4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
39 Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
40 nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
42 <cpu number>,...,<cpu number>
46 <cpu number>-<cpu number>
47 (must be a positive range in ascending order)
51 <cpu number>,...,<cpu number>-<cpu number>
53 Note that for the special case of a range one can split the range into equal
54 sized groups and for each group use some amount from the beginning of that
57 <cpu number>-cpu number>:<used size>/<group size>
59 For example one can add to the command line following parameter:
61 isolcpus=1,2,10-20,100-2000:2/25
63 where the final item represents CPUs 100,101,125,126,150,151,...
67 This document may not be entirely up to date and comprehensive. The command
68 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
69 module. Loadable modules, after being loaded into the running kernel, also
70 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
71 parameters may be changed at runtime by the command
72 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
74 The parameters listed below are only valid if certain kernel build options were
75 enabled and if respective hardware is present. The text in square brackets at
76 the beginning of each description states the restrictions within which a
77 parameter is applicable:
79 ACPI ACPI support is enabled.
80 AGP AGP (Accelerated Graphics Port) is enabled.
81 ALSA ALSA sound support is enabled.
82 APIC APIC support is enabled.
83 APM Advanced Power Management support is enabled.
84 ARM ARM architecture is enabled.
85 AVR32 AVR32 architecture is enabled.
86 AX25 Appropriate AX.25 support is enabled.
87 BLACKFIN Blackfin architecture is enabled.
88 CLK Common clock infrastructure is enabled.
89 CMA Contiguous Memory Area support is enabled.
90 DRM Direct Rendering Management support is enabled.
91 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
92 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
93 EFI EFI Partitioning (GPT) is enabled
94 EIDE EIDE/ATAPI support is enabled.
95 EVM Extended Verification Module
96 FB The frame buffer device is enabled.
97 FTRACE Function tracing enabled.
98 GCOV GCOV profiling is enabled.
99 HW Appropriate hardware is enabled.
100 IA-64 IA-64 architecture is enabled.
101 IMA Integrity measurement architecture is enabled.
102 IOSCHED More than one I/O scheduler is enabled.
103 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
104 IPV6 IPv6 support is enabled.
105 ISAPNP ISA PnP code is enabled.
106 ISDN Appropriate ISDN support is enabled.
107 JOY Appropriate joystick support is enabled.
108 KGDB Kernel debugger support is enabled.
109 KVM Kernel Virtual Machine support is enabled.
110 LIBATA Libata driver is enabled
111 LP Printer support is enabled.
112 LOOP Loopback device support is enabled.
113 M68k M68k architecture is enabled.
114 These options have more detailed description inside of
115 Documentation/m68k/kernel-options.txt.
116 MDA MDA console support is enabled.
117 MIPS MIPS architecture is enabled.
118 MOUSE Appropriate mouse support is enabled.
119 MSI Message Signaled Interrupts (PCI).
120 MTD MTD (Memory Technology Device) support is enabled.
121 NET Appropriate network support is enabled.
122 NUMA NUMA support is enabled.
123 NFS Appropriate NFS support is enabled.
124 OSS OSS sound support is enabled.
125 PV_OPS A paravirtualized kernel is enabled.
126 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
127 PARISC The PA-RISC architecture is enabled.
128 PCI PCI bus support is enabled.
129 PCIE PCI Express support is enabled.
130 PCMCIA The PCMCIA subsystem is enabled.
131 PNP Plug & Play support is enabled.
132 PPC PowerPC architecture is enabled.
133 PPT Parallel port support is enabled.
134 PS2 Appropriate PS/2 support is enabled.
135 RAM RAM disk support is enabled.
136 S390 S390 architecture is enabled.
137 SCSI Appropriate SCSI support is enabled.
138 A lot of drivers have their options described inside
139 the Documentation/scsi/ sub-directory.
140 SECURITY Different security models are enabled.
141 SELINUX SELinux support is enabled.
142 APPARMOR AppArmor support is enabled.
143 SERIAL Serial support is enabled.
144 SH SuperH architecture is enabled.
145 SMP The kernel is an SMP kernel.
146 SPARC Sparc architecture is enabled.
147 SWSUSP Software suspend (hibernation) is enabled.
148 SUSPEND System suspend states are enabled.
149 TPM TPM drivers are enabled.
150 TS Appropriate touchscreen support is enabled.
151 UMS USB Mass Storage support is enabled.
152 USB USB support is enabled.
153 USBHID USB Human Interface Device support is enabled.
154 V4L Video For Linux support is enabled.
155 VMMIO Driver for memory mapped virtio devices is enabled.
156 VGA The VGA console has been enabled.
157 VT Virtual terminal support is enabled.
158 WDT Watchdog support is enabled.
159 XT IBM PC/XT MFM hard disk support is enabled.
160 X86-32 X86-32, aka i386 architecture is enabled.
161 X86-64 X86-64 architecture is enabled.
162 More X86-64 boot options can be found in
163 Documentation/x86/x86_64/boot-options.txt .
164 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
165 X86_UV SGI UV support is enabled.
166 XEN Xen support is enabled
168 In addition, the following text indicates that the option:
170 BUGS= Relates to possible processor bugs on the said processor.
171 KNL Is a kernel start-up parameter.
172 BOOT Is a boot loader parameter.
174 Parameters denoted with BOOT are actually interpreted by the boot
175 loader, and have no meaning to the kernel directly.
176 Do not modify the syntax of boot loader parameters without extreme
177 need or coordination with <Documentation/x86/boot.txt>.
179 There are also arch-specific kernel-parameters not documented here.
180 See for example <Documentation/x86/x86_64/boot-options.txt>.
182 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
183 a trailing = on the name of any parameter states that that parameter will
184 be entered as an environment variable, whereas its absence indicates that
185 it will appear as a kernel argument readable via /proc/cmdline by programs
186 running once the system is up.
188 The number of kernel parameters is not limited, but the length of the
189 complete command line (parameters including spaces etc.) is limited to
190 a fixed number of characters. This limit depends on the architecture
191 and is between 256 and 4096 characters. It is defined in the file
192 ./include/asm/setup.h as COMMAND_LINE_SIZE.
194 Finally, the [KMG] suffix is commonly described after a number of kernel
195 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
196 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
197 bytes respectively. Such letter suffixes can also be entirely omitted.
200 acpi= [HW,ACPI,X86,ARM64]
201 Advanced Configuration and Power Interface
202 Format: { force | on | off | strict | noirq | rsdt |
204 force -- enable ACPI if default was off
205 on -- enable ACPI but allow fallback to DT [arm64]
206 off -- disable ACPI if default was on
207 noirq -- do not use ACPI for IRQ routing
208 strict -- Be less tolerant of platforms that are not
209 strictly ACPI specification compliant.
210 rsdt -- prefer RSDT over (default) XSDT
211 copy_dsdt -- copy DSDT to memory
212 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
215 See also Documentation/power/runtime_pm.txt, pci=noacpi
217 acpi_apic_instance= [ACPI, IOAPIC]
219 2: use 2nd APIC table, if available
220 1,0: use 1st APIC table
223 acpi_backlight= [HW,ACPI]
224 acpi_backlight=vendor
226 If set to vendor, prefer vendor specific driver
227 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
228 of the ACPI video.ko driver.
230 acpi_force_32bit_fadt_addr
231 force FADT to use 32 bit addresses rather than the
232 64 bit X_* addresses. Some firmware have broken 64
233 bit addresses for force ACPI ignore these and use
234 the older legacy 32 bit addresses.
236 acpica_no_return_repair [HW, ACPI]
237 Disable AML predefined validation mechanism
238 This mechanism can repair the evaluation result to make
239 the return objects more ACPI specification compliant.
240 This option is useful for developers to identify the
241 root cause of an AML interpreter issue when the issue
242 has something to do with the repair mechanism.
244 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
245 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
247 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
248 debug output. Bits in debug_layer correspond to a
249 _COMPONENT in an ACPI source file, e.g.,
250 #define _COMPONENT ACPI_PCI_COMPONENT
251 Bits in debug_level correspond to a level in
252 ACPI_DEBUG_PRINT statements, e.g.,
253 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
254 The debug_level mask defaults to "info". See
255 Documentation/acpi/debug.txt for more information about
256 debug layers and levels.
