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. Check 708 Documentation/kdump/kdump.txt for further details. 709 710 crashkernel=range1:size1[,range2:size2,...][@offset] 711 [KNL] Same as above, but depends on the memory 712 in the running system. The syntax of range is 713 start-[end] where start and end are both 714 a memory unit (amount[KMG]). See also 715 Documentation/kdump/kdump.txt for an example. 716 717 crashkernel=size[KMG],high 718 [KNL, x86_64] range could be above 4G. Allow kernel 719 to allocate physical memory region from top, so could 720 be above 4G if system have more than 4G ram installed. 721 Otherwise memory region will be allocated below 4G, if 722 available. 723 It will be ignored if crashkernel=X is specified. 724 crashkernel=size[KMG],low 725 [KNL, x86_64] range under 4G. When crashkernel=X,high 726 is passed, kernel could allocate physical memory region 727 above 4G, that cause second kernel crash on system 728 that require some amount of low memory, e.g. swiotlb 729 requires at least 64M+32K low memory, also enough extra 730 low memory is needed to make sure DMA buffers for 32-bit 731 devices won't run out. Kernel would try to allocate at 732 at least 256M below 4G automatically. 733 This one let user to specify own low range under 4G 734 for second kernel instead. 735 0: to disable low allocation. 736 It will be ignored when crashkernel=X,high is not used 737 or memory reserved is below 4G. 738 739 cryptomgr.notests 740 [KNL] Disable crypto self-tests 741 742 cs89x0_dma= [HW,NET] 743 Format: <dma> 744 745 cs89x0_media= [HW,NET] 746 Format: { rj45 | aui | bnc } 747 748 dasd= [HW,NET] 749 See header of drivers/s390/block/dasd_devmap.c. 750 751 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 752 (one device per port) 753 Format: <port#>,<type> 754 See also Documentation/input/devices/joystick-parport.rst 755 756 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 757 time. See 758 Documentation/admin-guide/dynamic-debug-howto.rst for 759 details. Deprecated, see dyndbg. 760 761 debug [KNL] Enable kernel debugging (events log level). 762 763 debug_boot_weak_hash 764 [KNL] Enable printing [hashed] pointers early in the 765 boot sequence. If enabled, we use a weak hash instead 766 of siphash to hash pointers. Use this option if you are 767 seeing instances of '(___ptrval___)') and need to see a 768 value (hashed pointer) instead. Cryptographically 769 insecure, please do not use on production kernels. 770 771 debug_locks_verbose= 772 [KNL] verbose self-tests 773 Format=<0|1> 774 Print debugging info while doing the locking API 775 self-tests. 776 We default to 0 (no extra messages), setting it to 777 1 will print _a lot_ more information - normally 778 only useful to kernel developers. 779 780 debug_objects [KNL] Enable object debugging 781 782 no_debug_objects 783 [KNL] Disable object debugging 784 785 debug_guardpage_minorder= 786 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 787 parameter allows control of the order of pages that will 788 be intentionally kept free (and hence protected) by the 789 buddy allocator. Bigger value increase the probability 790 of catching random memory corruption, but reduce the 791 amount of memory for normal system use. The maximum 792 possible value is MAX_ORDER/2. Setting this parameter 793 to 1 or 2 should be enough to identify most random 794 memory corruption problems caused by bugs in kernel or 795 driver code when a CPU writes to (or reads from) a 796 random memory location. Note that there exists a class 797 of memory corruptions problems caused by buggy H/W or 798 F/W or by drivers badly programing DMA (basically when 799 memory is written at bus level and the CPU MMU is 800 bypassed) which are not detectable by 801 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 802 tracking down these problems. 803 804 debug_pagealloc= 805 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 806 parameter enables the feature at boot time. In 807 default, it is disabled. We can avoid allocating huge 808 chunk of memory for debug pagealloc if we don't enable 809 it at boot time and the system will work mostly same 810 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 811 on: enable the feature 812 813 debugpat [X86] Enable PAT debugging 814 815 decnet.addr= [HW,NET] 816 Format: <area>[,<node>] 817 See also Documentation/networking/decnet.txt. 818 819 default_hugepagesz= 820 [same as hugepagesz=] The size of the default 821 HugeTLB page size. This is the size represented by 822 the legacy /proc/ hugepages APIs, used for SHM, and 823 default size when mounting hugetlbfs filesystems. 824 Defaults to the default architecture's huge page size 825 if not specified. 826 827 deferred_probe_timeout= 828 [KNL] Debugging option to set a timeout in seconds for 829 deferred probe to give up waiting on dependencies to 830 probe. Only specific dependencies (subsystems or 831 drivers) that have opted in will be ignored. A timeout of 0 832 will timeout at the end of initcalls. This option will also 833 dump out devices still on the deferred probe list after 834 retrying. 835 836 dhash_entries= [KNL] 837 Set number of hash buckets for dentry cache. 838 839 disable_1tb_segments [PPC] 840 Disables the use of 1TB hash page table segments. This 841 causes the kernel to fall back to 256MB segments which 842 can be useful when debugging issues that require an SLB 843 miss to occur. 844 845 disable= [IPV6] 846 See Documentation/networking/ipv6.txt. 847 848 hardened_usercopy= 849 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 850 hardening is enabled for this boot. Hardened 851 usercopy checking is used to protect the kernel 852 from reading or writing beyond known memory 853 allocation boundaries as a proactive defense 854 against bounds-checking flaws in the kernel's 855 copy_to_user()/copy_from_user() interface. 856 on Perform hardened usercopy checks (default). 857 off Disable hardened usercopy checks. 858 859 disable_radix [PPC] 860 Disable RADIX MMU mode on POWER9 861 862 disable_cpu_apicid= [X86,APIC,SMP] 863 Format: <int> 864 The number of initial APIC ID for the 865 corresponding CPU to be disabled at boot, 866 mostly used for the kdump 2nd kernel to 867 disable BSP to wake up multiple CPUs without 868 causing system reset or hang due to sending 869 INIT from AP to BSP. 870 871 perf_v4_pmi= [X86,INTEL] 872 Format: <bool> 873 Disable Intel PMU counter freezing feature. 874 The feature only exists starting from 875 Arch Perfmon v4 (Skylake and newer). 876 877 disable_ddw [PPC/PSERIES] 878 Disable Dynamic DMA Window support. Use this if 879 to workaround buggy firmware. 880 881 disable_ipv6= [IPV6] 882 See Documentation/networking/ipv6.txt. 883 884 disable_mtrr_cleanup [X86] 885 The kernel tries to adjust MTRR layout from continuous 886 to discrete, to make X server driver able to add WB 887 entry later. This parameter disables that. 888 889 disable_mtrr_trim [X86, Intel and AMD only] 890 By default the kernel will trim any uncacheable 891 memory out of your available memory pool based on 892 MTRR settings. This parameter disables that behavior, 893 possibly causing your machine to run very slowly. 894 895 disable_timer_pin_1 [X86] 896 Disable PIN 1 of APIC timer 897 Can be useful to work around chipset bugs. 898 899 dis_ucode_ldr [X86] Disable the microcode loader. 900 901 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 902 this option disables the debugging code at boot. 903 904 dma_debug_entries=<number> 905 This option allows to tune the number of preallocated 906 entries for DMA-API debugging code. One entry is 907 required per DMA-API allocation. Use this if the 908 DMA-API debugging code disables itself because the 909 architectural default is too low. 910 911 dma_debug_driver=<driver_name> 912 With this option the DMA-API debugging driver 913 filter feature can be enabled at boot time. Just 914 pass the driver to filter for as the parameter. 915 The filter can be disabled or changed to another 916 driver later using sysfs. 917 918 driver_async_probe= [KNL] 919 List of driver names to be probed asynchronously. 920 Format: <driver_name1>,<driver_name2>... 921 922 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 923 Broken monitors, graphic adapters, KVMs and EDIDless 924 panels may send no or incorrect EDID data sets. 925 This parameter allows to specify an EDID data sets 926 in the /lib/firmware directory that are used instead. 927 Generic built-in EDID data sets are used, if one of 928 edid/1024x768.bin, edid/1280x1024.bin, 929 edid/1680x1050.bin, or edid/1920x1080.bin is given 930 and no file with the same name exists. Details and 931 instructions how to build your own EDID data are 932 available in Documentation/EDID/HOWTO.txt. An EDID 933 data set will only be used for a particular connector, 934 if its name and a colon are prepended to the EDID 935 name. Each connector may use a unique EDID data 936 set by separating the files with a comma. An EDID 937 data set with no connector name will be used for 938 any connectors not explicitly specified. 939 940 dscc4.setup= [NET] 941 942 dt_cpu_ftrs= [PPC] 943 Format: {"off" | "known"} 944 Control how the dt_cpu_ftrs device-tree binding is 945 used for CPU feature discovery and setup (if it 946 exists). 947 off: Do not use it, fall back to legacy cpu table. 948 known: Do not pass through unknown features to guests 949 or userspace, only those that the kernel is aware of. 950 951 dump_apple_properties [X86] 952 Dump name and content of EFI device properties on 953 x86 Macs. Useful for driver authors to determine 954 what data is available or for reverse-engineering. 955 956 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 957 module.dyndbg[="val"] 958 Enable debug messages at boot time. See 959 Documentation/admin-guide/dynamic-debug-howto.rst 960 for details. 961 962 nompx [X86] Disables Intel Memory Protection Extensions. 963 See Documentation/x86/intel_mpx.txt for more 964 information about the feature. 965 966 nopku [X86] Disable Memory Protection Keys CPU feature found 967 in some Intel CPUs. 968 969 module.async_probe [KNL] 970 Enable asynchronous probe on this module. 971 972 early_ioremap_debug [KNL] 973 Enable debug messages in early_ioremap support. This 974 is useful for tracking down temporary early mappings 975 which are not unmapped. 976 977 earlycon= [KNL] Output early console device and options. 978 979 [ARM64] The early console is determined by the 980 stdout-path property in device tree's chosen node, 981 or determined by the ACPI SPCR table. 982 983 [X86] When used with no options the early console is 984 determined by the ACPI SPCR table. 985 986 cdns,<addr>[,options] 987 Start an early, polled-mode console on a Cadence 988 (xuartps) serial port at the specified address. Only 989 supported option is baud rate. If baud rate is not 990 specified, the serial port must already be setup and 991 configured. 992 993 uart[8250],io,<addr>[,options] 994 uart[8250],mmio,<addr>[,options] 995 uart[8250],mmio32,<addr>[,options] 996 uart[8250],mmio32be,<addr>[,options] 997 uart[8250],0x<addr>[,options] 998 Start an early, polled-mode console on the 8250/16550 999 UART at the specified I/O port or MMIO address. 1000 MMIO inter-register address stride is either 8-bit 1001 (mmio) or 32-bit (mmio32 or mmio32be). 1002 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1003 to be equivalent to 'mmio'. 'options' are specified 1004 in the same format described for "console=ttyS<n>"; if 1005 unspecified, the h/w is not initialized. 1006 1007 pl011,<addr> 1008 pl011,mmio32,<addr> 1009 Start an early, polled-mode console on a pl011 serial 1010 port at the specified address. The pl011 serial port 1011 must already be setup and configured. Options are not 1012 yet supported. If 'mmio32' is specified, then only 1013 the driver will use only 32-bit accessors to read/write 1014 the device registers. 1015 1016 meson,<addr> 1017 Start an early, polled-mode console on a meson serial 1018 port at the specified address. The serial port must 1019 already be setup and configured. Options are not yet 1020 supported. 1021 1022 msm_serial,<addr> 1023 Start an early, polled-mode console on an msm serial 1024 port at the specified address. The serial port 1025 must already be setup and configured. Options are not 1026 yet supported. 1027 1028 msm_serial_dm,<addr> 1029 Start an early, polled-mode console on an msm serial 1030 dm port at the specified address. The serial port 1031 must already be setup and configured. Options are not 1032 yet supported. 1033 1034 owl,<addr> 1035 Start an early, polled-mode console on a serial port 1036 of an Actions Semi SoC, such as S500 or S900, at the 1037 specified address. The serial port must already be 1038 setup and configured. Options are not yet supported. 1039 1040 rda,<addr> 1041 Start an early, polled-mode console on a serial port 1042 of an RDA Micro SoC, such as RDA8810PL, at the 1043 specified address. The serial port must already be 1044 setup and configured. Options are not yet supported. 1045 1046 smh Use ARM semihosting calls for early console. 1047 1048 s3c2410,<addr> 1049 s3c2412,<addr> 1050 s3c2440,<addr> 1051 s3c6400,<addr> 1052 s5pv210,<addr> 1053 exynos4210,<addr> 1054 Use early console provided by serial driver available 1055 on Samsung SoCs, requires selecting proper type and 1056 a correct base address of the selected UART port. The 1057 serial port must already be setup and configured. 1058 Options are not yet supported. 1059 1060 lantiq,<addr> 1061 Start an early, polled-mode console on a lantiq serial 1062 (lqasc) port at the specified address. The serial port 1063 must already be setup and configured. Options are not 1064 yet supported. 1065 1066 lpuart,<addr> 1067 lpuart32,<addr> 1068 Use early console provided by Freescale LP UART driver 1069 found on Freescale Vybrid and QorIQ LS1021A processors. 1070 A valid base address must be provided, and the serial 1071 port must already be setup and configured. 1072 1073 ar3700_uart,<addr> 1074 Start an early, polled-mode console on the 1075 Armada 3700 serial port at the specified 1076 address. The serial port must already be setup 1077 and configured. Options are not yet supported. 1078 1079 qcom_geni,<addr> 1080 Start an early, polled-mode console on a Qualcomm 1081 Generic Interface (GENI) based serial port at the 1082 specified address. The serial port must already be 1083 setup and configured. Options are not yet supported. 1084 1085 efifb,[options] 1086 Start an early, unaccelerated console on the EFI 1087 memory mapped framebuffer (if available). On cache 1088 coherent non-x86 systems that use system memory for 1089 the framebuffer, pass the 'ram' option so that it is 1090 mapped with the correct attributes. 1091 1092 earlyprintk= [X86,SH,ARM,M68k,S390] 1093 earlyprintk=vga 1094 earlyprintk=sclp 1095 earlyprintk=xen 1096 earlyprintk=serial[,ttySn[,baudrate]] 1097 earlyprintk=serial[,0x...[,baudrate]] 1098 earlyprintk=ttySn[,baudrate] 1099 earlyprintk=dbgp[debugController#] 1100 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1101 earlyprintk=xdbc[xhciController#] 1102 1103 earlyprintk is useful when the kernel crashes before 1104 the normal console is initialized. It is not enabled by 1105 default because it has some cosmetic problems. 1106 1107 Append ",keep" to not disable it when the real console 1108 takes over. 1109 1110 Only one of vga, efi, serial, or usb debug port can 1111 be used at a time. 1112 1113 Currently only ttyS0 and ttyS1 may be specified by 1114 name. Other I/O ports may be explicitly specified 1115 on some architectures (x86 and arm at least) by 1116 replacing ttySn with an I/O port address, like this: 1117 earlyprintk=serial,0x1008,115200 1118 You can find the port for a given device in 1119 /proc/tty/driver/serial: 1120 2: uart:ST16650V2 port:00001008 irq:18 ... 1121 1122 Interaction with the standard serial driver is not 1123 very good. 1124 1125 The VGA and EFI output is eventually overwritten by 1126 the real console. 1127 1128 The xen output can only be used by Xen PV guests. 1129 1130 The sclp output can only be used on s390. 1131 1132 The optional "force" to "pciserial" enables use of a 1133 PCI device even when its classcode is not of the 1134 UART class. 1135 1136 edac_report= [HW,EDAC] Control how to report EDAC event 1137 Format: {"on" | "off" | "force"} 1138 on: enable EDAC to report H/W event. May be overridden 1139 by other higher priority error reporting module. 1140 off: disable H/W event reporting through EDAC. 1141 force: enforce the use of EDAC to report H/W event. 1142 default: on. 1143 1144 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1145 ekgdboc=kbd 1146 1147 This is designed to be used in conjunction with 1148 the boot argument: earlyprintk=vga 1149 1150 edd= [EDD] 1151 Format: {"off" | "on" | "skip[mbr]"} 1152 1153 efi= [EFI] 1154 Format: { "old_map", "nochunk", "noruntime", "debug" } 1155 old_map [X86-64]: switch to the old ioremap-based EFI 1156 runtime services mapping. 32-bit still uses this one by 1157 default. 1158 nochunk: disable reading files in "chunks" in the EFI 1159 boot stub, as chunking can cause problems with some 1160 firmware implementations. 1161 noruntime : disable EFI runtime services support 1162 debug: enable misc debug output 1163 1164 efi_no_storage_paranoia [EFI; X86] 1165 Using this parameter you can use more than 50% of 1166 your efi variable storage. Use this parameter only if 1167 you are really sure that your UEFI does sane gc and 1168 fulfills the spec otherwise your board may brick. 1169 1170 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1171 Add arbitrary attribute to specific memory range by 1172 updating original EFI memory map. 1173 Region of memory which aa attribute is added to is 1174 from ss to ss+nn. 1175 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1176 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1177 attribute is added to range 0x100000000-0x180000000 and 1178 0x10a0000000-0x1120000000. 1179 1180 Using this parameter you can do debugging of EFI memmap 1181 related feature. For example, you can do debugging of 1182 Address Range Mirroring feature even if your box 1183 doesn't support it. 1184 1185 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1186 that is to be dynamically loaded by Linux. If there are 1187 multiple variables with the same name but with different 1188 vendor GUIDs, all of them will be loaded. See 1189 Documentation/acpi/ssdt-overlays.txt for details. 1190 1191 1192 eisa_irq_edge= [PARISC,HW] 1193 See header of drivers/parisc/eisa.c. 1194 1195 elanfreq= [X86-32] 1196 See comment before function elanfreq_setup() in 1197 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1198 1199 elevator= [IOSCHED] 1200 Format: {"cfq" | "deadline" | "noop"} 1201 See Documentation/block/cfq-iosched.txt and 1202 Documentation/block/deadline-iosched.txt for details. 1203 1204 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1205 Specifies physical address of start of kernel core 1206 image elf header and optionally the size. Generally 1207 kexec loader will pass this option to capture kernel. 1208 See Documentation/kdump/kdump.txt for details. 1209 1210 enable_mtrr_cleanup [X86] 1211 The kernel tries to adjust MTRR layout from continuous 1212 to discrete, to make X server driver able to add WB 1213 entry later. This parameter enables that. 1214 1215 enable_timer_pin_1 [X86] 1216 Enable PIN 1 of APIC timer 1217 Can be useful to work around chipset bugs 1218 (in particular on some ATI chipsets). 1219 The kernel tries to set a reasonable default. 1220 1221 enforcing [SELINUX] Set initial enforcing status. 1222 Format: {"0" | "1"} 1223 See security/selinux/Kconfig help text. 1224 0 -- permissive (log only, no denials). 1225 1 -- enforcing (deny and log). 1226 Default value is 0. 1227 Value can be changed at runtime via /selinux/enforce. 1228 1229 erst_disable [ACPI] 1230 Disable Error Record Serialization Table (ERST) 1231 support. 1232 1233 ether= [HW,NET] Ethernet cards parameters 1234 This option is obsoleted by the "netdev=" option, which 1235 has equivalent usage. See its documentation for details. 1236 1237 evm= [EVM] 1238 Format: { "fix" } 1239 Permit 'security.evm' to be updated regardless of 1240 current integrity status. 1241 1242 failslab= 1243 fail_page_alloc= 1244 fail_make_request=[KNL] 1245 General fault injection mechanism. 1246 Format: <interval>,<probability>,<space>,<times> 1247 See also Documentation/fault-injection/. 1248 1249 floppy= [HW] 1250 See Documentation/blockdev/floppy.txt. 1251 1252 force_pal_cache_flush 1253 [IA-64] Avoid check_sal_cache_flush which may hang on 1254 buggy SAL_CACHE_FLUSH implementations. Using this 1255 parameter will force ia64_sal_cache_flush to call 1256 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1257 1258 forcepae [X86-32] 1259 Forcefully enable Physical Address Extension (PAE). 