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 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/firmware-guide/acpi/debug.rst for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <int> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_rsdp= [ACPI,EFI,KEXEC] 140 Pass the RSDP address to the kernel, mostly used 141 on machines running EFI runtime service to boot the 142 second kernel for kdump. 143 144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 145 Format: To spoof as Windows 98: ="Microsoft Windows" 146 147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 148 of 2 which is mandated by ACPI 6) as the supported ACPI 149 specification revision (when using this switch, it may 150 be necessary to carry out a cold reboot _twice_ in a 151 row to make it take effect on the platform firmware). 152 153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 154 acpi_osi="string1" # add string1 155 acpi_osi="!string2" # remove string2 156 acpi_osi=!* # remove all strings 157 acpi_osi=! # disable all built-in OS vendor 158 strings 159 acpi_osi=!! # enable all built-in OS vendor 160 strings 161 acpi_osi= # disable all strings 162 163 'acpi_osi=!' can be used in combination with single or 164 multiple 'acpi_osi="string1"' to support specific OS 165 vendor string(s). Note that such command can only 166 affect the default state of the OS vendor strings, thus 167 it cannot affect the default state of the feature group 168 strings and the current state of the OS vendor strings, 169 specifying it multiple times through kernel command line 170 is meaningless. This command is useful when one do not 171 care about the state of the feature group strings which 172 should be controlled by the OSPM. 173 Examples: 174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 176 can make '_OSI("Windows 2000")' TRUE. 177 178 'acpi_osi=' cannot be used in combination with other 179 'acpi_osi=' command lines, the _OSI method will not 180 exist in the ACPI namespace. NOTE that such command can 181 only affect the _OSI support state, thus specifying it 182 multiple times through kernel command line is also 183 meaningless. 184 Examples: 185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 186 FALSE. 187 188 'acpi_osi=!*' can be used in combination with single or 189 multiple 'acpi_osi="string1"' to support specific 190 string(s). Note that such command can affect the 191 current state of both the OS vendor strings and the 192 feature group strings, thus specifying it multiple times 193 through kernel command line is meaningful. But it may 194 still not able to affect the final state of a string if 195 there are quirks related to this string. This command 196 is useful when one want to control the state of the 197 feature group strings to debug BIOS issues related to 198 the OSPM features. 199 Examples: 200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 201 '_OSI("Module Device")' FALSE. 202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 203 '_OSI("Module Device")' TRUE. 204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 205 equivalent to 206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 207 and 208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 209 they all will make '_OSI("Windows 2000")' TRUE. 210 211 acpi_pm_good [X86] 212 Override the pmtimer bug detection: force the kernel 213 to assume that this machine's pmtimer latches its value 214 and always returns good values. 215 216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 217 Format: { level | edge | high | low } 218 219 acpi_skip_timer_override [HW,ACPI] 220 Recognize and ignore IRQ0/pin2 Interrupt Override. 221 For broken nForce2 BIOS resulting in XT-PIC timer. 222 223 acpi_sleep= [HW,ACPI] Sleep options 224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 225 old_ordering, nonvs, sci_force_enable, nobl } 226 See Documentation/power/video.rst for information on 227 s3_bios and s3_mode. 228 s3_beep is for debugging; it makes the PC's speaker beep 229 as soon as the kernel's real-mode entry point is called. 230 s4_nohwsig prevents ACPI hardware signature from being 231 used during resume from hibernation. 232 old_ordering causes the ACPI 1.0 ordering of the _PTS 233 control method, with respect to putting devices into 234 low power states, to be enforced (the ACPI 2.0 ordering 235 of _PTS is used by default). 236 nonvs prevents the kernel from saving/restoring the 237 ACPI NVS memory during suspend/hibernation and resume. 238 sci_force_enable causes the kernel to set SCI_EN directly 239 on resume from S1/S3 (which is against the ACPI spec, 240 but some broken systems don't work without it). 241 nobl causes the internal blacklist of systems known to 242 behave incorrectly in some ways with respect to system 243 suspend and resume to be ignored (use wisely). 244 245 acpi_use_timer_override [HW,ACPI] 246 Use timer override. For some broken Nvidia NF5 boards 247 that require a timer override, but don't have HPET 248 249 add_efi_memmap [EFI; X86] Include EFI memory map in 250 kernel's map of available physical RAM. 251 252 agp= [AGP] 253 { off | try_unsupported } 254 off: disable AGP support 255 try_unsupported: try to drive unsupported chipsets 256 (may crash computer or cause data corruption) 257 258 ALSA [HW,ALSA] 259 See Documentation/sound/alsa-configuration.rst 260 261 alignment= [KNL,ARM] 262 Allow the default userspace alignment fault handler 263 behaviour to be specified. Bit 0 enables warnings, 264 bit 1 enables fixups, and bit 2 sends a segfault. 265 266 align_va_addr= [X86-64] 267 Align virtual addresses by clearing slice [14:12] when 268 allocating a VMA at process creation time. This option 269 gives you up to 3% performance improvement on AMD F15h 270 machines (where it is enabled by default) for a 271 CPU-intensive style benchmark, and it can vary highly in 272 a microbenchmark depending on workload and compiler. 273 274 32: only for 32-bit processes 275 64: only for 64-bit processes 276 on: enable for both 32- and 64-bit processes 277 off: disable for both 32- and 64-bit processes 278 279 alloc_snapshot [FTRACE] 280 Allocate the ftrace snapshot buffer on boot up when the 281 main buffer is allocated. This is handy if debugging 282 and you need to use tracing_snapshot() on boot up, and 283 do not want to use tracing_snapshot_alloc() as it needs 284 to be done where GFP_KERNEL allocations are allowed. 285 286 amd_iommu= [HW,X86-64] 287 Pass parameters to the AMD IOMMU driver in the system. 288 Possible values are: 289 fullflush - enable flushing of IO/TLB entries when 290 they are unmapped. Otherwise they are 291 flushed before they will be reused, which 292 is a lot of faster 293 off - do not initialize any AMD IOMMU found in 294 the system 295 force_isolation - Force device isolation for all 296 devices. The IOMMU driver is not 297 allowed anymore to lift isolation 298 requirements as needed. This option 299 does not override iommu=pt 300 301 amd_iommu_dump= [HW,X86-64] 302 Enable AMD IOMMU driver option to dump the ACPI table 303 for AMD IOMMU. With this option enabled, AMD IOMMU 304 driver will print ACPI tables for AMD IOMMU during 305 IOMMU initialization. 306 307 amd_iommu_intr= [HW,X86-64] 308 Specifies one of the following AMD IOMMU interrupt 309 remapping modes: 310 legacy - Use legacy interrupt remapping mode. 311 vapic - Use virtual APIC mode, which allows IOMMU 312 to inject interrupts directly into guest. 313 This mode requires kvm-amd.avic=1. 314 (Default when IOMMU HW support is present.) 315 316 amijoy.map= [HW,JOY] Amiga joystick support 317 Map of devices attached to JOY0DAT and JOY1DAT 318 Format: <a>,<b> 319 See also Documentation/input/joydev/joystick.rst 320 321 analog.map= [HW,JOY] Analog joystick and gamepad support 322 Specifies type or capabilities of an analog joystick 323 connected to one of 16 gameports 324 Format: <type1>,<type2>,..<type16> 325 326 apc= [HW,SPARC] 327 Power management functions (SPARCstation-4/5 + deriv.) 328 Format: noidle 329 Disable APC CPU standby support. SPARCstation-Fox does 330 not play well with APC CPU idle - disable it if you have 331 APC and your system crashes randomly. 332 333 apic= [APIC,X86] Advanced Programmable Interrupt Controller 334 Change the output verbosity while booting 335 Format: { quiet (default) | verbose | debug } 336 Change the amount of debugging information output 337 when initialising the APIC and IO-APIC components. 338 For X86-32, this can also be used to specify an APIC 339 driver name. 340 Format: apic=driver_name 341 Examples: apic=bigsmp 342 343 apic_extnmi= [APIC,X86] External NMI delivery setting 344 Format: { bsp (default) | all | none } 345 bsp: External NMI is delivered only to CPU 0 346 all: External NMIs are broadcast to all CPUs as a 347 backup of CPU 0 348 none: External NMI is masked for all CPUs. This is 349 useful so that a dump capture kernel won't be 350 shot down by NMI 351 352 autoconf= [IPV6] 353 See Documentation/networking/ipv6.txt. 354 355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 356 Limit apic dumping. The parameter defines the maximal 357 number of local apics being dumped. Also it is possible 358 to set it to "all" by meaning -- no limit here. 359 Format: { 1 (default) | 2 | ... | all }. 360 The parameter valid if only apic=debug or 361 apic=verbose is specified. 362 Example: apic=debug show_lapic=all 363 364 apm= [APM] Advanced Power Management 365 See header of arch/x86/kernel/apm_32.c. 366 367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 368 Format: <io>,<irq>,<nodeID> 369 370 ataflop= [HW,M68k] 371 372 atarimouse= [HW,MOUSE] Atari Mouse 373 374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 375 EzKey and similar keyboards 376 377 atkbd.reset= [HW] Reset keyboard during initialization 378 379 atkbd.set= [HW] Select keyboard code set 380 Format: <int> (2 = AT (default), 3 = PS/2) 381 382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 383 keyboards 384 385 atkbd.softraw= [HW] Choose between synthetic and real raw mode 386 Format: <bool> (0 = real, 1 = synthetic (default)) 387 388 atkbd.softrepeat= [HW] 389 Use software keyboard repeat 390 391 audit= [KNL] Enable the audit sub-system 392 Format: { "0" | "1" | "off" | "on" } 393 0 | off - kernel audit is disabled and can not be 394 enabled until the next reboot 395 unset - kernel audit is initialized but disabled and 396 will be fully enabled by the userspace auditd. 397 1 | on - kernel audit is initialized and partially 398 enabled, storing at most audit_backlog_limit 399 messages in RAM until it is fully enabled by the 400 userspace auditd. 401 Default: unset 402 403 audit_backlog_limit= [KNL] Set the audit queue size limit. 404 Format: <int> (must be >=0) 405 Default: 64 406 407 bau= [X86_UV] Enable the BAU on SGI UV. The default 408 behavior is to disable the BAU (i.e. bau=0). 409 Format: { "0" | "1" } 410 0 - Disable the BAU. 411 1 - Enable the BAU. 412 unset - Disable the BAU. 413 414 baycom_epp= [HW,AX25] 415 Format: <io>,<mode> 416 417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 418 Format: <io>,<mode> 419 See header of drivers/net/hamradio/baycom_par.c. 420 421 baycom_ser_fdx= [HW,AX25] 422 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 423 Format: <io>,<irq>,<mode>[,<baud>] 424 See header of drivers/net/hamradio/baycom_ser_fdx.c. 425 426 baycom_ser_hdx= [HW,AX25] 427 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 428 Format: <io>,<irq>,<mode> 429 See header of drivers/net/hamradio/baycom_ser_hdx.c. 430 431 blkdevparts= Manual partition parsing of block device(s) for 432 embedded devices based on command line input. 433 See Documentation/block/cmdline-partition.rst 434 435 boot_delay= Milliseconds to delay each printk during boot. 436 Values larger than 10 seconds (10000) are changed to 437 no delay (0). 438 Format: integer 439 440 bootmem_debug [KNL] Enable bootmem allocator debug messages. 441 442 bert_disable [ACPI] 443 Disable BERT OS support on buggy BIOSes. 444 445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 446 bttv.radio= Most important insmod options are available as 447 kernel args too. 448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 449 bttv.tuner= 450 451 bulk_remove=off [PPC] This parameter disables the use of the pSeries 452 firmware feature for flushing multiple hpte entries 453 at a time. 454 455 c101= [NET] Moxa C101 synchronous serial card 456 457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 458 Sometimes CPU hardware bugs make them report the cache 459 size incorrectly. The kernel will attempt work arounds 460 to fix known problems, but for some CPUs it is not 461 possible to determine what the correct size should be. 462 This option provides an override for these situations. 463 464 carrier_timeout= 465 [NET] Specifies amount of time (in seconds) that 466 the kernel should wait for a network carrier. By default 467 it waits 120 seconds. 468 469 ca_keys= [KEYS] This parameter identifies a specific key(s) on 470 the system trusted keyring to be used for certificate 471 trust validation. 472 format: { id:<keyid> | builtin } 473 474 cca= [MIPS] Override the kernel pages' cache coherency 475 algorithm. Accepted values range from 0 to 7 476 inclusive. See arch/mips/include/asm/pgtable-bits.h 477 for platform specific values (SB1, Loongson3 and 478 others). 479 480 ccw_timeout_log [S390] 481 See Documentation/s390/common_io.rst for details. 482 483 cgroup_disable= [KNL] Disable a particular controller 484 Format: {name of the controller(s) to disable} 485 The effects of cgroup_disable=foo are: 486 - foo isn't auto-mounted if you mount all cgroups in 487 a single hierarchy 488 - foo isn't visible as an individually mountable 489 subsystem 490 {Currently only "memory" controller deal with this and 491 cut the overhead, others just disable the usage. So 492 only cgroup_disable=memory is actually worthy} 493 494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 495 Format: { { controller | "all" | "named" } 496 [,{ controller | "all" | "named" }...] } 497 Like cgroup_disable, but only applies to cgroup v1; 498 the blacklisted controllers remain available in cgroup2. 499 "all" blacklists all controllers and "named" disables 500 named mounts. Specifying both "all" and "named" disables 501 all v1 hierarchies. 502 503 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 504 Format: <string> 505 nosocket -- Disable socket memory accounting. 506 nokmem -- Disable kernel memory accounting. 507 508 checkreqprot [SELINUX] Set initial checkreqprot flag value. 509 Format: { "0" | "1" } 510 See security/selinux/Kconfig help text. 511 0 -- check protection applied by kernel (includes 512 any implied execute protection). 513 1 -- check protection requested by application. 514 Default value is set via a kernel config option. 515 Value can be changed at runtime via 516 /selinux/checkreqprot. 517 518 cio_ignore= [S390] 519 See Documentation/s390/common_io.rst for details. 520 clk_ignore_unused 521 [CLK] 522 Prevents the clock framework from automatically gating 523 clocks that have not been explicitly enabled by a Linux 524 device driver but are enabled in hardware at reset or 525 by the bootloader/firmware. Note that this does not 526 force such clocks to be always-on nor does it reserve 527 those clocks in any way. This parameter is useful for 528 debug and development, but should not be needed on a 529 platform with proper driver support. For more 530 information, see Documentation/driver-api/clk.rst. 531 532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 533 [Deprecated] 534 Forces specified clocksource (if available) to be used 535 when calculating gettimeofday(). If specified 536 clocksource is not available, it defaults to PIT. 537 Format: { pit | tsc | cyclone | pmtmr } 538 539 clocksource= Override the default clocksource 540 Format: <string> 541 Override the default clocksource and use the clocksource 542 with the name specified. 543 Some clocksource names to choose from, depending on 544 the platform: 545 [all] jiffies (this is the base, fallback clocksource) 546 [ACPI] acpi_pm 547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 548 pxa_timer,timer3,32k_counter,timer0_1 549 [X86-32] pit,hpet,tsc; 550 scx200_hrt on Geode; cyclone on IBM x440 551 [MIPS] MIPS 552 [PARISC] cr16 553 [S390] tod 554 [SH] SuperH 555 [SPARC64] tick 556 [X86-64] hpet,tsc 557 558 clocksource.arm_arch_timer.evtstrm= 559 [ARM,ARM64] 560 Format: <bool> 561 Enable/disable the eventstream feature of the ARM 562 architected timer so that code using WFE-based polling 563 loops can be debugged more effectively on production 564 systems. 565 566 clearcpuid=BITNUM [X86] 567 Disable CPUID feature X for the kernel. See 568 arch/x86/include/asm/cpufeatures.h for the valid bit 569 numbers. Note the Linux specific bits are not necessarily 570 stable over kernel options, but the vendor specific 571 ones should be. 572 Also note that user programs calling CPUID directly 573 or using the feature without checking anything 574 will still see it. This just prevents it from 575 being used by the kernel or shown in /proc/cpuinfo. 576 Also note the kernel might malfunction if you disable 577 some critical bits. 578 579 cma=nn[MG]@[start[MG][-end[MG]]] 580 [ARM,X86,KNL] 581 Sets the size of kernel global memory area for 582 contiguous memory allocations and optionally the 583 placement constraint by the physical address range of 584 memory allocations. A value of 0 disables CMA 585 altogether. For more information, see 586 include/linux/dma-contiguous.h 587 588 cmo_free_hint= [PPC] Format: { yes | no } 589 Specify whether pages are marked as being inactive 590 when they are freed. This is used in CMO environments 591 to determine OS memory pressure for page stealing by 592 a hypervisor. 593 Default: yes 594 595 coherent_pool=nn[KMG] [ARM,KNL] 596 Sets the size of memory pool for coherent, atomic dma 597 allocations, by default set to 256K. 598 599 com20020= [HW,NET] ARCnet - COM20020 chipset 600 Format: 601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 602 603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 604 Format: <io>[,<irq>] 605 606 com90xx= [HW,NET] 607 ARCnet - COM90xx chipset (memory-mapped buffers) 608 Format: <io>[,<irq>[,<memstart>]] 609 610 condev= [HW,S390] console device 611 conmode= 612 613 console= [KNL] Output console device and options. 614 615 tty<n> Use the virtual console device <n>. 616 617 ttyS<n>[,options] 618 ttyUSB0[,options] 619 Use the specified serial port. The options are of 620 the form "bbbbpnf", where "bbbb" is the baud rate, 621 "p" is parity ("n", "o", or "e"), "n" is number of 622 bits, and "f" is flow control ("r" for RTS or 623 omit it). Default is "9600n8". 624 625 See Documentation/admin-guide/serial-console.rst for more 626 information. See 627 Documentation/networking/netconsole.txt for an 628 alternative. 629 630 uart[8250],io,<addr>[,options] 631 uart[8250],mmio,<addr>[,options] 632 uart[8250],mmio16,<addr>[,options] 633 uart[8250],mmio32,<addr>[,options] 634 uart[8250],0x<addr>[,options] 635 Start an early, polled-mode console on the 8250/16550 636 UART at the specified I/O port or MMIO address, 637 switching to the matching ttyS device later. 638 MMIO inter-register address stride is either 8-bit 639 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 641 to be equivalent to 'mmio'. 'options' are specified in 642 the same format described for ttyS above; if unspecified, 643 the h/w is not re-initialized. 644 645 hvc<n> Use the hypervisor console device <n>. This is for 646 both Xen and PowerPC hypervisors. 647 648 If the device connected to the port is not a TTY but a braille 649 device, prepend "brl," before the device type, for instance 650 console=brl,ttyS0 651 For now, only VisioBraille is supported. 652 653 console_msg_format= 654 [KNL] Change console messages format 655 default 656 By default we print messages on consoles in 657 "[time stamp] text\n" format (time stamp may not be 658 printed, depending on CONFIG_PRINTK_TIME or 659 `printk_time' param). 660 syslog 661 Switch to syslog format: "<%u>[time stamp] text\n" 662 IOW, each message will have a facility and loglevel 663 prefix. The format is similar to one used by syslog() 664 syscall, or to executing "dmesg -S --raw" or to reading 665 from /proc/kmsg. 666 667 consoleblank= [KNL] The console blank (screen saver) timeout in 668 seconds. A value of 0 disables the blank timer. 669 Defaults to 0. 670 671 coredump_filter= 672 [KNL] Change the default value for 673 /proc/<pid>/coredump_filter. 674 See also Documentation/filesystems/proc.txt. 675 676 coresight_cpu_debug.enable 677 [ARM,ARM64] 678 Format: <bool> 679 Enable/disable the CPU sampling based debugging. 680 0: default value, disable debugging 681 1: enable debugging at boot time 682 683 cpuidle.off=1 [CPU_IDLE] 684 disable the cpuidle sub-system 685 686 cpuidle.governor= 687 [CPU_IDLE] Name of the cpuidle governor to use. 688 689 cpufreq.off=1 [CPU_FREQ] 690 disable the cpufreq sub-system 691 692 cpu_init_udelay=N 693 [X86] Delay for N microsec between assert and de-assert 694 of APIC INIT to start processors. This delay occurs 695 on every CPU online, such as boot, and resume from suspend. 696 Default: 10000 697 698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 699 Format: 700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 701 702 crashkernel=size[KMG][@offset[KMG]] 703 [KNL] Using kexec, Linux can switch to a 'crash kernel' 704 upon panic. This parameter reserves the physical 705 memory region [offset, offset + size] for that kernel 706 image. If '@offset' is omitted, then a suitable offset 707 is selected automatically. 708 [KNL, x86_64] select a region under 4G first, and 709 fall back to reserve region above 4G when '@offset' 710 hasn't been specified. 711 See Documentation/admin-guide/kdump/kdump.rst for further details. 712 713 crashkernel=range1:size1[,range2:size2,...][@offset] 714 [KNL] Same as above, but depends on the memory 715 in the running system. The syntax of range is 716 start-[end] where start and end are both 717 a memory unit (amount[KMG]). See also 718 Documentation/admin-guide/kdump/kdump.rst for an example. 719 720 crashkernel=size[KMG],high 721 [KNL, x86_64] range could be above 4G. Allow kernel 722 to allocate physical memory region from top, so could 723 be above 4G if system have more than 4G ram installed. 724 Otherwise memory region will be allocated below 4G, if 725 available. 726 It will be ignored if crashkernel=X is specified. 727 crashkernel=size[KMG],low 728 [KNL, x86_64] range under 4G. When crashkernel=X,high 729 is passed, kernel could allocate physical memory region 730 above 4G, that cause second kernel crash on system 731 that require some amount of low memory, e.g. swiotlb 732 requires at least 64M+32K low memory, also enough extra 733 low memory is needed to make sure DMA buffers for 32-bit 734 devices won't run out. Kernel would try to allocate at 735 at least 256M below 4G automatically. 736 This one let user to specify own low range under 4G 737 for second kernel instead. 738 0: to disable low allocation. 739 It will be ignored when crashkernel=X,high is not used 740 or memory reserved is below 4G. 741 742 cryptomgr.notests 743 [KNL] Disable crypto self-tests 744 745 cs89x0_dma= [HW,NET] 746 Format: <dma> 747 748 cs89x0_media= [HW,NET] 749 Format: { rj45 | aui | bnc } 750 751 dasd= [HW,NET] 752 See header of drivers/s390/block/dasd_devmap.c. 753 754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 755 (one device per port) 756 Format: <port#>,<type> 757 See also Documentation/input/devices/joystick-parport.rst 758 759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 760 time. See 761 Documentation/admin-guide/dynamic-debug-howto.rst for 762 details. Deprecated, see dyndbg. 763 764 debug [KNL] Enable kernel debugging (events log level). 765 766 debug_boot_weak_hash 767 [KNL] Enable printing [hashed] pointers early in the 768 boot sequence. If enabled, we use a weak hash instead 769 of siphash to hash pointers. Use this option if you are 770 seeing instances of '(___ptrval___)') and need to see a 771 value (hashed pointer) instead. Cryptographically 772 insecure, please do not use on production kernels. 773 774 debug_locks_verbose= 775 [KNL] verbose self-tests 776 Format=<0|1> 777 Print debugging info while doing the locking API 778 self-tests. 779 We default to 0 (no extra messages), setting it to 780 1 will print _a lot_ more information - normally 781 only useful to kernel developers. 