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.txt, 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/acpi/debug.txt 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.txt 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.txt 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/CommonIO 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/CommonIO 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/kdump/kdump.txt 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/kdump/kdump.txt 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 809 parameter enables the feature at boot time. In 810 default, it is disabled. We can avoid allocating huge 811 chunk of memory for debug pagealloc if we don't enable 812 it at boot time and the system will work mostly same 813 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 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_cpu_apicid= [X86,APIC,SMP] 866 Format: <int> 867 The number of initial APIC ID for the 868 corresponding CPU to be disabled at boot, 869 mostly used for the kdump 2nd kernel to 870 disable BSP to wake up multiple CPUs without 871 causing system reset or hang due to sending 872 INIT from AP to BSP. 873 874 perf_v4_pmi= [X86,INTEL] 875 Format: <bool> 876 Disable Intel PMU counter freezing feature. 877 The feature only exists starting from 878 Arch Perfmon v4 (Skylake and newer). 879 880 disable_ddw [PPC/PSERIES] 881 Disable Dynamic DMA Window support. Use this if 882 to workaround buggy firmware. 883 884 disable_ipv6= [IPV6] 885 See Documentation/networking/ipv6.txt. 886 887 disable_mtrr_cleanup [X86] 888 The kernel tries to adjust MTRR layout from continuous 889 to discrete, to make X server driver able to add WB 890 entry later. This parameter disables that. 891 892 disable_mtrr_trim [X86, Intel and AMD only] 893 By default the kernel will trim any uncacheable 894 memory out of your available memory pool based on 895 MTRR settings. This parameter disables that behavior, 896 possibly causing your machine to run very slowly. 897 898 disable_timer_pin_1 [X86] 899 Disable PIN 1 of APIC timer 900 Can be useful to work around chipset bugs. 901 902 dis_ucode_ldr [X86] Disable the microcode loader. 903 904 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 905 this option disables the debugging code at boot. 906 907 dma_debug_entries=<number> 908 This option allows to tune the number of preallocated 909 entries for DMA-API debugging code. One entry is 910 required per DMA-API allocation. Use this if the 911 DMA-API debugging code disables itself because the 912 architectural default is too low. 913 914 dma_debug_driver=<driver_name> 915 With this option the DMA-API debugging driver 916 filter feature can be enabled at boot time. Just 917 pass the driver to filter for as the parameter. 918 The filter can be disabled or changed to another 919 driver later using sysfs. 920 921 driver_async_probe= [KNL] 922 List of driver names to be probed asynchronously. 923 Format: <driver_name1>,<driver_name2>... 924 925 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 926 Broken monitors, graphic adapters, KVMs and EDIDless 927 panels may send no or incorrect EDID data sets. 928 This parameter allows to specify an EDID data sets 929 in the /lib/firmware directory that are used instead. 930 Generic built-in EDID data sets are used, if one of 931 edid/1024x768.bin, edid/1280x1024.bin, 932 edid/1680x1050.bin, or edid/1920x1080.bin is given 933 and no file with the same name exists. Details and 934 instructions how to build your own EDID data are 935 available in Documentation/EDID/HOWTO.txt. An EDID 936 data set will only be used for a particular connector, 937 if its name and a colon are prepended to the EDID 938 name. Each connector may use a unique EDID data 939 set by separating the files with a comma. An EDID 940 data set with no connector name will be used for 941 any connectors not explicitly specified. 942 943 dscc4.setup= [NET] 944 945 dt_cpu_ftrs= [PPC] 946 Format: {"off" | "known"} 947 Control how the dt_cpu_ftrs device-tree binding is 948 used for CPU feature discovery and setup (if it 949 exists). 950 off: Do not use it, fall back to legacy cpu table. 951 known: Do not pass through unknown features to guests 952 or userspace, only those that the kernel is aware of. 953 954 dump_apple_properties [X86] 955 Dump name and content of EFI device properties on 956 x86 Macs. Useful for driver authors to determine 957 what data is available or for reverse-engineering. 958 959 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 960 module.dyndbg[="val"] 961 Enable debug messages at boot time. See 962 Documentation/admin-guide/dynamic-debug-howto.rst 963 for details. 964 965 nompx [X86] Disables Intel Memory Protection Extensions. 966 See Documentation/x86/intel_mpx.txt for more 967 information about the feature. 968 969 nopku [X86] Disable Memory Protection Keys CPU feature found 970 in some Intel CPUs. 971 972 module.async_probe [KNL] 973 Enable asynchronous probe on this module. 974 975 early_ioremap_debug [KNL] 976 Enable debug messages in early_ioremap support. This 977 is useful for tracking down temporary early mappings 978 which are not unmapped. 979 980 earlycon= [KNL] Output early console device and options. 981 982 [ARM64] The early console is determined by the 983 stdout-path property in device tree's chosen node, 984 or determined by the ACPI SPCR table. 985 986 [X86] When used with no options the early console is 987 determined by the ACPI SPCR table. 988 989 cdns,<addr>[,options] 990 Start an early, polled-mode console on a Cadence 991 (xuartps) serial port at the specified address. Only 992 supported option is baud rate. If baud rate is not 993 specified, the serial port must already be setup and 994 configured. 995 996 uart[8250],io,<addr>[,options] 997 uart[8250],mmio,<addr>[,options] 998 uart[8250],mmio32,<addr>[,options] 999 uart[8250],mmio32be,<addr>[,options] 1000 uart[8250],0x<addr>[,options] 1001 Start an early, polled-mode console on the 8250/16550 1002 UART at the specified I/O port or MMIO address. 1003 MMIO inter-register address stride is either 8-bit 1004 (mmio) or 32-bit (mmio32 or mmio32be). 1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1006 to be equivalent to 'mmio'. 'options' are specified 1007 in the same format described for "console=ttyS<n>"; if 1008 unspecified, the h/w is not initialized. 1009 1010 pl011,<addr> 1011 pl011,mmio32,<addr> 1012 Start an early, polled-mode console on a pl011 serial 1013 port at the specified address. The pl011 serial port 1014 must already be setup and configured. Options are not 1015 yet supported. If 'mmio32' is specified, then only 1016 the driver will use only 32-bit accessors to read/write 1017 the device registers. 1018 1019 meson,<addr> 1020 Start an early, polled-mode console on a meson serial 1021 port at the specified address. The serial port must 1022 already be setup and configured. Options are not yet 1023 supported. 1024 1025 msm_serial,<addr> 1026 Start an early, polled-mode console on an msm serial 1027 port at the specified address. The serial port 1028 must already be setup and configured. Options are not 1029 yet supported. 1030 1031 msm_serial_dm,<addr> 1032 Start an early, polled-mode console on an msm serial 1033 dm port at the specified address. The serial port 1034 must already be setup and configured. Options are not 1035 yet supported. 1036 1037 owl,<addr> 1038 Start an early, polled-mode console on a serial port 1039 of an Actions Semi SoC, such as S500 or S900, at the 1040 specified address. The serial port must already be 1041 setup and configured. Options are not yet supported. 1042 1043 rda,<addr> 1044 Start an early, polled-mode console on a serial port 1045 of an RDA Micro SoC, such as RDA8810PL, at the 1046 specified address. The serial port must already be 1047 setup and configured. Options are not yet supported. 1048 1049 smh Use ARM semihosting calls for early console. 1050 1051 s3c2410,<addr> 1052 s3c2412,<addr> 1053 s3c2440,<addr> 1054 s3c6400,<addr> 1055 s5pv210,<addr> 1056 exynos4210,<addr> 1057 Use early console provided by serial driver available 1058 on Samsung SoCs, requires selecting proper type and 1059 a correct base address of the selected UART port. The 1060 serial port must already be setup and configured. 1061 Options are not yet supported. 1062 1063 lantiq,<addr> 1064 Start an early, polled-mode console on a lantiq serial 1065 (lqasc) port at the specified address. The serial port 1066 must already be setup and configured. Options are not 1067 yet supported. 1068 1069 lpuart,<addr> 1070 lpuart32,<addr> 1071 Use early console provided by Freescale LP UART driver 1072 found on Freescale Vybrid and QorIQ LS1021A processors. 1073 A valid base address must be provided, and the serial 1074 port must already be setup and configured. 1075 1076 ar3700_uart,<addr> 1077 Start an early, polled-mode console on the 1078 Armada 3700 serial port at the specified 1079 address. The serial port must already be setup 1080 and configured. Options are not yet supported. 1081 1082 qcom_geni,<addr> 1083 Start an early, polled-mode console on a Qualcomm 1084 Generic Interface (GENI) based serial port at the 1085 specified address. The serial port must already be 1086 setup and configured. Options are not yet supported. 1087 1088 efifb,[options] 1089 Start an early, unaccelerated console on the EFI 1090 memory mapped framebuffer (if available). On cache 1091 coherent non-x86 systems that use system memory for 1092 the framebuffer, pass the 'ram' option so that it is 1093 mapped with the correct attributes. 1094 1095 earlyprintk= [X86,SH,ARM,M68k,S390] 1096 earlyprintk=vga 1097 earlyprintk=sclp 1098 earlyprintk=xen 1099 earlyprintk=serial[,ttySn[,baudrate]] 1100 earlyprintk=serial[,0x...[,baudrate]] 1101 earlyprintk=ttySn[,baudrate] 1102 earlyprintk=dbgp[debugController#] 1103 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1104 earlyprintk=xdbc[xhciController#] 1105 1106 earlyprintk is useful when the kernel crashes before 1107 the normal console is initialized. It is not enabled by 1108 default because it has some cosmetic problems. 1109 1110 Append ",keep" to not disable it when the real console 1111 takes over. 1112 1113 Only one of vga, efi, serial, or usb debug port can 1114 be used at a time. 1115 1116 Currently only ttyS0 and ttyS1 may be specified by 1117 name. Other I/O ports may be explicitly specified 1118 on some architectures (x86 and arm at least) by 1119 replacing ttySn with an I/O port address, like this: 1120 earlyprintk=serial,0x1008,115200 1121 You can find the port for a given device in 1122 /proc/tty/driver/serial: 1123 2: uart:ST16650V2 port:00001008 irq:18 ... 1124 1125 Interaction with the standard serial driver is not 1126 very good. 1127 1128 The VGA and EFI output is eventually overwritten by 1129 the real console. 1130 1131 The xen output can only be used by Xen PV guests. 1132 1133 The sclp output can only be used on s390. 1134 1135 The optional "force" to "pciserial" enables use of a 1136 PCI device even when its classcode is not of the 1137 UART class. 1138 1139 edac_report= [HW,EDAC] Control how to report EDAC event 1140 Format: {"on" | "off" | "force"} 1141 on: enable EDAC to report H/W event. May be overridden 1142 by other higher priority error reporting module. 1143 off: disable H/W event reporting through EDAC. 1144 force: enforce the use of EDAC to report H/W event. 1145 default: on. 1146 1147 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1148 ekgdboc=kbd 1149 1150 This is designed to be used in conjunction with 1151 the boot argument: earlyprintk=vga 1152 1153 edd= [EDD] 1154 Format: {"off" | "on" | "skip[mbr]"} 1155 1156 efi= [EFI] 1157 Format: { "old_map", "nochunk", "noruntime", "debug" } 1158 old_map [X86-64]: switch to the old ioremap-based EFI 1159 runtime services mapping. 32-bit still uses this one by 1160 default. 1161 nochunk: disable reading files in "chunks" in the EFI 1162 boot stub, as chunking can cause problems with some 1163 firmware implementations. 1164 noruntime : disable EFI runtime services support 1165 debug: enable misc debug output 1166 1167 efi_no_storage_paranoia [EFI; X86] 1168 Using this parameter you can use more than 50% of 1169 your efi variable storage. Use this parameter only if 1170 you are really sure that your UEFI does sane gc and 1171 fulfills the spec otherwise your board may brick. 1172 1173 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1174 Add arbitrary attribute to specific memory range by 1175 updating original EFI memory map. 1176 Region of memory which aa attribute is added to is 1177 from ss to ss+nn. 1178 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1179 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1180 attribute is added to range 0x100000000-0x180000000 and 1181 0x10a0000000-0x1120000000. 1182 1183 Using this parameter you can do debugging of EFI memmap 1184 related feature. For example, you can do debugging of 1185 Address Range Mirroring feature even if your box 1186 doesn't support it. 1187 1188 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1189 that is to be dynamically loaded by Linux. If there are 1190 multiple variables with the same name but with different 1191 vendor GUIDs, all of them will be loaded. See 1192 Documentation/acpi/ssdt-overlays.txt for details. 1193 1194 1195 eisa_irq_edge= [PARISC,HW] 1196 See header of drivers/parisc/eisa.c. 1197 1198 elanfreq= [X86-32] 1199 See comment before function elanfreq_setup() in 1200 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1201 1202 elevator= [IOSCHED] 1203 Format: { "mq-deadline" | "kyber" | "bfq" } 1204 See Documentation/block/deadline-iosched.txt, 1205 Documentation/block/kyber-iosched.txt and 1206 Documentation/block/bfq-iosched.txt for details. 1207 1208 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1209 Specifies physical address of start of kernel core 1210 image elf header and optionally the size. Generally 1211 kexec loader will pass this option to capture kernel. 1212 See Documentation/kdump/kdump.txt for details. 1213 1214 enable_mtrr_cleanup [X86] 1215 The kernel tries to adjust MTRR layout from continuous 1216 to discrete, to make X server driver able to add WB 1217 entry later. This parameter enables that. 1218 1219 enable_timer_pin_1 [X86] 1220 Enable PIN 1 of APIC timer 1221 Can be useful to work around chipset bugs 1222 (in particular on some ATI chipsets). 1223 The kernel tries to set a reasonable default. 1224 1225 enforcing [SELINUX] Set initial enforcing status. 1226 Format: {"0" | "1"} 1227 See security/selinux/Kconfig help text. 1228 0 -- permissive (log only, no denials). 1229 1 -- enforcing (deny and log). 1230 Default value is 0. 1231 Value can be changed at runtime via /selinux/enforce. 1232 1233 erst_disable [ACPI] 1234 Disable Error Record Serialization Table (ERST) 1235 support. 1236 1237 ether= [HW,NET] Ethernet cards parameters 1238 This option is obsoleted by the "netdev=" option, which 1239 has equivalent usage. See its documentation for details. 1240 1241 evm= [EVM] 1242 Format: { "fix" } 1243 Permit 'security.evm' to be updated regardless of 1244 current integrity status. 1245 1246 failslab= 1247 fail_page_alloc= 1248 fail_make_request=[KNL] 1249 General fault injection mechanism. 1250 Format: <interval>,<probability>,<space>,<times> 1251 See also Documentation/fault-injection/. 1252 1253 floppy= [HW] 1254 See Documentation/blockdev/floppy.txt. 1255 1256 force_pal_cache_flush 1257 [IA-64] Avoid check_sal_cache_flush which may hang on 1258 buggy SAL_CACHE_FLUSH implementations. Using this 1259 parameter will force ia64_sal_cache_flush to call 1260 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1261 1262 forcepae [X86-32] 1263 Forcefully enable Physical Address Extension (PAE). 1264 Many Pentium M systems disable PAE but may have a 1265 functionally usable PAE implementation. 1266 Warning: use of this parameter will taint the kernel 1267 and may cause unknown problems. 1268 1269 ftrace=[tracer] 1270 [FTRACE] will set and start the specified tracer 1271 as early as possible in order to facilitate early 1272 boot debugging. 1273 1274 ftrace_dump_on_oops[=orig_cpu] 1275 [FTRACE] will dump the trace buffers on oops. 1276 If no parameter is passed, ftrace will dump 1277 buffers of all CPUs, but if you pass orig_cpu, it will 1278 dump only the buffer of the CPU that triggered the 1279 oops. 1280 1281 ftrace_filter=[function-list] 1282 [FTRACE] Limit the functions traced by the function 1283 tracer at boot up. function-list is a comma separated 1284 list of functions. This list can be changed at run 1285 time by the set_ftrace_filter file in the debugfs 1286 tracing directory. 1287 1288 ftrace_notrace=[function-list] 1289 [FTRACE] Do not trace the functions specified in 1290 function-list. This list can be changed at run time 1291 by the set_ftrace_notrace file in the debugfs 1292 tracing directory. 1293 1294 ftrace_graph_filter=[function-list] 1295 [FTRACE] Limit the top level callers functions traced 1296 by the function graph tracer at boot up. 1297 function-list is a comma separated list of functions 1298 that can be changed at run time by the 1299 set_graph_function file in the debugfs tracing directory. 1300 1301 ftrace_graph_notrace=[function-list] 1302 [FTRACE] Do not trace from the functions specified in 1303 function-list. This list is a comma separated list of 1304 functions that can be changed at run time by the 1305 set_graph_notrace file in the debugfs tracing directory. 1306 1307 ftrace_graph_max_depth=<uint> 1308 [FTRACE] Used with the function graph tracer. This is 1309 the max depth it will trace into a function. This value 1310 can be changed at run time by the max_graph_depth file 1311 in the tracefs tracing directory. default: 0 (no limit) 1312 1313 gamecon.map[2|3]= 1314 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1315 support via parallel port (up to 5 devices per port) 1316 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1317 See also Documentation/input/devices/joystick-parport.rst 1318 1319 gamma= [HW,DRM] 1320 1321 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1322 Format: off | on 1323 default: on 1324 1325 gcov_persist= [GCOV] When non-zero (default), profiling data for 1326 kernel modules is saved and remains accessible via 1327 debugfs, even when the module is unloaded/reloaded. 1328 When zero, profiling data is discarded and associated 1329 debugfs files are removed at module unload time. 1330 1331 goldfish [X86] Enable the goldfish android emulator platform. 1332 Don't use this when you are not running on the 1333 android emulator 1334 1335 gpt [EFI] Forces disk with valid GPT signature but 1336 invalid Protective MBR to be treated as GPT. If the 1337 primary GPT is corrupted, it enables the backup/alternate 1338 GPT to be used instead. 1339 1340 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1341 the "Enable 0" bit of the configuration register. 1342 Format: 0 | 1 1343 Default: 0 1344 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1345 the "Enable 0" bit of the configuration register. 1346 Format: 0 | 1 1347 Default: 0 1348 grcan.select= [HW] Select which physical interface to use. 1349 Format: 0 | 1 1350 Default: 0 1351 grcan.txsize= [HW] Sets the size of the tx buffer. 1352 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1353 Default: 1024 1354 grcan.rxsize= [HW] Sets the size of the rx buffer. 1355 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1356 Default: 1024 1357 1358 gpio-mockup.gpio_mockup_ranges 1359 [HW] Sets the ranges of gpiochip of for this device. 1360 Format: <start1>,<end1>,<start2>,<end2>... 1361 1362 hardlockup_all_cpu_backtrace= 1363 [KNL] Should the hard-lockup detector generate 1364 backtraces on all cpus. 1365 Format: <integer> 1366 1367 hashdist= [KNL,NUMA] Large hashes allocated during boot 1368 are distributed across NUMA nodes. Defaults on 1369 for 64-bit NUMA, off otherwise. 1370 Format: 0 | 1 (for off | on) 1371 1372 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1373 1374 hd= [EIDE] (E)IDE hard drive subsystem geometry 1375 Format: <cyl>,<head>,<sect> 1376 1377 hest_disable [ACPI] 1378 Disable Hardware Error Source Table (HEST) support; 1379 corresponding firmware-first mode error processing 1380 logic will be disabled. 1381 1382 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1383 size of <nn>. This works even on boxes that have no 1384 highmem otherwise. This also works to reduce highmem 1385 size on bigger boxes. 1386 1387 highres= [KNL] Enable/disable high resolution timer mode. 1388 Valid parameters: "on", "off" 1389 Default: "on" 1390 1391 hisax= [HW,ISDN] 1392 See Documentation/isdn/README.HiSax. 