258 Enable processor driver info messages:
259 acpi.debug_layer=0x20000000
260 Enable PCI/PCI interrupt routing info messages:
261 acpi.debug_layer=0x400000
262 Enable AML "Debug" output, i.e., stores to the Debug
263 object while interpreting AML:
264 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
265 Enable all messages related to ACPI hardware:
266 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
268 Some values produce so much output that the system is
269 unusable. The "log_buf_len" parameter may be useful
270 if you need to capture more output.
272 acpi_enforce_resources= [ACPI]
273 { strict | lax | no }
274 Check for resource conflicts between native drivers
275 and ACPI OperationRegions (SystemIO and SystemMemory
276 only). IO ports and memory declared in ACPI might be
277 used by the ACPI subsystem in arbitrary AML code and
278 can interfere with legacy drivers.
279 strict (default): access to resources claimed by ACPI
280 is denied; legacy drivers trying to access reserved
281 resources will fail to bind to device using them.
282 lax: access to resources claimed by ACPI is allowed;
283 legacy drivers trying to access reserved resources
284 will bind successfully but a warning message is logged.
285 no: ACPI OperationRegions are not marked as reserved,
286 no further checks are performed.
288 acpi_force_table_verification [HW,ACPI]
289 Enable table checksum verification during early stage.
290 By default, this is disabled due to x86 early mapping
293 acpi_irq_balance [HW,ACPI]
294 ACPI will balance active IRQs
297 acpi_irq_nobalance [HW,ACPI]
298 ACPI will not move active IRQs (default)
301 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
302 Format: <irq>,<irq>...
304 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
306 Format: <irq>,<irq>...
308 acpi_mask_gpe= [HW,ACPI]
309 Due to the existence of _Lxx/_Exx, some GPEs triggered
310 by unsupported hardware/firmware features can result in
311 GPE floodings that cannot be automatically disabled by
313 This facility can be used to prevent such uncontrolled
317 acpi_no_auto_serialize [HW,ACPI]
318 Disable auto-serialization of AML methods
319 AML control methods that contain the opcodes to create
320 named objects will be marked as "Serialized" by the
321 auto-serialization feature.
322 This feature is enabled by default.
323 This option allows to turn off the feature.
325 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
328 acpi_no_static_ssdt [HW,ACPI]
329 Disable installation of static SSDTs at early boot time
330 By default, SSDTs contained in the RSDT/XSDT will be
331 installed automatically and they will appear under
332 /sys/firmware/acpi/tables.
333 This option turns off this feature.
334 Note that specifying this option does not affect
335 dynamic table installation which will install SSDT
336 tables to /sys/firmware/acpi/tables/dynamic.
338 acpi_no_watchdog [HW,ACPI,WDT]
339 Ignore the ACPI-based watchdog interface (WDAT) and let
340 a native driver control the watchdog device instead.
342 acpi_rsdp= [ACPI,EFI,KEXEC]
343 Pass the RSDP address to the kernel, mostly used
344 on machines running EFI runtime service to boot the
345 second kernel for kdump.
347 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
348 Format: To spoof as Windows 98: ="Microsoft Windows"
350 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
351 of 2 which is mandated by ACPI 6) as the supported ACPI
352 specification revision (when using this switch, it may
353 be necessary to carry out a cold reboot _twice_ in a
354 row to make it take effect on the platform firmware).
356 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
357 acpi_osi="string1" # add string1
358 acpi_osi="!string2" # remove string2
359 acpi_osi=!* # remove all strings
360 acpi_osi=! # disable all built-in OS vendor
362 acpi_osi=!! # enable all built-in OS vendor
364 acpi_osi= # disable all strings
366 'acpi_osi=!' can be used in combination with single or
367 multiple 'acpi_osi="string1"' to support specific OS
368 vendor string(s). Note that such command can only
369 affect the default state of the OS vendor strings, thus
370 it cannot affect the default state of the feature group
371 strings and the current state of the OS vendor strings,
372 specifying it multiple times through kernel command line
373 is meaningless. This command is useful when one do not
374 care about the state of the feature group strings which
375 should be controlled by the OSPM.
377 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
378 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
379 can make '_OSI("Windows 2000")' TRUE.
381 'acpi_osi=' cannot be used in combination with other
382 'acpi_osi=' command lines, the _OSI method will not
383 exist in the ACPI namespace. NOTE that such command can
384 only affect the _OSI support state, thus specifying it
385 multiple times through kernel command line is also
388 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
391 'acpi_osi=!*' can be used in combination with single or
392 multiple 'acpi_osi="string1"' to support specific
393 string(s). Note that such command can affect the
394 current state of both the OS vendor strings and the
395 feature group strings, thus specifying it multiple times
396 through kernel command line is meaningful. But it may
397 still not able to affect the final state of a string if
398 there are quirks related to this string. This command
399 is useful when one want to control the state of the
400 feature group strings to debug BIOS issues related to
403 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
404 '_OSI("Module Device")' FALSE.
405 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
406 '_OSI("Module Device")' TRUE.
407 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
409 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
411 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
412 they all will make '_OSI("Windows 2000")' TRUE.
415 Override the pmtimer bug detection: force the kernel
416 to assume that this machine's pmtimer latches its value
417 and always returns good values.
419 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
420 Format: { level | edge | high | low }
422 acpi_skip_timer_override [HW,ACPI]
423 Recognize and ignore IRQ0/pin2 Interrupt Override.
424 For broken nForce2 BIOS resulting in XT-PIC timer.
426 acpi_sleep= [HW,ACPI] Sleep options
427 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
428 old_ordering, nonvs, sci_force_enable }
429 See Documentation/power/video.txt for information on
431 s3_beep is for debugging; it makes the PC's speaker beep
432 as soon as the kernel's real-mode entry point is called.
433 s4_nohwsig prevents ACPI hardware signature from being
434 used during resume from hibernation.
435 old_ordering causes the ACPI 1.0 ordering of the _PTS
436 control method, with respect to putting devices into
437 low power states, to be enforced (the ACPI 2.0 ordering
438 of _PTS is used by default).
439 nonvs prevents the kernel from saving/restoring the
440 ACPI NVS memory during suspend/hibernation and resume.
441 sci_force_enable causes the kernel to set SCI_EN directly
442 on resume from S1/S3 (which is against the ACPI spec,
443 but some broken systems don't work without it).
445 acpi_use_timer_override [HW,ACPI]
446 Use timer override. For some broken Nvidia NF5 boards
447 that require a timer override, but don't have HPET
449 add_efi_memmap [EFI; X86] Include EFI memory map in
450 kernel's map of available physical RAM.
453 { off | try_unsupported }
454 off: disable AGP support
455 try_unsupported: try to drive unsupported chipsets
456 (may crash computer or cause data corruption)
459 See Documentation/sound/alsa/alsa-parameters.txt
462 Allow the default userspace alignment fault handler
463 behaviour to be specified. Bit 0 enables warnings,
464 bit 1 enables fixups, and bit 2 sends a segfault.
466 align_va_addr= [X86-64]
467 Align virtual addresses by clearing slice [14:12] when
468 allocating a VMA at process creation time. This option
469 gives you up to 3% performance improvement on AMD F15h
470 machines (where it is enabled by default) for a
471 CPU-intensive style benchmark, and it can vary highly in
472 a microbenchmark depending on workload and compiler.
474 32: only for 32-bit processes
475 64: only for 64-bit processes
476 on: enable for both 32- and 64-bit processes
477 off: disable for both 32- and 64-bit processes
479 alloc_snapshot [FTRACE]
480 Allocate the ftrace snapshot buffer on boot up when the
481 main buffer is allocated. This is handy if debugging
482 and you need to use tracing_snapshot() on boot up, and
483 do not want to use tracing_snapshot_alloc() as it needs
484 to be done where GFP_KERNEL allocations are allowed.