782 783 debug_objects [KNL] Enable object debugging 784 785 no_debug_objects 786 [KNL] Disable object debugging 787 788 debug_guardpage_minorder= 789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 790 parameter allows control of the order of pages that will 791 be intentionally kept free (and hence protected) by the 792 buddy allocator. Bigger value increase the probability 793 of catching random memory corruption, but reduce the 794 amount of memory for normal system use. The maximum 795 possible value is MAX_ORDER/2. Setting this parameter 796 to 1 or 2 should be enough to identify most random 797 memory corruption problems caused by bugs in kernel or 798 driver code when a CPU writes to (or reads from) a 799 random memory location. Note that there exists a class 800 of memory corruptions problems caused by buggy H/W or 801 F/W or by drivers badly programing DMA (basically when 802 memory is written at bus level and the CPU MMU is 803 bypassed) which are not detectable by 804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 805 tracking down these problems. 806 807 debug_pagealloc= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 809 enables the feature at boot time. By default, it is 810 disabled and the system will work mostly the same as a 811 kernel built without CONFIG_DEBUG_PAGEALLOC. 812 Note: to get most of debug_pagealloc error reports, it's 813 useful to also enable the page_owner functionality. 814 on: enable the feature 815 816 debugpat [X86] Enable PAT debugging 817 818 decnet.addr= [HW,NET] 819 Format: <area>[,<node>] 820 See also Documentation/networking/decnet.txt. 821 822 default_hugepagesz= 823 [same as hugepagesz=] The size of the default 824 HugeTLB page size. This is the size represented by 825 the legacy /proc/ hugepages APIs, used for SHM, and 826 default size when mounting hugetlbfs filesystems. 827 Defaults to the default architecture's huge page size 828 if not specified. 829 830 deferred_probe_timeout= 831 [KNL] Debugging option to set a timeout in seconds for 832 deferred probe to give up waiting on dependencies to 833 probe. Only specific dependencies (subsystems or 834 drivers) that have opted in will be ignored. A timeout of 0 835 will timeout at the end of initcalls. This option will also 836 dump out devices still on the deferred probe list after 837 retrying. 838 839 dhash_entries= [KNL] 840 Set number of hash buckets for dentry cache. 841 842 disable_1tb_segments [PPC] 843 Disables the use of 1TB hash page table segments. This 844 causes the kernel to fall back to 256MB segments which 845 can be useful when debugging issues that require an SLB 846 miss to occur. 847 848 disable= [IPV6] 849 See Documentation/networking/ipv6.txt. 850 851 hardened_usercopy= 852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 853 hardening is enabled for this boot. Hardened 854 usercopy checking is used to protect the kernel 855 from reading or writing beyond known memory 856 allocation boundaries as a proactive defense 857 against bounds-checking flaws in the kernel's 858 copy_to_user()/copy_from_user() interface. 859 on Perform hardened usercopy checks (default). 860 off Disable hardened usercopy checks. 861 862 disable_radix [PPC] 863 Disable RADIX MMU mode on POWER9 864 865 disable_tlbie [PPC] 866 Disable TLBIE instruction. Currently does not work 867 with KVM, with HASH MMU, or with coherent accelerators. 868 869 disable_cpu_apicid= [X86,APIC,SMP] 870 Format: <int> 871 The number of initial APIC ID for the 872 corresponding CPU to be disabled at boot, 873 mostly used for the kdump 2nd kernel to 874 disable BSP to wake up multiple CPUs without 875 causing system reset or hang due to sending 876 INIT from AP to BSP. 877 878 perf_v4_pmi= [X86,INTEL] 879 Format: <bool> 880 Disable Intel PMU counter freezing feature. 881 The feature only exists starting from 882 Arch Perfmon v4 (Skylake and newer). 883 884 disable_ddw [PPC/PSERIES] 885 Disable Dynamic DMA Window support. Use this if 886 to workaround buggy firmware. 887 888 disable_ipv6= [IPV6] 889 See Documentation/networking/ipv6.txt. 890 891 disable_mtrr_cleanup [X86] 892 The kernel tries to adjust MTRR layout from continuous 893 to discrete, to make X server driver able to add WB 894 entry later. This parameter disables that. 895 896 disable_mtrr_trim [X86, Intel and AMD only] 897 By default the kernel will trim any uncacheable 898 memory out of your available memory pool based on 899 MTRR settings. This parameter disables that behavior, 900 possibly causing your machine to run very slowly. 901 902 disable_timer_pin_1 [X86] 903 Disable PIN 1 of APIC timer 904 Can be useful to work around chipset bugs. 905 906 dis_ucode_ldr [X86] Disable the microcode loader. 907 908 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 909 this option disables the debugging code at boot. 910 911 dma_debug_entries=<number> 912 This option allows to tune the number of preallocated 913 entries for DMA-API debugging code. One entry is 914 required per DMA-API allocation. Use this if the 915 DMA-API debugging code disables itself because the 916 architectural default is too low. 917 918 dma_debug_driver=<driver_name> 919 With this option the DMA-API debugging driver 920 filter feature can be enabled at boot time. Just 921 pass the driver to filter for as the parameter. 922 The filter can be disabled or changed to another 923 driver later using sysfs. 924 925 driver_async_probe= [KNL] 926 List of driver names to be probed asynchronously. 927 Format: <driver_name1>,<driver_name2>... 928 929 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 930 Broken monitors, graphic adapters, KVMs and EDIDless 931 panels may send no or incorrect EDID data sets. 932 This parameter allows to specify an EDID data sets 933 in the /lib/firmware directory that are used instead. 934 Generic built-in EDID data sets are used, if one of 935 edid/1024x768.bin, edid/1280x1024.bin, 936 edid/1680x1050.bin, or edid/1920x1080.bin is given 937 and no file with the same name exists. Details and 938 instructions how to build your own EDID data are 939 available in Documentation/driver-api/edid.rst. An EDID 940 data set will only be used for a particular connector, 941 if its name and a colon are prepended to the EDID 942 name. Each connector may use a unique EDID data 943 set by separating the files with a comma. An EDID 944 data set with no connector name will be used for 945 any connectors not explicitly specified. 946 947 dscc4.setup= [NET] 948 949 dt_cpu_ftrs= [PPC] 950 Format: {"off" | "known"} 951 Control how the dt_cpu_ftrs device-tree binding is 952 used for CPU feature discovery and setup (if it 953 exists). 954 off: Do not use it, fall back to legacy cpu table. 955 known: Do not pass through unknown features to guests 956 or userspace, only those that the kernel is aware of. 957 958 dump_apple_properties [X86] 959 Dump name and content of EFI device properties on 960 x86 Macs. Useful for driver authors to determine 961 what data is available or for reverse-engineering. 962 963 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 964 module.dyndbg[="val"] 965 Enable debug messages at boot time. See 966 Documentation/admin-guide/dynamic-debug-howto.rst 967 for details. 968 969 nompx [X86] Disables Intel Memory Protection Extensions. 970 See Documentation/x86/intel_mpx.rst for more 971 information about the feature. 972 973 nopku [X86] Disable Memory Protection Keys CPU feature found 974 in some Intel CPUs. 975 976 module.async_probe [KNL] 977 Enable asynchronous probe on this module. 978 979 early_ioremap_debug [KNL] 980 Enable debug messages in early_ioremap support. This 981 is useful for tracking down temporary early mappings 982 which are not unmapped. 983 984 earlycon= [KNL] Output early console device and options. 985 986 [ARM64] The early console is determined by the 987 stdout-path property in device tree's chosen node, 988 or determined by the ACPI SPCR table. 989 990 [X86] When used with no options the early console is 991 determined by the ACPI SPCR table. 992 993 cdns,<addr>[,options] 994 Start an early, polled-mode console on a Cadence 995 (xuartps) serial port at the specified address. Only 996 supported option is baud rate. If baud rate is not 997 specified, the serial port must already be setup and 998 configured. 999 1000 uart[8250],io,<addr>[,options] 1001 uart[8250],mmio,<addr>[,options] 1002 uart[8250],mmio32,<addr>[,options] 1003 uart[8250],mmio32be,<addr>[,options] 1004 uart[8250],0x<addr>[,options] 1005 Start an early, polled-mode console on the 8250/16550 1006 UART at the specified I/O port or MMIO address. 1007 MMIO inter-register address stride is either 8-bit 1008 (mmio) or 32-bit (mmio32 or mmio32be). 1009 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1010 to be equivalent to 'mmio'. 'options' are specified 1011 in the same format described for "console=ttyS<n>"; if 1012 unspecified, the h/w is not initialized. 1013 1014 pl011,<addr> 1015 pl011,mmio32,<addr> 1016 Start an early, polled-mode console on a pl011 serial 1017 port at the specified address. The pl011 serial port 1018 must already be setup and configured. Options are not 1019 yet supported. If 'mmio32' is specified, then only 1020 the driver will use only 32-bit accessors to read/write 1021 the device registers. 1022 1023 meson,<addr> 1024 Start an early, polled-mode console on a meson serial 1025 port at the specified address. The serial port must 1026 already be setup and configured. Options are not yet 1027 supported. 1028 1029 msm_serial,<addr> 1030 Start an early, polled-mode console on an msm serial 1031 port at the specified address. The serial port 1032 must already be setup and configured. Options are not 1033 yet supported. 1034 1035 msm_serial_dm,<addr> 1036 Start an early, polled-mode console on an msm serial 1037 dm port at the specified address. The serial port 1038 must already be setup and configured. Options are not 1039 yet supported. 1040 1041 owl,<addr> 1042 Start an early, polled-mode console on a serial port 1043 of an Actions Semi SoC, such as S500 or S900, at the 1044 specified address. The serial port must already be 1045 setup and configured. Options are not yet supported. 1046 1047 rda,<addr> 1048 Start an early, polled-mode console on a serial port 1049 of an RDA Micro SoC, such as RDA8810PL, at the 1050 specified address. The serial port must already be 1051 setup and configured. Options are not yet supported. 1052 1053 sbi 1054 Use RISC-V SBI (Supervisor Binary Interface) for early 1055 console. 1056 1057 smh Use ARM semihosting calls for early console. 1058 1059 s3c2410,<addr> 1060 s3c2412,<addr> 1061 s3c2440,<addr> 1062 s3c6400,<addr> 1063 s5pv210,<addr> 1064 exynos4210,<addr> 1065 Use early console provided by serial driver available 1066 on Samsung SoCs, requires selecting proper type and 1067 a correct base address of the selected UART port. The 1068 serial port must already be setup and configured. 1069 Options are not yet supported. 1070 1071 lantiq,<addr> 1072 Start an early, polled-mode console on a lantiq serial 1073 (lqasc) port at the specified address. The serial port 1074 must already be setup and configured. Options are not 1075 yet supported. 1076 1077 lpuart,<addr> 1078 lpuart32,<addr> 1079 Use early console provided by Freescale LP UART driver 1080 found on Freescale Vybrid and QorIQ LS1021A processors. 1081 A valid base address must be provided, and the serial 1082 port must already be setup and configured. 1083 1084 ar3700_uart,<addr> 1085 Start an early, polled-mode console on the 1086 Armada 3700 serial port at the specified 1087 address. The serial port must already be setup 1088 and configured. Options are not yet supported. 1089 1090 qcom_geni,<addr> 1091 Start an early, polled-mode console on a Qualcomm 1092 Generic Interface (GENI) based serial port at the 1093 specified address. The serial port must already be 1094 setup and configured. Options are not yet supported. 1095 1096 efifb,[options] 1097 Start an early, unaccelerated console on the EFI 1098 memory mapped framebuffer (if available). On cache 1099 coherent non-x86 systems that use system memory for 1100 the framebuffer, pass the 'ram' option so that it is 1101 mapped with the correct attributes. 1102 1103 linflex,<addr> 1104 Use early console provided by Freescale LinFlex UART 1105 serial driver for NXP S32V234 SoCs. A valid base 1106 address must be provided, and the serial port must 1107 already be setup and configured. 1108 1109 earlyprintk= [X86,SH,ARM,M68k,S390] 1110 earlyprintk=vga 1111 earlyprintk=sclp 1112 earlyprintk=xen 1113 earlyprintk=serial[,ttySn[,baudrate]] 1114 earlyprintk=serial[,0x...[,baudrate]] 1115 earlyprintk=ttySn[,baudrate] 1116 earlyprintk=dbgp[debugController#] 1117 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1118 earlyprintk=xdbc[xhciController#] 1119 1120 earlyprintk is useful when the kernel crashes before 1121 the normal console is initialized. It is not enabled by 1122 default because it has some cosmetic problems. 1123 1124 Append ",keep" to not disable it when the real console 1125 takes over. 1126 1127 Only one of vga, efi, serial, or usb debug port can 1128 be used at a time. 1129 1130 Currently only ttyS0 and ttyS1 may be specified by 1131 name. Other I/O ports may be explicitly specified 1132 on some architectures (x86 and arm at least) by 1133 replacing ttySn with an I/O port address, like this: 1134 earlyprintk=serial,0x1008,115200 1135 You can find the port for a given device in 1136 /proc/tty/driver/serial: 1137 2: uart:ST16650V2 port:00001008 irq:18 ... 1138 1139 Interaction with the standard serial driver is not 1140 very good. 1141 1142 The VGA and EFI output is eventually overwritten by 1143 the real console. 1144 1145 The xen output can only be used by Xen PV guests. 1146 1147 The sclp output can only be used on s390. 1148 1149 The optional "force" to "pciserial" enables use of a 1150 PCI device even when its classcode is not of the 1151 UART class. 1152 1153 edac_report= [HW,EDAC] Control how to report EDAC event 1154 Format: {"on" | "off" | "force"} 1155 on: enable EDAC to report H/W event. May be overridden 1156 by other higher priority error reporting module. 1157 off: disable H/W event reporting through EDAC. 1158 force: enforce the use of EDAC to report H/W event. 1159 default: on. 1160 1161 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1162 ekgdboc=kbd 1163 1164 This is designed to be used in conjunction with 1165 the boot argument: earlyprintk=vga 1166 1167 edd= [EDD] 1168 Format: {"off" | "on" | "skip[mbr]"} 1169 1170 efi= [EFI] 1171 Format: { "old_map", "nochunk", "noruntime", "debug" } 1172 old_map [X86-64]: switch to the old ioremap-based EFI 1173 runtime services mapping. 32-bit still uses this one by 1174 default. 1175 nochunk: disable reading files in "chunks" in the EFI 1176 boot stub, as chunking can cause problems with some 1177 firmware implementations. 1178 noruntime : disable EFI runtime services support 1179 debug: enable misc debug output 1180 1181 efi_no_storage_paranoia [EFI; X86] 1182 Using this parameter you can use more than 50% of 1183 your efi variable storage. Use this parameter only if 1184 you are really sure that your UEFI does sane gc and 1185 fulfills the spec otherwise your board may brick. 1186 1187 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1188 Add arbitrary attribute to specific memory range by 1189 updating original EFI memory map. 1190 Region of memory which aa attribute is added to is 1191 from ss to ss+nn. 1192 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1193 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1194 attribute is added to range 0x100000000-0x180000000 and 1195 0x10a0000000-0x1120000000. 1196 1197 Using this parameter you can do debugging of EFI memmap 1198 related feature. For example, you can do debugging of 1199 Address Range Mirroring feature even if your box 1200 doesn't support it. 1201 1202 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1203 that is to be dynamically loaded by Linux. If there are 1204 multiple variables with the same name but with different 1205 vendor GUIDs, all of them will be loaded. See 1206 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1207 1208 1209 eisa_irq_edge= [PARISC,HW] 1210 See header of drivers/parisc/eisa.c. 1211 1212 elanfreq= [X86-32] 1213 See comment before function elanfreq_setup() in 1214 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1215 1216 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1217 Specifies physical address of start of kernel core 1218 image elf header and optionally the size. Generally 1219 kexec loader will pass this option to capture kernel. 1220 See Documentation/admin-guide/kdump/kdump.rst for details. 1221 1222 enable_mtrr_cleanup [X86] 1223 The kernel tries to adjust MTRR layout from continuous 1224 to discrete, to make X server driver able to add WB 1225 entry later. This parameter enables that. 1226 1227 enable_timer_pin_1 [X86] 1228 Enable PIN 1 of APIC timer 1229 Can be useful to work around chipset bugs 1230 (in particular on some ATI chipsets). 1231 The kernel tries to set a reasonable default. 1232 1233 enforcing [SELINUX] Set initial enforcing status. 1234 Format: {"0" | "1"} 1235 See security/selinux/Kconfig help text. 1236 0 -- permissive (log only, no denials). 1237 1 -- enforcing (deny and log). 1238 Default value is 0. 1239 Value can be changed at runtime via /selinux/enforce. 1240 1241 erst_disable [ACPI] 1242 Disable Error Record Serialization Table (ERST) 1243 support. 1244 1245 ether= [HW,NET] Ethernet cards parameters 1246 This option is obsoleted by the "netdev=" option, which 1247 has equivalent usage. See its documentation for details. 1248 1249 evm= [EVM] 1250 Format: { "fix" } 1251 Permit 'security.evm' to be updated regardless of 1252 current integrity status. 1253 1254 failslab= 1255 fail_page_alloc= 1256 fail_make_request=[KNL] 1257 General fault injection mechanism. 1258 Format: <interval>,<probability>,<space>,<times> 1259 See also Documentation/fault-injection/. 1260 1261 floppy= [HW] 1262 See Documentation/admin-guide/blockdev/floppy.rst. 1263 1264 force_pal_cache_flush 1265 [IA-64] Avoid check_sal_cache_flush which may hang on 1266 buggy SAL_CACHE_FLUSH implementations. Using this 1267 parameter will force ia64_sal_cache_flush to call 1268 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1269 1270 forcepae [X86-32] 1271 Forcefully enable Physical Address Extension (PAE). 1272 Many Pentium M systems disable PAE but may have a 1273 functionally usable PAE implementation. 1274 Warning: use of this parameter will taint the kernel 1275 and may cause unknown problems. 1276 1277 ftrace=[tracer] 1278 [FTRACE] will set and start the specified tracer 1279 as early as possible in order to facilitate early 1280 boot debugging. 1281 1282 ftrace_dump_on_oops[=orig_cpu] 1283 [FTRACE] will dump the trace buffers on oops. 1284 If no parameter is passed, ftrace will dump 1285 buffers of all CPUs, but if you pass orig_cpu, it will 1286 dump only the buffer of the CPU that triggered the 1287 oops. 1288 1289 ftrace_filter=[function-list] 1290 [FTRACE] Limit the functions traced by the function 1291 tracer at boot up. function-list is a comma separated 1292 list of functions. This list can be changed at run 1293 time by the set_ftrace_filter file in the debugfs 1294 tracing directory. 1295 1296 ftrace_notrace=[function-list] 1297 [FTRACE] Do not trace the functions specified in 1298 function-list. This list can be changed at run time 1299 by the set_ftrace_notrace file in the debugfs 1300 tracing directory. 1301 1302 ftrace_graph_filter=[function-list] 1303 [FTRACE] Limit the top level callers functions traced 1304 by the function graph tracer at boot up. 1305 function-list is a comma separated list of functions 1306 that can be changed at run time by the 1307 set_graph_function file in the debugfs tracing directory. 1308 1309 ftrace_graph_notrace=[function-list] 1310 [FTRACE] Do not trace from the functions specified in 1311 function-list. This list is a comma separated list of 1312 functions that can be changed at run time by the 1313 set_graph_notrace file in the debugfs tracing directory. 1314 1315 ftrace_graph_max_depth=<uint> 1316 [FTRACE] Used with the function graph tracer. This is 1317 the max depth it will trace into a function. This value 1318 can be changed at run time by the max_graph_depth file 1319 in the tracefs tracing directory. default: 0 (no limit) 1320 1321 gamecon.map[2|3]= 1322 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1323 support via parallel port (up to 5 devices per port) 1324 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1325 See also Documentation/input/devices/joystick-parport.rst 1326 1327 gamma= [HW,DRM] 1328 1329 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1330 Format: off | on 1331 default: on 1332 1333 gcov_persist= [GCOV] When non-zero (default), profiling data for 1334 kernel modules is saved and remains accessible via 1335 debugfs, even when the module is unloaded/reloaded. 1336 When zero, profiling data is discarded and associated 1337 debugfs files are removed at module unload time. 1338 1339 goldfish [X86] Enable the goldfish android emulator platform. 1340 Don't use this when you are not running on the 1341 android emulator 1342 1343 gpt [EFI] Forces disk with valid GPT signature but 1344 invalid Protective MBR to be treated as GPT. If the 1345 primary GPT is corrupted, it enables the backup/alternate 1346 GPT to be used instead. 1347 1348 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1349 the "Enable 0" bit of the configuration register. 1350 Format: 0 | 1 1351 Default: 0 1352 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1353 the "Enable 0" bit of the configuration register. 1354 Format: 0 | 1 1355 Default: 0 1356 grcan.select= [HW] Select which physical interface to use. 1357 Format: 0 | 1 1358 Default: 0 1359 grcan.txsize= [HW] Sets the size of the tx buffer. 1360 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1361 Default: 1024 1362 grcan.rxsize= [HW] Sets the size of the rx buffer. 1363 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1364 Default: 1024 1365 1366 gpio-mockup.gpio_mockup_ranges 1367 [HW] Sets the ranges of gpiochip of for this device. 1368 Format: <start1>,<end1>,<start2>,<end2>... 1369 1370 hardlockup_all_cpu_backtrace= 1371 [KNL] Should the hard-lockup detector generate 1372 backtraces on all cpus. 1373 Format: <integer> 1374 1375 hashdist= [KNL,NUMA] Large hashes allocated during boot 1376 are distributed across NUMA nodes. Defaults on 1377 for 64-bit NUMA, off otherwise. 1378 Format: 0 | 1 (for off | on) 1379 1380 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1381 1382 hd= [EIDE] (E)IDE hard drive subsystem geometry 1383 Format: <cyl>,<head>,<sect> 1384 1385 hest_disable [ACPI] 1386 Disable Hardware Error Source Table (HEST) support; 1387 corresponding firmware-first mode error processing 1388 logic will be disabled. 1389 1390 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1391 size of <nn>. This works even on boxes that have no 1392 highmem otherwise. This also works to reduce highmem 1393 size on bigger boxes. 1394 1395 highres= [KNL] Enable/disable high resolution timer mode. 1396 Valid parameters: "on", "off" 1397 Default: "on" 1398 1399 hlt [BUGS=ARM,SH] 1400 1401 hpet= [X86-32,HPET] option to control HPET usage 1402 Format: { enable (default) | disable | force | 1403 verbose } 1404 disable: disable HPET and use PIT instead 1405 force: allow force enabled of undocumented chips (ICH4, 1406 VIA, nVidia) 1407 verbose: show contents of HPET registers during setup 1408 1409 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1410 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1411 1412 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1413 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1414 On x86-64 and powerpc, this option can be specified 1415 multiple times interleaved with hugepages= to reserve 1416 huge pages of different sizes. Valid pages sizes on 1417 x86-64 are 2M (when the CPU supports "pse") and 1G 1418 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1419 1420 hung_task_panic= 1421 [KNL] Should the hung task detector generate panics. 1422 Format: <integer> 1423 1424 A nonzero value instructs the kernel to panic when a 1425 hung task is detected. The default value is controlled 1426 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1427 option. The value selected by this boot parameter can 1428 be changed later by the kernel.hung_task_panic sysctl. 1429 1430 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1431 terminal devices. Valid values: 0..8 1432 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1433 If specified, z/VM IUCV HVC accepts connections 1434 from listed z/VM user IDs only. 1435 1436 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1437 which allow the hypervisor to 'idle' the 1438 guest on lock contention. 1439 1440 keep_bootcon [KNL] 1441 Do not unregister boot console at start. This is only 1442 useful for debugging when something happens in the window 1443 between unregistering the boot console and initializing 1444 the real console. 