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-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2059 Default is 1 (enabled) 2060 2061 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2062 for all guests. 2063 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2064 2065 kvm-arm.vgic_v3_group0_trap= 2066 [KVM,ARM] Trap guest accesses to GICv3 group-0 2067 system registers 2068 2069 kvm-arm.vgic_v3_group1_trap= 2070 [KVM,ARM] Trap guest accesses to GICv3 group-1 2071 system registers 2072 2073 kvm-arm.vgic_v3_common_trap= 2074 [KVM,ARM] Trap guest accesses to GICv3 common 2075 system registers 2076 2077 kvm-arm.vgic_v4_enable= 2078 [KVM,ARM] Allow use of GICv4 for direct injection of 2079 LPIs. 2080 2081 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2082 (virtualized MMU) support on capable Intel chips. 2083 Default is 1 (enabled) 2084 2085 kvm-intel.emulate_invalid_guest_state= 2086 [KVM,Intel] Enable emulation of invalid guest states 2087 Default is 0 (disabled) 2088 2089 kvm-intel.flexpriority= 2090 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2091 Default is 1 (enabled) 2092 2093 kvm-intel.nested= 2094 [KVM,Intel] Enable VMX nesting (nVMX). 2095 Default is 0 (disabled) 2096 2097 kvm-intel.unrestricted_guest= 2098 [KVM,Intel] Disable unrestricted guest feature 2099 (virtualized real and unpaged mode) on capable 2100 Intel chips. Default is 1 (enabled) 2101 2102 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2103 CVE-2018-3620. 2104 2105 Valid arguments: never, cond, always 2106 2107 always: L1D cache flush on every VMENTER. 2108 cond: Flush L1D on VMENTER only when the code between 2109 VMEXIT and VMENTER can leak host memory. 2110 never: Disables the mitigation 2111 2112 Default is cond (do L1 cache flush in specific instances) 2113 2114 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2115 feature (tagged TLBs) on capable Intel chips. 2116 Default is 1 (enabled) 2117 2118 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2119 affected CPUs 2120 2121 The kernel PTE inversion protection is unconditionally 2122 enabled and cannot be disabled. 2123 2124 full 2125 Provides all available mitigations for the 2126 L1TF vulnerability. Disables SMT and 2127 enables all mitigations in the 2128 hypervisors, i.e. unconditional L1D flush. 2129 2130 SMT control and L1D flush control via the 2131 sysfs interface is still possible after 2132 boot. Hypervisors will issue a warning 2133 when the first VM is started in a 2134 potentially insecure configuration, 2135 i.e. SMT enabled or L1D flush disabled. 2136 2137 full,force 2138 Same as 'full', but disables SMT and L1D 2139 flush runtime control. Implies the 2140 'nosmt=force' command line option. 2141 (i.e. sysfs control of SMT is disabled.) 2142 2143 flush 2144 Leaves SMT enabled and enables the default 2145 hypervisor mitigation, i.e. conditional 2146 L1D flush. 2147 2148 SMT control and L1D flush control via the 2149 sysfs interface is still possible after 2150 boot. Hypervisors will issue a warning 2151 when the first VM is started in a 2152 potentially insecure configuration, 2153 i.e. SMT enabled or L1D flush disabled. 2154 2155 flush,nosmt 2156 2157 Disables SMT and enables the default 2158 hypervisor mitigation. 2159 2160 SMT control and L1D flush control via the 2161 sysfs interface is still possible after 2162 boot. Hypervisors will issue a warning 2163 when the first VM is started in a 2164 potentially insecure configuration, 2165 i.e. SMT enabled or L1D flush disabled. 2166 2167 flush,nowarn 2168 Same as 'flush', but hypervisors will not 2169 warn when a VM is started in a potentially 2170 insecure configuration. 2171 2172 off 2173 Disables hypervisor mitigations and doesn't 2174 emit any warnings. 2175 It also drops the swap size and available 2176 RAM limit restriction on both hypervisor and 2177 bare metal. 2178 2179 Default is 'flush'. 2180 2181 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2182 2183 l2cr= [PPC] 2184 2185 l3cr= [PPC] 2186 2187 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2188 disabled it. 2189 2190 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2191 value for LAPIC timer one-shot implementation. Default 2192 back to the programmable timer unit in the LAPIC. 2193 2194 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2195 in C2 power state. 2196 2197 libata.dma= [LIBATA] DMA control 2198 libata.dma=0 Disable all PATA and SATA DMA 2199 libata.dma=1 PATA and SATA Disk DMA only 2200 libata.dma=2 ATAPI (CDROM) DMA only 2201 libata.dma=4 Compact Flash DMA only 2202 Combinations also work, so libata.dma=3 enables DMA 2203 for disks and CDROMs, but not CFs. 2204 2205 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2206 libata.ignore_hpa=0 keep BIOS limits (default) 2207 libata.ignore_hpa=1 ignore limits, using full disk 2208 2209 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2210 when set. 2211 Format: <int> 2212 2213 libata.force= [LIBATA] Force configurations. The format is comma 2214 separated list of "[ID:]VAL" where ID is 2215 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2216 matching port, link or device. Basically, it matches 2217 the ATA ID string printed on console by libata. If 2218 the whole ID part is omitted, the last PORT and DEVICE 2219 values are used. If ID hasn't been specified yet, the 2220 configuration applies to all ports, links and devices. 2221 2222 If only DEVICE is omitted, the parameter applies to 2223 the port and all links and devices behind it. DEVICE 2224 number of 0 either selects the first device or the 2225 first fan-out link behind PMP device. It does not 2226 select the host link. DEVICE number of 15 selects the 2227 host link and device attached to it. 2228 2229 The VAL specifies the configuration to force. As long 2230 as there's no ambiguity shortcut notation is allowed. 2231 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2232 The following configurations can be forced. 2233 2234 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2235 Any ID with matching PORT is used. 2236 2237 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2238 2239 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2240 udma[/][16,25,33,44,66,100,133] notation is also 2241 allowed. 2242 2243 * [no]ncq: Turn on or off NCQ. 2244 2245 * [no]ncqtrim: Turn off queued DSM TRIM. 2246 2247 * nohrst, nosrst, norst: suppress hard, soft 2248 and both resets. 2249 2250 * rstonce: only attempt one reset during 2251 hot-unplug link recovery 2252 2253 * dump_id: dump IDENTIFY data. 2254 2255 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2256 2257 * disable: Disable this device. 2258 2259 If there are multiple matching configurations changing 2260 the same attribute, the last one is used. 2261 2262 memblock=debug [KNL] Enable memblock debug messages. 2263 2264 load_ramdisk= [RAM] List of ramdisks to load from floppy 2265 See Documentation/admin-guide/blockdev/ramdisk.rst. 2266 2267 lockd.nlm_grace_period=P [NFS] Assign grace period. 2268 Format: <integer> 2269 2270 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2271 Format: <integer> 2272 2273 lockd.nlm_timeout=T [NFS] Assign timeout value. 2274 Format: <integer> 2275 2276 lockd.nlm_udpport=M [NFS] Assign UDP port. 2277 Format: <integer> 2278 2279 lockdown= [SECURITY] 2280 { integrity | confidentiality } 2281 Enable the kernel lockdown feature. If set to 2282 integrity, kernel features that allow userland to 2283 modify the running kernel are disabled. If set to 2284 confidentiality, kernel features that allow userland 2285 to extract confidential information from the kernel 2286 are also disabled. 2287 2288 locktorture.nreaders_stress= [KNL] 2289 Set the number of locking read-acquisition kthreads. 2290 Defaults to being automatically set based on the 2291 number of online CPUs. 2292 2293 locktorture.nwriters_stress= [KNL] 2294 Set the number of locking write-acquisition kthreads. 2295 2296 locktorture.onoff_holdoff= [KNL] 2297 Set time (s) after boot for CPU-hotplug testing. 2298 2299 locktorture.onoff_interval= [KNL] 2300 Set time (s) between CPU-hotplug operations, or 2301 zero to disable CPU-hotplug testing. 2302 2303 locktorture.shuffle_interval= [KNL] 2304 Set task-shuffle interval (jiffies). Shuffling 2305 tasks allows some CPUs to go into dyntick-idle 2306 mode during the locktorture test. 2307 2308 locktorture.shutdown_secs= [KNL] 2309 Set time (s) after boot system shutdown. This 2310 is useful for hands-off automated testing. 2311 2312 locktorture.stat_interval= [KNL] 2313 Time (s) between statistics printk()s. 2314 2315 locktorture.stutter= [KNL] 2316 Time (s) to stutter testing, for example, 2317 specifying five seconds causes the test to run for 2318 five seconds, wait for five seconds, and so on. 2319 This tests the locking primitive's ability to 2320 transition abruptly to and from idle. 2321 2322 locktorture.torture_type= [KNL] 2323 Specify the locking implementation to test. 2324 2325 locktorture.verbose= [KNL] 2326 Enable additional printk() statements. 2327 2328 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2329 Format: <irq> 2330 2331 loglevel= All Kernel Messages with a loglevel smaller than the 2332 console loglevel will be printed to the console. It can 2333 also be changed with klogd or other programs. The 2334 loglevels are defined as follows: 2335 2336 0 (KERN_EMERG) system is unusable 2337 1 (KERN_ALERT) action must be taken immediately 2338 2 (KERN_CRIT) critical conditions 2339 3 (KERN_ERR) error conditions 2340 4 (KERN_WARNING) warning conditions 2341 5 (KERN_NOTICE) normal but significant condition 2342 6 (KERN_INFO) informational 2343 7 (KERN_DEBUG) debug-level messages 2344 2345 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2346 in bytes. n must be a power of two and greater 2347 than the minimal size. The minimal size is defined 2348 by LOG_BUF_SHIFT kernel config parameter. There is 2349 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2350 that allows to increase the default size depending on 2351 the number of CPUs. See init/Kconfig for more details. 2352 2353 logo.nologo [FB] Disables display of the built-in Linux logo. 2354 This may be used to provide more screen space for 2355 kernel log messages and is useful when debugging 2356 kernel boot problems. 2357 2358 lp=0 [LP] Specify parallel ports to use, e.g, 2359 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2360 lp=reset first parallel port). 'lp=0' disables the 2361 lp=auto printer driver. 'lp=reset' (which can be 2362 specified in addition to the ports) causes 2363 attached printers to be reset. Using 2364 lp=port1,port2,... specifies the parallel ports 2365 to associate lp devices with, starting with 2366 lp0. A port specification may be 'none' to skip 2367 that lp device, or a parport name such as 2368 'parport0'. Specifying 'lp=auto' instead of a 2369 port specification list means that device IDs 2370 from each port should be examined, to see if 2371 an IEEE 1284-compliant printer is attached; if 2372 so, the driver will manage that printer. 2373 See also header of drivers/char/lp.c. 2374 2375 lpj=n [KNL] 2376 Sets loops_per_jiffy to given constant, thus avoiding 2377 time-consuming boot-time autodetection (up to 250 ms per 2378 CPU). 0 enables autodetection (default). To determine 2379 the correct value for your kernel, boot with normal 2380 autodetection and see what value is printed. Note that 2381 on SMP systems the preset will be applied to all CPUs, 2382 which is likely to cause problems if your CPUs need 2383 significantly divergent settings. An incorrect value 2384 will cause delays in the kernel to be wrong, leading to 2385 unpredictable I/O errors and other breakage. Although 2386 unlikely, in the extreme case this might damage your 2387 hardware. 2388 2389 ltpc= [NET] 2390 Format: <io>,<irq>,<dma> 2391 2392 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2393 2394 lsm=lsm1,...,lsmN 2395 [SECURITY] Choose order of LSM initialization. This 2396 overrides CONFIG_LSM, and the "security=" parameter. 2397 2398 machvec= [IA-64] Force the use of a particular machine-vector 2399 (machvec) in a generic kernel. 2400 Example: machvec=hpzx1 2401 2402 machtype= [Loongson] Share the same kernel image file between different 2403 yeeloong laptop. 2404 Example: machtype=lemote-yeeloong-2f-7inch 2405 2406 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2407 than or equal to this physical address is ignored. 2408 2409 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2410 will bring up during bootup. maxcpus=n : n >= 0 limits 2411 the kernel to bring up 'n' processors. Surely after 2412 bootup you can bring up the other plugged cpu by executing 2413 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2414 only takes effect during system bootup. 2415 While n=0 is a special case, it is equivalent to "nosmp", 2416 which also disables the IO APIC. 2417 2418 max_loop= [LOOP] The number of loop block devices that get 2419 (loop.max_loop) unconditionally pre-created at init time. The default 2420 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2421 of statically allocating a predefined number, loop 2422 devices can be requested on-demand with the 2423 /dev/loop-control interface. 2424 2425 mce [X86-32] Machine Check Exception 2426 2427 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2428 2429 md= [HW] RAID subsystems devices and level 2430 See Documentation/admin-guide/md.rst. 2431 2432 mdacon= [MDA] 2433 Format: <first>,<last> 2434 Specifies range of consoles to be captured by the MDA. 2435 2436 mds= [X86,INTEL] 2437 Control mitigation for the Micro-architectural Data 2438 Sampling (MDS) vulnerability. 2439 2440 Certain CPUs are vulnerable to an exploit against CPU 2441 internal buffers which can forward information to a 2442 disclosure gadget under certain conditions. 2443 2444 In vulnerable processors, the speculatively 2445 forwarded data can be used in a cache side channel 2446 attack, to access data to which the attacker does 2447 not have direct access. 2448 2449 This parameter controls the MDS mitigation. The 2450 options are: 2451 2452 full - Enable MDS mitigation on vulnerable CPUs 2453 full,nosmt - Enable MDS mitigation and disable 2454 SMT on vulnerable CPUs 2455 off - Unconditionally disable MDS mitigation 2456 2457 Not specifying this option is equivalent to 2458 mds=full. 2459 2460 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2461 2462 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2463 Amount of memory to be used when the kernel is not able 2464 to see the whole system memory or for test. 2465 [X86] Work as limiting max address. Use together 2466 with memmap= to avoid physical address space collisions. 2467 Without memmap= PCI devices could be placed at addresses 2468 belonging to unused RAM. 2469 2470 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2471 memory. 2472 2473 memchunk=nn[KMG] 2474 [KNL,SH] Allow user to override the default size for 2475 per-device physically contiguous DMA buffers. 2476 2477 memhp_default_state=online/offline 2478 [KNL] Set the initial state for the memory hotplug 2479 onlining policy. If not specified, the default value is 2480 set according to the 2481 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2482 option. 2483 See Documentation/admin-guide/mm/memory-hotplug.rst. 2484 2485 memmap=exactmap [KNL,X86] Enable setting of an exact 2486 E820 memory map, as specified by the user. 2487 Such memmap=exactmap lines can be constructed based on 2488 BIOS output or other requirements. See the memmap=nn@ss 2489 option description. 