1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.txt, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/acpi/debug.txt for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <int> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_rsdp= [ACPI,EFI,KEXEC] 140 Pass the RSDP address to the kernel, mostly used 141 on machines running EFI runtime service to boot the 142 second kernel for kdump. 143 144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 145 Format: To spoof as Windows 98: ="Microsoft Windows" 146 147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 148 of 2 which is mandated by ACPI 6) as the supported ACPI 149 specification revision (when using this switch, it may 150 be necessary to carry out a cold reboot _twice_ in a 151 row to make it take effect on the platform firmware). 152 153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 154 acpi_osi="string1" # add string1 155 acpi_osi="!string2" # remove string2 156 acpi_osi=!* # remove all strings 157 acpi_osi=! # disable all built-in OS vendor 158 strings 159 acpi_osi=!! # enable all built-in OS vendor 160 strings 161 acpi_osi= # disable all strings 162 163 'acpi_osi=!' can be used in combination with single or 164 multiple 'acpi_osi="string1"' to support specific OS 165 vendor string(s). Note that such command can only 166 affect the default state of the OS vendor strings, thus 167 it cannot affect the default state of the feature group 168 strings and the current state of the OS vendor strings, 169 specifying it multiple times through kernel command line 170 is meaningless. This command is useful when one do not 171 care about the state of the feature group strings which 172 should be controlled by the OSPM. 173 Examples: 174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 176 can make '_OSI("Windows 2000")' TRUE. 177 178 'acpi_osi=' cannot be used in combination with other 179 'acpi_osi=' command lines, the _OSI method will not 180 exist in the ACPI namespace. NOTE that such command can 181 only affect the _OSI support state, thus specifying it 182 multiple times through kernel command line is also 183 meaningless. 184 Examples: 185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 186 FALSE. 187 188 'acpi_osi=!*' can be used in combination with single or 189 multiple 'acpi_osi="string1"' to support specific 190 string(s). Note that such command can affect the 191 current state of both the OS vendor strings and the 192 feature group strings, thus specifying it multiple times 193 through kernel command line is meaningful. But it may 194 still not able to affect the final state of a string if 195 there are quirks related to this string. This command 196 is useful when one want to control the state of the 197 feature group strings to debug BIOS issues related to 198 the OSPM features. 199 Examples: 200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 201 '_OSI("Module Device")' FALSE. 202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 203 '_OSI("Module Device")' TRUE. 204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 205 equivalent to 206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 207 and 208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 209 they all will make '_OSI("Windows 2000")' TRUE. 210 211 acpi_pm_good [X86] 212 Override the pmtimer bug detection: force the kernel 213 to assume that this machine's pmtimer latches its value 214 and always returns good values. 215 216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 217 Format: { level | edge | high | low } 218 219 acpi_skip_timer_override [HW,ACPI] 220 Recognize and ignore IRQ0/pin2 Interrupt Override. 221 For broken nForce2 BIOS resulting in XT-PIC timer. 222 223 acpi_sleep= [HW,ACPI] Sleep options 224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 225 old_ordering, nonvs, sci_force_enable, nobl } 226 See Documentation/power/video.txt for information on 227 s3_bios and s3_mode. 228 s3_beep is for debugging; it makes the PC's speaker beep 229 as soon as the kernel's real-mode entry point is called. 230 s4_nohwsig prevents ACPI hardware signature from being 231 used during resume from hibernation. 232 old_ordering causes the ACPI 1.0 ordering of the _PTS 233 control method, with respect to putting devices into 234 low power states, to be enforced (the ACPI 2.0 ordering 235 of _PTS is used by default). 236 nonvs prevents the kernel from saving/restoring the 237 ACPI NVS memory during suspend/hibernation and resume. 238 sci_force_enable causes the kernel to set SCI_EN directly 239 on resume from S1/S3 (which is against the ACPI spec, 240 but some broken systems don't work without it). 241 nobl causes the internal blacklist of systems known to 242 behave incorrectly in some ways with respect to system 243 suspend and resume to be ignored (use wisely). 244 245 acpi_use_timer_override [HW,ACPI] 246 Use timer override. For some broken Nvidia NF5 boards 247 that require a timer override, but don't have HPET 248 249 add_efi_memmap [EFI; X86] Include EFI memory map in 250 kernel's map of available physical RAM. 251 252 agp= [AGP] 253 { off | try_unsupported } 254 off: disable AGP support 255 try_unsupported: try to drive unsupported chipsets 256 (may crash computer or cause data corruption) 257 258 ALSA [HW,ALSA] 259 See Documentation/sound/alsa-configuration.rst 260 261 alignment= [KNL,ARM] 262 Allow the default userspace alignment fault handler 263 behaviour to be specified. Bit 0 enables warnings, 264 bit 1 enables fixups, and bit 2 sends a segfault. 265 266 align_va_addr= [X86-64] 267 Align virtual addresses by clearing slice [14:12] when 268 allocating a VMA at process creation time. This option 269 gives you up to 3% performance improvement on AMD F15h 270 machines (where it is enabled by default) for a 271 CPU-intensive style benchmark, and it can vary highly in 272 a microbenchmark depending on workload and compiler. 273 274 32: only for 32-bit processes 275 64: only for 64-bit processes 276 on: enable for both 32- and 64-bit processes 277 off: disable for both 32- and 64-bit processes 278 279 alloc_snapshot [FTRACE] 280 Allocate the ftrace snapshot buffer on boot up when the 281 main buffer is allocated. This is handy if debugging 282 and you need to use tracing_snapshot() on boot up, and 283 do not want to use tracing_snapshot_alloc() as it needs 284 to be done where GFP_KERNEL allocations are allowed. 285 286 amd_iommu= [HW,X86-64] 287 Pass parameters to the AMD IOMMU driver in the system. 288 Possible values are: 289 fullflush - enable flushing of IO/TLB entries when 290 they are unmapped. Otherwise they are 291 flushed before they will be reused, which 292 is a lot of faster 293 off - do not initialize any AMD IOMMU found in 294 the system 295 force_isolation - Force device isolation for all 296 devices. The IOMMU driver is not 297 allowed anymore to lift isolation 298 requirements as needed. This option 299 does not override iommu=pt 300 301 amd_iommu_dump= [HW,X86-64] 302 Enable AMD IOMMU driver option to dump the ACPI table 303 for AMD IOMMU. With this option enabled, AMD IOMMU 304 driver will print ACPI tables for AMD IOMMU during 305 IOMMU initialization. 306 307 amd_iommu_intr= [HW,X86-64] 308 Specifies one of the following AMD IOMMU interrupt 309 remapping modes: 310 legacy - Use legacy interrupt remapping mode. 311 vapic - Use virtual APIC mode, which allows IOMMU 312 to inject interrupts directly into guest. 313 This mode requires kvm-amd.avic=1. 314 (Default when IOMMU HW support is present.) 315 316 amijoy.map= [HW,JOY] Amiga joystick support 317 Map of devices attached to JOY0DAT and JOY1DAT 318 Format: <a>,<b> 319 See also Documentation/input/joydev/joystick.rst 320 321 analog.map= [HW,JOY] Analog joystick and gamepad support 322 Specifies type or capabilities of an analog joystick 323 connected to one of 16 gameports 324 Format: <type1>,<type2>,..<type16> 325 326 apc= [HW,SPARC] 327 Power management functions (SPARCstation-4/5 + deriv.) 328 Format: noidle 329 Disable APC CPU standby support. SPARCstation-Fox does 330 not play well with APC CPU idle - disable it if you have 331 APC and your system crashes randomly. 332 333 apic= [APIC,X86] Advanced Programmable Interrupt Controller 334 Change the output verbosity while booting 335 Format: { quiet (default) | verbose | debug } 336 Change the amount of debugging information output 337 when initialising the APIC and IO-APIC components. 338 For X86-32, this can also be used to specify an APIC 339 driver name. 340 Format: apic=driver_name 341 Examples: apic=bigsmp 342 343 apic_extnmi= [APIC,X86] External NMI delivery setting 344 Format: { bsp (default) | all | none } 345 bsp: External NMI is delivered only to CPU 0 346 all: External NMIs are broadcast to all CPUs as a 347 backup of CPU 0 348 none: External NMI is masked for all CPUs. This is 349 useful so that a dump capture kernel won't be 350 shot down by NMI 351 352 autoconf= [IPV6] 353 See Documentation/networking/ipv6.txt. 354 355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 356 Limit apic dumping. The parameter defines the maximal 357 number of local apics being dumped. Also it is possible 358 to set it to "all" by meaning -- no limit here. 359 Format: { 1 (default) | 2 | ... | all }. 360 The parameter valid if only apic=debug or 361 apic=verbose is specified. 362 Example: apic=debug show_lapic=all 363 364 apm= [APM] Advanced Power Management 365 See header of arch/x86/kernel/apm_32.c. 366 367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 368 Format: <io>,<irq>,<nodeID> 369 370 ataflop= [HW,M68k] 371 372 atarimouse= [HW,MOUSE] Atari Mouse 373 374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 375 EzKey and similar keyboards 376 377 atkbd.reset= [HW] Reset keyboard during initialization 378 379 atkbd.set= [HW] Select keyboard code set 380 Format: <int> (2 = AT (default), 3 = PS/2) 381 382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 383 keyboards 384 385 atkbd.softraw= [HW] Choose between synthetic and real raw mode 386 Format: <bool> (0 = real, 1 = synthetic (default)) 387 388 atkbd.softrepeat= [HW] 389 Use software keyboard repeat 390 391 audit= [KNL] Enable the audit sub-system 392 Format: { "0" | "1" | "off" | "on" } 393 0 | off - kernel audit is disabled and can not be 394 enabled until the next reboot 395 unset - kernel audit is initialized but disabled and 396 will be fully enabled by the userspace auditd. 397 1 | on - kernel audit is initialized and partially 398 enabled, storing at most audit_backlog_limit 399 messages in RAM until it is fully enabled by the 400 userspace auditd. 401 Default: unset 402 403 audit_backlog_limit= [KNL] Set the audit queue size limit. 404 Format: <int> (must be >=0) 405 Default: 64 406 407 bau= [X86_UV] Enable the BAU on SGI UV. The default 408 behavior is to disable the BAU (i.e. bau=0). 409 Format: { "0" | "1" } 410 0 - Disable the BAU. 411 1 - Enable the BAU. 412 unset - Disable the BAU. 413 414 baycom_epp= [HW,AX25] 415 Format: <io>,<mode> 416 417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 418 Format: <io>,<mode> 419 See header of drivers/net/hamradio/baycom_par.c. 420 421 baycom_ser_fdx= [HW,AX25] 422 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 423 Format: <io>,<irq>,<mode>[,<baud>] 424 See header of drivers/net/hamradio/baycom_ser_fdx.c. 425 426 baycom_ser_hdx= [HW,AX25] 427 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 428 Format: <io>,<irq>,<mode> 429 See header of drivers/net/hamradio/baycom_ser_hdx.c. 430 431 blkdevparts= Manual partition parsing of block device(s) for 432 embedded devices based on command line input. 433 See Documentation/block/cmdline-partition.txt 434 435 boot_delay= Milliseconds to delay each printk during boot. 436 Values larger than 10 seconds (10000) are changed to 437 no delay (0). 438 Format: integer 439 440 bootmem_debug [KNL] Enable bootmem allocator debug messages. 441 442 bert_disable [ACPI] 443 Disable BERT OS support on buggy BIOSes. 444 445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 446 bttv.radio= Most important insmod options are available as 447 kernel args too. 448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 449 bttv.tuner= 450 451 bulk_remove=off [PPC] This parameter disables the use of the pSeries 452 firmware feature for flushing multiple hpte entries 453 at a time. 454 455 c101= [NET] Moxa C101 synchronous serial card 456 457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 458 Sometimes CPU hardware bugs make them report the cache 459 size incorrectly. The kernel will attempt work arounds 460 to fix known problems, but for some CPUs it is not 461 possible to determine what the correct size should be. 462 This option provides an override for these situations. 463 464 carrier_timeout= 465 [NET] Specifies amount of time (in seconds) that 466 the kernel should wait for a network carrier. By default 467 it waits 120 seconds. 468 469 ca_keys= [KEYS] This parameter identifies a specific key(s) on 470 the system trusted keyring to be used for certificate 471 trust validation. 472 format: { id:<keyid> | builtin } 473 474 cca= [MIPS] Override the kernel pages' cache coherency 475 algorithm. Accepted values range from 0 to 7 476 inclusive. See arch/mips/include/asm/pgtable-bits.h 477 for platform specific values (SB1, Loongson3 and 478 others). 479 480 ccw_timeout_log [S390] 481 See Documentation/s390/CommonIO for details. 482 483 cgroup_disable= [KNL] Disable a particular controller 484 Format: {name of the controller(s) to disable} 485 The effects of cgroup_disable=foo are: 486 - foo isn't auto-mounted if you mount all cgroups in 487 a single hierarchy 488 - foo isn't visible as an individually mountable 489 subsystem 490 {Currently only "memory" controller deal with this and 491 cut the overhead, others just disable the usage. So 492 only cgroup_disable=memory is actually worthy} 493 494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 495 Format: { { controller | "all" | "named" } 496 [,{ controller | "all" | "named" }...] } 497 Like cgroup_disable, but only applies to cgroup v1; 498 the blacklisted controllers remain available in cgroup2. 499 "all" blacklists all controllers and "named" disables 500 named mounts. Specifying both "all" and "named" disables 501 all v1 hierarchies. 502 503 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 504 Format: <string> 505 nosocket -- Disable socket memory accounting. 506 nokmem -- Disable kernel memory accounting. 507 508 checkreqprot [SELINUX] Set initial checkreqprot flag value. 509 Format: { "0" | "1" } 510 See security/selinux/Kconfig help text. 511 0 -- check protection applied by kernel (includes 512 any implied execute protection). 513 1 -- check protection requested by application. 514 Default value is set via a kernel config option. 515 Value can be changed at runtime via 516 /selinux/checkreqprot. 517 518 cio_ignore= [S390] 519 See Documentation/s390/CommonIO for details. 520 clk_ignore_unused 521 [CLK] 522 Prevents the clock framework from automatically gating 523 clocks that have not been explicitly enabled by a Linux 524 device driver but are enabled in hardware at reset or 525 by the bootloader/firmware. Note that this does not 526 force such clocks to be always-on nor does it reserve 527 those clocks in any way. This parameter is useful for 528 debug and development, but should not be needed on a 529 platform with proper driver support. For more 530 information, see Documentation/driver-api/clk.rst. 531 532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 533 [Deprecated] 534 Forces specified clocksource (if available) to be used 535 when calculating gettimeofday(). If specified 536 clocksource is not available, it defaults to PIT. 537 Format: { pit | tsc | cyclone | pmtmr } 538 539 clocksource= Override the default clocksource 540 Format: <string> 541 Override the default clocksource and use the clocksource 542 with the name specified. 543 Some clocksource names to choose from, depending on 544 the platform: 545 [all] jiffies (this is the base, fallback clocksource) 546 [ACPI] acpi_pm 547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 548 pxa_timer,timer3,32k_counter,timer0_1 549 [X86-32] pit,hpet,tsc; 550 scx200_hrt on Geode; cyclone on IBM x440 551 [MIPS] MIPS 552 [PARISC] cr16 553 [S390] tod 554 [SH] SuperH 555 [SPARC64] tick 556 [X86-64] hpet,tsc 557 558 clocksource.arm_arch_timer.evtstrm= 559 [ARM,ARM64] 560 Format: <bool> 561 Enable/disable the eventstream feature of the ARM 562 architected timer so that code using WFE-based polling 563 loops can be debugged more effectively on production 564 systems. 565 566 clearcpuid=BITNUM [X86] 567 Disable CPUID feature X for the kernel. See 568 arch/x86/include/asm/cpufeatures.h for the valid bit 569 numbers. Note the Linux specific bits are not necessarily 570 stable over kernel options, but the vendor specific 571 ones should be. 572 Also note that user programs calling CPUID directly 573 or using the feature without checking anything 574 will still see it. This just prevents it from 575 being used by the kernel or shown in /proc/cpuinfo. 576 Also note the kernel might malfunction if you disable 577 some critical bits. 578 579 cma=nn[MG]@[start[MG][-end[MG]]] 580 [ARM,X86,KNL] 581 Sets the size of kernel global memory area for 582 contiguous memory allocations and optionally the 583 placement constraint by the physical address range of 584 memory allocations. A value of 0 disables CMA 585 altogether. For more information, see 586 include/linux/dma-contiguous.h 587 588 cmo_free_hint= [PPC] Format: { yes | no } 589 Specify whether pages are marked as being inactive 590 when they are freed. This is used in CMO environments 591 to determine OS memory pressure for page stealing by 592 a hypervisor. 593 Default: yes 594 595 coherent_pool=nn[KMG] [ARM,KNL] 596 Sets the size of memory pool for coherent, atomic dma 597 allocations, by default set to 256K. 598 599 com20020= [HW,NET] ARCnet - COM20020 chipset 600 Format: 601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 602 603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 604 Format: <io>[,<irq>] 605 606 com90xx= [HW,NET] 607 ARCnet - COM90xx chipset (memory-mapped buffers) 608 Format: <io>[,<irq>[,<memstart>]] 609 610 condev= [HW,S390] console device 611 conmode= 612 613 console= [KNL] Output console device and options. 614 615 tty<n> Use the virtual console device <n>. 616 617 ttyS<n>[,options] 618 ttyUSB0[,options] 619 Use the specified serial port. The options are of 620 the form "bbbbpnf", where "bbbb" is the baud rate, 621 "p" is parity ("n", "o", or "e"), "n" is number of 622 bits, and "f" is flow control ("r" for RTS or 623 omit it). Default is "9600n8". 624 625 See Documentation/admin-guide/serial-console.rst for more 626 information. See 627 Documentation/networking/netconsole.txt for an 628 alternative. 629 630 uart[8250],io,<addr>[,options] 631 uart[8250],mmio,<addr>[,options] 632 uart[8250],mmio16,<addr>[,options] 633 uart[8250],mmio32,<addr>[,options] 634 uart[8250],0x<addr>[,options] 635 Start an early, polled-mode console on the 8250/16550 636 UART at the specified I/O port or MMIO address, 637 switching to the matching ttyS device later. 638 MMIO inter-register address stride is either 8-bit 639 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 641 to be equivalent to 'mmio'. 'options' are specified in 642 the same format described for ttyS above; if unspecified, 643 the h/w is not re-initialized. 644 645 hvc<n> Use the hypervisor console device <n>. This is for 646 both Xen and PowerPC hypervisors. 647 648 If the device connected to the port is not a TTY but a braille 649 device, prepend "brl," before the device type, for instance 650 console=brl,ttyS0 651 For now, only VisioBraille is supported. 652 653 console_msg_format= 654 [KNL] Change console messages format 655 default 656 By default we print messages on consoles in 657 "[time stamp] text\n" format (time stamp may not be 658 printed, depending on CONFIG_PRINTK_TIME or 659 `printk_time' param). 660 syslog 661 Switch to syslog format: "<%u>[time stamp] text\n" 662 IOW, each message will have a facility and loglevel 663 prefix. The format is similar to one used by syslog() 664 syscall, or to executing "dmesg -S --raw" or to reading 665 from /proc/kmsg. 666 667 consoleblank= [KNL] The console blank (screen saver) timeout in 668 seconds. A value of 0 disables the blank timer. 669 Defaults to 0. 670 671 coredump_filter= 672 [KNL] Change the default value for 673 /proc/<pid>/coredump_filter. 674 See also Documentation/filesystems/proc.txt. 675 676 coresight_cpu_debug.enable 677 [ARM,ARM64] 678 Format: <bool> 679 Enable/disable the CPU sampling based debugging. 680 0: default value, disable debugging 681 1: enable debugging at boot time 682 683 cpuidle.off=1 [CPU_IDLE] 684 disable the cpuidle sub-system 685 686 cpuidle.governor= 687 [CPU_IDLE] Name of the cpuidle governor to use. 688 689 cpufreq.off=1 [CPU_FREQ] 690 disable the cpufreq sub-system 691 692 cpu_init_udelay=N 693 [X86] Delay for N microsec between assert and de-assert 694 of APIC INIT to start processors. This delay occurs 695 on every CPU online, such as boot, and resume from suspend. 696 Default: 10000 697 698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 699 Format: 700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 701 702 crashkernel=size[KMG][@offset[KMG]] 703 [KNL] Using kexec, Linux can switch to a 'crash kernel' 704 upon panic. This parameter reserves the physical 705 memory region [offset, offset + size] for that kernel 706 image. If '@offset' is omitted, then a suitable offset 707 is selected automatically. 708 [KNL, x86_64] select a region under 4G first, and 709 fall back to reserve region above 4G when '@offset' 710 hasn't been specified. 711 See Documentation/kdump/kdump.txt for further details. 712 713 crashkernel=range1:size1[,range2:size2,...][@offset] 714 [KNL] Same as above, but depends on the memory 715 in the running system. The syntax of range is 716 start-[end] where start and end are both 717 a memory unit (amount[KMG]). See also 718 Documentation/kdump/kdump.txt for an example. 719 720 crashkernel=size[KMG],high 721 [KNL, x86_64] range could be above 4G. Allow kernel 722 to allocate physical memory region from top, so could 723 be above 4G if system have more than 4G ram installed. 724 Otherwise memory region will be allocated below 4G, if 725 available. 726 It will be ignored if crashkernel=X is specified. 727 crashkernel=size[KMG],low 728 [KNL, x86_64] range under 4G. When crashkernel=X,high 729 is passed, kernel could allocate physical memory region 730 above 4G, that cause second kernel crash on system 731 that require some amount of low memory, e.g. swiotlb 732 requires at least 64M+32K low memory, also enough extra 733 low memory is needed to make sure DMA buffers for 32-bit 734 devices won't run out. Kernel would try to allocate at 735 at least 256M below 4G automatically. 736 This one let user to specify own low range under 4G 737 for second kernel instead. 738 0: to disable low allocation. 739 It will be ignored when crashkernel=X,high is not used 740 or memory reserved is below 4G. 741 742 cryptomgr.notests 743 [KNL] Disable crypto self-tests 744 745 cs89x0_dma= [HW,NET] 746 Format: <dma> 747 748 cs89x0_media= [HW,NET] 749 Format: { rj45 | aui | bnc } 750 751 dasd= [HW,NET] 752 See header of drivers/s390/block/dasd_devmap.c. 753 754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 755 (one device per port) 756 Format: <port#>,<type> 757 See also Documentation/input/devices/joystick-parport.rst 758 759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 760 time. See 761 Documentation/admin-guide/dynamic-debug-howto.rst for 762 details. Deprecated, see dyndbg. 763 764 debug [KNL] Enable kernel debugging (events log level). 765 766 debug_boot_weak_hash 767 [KNL] Enable printing [hashed] pointers early in the 768 boot sequence. If enabled, we use a weak hash instead 769 of siphash to hash pointers. Use this option if you are 770 seeing instances of '(___ptrval___)') and need to see a 771 value (hashed pointer) instead. Cryptographically 772 insecure, please do not use on production kernels. 