1445 1446 i2c_bus= [HW] Override the default board specific I2C bus speed 1447 or register an additional I2C bus that is not 1448 registered from board initialization code. 1449 Format: 1450 <bus_id>,<clkrate> 1451 1452 i8042.debug [HW] Toggle i8042 debug mode 1453 i8042.unmask_kbd_data 1454 [HW] Enable printing of interrupt data from the KBD port 1455 (disabled by default, and as a pre-condition 1456 requires that i8042.debug=1 be enabled) 1457 i8042.direct [HW] Put keyboard port into non-translated mode 1458 i8042.dumbkbd [HW] Pretend that controller can only read data from 1459 keyboard and cannot control its state 1460 (Don't attempt to blink the leds) 1461 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1462 i8042.nokbd [HW] Don't check/create keyboard port 1463 i8042.noloop [HW] Disable the AUX Loopback command while probing 1464 for the AUX port 1465 i8042.nomux [HW] Don't check presence of an active multiplexing 1466 controller 1467 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1468 controllers 1469 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1470 i8042.reset [HW] Reset the controller during init, cleanup and 1471 suspend-to-ram transitions, only during s2r 1472 transitions, or never reset 1473 Format: { 1 | Y | y | 0 | N | n } 1474 1, Y, y: always reset controller 1475 0, N, n: don't ever reset controller 1476 Default: only on s2r transitions on x86; most other 1477 architectures force reset to be always executed 1478 i8042.unlock [HW] Unlock (ignore) the keylock 1479 i8042.kbdreset [HW] Reset device connected to KBD port 1480 1481 i810= [HW,DRM] 1482 1483 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1484 indicates that the driver is running on unsupported 1485 hardware. 1486 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1487 does not match list of supported models. 1488 i8k.power_status 1489 [HW] Report power status in /proc/i8k 1490 (disabled by default) 1491 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1492 capability is set. 1493 1494 i915.invert_brightness= 1495 [DRM] Invert the sense of the variable that is used to 1496 set the brightness of the panel backlight. Normally a 1497 brightness value of 0 indicates backlight switched off, 1498 and the maximum of the brightness value sets the backlight 1499 to maximum brightness. If this parameter is set to 0 1500 (default) and the machine requires it, or this parameter 1501 is set to 1, a brightness value of 0 sets the backlight 1502 to maximum brightness, and the maximum of the brightness 1503 value switches the backlight off. 1504 -1 -- never invert brightness 1505 0 -- machine default 1506 1 -- force brightness inversion 1507 1508 icn= [HW,ISDN] 1509 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1510 1511 ide-core.nodma= [HW] (E)IDE subsystem 1512 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1513 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1514 .cdrom .chs .ignore_cable are additional options 1515 See Documentation/ide/ide.rst. 1516 1517 ide-generic.probe-mask= [HW] (E)IDE subsystem 1518 Format: <int> 1519 Probe mask for legacy ISA IDE ports. Depending on 1520 platform up to 6 ports are supported, enabled by 1521 setting corresponding bits in the mask to 1. The 1522 default value is 0x0, which has a special meaning. 1523 On systems that have PCI, it triggers scanning the 1524 PCI bus for the first and the second port, which 1525 are then probed. On systems without PCI the value 1526 of 0x0 enables probing the two first ports as if it 1527 was 0x3. 1528 1529 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1530 Claim all unknown PCI IDE storage controllers. 1531 1532 idle= [X86] 1533 Format: idle=poll, idle=halt, idle=nomwait 1534 Poll forces a polling idle loop that can slightly 1535 improve the performance of waking up a idle CPU, but 1536 will use a lot of power and make the system run hot. 1537 Not recommended. 1538 idle=halt: Halt is forced to be used for CPU idle. 1539 In such case C2/C3 won't be used again. 1540 idle=nomwait: Disable mwait for CPU C-states 1541 1542 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1543 Format: { strict | legacy | 2008 | relaxed } 1544 Default: strict 1545 1546 Choose which programs will be accepted for execution 1547 based on the IEEE 754 NaN encoding(s) supported by 1548 the FPU and the NaN encoding requested with the value 1549 of an ELF file header flag individually set by each 1550 binary. Hardware implementations are permitted to 1551 support either or both of the legacy and the 2008 NaN 1552 encoding mode. 1553 1554 Available settings are as follows: 1555 strict accept binaries that request a NaN encoding 1556 supported by the FPU 1557 legacy only accept legacy-NaN binaries, if supported 1558 by the FPU 1559 2008 only accept 2008-NaN binaries, if supported 1560 by the FPU 1561 relaxed accept any binaries regardless of whether 1562 supported by the FPU 1563 1564 The FPU emulator is always able to support both NaN 1565 encodings, so if no FPU hardware is present or it has 1566 been disabled with 'nofpu', then the settings of 1567 'legacy' and '2008' strap the emulator accordingly, 1568 'relaxed' straps the emulator for both legacy-NaN and 1569 2008-NaN, whereas 'strict' enables legacy-NaN only on 1570 legacy processors and both NaN encodings on MIPS32 or 1571 MIPS64 CPUs. 1572 1573 The setting for ABS.fmt/NEG.fmt instruction execution 1574 mode generally follows that for the NaN encoding, 1575 except where unsupported by hardware. 1576 1577 ignore_loglevel [KNL] 1578 Ignore loglevel setting - this will print /all/ 1579 kernel messages to the console. Useful for debugging. 1580 We also add it as printk module parameter, so users 1581 could change it dynamically, usually by 1582 /sys/module/printk/parameters/ignore_loglevel. 1583 1584 ignore_rlimit_data 1585 Ignore RLIMIT_DATA setting for data mappings, 1586 print warning at first misuse. Can be changed via 1587 /sys/module/kernel/parameters/ignore_rlimit_data. 1588 1589 ihash_entries= [KNL] 1590 Set number of hash buckets for inode cache. 1591 1592 ima_appraise= [IMA] appraise integrity measurements 1593 Format: { "off" | "enforce" | "fix" | "log" } 1594 default: "enforce" 1595 1596 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1597 The builtin appraise policy appraises all files 1598 owned by uid=0. 1599 1600 ima_canonical_fmt [IMA] 1601 Use the canonical format for the binary runtime 1602 measurements, instead of host native format. 1603 1604 ima_hash= [IMA] 1605 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1606 | sha512 | ... } 1607 default: "sha1" 1608 1609 The list of supported hash algorithms is defined 1610 in crypto/hash_info.h. 1611 1612 ima_policy= [IMA] 1613 The builtin policies to load during IMA setup. 1614 Format: "tcb | appraise_tcb | secure_boot | 1615 fail_securely" 1616 1617 The "tcb" policy measures all programs exec'd, files 1618 mmap'd for exec, and all files opened with the read 1619 mode bit set by either the effective uid (euid=0) or 1620 uid=0. 1621 1622 The "appraise_tcb" policy appraises the integrity of 1623 all files owned by root. 1624 1625 The "secure_boot" policy appraises the integrity 1626 of files (eg. kexec kernel image, kernel modules, 1627 firmware, policy, etc) based on file signatures. 1628 1629 The "fail_securely" policy forces file signature 1630 verification failure also on privileged mounted 1631 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1632 flag. 1633 1634 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1635 Load a policy which meets the needs of the Trusted 1636 Computing Base. This means IMA will measure all 1637 programs exec'd, files mmap'd for exec, and all files 1638 opened for read by uid=0. 1639 1640 ima_template= [IMA] 1641 Select one of defined IMA measurements template formats. 1642 Formats: { "ima" | "ima-ng" | "ima-sig" } 1643 Default: "ima-ng" 1644 1645 ima_template_fmt= 1646 [IMA] Define a custom template format. 1647 Format: { "field1|...|fieldN" } 1648 1649 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1650 Format: <min_file_size> 1651 Set the minimal file size for using asynchronous hash. 1652 If left unspecified, ahash usage is disabled. 1653 1654 ahash performance varies for different data sizes on 1655 different crypto accelerators. This option can be used 1656 to achieve the best performance for a particular HW. 1657 1658 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1659 Format: <bufsize> 1660 Set hashing buffer size. Default: 4k. 1661 1662 ahash performance varies for different chunk sizes on 1663 different crypto accelerators. This option can be used 1664 to achieve best performance for particular HW. 1665 1666 init= [KNL] 1667 Format: <full_path> 1668 Run specified binary instead of /sbin/init as init 1669 process. 1670 1671 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1672 for working out where the kernel is dying during 1673 startup. 1674 1675 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1676 initcall functions. Useful for debugging built-in 1677 modules and initcalls. 1678 1679 initrd= [BOOT] Specify the location of the initial ramdisk 1680 1681 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1682 zeroes. 1683 Format: 0 | 1 1684 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1685 1686 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1687 Format: 0 | 1 1688 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1689 1690 init_pkru= [x86] Specify the default memory protection keys rights 1691 register contents for all processes. 0x55555554 by 1692 default (disallow access to all but pkey 0). Can 1693 override in debugfs after boot. 1694 1695 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1696 Format: <irq> 1697 1698 int_pln_enable [x86] Enable power limit notification interrupt 1699 1700 integrity_audit=[IMA] 1701 Format: { "0" | "1" } 1702 0 -- basic integrity auditing messages. (Default) 1703 1 -- additional integrity auditing messages. 1704 1705 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1706 on 1707 Enable intel iommu driver. 1708 off 1709 Disable intel iommu driver. 1710 igfx_off [Default Off] 1711 By default, gfx is mapped as normal device. If a gfx 1712 device has a dedicated DMAR unit, the DMAR unit is 1713 bypassed by not enabling DMAR with this option. In 1714 this case, gfx device will use physical address for 1715 DMA. 1716 forcedac [x86_64] 1717 With this option iommu will not optimize to look 1718 for io virtual address below 32-bit forcing dual 1719 address cycle on pci bus for cards supporting greater 1720 than 32-bit addressing. The default is to look 1721 for translation below 32-bit and if not available 1722 then look in the higher range. 1723 strict [Default Off] 1724 With this option on every unmap_single operation will 1725 result in a hardware IOTLB flush operation as opposed 1726 to batching them for performance. 1727 sp_off [Default Off] 1728 By default, super page will be supported if Intel IOMMU 1729 has the capability. With this option, super page will 1730 not be supported. 1731 sm_on [Default Off] 1732 By default, scalable mode will be disabled even if the 1733 hardware advertises that it has support for the scalable 1734 mode translation. With this option set, scalable mode 1735 will be used on hardware which claims to support it. 1736 tboot_noforce [Default Off] 1737 Do not force the Intel IOMMU enabled under tboot. 1738 By default, tboot will force Intel IOMMU on, which 1739 could harm performance of some high-throughput 1740 devices like 40GBit network cards, even if identity 1741 mapping is enabled. 1742 Note that using this option lowers the security 1743 provided by tboot because it makes the system 1744 vulnerable to DMA attacks. 1745 nobounce [Default off] 1746 Disable bounce buffer for unstrusted devices such as 1747 the Thunderbolt devices. This will treat the untrusted 1748 devices as the trusted ones, hence might expose security 1749 risks of DMA attacks. 1750 1751 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1752 0 disables intel_idle and fall back on acpi_idle. 1753 1 to 9 specify maximum depth of C-state. 1754 1755 intel_pstate= [X86] 1756 disable 1757 Do not enable intel_pstate as the default 1758 scaling driver for the supported processors 1759 passive 1760 Use intel_pstate as a scaling driver, but configure it 1761 to work with generic cpufreq governors (instead of 1762 enabling its internal governor). This mode cannot be 1763 used along with the hardware-managed P-states (HWP) 1764 feature. 1765 force 1766 Enable intel_pstate on systems that prohibit it by default 1767 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1768 instead of acpi-cpufreq may disable platform features, such 1769 as thermal controls and power capping, that rely on ACPI 1770 P-States information being indicated to OSPM and therefore 1771 should be used with caution. This option does not work with 1772 processors that aren't supported by the intel_pstate driver 1773 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1774 no_hwp 1775 Do not enable hardware P state control (HWP) 1776 if available. 1777 hwp_only 1778 Only load intel_pstate on systems which support 1779 hardware P state control (HWP) if available. 1780 support_acpi_ppc 1781 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1782 Description Table, specifies preferred power management 1783 profile as "Enterprise Server" or "Performance Server", 1784 then this feature is turned on by default. 1785 per_cpu_perf_limits 1786 Allow per-logical-CPU P-State performance control limits using 1787 cpufreq sysfs interface 1788 1789 intremap= [X86-64, Intel-IOMMU] 1790 on enable Interrupt Remapping (default) 1791 off disable Interrupt Remapping 1792 nosid disable Source ID checking 1793 no_x2apic_optout 1794 BIOS x2APIC opt-out request will be ignored 1795 nopost disable Interrupt Posting 1796 1797 iomem= Disable strict checking of access to MMIO memory 1798 strict regions from userspace. 1799 relaxed 1800 1801 iommu= [x86] 1802 off 1803 force 1804 noforce 1805 biomerge 1806 panic 1807 nopanic 1808 merge 1809 nomerge 1810 soft 1811 pt [x86] 1812 nopt [x86] 1813 nobypass [PPC/POWERNV] 1814 Disable IOMMU bypass, using IOMMU for PCI devices. 1815 1816 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1817 Format: { "0" | "1" } 1818 0 - Lazy mode. 1819 Request that DMA unmap operations use deferred 1820 invalidation of hardware TLBs, for increased 1821 throughput at the cost of reduced device isolation. 1822 Will fall back to strict mode if not supported by 1823 the relevant IOMMU driver. 1824 1 - Strict mode (default). 1825 DMA unmap operations invalidate IOMMU hardware TLBs 1826 synchronously. 1827 1828 iommu.passthrough= 1829 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1830 Format: { "0" | "1" } 1831 0 - Use IOMMU translation for DMA. 1832 1 - Bypass the IOMMU for DMA. 1833 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1834 1835 io7= [HW] IO7 for Marvel based alpha systems 1836 See comment before marvel_specify_io7 in 1837 arch/alpha/kernel/core_marvel.c. 1838 1839 io_delay= [X86] I/O delay method 1840 0x80 1841 Standard port 0x80 based delay 1842 0xed 1843 Alternate port 0xed based delay (needed on some systems) 1844 udelay 1845 Simple two microseconds delay 1846 none 1847 No delay 1848 1849 ip= [IP_PNP] 1850 See Documentation/filesystems/nfs/nfsroot.txt. 1851 1852 ipcmni_extend [KNL] Extend the maximum number of unique System V 1853 IPC identifiers from 32,768 to 16,777,216. 1854 1855 irqaffinity= [SMP] Set the default irq affinity mask 1856 The argument is a cpu list, as described above. 1857 1858 irqchip.gicv2_force_probe= 1859 [ARM, ARM64] 1860 Format: <bool> 1861 Force the kernel to look for the second 4kB page 1862 of a GICv2 controller even if the memory range 1863 exposed by the device tree is too small. 1864 1865 irqchip.gicv3_nolpi= 1866 [ARM, ARM64] 1867 Force the kernel to ignore the availability of 1868 LPIs (and by consequence ITSs). Intended for system 1869 that use the kernel as a bootloader, and thus want 1870 to let secondary kernels in charge of setting up 1871 LPIs. 1872 1873 irqchip.gicv3_pseudo_nmi= [ARM64] 1874 Enables support for pseudo-NMIs in the kernel. This 1875 requires the kernel to be built with 1876 CONFIG_ARM64_PSEUDO_NMI. 1877 1878 irqfixup [HW] 1879 When an interrupt is not handled search all handlers 1880 for it. Intended to get systems with badly broken 1881 firmware running. 1882 1883 irqpoll [HW] 1884 When an interrupt is not handled search all handlers 1885 for it. Also check all handlers each timer 1886 interrupt. Intended to get systems with badly broken 1887 firmware running. 1888 1889 isapnp= [ISAPNP] 1890 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1891 1892 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1893 [Deprecated - use cpusets instead] 1894 Format: [flag-list,]<cpu-list> 1895 1896 Specify one or more CPUs to isolate from disturbances 1897 specified in the flag list (default: domain): 1898 1899 nohz 1900 Disable the tick when a single task runs. 1901 1902 A residual 1Hz tick is offloaded to workqueues, which you 1903 need to affine to housekeeping through the global 1904 workqueue's affinity configured via the 1905 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1906 by using the 'domain' flag described below. 1907 1908 NOTE: by default the global workqueue runs on all CPUs, 1909 so to protect individual CPUs the 'cpumask' file has to 1910 be configured manually after bootup. 1911 1912 domain 1913 Isolate from the general SMP balancing and scheduling 1914 algorithms. Note that performing domain isolation this way 1915 is irreversible: it's not possible to bring back a CPU to 1916 the domains once isolated through isolcpus. It's strongly 1917 advised to use cpusets instead to disable scheduler load 1918 balancing through the "cpuset.sched_load_balance" file. 1919 It offers a much more flexible interface where CPUs can 1920 move in and out of an isolated set anytime. 1921 1922 You can move a process onto or off an "isolated" CPU via 1923 the CPU affinity syscalls or cpuset. 1924 <cpu number> begins at 0 and the maximum value is 1925 "number of CPUs in system - 1". 1926 1927 The format of <cpu-list> is described above. 1928 1929 1930 1931 iucv= [HW,NET] 1932 1933 ivrs_ioapic [HW,X86_64] 1934 Provide an override to the IOAPIC-ID<->DEVICE-ID 1935 mapping provided in the IVRS ACPI table. For 1936 example, to map IOAPIC-ID decimal 10 to 1937 PCI device 00:14.0 write the parameter as: 1938 ivrs_ioapic[10]=00:14.0 1939 1940 ivrs_hpet [HW,X86_64] 1941 Provide an override to the HPET-ID<->DEVICE-ID 1942 mapping provided in the IVRS ACPI table. For 1943 example, to map HPET-ID decimal 0 to 1944 PCI device 00:14.0 write the parameter as: 1945 ivrs_hpet[0]=00:14.0 1946 1947 ivrs_acpihid [HW,X86_64] 1948 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1949 mapping provided in the IVRS ACPI table. For 1950 example, to map UART-HID:UID AMD0020:0 to 1951 PCI device 00:14.5 write the parameter as: 1952 ivrs_acpihid[00:14.5]=AMD0020:0 1953 1954 js= [HW,JOY] Analog joystick 1955 See Documentation/input/joydev/joystick.rst. 1956 1957 nokaslr [KNL] 1958 When CONFIG_RANDOMIZE_BASE is set, this disables 1959 kernel and module base offset ASLR (Address Space 1960 Layout Randomization). 1961 1962 kasan_multi_shot 1963 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1964 report on every invalid memory access. Without this 1965 parameter KASAN will print report only for the first 1966 invalid access. 1967 1968 keepinitrd [HW,ARM] 1969 1970 kernelcore= [KNL,X86,IA-64,PPC] 1971 Format: nn[KMGTPE] | nn% | "mirror" 1972 This parameter specifies the amount of memory usable by 1973 the kernel for non-movable allocations. The requested 1974 amount is spread evenly throughout all nodes in the 1975 system as ZONE_NORMAL. The remaining memory is used for 1976 movable memory in its own zone, ZONE_MOVABLE. In the 1977 event, a node is too small to have both ZONE_NORMAL and 1978 ZONE_MOVABLE, kernelcore memory will take priority and 1979 other nodes will have a larger ZONE_MOVABLE. 1980 1981 ZONE_MOVABLE is used for the allocation of pages that 1982 may be reclaimed or moved by the page migration 1983 subsystem. Note that allocations like PTEs-from-HighMem 1984 still use the HighMem zone if it exists, and the Normal 1985 zone if it does not. 1986 1987 It is possible to specify the exact amount of memory in 1988 the form of "nn[KMGTPE]", a percentage of total system 1989 memory in the form of "nn%", or "mirror". If "mirror" 1990 option is specified, mirrored (reliable) memory is used 1991 for non-movable allocations and remaining memory is used 1992 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1993 are exclusive, so you cannot specify multiple forms. 1994 1995 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1996 Format: <Controller#>[,poll interval] 1997 The controller # is the number of the ehci usb debug 1998 port as it is probed via PCI. The poll interval is 1999 optional and is the number seconds in between 2000 each poll cycle to the debug port in case you need 2001 the functionality for interrupting the kernel with 2002 gdb or control-c on the dbgp connection. When 2003 not using this parameter you use sysrq-g to break into 2004 the kernel debugger. 2005 2006 kgdboc= [KGDB,HW] kgdb over consoles. 2007 Requires a tty driver that supports console polling, 2008 or a supported polling keyboard driver (non-usb). 2009 Serial only format: <serial_device>[,baud] 2010 keyboard only format: kbd 2011 keyboard and serial format: kbd,<serial_device>[,baud] 2012 Optional Kernel mode setting: 2013 kms, kbd format: kms,kbd 2014 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2015 2016 kgdbwait [KGDB] Stop kernel execution and enter the 2017 kernel debugger at the earliest opportunity. 2018 2019 kmac= [MIPS] korina ethernet MAC address. 2020 Configure the RouterBoard 532 series on-chip 2021 Ethernet adapter MAC address. 2022 2023 kmemleak= [KNL] Boot-time kmemleak enable/disable 2024 Valid arguments: on, off 2025 Default: on 2026 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2027 the default is off. 2028 2029 kprobe_event=[probe-list] 2030 [FTRACE] Add kprobe events and enable at boot time. 2031 The probe-list is a semicolon delimited list of probe 2032 definitions. Each definition is same as kprobe_events 2033 interface, but the parameters are comma delimited. 2034 For example, to add a kprobe event on vfs_read with 2035 arg1 and arg2, add to the command line; 2036 2037 kprobe_event=p,vfs_read,$arg1,$arg2 2038 2039 See also Documentation/trace/kprobetrace.rst "Kernel 2040 Boot Parameter" section. 2041 2042 kpti= [ARM64] Control page table isolation of user 2043 and kernel address spaces. 2044 Default: enabled on cores which need mitigation. 2045 0: force disabled 2046 1: force enabled 2047 2048 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2049 Default is 0 (don't ignore, but inject #GP) 2050 2051 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2052 Default is false (don't support). 2053 2054 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2055 KVM MMU at runtime. 2056 Default is 0 (off) 2057 2058 kvm.nx_huge_pages= 2059 [KVM] Controls the software workaround for the 2060 X86_BUG_ITLB_MULTIHIT bug. 2061 force : Always deploy workaround. 2062 off : Never deploy workaround. 2063 auto : Deploy workaround based on the presence of 2064 X86_BUG_ITLB_MULTIHIT. 2065 2066 Default is 'auto'. 2067 2068 If the software workaround is enabled for the host, 2069 guests do need not to enable it for nested guests. 2070 2071 kvm.nx_huge_pages_recovery_ratio= 2072 [KVM] Controls how many 4KiB pages are periodically zapped 2073 back to huge pages. 0 disables the recovery, otherwise if 2074 the value is N KVM will zap 1/Nth of the 4KiB pages every 2075 minute. The default is 60. 2076 2077 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2078 Default is 1 (enabled) 2079 2080 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2081 for all guests. 2082 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2083 2084 kvm-arm.vgic_v3_group0_trap= 2085 [KVM,ARM] Trap guest accesses to GICv3 group-0 2086 system registers 2087 2088 kvm-arm.vgic_v3_group1_trap= 2089 [KVM,ARM] Trap guest accesses to GICv3 group-1 2090 system registers 2091 2092 kvm-arm.vgic_v3_common_trap= 2093 [KVM,ARM] Trap guest accesses to GICv3 common 2094 system registers 2095 2096 kvm-arm.vgic_v4_enable= 2097 [KVM,ARM] Allow use of GICv4 for direct injection of 2098 LPIs. 2099 2100 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2101 (virtualized MMU) support on capable Intel chips. 2102 Default is 1 (enabled) 2103 2104 kvm-intel.emulate_invalid_guest_state= 2105 [KVM,Intel] Enable emulation of invalid guest states 2106 Default is 0 (disabled) 2107 2108 kvm-intel.flexpriority= 2109 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2110 Default is 1 (enabled) 2111 2112 kvm-intel.nested= 2113 [KVM,Intel] Enable VMX nesting (nVMX). 2114 Default is 0 (disabled) 2115 2116 kvm-intel.unrestricted_guest= 2117 [KVM,Intel] Disable unrestricted guest feature 2118 (virtualized real and unpaged mode) on capable 2119 Intel chips. Default is 1 (enabled) 2120 2121 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2122 CVE-2018-3620. 