2490 2491 memmap=nn[KMG]@ss[KMG] 2492 [KNL] Force usage of a specific region of memory. 2493 Region of memory to be used is from ss to ss+nn. 2494 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2495 which limits max address to nn[KMG]. 2496 Multiple different regions can be specified, 2497 comma delimited. 2498 Example: 2499 memmap=100M@2G,100M#3G,1G!1024G 2500 2501 memmap=nn[KMG]#ss[KMG] 2502 [KNL,ACPI] Mark specific memory as ACPI data. 2503 Region of memory to be marked is from ss to ss+nn. 2504 2505 memmap=nn[KMG]$ss[KMG] 2506 [KNL,ACPI] Mark specific memory as reserved. 2507 Region of memory to be reserved is from ss to ss+nn. 2508 Example: Exclude memory from 0x18690000-0x1869ffff 2509 memmap=64K$0x18690000 2510 or 2511 memmap=0x10000$0x18690000 2512 Some bootloaders may need an escape character before '$', 2513 like Grub2, otherwise '$' and the following number 2514 will be eaten. 2515 2516 memmap=nn[KMG]!ss[KMG] 2517 [KNL,X86] Mark specific memory as protected. 2518 Region of memory to be used, from ss to ss+nn. 2519 The memory region may be marked as e820 type 12 (0xc) 2520 and is NVDIMM or ADR memory. 2521 2522 memmap=<size>%<offset>-<oldtype>+<newtype> 2523 [KNL,ACPI] Convert memory within the specified region 2524 from <oldtype> to <newtype>. If "-<oldtype>" is left 2525 out, the whole region will be marked as <newtype>, 2526 even if previously unavailable. If "+<newtype>" is left 2527 out, matching memory will be removed. Types are 2528 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2529 3 = ACPI, 12 = PRAM. 2530 2531 memory_corruption_check=0/1 [X86] 2532 Some BIOSes seem to corrupt the first 64k of 2533 memory when doing things like suspend/resume. 2534 Setting this option will scan the memory 2535 looking for corruption. Enabling this will 2536 both detect corruption and prevent the kernel 2537 from using the memory being corrupted. 2538 However, its intended as a diagnostic tool; if 2539 repeatable BIOS-originated corruption always 2540 affects the same memory, you can use memmap= 2541 to prevent the kernel from using that memory. 2542 2543 memory_corruption_check_size=size [X86] 2544 By default it checks for corruption in the low 2545 64k, making this memory unavailable for normal 2546 use. Use this parameter to scan for 2547 corruption in more or less memory. 2548 2549 memory_corruption_check_period=seconds [X86] 2550 By default it checks for corruption every 60 2551 seconds. Use this parameter to check at some 2552 other rate. 0 disables periodic checking. 2553 2554 memtest= [KNL,X86,ARM,PPC] Enable memtest 2555 Format: <integer> 2556 default : 0 <disable> 2557 Specifies the number of memtest passes to be 2558 performed. Each pass selects another test 2559 pattern from a given set of patterns. Memtest 2560 fills the memory with this pattern, validates 2561 memory contents and reserves bad memory 2562 regions that are detected. 2563 2564 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2565 Valid arguments: on, off 2566 Default (depends on kernel configuration option): 2567 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2568 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2569 mem_encrypt=on: Activate SME 2570 mem_encrypt=off: Do not activate SME 2571 2572 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2573 for details on when memory encryption can be activated. 2574 2575 mem_sleep_default= [SUSPEND] Default system suspend mode: 2576 s2idle - Suspend-To-Idle 2577 shallow - Power-On Suspend or equivalent (if supported) 2578 deep - Suspend-To-RAM or equivalent (if supported) 2579 See Documentation/admin-guide/pm/sleep-states.rst. 2580 2581 meye.*= [HW] Set MotionEye Camera parameters 2582 See Documentation/media/v4l-drivers/meye.rst. 2583 2584 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2585 Multi-Function General Purpose Timers on AMD Geode 2586 platforms. 2587 2588 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2589 the BIOS has incorrectly applied a workaround. TinyBIOS 2590 version 0.98 is known to be affected, 0.99 fixes the 2591 problem by letting the user disable the workaround. 2592 2593 mga= [HW,DRM] 2594 2595 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2596 physical address is ignored. 2597 2598 mini2440= [ARM,HW,KNL] 2599 Format:[0..2][b][c][t] 2600 Default: "0tb" 2601 MINI2440 configuration specification: 2602 0 - The attached screen is the 3.5" TFT 2603 1 - The attached screen is the 7" TFT 2604 2 - The VGA Shield is attached (1024x768) 2605 Leaving out the screen size parameter will not load 2606 the TFT driver, and the framebuffer will be left 2607 unconfigured. 2608 b - Enable backlight. The TFT backlight pin will be 2609 linked to the kernel VESA blanking code and a GPIO 2610 LED. This parameter is not necessary when using the 2611 VGA shield. 2612 c - Enable the s3c camera interface. 2613 t - Reserved for enabling touchscreen support. The 2614 touchscreen support is not enabled in the mainstream 2615 kernel as of 2.6.30, a preliminary port can be found 2616 in the "bleeding edge" mini2440 support kernel at 2617 http://repo.or.cz/w/linux-2.6/mini2440.git 2618 2619 mitigations= 2620 [X86,PPC,S390,ARM64] Control optional mitigations for 2621 CPU vulnerabilities. This is a set of curated, 2622 arch-independent options, each of which is an 2623 aggregation of existing arch-specific options. 2624 2625 off 2626 Disable all optional CPU mitigations. This 2627 improves system performance, but it may also 2628 expose users to several CPU vulnerabilities. 2629 Equivalent to: nopti [X86,PPC] 2630 kpti=0 [ARM64] 2631 nospectre_v1 [X86,PPC] 2632 nobp=0 [S390] 2633 nospectre_v2 [X86,PPC,S390,ARM64] 2634 spectre_v2_user=off [X86] 2635 spec_store_bypass_disable=off [X86,PPC] 2636 ssbd=force-off [ARM64] 2637 l1tf=off [X86] 2638 mds=off [X86] 2639 2640 auto (default) 2641 Mitigate all CPU vulnerabilities, but leave SMT 2642 enabled, even if it's vulnerable. This is for 2643 users who don't want to be surprised by SMT 2644 getting disabled across kernel upgrades, or who 2645 have other ways of avoiding SMT-based attacks. 2646 Equivalent to: (default behavior) 2647 2648 auto,nosmt 2649 Mitigate all CPU vulnerabilities, disabling SMT 2650 if needed. This is for users who always want to 2651 be fully mitigated, even if it means losing SMT. 2652 Equivalent to: l1tf=flush,nosmt [X86] 2653 mds=full,nosmt [X86] 2654 2655 mminit_loglevel= 2656 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2657 parameter allows control of the logging verbosity for 2658 the additional memory initialisation checks. A value 2659 of 0 disables mminit logging and a level of 4 will 2660 log everything. Information is printed at KERN_DEBUG 2661 so loglevel=8 may also need to be specified. 2662 2663 module.sig_enforce 2664 [KNL] When CONFIG_MODULE_SIG is set, this means that 2665 modules without (valid) signatures will fail to load. 2666 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2667 is always true, so this option does nothing. 2668 2669 module_blacklist= [KNL] Do not load a comma-separated list of 2670 modules. Useful for debugging problem modules. 2671 2672 mousedev.tap_time= 2673 [MOUSE] Maximum time between finger touching and 2674 leaving touchpad surface for touch to be considered 2675 a tap and be reported as a left button click (for 2676 touchpads working in absolute mode only). 2677 Format: <msecs> 2678 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2679 reporting absolute coordinates, such as tablets 2680 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2681 reporting absolute coordinates, such as tablets 2682 2683 movablecore= [KNL,X86,IA-64,PPC] 2684 Format: nn[KMGTPE] | nn% 2685 This parameter is the complement to kernelcore=, it 2686 specifies the amount of memory used for migratable 2687 allocations. If both kernelcore and movablecore is 2688 specified, then kernelcore will be at *least* the 2689 specified value but may be more. If movablecore on its 2690 own is specified, the administrator must be careful 2691 that the amount of memory usable for all allocations 2692 is not too small. 2693 2694 movable_node [KNL] Boot-time switch to make hotplugable memory 2695 NUMA nodes to be movable. This means that the memory 2696 of such nodes will be usable only for movable 2697 allocations which rules out almost all kernel 2698 allocations. Use with caution! 2699 2700 MTD_Partition= [MTD] 2701 Format: <name>,<region-number>,<size>,<offset> 2702 2703 MTD_Region= [MTD] Format: 2704 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2705 2706 mtdparts= [MTD] 2707 See drivers/mtd/cmdlinepart.c. 2708 2709 multitce=off [PPC] This parameter disables the use of the pSeries 2710 firmware feature for updating multiple TCE entries 2711 at a time. 2712 2713 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2714 2715 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2716 2717 boundary - index of last SLC block on Flex-OneNAND. 2718 The remaining blocks are configured as MLC blocks. 2719 lock - Configure if Flex-OneNAND boundary should be locked. 2720 Once locked, the boundary cannot be changed. 2721 1 indicates lock status, 0 indicates unlock status. 2722 2723 mtdset= [ARM] 2724 ARM/S3C2412 JIVE boot control 2725 2726 See arch/arm/mach-s3c2412/mach-jive.c 2727 2728 mtouchusb.raw_coordinates= 2729 [HW] Make the MicroTouch USB driver use raw coordinates 2730 ('y', default) or cooked coordinates ('n') 2731 2732 mtrr_chunk_size=nn[KMG] [X86] 2733 used for mtrr cleanup. It is largest continuous chunk 2734 that could hold holes aka. UC entries. 2735 2736 mtrr_gran_size=nn[KMG] [X86] 2737 Used for mtrr cleanup. It is granularity of mtrr block. 2738 Default is 1. 2739 Large value could prevent small alignment from 2740 using up MTRRs. 2741 2742 mtrr_spare_reg_nr=n [X86] 2743 Format: <integer> 2744 Range: 0,7 : spare reg number 2745 Default : 1 2746 Used for mtrr cleanup. It is spare mtrr entries number. 2747 Set to 2 or more if your graphical card needs more. 2748 2749 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2750 2751 netdev= [NET] Network devices parameters 2752 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2753 Note that mem_start is often overloaded to mean 2754 something different and driver-specific. 2755 This usage is only documented in each driver source 2756 file if at all. 2757 2758 nf_conntrack.acct= 2759 [NETFILTER] Enable connection tracking flow accounting 2760 0 to disable accounting 2761 1 to enable accounting 2762 Default value is 0. 2763 2764 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2765 See Documentation/filesystems/nfs/nfsroot.txt. 2766 2767 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2768 See Documentation/filesystems/nfs/nfsroot.txt. 2769 2770 nfsrootdebug [NFS] enable nfsroot debugging messages. 2771 See Documentation/filesystems/nfs/nfsroot.txt. 2772 2773 nfs.callback_nr_threads= 2774 [NFSv4] set the total number of threads that the 2775 NFS client will assign to service NFSv4 callback 2776 requests. 2777 2778 nfs.callback_tcpport= 2779 [NFS] set the TCP port on which the NFSv4 callback 2780 channel should listen. 2781 2782 nfs.cache_getent= 2783 [NFS] sets the pathname to the program which is used 2784 to update the NFS client cache entries. 2785 2786 nfs.cache_getent_timeout= 2787 [NFS] sets the timeout after which an attempt to 2788 update a cache entry is deemed to have failed. 2789 2790 nfs.idmap_cache_timeout= 2791 [NFS] set the maximum lifetime for idmapper cache 2792 entries. 2793 2794 nfs.enable_ino64= 2795 [NFS] enable 64-bit inode numbers. 2796 If zero, the NFS client will fake up a 32-bit inode 2797 number for the readdir() and stat() syscalls instead 2798 of returning the full 64-bit number. 2799 The default is to return 64-bit inode numbers. 2800 2801 nfs.max_session_cb_slots= 2802 [NFSv4.1] Sets the maximum number of session 2803 slots the client will assign to the callback 2804 channel. This determines the maximum number of 2805 callbacks the client will process in parallel for 2806 a particular server. 2807 2808 nfs.max_session_slots= 2809 [NFSv4.1] Sets the maximum number of session slots 2810 the client will attempt to negotiate with the server. 2811 This limits the number of simultaneous RPC requests 2812 that the client can send to the NFSv4.1 server. 2813 Note that there is little point in setting this 2814 value higher than the max_tcp_slot_table_limit. 2815 2816 nfs.nfs4_disable_idmapping= 2817 [NFSv4] When set to the default of '1', this option 2818 ensures that both the RPC level authentication 2819 scheme and the NFS level operations agree to use 2820 numeric uids/gids if the mount is using the 2821 'sec=sys' security flavour. In effect it is 2822 disabling idmapping, which can make migration from 2823 legacy NFSv2/v3 systems to NFSv4 easier. 2824 Servers that do not support this mode of operation 2825 will be autodetected by the client, and it will fall 2826 back to using the idmapper. 2827 To turn off this behaviour, set the value to '0'. 2828 nfs.nfs4_unique_id= 2829 [NFS4] Specify an additional fixed unique ident- 2830 ification string that NFSv4 clients can insert into 2831 their nfs_client_id4 string. This is typically a 2832 UUID that is generated at system install time. 2833 2834 nfs.send_implementation_id = 2835 [NFSv4.1] Send client implementation identification 2836 information in exchange_id requests. 2837 If zero, no implementation identification information 2838 will be sent. 2839 The default is to send the implementation identification 2840 information. 2841 2842 nfs.recover_lost_locks = 2843 [NFSv4] Attempt to recover locks that were lost due 2844 to a lease timeout on the server. Please note that 2845 doing this risks data corruption, since there are 2846 no guarantees that the file will remain unchanged 2847 after the locks are lost. 2848 If you want to enable the kernel legacy behaviour of 2849 attempting to recover these locks, then set this 2850 parameter to '1'. 2851 The default parameter value of '0' causes the kernel 2852 not to attempt recovery of lost locks. 2853 2854 nfs4.layoutstats_timer = 2855 [NFSv4.2] Change the rate at which the kernel sends 2856 layoutstats to the pNFS metadata server. 2857 2858 Setting this to value to 0 causes the kernel to use 2859 whatever value is the default set by the layout 2860 driver. A non-zero value sets the minimum interval 2861 in seconds between layoutstats transmissions. 2862 2863 nfsd.nfs4_disable_idmapping= 2864 [NFSv4] When set to the default of '1', the NFSv4 2865 server will return only numeric uids and gids to 2866 clients using auth_sys, and will accept numeric uids 2867 and gids from such clients. This is intended to ease 2868 migration from NFSv2/v3. 2869 2870 nmi_debug= [KNL,SH] Specify one or more actions to take 2871 when a NMI is triggered. 2872 Format: [state][,regs][,debounce][,die] 2873 2874 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2875 Format: [panic,][nopanic,][num] 2876 Valid num: 0 or 1 2877 0 - turn hardlockup detector in nmi_watchdog off 2878 1 - turn hardlockup detector in nmi_watchdog on 2879 When panic is specified, panic when an NMI watchdog 2880 timeout occurs (or 'nopanic' to not panic on an NMI 2881 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 2882 To disable both hard and soft lockup detectors, 2883 please see 'nowatchdog'. 2884 This is useful when you use a panic=... timeout and 2885 need the box quickly up again. 