echo the option name into 5001 5002 /sys/kernel/debug/tracing/trace_options 5003 5004 For example, to enable stacktrace option (to dump the 5005 stack trace of each event), add to the command line: 5006 5007 trace_options=stacktrace 5008 5009 See also Documentation/trace/ftrace.rst "trace options" 5010 section. 5011 5012 tp_printk[FTRACE] 5013 Have the tracepoints sent to printk as well as the 5014 tracing ring buffer. This is useful for early boot up 5015 where the system hangs or reboots and does not give the 5016 option for reading the tracing buffer or performing a 5017 ftrace_dump_on_oops. 5018 5019 To turn off having tracepoints sent to printk, 5020 echo 0 > /proc/sys/kernel/tracepoint_printk 5021 Note, echoing 1 into this file without the 5022 tracepoint_printk kernel cmdline option has no effect. 5023 5024 ** CAUTION ** 5025 5026 Having tracepoints sent to printk() and activating high 5027 frequency tracepoints such as irq or sched, can cause 5028 the system to live lock. 5029 5030 traceoff_on_warning 5031 [FTRACE] enable this option to disable tracing when a 5032 warning is hit. This turns off "tracing_on". Tracing can 5033 be enabled again by echoing '1' into the "tracing_on" 5034 file located in /sys/kernel/debug/tracing/ 5035 5036 This option is useful, as it disables the trace before 5037 the WARNING dump is called, which prevents the trace to 5038 be filled with content caused by the warning output. 5039 5040 This option can also be set at run time via the sysctl 5041 option: kernel/traceoff_on_warning 5042 5043 transparent_hugepage= 5044 [KNL] 5045 Format: [always|madvise|never] 5046 Can be used to control the default behavior of the system 5047 with respect to transparent hugepages. 5048 See Documentation/admin-guide/mm/transhuge.rst 5049 for more details. 5050 5051 tsc= Disable clocksource stability checks for TSC. 5052 Format: <string> 5053 [x86] reliable: mark tsc clocksource as reliable, this 5054 disables clocksource verification at runtime, as well 5055 as the stability checks done at bootup. Used to enable 5056 high-resolution timer mode on older hardware, and in 5057 virtualized environment. 5058 [x86] noirqtime: Do not use TSC to do irq accounting. 5059 Used to run time disable IRQ_TIME_ACCOUNTING on any 5060 platforms where RDTSC is slow and this accounting 5061 can add overhead. 5062 [x86] unstable: mark the TSC clocksource as unstable, this 5063 marks the TSC unconditionally unstable at bootup and 5064 avoids any further wobbles once the TSC watchdog notices. 5065 [x86] nowatchdog: disable clocksource watchdog. Used 5066 in situations with strict latency requirements (where 5067 interruptions from clocksource watchdog are not 5068 acceptable). 5069 5070 tsx= [X86] Control Transactional Synchronization 5071 Extensions (TSX) feature in Intel processors that 5072 support TSX control. 5073 5074 This parameter controls the TSX feature. The options are: 5075 5076 on - Enable TSX on the system. Although there are 5077 mitigations for all known security vulnerabilities, 5078 TSX has been known to be an accelerator for 5079 several previous speculation-related CVEs, and 5080 so there may be unknown security risks associated 5081 with leaving it enabled. 5082 5083 off - Disable TSX on the system. (Note that this 5084 option takes effect only on newer CPUs which are 5085 not vulnerable to MDS, i.e., have 5086 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5087 the new IA32_TSX_CTRL MSR through a microcode 5088 update. This new MSR allows for the reliable 5089 deactivation of the TSX functionality.) 5090 5091 auto - Disable TSX if X86_BUG_TAA is present, 5092 otherwise enable TSX on the system. 5093 5094 Not specifying this option is equivalent to tsx=off. 5095 5096 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5097 for more details. 5098 5099 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5100 Abort (TAA) vulnerability. 5101 5102 Similar to Micro-architectural Data Sampling (MDS) 5103 certain CPUs that support Transactional 5104 Synchronization Extensions (TSX) are vulnerable to an 5105 exploit against CPU internal buffers which can forward 5106 information to a disclosure gadget under certain 5107 conditions. 