773 774 debug_locks_verbose= 775 [KNL] verbose self-tests 776 Format=<0|1> 777 Print debugging info while doing the locking API 778 self-tests. 779 We default to 0 (no extra messages), setting it to 780 1 will print _a lot_ more information - normally 781 only useful to kernel developers. 782 783 debug_objects [KNL] Enable object debugging 784 785 no_debug_objects 786 [KNL] Disable object debugging 787 788 debug_guardpage_minorder= 789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 790 parameter allows control of the order of pages that will 791 be intentionally kept free (and hence protected) by the 792 buddy allocator. Bigger value increase the probability 793 of catching random memory corruption, but reduce the 794 amount of memory for normal system use. The maximum 795 possible value is MAX_ORDER/2. Setting this parameter 796 to 1 or 2 should be enough to identify most random 797 memory corruption problems caused by bugs in kernel or 798 driver code when a CPU writes to (or reads from) a 799 random memory location. Note that there exists a class 800 of memory corruptions problems caused by buggy H/W or 801 F/W or by drivers badly programing DMA (basically when 802 memory is written at bus level and the CPU MMU is 803 bypassed) which are not detectable by 804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 805 tracking down these problems. 806 807 debug_pagealloc= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 809 parameter enables the feature at boot time. In 810 default, it is disabled. We can avoid allocating huge 811 chunk of memory for debug pagealloc if we don't enable 812 it at boot time and the system will work mostly same 813 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 814 on: enable the feature 815 816 debugpat [X86] Enable PAT debugging 817 818 decnet.addr= [HW,NET] 819 Format: <area>[,<node>] 820 See also Documentation/networking/decnet.txt. 821 822 default_hugepagesz= 823 [same as hugepagesz=] The size of the default 824 HugeTLB page size. This is the size represented by 825 the legacy /proc/ hugepages APIs, used for SHM, and 826 default size when mounting hugetlbfs filesystems. 827 Defaults to the default architecture's huge page size 828 if not specified. 829 830 deferred_probe_timeout= 831 [KNL] Debugging option to set a timeout in seconds for 832 deferred probe to give up waiting on dependencies to 833 probe. Only specific dependencies (subsystems or 834 drivers) that have opted in will be ignored. A timeout of 0 835 will timeout at the end of initcalls. This option will also 836 dump out devices still on the deferred probe list after 837 retrying. 838 839 dhash_entries= [KNL] 840 Set number of hash buckets for dentry cache. 841 842 disable_1tb_segments [PPC] 843 Disables the use of 1TB hash page table segments. This 844 causes the kernel to fall back to 256MB segments which 845 can be useful when debugging issues that require an SLB 846 miss to occur. 847 848 disable= [IPV6] 849 See Documentation/networking/ipv6.txt. 850 851 hardened_usercopy= 852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 853 hardening is enabled for this boot. Hardened 854 usercopy checking is used to protect the kernel 855 from reading or writing beyond known memory 856 allocation boundaries as a proactive defense 857 against bounds-checking flaws in the kernel's 858 copy_to_user()/copy_from_user() interface. 859 on Perform hardened usercopy checks (default). 860 off Disable hardened usercopy checks. 861 862 disable_radix [PPC] 863 Disable RADIX MMU mode on POWER9 864 865 disable_cpu_apicid= [X86,APIC,SMP] 866 Format: <int> 867 The number of initial APIC ID for the 868 corresponding CPU to be disabled at boot, 869 mostly used for the kdump 2nd kernel to 870 disable BSP to wake up multiple CPUs without 871 causing system reset or hang due to sending 872 INIT from AP to BSP. 873 874 perf_v4_pmi= [X86,INTEL] 875 Format: <bool> 876 Disable Intel PMU counter freezing feature. 877 The feature only exists starting from 878 Arch Perfmon v4 (Skylake and newer). 879 880 disable_ddw [PPC/PSERIES] 881 Disable Dynamic DMA Window support. Use this if 882 to workaround buggy firmware. 883 884 disable_ipv6= [IPV6] 885 See Documentation/networking/ipv6.txt. 886 887 disable_mtrr_cleanup [X86] 888 The kernel tries to adjust MTRR layout from continuous 889 to discrete, to make X server driver able to add WB 890 entry later. This parameter disables that. 891 892 disable_mtrr_trim [X86, Intel and AMD only] 893 By default the kernel will trim any uncacheable 894 memory out of your available memory pool based on 895 MTRR settings. This parameter disables that behavior, 896 possibly causing your machine to run very slowly. 897 898 disable_timer_pin_1 [X86] 899 Disable PIN 1 of APIC timer 900 Can be useful to work around chipset bugs. 901 902 dis_ucode_ldr [X86] Disable the microcode loader. 903 904 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 905 this option disables the debugging code at boot. 906 907 dma_debug_entries=<number> 908 This option allows to tune the number of preallocated 909 entries for DMA-API debugging code. One entry is 910 required per DMA-API allocation. Use this if the 911 DMA-API debugging code disables itself because the 912 architectural default is too low. 913 914 dma_debug_driver=<driver_name> 915 With this option the DMA-API debugging driver 916 filter feature can be enabled at boot time. Just 917 pass the driver to filter for as the parameter. 918 The filter can be disabled or changed to another 919 driver later using sysfs. 920 921 driver_async_probe= [KNL] 922 List of driver names to be probed asynchronously. 923 Format: <driver_name1>,<driver_name2>... 924 925 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 926 Broken monitors, graphic adapters, KVMs and EDIDless 927 panels may send no or incorrect EDID data sets. 928 This parameter allows to specify an EDID data sets 929 in the /lib/firmware directory that are used instead. 930 Generic built-in EDID data sets are used, if one of 931 edid/1024x768.bin, edid/1280x1024.bin, 932 edid/1680x1050.bin, or edid/1920x1080.bin is given 933 and no file with the same name exists. Details and 934 instructions how to build your own EDID data are 935 available in Documentation/EDID/HOWTO.txt. An EDID 936 data set will only be used for a particular connector, 937 if its name and a colon are prepended to the EDID 938 name. Each connector may use a unique EDID data 939 set by separating the files with a comma. An EDID 940 data set with no connector name will be used for 941 any connectors not explicitly specified. 942 943 dscc4.setup= [NET] 944 945 dt_cpu_ftrs= [PPC] 946 Format: {"off" | "known"} 947 Control how the dt_cpu_ftrs device-tree binding is 948 used for CPU feature discovery and setup (if it 949 exists). 950 off: Do not use it, fall back to legacy cpu table. 951 known: Do not pass through unknown features to guests 952 or userspace, only those that the kernel is aware of. 953 954 dump_apple_properties [X86] 955 Dump name and content of EFI device properties on 956 x86 Macs. Useful for driver authors to determine 957 what data is available or for reverse-engineering. 958 959 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 960 module.dyndbg[="val"] 961 Enable debug messages at boot time. See 962 Documentation/admin-guide/dynamic-debug-howto.rst 963 for details. 964 965 nompx [X86] Disables Intel Memory Protection Extensions. 966 See Documentation/x86/intel_mpx.txt for more 967 information about the feature. 968 969 nopku [X86] Disable Memory Protection Keys CPU feature found 970 in some Intel CPUs. 971 972 module.async_probe [KNL] 973 Enable asynchronous probe on this module. 974 975 early_ioremap_debug [KNL] 976 Enable debug messages in early_ioremap support. This 977 is useful for tracking down temporary early mappings 978 which are not unmapped. 979 980 earlycon= [KNL] Output early console device and options. 981 982 [ARM64] The early console is determined by the 983 stdout-path property in device tree's chosen node, 984 or determined by the ACPI SPCR table. 985 986 [X86] When used with no options the early console is 987 determined by the ACPI SPCR table. 988 989 cdns,<addr>[,options] 990 Start an early, polled-mode console on a Cadence 991 (xuartps) serial port at the specified address. Only 992 supported option is baud rate. If baud rate is not 993 specified, the serial port must already be setup and 994 configured. 995 996 uart[8250],io,<addr>[,options] 997 uart[8250],mmio,<addr>[,options] 998 uart[8250],mmio32,<addr>[,options] 999 uart[8250],mmio32be,<addr>[,options] 1000 uart[8250],0x<addr>[,options] 1001 Start an early, polled-mode console on the 8250/16550 1002 UART at the specified I/O port or MMIO address. 1003 MMIO inter-register address stride is either 8-bit 1004 (mmio) or 32-bit (mmio32 or mmio32be). 1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1006 to be equivalent to 'mmio'. 'options' are specified 1007 in the same format described for "console=ttyS<n>"; if 1008 unspecified, the h/w is not initialized. 1009 1010 pl011,<addr> 1011 pl011,mmio32,<addr> 1012 Start an early, polled-mode console on a pl011 serial 1013 port at the specified address. The pl011 serial port 1014 must already be setup and configured. Options are not 1015 yet supported. If 'mmio32' is specified, then only 1016 the driver will use only 32-bit accessors to read/write 1017 the device registers. 1018 1019 meson,<addr> 1020 Start an early, polled-mode console on a meson serial 1021 port at the specified address. The serial port must 1022 already be setup and configured. Options are not yet 1023 supported. 1024 1025 msm_serial,<addr> 1026 Start an early, polled-mode console on an msm serial 1027 port at the specified address. The serial port 1028 must already be setup and configured. Options are not 1029 yet supported. 1030 1031 msm_serial_dm,<addr> 1032 Start an early, polled-mode console on an msm serial 1033 dm port at the specified address. The serial port 1034 must already be setup and configured. Options are not 1035 yet supported. 1036 1037 owl,<addr> 1038 Start an early, polled-mode console on a serial port 1039 of an Actions Semi SoC, such as S500 or S900, at the 1040 specified address. The serial port must already be 1041 setup and configured. Options are not yet supported. 1042 1043 rda,<addr> 1044 Start an early, polled-mode console on a serial port 1045 of an RDA Micro SoC, such as RDA8810PL, at the 1046 specified address. The serial port must already be 1047 setup and configured. Options are not yet supported. 1048 1049 smh Use ARM semihosting calls for early console. 1050 1051 s3c2410,<addr> 1052 s3c2412,<addr> 1053 s3c2440,<addr> 1054 s3c6400,<addr> 1055 s5pv210,<addr> 1056 exynos4210,<addr> 1057 Use early console provided by serial driver available 1058 on Samsung SoCs, requires selecting proper type and 1059 a correct base address of the selected UART port. The 1060 serial port must already be setup and configured. 1061 Options are not yet supported. 1062 1063 lantiq,<addr> 1064 Start an early, polled-mode console on a lantiq serial 1065 (lqasc) port at the specified address. The serial port 1066 must already be setup and configured. Options are not 1067 yet supported. 1068 1069 lpuart,<addr> 1070 lpuart32,<addr> 1071 Use early console provided by Freescale LP UART driver 1072 found on Freescale Vybrid and QorIQ LS1021A processors. 1073 A valid base address must be provided, and the serial 1074 port must already be setup and configured. 1075 1076 ar3700_uart,<addr> 1077 Start an early, polled-mode console on the 1078 Armada 3700 serial port at the specified 1079 address. The serial port must already be setup 1080 and configured. Options are not yet supported. 1081 1082 qcom_geni,<addr> 1083 Start an early, polled-mode console on a Qualcomm 1084 Generic Interface (GENI) based serial port at the 1085 specified address. The serial port must already be 1086 setup and configured. Options are not yet supported. 1087 1088 efifb,[options] 1089 Start an early, unaccelerated console on the EFI 1090 memory mapped framebuffer (if available). On cache 1091 coherent non-x86 systems that use system memory for 1092 the framebuffer, pass the 'ram' option so that it is 1093 mapped with the correct attributes. 1094 1095 earlyprintk= [X86,SH,ARM,M68k,S390] 1096 earlyprintk=vga 1097 earlyprintk=sclp 1098 earlyprintk=xen 1099 earlyprintk=serial[,ttySn[,baudrate]] 1100 earlyprintk=serial[,0x...[,baudrate]] 1101 earlyprintk=ttySn[,baudrate] 1102 earlyprintk=dbgp[debugController#] 1103 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1104 earlyprintk=xdbc[xhciController#] 1105 1106 earlyprintk is useful when the kernel crashes before 1107 the normal console is initialized. It is not enabled by 1108 default because it has some cosmetic problems. 1109 1110 Append ",keep" to not disable it when the real console 1111 takes over. 1112 1113 Only one of vga, efi, serial, or usb debug port can 1114 be used at a time. 1115 1116 Currently only ttyS0 and ttyS1 may be specified by 1117 name. Other I/O ports may be explicitly specified 1118 on some architectures (x86 and arm at least) by 1119 replacing ttySn with an I/O port address, like this: 1120 earlyprintk=serial,0x1008,115200 1121 You can find the port for a given device in 1122 /proc/tty/driver/serial: 1123 2: uart:ST16650V2 port:00001008 irq:18 ... 1124 1125 Interaction with the standard serial driver is not 1126 very good. 1127 1128 The VGA and EFI output is eventually overwritten by 1129 the real console. 1130 1131 The xen output can only be used by Xen PV guests. 1132 1133 The sclp output can only be used on s390. 1134 1135 The optional "force" to "pciserial" enables use of a 1136 PCI device even when its classcode is not of the 1137 UART class. 1138 1139 edac_report= [HW,EDAC] Control how to report EDAC event 1140 Format: {"on" | "off" | "force"} 1141 on: enable EDAC to report H/W event. May be overridden 1142 by other higher priority error reporting module. 1143 off: disable H/W event reporting through EDAC. 1144 force: enforce the use of EDAC to report H/W event. 1145 default: on. 1146 1147 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1148 ekgdboc=kbd 1149 1150 This is designed to be used in conjunction with 1151 the boot argument: earlyprintk=vga 1152 1153 edd= [EDD] 1154 Format: {"off" | "on" | "skip[mbr]"} 1155 1156 efi= [EFI] 1157 Format: { "old_map", "nochunk", "noruntime", "debug" } 1158 old_map [X86-64]: switch to the old ioremap-based EFI 1159 runtime services mapping. 32-bit still uses this one by 1160 default. 1161 nochunk: disable reading files in "chunks" in the EFI 1162 boot stub, as chunking can cause problems with some 1163 firmware implementations. 1164 noruntime : disable EFI runtime services support 1165 debug: enable misc debug output 1166 1167 efi_no_storage_paranoia [EFI; X86] 1168 Using this parameter you can use more than 50% of 1169 your efi variable storage. Use this parameter only if 1170 you are really sure that your UEFI does sane gc and 1171 fulfills the spec otherwise your board may brick. 1172 1173 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1174 Add arbitrary attribute to specific memory range by 1175 updating original EFI memory map. 1176 Region of memory which aa attribute is added to is 1177 from ss to ss+nn. 1178 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1179 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1180 attribute is added to range 0x100000000-0x180000000 and 1181 0x10a0000000-0x1120000000. 1182 1183 Using this parameter you can do debugging of EFI memmap 1184 related feature. For example, you can do debugging of 1185 Address Range Mirroring feature even if your box 1186 doesn't support it. 1187 1188 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1189 that is to be dynamically loaded by Linux. If there are 1190 multiple variables with the same name but with different 1191 vendor GUIDs, all of them will be loaded. See 1192 Documentation/acpi/ssdt-overlays.txt for details. 1193 1194 1195 eisa_irq_edge= [PARISC,HW] 1196 See header of drivers/parisc/eisa.c. 1197 1198 elanfreq= [X86-32] 1199 See comment before function elanfreq_setup() in 1200 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1201 1202 elevator= [IOSCHED] 1203 Format: { "mq-deadline" | "kyber" | "bfq" } 1204 See Documentation/block/deadline-iosched.txt, 1205 Documentation/block/kyber-iosched.txt and 1206 Documentation/block/bfq-iosched.txt for details. 1207 1208 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1209 Specifies physical address of start of kernel core 1210 image elf header and optionally the size. Generally 1211 kexec loader will pass this option to capture kernel. 1212 See Documentation/kdump/kdump.txt for details. 1213 1214 enable_mtrr_cleanup [X86] 1215 The kernel tries to adjust MTRR layout from continuous 1216 to discrete, to make X server driver able to add WB 1217 entry later. This parameter enables that. 1218 1219 enable_timer_pin_1 [X86] 1220 Enable PIN 1 of APIC timer 1221 Can be useful to work around chipset bugs 1222 (in particular on some ATI chipsets). 1223 The kernel tries to set a reasonable default. 1224 1225 enforcing [SELINUX] Set initial enforcing status. 1226 Format: {"0" | "1"} 1227 See security/selinux/Kconfig help text. 1228 0 -- permissive (log only, no denials). 1229 1 -- enforcing (deny and log). 1230 Default value is 0. 1231 Value can be changed at runtime via /selinux/enforce. 1232 1233 erst_disable [ACPI] 1234 Disable Error Record Serialization Table (ERST) 1235 support. 1236 1237 ether= [HW,NET] Ethernet cards parameters 1238 This option is obsoleted by the "netdev=" option, which 1239 has equivalent usage. See its documentation for details. 1240 1241 evm= [EVM] 1242 Format: { "fix" } 1243 Permit 'security.evm' to be updated regardless of 1244 current integrity status. 1245 1246 failslab= 1247 fail_page_alloc= 1248 fail_make_request=[KNL] 1249 General fault injection mechanism. 1250 Format: <interval>,<probability>,<space>,<times> 1251 See also Documentation/fault-injection/. 1252 1253 floppy= [HW] 1254 See Documentation/blockdev/floppy.txt. 1255 1256 force_pal_cache_flush 1257 [IA-64] Avoid check_sal_cache_flush which may hang on 1258 buggy SAL_CACHE_FLUSH implementations. Using this 1259 parameter will force ia64_sal_cache_flush to call 1260 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1261 1262 forcepae [X86-32] 1263 Forcefully enable Physical Address Extension (PAE). 1264 Many Pentium M systems disable PAE but may have a 1265 functionally usable PAE implementation. 1266 Warning: use of this parameter will taint the kernel 1267 and may cause unknown problems. 1268 1269 ftrace=[tracer] 1270 [FTRACE] will set and start the specified tracer 1271 as early as possible in order to facilitate early 1272 boot debugging. 1273 1274 ftrace_dump_on_oops[=orig_cpu] 1275 [FTRACE] will dump the trace buffers on oops. 1276 If no parameter is passed, ftrace will dump 1277 buffers of all CPUs, but if you pass orig_cpu, it will 1278 dump only the buffer of the CPU that triggered the 1279 oops. 1280 1281 ftrace_filter=[function-list] 1282 [FTRACE] Limit the functions traced by the function 1283 tracer at boot up. function-list is a comma separated 1284 list of functions. This list can be changed at run 1285 time by the set_ftrace_filter file in the debugfs 1286 tracing directory. 1287 1288 ftrace_notrace=[function-list] 1289 [FTRACE] Do not trace the functions specified in 1290 function-list. This list can be changed at run time 1291 by the set_ftrace_notrace file in the debugfs 1292 tracing directory. 1293 1294 ftrace_graph_filter=[function-list] 1295 [FTRACE] Limit the top level callers functions traced 1296 by the function graph tracer at boot up. 1297 function-list is a comma separated list of functions 1298 that can be changed at run time by the 1299 set_graph_function file in the debugfs tracing directory. 1300 1301 ftrace_graph_notrace=[function-list] 1302 [FTRACE] Do not trace from the functions specified in 1303 function-list. This list is a comma separated list of 1304 functions that can be changed at run time by the 1305 set_graph_notrace file in the debugfs tracing directory. 1306 1307 ftrace_graph_max_depth=<uint> 1308 [FTRACE] Used with the function graph tracer. This is 1309 the max depth it will trace into a function. This value 1310 can be changed at run time by the max_graph_depth file 1311 in the tracefs tracing directory. default: 0 (no limit) 1312 1313 gamecon.map[2|3]= 1314 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1315 support via parallel port (up to 5 devices per port) 1316 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1317 See also Documentation/input/devices/joystick-parport.rst 1318 1319 gamma= [HW,DRM] 1320 1321 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1322 Format: off | on 1323 default: on 1324 1325 gcov_persist= [GCOV] When non-zero (default), profiling data for 1326 kernel modules is saved and remains accessible via 1327 debugfs, even when the module is unloaded/reloaded. 1328 When zero, profiling data is discarded and associated 1329 debugfs files are removed at module unload time. 1330 1331 goldfish [X86] Enable the goldfish android emulator platform. 1332 Don't use this when you are not running on the 1333 android emulator 1334 1335 gpt [EFI] Forces disk with valid GPT signature but 1336 invalid Protective MBR to be treated as GPT. If the 1337 primary GPT is corrupted, it enables the backup/alternate 1338 GPT to be used instead. 1339 1340 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1341 the "Enable 0" bit of the configuration register. 1342 Format: 0 | 1 1343 Default: 0 1344 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1345 the "Enable 0" bit of the configuration register. 1346 Format: 0 | 1 1347 Default: 0 1348 grcan.select= [HW] Select which physical interface to use. 1349 Format: 0 | 1 1350 Default: 0 1351 grcan.txsize= [HW] Sets the size of the tx buffer. 1352 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1353 Default: 1024 1354 grcan.rxsize= [HW] Sets the size of the rx buffer. 1355 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1356 Default: 1024 1357 1358 gpio-mockup.gpio_mockup_ranges 1359 [HW] Sets the ranges of gpiochip of for this device. 1360 Format: <start1>,<end1>,<start2>,<end2>... 1361 1362 hardlockup_all_cpu_backtrace= 1363 [KNL] Should the hard-lockup detector generate 1364 backtraces on all cpus. 1365 Format: <integer> 1366 1367 hashdist= [KNL,NUMA] Large hashes allocated during boot 1368 are distributed across NUMA nodes. Defaults on 1369 for 64-bit NUMA, off otherwise. 1370 Format: 0 | 1 (for off | on) 1371 1372 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1373 1374 hd= [EIDE] (E)IDE hard drive subsystem geometry 1375 Format: <cyl>,<head>,<sect> 1376 1377 hest_disable [ACPI] 1378 Disable Hardware Error Source Table (HEST) support; 1379 corresponding firmware-first mode error processing 1380 logic will be disabled. 1381 1382 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1383 size of <nn>. This works even on boxes that have no 1384 highmem otherwise. This also works to reduce highmem 1385 size on bigger boxes. 1386 1387 highres= [KNL] Enable/disable high resolution timer mode. 1388 Valid parameters: "on", "off" 1389 Default: "on" 1390 1391 hisax= [HW,ISDN] 1392 See Documentation/isdn/README.HiSax. 1393 1394 hlt [BUGS=ARM,SH] 1395 1396 hpet= [X86-32,HPET] option to control HPET usage 1397 Format: { enable (default) | disable | force | 1398 verbose } 1399 disable: disable HPET and use PIT instead 1400 force: allow force enabled of undocumented chips (ICH4, 1401 VIA, nVidia) 1402 verbose: show contents of HPET registers during setup 1403 1404 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1405 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1406 1407 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1408 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1409 On x86-64 and powerpc, this option can be specified 1410 multiple times interleaved with hugepages= to reserve 1411 huge pages of different sizes. Valid pages sizes on 1412 x86-64 are 2M (when the CPU supports "pse") and 1G 1413 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1414 1415 hung_task_panic= 1416 [KNL] Should the hung task detector generate panics. 