2886 2887 These settings can be accessed at runtime via 2888 the nmi_watchdog and hardlockup_panic sysctls. 2889 2890 netpoll.carrier_timeout= 2891 [NET] Specifies amount of time (in seconds) that 2892 netpoll should wait for a carrier. By default netpoll 2893 waits 4 seconds. 2894 2895 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2896 emulation library even if a 387 maths coprocessor 2897 is present. 2898 2899 no5lvl [X86-64] Disable 5-level paging mode. Forces 2900 kernel to use 4-level paging instead. 2901 2902 no_console_suspend 2903 [HW] Never suspend the console 2904 Disable suspending of consoles during suspend and 2905 hibernate operations. Once disabled, debugging 2906 messages can reach various consoles while the rest 2907 of the system is being put to sleep (ie, while 2908 debugging driver suspend/resume hooks). This may 2909 not work reliably with all consoles, but is known 2910 to work with serial and VGA consoles. 2911 To facilitate more flexible debugging, we also add 2912 console_suspend, a printk module parameter to control 2913 it. Users could use console_suspend (usually 2914 /sys/module/printk/parameters/console_suspend) to 2915 turn on/off it dynamically. 2916 2917 novmcoredd [KNL,KDUMP] 2918 Disable device dump. Device dump allows drivers to 2919 append dump data to vmcore so you can collect driver 2920 specified debug info. Drivers can append the data 2921 without any limit and this data is stored in memory, 2922 so this may cause significant memory stress. Disabling 2923 device dump can help save memory but the driver debug 2924 data will be no longer available. This parameter 2925 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 2926 is set. 2927 2928 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2929 caches in the slab allocator. Saves per-node memory, 2930 but will impact performance. 2931 2932 noalign [KNL,ARM] 2933 2934 noaltinstr [S390] Disables alternative instructions patching 2935 (CPU alternatives feature). 2936 2937 noapic [SMP,APIC] Tells the kernel to not make use of any 2938 IOAPICs that may be present in the system. 2939 2940 noautogroup Disable scheduler automatic task group creation. 2941 2942 nobats [PPC] Do not use BATs for mapping kernel lowmem 2943 on "Classic" PPC cores. 2944 2945 nocache [ARM] 2946 2947 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2948 2949 nodelayacct [KNL] Disable per-task delay accounting 2950 2951 nodsp [SH] Disable hardware DSP at boot time. 2952 2953 noefi Disable EFI runtime services support. 2954 2955 noexec [IA-64] 2956 2957 noexec [X86] 2958 On X86-32 available only on PAE configured kernels. 2959 noexec=on: enable non-executable mappings (default) 2960 noexec=off: disable non-executable mappings 2961 2962 nosmap [X86,PPC] 2963 Disable SMAP (Supervisor Mode Access Prevention) 2964 even if it is supported by processor. 2965 2966 nosmep [X86,PPC] 2967 Disable SMEP (Supervisor Mode Execution Prevention) 2968 even if it is supported by processor. 2969 2970 noexec32 [X86-64] 2971 This affects only 32-bit executables. 2972 noexec32=on: enable non-executable mappings (default) 2973 read doesn't imply executable mappings 2974 noexec32=off: disable non-executable mappings 2975 read implies executable mappings 2976 2977 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2978 2979 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2980 register save and restore. The kernel will only save 2981 legacy floating-point registers on task switch. 2982 2983 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 2984 2985 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2986 Equivalent to smt=1. 2987 2988 [KNL,x86] Disable symmetric multithreading (SMT). 2989 nosmt=force: Force disable SMT, cannot be undone 2990 via the sysfs control file. 2991 2992 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 2993 (bounds check bypass). With this option data leaks are 2994 possible in the system. 2995 2996 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 2997 the Spectre variant 2 (indirect branch prediction) 2998 vulnerability. System may allow data leaks with this 2999 option. 3000 3001 nospec_store_bypass_disable 3002 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3003 3004 noxsave [BUGS=X86] Disables x86 extended register state save 3005 and restore using xsave. The kernel will fallback to 3006 enabling legacy floating-point and sse state. 3007 3008 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3009 register states. The kernel will fall back to use 3010 xsave to save the states. By using this parameter, 3011 performance of saving the states is degraded because 3012 xsave doesn't support modified optimization while 3013 xsaveopt supports it on xsaveopt enabled systems. 3014 3015 noxsaves [X86] Disables xsaves and xrstors used in saving and 3016 restoring x86 extended register state in compacted 3017 form of xsave area. The kernel will fall back to use 3018 xsaveopt and xrstor to save and restore the states 3019 in standard form of xsave area. By using this 3020 parameter, xsave area per process might occupy more 3021 memory on xsaves enabled systems. 3022 3023 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3024 wfi(ARM) instruction doesn't work correctly and not to 3025 use it. This is also useful when using JTAG debugger. 3026 3027 no_file_caps Tells the kernel not to honor file capabilities. The 3028 only way then for a file to be executed with privilege 3029 is to be setuid root or executed by root. 3030 3031 nohalt [IA-64] Tells the kernel not to use the power saving 3032 function PAL_HALT_LIGHT when idle. This increases 3033 power-consumption. On the positive side, it reduces 3034 interrupt wake-up latency, which may improve performance 3035 in certain environments such as networked servers or 3036 real-time systems. 3037 3038 nohibernate [HIBERNATION] Disable hibernation and resume. 3039 3040 nohz= [KNL] Boottime enable/disable dynamic ticks 3041 Valid arguments: on, off 3042 Default: on 3043 3044 nohz_full= [KNL,BOOT,SMP,ISOL] 3045 The argument is a cpu list, as described above. 3046 In kernels built with CONFIG_NO_HZ_FULL=y, set 3047 the specified list of CPUs whose tick will be stopped 3048 whenever possible. The boot CPU will be forced outside 3049 the range to maintain the timekeeping. Any CPUs 3050 in this list will have their RCU callbacks offloaded, 3051 just as if they had also been called out in the 3052 rcu_nocbs= boot parameter. 3053 3054 noiotrap [SH] Disables trapped I/O port accesses. 3055 3056 noirqdebug [X86-32] Disables the code which attempts to detect and 3057 disable unhandled interrupt sources. 3058 3059 no_timer_check [X86,APIC] Disables the code which tests for 3060 broken timer IRQ sources. 3061 3062 noisapnp [ISAPNP] Disables ISA PnP code. 3063 3064 noinitrd [RAM] Tells the kernel not to load any configured 3065 initial RAM disk. 3066 3067 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3068 remapping. 3069 [Deprecated - use intremap=off] 3070 3071 nointroute [IA-64] 3072 3073 noinvpcid [X86] Disable the INVPCID cpu feature. 3074 3075 nojitter [IA-64] Disables jitter checking for ITC timers. 3076 3077 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3078 3079 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3080 fault handling. 3081 3082 no-vmw-sched-clock 3083 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3084 clock and use the default one. 3085 3086 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3087 steal time is computed, but won't influence scheduler 3088 behaviour 3089 3090 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3091 3092 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3093 3094 noltlbs [PPC] Do not use large page/tlb entries for kernel 3095 lowmem mapping on PPC40x and PPC8xx 3096 3097 nomca [IA-64] Disable machine check abort handling 3098 3099 nomce [X86-32] Disable Machine Check Exception 3100 3101 nomfgpt [X86-32] Disable Multi-Function General Purpose 3102 Timer usage (for AMD Geode machines). 3103 3104 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3105 shutdown the other cpus. Instead use the REBOOT_VECTOR 3106 irq. 3107 3108 nomodule Disable module load 3109 3110 nopat [X86] Disable PAT (page attribute table extension of 3111 pagetables) support. 3112 3113 nopcid [X86-64] Disable the PCID cpu feature. 3114 3115 norandmaps Don't use address space randomization. Equivalent to 3116 echo 0 > /proc/sys/kernel/randomize_va_space 3117 3118 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3119 with UP alternatives 3120 3121 nordrand [X86] Disable kernel use of the RDRAND and 3122 RDSEED instructions even if they are supported 3123 by the processor. RDRAND and RDSEED are still 3124 available to user space applications. 3125 3126 noresume [SWSUSP] Disables resume and restores original swap 3127 space. 3128 3129 no-scroll [VGA] Disables scrollback. 3130 This is required for the Braillex ib80-piezo Braille 3131 reader made by F.H. Papenmeier (Germany). 3132 3133 nosbagart [IA-64] 3134 3135 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3136 3137 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3138 and disable the IO APIC. legacy for "maxcpus=0". 3139 3140 nosoftlockup [KNL] Disable the soft-lockup detector. 3141 3142 nosync [HW,M68K] Disables sync negotiation for all devices. 3143 3144 nowatchdog [KNL] Disable both lockup detectors, i.e. 3145 soft-lockup and NMI watchdog (hard-lockup). 3146 3147 nowb [ARM] 3148 3149 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3150 3151 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3152 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3153 Some features depend on CPU0. Known dependencies are: 3154 1. Resume from suspend/hibernate depends on CPU0. 3155 Suspend/hibernate will fail if CPU0 is offline and you 3156 need to online CPU0 before suspend/hibernate. 3157 2. PIC interrupts also depend on CPU0. CPU0 can't be 3158 removed if a PIC interrupt is detected. 3159 It's said poweroff/reboot may depend on CPU0 on some 3160 machines although I haven't seen such issues so far 3161 after CPU0 is offline on a few tested machines. 3162 If the dependencies are under your control, you can 3163 turn on cpu0_hotplug. 3164 3165 nps_mtm_hs_ctr= [KNL,ARC] 3166 This parameter sets the maximum duration, in 3167 cycles, each HW thread of the CTOP can run 3168 without interruptions, before HW switches it. 3169 The actual maximum duration is 16 times this 3170 parameter's value. 3171 Format: integer between 1 and 255 3172 Default: 255 3173 3174 nptcg= [IA-64] Override max number of concurrent global TLB 3175 purges which is reported from either PAL_VM_SUMMARY or 3176 SAL PALO. 3177 3178 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3179 could support. nr_cpus=n : n >= 1 limits the kernel to 3180 support 'n' processors. It could be larger than the 3181 number of already plugged CPU during bootup, later in 3182 runtime you can physically add extra cpu until it reaches 3183 n. So during boot up some boot time memory for per-cpu 3184 variables need be pre-allocated for later physical cpu 3185 hot plugging. 3186 3187 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3188 3189 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3190 Allowed values are enable and disable 3191 3192 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3193 'node', 'default' can be specified 3194 This can be set from sysctl after boot. 3195 See Documentation/admin-guide/sysctl/vm.rst for details. 3196 3197 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3198 See Documentation/debugging-via-ohci1394.txt for more 3199 info. 3200 3201 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3202 Rather than timing out after 20 ms if an EC 3203 command is not properly ACKed, override the length 3204 of the timeout. We have interrupts disabled while 3205 waiting for the ACK, so if this is set too high 3206 interrupts *may* be lost! 3207 3208 omap_mux= [OMAP] Override bootloader pin multiplexing. 3209 Format: <mux_mode0.mode_name=value>... 3210 For example, to override I2C bus2: 3211 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3212 3213 oprofile.timer= [HW] 3214 Use timer interrupt instead of performance counters 3215 3216 oprofile.cpu_type= Force an oprofile cpu type 3217 This might be useful if you have an older oprofile 3218 userland or if you want common events. 3219 Format: { arch_perfmon } 3220 arch_perfmon: [X86] Force use of architectural 3221 perfmon on Intel CPUs instead of the 3222 CPU specific event set. 3223 timer: [X86] Force use of architectural NMI 3224 timer mode (see also oprofile.timer 3225 for generic hr timer mode) 3226 3227 oops=panic Always panic on oopses. Default is to just kill the 3228 process, but there is a small probability of 3229 deadlocking the machine. 3230 This will also cause panics on machine check exceptions. 3231 Useful together with panic=30 to trigger a reboot. 3232 3233 page_alloc.shuffle= 3234 [KNL] Boolean flag to control whether the page allocator 3235 should randomize its free lists. The randomization may 3236 be automatically enabled if the kernel detects it is 3237 running on a platform with a direct-mapped memory-side 3238 cache, and this parameter can be used to 3239 override/disable that behavior. The state of the flag 3240 can be read from sysfs at: 3241 /sys/module/page_alloc/parameters/shuffle. 3242 3243 page_owner= [KNL] Boot-time page_owner enabling option. 3244 Storage of the information about who allocated 3245 each page is disabled in default. With this switch, 3246 we can turn it on. 3247 on: enable the feature 3248 3249 page_poison= [KNL] Boot-time parameter changing the state of 3250 poisoning on the buddy allocator, available with 3251 CONFIG_PAGE_POISONING=y. 3252 off: turn off poisoning (default) 3253 on: turn on poisoning 3254 3255 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3256 timeout > 0: seconds before rebooting 3257 timeout = 0: wait forever 3258 timeout < 0: reboot immediately 3259 Format: <timeout> 3260 3261 panic_print= Bitmask for printing system info when panic happens. 3262 User can chose combination of the following bits: 3263 bit 0: print all tasks info 3264 bit 1: print system memory info 3265 bit 2: print timer info 3266 bit 3: print locks info if CONFIG_LOCKDEP is on 3267 bit 4: print ftrace buffer 3268 bit 5: print all printk messages in buffer 3269 3270 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3271 on a WARN(). 3272 3273 crash_kexec_post_notifiers 3274 Run kdump after running panic-notifiers and dumping 3275 kmsg. This only for the users who doubt kdump always 3276 succeeds in any situation. 3277 Note that this also increases risks of kdump failure, 3278 because some panic notifiers can make the crashed 3279 kernel more unstable. 3280 3281 parkbd.port= [HW] Parallel port number the keyboard adapter is 3282 connected to, default is 0. 3283 Format: <parport#> 3284 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3285 0 for XT, 1 for AT (default is AT). 3286 Format: <mode> 3287 3288 parport= [HW,PPT] Specify parallel ports. 0 disables. 3289 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3290 Use 'auto' to force the driver to use any 3291 IRQ/DMA settings detected (the default is to 3292 ignore detected IRQ/DMA settings because of 3293 possible conflicts). You can specify the base 3294 address, IRQ, and DMA settings; IRQ and DMA 3295 should be numbers, or 'auto' (for using detected 3296 settings on that particular port), or 'nofifo' 3297 (to avoid using a FIFO even if it is detected). 