1393 1394 hlt [BUGS=ARM,SH] 1395 1396 hpet= [X86-32,HPET] option to control HPET usage 1397 Format: { enable (default) | disable | force | 1398 verbose } 1399 disable: disable HPET and use PIT instead 1400 force: allow force enabled of undocumented chips (ICH4, 1401 VIA, nVidia) 1402 verbose: show contents of HPET registers during setup 1403 1404 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1405 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1406 1407 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1408 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1409 On x86-64 and powerpc, this option can be specified 1410 multiple times interleaved with hugepages= to reserve 1411 huge pages of different sizes. Valid pages sizes on 1412 x86-64 are 2M (when the CPU supports "pse") and 1G 1413 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1414 1415 hung_task_panic= 1416 [KNL] Should the hung task detector generate panics. 1417 Format: <integer> 1418 1419 A nonzero value instructs the kernel to panic when a 1420 hung task is detected. The default value is controlled 1421 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1422 option. The value selected by this boot parameter can 1423 be changed later by the kernel.hung_task_panic sysctl. 1424 1425 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1426 terminal devices. Valid values: 0..8 1427 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1428 If specified, z/VM IUCV HVC accepts connections 1429 from listed z/VM user IDs only. 1430 1431 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1432 which allow the hypervisor to 'idle' the 1433 guest on lock contention. 1434 1435 keep_bootcon [KNL] 1436 Do not unregister boot console at start. This is only 1437 useful for debugging when something happens in the window 1438 between unregistering the boot console and initializing 1439 the real console. 1440 1441 i2c_bus= [HW] Override the default board specific I2C bus speed 1442 or register an additional I2C bus that is not 1443 registered from board initialization code. 1444 Format: 1445 <bus_id>,<clkrate> 1446 1447 i8042.debug [HW] Toggle i8042 debug mode 1448 i8042.unmask_kbd_data 1449 [HW] Enable printing of interrupt data from the KBD port 1450 (disabled by default, and as a pre-condition 1451 requires that i8042.debug=1 be enabled) 1452 i8042.direct [HW] Put keyboard port into non-translated mode 1453 i8042.dumbkbd [HW] Pretend that controller can only read data from 1454 keyboard and cannot control its state 1455 (Don't attempt to blink the leds) 1456 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1457 i8042.nokbd [HW] Don't check/create keyboard port 1458 i8042.noloop [HW] Disable the AUX Loopback command while probing 1459 for the AUX port 1460 i8042.nomux [HW] Don't check presence of an active multiplexing 1461 controller 1462 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1463 controllers 1464 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1465 i8042.reset [HW] Reset the controller during init, cleanup and 1466 suspend-to-ram transitions, only during s2r 1467 transitions, or never reset 1468 Format: { 1 | Y | y | 0 | N | n } 1469 1, Y, y: always reset controller 1470 0, N, n: don't ever reset controller 1471 Default: only on s2r transitions on x86; most other 1472 architectures force reset to be always executed 1473 i8042.unlock [HW] Unlock (ignore) the keylock 1474 i8042.kbdreset [HW] Reset device connected to KBD port 1475 1476 i810= [HW,DRM] 1477 1478 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1479 indicates that the driver is running on unsupported 1480 hardware. 1481 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1482 does not match list of supported models. 1483 i8k.power_status 1484 [HW] Report power status in /proc/i8k 1485 (disabled by default) 1486 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1487 capability is set. 1488 1489 i915.invert_brightness= 1490 [DRM] Invert the sense of the variable that is used to 1491 set the brightness of the panel backlight. Normally a 1492 brightness value of 0 indicates backlight switched off, 1493 and the maximum of the brightness value sets the backlight 1494 to maximum brightness. If this parameter is set to 0 1495 (default) and the machine requires it, or this parameter 1496 is set to 1, a brightness value of 0 sets the backlight 1497 to maximum brightness, and the maximum of the brightness 1498 value switches the backlight off. 1499 -1 -- never invert brightness 1500 0 -- machine default 1501 1 -- force brightness inversion 1502 1503 icn= [HW,ISDN] 1504 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1505 1506 ide-core.nodma= [HW] (E)IDE subsystem 1507 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1508 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1509 .cdrom .chs .ignore_cable are additional options 1510 See Documentation/ide/ide.txt. 1511 1512 ide-generic.probe-mask= [HW] (E)IDE subsystem 1513 Format: <int> 1514 Probe mask for legacy ISA IDE ports. Depending on 1515 platform up to 6 ports are supported, enabled by 1516 setting corresponding bits in the mask to 1. The 1517 default value is 0x0, which has a special meaning. 1518 On systems that have PCI, it triggers scanning the 1519 PCI bus for the first and the second port, which 1520 are then probed. On systems without PCI the value 1521 of 0x0 enables probing the two first ports as if it 1522 was 0x3. 1523 1524 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1525 Claim all unknown PCI IDE storage controllers. 1526 1527 idle= [X86] 1528 Format: idle=poll, idle=halt, idle=nomwait 1529 Poll forces a polling idle loop that can slightly 1530 improve the performance of waking up a idle CPU, but 1531 will use a lot of power and make the system run hot. 1532 Not recommended. 1533 idle=halt: Halt is forced to be used for CPU idle. 1534 In such case C2/C3 won't be used again. 1535 idle=nomwait: Disable mwait for CPU C-states 1536 1537 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1538 Format: { strict | legacy | 2008 | relaxed } 1539 Default: strict 1540 1541 Choose which programs will be accepted for execution 1542 based on the IEEE 754 NaN encoding(s) supported by 1543 the FPU and the NaN encoding requested with the value 1544 of an ELF file header flag individually set by each 1545 binary. Hardware implementations are permitted to 1546 support either or both of the legacy and the 2008 NaN 1547 encoding mode. 1548 1549 Available settings are as follows: 1550 strict accept binaries that request a NaN encoding 1551 supported by the FPU 1552 legacy only accept legacy-NaN binaries, if supported 1553 by the FPU 1554 2008 only accept 2008-NaN binaries, if supported 1555 by the FPU 1556 relaxed accept any binaries regardless of whether 1557 supported by the FPU 1558 1559 The FPU emulator is always able to support both NaN 1560 encodings, so if no FPU hardware is present or it has 1561 been disabled with 'nofpu', then the settings of 1562 'legacy' and '2008' strap the emulator accordingly, 1563 'relaxed' straps the emulator for both legacy-NaN and 1564 2008-NaN, whereas 'strict' enables legacy-NaN only on 1565 legacy processors and both NaN encodings on MIPS32 or 1566 MIPS64 CPUs. 1567 1568 The setting for ABS.fmt/NEG.fmt instruction execution 1569 mode generally follows that for the NaN encoding, 1570 except where unsupported by hardware. 1571 1572 ignore_loglevel [KNL] 1573 Ignore loglevel setting - this will print /all/ 1574 kernel messages to the console. Useful for debugging. 1575 We also add it as printk module parameter, so users 1576 could change it dynamically, usually by 1577 /sys/module/printk/parameters/ignore_loglevel. 1578 1579 ignore_rlimit_data 1580 Ignore RLIMIT_DATA setting for data mappings, 1581 print warning at first misuse. Can be changed via 1582 /sys/module/kernel/parameters/ignore_rlimit_data. 1583 1584 ihash_entries= [KNL] 1585 Set number of hash buckets for inode cache. 1586 1587 ima_appraise= [IMA] appraise integrity measurements 1588 Format: { "off" | "enforce" | "fix" | "log" } 1589 default: "enforce" 1590 1591 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1592 The builtin appraise policy appraises all files 1593 owned by uid=0. 1594 1595 ima_canonical_fmt [IMA] 1596 Use the canonical format for the binary runtime 1597 measurements, instead of host native format. 1598 1599 ima_hash= [IMA] 1600 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1601 | sha512 | ... } 1602 default: "sha1" 1603 1604 The list of supported hash algorithms is defined 1605 in crypto/hash_info.h. 1606 1607 ima_policy= [IMA] 1608 The builtin policies to load during IMA setup. 1609 Format: "tcb | appraise_tcb | secure_boot | 1610 fail_securely" 1611 1612 The "tcb" policy measures all programs exec'd, files 1613 mmap'd for exec, and all files opened with the read 1614 mode bit set by either the effective uid (euid=0) or 1615 uid=0. 1616 1617 The "appraise_tcb" policy appraises the integrity of 1618 all files owned by root. 1619 1620 The "secure_boot" policy appraises the integrity 1621 of files (eg. kexec kernel image, kernel modules, 1622 firmware, policy, etc) based on file signatures. 1623 1624 The "fail_securely" policy forces file signature 1625 verification failure also on privileged mounted 1626 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1627 flag. 1628 1629 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1630 Load a policy which meets the needs of the Trusted 1631 Computing Base. This means IMA will measure all 1632 programs exec'd, files mmap'd for exec, and all files 1633 opened for read by uid=0. 1634 1635 ima_template= [IMA] 1636 Select one of defined IMA measurements template formats. 1637 Formats: { "ima" | "ima-ng" | "ima-sig" } 1638 Default: "ima-ng" 1639 1640 ima_template_fmt= 1641 [IMA] Define a custom template format. 1642 Format: { "field1|...|fieldN" } 1643 1644 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1645 Format: <min_file_size> 1646 Set the minimal file size for using asynchronous hash. 1647 If left unspecified, ahash usage is disabled. 1648 1649 ahash performance varies for different data sizes on 1650 different crypto accelerators. This option can be used 1651 to achieve the best performance for a particular HW. 1652 1653 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1654 Format: <bufsize> 1655 Set hashing buffer size. Default: 4k. 1656 1657 ahash performance varies for different chunk sizes on 1658 different crypto accelerators. This option can be used 1659 to achieve best performance for particular HW. 1660 1661 init= [KNL] 1662 Format: <full_path> 1663 Run specified binary instead of /sbin/init as init 1664 process. 1665 1666 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1667 for working out where the kernel is dying during 1668 startup. 1669 1670 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1671 initcall functions. Useful for debugging built-in 1672 modules and initcalls. 1673 1674 initrd= [BOOT] Specify the location of the initial ramdisk 1675 1676 init_pkru= [x86] Specify the default memory protection keys rights 1677 register contents for all processes. 0x55555554 by 1678 default (disallow access to all but pkey 0). Can 1679 override in debugfs after boot. 1680 1681 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1682 Format: <irq> 1683 1684 int_pln_enable [x86] Enable power limit notification interrupt 1685 1686 integrity_audit=[IMA] 1687 Format: { "0" | "1" } 1688 0 -- basic integrity auditing messages. (Default) 1689 1 -- additional integrity auditing messages. 1690 1691 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1692 on 1693 Enable intel iommu driver. 1694 off 1695 Disable intel iommu driver. 1696 igfx_off [Default Off] 1697 By default, gfx is mapped as normal device. If a gfx 1698 device has a dedicated DMAR unit, the DMAR unit is 1699 bypassed by not enabling DMAR with this option. In 1700 this case, gfx device will use physical address for 1701 DMA. 1702 forcedac [x86_64] 1703 With this option iommu will not optimize to look 1704 for io virtual address below 32-bit forcing dual 1705 address cycle on pci bus for cards supporting greater 1706 than 32-bit addressing. The default is to look 1707 for translation below 32-bit and if not available 1708 then look in the higher range. 1709 strict [Default Off] 1710 With this option on every unmap_single operation will 1711 result in a hardware IOTLB flush operation as opposed 1712 to batching them for performance. 1713 sp_off [Default Off] 1714 By default, super page will be supported if Intel IOMMU 1715 has the capability. With this option, super page will 1716 not be supported. 1717 sm_on [Default Off] 1718 By default, scalable mode will be disabled even if the 1719 hardware advertises that it has support for the scalable 1720 mode translation. With this option set, scalable mode 1721 will be used on hardware which claims to support it. 1722 tboot_noforce [Default Off] 1723 Do not force the Intel IOMMU enabled under tboot. 1724 By default, tboot will force Intel IOMMU on, which 1725 could harm performance of some high-throughput 1726 devices like 40GBit network cards, even if identity 1727 mapping is enabled. 1728 Note that using this option lowers the security 1729 provided by tboot because it makes the system 1730 vulnerable to DMA attacks. 1731 1732 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1733 0 disables intel_idle and fall back on acpi_idle. 1734 1 to 9 specify maximum depth of C-state. 1735 1736 intel_pstate= [X86] 1737 disable 1738 Do not enable intel_pstate as the default 1739 scaling driver for the supported processors 1740 passive 1741 Use intel_pstate as a scaling driver, but configure it 1742 to work with generic cpufreq governors (instead of 1743 enabling its internal governor). This mode cannot be 1744 used along with the hardware-managed P-states (HWP) 1745 feature. 1746 force 1747 Enable intel_pstate on systems that prohibit it by default 1748 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1749 instead of acpi-cpufreq may disable platform features, such 1750 as thermal controls and power capping, that rely on ACPI 1751 P-States information being indicated to OSPM and therefore 1752 should be used with caution. This option does not work with 1753 processors that aren't supported by the intel_pstate driver 1754 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1755 no_hwp 1756 Do not enable hardware P state control (HWP) 1757 if available. 1758 hwp_only 1759 Only load intel_pstate on systems which support 1760 hardware P state control (HWP) if available. 1761 support_acpi_ppc 1762 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1763 Description Table, specifies preferred power management 1764 profile as "Enterprise Server" or "Performance Server", 1765 then this feature is turned on by default. 1766 per_cpu_perf_limits 1767 Allow per-logical-CPU P-State performance control limits using 1768 cpufreq sysfs interface 1769 1770 intremap= [X86-64, Intel-IOMMU] 1771 on enable Interrupt Remapping (default) 1772 off disable Interrupt Remapping 1773 nosid disable Source ID checking 1774 no_x2apic_optout 1775 BIOS x2APIC opt-out request will be ignored 1776 nopost disable Interrupt Posting 1777 1778 iomem= Disable strict checking of access to MMIO memory 1779 strict regions from userspace. 1780 relaxed 1781 1782 iommu= [x86] 1783 off 1784 force 1785 noforce 1786 biomerge 1787 panic 1788 nopanic 1789 merge 1790 nomerge 1791 soft 1792 pt [x86] 1793 nopt [x86] 1794 nobypass [PPC/POWERNV] 1795 Disable IOMMU bypass, using IOMMU for PCI devices. 1796 1797 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1798 Format: { "0" | "1" } 1799 0 - Lazy mode. 1800 Request that DMA unmap operations use deferred 1801 invalidation of hardware TLBs, for increased 1802 throughput at the cost of reduced device isolation. 1803 Will fall back to strict mode if not supported by 1804 the relevant IOMMU driver. 1805 1 - Strict mode (default). 1806 DMA unmap operations invalidate IOMMU hardware TLBs 1807 synchronously. 1808 1809 iommu.passthrough= 1810 [ARM64] Configure DMA to bypass the IOMMU by default. 1811 Format: { "0" | "1" } 1812 0 - Use IOMMU translation for DMA. 1813 1 - Bypass the IOMMU for DMA. 1814 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1815 1816 io7= [HW] IO7 for Marvel based alpha systems 1817 See comment before marvel_specify_io7 in 1818 arch/alpha/kernel/core_marvel.c. 1819 1820 io_delay= [X86] I/O delay method 1821 0x80 1822 Standard port 0x80 based delay 1823 0xed 1824 Alternate port 0xed based delay (needed on some systems) 1825 udelay 1826 Simple two microseconds delay 1827 none 1828 No delay 1829 1830 ip= [IP_PNP] 1831 See Documentation/filesystems/nfs/nfsroot.txt. 1832 1833 ipcmni_extend [KNL] Extend the maximum number of unique System V 1834 IPC identifiers from 32,768 to 16,777,216. 1835 1836 irqaffinity= [SMP] Set the default irq affinity mask 1837 The argument is a cpu list, as described above. 1838 1839 irqchip.gicv2_force_probe= 1840 [ARM, ARM64] 1841 Format: <bool> 1842 Force the kernel to look for the second 4kB page 1843 of a GICv2 controller even if the memory range 1844 exposed by the device tree is too small. 1845 1846 irqchip.gicv3_nolpi= 1847 [ARM, ARM64] 1848 Force the kernel to ignore the availability of 1849 LPIs (and by consequence ITSs). Intended for system 1850 that use the kernel as a bootloader, and thus want 1851 to let secondary kernels in charge of setting up 1852 LPIs. 1853 1854 irqchip.gicv3_pseudo_nmi= [ARM64] 1855 Enables support for pseudo-NMIs in the kernel. This 1856 requires the kernel to be built with 1857 CONFIG_ARM64_PSEUDO_NMI. 1858 1859 irqfixup [HW] 1860 When an interrupt is not handled search all handlers 1861 for it. Intended to get systems with badly broken 1862 firmware running. 1863 1864 irqpoll [HW] 1865 When an interrupt is not handled search all handlers 1866 for it. Also check all handlers each timer 1867 interrupt. Intended to get systems with badly broken 1868 firmware running. 1869 1870 isapnp= [ISAPNP] 1871 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1872 1873 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1874 [Deprecated - use cpusets instead] 1875 Format: [flag-list,]<cpu-list> 1876 1877 Specify one or more CPUs to isolate from disturbances 1878 specified in the flag list (default: domain): 1879 1880 nohz 1881 Disable the tick when a single task runs. 1882 1883 A residual 1Hz tick is offloaded to workqueues, which you 1884 need to affine to housekeeping through the global 1885 workqueue's affinity configured via the 1886 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1887 by using the 'domain' flag described below. 1888 1889 NOTE: by default the global workqueue runs on all CPUs, 1890 so to protect individual CPUs the 'cpumask' file has to 1891 be configured manually after bootup. 1892 1893 domain 1894 Isolate from the general SMP balancing and scheduling 1895 algorithms. Note that performing domain isolation this way 1896 is irreversible: it's not possible to bring back a CPU to 1897 the domains once isolated through isolcpus. It's strongly 1898 advised to use cpusets instead to disable scheduler load 1899 balancing through the "cpuset.sched_load_balance" file. 1900 It offers a much more flexible interface where CPUs can 1901 move in and out of an isolated set anytime. 1902 1903 You can move a process onto or off an "isolated" CPU via 1904 the CPU affinity syscalls or cpuset. 1905 <cpu number> begins at 0 and the maximum value is 1906 "number of CPUs in system - 1". 1907 1908 The format of <cpu-list> is described above. 1909 1910 1911 1912 iucv= [HW,NET] 1913 1914 ivrs_ioapic [HW,X86_64] 1915 Provide an override to the IOAPIC-ID<->DEVICE-ID 1916 mapping provided in the IVRS ACPI table. For 1917 example, to map IOAPIC-ID decimal 10 to 1918 PCI device 00:14.0 write the parameter as: 1919 ivrs_ioapic[10]=00:14.0 1920 1921 ivrs_hpet [HW,X86_64] 1922 Provide an override to the HPET-ID<->DEVICE-ID 1923 mapping provided in the IVRS ACPI table. For 1924 example, to map HPET-ID decimal 0 to 1925 PCI device 00:14.0 write the parameter as: 1926 ivrs_hpet[0]=00:14.0 1927 1928 ivrs_acpihid [HW,X86_64] 1929 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1930 mapping provided in the IVRS ACPI table. For 1931 example, to map UART-HID:UID AMD0020:0 to 1932 PCI device 00:14.5 write the parameter as: 1933 ivrs_acpihid[00:14.5]=AMD0020:0 1934 1935 js= [HW,JOY] Analog joystick 1936 See Documentation/input/joydev/joystick.rst. 1937 1938 nokaslr [KNL] 1939 When CONFIG_RANDOMIZE_BASE is set, this disables 1940 kernel and module base offset ASLR (Address Space 1941 Layout Randomization). 1942 1943 kasan_multi_shot 1944 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1945 report on every invalid memory access. Without this 1946 parameter KASAN will print report only for the first 1947 invalid access. 