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