5108 5109 In vulnerable processors, the speculatively forwarded 5110 data can be used in a cache side channel attack, to 5111 access data to which the attacker does not have direct 5112 access. 5113 5114 This parameter controls the TAA mitigation. The 5115 options are: 5116 5117 full - Enable TAA mitigation on vulnerable CPUs 5118 if TSX is enabled. 5119 5120 full,nosmt - Enable TAA mitigation and disable SMT on 5121 vulnerable CPUs. If TSX is disabled, SMT 5122 is not disabled because CPU is not 5123 vulnerable to cross-thread TAA attacks. 5124 off - Unconditionally disable TAA mitigation 5125 5126 On MDS-affected machines, tsx_async_abort=off can be 5127 prevented by an active MDS mitigation as both vulnerabilities 5128 are mitigated with the same mechanism so in order to disable 5129 this mitigation, you need to specify mds=off too. 5130 5131 Not specifying this option is equivalent to 5132 tsx_async_abort=full. On CPUs which are MDS affected 5133 and deploy MDS mitigation, TAA mitigation is not 5134 required and doesn't provide any additional 5135 mitigation. 5136 5137 For details see: 5138 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5139 5140 turbografx.map[2|3]= [HW,JOY] 5141 TurboGraFX parallel port interface 5142 Format: 5143 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5144 See also Documentation/input/devices/joystick-parport.rst 5145 5146 udbg-immortal [PPC] When debugging early kernel crashes that 5147 happen after console_init() and before a proper 5148 console driver takes over, this boot options might 5149 help "seeing" what's going on. 5150 5151 uhash_entries= [KNL,NET] 5152 Set number of hash buckets for UDP/UDP-Lite connections 5153 5154 uhci-hcd.ignore_oc= 5155 [USB] Ignore overcurrent events (default N). 5156 Some badly-designed motherboards generate lots of 5157 bogus events, for ports that aren't wired to 5158 anything. Set this parameter to avoid log spamming. 5159 Note that genuine overcurrent events won't be 5160 reported either. 5161 5162 unknown_nmi_panic 5163 [X86] Cause panic on unknown NMI. 5164 5165 usbcore.authorized_default= 5166 [USB] Default USB device authorization: 5167 (default -1 = authorized except for wireless USB, 5168 0 = not authorized, 1 = authorized, 2 = authorized 5169 if device connected to internal port) 5170 5171 usbcore.autosuspend= 5172 [USB] The autosuspend time delay (in seconds) used 5173 for newly-detected USB devices (default 2). This 5174 is the time required before an idle device will be 5175 autosuspended. Devices for which the delay is set 5176 to a negative value won't be autosuspended at all. 5177 5178 usbcore.usbfs_snoop= 5179 [USB] Set to log all usbfs traffic (default 0 = off). 5180 5181 usbcore.usbfs_snoop_max= 5182 [USB] Maximum number of bytes to snoop in each URB 5183 (default = 65536). 5184 5185 usbcore.blinkenlights= 5186 [USB] Set to cycle leds on hubs (default 0 = off). 5187 5188 usbcore.old_scheme_first= 5189 [USB] Start with the old device initialization 5190 scheme, applies only to low and full-speed devices 5191 (default 0 = off). 5192 5193 usbcore.usbfs_memory_mb= 5194 [USB] Memory limit (in MB) for buffers allocated by 5195 usbfs (default = 16, 0 = max = 2047). 5196 5197 usbcore.use_both_schemes= 5198 [USB] Try the other device initialization scheme 5199 if the first one fails (default 1 = enabled). 5200 5201 usbcore.initial_descriptor_timeout= 5202 [USB] Specifies timeout for the initial 64-byte 5203 USB_REQ_GET_DESCRIPTOR request in milliseconds 5204 (default 5000 = 5.0 seconds). 