1948 1949 keepinitrd [HW,ARM] 1950 1951 kernelcore= [KNL,X86,IA-64,PPC] 1952 Format: nn[KMGTPE] | nn% | "mirror" 1953 This parameter specifies the amount of memory usable by 1954 the kernel for non-movable allocations. The requested 1955 amount is spread evenly throughout all nodes in the 1956 system as ZONE_NORMAL. The remaining memory is used for 1957 movable memory in its own zone, ZONE_MOVABLE. In the 1958 event, a node is too small to have both ZONE_NORMAL and 1959 ZONE_MOVABLE, kernelcore memory will take priority and 1960 other nodes will have a larger ZONE_MOVABLE. 1961 1962 ZONE_MOVABLE is used for the allocation of pages that 1963 may be reclaimed or moved by the page migration 1964 subsystem. Note that allocations like PTEs-from-HighMem 1965 still use the HighMem zone if it exists, and the Normal 1966 zone if it does not. 1967 1968 It is possible to specify the exact amount of memory in 1969 the form of "nn[KMGTPE]", a percentage of total system 1970 memory in the form of "nn%", or "mirror". If "mirror" 1971 option is specified, mirrored (reliable) memory is used 1972 for non-movable allocations and remaining memory is used 1973 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1974 are exclusive, so you cannot specify multiple forms. 1975 1976 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1977 Format: <Controller#>[,poll interval] 1978 The controller # is the number of the ehci usb debug 1979 port as it is probed via PCI. The poll interval is 1980 optional and is the number seconds in between 1981 each poll cycle to the debug port in case you need 1982 the functionality for interrupting the kernel with 1983 gdb or control-c on the dbgp connection. When 1984 not using this parameter you use sysrq-g to break into 1985 the kernel debugger. 1986 1987 kgdboc= [KGDB,HW] kgdb over consoles. 1988 Requires a tty driver that supports console polling, 1989 or a supported polling keyboard driver (non-usb). 1990 Serial only format: <serial_device>[,baud] 1991 keyboard only format: kbd 1992 keyboard and serial format: kbd,<serial_device>[,baud] 1993 Optional Kernel mode setting: 1994 kms, kbd format: kms,kbd 1995 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1996 1997 kgdbwait [KGDB] Stop kernel execution and enter the 1998 kernel debugger at the earliest opportunity. 1999 2000 kmac= [MIPS] korina ethernet MAC address. 2001 Configure the RouterBoard 532 series on-chip 2002 Ethernet adapter MAC address. 2003 2004 kmemleak= [KNL] Boot-time kmemleak enable/disable 2005 Valid arguments: on, off 2006 Default: on 2007 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2008 the default is off. 2009 2010 kpti= [ARM64] Control page table isolation of user 2011 and kernel address spaces. 2012 Default: enabled on cores which need mitigation. 2013 0: force disabled 2014 1: force enabled 2015 2016 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2017 Default is 0 (don't ignore, but inject #GP) 2018 2019 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2020 Default is false (don't support). 2021 2022 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2023 KVM MMU at runtime. 2024 Default is 0 (off) 2025 2026 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2027 Default is 1 (enabled) 2028 2029 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2030 for all guests. 2031 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2032 2033 kvm-arm.vgic_v3_group0_trap= 2034 [KVM,ARM] Trap guest accesses to GICv3 group-0 2035 system registers 2036 2037 kvm-arm.vgic_v3_group1_trap= 2038 [KVM,ARM] Trap guest accesses to GICv3 group-1 2039 system registers 2040 2041 kvm-arm.vgic_v3_common_trap= 2042 [KVM,ARM] Trap guest accesses to GICv3 common 2043 system registers 2044 2045 kvm-arm.vgic_v4_enable= 2046 [KVM,ARM] Allow use of GICv4 for direct injection of 2047 LPIs. 2048 2049 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2050 (virtualized MMU) support on capable Intel chips. 2051 Default is 1 (enabled) 2052 2053 kvm-intel.emulate_invalid_guest_state= 2054 [KVM,Intel] Enable emulation of invalid guest states 2055 Default is 0 (disabled) 2056 2057 kvm-intel.flexpriority= 2058 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2059 Default is 1 (enabled) 2060 2061 kvm-intel.nested= 2062 [KVM,Intel] Enable VMX nesting (nVMX). 2063 Default is 0 (disabled) 2064 2065 kvm-intel.unrestricted_guest= 2066 [KVM,Intel] Disable unrestricted guest feature 2067 (virtualized real and unpaged mode) on capable 2068 Intel chips. Default is 1 (enabled) 2069 2070 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2071 CVE-2018-3620. 2072 2073 Valid arguments: never, cond, always 2074 2075 always: L1D cache flush on every VMENTER. 2076 cond: Flush L1D on VMENTER only when the code between 2077 VMEXIT and VMENTER can leak host memory. 2078 never: Disables the mitigation 2079 2080 Default is cond (do L1 cache flush in specific instances) 2081 2082 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2083 feature (tagged TLBs) on capable Intel chips. 2084 Default is 1 (enabled) 2085 2086 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2087 affected CPUs 2088 2089 The kernel PTE inversion protection is unconditionally 2090 enabled and cannot be disabled. 2091 2092 full 2093 Provides all available mitigations for the 2094 L1TF vulnerability. Disables SMT and 2095 enables all mitigations in the 2096 hypervisors, i.e. unconditional L1D flush. 2097 2098 SMT control and L1D flush control via the 2099 sysfs interface is still possible after 2100 boot. Hypervisors will issue a warning 2101 when the first VM is started in a 2102 potentially insecure configuration, 2103 i.e. SMT enabled or L1D flush disabled. 2104 2105 full,force 2106 Same as 'full', but disables SMT and L1D 2107 flush runtime control. Implies the 2108 'nosmt=force' command line option. 2109 (i.e. sysfs control of SMT is disabled.) 2110 2111 flush 2112 Leaves SMT enabled and enables the default 2113 hypervisor mitigation, i.e. conditional 2114 L1D flush. 2115 2116 SMT control and L1D flush control via the 2117 sysfs interface is still possible after 2118 boot. Hypervisors will issue a warning 2119 when the first VM is started in a 2120 potentially insecure configuration, 2121 i.e. SMT enabled or L1D flush disabled. 2122 2123 flush,nosmt 2124 2125 Disables SMT and enables the default 2126 hypervisor mitigation. 2127 2128 SMT control and L1D flush control via the 2129 sysfs interface is still possible after 2130 boot. Hypervisors will issue a warning 2131 when the first VM is started in a 2132 potentially insecure configuration, 2133 i.e. SMT enabled or L1D flush disabled. 2134 2135 flush,nowarn 2136 Same as 'flush', but hypervisors will not 2137 warn when a VM is started in a potentially 2138 insecure configuration. 2139 2140 off 2141 Disables hypervisor mitigations and doesn't 2142 emit any warnings. 2143 It also drops the swap size and available 2144 RAM limit restriction on both hypervisor and 2145 bare metal. 2146 2147 Default is 'flush'. 2148 2149 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2150 2151 l2cr= [PPC] 2152 2153 l3cr= [PPC] 2154 2155 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2156 disabled it. 2157 2158 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2159 value for LAPIC timer one-shot implementation. Default 2160 back to the programmable timer unit in the LAPIC. 2161 2162 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2163 in C2 power state. 2164 2165 libata.dma= [LIBATA] DMA control 2166 libata.dma=0 Disable all PATA and SATA DMA 2167 libata.dma=1 PATA and SATA Disk DMA only 2168 libata.dma=2 ATAPI (CDROM) DMA only 2169 libata.dma=4 Compact Flash DMA only 2170 Combinations also work, so libata.dma=3 enables DMA 2171 for disks and CDROMs, but not CFs. 2172 2173 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2174 libata.ignore_hpa=0 keep BIOS limits (default) 2175 libata.ignore_hpa=1 ignore limits, using full disk 2176 2177 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2178 when set. 2179 Format: <int> 2180 2181 libata.force= [LIBATA] Force configurations. The format is comma 2182 separated list of "[ID:]VAL" where ID is 2183 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2184 matching port, link or device. Basically, it matches 2185 the ATA ID string printed on console by libata. If 2186 the whole ID part is omitted, the last PORT and DEVICE 2187 values are used. If ID hasn't been specified yet, the 2188 configuration applies to all ports, links and devices. 2189 2190 If only DEVICE is omitted, the parameter applies to 2191 the port and all links and devices behind it. DEVICE 2192 number of 0 either selects the first device or the 2193 first fan-out link behind PMP device. It does not 2194 select the host link. DEVICE number of 15 selects the 2195 host link and device attached to it. 2196 2197 The VAL specifies the configuration to force. As long 2198 as there's no ambiguity shortcut notation is allowed. 2199 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2200 The following configurations can be forced. 2201 2202 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2203 Any ID with matching PORT is used. 2204 2205 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2206 2207 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2208 udma[/][16,25,33,44,66,100,133] notation is also 2209 allowed. 2210 2211 * [no]ncq: Turn on or off NCQ. 2212 2213 * [no]ncqtrim: Turn off queued DSM TRIM. 2214 2215 * nohrst, nosrst, norst: suppress hard, soft 2216 and both resets. 2217 2218 * rstonce: only attempt one reset during 2219 hot-unplug link recovery 2220 2221 * dump_id: dump IDENTIFY data. 2222 2223 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2224 2225 * disable: Disable this device. 2226 2227 If there are multiple matching configurations changing 2228 the same attribute, the last one is used. 2229 2230 memblock=debug [KNL] Enable memblock debug messages. 2231 2232 load_ramdisk= [RAM] List of ramdisks to load from floppy 2233 See Documentation/blockdev/ramdisk.txt. 2234 2235 lockd.nlm_grace_period=P [NFS] Assign grace period. 2236 Format: <integer> 2237 2238 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2239 Format: <integer> 2240 2241 lockd.nlm_timeout=T [NFS] Assign timeout value. 2242 Format: <integer> 2243 2244 lockd.nlm_udpport=M [NFS] Assign UDP port. 2245 Format: <integer> 2246 2247 lockdown= [SECURITY] 2248 { integrity | confidentiality } 2249 Enable the kernel lockdown feature. If set to 2250 integrity, kernel features that allow userland to 2251 modify the running kernel are disabled. If set to 2252 confidentiality, kernel features that allow userland 2253 to extract confidential information from the kernel 2254 are also disabled. 2255 2256 locktorture.nreaders_stress= [KNL] 2257 Set the number of locking read-acquisition kthreads. 2258 Defaults to being automatically set based on the 2259 number of online CPUs. 2260 2261 locktorture.nwriters_stress= [KNL] 2262 Set the number of locking write-acquisition kthreads. 2263 2264 locktorture.onoff_holdoff= [KNL] 2265 Set time (s) after boot for CPU-hotplug testing. 2266 2267 locktorture.onoff_interval= [KNL] 2268 Set time (s) between CPU-hotplug operations, or 2269 zero to disable CPU-hotplug testing. 2270 2271 locktorture.shuffle_interval= [KNL] 2272 Set task-shuffle interval (jiffies). Shuffling 2273 tasks allows some CPUs to go into dyntick-idle 2274 mode during the locktorture test. 2275 2276 locktorture.shutdown_secs= [KNL] 2277 Set time (s) after boot system shutdown. This 2278 is useful for hands-off automated testing. 2279 2280 locktorture.stat_interval= [KNL] 2281 Time (s) between statistics printk()s. 2282 2283 locktorture.stutter= [KNL] 2284 Time (s) to stutter testing, for example, 2285 specifying five seconds causes the test to run for 2286 five seconds, wait for five seconds, and so on. 2287 This tests the locking primitive's ability to 2288 transition abruptly to and from idle. 2289 2290 locktorture.torture_type= [KNL] 2291 Specify the locking implementation to test. 2292 2293 locktorture.verbose= [KNL] 2294 Enable additional printk() statements. 2295 2296 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2297 Format: <irq> 2298 2299 loglevel= All Kernel Messages with a loglevel smaller than the 2300 console loglevel will be printed to the console. It can 2301 also be changed with klogd or other programs. The 2302 loglevels are defined as follows: 2303 2304 0 (KERN_EMERG) system is unusable 2305 1 (KERN_ALERT) action must be taken immediately 2306 2 (KERN_CRIT) critical conditions 2307 3 (KERN_ERR) error conditions 2308 4 (KERN_WARNING) warning conditions 2309 5 (KERN_NOTICE) normal but significant condition 2310 6 (KERN_INFO) informational 2311 7 (KERN_DEBUG) debug-level messages 2312 2313 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2314 in bytes. n must be a power of two and greater 2315 than the minimal size. The minimal size is defined 2316 by LOG_BUF_SHIFT kernel config parameter. There is 2317 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2318 that allows to increase the default size depending on 2319 the number of CPUs. See init/Kconfig for more details. 2320 2321 logo.nologo [FB] Disables display of the built-in Linux logo. 2322 This may be used to provide more screen space for 2323 kernel log messages and is useful when debugging 2324 kernel boot problems. 2325 2326 lp=0 [LP] Specify parallel ports to use, e.g, 2327 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2328 lp=reset first parallel port). 'lp=0' disables the 2329 lp=auto printer driver. 'lp=reset' (which can be 2330 specified in addition to the ports) causes 2331 attached printers to be reset. Using 2332 lp=port1,port2,... specifies the parallel ports 2333 to associate lp devices with, starting with 2334 lp0. A port specification may be 'none' to skip 2335 that lp device, or a parport name such as 2336 'parport0'. Specifying 'lp=auto' instead of a 2337 port specification list means that device IDs 2338 from each port should be examined, to see if 2339 an IEEE 1284-compliant printer is attached; if 2340 so, the driver will manage that printer. 2341 See also header of drivers/char/lp.c. 2342 2343 lpj=n [KNL] 2344 Sets loops_per_jiffy to given constant, thus avoiding 2345 time-consuming boot-time autodetection (up to 250 ms per 2346 CPU). 0 enables autodetection (default). To determine 2347 the correct value for your kernel, boot with normal 2348 autodetection and see what value is printed. Note that 2349 on SMP systems the preset will be applied to all CPUs, 2350 which is likely to cause problems if your CPUs need 2351 significantly divergent settings. An incorrect value 2352 will cause delays in the kernel to be wrong, leading to 2353 unpredictable I/O errors and other breakage. Although 2354 unlikely, in the extreme case this might damage your 2355 hardware. 2356 2357 ltpc= [NET] 2358 Format: <io>,<irq>,<dma> 2359 2360 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2361 2362 lsm=lsm1,...,lsmN 2363 [SECURITY] Choose order of LSM initialization. This 2364 overrides CONFIG_LSM, and the "security=" parameter. 2365 2366 machvec= [IA-64] Force the use of a particular machine-vector 2367 (machvec) in a generic kernel. 2368 Example: machvec=hpzx1_swiotlb 2369 2370 machtype= [Loongson] Share the same kernel image file between different 2371 yeeloong laptop. 2372 Example: machtype=lemote-yeeloong-2f-7inch 2373 2374 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2375 than or equal to this physical address is ignored. 2376 2377 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2378 will bring up during bootup. maxcpus=n : n >= 0 limits 2379 the kernel to bring up 'n' processors. Surely after 2380 bootup you can bring up the other plugged cpu by executing 2381 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2382 only takes effect during system bootup. 2383 While n=0 is a special case, it is equivalent to "nosmp", 2384 which also disables the IO APIC. 2385 2386 max_loop= [LOOP] The number of loop block devices that get 2387 (loop.max_loop) unconditionally pre-created at init time. The default 2388 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2389 of statically allocating a predefined number, loop 2390 devices can be requested on-demand with the 2391 /dev/loop-control interface. 2392 2393 mce [X86-32] Machine Check Exception 2394 2395 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2396 2397 md= [HW] RAID subsystems devices and level 2398 See Documentation/admin-guide/md.rst. 2399 2400 mdacon= [MDA] 2401 Format: <first>,<last> 2402 Specifies range of consoles to be captured by the MDA. 2403 2404 mds= [X86,INTEL] 2405 Control mitigation for the Micro-architectural Data 2406 Sampling (MDS) vulnerability. 2407 2408 Certain CPUs are vulnerable to an exploit against CPU 2409 internal buffers which can forward information to a 2410 disclosure gadget under certain conditions. 2411 2412 In vulnerable processors, the speculatively 2413 forwarded data can be used in a cache side channel 2414 attack, to access data to which the attacker does 2415 not have direct access. 2416 2417 This parameter controls the MDS mitigation. The 2418 options are: 2419 2420 full - Enable MDS mitigation on vulnerable CPUs 2421 full,nosmt - Enable MDS mitigation and disable 2422 SMT on vulnerable CPUs 2423 off - Unconditionally disable MDS mitigation 2424 2425 Not specifying this option is equivalent to 2426 mds=full. 2427 2428 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2429 2430 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2431 Amount of memory to be used when the kernel is not able 2432 to see the whole system memory or for test. 2433 [X86] Work as limiting max address. Use together 2434 with memmap= to avoid physical address space collisions. 2435 Without memmap= PCI devices could be placed at addresses 2436 belonging to unused RAM. 2437 2438 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2439 memory. 2440 2441 memchunk=nn[KMG] 2442 [KNL,SH] Allow user to override the default size for 2443 per-device physically contiguous DMA buffers. 2444 2445 memhp_default_state=online/offline 2446 [KNL] Set the initial state for the memory hotplug 2447 onlining policy. If not specified, the default value is 2448 set according to the 2449 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2450 option. 2451 See Documentation/memory-hotplug.txt. 2452 2453 memmap=exactmap [KNL,X86] Enable setting of an exact 2454 E820 memory map, as specified by the user. 2455 Such memmap=exactmap lines can be constructed based on 2456 BIOS output or other requirements. See the memmap=nn@ss 2457 option description. 2458 2459 memmap=nn[KMG]@ss[KMG] 2460 [KNL] Force usage of a specific region of memory. 2461 Region of memory to be used is from ss to ss+nn. 2462 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2463 which limits max address to nn[KMG]. 2464 Multiple different regions can be specified, 2465 comma delimited. 2466 Example: 2467 memmap=100M@2G,100M#3G,1G!1024G 2468 2469 memmap=nn[KMG]#ss[KMG] 2470 [KNL,ACPI] Mark specific memory as ACPI data. 2471 Region of memory to be marked is from ss to ss+nn. 2472 2473 memmap=nn[KMG]$ss[KMG] 2474 [KNL,ACPI] Mark specific memory as reserved. 2475 Region of memory to be reserved is from ss to ss+nn. 2476 Example: Exclude memory from 0x18690000-0x1869ffff 2477 memmap=64K$0x18690000 2478 or 2479 memmap=0x10000$0x18690000 2480 Some bootloaders may need an escape character before '$', 2481 like Grub2, otherwise '$' and the following number 2482 will be eaten. 2483 2484 memmap=nn[KMG]!ss[KMG] 2485 [KNL,X86] Mark specific memory as protected. 2486 Region of memory to be used, from ss to ss+nn. 2487 The memory region may be marked as e820 type 12 (0xc) 2488 and is NVDIMM or ADR memory. 2489 2490 memmap=<size>%<offset>-<oldtype>+<newtype> 2491 [KNL,ACPI] Convert memory within the specified region 2492 from <oldtype> to <newtype>. If "-<oldtype>" is left 2493 out, the whole region will be marked as <newtype>, 2494 even if previously unavailable. If "+<newtype>" is left 2495 out, matching memory will be removed. Types are 2496 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2497 3 = ACPI, 12 = PRAM. 2498 2499 memory_corruption_check=0/1 [X86] 2500 Some BIOSes seem to corrupt the first 64k of 2501 memory when doing things like suspend/resume. 2502 Setting this option will scan the memory 2503 looking for corruption. Enabling this will 2504 both detect corruption and prevent the kernel 2505 from using the memory being corrupted. 2506 However, its intended as a diagnostic tool; if 2507 repeatable BIOS-originated corruption always 2508 affects the same memory, you can use memmap= 2509 to prevent the kernel from using that memory. 