486 amd_iommu= [HW,X86-64]
487 Pass parameters to the AMD IOMMU driver in the system.
489 fullflush - enable flushing of IO/TLB entries when
490 they are unmapped. Otherwise they are
491 flushed before they will be reused, which
493 off - do not initialize any AMD IOMMU found in
495 force_isolation - Force device isolation for all
496 devices. The IOMMU driver is not
497 allowed anymore to lift isolation
498 requirements as needed. This option
499 does not override iommu=pt
501 amd_iommu_dump= [HW,X86-64]
502 Enable AMD IOMMU driver option to dump the ACPI table
503 for AMD IOMMU. With this option enabled, AMD IOMMU
504 driver will print ACPI tables for AMD IOMMU during
505 IOMMU initialization.
507 amd_iommu_intr= [HW,X86-64]
508 Specifies one of the following AMD IOMMU interrupt
510 legacy - Use legacy interrupt remapping mode.
511 vapic - Use virtual APIC mode, which allows IOMMU
512 to inject interrupts directly into guest.
513 This mode requires kvm-amd.avic=1.
514 (Default when IOMMU HW support is present.)
516 amijoy.map= [HW,JOY] Amiga joystick support
517 Map of devices attached to JOY0DAT and JOY1DAT
519 See also Documentation/input/joystick.txt
521 analog.map= [HW,JOY] Analog joystick and gamepad support
522 Specifies type or capabilities of an analog joystick
523 connected to one of 16 gameports
524 Format: <type1>,<type2>,..<type16>
527 Power management functions (SPARCstation-4/5 + deriv.)
529 Disable APC CPU standby support. SPARCstation-Fox does
530 not play well with APC CPU idle - disable it if you have
531 APC and your system crashes randomly.
533 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
534 Change the output verbosity whilst booting
535 Format: { quiet (default) | verbose | debug }
536 Change the amount of debugging information output
537 when initialising the APIC and IO-APIC components.
539 apic_extnmi= [APIC,X86] External NMI delivery setting
540 Format: { bsp (default) | all | none }
541 bsp: External NMI is delivered only to CPU 0
542 all: External NMIs are broadcast to all CPUs as a
544 none: External NMI is masked for all CPUs. This is
545 useful so that a dump capture kernel won't be
549 See Documentation/networking/ipv6.txt.
551 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
552 Limit apic dumping. The parameter defines the maximal
553 number of local apics being dumped. Also it is possible
554 to set it to "all" by meaning -- no limit here.
555 Format: { 1 (default) | 2 | ... | all }.
556 The parameter valid if only apic=debug or
557 apic=verbose is specified.
558 Example: apic=debug show_lapic=all
560 apm= [APM] Advanced Power Management
561 See header of arch/x86/kernel/apm_32.c.
563 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
564 Format: <io>,<irq>,<nodeID>
568 atarimouse= [HW,MOUSE] Atari Mouse
570 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
571 EzKey and similar keyboards
573 atkbd.reset= [HW] Reset keyboard during initialization
575 atkbd.set= [HW] Select keyboard code set
576 Format: <int> (2 = AT (default), 3 = PS/2)
578 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
581 atkbd.softraw= [HW] Choose between synthetic and real raw mode
582 Format: <bool> (0 = real, 1 = synthetic (default))
584 atkbd.softrepeat= [HW]
585 Use software keyboard repeat
587 audit= [KNL] Enable the audit sub-system
588 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
589 0 - kernel audit is disabled and can not be enabled
590 until the next reboot
591 unset - kernel audit is initialized but disabled and
592 will be fully enabled by the userspace auditd.
593 1 - kernel audit is initialized and partially enabled,
594 storing at most audit_backlog_limit messages in
595 RAM until it is fully enabled by the userspace
599 audit_backlog_limit= [KNL] Set the audit queue size limit.
600 Format: <int> (must be >=0)
603 bau= [X86_UV] Enable the BAU on SGI UV. The default
604 behavior is to disable the BAU (i.e. bau=0).
605 Format: { "0" | "1" }
608 unset - Disable the BAU.
610 baycom_epp= [HW,AX25]
613 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
615 See header of drivers/net/hamradio/baycom_par.c.
617 baycom_ser_fdx= [HW,AX25]
618 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
619 Format: <io>,<irq>,<mode>[,<baud>]
620 See header of drivers/net/hamradio/baycom_ser_fdx.c.
622 baycom_ser_hdx= [HW,AX25]
623 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
624 Format: <io>,<irq>,<mode>
625 See header of drivers/net/hamradio/baycom_ser_hdx.c.
627 blkdevparts= Manual partition parsing of block device(s) for
628 embedded devices based on command line input.
629 See Documentation/block/cmdline-partition.txt
631 boot_delay= Milliseconds to delay each printk during boot.
632 Values larger than 10 seconds (10000) are changed to
636 bootmem_debug [KNL] Enable bootmem allocator debug messages.
639 Disable BERT OS support on buggy BIOSes.
641 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
642 bttv.radio= Most important insmod options are available as
644 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
647 bulk_remove=off [PPC] This parameter disables the use of the pSeries
648 firmware feature for flushing multiple hpte entries
651 c101= [NET] Moxa C101 synchronous serial card
653 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
654 Sometimes CPU hardware bugs make them report the cache
655 size incorrectly. The kernel will attempt work arounds
656 to fix known problems, but for some CPUs it is not
657 possible to determine what the correct size should be.
658 This option provides an override for these situations.
660 ca_keys= [KEYS] This parameter identifies a specific key(s) on
661 the system trusted keyring to be used for certificate
663 format: { id:<keyid> | builtin }
665 cca= [MIPS] Override the kernel pages' cache coherency
666 algorithm. Accepted values range from 0 to 7
667 inclusive. See arch/mips/include/asm/pgtable-bits.h
668 for platform specific values (SB1, Loongson3 and
671 ccw_timeout_log [S390]
672 See Documentation/s390/CommonIO for details.
674 cgroup_disable= [KNL] Disable a particular controller
675 Format: {name of the controller(s) to disable}
676 The effects of cgroup_disable=foo are:
677 - foo isn't auto-mounted if you mount all cgroups in
679 - foo isn't visible as an individually mountable
681 {Currently only "memory" controller deal with this and
682 cut the overhead, others just disable the usage. So
683 only cgroup_disable=memory is actually worthy}
685 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
686 Format: { controller[,controller...] | "all" }
687 Like cgroup_disable, but only applies to cgroup v1;
688 the blacklisted controllers remain available in cgroup2.
690 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
692 nosocket -- Disable socket memory accounting.
693 nokmem -- Disable kernel memory accounting.
695 checkreqprot [SELINUX] Set initial checkreqprot flag value.
696 Format: { "0" | "1" }
697 See security/selinux/Kconfig help text.
698 0 -- check protection applied by kernel (includes
699 any implied execute protection).
700 1 -- check protection requested by application.
701 Default value is set via a kernel config option.
702 Value can be changed at runtime via
703 /selinux/checkreqprot.
706 See Documentation/s390/CommonIO for details.
709 Prevents the clock framework from automatically gating
710 clocks that have not been explicitly enabled by a Linux
711 device driver but are enabled in hardware at reset or
712 by the bootloader/firmware. Note that this does not
713 force such clocks to be always-on nor does it reserve
714 those clocks in any way. This parameter is useful for
715 debug and development, but should not be needed on a
716 platform with proper driver support. For more
717 information, see Documentation/clk.txt.
719 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
721 Forces specified clocksource (if available) to be used
722 when calculating gettimeofday(). If specified
723 clocksource is not available, it defaults to PIT.
724 Format: { pit | tsc | cyclone | pmtmr }
726 clocksource= Override the default clocksource
728 Override the default clocksource and use the clocksource
729 with the name specified.
730 Some clocksource names to choose from, depending on
732 [all] jiffies (this is the base, fallback clocksource)
734 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
735 pxa_timer,timer3,32k_counter,timer0_1
737 [X86-32] pit,hpet,tsc;
738 scx200_hrt on Geode; cyclone on IBM x440
746 clocksource.arm_arch_timer.evtstrm=
749 Enable/disable the eventstream feature of the ARM
750 architected timer so that code using WFE-based polling
751 loops can be debugged more effectively on production
754 clocksource.arm_arch_timer.fsl-a008585=
757 Enable/disable the workaround of Freescale/NXP
758 erratum A-008585. This can be useful for KVM
759 guests, if the guest device tree doesn't show the
760 erratum. If unspecified, the workaround is
761 enabled based on the device tree.