1260 Many Pentium M systems disable PAE but may have a 1261 functionally usable PAE implementation. 1262 Warning: use of this parameter will taint the kernel 1263 and may cause unknown problems. 1264 1265 ftrace=[tracer] 1266 [FTRACE] will set and start the specified tracer 1267 as early as possible in order to facilitate early 1268 boot debugging. 1269 1270 ftrace_dump_on_oops[=orig_cpu] 1271 [FTRACE] will dump the trace buffers on oops. 1272 If no parameter is passed, ftrace will dump 1273 buffers of all CPUs, but if you pass orig_cpu, it will 1274 dump only the buffer of the CPU that triggered the 1275 oops. 1276 1277 ftrace_filter=[function-list] 1278 [FTRACE] Limit the functions traced by the function 1279 tracer at boot up. function-list is a comma separated 1280 list of functions. This list can be changed at run 1281 time by the set_ftrace_filter file in the debugfs 1282 tracing directory. 1283 1284 ftrace_notrace=[function-list] 1285 [FTRACE] Do not trace the functions specified in 1286 function-list. This list can be changed at run time 1287 by the set_ftrace_notrace file in the debugfs 1288 tracing directory. 1289 1290 ftrace_graph_filter=[function-list] 1291 [FTRACE] Limit the top level callers functions traced 1292 by the function graph tracer at boot up. 1293 function-list is a comma separated list of functions 1294 that can be changed at run time by the 1295 set_graph_function file in the debugfs tracing directory. 1296 1297 ftrace_graph_notrace=[function-list] 1298 [FTRACE] Do not trace from the functions specified in 1299 function-list. This list is a comma separated list of 1300 functions that can be changed at run time by the 1301 set_graph_notrace file in the debugfs tracing directory. 1302 1303 ftrace_graph_max_depth=<uint> 1304 [FTRACE] Used with the function graph tracer. This is 1305 the max depth it will trace into a function. This value 1306 can be changed at run time by the max_graph_depth file 1307 in the tracefs tracing directory. default: 0 (no limit) 1308 1309 gamecon.map[2|3]= 1310 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1311 support via parallel port (up to 5 devices per port) 1312 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1313 See also Documentation/input/devices/joystick-parport.rst 1314 1315 gamma= [HW,DRM] 1316 1317 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1318 Format: off | on 1319 default: on 1320 1321 gcov_persist= [GCOV] When non-zero (default), profiling data for 1322 kernel modules is saved and remains accessible via 1323 debugfs, even when the module is unloaded/reloaded. 1324 When zero, profiling data is discarded and associated 1325 debugfs files are removed at module unload time. 1326 1327 goldfish [X86] Enable the goldfish android emulator platform. 1328 Don't use this when you are not running on the 1329 android emulator 1330 1331 gpt [EFI] Forces disk with valid GPT signature but 1332 invalid Protective MBR to be treated as GPT. If the 1333 primary GPT is corrupted, it enables the backup/alternate 1334 GPT to be used instead. 1335 1336 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1337 the "Enable 0" bit of the configuration register. 1338 Format: 0 | 1 1339 Default: 0 1340 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1341 the "Enable 0" bit of the configuration register. 1342 Format: 0 | 1 1343 Default: 0 1344 grcan.select= [HW] Select which physical interface to use. 1345 Format: 0 | 1 1346 Default: 0 1347 grcan.txsize= [HW] Sets the size of the tx buffer. 1348 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1349 Default: 1024 1350 grcan.rxsize= [HW] Sets the size of the rx buffer. 1351 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1352 Default: 1024 1353 1354 gpio-mockup.gpio_mockup_ranges 1355 [HW] Sets the ranges of gpiochip of for this device. 1356 Format: <start1>,<end1>,<start2>,<end2>... 1357 1358 hardlockup_all_cpu_backtrace= 1359 [KNL] Should the hard-lockup detector generate 1360 backtraces on all cpus. 1361 Format: <integer> 1362 1363 hashdist= [KNL,NUMA] Large hashes allocated during boot 1364 are distributed across NUMA nodes. Defaults on 1365 for 64-bit NUMA, off otherwise. 1366 Format: 0 | 1 (for off | on) 1367 1368 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1369 1370 hd= [EIDE] (E)IDE hard drive subsystem geometry 1371 Format: <cyl>,<head>,<sect> 1372 1373 hest_disable [ACPI] 1374 Disable Hardware Error Source Table (HEST) support; 1375 corresponding firmware-first mode error processing 1376 logic will be disabled. 1377 1378 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1379 size of <nn>. This works even on boxes that have no 1380 highmem otherwise. This also works to reduce highmem 1381 size on bigger boxes. 1382 1383 highres= [KNL] Enable/disable high resolution timer mode. 1384 Valid parameters: "on", "off" 1385 Default: "on" 1386 1387 hisax= [HW,ISDN] 1388 See Documentation/isdn/README.HiSax. 1389 1390 hlt [BUGS=ARM,SH] 1391 1392 hpet= [X86-32,HPET] option to control HPET usage 1393 Format: { enable (default) | disable | force | 1394 verbose } 1395 disable: disable HPET and use PIT instead 1396 force: allow force enabled of undocumented chips (ICH4, 1397 VIA, nVidia) 1398 verbose: show contents of HPET registers during setup 1399 1400 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1401 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1402 1403 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1404 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1405 On x86-64 and powerpc, this option can be specified 1406 multiple times interleaved with hugepages= to reserve 1407 huge pages of different sizes. Valid pages sizes on 1408 x86-64 are 2M (when the CPU supports "pse") and 1G 1409 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1410 1411 hung_task_panic= 1412 [KNL] Should the hung task detector generate panics. 1413 Format: <integer> 1414 1415 A nonzero value instructs the kernel to panic when a 1416 hung task is detected. The default value is controlled 1417 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1418 option. The value selected by this boot parameter can 1419 be changed later by the kernel.hung_task_panic sysctl. 1420 1421 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1422 terminal devices. Valid values: 0..8 1423 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1424 If specified, z/VM IUCV HVC accepts connections 1425 from listed z/VM user IDs only. 1426 1427 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1428 which allow the hypervisor to 'idle' the 1429 guest on lock contention. 1430 1431 keep_bootcon [KNL] 1432 Do not unregister boot console at start. This is only 1433 useful for debugging when something happens in the window 1434 between unregistering the boot console and initializing 1435 the real console. 1436 1437 i2c_bus= [HW] Override the default board specific I2C bus speed 1438 or register an additional I2C bus that is not 1439 registered from board initialization code. 1440 Format: 1441 <bus_id>,<clkrate> 1442 1443 i8042.debug [HW] Toggle i8042 debug mode 1444 i8042.unmask_kbd_data 1445 [HW] Enable printing of interrupt data from the KBD port 1446 (disabled by default, and as a pre-condition 1447 requires that i8042.debug=1 be enabled) 1448 i8042.direct [HW] Put keyboard port into non-translated mode 1449 i8042.dumbkbd [HW] Pretend that controller can only read data from 1450 keyboard and cannot control its state 1451 (Don't attempt to blink the leds) 1452 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1453 i8042.nokbd [HW] Don't check/create keyboard port 1454 i8042.noloop [HW] Disable the AUX Loopback command while probing 1455 for the AUX port 1456 i8042.nomux [HW] Don't check presence of an active multiplexing 1457 controller 1458 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1459 controllers 1460 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1461 i8042.reset [HW] Reset the controller during init, cleanup and 1462 suspend-to-ram transitions, only during s2r 1463 transitions, or never reset 1464 Format: { 1 | Y | y | 0 | N | n } 1465 1, Y, y: always reset controller 1466 0, N, n: don't ever reset controller 1467 Default: only on s2r transitions on x86; most other 1468 architectures force reset to be always executed 1469 i8042.unlock [HW] Unlock (ignore) the keylock 1470 i8042.kbdreset [HW] Reset device connected to KBD port 1471 1472 i810= [HW,DRM] 1473 1474 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1475 indicates that the driver is running on unsupported 1476 hardware. 1477 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1478 does not match list of supported models. 1479 i8k.power_status 1480 [HW] Report power status in /proc/i8k 1481 (disabled by default) 1482 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1483 capability is set. 1484 1485 i915.invert_brightness= 1486 [DRM] Invert the sense of the variable that is used to 1487 set the brightness of the panel backlight. Normally a 1488 brightness value of 0 indicates backlight switched off, 1489 and the maximum of the brightness value sets the backlight 1490 to maximum brightness. If this parameter is set to 0 1491 (default) and the machine requires it, or this parameter 1492 is set to 1, a brightness value of 0 sets the backlight 1493 to maximum brightness, and the maximum of the brightness 1494 value switches the backlight off. 1495 -1 -- never invert brightness 1496 0 -- machine default 1497 1 -- force brightness inversion 1498 1499 icn= [HW,ISDN] 1500 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1501 1502 ide-core.nodma= [HW] (E)IDE subsystem 1503 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1504 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1505 .cdrom .chs .ignore_cable are additional options 1506 See Documentation/ide/ide.txt. 1507 1508 ide-generic.probe-mask= [HW] (E)IDE subsystem 1509 Format: <int> 1510 Probe mask for legacy ISA IDE ports. Depending on 1511 platform up to 6 ports are supported, enabled by 1512 setting corresponding bits in the mask to 1. The 1513 default value is 0x0, which has a special meaning. 1514 On systems that have PCI, it triggers scanning the 1515 PCI bus for the first and the second port, which 1516 are then probed. On systems without PCI the value 1517 of 0x0 enables probing the two first ports as if it 1518 was 0x3. 1519 1520 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1521 Claim all unknown PCI IDE storage controllers. 1522 1523 idle= [X86] 1524 Format: idle=poll, idle=halt, idle=nomwait 1525 Poll forces a polling idle loop that can slightly 1526 improve the performance of waking up a idle CPU, but 1527 will use a lot of power and make the system run hot. 1528 Not recommended. 1529 idle=halt: Halt is forced to be used for CPU idle. 1530 In such case C2/C3 won't be used again. 1531 idle=nomwait: Disable mwait for CPU C-states 1532 1533 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1534 Format: { strict | legacy | 2008 | relaxed } 1535 Default: strict 1536 1537 Choose which programs will be accepted for execution 1538 based on the IEEE 754 NaN encoding(s) supported by 1539 the FPU and the NaN encoding requested with the value 1540 of an ELF file header flag individually set by each 1541 binary. Hardware implementations are permitted to 1542 support either or both of the legacy and the 2008 NaN 1543 encoding mode. 1544 1545 Available settings are as follows: 1546 strict accept binaries that request a NaN encoding 1547 supported by the FPU 1548 legacy only accept legacy-NaN binaries, if supported 1549 by the FPU 1550 2008 only accept 2008-NaN binaries, if supported 1551 by the FPU 1552 relaxed accept any binaries regardless of whether 1553 supported by the FPU 1554 1555 The FPU emulator is always able to support both NaN 1556 encodings, so if no FPU hardware is present or it has 1557 been disabled with 'nofpu', then the settings of 1558 'legacy' and '2008' strap the emulator accordingly, 1559 'relaxed' straps the emulator for both legacy-NaN and 1560 2008-NaN, whereas 'strict' enables legacy-NaN only on 1561 legacy processors and both NaN encodings on MIPS32 or 1562 MIPS64 CPUs. 1563 1564 The setting for ABS.fmt/NEG.fmt instruction execution 1565 mode generally follows that for the NaN encoding, 1566 except where unsupported by hardware. 1567 1568 ignore_loglevel [KNL] 1569 Ignore loglevel setting - this will print /all/ 1570 kernel messages to the console. Useful for debugging. 1571 We also add it as printk module parameter, so users 1572 could change it dynamically, usually by 1573 /sys/module/printk/parameters/ignore_loglevel. 1574 1575 ignore_rlimit_data 1576 Ignore RLIMIT_DATA setting for data mappings, 1577 print warning at first misuse. Can be changed via 1578 /sys/module/kernel/parameters/ignore_rlimit_data. 1579 1580 ihash_entries= [KNL] 1581 Set number of hash buckets for inode cache. 1582 1583 ima_appraise= [IMA] appraise integrity measurements 1584 Format: { "off" | "enforce" | "fix" | "log" } 1585 default: "enforce" 1586 1587 ima_appraise_tcb [IMA] 1588 The builtin appraise policy appraises all files 1589 owned by uid=0. 1590 1591 ima_canonical_fmt [IMA] 1592 Use the canonical format for the binary runtime 1593 measurements, instead of host native format. 1594 1595 ima_hash= [IMA] 1596 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1597 | sha512 | ... } 1598 default: "sha1" 1599 1600 The list of supported hash algorithms is defined 1601 in crypto/hash_info.h. 1602 1603 ima_policy= [IMA] 1604 The builtin policies to load during IMA setup. 1605 Format: "tcb | appraise_tcb | secure_boot | 1606 fail_securely" 1607 1608 The "tcb" policy measures all programs exec'd, files 1609 mmap'd for exec, and all files opened with the read 1610 mode bit set by either the effective uid (euid=0) or 1611 uid=0. 1612 1613 The "appraise_tcb" policy appraises the integrity of 1614 all files owned by root. (This is the equivalent 1615 of ima_appraise_tcb.) 1616 1617 The "secure_boot" policy appraises the integrity 1618 of files (eg. kexec kernel image, kernel modules, 1619 firmware, policy, etc) based on file signatures. 1620 1621 The "fail_securely" policy forces file signature 1622 verification failure also on privileged mounted 1623 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1624 flag. 1625 1626 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1627 Load a policy which meets the needs of the Trusted 1628 Computing Base. This means IMA will measure all 1629 programs exec'd, files mmap'd for exec, and all files 1630 opened for read by uid=0. 1631 1632 ima_template= [IMA] 1633 Select one of defined IMA measurements template formats. 1634 Formats: { "ima" | "ima-ng" | "ima-sig" } 1635 Default: "ima-ng" 1636 1637 ima_template_fmt= 1638 [IMA] Define a custom template format. 1639 Format: { "field1|...|fieldN" } 1640 1641 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1642 Format: <min_file_size> 1643 Set the minimal file size for using asynchronous hash. 1644 If left unspecified, ahash usage is disabled. 1645 1646 ahash performance varies for different data sizes on 1647 different crypto accelerators. This option can be used 1648 to achieve the best performance for a particular HW. 1649 1650 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1651 Format: <bufsize> 1652 Set hashing buffer size. Default: 4k. 1653 1654 ahash performance varies for different chunk sizes on 1655 different crypto accelerators. This option can be used 1656 to achieve best performance for particular HW. 1657 1658 init= [KNL] 1659 Format: <full_path> 1660 Run specified binary instead of /sbin/init as init 1661 process. 1662 1663 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1664 for working out where the kernel is dying during 1665 startup. 1666 1667 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1668 initcall functions. Useful for debugging built-in 1669 modules and initcalls. 1670 1671 initrd= [BOOT] Specify the location of the initial ramdisk 1672 1673 init_pkru= [x86] Specify the default memory protection keys rights 1674 register contents for all processes. 0x55555554 by 1675 default (disallow access to all but pkey 0). Can 1676 override in debugfs after boot. 1677 1678 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1679 Format: <irq> 1680 1681 int_pln_enable [x86] Enable power limit notification interrupt 1682 1683 integrity_audit=[IMA] 1684 Format: { "0" | "1" } 1685 0 -- basic integrity auditing messages. (Default) 1686 1 -- additional integrity auditing messages. 1687 1688 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1689 on 1690 Enable intel iommu driver. 1691 off 1692 Disable intel iommu driver. 1693 igfx_off [Default Off] 1694 By default, gfx is mapped as normal device. If a gfx 1695 device has a dedicated DMAR unit, the DMAR unit is 1696 bypassed by not enabling DMAR with this option. In 1697 this case, gfx device will use physical address for 1698 DMA. 1699 forcedac [x86_64] 1700 With this option iommu will not optimize to look 1701 for io virtual address below 32-bit forcing dual 1702 address cycle on pci bus for cards supporting greater 1703 than 32-bit addressing. The default is to look 1704 for translation below 32-bit and if not available 1705 then look in the higher range. 1706 strict [Default Off] 1707 With this option on every unmap_single operation will 1708 result in a hardware IOTLB flush operation as opposed 1709 to batching them for performance. 1710 sp_off [Default Off] 1711 By default, super page will be supported if Intel IOMMU 1712 has the capability. With this option, super page will 1713 not be supported. 1714 sm_on [Default Off] 1715 By default, scalable mode will be disabled even if the 1716 hardware advertises that it has support for the scalable 1717 mode translation. With this option set, scalable mode 1718 will be used on hardware which claims to support it. 1719 tboot_noforce [Default Off] 1720 Do not force the Intel IOMMU enabled under tboot. 1721 By default, tboot will force Intel IOMMU on, which 1722 could harm performance of some high-throughput 1723 devices like 40GBit network cards, even if identity 1724 mapping is enabled. 1725 Note that using this option lowers the security 1726 provided by tboot because it makes the system 1727 vulnerable to DMA attacks. 1728 1729 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1730 0 disables intel_idle and fall back on acpi_idle. 1731 1 to 9 specify maximum depth of C-state. 1732 1733 intel_pstate= [X86] 1734 disable 1735 Do not enable intel_pstate as the default 1736 scaling driver for the supported processors 1737 passive 1738 Use intel_pstate as a scaling driver, but configure it 1739 to work with generic cpufreq governors (instead of 1740 enabling its internal governor). This mode cannot be 1741 used along with the hardware-managed P-states (HWP) 1742 feature. 1743 force 1744 Enable intel_pstate on systems that prohibit it by default 1745 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1746 instead of acpi-cpufreq may disable platform features, such 1747 as thermal controls and power capping, that rely on ACPI 1748 P-States information being indicated to OSPM and therefore 1749 should be used with caution. This option does not work with 1750 processors that aren't supported by the intel_pstate driver 1751 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1752 no_hwp 1753 Do not enable hardware P state control (HWP) 1754 if available. 1755 hwp_only 1756 Only load intel_pstate on systems which support 1757 hardware P state control (HWP) if available. 1758 support_acpi_ppc 1759 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1760 Description Table, specifies preferred power management 1761 profile as "Enterprise Server" or "Performance Server", 1762 then this feature is turned on by default. 1763 per_cpu_perf_limits 1764 Allow per-logical-CPU P-State performance control limits using 1765 cpufreq sysfs interface 1766 1767 intremap= [X86-64, Intel-IOMMU] 1768 on enable Interrupt Remapping (default) 1769 off disable Interrupt Remapping 1770 nosid disable Source ID checking 1771 no_x2apic_optout 1772 BIOS x2APIC opt-out request will be ignored 1773 nopost disable Interrupt Posting 1774 1775 iomem= Disable strict checking of access to MMIO memory 1776 strict regions from userspace. 1777 relaxed 1778 1779 iommu= [x86] 1780 off 1781 force 1782 noforce 1783 biomerge 1784 panic 1785 nopanic 1786 merge 1787 nomerge 1788 soft 1789 pt [x86] 1790 nopt [x86] 1791 nobypass [PPC/POWERNV] 1792 Disable IOMMU bypass, using IOMMU for PCI devices. 1793 1794 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1795 Format: { "0" | "1" } 1796 0 - Lazy mode. 1797 Request that DMA unmap operations use deferred 1798 invalidation of hardware TLBs, for increased 1799 throughput at the cost of reduced device isolation. 1800 Will fall back to strict mode if not supported by 1801 the relevant IOMMU driver. 