2510 2511 memory_corruption_check_size=size [X86] 2512 By default it checks for corruption in the low 2513 64k, making this memory unavailable for normal 2514 use. Use this parameter to scan for 2515 corruption in more or less memory. 2516 2517 memory_corruption_check_period=seconds [X86] 2518 By default it checks for corruption every 60 2519 seconds. Use this parameter to check at some 2520 other rate. 0 disables periodic checking. 2521 2522 memtest= [KNL,X86,ARM,PPC] Enable memtest 2523 Format: <integer> 2524 default : 0 <disable> 2525 Specifies the number of memtest passes to be 2526 performed. Each pass selects another test 2527 pattern from a given set of patterns. Memtest 2528 fills the memory with this pattern, validates 2529 memory contents and reserves bad memory 2530 regions that are detected. 2531 2532 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2533 Valid arguments: on, off 2534 Default (depends on kernel configuration option): 2535 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2536 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2537 mem_encrypt=on: Activate SME 2538 mem_encrypt=off: Do not activate SME 2539 2540 Refer to Documentation/x86/amd-memory-encryption.txt 2541 for details on when memory encryption can be activated. 2542 2543 mem_sleep_default= [SUSPEND] Default system suspend mode: 2544 s2idle - Suspend-To-Idle 2545 shallow - Power-On Suspend or equivalent (if supported) 2546 deep - Suspend-To-RAM or equivalent (if supported) 2547 See Documentation/admin-guide/pm/sleep-states.rst. 2548 2549 meye.*= [HW] Set MotionEye Camera parameters 2550 See Documentation/media/v4l-drivers/meye.rst. 2551 2552 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2553 Multi-Function General Purpose Timers on AMD Geode 2554 platforms. 2555 2556 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2557 the BIOS has incorrectly applied a workaround. TinyBIOS 2558 version 0.98 is known to be affected, 0.99 fixes the 2559 problem by letting the user disable the workaround. 2560 2561 mga= [HW,DRM] 2562 2563 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2564 physical address is ignored. 2565 2566 mini2440= [ARM,HW,KNL] 2567 Format:[0..2][b][c][t] 2568 Default: "0tb" 2569 MINI2440 configuration specification: 2570 0 - The attached screen is the 3.5" TFT 2571 1 - The attached screen is the 7" TFT 2572 2 - The VGA Shield is attached (1024x768) 2573 Leaving out the screen size parameter will not load 2574 the TFT driver, and the framebuffer will be left 2575 unconfigured. 2576 b - Enable backlight. The TFT backlight pin will be 2577 linked to the kernel VESA blanking code and a GPIO 2578 LED. This parameter is not necessary when using the 2579 VGA shield. 2580 c - Enable the s3c camera interface. 2581 t - Reserved for enabling touchscreen support. The 2582 touchscreen support is not enabled in the mainstream 2583 kernel as of 2.6.30, a preliminary port can be found 2584 in the "bleeding edge" mini2440 support kernel at 2585 http://repo.or.cz/w/linux-2.6/mini2440.git 2586 2587 mitigations= 2588 [X86,PPC,S390,ARM64] Control optional mitigations for 2589 CPU vulnerabilities. This is a set of curated, 2590 arch-independent options, each of which is an 2591 aggregation of existing arch-specific options. 2592 2593 off 2594 Disable all optional CPU mitigations. This 2595 improves system performance, but it may also 2596 expose users to several CPU vulnerabilities. 2597 Equivalent to: nopti [X86,PPC] 2598 kpti=0 [ARM64] 2599 nospectre_v1 [PPC] 2600 nobp=0 [S390] 2601 nospectre_v2 [X86,PPC,S390,ARM64] 2602 spectre_v2_user=off [X86] 2603 spec_store_bypass_disable=off [X86,PPC] 2604 ssbd=force-off [ARM64] 2605 l1tf=off [X86] 2606 mds=off [X86] 2607 2608 auto (default) 2609 Mitigate all CPU vulnerabilities, but leave SMT 2610 enabled, even if it's vulnerable. This is for 2611 users who don't want to be surprised by SMT 2612 getting disabled across kernel upgrades, or who 2613 have other ways of avoiding SMT-based attacks. 2614 Equivalent to: (default behavior) 2615 2616 auto,nosmt 2617 Mitigate all CPU vulnerabilities, disabling SMT 2618 if needed. This is for users who always want to 2619 be fully mitigated, even if it means losing SMT. 2620 Equivalent to: l1tf=flush,nosmt [X86] 2621 mds=full,nosmt [X86] 2622 2623 mminit_loglevel= 2624 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2625 parameter allows control of the logging verbosity for 2626 the additional memory initialisation checks. A value 2627 of 0 disables mminit logging and a level of 4 will 2628 log everything. Information is printed at KERN_DEBUG 2629 so loglevel=8 may also need to be specified. 2630 2631 module.sig_enforce 2632 [KNL] When CONFIG_MODULE_SIG is set, this means that 2633 modules without (valid) signatures will fail to load. 2634 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2635 is always true, so this option does nothing. 2636 2637 module_blacklist= [KNL] Do not load a comma-separated list of 2638 modules. Useful for debugging problem modules. 2639 2640 mousedev.tap_time= 2641 [MOUSE] Maximum time between finger touching and 2642 leaving touchpad surface for touch to be considered 2643 a tap and be reported as a left button click (for 2644 touchpads working in absolute mode only). 2645 Format: <msecs> 2646 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2647 reporting absolute coordinates, such as tablets 2648 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2649 reporting absolute coordinates, such as tablets 2650 2651 movablecore= [KNL,X86,IA-64,PPC] 2652 Format: nn[KMGTPE] | nn% 2653 This parameter is the complement to kernelcore=, it 2654 specifies the amount of memory used for migratable 2655 allocations. If both kernelcore and movablecore is 2656 specified, then kernelcore will be at *least* the 2657 specified value but may be more. If movablecore on its 2658 own is specified, the administrator must be careful 2659 that the amount of memory usable for all allocations 2660 is not too small. 2661 2662 movable_node [KNL] Boot-time switch to make hotplugable memory 2663 NUMA nodes to be movable. This means that the memory 2664 of such nodes will be usable only for movable 2665 allocations which rules out almost all kernel 2666 allocations. Use with caution! 2667 2668 MTD_Partition= [MTD] 2669 Format: <name>,<region-number>,<size>,<offset> 2670 2671 MTD_Region= [MTD] Format: 2672 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2673 2674 mtdparts= [MTD] 2675 See drivers/mtd/cmdlinepart.c. 2676 2677 multitce=off [PPC] This parameter disables the use of the pSeries 2678 firmware feature for updating multiple TCE entries 2679 at a time. 2680 2681 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2682 2683 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2684 2685 boundary - index of last SLC block on Flex-OneNAND. 2686 The remaining blocks are configured as MLC blocks. 2687 lock - Configure if Flex-OneNAND boundary should be locked. 2688 Once locked, the boundary cannot be changed. 2689 1 indicates lock status, 0 indicates unlock status. 2690 2691 mtdset= [ARM] 2692 ARM/S3C2412 JIVE boot control 2693 2694 See arch/arm/mach-s3c2412/mach-jive.c 2695 2696 mtouchusb.raw_coordinates= 2697 [HW] Make the MicroTouch USB driver use raw coordinates 2698 ('y', default) or cooked coordinates ('n') 2699 2700 mtrr_chunk_size=nn[KMG] [X86] 2701 used for mtrr cleanup. It is largest continuous chunk 2702 that could hold holes aka. UC entries. 2703 2704 mtrr_gran_size=nn[KMG] [X86] 2705 Used for mtrr cleanup. It is granularity of mtrr block. 2706 Default is 1. 2707 Large value could prevent small alignment from 2708 using up MTRRs. 2709 2710 mtrr_spare_reg_nr=n [X86] 2711 Format: <integer> 2712 Range: 0,7 : spare reg number 2713 Default : 1 2714 Used for mtrr cleanup. It is spare mtrr entries number. 2715 Set to 2 or more if your graphical card needs more. 2716 2717 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2718 2719 netdev= [NET] Network devices parameters 2720 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2721 Note that mem_start is often overloaded to mean 2722 something different and driver-specific. 2723 This usage is only documented in each driver source 2724 file if at all. 2725 2726 nf_conntrack.acct= 2727 [NETFILTER] Enable connection tracking flow accounting 2728 0 to disable accounting 2729 1 to enable accounting 2730 Default value is 0. 2731 2732 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2733 See Documentation/filesystems/nfs/nfsroot.txt. 2734 2735 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2736 See Documentation/filesystems/nfs/nfsroot.txt. 2737 2738 nfsrootdebug [NFS] enable nfsroot debugging messages. 2739 See Documentation/filesystems/nfs/nfsroot.txt. 2740 2741 nfs.callback_nr_threads= 2742 [NFSv4] set the total number of threads that the 2743 NFS client will assign to service NFSv4 callback 2744 requests. 2745 2746 nfs.callback_tcpport= 2747 [NFS] set the TCP port on which the NFSv4 callback 2748 channel should listen. 2749 2750 nfs.cache_getent= 2751 [NFS] sets the pathname to the program which is used 2752 to update the NFS client cache entries. 2753 2754 nfs.cache_getent_timeout= 2755 [NFS] sets the timeout after which an attempt to 2756 update a cache entry is deemed to have failed. 2757 2758 nfs.idmap_cache_timeout= 2759 [NFS] set the maximum lifetime for idmapper cache 2760 entries. 2761 2762 nfs.enable_ino64= 2763 [NFS] enable 64-bit inode numbers. 2764 If zero, the NFS client will fake up a 32-bit inode 2765 number for the readdir() and stat() syscalls instead 2766 of returning the full 64-bit number. 2767 The default is to return 64-bit inode numbers. 2768 2769 nfs.max_session_cb_slots= 2770 [NFSv4.1] Sets the maximum number of session 2771 slots the client will assign to the callback 2772 channel. This determines the maximum number of 2773 callbacks the client will process in parallel for 2774 a particular server. 2775 2776 nfs.max_session_slots= 2777 [NFSv4.1] Sets the maximum number of session slots 2778 the client will attempt to negotiate with the server. 2779 This limits the number of simultaneous RPC requests 2780 that the client can send to the NFSv4.1 server. 2781 Note that there is little point in setting this 2782 value higher than the max_tcp_slot_table_limit. 2783 2784 nfs.nfs4_disable_idmapping= 2785 [NFSv4] When set to the default of '1', this option 2786 ensures that both the RPC level authentication 2787 scheme and the NFS level operations agree to use 2788 numeric uids/gids if the mount is using the 2789 'sec=sys' security flavour. In effect it is 2790 disabling idmapping, which can make migration from 2791 legacy NFSv2/v3 systems to NFSv4 easier. 2792 Servers that do not support this mode of operation 2793 will be autodetected by the client, and it will fall 2794 back to using the idmapper. 2795 To turn off this behaviour, set the value to '0'. 2796 nfs.nfs4_unique_id= 2797 [NFS4] Specify an additional fixed unique ident- 2798 ification string that NFSv4 clients can insert into 2799 their nfs_client_id4 string. This is typically a 2800 UUID that is generated at system install time. 2801 2802 nfs.send_implementation_id = 2803 [NFSv4.1] Send client implementation identification 2804 information in exchange_id requests. 2805 If zero, no implementation identification information 2806 will be sent. 2807 The default is to send the implementation identification 2808 information. 2809 2810 nfs.recover_lost_locks = 2811 [NFSv4] Attempt to recover locks that were lost due 2812 to a lease timeout on the server. Please note that 2813 doing this risks data corruption, since there are 2814 no guarantees that the file will remain unchanged 2815 after the locks are lost. 2816 If you want to enable the kernel legacy behaviour of 2817 attempting to recover these locks, then set this 2818 parameter to '1'. 2819 The default parameter value of '0' causes the kernel 2820 not to attempt recovery of lost locks. 2821 2822 nfs4.layoutstats_timer = 2823 [NFSv4.2] Change the rate at which the kernel sends 2824 layoutstats to the pNFS metadata server. 2825 2826 Setting this to value to 0 causes the kernel to use 2827 whatever value is the default set by the layout 2828 driver. A non-zero value sets the minimum interval 2829 in seconds between layoutstats transmissions. 2830 2831 nfsd.nfs4_disable_idmapping= 2832 [NFSv4] When set to the default of '1', the NFSv4 2833 server will return only numeric uids and gids to 2834 clients using auth_sys, and will accept numeric uids 2835 and gids from such clients. This is intended to ease 2836 migration from NFSv2/v3. 2837 2838 nmi_debug= [KNL,SH] Specify one or more actions to take 2839 when a NMI is triggered. 2840 Format: [state][,regs][,debounce][,die] 2841 2842 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2843 Format: [panic,][nopanic,][num] 2844 Valid num: 0 or 1 2845 0 - turn hardlockup detector in nmi_watchdog off 2846 1 - turn hardlockup detector in nmi_watchdog on 2847 When panic is specified, panic when an NMI watchdog 2848 timeout occurs (or 'nopanic' to override the opposite 2849 default). To disable both hard and soft lockup detectors, 2850 please see 'nowatchdog'. 2851 This is useful when you use a panic=... timeout and 2852 need the box quickly up again. 2853 2854 These settings can be accessed at runtime via 2855 the nmi_watchdog and hardlockup_panic sysctls. 2856 2857 netpoll.carrier_timeout= 2858 [NET] Specifies amount of time (in seconds) that 2859 netpoll should wait for a carrier. By default netpoll 2860 waits 4 seconds. 2861 2862 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2863 emulation library even if a 387 maths coprocessor 2864 is present. 2865 2866 no5lvl [X86-64] Disable 5-level paging mode. Forces 2867 kernel to use 4-level paging instead. 2868 2869 no_console_suspend 2870 [HW] Never suspend the console 2871 Disable suspending of consoles during suspend and 2872 hibernate operations. Once disabled, debugging 2873 messages can reach various consoles while the rest 2874 of the system is being put to sleep (ie, while 2875 debugging driver suspend/resume hooks). This may 2876 not work reliably with all consoles, but is known 2877 to work with serial and VGA consoles. 2878 To facilitate more flexible debugging, we also add 2879 console_suspend, a printk module parameter to control 2880 it. Users could use console_suspend (usually 2881 /sys/module/printk/parameters/console_suspend) to 2882 turn on/off it dynamically. 2883 2884 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2885 caches in the slab allocator. Saves per-node memory, 2886 but will impact performance. 2887 2888 noalign [KNL,ARM] 2889 2890 noaltinstr [S390] Disables alternative instructions patching 2891 (CPU alternatives feature). 2892 2893 noapic [SMP,APIC] Tells the kernel to not make use of any 2894 IOAPICs that may be present in the system. 2895 2896 noautogroup Disable scheduler automatic task group creation. 2897 2898 nobats [PPC] Do not use BATs for mapping kernel lowmem 2899 on "Classic" PPC cores. 2900 2901 nocache [ARM] 2902 2903 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2904 2905 nodelayacct [KNL] Disable per-task delay accounting 2906 2907 nodsp [SH] Disable hardware DSP at boot time. 2908 2909 noefi Disable EFI runtime services support. 2910 2911 noexec [IA-64] 2912 2913 noexec [X86] 2914 On X86-32 available only on PAE configured kernels. 2915 noexec=on: enable non-executable mappings (default) 2916 noexec=off: disable non-executable mappings 2917 2918 nosmap [X86,PPC] 2919 Disable SMAP (Supervisor Mode Access Prevention) 2920 even if it is supported by processor. 2921 2922 nosmep [X86,PPC] 2923 Disable SMEP (Supervisor Mode Execution Prevention) 2924 even if it is supported by processor. 2925 2926 noexec32 [X86-64] 2927 This affects only 32-bit executables. 2928 noexec32=on: enable non-executable mappings (default) 2929 read doesn't imply executable mappings 2930 noexec32=off: disable non-executable mappings 2931 read implies executable mappings 2932 2933 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2934 2935 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2936 register save and restore. The kernel will only save 2937 legacy floating-point registers on task switch. 2938 2939 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2940 2941 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2942 Equivalent to smt=1. 2943 2944 [KNL,x86] Disable symmetric multithreading (SMT). 2945 nosmt=force: Force disable SMT, cannot be undone 2946 via the sysfs control file. 2947 2948 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds 2949 check bypass). With this option data leaks are possible 2950 in the system. 2951 2952 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 2953 the Spectre variant 2 (indirect branch prediction) 2954 vulnerability. System may allow data leaks with this 2955 option. 2956 2957 nospec_store_bypass_disable 2958 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2959 2960 noxsave [BUGS=X86] Disables x86 extended register state save 2961 and restore using xsave. The kernel will fallback to 2962 enabling legacy floating-point and sse state. 2963 2964 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2965 register states. The kernel will fall back to use 2966 xsave to save the states. By using this parameter, 2967 performance of saving the states is degraded because 2968 xsave doesn't support modified optimization while 2969 xsaveopt supports it on xsaveopt enabled systems. 2970 2971 noxsaves [X86] Disables xsaves and xrstors used in saving and 2972 restoring x86 extended register state in compacted 2973 form of xsave area. The kernel will fall back to use 2974 xsaveopt and xrstor to save and restore the states 2975 in standard form of xsave area. By using this 2976 parameter, xsave area per process might occupy more 2977 memory on xsaves enabled systems. 2978 2979 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2980 wfi(ARM) instruction doesn't work correctly and not to 2981 use it. This is also useful when using JTAG debugger. 2982 2983 no_file_caps Tells the kernel not to honor file capabilities. The 2984 only way then for a file to be executed with privilege 2985 is to be setuid root or executed by root. 2986 2987 nohalt [IA-64] Tells the kernel not to use the power saving 2988 function PAL_HALT_LIGHT when idle. This increases 2989 power-consumption. On the positive side, it reduces 2990 interrupt wake-up latency, which may improve performance 2991 in certain environments such as networked servers or 2992 real-time systems. 2993 2994 nohibernate [HIBERNATION] Disable hibernation and resume. 2995 2996 nohz= [KNL] Boottime enable/disable dynamic ticks 2997 Valid arguments: on, off 2998 Default: on 2999 3000 nohz_full= [KNL,BOOT,SMP,ISOL] 3001 The argument is a cpu list, as described above. 3002 In kernels built with CONFIG_NO_HZ_FULL=y, set 3003 the specified list of CPUs whose tick will be stopped 3004 whenever possible. The boot CPU will be forced outside 3005 the range to maintain the timekeeping. Any CPUs 3006 in this list will have their RCU callbacks offloaded, 3007 just as if they had also been called out in the 3008 rcu_nocbs= boot parameter. 3009 3010 noiotrap [SH] Disables trapped I/O port accesses. 3011 3012 noirqdebug [X86-32] Disables the code which attempts to detect and 3013 disable unhandled interrupt sources. 3014 3015 no_timer_check [X86,APIC] Disables the code which tests for 3016 broken timer IRQ sources. 3017 3018 noisapnp [ISAPNP] Disables ISA PnP code. 3019 3020 noinitrd [RAM] Tells the kernel not to load any configured 3021 initial RAM disk. 3022 3023 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3024 remapping. 3025 [Deprecated - use intremap=off] 3026 3027 nointroute [IA-64] 3028 3029 noinvpcid [X86] Disable the INVPCID cpu feature. 3030 3031 nojitter [IA-64] Disables jitter checking for ITC timers. 3032 3033 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3034 3035 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3036 fault handling. 3037 3038 no-vmw-sched-clock 3039 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3040 clock and use the default one. 3041 3042 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3043 steal time is computed, but won't influence scheduler 3044 behaviour 3045 3046 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3047 3048 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3049 3050 noltlbs [PPC] Do not use large page/tlb entries for kernel 3051 lowmem mapping on PPC40x and PPC8xx 3052 3053 nomca [IA-64] Disable machine check abort handling 3054 3055 nomce [X86-32] Disable Machine Check Exception 3056 3057 nomfgpt [X86-32] Disable Multi-Function General Purpose 3058 Timer usage (for AMD Geode machines). 