1417 Format: <integer> 1418 1419 A nonzero value instructs the kernel to panic when a 1420 hung task is detected. The default value is controlled 1421 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1422 option. The value selected by this boot parameter can 1423 be changed later by the kernel.hung_task_panic sysctl. 1424 1425 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1426 terminal devices. Valid values: 0..8 1427 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1428 If specified, z/VM IUCV HVC accepts connections 1429 from listed z/VM user IDs only. 1430 1431 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1432 which allow the hypervisor to 'idle' the 1433 guest on lock contention. 1434 1435 keep_bootcon [KNL] 1436 Do not unregister boot console at start. This is only 1437 useful for debugging when something happens in the window 1438 between unregistering the boot console and initializing 1439 the real console. 1440 1441 i2c_bus= [HW] Override the default board specific I2C bus speed 1442 or register an additional I2C bus that is not 1443 registered from board initialization code. 1444 Format: 1445 <bus_id>,<clkrate> 1446 1447 i8042.debug [HW] Toggle i8042 debug mode 1448 i8042.unmask_kbd_data 1449 [HW] Enable printing of interrupt data from the KBD port 1450 (disabled by default, and as a pre-condition 1451 requires that i8042.debug=1 be enabled) 1452 i8042.direct [HW] Put keyboard port into non-translated mode 1453 i8042.dumbkbd [HW] Pretend that controller can only read data from 1454 keyboard and cannot control its state 1455 (Don't attempt to blink the leds) 1456 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1457 i8042.nokbd [HW] Don't check/create keyboard port 1458 i8042.noloop [HW] Disable the AUX Loopback command while probing 1459 for the AUX port 1460 i8042.nomux [HW] Don't check presence of an active multiplexing 1461 controller 1462 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1463 controllers 1464 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1465 i8042.reset [HW] Reset the controller during init, cleanup and 1466 suspend-to-ram transitions, only during s2r 1467 transitions, or never reset 1468 Format: { 1 | Y | y | 0 | N | n } 1469 1, Y, y: always reset controller 1470 0, N, n: don't ever reset controller 1471 Default: only on s2r transitions on x86; most other 1472 architectures force reset to be always executed 1473 i8042.unlock [HW] Unlock (ignore) the keylock 1474 i8042.kbdreset [HW] Reset device connected to KBD port 1475 1476 i810= [HW,DRM] 1477 1478 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1479 indicates that the driver is running on unsupported 1480 hardware. 1481 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1482 does not match list of supported models. 1483 i8k.power_status 1484 [HW] Report power status in /proc/i8k 1485 (disabled by default) 1486 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1487 capability is set. 1488 1489 i915.invert_brightness= 1490 [DRM] Invert the sense of the variable that is used to 1491 set the brightness of the panel backlight. Normally a 1492 brightness value of 0 indicates backlight switched off, 1493 and the maximum of the brightness value sets the backlight 1494 to maximum brightness. If this parameter is set to 0 1495 (default) and the machine requires it, or this parameter 1496 is set to 1, a brightness value of 0 sets the backlight 1497 to maximum brightness, and the maximum of the brightness 1498 value switches the backlight off. 1499 -1 -- never invert brightness 1500 0 -- machine default 1501 1 -- force brightness inversion 1502 1503 icn= [HW,ISDN] 1504 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1505 1506 ide-core.nodma= [HW] (E)IDE subsystem 1507 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1508 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1509 .cdrom .chs .ignore_cable are additional options 1510 See Documentation/ide/ide.txt. 1511 1512 ide-generic.probe-mask= [HW] (E)IDE subsystem 1513 Format: <int> 1514 Probe mask for legacy ISA IDE ports. Depending on 1515 platform up to 6 ports are supported, enabled by 1516 setting corresponding bits in the mask to 1. The 1517 default value is 0x0, which has a special meaning. 1518 On systems that have PCI, it triggers scanning the 1519 PCI bus for the first and the second port, which 1520 are then probed. On systems without PCI the value 1521 of 0x0 enables probing the two first ports as if it 1522 was 0x3. 1523 1524 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1525 Claim all unknown PCI IDE storage controllers. 1526 1527 idle= [X86] 1528 Format: idle=poll, idle=halt, idle=nomwait 1529 Poll forces a polling idle loop that can slightly 1530 improve the performance of waking up a idle CPU, but 1531 will use a lot of power and make the system run hot. 1532 Not recommended. 1533 idle=halt: Halt is forced to be used for CPU idle. 1534 In such case C2/C3 won't be used again. 1535 idle=nomwait: Disable mwait for CPU C-states 1536 1537 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1538 Format: { strict | legacy | 2008 | relaxed } 1539 Default: strict 1540 1541 Choose which programs will be accepted for execution 1542 based on the IEEE 754 NaN encoding(s) supported by 1543 the FPU and the NaN encoding requested with the value 1544 of an ELF file header flag individually set by each 1545 binary. Hardware implementations are permitted to 1546 support either or both of the legacy and the 2008 NaN 1547 encoding mode. 1548 1549 Available settings are as follows: 1550 strict accept binaries that request a NaN encoding 1551 supported by the FPU 1552 legacy only accept legacy-NaN binaries, if supported 1553 by the FPU 1554 2008 only accept 2008-NaN binaries, if supported 1555 by the FPU 1556 relaxed accept any binaries regardless of whether 1557 supported by the FPU 1558 1559 The FPU emulator is always able to support both NaN 1560 encodings, so if no FPU hardware is present or it has 1561 been disabled with 'nofpu', then the settings of 1562 'legacy' and '2008' strap the emulator accordingly, 1563 'relaxed' straps the emulator for both legacy-NaN and 1564 2008-NaN, whereas 'strict' enables legacy-NaN only on 1565 legacy processors and both NaN encodings on MIPS32 or 1566 MIPS64 CPUs. 1567 1568 The setting for ABS.fmt/NEG.fmt instruction execution 1569 mode generally follows that for the NaN encoding, 1570 except where unsupported by hardware. 1571 1572 ignore_loglevel [KNL] 1573 Ignore loglevel setting - this will print /all/ 1574 kernel messages to the console. Useful for debugging. 1575 We also add it as printk module parameter, so users 1576 could change it dynamically, usually by 1577 /sys/module/printk/parameters/ignore_loglevel. 1578 1579 ignore_rlimit_data 1580 Ignore RLIMIT_DATA setting for data mappings, 1581 print warning at first misuse. Can be changed via 1582 /sys/module/kernel/parameters/ignore_rlimit_data. 1583 1584 ihash_entries= [KNL] 1585 Set number of hash buckets for inode cache. 1586 1587 ima_appraise= [IMA] appraise integrity measurements 1588 Format: { "off" | "enforce" | "fix" | "log" } 1589 default: "enforce" 1590 1591 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1592 The builtin appraise policy appraises all files 1593 owned by uid=0. 1594 1595 ima_canonical_fmt [IMA] 1596 Use the canonical format for the binary runtime 1597 measurements, instead of host native format. 1598 1599 ima_hash= [IMA] 1600 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1601 | sha512 | ... } 1602 default: "sha1" 1603 1604 The list of supported hash algorithms is defined 1605 in crypto/hash_info.h. 1606 1607 ima_policy= [IMA] 1608 The builtin policies to load during IMA setup. 1609 Format: "tcb | appraise_tcb | secure_boot | 1610 fail_securely" 1611 1612 The "tcb" policy measures all programs exec'd, files 1613 mmap'd for exec, and all files opened with the read 1614 mode bit set by either the effective uid (euid=0) or 1615 uid=0. 1616 1617 The "appraise_tcb" policy appraises the integrity of 1618 all files owned by root. 1619 1620 The "secure_boot" policy appraises the integrity 1621 of files (eg. kexec kernel image, kernel modules, 1622 firmware, policy, etc) based on file signatures. 1623 1624 The "fail_securely" policy forces file signature 1625 verification failure also on privileged mounted 1626 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1627 flag. 1628 1629 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1630 Load a policy which meets the needs of the Trusted 1631 Computing Base. This means IMA will measure all 1632 programs exec'd, files mmap'd for exec, and all files 1633 opened for read by uid=0. 1634 1635 ima_template= [IMA] 1636 Select one of defined IMA measurements template formats. 1637 Formats: { "ima" | "ima-ng" | "ima-sig" } 1638 Default: "ima-ng" 1639 1640 ima_template_fmt= 1641 [IMA] Define a custom template format. 1642 Format: { "field1|...|fieldN" } 1643 1644 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1645 Format: <min_file_size> 1646 Set the minimal file size for using asynchronous hash. 1647 If left unspecified, ahash usage is disabled. 1648 1649 ahash performance varies for different data sizes on 1650 different crypto accelerators. This option can be used 1651 to achieve the best performance for a particular HW. 1652 1653 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1654 Format: <bufsize> 1655 Set hashing buffer size. Default: 4k. 1656 1657 ahash performance varies for different chunk sizes on 1658 different crypto accelerators. This option can be used 1659 to achieve best performance for particular HW. 1660 1661 init= [KNL] 1662 Format: <full_path> 1663 Run specified binary instead of /sbin/init as init 1664 process. 1665 1666 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1667 for working out where the kernel is dying during 1668 startup. 1669 1670 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1671 initcall functions. Useful for debugging built-in 1672 modules and initcalls. 1673 1674 initrd= [BOOT] Specify the location of the initial ramdisk 1675 1676 init_pkru= [x86] Specify the default memory protection keys rights 1677 register contents for all processes. 0x55555554 by 1678 default (disallow access to all but pkey 0). Can 1679 override in debugfs after boot. 1680 1681 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1682 Format: <irq> 1683 1684 int_pln_enable [x86] Enable power limit notification interrupt 1685 1686 integrity_audit=[IMA] 1687 Format: { "0" | "1" } 1688 0 -- basic integrity auditing messages. (Default) 1689 1 -- additional integrity auditing messages. 1690 1691 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1692 on 1693 Enable intel iommu driver. 1694 off 1695 Disable intel iommu driver. 1696 igfx_off [Default Off] 1697 By default, gfx is mapped as normal device. If a gfx 1698 device has a dedicated DMAR unit, the DMAR unit is 1699 bypassed by not enabling DMAR with this option. In 1700 this case, gfx device will use physical address for 1701 DMA. 1702 forcedac [x86_64] 1703 With this option iommu will not optimize to look 1704 for io virtual address below 32-bit forcing dual 1705 address cycle on pci bus for cards supporting greater 1706 than 32-bit addressing. The default is to look 1707 for translation below 32-bit and if not available 1708 then look in the higher range. 1709 strict [Default Off] 1710 With this option on every unmap_single operation will 1711 result in a hardware IOTLB flush operation as opposed 1712 to batching them for performance. 1713 sp_off [Default Off] 1714 By default, super page will be supported if Intel IOMMU 1715 has the capability. With this option, super page will 1716 not be supported. 1717 sm_on [Default Off] 1718 By default, scalable mode will be disabled even if the 1719 hardware advertises that it has support for the scalable 1720 mode translation. With this option set, scalable mode 1721 will be used on hardware which claims to support it. 1722 tboot_noforce [Default Off] 1723 Do not force the Intel IOMMU enabled under tboot. 1724 By default, tboot will force Intel IOMMU on, which 1725 could harm performance of some high-throughput 1726 devices like 40GBit network cards, even if identity 1727 mapping is enabled. 1728 Note that using this option lowers the security 1729 provided by tboot because it makes the system 1730 vulnerable to DMA attacks. 1731 1732 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1733 0 disables intel_idle and fall back on acpi_idle. 1734 1 to 9 specify maximum depth of C-state. 1735 1736 intel_pstate= [X86] 1737 disable 1738 Do not enable intel_pstate as the default 1739 scaling driver for the supported processors 1740 passive 1741 Use intel_pstate as a scaling driver, but configure it 1742 to work with generic cpufreq governors (instead of 1743 enabling its internal governor). This mode cannot be 1744 used along with the hardware-managed P-states (HWP) 1745 feature. 1746 force 1747 Enable intel_pstate on systems that prohibit it by default 1748 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1749 instead of acpi-cpufreq may disable platform features, such 1750 as thermal controls and power capping, that rely on ACPI 1751 P-States information being indicated to OSPM and therefore 1752 should be used with caution. This option does not work with 1753 processors that aren't supported by the intel_pstate driver 1754 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1755 no_hwp 1756 Do not enable hardware P state control (HWP) 1757 if available. 1758 hwp_only 1759 Only load intel_pstate on systems which support 1760 hardware P state control (HWP) if available. 1761 support_acpi_ppc 1762 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1763 Description Table, specifies preferred power management 1764 profile as "Enterprise Server" or "Performance Server", 1765 then this feature is turned on by default. 1766 per_cpu_perf_limits 1767 Allow per-logical-CPU P-State performance control limits using 1768 cpufreq sysfs interface 1769 1770 intremap= [X86-64, Intel-IOMMU] 1771 on enable Interrupt Remapping (default) 1772 off disable Interrupt Remapping 1773 nosid disable Source ID checking 1774 no_x2apic_optout 1775 BIOS x2APIC opt-out request will be ignored 1776 nopost disable Interrupt Posting 1777 1778 iomem= Disable strict checking of access to MMIO memory 1779 strict regions from userspace. 1780 relaxed 1781 1782 iommu= [x86] 1783 off 1784 force 1785 noforce 1786 biomerge 1787 panic 1788 nopanic 1789 merge 1790 nomerge 1791 soft 1792 pt [x86] 1793 nopt [x86] 1794 nobypass [PPC/POWERNV] 1795 Disable IOMMU bypass, using IOMMU for PCI devices. 1796 1797 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1798 Format: { "0" | "1" } 1799 0 - Lazy mode. 1800 Request that DMA unmap operations use deferred 1801 invalidation of hardware TLBs, for increased 1802 throughput at the cost of reduced device isolation. 1803 Will fall back to strict mode if not supported by 1804 the relevant IOMMU driver. 1805 1 - Strict mode (default). 1806 DMA unmap operations invalidate IOMMU hardware TLBs 1807 synchronously. 1808 1809 iommu.passthrough= 1810 [ARM64] Configure DMA to bypass the IOMMU by default. 1811 Format: { "0" | "1" } 1812 0 - Use IOMMU translation for DMA. 1813 1 - Bypass the IOMMU for DMA. 1814 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1815 1816 io7= [HW] IO7 for Marvel based alpha systems 1817 See comment before marvel_specify_io7 in 1818 arch/alpha/kernel/core_marvel.c. 1819 1820 io_delay= [X86] I/O delay method 1821 0x80 1822 Standard port 0x80 based delay 1823 0xed 1824 Alternate port 0xed based delay (needed on some systems) 1825 udelay 1826 Simple two microseconds delay 1827 none 1828 No delay 1829 1830 ip= [IP_PNP] 1831 See Documentation/filesystems/nfs/nfsroot.txt. 1832 1833 ipcmni_extend [KNL] Extend the maximum number of unique System V 1834 IPC identifiers from 32,768 to 16,777,216. 1835 1836 irqaffinity= [SMP] Set the default irq affinity mask 1837 The argument is a cpu list, as described above. 1838 1839 irqchip.gicv2_force_probe= 1840 [ARM, ARM64] 1841 Format: <bool> 1842 Force the kernel to look for the second 4kB page 1843 of a GICv2 controller even if the memory range 1844 exposed by the device tree is too small. 1845 1846 irqchip.gicv3_nolpi= 1847 [ARM, ARM64] 1848 Force the kernel to ignore the availability of 1849 LPIs (and by consequence ITSs). Intended for system 1850 that use the kernel as a bootloader, and thus want 1851 to let secondary kernels in charge of setting up 1852 LPIs. 1853 1854 irqchip.gicv3_pseudo_nmi= [ARM64] 1855 Enables support for pseudo-NMIs in the kernel. This 1856 requires the kernel to be built with 1857 CONFIG_ARM64_PSEUDO_NMI. 1858 1859 irqfixup [HW] 1860 When an interrupt is not handled search all handlers 1861 for it. Intended to get systems with badly broken 1862 firmware running. 1863 1864 irqpoll [HW] 1865 When an interrupt is not handled search all handlers 1866 for it. Also check all handlers each timer 1867 interrupt. Intended to get systems with badly broken 1868 firmware running. 1869 1870 isapnp= [ISAPNP] 1871 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1872 1873 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1874 [Deprecated - use cpusets instead] 1875 Format: [flag-list,]<cpu-list> 1876 1877 Specify one or more CPUs to isolate from disturbances 1878 specified in the flag list (default: domain): 1879 1880 nohz 1881 Disable the tick when a single task runs. 1882 1883 A residual 1Hz tick is offloaded to workqueues, which you 1884 need to affine to housekeeping through the global 1885 workqueue's affinity configured via the 1886 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1887 by using the 'domain' flag described below. 1888 1889 NOTE: by default the global workqueue runs on all CPUs, 1890 so to protect individual CPUs the 'cpumask' file has to 1891 be configured manually after bootup. 1892 1893 domain 1894 Isolate from the general SMP balancing and scheduling 1895 algorithms. Note that performing domain isolation this way 1896 is irreversible: it's not possible to bring back a CPU to 1897 the domains once isolated through isolcpus. It's strongly 1898 advised to use cpusets instead to disable scheduler load 1899 balancing through the "cpuset.sched_load_balance" file. 1900 It offers a much more flexible interface where CPUs can 1901 move in and out of an isolated set anytime. 1902 1903 You can move a process onto or off an "isolated" CPU via 1904 the CPU affinity syscalls or cpuset. 1905 <cpu number> begins at 0 and the maximum value is 1906 "number of CPUs in system - 1". 1907 1908 The format of <cpu-list> is described above. 1909 1910 1911 1912 iucv= [HW,NET] 1913 1914 ivrs_ioapic [HW,X86_64] 1915 Provide an override to the IOAPIC-ID<->DEVICE-ID 1916 mapping provided in the IVRS ACPI table. For 1917 example, to map IOAPIC-ID decimal 10 to 1918 PCI device 00:14.0 write the parameter as: 1919 ivrs_ioapic[10]=00:14.0 1920 1921 ivrs_hpet [HW,X86_64] 1922 Provide an override to the HPET-ID<->DEVICE-ID 1923 mapping provided in the IVRS ACPI table. For 1924 example, to map HPET-ID decimal 0 to 1925 PCI device 00:14.0 write the parameter as: 1926 ivrs_hpet[0]=00:14.0 1927 1928 ivrs_acpihid [HW,X86_64] 1929 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1930 mapping provided in the IVRS ACPI table. For 1931 example, to map UART-HID:UID AMD0020:0 to 1932 PCI device 00:14.5 write the parameter as: 1933 ivrs_acpihid[00:14.5]=AMD0020:0 1934 1935 js= [HW,JOY] Analog joystick 1936 See Documentation/input/joydev/joystick.rst. 1937 1938 nokaslr [KNL] 1939 When CONFIG_RANDOMIZE_BASE is set, this disables 1940 kernel and module base offset ASLR (Address Space 1941 Layout Randomization). 1942 1943 kasan_multi_shot 1944 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1945 report on every invalid memory access. Without this 1946 parameter KASAN will print report only for the first 1947 invalid access. 1948 1949 keepinitrd [HW,ARM] 1950 1951 kernelcore= [KNL,X86,IA-64,PPC] 1952 Format: nn[KMGTPE] | nn% | "mirror" 1953 This parameter specifies the amount of memory usable by 1954 the kernel for non-movable allocations. The requested 1955 amount is spread evenly throughout all nodes in the 1956 system as ZONE_NORMAL. The remaining memory is used for 1957 movable memory in its own zone, ZONE_MOVABLE. In the 1958 event, a node is too small to have both ZONE_NORMAL and 1959 ZONE_MOVABLE, kernelcore memory will take priority and 1960 other nodes will have a larger ZONE_MOVABLE. 1961 1962 ZONE_MOVABLE is used for the allocation of pages that 1963 may be reclaimed or moved by the page migration 1964 subsystem. Note that allocations like PTEs-from-HighMem 1965 still use the HighMem zone if it exists, and the Normal 1966 zone if it does not. 1967 1968 It is possible to specify the exact amount of memory in 1969 the form of "nn[KMGTPE]", a percentage of total system 1970 memory in the form of "nn%", or "mirror". If "mirror" 1971 option is specified, mirrored (reliable) memory is used 1972 for non-movable allocations and remaining memory is used 1973 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1974 are exclusive, so you cannot specify multiple forms. 1975 1976 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1977 Format: <Controller#>[,poll interval] 1978 The controller # is the number of the ehci usb debug 1979 port as it is probed via PCI. The poll interval is 1980 optional and is the number seconds in between 1981 each poll cycle to the debug port in case you need 1982 the functionality for interrupting the kernel with 1983 gdb or control-c on the dbgp connection. When 1984 not using this parameter you use sysrq-g to break into 1985 the kernel debugger. 1986 1987 kgdboc= [KGDB,HW] kgdb over consoles. 1988 Requires a tty driver that supports console polling, 1989 or a supported polling keyboard driver (non-usb). 1990 Serial only format: <serial_device>[,baud] 1991 keyboard only format: kbd 1992 keyboard and serial format: kbd,<serial_device>[,baud] 1993 Optional Kernel mode setting: 1994 kms, kbd format: kms,kbd 1995 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1996 1997 kgdbwait [KGDB] Stop kernel execution and enter the 1998 kernel debugger at the earliest opportunity. 1999 2000 kmac= [MIPS] korina ethernet MAC address. 2001 Configure the RouterBoard 532 series on-chip 2002 Ethernet adapter MAC address. 2003 2004 kmemleak= [KNL] Boot-time kmemleak enable/disable 2005 Valid arguments: on, off 2006 Default: on 2007 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2008 the default is off. 2009 2010 kpti= [ARM64] Control page table isolation of user 2011 and kernel address spaces. 2012 Default: enabled on cores which need mitigation. 2013 0: force disabled 2014 1: force enabled 2015 2016 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2017 Default is 0 (don't ignore, but inject #GP) 2018 2019 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2020 Default is false (don't support). 2021 2022 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2023 KVM MMU at runtime. 2024 Default is 0 (off) 2025 2026 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2027 Default is 1 (enabled) 2028 2029 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2030 for all guests. 2031 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2032 2033 kvm-arm.vgic_v3_group0_trap= 2034 [KVM,ARM] Trap guest accesses to GICv3 group-0 2035 system registers 2036 2037 kvm-arm.vgic_v3_group1_trap= 2038 [KVM,ARM] Trap guest accesses to GICv3 group-1 2039 system registers 2040 2041 kvm-arm.vgic_v3_common_trap= 2042 [KVM,ARM] Trap guest accesses to GICv3 common 2043 system registers 2044 2045 kvm-arm.vgic_v4_enable= 2046 [KVM,ARM] Allow use of GICv4 for direct injection of 2047 LPIs. 2048 2049 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2050 (virtualized MMU) support on capable Intel chips. 