1802 1 - Strict mode (default). 1803 DMA unmap operations invalidate IOMMU hardware TLBs 1804 synchronously. 1805 1806 iommu.passthrough= 1807 [ARM64] Configure DMA to bypass the IOMMU by default. 1808 Format: { "0" | "1" } 1809 0 - Use IOMMU translation for DMA. 1810 1 - Bypass the IOMMU for DMA. 1811 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1812 1813 io7= [HW] IO7 for Marvel based alpha systems 1814 See comment before marvel_specify_io7 in 1815 arch/alpha/kernel/core_marvel.c. 1816 1817 io_delay= [X86] I/O delay method 1818 0x80 1819 Standard port 0x80 based delay 1820 0xed 1821 Alternate port 0xed based delay (needed on some systems) 1822 udelay 1823 Simple two microseconds delay 1824 none 1825 No delay 1826 1827 ip= [IP_PNP] 1828 See Documentation/filesystems/nfs/nfsroot.txt. 1829 1830 irqaffinity= [SMP] Set the default irq affinity mask 1831 The argument is a cpu list, as described above. 1832 1833 irqchip.gicv2_force_probe= 1834 [ARM, ARM64] 1835 Format: <bool> 1836 Force the kernel to look for the second 4kB page 1837 of a GICv2 controller even if the memory range 1838 exposed by the device tree is too small. 1839 1840 irqchip.gicv3_nolpi= 1841 [ARM, ARM64] 1842 Force the kernel to ignore the availability of 1843 LPIs (and by consequence ITSs). Intended for system 1844 that use the kernel as a bootloader, and thus want 1845 to let secondary kernels in charge of setting up 1846 LPIs. 1847 1848 irqfixup [HW] 1849 When an interrupt is not handled search all handlers 1850 for it. Intended to get systems with badly broken 1851 firmware running. 1852 1853 irqpoll [HW] 1854 When an interrupt is not handled search all handlers 1855 for it. Also check all handlers each timer 1856 interrupt. Intended to get systems with badly broken 1857 firmware running. 1858 1859 isapnp= [ISAPNP] 1860 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1861 1862 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1863 [Deprecated - use cpusets instead] 1864 Format: [flag-list,]<cpu-list> 1865 1866 Specify one or more CPUs to isolate from disturbances 1867 specified in the flag list (default: domain): 1868 1869 nohz 1870 Disable the tick when a single task runs. 1871 1872 A residual 1Hz tick is offloaded to workqueues, which you 1873 need to affine to housekeeping through the global 1874 workqueue's affinity configured via the 1875 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1876 by using the 'domain' flag described below. 1877 1878 NOTE: by default the global workqueue runs on all CPUs, 1879 so to protect individual CPUs the 'cpumask' file has to 1880 be configured manually after bootup. 1881 1882 domain 1883 Isolate from the general SMP balancing and scheduling 1884 algorithms. Note that performing domain isolation this way 1885 is irreversible: it's not possible to bring back a CPU to 1886 the domains once isolated through isolcpus. It's strongly 1887 advised to use cpusets instead to disable scheduler load 1888 balancing through the "cpuset.sched_load_balance" file. 1889 It offers a much more flexible interface where CPUs can 1890 move in and out of an isolated set anytime. 1891 1892 You can move a process onto or off an "isolated" CPU via 1893 the CPU affinity syscalls or cpuset. 1894 <cpu number> begins at 0 and the maximum value is 1895 "number of CPUs in system - 1". 1896 1897 The format of <cpu-list> is described above. 1898 1899 1900 1901 iucv= [HW,NET] 1902 1903 ivrs_ioapic [HW,X86_64] 1904 Provide an override to the IOAPIC-ID<->DEVICE-ID 1905 mapping provided in the IVRS ACPI table. For 1906 example, to map IOAPIC-ID decimal 10 to 1907 PCI device 00:14.0 write the parameter as: 1908 ivrs_ioapic[10]=00:14.0 1909 1910 ivrs_hpet [HW,X86_64] 1911 Provide an override to the HPET-ID<->DEVICE-ID 1912 mapping provided in the IVRS ACPI table. For 1913 example, to map HPET-ID decimal 0 to 1914 PCI device 00:14.0 write the parameter as: 1915 ivrs_hpet[0]=00:14.0 1916 1917 ivrs_acpihid [HW,X86_64] 1918 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1919 mapping provided in the IVRS ACPI table. For 1920 example, to map UART-HID:UID AMD0020:0 to 1921 PCI device 00:14.5 write the parameter as: 1922 ivrs_acpihid[00:14.5]=AMD0020:0 1923 1924 js= [HW,JOY] Analog joystick 1925 See Documentation/input/joydev/joystick.rst. 1926 1927 nokaslr [KNL] 1928 When CONFIG_RANDOMIZE_BASE is set, this disables 1929 kernel and module base offset ASLR (Address Space 1930 Layout Randomization). 1931 1932 kasan_multi_shot 1933 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1934 report on every invalid memory access. Without this 1935 parameter KASAN will print report only for the first 1936 invalid access. 1937 1938 keepinitrd [HW,ARM] 1939 1940 kernelcore= [KNL,X86,IA-64,PPC] 1941 Format: nn[KMGTPE] | nn% | "mirror" 1942 This parameter specifies the amount of memory usable by 1943 the kernel for non-movable allocations. The requested 1944 amount is spread evenly throughout all nodes in the 1945 system as ZONE_NORMAL. The remaining memory is used for 1946 movable memory in its own zone, ZONE_MOVABLE. In the 1947 event, a node is too small to have both ZONE_NORMAL and 1948 ZONE_MOVABLE, kernelcore memory will take priority and 1949 other nodes will have a larger ZONE_MOVABLE. 1950 1951 ZONE_MOVABLE is used for the allocation of pages that 1952 may be reclaimed or moved by the page migration 1953 subsystem. Note that allocations like PTEs-from-HighMem 1954 still use the HighMem zone if it exists, and the Normal 1955 zone if it does not. 1956 1957 It is possible to specify the exact amount of memory in 1958 the form of "nn[KMGTPE]", a percentage of total system 1959 memory in the form of "nn%", or "mirror". If "mirror" 1960 option is specified, mirrored (reliable) memory is used 1961 for non-movable allocations and remaining memory is used 1962 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1963 are exclusive, so you cannot specify multiple forms. 1964 1965 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1966 Format: <Controller#>[,poll interval] 1967 The controller # is the number of the ehci usb debug 1968 port as it is probed via PCI. The poll interval is 1969 optional and is the number seconds in between 1970 each poll cycle to the debug port in case you need 1971 the functionality for interrupting the kernel with 1972 gdb or control-c on the dbgp connection. When 1973 not using this parameter you use sysrq-g to break into 1974 the kernel debugger. 1975 1976 kgdboc= [KGDB,HW] kgdb over consoles. 1977 Requires a tty driver that supports console polling, 1978 or a supported polling keyboard driver (non-usb). 1979 Serial only format: <serial_device>[,baud] 1980 keyboard only format: kbd 1981 keyboard and serial format: kbd,<serial_device>[,baud] 1982 Optional Kernel mode setting: 1983 kms, kbd format: kms,kbd 1984 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1985 1986 kgdbwait [KGDB] Stop kernel execution and enter the 1987 kernel debugger at the earliest opportunity. 1988 1989 kmac= [MIPS] korina ethernet MAC address. 1990 Configure the RouterBoard 532 series on-chip 1991 Ethernet adapter MAC address. 1992 1993 kmemleak= [KNL] Boot-time kmemleak enable/disable 1994 Valid arguments: on, off 1995 Default: on 1996 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1997 the default is off. 1998 1999 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2000 Default is 0 (don't ignore, but inject #GP) 2001 2002 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2003 Default is false (don't support). 2004 2005 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2006 KVM MMU at runtime. 2007 Default is 0 (off) 2008 2009 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2010 Default is 1 (enabled) 2011 2012 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2013 for all guests. 2014 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2015 2016 kvm-arm.vgic_v3_group0_trap= 2017 [KVM,ARM] Trap guest accesses to GICv3 group-0 2018 system registers 2019 2020 kvm-arm.vgic_v3_group1_trap= 2021 [KVM,ARM] Trap guest accesses to GICv3 group-1 2022 system registers 2023 2024 kvm-arm.vgic_v3_common_trap= 2025 [KVM,ARM] Trap guest accesses to GICv3 common 2026 system registers 2027 2028 kvm-arm.vgic_v4_enable= 2029 [KVM,ARM] Allow use of GICv4 for direct injection of 2030 LPIs. 2031 2032 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2033 (virtualized MMU) support on capable Intel chips. 2034 Default is 1 (enabled) 2035 2036 kvm-intel.emulate_invalid_guest_state= 2037 [KVM,Intel] Enable emulation of invalid guest states 2038 Default is 0 (disabled) 2039 2040 kvm-intel.flexpriority= 2041 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2042 Default is 1 (enabled) 2043 2044 kvm-intel.nested= 2045 [KVM,Intel] Enable VMX nesting (nVMX). 2046 Default is 0 (disabled) 2047 2048 kvm-intel.unrestricted_guest= 2049 [KVM,Intel] Disable unrestricted guest feature 2050 (virtualized real and unpaged mode) on capable 2051 Intel chips. Default is 1 (enabled) 2052 2053 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2054 CVE-2018-3620. 2055 2056 Valid arguments: never, cond, always 2057 2058 always: L1D cache flush on every VMENTER. 2059 cond: Flush L1D on VMENTER only when the code between 2060 VMEXIT and VMENTER can leak host memory. 2061 never: Disables the mitigation 2062 2063 Default is cond (do L1 cache flush in specific instances) 2064 2065 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2066 feature (tagged TLBs) on capable Intel chips. 2067 Default is 1 (enabled) 2068 2069 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2070 affected CPUs 2071 2072 The kernel PTE inversion protection is unconditionally 2073 enabled and cannot be disabled. 2074 2075 full 2076 Provides all available mitigations for the 2077 L1TF vulnerability. Disables SMT and 2078 enables all mitigations in the 2079 hypervisors, i.e. unconditional L1D flush. 2080 2081 SMT control and L1D flush control via the 2082 sysfs interface is still possible after 2083 boot. Hypervisors will issue a warning 2084 when the first VM is started in a 2085 potentially insecure configuration, 2086 i.e. SMT enabled or L1D flush disabled. 2087 2088 full,force 2089 Same as 'full', but disables SMT and L1D 2090 flush runtime control. Implies the 2091 'nosmt=force' command line option. 2092 (i.e. sysfs control of SMT is disabled.) 2093 2094 flush 2095 Leaves SMT enabled and enables the default 2096 hypervisor mitigation, i.e. conditional 2097 L1D flush. 2098 2099 SMT control and L1D flush control via the 2100 sysfs interface is still possible after 2101 boot. Hypervisors will issue a warning 2102 when the first VM is started in a 2103 potentially insecure configuration, 2104 i.e. SMT enabled or L1D flush disabled. 2105 2106 flush,nosmt 2107 2108 Disables SMT and enables the default 2109 hypervisor mitigation. 2110 2111 SMT control and L1D flush control via the 2112 sysfs interface is still possible after 2113 boot. Hypervisors will issue a warning 2114 when the first VM is started in a 2115 potentially insecure configuration, 2116 i.e. SMT enabled or L1D flush disabled. 2117 2118 flush,nowarn 2119 Same as 'flush', but hypervisors will not 2120 warn when a VM is started in a potentially 2121 insecure configuration. 2122 2123 off 2124 Disables hypervisor mitigations and doesn't 2125 emit any warnings. 2126 It also drops the swap size and available 2127 RAM limit restriction on both hypervisor and 2128 bare metal. 2129 2130 Default is 'flush'. 2131 2132 For details see: Documentation/admin-guide/l1tf.rst 2133 2134 l2cr= [PPC] 2135 2136 l3cr= [PPC] 2137 2138 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2139 disabled it. 2140 2141 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2142 value for LAPIC timer one-shot implementation. Default 2143 back to the programmable timer unit in the LAPIC. 2144 2145 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2146 in C2 power state. 2147 2148 libata.dma= [LIBATA] DMA control 2149 libata.dma=0 Disable all PATA and SATA DMA 2150 libata.dma=1 PATA and SATA Disk DMA only 2151 libata.dma=2 ATAPI (CDROM) DMA only 2152 libata.dma=4 Compact Flash DMA only 2153 Combinations also work, so libata.dma=3 enables DMA 2154 for disks and CDROMs, but not CFs. 2155 2156 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2157 libata.ignore_hpa=0 keep BIOS limits (default) 2158 libata.ignore_hpa=1 ignore limits, using full disk 2159 2160 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2161 when set. 2162 Format: <int> 2163 2164 libata.force= [LIBATA] Force configurations. The format is comma 2165 separated list of "[ID:]VAL" where ID is 2166 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2167 matching port, link or device. Basically, it matches 2168 the ATA ID string printed on console by libata. If 2169 the whole ID part is omitted, the last PORT and DEVICE 2170 values are used. If ID hasn't been specified yet, the 2171 configuration applies to all ports, links and devices. 2172 2173 If only DEVICE is omitted, the parameter applies to 2174 the port and all links and devices behind it. DEVICE 2175 number of 0 either selects the first device or the 2176 first fan-out link behind PMP device. It does not 2177 select the host link. DEVICE number of 15 selects the 2178 host link and device attached to it. 2179 2180 The VAL specifies the configuration to force. As long 2181 as there's no ambiguity shortcut notation is allowed. 2182 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2183 The following configurations can be forced. 2184 2185 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2186 Any ID with matching PORT is used. 2187 2188 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2189 2190 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2191 udma[/][16,25,33,44,66,100,133] notation is also 2192 allowed. 2193 2194 * [no]ncq: Turn on or off NCQ. 2195 2196 * [no]ncqtrim: Turn off queued DSM TRIM. 2197 2198 * nohrst, nosrst, norst: suppress hard, soft 2199 and both resets. 2200 2201 * rstonce: only attempt one reset during 2202 hot-unplug link recovery 2203 2204 * dump_id: dump IDENTIFY data. 2205 2206 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2207 2208 * disable: Disable this device. 2209 2210 If there are multiple matching configurations changing 2211 the same attribute, the last one is used. 2212 2213 memblock=debug [KNL] Enable memblock debug messages. 2214 2215 load_ramdisk= [RAM] List of ramdisks to load from floppy 2216 See Documentation/blockdev/ramdisk.txt. 2217 2218 lockd.nlm_grace_period=P [NFS] Assign grace period. 2219 Format: <integer> 2220 2221 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2222 Format: <integer> 2223 2224 lockd.nlm_timeout=T [NFS] Assign timeout value. 2225 Format: <integer> 2226 2227 lockd.nlm_udpport=M [NFS] Assign UDP port. 2228 Format: <integer> 2229 2230 locktorture.nreaders_stress= [KNL] 2231 Set the number of locking read-acquisition kthreads. 2232 Defaults to being automatically set based on the 2233 number of online CPUs. 2234 2235 locktorture.nwriters_stress= [KNL] 2236 Set the number of locking write-acquisition kthreads. 2237 2238 locktorture.onoff_holdoff= [KNL] 2239 Set time (s) after boot for CPU-hotplug testing. 2240 2241 locktorture.onoff_interval= [KNL] 2242 Set time (s) between CPU-hotplug operations, or 2243 zero to disable CPU-hotplug testing. 2244 2245 locktorture.shuffle_interval= [KNL] 2246 Set task-shuffle interval (jiffies). Shuffling 2247 tasks allows some CPUs to go into dyntick-idle 2248 mode during the locktorture test. 2249 2250 locktorture.shutdown_secs= [KNL] 2251 Set time (s) after boot system shutdown. This 2252 is useful for hands-off automated testing. 2253 2254 locktorture.stat_interval= [KNL] 2255 Time (s) between statistics printk()s. 2256 2257 locktorture.stutter= [KNL] 2258 Time (s) to stutter testing, for example, 2259 specifying five seconds causes the test to run for 2260 five seconds, wait for five seconds, and so on. 2261 This tests the locking primitive's ability to 2262 transition abruptly to and from idle. 2263 2264 locktorture.torture_type= [KNL] 2265 Specify the locking implementation to test. 2266 2267 locktorture.verbose= [KNL] 2268 Enable additional printk() statements. 2269 2270 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2271 Format: <irq> 2272 2273 loglevel= All Kernel Messages with a loglevel smaller than the 2274 console loglevel will be printed to the console. It can 2275 also be changed with klogd or other programs. The 2276 loglevels are defined as follows: 2277 2278 0 (KERN_EMERG) system is unusable 2279 1 (KERN_ALERT) action must be taken immediately 2280 2 (KERN_CRIT) critical conditions 2281 3 (KERN_ERR) error conditions 2282 4 (KERN_WARNING) warning conditions 2283 5 (KERN_NOTICE) normal but significant condition 2284 6 (KERN_INFO) informational 2285 7 (KERN_DEBUG) debug-level messages 2286 2287 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2288 in bytes. n must be a power of two and greater 2289 than the minimal size. The minimal size is defined 2290 by LOG_BUF_SHIFT kernel config parameter. There is 2291 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2292 that allows to increase the default size depending on 2293 the number of CPUs. See init/Kconfig for more details. 2294 2295 logo.nologo [FB] Disables display of the built-in Linux logo. 2296 This may be used to provide more screen space for 2297 kernel log messages and is useful when debugging 2298 kernel boot problems. 2299 2300 lp=0 [LP] Specify parallel ports to use, e.g, 2301 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2302 lp=reset first parallel port). 'lp=0' disables the 2303 lp=auto printer driver. 'lp=reset' (which can be 2304 specified in addition to the ports) causes 2305 attached printers to be reset. Using 2306 lp=port1,port2,... specifies the parallel ports 2307 to associate lp devices with, starting with 2308 lp0. A port specification may be 'none' to skip 2309 that lp device, or a parport name such as 2310 'parport0'. Specifying 'lp=auto' instead of a 2311 port specification list means that device IDs 2312 from each port should be examined, to see if 2313 an IEEE 1284-compliant printer is attached; if 2314 so, the driver will manage that printer. 2315 See also header of drivers/char/lp.c. 2316 2317 lpj=n [KNL] 2318 Sets loops_per_jiffy to given constant, thus avoiding 2319 time-consuming boot-time autodetection (up to 250 ms per 2320 CPU). 0 enables autodetection (default). To determine 2321 the correct value for your kernel, boot with normal 2322 autodetection and see what value is printed. Note that 2323 on SMP systems the preset will be applied to all CPUs, 2324 which is likely to cause problems if your CPUs need 2325 significantly divergent settings. An incorrect value 2326 will cause delays in the kernel to be wrong, leading to 2327 unpredictable I/O errors and other breakage. Although 2328 unlikely, in the extreme case this might damage your 2329 hardware. 2330 2331 ltpc= [NET] 2332 Format: <io>,<irq>,<dma> 2333 2334 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2335 2336 machvec= [IA-64] Force the use of a particular machine-vector 2337 (machvec) in a generic kernel. 2338 Example: machvec=hpzx1_swiotlb 2339 2340 machtype= [Loongson] Share the same kernel image file between different 2341 yeeloong laptop. 2342 Example: machtype=lemote-yeeloong-2f-7inch 2343 2344 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2345 than or equal to this physical address is ignored. 2346 2347 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2348 will bring up during bootup. maxcpus=n : n >= 0 limits 2349 the kernel to bring up 'n' processors. Surely after 2350 bootup you can bring up the other plugged cpu by executing 2351 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2352 only takes effect during system bootup. 2353 While n=0 is a special case, it is equivalent to "nosmp", 2354 which also disables the IO APIC. 2355 2356 max_loop= [LOOP] The number of loop block devices that get 2357 (loop.max_loop) unconditionally pre-created at init time. The default 2358 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2359 of statically allocating a predefined number, loop 2360 devices can be requested on-demand with the 2361 /dev/loop-control interface. 2362 2363 mce [X86-32] Machine Check Exception 2364 2365 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2366 2367 md= [HW] RAID subsystems devices and level 2368 See Documentation/admin-guide/md.rst. 2369 2370 mdacon= [MDA] 2371 Format: <first>,<last> 2372 Specifies range of consoles to be captured by the MDA. 2373 2374 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2375 Amount of memory to be used when the kernel is not able 2376 to see the whole system memory or for test. 2377 [X86] Work as limiting max address. Use together 2378 with memmap= to avoid physical address space collisions. 