3059 3060 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3061 shutdown the other cpus. Instead use the REBOOT_VECTOR 3062 irq. 3063 3064 nomodule Disable module load 3065 3066 nopat [X86] Disable PAT (page attribute table extension of 3067 pagetables) support. 3068 3069 nopcid [X86-64] Disable the PCID cpu feature. 3070 3071 norandmaps Don't use address space randomization. Equivalent to 3072 echo 0 > /proc/sys/kernel/randomize_va_space 3073 3074 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3075 with UP alternatives 3076 3077 nordrand [X86] Disable kernel use of the RDRAND and 3078 RDSEED instructions even if they are supported 3079 by the processor. RDRAND and RDSEED are still 3080 available to user space applications. 3081 3082 noresume [SWSUSP] Disables resume and restores original swap 3083 space. 3084 3085 no-scroll [VGA] Disables scrollback. 3086 This is required for the Braillex ib80-piezo Braille 3087 reader made by F.H. Papenmeier (Germany). 3088 3089 nosbagart [IA-64] 3090 3091 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3092 3093 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3094 and disable the IO APIC. legacy for "maxcpus=0". 3095 3096 nosoftlockup [KNL] Disable the soft-lockup detector. 3097 3098 nosync [HW,M68K] Disables sync negotiation for all devices. 3099 3100 nowatchdog [KNL] Disable both lockup detectors, i.e. 3101 soft-lockup and NMI watchdog (hard-lockup). 3102 3103 nowb [ARM] 3104 3105 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3106 3107 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3108 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3109 Some features depend on CPU0. Known dependencies are: 3110 1. Resume from suspend/hibernate depends on CPU0. 3111 Suspend/hibernate will fail if CPU0 is offline and you 3112 need to online CPU0 before suspend/hibernate. 3113 2. PIC interrupts also depend on CPU0. CPU0 can't be 3114 removed if a PIC interrupt is detected. 3115 It's said poweroff/reboot may depend on CPU0 on some 3116 machines although I haven't seen such issues so far 3117 after CPU0 is offline on a few tested machines. 3118 If the dependencies are under your control, you can 3119 turn on cpu0_hotplug. 3120 3121 nps_mtm_hs_ctr= [KNL,ARC] 3122 This parameter sets the maximum duration, in 3123 cycles, each HW thread of the CTOP can run 3124 without interruptions, before HW switches it. 3125 The actual maximum duration is 16 times this 3126 parameter's value. 3127 Format: integer between 1 and 255 3128 Default: 255 3129 3130 nptcg= [IA-64] Override max number of concurrent global TLB 3131 purges which is reported from either PAL_VM_SUMMARY or 3132 SAL PALO. 3133 3134 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3135 could support. nr_cpus=n : n >= 1 limits the kernel to 3136 support 'n' processors. It could be larger than the 3137 number of already plugged CPU during bootup, later in 3138 runtime you can physically add extra cpu until it reaches 3139 n. So during boot up some boot time memory for per-cpu 3140 variables need be pre-allocated for later physical cpu 3141 hot plugging. 3142 3143 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3144 3145 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3146 Allowed values are enable and disable 3147 3148 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3149 'node', 'default' can be specified 3150 This can be set from sysctl after boot. 3151 See Documentation/sysctl/vm.txt for details. 3152 3153 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3154 See Documentation/debugging-via-ohci1394.txt for more 3155 info. 3156 3157 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3158 Rather than timing out after 20 ms if an EC 3159 command is not properly ACKed, override the length 3160 of the timeout. We have interrupts disabled while 3161 waiting for the ACK, so if this is set too high 3162 interrupts *may* be lost! 3163 3164 omap_mux= [OMAP] Override bootloader pin multiplexing. 3165 Format: <mux_mode0.mode_name=value>... 3166 For example, to override I2C bus2: 3167 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3168 3169 oprofile.timer= [HW] 3170 Use timer interrupt instead of performance counters 3171 3172 oprofile.cpu_type= Force an oprofile cpu type 3173 This might be useful if you have an older oprofile 3174 userland or if you want common events. 3175 Format: { arch_perfmon } 3176 arch_perfmon: [X86] Force use of architectural 3177 perfmon on Intel CPUs instead of the 3178 CPU specific event set. 3179 timer: [X86] Force use of architectural NMI 3180 timer mode (see also oprofile.timer 3181 for generic hr timer mode) 3182 3183 oops=panic Always panic on oopses. Default is to just kill the 3184 process, but there is a small probability of 3185 deadlocking the machine. 3186 This will also cause panics on machine check exceptions. 3187 Useful together with panic=30 to trigger a reboot. 3188 3189 page_alloc.shuffle= 3190 [KNL] Boolean flag to control whether the page allocator 3191 should randomize its free lists. The randomization may 3192 be automatically enabled if the kernel detects it is 3193 running on a platform with a direct-mapped memory-side 3194 cache, and this parameter can be used to 3195 override/disable that behavior. The state of the flag 3196 can be read from sysfs at: 3197 /sys/module/page_alloc/parameters/shuffle. 3198 3199 page_owner= [KNL] Boot-time page_owner enabling option. 3200 Storage of the information about who allocated 3201 each page is disabled in default. With this switch, 3202 we can turn it on. 3203 on: enable the feature 3204 3205 page_poison= [KNL] Boot-time parameter changing the state of 3206 poisoning on the buddy allocator, available with 3207 CONFIG_PAGE_POISONING=y. 3208 off: turn off poisoning (default) 3209 on: turn on poisoning 3210 3211 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3212 timeout > 0: seconds before rebooting 3213 timeout = 0: wait forever 3214 timeout < 0: reboot immediately 3215 Format: <timeout> 3216 3217 panic_print= Bitmask for printing system info when panic happens. 3218 User can chose combination of the following bits: 3219 bit 0: print all tasks info 3220 bit 1: print system memory info 3221 bit 2: print timer info 3222 bit 3: print locks info if CONFIG_LOCKDEP is on 3223 bit 4: print ftrace buffer 3224 bit 5: print all printk messages in buffer 3225 3226 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3227 on a WARN(). 3228 3229 crash_kexec_post_notifiers 3230 Run kdump after running panic-notifiers and dumping 3231 kmsg. This only for the users who doubt kdump always 3232 succeeds in any situation. 3233 Note that this also increases risks of kdump failure, 3234 because some panic notifiers can make the crashed 3235 kernel more unstable. 3236 3237 parkbd.port= [HW] Parallel port number the keyboard adapter is 3238 connected to, default is 0. 3239 Format: <parport#> 3240 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3241 0 for XT, 1 for AT (default is AT). 3242 Format: <mode> 3243 3244 parport= [HW,PPT] Specify parallel ports. 0 disables. 3245 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3246 Use 'auto' to force the driver to use any 3247 IRQ/DMA settings detected (the default is to 3248 ignore detected IRQ/DMA settings because of 3249 possible conflicts). You can specify the base 3250 address, IRQ, and DMA settings; IRQ and DMA 3251 should be numbers, or 'auto' (for using detected 3252 settings on that particular port), or 'nofifo' 3253 (to avoid using a FIFO even if it is detected). 3254 Parallel ports are assigned in the order they 3255 are specified on the command line, starting 3256 with parport0. 3257 3258 parport_init_mode= [HW,PPT] 3259 Configure VIA parallel port to operate in 3260 a specific mode. This is necessary on Pegasos 3261 computer where firmware has no options for setting 3262 up parallel port mode and sets it to spp. 3263 Currently this function knows 686a and 8231 chips. 3264 Format: [spp|ps2|epp|ecp|ecpepp] 3265 3266 pause_on_oops= 3267 Halt all CPUs after the first oops has been printed for 3268 the specified number of seconds. This is to be used if 3269 your oopses keep scrolling off the screen. 3270 3271 pcbit= [HW,ISDN] 3272 3273 pcd. [PARIDE] 3274 See header of drivers/block/paride/pcd.c. 3275 See also Documentation/blockdev/paride.txt. 3276 3277 pci=option[,option...] [PCI] various PCI subsystem options. 3278 3279 Some options herein operate on a specific device 3280 or a set of devices (<pci_dev>). These are 3281 specified in one of the following formats: 3282 3283 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3284 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3285 3286 Note: the first format specifies a PCI 3287 bus/device/function address which may change 3288 if new hardware is inserted, if motherboard 3289 firmware changes, or due to changes caused 3290 by other kernel parameters. If the 3291 domain is left unspecified, it is 3292 taken to be zero. Optionally, a path 3293 to a device through multiple device/function 3294 addresses can be specified after the base 3295 address (this is more robust against 3296 renumbering issues). The second format 3297 selects devices using IDs from the 3298 configuration space which may match multiple 3299 devices in the system. 3300 3301 earlydump dump PCI config space before the kernel 3302 changes anything 3303 off [X86] don't probe for the PCI bus 3304 bios [X86-32] force use of PCI BIOS, don't access 3305 the hardware directly. Use this if your machine 3306 has a non-standard PCI host bridge. 3307 nobios [X86-32] disallow use of PCI BIOS, only direct 3308 hardware access methods are allowed. Use this 3309 if you experience crashes upon bootup and you 3310 suspect they are caused by the BIOS. 3311 conf1 [X86] Force use of PCI Configuration Access 3312 Mechanism 1 (config address in IO port 0xCF8, 3313 data in IO port 0xCFC, both 32-bit). 3314 conf2 [X86] Force use of PCI Configuration Access 3315 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3316 the function, IO port 0xCFA, also 8-bit, sets 3317 bus number. The config space is then accessed 3318 through ports 0xC000-0xCFFF). 3319 See http://wiki.osdev.org/PCI for more info 3320 on the configuration access mechanisms. 3321 noaer [PCIE] If the PCIEAER kernel config parameter is 3322 enabled, this kernel boot option can be used to 3323 disable the use of PCIE advanced error reporting. 3324 nodomains [PCI] Disable support for multiple PCI 3325 root domains (aka PCI segments, in ACPI-speak). 3326 nommconf [X86] Disable use of MMCONFIG for PCI 3327 Configuration 3328 check_enable_amd_mmconf [X86] check for and enable 3329 properly configured MMIO access to PCI 3330 config space on AMD family 10h CPU 3331 nomsi [MSI] If the PCI_MSI kernel config parameter is 3332 enabled, this kernel boot option can be used to 3333 disable the use of MSI interrupts system-wide. 3334 noioapicquirk [APIC] Disable all boot interrupt quirks. 3335 Safety option to keep boot IRQs enabled. This 3336 should never be necessary. 3337 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3338 primary IO-APIC for bridges that cannot disable 3339 boot IRQs. This fixes a source of spurious IRQs 3340 when the system masks IRQs. 3341 noioapicreroute [APIC] Disable workaround that uses the 3342 boot IRQ equivalent of an IRQ that connects to 3343 a chipset where boot IRQs cannot be disabled. 3344 The opposite of ioapicreroute. 3345 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3346 routing table. These calls are known to be buggy 3347 on several machines and they hang the machine 3348 when used, but on other computers it's the only 3349 way to get the interrupt routing table. Try 3350 this option if the kernel is unable to allocate 3351 IRQs or discover secondary PCI buses on your 3352 motherboard. 3353 rom [X86] Assign address space to expansion ROMs. 3354 Use with caution as certain devices share 3355 address decoders between ROMs and other 3356 resources. 3357 norom [X86] Do not assign address space to 3358 expansion ROMs that do not already have 3359 BIOS assigned address ranges. 3360 nobar [X86] Do not assign address space to the 3361 BARs that weren't assigned by the BIOS. 3362 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3363 assigned automatically to PCI devices. You can 3364 make the kernel exclude IRQs of your ISA cards 3365 this way. 3366 pirqaddr=0xAAAAA [X86] Specify the physical address 3367 of the PIRQ table (normally generated 3368 by the BIOS) if it is outside the 3369 F0000h-100000h range. 3370 lastbus=N [X86] Scan all buses thru bus #N. Can be 3371 useful if the kernel is unable to find your 3372 secondary buses and you want to tell it 3373 explicitly which ones they are. 3374 assign-busses [X86] Always assign all PCI bus 3375 numbers ourselves, overriding 3376 whatever the firmware may have done. 3377 usepirqmask [X86] Honor the possible IRQ mask stored 3378 in the BIOS $PIR table. This is needed on 3379 some systems with broken BIOSes, notably 3380 some HP Pavilion N5400 and Omnibook XE3 3381 notebooks. This will have no effect if ACPI 3382 IRQ routing is enabled. 3383 noacpi [X86] Do not use ACPI for IRQ routing 3384 or for PCI scanning. 3385 use_crs [X86] Use PCI host bridge window information 3386 from ACPI. On BIOSes from 2008 or later, this 3387 is enabled by default. If you need to use this, 3388 please report a bug. 3389 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3390 If you need to use this, please report a bug. 3391 routeirq Do IRQ routing for all PCI devices. 3392 This is normally done in pci_enable_device(), 3393 so this option is a temporary workaround 3394 for broken drivers that don't call it. 3395 skip_isa_align [X86] do not align io start addr, so can 3396 handle more pci cards 3397 noearly [X86] Don't do any early type 1 scanning. 3398 This might help on some broken boards which 3399 machine check when some devices' config space 3400 is read. But various workarounds are disabled 3401 and some IOMMU drivers will not work. 3402 bfsort Sort PCI devices into breadth-first order. 3403 This sorting is done to get a device 3404 order compatible with older (<= 2.4) kernels. 3405 nobfsort Don't sort PCI devices into breadth-first order. 3406 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3407 tuning and use the BIOS-configured MPS defaults. 3408 pcie_bus_safe Set every device's MPS to the largest value 3409 supported by all devices below the root complex. 3410 pcie_bus_perf Set device MPS to the largest allowable MPS 3411 based on its parent bus. Also set MRRS (Max 3412 Read Request Size) to the largest supported 3413 value (no larger than the MPS that the device 3414 or bus can support) for best performance. 3415 pcie_bus_peer2peer Set every device's MPS to 128B, which 3416 every device is guaranteed to support. This 3417 configuration allows peer-to-peer DMA between 3418 any pair of devices, possibly at the cost of 3419 reduced performance. This also guarantees 3420 that hot-added devices will work. 3421 cbiosize=nn[KMG] The fixed amount of bus space which is 3422 reserved for the CardBus bridge's IO window. 3423 The default value is 256 bytes. 3424 cbmemsize=nn[KMG] The fixed amount of bus space which is 3425 reserved for the CardBus bridge's memory 3426 window. The default value is 64 megabytes. 3427 resource_alignment= 3428 Format: 3429 [<order of align>@]<pci_dev>[; ...] 3430 Specifies alignment and device to reassign 3431 aligned memory resources. How to 3432 specify the device is described above. 3433 If <order of align> is not specified, 3434 PAGE_SIZE is used as alignment. 3435 PCI-PCI bridge can be specified, if resource 3436 windows need to be expanded. 3437 To specify the alignment for several 3438 instances of a device, the PCI vendor, 3439 device, subvendor, and subdevice may be 3440 specified, e.g., 4096@pci:8086:9c22:103c:198f 3441 ecrc= Enable/disable PCIe ECRC (transaction layer 3442 end-to-end CRC checking). 3443 bios: Use BIOS/firmware settings. This is the 3444 the default. 3445 off: Turn ECRC off 3446 on: Turn ECRC on. 3447 hpiosize=nn[KMG] The fixed amount of bus space which is 3448 reserved for hotplug bridge's IO window. 3449 Default size is 256 bytes. 3450 hpmemsize=nn[KMG] The fixed amount of bus space which is 3451 reserved for hotplug bridge's memory window. 3452 Default size is 2 megabytes. 3453 hpbussize=nn The minimum amount of additional bus numbers 3454 reserved for buses below a hotplug bridge. 3455 Default is 1. 3456 realloc= Enable/disable reallocating PCI bridge resources 3457 if allocations done by BIOS are too small to 3458 accommodate resources required by all child 3459 devices. 3460 off: Turn realloc off 3461 on: Turn realloc on 3462 realloc same as realloc=on 3463 noari do not use PCIe ARI. 3464 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3465 do not use PCIe ATS (and IOMMU device IOTLB). 3466 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3467 only look for one device below a PCIe downstream 3468 port. 3469 big_root_window Try to add a big 64bit memory window to the PCIe 3470 root complex on AMD CPUs. Some GFX hardware 3471 can resize a BAR to allow access to all VRAM. 3472 Adding the window is slightly risky (it may 3473 conflict with unreported devices), so this 3474 taints the kernel. 3475 disable_acs_redir=<pci_dev>[; ...] 3476 Specify one or more PCI devices (in the format 3477 specified above) separated by semicolons. 3478 Each device specified will have the PCI ACS 3479 redirect capabilities forced off which will 3480 allow P2P traffic between devices through 3481 bridges without forcing it upstream. Note: 3482 this removes isolation between devices and 3483 may put more devices in an IOMMU group. 3484 force_floating [S390] Force usage of floating interrupts. 3485 nomio [S390] Do not use MIO instructions. 3486 3487 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3488 Management. 3489 off Disable ASPM. 3490 force Enable ASPM even on devices that claim not to support it. 3491 WARNING: Forcing ASPM on may cause system lockups. 3492 3493 pcie_ports= [PCIE] PCIe port services handling: 3494 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3495 even if the platform doesn't give the OS permission to 3496 use them. This may cause conflicts if the platform 3497 also tries to use these services. 3498 compat Disable native PCIe services (PME, AER, DPC, PCIe 3499 hotplug). 3500 3501 pcie_port_pm= [PCIE] PCIe port power management handling: 3502 off Disable power management of all PCIe ports 3503 force Forcibly enable power management of all PCIe ports 3504 3505 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3506 nomsi Do not use MSI for native PCIe PME signaling (this makes 3507 all PCIe root ports use INTx for all services). 3508 3509 pcmv= [HW,PCMCIA] BadgePAD 4 3510 3511 pd_ignore_unused 3512 [PM] 3513 Keep all power-domains already enabled by bootloader on, 3514 even if no driver has claimed them. This is useful 3515 for debug and development, but should not be 3516 needed on a platform with proper driver support. 3517 3518 pd. [PARIDE] 3519 See Documentation/blockdev/paride.txt. 3520 3521 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3522 boot time. 3523 Format: { 0 | 1 } 3524 See arch/parisc/kernel/pdc_chassis.c 3525 3526 percpu_alloc= Select which percpu first chunk allocator to use. 3527 Currently supported values are "embed" and "page". 3528 Archs may support subset or none of the selections. 3529 See comments in mm/percpu.c for details on each 3530 allocator. This parameter is primarily for debugging 3531 and performance comparison. 3532 3533 pf. [PARIDE] 3534 See Documentation/blockdev/paride.txt. 3535 3536 pg. [PARIDE] 3537 See Documentation/blockdev/paride.txt. 3538 3539 pirq= [SMP,APIC] Manual mp-table setup 3540 See Documentation/x86/i386/IO-APIC.txt. 3541 3542 plip= [PPT,NET] Parallel port network link 3543 Format: { parport<nr> | timid | 0 } 3544 See also Documentation/admin-guide/parport.rst. 3545 3546 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3547 Override pmtimer IOPort with a hex value. 3548 e.g. pmtmr=0x508 3549 3550 pnp.debug=1 [PNP] 3551 Enable PNP debug messages (depends on the 3552 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3553 via /sys/module/pnp/parameters/debug. We always show 3554 current resource usage; turning this on also shows 3555 possible settings and some assignment information. 3556 3557 pnpacpi= [ACPI] 3558 { off } 3559 3560 pnpbios= [ISAPNP] 3561 { on | off | curr | res | no-curr | no-res } 3562 3563 pnp_reserve_irq= 3564 [ISAPNP] Exclude IRQs for the autoconfiguration 3565 3566 pnp_reserve_dma= 3567 [ISAPNP] Exclude DMAs for the autoconfiguration 3568 3569 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3570 Ranges are in pairs (I/O port base and size). 