763 clearcpuid=BITNUM [X86]
764 Disable CPUID feature X for the kernel. See
765 arch/x86/include/asm/cpufeatures.h for the valid bit
766 numbers. Note the Linux specific bits are not necessarily
767 stable over kernel options, but the vendor specific
769 Also note that user programs calling CPUID directly
770 or using the feature without checking anything
771 will still see it. This just prevents it from
772 being used by the kernel or shown in /proc/cpuinfo.
773 Also note the kernel might malfunction if you disable
776 cma=nn[MG]@[start[MG][-end[MG]]]
778 Sets the size of kernel global memory area for
779 contiguous memory allocations and optionally the
780 placement constraint by the physical address range of
781 memory allocations. A value of 0 disables CMA
782 altogether. For more information, see
783 include/linux/dma-contiguous.h
785 cmo_free_hint= [PPC] Format: { yes | no }
786 Specify whether pages are marked as being inactive
787 when they are freed. This is used in CMO environments
788 to determine OS memory pressure for page stealing by
792 coherent_pool=nn[KMG] [ARM,KNL]
793 Sets the size of memory pool for coherent, atomic dma
794 allocations, by default set to 256K.
796 code_bytes [X86] How many bytes of object code to print
801 com20020= [HW,NET] ARCnet - COM20020 chipset
803 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
805 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
809 ARCnet - COM90xx chipset (memory-mapped buffers)
810 Format: <io>[,<irq>[,<memstart>]]
812 condev= [HW,S390] console device
815 console= [KNL] Output console device and options.
817 tty<n> Use the virtual console device <n>.
821 Use the specified serial port. The options are of
822 the form "bbbbpnf", where "bbbb" is the baud rate,
823 "p" is parity ("n", "o", or "e"), "n" is number of
824 bits, and "f" is flow control ("r" for RTS or
825 omit it). Default is "9600n8".
827 See Documentation/serial-console.txt for more
829 Documentation/networking/netconsole.txt for an
832 uart[8250],io,<addr>[,options]
833 uart[8250],mmio,<addr>[,options]
834 uart[8250],mmio16,<addr>[,options]
835 uart[8250],mmio32,<addr>[,options]
836 uart[8250],0x<addr>[,options]
837 Start an early, polled-mode console on the 8250/16550
838 UART at the specified I/O port or MMIO address,
839 switching to the matching ttyS device later.
840 MMIO inter-register address stride is either 8-bit
841 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
842 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
843 to be equivalent to 'mmio'. 'options' are specified in
844 the same format described for ttyS above; if unspecified,
845 the h/w is not re-initialized.
847 hvc<n> Use the hypervisor console device <n>. This is for
848 both Xen and PowerPC hypervisors.
850 If the device connected to the port is not a TTY but a braille
851 device, prepend "brl," before the device type, for instance
853 For now, only VisioBraille is supported.
855 consoleblank= [KNL] The console blank (screen saver) timeout in
856 seconds. Defaults to 10*60 = 10mins. A value of 0
857 disables the blank timer.
860 [KNL] Change the default value for
861 /proc/<pid>/coredump_filter.
862 See also Documentation/filesystems/proc.txt.
864 cpuidle.off=1 [CPU_IDLE]
865 disable the cpuidle sub-system
868 [X86] Delay for N microsec between assert and de-assert
869 of APIC INIT to start processors. This delay occurs
870 on every CPU online, such as boot, and resume from suspend.
873 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
875 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
877 crashkernel=size[KMG][@offset[KMG]]
878 [KNL] Using kexec, Linux can switch to a 'crash kernel'
879 upon panic. This parameter reserves the physical
880 memory region [offset, offset + size] for that kernel
881 image. If '@offset' is omitted, then a suitable offset
882 is selected automatically. Check
883 Documentation/kdump/kdump.txt for further details.
885 crashkernel=range1:size1[,range2:size2,...][@offset]
886 [KNL] Same as above, but depends on the memory
887 in the running system. The syntax of range is
888 start-[end] where start and end are both
889 a memory unit (amount[KMG]). See also
890 Documentation/kdump/kdump.txt for an example.
892 crashkernel=size[KMG],high
893 [KNL, x86_64] range could be above 4G. Allow kernel
894 to allocate physical memory region from top, so could
895 be above 4G if system have more than 4G ram installed.
896 Otherwise memory region will be allocated below 4G, if
898 It will be ignored if crashkernel=X is specified.
899 crashkernel=size[KMG],low
900 [KNL, x86_64] range under 4G. When crashkernel=X,high
901 is passed, kernel could allocate physical memory region
902 above 4G, that cause second kernel crash on system
903 that require some amount of low memory, e.g. swiotlb
904 requires at least 64M+32K low memory, also enough extra
905 low memory is needed to make sure DMA buffers for 32-bit
906 devices won't run out. Kernel would try to allocate at
907 at least 256M below 4G automatically.
908 This one let user to specify own low range under 4G
909 for second kernel instead.
910 0: to disable low allocation.
911 It will be ignored when crashkernel=X,high is not used
912 or memory reserved is below 4G.
915 [KNL] Disable crypto self-tests
920 cs89x0_media= [HW,NET]
921 Format: { rj45 | aui | bnc }
924 See header of drivers/s390/block/dasd_devmap.c.
926 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
927 (one device per port)
928 Format: <port#>,<type>
929 See also Documentation/input/joystick-parport.txt
931 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
932 time. See Documentation/dynamic-debug-howto.txt for
933 details. Deprecated, see dyndbg.
935 debug [KNL] Enable kernel debugging (events log level).
938 [KNL] verbose self-tests
940 Print debugging info while doing the locking API
942 We default to 0 (no extra messages), setting it to
943 1 will print _a lot_ more information - normally
944 only useful to kernel developers.
946 debug_objects [KNL] Enable object debugging
949 [KNL] Disable object debugging
951 debug_guardpage_minorder=
952 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
953 parameter allows control of the order of pages that will
954 be intentionally kept free (and hence protected) by the
955 buddy allocator. Bigger value increase the probability
956 of catching random memory corruption, but reduce the
957 amount of memory for normal system use. The maximum
958 possible value is MAX_ORDER/2. Setting this parameter
959 to 1 or 2 should be enough to identify most random
960 memory corruption problems caused by bugs in kernel or
961 driver code when a CPU writes to (or reads from) a
962 random memory location. Note that there exists a class
963 of memory corruptions problems caused by buggy H/W or
964 F/W or by drivers badly programing DMA (basically when
965 memory is written at bus level and the CPU MMU is
966 bypassed) which are not detectable by
967 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
968 tracking down these problems.
971 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
972 parameter enables the feature at boot time. In
973 default, it is disabled. We can avoid allocating huge
974 chunk of memory for debug pagealloc if we don't enable
975 it at boot time and the system will work mostly same
976 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
977 on: enable the feature
979 debugpat [X86] Enable PAT debugging
981 decnet.addr= [HW,NET]
982 Format: <area>[,<node>]
983 See also Documentation/networking/decnet.txt.
986 [same as hugepagesz=] The size of the default
987 HugeTLB page size. This is the size represented by
988 the legacy /proc/ hugepages APIs, used for SHM, and
989 default size when mounting hugetlbfs filesystems.
990 Defaults to the default architecture's huge page size
994 Set number of hash buckets for dentry cache.
996 disable_1tb_segments [PPC]
997 Disables the use of 1TB hash page table segments. This
998 causes the kernel to fall back to 256MB segments which
999 can be useful when debugging issues that require an SLB
1003 See Documentation/networking/ipv6.txt.
1006 Disable RADIX MMU mode on POWER9
1008 disable_cpu_apicid= [X86,APIC,SMP]
1010 The number of initial APIC ID for the
1011 corresponding CPU to be disabled at boot,
1012 mostly used for the kdump 2nd kernel to
1013 disable BSP to wake up multiple CPUs without
1014 causing system reset or hang due to sending
1015 INIT from AP to BSP.
1017 disable_ddw [PPC/PSERIES]
1018 Disable Dynamic DMA Window support. Use this if
1019 to workaround buggy firmware.
1021 disable_ipv6= [IPV6]
1022 See Documentation/networking/ipv6.txt.
1024 disable_mtrr_cleanup [X86]
1025 The kernel tries to adjust MTRR layout from continuous
1026 to discrete, to make X server driver able to add WB
1027 entry later. This parameter disables that.