2379 Without memmap= PCI devices could be placed at addresses 2380 belonging to unused RAM. 2381 2382 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2383 memory. 2384 2385 memchunk=nn[KMG] 2386 [KNL,SH] Allow user to override the default size for 2387 per-device physically contiguous DMA buffers. 2388 2389 memhp_default_state=online/offline 2390 [KNL] Set the initial state for the memory hotplug 2391 onlining policy. If not specified, the default value is 2392 set according to the 2393 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2394 option. 2395 See Documentation/memory-hotplug.txt. 2396 2397 memmap=exactmap [KNL,X86] Enable setting of an exact 2398 E820 memory map, as specified by the user. 2399 Such memmap=exactmap lines can be constructed based on 2400 BIOS output or other requirements. See the memmap=nn@ss 2401 option description. 2402 2403 memmap=nn[KMG]@ss[KMG] 2404 [KNL] Force usage of a specific region of memory. 2405 Region of memory to be used is from ss to ss+nn. 2406 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2407 which limits max address to nn[KMG]. 2408 Multiple different regions can be specified, 2409 comma delimited. 2410 Example: 2411 memmap=100M@2G,100M#3G,1G!1024G 2412 2413 memmap=nn[KMG]#ss[KMG] 2414 [KNL,ACPI] Mark specific memory as ACPI data. 2415 Region of memory to be marked is from ss to ss+nn. 2416 2417 memmap=nn[KMG]$ss[KMG] 2418 [KNL,ACPI] Mark specific memory as reserved. 2419 Region of memory to be reserved is from ss to ss+nn. 2420 Example: Exclude memory from 0x18690000-0x1869ffff 2421 memmap=64K$0x18690000 2422 or 2423 memmap=0x10000$0x18690000 2424 Some bootloaders may need an escape character before '$', 2425 like Grub2, otherwise '$' and the following number 2426 will be eaten. 2427 2428 memmap=nn[KMG]!ss[KMG] 2429 [KNL,X86] Mark specific memory as protected. 2430 Region of memory to be used, from ss to ss+nn. 2431 The memory region may be marked as e820 type 12 (0xc) 2432 and is NVDIMM or ADR memory. 2433 2434 memmap=<size>%<offset>-<oldtype>+<newtype> 2435 [KNL,ACPI] Convert memory within the specified region 2436 from <oldtype> to <newtype>. If "-<oldtype>" is left 2437 out, the whole region will be marked as <newtype>, 2438 even if previously unavailable. If "+<newtype>" is left 2439 out, matching memory will be removed. Types are 2440 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2441 3 = ACPI, 12 = PRAM. 2442 2443 memory_corruption_check=0/1 [X86] 2444 Some BIOSes seem to corrupt the first 64k of 2445 memory when doing things like suspend/resume. 2446 Setting this option will scan the memory 2447 looking for corruption. Enabling this will 2448 both detect corruption and prevent the kernel 2449 from using the memory being corrupted. 2450 However, its intended as a diagnostic tool; if 2451 repeatable BIOS-originated corruption always 2452 affects the same memory, you can use memmap= 2453 to prevent the kernel from using that memory. 2454 2455 memory_corruption_check_size=size [X86] 2456 By default it checks for corruption in the low 2457 64k, making this memory unavailable for normal 2458 use. Use this parameter to scan for 2459 corruption in more or less memory. 2460 2461 memory_corruption_check_period=seconds [X86] 2462 By default it checks for corruption every 60 2463 seconds. Use this parameter to check at some 2464 other rate. 0 disables periodic checking. 2465 2466 memtest= [KNL,X86,ARM,PPC] Enable memtest 2467 Format: <integer> 2468 default : 0 <disable> 2469 Specifies the number of memtest passes to be 2470 performed. Each pass selects another test 2471 pattern from a given set of patterns. Memtest 2472 fills the memory with this pattern, validates 2473 memory contents and reserves bad memory 2474 regions that are detected. 2475 2476 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2477 Valid arguments: on, off 2478 Default (depends on kernel configuration option): 2479 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2480 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2481 mem_encrypt=on: Activate SME 2482 mem_encrypt=off: Do not activate SME 2483 2484 Refer to Documentation/x86/amd-memory-encryption.txt 2485 for details on when memory encryption can be activated. 2486 2487 mem_sleep_default= [SUSPEND] Default system suspend mode: 2488 s2idle - Suspend-To-Idle 2489 shallow - Power-On Suspend or equivalent (if supported) 2490 deep - Suspend-To-RAM or equivalent (if supported) 2491 See Documentation/admin-guide/pm/sleep-states.rst. 2492 2493 meye.*= [HW] Set MotionEye Camera parameters 2494 See Documentation/media/v4l-drivers/meye.rst. 2495 2496 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2497 Multi-Function General Purpose Timers on AMD Geode 2498 platforms. 2499 2500 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2501 the BIOS has incorrectly applied a workaround. TinyBIOS 2502 version 0.98 is known to be affected, 0.99 fixes the 2503 problem by letting the user disable the workaround. 2504 2505 mga= [HW,DRM] 2506 2507 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2508 physical address is ignored. 2509 2510 mini2440= [ARM,HW,KNL] 2511 Format:[0..2][b][c][t] 2512 Default: "0tb" 2513 MINI2440 configuration specification: 2514 0 - The attached screen is the 3.5" TFT 2515 1 - The attached screen is the 7" TFT 2516 2 - The VGA Shield is attached (1024x768) 2517 Leaving out the screen size parameter will not load 2518 the TFT driver, and the framebuffer will be left 2519 unconfigured. 2520 b - Enable backlight. The TFT backlight pin will be 2521 linked to the kernel VESA blanking code and a GPIO 2522 LED. This parameter is not necessary when using the 2523 VGA shield. 2524 c - Enable the s3c camera interface. 2525 t - Reserved for enabling touchscreen support. The 2526 touchscreen support is not enabled in the mainstream 2527 kernel as of 2.6.30, a preliminary port can be found 2528 in the "bleeding edge" mini2440 support kernel at 2529 http://repo.or.cz/w/linux-2.6/mini2440.git 2530 2531 mminit_loglevel= 2532 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2533 parameter allows control of the logging verbosity for 2534 the additional memory initialisation checks. A value 2535 of 0 disables mminit logging and a level of 4 will 2536 log everything. Information is printed at KERN_DEBUG 2537 so loglevel=8 may also need to be specified. 2538 2539 module.sig_enforce 2540 [KNL] When CONFIG_MODULE_SIG is set, this means that 2541 modules without (valid) signatures will fail to load. 2542 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2543 is always true, so this option does nothing. 2544 2545 module_blacklist= [KNL] Do not load a comma-separated list of 2546 modules. Useful for debugging problem modules. 2547 2548 mousedev.tap_time= 2549 [MOUSE] Maximum time between finger touching and 2550 leaving touchpad surface for touch to be considered 2551 a tap and be reported as a left button click (for 2552 touchpads working in absolute mode only). 2553 Format: <msecs> 2554 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2555 reporting absolute coordinates, such as tablets 2556 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2557 reporting absolute coordinates, such as tablets 2558 2559 movablecore= [KNL,X86,IA-64,PPC] 2560 Format: nn[KMGTPE] | nn% 2561 This parameter is the complement to kernelcore=, it 2562 specifies the amount of memory used for migratable 2563 allocations. If both kernelcore and movablecore is 2564 specified, then kernelcore will be at *least* the 2565 specified value but may be more. If movablecore on its 2566 own is specified, the administrator must be careful 2567 that the amount of memory usable for all allocations 2568 is not too small. 2569 2570 movable_node [KNL] Boot-time switch to make hotplugable memory 2571 NUMA nodes to be movable. This means that the memory 2572 of such nodes will be usable only for movable 2573 allocations which rules out almost all kernel 2574 allocations. Use with caution! 2575 2576 MTD_Partition= [MTD] 2577 Format: <name>,<region-number>,<size>,<offset> 2578 2579 MTD_Region= [MTD] Format: 2580 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2581 2582 mtdparts= [MTD] 2583 See drivers/mtd/cmdlinepart.c. 2584 2585 multitce=off [PPC] This parameter disables the use of the pSeries 2586 firmware feature for updating multiple TCE entries 2587 at a time. 2588 2589 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2590 2591 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2592 2593 boundary - index of last SLC block on Flex-OneNAND. 2594 The remaining blocks are configured as MLC blocks. 2595 lock - Configure if Flex-OneNAND boundary should be locked. 2596 Once locked, the boundary cannot be changed. 2597 1 indicates lock status, 0 indicates unlock status. 2598 2599 mtdset= [ARM] 2600 ARM/S3C2412 JIVE boot control 2601 2602 See arch/arm/mach-s3c2412/mach-jive.c 2603 2604 mtouchusb.raw_coordinates= 2605 [HW] Make the MicroTouch USB driver use raw coordinates 2606 ('y', default) or cooked coordinates ('n') 2607 2608 mtrr_chunk_size=nn[KMG] [X86] 2609 used for mtrr cleanup. It is largest continuous chunk 2610 that could hold holes aka. UC entries. 2611 2612 mtrr_gran_size=nn[KMG] [X86] 2613 Used for mtrr cleanup. It is granularity of mtrr block. 2614 Default is 1. 2615 Large value could prevent small alignment from 2616 using up MTRRs. 2617 2618 mtrr_spare_reg_nr=n [X86] 2619 Format: <integer> 2620 Range: 0,7 : spare reg number 2621 Default : 1 2622 Used for mtrr cleanup. It is spare mtrr entries number. 2623 Set to 2 or more if your graphical card needs more. 2624 2625 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2626 2627 netdev= [NET] Network devices parameters 2628 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2629 Note that mem_start is often overloaded to mean 2630 something different and driver-specific. 2631 This usage is only documented in each driver source 2632 file if at all. 2633 2634 nf_conntrack.acct= 2635 [NETFILTER] Enable connection tracking flow accounting 2636 0 to disable accounting 2637 1 to enable accounting 2638 Default value is 0. 2639 2640 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2641 See Documentation/filesystems/nfs/nfsroot.txt. 2642 2643 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2644 See Documentation/filesystems/nfs/nfsroot.txt. 2645 2646 nfsrootdebug [NFS] enable nfsroot debugging messages. 2647 See Documentation/filesystems/nfs/nfsroot.txt. 2648 2649 nfs.callback_nr_threads= 2650 [NFSv4] set the total number of threads that the 2651 NFS client will assign to service NFSv4 callback 2652 requests. 2653 2654 nfs.callback_tcpport= 2655 [NFS] set the TCP port on which the NFSv4 callback 2656 channel should listen. 2657 2658 nfs.cache_getent= 2659 [NFS] sets the pathname to the program which is used 2660 to update the NFS client cache entries. 2661 2662 nfs.cache_getent_timeout= 2663 [NFS] sets the timeout after which an attempt to 2664 update a cache entry is deemed to have failed. 2665 2666 nfs.idmap_cache_timeout= 2667 [NFS] set the maximum lifetime for idmapper cache 2668 entries. 2669 2670 nfs.enable_ino64= 2671 [NFS] enable 64-bit inode numbers. 2672 If zero, the NFS client will fake up a 32-bit inode 2673 number for the readdir() and stat() syscalls instead 2674 of returning the full 64-bit number. 2675 The default is to return 64-bit inode numbers. 2676 2677 nfs.max_session_cb_slots= 2678 [NFSv4.1] Sets the maximum number of session 2679 slots the client will assign to the callback 2680 channel. This determines the maximum number of 2681 callbacks the client will process in parallel for 2682 a particular server. 2683 2684 nfs.max_session_slots= 2685 [NFSv4.1] Sets the maximum number of session slots 2686 the client will attempt to negotiate with the server. 2687 This limits the number of simultaneous RPC requests 2688 that the client can send to the NFSv4.1 server. 2689 Note that there is little point in setting this 2690 value higher than the max_tcp_slot_table_limit. 2691 2692 nfs.nfs4_disable_idmapping= 2693 [NFSv4] When set to the default of '1', this option 2694 ensures that both the RPC level authentication 2695 scheme and the NFS level operations agree to use 2696 numeric uids/gids if the mount is using the 2697 'sec=sys' security flavour. In effect it is 2698 disabling idmapping, which can make migration from 2699 legacy NFSv2/v3 systems to NFSv4 easier. 2700 Servers that do not support this mode of operation 2701 will be autodetected by the client, and it will fall 2702 back to using the idmapper. 2703 To turn off this behaviour, set the value to '0'. 2704 nfs.nfs4_unique_id= 2705 [NFS4] Specify an additional fixed unique ident- 2706 ification string that NFSv4 clients can insert into 2707 their nfs_client_id4 string. This is typically a 2708 UUID that is generated at system install time. 2709 2710 nfs.send_implementation_id = 2711 [NFSv4.1] Send client implementation identification 2712 information in exchange_id requests. 2713 If zero, no implementation identification information 2714 will be sent. 2715 The default is to send the implementation identification 2716 information. 2717 2718 nfs.recover_lost_locks = 2719 [NFSv4] Attempt to recover locks that were lost due 2720 to a lease timeout on the server. Please note that 2721 doing this risks data corruption, since there are 2722 no guarantees that the file will remain unchanged 2723 after the locks are lost. 2724 If you want to enable the kernel legacy behaviour of 2725 attempting to recover these locks, then set this 2726 parameter to '1'. 2727 The default parameter value of '0' causes the kernel 2728 not to attempt recovery of lost locks. 2729 2730 nfs4.layoutstats_timer = 2731 [NFSv4.2] Change the rate at which the kernel sends 2732 layoutstats to the pNFS metadata server. 2733 2734 Setting this to value to 0 causes the kernel to use 2735 whatever value is the default set by the layout 2736 driver. A non-zero value sets the minimum interval 2737 in seconds between layoutstats transmissions. 2738 2739 nfsd.nfs4_disable_idmapping= 2740 [NFSv4] When set to the default of '1', the NFSv4 2741 server will return only numeric uids and gids to 2742 clients using auth_sys, and will accept numeric uids 2743 and gids from such clients. This is intended to ease 2744 migration from NFSv2/v3. 2745 2746 nmi_debug= [KNL,SH] Specify one or more actions to take 2747 when a NMI is triggered. 2748 Format: [state][,regs][,debounce][,die] 2749 2750 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2751 Format: [panic,][nopanic,][num] 2752 Valid num: 0 or 1 2753 0 - turn hardlockup detector in nmi_watchdog off 2754 1 - turn hardlockup detector in nmi_watchdog on 2755 When panic is specified, panic when an NMI watchdog 2756 timeout occurs (or 'nopanic' to override the opposite 2757 default). To disable both hard and soft lockup detectors, 2758 please see 'nowatchdog'. 2759 This is useful when you use a panic=... timeout and 2760 need the box quickly up again. 2761 2762 These settings can be accessed at runtime via 2763 the nmi_watchdog and hardlockup_panic sysctls. 2764 2765 netpoll.carrier_timeout= 2766 [NET] Specifies amount of time (in seconds) that 2767 netpoll should wait for a carrier. By default netpoll 2768 waits 4 seconds. 2769 2770 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2771 emulation library even if a 387 maths coprocessor 2772 is present. 2773 2774 no5lvl [X86-64] Disable 5-level paging mode. Forces 2775 kernel to use 4-level paging instead. 2776 2777 no_console_suspend 2778 [HW] Never suspend the console 2779 Disable suspending of consoles during suspend and 2780 hibernate operations. Once disabled, debugging 2781 messages can reach various consoles while the rest 2782 of the system is being put to sleep (ie, while 2783 debugging driver suspend/resume hooks). This may 2784 not work reliably with all consoles, but is known 2785 to work with serial and VGA consoles. 2786 To facilitate more flexible debugging, we also add 2787 console_suspend, a printk module parameter to control 2788 it. Users could use console_suspend (usually 2789 /sys/module/printk/parameters/console_suspend) to 2790 turn on/off it dynamically. 2791 2792 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2793 caches in the slab allocator. Saves per-node memory, 2794 but will impact performance. 2795 2796 noalign [KNL,ARM] 2797 2798 noaltinstr [S390] Disables alternative instructions patching 2799 (CPU alternatives feature). 2800 2801 noapic [SMP,APIC] Tells the kernel to not make use of any 2802 IOAPICs that may be present in the system. 2803 2804 noautogroup Disable scheduler automatic task group creation. 2805 2806 nobats [PPC] Do not use BATs for mapping kernel lowmem 2807 on "Classic" PPC cores. 2808 2809 nocache [ARM] 2810 2811 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2812 2813 nodelayacct [KNL] Disable per-task delay accounting 2814 2815 nodsp [SH] Disable hardware DSP at boot time. 2816 2817 noefi Disable EFI runtime services support. 2818 2819 noexec [IA-64] 2820 2821 noexec [X86] 2822 On X86-32 available only on PAE configured kernels. 2823 noexec=on: enable non-executable mappings (default) 2824 noexec=off: disable non-executable mappings 2825 2826 nosmap [X86] 2827 Disable SMAP (Supervisor Mode Access Prevention) 2828 even if it is supported by processor. 2829 2830 nosmep [X86] 2831 Disable SMEP (Supervisor Mode Execution Prevention) 2832 even if it is supported by processor. 2833 2834 noexec32 [X86-64] 2835 This affects only 32-bit executables. 2836 noexec32=on: enable non-executable mappings (default) 2837 read doesn't imply executable mappings 2838 noexec32=off: disable non-executable mappings 2839 read implies executable mappings 2840 2841 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2842 2843 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2844 register save and restore. The kernel will only save 2845 legacy floating-point registers on task switch. 2846 2847 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2848 2849 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2850 Equivalent to smt=1. 2851 2852 [KNL,x86] Disable symmetric multithreading (SMT). 2853 nosmt=force: Force disable SMT, cannot be undone 2854 via the sysfs control file. 2855 2856 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds 2857 check bypass). With this option data leaks are possible 2858 in the system. 2859 2860 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2 2861 (indirect branch prediction) vulnerability. System may 2862 allow data leaks with this option, which is equivalent 2863 to spectre_v2=off. 2864 2865 nospec_store_bypass_disable 2866 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2867 2868 noxsave [BUGS=X86] Disables x86 extended register state save 2869 and restore using xsave. The kernel will fallback to 2870 enabling legacy floating-point and sse state. 2871 2872 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2873 register states. The kernel will fall back to use 2874 xsave to save the states. By using this parameter, 2875 performance of saving the states is degraded because 2876 xsave doesn't support modified optimization while 2877 xsaveopt supports it on xsaveopt enabled systems. 2878 2879 noxsaves [X86] Disables xsaves and xrstors used in saving and 2880 restoring x86 extended register state in compacted 2881 form of xsave area. The kernel will fall back to use 2882 xsaveopt and xrstor to save and restore the states 2883 in standard form of xsave area. By using this 2884 parameter, xsave area per process might occupy more 2885 memory on xsaves enabled systems. 2886 2887 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2888 wfi(ARM) instruction doesn't work correctly and not to 2889 use it. This is also useful when using JTAG debugger. 2890 2891 no_file_caps Tells the kernel not to honor file capabilities. The 2892 only way then for a file to be executed with privilege 2893 is to be setuid root or executed by root. 2894 2895 nohalt [IA-64] Tells the kernel not to use the power saving 2896 function PAL_HALT_LIGHT when idle. This increases 2897 power-consumption. On the positive side, it reduces 2898 interrupt wake-up latency, which may improve performance 2899 in certain environments such as networked servers or 2900 real-time systems. 2901 2902 nohibernate [HIBERNATION] Disable hibernation and resume. 2903 2904 nohz= [KNL] Boottime enable/disable dynamic ticks 2905 Valid arguments: on, off 2906 Default: on 2907 2908 nohz_full= [KNL,BOOT,SMP,ISOL] 2909 The argument is a cpu list, as described above. 2910 In kernels built with CONFIG_NO_HZ_FULL=y, set 2911 the specified list of CPUs whose tick will be stopped 2912 whenever possible. The boot CPU will be forced outside 2913 the range to maintain the timekeeping. Any CPUs 2914 in this list will have their RCU callbacks offloaded, 2915 just as if they had also been called out in the 2916 rcu_nocbs= boot parameter. 