3298 Parallel ports are assigned in the order they 3299 are specified on the command line, starting 3300 with parport0. 3301 3302 parport_init_mode= [HW,PPT] 3303 Configure VIA parallel port to operate in 3304 a specific mode. This is necessary on Pegasos 3305 computer where firmware has no options for setting 3306 up parallel port mode and sets it to spp. 3307 Currently this function knows 686a and 8231 chips. 3308 Format: [spp|ps2|epp|ecp|ecpepp] 3309 3310 pause_on_oops= 3311 Halt all CPUs after the first oops has been printed for 3312 the specified number of seconds. This is to be used if 3313 your oopses keep scrolling off the screen. 3314 3315 pcbit= [HW,ISDN] 3316 3317 pcd. [PARIDE] 3318 See header of drivers/block/paride/pcd.c. 3319 See also Documentation/admin-guide/blockdev/paride.rst. 3320 3321 pci=option[,option...] [PCI] various PCI subsystem options. 3322 3323 Some options herein operate on a specific device 3324 or a set of devices (<pci_dev>). These are 3325 specified in one of the following formats: 3326 3327 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3328 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3329 3330 Note: the first format specifies a PCI 3331 bus/device/function address which may change 3332 if new hardware is inserted, if motherboard 3333 firmware changes, or due to changes caused 3334 by other kernel parameters. If the 3335 domain is left unspecified, it is 3336 taken to be zero. Optionally, a path 3337 to a device through multiple device/function 3338 addresses can be specified after the base 3339 address (this is more robust against 3340 renumbering issues). The second format 3341 selects devices using IDs from the 3342 configuration space which may match multiple 3343 devices in the system. 3344 3345 earlydump dump PCI config space before the kernel 3346 changes anything 3347 off [X86] don't probe for the PCI bus 3348 bios [X86-32] force use of PCI BIOS, don't access 3349 the hardware directly. Use this if your machine 3350 has a non-standard PCI host bridge. 3351 nobios [X86-32] disallow use of PCI BIOS, only direct 3352 hardware access methods are allowed. Use this 3353 if you experience crashes upon bootup and you 3354 suspect they are caused by the BIOS. 3355 conf1 [X86] Force use of PCI Configuration Access 3356 Mechanism 1 (config address in IO port 0xCF8, 3357 data in IO port 0xCFC, both 32-bit). 3358 conf2 [X86] Force use of PCI Configuration Access 3359 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3360 the function, IO port 0xCFA, also 8-bit, sets 3361 bus number. The config space is then accessed 3362 through ports 0xC000-0xCFFF). 3363 See http://wiki.osdev.org/PCI for more info 3364 on the configuration access mechanisms. 3365 noaer [PCIE] If the PCIEAER kernel config parameter is 3366 enabled, this kernel boot option can be used to 3367 disable the use of PCIE advanced error reporting. 3368 nodomains [PCI] Disable support for multiple PCI 3369 root domains (aka PCI segments, in ACPI-speak). 3370 nommconf [X86] Disable use of MMCONFIG for PCI 3371 Configuration 3372 check_enable_amd_mmconf [X86] check for and enable 3373 properly configured MMIO access to PCI 3374 config space on AMD family 10h CPU 3375 nomsi [MSI] If the PCI_MSI kernel config parameter is 3376 enabled, this kernel boot option can be used to 3377 disable the use of MSI interrupts system-wide. 3378 noioapicquirk [APIC] Disable all boot interrupt quirks. 3379 Safety option to keep boot IRQs enabled. This 3380 should never be necessary. 3381 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3382 primary IO-APIC for bridges that cannot disable 3383 boot IRQs. This fixes a source of spurious IRQs 3384 when the system masks IRQs. 3385 noioapicreroute [APIC] Disable workaround that uses the 3386 boot IRQ equivalent of an IRQ that connects to 3387 a chipset where boot IRQs cannot be disabled. 3388 The opposite of ioapicreroute. 3389 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3390 routing table. These calls are known to be buggy 3391 on several machines and they hang the machine 3392 when used, but on other computers it's the only 3393 way to get the interrupt routing table. Try 3394 this option if the kernel is unable to allocate 3395 IRQs or discover secondary PCI buses on your 3396 motherboard. 3397 rom [X86] Assign address space to expansion ROMs. 3398 Use with caution as certain devices share 3399 address decoders between ROMs and other 3400 resources. 3401 norom [X86] Do not assign address space to 3402 expansion ROMs that do not already have 3403 BIOS assigned address ranges. 3404 nobar [X86] Do not assign address space to the 3405 BARs that weren't assigned by the BIOS. 3406 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3407 assigned automatically to PCI devices. You can 3408 make the kernel exclude IRQs of your ISA cards 3409 this way. 3410 pirqaddr=0xAAAAA [X86] Specify the physical address 3411 of the PIRQ table (normally generated 3412 by the BIOS) if it is outside the 3413 F0000h-100000h range. 3414 lastbus=N [X86] Scan all buses thru bus #N. Can be 3415 useful if the kernel is unable to find your 3416 secondary buses and you want to tell it 3417 explicitly which ones they are. 3418 assign-busses [X86] Always assign all PCI bus 3419 numbers ourselves, overriding 3420 whatever the firmware may have done. 3421 usepirqmask [X86] Honor the possible IRQ mask stored 3422 in the BIOS $PIR table. This is needed on 3423 some systems with broken BIOSes, notably 3424 some HP Pavilion N5400 and Omnibook XE3 3425 notebooks. This will have no effect if ACPI 3426 IRQ routing is enabled. 3427 noacpi [X86] Do not use ACPI for IRQ routing 3428 or for PCI scanning. 3429 use_crs [X86] Use PCI host bridge window information 3430 from ACPI. On BIOSes from 2008 or later, this 3431 is enabled by default. If you need to use this, 3432 please report a bug. 3433 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3434 If you need to use this, please report a bug. 3435 routeirq Do IRQ routing for all PCI devices. 3436 This is normally done in pci_enable_device(), 3437 so this option is a temporary workaround 3438 for broken drivers that don't call it. 3439 skip_isa_align [X86] do not align io start addr, so can 3440 handle more pci cards 3441 noearly [X86] Don't do any early type 1 scanning. 3442 This might help on some broken boards which 3443 machine check when some devices' config space 3444 is read. But various workarounds are disabled 3445 and some IOMMU drivers will not work. 3446 bfsort Sort PCI devices into breadth-first order. 3447 This sorting is done to get a device 3448 order compatible with older (<= 2.4) kernels. 3449 nobfsort Don't sort PCI devices into breadth-first order. 3450 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3451 tuning and use the BIOS-configured MPS defaults. 3452 pcie_bus_safe Set every device's MPS to the largest value 3453 supported by all devices below the root complex. 3454 pcie_bus_perf Set device MPS to the largest allowable MPS 3455 based on its parent bus. Also set MRRS (Max 3456 Read Request Size) to the largest supported 3457 value (no larger than the MPS that the device 3458 or bus can support) for best performance. 3459 pcie_bus_peer2peer Set every device's MPS to 128B, which 3460 every device is guaranteed to support. This 3461 configuration allows peer-to-peer DMA between 3462 any pair of devices, possibly at the cost of 3463 reduced performance. This also guarantees 3464 that hot-added devices will work. 3465 cbiosize=nn[KMG] The fixed amount of bus space which is 3466 reserved for the CardBus bridge's IO window. 3467 The default value is 256 bytes. 3468 cbmemsize=nn[KMG] The fixed amount of bus space which is 3469 reserved for the CardBus bridge's memory 3470 window. The default value is 64 megabytes. 3471 resource_alignment= 3472 Format: 3473 [<order of align>@]<pci_dev>[; ...] 3474 Specifies alignment and device to reassign 3475 aligned memory resources. How to 3476 specify the device is described above. 3477 If <order of align> is not specified, 3478 PAGE_SIZE is used as alignment. 3479 A PCI-PCI bridge can be specified if resource 3480 windows need to be expanded. 3481 To specify the alignment for several 3482 instances of a device, the PCI vendor, 3483 device, subvendor, and subdevice may be 3484 specified, e.g., 12@pci:8086:9c22:103c:198f 3485 for 4096-byte alignment. 3486 ecrc= Enable/disable PCIe ECRC (transaction layer 3487 end-to-end CRC checking). 3488 bios: Use BIOS/firmware settings. This is the 3489 the default. 3490 off: Turn ECRC off 3491 on: Turn ECRC on. 3492 hpiosize=nn[KMG] The fixed amount of bus space which is 3493 reserved for hotplug bridge's IO window. 3494 Default size is 256 bytes. 3495 hpmemsize=nn[KMG] The fixed amount of bus space which is 3496 reserved for hotplug bridge's memory window. 3497 Default size is 2 megabytes. 3498 hpbussize=nn The minimum amount of additional bus numbers 3499 reserved for buses below a hotplug bridge. 3500 Default is 1. 3501 realloc= Enable/disable reallocating PCI bridge resources 3502 if allocations done by BIOS are too small to 3503 accommodate resources required by all child 3504 devices. 3505 off: Turn realloc off 3506 on: Turn realloc on 3507 realloc same as realloc=on 3508 noari do not use PCIe ARI. 3509 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3510 do not use PCIe ATS (and IOMMU device IOTLB). 3511 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3512 only look for one device below a PCIe downstream 3513 port. 3514 big_root_window Try to add a big 64bit memory window to the PCIe 3515 root complex on AMD CPUs. Some GFX hardware 3516 can resize a BAR to allow access to all VRAM. 3517 Adding the window is slightly risky (it may 3518 conflict with unreported devices), so this 3519 taints the kernel. 3520 disable_acs_redir=<pci_dev>[; ...] 3521 Specify one or more PCI devices (in the format 3522 specified above) separated by semicolons. 3523 Each device specified will have the PCI ACS 3524 redirect capabilities forced off which will 3525 allow P2P traffic between devices through 3526 bridges without forcing it upstream. Note: 3527 this removes isolation between devices and 3528 may put more devices in an IOMMU group. 3529 force_floating [S390] Force usage of floating interrupts. 3530 nomio [S390] Do not use MIO instructions. 3531 3532 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3533 Management. 3534 off Disable ASPM. 3535 force Enable ASPM even on devices that claim not to support it. 3536 WARNING: Forcing ASPM on may cause system lockups. 3537 3538 pcie_ports= [PCIE] PCIe port services handling: 3539 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3540 even if the platform doesn't give the OS permission to 3541 use them. This may cause conflicts if the platform 3542 also tries to use these services. 3543 compat Disable native PCIe services (PME, AER, DPC, PCIe 3544 hotplug). 3545 3546 pcie_port_pm= [PCIE] PCIe port power management handling: 3547 off Disable power management of all PCIe ports 3548 force Forcibly enable power management of all PCIe ports 3549 3550 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3551 nomsi Do not use MSI for native PCIe PME signaling (this makes 3552 all PCIe root ports use INTx for all services). 3553 3554 pcmv= [HW,PCMCIA] BadgePAD 4 3555 3556 pd_ignore_unused 3557 [PM] 3558 Keep all power-domains already enabled by bootloader on, 3559 even if no driver has claimed them. This is useful 3560 for debug and development, but should not be 3561 needed on a platform with proper driver support. 3562 3563 pd. [PARIDE] 3564 See Documentation/admin-guide/blockdev/paride.rst. 3565 3566 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3567 boot time. 3568 Format: { 0 | 1 } 3569 See arch/parisc/kernel/pdc_chassis.c 3570 3571 percpu_alloc= Select which percpu first chunk allocator to use. 3572 Currently supported values are "embed" and "page". 3573 Archs may support subset or none of the selections. 3574 See comments in mm/percpu.c for details on each 3575 allocator. This parameter is primarily for debugging 3576 and performance comparison. 3577 3578 pf. [PARIDE] 3579 See Documentation/admin-guide/blockdev/paride.rst. 3580 3581 pg. [PARIDE] 3582 See Documentation/admin-guide/blockdev/paride.rst. 3583 3584 pirq= [SMP,APIC] Manual mp-table setup 3585 See Documentation/x86/i386/IO-APIC.rst. 3586 3587 plip= [PPT,NET] Parallel port network link 3588 Format: { parport<nr> | timid | 0 } 3589 See also Documentation/admin-guide/parport.rst. 3590 3591 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3592 Override pmtimer IOPort with a hex value. 3593 e.g. pmtmr=0x508 3594 3595 pnp.debug=1 [PNP] 3596 Enable PNP debug messages (depends on the 3597 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3598 via /sys/module/pnp/parameters/debug. We always show 3599 current resource usage; turning this on also shows 3600 possible settings and some assignment information. 3601 3602 pnpacpi= [ACPI] 3603 { off } 3604 3605 pnpbios= [ISAPNP] 3606 { on | off | curr | res | no-curr | no-res } 3607 3608 pnp_reserve_irq= 3609 [ISAPNP] Exclude IRQs for the autoconfiguration 3610 3611 pnp_reserve_dma= 3612 [ISAPNP] Exclude DMAs for the autoconfiguration 3613 3614 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3615 Ranges are in pairs (I/O port base and size). 3616 3617 pnp_reserve_mem= 3618 [ISAPNP] Exclude memory regions for the 3619 autoconfiguration. 3620 Ranges are in pairs (memory base and size). 3621 3622 ports= [IP_VS_FTP] IPVS ftp helper module 3623 Default is 21. 3624 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3625 may be specified. 3626 Format: <port>,<port>.... 3627 3628 powersave=off [PPC] This option disables power saving features. 3629 It specifically disables cpuidle and sets the 3630 platform machine description specific power_save 3631 function to NULL. On Idle the CPU just reduces 3632 execution priority. 3633 3634 ppc_strict_facility_enable 3635 [PPC] This option catches any kernel floating point, 3636 Altivec, VSX and SPE outside of regions specifically 3637 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3638 There is some performance impact when enabling this. 3639 3640 ppc_tm= [PPC] 3641 Format: {"off"} 3642 Disable Hardware Transactional Memory 3643 3644 print-fatal-signals= 3645 [KNL] debug: print fatal signals 3646 3647 If enabled, warn about various signal handling 3648 related application anomalies: too many signals, 3649 too many POSIX.1 timers, fatal signals causing a 3650 coredump - etc. 3651 3652 If you hit the warning due to signal overflow, 3653 you might want to try "ulimit -i unlimited". 3654 3655 default: off. 3656 3657 printk.always_kmsg_dump= 3658 Trigger kmsg_dump for cases other than kernel oops or 3659 panics 3660 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3661 default: disabled 3662 3663 printk.devkmsg={on,off,ratelimit} 3664 Control writing to /dev/kmsg. 3665 on - unlimited logging to /dev/kmsg from userspace 3666 off - logging to /dev/kmsg disabled 3667 ratelimit - ratelimit the logging 3668 Default: ratelimit 3669 3670 printk.time= Show timing data prefixed to each printk message line 3671 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3672 3673 processor.max_cstate= [HW,ACPI] 3674 Limit processor to maximum C-state 3675 max_cstate=9 overrides any DMI blacklist limit. 