3571 3572 pnp_reserve_mem= 3573 [ISAPNP] Exclude memory regions for the 3574 autoconfiguration. 3575 Ranges are in pairs (memory base and size). 3576 3577 ports= [IP_VS_FTP] IPVS ftp helper module 3578 Default is 21. 3579 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3580 may be specified. 3581 Format: <port>,<port>.... 3582 3583 powersave=off [PPC] This option disables power saving features. 3584 It specifically disables cpuidle and sets the 3585 platform machine description specific power_save 3586 function to NULL. On Idle the CPU just reduces 3587 execution priority. 3588 3589 ppc_strict_facility_enable 3590 [PPC] This option catches any kernel floating point, 3591 Altivec, VSX and SPE outside of regions specifically 3592 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3593 There is some performance impact when enabling this. 3594 3595 ppc_tm= [PPC] 3596 Format: {"off"} 3597 Disable Hardware Transactional Memory 3598 3599 print-fatal-signals= 3600 [KNL] debug: print fatal signals 3601 3602 If enabled, warn about various signal handling 3603 related application anomalies: too many signals, 3604 too many POSIX.1 timers, fatal signals causing a 3605 coredump - etc. 3606 3607 If you hit the warning due to signal overflow, 3608 you might want to try "ulimit -i unlimited". 3609 3610 default: off. 3611 3612 printk.always_kmsg_dump= 3613 Trigger kmsg_dump for cases other than kernel oops or 3614 panics 3615 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3616 default: disabled 3617 3618 printk.devkmsg={on,off,ratelimit} 3619 Control writing to /dev/kmsg. 3620 on - unlimited logging to /dev/kmsg from userspace 3621 off - logging to /dev/kmsg disabled 3622 ratelimit - ratelimit the logging 3623 Default: ratelimit 3624 3625 printk.time= Show timing data prefixed to each printk message line 3626 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3627 3628 processor.max_cstate= [HW,ACPI] 3629 Limit processor to maximum C-state 3630 max_cstate=9 overrides any DMI blacklist limit. 3631 3632 processor.nocst [HW,ACPI] 3633 Ignore the _CST method to determine C-states, 3634 instead using the legacy FADT method 3635 3636 profile= [KNL] Enable kernel profiling via /proc/profile 3637 Format: [<profiletype>,]<number> 3638 Param: <profiletype>: "schedule", "sleep", or "kvm" 3639 [defaults to kernel profiling] 3640 Param: "schedule" - profile schedule points. 3641 Param: "sleep" - profile D-state sleeping (millisecs). 3642 Requires CONFIG_SCHEDSTATS 3643 Param: "kvm" - profile VM exits. 3644 Param: <number> - step/bucket size as a power of 2 for 3645 statistical time based profiling. 3646 3647 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3648 before loading. 3649 See Documentation/blockdev/ramdisk.txt. 3650 3651 psi= [KNL] Enable or disable pressure stall information 3652 tracking. 3653 Format: <bool> 3654 3655 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3656 probe for; one of (bare|imps|exps|lifebook|any). 3657 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3658 per second. 3659 psmouse.resetafter= [HW,MOUSE] 3660 Try to reset the device after so many bad packets 3661 (0 = never). 3662 psmouse.resolution= 3663 [HW,MOUSE] Set desired mouse resolution, in dpi. 3664 psmouse.smartscroll= 3665 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3666 0 = disabled, 1 = enabled (default). 3667 3668 pstore.backend= Specify the name of the pstore backend to use 3669 3670 pt. [PARIDE] 3671 See Documentation/blockdev/paride.txt. 3672 3673 pti= [X86_64] Control Page Table Isolation of user and 3674 kernel address spaces. Disabling this feature 3675 removes hardening, but improves performance of 3676 system calls and interrupts. 3677 3678 on - unconditionally enable 3679 off - unconditionally disable 3680 auto - kernel detects whether your CPU model is 3681 vulnerable to issues that PTI mitigates 3682 3683 Not specifying this option is equivalent to pti=auto. 3684 3685 nopti [X86_64] 3686 Equivalent to pti=off 3687 3688 pty.legacy_count= 3689 [KNL] Number of legacy pty's. Overwrites compiled-in 3690 default number. 3691 3692 quiet [KNL] Disable most log messages 3693 3694 r128= [HW,DRM] 3695 3696 raid= [HW,RAID] 3697 See Documentation/admin-guide/md.rst. 3698 3699 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3700 See Documentation/blockdev/ramdisk.txt. 3701 3702 random.trust_cpu={on,off} 3703 [KNL] Enable or disable trusting the use of the 3704 CPU's random number generator (if available) to 3705 fully seed the kernel's CRNG. Default is controlled 3706 by CONFIG_RANDOM_TRUST_CPU. 3707 3708 ras=option[,option,...] [KNL] RAS-specific options 3709 3710 cec_disable [X86] 3711 Disable the Correctable Errors Collector, 3712 see CONFIG_RAS_CEC help text. 3713 3714 rcu_nocbs= [KNL] 3715 The argument is a cpu list, as described above, 3716 except that the string "all" can be used to 3717 specify every CPU on the system. 3718 3719 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3720 the specified list of CPUs to be no-callback CPUs. 3721 Invocation of these CPUs' RCU callbacks will be 3722 offloaded to "rcuox/N" kthreads created for that 3723 purpose, where "x" is "p" for RCU-preempt, and 3724 "s" for RCU-sched, and "N" is the CPU number. 3725 This reduces OS jitter on the offloaded CPUs, 3726 which can be useful for HPC and real-time 3727 workloads. It can also improve energy efficiency 3728 for asymmetric multiprocessors. 3729 3730 rcu_nocb_poll [KNL] 3731 Rather than requiring that offloaded CPUs 3732 (specified by rcu_nocbs= above) explicitly 3733 awaken the corresponding "rcuoN" kthreads, 3734 make these kthreads poll for callbacks. 3735 This improves the real-time response for the 3736 offloaded CPUs by relieving them of the need to 3737 wake up the corresponding kthread, but degrades 3738 energy efficiency by requiring that the kthreads 3739 periodically wake up to do the polling. 3740 3741 rcutree.blimit= [KNL] 3742 Set maximum number of finished RCU callbacks to 3743 process in one batch. 3744 3745 rcutree.dump_tree= [KNL] 3746 Dump the structure of the rcu_node combining tree 3747 out at early boot. This is used for diagnostic 3748 purposes, to verify correct tree setup. 3749 3750 rcutree.gp_cleanup_delay= [KNL] 3751 Set the number of jiffies to delay each step of 3752 RCU grace-period cleanup. 3753 3754 rcutree.gp_init_delay= [KNL] 3755 Set the number of jiffies to delay each step of 3756 RCU grace-period initialization. 3757 3758 rcutree.gp_preinit_delay= [KNL] 3759 Set the number of jiffies to delay each step of 3760 RCU grace-period pre-initialization, that is, 3761 the propagation of recent CPU-hotplug changes up 3762 the rcu_node combining tree. 3763 3764 rcutree.rcu_fanout_exact= [KNL] 3765 Disable autobalancing of the rcu_node combining 3766 tree. This is used by rcutorture, and might 3767 possibly be useful for architectures having high 3768 cache-to-cache transfer latencies. 3769 3770 rcutree.rcu_fanout_leaf= [KNL] 3771 Change the number of CPUs assigned to each 3772 leaf rcu_node structure. Useful for very 3773 large systems, which will choose the value 64, 3774 and for NUMA systems with large remote-access 3775 latencies, which will choose a value aligned 3776 with the appropriate hardware boundaries. 3777 3778 rcutree.jiffies_till_first_fqs= [KNL] 3779 Set delay from grace-period initialization to 3780 first attempt to force quiescent states. 3781 Units are jiffies, minimum value is zero, 3782 and maximum value is HZ. 3783 3784 rcutree.jiffies_till_next_fqs= [KNL] 3785 Set delay between subsequent attempts to force 3786 quiescent states. Units are jiffies, minimum 3787 value is one, and maximum value is HZ. 3788 3789 rcutree.jiffies_till_sched_qs= [KNL] 3790 Set required age in jiffies for a 3791 given grace period before RCU starts 3792 soliciting quiescent-state help from 3793 rcu_note_context_switch() and cond_resched(). 3794 If not specified, the kernel will calculate 3795 a value based on the most recent settings 3796 of rcutree.jiffies_till_first_fqs 3797 and rcutree.jiffies_till_next_fqs. 3798 This calculated value may be viewed in 3799 rcutree.jiffies_to_sched_qs. Any attempt to set 3800 rcutree.jiffies_to_sched_qs will be cheerfully 3801 overwritten. 3802 3803 rcutree.kthread_prio= [KNL,BOOT] 3804 Set the SCHED_FIFO priority of the RCU per-CPU 3805 kthreads (rcuc/N). This value is also used for 3806 the priority of the RCU boost threads (rcub/N) 3807 and for the RCU grace-period kthreads (rcu_bh, 3808 rcu_preempt, and rcu_sched). If RCU_BOOST is 3809 set, valid values are 1-99 and the default is 1 3810 (the least-favored priority). Otherwise, when 3811 RCU_BOOST is not set, valid values are 0-99 and 3812 the default is zero (non-realtime operation). 3813 3814 rcutree.rcu_nocb_leader_stride= [KNL] 3815 Set the number of NOCB kthread groups, which 3816 defaults to the square root of the number of 3817 CPUs. Larger numbers reduces the wakeup overhead 3818 on the per-CPU grace-period kthreads, but increases 3819 that same overhead on each group's leader. 3820 3821 rcutree.qhimark= [KNL] 3822 Set threshold of queued RCU callbacks beyond which 3823 batch limiting is disabled. 3824 3825 rcutree.qlowmark= [KNL] 3826 Set threshold of queued RCU callbacks below which 3827 batch limiting is re-enabled. 3828 3829 rcutree.rcu_idle_gp_delay= [KNL] 3830 Set wakeup interval for idle CPUs that have 3831 RCU callbacks (RCU_FAST_NO_HZ=y). 3832 3833 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3834 Set wakeup interval for idle CPUs that have 3835 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3836 Lazy RCU callbacks are those which RCU can 3837 prove do nothing more than free memory. 3838 3839 rcutree.rcu_kick_kthreads= [KNL] 3840 Cause the grace-period kthread to get an extra 3841 wake_up() if it sleeps three times longer than 3842 it should at force-quiescent-state time. 3843 This wake_up() will be accompanied by a 3844 WARN_ONCE() splat and an ftrace_dump(). 3845 3846 rcutree.sysrq_rcu= [KNL] 3847 Commandeer a sysrq key to dump out Tree RCU's 3848 rcu_node tree with an eye towards determining 3849 why a new grace period has not yet started. 3850 3851 rcuperf.gp_async= [KNL] 3852 Measure performance of asynchronous 3853 grace-period primitives such as call_rcu(). 3854 3855 rcuperf.gp_async_max= [KNL] 3856 Specify the maximum number of outstanding 3857 callbacks per writer thread. When a writer 3858 thread exceeds this limit, it invokes the 3859 corresponding flavor of rcu_barrier() to allow 3860 previously posted callbacks to drain. 3861 3862 rcuperf.gp_exp= [KNL] 3863 Measure performance of expedited synchronous 3864 grace-period primitives. 3865 3866 rcuperf.holdoff= [KNL] 3867 Set test-start holdoff period. The purpose of 3868 this parameter is to delay the start of the 3869 test until boot completes in order to avoid 3870 interference. 3871 3872 rcuperf.nreaders= [KNL] 3873 Set number of RCU readers. The value -1 selects 3874 N, where N is the number of CPUs. A value 3875 "n" less than -1 selects N-n+1, where N is again 3876 the number of CPUs. For example, -2 selects N 3877 (the number of CPUs), -3 selects N+1, and so on. 3878 A value of "n" less than or equal to -N selects 3879 a single reader. 3880 3881 rcuperf.nwriters= [KNL] 3882 Set number of RCU writers. The values operate 3883 the same as for rcuperf.nreaders. 3884 N, where N is the number of CPUs 3885 3886 rcuperf.perf_type= [KNL] 3887 Specify the RCU implementation to test. 3888 3889 rcuperf.shutdown= [KNL] 3890 Shut the system down after performance tests 3891 complete. This is useful for hands-off automated 3892 testing. 3893 3894 rcuperf.verbose= [KNL] 3895 Enable additional printk() statements. 3896 3897 rcuperf.writer_holdoff= [KNL] 3898 Write-side holdoff between grace periods, 3899 in microseconds. The default of zero says 3900 no holdoff. 3901 3902 rcutorture.fqs_duration= [KNL] 3903 Set duration of force_quiescent_state bursts 3904 in microseconds. 3905 3906 rcutorture.fqs_holdoff= [KNL] 3907 Set holdoff time within force_quiescent_state bursts 3908 in microseconds. 3909 3910 rcutorture.fqs_stutter= [KNL] 3911 Set wait time between force_quiescent_state bursts 3912 in seconds. 3913 3914 rcutorture.fwd_progress= [KNL] 3915 Enable RCU grace-period forward-progress testing 3916 for the types of RCU supporting this notion. 3917 3918 rcutorture.fwd_progress_div= [KNL] 3919 Specify the fraction of a CPU-stall-warning 3920 period to do tight-loop forward-progress testing. 3921 3922 rcutorture.fwd_progress_holdoff= [KNL] 3923 Number of seconds to wait between successive 3924 forward-progress tests. 3925 3926 rcutorture.fwd_progress_need_resched= [KNL] 3927 Enclose cond_resched() calls within checks for 3928 need_resched() during tight-loop forward-progress 3929 testing. 3930 3931 rcutorture.gp_cond= [KNL] 3932 Use conditional/asynchronous update-side 3933 primitives, if available. 3934 3935 rcutorture.gp_exp= [KNL] 3936 Use expedited update-side primitives, if available. 3937 3938 rcutorture.gp_normal= [KNL] 3939 Use normal (non-expedited) asynchronous 3940 update-side primitives, if available. 3941 3942 rcutorture.gp_sync= [KNL] 3943 Use normal (non-expedited) synchronous 3944 update-side primitives, if available. If all 3945 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3946 rcutorture.gp_normal=, and rcutorture.gp_sync= 3947 are zero, rcutorture acts as if is interpreted 3948 they are all non-zero. 3949 3950 rcutorture.n_barrier_cbs= [KNL] 3951 Set callbacks/threads for rcu_barrier() testing. 3952 3953 rcutorture.nfakewriters= [KNL] 3954 Set number of concurrent RCU writers. These just 3955 stress RCU, they don't participate in the actual 3956 test, hence the "fake". 3957 3958 rcutorture.nreaders= [KNL] 3959 Set number of RCU readers. The value -1 selects 3960 N-1, where N is the number of CPUs. A value 3961 "n" less than -1 selects N-n-2, where N is again 3962 the number of CPUs. For example, -2 selects N 3963 (the number of CPUs), -3 selects N+1, and so on. 3964 3965 rcutorture.object_debug= [KNL] 3966 Enable debug-object double-call_rcu() testing. 3967 3968 rcutorture.onoff_holdoff= [KNL] 3969 Set time (s) after boot for CPU-hotplug testing. 3970 3971 rcutorture.onoff_interval= [KNL] 3972 Set time (jiffies) between CPU-hotplug operations, 3973 or zero to disable CPU-hotplug testing. 3974 3975 rcutorture.shuffle_interval= [KNL] 3976 Set task-shuffle interval (s). Shuffling tasks 3977 allows some CPUs to go into dyntick-idle mode 3978 during the rcutorture test. 3979 3980 rcutorture.shutdown_secs= [KNL] 3981 Set time (s) after boot system shutdown. This 3982 is useful for hands-off automated testing. 3983 3984 rcutorture.stall_cpu= [KNL] 3985 Duration of CPU stall (s) to test RCU CPU stall 3986 warnings, zero to disable. 3987 3988 rcutorture.stall_cpu_holdoff= [KNL] 3989 Time to wait (s) after boot before inducing stall. 3990 3991 rcutorture.stall_cpu_irqsoff= [KNL] 3992 Disable interrupts while stalling if set. 3993 3994 rcutorture.stat_interval= [KNL] 3995 Time (s) between statistics printk()s. 3996 3997 rcutorture.stutter= [KNL] 3998 Time (s) to stutter testing, for example, specifying 3999 five seconds causes the test to run for five seconds, 4000 wait for five seconds, and so on. This tests RCU's 4001 ability to transition abruptly to and from idle. 4002 4003 rcutorture.test_boost= [KNL] 4004 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4005 "Maybe" means test if the RCU implementation 4006 under test support RCU priority boosting. 4007 4008 rcutorture.test_boost_duration= [KNL] 4009 Duration (s) of each individual boost test. 4010 4011 rcutorture.test_boost_interval= [KNL] 4012 Interval (s) between each boost test. 4013 4014 rcutorture.test_no_idle_hz= [KNL] 4015 Test RCU's dyntick-idle handling. See also the 4016 rcutorture.shuffle_interval parameter. 4017 4018 rcutorture.torture_type= [KNL] 4019 Specify the RCU implementation to test. 4020 4021 rcutorture.verbose= [KNL] 4022 Enable additional printk() statements. 4023 4024 rcupdate.rcu_cpu_stall_suppress= [KNL] 4025 Suppress RCU CPU stall warning messages. 4026 4027 rcupdate.rcu_cpu_stall_timeout= [KNL] 4028 Set timeout for RCU CPU stall warning messages. 4029 4030 rcupdate.rcu_expedited= [KNL] 4031 Use expedited grace-period primitives, for 4032 example, synchronize_rcu_expedited() instead 4033 of synchronize_rcu(). This reduces latency, 4034 but can increase CPU utilization, degrade 4035 real-time latency, and degrade energy efficiency. 4036 No effect on CONFIG_TINY_RCU kernels. 4037 4038 rcupdate.rcu_normal= [KNL] 4039 Use only normal grace-period primitives, 4040 for example, synchronize_rcu() instead of 4041 synchronize_rcu_expedited(). This improves 4042 real-time latency, CPU utilization, and 4043 energy efficiency, but can expose users to 4044 increased grace-period latency. This parameter 4045 overrides rcupdate.rcu_expedited. No effect on 4046 CONFIG_TINY_RCU kernels. 4047 4048 rcupdate.rcu_normal_after_boot= [KNL] 4049 Once boot has completed (that is, after 4050 rcu_end_inkernel_boot() has been invoked), use 4051 only normal grace-period primitives. No effect 4052 on CONFIG_TINY_RCU kernels. 4053 4054 rcupdate.rcu_task_stall_timeout= [KNL] 4055 Set timeout in jiffies for RCU task stall warning 4056 messages. Disable with a value less than or equal 4057 to zero. 4058 4059 rcupdate.rcu_self_test= [KNL] 4060 Run the RCU early boot self tests 4061 4062 rdinit= [KNL] 4063 Format: <full_path> 4064 Run specified binary instead of /init from the ramdisk, 4065 used for early userspace startup. See initrd. 4066 4067 rdt= [HW,X86,RDT] 4068 Turn on/off individual RDT features. List is: 4069 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4070 mba. 4071 E.g. to turn on cmt and turn off mba use: 4072 rdt=cmt,!mba 4073 4074 reboot= [KNL] 4075 Format (x86 or x86_64): 4076 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4077 [[,]s[mp]#### \ 4078 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4079 [[,]f[orce] 4080 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4081 (prefix with 'panic_' to set mode for panic 4082 reboot only), 4083 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4084 reboot_force is either force or not specified, 4085 reboot_cpu is s[mp]#### with #### being the processor 4086 to be used for rebooting. 4087 4088 relax_domain_level= 4089 [KNL, SMP] Set scheduler's default relax_domain_level. 4090 See Documentation/cgroup-v1/cpusets.txt. 4091 4092 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4093 Format: <base1>,<size1>[,<base2>,<size2>,...] 4094 Reserve I/O ports or memory so the kernel won't use 4095 them. If <base> is less than 0x10000, the region 4096 is assumed to be I/O ports; otherwise it is memory. 4097 4098 reservetop= [X86-32] 4099 Format: nn[KMG] 4100 Reserves a hole at the top of the kernel virtual 4101 address space. 4102 4103 reservelow= [X86] 4104 Format: nn[K] 4105 Set the amount of memory to reserve for BIOS at 4106 the bottom of the address space. 4107 4108 reset_devices [KNL] Force drivers to reset the underlying device 4109 during initialization. 4110 4111 resume= [SWSUSP] 4112 Specify the partition device for software suspend 4113 Format: 4114 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4115 4116 resume_offset= [SWSUSP] 4117 Specify the offset from the beginning of the partition 4118 given by "resume=" at which the swap header is located, 4119 in <PAGE_SIZE> units (needed only for swap files). 4120 See Documentation/power/swsusp-and-swap-files.txt 4121 4122 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4123 read the resume files 4124 4125 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4126 Useful for devices that are detected asynchronously 4127 (e.g. USB and MMC devices). 4128 4129 hibernate= [HIBERNATION] 4130 noresume Don't check if there's a hibernation image 4131 present during boot. 4132 nocompress Don't compress/decompress hibernation images. 4133 no Disable hibernation and resume. 4134 protect_image Turn on image protection during restoration 4135 (that will set all pages holding image data 4136 during restoration read-only). 4137 4138 retain_initrd [RAM] Keep initrd memory after extraction 4139 4140 rfkill.default_state= 4141 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4142 etc. communication is blocked by default. 4143 1 Unblocked. 4144 4145 rfkill.master_switch_mode= 4146 0 The "airplane mode" button does nothing. 4147 1 The "airplane mode" button toggles between everything 4148 blocked and the previous configuration. 4149 2 The "airplane mode" button toggles between everything 4150 blocked and everything unblocked. 4151 4152 rhash_entries= [KNL,NET] 4153 Set number of hash buckets for route cache 4154 4155 ring3mwait=disable 4156 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4157 CPUs. 4158 4159 ro [KNL] Mount root device read-only on boot 4160 4161 rodata= [KNL] 4162 on Mark read-only kernel memory as read-only (default). 