2123 2124 Valid arguments: never, cond, always 2125 2126 always: L1D cache flush on every VMENTER. 2127 cond: Flush L1D on VMENTER only when the code between 2128 VMEXIT and VMENTER can leak host memory. 2129 never: Disables the mitigation 2130 2131 Default is cond (do L1 cache flush in specific instances) 2132 2133 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2134 feature (tagged TLBs) on capable Intel chips. 2135 Default is 1 (enabled) 2136 2137 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2138 affected CPUs 2139 2140 The kernel PTE inversion protection is unconditionally 2141 enabled and cannot be disabled. 2142 2143 full 2144 Provides all available mitigations for the 2145 L1TF vulnerability. Disables SMT and 2146 enables all mitigations in the 2147 hypervisors, i.e. unconditional L1D flush. 2148 2149 SMT control and L1D flush control via the 2150 sysfs interface is still possible after 2151 boot. Hypervisors will issue a warning 2152 when the first VM is started in a 2153 potentially insecure configuration, 2154 i.e. SMT enabled or L1D flush disabled. 2155 2156 full,force 2157 Same as 'full', but disables SMT and L1D 2158 flush runtime control. Implies the 2159 'nosmt=force' command line option. 2160 (i.e. sysfs control of SMT is disabled.) 2161 2162 flush 2163 Leaves SMT enabled and enables the default 2164 hypervisor mitigation, i.e. conditional 2165 L1D flush. 2166 2167 SMT control and L1D flush control via the 2168 sysfs interface is still possible after 2169 boot. Hypervisors will issue a warning 2170 when the first VM is started in a 2171 potentially insecure configuration, 2172 i.e. SMT enabled or L1D flush disabled. 2173 2174 flush,nosmt 2175 2176 Disables SMT and enables the default 2177 hypervisor mitigation. 2178 2179 SMT control and L1D flush control via the 2180 sysfs interface is still possible after 2181 boot. Hypervisors will issue a warning 2182 when the first VM is started in a 2183 potentially insecure configuration, 2184 i.e. SMT enabled or L1D flush disabled. 2185 2186 flush,nowarn 2187 Same as 'flush', but hypervisors will not 2188 warn when a VM is started in a potentially 2189 insecure configuration. 2190 2191 off 2192 Disables hypervisor mitigations and doesn't 2193 emit any warnings. 2194 It also drops the swap size and available 2195 RAM limit restriction on both hypervisor and 2196 bare metal. 2197 2198 Default is 'flush'. 2199 2200 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2201 2202 l2cr= [PPC] 2203 2204 l3cr= [PPC] 2205 2206 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2207 disabled it. 2208 2209 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2210 value for LAPIC timer one-shot implementation. Default 2211 back to the programmable timer unit in the LAPIC. 2212 2213 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2214 in C2 power state. 2215 2216 libata.dma= [LIBATA] DMA control 2217 libata.dma=0 Disable all PATA and SATA DMA 2218 libata.dma=1 PATA and SATA Disk DMA only 2219 libata.dma=2 ATAPI (CDROM) DMA only 2220 libata.dma=4 Compact Flash DMA only 2221 Combinations also work, so libata.dma=3 enables DMA 2222 for disks and CDROMs, but not CFs. 2223 2224 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2225 libata.ignore_hpa=0 keep BIOS limits (default) 2226 libata.ignore_hpa=1 ignore limits, using full disk 2227 2228 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2229 when set. 2230 Format: <int> 2231 2232 libata.force= [LIBATA] Force configurations. The format is comma 2233 separated list of "[ID:]VAL" where ID is 2234 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2235 matching port, link or device. Basically, it matches 2236 the ATA ID string printed on console by libata. If 2237 the whole ID part is omitted, the last PORT and DEVICE 2238 values are used. If ID hasn't been specified yet, the 2239 configuration applies to all ports, links and devices. 2240 2241 If only DEVICE is omitted, the parameter applies to 2242 the port and all links and devices behind it. DEVICE 2243 number of 0 either selects the first device or the 2244 first fan-out link behind PMP device. It does not 2245 select the host link. DEVICE number of 15 selects the 2246 host link and device attached to it. 2247 2248 The VAL specifies the configuration to force. As long 2249 as there's no ambiguity shortcut notation is allowed. 2250 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2251 The following configurations can be forced. 2252 2253 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2254 Any ID with matching PORT is used. 2255 2256 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2257 2258 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2259 udma[/][16,25,33,44,66,100,133] notation is also 2260 allowed. 2261 2262 * [no]ncq: Turn on or off NCQ. 2263 2264 * [no]ncqtrim: Turn off queued DSM TRIM. 2265 2266 * nohrst, nosrst, norst: suppress hard, soft 2267 and both resets. 2268 2269 * rstonce: only attempt one reset during 2270 hot-unplug link recovery 2271 2272 * dump_id: dump IDENTIFY data. 2273 2274 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2275 2276 * disable: Disable this device. 2277 2278 If there are multiple matching configurations changing 2279 the same attribute, the last one is used. 2280 2281 memblock=debug [KNL] Enable memblock debug messages. 2282 2283 load_ramdisk= [RAM] List of ramdisks to load from floppy 2284 See Documentation/admin-guide/blockdev/ramdisk.rst. 2285 2286 lockd.nlm_grace_period=P [NFS] Assign grace period. 2287 Format: <integer> 2288 2289 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2290 Format: <integer> 2291 2292 lockd.nlm_timeout=T [NFS] Assign timeout value. 2293 Format: <integer> 2294 2295 lockd.nlm_udpport=M [NFS] Assign UDP port. 2296 Format: <integer> 2297 2298 lockdown= [SECURITY] 2299 { integrity | confidentiality } 2300 Enable the kernel lockdown feature. If set to 2301 integrity, kernel features that allow userland to 2302 modify the running kernel are disabled. If set to 2303 confidentiality, kernel features that allow userland 2304 to extract confidential information from the kernel 2305 are also disabled. 2306 2307 locktorture.nreaders_stress= [KNL] 2308 Set the number of locking read-acquisition kthreads. 2309 Defaults to being automatically set based on the 2310 number of online CPUs. 2311 2312 locktorture.nwriters_stress= [KNL] 2313 Set the number of locking write-acquisition kthreads. 2314 2315 locktorture.onoff_holdoff= [KNL] 2316 Set time (s) after boot for CPU-hotplug testing. 2317 2318 locktorture.onoff_interval= [KNL] 2319 Set time (s) between CPU-hotplug operations, or 2320 zero to disable CPU-hotplug testing. 2321 2322 locktorture.shuffle_interval= [KNL] 2323 Set task-shuffle interval (jiffies). Shuffling 2324 tasks allows some CPUs to go into dyntick-idle 2325 mode during the locktorture test. 2326 2327 locktorture.shutdown_secs= [KNL] 2328 Set time (s) after boot system shutdown. This 2329 is useful for hands-off automated testing. 2330 2331 locktorture.stat_interval= [KNL] 2332 Time (s) between statistics printk()s. 2333 2334 locktorture.stutter= [KNL] 2335 Time (s) to stutter testing, for example, 2336 specifying five seconds causes the test to run for 2337 five seconds, wait for five seconds, and so on. 2338 This tests the locking primitive's ability to 2339 transition abruptly to and from idle. 2340 2341 locktorture.torture_type= [KNL] 2342 Specify the locking implementation to test. 2343 2344 locktorture.verbose= [KNL] 2345 Enable additional printk() statements. 2346 2347 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2348 Format: <irq> 2349 2350 loglevel= All Kernel Messages with a loglevel smaller than the 2351 console loglevel will be printed to the console. It can 2352 also be changed with klogd or other programs. The 2353 loglevels are defined as follows: 2354 2355 0 (KERN_EMERG) system is unusable 2356 1 (KERN_ALERT) action must be taken immediately 2357 2 (KERN_CRIT) critical conditions 2358 3 (KERN_ERR) error conditions 2359 4 (KERN_WARNING) warning conditions 2360 5 (KERN_NOTICE) normal but significant condition 2361 6 (KERN_INFO) informational 2362 7 (KERN_DEBUG) debug-level messages 2363 2364 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2365 in bytes. n must be a power of two and greater 2366 than the minimal size. The minimal size is defined 2367 by LOG_BUF_SHIFT kernel config parameter. There is 2368 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2369 that allows to increase the default size depending on 2370 the number of CPUs. See init/Kconfig for more details. 2371 2372 logo.nologo [FB] Disables display of the built-in Linux logo. 2373 This may be used to provide more screen space for 2374 kernel log messages and is useful when debugging 2375 kernel boot problems. 2376 2377 lp=0 [LP] Specify parallel ports to use, e.g, 2378 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2379 lp=reset first parallel port). 'lp=0' disables the 2380 lp=auto printer driver. 'lp=reset' (which can be 2381 specified in addition to the ports) causes 2382 attached printers to be reset. Using 2383 lp=port1,port2,... specifies the parallel ports 2384 to associate lp devices with, starting with 2385 lp0. A port specification may be 'none' to skip 2386 that lp device, or a parport name such as 2387 'parport0'. Specifying 'lp=auto' instead of a 2388 port specification list means that device IDs 2389 from each port should be examined, to see if 2390 an IEEE 1284-compliant printer is attached; if 2391 so, the driver will manage that printer. 2392 See also header of drivers/char/lp.c. 2393 2394 lpj=n [KNL] 2395 Sets loops_per_jiffy to given constant, thus avoiding 2396 time-consuming boot-time autodetection (up to 250 ms per 2397 CPU). 0 enables autodetection (default). To determine 2398 the correct value for your kernel, boot with normal 2399 autodetection and see what value is printed. Note that 2400 on SMP systems the preset will be applied to all CPUs, 2401 which is likely to cause problems if your CPUs need 2402 significantly divergent settings. An incorrect value 2403 will cause delays in the kernel to be wrong, leading to 2404 unpredictable I/O errors and other breakage. Although 2405 unlikely, in the extreme case this might damage your 2406 hardware. 2407 2408 ltpc= [NET] 2409 Format: <io>,<irq>,<dma> 2410 2411 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2412 2413 lsm=lsm1,...,lsmN 2414 [SECURITY] Choose order of LSM initialization. This 2415 overrides CONFIG_LSM, and the "security=" parameter. 2416 2417 machvec= [IA-64] Force the use of a particular machine-vector 2418 (machvec) in a generic kernel. 2419 Example: machvec=hpzx1 2420 2421 machtype= [Loongson] Share the same kernel image file between different 2422 yeeloong laptop. 2423 Example: machtype=lemote-yeeloong-2f-7inch 2424 2425 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2426 than or equal to this physical address is ignored. 2427 2428 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2429 will bring up during bootup. maxcpus=n : n >= 0 limits 2430 the kernel to bring up 'n' processors. Surely after 2431 bootup you can bring up the other plugged cpu by executing 2432 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2433 only takes effect during system bootup. 2434 While n=0 is a special case, it is equivalent to "nosmp", 2435 which also disables the IO APIC. 2436 2437 max_loop= [LOOP] The number of loop block devices that get 2438 (loop.max_loop) unconditionally pre-created at init time. The default 2439 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2440 of statically allocating a predefined number, loop 2441 devices can be requested on-demand with the 2442 /dev/loop-control interface. 2443 2444 mce [X86-32] Machine Check Exception 2445 2446 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2447 2448 md= [HW] RAID subsystems devices and level 2449 See Documentation/admin-guide/md.rst. 2450 2451 mdacon= [MDA] 2452 Format: <first>,<last> 2453 Specifies range of consoles to be captured by the MDA. 2454 2455 mds= [X86,INTEL] 2456 Control mitigation for the Micro-architectural Data 2457 Sampling (MDS) vulnerability. 2458 2459 Certain CPUs are vulnerable to an exploit against CPU 2460 internal buffers which can forward information to a 2461 disclosure gadget under certain conditions. 2462 2463 In vulnerable processors, the speculatively 2464 forwarded data can be used in a cache side channel 2465 attack, to access data to which the attacker does 2466 not have direct access. 2467 2468 This parameter controls the MDS mitigation. The 2469 options are: 2470 2471 full - Enable MDS mitigation on vulnerable CPUs 2472 full,nosmt - Enable MDS mitigation and disable 2473 SMT on vulnerable CPUs 2474 off - Unconditionally disable MDS mitigation 2475 2476 Not specifying this option is equivalent to 2477 mds=full. 2478 2479 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2480 2481 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2482 Amount of memory to be used when the kernel is not able 2483 to see the whole system memory or for test. 2484 [X86] Work as limiting max address. Use together 2485 with memmap= to avoid physical address space collisions. 2486 Without memmap= PCI devices could be placed at addresses 2487 belonging to unused RAM. 2488 2489 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2490 memory. 2491 2492 memchunk=nn[KMG] 2493 [KNL,SH] Allow user to override the default size for 2494 per-device physically contiguous DMA buffers. 2495 2496 memhp_default_state=online/offline 2497 [KNL] Set the initial state for the memory hotplug 2498 onlining policy. If not specified, the default value is 2499 set according to the 2500 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2501 option. 2502 See Documentation/admin-guide/mm/memory-hotplug.rst. 2503 2504 memmap=exactmap [KNL,X86] Enable setting of an exact 2505 E820 memory map, as specified by the user. 2506 Such memmap=exactmap lines can be constructed based on 2507 BIOS output or other requirements. See the memmap=nn@ss 2508 option description. 2509 2510 memmap=nn[KMG]@ss[KMG] 2511 [KNL] Force usage of a specific region of memory. 2512 Region of memory to be used is from ss to ss+nn. 2513 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2514 which limits max address to nn[KMG]. 2515 Multiple different regions can be specified, 2516 comma delimited. 2517 Example: 2518 memmap=100M@2G,100M#3G,1G!1024G 2519 2520 memmap=nn[KMG]#ss[KMG] 2521 [KNL,ACPI] Mark specific memory as ACPI data. 2522 Region of memory to be marked is from ss to ss+nn. 2523 2524 memmap=nn[KMG]$ss[KMG] 2525 [KNL,ACPI] Mark specific memory as reserved. 2526 Region of memory to be reserved is from ss to ss+nn. 2527 Example: Exclude memory from 0x18690000-0x1869ffff 2528 memmap=64K$0x18690000 2529 or 2530 memmap=0x10000$0x18690000 2531 Some bootloaders may need an escape character before '$', 2532 like Grub2, otherwise '$' and the following number 2533 will be eaten. 2534 2535 memmap=nn[KMG]!ss[KMG] 2536 [KNL,X86] Mark specific memory as protected. 2537 Region of memory to be used, from ss to ss+nn. 2538 The memory region may be marked as e820 type 12 (0xc) 2539 and is NVDIMM or ADR memory. 2540 2541 memmap=<size>%<offset>-<oldtype>+<newtype> 2542 [KNL,ACPI] Convert memory within the specified region 2543 from <oldtype> to <newtype>. If "-<oldtype>" is left 2544 out, the whole region will be marked as <newtype>, 2545 even if previously unavailable. If "+<newtype>" is left 2546 out, matching memory will be removed. Types are 2547 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2548 3 = ACPI, 12 = PRAM. 2549 2550 memory_corruption_check=0/1 [X86] 2551 Some BIOSes seem to corrupt the first 64k of 2552 memory when doing things like suspend/resume. 2553 Setting this option will scan the memory 2554 looking for corruption. Enabling this will 2555 both detect corruption and prevent the kernel 2556 from using the memory being corrupted. 2557 However, its intended as a diagnostic tool; if 2558 repeatable BIOS-originated corruption always 2559 affects the same memory, you can use memmap= 2560 to prevent the kernel from using that memory. 2561 2562 memory_corruption_check_size=size [X86] 2563 By default it checks for corruption in the low 2564 64k, making this memory unavailable for normal 2565 use. Use this parameter to scan for 2566 corruption in more or less memory. 2567 2568 memory_corruption_check_period=seconds [X86] 2569 By default it checks for corruption every 60 2570 seconds. Use this parameter to check at some 2571 other rate. 0 disables periodic checking. 2572 2573 memtest= [KNL,X86,ARM,PPC] Enable memtest 2574 Format: <integer> 2575 default : 0 <disable> 2576 Specifies the number of memtest passes to be 2577 performed. Each pass selects another test 2578 pattern from a given set of patterns. Memtest 2579 fills the memory with this pattern, validates 2580 memory contents and reserves bad memory 2581 regions that are detected. 2582 2583 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2584 Valid arguments: on, off 2585 Default (depends on kernel configuration option): 2586 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2587 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2588 mem_encrypt=on: Activate SME 2589 mem_encrypt=off: Do not activate SME 2590 2591 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2592 for details on when memory encryption can be activated. 2593 2594 mem_sleep_default= [SUSPEND] Default system suspend mode: 2595 s2idle - Suspend-To-Idle 2596 shallow - Power-On Suspend or equivalent (if supported) 2597 deep - Suspend-To-RAM or equivalent (if supported) 2598 See Documentation/admin-guide/pm/sleep-states.rst. 2599 2600 meye.*= [HW] Set MotionEye Camera parameters 2601 See Documentation/media/v4l-drivers/meye.rst. 2602 2603 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2604 Multi-Function General Purpose Timers on AMD Geode 2605 platforms. 2606 2607 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2608 the BIOS has incorrectly applied a workaround. TinyBIOS 2609 version 0.98 is known to be affected, 0.99 fixes the 2610 problem by letting the user disable the workaround. 2611 2612 mga= [HW,DRM] 2613 2614 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2615 physical address is ignored. 2616 2617 mini2440= [ARM,HW,KNL] 2618 Format:[0..2][b][c][t] 2619 Default: "0tb" 2620 MINI2440 configuration specification: 2621 0 - The attached screen is the 3.5" TFT 2622 1 - The attached screen is the 7" TFT 2623 2 - The VGA Shield is attached (1024x768) 2624 Leaving out the screen size parameter will not load 2625 the TFT driver, and the framebuffer will be left 2626 unconfigured. 2627 b - Enable backlight. The TFT backlight pin will be 2628 linked to the kernel VESA blanking code and a GPIO 2629 LED. This parameter is not necessary when using the 2630 VGA shield. 2631 c - Enable the s3c camera interface. 2632 t - Reserved for enabling touchscreen support. The 2633 touchscreen support is not enabled in the mainstream 2634 kernel as of 2.6.30, a preliminary port can be found 2635 in the "bleeding edge" mini2440 support kernel at 2636 http://repo.or.cz/w/linux-2.6/mini2440.git 2637 2638 mitigations= 2639 [X86,PPC,S390,ARM64] Control optional mitigations for 2640 CPU vulnerabilities. This is a set of curated, 2641 arch-independent options, each of which is an 2642 aggregation of existing arch-specific options. 2643 2644 off 2645 Disable all optional CPU mitigations. This 2646 improves system performance, but it may also 2647 expose users to several CPU vulnerabilities. 2648 Equivalent to: nopti [X86,PPC] 2649 kpti=0 [ARM64] 2650 nospectre_v1 [X86,PPC] 2651 nobp=0 [S390] 2652 nospectre_v2 [X86,PPC,S390,ARM64] 2653 spectre_v2_user=off [X86] 2654 spec_store_bypass_disable=off [X86,PPC] 2655 ssbd=force-off [ARM64] 2656 l1tf=off [X86] 2657 mds=off [X86] 2658 tsx_async_abort=off [X86] 2659 kvm.nx_huge_pages=off [X86] 2660 2661 Exceptions: 2662 This does not have any effect on 2663 kvm.nx_huge_pages when 2664 kvm.nx_huge_pages=force. 2665 2666 auto (default) 2667 Mitigate all CPU vulnerabilities, but leave SMT 2668 enabled, even if it's vulnerable. This is for 2669 users who don't want to be surprised by SMT 2670 getting disabled across kernel upgrades, or who 2671 have other ways of avoiding SMT-based attacks. 2672 Equivalent to: (default behavior) 2673 2674 auto,nosmt 2675 Mitigate all CPU vulnerabilities, disabling SMT 2676 if needed. This is for users who always want to 2677 be fully mitigated, even if it means losing SMT. 2678 Equivalent to: l1tf=flush,nosmt [X86] 2679 mds=full,nosmt [X86] 2680 tsx_async_abort=full,nosmt [X86] 2681 2682 mminit_loglevel= 2683 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2684 parameter allows control of the logging verbosity for 2685 the additional memory initialisation checks. A value 2686 of 0 disables mminit logging and a level of 4 will 2687 log everything. Information is printed at KERN_DEBUG 2688 so loglevel=8 may also need to be specified. 2689 2690 module.sig_enforce 2691 [KNL] When CONFIG_MODULE_SIG is set, this means that 2692 modules without (valid) signatures will fail to load. 2693 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2694 is always true, so this option does nothing. 2695 2696 module_blacklist= [KNL] Do not load a comma-separated list of 2697 modules. Useful for debugging problem modules. 2698 2699 mousedev.tap_time= 2700 [MOUSE] Maximum time between finger touching and 2701 leaving touchpad surface for touch to be considered 2702 a tap and be reported as a left button click (for 2703 touchpads working in absolute mode only). 2704 Format: <msecs> 2705 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2706 reporting absolute coordinates, such as tablets 2707 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2708 reporting absolute coordinates, such as tablets 2709 2710 movablecore= [KNL,X86,IA-64,PPC] 2711 Format: nn[KMGTPE] | nn% 2712 This parameter is the complement to kernelcore=, it 2713 specifies the amount of memory used for migratable 2714 allocations. If both kernelcore and movablecore is 2715 specified, then kernelcore will be at *least* the 2716 specified value but may be more. If movablecore on its 2717 own is specified, the administrator must be careful 2718 that the amount of memory usable for all allocations 2719 is not too small. 2720 2721 movable_node [KNL] Boot-time switch to make hotplugable memory 2722 NUMA nodes to be movable. This means that the memory 2723 of such nodes will be usable only for movable 2724 allocations which rules out almost all kernel 2725 allocations. Use with caution! 2726 2727 MTD_Partition= [MTD] 2728 Format: <name>,<region-number>,<size>,<offset> 2729 2730 MTD_Region= [MTD] Format: 2731 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2732 2733 mtdparts= [MTD] 2734 See drivers/mtd/cmdlinepart.c. 2735 2736 multitce=off [PPC] This parameter disables the use of the pSeries 2737 firmware feature for updating multiple TCE entries 2738 at a time. 2739 2740 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2741 2742 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2743 2744 boundary - index of last SLC block on Flex-OneNAND. 2745 The remaining blocks are configured as MLC blocks. 2746 lock - Configure if Flex-OneNAND boundary should be locked. 2747 Once locked, the boundary cannot be changed. 2748 1 indicates lock status, 0 indicates unlock status. 2749 2750 mtdset= [ARM] 2751 ARM/S3C2412 JIVE boot control 2752 2753 See arch/arm/mach-s3c2412/mach-jive.c 2754 2755 mtouchusb.raw_coordinates= 2756 [HW] Make the MicroTouch USB driver use raw coordinates 2757 ('y', default) or cooked coordinates ('n') 2758 2759 mtrr_chunk_size=nn[KMG] [X86] 2760 used for mtrr cleanup. It is largest continuous chunk 2761 that could hold holes aka. UC entries. 2762 2763 mtrr_gran_size=nn[KMG] [X86] 2764 Used for mtrr cleanup. It is granularity of mtrr block. 2765 Default is 1. 2766 Large value could prevent small alignment from 2767 using up MTRRs. 2768 2769 mtrr_spare_reg_nr=n [X86] 2770 Format: <integer> 2771 Range: 0,7 : spare reg number 2772 Default : 1 2773 Used for mtrr cleanup. It is spare mtrr entries number. 2774 Set to 2 or more if your graphical card needs more. 2775 2776 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2777 2778 netdev= [NET] Network devices parameters 2779 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2780 Note that mem_start is often overloaded to mean 2781 something different and driver-specific. 2782 This usage is only documented in each driver source 2783 file if at all. 2784 2785 nf_conntrack.acct= 2786 [NETFILTER] Enable connection tracking flow accounting 2787 0 to disable accounting 2788 1 to enable accounting 2789 Default value is 0. 2790 2791 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2792 See Documentation/filesystems/nfs/nfsroot.txt. 2793 2794 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2795 See Documentation/filesystems/nfs/nfsroot.txt. 2796 2797 nfsrootdebug [NFS] enable nfsroot debugging messages. 