1029 disable_mtrr_trim [X86, Intel and AMD only]
1030 By default the kernel will trim any uncacheable
1031 memory out of your available memory pool based on
1032 MTRR settings. This parameter disables that behavior,
1033 possibly causing your machine to run very slowly.
1035 disable_timer_pin_1 [X86]
1036 Disable PIN 1 of APIC timer
1037 Can be useful to work around chipset bugs.
1039 dis_ucode_ldr [X86] Disable the microcode loader.
1041 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1042 this option disables the debugging code at boot.
1044 dma_debug_entries=<number>
1045 This option allows to tune the number of preallocated
1046 entries for DMA-API debugging code. One entry is
1047 required per DMA-API allocation. Use this if the
1048 DMA-API debugging code disables itself because the
1049 architectural default is too low.
1051 dma_debug_driver=<driver_name>
1052 With this option the DMA-API debugging driver
1053 filter feature can be enabled at boot time. Just
1054 pass the driver to filter for as the parameter.
1055 The filter can be disabled or changed to another
1056 driver later using sysfs.
1058 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1059 Broken monitors, graphic adapters, KVMs and EDIDless
1060 panels may send no or incorrect EDID data sets.
1061 This parameter allows to specify an EDID data sets
1062 in the /lib/firmware directory that are used instead.
1063 Generic built-in EDID data sets are used, if one of
1064 edid/1024x768.bin, edid/1280x1024.bin,
1065 edid/1680x1050.bin, or edid/1920x1080.bin is given
1066 and no file with the same name exists. Details and
1067 instructions how to build your own EDID data are
1068 available in Documentation/EDID/HOWTO.txt. An EDID
1069 data set will only be used for a particular connector,
1070 if its name and a colon are prepended to the EDID
1071 name. Each connector may use a unique EDID data
1072 set by separating the files with a comma. An EDID
1073 data set with no connector name will be used for
1074 any connectors not explicitly specified.
1078 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1079 module.dyndbg[="val"]
1080 Enable debug messages at boot time. See
1081 Documentation/dynamic-debug-howto.txt for details.
1083 nompx [X86] Disables Intel Memory Protection Extensions.
1084 See Documentation/x86/intel_mpx.txt for more
1085 information about the feature.
1087 nopku [X86] Disable Memory Protection Keys CPU feature found
1090 module.async_probe [KNL]
1091 Enable asynchronous probe on this module.
1093 early_ioremap_debug [KNL]
1094 Enable debug messages in early_ioremap support. This
1095 is useful for tracking down temporary early mappings
1096 which are not unmapped.
1098 earlycon= [KNL] Output early console device and options.
1100 When used with no options, the early console is
1101 determined by the stdout-path property in device
1104 cdns,<addr>[,options]
1105 Start an early, polled-mode console on a Cadence
1106 (xuartps) serial port at the specified address. Only
1107 supported option is baud rate. If baud rate is not
1108 specified, the serial port must already be setup and
1111 uart[8250],io,<addr>[,options]
1112 uart[8250],mmio,<addr>[,options]
1113 uart[8250],mmio32,<addr>[,options]
1114 uart[8250],mmio32be,<addr>[,options]
1115 uart[8250],0x<addr>[,options]
1116 Start an early, polled-mode console on the 8250/16550
1117 UART at the specified I/O port or MMIO address.
1118 MMIO inter-register address stride is either 8-bit
1119 (mmio) or 32-bit (mmio32 or mmio32be).
1120 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1121 to be equivalent to 'mmio'. 'options' are specified
1122 in the same format described for "console=ttyS<n>"; if
1123 unspecified, the h/w is not initialized.
1127 Start an early, polled-mode console on a pl011 serial
1128 port at the specified address. The pl011 serial port
1129 must already be setup and configured. Options are not
1130 yet supported. If 'mmio32' is specified, then only
1131 the driver will use only 32-bit accessors to read/write
1132 the device registers.
1135 Start an early, polled-mode console on a meson serial
1136 port at the specified address. The serial port must
1137 already be setup and configured. Options are not yet
1141 Start an early, polled-mode console on an msm serial
1142 port at the specified address. The serial port
1143 must already be setup and configured. Options are not
1146 msm_serial_dm,<addr>
1147 Start an early, polled-mode console on an msm serial
1148 dm port at the specified address. The serial port
1149 must already be setup and configured. Options are not
1152 smh Use ARM semihosting calls for early console.
1160 Use early console provided by serial driver available
1161 on Samsung SoCs, requires selecting proper type and
1162 a correct base address of the selected UART port. The
1163 serial port must already be setup and configured.
1164 Options are not yet supported.
1168 Use early console provided by Freescale LP UART driver
1169 found on Freescale Vybrid and QorIQ LS1021A processors.
1170 A valid base address must be provided, and the serial
1171 port must already be setup and configured.
1173 armada3700_uart,<addr>
1174 Start an early, polled-mode console on the
1175 Armada 3700 serial port at the specified
1176 address. The serial port must already be setup
1177 and configured. Options are not yet supported.
1179 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1183 earlyprintk=serial[,ttySn[,baudrate]]
1184 earlyprintk=serial[,0x...[,baudrate]]
1185 earlyprintk=ttySn[,baudrate]
1186 earlyprintk=dbgp[debugController#]
1187 earlyprintk=pciserial,bus:device.function[,baudrate]
1189 earlyprintk is useful when the kernel crashes before
1190 the normal console is initialized. It is not enabled by
1191 default because it has some cosmetic problems.
1193 Append ",keep" to not disable it when the real console
1196 Only one of vga, efi, serial, or usb debug port can
1199 Currently only ttyS0 and ttyS1 may be specified by
1200 name. Other I/O ports may be explicitly specified
1201 on some architectures (x86 and arm at least) by
1202 replacing ttySn with an I/O port address, like this:
1203 earlyprintk=serial,0x1008,115200
1204 You can find the port for a given device in
1205 /proc/tty/driver/serial:
1206 2: uart:ST16650V2 port:00001008 irq:18 ...
1208 Interaction with the standard serial driver is not
1211 The VGA and EFI output is eventually overwritten by
1214 The xen output can only be used by Xen PV guests.
1216 edac_report= [HW,EDAC] Control how to report EDAC event
1217 Format: {"on" | "off" | "force"}
1218 on: enable EDAC to report H/W event. May be overridden
1219 by other higher priority error reporting module.
1220 off: disable H/W event reporting through EDAC.
1221 force: enforce the use of EDAC to report H/W event.
1224 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1227 This is designed to be used in conjunction with
1228 the boot argument: earlyprintk=vga
1231 Format: {"off" | "on" | "skip[mbr]"}
1234 Format: { "old_map", "nochunk", "noruntime", "debug" }
1235 old_map [X86-64]: switch to the old ioremap-based EFI
1236 runtime services mapping. 32-bit still uses this one by
1238 nochunk: disable reading files in "chunks" in the EFI
1239 boot stub, as chunking can cause problems with some
1240 firmware implementations.
1241 noruntime : disable EFI runtime services support
1242 debug: enable misc debug output
1244 efi_no_storage_paranoia [EFI; X86]
1245 Using this parameter you can use more than 50% of
1246 your efi variable storage. Use this parameter only if
1247 you are really sure that your UEFI does sane gc and
1248 fulfills the spec otherwise your board may brick.
1250 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1251 Add arbitrary attribute to specific memory range by
1252 updating original EFI memory map.
1253 Region of memory which aa attribute is added to is
1255 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1256 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1257 attribute is added to range 0x100000000-0x180000000 and
1258 0x10a0000000-0x1120000000.
1260 Using this parameter you can do debugging of EFI memmap
1261 related feature. For example, you can do debugging of
1262 Address Range Mirroring feature even if your box
1265 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1266 that is to be dynamically loaded by Linux. If there are
1267 multiple variables with the same name but with different
1268 vendor GUIDs, all of them will be loaded. See
1269 Documentation/acpi/ssdt-overlays.txt for details.
1272 eisa_irq_edge= [PARISC,HW]
1273 See header of drivers/parisc/eisa.c.
1276 See comment before function elanfreq_setup() in
1277 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1280 Format: {"cfq" | "deadline" | "noop"}
1281 See Documentation/block/cfq-iosched.txt and
1282 Documentation/block/deadline-iosched.txt for details.
1284 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1285 Specifies physical address of start of kernel core
1286 image elf header and optionally the size. Generally
1287 kexec loader will pass this option to capture kernel.