5205 5206 usbcore.nousb [USB] Disable the USB subsystem 5207 5208 usbcore.quirks= 5209 [USB] A list of quirk entries to augment the built-in 5210 usb core quirk list. List entries are separated by 5211 commas. Each entry has the form 5212 VendorID:ProductID:Flags. The IDs are 4-digit hex 5213 numbers and Flags is a set of letters. Each letter 5214 will change the built-in quirk; setting it if it is 5215 clear and clearing it if it is set. The letters have 5216 the following meanings: 5217 a = USB_QUIRK_STRING_FETCH_255 (string 5218 descriptors must not be fetched using 5219 a 255-byte read); 5220 b = USB_QUIRK_RESET_RESUME (device can't resume 5221 correctly so reset it instead); 5222 c = USB_QUIRK_NO_SET_INTF (device can't handle 5223 Set-Interface requests); 5224 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5225 handle its Configuration or Interface 5226 strings); 5227 e = USB_QUIRK_RESET (device can't be reset 5228 (e.g morph devices), don't use reset); 5229 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5230 more interface descriptions than the 5231 bNumInterfaces count, and can't handle 5232 talking to these interfaces); 5233 g = USB_QUIRK_DELAY_INIT (device needs a pause 5234 during initialization, after we read 5235 the device descriptor); 5236 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5237 high speed and super speed interrupt 5238 endpoints, the USB 2.0 and USB 3.0 spec 5239 require the interval in microframes (1 5240 microframe = 125 microseconds) to be 5241 calculated as interval = 2 ^ 5242 (bInterval-1). 5243 Devices with this quirk report their 5244 bInterval as the result of this 5245 calculation instead of the exponent 5246 variable used in the calculation); 5247 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5248 handle device_qualifier descriptor 5249 requests); 5250 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5251 generates spurious wakeup, ignore 5252 remote wakeup capability); 5253 k = USB_QUIRK_NO_LPM (device can't handle Link 5254 Power Management); 5255 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5256 (Device reports its bInterval as linear 5257 frames instead of the USB 2.0 5258 calculation); 5259 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5260 to be disconnected before suspend to 5261 prevent spurious wakeup); 5262 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5263 pause after every control message); 5264 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5265 delay after resetting its port); 5266 Example: quirks=0781:5580:bk,0a5c:5834:gij 5267 5268 usbhid.mousepoll= 5269 [USBHID] The interval which mice are to be polled at. 5270 5271 usbhid.jspoll= 5272 [USBHID] The interval which joysticks are to be polled at. 5273 5274 usbhid.kbpoll= 5275 [USBHID] The interval which keyboards are to be polled at. 5276 5277 usb-storage.delay_use= 5278 [UMS] The delay in seconds before a new device is 5279 scanned for Logical Units (default 1). 5280 5281 usb-storage.quirks= 5282 [UMS] A list of quirks entries to supplement or 5283 override the built-in unusual_devs list. List 5284 entries are separated by commas. Each entry has 5285 the form VID:PID:Flags where VID and PID are Vendor 5286 and Product ID values (4-digit hex numbers) and 5287 Flags is a set of characters, each corresponding 5288 to a common usb-storage quirk flag as follows: 5289 a = SANE_SENSE (collect more than 18 bytes 5290 of sense data, not on uas); 5291 b = BAD_SENSE (don't collect more than 18 5292 bytes of sense data, not on uas); 5293 c = FIX_CAPACITY (decrease the reported 5294 device capacity by one sector); 5295 d = NO_READ_DISC_INFO (don't use 5296 READ_DISC_INFO command, not on uas); 5297 e = NO_READ_CAPACITY_16 (don't use 5298 READ_CAPACITY_16 command); 5299 f = NO_REPORT_OPCODES (don't use report opcodes 5300 command, uas only); 5301 g = MAX_SECTORS_240 (don't transfer more than 5302 240 sectors at a time, uas only); 5303 h = CAPACITY_HEURISTICS (decrease the 5304 reported device capacity by one 5305 sector if the number is odd); 5306 i = IGNORE_DEVICE (don't bind to this 5307 device); 5308 j = NO_REPORT_LUNS (don't use report luns 5309 command, uas only); 5310 l = NOT_LOCKABLE (don't try to lock and 5311 unlock ejectable media, not on uas); 5312 m = MAX_SECTORS_64 (don't transfer more 5313 than 64 sectors = 32 KB at a time, 5314 not on uas); 5315 n = INITIAL_READ10 (force a retry of the 5316 initial READ(10) command, not on uas); 5317 o = CAPACITY_OK (accept the capacity 5318 reported by the device, not on uas); 5319 p = WRITE_CACHE (the device cache is ON 5320 by default, not on uas); 5321 r = IGNORE_RESIDUE (the device reports 5322 bogus residue values, not on uas); 5323 s = SINGLE_LUN (the device has only one 5324 Logical Unit); 5325 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5326 commands, uas only); 5327 u = IGNORE_UAS (don't bind to the uas driver); 5328 w = NO_WP_DETECT (don't test whether the 5329 medium is write-protected). 