2798 See Documentation/filesystems/nfs/nfsroot.txt. 2799 2800 nfs.callback_nr_threads= 2801 [NFSv4] set the total number of threads that the 2802 NFS client will assign to service NFSv4 callback 2803 requests. 2804 2805 nfs.callback_tcpport= 2806 [NFS] set the TCP port on which the NFSv4 callback 2807 channel should listen. 2808 2809 nfs.cache_getent= 2810 [NFS] sets the pathname to the program which is used 2811 to update the NFS client cache entries. 2812 2813 nfs.cache_getent_timeout= 2814 [NFS] sets the timeout after which an attempt to 2815 update a cache entry is deemed to have failed. 2816 2817 nfs.idmap_cache_timeout= 2818 [NFS] set the maximum lifetime for idmapper cache 2819 entries. 2820 2821 nfs.enable_ino64= 2822 [NFS] enable 64-bit inode numbers. 2823 If zero, the NFS client will fake up a 32-bit inode 2824 number for the readdir() and stat() syscalls instead 2825 of returning the full 64-bit number. 2826 The default is to return 64-bit inode numbers. 2827 2828 nfs.max_session_cb_slots= 2829 [NFSv4.1] Sets the maximum number of session 2830 slots the client will assign to the callback 2831 channel. This determines the maximum number of 2832 callbacks the client will process in parallel for 2833 a particular server. 2834 2835 nfs.max_session_slots= 2836 [NFSv4.1] Sets the maximum number of session slots 2837 the client will attempt to negotiate with the server. 2838 This limits the number of simultaneous RPC requests 2839 that the client can send to the NFSv4.1 server. 2840 Note that there is little point in setting this 2841 value higher than the max_tcp_slot_table_limit. 2842 2843 nfs.nfs4_disable_idmapping= 2844 [NFSv4] When set to the default of '1', this option 2845 ensures that both the RPC level authentication 2846 scheme and the NFS level operations agree to use 2847 numeric uids/gids if the mount is using the 2848 'sec=sys' security flavour. In effect it is 2849 disabling idmapping, which can make migration from 2850 legacy NFSv2/v3 systems to NFSv4 easier. 2851 Servers that do not support this mode of operation 2852 will be autodetected by the client, and it will fall 2853 back to using the idmapper. 2854 To turn off this behaviour, set the value to '0'. 2855 nfs.nfs4_unique_id= 2856 [NFS4] Specify an additional fixed unique ident- 2857 ification string that NFSv4 clients can insert into 2858 their nfs_client_id4 string. This is typically a 2859 UUID that is generated at system install time. 2860 2861 nfs.send_implementation_id = 2862 [NFSv4.1] Send client implementation identification 2863 information in exchange_id requests. 2864 If zero, no implementation identification information 2865 will be sent. 2866 The default is to send the implementation identification 2867 information. 2868 2869 nfs.recover_lost_locks = 2870 [NFSv4] Attempt to recover locks that were lost due 2871 to a lease timeout on the server. Please note that 2872 doing this risks data corruption, since there are 2873 no guarantees that the file will remain unchanged 2874 after the locks are lost. 2875 If you want to enable the kernel legacy behaviour of 2876 attempting to recover these locks, then set this 2877 parameter to '1'. 2878 The default parameter value of '0' causes the kernel 2879 not to attempt recovery of lost locks. 2880 2881 nfs4.layoutstats_timer = 2882 [NFSv4.2] Change the rate at which the kernel sends 2883 layoutstats to the pNFS metadata server. 2884 2885 Setting this to value to 0 causes the kernel to use 2886 whatever value is the default set by the layout 2887 driver. A non-zero value sets the minimum interval 2888 in seconds between layoutstats transmissions. 2889 2890 nfsd.nfs4_disable_idmapping= 2891 [NFSv4] When set to the default of '1', the NFSv4 2892 server will return only numeric uids and gids to 2893 clients using auth_sys, and will accept numeric uids 2894 and gids from such clients. This is intended to ease 2895 migration from NFSv2/v3. 2896 2897 nmi_debug= [KNL,SH] Specify one or more actions to take 2898 when a NMI is triggered. 2899 Format: [state][,regs][,debounce][,die] 2900 2901 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2902 Format: [panic,][nopanic,][num] 2903 Valid num: 0 or 1 2904 0 - turn hardlockup detector in nmi_watchdog off 2905 1 - turn hardlockup detector in nmi_watchdog on 2906 When panic is specified, panic when an NMI watchdog 2907 timeout occurs (or 'nopanic' to not panic on an NMI 2908 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 2909 To disable both hard and soft lockup detectors, 2910 please see 'nowatchdog'. 2911 This is useful when you use a panic=... timeout and 2912 need the box quickly up again. 2913 2914 These settings can be accessed at runtime via 2915 the nmi_watchdog and hardlockup_panic sysctls. 2916 2917 netpoll.carrier_timeout= 2918 [NET] Specifies amount of time (in seconds) that 2919 netpoll should wait for a carrier. By default netpoll 2920 waits 4 seconds. 2921 2922 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2923 emulation library even if a 387 maths coprocessor 2924 is present. 2925 2926 no5lvl [X86-64] Disable 5-level paging mode. Forces 2927 kernel to use 4-level paging instead. 2928 2929 no_console_suspend 2930 [HW] Never suspend the console 2931 Disable suspending of consoles during suspend and 2932 hibernate operations. Once disabled, debugging 2933 messages can reach various consoles while the rest 2934 of the system is being put to sleep (ie, while 2935 debugging driver suspend/resume hooks). This may 2936 not work reliably with all consoles, but is known 2937 to work with serial and VGA consoles. 2938 To facilitate more flexible debugging, we also add 2939 console_suspend, a printk module parameter to control 2940 it. Users could use console_suspend (usually 2941 /sys/module/printk/parameters/console_suspend) to 2942 turn on/off it dynamically. 2943 2944 novmcoredd [KNL,KDUMP] 2945 Disable device dump. Device dump allows drivers to 2946 append dump data to vmcore so you can collect driver 2947 specified debug info. Drivers can append the data 2948 without any limit and this data is stored in memory, 2949 so this may cause significant memory stress. Disabling 2950 device dump can help save memory but the driver debug 2951 data will be no longer available. This parameter 2952 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 2953 is set. 2954 2955 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2956 caches in the slab allocator. Saves per-node memory, 2957 but will impact performance. 2958 2959 noalign [KNL,ARM] 2960 2961 noaltinstr [S390] Disables alternative instructions patching 2962 (CPU alternatives feature). 2963 2964 noapic [SMP,APIC] Tells the kernel to not make use of any 2965 IOAPICs that may be present in the system. 2966 2967 noautogroup Disable scheduler automatic task group creation. 2968 2969 nobats [PPC] Do not use BATs for mapping kernel lowmem 2970 on "Classic" PPC cores. 2971 2972 nocache [ARM] 2973 2974 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2975 2976 nodelayacct [KNL] Disable per-task delay accounting 2977 2978 nodsp [SH] Disable hardware DSP at boot time. 2979 2980 noefi Disable EFI runtime services support. 2981 2982 noexec [IA-64] 2983 2984 noexec [X86] 2985 On X86-32 available only on PAE configured kernels. 2986 noexec=on: enable non-executable mappings (default) 2987 noexec=off: disable non-executable mappings 2988 2989 nosmap [X86,PPC] 2990 Disable SMAP (Supervisor Mode Access Prevention) 2991 even if it is supported by processor. 2992 2993 nosmep [X86,PPC] 2994 Disable SMEP (Supervisor Mode Execution Prevention) 2995 even if it is supported by processor. 2996 2997 noexec32 [X86-64] 2998 This affects only 32-bit executables. 2999 noexec32=on: enable non-executable mappings (default) 3000 read doesn't imply executable mappings 3001 noexec32=off: disable non-executable mappings 3002 read implies executable mappings 3003 3004 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3005 3006 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3007 register save and restore. The kernel will only save 3008 legacy floating-point registers on task switch. 3009 3010 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3011 3012 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3013 Equivalent to smt=1. 3014 3015 [KNL,x86] Disable symmetric multithreading (SMT). 3016 nosmt=force: Force disable SMT, cannot be undone 3017 via the sysfs control file. 3018 3019 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3020 (bounds check bypass). With this option data leaks are 3021 possible in the system. 3022 3023 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3024 the Spectre variant 2 (indirect branch prediction) 3025 vulnerability. System may allow data leaks with this 3026 option. 3027 3028 nospec_store_bypass_disable 3029 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3030 3031 noxsave [BUGS=X86] Disables x86 extended register state save 3032 and restore using xsave. The kernel will fallback to 3033 enabling legacy floating-point and sse state. 3034 3035 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3036 register states. The kernel will fall back to use 3037 xsave to save the states. By using this parameter, 3038 performance of saving the states is degraded because 3039 xsave doesn't support modified optimization while 3040 xsaveopt supports it on xsaveopt enabled systems. 3041 3042 noxsaves [X86] Disables xsaves and xrstors used in saving and 3043 restoring x86 extended register state in compacted 3044 form of xsave area. The kernel will fall back to use 3045 xsaveopt and xrstor to save and restore the states 3046 in standard form of xsave area. By using this 3047 parameter, xsave area per process might occupy more 3048 memory on xsaves enabled systems. 3049 3050 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3051 wfi(ARM) instruction doesn't work correctly and not to 3052 use it. This is also useful when using JTAG debugger. 3053 3054 no_file_caps Tells the kernel not to honor file capabilities. The 3055 only way then for a file to be executed with privilege 3056 is to be setuid root or executed by root. 3057 3058 nohalt [IA-64] Tells the kernel not to use the power saving 3059 function PAL_HALT_LIGHT when idle. This increases 3060 power-consumption. On the positive side, it reduces 3061 interrupt wake-up latency, which may improve performance 3062 in certain environments such as networked servers or 3063 real-time systems. 3064 3065 nohibernate [HIBERNATION] Disable hibernation and resume. 3066 3067 nohz= [KNL] Boottime enable/disable dynamic ticks 3068 Valid arguments: on, off 3069 Default: on 3070 3071 nohz_full= [KNL,BOOT,SMP,ISOL] 3072 The argument is a cpu list, as described above. 3073 In kernels built with CONFIG_NO_HZ_FULL=y, set 3074 the specified list of CPUs whose tick will be stopped 3075 whenever possible. The boot CPU will be forced outside 3076 the range to maintain the timekeeping. Any CPUs 3077 in this list will have their RCU callbacks offloaded, 3078 just as if they had also been called out in the 3079 rcu_nocbs= boot parameter. 3080 3081 noiotrap [SH] Disables trapped I/O port accesses. 3082 3083 noirqdebug [X86-32] Disables the code which attempts to detect and 3084 disable unhandled interrupt sources. 3085 3086 no_timer_check [X86,APIC] Disables the code which tests for 3087 broken timer IRQ sources. 3088 3089 noisapnp [ISAPNP] Disables ISA PnP code. 3090 3091 noinitrd [RAM] Tells the kernel not to load any configured 3092 initial RAM disk. 3093 3094 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3095 remapping. 3096 [Deprecated - use intremap=off] 3097 3098 nointroute [IA-64] 3099 3100 noinvpcid [X86] Disable the INVPCID cpu feature. 3101 3102 nojitter [IA-64] Disables jitter checking for ITC timers. 3103 3104 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3105 3106 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3107 fault handling. 3108 3109 no-vmw-sched-clock 3110 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3111 clock and use the default one. 3112 3113 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3114 steal time is computed, but won't influence scheduler 3115 behaviour 3116 3117 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3118 3119 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3120 3121 noltlbs [PPC] Do not use large page/tlb entries for kernel 3122 lowmem mapping on PPC40x and PPC8xx 3123 3124 nomca [IA-64] Disable machine check abort handling 3125 3126 nomce [X86-32] Disable Machine Check Exception 3127 3128 nomfgpt [X86-32] Disable Multi-Function General Purpose 3129 Timer usage (for AMD Geode machines). 3130 3131 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3132 shutdown the other cpus. Instead use the REBOOT_VECTOR 3133 irq. 3134 3135 nomodule Disable module load 3136 3137 nopat [X86] Disable PAT (page attribute table extension of 3138 pagetables) support. 3139 3140 nopcid [X86-64] Disable the PCID cpu feature. 3141 3142 norandmaps Don't use address space randomization. Equivalent to 3143 echo 0 > /proc/sys/kernel/randomize_va_space 3144 3145 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3146 with UP alternatives 3147 3148 nordrand [X86] Disable kernel use of the RDRAND and 3149 RDSEED instructions even if they are supported 3150 by the processor. RDRAND and RDSEED are still 3151 available to user space applications. 3152 3153 noresume [SWSUSP] Disables resume and restores original swap 3154 space. 3155 3156 no-scroll [VGA] Disables scrollback. 3157 This is required for the Braillex ib80-piezo Braille 3158 reader made by F.H. Papenmeier (Germany). 3159 3160 nosbagart [IA-64] 3161 3162 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3163 3164 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3165 and disable the IO APIC. legacy for "maxcpus=0". 3166 3167 nosoftlockup [KNL] Disable the soft-lockup detector. 3168 3169 nosync [HW,M68K] Disables sync negotiation for all devices. 3170 3171 nowatchdog [KNL] Disable both lockup detectors, i.e. 3172 soft-lockup and NMI watchdog (hard-lockup). 3173 3174 nowb [ARM] 3175 3176 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3177 3178 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3179 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3180 Some features depend on CPU0. Known dependencies are: 3181 1. Resume from suspend/hibernate depends on CPU0. 3182 Suspend/hibernate will fail if CPU0 is offline and you 3183 need to online CPU0 before suspend/hibernate. 3184 2. PIC interrupts also depend on CPU0. CPU0 can't be 3185 removed if a PIC interrupt is detected. 3186 It's said poweroff/reboot may depend on CPU0 on some 3187 machines although I haven't seen such issues so far 3188 after CPU0 is offline on a few tested machines. 3189 If the dependencies are under your control, you can 3190 turn on cpu0_hotplug. 3191 3192 nps_mtm_hs_ctr= [KNL,ARC] 3193 This parameter sets the maximum duration, in 3194 cycles, each HW thread of the CTOP can run 3195 without interruptions, before HW switches it. 3196 The actual maximum duration is 16 times this 3197 parameter's value. 3198 Format: integer between 1 and 255 3199 Default: 255 3200 3201 nptcg= [IA-64] Override max number of concurrent global TLB 3202 purges which is reported from either PAL_VM_SUMMARY or 3203 SAL PALO. 3204 3205 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3206 could support. nr_cpus=n : n >= 1 limits the kernel to 3207 support 'n' processors. It could be larger than the 3208 number of already plugged CPU during bootup, later in 3209 runtime you can physically add extra cpu until it reaches 3210 n. So during boot up some boot time memory for per-cpu 3211 variables need be pre-allocated for later physical cpu 3212 hot plugging. 3213 3214 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3215 3216 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3217 Allowed values are enable and disable 3218 3219 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3220 'node', 'default' can be specified 3221 This can be set from sysctl after boot. 3222 See Documentation/admin-guide/sysctl/vm.rst for details. 3223 3224 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3225 See Documentation/debugging-via-ohci1394.txt for more 3226 info. 3227 3228 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3229 Rather than timing out after 20 ms if an EC 3230 command is not properly ACKed, override the length 3231 of the timeout. We have interrupts disabled while 3232 waiting for the ACK, so if this is set too high 3233 interrupts *may* be lost! 3234 3235 omap_mux= [OMAP] Override bootloader pin multiplexing. 3236 Format: <mux_mode0.mode_name=value>... 3237 For example, to override I2C bus2: 3238 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3239 3240 oprofile.timer= [HW] 3241 Use timer interrupt instead of performance counters 3242 3243 oprofile.cpu_type= Force an oprofile cpu type 3244 This might be useful if you have an older oprofile 3245 userland or if you want common events. 3246 Format: { arch_perfmon } 3247 arch_perfmon: [X86] Force use of architectural 3248 perfmon on Intel CPUs instead of the 3249 CPU specific event set. 3250 timer: [X86] Force use of architectural NMI 3251 timer mode (see also oprofile.timer 3252 for generic hr timer mode) 3253 3254 oops=panic Always panic on oopses. Default is to just kill the 3255 process, but there is a small probability of 3256 deadlocking the machine. 3257 This will also cause panics on machine check exceptions. 3258 Useful together with panic=30 to trigger a reboot. 3259 3260 page_alloc.shuffle= 3261 [KNL] Boolean flag to control whether the page allocator 3262 should randomize its free lists. The randomization may 3263 be automatically enabled if the kernel detects it is 3264 running on a platform with a direct-mapped memory-side 3265 cache, and this parameter can be used to 3266 override/disable that behavior. The state of the flag 3267 can be read from sysfs at: 3268 /sys/module/page_alloc/parameters/shuffle. 3269 3270 page_owner= [KNL] Boot-time page_owner enabling option. 3271 Storage of the information about who allocated 3272 each page is disabled in default. With this switch, 3273 we can turn it on. 3274 on: enable the feature 3275 3276 page_poison= [KNL] Boot-time parameter changing the state of 3277 poisoning on the buddy allocator, available with 3278 CONFIG_PAGE_POISONING=y. 3279 off: turn off poisoning (default) 3280 on: turn on poisoning 3281 3282 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3283 timeout > 0: seconds before rebooting 3284 timeout = 0: wait forever 3285 timeout < 0: reboot immediately 3286 Format: <timeout> 3287 3288 panic_print= Bitmask for printing system info when panic happens. 3289 User can chose combination of the following bits: 3290 bit 0: print all tasks info 3291 bit 1: print system memory info 3292 bit 2: print timer info 3293 bit 3: print locks info if CONFIG_LOCKDEP is on 3294 bit 4: print ftrace buffer 3295 bit 5: print all printk messages in buffer 3296 3297 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3298 on a WARN(). 3299 3300 crash_kexec_post_notifiers 3301 Run kdump after running panic-notifiers and dumping 3302 kmsg. This only for the users who doubt kdump always 3303 succeeds in any situation. 3304 Note that this also increases risks of kdump failure, 3305 because some panic notifiers can make the crashed 3306 kernel more unstable. 3307 3308 parkbd.port= [HW] Parallel port number the keyboard adapter is 3309 connected to, default is 0. 3310 Format: <parport#> 3311 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3312 0 for XT, 1 for AT (default is AT). 3313 Format: <mode> 3314 3315 parport= [HW,PPT] Specify parallel ports. 0 disables. 3316 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3317 Use 'auto' to force the driver to use any 3318 IRQ/DMA settings detected (the default is to 3319 ignore detected IRQ/DMA settings because of 3320 possible conflicts). You can specify the base 3321 address, IRQ, and DMA settings; IRQ and DMA 3322 should be numbers, or 'auto' (for using detected 3323 settings on that particular port), or 'nofifo' 3324 (to avoid using a FIFO even if it is detected). 3325 Parallel ports are assigned in the order they 3326 are specified on the command line, starting 3327 with parport0. 3328 3329 parport_init_mode= [HW,PPT] 3330 Configure VIA parallel port to operate in 3331 a specific mode. This is necessary on Pegasos 3332 computer where firmware has no options for setting 3333 up parallel port mode and sets it to spp. 3334 Currently this function knows 686a and 8231 chips. 3335 Format: [spp|ps2|epp|ecp|ecpepp] 3336 3337 pause_on_oops= 3338 Halt all CPUs after the first oops has been printed for 3339 the specified number of seconds. This is to be used if 3340 your oopses keep scrolling off the screen. 3341 3342 pcbit= [HW,ISDN] 3343 3344 pcd. [PARIDE] 3345 See header of drivers/block/paride/pcd.c. 3346 See also Documentation/admin-guide/blockdev/paride.rst. 3347 3348 pci=option[,option...] [PCI] various PCI subsystem options. 3349 3350 Some options herein operate on a specific device 3351 or a set of devices (<pci_dev>). These are 3352 specified in one of the following formats: 3353 3354 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3355 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3356 3357 Note: the first format specifies a PCI 3358 bus/device/function address which may change 3359 if new hardware is inserted, if motherboard 3360 firmware changes, or due to changes caused 3361 by other kernel parameters. If the 3362 domain is left unspecified, it is 3363 taken to be zero. Optionally, a path 3364 to a device through multiple device/function 3365 addresses can be specified after the base 3366 address (this is more robust against 3367 renumbering issues). The second format 3368 selects devices using IDs from the 3369 configuration space which may match multiple 3370 devices in the system. 3371 3372 earlydump dump PCI config space before the kernel 3373 changes anything 3374 off [X86] don't probe for the PCI bus 3375 bios [X86-32] force use of PCI BIOS, don't access 3376 the hardware directly. Use this if your machine 3377 has a non-standard PCI host bridge. 3378 nobios [X86-32] disallow use of PCI BIOS, only direct 3379 hardware access methods are allowed. Use this 3380 if you experience crashes upon bootup and you 3381 suspect they are caused by the BIOS. 3382 conf1 [X86] Force use of PCI Configuration Access 3383 Mechanism 1 (config address in IO port 0xCF8, 3384 data in IO port 0xCFC, both 32-bit). 3385 conf2 [X86] Force use of PCI Configuration Access 3386 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3387 the function, IO port 0xCFA, also 8-bit, sets 3388 bus number. The config space is then accessed 3389 through ports 0xC000-0xCFFF). 3390 See http://wiki.osdev.org/PCI for more info 3391 on the configuration access mechanisms. 3392 noaer [PCIE] If the PCIEAER kernel config parameter is 3393 enabled, this kernel boot option can be used to 3394 disable the use of PCIE advanced error reporting. 3395 nodomains [PCI] Disable support for multiple PCI 3396 root domains (aka PCI segments, in ACPI-speak). 3397 nommconf [X86] Disable use of MMCONFIG for PCI 3398 Configuration 3399 check_enable_amd_mmconf [X86] check for and enable 3400 properly configured MMIO access to PCI 3401 config space on AMD family 10h CPU 3402 nomsi [MSI] If the PCI_MSI kernel config parameter is 3403 enabled, this kernel boot option can be used to 3404 disable the use of MSI interrupts system-wide. 3405 noioapicquirk [APIC] Disable all boot interrupt quirks. 3406 Safety option to keep boot IRQs enabled. This 3407 should never be necessary. 3408 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3409 primary IO-APIC for bridges that cannot disable 3410 boot IRQs. This fixes a source of spurious IRQs 3411 when the system masks IRQs. 3412 noioapicreroute [APIC] Disable workaround that uses the 3413 boot IRQ equivalent of an IRQ that connects to 3414 a chipset where boot IRQs cannot be disabled. 3415 The opposite of ioapicreroute. 3416 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3417 routing table. These calls are known to be buggy 3418 on several machines and they hang the machine 3419 when used, but on other computers it's the only 3420 way to get the interrupt routing table. Try 3421 this option if the kernel is unable to allocate 3422 IRQs or discover secondary PCI buses on your 3423 motherboard. 3424 rom [X86] Assign address space to expansion ROMs. 3425 Use with caution as certain devices share 3426 address decoders between ROMs and other 3427 resources. 3428 norom [X86] Do not assign address space to 3429 expansion ROMs that do not already have 3430 BIOS assigned address ranges. 