2051 Default is 1 (enabled) 2052 2053 kvm-intel.emulate_invalid_guest_state= 2054 [KVM,Intel] Enable emulation of invalid guest states 2055 Default is 0 (disabled) 2056 2057 kvm-intel.flexpriority= 2058 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2059 Default is 1 (enabled) 2060 2061 kvm-intel.nested= 2062 [KVM,Intel] Enable VMX nesting (nVMX). 2063 Default is 0 (disabled) 2064 2065 kvm-intel.unrestricted_guest= 2066 [KVM,Intel] Disable unrestricted guest feature 2067 (virtualized real and unpaged mode) on capable 2068 Intel chips. Default is 1 (enabled) 2069 2070 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2071 CVE-2018-3620. 2072 2073 Valid arguments: never, cond, always 2074 2075 always: L1D cache flush on every VMENTER. 2076 cond: Flush L1D on VMENTER only when the code between 2077 VMEXIT and VMENTER can leak host memory. 2078 never: Disables the mitigation 2079 2080 Default is cond (do L1 cache flush in specific instances) 2081 2082 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2083 feature (tagged TLBs) on capable Intel chips. 2084 Default is 1 (enabled) 2085 2086 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2087 affected CPUs 2088 2089 The kernel PTE inversion protection is unconditionally 2090 enabled and cannot be disabled. 2091 2092 full 2093 Provides all available mitigations for the 2094 L1TF vulnerability. Disables SMT and 2095 enables all mitigations in the 2096 hypervisors, i.e. unconditional L1D flush. 2097 2098 SMT control and L1D flush control via the 2099 sysfs interface is still possible after 2100 boot. Hypervisors will issue a warning 2101 when the first VM is started in a 2102 potentially insecure configuration, 2103 i.e. SMT enabled or L1D flush disabled. 2104 2105 full,force 2106 Same as 'full', but disables SMT and L1D 2107 flush runtime control. Implies the 2108 'nosmt=force' command line option. 2109 (i.e. sysfs control of SMT is disabled.) 2110 2111 flush 2112 Leaves SMT enabled and enables the default 2113 hypervisor mitigation, i.e. conditional 2114 L1D flush. 2115 2116 SMT control and L1D flush control via the 2117 sysfs interface is still possible after 2118 boot. Hypervisors will issue a warning 2119 when the first VM is started in a 2120 potentially insecure configuration, 2121 i.e. SMT enabled or L1D flush disabled. 2122 2123 flush,nosmt 2124 2125 Disables SMT and enables the default 2126 hypervisor mitigation. 2127 2128 SMT control and L1D flush control via the 2129 sysfs interface is still possible after 2130 boot. Hypervisors will issue a warning 2131 when the first VM is started in a 2132 potentially insecure configuration, 2133 i.e. SMT enabled or L1D flush disabled. 2134 2135 flush,nowarn 2136 Same as 'flush', but hypervisors will not 2137 warn when a VM is started in a potentially 2138 insecure configuration. 2139 2140 off 2141 Disables hypervisor mitigations and doesn't 2142 emit any warnings. 2143 It also drops the swap size and available 2144 RAM limit restriction on both hypervisor and 2145 bare metal. 2146 2147 Default is 'flush'. 2148 2149 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2150 2151 l2cr= [PPC] 2152 2153 l3cr= [PPC] 2154 2155 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2156 disabled it. 2157 2158 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2159 value for LAPIC timer one-shot implementation. Default 2160 back to the programmable timer unit in the LAPIC. 2161 2162 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2163 in C2 power state. 2164 2165 libata.dma= [LIBATA] DMA control 2166 libata.dma=0 Disable all PATA and SATA DMA 2167 libata.dma=1 PATA and SATA Disk DMA only 2168 libata.dma=2 ATAPI (CDROM) DMA only 2169 libata.dma=4 Compact Flash DMA only 2170 Combinations also work, so libata.dma=3 enables DMA 2171 for disks and CDROMs, but not CFs. 2172 2173 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2174 libata.ignore_hpa=0 keep BIOS limits (default) 2175 libata.ignore_hpa=1 ignore limits, using full disk 2176 2177 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2178 when set. 2179 Format: <int> 2180 2181 libata.force= [LIBATA] Force configurations. The format is comma 2182 separated list of "[ID:]VAL" where ID is 2183 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2184 matching port, link or device. Basically, it matches 2185 the ATA ID string printed on console by libata. If 2186 the whole ID part is omitted, the last PORT and DEVICE 2187 values are used. If ID hasn't been specified yet, the 2188 configuration applies to all ports, links and devices. 2189 2190 If only DEVICE is omitted, the parameter applies to 2191 the port and all links and devices behind it. DEVICE 2192 number of 0 either selects the first device or the 2193 first fan-out link behind PMP device. It does not 2194 select the host link. DEVICE number of 15 selects the 2195 host link and device attached to it. 2196 2197 The VAL specifies the configuration to force. As long 2198 as there's no ambiguity shortcut notation is allowed. 2199 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2200 The following configurations can be forced. 2201 2202 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2203 Any ID with matching PORT is used. 2204 2205 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2206 2207 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2208 udma[/][16,25,33,44,66,100,133] notation is also 2209 allowed. 2210 2211 * [no]ncq: Turn on or off NCQ. 2212 2213 * [no]ncqtrim: Turn off queued DSM TRIM. 2214 2215 * nohrst, nosrst, norst: suppress hard, soft 2216 and both resets. 2217 2218 * rstonce: only attempt one reset during 2219 hot-unplug link recovery 2220 2221 * dump_id: dump IDENTIFY data. 2222 2223 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2224 2225 * disable: Disable this device. 2226 2227 If there are multiple matching configurations changing 2228 the same attribute, the last one is used. 2229 2230 memblock=debug [KNL] Enable memblock debug messages. 2231 2232 load_ramdisk= [RAM] List of ramdisks to load from floppy 2233 See Documentation/blockdev/ramdisk.txt. 2234 2235 lockd.nlm_grace_period=P [NFS] Assign grace period. 2236 Format: <integer> 2237 2238 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2239 Format: <integer> 2240 2241 lockd.nlm_timeout=T [NFS] Assign timeout value. 2242 Format: <integer> 2243 2244 lockd.nlm_udpport=M [NFS] Assign UDP port. 2245 Format: <integer> 2246 2247 locktorture.nreaders_stress= [KNL] 2248 Set the number of locking read-acquisition kthreads. 2249 Defaults to being automatically set based on the 2250 number of online CPUs. 2251 2252 locktorture.nwriters_stress= [KNL] 2253 Set the number of locking write-acquisition kthreads. 2254 2255 locktorture.onoff_holdoff= [KNL] 2256 Set time (s) after boot for CPU-hotplug testing. 2257 2258 locktorture.onoff_interval= [KNL] 2259 Set time (s) between CPU-hotplug operations, or 2260 zero to disable CPU-hotplug testing. 2261 2262 locktorture.shuffle_interval= [KNL] 2263 Set task-shuffle interval (jiffies). Shuffling 2264 tasks allows some CPUs to go into dyntick-idle 2265 mode during the locktorture test. 2266 2267 locktorture.shutdown_secs= [KNL] 2268 Set time (s) after boot system shutdown. This 2269 is useful for hands-off automated testing. 2270 2271 locktorture.stat_interval= [KNL] 2272 Time (s) between statistics printk()s. 2273 2274 locktorture.stutter= [KNL] 2275 Time (s) to stutter testing, for example, 2276 specifying five seconds causes the test to run for 2277 five seconds, wait for five seconds, and so on. 2278 This tests the locking primitive's ability to 2279 transition abruptly to and from idle. 2280 2281 locktorture.torture_type= [KNL] 2282 Specify the locking implementation to test. 2283 2284 locktorture.verbose= [KNL] 2285 Enable additional printk() statements. 2286 2287 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2288 Format: <irq> 2289 2290 loglevel= All Kernel Messages with a loglevel smaller than the 2291 console loglevel will be printed to the console. It can 2292 also be changed with klogd or other programs. The 2293 loglevels are defined as follows: 2294 2295 0 (KERN_EMERG) system is unusable 2296 1 (KERN_ALERT) action must be taken immediately 2297 2 (KERN_CRIT) critical conditions 2298 3 (KERN_ERR) error conditions 2299 4 (KERN_WARNING) warning conditions 2300 5 (KERN_NOTICE) normal but significant condition 2301 6 (KERN_INFO) informational 2302 7 (KERN_DEBUG) debug-level messages 2303 2304 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2305 in bytes. n must be a power of two and greater 2306 than the minimal size. The minimal size is defined 2307 by LOG_BUF_SHIFT kernel config parameter. There is 2308 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2309 that allows to increase the default size depending on 2310 the number of CPUs. See init/Kconfig for more details. 2311 2312 logo.nologo [FB] Disables display of the built-in Linux logo. 2313 This may be used to provide more screen space for 2314 kernel log messages and is useful when debugging 2315 kernel boot problems. 2316 2317 lp=0 [LP] Specify parallel ports to use, e.g, 2318 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2319 lp=reset first parallel port). 'lp=0' disables the 2320 lp=auto printer driver. 'lp=reset' (which can be 2321 specified in addition to the ports) causes 2322 attached printers to be reset. Using 2323 lp=port1,port2,... specifies the parallel ports 2324 to associate lp devices with, starting with 2325 lp0. A port specification may be 'none' to skip 2326 that lp device, or a parport name such as 2327 'parport0'. Specifying 'lp=auto' instead of a 2328 port specification list means that device IDs 2329 from each port should be examined, to see if 2330 an IEEE 1284-compliant printer is attached; if 2331 so, the driver will manage that printer. 2332 See also header of drivers/char/lp.c. 2333 2334 lpj=n [KNL] 2335 Sets loops_per_jiffy to given constant, thus avoiding 2336 time-consuming boot-time autodetection (up to 250 ms per 2337 CPU). 0 enables autodetection (default). To determine 2338 the correct value for your kernel, boot with normal 2339 autodetection and see what value is printed. Note that 2340 on SMP systems the preset will be applied to all CPUs, 2341 which is likely to cause problems if your CPUs need 2342 significantly divergent settings. An incorrect value 2343 will cause delays in the kernel to be wrong, leading to 2344 unpredictable I/O errors and other breakage. Although 2345 unlikely, in the extreme case this might damage your 2346 hardware. 2347 2348 ltpc= [NET] 2349 Format: <io>,<irq>,<dma> 2350 2351 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2352 2353 lsm=lsm1,...,lsmN 2354 [SECURITY] Choose order of LSM initialization. This 2355 overrides CONFIG_LSM, and the "security=" parameter. 2356 2357 machvec= [IA-64] Force the use of a particular machine-vector 2358 (machvec) in a generic kernel. 2359 Example: machvec=hpzx1_swiotlb 2360 2361 machtype= [Loongson] Share the same kernel image file between different 2362 yeeloong laptop. 2363 Example: machtype=lemote-yeeloong-2f-7inch 2364 2365 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2366 than or equal to this physical address is ignored. 2367 2368 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2369 will bring up during bootup. maxcpus=n : n >= 0 limits 2370 the kernel to bring up 'n' processors. Surely after 2371 bootup you can bring up the other plugged cpu by executing 2372 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2373 only takes effect during system bootup. 2374 While n=0 is a special case, it is equivalent to "nosmp", 2375 which also disables the IO APIC. 2376 2377 max_loop= [LOOP] The number of loop block devices that get 2378 (loop.max_loop) unconditionally pre-created at init time. The default 2379 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2380 of statically allocating a predefined number, loop 2381 devices can be requested on-demand with the 2382 /dev/loop-control interface. 2383 2384 mce [X86-32] Machine Check Exception 2385 2386 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2387 2388 md= [HW] RAID subsystems devices and level 2389 See Documentation/admin-guide/md.rst. 2390 2391 mdacon= [MDA] 2392 Format: <first>,<last> 2393 Specifies range of consoles to be captured by the MDA. 2394 2395 mds= [X86,INTEL] 2396 Control mitigation for the Micro-architectural Data 2397 Sampling (MDS) vulnerability. 2398 2399 Certain CPUs are vulnerable to an exploit against CPU 2400 internal buffers which can forward information to a 2401 disclosure gadget under certain conditions. 2402 2403 In vulnerable processors, the speculatively 2404 forwarded data can be used in a cache side channel 2405 attack, to access data to which the attacker does 2406 not have direct access. 2407 2408 This parameter controls the MDS mitigation. The 2409 options are: 2410 2411 full - Enable MDS mitigation on vulnerable CPUs 2412 full,nosmt - Enable MDS mitigation and disable 2413 SMT on vulnerable CPUs 2414 off - Unconditionally disable MDS mitigation 2415 2416 Not specifying this option is equivalent to 2417 mds=full. 2418 2419 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2420 2421 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2422 Amount of memory to be used when the kernel is not able 2423 to see the whole system memory or for test. 2424 [X86] Work as limiting max address. Use together 2425 with memmap= to avoid physical address space collisions. 2426 Without memmap= PCI devices could be placed at addresses 2427 belonging to unused RAM. 2428 2429 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2430 memory. 2431 2432 memchunk=nn[KMG] 2433 [KNL,SH] Allow user to override the default size for 2434 per-device physically contiguous DMA buffers. 2435 2436 memhp_default_state=online/offline 2437 [KNL] Set the initial state for the memory hotplug 2438 onlining policy. If not specified, the default value is 2439 set according to the 2440 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2441 option. 2442 See Documentation/memory-hotplug.txt. 2443 2444 memmap=exactmap [KNL,X86] Enable setting of an exact 2445 E820 memory map, as specified by the user. 2446 Such memmap=exactmap lines can be constructed based on 2447 BIOS output or other requirements. See the memmap=nn@ss 2448 option description. 2449 2450 memmap=nn[KMG]@ss[KMG] 2451 [KNL] Force usage of a specific region of memory. 2452 Region of memory to be used is from ss to ss+nn. 2453 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2454 which limits max address to nn[KMG]. 2455 Multiple different regions can be specified, 2456 comma delimited. 2457 Example: 2458 memmap=100M@2G,100M#3G,1G!1024G 2459 2460 memmap=nn[KMG]#ss[KMG] 2461 [KNL,ACPI] Mark specific memory as ACPI data. 2462 Region of memory to be marked is from ss to ss+nn. 2463 2464 memmap=nn[KMG]$ss[KMG] 2465 [KNL,ACPI] Mark specific memory as reserved. 2466 Region of memory to be reserved is from ss to ss+nn. 2467 Example: Exclude memory from 0x18690000-0x1869ffff 2468 memmap=64K$0x18690000 2469 or 2470 memmap=0x10000$0x18690000 2471 Some bootloaders may need an escape character before '$', 2472 like Grub2, otherwise '$' and the following number 2473 will be eaten. 2474 2475 memmap=nn[KMG]!ss[KMG] 2476 [KNL,X86] Mark specific memory as protected. 2477 Region of memory to be used, from ss to ss+nn. 2478 The memory region may be marked as e820 type 12 (0xc) 2479 and is NVDIMM or ADR memory. 2480 2481 memmap=<size>%<offset>-<oldtype>+<newtype> 2482 [KNL,ACPI] Convert memory within the specified region 2483 from <oldtype> to <newtype>. If "-<oldtype>" is left 2484 out, the whole region will be marked as <newtype>, 2485 even if previously unavailable. If "+<newtype>" is left 2486 out, matching memory will be removed. Types are 2487 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2488 3 = ACPI, 12 = PRAM. 2489 2490 memory_corruption_check=0/1 [X86] 2491 Some BIOSes seem to corrupt the first 64k of 2492 memory when doing things like suspend/resume. 2493 Setting this option will scan the memory 2494 looking for corruption. Enabling this will 2495 both detect corruption and prevent the kernel 2496 from using the memory being corrupted. 2497 However, its intended as a diagnostic tool; if 2498 repeatable BIOS-originated corruption always 2499 affects the same memory, you can use memmap= 2500 to prevent the kernel from using that memory. 2501 2502 memory_corruption_check_size=size [X86] 2503 By default it checks for corruption in the low 2504 64k, making this memory unavailable for normal 2505 use. Use this parameter to scan for 2506 corruption in more or less memory. 2507 2508 memory_corruption_check_period=seconds [X86] 2509 By default it checks for corruption every 60 2510 seconds. Use this parameter to check at some 2511 other rate. 0 disables periodic checking. 2512 2513 memtest= [KNL,X86,ARM,PPC] Enable memtest 2514 Format: <integer> 2515 default : 0 <disable> 2516 Specifies the number of memtest passes to be 2517 performed. Each pass selects another test 2518 pattern from a given set of patterns. Memtest 2519 fills the memory with this pattern, validates 2520 memory contents and reserves bad memory 2521 regions that are detected. 2522 2523 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2524 Valid arguments: on, off 2525 Default (depends on kernel configuration option): 2526 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2527 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2528 mem_encrypt=on: Activate SME 2529 mem_encrypt=off: Do not activate SME 2530 2531 Refer to Documentation/x86/amd-memory-encryption.txt 2532 for details on when memory encryption can be activated. 2533 2534 mem_sleep_default= [SUSPEND] Default system suspend mode: 2535 s2idle - Suspend-To-Idle 2536 shallow - Power-On Suspend or equivalent (if supported) 2537 deep - Suspend-To-RAM or equivalent (if supported) 2538 See Documentation/admin-guide/pm/sleep-states.rst. 2539 2540 meye.*= [HW] Set MotionEye Camera parameters 2541 See Documentation/media/v4l-drivers/meye.rst. 2542 2543 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2544 Multi-Function General Purpose Timers on AMD Geode 2545 platforms. 2546 2547 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2548 the BIOS has incorrectly applied a workaround. TinyBIOS 2549 version 0.98 is known to be affected, 0.99 fixes the 2550 problem by letting the user disable the workaround. 2551 2552 mga= [HW,DRM] 2553 2554 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2555 physical address is ignored. 2556 2557 mini2440= [ARM,HW,KNL] 2558 Format:[0..2][b][c][t] 2559 Default: "0tb" 2560 MINI2440 configuration specification: 2561 0 - The attached screen is the 3.5" TFT 2562 1 - The attached screen is the 7" TFT 2563 2 - The VGA Shield is attached (1024x768) 2564 Leaving out the screen size parameter will not load 2565 the TFT driver, and the framebuffer will be left 2566 unconfigured. 2567 b - Enable backlight. The TFT backlight pin will be 2568 linked to the kernel VESA blanking code and a GPIO 2569 LED. This parameter is not necessary when using the 2570 VGA shield. 2571 c - Enable the s3c camera interface. 2572 t - Reserved for enabling touchscreen support. The 2573 touchscreen support is not enabled in the mainstream 2574 kernel as of 2.6.30, a preliminary port can be found 2575 in the "bleeding edge" mini2440 support kernel at 2576 http://repo.or.cz/w/linux-2.6/mini2440.git 2577 2578 mitigations= 2579 [X86,PPC,S390,ARM64] Control optional mitigations for 2580 CPU vulnerabilities. This is a set of curated, 2581 arch-independent options, each of which is an 2582 aggregation of existing arch-specific options. 2583 2584 off 2585 Disable all optional CPU mitigations. This 2586 improves system performance, but it may also 2587 expose users to several CPU vulnerabilities. 2588 Equivalent to: nopti [X86,PPC] 2589 kpti=0 [ARM64] 2590 nospectre_v1 [PPC] 2591 nobp=0 [S390] 2592 nospectre_v2 [X86,PPC,S390,ARM64] 2593 spectre_v2_user=off [X86] 2594 spec_store_bypass_disable=off [X86,PPC] 2595 ssbd=force-off [ARM64] 2596 l1tf=off [X86] 2597 mds=off [X86] 2598 2599 auto (default) 2600 Mitigate all CPU vulnerabilities, but leave SMT 2601 enabled, even if it's vulnerable. This is for 2602 users who don't want to be surprised by SMT 2603 getting disabled across kernel upgrades, or who 2604 have other ways of avoiding SMT-based attacks. 2605 Equivalent to: (default behavior) 2606 2607 auto,nosmt 2608 Mitigate all CPU vulnerabilities, disabling SMT 2609 if needed. This is for users who always want to 2610 be fully mitigated, even if it means losing SMT. 2611 Equivalent to: l1tf=flush,nosmt [X86] 2612 mds=full,nosmt [X86] 2613 2614 mminit_loglevel= 2615 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2616 parameter allows control of the logging verbosity for 2617 the additional memory initialisation checks. A value 2618 of 0 disables mminit logging and a level of 4 will 2619 log everything. Information is printed at KERN_DEBUG 2620 so loglevel=8 may also need to be specified. 2621 2622 module.sig_enforce 2623 [KNL] When CONFIG_MODULE_SIG is set, this means that 2624 modules without (valid) signatures will fail to load. 2625 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2626 is always true, so this option does nothing. 2627 2628 module_blacklist= [KNL] Do not load a comma-separated list of 2629 modules. Useful for debugging problem modules. 2630 2631 mousedev.tap_time= 2632 [MOUSE] Maximum time between finger touching and 2633 leaving touchpad surface for touch to be considered 2634 a tap and be reported as a left button click (for 2635 touchpads working in absolute mode only). 2636 Format: <msecs> 2637 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2638 reporting absolute coordinates, such as tablets 2639 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2640 reporting absolute coordinates, such as tablets 2641 2642 movablecore= [KNL,X86,IA-64,PPC] 2643 Format: nn[KMGTPE] | nn% 2644 This parameter is the complement to kernelcore=, it 2645 specifies the amount of memory used for migratable 2646 allocations. If both kernelcore and movablecore is 2647 specified, then kernelcore will be at *least* the 2648 specified value but may be more. If movablecore on its 2649 own is specified, the administrator must be careful 2650 that the amount of memory usable for all allocations 2651 is not too small. 2652 2653 movable_node [KNL] Boot-time switch to make hotplugable memory 2654 NUMA nodes to be movable. This means that the memory 2655 of such nodes will be usable only for movable 2656 allocations which rules out almost all kernel 2657 allocations. Use with caution! 2658 2659 MTD_Partition= [MTD] 2660 Format: <name>,<region-number>,<size>,<offset> 2661 2662 MTD_Region= [MTD] Format: 2663 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2664 2665 mtdparts= [MTD] 2666 See drivers/mtd/cmdlinepart.c. 2667 2668 multitce=off [PPC] This parameter disables the use of the pSeries 2669 firmware feature for updating multiple TCE entries 2670 at a time. 2671 2672 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2673 2674 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2675 2676 boundary - index of last SLC block on Flex-OneNAND. 2677 The remaining blocks are configured as MLC blocks. 2678 lock - Configure if Flex-OneNAND boundary should be locked. 2679 Once locked, the boundary cannot be changed. 2680 1 indicates lock status, 0 indicates unlock status. 2681 2682 mtdset= [ARM] 2683 ARM/S3C2412 JIVE boot control 2684 2685 See arch/arm/mach-s3c2412/mach-jive.c 2686 2687 mtouchusb.raw_coordinates= 2688 [HW] Make the MicroTouch USB driver use raw coordinates 2689 ('y', default) or cooked coordinates ('n') 2690 2691 mtrr_chunk_size=nn[KMG] [X86] 2692 used for mtrr cleanup. It is largest continuous chunk 2693 that could hold holes aka. UC entries. 2694 2695 mtrr_gran_size=nn[KMG] [X86] 2696 Used for mtrr cleanup. It is granularity of mtrr block. 