5330 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5331 even if the device claims no cache, 5332 not on uas) 5333 Example: quirks=0419:aaf5:rl,0421:0433:rc 5334 5335 user_debug= [KNL,ARM] 5336 Format: <int> 5337 See arch/arm/Kconfig.debug help text. 5338 1 - undefined instruction events 5339 2 - system calls 5340 4 - invalid data aborts 5341 8 - SIGSEGV faults 5342 16 - SIGBUS faults 5343 Example: user_debug=31 5344 5345 userpte= 5346 [X86] Flags controlling user PTE allocations. 5347 5348 nohigh = do not allocate PTE pages in 5349 HIGHMEM regardless of setting 5350 of CONFIG_HIGHPTE. 5351 5352 vdso= [X86,SH] 5353 On X86_32, this is an alias for vdso32=. Otherwise: 5354 5355 vdso=1: enable VDSO (the default) 5356 vdso=0: disable VDSO mapping 5357 5358 vdso32= [X86] Control the 32-bit vDSO 5359 vdso32=1: enable 32-bit VDSO 5360 vdso32=0 or vdso32=2: disable 32-bit VDSO 5361 5362 See the help text for CONFIG_COMPAT_VDSO for more 5363 details. If CONFIG_COMPAT_VDSO is set, the default is 5364 vdso32=0; otherwise, the default is vdso32=1. 5365 5366 For compatibility with older kernels, vdso32=2 is an 5367 alias for vdso32=0. 5368 5369 Try vdso32=0 if you encounter an error that says: 5370 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5371 5372 vector= [IA-64,SMP] 5373 vector=percpu: enable percpu vector domain 5374 5375 video= [FB] Frame buffer configuration 5376 See Documentation/fb/modedb.rst. 5377 5378 video.brightness_switch_enabled= [0,1] 5379 If set to 1, on receiving an ACPI notify event 5380 generated by hotkey, video driver will adjust brightness 5381 level and then send out the event to user space through 5382 the allocated input device; If set to 0, video driver 5383 will only send out the event without touching backlight 5384 brightness level. 5385 default: 1 5386 5387 virtio_mmio.device= 5388 [VMMIO] Memory mapped virtio (platform) device. 5389 5390 <size>@<baseaddr>:<irq>[:<id>] 5391 where: 5392 <size> := size (can use standard suffixes 5393 like K, M and G) 5394 <baseaddr> := physical base address 5395 <irq> := interrupt number (as passed to 5396 request_irq()) 5397 <id> := (optional) platform device id 5398 example: 5399 virtio_mmio.device=1K@0x100b0000:48:7 5400 5401 Can be used multiple times for multiple devices. 5402 5403 vga= [BOOT,X86-32] Select a particular video mode 5404 See Documentation/x86/boot.rst and 5405 Documentation/admin-guide/svga.rst. 5406 Use vga=ask for menu. 5407 This is actually a boot loader parameter; the value is 5408 passed to the kernel using a special protocol. 5409 5410 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5411 May slow down system boot speed, especially when 5412 enabled on systems with a large amount of memory. 5413 All options are enabled by default, and this 5414 interface is meant to allow for selectively 5415 enabling or disabling specific virtual memory 5416 debugging features. 5417 5418 Available options are: 5419 P Enable page structure init time poisoning 5420 - Disable all of the above options 5421 5422 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5423 size of <nn>. This can be used to increase the 5424 minimum size (128MB on x86). It can also be used to 5425 decrease the size and leave more room for directly 5426 mapped kernel RAM. 5427 5428 vmcp_cma=nn[MG] [KNL,S390] 5429 Sets the memory size reserved for contiguous memory 5430 allocations for the vmcp device driver. 5431 5432 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5433 Format: <command> 5434 5435 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5436 Format: <command> 5437 5438 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5439 Format: <command> 5440 5441 vsyscall= [X86-64] 5442 Controls the behavior of vsyscalls (i.e. calls to 5443 fixed addresses of 0xffffffffff600x00 from legacy 5444 code). Most statically-linked binaries and older 5445 versions of glibc use these calls. Because these 5446 functions are at fixed addresses, they make nice 5447 targets for exploits that can control RIP. 5448 5449 emulate [default] Vsyscalls turn into traps and are 5450 emulated reasonably safely. The vsyscall 5451 page is readable. 