3676 3677 processor.nocst [HW,ACPI] 3678 Ignore the _CST method to determine C-states, 3679 instead using the legacy FADT method 3680 3681 profile= [KNL] Enable kernel profiling via /proc/profile 3682 Format: [<profiletype>,]<number> 3683 Param: <profiletype>: "schedule", "sleep", or "kvm" 3684 [defaults to kernel profiling] 3685 Param: "schedule" - profile schedule points. 3686 Param: "sleep" - profile D-state sleeping (millisecs). 3687 Requires CONFIG_SCHEDSTATS 3688 Param: "kvm" - profile VM exits. 3689 Param: <number> - step/bucket size as a power of 2 for 3690 statistical time based profiling. 3691 3692 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3693 before loading. 3694 See Documentation/admin-guide/blockdev/ramdisk.rst. 3695 3696 psi= [KNL] Enable or disable pressure stall information 3697 tracking. 3698 Format: <bool> 3699 3700 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3701 probe for; one of (bare|imps|exps|lifebook|any). 3702 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3703 per second. 3704 psmouse.resetafter= [HW,MOUSE] 3705 Try to reset the device after so many bad packets 3706 (0 = never). 3707 psmouse.resolution= 3708 [HW,MOUSE] Set desired mouse resolution, in dpi. 3709 psmouse.smartscroll= 3710 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3711 0 = disabled, 1 = enabled (default). 3712 3713 pstore.backend= Specify the name of the pstore backend to use 3714 3715 pt. [PARIDE] 3716 See Documentation/admin-guide/blockdev/paride.rst. 3717 3718 pti= [X86_64] Control Page Table Isolation of user and 3719 kernel address spaces. Disabling this feature 3720 removes hardening, but improves performance of 3721 system calls and interrupts. 3722 3723 on - unconditionally enable 3724 off - unconditionally disable 3725 auto - kernel detects whether your CPU model is 3726 vulnerable to issues that PTI mitigates 3727 3728 Not specifying this option is equivalent to pti=auto. 3729 3730 nopti [X86_64] 3731 Equivalent to pti=off 3732 3733 pty.legacy_count= 3734 [KNL] Number of legacy pty's. Overwrites compiled-in 3735 default number. 3736 3737 quiet [KNL] Disable most log messages 3738 3739 r128= [HW,DRM] 3740 3741 raid= [HW,RAID] 3742 See Documentation/admin-guide/md.rst. 3743 3744 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3745 See Documentation/admin-guide/blockdev/ramdisk.rst. 3746 3747 random.trust_cpu={on,off} 3748 [KNL] Enable or disable trusting the use of the 3749 CPU's random number generator (if available) to 3750 fully seed the kernel's CRNG. Default is controlled 3751 by CONFIG_RANDOM_TRUST_CPU. 3752 3753 ras=option[,option,...] [KNL] RAS-specific options 3754 3755 cec_disable [X86] 3756 Disable the Correctable Errors Collector, 3757 see CONFIG_RAS_CEC help text. 3758 3759 rcu_nocbs= [KNL] 3760 The argument is a cpu list, as described above, 3761 except that the string "all" can be used to 3762 specify every CPU on the system. 3763 3764 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3765 the specified list of CPUs to be no-callback CPUs. 3766 Invocation of these CPUs' RCU callbacks will be 3767 offloaded to "rcuox/N" kthreads created for that 3768 purpose, where "x" is "p" for RCU-preempt, and 3769 "s" for RCU-sched, and "N" is the CPU number. 3770 This reduces OS jitter on the offloaded CPUs, 3771 which can be useful for HPC and real-time 3772 workloads. It can also improve energy efficiency 3773 for asymmetric multiprocessors. 3774 3775 rcu_nocb_poll [KNL] 3776 Rather than requiring that offloaded CPUs 3777 (specified by rcu_nocbs= above) explicitly 3778 awaken the corresponding "rcuoN" kthreads, 3779 make these kthreads poll for callbacks. 3780 This improves the real-time response for the 3781 offloaded CPUs by relieving them of the need to 3782 wake up the corresponding kthread, but degrades 3783 energy efficiency by requiring that the kthreads 3784 periodically wake up to do the polling. 3785 3786 rcutree.blimit= [KNL] 3787 Set maximum number of finished RCU callbacks to 3788 process in one batch. 3789 3790 rcutree.dump_tree= [KNL] 3791 Dump the structure of the rcu_node combining tree 3792 out at early boot. This is used for diagnostic 3793 purposes, to verify correct tree setup. 3794 3795 rcutree.gp_cleanup_delay= [KNL] 3796 Set the number of jiffies to delay each step of 3797 RCU grace-period cleanup. 3798 3799 rcutree.gp_init_delay= [KNL] 3800 Set the number of jiffies to delay each step of 3801 RCU grace-period initialization. 3802 3803 rcutree.gp_preinit_delay= [KNL] 3804 Set the number of jiffies to delay each step of 3805 RCU grace-period pre-initialization, that is, 3806 the propagation of recent CPU-hotplug changes up 3807 the rcu_node combining tree. 3808 3809 rcutree.use_softirq= [KNL] 3810 If set to zero, move all RCU_SOFTIRQ processing to 3811 per-CPU rcuc kthreads. Defaults to a non-zero 3812 value, meaning that RCU_SOFTIRQ is used by default. 3813 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3814 3815 rcutree.rcu_fanout_exact= [KNL] 3816 Disable autobalancing of the rcu_node combining 3817 tree. This is used by rcutorture, and might 3818 possibly be useful for architectures having high 3819 cache-to-cache transfer latencies. 3820 3821 rcutree.rcu_fanout_leaf= [KNL] 3822 Change the number of CPUs assigned to each 3823 leaf rcu_node structure. Useful for very 3824 large systems, which will choose the value 64, 3825 and for NUMA systems with large remote-access 3826 latencies, which will choose a value aligned 3827 with the appropriate hardware boundaries. 3828 3829 rcutree.jiffies_till_first_fqs= [KNL] 3830 Set delay from grace-period initialization to 3831 first attempt to force quiescent states. 3832 Units are jiffies, minimum value is zero, 3833 and maximum value is HZ. 3834 3835 rcutree.jiffies_till_next_fqs= [KNL] 3836 Set delay between subsequent attempts to force 3837 quiescent states. Units are jiffies, minimum 3838 value is one, and maximum value is HZ. 3839 3840 rcutree.jiffies_till_sched_qs= [KNL] 3841 Set required age in jiffies for a 3842 given grace period before RCU starts 3843 soliciting quiescent-state help from 3844 rcu_note_context_switch() and cond_resched(). 3845 If not specified, the kernel will calculate 3846 a value based on the most recent settings 3847 of rcutree.jiffies_till_first_fqs 3848 and rcutree.jiffies_till_next_fqs. 3849 This calculated value may be viewed in 3850 rcutree.jiffies_to_sched_qs. Any attempt to set 3851 rcutree.jiffies_to_sched_qs will be cheerfully 3852 overwritten. 3853 3854 rcutree.kthread_prio= [KNL,BOOT] 3855 Set the SCHED_FIFO priority of the RCU per-CPU 3856 kthreads (rcuc/N). This value is also used for 3857 the priority of the RCU boost threads (rcub/N) 3858 and for the RCU grace-period kthreads (rcu_bh, 3859 rcu_preempt, and rcu_sched). If RCU_BOOST is 3860 set, valid values are 1-99 and the default is 1 3861 (the least-favored priority). Otherwise, when 3862 RCU_BOOST is not set, valid values are 0-99 and 3863 the default is zero (non-realtime operation). 3864 3865 rcutree.rcu_nocb_gp_stride= [KNL] 3866 Set the number of NOCB callback kthreads in 3867 each group, which defaults to the square root 3868 of the number of CPUs. Larger numbers reduce 3869 the wakeup overhead on the global grace-period 3870 kthread, but increases that same overhead on 3871 each group's NOCB grace-period kthread. 3872 3873 rcutree.qhimark= [KNL] 3874 Set threshold of queued RCU callbacks beyond which 3875 batch limiting is disabled. 3876 3877 rcutree.qlowmark= [KNL] 3878 Set threshold of queued RCU callbacks below which 3879 batch limiting is re-enabled. 3880 3881 rcutree.rcu_idle_gp_delay= [KNL] 3882 Set wakeup interval for idle CPUs that have 3883 RCU callbacks (RCU_FAST_NO_HZ=y). 3884 3885 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3886 Set wakeup interval for idle CPUs that have 3887 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3888 Lazy RCU callbacks are those which RCU can 3889 prove do nothing more than free memory. 3890 3891 rcutree.rcu_kick_kthreads= [KNL] 3892 Cause the grace-period kthread to get an extra 3893 wake_up() if it sleeps three times longer than 3894 it should at force-quiescent-state time. 3895 This wake_up() will be accompanied by a 3896 WARN_ONCE() splat and an ftrace_dump(). 3897 3898 rcutree.sysrq_rcu= [KNL] 3899 Commandeer a sysrq key to dump out Tree RCU's 3900 rcu_node tree with an eye towards determining 3901 why a new grace period has not yet started. 3902 3903 rcuperf.gp_async= [KNL] 3904 Measure performance of asynchronous 3905 grace-period primitives such as call_rcu(). 3906 3907 rcuperf.gp_async_max= [KNL] 3908 Specify the maximum number of outstanding 3909 callbacks per writer thread. When a writer 3910 thread exceeds this limit, it invokes the 3911 corresponding flavor of rcu_barrier() to allow 3912 previously posted callbacks to drain. 3913 3914 rcuperf.gp_exp= [KNL] 3915 Measure performance of expedited synchronous 3916 grace-period primitives. 3917 3918 rcuperf.holdoff= [KNL] 3919 Set test-start holdoff period. The purpose of 3920 this parameter is to delay the start of the 3921 test until boot completes in order to avoid 3922 interference. 3923 3924 rcuperf.nreaders= [KNL] 3925 Set number of RCU readers. The value -1 selects 3926 N, where N is the number of CPUs. A value 3927 "n" less than -1 selects N-n+1, where N is again 3928 the number of CPUs. For example, -2 selects N 3929 (the number of CPUs), -3 selects N+1, and so on. 3930 A value of "n" less than or equal to -N selects 3931 a single reader. 3932 3933 rcuperf.nwriters= [KNL] 3934 Set number of RCU writers. The values operate 3935 the same as for rcuperf.nreaders. 3936 N, where N is the number of CPUs 3937 3938 rcuperf.perf_type= [KNL] 3939 Specify the RCU implementation to test. 3940 3941 rcuperf.shutdown= [KNL] 3942 Shut the system down after performance tests 3943 complete. This is useful for hands-off automated 3944 testing. 3945 3946 rcuperf.verbose= [KNL] 3947 Enable additional printk() statements. 3948 3949 rcuperf.writer_holdoff= [KNL] 3950 Write-side holdoff between grace periods, 3951 in microseconds. The default of zero says 3952 no holdoff. 3953 3954 rcutorture.fqs_duration= [KNL] 3955 Set duration of force_quiescent_state bursts 3956 in microseconds. 3957 3958 rcutorture.fqs_holdoff= [KNL] 3959 Set holdoff time within force_quiescent_state bursts 3960 in microseconds. 3961 3962 rcutorture.fqs_stutter= [KNL] 3963 Set wait time between force_quiescent_state bursts 3964 in seconds. 3965 3966 rcutorture.fwd_progress= [KNL] 3967 Enable RCU grace-period forward-progress testing 3968 for the types of RCU supporting this notion. 3969 3970 rcutorture.fwd_progress_div= [KNL] 3971 Specify the fraction of a CPU-stall-warning 3972 period to do tight-loop forward-progress testing. 3973 3974 rcutorture.fwd_progress_holdoff= [KNL] 3975 Number of seconds to wait between successive 3976 forward-progress tests. 3977 3978 rcutorture.fwd_progress_need_resched= [KNL] 3979 Enclose cond_resched() calls within checks for 3980 need_resched() during tight-loop forward-progress 3981 testing. 3982 3983 rcutorture.gp_cond= [KNL] 3984 Use conditional/asynchronous update-side 3985 primitives, if available. 3986 3987 rcutorture.gp_exp= [KNL] 3988 Use expedited update-side primitives, if available. 3989 3990 rcutorture.gp_normal= [KNL] 3991 Use normal (non-expedited) asynchronous 3992 update-side primitives, if available. 3993 3994 rcutorture.gp_sync= [KNL] 3995 Use normal (non-expedited) synchronous 3996 update-side primitives, if available. If all 3997 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3998 rcutorture.gp_normal=, and rcutorture.gp_sync= 3999 are zero, rcutorture acts as if is interpreted 4000 they are all non-zero. 4001 4002 rcutorture.n_barrier_cbs= [KNL] 4003 Set callbacks/threads for rcu_barrier() testing. 4004 4005 rcutorture.nfakewriters= [KNL] 4006 Set number of concurrent RCU writers. These just 4007 stress RCU, they don't participate in the actual 4008 test, hence the "fake". 4009 4010 rcutorture.nreaders= [KNL] 4011 Set number of RCU readers. The value -1 selects 4012 N-1, where N is the number of CPUs. A value 4013 "n" less than -1 selects N-n-2, where N is again 4014 the number of CPUs. For example, -2 selects N 4015 (the number of CPUs), -3 selects N+1, and so on. 4016 4017 rcutorture.object_debug= [KNL] 4018 Enable debug-object double-call_rcu() testing. 4019 4020 rcutorture.onoff_holdoff= [KNL] 4021 Set time (s) after boot for CPU-hotplug testing. 4022 4023 rcutorture.onoff_interval= [KNL] 4024 Set time (jiffies) between CPU-hotplug operations, 4025 or zero to disable CPU-hotplug testing. 4026 4027 rcutorture.shuffle_interval= [KNL] 4028 Set task-shuffle interval (s). Shuffling tasks 4029 allows some CPUs to go into dyntick-idle mode 4030 during the rcutorture test. 4031 4032 rcutorture.shutdown_secs= [KNL] 4033 Set time (s) after boot system shutdown. This 4034 is useful for hands-off automated testing. 4035 4036 rcutorture.stall_cpu= [KNL] 4037 Duration of CPU stall (s) to test RCU CPU stall 4038 warnings, zero to disable. 4039 4040 rcutorture.stall_cpu_holdoff= [KNL] 4041 Time to wait (s) after boot before inducing stall. 4042 4043 rcutorture.stall_cpu_irqsoff= [KNL] 4044 Disable interrupts while stalling if set. 4045 4046 rcutorture.stat_interval= [KNL] 4047 Time (s) between statistics printk()s. 4048 4049 rcutorture.stutter= [KNL] 4050 Time (s) to stutter testing, for example, specifying 4051 five seconds causes the test to run for five seconds, 4052 wait for five seconds, and so on. This tests RCU's 4053 ability to transition abruptly to and from idle. 4054 4055 rcutorture.test_boost= [KNL] 4056 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4057 "Maybe" means test if the RCU implementation 4058 under test support RCU priority boosting. 4059 4060 rcutorture.test_boost_duration= [KNL] 4061 Duration (s) of each individual boost test. 4062 4063 rcutorture.test_boost_interval= [KNL] 4064 Interval (s) between each boost test. 4065 4066 rcutorture.test_no_idle_hz= [KNL] 4067 Test RCU's dyntick-idle handling. See also the 4068 rcutorture.shuffle_interval parameter. 4069 4070 rcutorture.torture_type= [KNL] 4071 Specify the RCU implementation to test. 4072 4073 rcutorture.verbose= [KNL] 4074 Enable additional printk() statements. 4075 4076 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4077 Dump ftrace buffer after reporting RCU CPU 4078 stall warning. 4079 4080 rcupdate.rcu_cpu_stall_suppress= [KNL] 4081 Suppress RCU CPU stall warning messages. 4082 4083 rcupdate.rcu_cpu_stall_timeout= [KNL] 4084 Set timeout for RCU CPU stall warning messages. 4085 4086 rcupdate.rcu_expedited= [KNL] 4087 Use expedited grace-period primitives, for 4088 example, synchronize_rcu_expedited() instead 4089 of synchronize_rcu(). This reduces latency, 4090 but can increase CPU utilization, degrade 4091 real-time latency, and degrade energy efficiency. 4092 No effect on CONFIG_TINY_RCU kernels. 4093 4094 rcupdate.rcu_normal= [KNL] 4095 Use only normal grace-period primitives, 4096 for example, synchronize_rcu() instead of 4097 synchronize_rcu_expedited(). This improves 4098 real-time latency, CPU utilization, and 4099 energy efficiency, but can expose users to 4100 increased grace-period latency. This parameter 4101 overrides rcupdate.rcu_expedited. No effect on 4102 CONFIG_TINY_RCU kernels. 4103 4104 rcupdate.rcu_normal_after_boot= [KNL] 4105 Once boot has completed (that is, after 4106 rcu_end_inkernel_boot() has been invoked), use 4107 only normal grace-period primitives. No effect 4108 on CONFIG_TINY_RCU kernels. 