1288 See Documentation/kdump/kdump.txt for details.
1290 enable_mtrr_cleanup [X86]
1291 The kernel tries to adjust MTRR layout from continuous
1292 to discrete, to make X server driver able to add WB
1293 entry later. This parameter enables that.
1295 enable_timer_pin_1 [X86]
1296 Enable PIN 1 of APIC timer
1297 Can be useful to work around chipset bugs
1298 (in particular on some ATI chipsets).
1299 The kernel tries to set a reasonable default.
1301 enforcing [SELINUX] Set initial enforcing status.
1303 See security/selinux/Kconfig help text.
1304 0 -- permissive (log only, no denials).
1305 1 -- enforcing (deny and log).
1307 Value can be changed at runtime via /selinux/enforce.
1310 Disable Error Record Serialization Table (ERST)
1313 ether= [HW,NET] Ethernet cards parameters
1314 This option is obsoleted by the "netdev=" option, which
1315 has equivalent usage. See its documentation for details.
1319 Permit 'security.evm' to be updated regardless of
1320 current integrity status.
1324 fail_make_request=[KNL]
1325 General fault injection mechanism.
1326 Format: <interval>,<probability>,<space>,<times>
1327 See also Documentation/fault-injection/.
1330 See Documentation/blockdev/floppy.txt.
1332 force_pal_cache_flush
1333 [IA-64] Avoid check_sal_cache_flush which may hang on
1334 buggy SAL_CACHE_FLUSH implementations. Using this
1335 parameter will force ia64_sal_cache_flush to call
1336 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1339 Forcefully enable Physical Address Extension (PAE).
1340 Many Pentium M systems disable PAE but may have a
1341 functionally usable PAE implementation.
1342 Warning: use of this parameter will taint the kernel
1343 and may cause unknown problems.
1346 [FTRACE] will set and start the specified tracer
1347 as early as possible in order to facilitate early
1350 ftrace_dump_on_oops[=orig_cpu]
1351 [FTRACE] will dump the trace buffers on oops.
1352 If no parameter is passed, ftrace will dump
1353 buffers of all CPUs, but if you pass orig_cpu, it will
1354 dump only the buffer of the CPU that triggered the
1357 ftrace_filter=[function-list]
1358 [FTRACE] Limit the functions traced by the function
1359 tracer at boot up. function-list is a comma separated
1360 list of functions. This list can be changed at run
1361 time by the set_ftrace_filter file in the debugfs
1364 ftrace_notrace=[function-list]
1365 [FTRACE] Do not trace the functions specified in
1366 function-list. This list can be changed at run time
1367 by the set_ftrace_notrace file in the debugfs
1370 ftrace_graph_filter=[function-list]
1371 [FTRACE] Limit the top level callers functions traced
1372 by the function graph tracer at boot up.
1373 function-list is a comma separated list of functions
1374 that can be changed at run time by the
1375 set_graph_function file in the debugfs tracing directory.
1377 ftrace_graph_notrace=[function-list]
1378 [FTRACE] Do not trace from the functions specified in
1379 function-list. This list is a comma separated list of
1380 functions that can be changed at run time by the
1381 set_graph_notrace file in the debugfs tracing directory.
1384 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1385 support via parallel port (up to 5 devices per port)
1386 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1387 See also Documentation/input/joystick-parport.txt
1391 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1395 gcov_persist= [GCOV] When non-zero (default), profiling data for
1396 kernel modules is saved and remains accessible via
1397 debugfs, even when the module is unloaded/reloaded.
1398 When zero, profiling data is discarded and associated
1399 debugfs files are removed at module unload time.
1401 goldfish [X86] Enable the goldfish android emulator platform.
1402 Don't use this when you are not running on the
1405 gpt [EFI] Forces disk with valid GPT signature but
1406 invalid Protective MBR to be treated as GPT. If the
1407 primary GPT is corrupted, it enables the backup/alternate
1408 GPT to be used instead.
1410 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1411 the "Enable 0" bit of the configuration register.
1414 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1415 the "Enable 0" bit of the configuration register.
1418 grcan.select= [HW] Select which physical interface to use.
1421 grcan.txsize= [HW] Sets the size of the tx buffer.
1422 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1424 grcan.rxsize= [HW] Sets the size of the rx buffer.
1425 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1428 gpio-mockup.gpio_mockup_ranges
1429 [HW] Sets the ranges of gpiochip of for this device.
1430 Format: <start1>,<end1>,<start2>,<end2>...
1432 hardlockup_all_cpu_backtrace=
1433 [KNL] Should the hard-lockup detector generate
1434 backtraces on all cpus.
1437 hashdist= [KNL,NUMA] Large hashes allocated during boot
1438 are distributed across NUMA nodes. Defaults on
1439 for 64-bit NUMA, off otherwise.
1440 Format: 0 | 1 (for off | on)
1442 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1444 hd= [EIDE] (E)IDE hard drive subsystem geometry
1445 Format: <cyl>,<head>,<sect>
1448 Disable Hardware Error Source Table (HEST) support;
1449 corresponding firmware-first mode error processing
1450 logic will be disabled.
1452 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1453 size of <nn>. This works even on boxes that have no
1454 highmem otherwise. This also works to reduce highmem
1455 size on bigger boxes.
1457 highres= [KNL] Enable/disable high resolution timer mode.
1458 Valid parameters: "on", "off"
1462 See Documentation/isdn/README.HiSax.
1466 hpet= [X86-32,HPET] option to control HPET usage
1467 Format: { enable (default) | disable | force |
1469 disable: disable HPET and use PIT instead
1470 force: allow force enabled of undocumented chips (ICH4,
1472 verbose: show contents of HPET registers during setup
1474 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1475 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1477 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1478 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1479 On x86-64 and powerpc, this option can be specified
1480 multiple times interleaved with hugepages= to reserve
1481 huge pages of different sizes. Valid pages sizes on
1482 x86-64 are 2M (when the CPU supports "pse") and 1G
1483 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1485 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1486 terminal devices. Valid values: 0..8
1487 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1488 If specified, z/VM IUCV HVC accepts connections
1489 from listed z/VM user IDs only.
1491 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1492 hardware thread id mappings.
1493 Format: <cpu>:<hwthread>
1496 Do not unregister boot console at start. This is only
1497 useful for debugging when something happens in the window
1498 between unregistering the boot console and initializing
1501 i2c_bus= [HW] Override the default board specific I2C bus speed
1502 or register an additional I2C bus that is not
1503 registered from board initialization code.
1507 i8042.debug [HW] Toggle i8042 debug mode
1508 i8042.unmask_kbd_data
1509 [HW] Enable printing of interrupt data from the KBD port
1510 (disabled by default, and as a pre-condition
1511 requires that i8042.debug=1 be enabled)
1512 i8042.direct [HW] Put keyboard port into non-translated mode
1513 i8042.dumbkbd [HW] Pretend that controller can only read data from
1514 keyboard and cannot control its state
1515 (Don't attempt to blink the leds)
1516 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1517 i8042.nokbd [HW] Don't check/create keyboard port
1518 i8042.noloop [HW] Disable the AUX Loopback command while probing
1520 i8042.nomux [HW] Don't check presence of an active multiplexing
1522 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1524 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1525 i8042.reset [HW] Reset the controller during init, cleanup and
1526 suspend-to-ram transitions, only during s2r
1527 transitions, or never reset
1528 Format: { 1 | Y | y | 0 | N | n }
1529 1, Y, y: always reset controller
1530 0, N, n: don't ever reset controller
1531 Default: only on s2r transitions on x86; most other
1532 architectures force reset to be always executed
1533 i8042.unlock [HW] Unlock (ignore) the keylock
1534 i8042.kbdreset [HW] Reset device connected to KBD port
1538 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1539 indicates that the driver is running on unsupported
1541 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1542 does not match list of supported models.