2917 2918 noiotrap [SH] Disables trapped I/O port accesses. 2919 2920 noirqdebug [X86-32] Disables the code which attempts to detect and 2921 disable unhandled interrupt sources. 2922 2923 no_timer_check [X86,APIC] Disables the code which tests for 2924 broken timer IRQ sources. 2925 2926 noisapnp [ISAPNP] Disables ISA PnP code. 2927 2928 noinitrd [RAM] Tells the kernel not to load any configured 2929 initial RAM disk. 2930 2931 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2932 remapping. 2933 [Deprecated - use intremap=off] 2934 2935 nointroute [IA-64] 2936 2937 noinvpcid [X86] Disable the INVPCID cpu feature. 2938 2939 nojitter [IA-64] Disables jitter checking for ITC timers. 2940 2941 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2942 2943 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2944 fault handling. 2945 2946 no-vmw-sched-clock 2947 [X86,PV_OPS] Disable paravirtualized VMware scheduler 2948 clock and use the default one. 2949 2950 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2951 steal time is computed, but won't influence scheduler 2952 behaviour 2953 2954 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2955 2956 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2957 2958 noltlbs [PPC] Do not use large page/tlb entries for kernel 2959 lowmem mapping on PPC40x and PPC8xx 2960 2961 nomca [IA-64] Disable machine check abort handling 2962 2963 nomce [X86-32] Disable Machine Check Exception 2964 2965 nomfgpt [X86-32] Disable Multi-Function General Purpose 2966 Timer usage (for AMD Geode machines). 2967 2968 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2969 shutdown the other cpus. Instead use the REBOOT_VECTOR 2970 irq. 2971 2972 nomodule Disable module load 2973 2974 nopat [X86] Disable PAT (page attribute table extension of 2975 pagetables) support. 2976 2977 nopcid [X86-64] Disable the PCID cpu feature. 2978 2979 norandmaps Don't use address space randomization. Equivalent to 2980 echo 0 > /proc/sys/kernel/randomize_va_space 2981 2982 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2983 with UP alternatives 2984 2985 nordrand [X86] Disable kernel use of the RDRAND and 2986 RDSEED instructions even if they are supported 2987 by the processor. RDRAND and RDSEED are still 2988 available to user space applications. 2989 2990 noresume [SWSUSP] Disables resume and restores original swap 2991 space. 2992 2993 no-scroll [VGA] Disables scrollback. 2994 This is required for the Braillex ib80-piezo Braille 2995 reader made by F.H. Papenmeier (Germany). 2996 2997 nosbagart [IA-64] 2998 2999 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3000 3001 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3002 and disable the IO APIC. legacy for "maxcpus=0". 3003 3004 nosoftlockup [KNL] Disable the soft-lockup detector. 3005 3006 nosync [HW,M68K] Disables sync negotiation for all devices. 3007 3008 nowatchdog [KNL] Disable both lockup detectors, i.e. 3009 soft-lockup and NMI watchdog (hard-lockup). 3010 3011 nowb [ARM] 3012 3013 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3014 3015 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3016 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3017 Some features depend on CPU0. Known dependencies are: 3018 1. Resume from suspend/hibernate depends on CPU0. 3019 Suspend/hibernate will fail if CPU0 is offline and you 3020 need to online CPU0 before suspend/hibernate. 3021 2. PIC interrupts also depend on CPU0. CPU0 can't be 3022 removed if a PIC interrupt is detected. 3023 It's said poweroff/reboot may depend on CPU0 on some 3024 machines although I haven't seen such issues so far 3025 after CPU0 is offline on a few tested machines. 3026 If the dependencies are under your control, you can 3027 turn on cpu0_hotplug. 3028 3029 nps_mtm_hs_ctr= [KNL,ARC] 3030 This parameter sets the maximum duration, in 3031 cycles, each HW thread of the CTOP can run 3032 without interruptions, before HW switches it. 3033 The actual maximum duration is 16 times this 3034 parameter's value. 3035 Format: integer between 1 and 255 3036 Default: 255 3037 3038 nptcg= [IA-64] Override max number of concurrent global TLB 3039 purges which is reported from either PAL_VM_SUMMARY or 3040 SAL PALO. 3041 3042 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3043 could support. nr_cpus=n : n >= 1 limits the kernel to 3044 support 'n' processors. It could be larger than the 3045 number of already plugged CPU during bootup, later in 3046 runtime you can physically add extra cpu until it reaches 3047 n. So during boot up some boot time memory for per-cpu 3048 variables need be pre-allocated for later physical cpu 3049 hot plugging. 3050 3051 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3052 3053 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3054 Allowed values are enable and disable 3055 3056 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3057 'node', 'default' can be specified 3058 This can be set from sysctl after boot. 3059 See Documentation/sysctl/vm.txt for details. 3060 3061 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3062 See Documentation/debugging-via-ohci1394.txt for more 3063 info. 3064 3065 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3066 Rather than timing out after 20 ms if an EC 3067 command is not properly ACKed, override the length 3068 of the timeout. We have interrupts disabled while 3069 waiting for the ACK, so if this is set too high 3070 interrupts *may* be lost! 3071 3072 omap_mux= [OMAP] Override bootloader pin multiplexing. 3073 Format: <mux_mode0.mode_name=value>... 3074 For example, to override I2C bus2: 3075 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3076 3077 oprofile.timer= [HW] 3078 Use timer interrupt instead of performance counters 3079 3080 oprofile.cpu_type= Force an oprofile cpu type 3081 This might be useful if you have an older oprofile 3082 userland or if you want common events. 3083 Format: { arch_perfmon } 3084 arch_perfmon: [X86] Force use of architectural 3085 perfmon on Intel CPUs instead of the 3086 CPU specific event set. 3087 timer: [X86] Force use of architectural NMI 3088 timer mode (see also oprofile.timer 3089 for generic hr timer mode) 3090 3091 oops=panic Always panic on oopses. Default is to just kill the 3092 process, but there is a small probability of 3093 deadlocking the machine. 3094 This will also cause panics on machine check exceptions. 3095 Useful together with panic=30 to trigger a reboot. 3096 3097 page_owner= [KNL] Boot-time page_owner enabling option. 3098 Storage of the information about who allocated 3099 each page is disabled in default. With this switch, 3100 we can turn it on. 3101 on: enable the feature 3102 3103 page_poison= [KNL] Boot-time parameter changing the state of 3104 poisoning on the buddy allocator, available with 3105 CONFIG_PAGE_POISONING=y. 3106 off: turn off poisoning (default) 3107 on: turn on poisoning 3108 3109 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3110 timeout > 0: seconds before rebooting 3111 timeout = 0: wait forever 3112 timeout < 0: reboot immediately 3113 Format: <timeout> 3114 3115 panic_print= Bitmask for printing system info when panic happens. 3116 User can chose combination of the following bits: 3117 bit 0: print all tasks info 3118 bit 1: print system memory info 3119 bit 2: print timer info 3120 bit 3: print locks info if CONFIG_LOCKDEP is on 3121 bit 4: print ftrace buffer 3122 3123 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3124 on a WARN(). 3125 3126 crash_kexec_post_notifiers 3127 Run kdump after running panic-notifiers and dumping 3128 kmsg. This only for the users who doubt kdump always 3129 succeeds in any situation. 3130 Note that this also increases risks of kdump failure, 3131 because some panic notifiers can make the crashed 3132 kernel more unstable. 3133 3134 parkbd.port= [HW] Parallel port number the keyboard adapter is 3135 connected to, default is 0. 3136 Format: <parport#> 3137 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3138 0 for XT, 1 for AT (default is AT). 3139 Format: <mode> 3140 3141 parport= [HW,PPT] Specify parallel ports. 0 disables. 3142 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3143 Use 'auto' to force the driver to use any 3144 IRQ/DMA settings detected (the default is to 3145 ignore detected IRQ/DMA settings because of 3146 possible conflicts). You can specify the base 3147 address, IRQ, and DMA settings; IRQ and DMA 3148 should be numbers, or 'auto' (for using detected 3149 settings on that particular port), or 'nofifo' 3150 (to avoid using a FIFO even if it is detected). 3151 Parallel ports are assigned in the order they 3152 are specified on the command line, starting 3153 with parport0. 3154 3155 parport_init_mode= [HW,PPT] 3156 Configure VIA parallel port to operate in 3157 a specific mode. This is necessary on Pegasos 3158 computer where firmware has no options for setting 3159 up parallel port mode and sets it to spp. 3160 Currently this function knows 686a and 8231 chips. 3161 Format: [spp|ps2|epp|ecp|ecpepp] 3162 3163 pause_on_oops= 3164 Halt all CPUs after the first oops has been printed for 3165 the specified number of seconds. This is to be used if 3166 your oopses keep scrolling off the screen. 3167 3168 pcbit= [HW,ISDN] 3169 3170 pcd. [PARIDE] 3171 See header of drivers/block/paride/pcd.c. 3172 See also Documentation/blockdev/paride.txt. 3173 3174 pci=option[,option...] [PCI] various PCI subsystem options. 3175 3176 Some options herein operate on a specific device 3177 or a set of devices (<pci_dev>). These are 3178 specified in one of the following formats: 3179 3180 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3181 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3182 3183 Note: the first format specifies a PCI 3184 bus/device/function address which may change 3185 if new hardware is inserted, if motherboard 3186 firmware changes, or due to changes caused 3187 by other kernel parameters. If the 3188 domain is left unspecified, it is 3189 taken to be zero. Optionally, a path 3190 to a device through multiple device/function 3191 addresses can be specified after the base 3192 address (this is more robust against 3193 renumbering issues). The second format 3194 selects devices using IDs from the 3195 configuration space which may match multiple 3196 devices in the system. 3197 3198 earlydump dump PCI config space before the kernel 3199 changes anything 3200 off [X86] don't probe for the PCI bus 3201 bios [X86-32] force use of PCI BIOS, don't access 3202 the hardware directly. Use this if your machine 3203 has a non-standard PCI host bridge. 3204 nobios [X86-32] disallow use of PCI BIOS, only direct 3205 hardware access methods are allowed. Use this 3206 if you experience crashes upon bootup and you 3207 suspect they are caused by the BIOS. 3208 conf1 [X86] Force use of PCI Configuration Access 3209 Mechanism 1 (config address in IO port 0xCF8, 3210 data in IO port 0xCFC, both 32-bit). 3211 conf2 [X86] Force use of PCI Configuration Access 3212 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3213 the function, IO port 0xCFA, also 8-bit, sets 3214 bus number. The config space is then accessed 3215 through ports 0xC000-0xCFFF). 3216 See http://wiki.osdev.org/PCI for more info 3217 on the configuration access mechanisms. 3218 noaer [PCIE] If the PCIEAER kernel config parameter is 3219 enabled, this kernel boot option can be used to 3220 disable the use of PCIE advanced error reporting. 3221 nodomains [PCI] Disable support for multiple PCI 3222 root domains (aka PCI segments, in ACPI-speak). 3223 nommconf [X86] Disable use of MMCONFIG for PCI 3224 Configuration 3225 check_enable_amd_mmconf [X86] check for and enable 3226 properly configured MMIO access to PCI 3227 config space on AMD family 10h CPU 3228 nomsi [MSI] If the PCI_MSI kernel config parameter is 3229 enabled, this kernel boot option can be used to 3230 disable the use of MSI interrupts system-wide. 3231 noioapicquirk [APIC] Disable all boot interrupt quirks. 3232 Safety option to keep boot IRQs enabled. This 3233 should never be necessary. 3234 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3235 primary IO-APIC for bridges that cannot disable 3236 boot IRQs. This fixes a source of spurious IRQs 3237 when the system masks IRQs. 3238 noioapicreroute [APIC] Disable workaround that uses the 3239 boot IRQ equivalent of an IRQ that connects to 3240 a chipset where boot IRQs cannot be disabled. 3241 The opposite of ioapicreroute. 3242 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3243 routing table. These calls are known to be buggy 3244 on several machines and they hang the machine 3245 when used, but on other computers it's the only 3246 way to get the interrupt routing table. Try 3247 this option if the kernel is unable to allocate 3248 IRQs or discover secondary PCI buses on your 3249 motherboard. 3250 rom [X86] Assign address space to expansion ROMs. 3251 Use with caution as certain devices share 3252 address decoders between ROMs and other 3253 resources. 3254 norom [X86] Do not assign address space to 3255 expansion ROMs that do not already have 3256 BIOS assigned address ranges. 3257 nobar [X86] Do not assign address space to the 3258 BARs that weren't assigned by the BIOS. 3259 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3260 assigned automatically to PCI devices. You can 3261 make the kernel exclude IRQs of your ISA cards 3262 this way. 3263 pirqaddr=0xAAAAA [X86] Specify the physical address 3264 of the PIRQ table (normally generated 3265 by the BIOS) if it is outside the 3266 F0000h-100000h range. 3267 lastbus=N [X86] Scan all buses thru bus #N. Can be 3268 useful if the kernel is unable to find your 3269 secondary buses and you want to tell it 3270 explicitly which ones they are. 3271 assign-busses [X86] Always assign all PCI bus 3272 numbers ourselves, overriding 3273 whatever the firmware may have done. 3274 usepirqmask [X86] Honor the possible IRQ mask stored 3275 in the BIOS $PIR table. This is needed on 3276 some systems with broken BIOSes, notably 3277 some HP Pavilion N5400 and Omnibook XE3 3278 notebooks. This will have no effect if ACPI 3279 IRQ routing is enabled. 3280 noacpi [X86] Do not use ACPI for IRQ routing 3281 or for PCI scanning. 3282 use_crs [X86] Use PCI host bridge window information 3283 from ACPI. On BIOSes from 2008 or later, this 3284 is enabled by default. If you need to use this, 3285 please report a bug. 3286 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3287 If you need to use this, please report a bug. 3288 routeirq Do IRQ routing for all PCI devices. 3289 This is normally done in pci_enable_device(), 3290 so this option is a temporary workaround 3291 for broken drivers that don't call it. 3292 skip_isa_align [X86] do not align io start addr, so can 3293 handle more pci cards 3294 noearly [X86] Don't do any early type 1 scanning. 3295 This might help on some broken boards which 3296 machine check when some devices' config space 3297 is read. But various workarounds are disabled 3298 and some IOMMU drivers will not work. 3299 bfsort Sort PCI devices into breadth-first order. 3300 This sorting is done to get a device 3301 order compatible with older (<= 2.4) kernels. 3302 nobfsort Don't sort PCI devices into breadth-first order. 3303 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3304 tuning and use the BIOS-configured MPS defaults. 3305 pcie_bus_safe Set every device's MPS to the largest value 3306 supported by all devices below the root complex. 3307 pcie_bus_perf Set device MPS to the largest allowable MPS 3308 based on its parent bus. Also set MRRS (Max 3309 Read Request Size) to the largest supported 3310 value (no larger than the MPS that the device 3311 or bus can support) for best performance. 3312 pcie_bus_peer2peer Set every device's MPS to 128B, which 3313 every device is guaranteed to support. This 3314 configuration allows peer-to-peer DMA between 3315 any pair of devices, possibly at the cost of 3316 reduced performance. This also guarantees 3317 that hot-added devices will work. 3318 cbiosize=nn[KMG] The fixed amount of bus space which is 3319 reserved for the CardBus bridge's IO window. 3320 The default value is 256 bytes. 3321 cbmemsize=nn[KMG] The fixed amount of bus space which is 3322 reserved for the CardBus bridge's memory 3323 window. The default value is 64 megabytes. 3324 resource_alignment= 3325 Format: 3326 [<order of align>@]<pci_dev>[; ...] 3327 Specifies alignment and device to reassign 3328 aligned memory resources. How to 3329 specify the device is described above. 3330 If <order of align> is not specified, 3331 PAGE_SIZE is used as alignment. 3332 PCI-PCI bridge can be specified, if resource 3333 windows need to be expanded. 3334 To specify the alignment for several 3335 instances of a device, the PCI vendor, 3336 device, subvendor, and subdevice may be 3337 specified, e.g., 4096@pci:8086:9c22:103c:198f 3338 ecrc= Enable/disable PCIe ECRC (transaction layer 3339 end-to-end CRC checking). 3340 bios: Use BIOS/firmware settings. This is the 3341 the default. 3342 off: Turn ECRC off 3343 on: Turn ECRC on. 3344 hpiosize=nn[KMG] The fixed amount of bus space which is 3345 reserved for hotplug bridge's IO window. 3346 Default size is 256 bytes. 3347 hpmemsize=nn[KMG] The fixed amount of bus space which is 3348 reserved for hotplug bridge's memory window. 3349 Default size is 2 megabytes. 3350 hpbussize=nn The minimum amount of additional bus numbers 3351 reserved for buses below a hotplug bridge. 3352 Default is 1. 3353 realloc= Enable/disable reallocating PCI bridge resources 3354 if allocations done by BIOS are too small to 3355 accommodate resources required by all child 3356 devices. 3357 off: Turn realloc off 3358 on: Turn realloc on 3359 realloc same as realloc=on 3360 noari do not use PCIe ARI. 3361 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3362 do not use PCIe ATS (and IOMMU device IOTLB). 3363 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3364 only look for one device below a PCIe downstream 3365 port. 3366 big_root_window Try to add a big 64bit memory window to the PCIe 3367 root complex on AMD CPUs. Some GFX hardware 3368 can resize a BAR to allow access to all VRAM. 3369 Adding the window is slightly risky (it may 3370 conflict with unreported devices), so this 3371 taints the kernel. 3372 disable_acs_redir=<pci_dev>[; ...] 3373 Specify one or more PCI devices (in the format 3374 specified above) separated by semicolons. 3375 Each device specified will have the PCI ACS 3376 redirect capabilities forced off which will 3377 allow P2P traffic between devices through 3378 bridges without forcing it upstream. Note: 3379 this removes isolation between devices and 3380 may put more devices in an IOMMU group. 3381 3382 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3383 Management. 3384 off Disable ASPM. 3385 force Enable ASPM even on devices that claim not to support it. 3386 WARNING: Forcing ASPM on may cause system lockups. 3387 3388 pcie_ports= [PCIE] PCIe port services handling: 3389 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3390 even if the platform doesn't give the OS permission to 3391 use them. This may cause conflicts if the platform 3392 also tries to use these services. 3393 compat Disable native PCIe services (PME, AER, DPC, PCIe 3394 hotplug). 3395 3396 pcie_port_pm= [PCIE] PCIe port power management handling: 3397 off Disable power management of all PCIe ports 3398 force Forcibly enable power management of all PCIe ports 3399 3400 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3401 nomsi Do not use MSI for native PCIe PME signaling (this makes 3402 all PCIe root ports use INTx for all services). 3403 3404 pcmv= [HW,PCMCIA] BadgePAD 4 3405 3406 pd_ignore_unused 3407 [PM] 3408 Keep all power-domains already enabled by bootloader on, 3409 even if no driver has claimed them. This is useful 3410 for debug and development, but should not be 3411 needed on a platform with proper driver support. 3412 3413 pd. [PARIDE] 3414 See Documentation/blockdev/paride.txt. 3415 3416 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3417 boot time. 3418 Format: { 0 | 1 } 3419 See arch/parisc/kernel/pdc_chassis.c 3420 3421 percpu_alloc= Select which percpu first chunk allocator to use. 3422 Currently supported values are "embed" and "page". 3423 Archs may support subset or none of the selections. 3424 See comments in mm/percpu.c for details on each 3425 allocator. This parameter is primarily for debugging 3426 and performance comparison. 