5452 5453 xonly Vsyscalls turn into traps and are 5454 emulated reasonably safely. The vsyscall 5455 page is not readable. 5456 5457 none Vsyscalls don't work at all. This makes 5458 them quite hard to use for exploits but 5459 might break your system. 5460 5461 vt.color= [VT] Default text color. 5462 Format: 0xYX, X = foreground, Y = background. 5463 Default: 0x07 = light gray on black. 5464 5465 vt.cur_default= [VT] Default cursor shape. 5466 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5467 the parameters of the <Esc>[?A;B;Cc escape sequence; 5468 see VGA-softcursor.txt. Default: 2 = underline. 5469 5470 vt.default_blu= [VT] 5471 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5472 Change the default blue palette of the console. 5473 This is a 16-member array composed of values 5474 ranging from 0-255. 5475 5476 vt.default_grn= [VT] 5477 Format: <green0>,<green1>,<green2>,...,<green15> 5478 Change the default green palette of the console. 5479 This is a 16-member array composed of values 5480 ranging from 0-255. 5481 5482 vt.default_red= [VT] 5483 Format: <red0>,<red1>,<red2>,...,<red15> 5484 Change the default red palette of the console. 5485 This is a 16-member array composed of values 5486 ranging from 0-255. 5487 5488 vt.default_utf8= 5489 [VT] 5490 Format=<0|1> 5491 Set system-wide default UTF-8 mode for all tty's. 5492 Default is 1, i.e. UTF-8 mode is enabled for all 5493 newly opened terminals. 5494 5495 vt.global_cursor_default= 5496 [VT] 5497 Format=<-1|0|1> 5498 Set system-wide default for whether a cursor 5499 is shown on new VTs. Default is -1, 5500 i.e. cursors will be created by default unless 5501 overridden by individual drivers. 0 will hide 5502 cursors, 1 will display them. 5503 5504 vt.italic= [VT] Default color for italic text; 0-15. 5505 Default: 2 = green. 5506 5507 vt.underline= [VT] Default color for underlined text; 0-15. 5508 Default: 3 = cyan. 5509 5510 watchdog timers [HW,WDT] For information on watchdog timers, 5511 see Documentation/watchdog/watchdog-parameters.rst 5512 or other driver-specific files in the 5513 Documentation/watchdog/ directory. 5514 5515 watchdog_thresh= 5516 [KNL] 5517 Set the hard lockup detector stall duration 5518 threshold in seconds. The soft lockup detector 5519 threshold is set to twice the value. A value of 0 5520 disables both lockup detectors. Default is 10 5521 seconds. 5522 5523 workqueue.watchdog_thresh= 5524 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5525 warn stall conditions and dump internal state to 5526 help debugging. 0 disables workqueue stall 5527 detection; otherwise, it's the stall threshold 5528 duration in seconds. The default value is 30 and 5529 it can be updated at runtime by writing to the 5530 corresponding sysfs file. 5531 5532 workqueue.disable_numa 5533 By default, all work items queued to unbound 5534 workqueues are affine to the NUMA nodes they're 5535 issued on, which results in better behavior in 5536 general. If NUMA affinity needs to be disabled for 5537 whatever reason, this option can be used. Note 5538 that this also can be controlled per-workqueue for 5539 workqueues visible under /sys/bus/workqueue/. 5540 5541 workqueue.power_efficient 5542 Per-cpu workqueues are generally preferred because 5543 they show better performance thanks to cache 5544 locality; unfortunately, per-cpu workqueues tend to 5545 be more power hungry than unbound workqueues. 5546 5547 Enabling this makes the per-cpu workqueues which 5548 were observed to contribute significantly to power 5549 consumption unbound, leading to measurably lower 5550 power usage at the cost of small performance 5551 overhead. 5552 5553 The default value of this parameter is determined by 5554 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5555 5556 workqueue.debug_force_rr_cpu 5557 Workqueue used to implicitly guarantee that work 5558 items queued without explicit CPU specified are put 5559 on the local CPU. This guarantee is no longer true 5560 and while local CPU is still preferred work items 5561 may be put on foreign CPUs. This debug option 5562 forces round-robin CPU selection to flush out 5563 usages which depend on the now broken guarantee. 