4109 4110 rcupdate.rcu_task_stall_timeout= [KNL] 4111 Set timeout in jiffies for RCU task stall warning 4112 messages. Disable with a value less than or equal 4113 to zero. 4114 4115 rcupdate.rcu_self_test= [KNL] 4116 Run the RCU early boot self tests 4117 4118 rdinit= [KNL] 4119 Format: <full_path> 4120 Run specified binary instead of /init from the ramdisk, 4121 used for early userspace startup. See initrd. 4122 4123 rdrand= [X86] 4124 force - Override the decision by the kernel to hide the 4125 advertisement of RDRAND support (this affects 4126 certain AMD processors because of buggy BIOS 4127 support, specifically around the suspend/resume 4128 path). 4129 4130 rdt= [HW,X86,RDT] 4131 Turn on/off individual RDT features. List is: 4132 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4133 mba. 4134 E.g. to turn on cmt and turn off mba use: 4135 rdt=cmt,!mba 4136 4137 reboot= [KNL] 4138 Format (x86 or x86_64): 4139 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4140 [[,]s[mp]#### \ 4141 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4142 [[,]f[orce] 4143 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4144 (prefix with 'panic_' to set mode for panic 4145 reboot only), 4146 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4147 reboot_force is either force or not specified, 4148 reboot_cpu is s[mp]#### with #### being the processor 4149 to be used for rebooting. 4150 4151 relax_domain_level= 4152 [KNL, SMP] Set scheduler's default relax_domain_level. 4153 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4154 4155 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4156 Format: <base1>,<size1>[,<base2>,<size2>,...] 4157 Reserve I/O ports or memory so the kernel won't use 4158 them. If <base> is less than 0x10000, the region 4159 is assumed to be I/O ports; otherwise it is memory. 4160 4161 reservetop= [X86-32] 4162 Format: nn[KMG] 4163 Reserves a hole at the top of the kernel virtual 4164 address space. 4165 4166 reservelow= [X86] 4167 Format: nn[K] 4168 Set the amount of memory to reserve for BIOS at 4169 the bottom of the address space. 4170 4171 reset_devices [KNL] Force drivers to reset the underlying device 4172 during initialization. 4173 4174 resume= [SWSUSP] 4175 Specify the partition device for software suspend 4176 Format: 4177 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4178 4179 resume_offset= [SWSUSP] 4180 Specify the offset from the beginning of the partition 4181 given by "resume=" at which the swap header is located, 4182 in <PAGE_SIZE> units (needed only for swap files). 4183 See Documentation/power/swsusp-and-swap-files.rst 4184 4185 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4186 read the resume files 4187 4188 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4189 Useful for devices that are detected asynchronously 4190 (e.g. USB and MMC devices). 4191 4192 hibernate= [HIBERNATION] 4193 noresume Don't check if there's a hibernation image 4194 present during boot. 4195 nocompress Don't compress/decompress hibernation images. 4196 no Disable hibernation and resume. 4197 protect_image Turn on image protection during restoration 4198 (that will set all pages holding image data 4199 during restoration read-only). 4200 4201 retain_initrd [RAM] Keep initrd memory after extraction 4202 4203 rfkill.default_state= 4204 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4205 etc. communication is blocked by default. 4206 1 Unblocked. 4207 4208 rfkill.master_switch_mode= 4209 0 The "airplane mode" button does nothing. 4210 1 The "airplane mode" button toggles between everything 4211 blocked and the previous configuration. 4212 2 The "airplane mode" button toggles between everything 4213 blocked and everything unblocked. 4214 4215 rhash_entries= [KNL,NET] 4216 Set number of hash buckets for route cache 4217 4218 ring3mwait=disable 4219 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4220 CPUs. 4221 4222 ro [KNL] Mount root device read-only on boot 4223 4224 rodata= [KNL] 4225 on Mark read-only kernel memory as read-only (default). 4226 off Leave read-only kernel memory writable for debugging. 4227 4228 rockchip.usb_uart 4229 Enable the uart passthrough on the designated usb port 4230 on Rockchip SoCs. When active, the signals of the 4231 debug-uart get routed to the D+ and D- pins of the usb 4232 port and the regular usb controller gets disabled. 4233 4234 root= [KNL] Root filesystem 4235 See name_to_dev_t comment in init/do_mounts.c. 4236 4237 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4238 mount the root filesystem 4239 4240 rootflags= [KNL] Set root filesystem mount option string 4241 4242 rootfstype= [KNL] Set root filesystem type 4243 4244 rootwait [KNL] Wait (indefinitely) for root device to show up. 4245 Useful for devices that are detected asynchronously 4246 (e.g. USB and MMC devices). 4247 4248 rproc_mem=nn[KMG][@address] 4249 [KNL,ARM,CMA] Remoteproc physical memory block. 4250 Memory area to be used by remote processor image, 4251 managed by CMA. 4252 4253 rw [KNL] Mount root device read-write on boot 4254 4255 S [KNL] Run init in single mode 4256 4257 s390_iommu= [HW,S390] 4258 Set s390 IOTLB flushing mode 4259 strict 4260 With strict flushing every unmap operation will result in 4261 an IOTLB flush. Default is lazy flushing before reuse, 4262 which is faster. 4263 4264 sa1100ir [NET] 4265 See drivers/net/irda/sa1100_ir.c. 4266 4267 sbni= [NET] Granch SBNI12 leased line adapter 4268 4269 sched_debug [KNL] Enables verbose scheduler debug messages. 4270 4271 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4272 Allowed values are enable and disable. This feature 4273 incurs a small amount of overhead in the scheduler 4274 but is useful for debugging and performance tuning. 4275 4276 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4277 xtime_lock contention on larger systems, and/or RCU lock 4278 contention on all systems with CONFIG_MAXSMP set. 4279 Format: { "0" | "1" } 4280 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4281 1 -- enable. 4282 Note: increases power consumption, thus should only be 4283 enabled if running jitter sensitive (HPC/RT) workloads. 4284 4285 security= [SECURITY] Choose a legacy "major" security module to 4286 enable at boot. This has been deprecated by the 4287 "lsm=" parameter. 4288 4289 selinux= [SELINUX] Disable or enable SELinux at boot time. 4290 Format: { "0" | "1" } 4291 See security/selinux/Kconfig help text. 4292 0 -- disable. 4293 1 -- enable. 4294 Default value is set via kernel config option. 4295 If enabled at boot time, /selinux/disable can be used 4296 later to disable prior to initial policy load. 4297 4298 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4299 Format: { "0" | "1" } 4300 See security/apparmor/Kconfig help text 4301 0 -- disable. 4302 1 -- enable. 4303 Default value is set via kernel config option. 4304 4305 serialnumber [BUGS=X86-32] 4306 4307 shapers= [NET] 4308 Maximal number of shapers. 4309 4310 simeth= [IA-64] 4311 simscsi= 4312 4313 slram= [HW,MTD] 4314 4315 slab_nomerge [MM] 4316 Disable merging of slabs with similar size. May be 4317 necessary if there is some reason to distinguish 4318 allocs to different slabs, especially in hardened 4319 environments where the risk of heap overflows and 4320 layout control by attackers can usually be 4321 frustrated by disabling merging. This will reduce 4322 most of the exposure of a heap attack to a single 4323 cache (risks via metadata attacks are mostly 4324 unchanged). Debug options disable merging on their 4325 own. 4326 For more information see Documentation/vm/slub.rst. 4327 4328 slab_max_order= [MM, SLAB] 4329 Determines the maximum allowed order for slabs. 4330 A high setting may cause OOMs due to memory 4331 fragmentation. Defaults to 1 for systems with 4332 more than 32MB of RAM, 0 otherwise. 4333 4334 slub_debug[=options[,slabs]] [MM, SLUB] 4335 Enabling slub_debug allows one to determine the 4336 culprit if slab objects become corrupted. Enabling 4337 slub_debug can create guard zones around objects and 4338 may poison objects when not in use. Also tracks the 4339 last alloc / free. For more information see 4340 Documentation/vm/slub.rst. 4341 4342 slub_memcg_sysfs= [MM, SLUB] 4343 Determines whether to enable sysfs directories for 4344 memory cgroup sub-caches. 1 to enable, 0 to disable. 4345 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4346 Enabling this can lead to a very high number of debug 4347 directories and files being created under 4348 /sys/kernel/slub. 4349 4350 slub_max_order= [MM, SLUB] 4351 Determines the maximum allowed order for slabs. 4352 A high setting may cause OOMs due to memory 4353 fragmentation. For more information see 4354 Documentation/vm/slub.rst. 4355 4356 slub_min_objects= [MM, SLUB] 4357 The minimum number of objects per slab. SLUB will 4358 increase the slab order up to slub_max_order to 4359 generate a sufficiently large slab able to contain 4360 the number of objects indicated. The higher the number 4361 of objects the smaller the overhead of tracking slabs 4362 and the less frequently locks need to be acquired. 4363 For more information see Documentation/vm/slub.rst. 4364 4365 slub_min_order= [MM, SLUB] 4366 Determines the minimum page order for slabs. Must be 4367 lower than slub_max_order. 4368 For more information see Documentation/vm/slub.rst. 4369 4370 slub_nomerge [MM, SLUB] 4371 Same with slab_nomerge. This is supported for legacy. 4372 See slab_nomerge for more information. 4373 4374 smart2= [HW] 4375 Format: <io1>[,<io2>[,...,<io8>]] 4376 4377 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4378 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4379 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4380 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4381 smsc-ircc2.ircc_irq= [HW] IRQ line 4382 smsc-ircc2.ircc_dma= [HW] DMA channel 4383 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4384 0: Toshiba Satellite 1800 (GP data pin select) 4385 1: Fast pin select (default) 4386 2: ATC IRMode 4387 4388 smt [KNL,S390] Set the maximum number of threads (logical 4389 CPUs) to use per physical CPU on systems capable of 4390 symmetric multithreading (SMT). Will be capped to the 4391 actual hardware limit. 4392 Format: <integer> 4393 Default: -1 (no limit) 4394 4395 softlockup_panic= 4396 [KNL] Should the soft-lockup detector generate panics. 4397 Format: <integer> 4398 4399 A nonzero value instructs the soft-lockup detector 4400 to panic the machine when a soft-lockup occurs. This 4401 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4402 which is the respective build-time switch to that 4403 functionality. 4404 4405 softlockup_all_cpu_backtrace= 4406 [KNL] Should the soft-lockup detector generate 4407 backtraces on all cpus. 4408 Format: <integer> 4409 4410 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4411 See Documentation/admin-guide/laptops/sonypi.rst 4412 4413 spectre_v2= [X86] Control mitigation of Spectre variant 2 4414 (indirect branch speculation) vulnerability. 4415 The default operation protects the kernel from 4416 user space attacks. 4417 4418 on - unconditionally enable, implies 4419 spectre_v2_user=on 4420 off - unconditionally disable, implies 4421 spectre_v2_user=off 4422 auto - kernel detects whether your CPU model is 4423 vulnerable 4424 4425 Selecting 'on' will, and 'auto' may, choose a 4426 mitigation method at run time according to the 4427 CPU, the available microcode, the setting of the 4428 CONFIG_RETPOLINE configuration option, and the 4429 compiler with which the kernel was built. 4430 4431 Selecting 'on' will also enable the mitigation 4432 against user space to user space task attacks. 4433 4434 Selecting 'off' will disable both the kernel and 4435 the user space protections. 4436 4437 Specific mitigations can also be selected manually: 4438 4439 retpoline - replace indirect branches 4440 retpoline,generic - google's original retpoline 4441 retpoline,amd - AMD-specific minimal thunk 4442 4443 Not specifying this option is equivalent to 4444 spectre_v2=auto. 4445 4446 spectre_v2_user= 4447 [X86] Control mitigation of Spectre variant 2 4448 (indirect branch speculation) vulnerability between 4449 user space tasks 4450 4451 on - Unconditionally enable mitigations. Is 4452 enforced by spectre_v2=on 4453 4454 off - Unconditionally disable mitigations. Is 4455 enforced by spectre_v2=off 4456 4457 prctl - Indirect branch speculation is enabled, 4458 but mitigation can be enabled via prctl 4459 per thread. The mitigation control state 4460 is inherited on fork. 4461 4462 prctl,ibpb 4463 - Like "prctl" above, but only STIBP is 4464 controlled per thread. IBPB is issued 4465 always when switching between different user 4466 space processes. 4467 4468 seccomp 4469 - Same as "prctl" above, but all seccomp 4470 threads will enable the mitigation unless 4471 they explicitly opt out. 4472 4473 seccomp,ibpb 4474 - Like "seccomp" above, but only STIBP is 4475 controlled per thread. IBPB is issued 4476 always when switching between different 4477 user space processes. 4478 4479 auto - Kernel selects the mitigation depending on 4480 the available CPU features and vulnerability. 4481 4482 Default mitigation: 4483 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4484 4485 Not specifying this option is equivalent to 4486 spectre_v2_user=auto. 4487 4488 spec_store_bypass_disable= 4489 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4490 (Speculative Store Bypass vulnerability) 4491 4492 Certain CPUs are vulnerable to an exploit against a 4493 a common industry wide performance optimization known 4494 as "Speculative Store Bypass" in which recent stores 4495 to the same memory location may not be observed by 4496 later loads during speculative execution. The idea 4497 is that such stores are unlikely and that they can 4498 be detected prior to instruction retirement at the 4499 end of a particular speculation execution window. 4500 4501 In vulnerable processors, the speculatively forwarded 4502 store can be used in a cache side channel attack, for 4503 example to read memory to which the attacker does not 4504 directly have access (e.g. inside sandboxed code). 4505 4506 This parameter controls whether the Speculative Store 4507 Bypass optimization is used. 4508 4509 On x86 the options are: 4510 4511 on - Unconditionally disable Speculative Store Bypass 4512 off - Unconditionally enable Speculative Store Bypass 4513 auto - Kernel detects whether the CPU model contains an 4514 implementation of Speculative Store Bypass and 4515 picks the most appropriate mitigation. If the 4516 CPU is not vulnerable, "off" is selected. If the 4517 CPU is vulnerable the default mitigation is 4518 architecture and Kconfig dependent. See below. 4519 prctl - Control Speculative Store Bypass per thread 4520 via prctl. Speculative Store Bypass is enabled 4521 for a process by default. The state of the control 4522 is inherited on fork. 4523 seccomp - Same as "prctl" above, but all seccomp threads 4524 will disable SSB unless they explicitly opt out. 4525 4526 Default mitigations: 4527 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4528 4529 On powerpc the options are: 4530 4531 on,auto - On Power8 and Power9 insert a store-forwarding 4532 barrier on kernel entry and exit. On Power7 4533 perform a software flush on kernel entry and 4534 exit. 4535 off - No action. 