3427 3428 pf. [PARIDE] 3429 See Documentation/blockdev/paride.txt. 3430 3431 pg. [PARIDE] 3432 See Documentation/blockdev/paride.txt. 3433 3434 pirq= [SMP,APIC] Manual mp-table setup 3435 See Documentation/x86/i386/IO-APIC.txt. 3436 3437 plip= [PPT,NET] Parallel port network link 3438 Format: { parport<nr> | timid | 0 } 3439 See also Documentation/admin-guide/parport.rst. 3440 3441 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3442 Override pmtimer IOPort with a hex value. 3443 e.g. pmtmr=0x508 3444 3445 pnp.debug=1 [PNP] 3446 Enable PNP debug messages (depends on the 3447 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3448 via /sys/module/pnp/parameters/debug. We always show 3449 current resource usage; turning this on also shows 3450 possible settings and some assignment information. 3451 3452 pnpacpi= [ACPI] 3453 { off } 3454 3455 pnpbios= [ISAPNP] 3456 { on | off | curr | res | no-curr | no-res } 3457 3458 pnp_reserve_irq= 3459 [ISAPNP] Exclude IRQs for the autoconfiguration 3460 3461 pnp_reserve_dma= 3462 [ISAPNP] Exclude DMAs for the autoconfiguration 3463 3464 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3465 Ranges are in pairs (I/O port base and size). 3466 3467 pnp_reserve_mem= 3468 [ISAPNP] Exclude memory regions for the 3469 autoconfiguration. 3470 Ranges are in pairs (memory base and size). 3471 3472 ports= [IP_VS_FTP] IPVS ftp helper module 3473 Default is 21. 3474 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3475 may be specified. 3476 Format: <port>,<port>.... 3477 3478 powersave=off [PPC] This option disables power saving features. 3479 It specifically disables cpuidle and sets the 3480 platform machine description specific power_save 3481 function to NULL. On Idle the CPU just reduces 3482 execution priority. 3483 3484 ppc_strict_facility_enable 3485 [PPC] This option catches any kernel floating point, 3486 Altivec, VSX and SPE outside of regions specifically 3487 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3488 There is some performance impact when enabling this. 3489 3490 ppc_tm= [PPC] 3491 Format: {"off"} 3492 Disable Hardware Transactional Memory 3493 3494 print-fatal-signals= 3495 [KNL] debug: print fatal signals 3496 3497 If enabled, warn about various signal handling 3498 related application anomalies: too many signals, 3499 too many POSIX.1 timers, fatal signals causing a 3500 coredump - etc. 3501 3502 If you hit the warning due to signal overflow, 3503 you might want to try "ulimit -i unlimited". 3504 3505 default: off. 3506 3507 printk.always_kmsg_dump= 3508 Trigger kmsg_dump for cases other than kernel oops or 3509 panics 3510 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3511 default: disabled 3512 3513 printk.devkmsg={on,off,ratelimit} 3514 Control writing to /dev/kmsg. 3515 on - unlimited logging to /dev/kmsg from userspace 3516 off - logging to /dev/kmsg disabled 3517 ratelimit - ratelimit the logging 3518 Default: ratelimit 3519 3520 printk.time= Show timing data prefixed to each printk message line 3521 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3522 3523 processor.max_cstate= [HW,ACPI] 3524 Limit processor to maximum C-state 3525 max_cstate=9 overrides any DMI blacklist limit. 3526 3527 processor.nocst [HW,ACPI] 3528 Ignore the _CST method to determine C-states, 3529 instead using the legacy FADT method 3530 3531 profile= [KNL] Enable kernel profiling via /proc/profile 3532 Format: [<profiletype>,]<number> 3533 Param: <profiletype>: "schedule", "sleep", or "kvm" 3534 [defaults to kernel profiling] 3535 Param: "schedule" - profile schedule points. 3536 Param: "sleep" - profile D-state sleeping (millisecs). 3537 Requires CONFIG_SCHEDSTATS 3538 Param: "kvm" - profile VM exits. 3539 Param: <number> - step/bucket size as a power of 2 for 3540 statistical time based profiling. 3541 3542 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3543 before loading. 3544 See Documentation/blockdev/ramdisk.txt. 3545 3546 psi= [KNL] Enable or disable pressure stall information 3547 tracking. 3548 Format: <bool> 3549 3550 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3551 probe for; one of (bare|imps|exps|lifebook|any). 3552 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3553 per second. 3554 psmouse.resetafter= [HW,MOUSE] 3555 Try to reset the device after so many bad packets 3556 (0 = never). 3557 psmouse.resolution= 3558 [HW,MOUSE] Set desired mouse resolution, in dpi. 3559 psmouse.smartscroll= 3560 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3561 0 = disabled, 1 = enabled (default). 3562 3563 pstore.backend= Specify the name of the pstore backend to use 3564 3565 pt. [PARIDE] 3566 See Documentation/blockdev/paride.txt. 3567 3568 pti= [X86_64] Control Page Table Isolation of user and 3569 kernel address spaces. Disabling this feature 3570 removes hardening, but improves performance of 3571 system calls and interrupts. 3572 3573 on - unconditionally enable 3574 off - unconditionally disable 3575 auto - kernel detects whether your CPU model is 3576 vulnerable to issues that PTI mitigates 3577 3578 Not specifying this option is equivalent to pti=auto. 3579 3580 nopti [X86_64] 3581 Equivalent to pti=off 3582 3583 pty.legacy_count= 3584 [KNL] Number of legacy pty's. Overwrites compiled-in 3585 default number. 3586 3587 quiet [KNL] Disable most log messages 3588 3589 r128= [HW,DRM] 3590 3591 raid= [HW,RAID] 3592 See Documentation/admin-guide/md.rst. 3593 3594 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3595 See Documentation/blockdev/ramdisk.txt. 3596 3597 random.trust_cpu={on,off} 3598 [KNL] Enable or disable trusting the use of the 3599 CPU's random number generator (if available) to 3600 fully seed the kernel's CRNG. Default is controlled 3601 by CONFIG_RANDOM_TRUST_CPU. 3602 3603 ras=option[,option,...] [KNL] RAS-specific options 3604 3605 cec_disable [X86] 3606 Disable the Correctable Errors Collector, 3607 see CONFIG_RAS_CEC help text. 3608 3609 rcu_nocbs= [KNL] 3610 The argument is a cpu list, as described above. 3611 3612 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3613 the specified list of CPUs to be no-callback CPUs. 3614 Invocation of these CPUs' RCU callbacks will be 3615 offloaded to "rcuox/N" kthreads created for that 3616 purpose, where "x" is "p" for RCU-preempt, and 3617 "s" for RCU-sched, and "N" is the CPU number. 3618 This reduces OS jitter on the offloaded CPUs, 3619 which can be useful for HPC and real-time 3620 workloads. It can also improve energy efficiency 3621 for asymmetric multiprocessors. 3622 3623 rcu_nocb_poll [KNL] 3624 Rather than requiring that offloaded CPUs 3625 (specified by rcu_nocbs= above) explicitly 3626 awaken the corresponding "rcuoN" kthreads, 3627 make these kthreads poll for callbacks. 3628 This improves the real-time response for the 3629 offloaded CPUs by relieving them of the need to 3630 wake up the corresponding kthread, but degrades 3631 energy efficiency by requiring that the kthreads 3632 periodically wake up to do the polling. 3633 3634 rcutree.blimit= [KNL] 3635 Set maximum number of finished RCU callbacks to 3636 process in one batch. 3637 3638 rcutree.dump_tree= [KNL] 3639 Dump the structure of the rcu_node combining tree 3640 out at early boot. This is used for diagnostic 3641 purposes, to verify correct tree setup. 3642 3643 rcutree.gp_cleanup_delay= [KNL] 3644 Set the number of jiffies to delay each step of 3645 RCU grace-period cleanup. 3646 3647 rcutree.gp_init_delay= [KNL] 3648 Set the number of jiffies to delay each step of 3649 RCU grace-period initialization. 3650 3651 rcutree.gp_preinit_delay= [KNL] 3652 Set the number of jiffies to delay each step of 3653 RCU grace-period pre-initialization, that is, 3654 the propagation of recent CPU-hotplug changes up 3655 the rcu_node combining tree. 3656 3657 rcutree.rcu_fanout_exact= [KNL] 3658 Disable autobalancing of the rcu_node combining 3659 tree. This is used by rcutorture, and might 3660 possibly be useful for architectures having high 3661 cache-to-cache transfer latencies. 3662 3663 rcutree.rcu_fanout_leaf= [KNL] 3664 Change the number of CPUs assigned to each 3665 leaf rcu_node structure. Useful for very 3666 large systems, which will choose the value 64, 3667 and for NUMA systems with large remote-access 3668 latencies, which will choose a value aligned 3669 with the appropriate hardware boundaries. 3670 3671 rcutree.jiffies_till_first_fqs= [KNL] 3672 Set delay from grace-period initialization to 3673 first attempt to force quiescent states. 3674 Units are jiffies, minimum value is zero, 3675 and maximum value is HZ. 3676 3677 rcutree.jiffies_till_next_fqs= [KNL] 3678 Set delay between subsequent attempts to force 3679 quiescent states. Units are jiffies, minimum 3680 value is one, and maximum value is HZ. 3681 3682 rcutree.jiffies_till_sched_qs= [KNL] 3683 Set required age in jiffies for a 3684 given grace period before RCU starts 3685 soliciting quiescent-state help from 3686 rcu_note_context_switch() and cond_resched(). 3687 If not specified, the kernel will calculate 3688 a value based on the most recent settings 3689 of rcutree.jiffies_till_first_fqs 3690 and rcutree.jiffies_till_next_fqs. 3691 This calculated value may be viewed in 3692 rcutree.jiffies_to_sched_qs. Any attempt to set 3693 rcutree.jiffies_to_sched_qs will be cheerfully 3694 overwritten. 3695 3696 rcutree.kthread_prio= [KNL,BOOT] 3697 Set the SCHED_FIFO priority of the RCU per-CPU 3698 kthreads (rcuc/N). This value is also used for 3699 the priority of the RCU boost threads (rcub/N) 3700 and for the RCU grace-period kthreads (rcu_bh, 3701 rcu_preempt, and rcu_sched). If RCU_BOOST is 3702 set, valid values are 1-99 and the default is 1 3703 (the least-favored priority). Otherwise, when 3704 RCU_BOOST is not set, valid values are 0-99 and 3705 the default is zero (non-realtime operation). 3706 3707 rcutree.rcu_nocb_leader_stride= [KNL] 3708 Set the number of NOCB kthread groups, which 3709 defaults to the square root of the number of 3710 CPUs. Larger numbers reduces the wakeup overhead 3711 on the per-CPU grace-period kthreads, but increases 3712 that same overhead on each group's leader. 3713 3714 rcutree.qhimark= [KNL] 3715 Set threshold of queued RCU callbacks beyond which 3716 batch limiting is disabled. 3717 3718 rcutree.qlowmark= [KNL] 3719 Set threshold of queued RCU callbacks below which 3720 batch limiting is re-enabled. 3721 3722 rcutree.rcu_idle_gp_delay= [KNL] 3723 Set wakeup interval for idle CPUs that have 3724 RCU callbacks (RCU_FAST_NO_HZ=y). 3725 3726 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3727 Set wakeup interval for idle CPUs that have 3728 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3729 Lazy RCU callbacks are those which RCU can 3730 prove do nothing more than free memory. 3731 3732 rcutree.rcu_kick_kthreads= [KNL] 3733 Cause the grace-period kthread to get an extra 3734 wake_up() if it sleeps three times longer than 3735 it should at force-quiescent-state time. 3736 This wake_up() will be accompanied by a 3737 WARN_ONCE() splat and an ftrace_dump(). 3738 3739 rcutree.sysrq_rcu= [KNL] 3740 Commandeer a sysrq key to dump out Tree RCU's 3741 rcu_node tree with an eye towards determining 3742 why a new grace period has not yet started. 3743 3744 rcuperf.gp_async= [KNL] 3745 Measure performance of asynchronous 3746 grace-period primitives such as call_rcu(). 3747 3748 rcuperf.gp_async_max= [KNL] 3749 Specify the maximum number of outstanding 3750 callbacks per writer thread. When a writer 3751 thread exceeds this limit, it invokes the 3752 corresponding flavor of rcu_barrier() to allow 3753 previously posted callbacks to drain. 3754 3755 rcuperf.gp_exp= [KNL] 3756 Measure performance of expedited synchronous 3757 grace-period primitives. 3758 3759 rcuperf.holdoff= [KNL] 3760 Set test-start holdoff period. The purpose of 3761 this parameter is to delay the start of the 3762 test until boot completes in order to avoid 3763 interference. 3764 3765 rcuperf.nreaders= [KNL] 3766 Set number of RCU readers. The value -1 selects 3767 N, where N is the number of CPUs. A value 3768 "n" less than -1 selects N-n+1, where N is again 3769 the number of CPUs. For example, -2 selects N 3770 (the number of CPUs), -3 selects N+1, and so on. 3771 A value of "n" less than or equal to -N selects 3772 a single reader. 3773 3774 rcuperf.nwriters= [KNL] 3775 Set number of RCU writers. The values operate 3776 the same as for rcuperf.nreaders. 3777 N, where N is the number of CPUs 3778 3779 rcuperf.perf_type= [KNL] 3780 Specify the RCU implementation to test. 3781 3782 rcuperf.shutdown= [KNL] 3783 Shut the system down after performance tests 3784 complete. This is useful for hands-off automated 3785 testing. 3786 3787 rcuperf.verbose= [KNL] 3788 Enable additional printk() statements. 3789 3790 rcuperf.writer_holdoff= [KNL] 3791 Write-side holdoff between grace periods, 3792 in microseconds. The default of zero says 3793 no holdoff. 3794 3795 rcutorture.fqs_duration= [KNL] 3796 Set duration of force_quiescent_state bursts 3797 in microseconds. 3798 3799 rcutorture.fqs_holdoff= [KNL] 3800 Set holdoff time within force_quiescent_state bursts 3801 in microseconds. 3802 3803 rcutorture.fqs_stutter= [KNL] 3804 Set wait time between force_quiescent_state bursts 3805 in seconds. 3806 3807 rcutorture.fwd_progress= [KNL] 3808 Enable RCU grace-period forward-progress testing 3809 for the types of RCU supporting this notion. 3810 3811 rcutorture.fwd_progress_div= [KNL] 3812 Specify the fraction of a CPU-stall-warning 3813 period to do tight-loop forward-progress testing. 3814 3815 rcutorture.fwd_progress_holdoff= [KNL] 3816 Number of seconds to wait between successive 3817 forward-progress tests. 3818 3819 rcutorture.fwd_progress_need_resched= [KNL] 3820 Enclose cond_resched() calls within checks for 3821 need_resched() during tight-loop forward-progress 3822 testing. 3823 3824 rcutorture.gp_cond= [KNL] 3825 Use conditional/asynchronous update-side 3826 primitives, if available. 3827 3828 rcutorture.gp_exp= [KNL] 3829 Use expedited update-side primitives, if available. 3830 3831 rcutorture.gp_normal= [KNL] 3832 Use normal (non-expedited) asynchronous 3833 update-side primitives, if available. 3834 3835 rcutorture.gp_sync= [KNL] 3836 Use normal (non-expedited) synchronous 3837 update-side primitives, if available. If all 3838 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3839 rcutorture.gp_normal=, and rcutorture.gp_sync= 3840 are zero, rcutorture acts as if is interpreted 3841 they are all non-zero. 3842 3843 rcutorture.n_barrier_cbs= [KNL] 3844 Set callbacks/threads for rcu_barrier() testing. 3845 3846 rcutorture.nfakewriters= [KNL] 3847 Set number of concurrent RCU writers. These just 3848 stress RCU, they don't participate in the actual 3849 test, hence the "fake". 3850 3851 rcutorture.nreaders= [KNL] 3852 Set number of RCU readers. The value -1 selects 3853 N-1, where N is the number of CPUs. A value 3854 "n" less than -1 selects N-n-2, where N is again 3855 the number of CPUs. For example, -2 selects N 3856 (the number of CPUs), -3 selects N+1, and so on. 3857 3858 rcutorture.object_debug= [KNL] 3859 Enable debug-object double-call_rcu() testing. 3860 3861 rcutorture.onoff_holdoff= [KNL] 3862 Set time (s) after boot for CPU-hotplug testing. 3863 3864 rcutorture.onoff_interval= [KNL] 3865 Set time (jiffies) between CPU-hotplug operations, 3866 or zero to disable CPU-hotplug testing. 3867 3868 rcutorture.shuffle_interval= [KNL] 3869 Set task-shuffle interval (s). Shuffling tasks 3870 allows some CPUs to go into dyntick-idle mode 3871 during the rcutorture test. 3872 3873 rcutorture.shutdown_secs= [KNL] 3874 Set time (s) after boot system shutdown. This 3875 is useful for hands-off automated testing. 3876 3877 rcutorture.stall_cpu= [KNL] 3878 Duration of CPU stall (s) to test RCU CPU stall 3879 warnings, zero to disable. 3880 3881 rcutorture.stall_cpu_holdoff= [KNL] 3882 Time to wait (s) after boot before inducing stall. 3883 3884 rcutorture.stall_cpu_irqsoff= [KNL] 3885 Disable interrupts while stalling if set. 3886 3887 rcutorture.stat_interval= [KNL] 3888 Time (s) between statistics printk()s. 3889 3890 rcutorture.stutter= [KNL] 3891 Time (s) to stutter testing, for example, specifying 3892 five seconds causes the test to run for five seconds, 3893 wait for five seconds, and so on. This tests RCU's 3894 ability to transition abruptly to and from idle. 3895 3896 rcutorture.test_boost= [KNL] 3897 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3898 "Maybe" means test if the RCU implementation 3899 under test support RCU priority boosting. 3900 3901 rcutorture.test_boost_duration= [KNL] 3902 Duration (s) of each individual boost test. 3903 3904 rcutorture.test_boost_interval= [KNL] 3905 Interval (s) between each boost test. 3906 3907 rcutorture.test_no_idle_hz= [KNL] 3908 Test RCU's dyntick-idle handling. See also the 3909 rcutorture.shuffle_interval parameter. 3910 3911 rcutorture.torture_type= [KNL] 3912 Specify the RCU implementation to test. 3913 3914 rcutorture.verbose= [KNL] 3915 Enable additional printk() statements. 3916 3917 rcupdate.rcu_cpu_stall_suppress= [KNL] 3918 Suppress RCU CPU stall warning messages. 3919 3920 rcupdate.rcu_cpu_stall_timeout= [KNL] 3921 Set timeout for RCU CPU stall warning messages. 3922 3923 rcupdate.rcu_expedited= [KNL] 3924 Use expedited grace-period primitives, for 3925 example, synchronize_rcu_expedited() instead 3926 of synchronize_rcu(). This reduces latency, 3927 but can increase CPU utilization, degrade 3928 real-time latency, and degrade energy efficiency. 3929 No effect on CONFIG_TINY_RCU kernels. 3930 3931 rcupdate.rcu_normal= [KNL] 3932 Use only normal grace-period primitives, 3933 for example, synchronize_rcu() instead of 3934 synchronize_rcu_expedited(). This improves 3935 real-time latency, CPU utilization, and 3936 energy efficiency, but can expose users to 3937 increased grace-period latency. This parameter 3938 overrides rcupdate.rcu_expedited. No effect on 3939 CONFIG_TINY_RCU kernels. 3940 3941 rcupdate.rcu_normal_after_boot= [KNL] 3942 Once boot has completed (that is, after 3943 rcu_end_inkernel_boot() has been invoked), use 3944 only normal grace-period primitives. No effect 3945 on CONFIG_TINY_RCU kernels. 3946 3947 rcupdate.rcu_task_stall_timeout= [KNL] 3948 Set timeout in jiffies for RCU task stall warning 3949 messages. Disable with a value less than or equal 3950 to zero. 3951 3952 rcupdate.rcu_self_test= [KNL] 3953 Run the RCU early boot self tests 3954 3955 rdinit= [KNL] 3956 Format: <full_path> 3957 Run specified binary instead of /init from the ramdisk, 3958 used for early userspace startup. See initrd. 3959 3960 rdt= [HW,X86,RDT] 3961 Turn on/off individual RDT features. List is: 3962 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 3963 mba. 3964 E.g. to turn on cmt and turn off mba use: 3965 rdt=cmt,!mba 3966 3967 reboot= [KNL] 3968 Format (x86 or x86_64): 3969 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3970 [[,]s[mp]#### \ 3971 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3972 [[,]f[orce] 3973 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3974 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3975 reboot_force is either force or not specified, 3976 reboot_cpu is s[mp]#### with #### being the processor 3977 to be used for rebooting. 3978 3979 relax_domain_level= 3980 [KNL, SMP] Set scheduler's default relax_domain_level. 3981 See Documentation/cgroup-v1/cpusets.txt. 3982 3983 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 3984 Format: <base1>,<size1>[,<base2>,<size2>,...] 3985 Reserve I/O ports or memory so the kernel won't use 3986 them. If <base> is less than 0x10000, the region 3987 is assumed to be I/O ports; otherwise it is memory. 3988 3989 reservetop= [X86-32] 3990 Format: nn[KMG] 3991 Reserves a hole at the top of the kernel virtual 3992 address space. 3993 3994 reservelow= [X86] 3995 Format: nn[K] 3996 Set the amount of memory to reserve for BIOS at 3997 the bottom of the address space. 3998 3999 reset_devices [KNL] Force drivers to reset the underlying device 4000 during initialization. 4001 4002 resume= [SWSUSP] 4003 Specify the partition device for software suspend 4004 Format: 4005 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4006 4007 resume_offset= [SWSUSP] 4008 Specify the offset from the beginning of the partition 4009 given by "resume=" at which the swap header is located, 4010 in <PAGE_SIZE> units (needed only for swap files). 4011 See Documentation/power/swsusp-and-swap-files.txt 4012 4013 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4014 read the resume files 4015 4016 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4017 Useful for devices that are detected asynchronously 4018 (e.g. USB and MMC devices). 4019 4020 hibernate= [HIBERNATION] 4021 noresume Don't check if there's a hibernation image 4022 present during boot. 4023 nocompress Don't compress/decompress hibernation images. 4024 no Disable hibernation and resume. 4025 protect_image Turn on image protection during restoration 4026 (that will set all pages holding image data 4027 during restoration read-only). 