4163 off Leave read-only kernel memory writable for debugging. 4164 4165 rockchip.usb_uart 4166 Enable the uart passthrough on the designated usb port 4167 on Rockchip SoCs. When active, the signals of the 4168 debug-uart get routed to the D+ and D- pins of the usb 4169 port and the regular usb controller gets disabled. 4170 4171 root= [KNL] Root filesystem 4172 See name_to_dev_t comment in init/do_mounts.c. 4173 4174 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4175 mount the root filesystem 4176 4177 rootflags= [KNL] Set root filesystem mount option string 4178 4179 rootfstype= [KNL] Set root filesystem type 4180 4181 rootwait [KNL] Wait (indefinitely) for root device to show up. 4182 Useful for devices that are detected asynchronously 4183 (e.g. USB and MMC devices). 4184 4185 rproc_mem=nn[KMG][@address] 4186 [KNL,ARM,CMA] Remoteproc physical memory block. 4187 Memory area to be used by remote processor image, 4188 managed by CMA. 4189 4190 rw [KNL] Mount root device read-write on boot 4191 4192 S [KNL] Run init in single mode 4193 4194 s390_iommu= [HW,S390] 4195 Set s390 IOTLB flushing mode 4196 strict 4197 With strict flushing every unmap operation will result in 4198 an IOTLB flush. Default is lazy flushing before reuse, 4199 which is faster. 4200 4201 sa1100ir [NET] 4202 See drivers/net/irda/sa1100_ir.c. 4203 4204 sbni= [NET] Granch SBNI12 leased line adapter 4205 4206 sched_debug [KNL] Enables verbose scheduler debug messages. 4207 4208 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4209 Allowed values are enable and disable. This feature 4210 incurs a small amount of overhead in the scheduler 4211 but is useful for debugging and performance tuning. 4212 4213 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4214 xtime_lock contention on larger systems, and/or RCU lock 4215 contention on all systems with CONFIG_MAXSMP set. 4216 Format: { "0" | "1" } 4217 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4218 1 -- enable. 4219 Note: increases power consumption, thus should only be 4220 enabled if running jitter sensitive (HPC/RT) workloads. 4221 4222 security= [SECURITY] Choose a legacy "major" security module to 4223 enable at boot. This has been deprecated by the 4224 "lsm=" parameter. 4225 4226 selinux= [SELINUX] Disable or enable SELinux at boot time. 4227 Format: { "0" | "1" } 4228 See security/selinux/Kconfig help text. 4229 0 -- disable. 4230 1 -- enable. 4231 Default value is set via kernel config option. 4232 If enabled at boot time, /selinux/disable can be used 4233 later to disable prior to initial policy load. 4234 4235 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4236 Format: { "0" | "1" } 4237 See security/apparmor/Kconfig help text 4238 0 -- disable. 4239 1 -- enable. 4240 Default value is set via kernel config option. 4241 4242 serialnumber [BUGS=X86-32] 4243 4244 shapers= [NET] 4245 Maximal number of shapers. 4246 4247 simeth= [IA-64] 4248 simscsi= 4249 4250 slram= [HW,MTD] 4251 4252 slab_nomerge [MM] 4253 Disable merging of slabs with similar size. May be 4254 necessary if there is some reason to distinguish 4255 allocs to different slabs, especially in hardened 4256 environments where the risk of heap overflows and 4257 layout control by attackers can usually be 4258 frustrated by disabling merging. This will reduce 4259 most of the exposure of a heap attack to a single 4260 cache (risks via metadata attacks are mostly 4261 unchanged). Debug options disable merging on their 4262 own. 4263 For more information see Documentation/vm/slub.rst. 4264 4265 slab_max_order= [MM, SLAB] 4266 Determines the maximum allowed order for slabs. 4267 A high setting may cause OOMs due to memory 4268 fragmentation. Defaults to 1 for systems with 4269 more than 32MB of RAM, 0 otherwise. 4270 4271 slub_debug[=options[,slabs]] [MM, SLUB] 4272 Enabling slub_debug allows one to determine the 4273 culprit if slab objects become corrupted. Enabling 4274 slub_debug can create guard zones around objects and 4275 may poison objects when not in use. Also tracks the 4276 last alloc / free. For more information see 4277 Documentation/vm/slub.rst. 4278 4279 slub_memcg_sysfs= [MM, SLUB] 4280 Determines whether to enable sysfs directories for 4281 memory cgroup sub-caches. 1 to enable, 0 to disable. 4282 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4283 Enabling this can lead to a very high number of debug 4284 directories and files being created under 4285 /sys/kernel/slub. 4286 4287 slub_max_order= [MM, SLUB] 4288 Determines the maximum allowed order for slabs. 4289 A high setting may cause OOMs due to memory 4290 fragmentation. For more information see 4291 Documentation/vm/slub.rst. 4292 4293 slub_min_objects= [MM, SLUB] 4294 The minimum number of objects per slab. SLUB will 4295 increase the slab order up to slub_max_order to 4296 generate a sufficiently large slab able to contain 4297 the number of objects indicated. The higher the number 4298 of objects the smaller the overhead of tracking slabs 4299 and the less frequently locks need to be acquired. 4300 For more information see Documentation/vm/slub.rst. 4301 4302 slub_min_order= [MM, SLUB] 4303 Determines the minimum page order for slabs. Must be 4304 lower than slub_max_order. 4305 For more information see Documentation/vm/slub.rst. 4306 4307 slub_nomerge [MM, SLUB] 4308 Same with slab_nomerge. This is supported for legacy. 4309 See slab_nomerge for more information. 4310 4311 smart2= [HW] 4312 Format: <io1>[,<io2>[,...,<io8>]] 4313 4314 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4315 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4316 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4317 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4318 smsc-ircc2.ircc_irq= [HW] IRQ line 4319 smsc-ircc2.ircc_dma= [HW] DMA channel 4320 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4321 0: Toshiba Satellite 1800 (GP data pin select) 4322 1: Fast pin select (default) 4323 2: ATC IRMode 4324 4325 smt [KNL,S390] Set the maximum number of threads (logical 4326 CPUs) to use per physical CPU on systems capable of 4327 symmetric multithreading (SMT). Will be capped to the 4328 actual hardware limit. 4329 Format: <integer> 4330 Default: -1 (no limit) 4331 4332 softlockup_panic= 4333 [KNL] Should the soft-lockup detector generate panics. 4334 Format: <integer> 4335 4336 A nonzero value instructs the soft-lockup detector 4337 to panic the machine when a soft-lockup occurs. This 4338 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4339 which is the respective build-time switch to that 4340 functionality. 4341 4342 softlockup_all_cpu_backtrace= 4343 [KNL] Should the soft-lockup detector generate 4344 backtraces on all cpus. 4345 Format: <integer> 4346 4347 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4348 See Documentation/laptops/sonypi.txt 4349 4350 spectre_v2= [X86] Control mitigation of Spectre variant 2 4351 (indirect branch speculation) vulnerability. 4352 The default operation protects the kernel from 4353 user space attacks. 4354 4355 on - unconditionally enable, implies 4356 spectre_v2_user=on 4357 off - unconditionally disable, implies 4358 spectre_v2_user=off 4359 auto - kernel detects whether your CPU model is 4360 vulnerable 4361 4362 Selecting 'on' will, and 'auto' may, choose a 4363 mitigation method at run time according to the 4364 CPU, the available microcode, the setting of the 4365 CONFIG_RETPOLINE configuration option, and the 4366 compiler with which the kernel was built. 4367 4368 Selecting 'on' will also enable the mitigation 4369 against user space to user space task attacks. 4370 4371 Selecting 'off' will disable both the kernel and 4372 the user space protections. 4373 4374 Specific mitigations can also be selected manually: 4375 4376 retpoline - replace indirect branches 4377 retpoline,generic - google's original retpoline 4378 retpoline,amd - AMD-specific minimal thunk 4379 4380 Not specifying this option is equivalent to 4381 spectre_v2=auto. 4382 4383 spectre_v2_user= 4384 [X86] Control mitigation of Spectre variant 2 4385 (indirect branch speculation) vulnerability between 4386 user space tasks 4387 4388 on - Unconditionally enable mitigations. Is 4389 enforced by spectre_v2=on 4390 4391 off - Unconditionally disable mitigations. Is 4392 enforced by spectre_v2=off 4393 4394 prctl - Indirect branch speculation is enabled, 4395 but mitigation can be enabled via prctl 4396 per thread. The mitigation control state 4397 is inherited on fork. 4398 4399 prctl,ibpb 4400 - Like "prctl" above, but only STIBP is 4401 controlled per thread. IBPB is issued 4402 always when switching between different user 4403 space processes. 4404 4405 seccomp 4406 - Same as "prctl" above, but all seccomp 4407 threads will enable the mitigation unless 4408 they explicitly opt out. 4409 4410 seccomp,ibpb 4411 - Like "seccomp" above, but only STIBP is 4412 controlled per thread. IBPB is issued 4413 always when switching between different 4414 user space processes. 4415 4416 auto - Kernel selects the mitigation depending on 4417 the available CPU features and vulnerability. 4418 4419 Default mitigation: 4420 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4421 4422 Not specifying this option is equivalent to 4423 spectre_v2_user=auto. 4424 4425 spec_store_bypass_disable= 4426 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4427 (Speculative Store Bypass vulnerability) 4428 4429 Certain CPUs are vulnerable to an exploit against a 4430 a common industry wide performance optimization known 4431 as "Speculative Store Bypass" in which recent stores 4432 to the same memory location may not be observed by 4433 later loads during speculative execution. The idea 4434 is that such stores are unlikely and that they can 4435 be detected prior to instruction retirement at the 4436 end of a particular speculation execution window. 4437 4438 In vulnerable processors, the speculatively forwarded 4439 store can be used in a cache side channel attack, for 4440 example to read memory to which the attacker does not 4441 directly have access (e.g. inside sandboxed code). 4442 4443 This parameter controls whether the Speculative Store 4444 Bypass optimization is used. 4445 4446 On x86 the options are: 4447 4448 on - Unconditionally disable Speculative Store Bypass 4449 off - Unconditionally enable Speculative Store Bypass 4450 auto - Kernel detects whether the CPU model contains an 4451 implementation of Speculative Store Bypass and 4452 picks the most appropriate mitigation. If the 4453 CPU is not vulnerable, "off" is selected. If the 4454 CPU is vulnerable the default mitigation is 4455 architecture and Kconfig dependent. See below. 4456 prctl - Control Speculative Store Bypass per thread 4457 via prctl. Speculative Store Bypass is enabled 4458 for a process by default. The state of the control 4459 is inherited on fork. 4460 seccomp - Same as "prctl" above, but all seccomp threads 4461 will disable SSB unless they explicitly opt out. 4462 4463 Default mitigations: 4464 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4465 4466 On powerpc the options are: 4467 4468 on,auto - On Power8 and Power9 insert a store-forwarding 4469 barrier on kernel entry and exit. On Power7 4470 perform a software flush on kernel entry and 4471 exit. 4472 off - No action. 4473 4474 Not specifying this option is equivalent to 4475 spec_store_bypass_disable=auto. 4476 4477 spia_io_base= [HW,MTD] 4478 spia_fio_base= 4479 spia_pedr= 4480 spia_peddr= 4481 4482 srcutree.counter_wrap_check [KNL] 4483 Specifies how frequently to check for 4484 grace-period sequence counter wrap for the 4485 srcu_data structure's ->srcu_gp_seq_needed field. 4486 The greater the number of bits set in this kernel 4487 parameter, the less frequently counter wrap will 4488 be checked for. Note that the bottom two bits 4489 are ignored. 4490 4491 srcutree.exp_holdoff [KNL] 4492 Specifies how many nanoseconds must elapse 4493 since the end of the last SRCU grace period for 4494 a given srcu_struct until the next normal SRCU 4495 grace period will be considered for automatic 4496 expediting. Set to zero to disable automatic 4497 expediting. 4498 4499 ssbd= [ARM64,HW] 4500 Speculative Store Bypass Disable control 4501 4502 On CPUs that are vulnerable to the Speculative 4503 Store Bypass vulnerability and offer a 4504 firmware based mitigation, this parameter 4505 indicates how the mitigation should be used: 4506 4507 force-on: Unconditionally enable mitigation for 4508 for both kernel and userspace 4509 force-off: Unconditionally disable mitigation for 4510 for both kernel and userspace 4511 kernel: Always enable mitigation in the 4512 kernel, and offer a prctl interface 4513 to allow userspace to register its 4514 interest in being mitigated too. 4515 4516 stack_guard_gap= [MM] 4517 override the default stack gap protection. The value 4518 is in page units and it defines how many pages prior 4519 to (for stacks growing down) resp. after (for stacks 4520 growing up) the main stack are reserved for no other 4521 mapping. Default value is 256 pages. 4522 4523 stacktrace [FTRACE] 4524 Enabled the stack tracer on boot up. 4525 4526 stacktrace_filter=[function-list] 4527 [FTRACE] Limit the functions that the stack tracer 4528 will trace at boot up. function-list is a comma separated 4529 list of functions. This list can be changed at run 4530 time by the stack_trace_filter file in the debugfs 4531 tracing directory. Note, this enables stack tracing 4532 and the stacktrace above is not needed. 4533 4534 sti= [PARISC,HW] 4535 Format: <num> 4536 Set the STI (builtin display/keyboard on the HP-PARISC 4537 machines) console (graphic card) which should be used 4538 as the initial boot-console. 4539 See also comment in drivers/video/console/sticore.c. 4540 4541 sti_font= [HW] 4542 See comment in drivers/video/console/sticore.c. 4543 4544 stifb= [HW] 4545 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4546 4547 sunrpc.min_resvport= 4548 sunrpc.max_resvport= 4549 [NFS,SUNRPC] 4550 SunRPC servers often require that client requests 4551 originate from a privileged port (i.e. a port in the 4552 range 0 < portnr < 1024). 4553 An administrator who wishes to reserve some of these 4554 ports for other uses may adjust the range that the 4555 kernel's sunrpc client considers to be privileged 4556 using these two parameters to set the minimum and 4557 maximum port values. 4558 4559 sunrpc.svc_rpc_per_connection_limit= 4560 [NFS,SUNRPC] 4561 Limit the number of requests that the server will 4562 process in parallel from a single connection. 4563 The default value is 0 (no limit). 4564 4565 sunrpc.pool_mode= 4566 [NFS] 4567 Control how the NFS server code allocates CPUs to 4568 service thread pools. Depending on how many NICs 4569 you have and where their interrupts are bound, this 4570 option will affect which CPUs will do NFS serving. 4571 Note: this parameter cannot be changed while the 4572 NFS server is running. 4573 4574 auto the server chooses an appropriate mode 4575 automatically using heuristics 4576 global a single global pool contains all CPUs 4577 percpu one pool for each CPU 4578 pernode one pool for each NUMA node (equivalent 4579 to global on non-NUMA machines) 4580 4581 sunrpc.tcp_slot_table_entries= 4582 sunrpc.udp_slot_table_entries= 4583 [NFS,SUNRPC] 4584 Sets the upper limit on the number of simultaneous 4585 RPC calls that can be sent from the client to a 4586 server. Increasing these values may allow you to 4587 improve throughput, but will also increase the 4588 amount of memory reserved for use by the client. 4589 4590 suspend.pm_test_delay= 4591 [SUSPEND] 4592 Sets the number of seconds to remain in a suspend test 4593 mode before resuming the system (see 4594 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4595 is set. Default value is 5. 4596 4597 swapaccount=[0|1] 4598 [KNL] Enable accounting of swap in memory resource 4599 controller if no parameter or 1 is given or disable 4600 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4601 4602 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4603 Format: { <int> | force | noforce } 4604 <int> -- Number of I/O TLB slabs 4605 force -- force using of bounce buffers even if they 4606 wouldn't be automatically used by the kernel 4607 noforce -- Never use bounce buffers (for debugging) 4608 4609 switches= [HW,M68k] 4610 4611 sysfs.deprecated=0|1 [KNL] 4612 Enable/disable old style sysfs layout for old udev 4613 on older distributions. When this option is enabled 4614 very new udev will not work anymore. When this option 4615 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4616 in older udev will not work anymore. 4617 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4618 the kernel configuration. 4619 4620 sysrq_always_enabled 4621 [KNL] 4622 Ignore sysrq setting - this boot parameter will 4623 neutralize any effect of /proc/sys/kernel/sysrq. 4624 Useful for debugging. 4625 4626 tcpmhash_entries= [KNL,NET] 4627 Set the number of tcp_metrics_hash slots. 4628 Default value is 8192 or 16384 depending on total 4629 ram pages. This is used to specify the TCP metrics 4630 cache size. See Documentation/networking/ip-sysctl.txt 4631 "tcp_no_metrics_save" section for more details. 4632 4633 tdfx= [HW,DRM] 4634 4635 test_suspend= [SUSPEND][,N] 4636 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4637 standby suspend) or "freeze" (for suspend type freeze) 4638 as the system sleep state during system startup with 4639 the optional capability to repeat N number of times. 4640 The system is woken from this state using a 4641 wakeup-capable RTC alarm. 4642 4643 thash_entries= [KNL,NET] 4644 Set number of hash buckets for TCP connection 4645 4646 thermal.act= [HW,ACPI] 4647 -1: disable all active trip points in all thermal zones 4648 <degrees C>: override all lowest active trip points 4649 4650 thermal.crt= [HW,ACPI] 4651 -1: disable all critical trip points in all thermal zones 4652 <degrees C>: override all critical trip points 4653 4654 thermal.nocrt= [HW,ACPI] 4655 Set to disable actions on ACPI thermal zone 4656 critical and hot trip points. 4657 4658 thermal.off= [HW,ACPI] 4659 1: disable ACPI thermal control 4660 4661 thermal.psv= [HW,ACPI] 4662 -1: disable all passive trip points 4663 <degrees C>: override all passive trip points to this 4664 value 4665 4666 thermal.tzp= [HW,ACPI] 4667 Specify global default ACPI thermal zone polling rate 4668 <deci-seconds>: poll all this frequency 4669 0: no polling (default) 4670 4671 threadirqs [KNL] 4672 Force threading of all interrupt handlers except those 4673 marked explicitly IRQF_NO_THREAD. 4674 4675 tmem [KNL,XEN] 4676 Enable the Transcendent memory driver if built-in. 4677 4678 tmem.cleancache=0|1 [KNL, XEN] 4679 Default is on (1). Disable the usage of the cleancache 4680 API to send anonymous pages to the hypervisor. 4681 4682 tmem.frontswap=0|1 [KNL, XEN] 4683 Default is on (1). Disable the usage of the frontswap 4684 API to send swap pages to the hypervisor. If disabled 4685 the selfballooning and selfshrinking are force disabled. 4686 4687 tmem.selfballooning=0|1 [KNL, XEN] 4688 Default is on (1). Disable the driving of swap pages 4689 to the hypervisor. 4690 4691 tmem.selfshrinking=0|1 [KNL, XEN] 4692 Default is on (1). Partial swapoff that immediately 4693 transfers pages from Xen hypervisor back to the 4694 kernel based on different criteria. 4695 4696 topology= [S390] 4697 Format: {off | on} 4698 Specify if the kernel should make use of the cpu 4699 topology information if the hardware supports this. 4700 The scheduler will make use of this information and 4701 e.g. base its process migration decisions on it. 4702 Default is on. 4703 4704 topology_updates= [KNL, PPC, NUMA] 4705 Format: {off} 4706 Specify if the kernel should ignore (off) 4707 topology updates sent by the hypervisor to this 4708 LPAR. 4709 4710 tp720= [HW,PS2] 4711 4712 tpm_suspend_pcr=[HW,TPM] 4713 Format: integer pcr id 4714 Specify that at suspend time, the tpm driver 4715 should extend the specified pcr with zeros, 4716 as a workaround for some chips which fail to 4717 flush the last written pcr on TPM_SaveState. 4718 This will guarantee that all the other pcrs 4719 are saved. 4720 4721 trace_buf_size=nn[KMG] 4722 [FTRACE] will set tracing buffer size on each cpu. 4723 4724 trace_event=[event-list] 4725 [FTRACE] Set and start specified trace events in order 4726 to facilitate early boot debugging. The event-list is a 4727 comma separated list of trace events to enable. See 4728 also Documentation/trace/events.rst 4729 4730 trace_options=[option-list] 4731 [FTRACE] Enable or disable tracer options at boot. 4732 The option-list is a comma delimited list of options 4733 that can be enabled or disabled just as if you were 4734 to echo the option name into 4735 4736 /sys/kernel/debug/tracing/trace_options 4737 4738 For example, to enable stacktrace option (to dump the 4739 stack trace of each event), add to the command line: 4740 4741 trace_options=stacktrace 4742 4743 See also Documentation/trace/ftrace.rst "trace options" 4744 section. 