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