2697 Default is 1. 2698 Large value could prevent small alignment from 2699 using up MTRRs. 2700 2701 mtrr_spare_reg_nr=n [X86] 2702 Format: <integer> 2703 Range: 0,7 : spare reg number 2704 Default : 1 2705 Used for mtrr cleanup. It is spare mtrr entries number. 2706 Set to 2 or more if your graphical card needs more. 2707 2708 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2709 2710 netdev= [NET] Network devices parameters 2711 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2712 Note that mem_start is often overloaded to mean 2713 something different and driver-specific. 2714 This usage is only documented in each driver source 2715 file if at all. 2716 2717 nf_conntrack.acct= 2718 [NETFILTER] Enable connection tracking flow accounting 2719 0 to disable accounting 2720 1 to enable accounting 2721 Default value is 0. 2722 2723 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2724 See Documentation/filesystems/nfs/nfsroot.txt. 2725 2726 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2727 See Documentation/filesystems/nfs/nfsroot.txt. 2728 2729 nfsrootdebug [NFS] enable nfsroot debugging messages. 2730 See Documentation/filesystems/nfs/nfsroot.txt. 2731 2732 nfs.callback_nr_threads= 2733 [NFSv4] set the total number of threads that the 2734 NFS client will assign to service NFSv4 callback 2735 requests. 2736 2737 nfs.callback_tcpport= 2738 [NFS] set the TCP port on which the NFSv4 callback 2739 channel should listen. 2740 2741 nfs.cache_getent= 2742 [NFS] sets the pathname to the program which is used 2743 to update the NFS client cache entries. 2744 2745 nfs.cache_getent_timeout= 2746 [NFS] sets the timeout after which an attempt to 2747 update a cache entry is deemed to have failed. 2748 2749 nfs.idmap_cache_timeout= 2750 [NFS] set the maximum lifetime for idmapper cache 2751 entries. 2752 2753 nfs.enable_ino64= 2754 [NFS] enable 64-bit inode numbers. 2755 If zero, the NFS client will fake up a 32-bit inode 2756 number for the readdir() and stat() syscalls instead 2757 of returning the full 64-bit number. 2758 The default is to return 64-bit inode numbers. 2759 2760 nfs.max_session_cb_slots= 2761 [NFSv4.1] Sets the maximum number of session 2762 slots the client will assign to the callback 2763 channel. This determines the maximum number of 2764 callbacks the client will process in parallel for 2765 a particular server. 2766 2767 nfs.max_session_slots= 2768 [NFSv4.1] Sets the maximum number of session slots 2769 the client will attempt to negotiate with the server. 2770 This limits the number of simultaneous RPC requests 2771 that the client can send to the NFSv4.1 server. 2772 Note that there is little point in setting this 2773 value higher than the max_tcp_slot_table_limit. 2774 2775 nfs.nfs4_disable_idmapping= 2776 [NFSv4] When set to the default of '1', this option 2777 ensures that both the RPC level authentication 2778 scheme and the NFS level operations agree to use 2779 numeric uids/gids if the mount is using the 2780 'sec=sys' security flavour. In effect it is 2781 disabling idmapping, which can make migration from 2782 legacy NFSv2/v3 systems to NFSv4 easier. 2783 Servers that do not support this mode of operation 2784 will be autodetected by the client, and it will fall 2785 back to using the idmapper. 2786 To turn off this behaviour, set the value to '0'. 2787 nfs.nfs4_unique_id= 2788 [NFS4] Specify an additional fixed unique ident- 2789 ification string that NFSv4 clients can insert into 2790 their nfs_client_id4 string. This is typically a 2791 UUID that is generated at system install time. 2792 2793 nfs.send_implementation_id = 2794 [NFSv4.1] Send client implementation identification 2795 information in exchange_id requests. 2796 If zero, no implementation identification information 2797 will be sent. 2798 The default is to send the implementation identification 2799 information. 2800 2801 nfs.recover_lost_locks = 2802 [NFSv4] Attempt to recover locks that were lost due 2803 to a lease timeout on the server. Please note that 2804 doing this risks data corruption, since there are 2805 no guarantees that the file will remain unchanged 2806 after the locks are lost. 2807 If you want to enable the kernel legacy behaviour of 2808 attempting to recover these locks, then set this 2809 parameter to '1'. 2810 The default parameter value of '0' causes the kernel 2811 not to attempt recovery of lost locks. 2812 2813 nfs4.layoutstats_timer = 2814 [NFSv4.2] Change the rate at which the kernel sends 2815 layoutstats to the pNFS metadata server. 2816 2817 Setting this to value to 0 causes the kernel to use 2818 whatever value is the default set by the layout 2819 driver. A non-zero value sets the minimum interval 2820 in seconds between layoutstats transmissions. 2821 2822 nfsd.nfs4_disable_idmapping= 2823 [NFSv4] When set to the default of '1', the NFSv4 2824 server will return only numeric uids and gids to 2825 clients using auth_sys, and will accept numeric uids 2826 and gids from such clients. This is intended to ease 2827 migration from NFSv2/v3. 2828 2829 nmi_debug= [KNL,SH] Specify one or more actions to take 2830 when a NMI is triggered. 2831 Format: [state][,regs][,debounce][,die] 2832 2833 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2834 Format: [panic,][nopanic,][num] 2835 Valid num: 0 or 1 2836 0 - turn hardlockup detector in nmi_watchdog off 2837 1 - turn hardlockup detector in nmi_watchdog on 2838 When panic is specified, panic when an NMI watchdog 2839 timeout occurs (or 'nopanic' to override the opposite 2840 default). To disable both hard and soft lockup detectors, 2841 please see 'nowatchdog'. 2842 This is useful when you use a panic=... timeout and 2843 need the box quickly up again. 2844 2845 These settings can be accessed at runtime via 2846 the nmi_watchdog and hardlockup_panic sysctls. 2847 2848 netpoll.carrier_timeout= 2849 [NET] Specifies amount of time (in seconds) that 2850 netpoll should wait for a carrier. By default netpoll 2851 waits 4 seconds. 2852 2853 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2854 emulation library even if a 387 maths coprocessor 2855 is present. 2856 2857 no5lvl [X86-64] Disable 5-level paging mode. Forces 2858 kernel to use 4-level paging instead. 2859 2860 no_console_suspend 2861 [HW] Never suspend the console 2862 Disable suspending of consoles during suspend and 2863 hibernate operations. Once disabled, debugging 2864 messages can reach various consoles while the rest 2865 of the system is being put to sleep (ie, while 2866 debugging driver suspend/resume hooks). This may 2867 not work reliably with all consoles, but is known 2868 to work with serial and VGA consoles. 2869 To facilitate more flexible debugging, we also add 2870 console_suspend, a printk module parameter to control 2871 it. Users could use console_suspend (usually 2872 /sys/module/printk/parameters/console_suspend) to 2873 turn on/off it dynamically. 2874 2875 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2876 caches in the slab allocator. Saves per-node memory, 2877 but will impact performance. 2878 2879 noalign [KNL,ARM] 2880 2881 noaltinstr [S390] Disables alternative instructions patching 2882 (CPU alternatives feature). 2883 2884 noapic [SMP,APIC] Tells the kernel to not make use of any 2885 IOAPICs that may be present in the system. 2886 2887 noautogroup Disable scheduler automatic task group creation. 2888 2889 nobats [PPC] Do not use BATs for mapping kernel lowmem 2890 on "Classic" PPC cores. 2891 2892 nocache [ARM] 2893 2894 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2895 2896 nodelayacct [KNL] Disable per-task delay accounting 2897 2898 nodsp [SH] Disable hardware DSP at boot time. 2899 2900 noefi Disable EFI runtime services support. 2901 2902 noexec [IA-64] 2903 2904 noexec [X86] 2905 On X86-32 available only on PAE configured kernels. 2906 noexec=on: enable non-executable mappings (default) 2907 noexec=off: disable non-executable mappings 2908 2909 nosmap [X86,PPC] 2910 Disable SMAP (Supervisor Mode Access Prevention) 2911 even if it is supported by processor. 2912 2913 nosmep [X86,PPC] 2914 Disable SMEP (Supervisor Mode Execution Prevention) 2915 even if it is supported by processor. 2916 2917 noexec32 [X86-64] 2918 This affects only 32-bit executables. 2919 noexec32=on: enable non-executable mappings (default) 2920 read doesn't imply executable mappings 2921 noexec32=off: disable non-executable mappings 2922 read implies executable mappings 2923 2924 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2925 2926 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2927 register save and restore. The kernel will only save 2928 legacy floating-point registers on task switch. 2929 2930 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2931 2932 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2933 Equivalent to smt=1. 2934 2935 [KNL,x86] Disable symmetric multithreading (SMT). 2936 nosmt=force: Force disable SMT, cannot be undone 2937 via the sysfs control file. 2938 2939 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds 2940 check bypass). With this option data leaks are possible 2941 in the system. 2942 2943 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 2944 the Spectre variant 2 (indirect branch prediction) 2945 vulnerability. System may allow data leaks with this 2946 option. 2947 2948 nospec_store_bypass_disable 2949 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2950 2951 noxsave [BUGS=X86] Disables x86 extended register state save 2952 and restore using xsave. The kernel will fallback to 2953 enabling legacy floating-point and sse state. 2954 2955 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2956 register states. The kernel will fall back to use 2957 xsave to save the states. By using this parameter, 2958 performance of saving the states is degraded because 2959 xsave doesn't support modified optimization while 2960 xsaveopt supports it on xsaveopt enabled systems. 2961 2962 noxsaves [X86] Disables xsaves and xrstors used in saving and 2963 restoring x86 extended register state in compacted 2964 form of xsave area. The kernel will fall back to use 2965 xsaveopt and xrstor to save and restore the states 2966 in standard form of xsave area. By using this 2967 parameter, xsave area per process might occupy more 2968 memory on xsaves enabled systems. 2969 2970 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2971 wfi(ARM) instruction doesn't work correctly and not to 2972 use it. This is also useful when using JTAG debugger. 2973 2974 no_file_caps Tells the kernel not to honor file capabilities. The 2975 only way then for a file to be executed with privilege 2976 is to be setuid root or executed by root. 2977 2978 nohalt [IA-64] Tells the kernel not to use the power saving 2979 function PAL_HALT_LIGHT when idle. This increases 2980 power-consumption. On the positive side, it reduces 2981 interrupt wake-up latency, which may improve performance 2982 in certain environments such as networked servers or 2983 real-time systems. 2984 2985 nohibernate [HIBERNATION] Disable hibernation and resume. 2986 2987 nohz= [KNL] Boottime enable/disable dynamic ticks 2988 Valid arguments: on, off 2989 Default: on 2990 2991 nohz_full= [KNL,BOOT,SMP,ISOL] 2992 The argument is a cpu list, as described above. 2993 In kernels built with CONFIG_NO_HZ_FULL=y, set 2994 the specified list of CPUs whose tick will be stopped 2995 whenever possible. The boot CPU will be forced outside 2996 the range to maintain the timekeeping. Any CPUs 2997 in this list will have their RCU callbacks offloaded, 2998 just as if they had also been called out in the 2999 rcu_nocbs= boot parameter. 3000 3001 noiotrap [SH] Disables trapped I/O port accesses. 3002 3003 noirqdebug [X86-32] Disables the code which attempts to detect and 3004 disable unhandled interrupt sources. 3005 3006 no_timer_check [X86,APIC] Disables the code which tests for 3007 broken timer IRQ sources. 3008 3009 noisapnp [ISAPNP] Disables ISA PnP code. 3010 3011 noinitrd [RAM] Tells the kernel not to load any configured 3012 initial RAM disk. 3013 3014 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3015 remapping. 3016 [Deprecated - use intremap=off] 3017 3018 nointroute [IA-64] 3019 3020 noinvpcid [X86] Disable the INVPCID cpu feature. 3021 3022 nojitter [IA-64] Disables jitter checking for ITC timers. 3023 3024 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3025 3026 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3027 fault handling. 3028 3029 no-vmw-sched-clock 3030 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3031 clock and use the default one. 3032 3033 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3034 steal time is computed, but won't influence scheduler 3035 behaviour 3036 3037 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3038 3039 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3040 3041 noltlbs [PPC] Do not use large page/tlb entries for kernel 3042 lowmem mapping on PPC40x and PPC8xx 3043 3044 nomca [IA-64] Disable machine check abort handling 3045 3046 nomce [X86-32] Disable Machine Check Exception 3047 3048 nomfgpt [X86-32] Disable Multi-Function General Purpose 3049 Timer usage (for AMD Geode machines). 3050 3051 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3052 shutdown the other cpus. Instead use the REBOOT_VECTOR 3053 irq. 3054 3055 nomodule Disable module load 3056 3057 nopat [X86] Disable PAT (page attribute table extension of 3058 pagetables) support. 3059 3060 nopcid [X86-64] Disable the PCID cpu feature. 3061 3062 norandmaps Don't use address space randomization. Equivalent to 3063 echo 0 > /proc/sys/kernel/randomize_va_space 3064 3065 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3066 with UP alternatives 3067 3068 nordrand [X86] Disable kernel use of the RDRAND and 3069 RDSEED instructions even if they are supported 3070 by the processor. RDRAND and RDSEED are still 3071 available to user space applications. 3072 3073 noresume [SWSUSP] Disables resume and restores original swap 3074 space. 3075 3076 no-scroll [VGA] Disables scrollback. 3077 This is required for the Braillex ib80-piezo Braille 3078 reader made by F.H. Papenmeier (Germany). 3079 3080 nosbagart [IA-64] 3081 3082 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3083 3084 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3085 and disable the IO APIC. legacy for "maxcpus=0". 3086 3087 nosoftlockup [KNL] Disable the soft-lockup detector. 3088 3089 nosync [HW,M68K] Disables sync negotiation for all devices. 3090 3091 nowatchdog [KNL] Disable both lockup detectors, i.e. 3092 soft-lockup and NMI watchdog (hard-lockup). 3093 3094 nowb [ARM] 3095 3096 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3097 3098 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3099 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3100 Some features depend on CPU0. Known dependencies are: 3101 1. Resume from suspend/hibernate depends on CPU0. 3102 Suspend/hibernate will fail if CPU0 is offline and you 3103 need to online CPU0 before suspend/hibernate. 3104 2. PIC interrupts also depend on CPU0. CPU0 can't be 3105 removed if a PIC interrupt is detected. 3106 It's said poweroff/reboot may depend on CPU0 on some 3107 machines although I haven't seen such issues so far 3108 after CPU0 is offline on a few tested machines. 3109 If the dependencies are under your control, you can 3110 turn on cpu0_hotplug. 3111 3112 nps_mtm_hs_ctr= [KNL,ARC] 3113 This parameter sets the maximum duration, in 3114 cycles, each HW thread of the CTOP can run 3115 without interruptions, before HW switches it. 3116 The actual maximum duration is 16 times this 3117 parameter's value. 3118 Format: integer between 1 and 255 3119 Default: 255 3120 3121 nptcg= [IA-64] Override max number of concurrent global TLB 3122 purges which is reported from either PAL_VM_SUMMARY or 3123 SAL PALO. 3124 3125 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3126 could support. nr_cpus=n : n >= 1 limits the kernel to 3127 support 'n' processors. It could be larger than the 3128 number of already plugged CPU during bootup, later in 3129 runtime you can physically add extra cpu until it reaches 3130 n. So during boot up some boot time memory for per-cpu 3131 variables need be pre-allocated for later physical cpu 3132 hot plugging. 3133 3134 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3135 3136 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3137 Allowed values are enable and disable 3138 3139 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3140 'node', 'default' can be specified 3141 This can be set from sysctl after boot. 3142 See Documentation/sysctl/vm.txt for details. 3143 3144 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3145 See Documentation/debugging-via-ohci1394.txt for more 3146 info. 3147 3148 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3149 Rather than timing out after 20 ms if an EC 3150 command is not properly ACKed, override the length 3151 of the timeout. We have interrupts disabled while 3152 waiting for the ACK, so if this is set too high 3153 interrupts *may* be lost! 3154 3155 omap_mux= [OMAP] Override bootloader pin multiplexing. 3156 Format: <mux_mode0.mode_name=value>... 3157 For example, to override I2C bus2: 3158 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3159 3160 oprofile.timer= [HW] 3161 Use timer interrupt instead of performance counters 3162 3163 oprofile.cpu_type= Force an oprofile cpu type 3164 This might be useful if you have an older oprofile 3165 userland or if you want common events. 3166 Format: { arch_perfmon } 3167 arch_perfmon: [X86] Force use of architectural 3168 perfmon on Intel CPUs instead of the 3169 CPU specific event set. 3170 timer: [X86] Force use of architectural NMI 3171 timer mode (see also oprofile.timer 3172 for generic hr timer mode) 3173 3174 oops=panic Always panic on oopses. Default is to just kill the 3175 process, but there is a small probability of 3176 deadlocking the machine. 3177 This will also cause panics on machine check exceptions. 3178 Useful together with panic=30 to trigger a reboot. 3179 3180 page_alloc.shuffle= 3181 [KNL] Boolean flag to control whether the page allocator 3182 should randomize its free lists. The randomization may 3183 be automatically enabled if the kernel detects it is 3184 running on a platform with a direct-mapped memory-side 3185 cache, and this parameter can be used to 3186 override/disable that behavior. The state of the flag 3187 can be read from sysfs at: 3188 /sys/module/page_alloc/parameters/shuffle. 3189 3190 page_owner= [KNL] Boot-time page_owner enabling option. 3191 Storage of the information about who allocated 3192 each page is disabled in default. With this switch, 3193 we can turn it on. 3194 on: enable the feature 3195 3196 page_poison= [KNL] Boot-time parameter changing the state of 3197 poisoning on the buddy allocator, available with 3198 CONFIG_PAGE_POISONING=y. 3199 off: turn off poisoning (default) 3200 on: turn on poisoning 3201 3202 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3203 timeout > 0: seconds before rebooting 3204 timeout = 0: wait forever 3205 timeout < 0: reboot immediately 3206 Format: <timeout> 3207 3208 panic_print= Bitmask for printing system info when panic happens. 3209 User can chose combination of the following bits: 3210 bit 0: print all tasks info 3211 bit 1: print system memory info 3212 bit 2: print timer info 3213 bit 3: print locks info if CONFIG_LOCKDEP is on 3214 bit 4: print ftrace buffer 3215 3216 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3217 on a WARN(). 3218 3219 crash_kexec_post_notifiers 3220 Run kdump after running panic-notifiers and dumping 3221 kmsg. This only for the users who doubt kdump always 3222 succeeds in any situation. 3223 Note that this also increases risks of kdump failure, 3224 because some panic notifiers can make the crashed 3225 kernel more unstable. 3226 3227 parkbd.port= [HW] Parallel port number the keyboard adapter is 3228 connected to, default is 0. 3229 Format: <parport#> 3230 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3231 0 for XT, 1 for AT (default is AT). 3232 Format: <mode> 3233 3234 parport= [HW,PPT] Specify parallel ports. 0 disables. 3235 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3236 Use 'auto' to force the driver to use any 3237 IRQ/DMA settings detected (the default is to 3238 ignore detected IRQ/DMA settings because of 3239 possible conflicts). You can specify the base 3240 address, IRQ, and DMA settings; IRQ and DMA 3241 should be numbers, or 'auto' (for using detected 3242 settings on that particular port), or 'nofifo' 3243 (to avoid using a FIFO even if it is detected). 3244 Parallel ports are assigned in the order they 3245 are specified on the command line, starting 3246 with parport0. 3247 3248 parport_init_mode= [HW,PPT] 3249 Configure VIA parallel port to operate in 3250 a specific mode. This is necessary on Pegasos 3251 computer where firmware has no options for setting 3252 up parallel port mode and sets it to spp. 3253 Currently this function knows 686a and 8231 chips. 3254 Format: [spp|ps2|epp|ecp|ecpepp] 3255 3256 pause_on_oops= 3257 Halt all CPUs after the first oops has been printed for 3258 the specified number of seconds. This is to be used if 3259 your oopses keep scrolling off the screen. 3260 3261 pcbit= [HW,ISDN] 3262 3263 pcd. [PARIDE] 3264 See header of drivers/block/paride/pcd.c. 3265 See also Documentation/blockdev/paride.txt. 3266 3267 pci=option[,option...] [PCI] various PCI subsystem options. 3268 3269 Some options herein operate on a specific device 3270 or a set of devices (<pci_dev>). These are 3271 specified in one of the following formats: 3272 3273 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3274 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3275 3276 Note: the first format specifies a PCI 3277 bus/device/function address which may change 3278 if new hardware is inserted, if motherboard 3279 firmware changes, or due to changes caused 3280 by other kernel parameters. If the 3281 domain is left unspecified, it is 3282 taken to be zero. Optionally, a path 3283 to a device through multiple device/function 3284 addresses can be specified after the base 3285 address (this is more robust against 3286 renumbering issues). The second format 3287 selects devices using IDs from the 3288 configuration space which may match multiple 3289 devices in the system. 3290 3291 earlydump dump PCI config space before the kernel 3292 changes anything 3293 off [X86] don't probe for the PCI bus 3294 bios [X86-32] force use of PCI BIOS, don't access 3295 the hardware directly. Use this if your machine 3296 has a non-standard PCI host bridge. 3297 nobios [X86-32] disallow use of PCI BIOS, only direct 3298 hardware access methods are allowed. Use this 3299 if you experience crashes upon bootup and you 3300 suspect they are caused by the BIOS. 3301 conf1 [X86] Force use of PCI Configuration Access 3302 Mechanism 1 (config address in IO port 0xCF8, 3303 data in IO port 0xCFC, both 32-bit). 3304 conf2 [X86] Force use of PCI Configuration Access 3305 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3306 the function, IO port 0xCFA, also 8-bit, sets 3307 bus number. The config space is then accessed 3308 through ports 0xC000-0xCFFF). 3309 See http://wiki.osdev.org/PCI for more info 3310 on the configuration access mechanisms. 3311 noaer [PCIE] If the PCIEAER kernel config parameter is 3312 enabled, this kernel boot option can be used to 3313 disable the use of PCIE advanced error reporting. 3314 nodomains [PCI] Disable support for multiple PCI 3315 root domains (aka PCI segments, in ACPI-speak). 3316 nommconf [X86] Disable use of MMCONFIG for PCI 3317 Configuration 3318 check_enable_amd_mmconf [X86] check for and enable 3319 properly configured MMIO access to PCI 3320 config space on AMD family 10h CPU 3321 nomsi [MSI] If the PCI_MSI kernel config parameter is 3322 enabled, this kernel boot option can be used to 3323 disable the use of MSI interrupts system-wide. 3324 noioapicquirk [APIC] Disable all boot interrupt quirks. 