3431 nobar [X86] Do not assign address space to the 3432 BARs that weren't assigned by the BIOS. 3433 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3434 assigned automatically to PCI devices. You can 3435 make the kernel exclude IRQs of your ISA cards 3436 this way. 3437 pirqaddr=0xAAAAA [X86] Specify the physical address 3438 of the PIRQ table (normally generated 3439 by the BIOS) if it is outside the 3440 F0000h-100000h range. 3441 lastbus=N [X86] Scan all buses thru bus #N. Can be 3442 useful if the kernel is unable to find your 3443 secondary buses and you want to tell it 3444 explicitly which ones they are. 3445 assign-busses [X86] Always assign all PCI bus 3446 numbers ourselves, overriding 3447 whatever the firmware may have done. 3448 usepirqmask [X86] Honor the possible IRQ mask stored 3449 in the BIOS $PIR table. This is needed on 3450 some systems with broken BIOSes, notably 3451 some HP Pavilion N5400 and Omnibook XE3 3452 notebooks. This will have no effect if ACPI 3453 IRQ routing is enabled. 3454 noacpi [X86] Do not use ACPI for IRQ routing 3455 or for PCI scanning. 3456 use_crs [X86] Use PCI host bridge window information 3457 from ACPI. On BIOSes from 2008 or later, this 3458 is enabled by default. If you need to use this, 3459 please report a bug. 3460 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3461 If you need to use this, please report a bug. 3462 routeirq Do IRQ routing for all PCI devices. 3463 This is normally done in pci_enable_device(), 3464 so this option is a temporary workaround 3465 for broken drivers that don't call it. 3466 skip_isa_align [X86] do not align io start addr, so can 3467 handle more pci cards 3468 noearly [X86] Don't do any early type 1 scanning. 3469 This might help on some broken boards which 3470 machine check when some devices' config space 3471 is read. But various workarounds are disabled 3472 and some IOMMU drivers will not work. 3473 bfsort Sort PCI devices into breadth-first order. 3474 This sorting is done to get a device 3475 order compatible with older (<= 2.4) kernels. 3476 nobfsort Don't sort PCI devices into breadth-first order. 3477 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3478 tuning and use the BIOS-configured MPS defaults. 3479 pcie_bus_safe Set every device's MPS to the largest value 3480 supported by all devices below the root complex. 3481 pcie_bus_perf Set device MPS to the largest allowable MPS 3482 based on its parent bus. Also set MRRS (Max 3483 Read Request Size) to the largest supported 3484 value (no larger than the MPS that the device 3485 or bus can support) for best performance. 3486 pcie_bus_peer2peer Set every device's MPS to 128B, which 3487 every device is guaranteed to support. This 3488 configuration allows peer-to-peer DMA between 3489 any pair of devices, possibly at the cost of 3490 reduced performance. This also guarantees 3491 that hot-added devices will work. 3492 cbiosize=nn[KMG] The fixed amount of bus space which is 3493 reserved for the CardBus bridge's IO window. 3494 The default value is 256 bytes. 3495 cbmemsize=nn[KMG] The fixed amount of bus space which is 3496 reserved for the CardBus bridge's memory 3497 window. The default value is 64 megabytes. 3498 resource_alignment= 3499 Format: 3500 [<order of align>@]<pci_dev>[; ...] 3501 Specifies alignment and device to reassign 3502 aligned memory resources. How to 3503 specify the device is described above. 3504 If <order of align> is not specified, 3505 PAGE_SIZE is used as alignment. 3506 A PCI-PCI bridge can be specified if resource 3507 windows need to be expanded. 3508 To specify the alignment for several 3509 instances of a device, the PCI vendor, 3510 device, subvendor, and subdevice may be 3511 specified, e.g., 12@pci:8086:9c22:103c:198f 3512 for 4096-byte alignment. 3513 ecrc= Enable/disable PCIe ECRC (transaction layer 3514 end-to-end CRC checking). 3515 bios: Use BIOS/firmware settings. This is the 3516 the default. 3517 off: Turn ECRC off 3518 on: Turn ECRC on. 3519 hpiosize=nn[KMG] The fixed amount of bus space which is 3520 reserved for hotplug bridge's IO window. 3521 Default size is 256 bytes. 3522 hpmemsize=nn[KMG] The fixed amount of bus space which is 3523 reserved for hotplug bridge's memory window. 3524 Default size is 2 megabytes. 3525 hpbussize=nn The minimum amount of additional bus numbers 3526 reserved for buses below a hotplug bridge. 3527 Default is 1. 3528 realloc= Enable/disable reallocating PCI bridge resources 3529 if allocations done by BIOS are too small to 3530 accommodate resources required by all child 3531 devices. 3532 off: Turn realloc off 3533 on: Turn realloc on 3534 realloc same as realloc=on 3535 noari do not use PCIe ARI. 3536 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3537 do not use PCIe ATS (and IOMMU device IOTLB). 3538 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3539 only look for one device below a PCIe downstream 3540 port. 3541 big_root_window Try to add a big 64bit memory window to the PCIe 3542 root complex on AMD CPUs. Some GFX hardware 3543 can resize a BAR to allow access to all VRAM. 3544 Adding the window is slightly risky (it may 3545 conflict with unreported devices), so this 3546 taints the kernel. 3547 disable_acs_redir=<pci_dev>[; ...] 3548 Specify one or more PCI devices (in the format 3549 specified above) separated by semicolons. 3550 Each device specified will have the PCI ACS 3551 redirect capabilities forced off which will 3552 allow P2P traffic between devices through 3553 bridges without forcing it upstream. Note: 3554 this removes isolation between devices and 3555 may put more devices in an IOMMU group. 3556 force_floating [S390] Force usage of floating interrupts. 3557 nomio [S390] Do not use MIO instructions. 3558 3559 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3560 Management. 3561 off Disable ASPM. 3562 force Enable ASPM even on devices that claim not to support it. 3563 WARNING: Forcing ASPM on may cause system lockups. 3564 3565 pcie_ports= [PCIE] PCIe port services handling: 3566 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3567 even if the platform doesn't give the OS permission to 3568 use them. This may cause conflicts if the platform 3569 also tries to use these services. 3570 compat Disable native PCIe services (PME, AER, DPC, PCIe 3571 hotplug). 3572 3573 pcie_port_pm= [PCIE] PCIe port power management handling: 3574 off Disable power management of all PCIe ports 3575 force Forcibly enable power management of all PCIe ports 3576 3577 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3578 nomsi Do not use MSI for native PCIe PME signaling (this makes 3579 all PCIe root ports use INTx for all services). 3580 3581 pcmv= [HW,PCMCIA] BadgePAD 4 3582 3583 pd_ignore_unused 3584 [PM] 3585 Keep all power-domains already enabled by bootloader on, 3586 even if no driver has claimed them. This is useful 3587 for debug and development, but should not be 3588 needed on a platform with proper driver support. 3589 3590 pd. [PARIDE] 3591 See Documentation/admin-guide/blockdev/paride.rst. 3592 3593 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3594 boot time. 3595 Format: { 0 | 1 } 3596 See arch/parisc/kernel/pdc_chassis.c 3597 3598 percpu_alloc= Select which percpu first chunk allocator to use. 3599 Currently supported values are "embed" and "page". 3600 Archs may support subset or none of the selections. 3601 See comments in mm/percpu.c for details on each 3602 allocator. This parameter is primarily for debugging 3603 and performance comparison. 3604 3605 pf. [PARIDE] 3606 See Documentation/admin-guide/blockdev/paride.rst. 3607 3608 pg. [PARIDE] 3609 See Documentation/admin-guide/blockdev/paride.rst. 3610 3611 pirq= [SMP,APIC] Manual mp-table setup 3612 See Documentation/x86/i386/IO-APIC.rst. 3613 3614 plip= [PPT,NET] Parallel port network link 3615 Format: { parport<nr> | timid | 0 } 3616 See also Documentation/admin-guide/parport.rst. 3617 3618 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3619 Override pmtimer IOPort with a hex value. 3620 e.g. pmtmr=0x508 3621 3622 pnp.debug=1 [PNP] 3623 Enable PNP debug messages (depends on the 3624 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3625 via /sys/module/pnp/parameters/debug. We always show 3626 current resource usage; turning this on also shows 3627 possible settings and some assignment information. 3628 3629 pnpacpi= [ACPI] 3630 { off } 3631 3632 pnpbios= [ISAPNP] 3633 { on | off | curr | res | no-curr | no-res } 3634 3635 pnp_reserve_irq= 3636 [ISAPNP] Exclude IRQs for the autoconfiguration 3637 3638 pnp_reserve_dma= 3639 [ISAPNP] Exclude DMAs for the autoconfiguration 3640 3641 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3642 Ranges are in pairs (I/O port base and size). 3643 3644 pnp_reserve_mem= 3645 [ISAPNP] Exclude memory regions for the 3646 autoconfiguration. 3647 Ranges are in pairs (memory base and size). 3648 3649 ports= [IP_VS_FTP] IPVS ftp helper module 3650 Default is 21. 3651 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3652 may be specified. 3653 Format: <port>,<port>.... 3654 3655 powersave=off [PPC] This option disables power saving features. 3656 It specifically disables cpuidle and sets the 3657 platform machine description specific power_save 3658 function to NULL. On Idle the CPU just reduces 3659 execution priority. 3660 3661 ppc_strict_facility_enable 3662 [PPC] This option catches any kernel floating point, 3663 Altivec, VSX and SPE outside of regions specifically 3664 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3665 There is some performance impact when enabling this. 3666 3667 ppc_tm= [PPC] 3668 Format: {"off"} 3669 Disable Hardware Transactional Memory 3670 3671 print-fatal-signals= 3672 [KNL] debug: print fatal signals 3673 3674 If enabled, warn about various signal handling 3675 related application anomalies: too many signals, 3676 too many POSIX.1 timers, fatal signals causing a 3677 coredump - etc. 3678 3679 If you hit the warning due to signal overflow, 3680 you might want to try "ulimit -i unlimited". 3681 3682 default: off. 3683 3684 printk.always_kmsg_dump= 3685 Trigger kmsg_dump for cases other than kernel oops or 3686 panics 3687 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3688 default: disabled 3689 3690 printk.devkmsg={on,off,ratelimit} 3691 Control writing to /dev/kmsg. 3692 on - unlimited logging to /dev/kmsg from userspace 3693 off - logging to /dev/kmsg disabled 3694 ratelimit - ratelimit the logging 3695 Default: ratelimit 3696 3697 printk.time= Show timing data prefixed to each printk message line 3698 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3699 3700 processor.max_cstate= [HW,ACPI] 3701 Limit processor to maximum C-state 3702 max_cstate=9 overrides any DMI blacklist limit. 3703 3704 processor.nocst [HW,ACPI] 3705 Ignore the _CST method to determine C-states, 3706 instead using the legacy FADT method 3707 3708 profile= [KNL] Enable kernel profiling via /proc/profile 3709 Format: [<profiletype>,]<number> 3710 Param: <profiletype>: "schedule", "sleep", or "kvm" 3711 [defaults to kernel profiling] 3712 Param: "schedule" - profile schedule points. 3713 Param: "sleep" - profile D-state sleeping (millisecs). 3714 Requires CONFIG_SCHEDSTATS 3715 Param: "kvm" - profile VM exits. 3716 Param: <number> - step/bucket size as a power of 2 for 3717 statistical time based profiling. 3718 3719 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3720 before loading. 3721 See Documentation/admin-guide/blockdev/ramdisk.rst. 3722 3723 psi= [KNL] Enable or disable pressure stall information 3724 tracking. 3725 Format: <bool> 3726 3727 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3728 probe for; one of (bare|imps|exps|lifebook|any). 3729 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3730 per second. 3731 psmouse.resetafter= [HW,MOUSE] 3732 Try to reset the device after so many bad packets 3733 (0 = never). 3734 psmouse.resolution= 3735 [HW,MOUSE] Set desired mouse resolution, in dpi. 3736 psmouse.smartscroll= 3737 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3738 0 = disabled, 1 = enabled (default). 3739 3740 pstore.backend= Specify the name of the pstore backend to use 3741 3742 pt. [PARIDE] 3743 See Documentation/admin-guide/blockdev/paride.rst. 3744 3745 pti= [X86_64] Control Page Table Isolation of user and 3746 kernel address spaces. Disabling this feature 3747 removes hardening, but improves performance of 3748 system calls and interrupts. 3749 3750 on - unconditionally enable 3751 off - unconditionally disable 3752 auto - kernel detects whether your CPU model is 3753 vulnerable to issues that PTI mitigates 3754 3755 Not specifying this option is equivalent to pti=auto. 3756 3757 nopti [X86_64] 3758 Equivalent to pti=off 3759 3760 pty.legacy_count= 3761 [KNL] Number of legacy pty's. Overwrites compiled-in 3762 default number. 3763 3764 quiet [KNL] Disable most log messages 3765 3766 r128= [HW,DRM] 3767 3768 raid= [HW,RAID] 3769 See Documentation/admin-guide/md.rst. 3770 3771 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3772 See Documentation/admin-guide/blockdev/ramdisk.rst. 3773 3774 random.trust_cpu={on,off} 3775 [KNL] Enable or disable trusting the use of the 3776 CPU's random number generator (if available) to 3777 fully seed the kernel's CRNG. Default is controlled 3778 by CONFIG_RANDOM_TRUST_CPU. 3779 3780 ras=option[,option,...] [KNL] RAS-specific options 3781 3782 cec_disable [X86] 3783 Disable the Correctable Errors Collector, 3784 see CONFIG_RAS_CEC help text. 3785 3786 rcu_nocbs= [KNL] 3787 The argument is a cpu list, as described above, 3788 except that the string "all" can be used to 3789 specify every CPU on the system. 3790 3791 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3792 the specified list of CPUs to be no-callback CPUs. 3793 Invocation of these CPUs' RCU callbacks will be 3794 offloaded to "rcuox/N" kthreads created for that 3795 purpose, where "x" is "p" for RCU-preempt, and 3796 "s" for RCU-sched, and "N" is the CPU number. 3797 This reduces OS jitter on the offloaded CPUs, 3798 which can be useful for HPC and real-time 3799 workloads. It can also improve energy efficiency 3800 for asymmetric multiprocessors. 3801 3802 rcu_nocb_poll [KNL] 3803 Rather than requiring that offloaded CPUs 3804 (specified by rcu_nocbs= above) explicitly 3805 awaken the corresponding "rcuoN" kthreads, 3806 make these kthreads poll for callbacks. 3807 This improves the real-time response for the 3808 offloaded CPUs by relieving them of the need to 3809 wake up the corresponding kthread, but degrades 3810 energy efficiency by requiring that the kthreads 3811 periodically wake up to do the polling. 3812 3813 rcutree.blimit= [KNL] 3814 Set maximum number of finished RCU callbacks to 3815 process in one batch. 3816 3817 rcutree.dump_tree= [KNL] 3818 Dump the structure of the rcu_node combining tree 3819 out at early boot. This is used for diagnostic 3820 purposes, to verify correct tree setup. 3821 3822 rcutree.gp_cleanup_delay= [KNL] 3823 Set the number of jiffies to delay each step of 3824 RCU grace-period cleanup. 3825 3826 rcutree.gp_init_delay= [KNL] 3827 Set the number of jiffies to delay each step of 3828 RCU grace-period initialization. 3829 3830 rcutree.gp_preinit_delay= [KNL] 3831 Set the number of jiffies to delay each step of 3832 RCU grace-period pre-initialization, that is, 3833 the propagation of recent CPU-hotplug changes up 3834 the rcu_node combining tree. 3835 3836 rcutree.use_softirq= [KNL] 3837 If set to zero, move all RCU_SOFTIRQ processing to 3838 per-CPU rcuc kthreads. Defaults to a non-zero 3839 value, meaning that RCU_SOFTIRQ is used by default. 3840 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3841 3842 rcutree.rcu_fanout_exact= [KNL] 3843 Disable autobalancing of the rcu_node combining 3844 tree. This is used by rcutorture, and might 3845 possibly be useful for architectures having high 3846 cache-to-cache transfer latencies. 3847 3848 rcutree.rcu_fanout_leaf= [KNL] 3849 Change the number of CPUs assigned to each 3850 leaf rcu_node structure. Useful for very 3851 large systems, which will choose the value 64, 3852 and for NUMA systems with large remote-access 3853 latencies, which will choose a value aligned 3854 with the appropriate hardware boundaries. 3855 3856 rcutree.jiffies_till_first_fqs= [KNL] 3857 Set delay from grace-period initialization to 3858 first attempt to force quiescent states. 3859 Units are jiffies, minimum value is zero, 3860 and maximum value is HZ. 3861 3862 rcutree.jiffies_till_next_fqs= [KNL] 3863 Set delay between subsequent attempts to force 3864 quiescent states. Units are jiffies, minimum 3865 value is one, and maximum value is HZ. 3866 3867 rcutree.jiffies_till_sched_qs= [KNL] 3868 Set required age in jiffies for a 3869 given grace period before RCU starts 3870 soliciting quiescent-state help from 3871 rcu_note_context_switch() and cond_resched(). 3872 If not specified, the kernel will calculate 3873 a value based on the most recent settings 3874 of rcutree.jiffies_till_first_fqs 3875 and rcutree.jiffies_till_next_fqs. 3876 This calculated value may be viewed in 3877 rcutree.jiffies_to_sched_qs. Any attempt to set 3878 rcutree.jiffies_to_sched_qs will be cheerfully 3879 overwritten. 3880 3881 rcutree.kthread_prio= [KNL,BOOT] 3882 Set the SCHED_FIFO priority of the RCU per-CPU 3883 kthreads (rcuc/N). This value is also used for 3884 the priority of the RCU boost threads (rcub/N) 3885 and for the RCU grace-period kthreads (rcu_bh, 3886 rcu_preempt, and rcu_sched). If RCU_BOOST is 3887 set, valid values are 1-99 and the default is 1 3888 (the least-favored priority). Otherwise, when 3889 RCU_BOOST is not set, valid values are 0-99 and 3890 the default is zero (non-realtime operation). 3891 3892 rcutree.rcu_nocb_gp_stride= [KNL] 3893 Set the number of NOCB callback kthreads in 3894 each group, which defaults to the square root 3895 of the number of CPUs. Larger numbers reduce 3896 the wakeup overhead on the global grace-period 3897 kthread, but increases that same overhead on 3898 each group's NOCB grace-period kthread. 3899 3900 rcutree.qhimark= [KNL] 3901 Set threshold of queued RCU callbacks beyond which 3902 batch limiting is disabled. 3903 3904 rcutree.qlowmark= [KNL] 3905 Set threshold of queued RCU callbacks below which 3906 batch limiting is re-enabled. 3907 3908 rcutree.rcu_idle_gp_delay= [KNL] 3909 Set wakeup interval for idle CPUs that have 3910 RCU callbacks (RCU_FAST_NO_HZ=y). 3911 3912 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3913 Set wakeup interval for idle CPUs that have 3914 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3915 Lazy RCU callbacks are those which RCU can 3916 prove do nothing more than free memory. 3917 3918 rcutree.rcu_kick_kthreads= [KNL] 3919 Cause the grace-period kthread to get an extra 3920 wake_up() if it sleeps three times longer than 3921 it should at force-quiescent-state time. 3922 This wake_up() will be accompanied by a 3923 WARN_ONCE() splat and an ftrace_dump(). 3924 3925 rcutree.sysrq_rcu= [KNL] 3926 Commandeer a sysrq key to dump out Tree RCU's 3927 rcu_node tree with an eye towards determining 3928 why a new grace period has not yet started. 3929 3930 rcuperf.gp_async= [KNL] 3931 Measure performance of asynchronous 3932 grace-period primitives such as call_rcu(). 3933 3934 rcuperf.gp_async_max= [KNL] 3935 Specify the maximum number of outstanding 3936 callbacks per writer thread. When a writer 3937 thread exceeds this limit, it invokes the 3938 corresponding flavor of rcu_barrier() to allow 3939 previously posted callbacks to drain. 3940 3941 rcuperf.gp_exp= [KNL] 3942 Measure performance of expedited synchronous 3943 grace-period primitives. 3944 3945 rcuperf.holdoff= [KNL] 3946 Set test-start holdoff period. The purpose of 3947 this parameter is to delay the start of the 3948 test until boot completes in order to avoid 3949 interference. 3950 3951 rcuperf.nreaders= [KNL] 3952 Set number of RCU readers. The value -1 selects 3953 N, where N is the number of CPUs. A value 3954 "n" less than -1 selects N-n+1, where N is again 3955 the number of CPUs. For example, -2 selects N 3956 (the number of CPUs), -3 selects N+1, and so on. 3957 A value of "n" less than or equal to -N selects 3958 a single reader. 3959 3960 rcuperf.nwriters= [KNL] 3961 Set number of RCU writers. The values operate 3962 the same as for rcuperf.nreaders. 3963 N, where N is the number of CPUs 3964 3965 rcuperf.perf_type= [KNL] 3966 Specify the RCU implementation to test. 3967 3968 rcuperf.shutdown= [KNL] 3969 Shut the system down after performance tests 3970 complete. This is useful for hands-off automated 3971 testing. 3972 3973 rcuperf.verbose= [KNL] 3974 Enable additional printk() statements. 3975 3976 rcuperf.writer_holdoff= [KNL] 3977 Write-side holdoff between grace periods, 3978 in microseconds. The default of zero says 3979 no holdoff. 3980 3981 rcutorture.fqs_duration= [KNL] 3982 Set duration of force_quiescent_state bursts 3983 in microseconds. 3984 3985 rcutorture.fqs_holdoff= [KNL] 3986 Set holdoff time within force_quiescent_state bursts 3987 in microseconds. 3988 3989 rcutorture.fqs_stutter= [KNL] 3990 Set wait time between force_quiescent_state bursts 3991 in seconds. 3992 3993 rcutorture.fwd_progress= [KNL] 3994 Enable RCU grace-period forward-progress testing 3995 for the types of RCU supporting this notion. 3996 3997 rcutorture.fwd_progress_div= [KNL] 3998 Specify the fraction of a CPU-stall-warning 3999 period to do tight-loop forward-progress testing. 4000 4001 rcutorture.fwd_progress_holdoff= [KNL] 4002 Number of seconds to wait between successive 4003 forward-progress tests. 4004 4005 rcutorture.fwd_progress_need_resched= [KNL] 4006 Enclose cond_resched() calls within checks for 4007 need_resched() during tight-loop forward-progress 4008 testing. 4009 4010 rcutorture.gp_cond= [KNL] 4011 Use conditional/asynchronous update-side 4012 primitives, if available. 4013 4014 rcutorture.gp_exp= [KNL] 4015 Use expedited update-side primitives, if available. 4016 4017 rcutorture.gp_normal= [KNL] 4018 Use normal (non-expedited) asynchronous 4019 update-side primitives, if available. 4020 4021 rcutorture.gp_sync= [KNL] 4022 Use normal (non-expedited) synchronous 4023 update-side primitives, if available. If all 4024 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4025 rcutorture.gp_normal=, and rcutorture.gp_sync= 4026 are zero, rcutorture acts as if is interpreted 4027 they are all non-zero. 4028 4029 rcutorture.n_barrier_cbs= [KNL] 4030 Set callbacks/threads for rcu_barrier() testing. 4031 4032 rcutorture.nfakewriters= [KNL] 4033 Set number of concurrent RCU writers. These just 4034 stress RCU, they don't participate in the actual 4035 test, hence the "fake". 4036 4037 rcutorture.nreaders= [KNL] 4038 Set number of RCU readers. The value -1 selects 4039 N-1, where N is the number of CPUs. A value 4040 "n" less than -1 selects N-n-2, where N is again 4041 the number of CPUs. For example, -2 selects N 4042 (the number of CPUs), -3 selects N+1, and so on. 4043 4044 rcutorture.object_debug= [KNL] 4045 Enable debug-object double-call_rcu() testing. 4046 4047 rcutorture.onoff_holdoff= [KNL] 4048 Set time (s) after boot for CPU-hotplug testing. 4049 4050 rcutorture.onoff_interval= [KNL] 4051 Set time (jiffies) between CPU-hotplug operations, 4052 or zero to disable CPU-hotplug testing. 4053 4054 rcutorture.shuffle_interval= [KNL] 4055 Set task-shuffle interval (s). Shuffling tasks 4056 allows some CPUs to go into dyntick-idle mode 4057 during the rcutorture test. 4058 4059 rcutorture.shutdown_secs= [KNL] 4060 Set time (s) after boot system shutdown. This 4061 is useful for hands-off automated testing. 4062 4063 rcutorture.stall_cpu= [KNL] 4064 Duration of CPU stall (s) to test RCU CPU stall 4065 warnings, zero to disable. 4066 4067 rcutorture.stall_cpu_holdoff= [KNL] 4068 Time to wait (s) after boot before inducing stall. 4069 4070 rcutorture.stall_cpu_irqsoff= [KNL] 4071 Disable interrupts while stalling if set. 4072 4073 rcutorture.stat_interval= [KNL] 4074 Time (s) between statistics printk()s. 4075 4076 rcutorture.stutter= [KNL] 4077 Time (s) to stutter testing, for example, specifying 4078 five seconds causes the test to run for five seconds, 4079 wait for five seconds, and so on. This tests RCU's 4080 ability to transition abruptly to and from idle. 4081 4082 rcutorture.test_boost= [KNL] 4083 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4084 "Maybe" means test if the RCU implementation 4085 under test support RCU priority boosting. 4086 4087 rcutorture.test_boost_duration= [KNL] 4088 Duration (s) of each individual boost test. 4089 4090 rcutorture.test_boost_interval= [KNL] 4091 Interval (s) between each boost test. 4092 4093 rcutorture.test_no_idle_hz= [KNL] 4094 Test RCU's dyntick-idle handling. See also the 4095 rcutorture.shuffle_interval parameter. 4096 4097 rcutorture.torture_type= [KNL] 4098 Specify the RCU implementation to test. 4099 4100 rcutorture.verbose= [KNL] 4101 Enable additional printk() statements. 4102 4103 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4104 Dump ftrace buffer after reporting RCU CPU 4105 stall warning. 