5564 When enabled, memory and cache locality will be 5565 impacted. 5566 5567 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5568 default x2apic cluster mode on platforms 5569 supporting x2apic. 5570 5571 x86_intel_mid_timer= [X86-32,APBT] 5572 Choose timer option for x86 Intel MID platform. 5573 Two valid options are apbt timer only and lapic timer 5574 plus one apbt timer for broadcast timer. 5575 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5576 5577 xen_512gb_limit [KNL,X86-64,XEN] 5578 Restricts the kernel running paravirtualized under Xen 5579 to use only up to 512 GB of RAM. The reason to do so is 5580 crash analysis tools and Xen tools for doing domain 5581 save/restore/migration must be enabled to handle larger 5582 domains. 5583 5584 xen_emul_unplug= [HW,X86,XEN] 5585 Unplug Xen emulated devices 5586 Format: [unplug0,][unplug1] 5587 ide-disks -- unplug primary master IDE devices 5588 aux-ide-disks -- unplug non-primary-master IDE devices 5589 nics -- unplug network devices 5590 all -- unplug all emulated devices (NICs and IDE disks) 5591 unnecessary -- unplugging emulated devices is 5592 unnecessary even if the host did not respond to 5593 the unplug protocol 5594 never -- do not unplug even if version check succeeds 5595 5596 xen_legacy_crash [X86,XEN] 5597 Crash from Xen panic notifier, without executing late 5598 panic() code such as dumping handler. 5599 5600 xen_nopvspin [X86,XEN] 5601 Disables the ticketlock slowpath using Xen PV 5602 optimizations. 5603 5604 xen_nopv [X86] 5605 Disables the PV optimizations forcing the HVM guest to 5606 run as generic HVM guest with no PV drivers. 5607 This option is obsoleted by the "nopv" option, which 5608 has equivalent effect for XEN platform. 5609 5610 xen_scrub_pages= [XEN] 5611 Boolean option to control scrubbing pages before giving them back 5612 to Xen, for use by other domains. Can be also changed at runtime 5613 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5614 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5615 5616 xen_timer_slop= [X86-64,XEN] 5617 Set the timer slop (in nanoseconds) for the virtual Xen 5618 timers (default is 100000). This adjusts the minimum 5619 delta of virtualized Xen timers, where lower values 5620 improve timer resolution at the expense of processing 5621 more timer interrupts. 5622 5623 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5624 Disables the PV optimizations forcing the guest to run 5625 as generic guest with no PV drivers. Currently support 5626 XEN HVM, KVM, HYPER_V and VMWARE guest. 5627 5628 xirc2ps_cs= [NET,PCMCIA] 5629 Format: 5630 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5631 5632 xive= [PPC] 5633 By default on POWER9 and above, the kernel will 5634 natively use the XIVE interrupt controller. This option 5635 allows the fallback firmware mode to be used: 5636 5637 off Fallback to firmware control of XIVE interrupt 5638 controller on both pseries and powernv 5639 platforms. Only useful on POWER9 and above. 5640 5641 xhci-hcd.quirks [USB,KNL] 5642 A hex value specifying bitmask with supplemental xhci 5643 host controller quirks. Meaning of each bit can be 5644 consulted in header drivers/usb/host/xhci.h. 5645 5646 xmon [PPC] 5647 Format: { early | on | rw | ro | off } 5648 Controls if xmon debugger is enabled. Default is off. 5649 Passing only "xmon" is equivalent to "xmon=early". 5650 early Call xmon as early as possible on boot; xmon 5651 debugger is called from setup_arch(). 5652 on xmon debugger hooks will be installed so xmon 5653 is only called on a kernel crash. Default mode, 5654 i.e. either "ro" or "rw" mode, is controlled 5655 with CONFIG_XMON_DEFAULT_RO_MODE. 5656 rw xmon debugger hooks will be installed so xmon 5657 is called only on a kernel crash, mode is write, 5658 meaning SPR registers, memory and, other data 5659 can be written using xmon commands. 5660 ro same as "rw" option above but SPR registers, 5661 memory, and other data can't be written using 5662 xmon commands. 5663 off xmon is disabled. 5664