3325 Safety option to keep boot IRQs enabled. This 3326 should never be necessary. 3327 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3328 primary IO-APIC for bridges that cannot disable 3329 boot IRQs. This fixes a source of spurious IRQs 3330 when the system masks IRQs. 3331 noioapicreroute [APIC] Disable workaround that uses the 3332 boot IRQ equivalent of an IRQ that connects to 3333 a chipset where boot IRQs cannot be disabled. 3334 The opposite of ioapicreroute. 3335 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3336 routing table. These calls are known to be buggy 3337 on several machines and they hang the machine 3338 when used, but on other computers it's the only 3339 way to get the interrupt routing table. Try 3340 this option if the kernel is unable to allocate 3341 IRQs or discover secondary PCI buses on your 3342 motherboard. 3343 rom [X86] Assign address space to expansion ROMs. 3344 Use with caution as certain devices share 3345 address decoders between ROMs and other 3346 resources. 3347 norom [X86] Do not assign address space to 3348 expansion ROMs that do not already have 3349 BIOS assigned address ranges. 3350 nobar [X86] Do not assign address space to the 3351 BARs that weren't assigned by the BIOS. 3352 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3353 assigned automatically to PCI devices. You can 3354 make the kernel exclude IRQs of your ISA cards 3355 this way. 3356 pirqaddr=0xAAAAA [X86] Specify the physical address 3357 of the PIRQ table (normally generated 3358 by the BIOS) if it is outside the 3359 F0000h-100000h range. 3360 lastbus=N [X86] Scan all buses thru bus #N. Can be 3361 useful if the kernel is unable to find your 3362 secondary buses and you want to tell it 3363 explicitly which ones they are. 3364 assign-busses [X86] Always assign all PCI bus 3365 numbers ourselves, overriding 3366 whatever the firmware may have done. 3367 usepirqmask [X86] Honor the possible IRQ mask stored 3368 in the BIOS $PIR table. This is needed on 3369 some systems with broken BIOSes, notably 3370 some HP Pavilion N5400 and Omnibook XE3 3371 notebooks. This will have no effect if ACPI 3372 IRQ routing is enabled. 3373 noacpi [X86] Do not use ACPI for IRQ routing 3374 or for PCI scanning. 3375 use_crs [X86] Use PCI host bridge window information 3376 from ACPI. On BIOSes from 2008 or later, this 3377 is enabled by default. If you need to use this, 3378 please report a bug. 3379 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3380 If you need to use this, please report a bug. 3381 routeirq Do IRQ routing for all PCI devices. 3382 This is normally done in pci_enable_device(), 3383 so this option is a temporary workaround 3384 for broken drivers that don't call it. 3385 skip_isa_align [X86] do not align io start addr, so can 3386 handle more pci cards 3387 noearly [X86] Don't do any early type 1 scanning. 3388 This might help on some broken boards which 3389 machine check when some devices' config space 3390 is read. But various workarounds are disabled 3391 and some IOMMU drivers will not work. 3392 bfsort Sort PCI devices into breadth-first order. 3393 This sorting is done to get a device 3394 order compatible with older (<= 2.4) kernels. 3395 nobfsort Don't sort PCI devices into breadth-first order. 3396 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3397 tuning and use the BIOS-configured MPS defaults. 3398 pcie_bus_safe Set every device's MPS to the largest value 3399 supported by all devices below the root complex. 3400 pcie_bus_perf Set device MPS to the largest allowable MPS 3401 based on its parent bus. Also set MRRS (Max 3402 Read Request Size) to the largest supported 3403 value (no larger than the MPS that the device 3404 or bus can support) for best performance. 3405 pcie_bus_peer2peer Set every device's MPS to 128B, which 3406 every device is guaranteed to support. This 3407 configuration allows peer-to-peer DMA between 3408 any pair of devices, possibly at the cost of 3409 reduced performance. This also guarantees 3410 that hot-added devices will work. 3411 cbiosize=nn[KMG] The fixed amount of bus space which is 3412 reserved for the CardBus bridge's IO window. 3413 The default value is 256 bytes. 3414 cbmemsize=nn[KMG] The fixed amount of bus space which is 3415 reserved for the CardBus bridge's memory 3416 window. The default value is 64 megabytes. 3417 resource_alignment= 3418 Format: 3419 [<order of align>@]<pci_dev>[; ...] 3420 Specifies alignment and device to reassign 3421 aligned memory resources. How to 3422 specify the device is described above. 3423 If <order of align> is not specified, 3424 PAGE_SIZE is used as alignment. 3425 PCI-PCI bridge can be specified, if resource 3426 windows need to be expanded. 3427 To specify the alignment for several 3428 instances of a device, the PCI vendor, 3429 device, subvendor, and subdevice may be 3430 specified, e.g., 4096@pci:8086:9c22:103c:198f 3431 ecrc= Enable/disable PCIe ECRC (transaction layer 3432 end-to-end CRC checking). 3433 bios: Use BIOS/firmware settings. This is the 3434 the default. 3435 off: Turn ECRC off 3436 on: Turn ECRC on. 3437 hpiosize=nn[KMG] The fixed amount of bus space which is 3438 reserved for hotplug bridge's IO window. 3439 Default size is 256 bytes. 3440 hpmemsize=nn[KMG] The fixed amount of bus space which is 3441 reserved for hotplug bridge's memory window. 3442 Default size is 2 megabytes. 3443 hpbussize=nn The minimum amount of additional bus numbers 3444 reserved for buses below a hotplug bridge. 3445 Default is 1. 3446 realloc= Enable/disable reallocating PCI bridge resources 3447 if allocations done by BIOS are too small to 3448 accommodate resources required by all child 3449 devices. 3450 off: Turn realloc off 3451 on: Turn realloc on 3452 realloc same as realloc=on 3453 noari do not use PCIe ARI. 3454 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3455 do not use PCIe ATS (and IOMMU device IOTLB). 3456 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3457 only look for one device below a PCIe downstream 3458 port. 3459 big_root_window Try to add a big 64bit memory window to the PCIe 3460 root complex on AMD CPUs. Some GFX hardware 3461 can resize a BAR to allow access to all VRAM. 3462 Adding the window is slightly risky (it may 3463 conflict with unreported devices), so this 3464 taints the kernel. 3465 disable_acs_redir=<pci_dev>[; ...] 3466 Specify one or more PCI devices (in the format 3467 specified above) separated by semicolons. 3468 Each device specified will have the PCI ACS 3469 redirect capabilities forced off which will 3470 allow P2P traffic between devices through 3471 bridges without forcing it upstream. Note: 3472 this removes isolation between devices and 3473 may put more devices in an IOMMU group. 3474 force_floating [S390] Force usage of floating interrupts. 3475 nomio [S390] Do not use MIO instructions. 3476 3477 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3478 Management. 3479 off Disable ASPM. 3480 force Enable ASPM even on devices that claim not to support it. 3481 WARNING: Forcing ASPM on may cause system lockups. 3482 3483 pcie_ports= [PCIE] PCIe port services handling: 3484 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3485 even if the platform doesn't give the OS permission to 3486 use them. This may cause conflicts if the platform 3487 also tries to use these services. 3488 compat Disable native PCIe services (PME, AER, DPC, PCIe 3489 hotplug). 3490 3491 pcie_port_pm= [PCIE] PCIe port power management handling: 3492 off Disable power management of all PCIe ports 3493 force Forcibly enable power management of all PCIe ports 3494 3495 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3496 nomsi Do not use MSI for native PCIe PME signaling (this makes 3497 all PCIe root ports use INTx for all services). 3498 3499 pcmv= [HW,PCMCIA] BadgePAD 4 3500 3501 pd_ignore_unused 3502 [PM] 3503 Keep all power-domains already enabled by bootloader on, 3504 even if no driver has claimed them. This is useful 3505 for debug and development, but should not be 3506 needed on a platform with proper driver support. 3507 3508 pd. [PARIDE] 3509 See Documentation/blockdev/paride.txt. 3510 3511 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3512 boot time. 3513 Format: { 0 | 1 } 3514 See arch/parisc/kernel/pdc_chassis.c 3515 3516 percpu_alloc= Select which percpu first chunk allocator to use. 3517 Currently supported values are "embed" and "page". 3518 Archs may support subset or none of the selections. 3519 See comments in mm/percpu.c for details on each 3520 allocator. This parameter is primarily for debugging 3521 and performance comparison. 3522 3523 pf. [PARIDE] 3524 See Documentation/blockdev/paride.txt. 3525 3526 pg. [PARIDE] 3527 See Documentation/blockdev/paride.txt. 3528 3529 pirq= [SMP,APIC] Manual mp-table setup 3530 See Documentation/x86/i386/IO-APIC.txt. 3531 3532 plip= [PPT,NET] Parallel port network link 3533 Format: { parport<nr> | timid | 0 } 3534 See also Documentation/admin-guide/parport.rst. 3535 3536 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3537 Override pmtimer IOPort with a hex value. 3538 e.g. pmtmr=0x508 3539 3540 pnp.debug=1 [PNP] 3541 Enable PNP debug messages (depends on the 3542 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3543 via /sys/module/pnp/parameters/debug. We always show 3544 current resource usage; turning this on also shows 3545 possible settings and some assignment information. 3546 3547 pnpacpi= [ACPI] 3548 { off } 3549 3550 pnpbios= [ISAPNP] 3551 { on | off | curr | res | no-curr | no-res } 3552 3553 pnp_reserve_irq= 3554 [ISAPNP] Exclude IRQs for the autoconfiguration 3555 3556 pnp_reserve_dma= 3557 [ISAPNP] Exclude DMAs for the autoconfiguration 3558 3559 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3560 Ranges are in pairs (I/O port base and size). 3561 3562 pnp_reserve_mem= 3563 [ISAPNP] Exclude memory regions for the 3564 autoconfiguration. 3565 Ranges are in pairs (memory base and size). 3566 3567 ports= [IP_VS_FTP] IPVS ftp helper module 3568 Default is 21. 3569 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3570 may be specified. 3571 Format: <port>,<port>.... 3572 3573 powersave=off [PPC] This option disables power saving features. 3574 It specifically disables cpuidle and sets the 3575 platform machine description specific power_save 3576 function to NULL. On Idle the CPU just reduces 3577 execution priority. 3578 3579 ppc_strict_facility_enable 3580 [PPC] This option catches any kernel floating point, 3581 Altivec, VSX and SPE outside of regions specifically 3582 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3583 There is some performance impact when enabling this. 3584 3585 ppc_tm= [PPC] 3586 Format: {"off"} 3587 Disable Hardware Transactional Memory 3588 3589 print-fatal-signals= 3590 [KNL] debug: print fatal signals 3591 3592 If enabled, warn about various signal handling 3593 related application anomalies: too many signals, 3594 too many POSIX.1 timers, fatal signals causing a 3595 coredump - etc. 3596 3597 If you hit the warning due to signal overflow, 3598 you might want to try "ulimit -i unlimited". 3599 3600 default: off. 3601 3602 printk.always_kmsg_dump= 3603 Trigger kmsg_dump for cases other than kernel oops or 3604 panics 3605 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3606 default: disabled 3607 3608 printk.devkmsg={on,off,ratelimit} 3609 Control writing to /dev/kmsg. 3610 on - unlimited logging to /dev/kmsg from userspace 3611 off - logging to /dev/kmsg disabled 3612 ratelimit - ratelimit the logging 3613 Default: ratelimit 3614 3615 printk.time= Show timing data prefixed to each printk message line 3616 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3617 3618 processor.max_cstate= [HW,ACPI] 3619 Limit processor to maximum C-state 3620 max_cstate=9 overrides any DMI blacklist limit. 3621 3622 processor.nocst [HW,ACPI] 3623 Ignore the _CST method to determine C-states, 3624 instead using the legacy FADT method 3625 3626 profile= [KNL] Enable kernel profiling via /proc/profile 3627 Format: [<profiletype>,]<number> 3628 Param: <profiletype>: "schedule", "sleep", or "kvm" 3629 [defaults to kernel profiling] 3630 Param: "schedule" - profile schedule points. 3631 Param: "sleep" - profile D-state sleeping (millisecs). 3632 Requires CONFIG_SCHEDSTATS 3633 Param: "kvm" - profile VM exits. 3634 Param: <number> - step/bucket size as a power of 2 for 3635 statistical time based profiling. 3636 3637 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3638 before loading. 3639 See Documentation/blockdev/ramdisk.txt. 3640 3641 psi= [KNL] Enable or disable pressure stall information 3642 tracking. 3643 Format: <bool> 3644 3645 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3646 probe for; one of (bare|imps|exps|lifebook|any). 3647 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3648 per second. 3649 psmouse.resetafter= [HW,MOUSE] 3650 Try to reset the device after so many bad packets 3651 (0 = never). 3652 psmouse.resolution= 3653 [HW,MOUSE] Set desired mouse resolution, in dpi. 3654 psmouse.smartscroll= 3655 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3656 0 = disabled, 1 = enabled (default). 3657 3658 pstore.backend= Specify the name of the pstore backend to use 3659 3660 pt. [PARIDE] 3661 See Documentation/blockdev/paride.txt. 3662 3663 pti= [X86_64] Control Page Table Isolation of user and 3664 kernel address spaces. Disabling this feature 3665 removes hardening, but improves performance of 3666 system calls and interrupts. 3667 3668 on - unconditionally enable 3669 off - unconditionally disable 3670 auto - kernel detects whether your CPU model is 3671 vulnerable to issues that PTI mitigates 3672 3673 Not specifying this option is equivalent to pti=auto. 3674 3675 nopti [X86_64] 3676 Equivalent to pti=off 3677 3678 pty.legacy_count= 3679 [KNL] Number of legacy pty's. Overwrites compiled-in 3680 default number. 3681 3682 quiet [KNL] Disable most log messages 3683 3684 r128= [HW,DRM] 3685 3686 raid= [HW,RAID] 3687 See Documentation/admin-guide/md.rst. 3688 3689 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3690 See Documentation/blockdev/ramdisk.txt. 3691 3692 random.trust_cpu={on,off} 3693 [KNL] Enable or disable trusting the use of the 3694 CPU's random number generator (if available) to 3695 fully seed the kernel's CRNG. Default is controlled 3696 by CONFIG_RANDOM_TRUST_CPU. 3697 3698 ras=option[,option,...] [KNL] RAS-specific options 3699 3700 cec_disable [X86] 3701 Disable the Correctable Errors Collector, 3702 see CONFIG_RAS_CEC help text. 3703 3704 rcu_nocbs= [KNL] 3705 The argument is a cpu list, as described above, 3706 except that the string "all" can be used to 3707 specify every CPU on the system. 3708 3709 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3710 the specified list of CPUs to be no-callback CPUs. 3711 Invocation of these CPUs' RCU callbacks will be 3712 offloaded to "rcuox/N" kthreads created for that 3713 purpose, where "x" is "p" for RCU-preempt, and 3714 "s" for RCU-sched, and "N" is the CPU number. 3715 This reduces OS jitter on the offloaded CPUs, 3716 which can be useful for HPC and real-time 3717 workloads. It can also improve energy efficiency 3718 for asymmetric multiprocessors. 3719 3720 rcu_nocb_poll [KNL] 3721 Rather than requiring that offloaded CPUs 3722 (specified by rcu_nocbs= above) explicitly 3723 awaken the corresponding "rcuoN" kthreads, 3724 make these kthreads poll for callbacks. 3725 This improves the real-time response for the 3726 offloaded CPUs by relieving them of the need to 3727 wake up the corresponding kthread, but degrades 3728 energy efficiency by requiring that the kthreads 3729 periodically wake up to do the polling. 3730 3731 rcutree.blimit= [KNL] 3732 Set maximum number of finished RCU callbacks to 3733 process in one batch. 3734 3735 rcutree.dump_tree= [KNL] 3736 Dump the structure of the rcu_node combining tree 3737 out at early boot. This is used for diagnostic 3738 purposes, to verify correct tree setup. 3739 3740 rcutree.gp_cleanup_delay= [KNL] 3741 Set the number of jiffies to delay each step of 3742 RCU grace-period cleanup. 3743 3744 rcutree.gp_init_delay= [KNL] 3745 Set the number of jiffies to delay each step of 3746 RCU grace-period initialization. 3747 3748 rcutree.gp_preinit_delay= [KNL] 3749 Set the number of jiffies to delay each step of 3750 RCU grace-period pre-initialization, that is, 3751 the propagation of recent CPU-hotplug changes up 3752 the rcu_node combining tree. 3753 3754 rcutree.rcu_fanout_exact= [KNL] 3755 Disable autobalancing of the rcu_node combining 3756 tree. This is used by rcutorture, and might 3757 possibly be useful for architectures having high 3758 cache-to-cache transfer latencies. 3759 3760 rcutree.rcu_fanout_leaf= [KNL] 3761 Change the number of CPUs assigned to each 3762 leaf rcu_node structure. Useful for very 3763 large systems, which will choose the value 64, 3764 and for NUMA systems with large remote-access 3765 latencies, which will choose a value aligned 3766 with the appropriate hardware boundaries. 3767 3768 rcutree.jiffies_till_first_fqs= [KNL] 3769 Set delay from grace-period initialization to 3770 first attempt to force quiescent states. 3771 Units are jiffies, minimum value is zero, 3772 and maximum value is HZ. 3773 3774 rcutree.jiffies_till_next_fqs= [KNL] 3775 Set delay between subsequent attempts to force 3776 quiescent states. Units are jiffies, minimum 3777 value is one, and maximum value is HZ. 3778 3779 rcutree.jiffies_till_sched_qs= [KNL] 3780 Set required age in jiffies for a 3781 given grace period before RCU starts 3782 soliciting quiescent-state help from 3783 rcu_note_context_switch() and cond_resched(). 3784 If not specified, the kernel will calculate 3785 a value based on the most recent settings 3786 of rcutree.jiffies_till_first_fqs 3787 and rcutree.jiffies_till_next_fqs. 3788 This calculated value may be viewed in 3789 rcutree.jiffies_to_sched_qs. Any attempt to set 3790 rcutree.jiffies_to_sched_qs will be cheerfully 3791 overwritten. 3792 3793 rcutree.kthread_prio= [KNL,BOOT] 3794 Set the SCHED_FIFO priority of the RCU per-CPU 3795 kthreads (rcuc/N). This value is also used for 3796 the priority of the RCU boost threads (rcub/N) 3797 and for the RCU grace-period kthreads (rcu_bh, 3798 rcu_preempt, and rcu_sched). If RCU_BOOST is 3799 set, valid values are 1-99 and the default is 1 3800 (the least-favored priority). Otherwise, when 3801 RCU_BOOST is not set, valid values are 0-99 and 3802 the default is zero (non-realtime operation). 3803 3804 rcutree.rcu_nocb_leader_stride= [KNL] 3805 Set the number of NOCB kthread groups, which 3806 defaults to the square root of the number of 3807 CPUs. Larger numbers reduces the wakeup overhead 3808 on the per-CPU grace-period kthreads, but increases 3809 that same overhead on each group's leader. 3810 3811 rcutree.qhimark= [KNL] 3812 Set threshold of queued RCU callbacks beyond which 3813 batch limiting is disabled. 3814 3815 rcutree.qlowmark= [KNL] 3816 Set threshold of queued RCU callbacks below which 3817 batch limiting is re-enabled. 3818 3819 rcutree.rcu_idle_gp_delay= [KNL] 3820 Set wakeup interval for idle CPUs that have 3821 RCU callbacks (RCU_FAST_NO_HZ=y). 3822 3823 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3824 Set wakeup interval for idle CPUs that have 3825 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3826 Lazy RCU callbacks are those which RCU can 3827 prove do nothing more than free memory. 3828 3829 rcutree.rcu_kick_kthreads= [KNL] 3830 Cause the grace-period kthread to get an extra 3831 wake_up() if it sleeps three times longer than 3832 it should at force-quiescent-state time. 3833 This wake_up() will be accompanied by a 3834 WARN_ONCE() splat and an ftrace_dump(). 3835 3836 rcutree.sysrq_rcu= [KNL] 3837 Commandeer a sysrq key to dump out Tree RCU's 3838 rcu_node tree with an eye towards determining 3839 why a new grace period has not yet started. 3840 3841 rcuperf.gp_async= [KNL] 3842 Measure performance of asynchronous 3843 grace-period primitives such as call_rcu(). 3844 3845 rcuperf.gp_async_max= [KNL] 3846 Specify the maximum number of outstanding 3847 callbacks per writer thread. When a writer 3848 thread exceeds this limit, it invokes the 3849 corresponding flavor of rcu_barrier() to allow 3850 previously posted callbacks to drain. 3851 3852 rcuperf.gp_exp= [KNL] 3853 Measure performance of expedited synchronous 3854 grace-period primitives. 3855 3856 rcuperf.holdoff= [KNL] 3857 Set test-start holdoff period. The purpose of 3858 this parameter is to delay the start of the 3859 test until boot completes in order to avoid 3860 interference. 3861 3862 rcuperf.nreaders= [KNL] 3863 Set number of RCU readers. The value -1 selects 3864 N, where N is the number of CPUs. A value 3865 "n" less than -1 selects N-n+1, where N is again 3866 the number of CPUs. For example, -2 selects N 3867 (the number of CPUs), -3 selects N+1, and so on. 3868 A value of "n" less than or equal to -N selects 3869 a single reader. 3870 3871 rcuperf.nwriters= [KNL] 3872 Set number of RCU writers. The values operate 3873 the same as for rcuperf.nreaders. 3874 N, where N is the number of CPUs 3875 3876 rcuperf.perf_type= [KNL] 3877 Specify the RCU implementation to test. 3878 3879 rcuperf.shutdown= [KNL] 3880 Shut the system down after performance tests 3881 complete. This is useful for hands-off automated 3882 testing. 3883 3884 rcuperf.verbose= [KNL] 3885 Enable additional printk() statements. 3886 3887 rcuperf.writer_holdoff= [KNL] 3888 Write-side holdoff between grace periods, 3889 in microseconds. The default of zero says 3890 no holdoff. 3891 3892 rcutorture.fqs_duration= [KNL] 3893 Set duration of force_quiescent_state bursts 3894 in microseconds. 3895 3896 rcutorture.fqs_holdoff= [KNL] 3897 Set holdoff time within force_quiescent_state bursts 3898 in microseconds. 3899 3900 rcutorture.fqs_stutter= [KNL] 3901 Set wait time between force_quiescent_state bursts 3902 in seconds. 3903 3904 rcutorture.fwd_progress= [KNL] 3905 Enable RCU grace-period forward-progress testing 3906 for the types of RCU supporting this notion. 3907 3908 rcutorture.fwd_progress_div= [KNL] 3909 Specify the fraction of a CPU-stall-warning 3910 period to do tight-loop forward-progress testing. 3911 3912 rcutorture.fwd_progress_holdoff= [KNL] 3913 Number of seconds to wait between successive 3914 forward-progress tests. 3915 3916 rcutorture.fwd_progress_need_resched= [KNL] 3917 Enclose cond_resched() calls within checks for 3918 need_resched() during tight-loop forward-progress 3919 testing. 3920 3921 rcutorture.gp_cond= [KNL] 3922 Use conditional/asynchronous update-side 3923 primitives, if available. 3924 3925 rcutorture.gp_exp= [KNL] 3926 Use expedited update-side primitives, if available. 3927 3928 rcutorture.gp_normal= [KNL] 3929 Use normal (non-expedited) asynchronous 3930 update-side primitives, if available. 3931 3932 rcutorture.gp_sync= [KNL] 3933 Use normal (non-expedited) synchronous 3934 update-side primitives, if available. If all 3935 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3936 rcutorture.gp_normal=, and rcutorture.gp_sync= 3937 are zero, rcutorture acts as if is interpreted 3938 they are all non-zero. 3939 3940 rcutorture.n_barrier_cbs= [KNL] 3941 Set callbacks/threads for rcu_barrier() testing. 3942 3943 rcutorture.nfakewriters= [KNL] 3944 Set number of concurrent RCU writers. These just 3945 stress RCU, they don't participate in the actual 3946 test, hence the "fake". 3947 3948 rcutorture.nreaders= [KNL] 3949 Set number of RCU readers. The value -1 selects 3950 N-1, where N is the number of CPUs. A value 3951 "n" less than -1 selects N-n-2, where N is again 3952 the number of CPUs. For example, -2 selects N 3953 (the number of CPUs), -3 selects N+1, and so on. 3954 3955 rcutorture.object_debug= [KNL] 3956 Enable debug-object double-call_rcu() testing. 3957 3958 rcutorture.onoff_holdoff= [KNL] 3959 Set time (s) after boot for CPU-hotplug testing. 