4106 4107 rcupdate.rcu_cpu_stall_suppress= [KNL] 4108 Suppress RCU CPU stall warning messages. 4109 4110 rcupdate.rcu_cpu_stall_timeout= [KNL] 4111 Set timeout for RCU CPU stall warning messages. 4112 4113 rcupdate.rcu_expedited= [KNL] 4114 Use expedited grace-period primitives, for 4115 example, synchronize_rcu_expedited() instead 4116 of synchronize_rcu(). This reduces latency, 4117 but can increase CPU utilization, degrade 4118 real-time latency, and degrade energy efficiency. 4119 No effect on CONFIG_TINY_RCU kernels. 4120 4121 rcupdate.rcu_normal= [KNL] 4122 Use only normal grace-period primitives, 4123 for example, synchronize_rcu() instead of 4124 synchronize_rcu_expedited(). This improves 4125 real-time latency, CPU utilization, and 4126 energy efficiency, but can expose users to 4127 increased grace-period latency. This parameter 4128 overrides rcupdate.rcu_expedited. No effect on 4129 CONFIG_TINY_RCU kernels. 4130 4131 rcupdate.rcu_normal_after_boot= [KNL] 4132 Once boot has completed (that is, after 4133 rcu_end_inkernel_boot() has been invoked), use 4134 only normal grace-period primitives. No effect 4135 on CONFIG_TINY_RCU kernels. 4136 4137 rcupdate.rcu_task_stall_timeout= [KNL] 4138 Set timeout in jiffies for RCU task stall warning 4139 messages. Disable with a value less than or equal 4140 to zero. 4141 4142 rcupdate.rcu_self_test= [KNL] 4143 Run the RCU early boot self tests 4144 4145 rdinit= [KNL] 4146 Format: <full_path> 4147 Run specified binary instead of /init from the ramdisk, 4148 used for early userspace startup. See initrd. 4149 4150 rdrand= [X86] 4151 force - Override the decision by the kernel to hide the 4152 advertisement of RDRAND support (this affects 4153 certain AMD processors because of buggy BIOS 4154 support, specifically around the suspend/resume 4155 path). 4156 4157 rdt= [HW,X86,RDT] 4158 Turn on/off individual RDT features. List is: 4159 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4160 mba. 4161 E.g. to turn on cmt and turn off mba use: 4162 rdt=cmt,!mba 4163 4164 reboot= [KNL] 4165 Format (x86 or x86_64): 4166 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4167 [[,]s[mp]#### \ 4168 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4169 [[,]f[orce] 4170 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4171 (prefix with 'panic_' to set mode for panic 4172 reboot only), 4173 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4174 reboot_force is either force or not specified, 4175 reboot_cpu is s[mp]#### with #### being the processor 4176 to be used for rebooting. 4177 4178 relax_domain_level= 4179 [KNL, SMP] Set scheduler's default relax_domain_level. 4180 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4181 4182 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4183 Format: <base1>,<size1>[,<base2>,<size2>,...] 4184 Reserve I/O ports or memory so the kernel won't use 4185 them. If <base> is less than 0x10000, the region 4186 is assumed to be I/O ports; otherwise it is memory. 4187 4188 reservetop= [X86-32] 4189 Format: nn[KMG] 4190 Reserves a hole at the top of the kernel virtual 4191 address space. 4192 4193 reservelow= [X86] 4194 Format: nn[K] 4195 Set the amount of memory to reserve for BIOS at 4196 the bottom of the address space. 4197 4198 reset_devices [KNL] Force drivers to reset the underlying device 4199 during initialization. 4200 4201 resume= [SWSUSP] 4202 Specify the partition device for software suspend 4203 Format: 4204 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4205 4206 resume_offset= [SWSUSP] 4207 Specify the offset from the beginning of the partition 4208 given by "resume=" at which the swap header is located, 4209 in <PAGE_SIZE> units (needed only for swap files). 4210 See Documentation/power/swsusp-and-swap-files.rst 4211 4212 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4213 read the resume files 4214 4215 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4216 Useful for devices that are detected asynchronously 4217 (e.g. USB and MMC devices). 4218 4219 hibernate= [HIBERNATION] 4220 noresume Don't check if there's a hibernation image 4221 present during boot. 4222 nocompress Don't compress/decompress hibernation images. 4223 no Disable hibernation and resume. 4224 protect_image Turn on image protection during restoration 4225 (that will set all pages holding image data 4226 during restoration read-only). 4227 4228 retain_initrd [RAM] Keep initrd memory after extraction 4229 4230 rfkill.default_state= 4231 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4232 etc. communication is blocked by default. 4233 1 Unblocked. 4234 4235 rfkill.master_switch_mode= 4236 0 The "airplane mode" button does nothing. 4237 1 The "airplane mode" button toggles between everything 4238 blocked and the previous configuration. 4239 2 The "airplane mode" button toggles between everything 4240 blocked and everything unblocked. 4241 4242 rhash_entries= [KNL,NET] 4243 Set number of hash buckets for route cache 4244 4245 ring3mwait=disable 4246 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4247 CPUs. 4248 4249 ro [KNL] Mount root device read-only on boot 4250 4251 rodata= [KNL] 4252 on Mark read-only kernel memory as read-only (default). 4253 off Leave read-only kernel memory writable for debugging. 4254 4255 rockchip.usb_uart 4256 Enable the uart passthrough on the designated usb port 4257 on Rockchip SoCs. When active, the signals of the 4258 debug-uart get routed to the D+ and D- pins of the usb 4259 port and the regular usb controller gets disabled. 4260 4261 root= [KNL] Root filesystem 4262 See name_to_dev_t comment in init/do_mounts.c. 4263 4264 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4265 mount the root filesystem 4266 4267 rootflags= [KNL] Set root filesystem mount option string 4268 4269 rootfstype= [KNL] Set root filesystem type 4270 4271 rootwait [KNL] Wait (indefinitely) for root device to show up. 4272 Useful for devices that are detected asynchronously 4273 (e.g. USB and MMC devices). 4274 4275 rproc_mem=nn[KMG][@address] 4276 [KNL,ARM,CMA] Remoteproc physical memory block. 4277 Memory area to be used by remote processor image, 4278 managed by CMA. 4279 4280 rw [KNL] Mount root device read-write on boot 4281 4282 S [KNL] Run init in single mode 4283 4284 s390_iommu= [HW,S390] 4285 Set s390 IOTLB flushing mode 4286 strict 4287 With strict flushing every unmap operation will result in 4288 an IOTLB flush. Default is lazy flushing before reuse, 4289 which is faster. 4290 4291 sa1100ir [NET] 4292 See drivers/net/irda/sa1100_ir.c. 4293 4294 sbni= [NET] Granch SBNI12 leased line adapter 4295 4296 sched_debug [KNL] Enables verbose scheduler debug messages. 4297 4298 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4299 Allowed values are enable and disable. This feature 4300 incurs a small amount of overhead in the scheduler 4301 but is useful for debugging and performance tuning. 4302 4303 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4304 xtime_lock contention on larger systems, and/or RCU lock 4305 contention on all systems with CONFIG_MAXSMP set. 4306 Format: { "0" | "1" } 4307 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4308 1 -- enable. 4309 Note: increases power consumption, thus should only be 4310 enabled if running jitter sensitive (HPC/RT) workloads. 4311 4312 security= [SECURITY] Choose a legacy "major" security module to 4313 enable at boot. This has been deprecated by the 4314 "lsm=" parameter. 4315 4316 selinux= [SELINUX] Disable or enable SELinux at boot time. 4317 Format: { "0" | "1" } 4318 See security/selinux/Kconfig help text. 4319 0 -- disable. 4320 1 -- enable. 4321 Default value is set via kernel config option. 4322 If enabled at boot time, /selinux/disable can be used 4323 later to disable prior to initial policy load. 4324 4325 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4326 Format: { "0" | "1" } 4327 See security/apparmor/Kconfig help text 4328 0 -- disable. 4329 1 -- enable. 4330 Default value is set via kernel config option. 4331 4332 serialnumber [BUGS=X86-32] 4333 4334 shapers= [NET] 4335 Maximal number of shapers. 4336 4337 simeth= [IA-64] 4338 simscsi= 4339 4340 slram= [HW,MTD] 4341 4342 slab_nomerge [MM] 4343 Disable merging of slabs with similar size. May be 4344 necessary if there is some reason to distinguish 4345 allocs to different slabs, especially in hardened 4346 environments where the risk of heap overflows and 4347 layout control by attackers can usually be 4348 frustrated by disabling merging. This will reduce 4349 most of the exposure of a heap attack to a single 4350 cache (risks via metadata attacks are mostly 4351 unchanged). Debug options disable merging on their 4352 own. 4353 For more information see Documentation/vm/slub.rst. 4354 4355 slab_max_order= [MM, SLAB] 4356 Determines the maximum allowed order for slabs. 4357 A high setting may cause OOMs due to memory 4358 fragmentation. Defaults to 1 for systems with 4359 more than 32MB of RAM, 0 otherwise. 4360 4361 slub_debug[=options[,slabs]] [MM, SLUB] 4362 Enabling slub_debug allows one to determine the 4363 culprit if slab objects become corrupted. Enabling 4364 slub_debug can create guard zones around objects and 4365 may poison objects when not in use. Also tracks the 4366 last alloc / free. For more information see 4367 Documentation/vm/slub.rst. 4368 4369 slub_memcg_sysfs= [MM, SLUB] 4370 Determines whether to enable sysfs directories for 4371 memory cgroup sub-caches. 1 to enable, 0 to disable. 4372 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4373 Enabling this can lead to a very high number of debug 4374 directories and files being created under 4375 /sys/kernel/slub. 4376 4377 slub_max_order= [MM, SLUB] 4378 Determines the maximum allowed order for slabs. 4379 A high setting may cause OOMs due to memory 4380 fragmentation. For more information see 4381 Documentation/vm/slub.rst. 4382 4383 slub_min_objects= [MM, SLUB] 4384 The minimum number of objects per slab. SLUB will 4385 increase the slab order up to slub_max_order to 4386 generate a sufficiently large slab able to contain 4387 the number of objects indicated. The higher the number 4388 of objects the smaller the overhead of tracking slabs 4389 and the less frequently locks need to be acquired. 4390 For more information see Documentation/vm/slub.rst. 4391 4392 slub_min_order= [MM, SLUB] 4393 Determines the minimum page order for slabs. Must be 4394 lower than slub_max_order. 4395 For more information see Documentation/vm/slub.rst. 4396 4397 slub_nomerge [MM, SLUB] 4398 Same with slab_nomerge. This is supported for legacy. 4399 See slab_nomerge for more information. 4400 4401 smart2= [HW] 4402 Format: <io1>[,<io2>[,...,<io8>]] 4403 4404 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4405 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4406 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4407 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4408 smsc-ircc2.ircc_irq= [HW] IRQ line 4409 smsc-ircc2.ircc_dma= [HW] DMA channel 4410 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4411 0: Toshiba Satellite 1800 (GP data pin select) 4412 1: Fast pin select (default) 4413 2: ATC IRMode 4414 4415 smt [KNL,S390] Set the maximum number of threads (logical 4416 CPUs) to use per physical CPU on systems capable of 4417 symmetric multithreading (SMT). Will be capped to the 4418 actual hardware limit. 4419 Format: <integer> 4420 Default: -1 (no limit) 4421 4422 softlockup_panic= 4423 [KNL] Should the soft-lockup detector generate panics. 4424 Format: <integer> 4425 4426 A nonzero value instructs the soft-lockup detector 4427 to panic the machine when a soft-lockup occurs. This 4428 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4429 which is the respective build-time switch to that 4430 functionality. 4431 4432 softlockup_all_cpu_backtrace= 4433 [KNL] Should the soft-lockup detector generate 4434 backtraces on all cpus. 4435 Format: <integer> 4436 4437 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4438 See Documentation/admin-guide/laptops/sonypi.rst 4439 4440 spectre_v2= [X86] Control mitigation of Spectre variant 2 4441 (indirect branch speculation) vulnerability. 4442 The default operation protects the kernel from 4443 user space attacks. 4444 4445 on - unconditionally enable, implies 4446 spectre_v2_user=on 4447 off - unconditionally disable, implies 4448 spectre_v2_user=off 4449 auto - kernel detects whether your CPU model is 4450 vulnerable 4451 4452 Selecting 'on' will, and 'auto' may, choose a 4453 mitigation method at run time according to the 4454 CPU, the available microcode, the setting of the 4455 CONFIG_RETPOLINE configuration option, and the 4456 compiler with which the kernel was built. 4457 4458 Selecting 'on' will also enable the mitigation 4459 against user space to user space task attacks. 4460 4461 Selecting 'off' will disable both the kernel and 4462 the user space protections. 4463 4464 Specific mitigations can also be selected manually: 4465 4466 retpoline - replace indirect branches 4467 retpoline,generic - google's original retpoline 4468 retpoline,amd - AMD-specific minimal thunk 4469 4470 Not specifying this option is equivalent to 4471 spectre_v2=auto. 4472 4473 spectre_v2_user= 4474 [X86] Control mitigation of Spectre variant 2 4475 (indirect branch speculation) vulnerability between 4476 user space tasks 4477 4478 on - Unconditionally enable mitigations. Is 4479 enforced by spectre_v2=on 4480 4481 off - Unconditionally disable mitigations. Is 4482 enforced by spectre_v2=off 4483 4484 prctl - Indirect branch speculation is enabled, 4485 but mitigation can be enabled via prctl 4486 per thread. The mitigation control state 4487 is inherited on fork. 4488 4489 prctl,ibpb 4490 - Like "prctl" above, but only STIBP is 4491 controlled per thread. IBPB is issued 4492 always when switching between different user 4493 space processes. 4494 4495 seccomp 4496 - Same as "prctl" above, but all seccomp 4497 threads will enable the mitigation unless 4498 they explicitly opt out. 4499 4500 seccomp,ibpb 4501 - Like "seccomp" above, but only STIBP is 4502 controlled per thread. IBPB is issued 4503 always when switching between different 4504 user space processes. 4505 4506 auto - Kernel selects the mitigation depending on 4507 the available CPU features and vulnerability. 4508 4509 Default mitigation: 4510 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4511 4512 Not specifying this option is equivalent to 4513 spectre_v2_user=auto. 4514 4515 spec_store_bypass_disable= 4516 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4517 (Speculative Store Bypass vulnerability) 4518 4519 Certain CPUs are vulnerable to an exploit against a 4520 a common industry wide performance optimization known 4521 as "Speculative Store Bypass" in which recent stores 4522 to the same memory location may not be observed by 4523 later loads during speculative execution. The idea 4524 is that such stores are unlikely and that they can 4525 be detected prior to instruction retirement at the 4526 end of a particular speculation execution window. 4527 4528 In vulnerable processors, the speculatively forwarded 4529 store can be used in a cache side channel attack, for 4530 example to read memory to which the attacker does not 4531 directly have access (e.g. inside sandboxed code). 4532 4533 This parameter controls whether the Speculative Store 4534 Bypass optimization is used. 4535 4536 On x86 the options are: 4537 4538 on - Unconditionally disable Speculative Store Bypass 4539 off - Unconditionally enable Speculative Store Bypass 4540 auto - Kernel detects whether the CPU model contains an 4541 implementation of Speculative Store Bypass and 4542 picks the most appropriate mitigation. If the 4543 CPU is not vulnerable, "off" is selected. If the 4544 CPU is vulnerable the default mitigation is 4545 architecture and Kconfig dependent. See below. 4546 prctl - Control Speculative Store Bypass per thread 4547 via prctl. Speculative Store Bypass is enabled 4548 for a process by default. The state of the control 4549 is inherited on fork. 4550 seccomp - Same as "prctl" above, but all seccomp threads 4551 will disable SSB unless they explicitly opt out. 4552 4553 Default mitigations: 4554 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4555 4556 On powerpc the options are: 4557 4558 on,auto - On Power8 and Power9 insert a store-forwarding 4559 barrier on kernel entry and exit. On Power7 4560 perform a software flush on kernel entry and 4561 exit. 4562 off - No action. 4563 4564 Not specifying this option is equivalent to 4565 spec_store_bypass_disable=auto. 4566 4567 spia_io_base= [HW,MTD] 4568 spia_fio_base= 4569 spia_pedr= 4570 spia_peddr= 4571 4572 srcutree.counter_wrap_check [KNL] 4573 Specifies how frequently to check for 4574 grace-period sequence counter wrap for the 4575 srcu_data structure's ->srcu_gp_seq_needed field. 4576 The greater the number of bits set in this kernel 4577 parameter, the less frequently counter wrap will 4578 be checked for. Note that the bottom two bits 4579 are ignored. 4580 4581 srcutree.exp_holdoff [KNL] 4582 Specifies how many nanoseconds must elapse 4583 since the end of the last SRCU grace period for 4584 a given srcu_struct until the next normal SRCU 4585 grace period will be considered for automatic 4586 expediting. Set to zero to disable automatic 4587 expediting. 4588 4589 ssbd= [ARM64,HW] 4590 Speculative Store Bypass Disable control 4591 4592 On CPUs that are vulnerable to the Speculative 4593 Store Bypass vulnerability and offer a 4594 firmware based mitigation, this parameter 4595 indicates how the mitigation should be used: 4596 4597 force-on: Unconditionally enable mitigation for 4598 for both kernel and userspace 4599 force-off: Unconditionally disable mitigation for 4600 for both kernel and userspace 4601 kernel: Always enable mitigation in the 4602 kernel, and offer a prctl interface 4603 to allow userspace to register its 4604 interest in being mitigated too. 4605 4606 stack_guard_gap= [MM] 4607 override the default stack gap protection. The value 4608 is in page units and it defines how many pages prior 4609 to (for stacks growing down) resp. after (for stacks 4610 growing up) the main stack are reserved for no other 4611 mapping. Default value is 256 pages. 4612 4613 stacktrace [FTRACE] 4614 Enabled the stack tracer on boot up. 4615 4616 stacktrace_filter=[function-list] 4617 [FTRACE] Limit the functions that the stack tracer 4618 will trace at boot up. function-list is a comma separated 4619 list of functions. This list can be changed at run 4620 time by the stack_trace_filter file in the debugfs 4621 tracing directory. Note, this enables stack tracing 4622 and the stacktrace above is not needed. 4623 4624 sti= [PARISC,HW] 4625 Format: <num> 4626 Set the STI (builtin display/keyboard on the HP-PARISC 4627 machines) console (graphic card) which should be used 4628 as the initial boot-console. 4629 See also comment in drivers/video/console/sticore.c. 4630 4631 sti_font= [HW] 4632 See comment in drivers/video/console/sticore.c. 4633 4634 stifb= [HW] 4635 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4636 4637 sunrpc.min_resvport= 4638 sunrpc.max_resvport= 4639 [NFS,SUNRPC] 4640 SunRPC servers often require that client requests 4641 originate from a privileged port (i.e. a port in the 4642 range 0 < portnr < 1024). 4643 An administrator who wishes to reserve some of these 4644 ports for other uses may adjust the range that the 4645 kernel's sunrpc client considers to be privileged 4646 using these two parameters to set the minimum and 4647 maximum port values. 4648 4649 sunrpc.svc_rpc_per_connection_limit= 4650 [NFS,SUNRPC] 4651 Limit the number of requests that the server will 4652 process in parallel from a single connection. 4653 The default value is 0 (no limit). 4654 4655 sunrpc.pool_mode= 4656 [NFS] 4657 Control how the NFS server code allocates CPUs to 4658 service thread pools. Depending on how many NICs 4659 you have and where their interrupts are bound, this 4660 option will affect which CPUs will do NFS serving. 4661 Note: this parameter cannot be changed while the 4662 NFS server is running. 4663 4664 auto the server chooses an appropriate mode 4665 automatically using heuristics 4666 global a single global pool contains all CPUs 4667 percpu one pool for each CPU 4668 pernode one pool for each NUMA node (equivalent 4669 to global on non-NUMA machines) 4670 4671 sunrpc.tcp_slot_table_entries= 4672 sunrpc.udp_slot_table_entries= 4673 [NFS,SUNRPC] 4674 Sets the upper limit on the number of simultaneous 4675 RPC calls that can be sent from the client to a 4676 server. Increasing these values may allow you to 4677 improve throughput, but will also increase the 4678 amount of memory reserved for use by the client. 4679 4680 suspend.pm_test_delay= 4681 [SUSPEND] 4682 Sets the number of seconds to remain in a suspend test 4683 mode before resuming the system (see 4684 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4685 is set. Default value is 5. 4686 4687 svm= [PPC] 4688 Format: { on | off | y | n | 1 | 0 } 4689 This parameter controls use of the Protected 4690 Execution Facility on pSeries. 4691 4692 swapaccount=[0|1] 4693 [KNL] Enable accounting of swap in memory resource 4694 controller if no parameter or 1 is given or disable 4695 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4696 4697 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4698 Format: { <int> | force | noforce } 4699 <int> -- Number of I/O TLB slabs 4700 force -- force using of bounce buffers even if they 4701 wouldn't be automatically used by the kernel 4702 noforce -- Never use bounce buffers (for debugging) 4703 4704 switches= [HW,M68k] 4705 4706 sysfs.deprecated=0|1 [KNL] 4707 Enable/disable old style sysfs layout for old udev 4708 on older distributions. When this option is enabled 4709 very new udev will not work anymore. When this option 4710 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4711 in older udev will not work anymore. 4712 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4713 the kernel configuration. 4714 4715 sysrq_always_enabled 4716 [KNL] 4717 Ignore sysrq setting - this boot parameter will 4718 neutralize any effect of /proc/sys/kernel/sysrq. 4719 Useful for debugging. 4720 4721 tcpmhash_entries= [KNL,NET] 4722 Set the number of tcp_metrics_hash slots. 4723 Default value is 8192 or 16384 depending on total 4724 ram pages. This is used to specify the TCP metrics 4725 cache size. See Documentation/networking/ip-sysctl.txt 4726 "tcp_no_metrics_save" section for more details. 4727 4728 tdfx= [HW,DRM] 4729 4730 test_suspend= [SUSPEND][,N] 4731 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4732 standby suspend) or "freeze" (for suspend type freeze) 4733 as the system sleep state during system startup with 4734 the optional capability to repeat N number of times. 4735 The system is woken from this state using a 4736 wakeup-capable RTC alarm. 4737 4738 thash_entries= [KNL,NET] 4739 Set number of hash buckets for TCP connection 4740 4741 thermal.act= [HW,ACPI] 4742 -1: disable all active trip points in all thermal zones 4743 <degrees C>: override all lowest active trip points 4744 4745 thermal.crt= [HW,ACPI] 4746 -1: disable all critical trip points in all thermal zones 4747 <degrees C>: override all critical trip points 4748 4749 thermal.nocrt= [HW,ACPI] 4750 Set to disable actions on ACPI thermal zone 4751 critical and hot trip points. 4752 4753 thermal.off= [HW,ACPI] 4754 1: disable ACPI thermal control 4755 4756 thermal.psv= [HW,ACPI] 4757 -1: disable all passive trip points 4758 <degrees C>: override all passive trip points to this 4759 value 4760 4761 thermal.tzp= [HW,ACPI] 4762 Specify global default ACPI thermal zone polling rate 4763 <deci-seconds>: poll all this frequency 4764 0: no polling (default) 4765 4766 threadirqs [KNL] 4767 Force threading of all interrupt handlers except those 4768 marked explicitly IRQF_NO_THREAD. 4769 4770 topology= [S390] 4771 Format: {off | on} 4772 Specify if the kernel should make use of the cpu 4773 topology information if the hardware supports this. 4774 The scheduler will make use of this information and 4775 e.g. base its process migration decisions on it. 4776 Default is on. 4777 4778 topology_updates= [KNL, PPC, NUMA] 4779 Format: {off} 4780 Specify if the kernel should ignore (off) 4781 topology updates sent by the hypervisor to this 4782 LPAR. 4783 4784 tp720= [HW,PS2] 4785 4786 tpm_suspend_pcr=[HW,TPM] 4787 Format: integer pcr id 4788 Specify that at suspend time, the tpm driver 4789 should extend the specified pcr with zeros, 4790 as a workaround for some chips which fail to 4791 flush the last written pcr on TPM_SaveState. 4792 This will guarantee that all the other pcrs 4793 are saved. 