4536 4537 Not specifying this option is equivalent to 4538 spec_store_bypass_disable=auto. 4539 4540 spia_io_base= [HW,MTD] 4541 spia_fio_base= 4542 spia_pedr= 4543 spia_peddr= 4544 4545 srcutree.counter_wrap_check [KNL] 4546 Specifies how frequently to check for 4547 grace-period sequence counter wrap for the 4548 srcu_data structure's ->srcu_gp_seq_needed field. 4549 The greater the number of bits set in this kernel 4550 parameter, the less frequently counter wrap will 4551 be checked for. Note that the bottom two bits 4552 are ignored. 4553 4554 srcutree.exp_holdoff [KNL] 4555 Specifies how many nanoseconds must elapse 4556 since the end of the last SRCU grace period for 4557 a given srcu_struct until the next normal SRCU 4558 grace period will be considered for automatic 4559 expediting. Set to zero to disable automatic 4560 expediting. 4561 4562 ssbd= [ARM64,HW] 4563 Speculative Store Bypass Disable control 4564 4565 On CPUs that are vulnerable to the Speculative 4566 Store Bypass vulnerability and offer a 4567 firmware based mitigation, this parameter 4568 indicates how the mitigation should be used: 4569 4570 force-on: Unconditionally enable mitigation for 4571 for both kernel and userspace 4572 force-off: Unconditionally disable mitigation for 4573 for both kernel and userspace 4574 kernel: Always enable mitigation in the 4575 kernel, and offer a prctl interface 4576 to allow userspace to register its 4577 interest in being mitigated too. 4578 4579 stack_guard_gap= [MM] 4580 override the default stack gap protection. The value 4581 is in page units and it defines how many pages prior 4582 to (for stacks growing down) resp. after (for stacks 4583 growing up) the main stack are reserved for no other 4584 mapping. Default value is 256 pages. 4585 4586 stacktrace [FTRACE] 4587 Enabled the stack tracer on boot up. 4588 4589 stacktrace_filter=[function-list] 4590 [FTRACE] Limit the functions that the stack tracer 4591 will trace at boot up. function-list is a comma separated 4592 list of functions. This list can be changed at run 4593 time by the stack_trace_filter file in the debugfs 4594 tracing directory. Note, this enables stack tracing 4595 and the stacktrace above is not needed. 4596 4597 sti= [PARISC,HW] 4598 Format: <num> 4599 Set the STI (builtin display/keyboard on the HP-PARISC 4600 machines) console (graphic card) which should be used 4601 as the initial boot-console. 4602 See also comment in drivers/video/console/sticore.c. 4603 4604 sti_font= [HW] 4605 See comment in drivers/video/console/sticore.c. 4606 4607 stifb= [HW] 4608 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4609 4610 sunrpc.min_resvport= 4611 sunrpc.max_resvport= 4612 [NFS,SUNRPC] 4613 SunRPC servers often require that client requests 4614 originate from a privileged port (i.e. a port in the 4615 range 0 < portnr < 1024). 4616 An administrator who wishes to reserve some of these 4617 ports for other uses may adjust the range that the 4618 kernel's sunrpc client considers to be privileged 4619 using these two parameters to set the minimum and 4620 maximum port values. 4621 4622 sunrpc.svc_rpc_per_connection_limit= 4623 [NFS,SUNRPC] 4624 Limit the number of requests that the server will 4625 process in parallel from a single connection. 4626 The default value is 0 (no limit). 4627 4628 sunrpc.pool_mode= 4629 [NFS] 4630 Control how the NFS server code allocates CPUs to 4631 service thread pools. Depending on how many NICs 4632 you have and where their interrupts are bound, this 4633 option will affect which CPUs will do NFS serving. 4634 Note: this parameter cannot be changed while the 4635 NFS server is running. 4636 4637 auto the server chooses an appropriate mode 4638 automatically using heuristics 4639 global a single global pool contains all CPUs 4640 percpu one pool for each CPU 4641 pernode one pool for each NUMA node (equivalent 4642 to global on non-NUMA machines) 4643 4644 sunrpc.tcp_slot_table_entries= 4645 sunrpc.udp_slot_table_entries= 4646 [NFS,SUNRPC] 4647 Sets the upper limit on the number of simultaneous 4648 RPC calls that can be sent from the client to a 4649 server. Increasing these values may allow you to 4650 improve throughput, but will also increase the 4651 amount of memory reserved for use by the client. 4652 4653 suspend.pm_test_delay= 4654 [SUSPEND] 4655 Sets the number of seconds to remain in a suspend test 4656 mode before resuming the system (see 4657 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4658 is set. Default value is 5. 4659 4660 svm= [PPC] 4661 Format: { on | off | y | n | 1 | 0 } 4662 This parameter controls use of the Protected 4663 Execution Facility on pSeries. 4664 4665 swapaccount=[0|1] 4666 [KNL] Enable accounting of swap in memory resource 4667 controller if no parameter or 1 is given or disable 4668 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4669 4670 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4671 Format: { <int> | force | noforce } 4672 <int> -- Number of I/O TLB slabs 4673 force -- force using of bounce buffers even if they 4674 wouldn't be automatically used by the kernel 4675 noforce -- Never use bounce buffers (for debugging) 4676 4677 switches= [HW,M68k] 4678 4679 sysfs.deprecated=0|1 [KNL] 4680 Enable/disable old style sysfs layout for old udev 4681 on older distributions. When this option is enabled 4682 very new udev will not work anymore. When this option 4683 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4684 in older udev will not work anymore. 4685 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4686 the kernel configuration. 4687 4688 sysrq_always_enabled 4689 [KNL] 4690 Ignore sysrq setting - this boot parameter will 4691 neutralize any effect of /proc/sys/kernel/sysrq. 4692 Useful for debugging. 4693 4694 tcpmhash_entries= [KNL,NET] 4695 Set the number of tcp_metrics_hash slots. 4696 Default value is 8192 or 16384 depending on total 4697 ram pages. This is used to specify the TCP metrics 4698 cache size. See Documentation/networking/ip-sysctl.txt 4699 "tcp_no_metrics_save" section for more details. 4700 4701 tdfx= [HW,DRM] 4702 4703 test_suspend= [SUSPEND][,N] 4704 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4705 standby suspend) or "freeze" (for suspend type freeze) 4706 as the system sleep state during system startup with 4707 the optional capability to repeat N number of times. 4708 The system is woken from this state using a 4709 wakeup-capable RTC alarm. 4710 4711 thash_entries= [KNL,NET] 4712 Set number of hash buckets for TCP connection 4713 4714 thermal.act= [HW,ACPI] 4715 -1: disable all active trip points in all thermal zones 4716 <degrees C>: override all lowest active trip points 4717 4718 thermal.crt= [HW,ACPI] 4719 -1: disable all critical trip points in all thermal zones 4720 <degrees C>: override all critical trip points 4721 4722 thermal.nocrt= [HW,ACPI] 4723 Set to disable actions on ACPI thermal zone 4724 critical and hot trip points. 4725 4726 thermal.off= [HW,ACPI] 4727 1: disable ACPI thermal control 4728 4729 thermal.psv= [HW,ACPI] 4730 -1: disable all passive trip points 4731 <degrees C>: override all passive trip points to this 4732 value 4733 4734 thermal.tzp= [HW,ACPI] 4735 Specify global default ACPI thermal zone polling rate 4736 <deci-seconds>: poll all this frequency 4737 0: no polling (default) 4738 4739 threadirqs [KNL] 4740 Force threading of all interrupt handlers except those 4741 marked explicitly IRQF_NO_THREAD. 4742 4743 topology= [S390] 4744 Format: {off | on} 4745 Specify if the kernel should make use of the cpu 4746 topology information if the hardware supports this. 4747 The scheduler will make use of this information and 4748 e.g. base its process migration decisions on it. 4749 Default is on. 4750 4751 topology_updates= [KNL, PPC, NUMA] 4752 Format: {off} 4753 Specify if the kernel should ignore (off) 4754 topology updates sent by the hypervisor to this 4755 LPAR. 4756 4757 tp720= [HW,PS2] 4758 4759 tpm_suspend_pcr=[HW,TPM] 4760 Format: integer pcr id 4761 Specify that at suspend time, the tpm driver 4762 should extend the specified pcr with zeros, 4763 as a workaround for some chips which fail to 4764 flush the last written pcr on TPM_SaveState. 4765 This will guarantee that all the other pcrs 4766 are saved. 4767 4768 trace_buf_size=nn[KMG] 4769 [FTRACE] will set tracing buffer size on each cpu. 4770 4771 trace_event=[event-list] 4772 [FTRACE] Set and start specified trace events in order 4773 to facilitate early boot debugging. The event-list is a 4774 comma separated list of trace events to enable. See 4775 also Documentation/trace/events.rst 4776 4777 trace_options=[option-list] 4778 [FTRACE] Enable or disable tracer options at boot. 4779 The option-list is a comma delimited list of options 4780 that can be enabled or disabled just as if you were 4781 to echo the option name into 4782 4783 /sys/kernel/debug/tracing/trace_options 4784 4785 For example, to enable stacktrace option (to dump the 4786 stack trace of each event), add to the command line: 4787 4788 trace_options=stacktrace 4789 4790 See also Documentation/trace/ftrace.rst "trace options" 4791 section. 4792 4793 tp_printk[FTRACE] 4794 Have the tracepoints sent to printk as well as the 4795 tracing ring buffer. This is useful for early boot up 4796 where the system hangs or reboots and does not give the 4797 option for reading the tracing buffer or performing a 4798 ftrace_dump_on_oops. 4799 4800 To turn off having tracepoints sent to printk, 4801 echo 0 > /proc/sys/kernel/tracepoint_printk 4802 Note, echoing 1 into this file without the 4803 tracepoint_printk kernel cmdline option has no effect. 4804 4805 ** CAUTION ** 4806 4807 Having tracepoints sent to printk() and activating high 4808 frequency tracepoints such as irq or sched, can cause 4809 the system to live lock. 4810 4811 traceoff_on_warning 4812 [FTRACE] enable this option to disable tracing when a 4813 warning is hit. This turns off "tracing_on". Tracing can 4814 be enabled again by echoing '1' into the "tracing_on" 4815 file located in /sys/kernel/debug/tracing/ 4816 4817 This option is useful, as it disables the trace before 4818 the WARNING dump is called, which prevents the trace to 4819 be filled with content caused by the warning output. 4820 4821 This option can also be set at run time via the sysctl 4822 option: kernel/traceoff_on_warning 4823 4824 transparent_hugepage= 4825 [KNL] 4826 Format: [always|madvise|never] 4827 Can be used to control the default behavior of the system 4828 with respect to transparent hugepages. 4829 See Documentation/admin-guide/mm/transhuge.rst 4830 for more details. 4831 4832 tsc= Disable clocksource stability checks for TSC. 4833 Format: <string> 4834 [x86] reliable: mark tsc clocksource as reliable, this 4835 disables clocksource verification at runtime, as well 4836 as the stability checks done at bootup. Used to enable 4837 high-resolution timer mode on older hardware, and in 4838 virtualized environment. 4839 [x86] noirqtime: Do not use TSC to do irq accounting. 4840 Used to run time disable IRQ_TIME_ACCOUNTING on any 4841 platforms where RDTSC is slow and this accounting 4842 can add overhead. 4843 [x86] unstable: mark the TSC clocksource as unstable, this 4844 marks the TSC unconditionally unstable at bootup and 4845 avoids any further wobbles once the TSC watchdog notices. 4846 [x86] nowatchdog: disable clocksource watchdog. Used 4847 in situations with strict latency requirements (where 4848 interruptions from clocksource watchdog are not 4849 acceptable). 4850 4851 turbografx.map[2|3]= [HW,JOY] 4852 TurboGraFX parallel port interface 4853 Format: 4854 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4855 See also Documentation/input/devices/joystick-parport.rst 4856 4857 udbg-immortal [PPC] When debugging early kernel crashes that 4858 happen after console_init() and before a proper 4859 console driver takes over, this boot options might 4860 help "seeing" what's going on. 4861 4862 uhash_entries= [KNL,NET] 4863 Set number of hash buckets for UDP/UDP-Lite connections 4864 4865 uhci-hcd.ignore_oc= 4866 [USB] Ignore overcurrent events (default N). 4867 Some badly-designed motherboards generate lots of 4868 bogus events, for ports that aren't wired to 4869 anything. Set this parameter to avoid log spamming. 4870 Note that genuine overcurrent events won't be 4871 reported either. 4872 4873 unknown_nmi_panic 4874 [X86] Cause panic on unknown NMI. 4875 4876 usbcore.authorized_default= 4877 [USB] Default USB device authorization: 4878 (default -1 = authorized except for wireless USB, 4879 0 = not authorized, 1 = authorized, 2 = authorized 4880 if device connected to internal port) 4881 4882 usbcore.autosuspend= 4883 [USB] The autosuspend time delay (in seconds) used 4884 for newly-detected USB devices (default 2). This 4885 is the time required before an idle device will be 4886 autosuspended. Devices for which the delay is set 4887 to a negative value won't be autosuspended at all. 4888 4889 usbcore.usbfs_snoop= 4890 [USB] Set to log all usbfs traffic (default 0 = off). 4891 4892 usbcore.usbfs_snoop_max= 4893 [USB] Maximum number of bytes to snoop in each URB 4894 (default = 65536). 4895 4896 usbcore.blinkenlights= 4897 [USB] Set to cycle leds on hubs (default 0 = off). 4898 4899 usbcore.old_scheme_first= 4900 [USB] Start with the old device initialization 4901 scheme, applies only to low and full-speed devices 4902 (default 0 = off). 4903 4904 usbcore.usbfs_memory_mb= 4905 [USB] Memory limit (in MB) for buffers allocated by 4906 usbfs (default = 16, 0 = max = 2047). 4907 4908 usbcore.use_both_schemes= 4909 [USB] Try the other device initialization scheme 4910 if the first one fails (default 1 = enabled). 4911 4912 usbcore.initial_descriptor_timeout= 4913 [USB] Specifies timeout for the initial 64-byte 4914 USB_REQ_GET_DESCRIPTOR request in milliseconds 4915 (default 5000 = 5.0 seconds). 4916 4917 usbcore.nousb [USB] Disable the USB subsystem 4918 4919 usbcore.quirks= 4920 [USB] A list of quirk entries to augment the built-in 4921 usb core quirk list. List entries are separated by 4922 commas. Each entry has the form 4923 VendorID:ProductID:Flags. The IDs are 4-digit hex 4924 numbers and Flags is a set of letters. Each letter 4925 will change the built-in quirk; setting it if it is 4926 clear and clearing it if it is set. The letters have 4927 the following meanings: 4928 a = USB_QUIRK_STRING_FETCH_255 (string 4929 descriptors must not be fetched using 4930 a 255-byte read); 4931 b = USB_QUIRK_RESET_RESUME (device can't resume 4932 correctly so reset it instead); 4933 c = USB_QUIRK_NO_SET_INTF (device can't handle 4934 Set-Interface requests); 4935 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4936 handle its Configuration or Interface 4937 strings); 4938 e = USB_QUIRK_RESET (device can't be reset 4939 (e.g morph devices), don't use reset); 4940 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4941 more interface descriptions than the 4942 bNumInterfaces count, and can't handle 4943 talking to these interfaces); 4944 g = USB_QUIRK_DELAY_INIT (device needs a pause 4945 during initialization, after we read 4946 the device descriptor); 4947 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4948 high speed and super speed interrupt 4949 endpoints, the USB 2.0 and USB 3.0 spec 4950 require the interval in microframes (1 4951 microframe = 125 microseconds) to be 4952 calculated as interval = 2 ^ 4953 (bInterval-1). 