3960 3961 rcutorture.onoff_interval= [KNL] 3962 Set time (jiffies) between CPU-hotplug operations, 3963 or zero to disable CPU-hotplug testing. 3964 3965 rcutorture.shuffle_interval= [KNL] 3966 Set task-shuffle interval (s). Shuffling tasks 3967 allows some CPUs to go into dyntick-idle mode 3968 during the rcutorture test. 3969 3970 rcutorture.shutdown_secs= [KNL] 3971 Set time (s) after boot system shutdown. This 3972 is useful for hands-off automated testing. 3973 3974 rcutorture.stall_cpu= [KNL] 3975 Duration of CPU stall (s) to test RCU CPU stall 3976 warnings, zero to disable. 3977 3978 rcutorture.stall_cpu_holdoff= [KNL] 3979 Time to wait (s) after boot before inducing stall. 3980 3981 rcutorture.stall_cpu_irqsoff= [KNL] 3982 Disable interrupts while stalling if set. 3983 3984 rcutorture.stat_interval= [KNL] 3985 Time (s) between statistics printk()s. 3986 3987 rcutorture.stutter= [KNL] 3988 Time (s) to stutter testing, for example, specifying 3989 five seconds causes the test to run for five seconds, 3990 wait for five seconds, and so on. This tests RCU's 3991 ability to transition abruptly to and from idle. 3992 3993 rcutorture.test_boost= [KNL] 3994 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3995 "Maybe" means test if the RCU implementation 3996 under test support RCU priority boosting. 3997 3998 rcutorture.test_boost_duration= [KNL] 3999 Duration (s) of each individual boost test. 4000 4001 rcutorture.test_boost_interval= [KNL] 4002 Interval (s) between each boost test. 4003 4004 rcutorture.test_no_idle_hz= [KNL] 4005 Test RCU's dyntick-idle handling. See also the 4006 rcutorture.shuffle_interval parameter. 4007 4008 rcutorture.torture_type= [KNL] 4009 Specify the RCU implementation to test. 4010 4011 rcutorture.verbose= [KNL] 4012 Enable additional printk() statements. 4013 4014 rcupdate.rcu_cpu_stall_suppress= [KNL] 4015 Suppress RCU CPU stall warning messages. 4016 4017 rcupdate.rcu_cpu_stall_timeout= [KNL] 4018 Set timeout for RCU CPU stall warning messages. 4019 4020 rcupdate.rcu_expedited= [KNL] 4021 Use expedited grace-period primitives, for 4022 example, synchronize_rcu_expedited() instead 4023 of synchronize_rcu(). This reduces latency, 4024 but can increase CPU utilization, degrade 4025 real-time latency, and degrade energy efficiency. 4026 No effect on CONFIG_TINY_RCU kernels. 4027 4028 rcupdate.rcu_normal= [KNL] 4029 Use only normal grace-period primitives, 4030 for example, synchronize_rcu() instead of 4031 synchronize_rcu_expedited(). This improves 4032 real-time latency, CPU utilization, and 4033 energy efficiency, but can expose users to 4034 increased grace-period latency. This parameter 4035 overrides rcupdate.rcu_expedited. No effect on 4036 CONFIG_TINY_RCU kernels. 4037 4038 rcupdate.rcu_normal_after_boot= [KNL] 4039 Once boot has completed (that is, after 4040 rcu_end_inkernel_boot() has been invoked), use 4041 only normal grace-period primitives. No effect 4042 on CONFIG_TINY_RCU kernels. 4043 4044 rcupdate.rcu_task_stall_timeout= [KNL] 4045 Set timeout in jiffies for RCU task stall warning 4046 messages. Disable with a value less than or equal 4047 to zero. 4048 4049 rcupdate.rcu_self_test= [KNL] 4050 Run the RCU early boot self tests 4051 4052 rdinit= [KNL] 4053 Format: <full_path> 4054 Run specified binary instead of /init from the ramdisk, 4055 used for early userspace startup. See initrd. 4056 4057 rdt= [HW,X86,RDT] 4058 Turn on/off individual RDT features. List is: 4059 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4060 mba. 4061 E.g. to turn on cmt and turn off mba use: 4062 rdt=cmt,!mba 4063 4064 reboot= [KNL] 4065 Format (x86 or x86_64): 4066 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4067 [[,]s[mp]#### \ 4068 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4069 [[,]f[orce] 4070 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4071 (prefix with 'panic_' to set mode for panic 4072 reboot only), 4073 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4074 reboot_force is either force or not specified, 4075 reboot_cpu is s[mp]#### with #### being the processor 4076 to be used for rebooting. 4077 4078 relax_domain_level= 4079 [KNL, SMP] Set scheduler's default relax_domain_level. 4080 See Documentation/cgroup-v1/cpusets.txt. 4081 4082 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4083 Format: <base1>,<size1>[,<base2>,<size2>,...] 4084 Reserve I/O ports or memory so the kernel won't use 4085 them. If <base> is less than 0x10000, the region 4086 is assumed to be I/O ports; otherwise it is memory. 4087 4088 reservetop= [X86-32] 4089 Format: nn[KMG] 4090 Reserves a hole at the top of the kernel virtual 4091 address space. 4092 4093 reservelow= [X86] 4094 Format: nn[K] 4095 Set the amount of memory to reserve for BIOS at 4096 the bottom of the address space. 4097 4098 reset_devices [KNL] Force drivers to reset the underlying device 4099 during initialization. 4100 4101 resume= [SWSUSP] 4102 Specify the partition device for software suspend 4103 Format: 4104 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4105 4106 resume_offset= [SWSUSP] 4107 Specify the offset from the beginning of the partition 4108 given by "resume=" at which the swap header is located, 4109 in <PAGE_SIZE> units (needed only for swap files). 4110 See Documentation/power/swsusp-and-swap-files.txt 4111 4112 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4113 read the resume files 4114 4115 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4116 Useful for devices that are detected asynchronously 4117 (e.g. USB and MMC devices). 4118 4119 hibernate= [HIBERNATION] 4120 noresume Don't check if there's a hibernation image 4121 present during boot. 4122 nocompress Don't compress/decompress hibernation images. 4123 no Disable hibernation and resume. 4124 protect_image Turn on image protection during restoration 4125 (that will set all pages holding image data 4126 during restoration read-only). 4127 4128 retain_initrd [RAM] Keep initrd memory after extraction 4129 4130 rfkill.default_state= 4131 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4132 etc. communication is blocked by default. 4133 1 Unblocked. 4134 4135 rfkill.master_switch_mode= 4136 0 The "airplane mode" button does nothing. 4137 1 The "airplane mode" button toggles between everything 4138 blocked and the previous configuration. 4139 2 The "airplane mode" button toggles between everything 4140 blocked and everything unblocked. 4141 4142 rhash_entries= [KNL,NET] 4143 Set number of hash buckets for route cache 4144 4145 ring3mwait=disable 4146 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4147 CPUs. 4148 4149 ro [KNL] Mount root device read-only on boot 4150 4151 rodata= [KNL] 4152 on Mark read-only kernel memory as read-only (default). 4153 off Leave read-only kernel memory writable for debugging. 4154 4155 rockchip.usb_uart 4156 Enable the uart passthrough on the designated usb port 4157 on Rockchip SoCs. When active, the signals of the 4158 debug-uart get routed to the D+ and D- pins of the usb 4159 port and the regular usb controller gets disabled. 4160 4161 root= [KNL] Root filesystem 4162 See name_to_dev_t comment in init/do_mounts.c. 4163 4164 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4165 mount the root filesystem 4166 4167 rootflags= [KNL] Set root filesystem mount option string 4168 4169 rootfstype= [KNL] Set root filesystem type 4170 4171 rootwait [KNL] Wait (indefinitely) for root device to show up. 4172 Useful for devices that are detected asynchronously 4173 (e.g. USB and MMC devices). 4174 4175 rproc_mem=nn[KMG][@address] 4176 [KNL,ARM,CMA] Remoteproc physical memory block. 4177 Memory area to be used by remote processor image, 4178 managed by CMA. 4179 4180 rw [KNL] Mount root device read-write on boot 4181 4182 S [KNL] Run init in single mode 4183 4184 s390_iommu= [HW,S390] 4185 Set s390 IOTLB flushing mode 4186 strict 4187 With strict flushing every unmap operation will result in 4188 an IOTLB flush. Default is lazy flushing before reuse, 4189 which is faster. 4190 4191 sa1100ir [NET] 4192 See drivers/net/irda/sa1100_ir.c. 4193 4194 sbni= [NET] Granch SBNI12 leased line adapter 4195 4196 sched_debug [KNL] Enables verbose scheduler debug messages. 4197 4198 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4199 Allowed values are enable and disable. This feature 4200 incurs a small amount of overhead in the scheduler 4201 but is useful for debugging and performance tuning. 4202 4203 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4204 xtime_lock contention on larger systems, and/or RCU lock 4205 contention on all systems with CONFIG_MAXSMP set. 4206 Format: { "0" | "1" } 4207 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4208 1 -- enable. 4209 Note: increases power consumption, thus should only be 4210 enabled if running jitter sensitive (HPC/RT) workloads. 4211 4212 security= [SECURITY] Choose a legacy "major" security module to 4213 enable at boot. This has been deprecated by the 4214 "lsm=" parameter. 4215 4216 selinux= [SELINUX] Disable or enable SELinux at boot time. 4217 Format: { "0" | "1" } 4218 See security/selinux/Kconfig help text. 4219 0 -- disable. 4220 1 -- enable. 4221 Default value is set via kernel config option. 4222 If enabled at boot time, /selinux/disable can be used 4223 later to disable prior to initial policy load. 4224 4225 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4226 Format: { "0" | "1" } 4227 See security/apparmor/Kconfig help text 4228 0 -- disable. 4229 1 -- enable. 4230 Default value is set via kernel config option. 4231 4232 serialnumber [BUGS=X86-32] 4233 4234 shapers= [NET] 4235 Maximal number of shapers. 4236 4237 simeth= [IA-64] 4238 simscsi= 4239 4240 slram= [HW,MTD] 4241 4242 slab_nomerge [MM] 4243 Disable merging of slabs with similar size. May be 4244 necessary if there is some reason to distinguish 4245 allocs to different slabs, especially in hardened 4246 environments where the risk of heap overflows and 4247 layout control by attackers can usually be 4248 frustrated by disabling merging. This will reduce 4249 most of the exposure of a heap attack to a single 4250 cache (risks via metadata attacks are mostly 4251 unchanged). Debug options disable merging on their 4252 own. 4253 For more information see Documentation/vm/slub.rst. 4254 4255 slab_max_order= [MM, SLAB] 4256 Determines the maximum allowed order for slabs. 4257 A high setting may cause OOMs due to memory 4258 fragmentation. Defaults to 1 for systems with 4259 more than 32MB of RAM, 0 otherwise. 4260 4261 slub_debug[=options[,slabs]] [MM, SLUB] 4262 Enabling slub_debug allows one to determine the 4263 culprit if slab objects become corrupted. Enabling 4264 slub_debug can create guard zones around objects and 4265 may poison objects when not in use. Also tracks the 4266 last alloc / free. For more information see 4267 Documentation/vm/slub.rst. 4268 4269 slub_memcg_sysfs= [MM, SLUB] 4270 Determines whether to enable sysfs directories for 4271 memory cgroup sub-caches. 1 to enable, 0 to disable. 4272 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4273 Enabling this can lead to a very high number of debug 4274 directories and files being created under 4275 /sys/kernel/slub. 4276 4277 slub_max_order= [MM, SLUB] 4278 Determines the maximum allowed order for slabs. 4279 A high setting may cause OOMs due to memory 4280 fragmentation. For more information see 4281 Documentation/vm/slub.rst. 4282 4283 slub_min_objects= [MM, SLUB] 4284 The minimum number of objects per slab. SLUB will 4285 increase the slab order up to slub_max_order to 4286 generate a sufficiently large slab able to contain 4287 the number of objects indicated. The higher the number 4288 of objects the smaller the overhead of tracking slabs 4289 and the less frequently locks need to be acquired. 4290 For more information see Documentation/vm/slub.rst. 4291 4292 slub_min_order= [MM, SLUB] 4293 Determines the minimum page order for slabs. Must be 4294 lower than slub_max_order. 4295 For more information see Documentation/vm/slub.rst. 4296 4297 slub_nomerge [MM, SLUB] 4298 Same with slab_nomerge. This is supported for legacy. 4299 See slab_nomerge for more information. 4300 4301 smart2= [HW] 4302 Format: <io1>[,<io2>[,...,<io8>]] 4303 4304 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4305 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4306 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4307 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4308 smsc-ircc2.ircc_irq= [HW] IRQ line 4309 smsc-ircc2.ircc_dma= [HW] DMA channel 4310 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4311 0: Toshiba Satellite 1800 (GP data pin select) 4312 1: Fast pin select (default) 4313 2: ATC IRMode 4314 4315 smt [KNL,S390] Set the maximum number of threads (logical 4316 CPUs) to use per physical CPU on systems capable of 4317 symmetric multithreading (SMT). Will be capped to the 4318 actual hardware limit. 4319 Format: <integer> 4320 Default: -1 (no limit) 4321 4322 softlockup_panic= 4323 [KNL] Should the soft-lockup detector generate panics. 4324 Format: <integer> 4325 4326 A nonzero value instructs the soft-lockup detector 4327 to panic the machine when a soft-lockup occurs. This 4328 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4329 which is the respective build-time switch to that 4330 functionality. 4331 4332 softlockup_all_cpu_backtrace= 4333 [KNL] Should the soft-lockup detector generate 4334 backtraces on all cpus. 4335 Format: <integer> 4336 4337 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4338 See Documentation/laptops/sonypi.txt 4339 4340 spectre_v2= [X86] Control mitigation of Spectre variant 2 4341 (indirect branch speculation) vulnerability. 4342 The default operation protects the kernel from 4343 user space attacks. 4344 4345 on - unconditionally enable, implies 4346 spectre_v2_user=on 4347 off - unconditionally disable, implies 4348 spectre_v2_user=off 4349 auto - kernel detects whether your CPU model is 4350 vulnerable 4351 4352 Selecting 'on' will, and 'auto' may, choose a 4353 mitigation method at run time according to the 4354 CPU, the available microcode, the setting of the 4355 CONFIG_RETPOLINE configuration option, and the 4356 compiler with which the kernel was built. 4357 4358 Selecting 'on' will also enable the mitigation 4359 against user space to user space task attacks. 4360 4361 Selecting 'off' will disable both the kernel and 4362 the user space protections. 4363 4364 Specific mitigations can also be selected manually: 4365 4366 retpoline - replace indirect branches 4367 retpoline,generic - google's original retpoline 4368 retpoline,amd - AMD-specific minimal thunk 4369 4370 Not specifying this option is equivalent to 4371 spectre_v2=auto. 4372 4373 spectre_v2_user= 4374 [X86] Control mitigation of Spectre variant 2 4375 (indirect branch speculation) vulnerability between 4376 user space tasks 4377 4378 on - Unconditionally enable mitigations. Is 4379 enforced by spectre_v2=on 4380 4381 off - Unconditionally disable mitigations. Is 4382 enforced by spectre_v2=off 4383 4384 prctl - Indirect branch speculation is enabled, 4385 but mitigation can be enabled via prctl 4386 per thread. The mitigation control state 4387 is inherited on fork. 4388 4389 prctl,ibpb 4390 - Like "prctl" above, but only STIBP is 4391 controlled per thread. IBPB is issued 4392 always when switching between different user 4393 space processes. 4394 4395 seccomp 4396 - Same as "prctl" above, but all seccomp 4397 threads will enable the mitigation unless 4398 they explicitly opt out. 4399 4400 seccomp,ibpb 4401 - Like "seccomp" above, but only STIBP is 4402 controlled per thread. IBPB is issued 4403 always when switching between different 4404 user space processes. 4405 4406 auto - Kernel selects the mitigation depending on 4407 the available CPU features and vulnerability. 4408 4409 Default mitigation: 4410 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4411 4412 Not specifying this option is equivalent to 4413 spectre_v2_user=auto. 4414 4415 spec_store_bypass_disable= 4416 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4417 (Speculative Store Bypass vulnerability) 4418 4419 Certain CPUs are vulnerable to an exploit against a 4420 a common industry wide performance optimization known 4421 as "Speculative Store Bypass" in which recent stores 4422 to the same memory location may not be observed by 4423 later loads during speculative execution. The idea 4424 is that such stores are unlikely and that they can 4425 be detected prior to instruction retirement at the 4426 end of a particular speculation execution window. 4427 4428 In vulnerable processors, the speculatively forwarded 4429 store can be used in a cache side channel attack, for 4430 example to read memory to which the attacker does not 4431 directly have access (e.g. inside sandboxed code). 4432 4433 This parameter controls whether the Speculative Store 4434 Bypass optimization is used. 4435 4436 On x86 the options are: 4437 4438 on - Unconditionally disable Speculative Store Bypass 4439 off - Unconditionally enable Speculative Store Bypass 4440 auto - Kernel detects whether the CPU model contains an 4441 implementation of Speculative Store Bypass and 4442 picks the most appropriate mitigation. If the 4443 CPU is not vulnerable, "off" is selected. If the 4444 CPU is vulnerable the default mitigation is 4445 architecture and Kconfig dependent. See below. 4446 prctl - Control Speculative Store Bypass per thread 4447 via prctl. Speculative Store Bypass is enabled 4448 for a process by default. The state of the control 4449 is inherited on fork. 4450 seccomp - Same as "prctl" above, but all seccomp threads 4451 will disable SSB unless they explicitly opt out. 4452 4453 Default mitigations: 4454 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4455 4456 On powerpc the options are: 4457 4458 on,auto - On Power8 and Power9 insert a store-forwarding 4459 barrier on kernel entry and exit. On Power7 4460 perform a software flush on kernel entry and 4461 exit. 4462 off - No action. 4463 4464 Not specifying this option is equivalent to 4465 spec_store_bypass_disable=auto. 4466 4467 spia_io_base= [HW,MTD] 4468 spia_fio_base= 4469 spia_pedr= 4470 spia_peddr= 4471 4472 srcutree.counter_wrap_check [KNL] 4473 Specifies how frequently to check for 4474 grace-period sequence counter wrap for the 4475 srcu_data structure's ->srcu_gp_seq_needed field. 4476 The greater the number of bits set in this kernel 4477 parameter, the less frequently counter wrap will 4478 be checked for. Note that the bottom two bits 4479 are ignored. 4480 4481 srcutree.exp_holdoff [KNL] 4482 Specifies how many nanoseconds must elapse 4483 since the end of the last SRCU grace period for 4484 a given srcu_struct until the next normal SRCU 4485 grace period will be considered for automatic 4486 expediting. Set to zero to disable automatic 4487 expediting. 4488 4489 ssbd= [ARM64,HW] 4490 Speculative Store Bypass Disable control 4491 4492 On CPUs that are vulnerable to the Speculative 4493 Store Bypass vulnerability and offer a 4494 firmware based mitigation, this parameter 4495 indicates how the mitigation should be used: 4496 4497 force-on: Unconditionally enable mitigation for 4498 for both kernel and userspace 4499 force-off: Unconditionally disable mitigation for 4500 for both kernel and userspace 4501 kernel: Always enable mitigation in the 4502 kernel, and offer a prctl interface 4503 to allow userspace to register its 4504 interest in being mitigated too. 4505 4506 stack_guard_gap= [MM] 4507 override the default stack gap protection. The value 4508 is in page units and it defines how many pages prior 4509 to (for stacks growing down) resp. after (for stacks 4510 growing up) the main stack are reserved for no other 4511 mapping. Default value is 256 pages. 4512 4513 stacktrace [FTRACE] 4514 Enabled the stack tracer on boot up. 4515 4516 stacktrace_filter=[function-list] 4517 [FTRACE] Limit the functions that the stack tracer 4518 will trace at boot up. function-list is a comma separated 4519 list of functions. This list can be changed at run 4520 time by the stack_trace_filter file in the debugfs 4521 tracing directory. Note, this enables stack tracing 4522 and the stacktrace above is not needed. 4523 4524 sti= [PARISC,HW] 4525 Format: <num> 4526 Set the STI (builtin display/keyboard on the HP-PARISC 4527 machines) console (graphic card) which should be used 4528 as the initial boot-console. 4529 See also comment in drivers/video/console/sticore.c. 4530 4531 sti_font= [HW] 4532 See comment in drivers/video/console/sticore.c. 4533 4534 stifb= [HW] 4535 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4536 4537 sunrpc.min_resvport= 4538 sunrpc.max_resvport= 4539 [NFS,SUNRPC] 4540 SunRPC servers often require that client requests 4541 originate from a privileged port (i.e. a port in the 4542 range 0 < portnr < 1024). 4543 An administrator who wishes to reserve some of these 4544 ports for other uses may adjust the range that the 4545 kernel's sunrpc client considers to be privileged 4546 using these two parameters to set the minimum and 4547 maximum port values. 4548 4549 sunrpc.svc_rpc_per_connection_limit= 4550 [NFS,SUNRPC] 4551 Limit the number of requests that the server will 4552 process in parallel from a single connection. 4553 The default value is 0 (no limit). 4554 4555 sunrpc.pool_mode= 4556 [NFS] 4557 Control how the NFS server code allocates CPUs to 4558 service thread pools. Depending on how many NICs 4559 you have and where their interrupts are bound, this 4560 option will affect which CPUs will do NFS serving. 4561 Note: this parameter cannot be changed while the 4562 NFS server is running. 4563 4564 auto the server chooses an appropriate mode 4565 automatically using heuristics 4566 global a single global pool contains all CPUs 4567 percpu one pool for each CPU 4568 pernode one pool for each NUMA node (equivalent 4569 to global on non-NUMA machines) 4570 4571 sunrpc.tcp_slot_table_entries= 4572 sunrpc.udp_slot_table_entries= 4573 [NFS,SUNRPC] 4574 Sets the upper limit on the number of simultaneous 4575 RPC calls that can be sent from the client to a 4576 server. Increasing these values may allow you to 4577 improve throughput, but will also increase the 4578 amount of memory reserved for use by the client. 4579 4580 suspend.pm_test_delay= 4581 [SUSPEND] 4582 Sets the number of seconds to remain in a suspend test 4583 mode before resuming the system (see 4584 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4585 is set. Default value is 5. 4586 4587 swapaccount=[0|1] 4588 [KNL] Enable accounting of swap in memory resource 4589 controller if no parameter or 1 is given or disable 4590 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4591 4592 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4593 Format: { <int> | force | noforce } 4594 <int> -- Number of I/O TLB slabs 4595 force -- force using of bounce buffers even if they 4596 wouldn't be automatically used by the kernel 4597 noforce -- Never use bounce buffers (for debugging) 4598 4599 switches= [HW,M68k] 4600 4601 sysfs.deprecated=0|1 [KNL] 4602 Enable/disable old style sysfs layout for old udev 4603 on older distributions. When this option is enabled 4604 very new udev will not work anymore. When this option 4605 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4606 in older udev will not work anymore. 4607 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4608 the kernel configuration. 4609 4610 sysrq_always_enabled 4611 [KNL] 4612 Ignore sysrq setting - this boot parameter will 4613 neutralize any effect of /proc/sys/kernel/sysrq. 4614 Useful for debugging. 4615 4616 tcpmhash_entries= [KNL,NET] 4617 Set the number of tcp_metrics_hash slots. 4618 Default value is 8192 or 16384 depending on total 4619 ram pages. This is used to specify the TCP metrics 4620 cache size. See Documentation/networking/ip-sysctl.txt 4621 "tcp_no_metrics_save" section for more details. 