4745 4746 tp_printk[FTRACE] 4747 Have the tracepoints sent to printk as well as the 4748 tracing ring buffer. This is useful for early boot up 4749 where the system hangs or reboots and does not give the 4750 option for reading the tracing buffer or performing a 4751 ftrace_dump_on_oops. 4752 4753 To turn off having tracepoints sent to printk, 4754 echo 0 > /proc/sys/kernel/tracepoint_printk 4755 Note, echoing 1 into this file without the 4756 tracepoint_printk kernel cmdline option has no effect. 4757 4758 ** CAUTION ** 4759 4760 Having tracepoints sent to printk() and activating high 4761 frequency tracepoints such as irq or sched, can cause 4762 the system to live lock. 4763 4764 traceoff_on_warning 4765 [FTRACE] enable this option to disable tracing when a 4766 warning is hit. This turns off "tracing_on". Tracing can 4767 be enabled again by echoing '1' into the "tracing_on" 4768 file located in /sys/kernel/debug/tracing/ 4769 4770 This option is useful, as it disables the trace before 4771 the WARNING dump is called, which prevents the trace to 4772 be filled with content caused by the warning output. 4773 4774 This option can also be set at run time via the sysctl 4775 option: kernel/traceoff_on_warning 4776 4777 transparent_hugepage= 4778 [KNL] 4779 Format: [always|madvise|never] 4780 Can be used to control the default behavior of the system 4781 with respect to transparent hugepages. 4782 See Documentation/admin-guide/mm/transhuge.rst 4783 for more details. 4784 4785 tsc= Disable clocksource stability checks for TSC. 4786 Format: <string> 4787 [x86] reliable: mark tsc clocksource as reliable, this 4788 disables clocksource verification at runtime, as well 4789 as the stability checks done at bootup. Used to enable 4790 high-resolution timer mode on older hardware, and in 4791 virtualized environment. 4792 [x86] noirqtime: Do not use TSC to do irq accounting. 4793 Used to run time disable IRQ_TIME_ACCOUNTING on any 4794 platforms where RDTSC is slow and this accounting 4795 can add overhead. 4796 [x86] unstable: mark the TSC clocksource as unstable, this 4797 marks the TSC unconditionally unstable at bootup and 4798 avoids any further wobbles once the TSC watchdog notices. 4799 [x86] nowatchdog: disable clocksource watchdog. Used 4800 in situations with strict latency requirements (where 4801 interruptions from clocksource watchdog are not 4802 acceptable). 4803 4804 turbografx.map[2|3]= [HW,JOY] 4805 TurboGraFX parallel port interface 4806 Format: 4807 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4808 See also Documentation/input/devices/joystick-parport.rst 4809 4810 udbg-immortal [PPC] When debugging early kernel crashes that 4811 happen after console_init() and before a proper 4812 console driver takes over, this boot options might 4813 help "seeing" what's going on. 4814 4815 uhash_entries= [KNL,NET] 4816 Set number of hash buckets for UDP/UDP-Lite connections 4817 4818 uhci-hcd.ignore_oc= 4819 [USB] Ignore overcurrent events (default N). 4820 Some badly-designed motherboards generate lots of 4821 bogus events, for ports that aren't wired to 4822 anything. Set this parameter to avoid log spamming. 4823 Note that genuine overcurrent events won't be 4824 reported either. 4825 4826 unknown_nmi_panic 4827 [X86] Cause panic on unknown NMI. 4828 4829 usbcore.authorized_default= 4830 [USB] Default USB device authorization: 4831 (default -1 = authorized except for wireless USB, 4832 0 = not authorized, 1 = authorized, 2 = authorized 4833 if device connected to internal port) 4834 4835 usbcore.autosuspend= 4836 [USB] The autosuspend time delay (in seconds) used 4837 for newly-detected USB devices (default 2). This 4838 is the time required before an idle device will be 4839 autosuspended. Devices for which the delay is set 4840 to a negative value won't be autosuspended at all. 4841 4842 usbcore.usbfs_snoop= 4843 [USB] Set to log all usbfs traffic (default 0 = off). 4844 4845 usbcore.usbfs_snoop_max= 4846 [USB] Maximum number of bytes to snoop in each URB 4847 (default = 65536). 4848 4849 usbcore.blinkenlights= 4850 [USB] Set to cycle leds on hubs (default 0 = off). 4851 4852 usbcore.old_scheme_first= 4853 [USB] Start with the old device initialization 4854 scheme, applies only to low and full-speed devices 4855 (default 0 = off). 4856 4857 usbcore.usbfs_memory_mb= 4858 [USB] Memory limit (in MB) for buffers allocated by 4859 usbfs (default = 16, 0 = max = 2047). 4860 4861 usbcore.use_both_schemes= 4862 [USB] Try the other device initialization scheme 4863 if the first one fails (default 1 = enabled). 4864 4865 usbcore.initial_descriptor_timeout= 4866 [USB] Specifies timeout for the initial 64-byte 4867 USB_REQ_GET_DESCRIPTOR request in milliseconds 4868 (default 5000 = 5.0 seconds). 4869 4870 usbcore.nousb [USB] Disable the USB subsystem 4871 4872 usbcore.quirks= 4873 [USB] A list of quirk entries to augment the built-in 4874 usb core quirk list. List entries are separated by 4875 commas. Each entry has the form 4876 VendorID:ProductID:Flags. The IDs are 4-digit hex 4877 numbers and Flags is a set of letters. Each letter 4878 will change the built-in quirk; setting it if it is 4879 clear and clearing it if it is set. The letters have 4880 the following meanings: 4881 a = USB_QUIRK_STRING_FETCH_255 (string 4882 descriptors must not be fetched using 4883 a 255-byte read); 4884 b = USB_QUIRK_RESET_RESUME (device can't resume 4885 correctly so reset it instead); 4886 c = USB_QUIRK_NO_SET_INTF (device can't handle 4887 Set-Interface requests); 4888 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4889 handle its Configuration or Interface 4890 strings); 4891 e = USB_QUIRK_RESET (device can't be reset 4892 (e.g morph devices), don't use reset); 4893 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4894 more interface descriptions than the 4895 bNumInterfaces count, and can't handle 4896 talking to these interfaces); 4897 g = USB_QUIRK_DELAY_INIT (device needs a pause 4898 during initialization, after we read 4899 the device descriptor); 4900 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4901 high speed and super speed interrupt 4902 endpoints, the USB 2.0 and USB 3.0 spec 4903 require the interval in microframes (1 4904 microframe = 125 microseconds) to be 4905 calculated as interval = 2 ^ 4906 (bInterval-1). 4907 Devices with this quirk report their 4908 bInterval as the result of this 4909 calculation instead of the exponent 4910 variable used in the calculation); 4911 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4912 handle device_qualifier descriptor 4913 requests); 4914 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4915 generates spurious wakeup, ignore 4916 remote wakeup capability); 4917 k = USB_QUIRK_NO_LPM (device can't handle Link 4918 Power Management); 4919 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4920 (Device reports its bInterval as linear 4921 frames instead of the USB 2.0 4922 calculation); 4923 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4924 to be disconnected before suspend to 4925 prevent spurious wakeup); 4926 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4927 pause after every control message); 4928 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4929 delay after resetting its port); 4930 Example: quirks=0781:5580:bk,0a5c:5834:gij 4931 4932 usbhid.mousepoll= 4933 [USBHID] The interval which mice are to be polled at. 4934 4935 usbhid.jspoll= 4936 [USBHID] The interval which joysticks are to be polled at. 4937 4938 usbhid.kbpoll= 4939 [USBHID] The interval which keyboards are to be polled at. 4940 4941 usb-storage.delay_use= 4942 [UMS] The delay in seconds before a new device is 4943 scanned for Logical Units (default 1). 4944 4945 usb-storage.quirks= 4946 [UMS] A list of quirks entries to supplement or 4947 override the built-in unusual_devs list. List 4948 entries are separated by commas. Each entry has 4949 the form VID:PID:Flags where VID and PID are Vendor 4950 and Product ID values (4-digit hex numbers) and 4951 Flags is a set of characters, each corresponding 4952 to a common usb-storage quirk flag as follows: 4953 a = SANE_SENSE (collect more than 18 bytes 4954 of sense data); 4955 b = BAD_SENSE (don't collect more than 18 4956 bytes of sense data); 4957 c = FIX_CAPACITY (decrease the reported 4958 device capacity by one sector); 4959 d = NO_READ_DISC_INFO (don't use 4960 READ_DISC_INFO command); 4961 e = NO_READ_CAPACITY_16 (don't use 4962 READ_CAPACITY_16 command); 4963 f = NO_REPORT_OPCODES (don't use report opcodes 4964 command, uas only); 4965 g = MAX_SECTORS_240 (don't transfer more than 4966 240 sectors at a time, uas only); 4967 h = CAPACITY_HEURISTICS (decrease the 4968 reported device capacity by one 4969 sector if the number is odd); 4970 i = IGNORE_DEVICE (don't bind to this 4971 device); 4972 j = NO_REPORT_LUNS (don't use report luns 4973 command, uas only); 4974 l = NOT_LOCKABLE (don't try to lock and 4975 unlock ejectable media); 4976 m = MAX_SECTORS_64 (don't transfer more 4977 than 64 sectors = 32 KB at a time); 4978 n = INITIAL_READ10 (force a retry of the 4979 initial READ(10) command); 4980 o = CAPACITY_OK (accept the capacity 4981 reported by the device); 4982 p = WRITE_CACHE (the device cache is ON 4983 by default); 4984 r = IGNORE_RESIDUE (the device reports 4985 bogus residue values); 4986 s = SINGLE_LUN (the device has only one 4987 Logical Unit); 4988 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4989 commands, uas only); 4990 u = IGNORE_UAS (don't bind to the uas driver); 4991 w = NO_WP_DETECT (don't test whether the 4992 medium is write-protected). 4993 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4994 even if the device claims no cache) 4995 Example: quirks=0419:aaf5:rl,0421:0433:rc 4996 4997 user_debug= [KNL,ARM] 4998 Format: <int> 4999 See arch/arm/Kconfig.debug help text. 5000 1 - undefined instruction events 5001 2 - system calls 5002 4 - invalid data aborts 5003 8 - SIGSEGV faults 5004 16 - SIGBUS faults 5005 Example: user_debug=31 5006 5007 userpte= 5008 [X86] Flags controlling user PTE allocations. 5009 5010 nohigh = do not allocate PTE pages in 5011 HIGHMEM regardless of setting 5012 of CONFIG_HIGHPTE. 5013 5014 vdso= [X86,SH] 5015 On X86_32, this is an alias for vdso32=. Otherwise: 5016 5017 vdso=1: enable VDSO (the default) 5018 vdso=0: disable VDSO mapping 5019 5020 vdso32= [X86] Control the 32-bit vDSO 5021 vdso32=1: enable 32-bit VDSO 5022 vdso32=0 or vdso32=2: disable 32-bit VDSO 5023 5024 See the help text for CONFIG_COMPAT_VDSO for more 5025 details. If CONFIG_COMPAT_VDSO is set, the default is 5026 vdso32=0; otherwise, the default is vdso32=1. 5027 5028 For compatibility with older kernels, vdso32=2 is an 5029 alias for vdso32=0. 5030 5031 Try vdso32=0 if you encounter an error that says: 5032 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5033 5034 vector= [IA-64,SMP] 5035 vector=percpu: enable percpu vector domain 5036 5037 video= [FB] Frame buffer configuration 5038 See Documentation/fb/modedb.txt. 5039 5040 video.brightness_switch_enabled= [0,1] 5041 If set to 1, on receiving an ACPI notify event 5042 generated by hotkey, video driver will adjust brightness 5043 level and then send out the event to user space through 5044 the allocated input device; If set to 0, video driver 5045 will only send out the event without touching backlight 5046 brightness level. 5047 default: 1 5048 5049 virtio_mmio.device= 5050 [VMMIO] Memory mapped virtio (platform) device. 5051 5052 <size>@<baseaddr>:<irq>[:<id>] 5053 where: 5054 <size> := size (can use standard suffixes 5055 like K, M and G) 5056 <baseaddr> := physical base address 5057 <irq> := interrupt number (as passed to 5058 request_irq()) 5059 <id> := (optional) platform device id 5060 example: 5061 virtio_mmio.device=1K@0x100b0000:48:7 5062 5063 Can be used multiple times for multiple devices. 5064 5065 vga= [BOOT,X86-32] Select a particular video mode 5066 See Documentation/x86/boot.txt and 5067 Documentation/svga.txt. 5068 Use vga=ask for menu. 5069 This is actually a boot loader parameter; the value is 5070 passed to the kernel using a special protocol. 5071 5072 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5073 May slow down system boot speed, especially when 5074 enabled on systems with a large amount of memory. 5075 All options are enabled by default, and this 5076 interface is meant to allow for selectively 5077 enabling or disabling specific virtual memory 5078 debugging features. 5079 5080 Available options are: 5081 P Enable page structure init time poisoning 5082 - Disable all of the above options 5083 5084 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5085 size of <nn>. This can be used to increase the 5086 minimum size (128MB on x86). It can also be used to 5087 decrease the size and leave more room for directly 5088 mapped kernel RAM. 5089 5090 vmcp_cma=nn[MG] [KNL,S390] 5091 Sets the memory size reserved for contiguous memory 5092 allocations for the vmcp device driver. 5093 5094 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5095 Format: <command> 5096 5097 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5098 Format: <command> 5099 5100 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5101 Format: <command> 5102 5103 vsyscall= [X86-64] 5104 Controls the behavior of vsyscalls (i.e. calls to 5105 fixed addresses of 0xffffffffff600x00 from legacy 5106 code). Most statically-linked binaries and older 5107 versions of glibc use these calls. Because these 5108 functions are at fixed addresses, they make nice 5109 targets for exploits that can control RIP. 5110 5111 emulate [default] Vsyscalls turn into traps and are 5112 emulated reasonably safely. 5113 5114 native Vsyscalls are native syscall instructions. 5115 This is a little bit faster than trapping 5116 and makes a few dynamic recompilers work 5117 better than they would in emulation mode. 5118 It also makes exploits much easier to write. 5119 5120 none Vsyscalls don't work at all. This makes 5121 them quite hard to use for exploits but 5122 might break your system. 5123 5124 vt.color= [VT] Default text color. 5125 Format: 0xYX, X = foreground, Y = background. 5126 Default: 0x07 = light gray on black. 5127 5128 vt.cur_default= [VT] Default cursor shape. 5129 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5130 the parameters of the <Esc>[?A;B;Cc escape sequence; 5131 see VGA-softcursor.txt. Default: 2 = underline. 5132 5133 vt.default_blu= [VT] 5134 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5135 Change the default blue palette of the console. 5136 This is a 16-member array composed of values 5137 ranging from 0-255. 5138 5139 vt.default_grn= [VT] 5140 Format: <green0>,<green1>,<green2>,...,<green15> 5141 Change the default green palette of the console. 5142 This is a 16-member array composed of values 5143 ranging from 0-255. 5144 5145 vt.default_red= [VT] 5146 Format: <red0>,<red1>,<red2>,...,<red15> 5147 Change the default red palette of the console. 5148 This is a 16-member array composed of values 5149 ranging from 0-255. 5150 5151 vt.default_utf8= 5152 [VT] 5153 Format=<0|1> 5154 Set system-wide default UTF-8 mode for all tty's. 5155 Default is 1, i.e. UTF-8 mode is enabled for all 5156 newly opened terminals. 5157 5158 vt.global_cursor_default= 5159 [VT] 5160 Format=<-1|0|1> 5161 Set system-wide default for whether a cursor 5162 is shown on new VTs. Default is -1, 5163 i.e. cursors will be created by default unless 5164 overridden by individual drivers. 0 will hide 5165 cursors, 1 will display them. 5166 5167 vt.italic= [VT] Default color for italic text; 0-15. 5168 Default: 2 = green. 5169 5170 vt.underline= [VT] Default color for underlined text; 0-15. 5171 Default: 3 = cyan. 5172 5173 watchdog timers [HW,WDT] For information on watchdog timers, 5174 see Documentation/watchdog/watchdog-parameters.txt 5175 or other driver-specific files in the 5176 Documentation/watchdog/ directory. 5177 5178 watchdog_thresh= 5179 [KNL] 5180 Set the hard lockup detector stall duration 5181 threshold in seconds. The soft lockup detector 5182 threshold is set to twice the value. A value of 0 5183 disables both lockup detectors. Default is 10 5184 seconds. 5185 5186 workqueue.watchdog_thresh= 5187 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5188 warn stall conditions and dump internal state to 5189 help debugging. 0 disables workqueue stall 5190 detection; otherwise, it's the stall threshold 5191 duration in seconds. The default value is 30 and 5192 it can be updated at runtime by writing to the 5193 corresponding sysfs file. 5194 5195 workqueue.disable_numa 5196 By default, all work items queued to unbound 5197 workqueues are affine to the NUMA nodes they're 5198 issued on, which results in better behavior in 5199 general. If NUMA affinity needs to be disabled for 5200 whatever reason, this option can be used. Note 5201 that this also can be controlled per-workqueue for 5202 workqueues visible under /sys/bus/workqueue/. 5203 5204 workqueue.power_efficient 5205 Per-cpu workqueues are generally preferred because 5206 they show better performance thanks to cache 5207 locality; unfortunately, per-cpu workqueues tend to 5208 be more power hungry than unbound workqueues. 5209 5210 Enabling this makes the per-cpu workqueues which 5211 were observed to contribute significantly to power 5212 consumption unbound, leading to measurably lower 5213 power usage at the cost of small performance 5214 overhead. 5215 5216 The default value of this parameter is determined by 5217 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5218 5219 workqueue.debug_force_rr_cpu 5220 Workqueue used to implicitly guarantee that work 5221 items queued without explicit CPU specified are put 5222 on the local CPU. This guarantee is no longer true 5223 and while local CPU is still preferred work items 5224 may be put on foreign CPUs. This debug option 5225 forces round-robin CPU selection to flush out 5226 usages which depend on the now broken guarantee. 5227 When enabled, memory and cache locality will be 5228 impacted. 5229 5230 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5231 default x2apic cluster mode on platforms 5232 supporting x2apic. 5233 5234 x86_intel_mid_timer= [X86-32,APBT] 5235 Choose timer option for x86 Intel MID platform. 5236 Two valid options are apbt timer only and lapic timer 5237 plus one apbt timer for broadcast timer. 5238 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5239 5240 xen_512gb_limit [KNL,X86-64,XEN] 5241 Restricts the kernel running paravirtualized under Xen 5242 to use only up to 512 GB of RAM. The reason to do so is 5243 crash analysis tools and Xen tools for doing domain 5244 save/restore/migration must be enabled to handle larger 5245 domains. 5246 5247 xen_emul_unplug= [HW,X86,XEN] 5248 Unplug Xen emulated devices 5249 Format: [unplug0,][unplug1] 5250 ide-disks -- unplug primary master IDE devices 5251 aux-ide-disks -- unplug non-primary-master IDE devices 5252 nics -- unplug network devices 5253 all -- unplug all emulated devices (NICs and IDE disks) 5254 unnecessary -- unplugging emulated devices is 5255 unnecessary even if the host did not respond to 5256 the unplug protocol 5257 never -- do not unplug even if version check succeeds 5258 5259 xen_nopvspin [X86,XEN] 5260 Disables the ticketlock slowpath using Xen PV 5261 optimizations. 5262 5263 xen_nopv [X86] 5264 Disables the PV optimizations forcing the HVM guest to 5265 run as generic HVM guest with no PV drivers. 5266 5267 xen_scrub_pages= [XEN] 5268 Boolean option to control scrubbing pages before giving them back 5269 to Xen, for use by other domains. Can be also changed at runtime 5270 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5271 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5272 5273 xen_timer_slop= [X86-64,XEN] 5274 Set the timer slop (in nanoseconds) for the virtual Xen 5275 timers (default is 100000). This adjusts the minimum 5276 delta of virtualized Xen timers, where lower values 5277 improve timer resolution at the expense of processing 5278 more timer interrupts. 5279 5280 xirc2ps_cs= [NET,PCMCIA] 5281 Format: 5282 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5283 5284 xhci-hcd.quirks [USB,KNL] 5285 A hex value specifying bitmask with supplemental xhci 5286 host controller quirks. Meaning of each bit can be 5287 consulted in header drivers/usb/host/xhci.h. 5288