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