4028 4029 retain_initrd [RAM] Keep initrd memory after extraction 4030 4031 rfkill.default_state= 4032 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4033 etc. communication is blocked by default. 4034 1 Unblocked. 4035 4036 rfkill.master_switch_mode= 4037 0 The "airplane mode" button does nothing. 4038 1 The "airplane mode" button toggles between everything 4039 blocked and the previous configuration. 4040 2 The "airplane mode" button toggles between everything 4041 blocked and everything unblocked. 4042 4043 rhash_entries= [KNL,NET] 4044 Set number of hash buckets for route cache 4045 4046 ring3mwait=disable 4047 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4048 CPUs. 4049 4050 ro [KNL] Mount root device read-only on boot 4051 4052 rodata= [KNL] 4053 on Mark read-only kernel memory as read-only (default). 4054 off Leave read-only kernel memory writable for debugging. 4055 4056 rockchip.usb_uart 4057 Enable the uart passthrough on the designated usb port 4058 on Rockchip SoCs. When active, the signals of the 4059 debug-uart get routed to the D+ and D- pins of the usb 4060 port and the regular usb controller gets disabled. 4061 4062 root= [KNL] Root filesystem 4063 See name_to_dev_t comment in init/do_mounts.c. 4064 4065 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4066 mount the root filesystem 4067 4068 rootflags= [KNL] Set root filesystem mount option string 4069 4070 rootfstype= [KNL] Set root filesystem type 4071 4072 rootwait [KNL] Wait (indefinitely) for root device to show up. 4073 Useful for devices that are detected asynchronously 4074 (e.g. USB and MMC devices). 4075 4076 rproc_mem=nn[KMG][@address] 4077 [KNL,ARM,CMA] Remoteproc physical memory block. 4078 Memory area to be used by remote processor image, 4079 managed by CMA. 4080 4081 rw [KNL] Mount root device read-write on boot 4082 4083 S [KNL] Run init in single mode 4084 4085 s390_iommu= [HW,S390] 4086 Set s390 IOTLB flushing mode 4087 strict 4088 With strict flushing every unmap operation will result in 4089 an IOTLB flush. Default is lazy flushing before reuse, 4090 which is faster. 4091 4092 sa1100ir [NET] 4093 See drivers/net/irda/sa1100_ir.c. 4094 4095 sbni= [NET] Granch SBNI12 leased line adapter 4096 4097 sched_debug [KNL] Enables verbose scheduler debug messages. 4098 4099 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4100 Allowed values are enable and disable. This feature 4101 incurs a small amount of overhead in the scheduler 4102 but is useful for debugging and performance tuning. 4103 4104 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4105 xtime_lock contention on larger systems, and/or RCU lock 4106 contention on all systems with CONFIG_MAXSMP set. 4107 Format: { "0" | "1" } 4108 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4109 1 -- enable. 4110 Note: increases power consumption, thus should only be 4111 enabled if running jitter sensitive (HPC/RT) workloads. 4112 4113 security= [SECURITY] Choose a security module to enable at boot. 4114 If this boot parameter is not specified, only the first 4115 security module asking for security registration will be 4116 loaded. An invalid security module name will be treated 4117 as if no module has been chosen. 4118 4119 selinux= [SELINUX] Disable or enable SELinux at boot time. 4120 Format: { "0" | "1" } 4121 See security/selinux/Kconfig help text. 4122 0 -- disable. 4123 1 -- enable. 4124 Default value is set via kernel config option. 4125 If enabled at boot time, /selinux/disable can be used 4126 later to disable prior to initial policy load. 4127 4128 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4129 Format: { "0" | "1" } 4130 See security/apparmor/Kconfig help text 4131 0 -- disable. 4132 1 -- enable. 4133 Default value is set via kernel config option. 4134 4135 serialnumber [BUGS=X86-32] 4136 4137 shapers= [NET] 4138 Maximal number of shapers. 4139 4140 simeth= [IA-64] 4141 simscsi= 4142 4143 slram= [HW,MTD] 4144 4145 slab_nomerge [MM] 4146 Disable merging of slabs with similar size. May be 4147 necessary if there is some reason to distinguish 4148 allocs to different slabs, especially in hardened 4149 environments where the risk of heap overflows and 4150 layout control by attackers can usually be 4151 frustrated by disabling merging. This will reduce 4152 most of the exposure of a heap attack to a single 4153 cache (risks via metadata attacks are mostly 4154 unchanged). Debug options disable merging on their 4155 own. 4156 For more information see Documentation/vm/slub.rst. 4157 4158 slab_max_order= [MM, SLAB] 4159 Determines the maximum allowed order for slabs. 4160 A high setting may cause OOMs due to memory 4161 fragmentation. Defaults to 1 for systems with 4162 more than 32MB of RAM, 0 otherwise. 4163 4164 slub_debug[=options[,slabs]] [MM, SLUB] 4165 Enabling slub_debug allows one to determine the 4166 culprit if slab objects become corrupted. Enabling 4167 slub_debug can create guard zones around objects and 4168 may poison objects when not in use. Also tracks the 4169 last alloc / free. For more information see 4170 Documentation/vm/slub.rst. 4171 4172 slub_memcg_sysfs= [MM, SLUB] 4173 Determines whether to enable sysfs directories for 4174 memory cgroup sub-caches. 1 to enable, 0 to disable. 4175 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4176 Enabling this can lead to a very high number of debug 4177 directories and files being created under 4178 /sys/kernel/slub. 4179 4180 slub_max_order= [MM, SLUB] 4181 Determines the maximum allowed order for slabs. 4182 A high setting may cause OOMs due to memory 4183 fragmentation. For more information see 4184 Documentation/vm/slub.rst. 4185 4186 slub_min_objects= [MM, SLUB] 4187 The minimum number of objects per slab. SLUB will 4188 increase the slab order up to slub_max_order to 4189 generate a sufficiently large slab able to contain 4190 the number of objects indicated. The higher the number 4191 of objects the smaller the overhead of tracking slabs 4192 and the less frequently locks need to be acquired. 4193 For more information see Documentation/vm/slub.rst. 4194 4195 slub_min_order= [MM, SLUB] 4196 Determines the minimum page order for slabs. Must be 4197 lower than slub_max_order. 4198 For more information see Documentation/vm/slub.rst. 4199 4200 slub_nomerge [MM, SLUB] 4201 Same with slab_nomerge. This is supported for legacy. 4202 See slab_nomerge for more information. 4203 4204 smart2= [HW] 4205 Format: <io1>[,<io2>[,...,<io8>]] 4206 4207 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4208 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4209 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4210 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4211 smsc-ircc2.ircc_irq= [HW] IRQ line 4212 smsc-ircc2.ircc_dma= [HW] DMA channel 4213 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4214 0: Toshiba Satellite 1800 (GP data pin select) 4215 1: Fast pin select (default) 4216 2: ATC IRMode 4217 4218 smt [KNL,S390] Set the maximum number of threads (logical 4219 CPUs) to use per physical CPU on systems capable of 4220 symmetric multithreading (SMT). Will be capped to the 4221 actual hardware limit. 4222 Format: <integer> 4223 Default: -1 (no limit) 4224 4225 softlockup_panic= 4226 [KNL] Should the soft-lockup detector generate panics. 4227 Format: <integer> 4228 4229 A nonzero value instructs the soft-lockup detector 4230 to panic the machine when a soft-lockup occurs. This 4231 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4232 which is the respective build-time switch to that 4233 functionality. 4234 4235 softlockup_all_cpu_backtrace= 4236 [KNL] Should the soft-lockup detector generate 4237 backtraces on all cpus. 4238 Format: <integer> 4239 4240 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4241 See Documentation/laptops/sonypi.txt 4242 4243 spectre_v2= [X86] Control mitigation of Spectre variant 2 4244 (indirect branch speculation) vulnerability. 4245 The default operation protects the kernel from 4246 user space attacks. 4247 4248 on - unconditionally enable, implies 4249 spectre_v2_user=on 4250 off - unconditionally disable, implies 4251 spectre_v2_user=off 4252 auto - kernel detects whether your CPU model is 4253 vulnerable 4254 4255 Selecting 'on' will, and 'auto' may, choose a 4256 mitigation method at run time according to the 4257 CPU, the available microcode, the setting of the 4258 CONFIG_RETPOLINE configuration option, and the 4259 compiler with which the kernel was built. 4260 4261 Selecting 'on' will also enable the mitigation 4262 against user space to user space task attacks. 4263 4264 Selecting 'off' will disable both the kernel and 4265 the user space protections. 4266 4267 Specific mitigations can also be selected manually: 4268 4269 retpoline - replace indirect branches 4270 retpoline,generic - google's original retpoline 4271 retpoline,amd - AMD-specific minimal thunk 4272 4273 Not specifying this option is equivalent to 4274 spectre_v2=auto. 4275 4276 spectre_v2_user= 4277 [X86] Control mitigation of Spectre variant 2 4278 (indirect branch speculation) vulnerability between 4279 user space tasks 4280 4281 on - Unconditionally enable mitigations. Is 4282 enforced by spectre_v2=on 4283 4284 off - Unconditionally disable mitigations. Is 4285 enforced by spectre_v2=off 4286 4287 prctl - Indirect branch speculation is enabled, 4288 but mitigation can be enabled via prctl 4289 per thread. The mitigation control state 4290 is inherited on fork. 4291 4292 prctl,ibpb 4293 - Like "prctl" above, but only STIBP is 4294 controlled per thread. IBPB is issued 4295 always when switching between different user 4296 space processes. 4297 4298 seccomp 4299 - Same as "prctl" above, but all seccomp 4300 threads will enable the mitigation unless 4301 they explicitly opt out. 4302 4303 seccomp,ibpb 4304 - Like "seccomp" above, but only STIBP is 4305 controlled per thread. IBPB is issued 4306 always when switching between different 4307 user space processes. 4308 4309 auto - Kernel selects the mitigation depending on 4310 the available CPU features and vulnerability. 4311 4312 Default mitigation: 4313 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4314 4315 Not specifying this option is equivalent to 4316 spectre_v2_user=auto. 4317 4318 spec_store_bypass_disable= 4319 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4320 (Speculative Store Bypass vulnerability) 4321 4322 Certain CPUs are vulnerable to an exploit against a 4323 a common industry wide performance optimization known 4324 as "Speculative Store Bypass" in which recent stores 4325 to the same memory location may not be observed by 4326 later loads during speculative execution. The idea 4327 is that such stores are unlikely and that they can 4328 be detected prior to instruction retirement at the 4329 end of a particular speculation execution window. 4330 4331 In vulnerable processors, the speculatively forwarded 4332 store can be used in a cache side channel attack, for 4333 example to read memory to which the attacker does not 4334 directly have access (e.g. inside sandboxed code). 4335 4336 This parameter controls whether the Speculative Store 4337 Bypass optimization is used. 4338 4339 On x86 the options are: 4340 4341 on - Unconditionally disable Speculative Store Bypass 4342 off - Unconditionally enable Speculative Store Bypass 4343 auto - Kernel detects whether the CPU model contains an 4344 implementation of Speculative Store Bypass and 4345 picks the most appropriate mitigation. If the 4346 CPU is not vulnerable, "off" is selected. If the 4347 CPU is vulnerable the default mitigation is 4348 architecture and Kconfig dependent. See below. 4349 prctl - Control Speculative Store Bypass per thread 4350 via prctl. Speculative Store Bypass is enabled 4351 for a process by default. The state of the control 4352 is inherited on fork. 4353 seccomp - Same as "prctl" above, but all seccomp threads 4354 will disable SSB unless they explicitly opt out. 4355 4356 Default mitigations: 4357 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4358 4359 On powerpc the options are: 4360 4361 on,auto - On Power8 and Power9 insert a store-forwarding 4362 barrier on kernel entry and exit. On Power7 4363 perform a software flush on kernel entry and 4364 exit. 4365 off - No action. 4366 4367 Not specifying this option is equivalent to 4368 spec_store_bypass_disable=auto. 4369 4370 spia_io_base= [HW,MTD] 4371 spia_fio_base= 4372 spia_pedr= 4373 spia_peddr= 4374 4375 srcutree.counter_wrap_check [KNL] 4376 Specifies how frequently to check for 4377 grace-period sequence counter wrap for the 4378 srcu_data structure's ->srcu_gp_seq_needed field. 4379 The greater the number of bits set in this kernel 4380 parameter, the less frequently counter wrap will 4381 be checked for. Note that the bottom two bits 4382 are ignored. 4383 4384 srcutree.exp_holdoff [KNL] 4385 Specifies how many nanoseconds must elapse 4386 since the end of the last SRCU grace period for 4387 a given srcu_struct until the next normal SRCU 4388 grace period will be considered for automatic 4389 expediting. Set to zero to disable automatic 4390 expediting. 4391 4392 ssbd= [ARM64,HW] 4393 Speculative Store Bypass Disable control 4394 4395 On CPUs that are vulnerable to the Speculative 4396 Store Bypass vulnerability and offer a 4397 firmware based mitigation, this parameter 4398 indicates how the mitigation should be used: 4399 4400 force-on: Unconditionally enable mitigation for 4401 for both kernel and userspace 4402 force-off: Unconditionally disable mitigation for 4403 for both kernel and userspace 4404 kernel: Always enable mitigation in the 4405 kernel, and offer a prctl interface 4406 to allow userspace to register its 4407 interest in being mitigated too. 4408 4409 stack_guard_gap= [MM] 4410 override the default stack gap protection. The value 4411 is in page units and it defines how many pages prior 4412 to (for stacks growing down) resp. after (for stacks 4413 growing up) the main stack are reserved for no other 4414 mapping. Default value is 256 pages. 4415 4416 stacktrace [FTRACE] 4417 Enabled the stack tracer on boot up. 4418 4419 stacktrace_filter=[function-list] 4420 [FTRACE] Limit the functions that the stack tracer 4421 will trace at boot up. function-list is a comma separated 4422 list of functions. This list can be changed at run 4423 time by the stack_trace_filter file in the debugfs 4424 tracing directory. Note, this enables stack tracing 4425 and the stacktrace above is not needed. 4426 4427 sti= [PARISC,HW] 4428 Format: <num> 4429 Set the STI (builtin display/keyboard on the HP-PARISC 4430 machines) console (graphic card) which should be used 4431 as the initial boot-console. 4432 See also comment in drivers/video/console/sticore.c. 4433 4434 sti_font= [HW] 4435 See comment in drivers/video/console/sticore.c. 4436 4437 stifb= [HW] 4438 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4439 4440 sunrpc.min_resvport= 4441 sunrpc.max_resvport= 4442 [NFS,SUNRPC] 4443 SunRPC servers often require that client requests 4444 originate from a privileged port (i.e. a port in the 4445 range 0 < portnr < 1024). 4446 An administrator who wishes to reserve some of these 4447 ports for other uses may adjust the range that the 4448 kernel's sunrpc client considers to be privileged 4449 using these two parameters to set the minimum and 4450 maximum port values. 4451 4452 sunrpc.svc_rpc_per_connection_limit= 4453 [NFS,SUNRPC] 4454 Limit the number of requests that the server will 4455 process in parallel from a single connection. 4456 The default value is 0 (no limit). 4457 4458 sunrpc.pool_mode= 4459 [NFS] 4460 Control how the NFS server code allocates CPUs to 4461 service thread pools. Depending on how many NICs 4462 you have and where their interrupts are bound, this 4463 option will affect which CPUs will do NFS serving. 4464 Note: this parameter cannot be changed while the 4465 NFS server is running. 4466 4467 auto the server chooses an appropriate mode 4468 automatically using heuristics 4469 global a single global pool contains all CPUs 4470 percpu one pool for each CPU 4471 pernode one pool for each NUMA node (equivalent 4472 to global on non-NUMA machines) 4473 4474 sunrpc.tcp_slot_table_entries= 4475 sunrpc.udp_slot_table_entries= 4476 [NFS,SUNRPC] 4477 Sets the upper limit on the number of simultaneous 4478 RPC calls that can be sent from the client to a 4479 server. Increasing these values may allow you to 4480 improve throughput, but will also increase the 4481 amount of memory reserved for use by the client. 4482 4483 suspend.pm_test_delay= 4484 [SUSPEND] 4485 Sets the number of seconds to remain in a suspend test 4486 mode before resuming the system (see 4487 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4488 is set. Default value is 5. 4489 4490 swapaccount=[0|1] 4491 [KNL] Enable accounting of swap in memory resource 4492 controller if no parameter or 1 is given or disable 4493 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4494 4495 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4496 Format: { <int> | force | noforce } 4497 <int> -- Number of I/O TLB slabs 4498 force -- force using of bounce buffers even if they 4499 wouldn't be automatically used by the kernel 4500 noforce -- Never use bounce buffers (for debugging) 4501 4502 switches= [HW,M68k] 4503 4504 sysfs.deprecated=0|1 [KNL] 4505 Enable/disable old style sysfs layout for old udev 4506 on older distributions. When this option is enabled 4507 very new udev will not work anymore. When this option 4508 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4509 in older udev will not work anymore. 4510 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4511 the kernel configuration. 4512 4513 sysrq_always_enabled 4514 [KNL] 4515 Ignore sysrq setting - this boot parameter will 4516 neutralize any effect of /proc/sys/kernel/sysrq. 4517 Useful for debugging. 4518 4519 tcpmhash_entries= [KNL,NET] 4520 Set the number of tcp_metrics_hash slots. 4521 Default value is 8192 or 16384 depending on total 4522 ram pages. This is used to specify the TCP metrics 4523 cache size. See Documentation/networking/ip-sysctl.txt 4524 "tcp_no_metrics_save" section for more details. 4525 4526 tdfx= [HW,DRM] 4527 4528 test_suspend= [SUSPEND][,N] 4529 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4530 standby suspend) or "freeze" (for suspend type freeze) 4531 as the system sleep state during system startup with 4532 the optional capability to repeat N number of times. 4533 The system is woken from this state using a 4534 wakeup-capable RTC alarm. 4535 4536 thash_entries= [KNL,NET] 4537 Set number of hash buckets for TCP connection 4538 4539 thermal.act= [HW,ACPI] 4540 -1: disable all active trip points in all thermal zones 4541 <degrees C>: override all lowest active trip points 4542 4543 thermal.crt= [HW,ACPI] 4544 -1: disable all critical trip points in all thermal zones 4545 <degrees C>: override all critical trip points 4546 4547 thermal.nocrt= [HW,ACPI] 4548 Set to disable actions on ACPI thermal zone 4549 critical and hot trip points. 4550 4551 thermal.off= [HW,ACPI] 4552 1: disable ACPI thermal control 4553 4554 thermal.psv= [HW,ACPI] 4555 -1: disable all passive trip points 4556 <degrees C>: override all passive trip points to this 4557 value 4558 4559 thermal.tzp= [HW,ACPI] 4560 Specify global default ACPI thermal zone polling rate 4561 <deci-seconds>: poll all this frequency 4562 0: no polling (default) 4563 4564 threadirqs [KNL] 4565 Force threading of all interrupt handlers except those 4566 marked explicitly IRQF_NO_THREAD. 4567 4568 tmem [KNL,XEN] 4569 Enable the Transcendent memory driver if built-in. 4570 4571 tmem.cleancache=0|1 [KNL, XEN] 4572 Default is on (1). Disable the usage of the cleancache 4573 API to send anonymous pages to the hypervisor. 4574 4575 tmem.frontswap=0|1 [KNL, XEN] 4576 Default is on (1). Disable the usage of the frontswap 4577 API to send swap pages to the hypervisor. If disabled 4578 the selfballooning and selfshrinking are force disabled. 4579 4580 tmem.selfballooning=0|1 [KNL, XEN] 4581 Default is on (1). Disable the driving of swap pages 4582 to the hypervisor. 4583 4584 tmem.selfshrinking=0|1 [KNL, XEN] 4585 Default is on (1). Partial swapoff that immediately 4586 transfers pages from Xen hypervisor back to the 4587 kernel based on different criteria. 4588 4589 topology= [S390] 4590 Format: {off | on} 4591 Specify if the kernel should make use of the cpu 4592 topology information if the hardware supports this. 4593 The scheduler will make use of this information and 4594 e.g. base its process migration decisions on it. 4595 Default is on. 4596 4597 topology_updates= [KNL, PPC, NUMA] 4598 Format: {off} 4599 Specify if the kernel should ignore (off) 4600 topology updates sent by the hypervisor to this 4601 LPAR. 4602 4603 tp720= [HW,PS2] 4604 4605 tpm_suspend_pcr=[HW,TPM] 4606 Format: integer pcr id 4607 Specify that at suspend time, the tpm driver 4608 should extend the specified pcr with zeros, 4609 as a workaround for some chips which fail to 4610 flush the last written pcr on TPM_SaveState. 