4622 4623 tdfx= [HW,DRM] 4624 4625 test_suspend= [SUSPEND][,N] 4626 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4627 standby suspend) or "freeze" (for suspend type freeze) 4628 as the system sleep state during system startup with 4629 the optional capability to repeat N number of times. 4630 The system is woken from this state using a 4631 wakeup-capable RTC alarm. 4632 4633 thash_entries= [KNL,NET] 4634 Set number of hash buckets for TCP connection 4635 4636 thermal.act= [HW,ACPI] 4637 -1: disable all active trip points in all thermal zones 4638 <degrees C>: override all lowest active trip points 4639 4640 thermal.crt= [HW,ACPI] 4641 -1: disable all critical trip points in all thermal zones 4642 <degrees C>: override all critical trip points 4643 4644 thermal.nocrt= [HW,ACPI] 4645 Set to disable actions on ACPI thermal zone 4646 critical and hot trip points. 4647 4648 thermal.off= [HW,ACPI] 4649 1: disable ACPI thermal control 4650 4651 thermal.psv= [HW,ACPI] 4652 -1: disable all passive trip points 4653 <degrees C>: override all passive trip points to this 4654 value 4655 4656 thermal.tzp= [HW,ACPI] 4657 Specify global default ACPI thermal zone polling rate 4658 <deci-seconds>: poll all this frequency 4659 0: no polling (default) 4660 4661 threadirqs [KNL] 4662 Force threading of all interrupt handlers except those 4663 marked explicitly IRQF_NO_THREAD. 4664 4665 tmem [KNL,XEN] 4666 Enable the Transcendent memory driver if built-in. 4667 4668 tmem.cleancache=0|1 [KNL, XEN] 4669 Default is on (1). Disable the usage of the cleancache 4670 API to send anonymous pages to the hypervisor. 4671 4672 tmem.frontswap=0|1 [KNL, XEN] 4673 Default is on (1). Disable the usage of the frontswap 4674 API to send swap pages to the hypervisor. If disabled 4675 the selfballooning and selfshrinking are force disabled. 4676 4677 tmem.selfballooning=0|1 [KNL, XEN] 4678 Default is on (1). Disable the driving of swap pages 4679 to the hypervisor. 4680 4681 tmem.selfshrinking=0|1 [KNL, XEN] 4682 Default is on (1). Partial swapoff that immediately 4683 transfers pages from Xen hypervisor back to the 4684 kernel based on different criteria. 4685 4686 topology= [S390] 4687 Format: {off | on} 4688 Specify if the kernel should make use of the cpu 4689 topology information if the hardware supports this. 4690 The scheduler will make use of this information and 4691 e.g. base its process migration decisions on it. 4692 Default is on. 4693 4694 topology_updates= [KNL, PPC, NUMA] 4695 Format: {off} 4696 Specify if the kernel should ignore (off) 4697 topology updates sent by the hypervisor to this 4698 LPAR. 4699 4700 tp720= [HW,PS2] 4701 4702 tpm_suspend_pcr=[HW,TPM] 4703 Format: integer pcr id 4704 Specify that at suspend time, the tpm driver 4705 should extend the specified pcr with zeros, 4706 as a workaround for some chips which fail to 4707 flush the last written pcr on TPM_SaveState. 4708 This will guarantee that all the other pcrs 4709 are saved. 4710 4711 trace_buf_size=nn[KMG] 4712 [FTRACE] will set tracing buffer size on each cpu. 4713 4714 trace_event=[event-list] 4715 [FTRACE] Set and start specified trace events in order 4716 to facilitate early boot debugging. The event-list is a 4717 comma separated list of trace events to enable. See 4718 also Documentation/trace/events.rst 4719 4720 trace_options=[option-list] 4721 [FTRACE] Enable or disable tracer options at boot. 4722 The option-list is a comma delimited list of options 4723 that can be enabled or disabled just as if you were 4724 to echo the option name into 4725 4726 /sys/kernel/debug/tracing/trace_options 4727 4728 For example, to enable stacktrace option (to dump the 4729 stack trace of each event), add to the command line: 4730 4731 trace_options=stacktrace 4732 4733 See also Documentation/trace/ftrace.rst "trace options" 4734 section. 4735 4736 tp_printk[FTRACE] 4737 Have the tracepoints sent to printk as well as the 4738 tracing ring buffer. This is useful for early boot up 4739 where the system hangs or reboots and does not give the 4740 option for reading the tracing buffer or performing a 4741 ftrace_dump_on_oops. 4742 4743 To turn off having tracepoints sent to printk, 4744 echo 0 > /proc/sys/kernel/tracepoint_printk 4745 Note, echoing 1 into this file without the 4746 tracepoint_printk kernel cmdline option has no effect. 4747 4748 ** CAUTION ** 4749 4750 Having tracepoints sent to printk() and activating high 4751 frequency tracepoints such as irq or sched, can cause 4752 the system to live lock. 4753 4754 traceoff_on_warning 4755 [FTRACE] enable this option to disable tracing when a 4756 warning is hit. This turns off "tracing_on". Tracing can 4757 be enabled again by echoing '1' into the "tracing_on" 4758 file located in /sys/kernel/debug/tracing/ 4759 4760 This option is useful, as it disables the trace before 4761 the WARNING dump is called, which prevents the trace to 4762 be filled with content caused by the warning output. 4763 4764 This option can also be set at run time via the sysctl 4765 option: kernel/traceoff_on_warning 4766 4767 transparent_hugepage= 4768 [KNL] 4769 Format: [always|madvise|never] 4770 Can be used to control the default behavior of the system 4771 with respect to transparent hugepages. 4772 See Documentation/admin-guide/mm/transhuge.rst 4773 for more details. 4774 4775 tsc= Disable clocksource stability checks for TSC. 4776 Format: <string> 4777 [x86] reliable: mark tsc clocksource as reliable, this 4778 disables clocksource verification at runtime, as well 4779 as the stability checks done at bootup. Used to enable 4780 high-resolution timer mode on older hardware, and in 4781 virtualized environment. 4782 [x86] noirqtime: Do not use TSC to do irq accounting. 4783 Used to run time disable IRQ_TIME_ACCOUNTING on any 4784 platforms where RDTSC is slow and this accounting 4785 can add overhead. 4786 [x86] unstable: mark the TSC clocksource as unstable, this 4787 marks the TSC unconditionally unstable at bootup and 4788 avoids any further wobbles once the TSC watchdog notices. 4789 [x86] nowatchdog: disable clocksource watchdog. Used 4790 in situations with strict latency requirements (where 4791 interruptions from clocksource watchdog are not 4792 acceptable). 4793 4794 turbografx.map[2|3]= [HW,JOY] 4795 TurboGraFX parallel port interface 4796 Format: 4797 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4798 See also Documentation/input/devices/joystick-parport.rst 4799 4800 udbg-immortal [PPC] When debugging early kernel crashes that 4801 happen after console_init() and before a proper 4802 console driver takes over, this boot options might 4803 help "seeing" what's going on. 4804 4805 uhash_entries= [KNL,NET] 4806 Set number of hash buckets for UDP/UDP-Lite connections 4807 4808 uhci-hcd.ignore_oc= 4809 [USB] Ignore overcurrent events (default N). 4810 Some badly-designed motherboards generate lots of 4811 bogus events, for ports that aren't wired to 4812 anything. Set this parameter to avoid log spamming. 4813 Note that genuine overcurrent events won't be 4814 reported either. 4815 4816 unknown_nmi_panic 4817 [X86] Cause panic on unknown NMI. 4818 4819 usbcore.authorized_default= 4820 [USB] Default USB device authorization: 4821 (default -1 = authorized except for wireless USB, 4822 0 = not authorized, 1 = authorized, 2 = authorized 4823 if device connected to internal port) 4824 4825 usbcore.autosuspend= 4826 [USB] The autosuspend time delay (in seconds) used 4827 for newly-detected USB devices (default 2). This 4828 is the time required before an idle device will be 4829 autosuspended. Devices for which the delay is set 4830 to a negative value won't be autosuspended at all. 4831 4832 usbcore.usbfs_snoop= 4833 [USB] Set to log all usbfs traffic (default 0 = off). 4834 4835 usbcore.usbfs_snoop_max= 4836 [USB] Maximum number of bytes to snoop in each URB 4837 (default = 65536). 4838 4839 usbcore.blinkenlights= 4840 [USB] Set to cycle leds on hubs (default 0 = off). 4841 4842 usbcore.old_scheme_first= 4843 [USB] Start with the old device initialization 4844 scheme, applies only to low and full-speed devices 4845 (default 0 = off). 4846 4847 usbcore.usbfs_memory_mb= 4848 [USB] Memory limit (in MB) for buffers allocated by 4849 usbfs (default = 16, 0 = max = 2047). 4850 4851 usbcore.use_both_schemes= 4852 [USB] Try the other device initialization scheme 4853 if the first one fails (default 1 = enabled). 4854 4855 usbcore.initial_descriptor_timeout= 4856 [USB] Specifies timeout for the initial 64-byte 4857 USB_REQ_GET_DESCRIPTOR request in milliseconds 4858 (default 5000 = 5.0 seconds). 4859 4860 usbcore.nousb [USB] Disable the USB subsystem 4861 4862 usbcore.quirks= 4863 [USB] A list of quirk entries to augment the built-in 4864 usb core quirk list. List entries are separated by 4865 commas. Each entry has the form 4866 VendorID:ProductID:Flags. The IDs are 4-digit hex 4867 numbers and Flags is a set of letters. Each letter 4868 will change the built-in quirk; setting it if it is 4869 clear and clearing it if it is set. The letters have 4870 the following meanings: 4871 a = USB_QUIRK_STRING_FETCH_255 (string 4872 descriptors must not be fetched using 4873 a 255-byte read); 4874 b = USB_QUIRK_RESET_RESUME (device can't resume 4875 correctly so reset it instead); 4876 c = USB_QUIRK_NO_SET_INTF (device can't handle 4877 Set-Interface requests); 4878 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4879 handle its Configuration or Interface 4880 strings); 4881 e = USB_QUIRK_RESET (device can't be reset 4882 (e.g morph devices), don't use reset); 4883 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4884 more interface descriptions than the 4885 bNumInterfaces count, and can't handle 4886 talking to these interfaces); 4887 g = USB_QUIRK_DELAY_INIT (device needs a pause 4888 during initialization, after we read 4889 the device descriptor); 4890 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4891 high speed and super speed interrupt 4892 endpoints, the USB 2.0 and USB 3.0 spec 4893 require the interval in microframes (1 4894 microframe = 125 microseconds) to be 4895 calculated as interval = 2 ^ 4896 (bInterval-1). 4897 Devices with this quirk report their 4898 bInterval as the result of this 4899 calculation instead of the exponent 4900 variable used in the calculation); 4901 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4902 handle device_qualifier descriptor 4903 requests); 4904 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4905 generates spurious wakeup, ignore 4906 remote wakeup capability); 4907 k = USB_QUIRK_NO_LPM (device can't handle Link 4908 Power Management); 4909 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4910 (Device reports its bInterval as linear 4911 frames instead of the USB 2.0 4912 calculation); 4913 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4914 to be disconnected before suspend to 4915 prevent spurious wakeup); 4916 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4917 pause after every control message); 4918 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4919 delay after resetting its port); 4920 Example: quirks=0781:5580:bk,0a5c:5834:gij 4921 4922 usbhid.mousepoll= 4923 [USBHID] The interval which mice are to be polled at. 4924 4925 usbhid.jspoll= 4926 [USBHID] The interval which joysticks are to be polled at. 4927 4928 usbhid.kbpoll= 4929 [USBHID] The interval which keyboards are to be polled at. 4930 4931 usb-storage.delay_use= 4932 [UMS] The delay in seconds before a new device is 4933 scanned for Logical Units (default 1). 4934 4935 usb-storage.quirks= 4936 [UMS] A list of quirks entries to supplement or 4937 override the built-in unusual_devs list. List 4938 entries are separated by commas. Each entry has 4939 the form VID:PID:Flags where VID and PID are Vendor 4940 and Product ID values (4-digit hex numbers) and 4941 Flags is a set of characters, each corresponding 4942 to a common usb-storage quirk flag as follows: 4943 a = SANE_SENSE (collect more than 18 bytes 4944 of sense data); 4945 b = BAD_SENSE (don't collect more than 18 4946 bytes of sense data); 4947 c = FIX_CAPACITY (decrease the reported 4948 device capacity by one sector); 4949 d = NO_READ_DISC_INFO (don't use 4950 READ_DISC_INFO command); 4951 e = NO_READ_CAPACITY_16 (don't use 4952 READ_CAPACITY_16 command); 4953 f = NO_REPORT_OPCODES (don't use report opcodes 4954 command, uas only); 4955 g = MAX_SECTORS_240 (don't transfer more than 4956 240 sectors at a time, uas only); 4957 h = CAPACITY_HEURISTICS (decrease the 4958 reported device capacity by one 4959 sector if the number is odd); 4960 i = IGNORE_DEVICE (don't bind to this 4961 device); 4962 j = NO_REPORT_LUNS (don't use report luns 4963 command, uas only); 4964 l = NOT_LOCKABLE (don't try to lock and 4965 unlock ejectable media); 4966 m = MAX_SECTORS_64 (don't transfer more 4967 than 64 sectors = 32 KB at a time); 4968 n = INITIAL_READ10 (force a retry of the 4969 initial READ(10) command); 4970 o = CAPACITY_OK (accept the capacity 4971 reported by the device); 4972 p = WRITE_CACHE (the device cache is ON 4973 by default); 4974 r = IGNORE_RESIDUE (the device reports 4975 bogus residue values); 4976 s = SINGLE_LUN (the device has only one 4977 Logical Unit); 4978 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4979 commands, uas only); 4980 u = IGNORE_UAS (don't bind to the uas driver); 4981 w = NO_WP_DETECT (don't test whether the 4982 medium is write-protected). 4983 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4984 even if the device claims no cache) 4985 Example: quirks=0419:aaf5:rl,0421:0433:rc 4986 4987 user_debug= [KNL,ARM] 4988 Format: <int> 4989 See arch/arm/Kconfig.debug help text. 4990 1 - undefined instruction events 4991 2 - system calls 4992 4 - invalid data aborts 4993 8 - SIGSEGV faults 4994 16 - SIGBUS faults 4995 Example: user_debug=31 4996 4997 userpte= 4998 [X86] Flags controlling user PTE allocations. 4999 5000 nohigh = do not allocate PTE pages in 5001 HIGHMEM regardless of setting 5002 of CONFIG_HIGHPTE. 5003 5004 vdso= [X86,SH] 5005 On X86_32, this is an alias for vdso32=. Otherwise: 5006 5007 vdso=1: enable VDSO (the default) 5008 vdso=0: disable VDSO mapping 5009 5010 vdso32= [X86] Control the 32-bit vDSO 5011 vdso32=1: enable 32-bit VDSO 5012 vdso32=0 or vdso32=2: disable 32-bit VDSO 5013 5014 See the help text for CONFIG_COMPAT_VDSO for more 5015 details. If CONFIG_COMPAT_VDSO is set, the default is 5016 vdso32=0; otherwise, the default is vdso32=1. 5017 5018 For compatibility with older kernels, vdso32=2 is an 5019 alias for vdso32=0. 5020 5021 Try vdso32=0 if you encounter an error that says: 5022 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5023 5024 vector= [IA-64,SMP] 5025 vector=percpu: enable percpu vector domain 5026 5027 video= [FB] Frame buffer configuration 5028 See Documentation/fb/modedb.txt. 5029 5030 video.brightness_switch_enabled= [0,1] 5031 If set to 1, on receiving an ACPI notify event 5032 generated by hotkey, video driver will adjust brightness 5033 level and then send out the event to user space through 5034 the allocated input device; If set to 0, video driver 5035 will only send out the event without touching backlight 5036 brightness level. 5037 default: 1 5038 5039 virtio_mmio.device= 5040 [VMMIO] Memory mapped virtio (platform) device. 5041 5042 <size>@<baseaddr>:<irq>[:<id>] 5043 where: 5044 <size> := size (can use standard suffixes 5045 like K, M and G) 5046 <baseaddr> := physical base address 5047 <irq> := interrupt number (as passed to 5048 request_irq()) 5049 <id> := (optional) platform device id 5050 example: 5051 virtio_mmio.device=1K@0x100b0000:48:7 5052 5053 Can be used multiple times for multiple devices. 5054 5055 vga= [BOOT,X86-32] Select a particular video mode 5056 See Documentation/x86/boot.txt and 5057 Documentation/svga.txt. 5058 Use vga=ask for menu. 5059 This is actually a boot loader parameter; the value is 5060 passed to the kernel using a special protocol. 5061 5062 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5063 May slow down system boot speed, especially when 5064 enabled on systems with a large amount of memory. 5065 All options are enabled by default, and this 5066 interface is meant to allow for selectively 5067 enabling or disabling specific virtual memory 5068 debugging features. 5069 5070 Available options are: 5071 P Enable page structure init time poisoning 5072 - Disable all of the above options 5073 5074 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5075 size of <nn>. This can be used to increase the 5076 minimum size (128MB on x86). It can also be used to 5077 decrease the size and leave more room for directly 5078 mapped kernel RAM. 5079 5080 vmcp_cma=nn[MG] [KNL,S390] 5081 Sets the memory size reserved for contiguous memory 5082 allocations for the vmcp device driver. 5083 5084 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5085 Format: <command> 5086 5087 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5088 Format: <command> 5089 5090 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5091 Format: <command> 5092 5093 vsyscall= [X86-64] 5094 Controls the behavior of vsyscalls (i.e. calls to 5095 fixed addresses of 0xffffffffff600x00 from legacy 5096 code). Most statically-linked binaries and older 5097 versions of glibc use these calls. Because these 5098 functions are at fixed addresses, they make nice 5099 targets for exploits that can control RIP. 5100 5101 emulate [default] Vsyscalls turn into traps and are 5102 emulated reasonably safely. 5103 5104 native Vsyscalls are native syscall instructions. 5105 This is a little bit faster than trapping 5106 and makes a few dynamic recompilers work 5107 better than they would in emulation mode. 5108 It also makes exploits much easier to write. 5109 5110 none Vsyscalls don't work at all. This makes 5111 them quite hard to use for exploits but 5112 might break your system. 5113 5114 vt.color= [VT] Default text color. 5115 Format: 0xYX, X = foreground, Y = background. 5116 Default: 0x07 = light gray on black. 5117 5118 vt.cur_default= [VT] Default cursor shape. 5119 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5120 the parameters of the <Esc>[?A;B;Cc escape sequence; 5121 see VGA-softcursor.txt. Default: 2 = underline. 5122 5123 vt.default_blu= [VT] 5124 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5125 Change the default blue palette of the console. 5126 This is a 16-member array composed of values 5127 ranging from 0-255. 5128 5129 vt.default_grn= [VT] 5130 Format: <green0>,<green1>,<green2>,...,<green15> 5131 Change the default green palette of the console. 5132 This is a 16-member array composed of values 5133 ranging from 0-255. 5134 5135 vt.default_red= [VT] 5136 Format: <red0>,<red1>,<red2>,...,<red15> 5137 Change the default red palette of the console. 5138 This is a 16-member array composed of values 5139 ranging from 0-255. 5140 5141 vt.default_utf8= 5142 [VT] 5143 Format=<0|1> 5144 Set system-wide default UTF-8 mode for all tty's. 5145 Default is 1, i.e. UTF-8 mode is enabled for all 5146 newly opened terminals. 5147 5148 vt.global_cursor_default= 5149 [VT] 5150 Format=<-1|0|1> 5151 Set system-wide default for whether a cursor 5152 is shown on new VTs. Default is -1, 5153 i.e. cursors will be created by default unless 5154 overridden by individual drivers. 0 will hide 5155 cursors, 1 will display them. 5156 5157 vt.italic= [VT] Default color for italic text; 0-15. 5158 Default: 2 = green. 5159 5160 vt.underline= [VT] Default color for underlined text; 0-15. 5161 Default: 3 = cyan. 5162 5163 watchdog timers [HW,WDT] For information on watchdog timers, 5164 see Documentation/watchdog/watchdog-parameters.txt 5165 or other driver-specific files in the 5166 Documentation/watchdog/ directory. 5167 5168 watchdog_thresh= 5169 [KNL] 5170 Set the hard lockup detector stall duration 5171 threshold in seconds. The soft lockup detector 5172 threshold is set to twice the value. A value of 0 5173 disables both lockup detectors. Default is 10 5174 seconds. 5175 5176 workqueue.watchdog_thresh= 5177 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5178 warn stall conditions and dump internal state to 5179 help debugging. 0 disables workqueue stall 5180 detection; otherwise, it's the stall threshold 5181 duration in seconds. The default value is 30 and 5182 it can be updated at runtime by writing to the 5183 corresponding sysfs file. 5184 5185 workqueue.disable_numa 5186 By default, all work items queued to unbound 5187 workqueues are affine to the NUMA nodes they're 5188 issued on, which results in better behavior in 5189 general. If NUMA affinity needs to be disabled for 5190 whatever reason, this option can be used. Note 5191 that this also can be controlled per-workqueue for 5192 workqueues visible under /sys/bus/workqueue/. 5193 5194 workqueue.power_efficient 5195 Per-cpu workqueues are generally preferred because 5196 they show better performance thanks to cache 5197 locality; unfortunately, per-cpu workqueues tend to 5198 be more power hungry than unbound workqueues. 5199 5200 Enabling this makes the per-cpu workqueues which 5201 were observed to contribute significantly to power 5202 consumption unbound, leading to measurably lower 5203 power usage at the cost of small performance 5204 overhead. 5205 5206 The default value of this parameter is determined by 5207 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5208 5209 workqueue.debug_force_rr_cpu 5210 Workqueue used to implicitly guarantee that work 5211 items queued without explicit CPU specified are put 5212 on the local CPU. This guarantee is no longer true 5213 and while local CPU is still preferred work items 5214 may be put on foreign CPUs. This debug option 5215 forces round-robin CPU selection to flush out 5216 usages which depend on the now broken guarantee. 5217 When enabled, memory and cache locality will be 5218 impacted. 5219 5220 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5221 default x2apic cluster mode on platforms 5222 supporting x2apic. 5223 5224 x86_intel_mid_timer= [X86-32,APBT] 5225 Choose timer option for x86 Intel MID platform. 5226 Two valid options are apbt timer only and lapic timer 5227 plus one apbt timer for broadcast timer. 5228 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5229 5230 xen_512gb_limit [KNL,X86-64,XEN] 5231 Restricts the kernel running paravirtualized under Xen 5232 to use only up to 512 GB of RAM. The reason to do so is 5233 crash analysis tools and Xen tools for doing domain 5234 save/restore/migration must be enabled to handle larger 5235 domains. 5236 5237 xen_emul_unplug= [HW,X86,XEN] 5238 Unplug Xen emulated devices 5239 Format: [unplug0,][unplug1] 5240 ide-disks -- unplug primary master IDE devices 5241 aux-ide-disks -- unplug non-primary-master IDE devices 5242 nics -- unplug network devices 5243 all -- unplug all emulated devices (NICs and IDE disks) 5244 unnecessary -- unplugging emulated devices is 5245 unnecessary even if the host did not respond to 5246 the unplug protocol 5247 never -- do not unplug even if version check succeeds 5248 5249 xen_nopvspin [X86,XEN] 5250 Disables the ticketlock slowpath using Xen PV 5251 optimizations. 5252 5253 xen_nopv [X86] 5254 Disables the PV optimizations forcing the HVM guest to 5255 run as generic HVM guest with no PV drivers. 5256 5257 xen_scrub_pages= [XEN] 5258 Boolean option to control scrubbing pages before giving them back 5259 to Xen, for use by other domains. Can be also changed at runtime 5260 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5261 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5262 5263 xen_timer_slop= [X86-64,XEN] 5264 Set the timer slop (in nanoseconds) for the virtual Xen 5265 timers (default is 100000). This adjusts the minimum 5266 delta of virtualized Xen timers, where lower values 5267 improve timer resolution at the expense of processing 5268 more timer interrupts. 5269 5270 xirc2ps_cs= [NET,PCMCIA] 5271 Format: 5272 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5273 5274 xhci-hcd.quirks [USB,KNL] 5275 A hex value specifying bitmask with supplemental xhci 5276 host controller quirks. Meaning of each bit can be 5277 consulted in header drivers/usb/host/xhci.h. 5278