4794 4795 trace_buf_size=nn[KMG] 4796 [FTRACE] will set tracing buffer size on each cpu. 4797 4798 trace_event=[event-list] 4799 [FTRACE] Set and start specified trace events in order 4800 to facilitate early boot debugging. The event-list is a 4801 comma separated list of trace events to enable. See 4802 also Documentation/trace/events.rst 4803 4804 trace_options=[option-list] 4805 [FTRACE] Enable or disable tracer options at boot. 4806 The option-list is a comma delimited list of options 4807 that can be enabled or disabled just as if you were 4808 to echo the option name into 4809 4810 /sys/kernel/debug/tracing/trace_options 4811 4812 For example, to enable stacktrace option (to dump the 4813 stack trace of each event), add to the command line: 4814 4815 trace_options=stacktrace 4816 4817 See also Documentation/trace/ftrace.rst "trace options" 4818 section. 4819 4820 tp_printk[FTRACE] 4821 Have the tracepoints sent to printk as well as the 4822 tracing ring buffer. This is useful for early boot up 4823 where the system hangs or reboots and does not give the 4824 option for reading the tracing buffer or performing a 4825 ftrace_dump_on_oops. 4826 4827 To turn off having tracepoints sent to printk, 4828 echo 0 > /proc/sys/kernel/tracepoint_printk 4829 Note, echoing 1 into this file without the 4830 tracepoint_printk kernel cmdline option has no effect. 4831 4832 ** CAUTION ** 4833 4834 Having tracepoints sent to printk() and activating high 4835 frequency tracepoints such as irq or sched, can cause 4836 the system to live lock. 4837 4838 traceoff_on_warning 4839 [FTRACE] enable this option to disable tracing when a 4840 warning is hit. This turns off "tracing_on". Tracing can 4841 be enabled again by echoing '1' into the "tracing_on" 4842 file located in /sys/kernel/debug/tracing/ 4843 4844 This option is useful, as it disables the trace before 4845 the WARNING dump is called, which prevents the trace to 4846 be filled with content caused by the warning output. 4847 4848 This option can also be set at run time via the sysctl 4849 option: kernel/traceoff_on_warning 4850 4851 transparent_hugepage= 4852 [KNL] 4853 Format: [always|madvise|never] 4854 Can be used to control the default behavior of the system 4855 with respect to transparent hugepages. 4856 See Documentation/admin-guide/mm/transhuge.rst 4857 for more details. 4858 4859 tsc= Disable clocksource stability checks for TSC. 4860 Format: <string> 4861 [x86] reliable: mark tsc clocksource as reliable, this 4862 disables clocksource verification at runtime, as well 4863 as the stability checks done at bootup. Used to enable 4864 high-resolution timer mode on older hardware, and in 4865 virtualized environment. 4866 [x86] noirqtime: Do not use TSC to do irq accounting. 4867 Used to run time disable IRQ_TIME_ACCOUNTING on any 4868 platforms where RDTSC is slow and this accounting 4869 can add overhead. 4870 [x86] unstable: mark the TSC clocksource as unstable, this 4871 marks the TSC unconditionally unstable at bootup and 4872 avoids any further wobbles once the TSC watchdog notices. 4873 [x86] nowatchdog: disable clocksource watchdog. Used 4874 in situations with strict latency requirements (where 4875 interruptions from clocksource watchdog are not 4876 acceptable). 4877 4878 tsx= [X86] Control Transactional Synchronization 4879 Extensions (TSX) feature in Intel processors that 4880 support TSX control. 4881 4882 This parameter controls the TSX feature. The options are: 4883 4884 on - Enable TSX on the system. Although there are 4885 mitigations for all known security vulnerabilities, 4886 TSX has been known to be an accelerator for 4887 several previous speculation-related CVEs, and 4888 so there may be unknown security risks associated 4889 with leaving it enabled. 4890 4891 off - Disable TSX on the system. (Note that this 4892 option takes effect only on newer CPUs which are 4893 not vulnerable to MDS, i.e., have 4894 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 4895 the new IA32_TSX_CTRL MSR through a microcode 4896 update. This new MSR allows for the reliable 4897 deactivation of the TSX functionality.) 4898 4899 auto - Disable TSX if X86_BUG_TAA is present, 4900 otherwise enable TSX on the system. 4901 4902 Not specifying this option is equivalent to tsx=off. 4903 4904 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 4905 for more details. 4906 4907 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 4908 Abort (TAA) vulnerability. 4909 4910 Similar to Micro-architectural Data Sampling (MDS) 4911 certain CPUs that support Transactional 4912 Synchronization Extensions (TSX) are vulnerable to an 4913 exploit against CPU internal buffers which can forward 4914 information to a disclosure gadget under certain 4915 conditions. 4916 4917 In vulnerable processors, the speculatively forwarded 4918 data can be used in a cache side channel attack, to 4919 access data to which the attacker does not have direct 4920 access. 4921 4922 This parameter controls the TAA mitigation. The 4923 options are: 4924 4925 full - Enable TAA mitigation on vulnerable CPUs 4926 if TSX is enabled. 4927 4928 full,nosmt - Enable TAA mitigation and disable SMT on 4929 vulnerable CPUs. If TSX is disabled, SMT 4930 is not disabled because CPU is not 4931 vulnerable to cross-thread TAA attacks. 4932 off - Unconditionally disable TAA mitigation 4933 4934 Not specifying this option is equivalent to 4935 tsx_async_abort=full. On CPUs which are MDS affected 4936 and deploy MDS mitigation, TAA mitigation is not 4937 required and doesn't provide any additional 4938 mitigation. 4939 4940 For details see: 4941 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 4942 4943 turbografx.map[2|3]= [HW,JOY] 4944 TurboGraFX parallel port interface 4945 Format: 4946 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4947 See also Documentation/input/devices/joystick-parport.rst 4948 4949 udbg-immortal [PPC] When debugging early kernel crashes that 4950 happen after console_init() and before a proper 4951 console driver takes over, this boot options might 4952 help "seeing" what's going on. 4953 4954 uhash_entries= [KNL,NET] 4955 Set number of hash buckets for UDP/UDP-Lite connections 4956 4957 uhci-hcd.ignore_oc= 4958 [USB] Ignore overcurrent events (default N). 4959 Some badly-designed motherboards generate lots of 4960 bogus events, for ports that aren't wired to 4961 anything. Set this parameter to avoid log spamming. 4962 Note that genuine overcurrent events won't be 4963 reported either. 4964 4965 unknown_nmi_panic 4966 [X86] Cause panic on unknown NMI. 4967 4968 usbcore.authorized_default= 4969 [USB] Default USB device authorization: 4970 (default -1 = authorized except for wireless USB, 4971 0 = not authorized, 1 = authorized, 2 = authorized 4972 if device connected to internal port) 4973 4974 usbcore.autosuspend= 4975 [USB] The autosuspend time delay (in seconds) used 4976 for newly-detected USB devices (default 2). This 4977 is the time required before an idle device will be 4978 autosuspended. Devices for which the delay is set 4979 to a negative value won't be autosuspended at all. 4980 4981 usbcore.usbfs_snoop= 4982 [USB] Set to log all usbfs traffic (default 0 = off). 4983 4984 usbcore.usbfs_snoop_max= 4985 [USB] Maximum number of bytes to snoop in each URB 4986 (default = 65536). 4987 4988 usbcore.blinkenlights= 4989 [USB] Set to cycle leds on hubs (default 0 = off). 4990 4991 usbcore.old_scheme_first= 4992 [USB] Start with the old device initialization 4993 scheme, applies only to low and full-speed devices 4994 (default 0 = off). 4995 4996 usbcore.usbfs_memory_mb= 4997 [USB] Memory limit (in MB) for buffers allocated by 4998 usbfs (default = 16, 0 = max = 2047). 4999 5000 usbcore.use_both_schemes= 5001 [USB] Try the other device initialization scheme 5002 if the first one fails (default 1 = enabled). 5003 5004 usbcore.initial_descriptor_timeout= 5005 [USB] Specifies timeout for the initial 64-byte 5006 USB_REQ_GET_DESCRIPTOR request in milliseconds 5007 (default 5000 = 5.0 seconds). 5008 5009 usbcore.nousb [USB] Disable the USB subsystem 5010 5011 usbcore.quirks= 5012 [USB] A list of quirk entries to augment the built-in 5013 usb core quirk list. List entries are separated by 5014 commas. Each entry has the form 5015 VendorID:ProductID:Flags. The IDs are 4-digit hex 5016 numbers and Flags is a set of letters. Each letter 5017 will change the built-in quirk; setting it if it is 5018 clear and clearing it if it is set. The letters have 5019 the following meanings: 5020 a = USB_QUIRK_STRING_FETCH_255 (string 5021 descriptors must not be fetched using 5022 a 255-byte read); 5023 b = USB_QUIRK_RESET_RESUME (device can't resume 5024 correctly so reset it instead); 5025 c = USB_QUIRK_NO_SET_INTF (device can't handle 5026 Set-Interface requests); 5027 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5028 handle its Configuration or Interface 5029 strings); 5030 e = USB_QUIRK_RESET (device can't be reset 5031 (e.g morph devices), don't use reset); 5032 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5033 more interface descriptions than the 5034 bNumInterfaces count, and can't handle 5035 talking to these interfaces); 5036 g = USB_QUIRK_DELAY_INIT (device needs a pause 5037 during initialization, after we read 5038 the device descriptor); 5039 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5040 high speed and super speed interrupt 5041 endpoints, the USB 2.0 and USB 3.0 spec 5042 require the interval in microframes (1 5043 microframe = 125 microseconds) to be 5044 calculated as interval = 2 ^ 5045 (bInterval-1). 5046 Devices with this quirk report their 5047 bInterval as the result of this 5048 calculation instead of the exponent 5049 variable used in the calculation); 5050 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5051 handle device_qualifier descriptor 5052 requests); 5053 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5054 generates spurious wakeup, ignore 5055 remote wakeup capability); 5056 k = USB_QUIRK_NO_LPM (device can't handle Link 5057 Power Management); 5058 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5059 (Device reports its bInterval as linear 5060 frames instead of the USB 2.0 5061 calculation); 5062 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5063 to be disconnected before suspend to 5064 prevent spurious wakeup); 5065 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5066 pause after every control message); 5067 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5068 delay after resetting its port); 5069 Example: quirks=0781:5580:bk,0a5c:5834:gij 5070 5071 usbhid.mousepoll= 5072 [USBHID] The interval which mice are to be polled at. 5073 5074 usbhid.jspoll= 5075 [USBHID] The interval which joysticks are to be polled at. 5076 5077 usbhid.kbpoll= 5078 [USBHID] The interval which keyboards are to be polled at. 5079 5080 usb-storage.delay_use= 5081 [UMS] The delay in seconds before a new device is 5082 scanned for Logical Units (default 1). 5083 5084 usb-storage.quirks= 5085 [UMS] A list of quirks entries to supplement or 5086 override the built-in unusual_devs list. List 5087 entries are separated by commas. Each entry has 5088 the form VID:PID:Flags where VID and PID are Vendor 5089 and Product ID values (4-digit hex numbers) and 5090 Flags is a set of characters, each corresponding 5091 to a common usb-storage quirk flag as follows: 5092 a = SANE_SENSE (collect more than 18 bytes 5093 of sense data); 5094 b = BAD_SENSE (don't collect more than 18 5095 bytes of sense data); 5096 c = FIX_CAPACITY (decrease the reported 5097 device capacity by one sector); 5098 d = NO_READ_DISC_INFO (don't use 5099 READ_DISC_INFO command); 5100 e = NO_READ_CAPACITY_16 (don't use 5101 READ_CAPACITY_16 command); 5102 f = NO_REPORT_OPCODES (don't use report opcodes 5103 command, uas only); 5104 g = MAX_SECTORS_240 (don't transfer more than 5105 240 sectors at a time, uas only); 5106 h = CAPACITY_HEURISTICS (decrease the 5107 reported device capacity by one 5108 sector if the number is odd); 5109 i = IGNORE_DEVICE (don't bind to this 5110 device); 5111 j = NO_REPORT_LUNS (don't use report luns 5112 command, uas only); 5113 l = NOT_LOCKABLE (don't try to lock and 5114 unlock ejectable media); 5115 m = MAX_SECTORS_64 (don't transfer more 5116 than 64 sectors = 32 KB at a time); 5117 n = INITIAL_READ10 (force a retry of the 5118 initial READ(10) command); 5119 o = CAPACITY_OK (accept the capacity 5120 reported by the device); 5121 p = WRITE_CACHE (the device cache is ON 5122 by default); 5123 r = IGNORE_RESIDUE (the device reports 5124 bogus residue values); 5125 s = SINGLE_LUN (the device has only one 5126 Logical Unit); 5127 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5128 commands, uas only); 5129 u = IGNORE_UAS (don't bind to the uas driver); 5130 w = NO_WP_DETECT (don't test whether the 5131 medium is write-protected). 5132 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5133 even if the device claims no cache) 5134 Example: quirks=0419:aaf5:rl,0421:0433:rc 5135 5136 user_debug= [KNL,ARM] 5137 Format: <int> 5138 See arch/arm/Kconfig.debug help text. 5139 1 - undefined instruction events 5140 2 - system calls 5141 4 - invalid data aborts 5142 8 - SIGSEGV faults 5143 16 - SIGBUS faults 5144 Example: user_debug=31 5145 5146 userpte= 5147 [X86] Flags controlling user PTE allocations. 5148 5149 nohigh = do not allocate PTE pages in 5150 HIGHMEM regardless of setting 5151 of CONFIG_HIGHPTE. 5152 5153 vdso= [X86,SH] 5154 On X86_32, this is an alias for vdso32=. Otherwise: 5155 5156 vdso=1: enable VDSO (the default) 5157 vdso=0: disable VDSO mapping 5158 5159 vdso32= [X86] Control the 32-bit vDSO 5160 vdso32=1: enable 32-bit VDSO 5161 vdso32=0 or vdso32=2: disable 32-bit VDSO 5162 5163 See the help text for CONFIG_COMPAT_VDSO for more 5164 details. If CONFIG_COMPAT_VDSO is set, the default is 5165 vdso32=0; otherwise, the default is vdso32=1. 5166 5167 For compatibility with older kernels, vdso32=2 is an 5168 alias for vdso32=0. 5169 5170 Try vdso32=0 if you encounter an error that says: 5171 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5172 5173 vector= [IA-64,SMP] 5174 vector=percpu: enable percpu vector domain 5175 5176 video= [FB] Frame buffer configuration 5177 See Documentation/fb/modedb.rst. 5178 5179 video.brightness_switch_enabled= [0,1] 5180 If set to 1, on receiving an ACPI notify event 5181 generated by hotkey, video driver will adjust brightness 5182 level and then send out the event to user space through 5183 the allocated input device; If set to 0, video driver 5184 will only send out the event without touching backlight 5185 brightness level. 5186 default: 1 5187 5188 virtio_mmio.device= 5189 [VMMIO] Memory mapped virtio (platform) device. 5190 5191 <size>@<baseaddr>:<irq>[:<id>] 5192 where: 5193 <size> := size (can use standard suffixes 5194 like K, M and G) 5195 <baseaddr> := physical base address 5196 <irq> := interrupt number (as passed to 5197 request_irq()) 5198 <id> := (optional) platform device id 5199 example: 5200 virtio_mmio.device=1K@0x100b0000:48:7 5201 5202 Can be used multiple times for multiple devices. 5203 5204 vga= [BOOT,X86-32] Select a particular video mode 5205 See Documentation/x86/boot.rst and 5206 Documentation/admin-guide/svga.rst. 5207 Use vga=ask for menu. 5208 This is actually a boot loader parameter; the value is 5209 passed to the kernel using a special protocol. 5210 5211 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5212 May slow down system boot speed, especially when 5213 enabled on systems with a large amount of memory. 5214 All options are enabled by default, and this 5215 interface is meant to allow for selectively 5216 enabling or disabling specific virtual memory 5217 debugging features. 5218 5219 Available options are: 5220 P Enable page structure init time poisoning 5221 - Disable all of the above options 5222 5223 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5224 size of <nn>. This can be used to increase the 5225 minimum size (128MB on x86). It can also be used to 5226 decrease the size and leave more room for directly 5227 mapped kernel RAM. 5228 5229 vmcp_cma=nn[MG] [KNL,S390] 5230 Sets the memory size reserved for contiguous memory 5231 allocations for the vmcp device driver. 5232 5233 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5234 Format: <command> 5235 5236 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5237 Format: <command> 5238 5239 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5240 Format: <command> 5241 5242 vsyscall= [X86-64] 5243 Controls the behavior of vsyscalls (i.e. calls to 5244 fixed addresses of 0xffffffffff600x00 from legacy 5245 code). Most statically-linked binaries and older 5246 versions of glibc use these calls. Because these 5247 functions are at fixed addresses, they make nice 5248 targets for exploits that can control RIP. 5249 5250 emulate [default] Vsyscalls turn into traps and are 5251 emulated reasonably safely. The vsyscall 5252 page is readable. 5253 5254 xonly Vsyscalls turn into traps and are 5255 emulated reasonably safely. The vsyscall 5256 page is not readable. 5257 5258 none Vsyscalls don't work at all. This makes 5259 them quite hard to use for exploits but 5260 might break your system. 5261 5262 vt.color= [VT] Default text color. 5263 Format: 0xYX, X = foreground, Y = background. 5264 Default: 0x07 = light gray on black. 5265 5266 vt.cur_default= [VT] Default cursor shape. 5267 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5268 the parameters of the <Esc>[?A;B;Cc escape sequence; 5269 see VGA-softcursor.txt. Default: 2 = underline. 5270 5271 vt.default_blu= [VT] 5272 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5273 Change the default blue palette of the console. 5274 This is a 16-member array composed of values 5275 ranging from 0-255. 5276 5277 vt.default_grn= [VT] 5278 Format: <green0>,<green1>,<green2>,...,<green15> 5279 Change the default green palette of the console. 5280 This is a 16-member array composed of values 5281 ranging from 0-255. 5282 5283 vt.default_red= [VT] 5284 Format: <red0>,<red1>,<red2>,...,<red15> 5285 Change the default red palette of the console. 5286 This is a 16-member array composed of values 5287 ranging from 0-255. 5288 5289 vt.default_utf8= 5290 [VT] 5291 Format=<0|1> 5292 Set system-wide default UTF-8 mode for all tty's. 5293 Default is 1, i.e. UTF-8 mode is enabled for all 5294 newly opened terminals. 5295 5296 vt.global_cursor_default= 5297 [VT] 5298 Format=<-1|0|1> 5299 Set system-wide default for whether a cursor 5300 is shown on new VTs. Default is -1, 5301 i.e. cursors will be created by default unless 5302 overridden by individual drivers. 0 will hide 5303 cursors, 1 will display them. 5304 5305 vt.italic= [VT] Default color for italic text; 0-15. 5306 Default: 2 = green. 5307 5308 vt.underline= [VT] Default color for underlined text; 0-15. 5309 Default: 3 = cyan. 5310 5311 watchdog timers [HW,WDT] For information on watchdog timers, 5312 see Documentation/watchdog/watchdog-parameters.rst 5313 or other driver-specific files in the 5314 Documentation/watchdog/ directory. 5315 5316 watchdog_thresh= 5317 [KNL] 5318 Set the hard lockup detector stall duration 5319 threshold in seconds. The soft lockup detector 5320 threshold is set to twice the value. A value of 0 5321 disables both lockup detectors. Default is 10 5322 seconds. 5323 5324 workqueue.watchdog_thresh= 5325 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5326 warn stall conditions and dump internal state to 5327 help debugging. 0 disables workqueue stall 5328 detection; otherwise, it's the stall threshold 5329 duration in seconds. The default value is 30 and 5330 it can be updated at runtime by writing to the 5331 corresponding sysfs file. 5332 5333 workqueue.disable_numa 5334 By default, all work items queued to unbound 5335 workqueues are affine to the NUMA nodes they're 5336 issued on, which results in better behavior in 5337 general. If NUMA affinity needs to be disabled for 5338 whatever reason, this option can be used. Note 5339 that this also can be controlled per-workqueue for 5340 workqueues visible under /sys/bus/workqueue/. 5341 5342 workqueue.power_efficient 5343 Per-cpu workqueues are generally preferred because 5344 they show better performance thanks to cache 5345 locality; unfortunately, per-cpu workqueues tend to 5346 be more power hungry than unbound workqueues. 5347 5348 Enabling this makes the per-cpu workqueues which 5349 were observed to contribute significantly to power 5350 consumption unbound, leading to measurably lower 5351 power usage at the cost of small performance 5352 overhead. 5353 5354 The default value of this parameter is determined by 5355 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5356 5357 workqueue.debug_force_rr_cpu 5358 Workqueue used to implicitly guarantee that work 5359 items queued without explicit CPU specified are put 5360 on the local CPU. This guarantee is no longer true 5361 and while local CPU is still preferred work items 5362 may be put on foreign CPUs. This debug option 5363 forces round-robin CPU selection to flush out 5364 usages which depend on the now broken guarantee. 5365 When enabled, memory and cache locality will be 5366 impacted. 5367 5368 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5369 default x2apic cluster mode on platforms 5370 supporting x2apic. 5371 5372 x86_intel_mid_timer= [X86-32,APBT] 5373 Choose timer option for x86 Intel MID platform. 5374 Two valid options are apbt timer only and lapic timer 5375 plus one apbt timer for broadcast timer. 5376 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5377 5378 xen_512gb_limit [KNL,X86-64,XEN] 5379 Restricts the kernel running paravirtualized under Xen 5380 to use only up to 512 GB of RAM. The reason to do so is 5381 crash analysis tools and Xen tools for doing domain 5382 save/restore/migration must be enabled to handle larger 5383 domains. 5384 5385 xen_emul_unplug= [HW,X86,XEN] 5386 Unplug Xen emulated devices 5387 Format: [unplug0,][unplug1] 5388 ide-disks -- unplug primary master IDE devices 5389 aux-ide-disks -- unplug non-primary-master IDE devices 5390 nics -- unplug network devices 5391 all -- unplug all emulated devices (NICs and IDE disks) 5392 unnecessary -- unplugging emulated devices is 5393 unnecessary even if the host did not respond to 5394 the unplug protocol 5395 never -- do not unplug even if version check succeeds 5396 5397 xen_legacy_crash [X86,XEN] 5398 Crash from Xen panic notifier, without executing late 5399 panic() code such as dumping handler. 5400 5401 xen_nopvspin [X86,XEN] 5402 Disables the ticketlock slowpath using Xen PV 5403 optimizations. 5404 5405 xen_nopv [X86] 5406 Disables the PV optimizations forcing the HVM guest to 5407 run as generic HVM guest with no PV drivers. 5408 This option is obsoleted by the "nopv" option, which 5409 has equivalent effect for XEN platform. 5410 5411 xen_scrub_pages= [XEN] 5412 Boolean option to control scrubbing pages before giving them back 5413 to Xen, for use by other domains. Can be also changed at runtime 5414 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5415 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5416 5417 xen_timer_slop= [X86-64,XEN] 5418 Set the timer slop (in nanoseconds) for the virtual Xen 5419 timers (default is 100000). This adjusts the minimum 5420 delta of virtualized Xen timers, where lower values 5421 improve timer resolution at the expense of processing 5422 more timer interrupts. 5423 5424 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5425 Disables the PV optimizations forcing the guest to run 5426 as generic guest with no PV drivers. Currently support 5427 XEN HVM, KVM, HYPER_V and VMWARE guest. 5428 5429 xirc2ps_cs= [NET,PCMCIA] 5430 Format: 5431 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5432 5433 xive= [PPC] 5434 By default on POWER9 and above, the kernel will 5435 natively use the XIVE interrupt controller. This option 5436 allows the fallback firmware mode to be used: 5437 5438 off Fallback to firmware control of XIVE interrupt 5439 controller on both pseries and powernv 5440 platforms. Only useful on POWER9 and above. 5441 5442 xhci-hcd.quirks [USB,KNL] 5443 A hex value specifying bitmask with supplemental xhci 5444 host controller quirks. Meaning of each bit can be 5445 consulted in header drivers/usb/host/xhci.h. 5446 5447 xmon [PPC] 5448 Format: { early | on | rw | ro | off } 5449 Controls if xmon debugger is enabled. Default is off. 5450 Passing only "xmon" is equivalent to "xmon=early". 5451 early Call xmon as early as possible on boot; xmon 5452 debugger is called from setup_arch(). 5453 on xmon debugger hooks will be installed so xmon 5454 is only called on a kernel crash. Default mode, 5455 i.e. either "ro" or "rw" mode, is controlled 5456 with CONFIG_XMON_DEFAULT_RO_MODE. 5457 rw xmon debugger hooks will be installed so xmon 5458 is called only on a kernel crash, mode is write, 5459 meaning SPR registers, memory and, other data 5460 can be written using xmon commands. 5461 ro same as "rw" option above but SPR registers, 5462 memory, and other data can't be written using 5463 xmon commands. 5464 off xmon is disabled. 5465