1544 [HW] Report power status in /proc/i8k
1545 (disabled by default)
1546 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1549 i915.invert_brightness=
1550 [DRM] Invert the sense of the variable that is used to
1551 set the brightness of the panel backlight. Normally a
1552 brightness value of 0 indicates backlight switched off,
1553 and the maximum of the brightness value sets the backlight
1554 to maximum brightness. If this parameter is set to 0
1555 (default) and the machine requires it, or this parameter
1556 is set to 1, a brightness value of 0 sets the backlight
1557 to maximum brightness, and the maximum of the brightness
1558 value switches the backlight off.
1559 -1 -- never invert brightness
1560 0 -- machine default
1561 1 -- force brightness inversion
1564 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1566 ide-core.nodma= [HW] (E)IDE subsystem
1567 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1568 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1569 .cdrom .chs .ignore_cable are additional options
1570 See Documentation/ide/ide.txt.
1572 ide-generic.probe-mask= [HW] (E)IDE subsystem
1574 Probe mask for legacy ISA IDE ports. Depending on
1575 platform up to 6 ports are supported, enabled by
1576 setting corresponding bits in the mask to 1. The
1577 default value is 0x0, which has a special meaning.
1578 On systems that have PCI, it triggers scanning the
1579 PCI bus for the first and the second port, which
1580 are then probed. On systems without PCI the value
1581 of 0x0 enables probing the two first ports as if it
1584 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1585 Claim all unknown PCI IDE storage controllers.
1588 Format: idle=poll, idle=halt, idle=nomwait
1589 Poll forces a polling idle loop that can slightly
1590 improve the performance of waking up a idle CPU, but
1591 will use a lot of power and make the system run hot.
1593 idle=halt: Halt is forced to be used for CPU idle.
1594 In such case C2/C3 won't be used again.
1595 idle=nomwait: Disable mwait for CPU C-states
1597 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1598 Format: { strict | legacy | 2008 | relaxed }
1601 Choose which programs will be accepted for execution
1602 based on the IEEE 754 NaN encoding(s) supported by
1603 the FPU and the NaN encoding requested with the value
1604 of an ELF file header flag individually set by each
1605 binary. Hardware implementations are permitted to
1606 support either or both of the legacy and the 2008 NaN
1609 Available settings are as follows:
1610 strict accept binaries that request a NaN encoding
1611 supported by the FPU
1612 legacy only accept legacy-NaN binaries, if supported
1614 2008 only accept 2008-NaN binaries, if supported
1616 relaxed accept any binaries regardless of whether
1617 supported by the FPU
1619 The FPU emulator is always able to support both NaN
1620 encodings, so if no FPU hardware is present or it has
1621 been disabled with 'nofpu', then the settings of
1622 'legacy' and '2008' strap the emulator accordingly,
1623 'relaxed' straps the emulator for both legacy-NaN and
1624 2008-NaN, whereas 'strict' enables legacy-NaN only on
1625 legacy processors and both NaN encodings on MIPS32 or
1628 The setting for ABS.fmt/NEG.fmt instruction execution
1629 mode generally follows that for the NaN encoding,
1630 except where unsupported by hardware.
1632 ignore_loglevel [KNL]
1633 Ignore loglevel setting - this will print /all/
1634 kernel messages to the console. Useful for debugging.
1635 We also add it as printk module parameter, so users
1636 could change it dynamically, usually by
1637 /sys/module/printk/parameters/ignore_loglevel.
1640 Ignore RLIMIT_DATA setting for data mappings,
1641 print warning at first misuse. Can be changed via
1642 /sys/module/kernel/parameters/ignore_rlimit_data.
1644 ihash_entries= [KNL]
1645 Set number of hash buckets for inode cache.
1647 ima_appraise= [IMA] appraise integrity measurements
1648 Format: { "off" | "enforce" | "fix" | "log" }
1651 ima_appraise_tcb [IMA]
1652 The builtin appraise policy appraises all files
1656 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1660 The list of supported hash algorithms is defined
1661 in crypto/hash_info.h.
1664 The builtin measurement policy to load during IMA
1665 setup. Specyfing "tcb" as the value, measures all
1666 programs exec'd, files mmap'd for exec, and all files
1667 opened with the read mode bit set by either the
1668 effective uid (euid=0) or uid=0.
1671 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1672 Load a policy which meets the needs of the Trusted
1673 Computing Base. This means IMA will measure all
1674 programs exec'd, files mmap'd for exec, and all files
1675 opened for read by uid=0.
1678 Select one of defined IMA measurements template formats.
1679 Formats: { "ima" | "ima-ng" | "ima-sig" }
1683 [IMA] Define a custom template format.
1684 Format: { "field1|...|fieldN" }
1686 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1687 Format: <min_file_size>
1688 Set the minimal file size for using asynchronous hash.
1689 If left unspecified, ahash usage is disabled.
1691 ahash performance varies for different data sizes on
1692 different crypto accelerators. This option can be used
1693 to achieve the best performance for a particular HW.
1695 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1697 Set hashing buffer size. Default: 4k.
1699 ahash performance varies for different chunk sizes on
1700 different crypto accelerators. This option can be used
1701 to achieve best performance for particular HW.
1705 Run specified binary instead of /sbin/init as init
1708 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1709 for working out where the kernel is dying during
1712 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1713 initcall functions. Useful for debugging built-in
1714 modules and initcalls.
1716 initrd= [BOOT] Specify the location of the initial ramdisk
1718 init_pkru= [x86] Specify the default memory protection keys rights
1719 register contents for all processes. 0x55555554 by
1720 default (disallow access to all but pkey 0). Can
1721 override in debugfs after boot.
1723 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1726 int_pln_enable [x86] Enable power limit notification interrupt
1728 integrity_audit=[IMA]
1729 Format: { "0" | "1" }
1730 0 -- basic integrity auditing messages. (Default)
1731 1 -- additional integrity auditing messages.
1733 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1735 Enable intel iommu driver.
1737 Disable intel iommu driver.
1738 igfx_off [Default Off]
1739 By default, gfx is mapped as normal device. If a gfx
1740 device has a dedicated DMAR unit, the DMAR unit is
1741 bypassed by not enabling DMAR with this option. In
1742 this case, gfx device will use physical address for
1745 With this option iommu will not optimize to look
1746 for io virtual address below 32-bit forcing dual
1747 address cycle on pci bus for cards supporting greater
1748 than 32-bit addressing. The default is to look
1749 for translation below 32-bit and if not available
1750 then look in the higher range.
1751 strict [Default Off]
1752 With this option on every unmap_single operation will
1753 result in a hardware IOTLB flush operation as opposed
1754 to batching them for performance.
1755 sp_off [Default Off]
1756 By default, super page will be supported if Intel IOMMU
1757 has the capability. With this option, super page will
1759 ecs_off [Default Off]
1760 By default, extended context tables will be supported if
1761 the hardware advertises that it has support both for the
1762 extended tables themselves, and also PASID support. With
1763 this option set, extended tables will not be used even
1764 on hardware which claims to support them.
1766 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1767 0 disables intel_idle and fall back on acpi_idle.
1768 1 to 9 specify maximum depth of C-state.
1772 Do not enable intel_pstate as the default
1773 scaling driver for the supported processors
1775 Enable intel_pstate on systems that prohibit it by default
1776 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1777 instead of acpi-cpufreq may disable platform features, such
1778 as thermal controls and power capping, that rely on ACPI
1779 P-States information being indicated to OSPM and therefore
1780 should be used with caution. This option does not work with
1781 processors that aren't supported by the intel_pstate driver
1782 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1784 Do not enable hardware P state control (HWP)
1787 Only load intel_pstate on systems which support
1788 hardware P state control (HWP) if available.
1790 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1791 Description Table, specifies preferred power management
1792 profile as "Enterprise Server" or "Performance Server",
1793 then this feature is turned on by default.
1795 intremap= [X86-64, Intel-IOMMU]
1796 on enable Interrupt Remapping (default)
1797 off disable Interrupt Remapping
1798 nosid disable Source ID checking
1800 BIOS x2APIC opt-out request will be ignored
1801 nopost disable Interrupt Posting
1803 iomem= Disable strict checking of access to MMIO memory
1804 strict regions from userspace.
1819 nobypass [PPC/POWERNV]
1820 Disable IOMMU bypass, using IOMMU for PCI devices.
1823 io7= [HW] IO7 for Marvel based alpha systems
1824 See comment before marvel_specify_io7 in
1825 arch/alpha/kernel/core_marvel.c.