4954 Devices with this quirk report their 4955 bInterval as the result of this 4956 calculation instead of the exponent 4957 variable used in the calculation); 4958 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4959 handle device_qualifier descriptor 4960 requests); 4961 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4962 generates spurious wakeup, ignore 4963 remote wakeup capability); 4964 k = USB_QUIRK_NO_LPM (device can't handle Link 4965 Power Management); 4966 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4967 (Device reports its bInterval as linear 4968 frames instead of the USB 2.0 4969 calculation); 4970 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4971 to be disconnected before suspend to 4972 prevent spurious wakeup); 4973 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4974 pause after every control message); 4975 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4976 delay after resetting its port); 4977 Example: quirks=0781:5580:bk,0a5c:5834:gij 4978 4979 usbhid.mousepoll= 4980 [USBHID] The interval which mice are to be polled at. 4981 4982 usbhid.jspoll= 4983 [USBHID] The interval which joysticks are to be polled at. 4984 4985 usbhid.kbpoll= 4986 [USBHID] The interval which keyboards are to be polled at. 4987 4988 usb-storage.delay_use= 4989 [UMS] The delay in seconds before a new device is 4990 scanned for Logical Units (default 1). 4991 4992 usb-storage.quirks= 4993 [UMS] A list of quirks entries to supplement or 4994 override the built-in unusual_devs list. List 4995 entries are separated by commas. Each entry has 4996 the form VID:PID:Flags where VID and PID are Vendor 4997 and Product ID values (4-digit hex numbers) and 4998 Flags is a set of characters, each corresponding 4999 to a common usb-storage quirk flag as follows: 5000 a = SANE_SENSE (collect more than 18 bytes 5001 of sense data); 5002 b = BAD_SENSE (don't collect more than 18 5003 bytes of sense data); 5004 c = FIX_CAPACITY (decrease the reported 5005 device capacity by one sector); 5006 d = NO_READ_DISC_INFO (don't use 5007 READ_DISC_INFO command); 5008 e = NO_READ_CAPACITY_16 (don't use 5009 READ_CAPACITY_16 command); 5010 f = NO_REPORT_OPCODES (don't use report opcodes 5011 command, uas only); 5012 g = MAX_SECTORS_240 (don't transfer more than 5013 240 sectors at a time, uas only); 5014 h = CAPACITY_HEURISTICS (decrease the 5015 reported device capacity by one 5016 sector if the number is odd); 5017 i = IGNORE_DEVICE (don't bind to this 5018 device); 5019 j = NO_REPORT_LUNS (don't use report luns 5020 command, uas only); 5021 l = NOT_LOCKABLE (don't try to lock and 5022 unlock ejectable media); 5023 m = MAX_SECTORS_64 (don't transfer more 5024 than 64 sectors = 32 KB at a time); 5025 n = INITIAL_READ10 (force a retry of the 5026 initial READ(10) command); 5027 o = CAPACITY_OK (accept the capacity 5028 reported by the device); 5029 p = WRITE_CACHE (the device cache is ON 5030 by default); 5031 r = IGNORE_RESIDUE (the device reports 5032 bogus residue values); 5033 s = SINGLE_LUN (the device has only one 5034 Logical Unit); 5035 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5036 commands, uas only); 5037 u = IGNORE_UAS (don't bind to the uas driver); 5038 w = NO_WP_DETECT (don't test whether the 5039 medium is write-protected). 5040 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5041 even if the device claims no cache) 5042 Example: quirks=0419:aaf5:rl,0421:0433:rc 5043 5044 user_debug= [KNL,ARM] 5045 Format: <int> 5046 See arch/arm/Kconfig.debug help text. 5047 1 - undefined instruction events 5048 2 - system calls 5049 4 - invalid data aborts 5050 8 - SIGSEGV faults 5051 16 - SIGBUS faults 5052 Example: user_debug=31 5053 5054 userpte= 5055 [X86] Flags controlling user PTE allocations. 5056 5057 nohigh = do not allocate PTE pages in 5058 HIGHMEM regardless of setting 5059 of CONFIG_HIGHPTE. 5060 5061 vdso= [X86,SH] 5062 On X86_32, this is an alias for vdso32=. Otherwise: 5063 5064 vdso=1: enable VDSO (the default) 5065 vdso=0: disable VDSO mapping 5066 5067 vdso32= [X86] Control the 32-bit vDSO 5068 vdso32=1: enable 32-bit VDSO 5069 vdso32=0 or vdso32=2: disable 32-bit VDSO 5070 5071 See the help text for CONFIG_COMPAT_VDSO for more 5072 details. If CONFIG_COMPAT_VDSO is set, the default is 5073 vdso32=0; otherwise, the default is vdso32=1. 5074 5075 For compatibility with older kernels, vdso32=2 is an 5076 alias for vdso32=0. 5077 5078 Try vdso32=0 if you encounter an error that says: 5079 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5080 5081 vector= [IA-64,SMP] 5082 vector=percpu: enable percpu vector domain 5083 5084 video= [FB] Frame buffer configuration 5085 See Documentation/fb/modedb.rst. 5086 5087 video.brightness_switch_enabled= [0,1] 5088 If set to 1, on receiving an ACPI notify event 5089 generated by hotkey, video driver will adjust brightness 5090 level and then send out the event to user space through 5091 the allocated input device; If set to 0, video driver 5092 will only send out the event without touching backlight 5093 brightness level. 5094 default: 1 5095 5096 virtio_mmio.device= 5097 [VMMIO] Memory mapped virtio (platform) device. 5098 5099 <size>@<baseaddr>:<irq>[:<id>] 5100 where: 5101 <size> := size (can use standard suffixes 5102 like K, M and G) 5103 <baseaddr> := physical base address 5104 <irq> := interrupt number (as passed to 5105 request_irq()) 5106 <id> := (optional) platform device id 5107 example: 5108 virtio_mmio.device=1K@0x100b0000:48:7 5109 5110 Can be used multiple times for multiple devices. 5111 5112 vga= [BOOT,X86-32] Select a particular video mode 5113 See Documentation/x86/boot.rst and 5114 Documentation/admin-guide/svga.rst. 5115 Use vga=ask for menu. 5116 This is actually a boot loader parameter; the value is 5117 passed to the kernel using a special protocol. 5118 5119 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5120 May slow down system boot speed, especially when 5121 enabled on systems with a large amount of memory. 5122 All options are enabled by default, and this 5123 interface is meant to allow for selectively 5124 enabling or disabling specific virtual memory 5125 debugging features. 5126 5127 Available options are: 5128 P Enable page structure init time poisoning 5129 - Disable all of the above options 5130 5131 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5132 size of <nn>. This can be used to increase the 5133 minimum size (128MB on x86). It can also be used to 5134 decrease the size and leave more room for directly 5135 mapped kernel RAM. 5136 5137 vmcp_cma=nn[MG] [KNL,S390] 5138 Sets the memory size reserved for contiguous memory 5139 allocations for the vmcp device driver. 5140 5141 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5142 Format: <command> 5143 5144 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5145 Format: <command> 5146 5147 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5148 Format: <command> 5149 5150 vsyscall= [X86-64] 5151 Controls the behavior of vsyscalls (i.e. calls to 5152 fixed addresses of 0xffffffffff600x00 from legacy 5153 code). Most statically-linked binaries and older 5154 versions of glibc use these calls. Because these 5155 functions are at fixed addresses, they make nice 5156 targets for exploits that can control RIP. 5157 5158 emulate [default] Vsyscalls turn into traps and are 5159 emulated reasonably safely. The vsyscall 5160 page is readable. 5161 5162 xonly Vsyscalls turn into traps and are 5163 emulated reasonably safely. The vsyscall 5164 page is not readable. 5165 5166 none Vsyscalls don't work at all. This makes 5167 them quite hard to use for exploits but 5168 might break your system. 5169 5170 vt.color= [VT] Default text color. 5171 Format: 0xYX, X = foreground, Y = background. 5172 Default: 0x07 = light gray on black. 5173 5174 vt.cur_default= [VT] Default cursor shape. 5175 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5176 the parameters of the <Esc>[?A;B;Cc escape sequence; 5177 see VGA-softcursor.txt. Default: 2 = underline. 5178 5179 vt.default_blu= [VT] 5180 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5181 Change the default blue palette of the console. 5182 This is a 16-member array composed of values 5183 ranging from 0-255. 5184 5185 vt.default_grn= [VT] 5186 Format: <green0>,<green1>,<green2>,...,<green15> 5187 Change the default green palette of the console. 5188 This is a 16-member array composed of values 5189 ranging from 0-255. 5190 5191 vt.default_red= [VT] 5192 Format: <red0>,<red1>,<red2>,...,<red15> 5193 Change the default red palette of the console. 5194 This is a 16-member array composed of values 5195 ranging from 0-255. 5196 5197 vt.default_utf8= 5198 [VT] 5199 Format=<0|1> 5200 Set system-wide default UTF-8 mode for all tty's. 5201 Default is 1, i.e. UTF-8 mode is enabled for all 5202 newly opened terminals. 5203 5204 vt.global_cursor_default= 5205 [VT] 5206 Format=<-1|0|1> 5207 Set system-wide default for whether a cursor 5208 is shown on new VTs. Default is -1, 5209 i.e. cursors will be created by default unless 5210 overridden by individual drivers. 0 will hide 5211 cursors, 1 will display them. 5212 5213 vt.italic= [VT] Default color for italic text; 0-15. 5214 Default: 2 = green. 5215 5216 vt.underline= [VT] Default color for underlined text; 0-15. 5217 Default: 3 = cyan. 5218 5219 watchdog timers [HW,WDT] For information on watchdog timers, 5220 see Documentation/watchdog/watchdog-parameters.rst 5221 or other driver-specific files in the 5222 Documentation/watchdog/ directory. 5223 5224 watchdog_thresh= 5225 [KNL] 5226 Set the hard lockup detector stall duration 5227 threshold in seconds. The soft lockup detector 5228 threshold is set to twice the value. A value of 0 5229 disables both lockup detectors. Default is 10 5230 seconds. 5231 5232 workqueue.watchdog_thresh= 5233 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5234 warn stall conditions and dump internal state to 5235 help debugging. 0 disables workqueue stall 5236 detection; otherwise, it's the stall threshold 5237 duration in seconds. The default value is 30 and 5238 it can be updated at runtime by writing to the 5239 corresponding sysfs file. 5240 5241 workqueue.disable_numa 5242 By default, all work items queued to unbound 5243 workqueues are affine to the NUMA nodes they're 5244 issued on, which results in better behavior in 5245 general. If NUMA affinity needs to be disabled for 5246 whatever reason, this option can be used. Note 5247 that this also can be controlled per-workqueue for 5248 workqueues visible under /sys/bus/workqueue/. 5249 5250 workqueue.power_efficient 5251 Per-cpu workqueues are generally preferred because 5252 they show better performance thanks to cache 5253 locality; unfortunately, per-cpu workqueues tend to 5254 be more power hungry than unbound workqueues. 5255 5256 Enabling this makes the per-cpu workqueues which 5257 were observed to contribute significantly to power 5258 consumption unbound, leading to measurably lower 5259 power usage at the cost of small performance 5260 overhead. 5261 5262 The default value of this parameter is determined by 5263 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5264 5265 workqueue.debug_force_rr_cpu 5266 Workqueue used to implicitly guarantee that work 5267 items queued without explicit CPU specified are put 5268 on the local CPU. This guarantee is no longer true 5269 and while local CPU is still preferred work items 5270 may be put on foreign CPUs. This debug option 5271 forces round-robin CPU selection to flush out 5272 usages which depend on the now broken guarantee. 5273 When enabled, memory and cache locality will be 5274 impacted. 5275 5276 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5277 default x2apic cluster mode on platforms 5278 supporting x2apic. 5279 5280 x86_intel_mid_timer= [X86-32,APBT] 5281 Choose timer option for x86 Intel MID platform. 5282 Two valid options are apbt timer only and lapic timer 5283 plus one apbt timer for broadcast timer. 5284 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5285 5286 xen_512gb_limit [KNL,X86-64,XEN] 5287 Restricts the kernel running paravirtualized under Xen 5288 to use only up to 512 GB of RAM. The reason to do so is 5289 crash analysis tools and Xen tools for doing domain 5290 save/restore/migration must be enabled to handle larger 5291 domains. 5292 5293 xen_emul_unplug= [HW,X86,XEN] 5294 Unplug Xen emulated devices 5295 Format: [unplug0,][unplug1] 5296 ide-disks -- unplug primary master IDE devices 5297 aux-ide-disks -- unplug non-primary-master IDE devices 5298 nics -- unplug network devices 5299 all -- unplug all emulated devices (NICs and IDE disks) 5300 unnecessary -- unplugging emulated devices is 5301 unnecessary even if the host did not respond to 5302 the unplug protocol 5303 never -- do not unplug even if version check succeeds 5304 5305 xen_nopvspin [X86,XEN] 5306 Disables the ticketlock slowpath using Xen PV 5307 optimizations. 5308 5309 xen_nopv [X86] 5310 Disables the PV optimizations forcing the HVM guest to 5311 run as generic HVM guest with no PV drivers. 5312 This option is obsoleted by the "nopv" option, which 5313 has equivalent effect for XEN platform. 5314 5315 xen_scrub_pages= [XEN] 5316 Boolean option to control scrubbing pages before giving them back 5317 to Xen, for use by other domains. Can be also changed at runtime 5318 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5319 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5320 5321 xen_timer_slop= [X86-64,XEN] 5322 Set the timer slop (in nanoseconds) for the virtual Xen 5323 timers (default is 100000). This adjusts the minimum 5324 delta of virtualized Xen timers, where lower values 5325 improve timer resolution at the expense of processing 5326 more timer interrupts. 5327 5328 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5329 Disables the PV optimizations forcing the guest to run 5330 as generic guest with no PV drivers. Currently support 5331 XEN HVM, KVM, HYPER_V and VMWARE guest. 5332 5333 xirc2ps_cs= [NET,PCMCIA] 5334 Format: 5335 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5336 5337 xive= [PPC] 5338 By default on POWER9 and above, the kernel will 5339 natively use the XIVE interrupt controller. This option 5340 allows the fallback firmware mode to be used: 5341 5342 off Fallback to firmware control of XIVE interrupt 5343 controller on both pseries and powernv 5344 platforms. Only useful on POWER9 and above. 5345 5346 xhci-hcd.quirks [USB,KNL] 5347 A hex value specifying bitmask with supplemental xhci 5348 host controller quirks. Meaning of each bit can be 5349 consulted in header drivers/usb/host/xhci.h. 5350 5351 xmon [PPC] 5352 Format: { early | on | rw | ro | off } 5353 Controls if xmon debugger is enabled. Default is off. 5354 Passing only "xmon" is equivalent to "xmon=early". 5355 early Call xmon as early as possible on boot; xmon 5356 debugger is called from setup_arch(). 5357 on xmon debugger hooks will be installed so xmon 5358 is only called on a kernel crash. Default mode, 5359 i.e. either "ro" or "rw" mode, is controlled 5360 with CONFIG_XMON_DEFAULT_RO_MODE. 5361 rw xmon debugger hooks will be installed so xmon 5362 is called only on a kernel crash, mode is write, 5363 meaning SPR registers, memory and, other data 5364 can be written using xmon commands. 5365 ro same as "rw" option above but SPR registers, 5366 memory, and other data can't be written using 5367 xmon commands. 5368 off xmon is disabled. 5369