4611 This will guarantee that all the other pcrs 4612 are saved. 4613 4614 trace_buf_size=nn[KMG] 4615 [FTRACE] will set tracing buffer size on each cpu. 4616 4617 trace_event=[event-list] 4618 [FTRACE] Set and start specified trace events in order 4619 to facilitate early boot debugging. The event-list is a 4620 comma separated list of trace events to enable. See 4621 also Documentation/trace/events.rst 4622 4623 trace_options=[option-list] 4624 [FTRACE] Enable or disable tracer options at boot. 4625 The option-list is a comma delimited list of options 4626 that can be enabled or disabled just as if you were 4627 to echo the option name into 4628 4629 /sys/kernel/debug/tracing/trace_options 4630 4631 For example, to enable stacktrace option (to dump the 4632 stack trace of each event), add to the command line: 4633 4634 trace_options=stacktrace 4635 4636 See also Documentation/trace/ftrace.rst "trace options" 4637 section. 4638 4639 tp_printk[FTRACE] 4640 Have the tracepoints sent to printk as well as the 4641 tracing ring buffer. This is useful for early boot up 4642 where the system hangs or reboots and does not give the 4643 option for reading the tracing buffer or performing a 4644 ftrace_dump_on_oops. 4645 4646 To turn off having tracepoints sent to printk, 4647 echo 0 > /proc/sys/kernel/tracepoint_printk 4648 Note, echoing 1 into this file without the 4649 tracepoint_printk kernel cmdline option has no effect. 4650 4651 ** CAUTION ** 4652 4653 Having tracepoints sent to printk() and activating high 4654 frequency tracepoints such as irq or sched, can cause 4655 the system to live lock. 4656 4657 traceoff_on_warning 4658 [FTRACE] enable this option to disable tracing when a 4659 warning is hit. This turns off "tracing_on". Tracing can 4660 be enabled again by echoing '1' into the "tracing_on" 4661 file located in /sys/kernel/debug/tracing/ 4662 4663 This option is useful, as it disables the trace before 4664 the WARNING dump is called, which prevents the trace to 4665 be filled with content caused by the warning output. 4666 4667 This option can also be set at run time via the sysctl 4668 option: kernel/traceoff_on_warning 4669 4670 transparent_hugepage= 4671 [KNL] 4672 Format: [always|madvise|never] 4673 Can be used to control the default behavior of the system 4674 with respect to transparent hugepages. 4675 See Documentation/admin-guide/mm/transhuge.rst 4676 for more details. 4677 4678 tsc= Disable clocksource stability checks for TSC. 4679 Format: <string> 4680 [x86] reliable: mark tsc clocksource as reliable, this 4681 disables clocksource verification at runtime, as well 4682 as the stability checks done at bootup. Used to enable 4683 high-resolution timer mode on older hardware, and in 4684 virtualized environment. 4685 [x86] noirqtime: Do not use TSC to do irq accounting. 4686 Used to run time disable IRQ_TIME_ACCOUNTING on any 4687 platforms where RDTSC is slow and this accounting 4688 can add overhead. 4689 [x86] unstable: mark the TSC clocksource as unstable, this 4690 marks the TSC unconditionally unstable at bootup and 4691 avoids any further wobbles once the TSC watchdog notices. 4692 4693 turbografx.map[2|3]= [HW,JOY] 4694 TurboGraFX parallel port interface 4695 Format: 4696 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4697 See also Documentation/input/devices/joystick-parport.rst 4698 4699 udbg-immortal [PPC] When debugging early kernel crashes that 4700 happen after console_init() and before a proper 4701 console driver takes over, this boot options might 4702 help "seeing" what's going on. 4703 4704 uhash_entries= [KNL,NET] 4705 Set number of hash buckets for UDP/UDP-Lite connections 4706 4707 uhci-hcd.ignore_oc= 4708 [USB] Ignore overcurrent events (default N). 4709 Some badly-designed motherboards generate lots of 4710 bogus events, for ports that aren't wired to 4711 anything. Set this parameter to avoid log spamming. 4712 Note that genuine overcurrent events won't be 4713 reported either. 4714 4715 unknown_nmi_panic 4716 [X86] Cause panic on unknown NMI. 4717 4718 usbcore.authorized_default= 4719 [USB] Default USB device authorization: 4720 (default -1 = authorized except for wireless USB, 4721 0 = not authorized, 1 = authorized, 2 = authorized 4722 if device connected to internal port) 4723 4724 usbcore.autosuspend= 4725 [USB] The autosuspend time delay (in seconds) used 4726 for newly-detected USB devices (default 2). This 4727 is the time required before an idle device will be 4728 autosuspended. Devices for which the delay is set 4729 to a negative value won't be autosuspended at all. 4730 4731 usbcore.usbfs_snoop= 4732 [USB] Set to log all usbfs traffic (default 0 = off). 4733 4734 usbcore.usbfs_snoop_max= 4735 [USB] Maximum number of bytes to snoop in each URB 4736 (default = 65536). 4737 4738 usbcore.blinkenlights= 4739 [USB] Set to cycle leds on hubs (default 0 = off). 4740 4741 usbcore.old_scheme_first= 4742 [USB] Start with the old device initialization 4743 scheme, applies only to low and full-speed devices 4744 (default 0 = off). 4745 4746 usbcore.usbfs_memory_mb= 4747 [USB] Memory limit (in MB) for buffers allocated by 4748 usbfs (default = 16, 0 = max = 2047). 4749 4750 usbcore.use_both_schemes= 4751 [USB] Try the other device initialization scheme 4752 if the first one fails (default 1 = enabled). 4753 4754 usbcore.initial_descriptor_timeout= 4755 [USB] Specifies timeout for the initial 64-byte 4756 USB_REQ_GET_DESCRIPTOR request in milliseconds 4757 (default 5000 = 5.0 seconds). 4758 4759 usbcore.nousb [USB] Disable the USB subsystem 4760 4761 usbcore.quirks= 4762 [USB] A list of quirk entries to augment the built-in 4763 usb core quirk list. List entries are separated by 4764 commas. Each entry has the form 4765 VendorID:ProductID:Flags. The IDs are 4-digit hex 4766 numbers and Flags is a set of letters. Each letter 4767 will change the built-in quirk; setting it if it is 4768 clear and clearing it if it is set. The letters have 4769 the following meanings: 4770 a = USB_QUIRK_STRING_FETCH_255 (string 4771 descriptors must not be fetched using 4772 a 255-byte read); 4773 b = USB_QUIRK_RESET_RESUME (device can't resume 4774 correctly so reset it instead); 4775 c = USB_QUIRK_NO_SET_INTF (device can't handle 4776 Set-Interface requests); 4777 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4778 handle its Configuration or Interface 4779 strings); 4780 e = USB_QUIRK_RESET (device can't be reset 4781 (e.g morph devices), don't use reset); 4782 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4783 more interface descriptions than the 4784 bNumInterfaces count, and can't handle 4785 talking to these interfaces); 4786 g = USB_QUIRK_DELAY_INIT (device needs a pause 4787 during initialization, after we read 4788 the device descriptor); 4789 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4790 high speed and super speed interrupt 4791 endpoints, the USB 2.0 and USB 3.0 spec 4792 require the interval in microframes (1 4793 microframe = 125 microseconds) to be 4794 calculated as interval = 2 ^ 4795 (bInterval-1). 4796 Devices with this quirk report their 4797 bInterval as the result of this 4798 calculation instead of the exponent 4799 variable used in the calculation); 4800 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4801 handle device_qualifier descriptor 4802 requests); 4803 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4804 generates spurious wakeup, ignore 4805 remote wakeup capability); 4806 k = USB_QUIRK_NO_LPM (device can't handle Link 4807 Power Management); 4808 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4809 (Device reports its bInterval as linear 4810 frames instead of the USB 2.0 4811 calculation); 4812 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4813 to be disconnected before suspend to 4814 prevent spurious wakeup); 4815 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4816 pause after every control message); 4817 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4818 delay after resetting its port); 4819 Example: quirks=0781:5580:bk,0a5c:5834:gij 4820 4821 usbhid.mousepoll= 4822 [USBHID] The interval which mice are to be polled at. 4823 4824 usbhid.jspoll= 4825 [USBHID] The interval which joysticks are to be polled at. 4826 4827 usbhid.kbpoll= 4828 [USBHID] The interval which keyboards are to be polled at. 4829 4830 usb-storage.delay_use= 4831 [UMS] The delay in seconds before a new device is 4832 scanned for Logical Units (default 1). 4833 4834 usb-storage.quirks= 4835 [UMS] A list of quirks entries to supplement or 4836 override the built-in unusual_devs list. List 4837 entries are separated by commas. Each entry has 4838 the form VID:PID:Flags where VID and PID are Vendor 4839 and Product ID values (4-digit hex numbers) and 4840 Flags is a set of characters, each corresponding 4841 to a common usb-storage quirk flag as follows: 4842 a = SANE_SENSE (collect more than 18 bytes 4843 of sense data); 4844 b = BAD_SENSE (don't collect more than 18 4845 bytes of sense data); 4846 c = FIX_CAPACITY (decrease the reported 4847 device capacity by one sector); 4848 d = NO_READ_DISC_INFO (don't use 4849 READ_DISC_INFO command); 4850 e = NO_READ_CAPACITY_16 (don't use 4851 READ_CAPACITY_16 command); 4852 f = NO_REPORT_OPCODES (don't use report opcodes 4853 command, uas only); 4854 g = MAX_SECTORS_240 (don't transfer more than 4855 240 sectors at a time, uas only); 4856 h = CAPACITY_HEURISTICS (decrease the 4857 reported device capacity by one 4858 sector if the number is odd); 4859 i = IGNORE_DEVICE (don't bind to this 4860 device); 4861 j = NO_REPORT_LUNS (don't use report luns 4862 command, uas only); 4863 l = NOT_LOCKABLE (don't try to lock and 4864 unlock ejectable media); 4865 m = MAX_SECTORS_64 (don't transfer more 4866 than 64 sectors = 32 KB at a time); 4867 n = INITIAL_READ10 (force a retry of the 4868 initial READ(10) command); 4869 o = CAPACITY_OK (accept the capacity 4870 reported by the device); 4871 p = WRITE_CACHE (the device cache is ON 4872 by default); 4873 r = IGNORE_RESIDUE (the device reports 4874 bogus residue values); 4875 s = SINGLE_LUN (the device has only one 4876 Logical Unit); 4877 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4878 commands, uas only); 4879 u = IGNORE_UAS (don't bind to the uas driver); 4880 w = NO_WP_DETECT (don't test whether the 4881 medium is write-protected). 4882 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4883 even if the device claims no cache) 4884 Example: quirks=0419:aaf5:rl,0421:0433:rc 4885 4886 user_debug= [KNL,ARM] 4887 Format: <int> 4888 See arch/arm/Kconfig.debug help text. 4889 1 - undefined instruction events 4890 2 - system calls 4891 4 - invalid data aborts 4892 8 - SIGSEGV faults 4893 16 - SIGBUS faults 4894 Example: user_debug=31 4895 4896 userpte= 4897 [X86] Flags controlling user PTE allocations. 4898 4899 nohigh = do not allocate PTE pages in 4900 HIGHMEM regardless of setting 4901 of CONFIG_HIGHPTE. 4902 4903 vdso= [X86,SH] 4904 On X86_32, this is an alias for vdso32=. Otherwise: 4905 4906 vdso=1: enable VDSO (the default) 4907 vdso=0: disable VDSO mapping 4908 4909 vdso32= [X86] Control the 32-bit vDSO 4910 vdso32=1: enable 32-bit VDSO 4911 vdso32=0 or vdso32=2: disable 32-bit VDSO 4912 4913 See the help text for CONFIG_COMPAT_VDSO for more 4914 details. If CONFIG_COMPAT_VDSO is set, the default is 4915 vdso32=0; otherwise, the default is vdso32=1. 4916 4917 For compatibility with older kernels, vdso32=2 is an 4918 alias for vdso32=0. 4919 4920 Try vdso32=0 if you encounter an error that says: 4921 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4922 4923 vector= [IA-64,SMP] 4924 vector=percpu: enable percpu vector domain 4925 4926 video= [FB] Frame buffer configuration 4927 See Documentation/fb/modedb.txt. 4928 4929 video.brightness_switch_enabled= [0,1] 4930 If set to 1, on receiving an ACPI notify event 4931 generated by hotkey, video driver will adjust brightness 4932 level and then send out the event to user space through 4933 the allocated input device; If set to 0, video driver 4934 will only send out the event without touching backlight 4935 brightness level. 4936 default: 1 4937 4938 virtio_mmio.device= 4939 [VMMIO] Memory mapped virtio (platform) device. 4940 4941 <size>@<baseaddr>:<irq>[:<id>] 4942 where: 4943 <size> := size (can use standard suffixes 4944 like K, M and G) 4945 <baseaddr> := physical base address 4946 <irq> := interrupt number (as passed to 4947 request_irq()) 4948 <id> := (optional) platform device id 4949 example: 4950 virtio_mmio.device=1K@0x100b0000:48:7 4951 4952 Can be used multiple times for multiple devices. 4953 4954 vga= [BOOT,X86-32] Select a particular video mode 4955 See Documentation/x86/boot.txt and 4956 Documentation/svga.txt. 4957 Use vga=ask for menu. 4958 This is actually a boot loader parameter; the value is 4959 passed to the kernel using a special protocol. 4960 4961 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 4962 May slow down system boot speed, especially when 4963 enabled on systems with a large amount of memory. 4964 All options are enabled by default, and this 4965 interface is meant to allow for selectively 4966 enabling or disabling specific virtual memory 4967 debugging features. 4968 4969 Available options are: 4970 P Enable page structure init time poisoning 4971 - Disable all of the above options 4972 4973 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4974 size of <nn>. This can be used to increase the 4975 minimum size (128MB on x86). It can also be used to 4976 decrease the size and leave more room for directly 4977 mapped kernel RAM. 4978 4979 vmcp_cma=nn[MG] [KNL,S390] 4980 Sets the memory size reserved for contiguous memory 4981 allocations for the vmcp device driver. 4982 4983 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4984 Format: <command> 4985 4986 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4987 Format: <command> 4988 4989 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4990 Format: <command> 4991 4992 vsyscall= [X86-64] 4993 Controls the behavior of vsyscalls (i.e. calls to 4994 fixed addresses of 0xffffffffff600x00 from legacy 4995 code). Most statically-linked binaries and older 4996 versions of glibc use these calls. Because these 4997 functions are at fixed addresses, they make nice 4998 targets for exploits that can control RIP. 4999 5000 emulate [default] Vsyscalls turn into traps and are 5001 emulated reasonably safely. 5002 5003 native Vsyscalls are native syscall instructions. 5004 This is a little bit faster than trapping 5005 and makes a few dynamic recompilers work 5006 better than they would in emulation mode. 5007 It also makes exploits much easier to write. 5008 5009 none Vsyscalls don't work at all. This makes 5010 them quite hard to use for exploits but 5011 might break your system. 5012 5013 vt.color= [VT] Default text color. 5014 Format: 0xYX, X = foreground, Y = background. 5015 Default: 0x07 = light gray on black. 5016 5017 vt.cur_default= [VT] Default cursor shape. 5018 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5019 the parameters of the <Esc>[?A;B;Cc escape sequence; 5020 see VGA-softcursor.txt. Default: 2 = underline. 5021 5022 vt.default_blu= [VT] 5023 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5024 Change the default blue palette of the console. 5025 This is a 16-member array composed of values 5026 ranging from 0-255. 5027 5028 vt.default_grn= [VT] 5029 Format: <green0>,<green1>,<green2>,...,<green15> 5030 Change the default green palette of the console. 5031 This is a 16-member array composed of values 5032 ranging from 0-255. 5033 5034 vt.default_red= [VT] 5035 Format: <red0>,<red1>,<red2>,...,<red15> 5036 Change the default red palette of the console. 5037 This is a 16-member array composed of values 5038 ranging from 0-255. 5039 5040 vt.default_utf8= 5041 [VT] 5042 Format=<0|1> 5043 Set system-wide default UTF-8 mode for all tty's. 5044 Default is 1, i.e. UTF-8 mode is enabled for all 5045 newly opened terminals. 5046 5047 vt.global_cursor_default= 5048 [VT] 5049 Format=<-1|0|1> 5050 Set system-wide default for whether a cursor 5051 is shown on new VTs. Default is -1, 5052 i.e. cursors will be created by default unless 5053 overridden by individual drivers. 0 will hide 5054 cursors, 1 will display them. 5055 5056 vt.italic= [VT] Default color for italic text; 0-15. 5057 Default: 2 = green. 5058 5059 vt.underline= [VT] Default color for underlined text; 0-15. 5060 Default: 3 = cyan. 5061 5062 watchdog timers [HW,WDT] For information on watchdog timers, 5063 see Documentation/watchdog/watchdog-parameters.txt 5064 or other driver-specific files in the 5065 Documentation/watchdog/ directory. 5066 5067 workqueue.watchdog_thresh= 5068 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5069 warn stall conditions and dump internal state to 5070 help debugging. 0 disables workqueue stall 5071 detection; otherwise, it's the stall threshold 5072 duration in seconds. The default value is 30 and 5073 it can be updated at runtime by writing to the 5074 corresponding sysfs file. 5075 5076 workqueue.disable_numa 5077 By default, all work items queued to unbound 5078 workqueues are affine to the NUMA nodes they're 5079 issued on, which results in better behavior in 5080 general. If NUMA affinity needs to be disabled for 5081 whatever reason, this option can be used. Note 5082 that this also can be controlled per-workqueue for 5083 workqueues visible under /sys/bus/workqueue/. 5084 5085 workqueue.power_efficient 5086 Per-cpu workqueues are generally preferred because 5087 they show better performance thanks to cache 5088 locality; unfortunately, per-cpu workqueues tend to 5089 be more power hungry than unbound workqueues. 5090 5091 Enabling this makes the per-cpu workqueues which 5092 were observed to contribute significantly to power 5093 consumption unbound, leading to measurably lower 5094 power usage at the cost of small performance 5095 overhead. 5096 5097 The default value of this parameter is determined by 5098 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5099 5100 workqueue.debug_force_rr_cpu 5101 Workqueue used to implicitly guarantee that work 5102 items queued without explicit CPU specified are put 5103 on the local CPU. This guarantee is no longer true 5104 and while local CPU is still preferred work items 5105 may be put on foreign CPUs. This debug option 5106 forces round-robin CPU selection to flush out 5107 usages which depend on the now broken guarantee. 5108 When enabled, memory and cache locality will be 5109 impacted. 5110 5111 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5112 default x2apic cluster mode on platforms 5113 supporting x2apic. 5114 5115 x86_intel_mid_timer= [X86-32,APBT] 5116 Choose timer option for x86 Intel MID platform. 5117 Two valid options are apbt timer only and lapic timer 5118 plus one apbt timer for broadcast timer. 5119 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5120 5121 xen_512gb_limit [KNL,X86-64,XEN] 5122 Restricts the kernel running paravirtualized under Xen 5123 to use only up to 512 GB of RAM. The reason to do so is 5124 crash analysis tools and Xen tools for doing domain 5125 save/restore/migration must be enabled to handle larger 5126 domains. 5127 5128 xen_emul_unplug= [HW,X86,XEN] 5129 Unplug Xen emulated devices 5130 Format: [unplug0,][unplug1] 5131 ide-disks -- unplug primary master IDE devices 5132 aux-ide-disks -- unplug non-primary-master IDE devices 5133 nics -- unplug network devices 5134 all -- unplug all emulated devices (NICs and IDE disks) 5135 unnecessary -- unplugging emulated devices is 5136 unnecessary even if the host did not respond to 5137 the unplug protocol 5138 never -- do not unplug even if version check succeeds 5139 5140 xen_nopvspin [X86,XEN] 5141 Disables the ticketlock slowpath using Xen PV 5142 optimizations. 5143 5144 xen_nopv [X86] 5145 Disables the PV optimizations forcing the HVM guest to 5146 run as generic HVM guest with no PV drivers. 5147 5148 xen_scrub_pages= [XEN] 5149 Boolean option to control scrubbing pages before giving them back 5150 to Xen, for use by other domains. Can be also changed at runtime 5151 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5152 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5153 5154 xirc2ps_cs= [NET,PCMCIA] 5155 Format: 5156 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5157 5158 xhci-hcd.quirks [USB,KNL] 5159 A hex value specifying bitmask with supplemental xhci 5160 host controller quirks. Meaning of each bit can be 5161 consulted in header drivers/usb/host/xhci.h. 5162