1827 io_delay= [X86] I/O delay method
1829 Standard port 0x80 based delay
1831 Alternate port 0xed based delay (needed on some systems)
1833 Simple two microseconds delay
1838 See Documentation/filesystems/nfs/nfsroot.txt.
1840 irqaffinity= [SMP] Set the default irq affinity mask
1841 The argument is a cpu list, as described above.
1844 When an interrupt is not handled search all handlers
1845 for it. Intended to get systems with badly broken
1849 When an interrupt is not handled search all handlers
1850 for it. Also check all handlers each timer
1851 interrupt. Intended to get systems with badly broken
1855 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1857 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1858 The argument is a cpu list, as described above.
1860 This option can be used to specify one or more CPUs
1861 to isolate from the general SMP balancing and scheduling
1862 algorithms. You can move a process onto or off an
1863 "isolated" CPU via the CPU affinity syscalls or cpuset.
1864 <cpu number> begins at 0 and the maximum value is
1865 "number of CPUs in system - 1".
1867 This option is the preferred way to isolate CPUs. The
1868 alternative -- manually setting the CPU mask of all
1869 tasks in the system -- can cause problems and
1870 suboptimal load balancer performance.
1874 ivrs_ioapic [HW,X86_64]
1875 Provide an override to the IOAPIC-ID<->DEVICE-ID
1876 mapping provided in the IVRS ACPI table. For
1877 example, to map IOAPIC-ID decimal 10 to
1878 PCI device 00:14.0 write the parameter as:
1879 ivrs_ioapic[10]=00:14.0
1881 ivrs_hpet [HW,X86_64]
1882 Provide an override to the HPET-ID<->DEVICE-ID
1883 mapping provided in the IVRS ACPI table. For
1884 example, to map HPET-ID decimal 0 to
1885 PCI device 00:14.0 write the parameter as:
1886 ivrs_hpet[0]=00:14.0
1888 ivrs_acpihid [HW,X86_64]
1889 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1890 mapping provided in the IVRS ACPI table. For
1891 example, to map UART-HID:UID AMD0020:0 to
1892 PCI device 00:14.5 write the parameter as:
1893 ivrs_acpihid[00:14.5]=AMD0020:0
1895 js= [HW,JOY] Analog joystick
1896 See Documentation/input/joystick.txt.
1899 When CONFIG_RANDOMIZE_BASE is set, this disables
1900 kernel and module base offset ASLR (Address Space
1901 Layout Randomization).
1905 kernelcore= [KNL,X86,IA-64,PPC]
1906 Format: nn[KMGTPE] | "mirror"
1908 specifies the amount of memory usable by the kernel
1909 for non-movable allocations. The requested amount is
1910 spread evenly throughout all nodes in the system. The
1911 remaining memory in each node is used for Movable
1912 pages. In the event, a node is too small to have both
1913 kernelcore and Movable pages, kernelcore pages will
1914 take priority and other nodes will have a larger number
1915 of Movable pages. The Movable zone is used for the
1916 allocation of pages that may be reclaimed or moved
1917 by the page migration subsystem. This means that
1918 HugeTLB pages may not be allocated from this zone.
1919 Note that allocations like PTEs-from-HighMem still
1920 use the HighMem zone if it exists, and the Normal
1921 zone if it does not.
1923 Instead of specifying the amount of memory (nn[KMGTPE]),
1924 you can specify "mirror" option. In case "mirror"
1925 option is specified, mirrored (reliable) memory is used
1926 for non-movable allocations and remaining memory is used
1927 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1928 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1931 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1932 Format: <Controller#>[,poll interval]
1933 The controller # is the number of the ehci usb debug
1934 port as it is probed via PCI. The poll interval is
1935 optional and is the number seconds in between
1936 each poll cycle to the debug port in case you need
1937 the functionality for interrupting the kernel with
1938 gdb or control-c on the dbgp connection. When
1939 not using this parameter you use sysrq-g to break into
1940 the kernel debugger.
1942 kgdboc= [KGDB,HW] kgdb over consoles.
1943 Requires a tty driver that supports console polling,
1944 or a supported polling keyboard driver (non-usb).
1945 Serial only format: <serial_device>[,baud]
1946 keyboard only format: kbd
1947 keyboard and serial format: kbd,<serial_device>[,baud]
1948 Optional Kernel mode setting:
1949 kms, kbd format: kms,kbd
1950 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1952 kgdbwait [KGDB] Stop kernel execution and enter the
1953 kernel debugger at the earliest opportunity.
1955 kmac= [MIPS] korina ethernet MAC address.
1956 Configure the RouterBoard 532 series on-chip
1957 Ethernet adapter MAC address.
1959 kmemleak= [KNL] Boot-time kmemleak enable/disable
1960 Valid arguments: on, off
1962 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1965 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1966 Valid arguments: 0, 1, 2
1967 kmemcheck=0 (disabled)
1968 kmemcheck=1 (enabled)
1969 kmemcheck=2 (one-shot mode)
1970 Default: 2 (one-shot mode)
1972 kpti= [ARM64] Control page table isolation of user
1973 and kernel address spaces.
1974 Default: enabled on cores which need mitigation.
1978 kstack=N [X86] Print N words from the kernel stack
1981 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1982 Default is 0 (don't ignore, but inject #GP)
1984 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1989 [KVM] Controls the software workaround for the
1990 X86_BUG_ITLB_MULTIHIT bug.
1991 force : Always deploy workaround.
1992 off : Never deploy workaround.
1993 auto : Deploy workaround based on the presence of
1994 X86_BUG_ITLB_MULTIHIT.
1998 If the software workaround is enabled for the host,
1999 guests do need not to enable it for nested guests.
2001 kvm.nx_huge_pages_recovery_ratio=
2002 [KVM] Controls how many 4KiB pages are periodically zapped
2003 back to huge pages. 0 disables the recovery, otherwise if
2004 the value is N KVM will zap 1/Nth of the 4KiB pages every
2005 minute. The default is 60.
2007 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2008 Default is 1 (enabled)
2010 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2012 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2014 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2015 (virtualized MMU) support on capable Intel chips.
2016 Default is 1 (enabled)
2018 kvm-intel.emulate_invalid_guest_state=
2019 [KVM,Intel] Enable emulation of invalid guest states
2020 Default is 0 (disabled)
2022 kvm-intel.flexpriority=
2023 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2024 Default is 1 (enabled)
2027 [KVM,Intel] Enable VMX nesting (nVMX).
2028 Default is 0 (disabled)
2030 kvm-intel.unrestricted_guest=
2031 [KVM,Intel] Disable unrestricted guest feature
2032 (virtualized real and unpaged mode) on capable
2033 Intel chips. Default is 1 (enabled)
2035 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2038 Valid arguments: never, cond, always
2040 always: L1D cache flush on every VMENTER.
2041 cond: Flush L1D on VMENTER only when the code between
2042 VMEXIT and VMENTER can leak host memory.
2043 never: Disables the mitigation
2045 Default is cond (do L1 cache flush in specific instances)
2047 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2048 feature (tagged TLBs) on capable Intel chips.
2049 Default is 1 (enabled)
2051 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2054 The kernel PTE inversion protection is unconditionally
2055 enabled and cannot be disabled.
2058 Provides all available mitigations for the
2059 L1TF vulnerability. Disables SMT and
2060 enables all mitigations in the
2061 hypervisors, i.e. unconditional L1D flush.
2063 SMT control and L1D flush control via the
2064 sysfs interface is still possible after
2065 boot. Hypervisors will issue a warning
2066 when the first VM is started in a
2067 potentially insecure configuration,
2068 i.e. SMT enabled or L1D flush disabled.
2071 Same as 'full', but disables SMT and L1D
2072 flush runtime control. Implies the
2073 'nosmt=force' command line option.
2074 (i.e. sysfs control of SMT is disabled.)
2077 Leaves SMT enabled and enables the default
2078 hypervisor mitigation, i.e. conditional
2081 SMT control and L1D flush control via the
2082 sysfs interface is still possible after
2083 boot. Hypervisors will issue a warning
2084 when the first VM is started in a
2085 potentially insecure configuration,
2086 i.e. SMT enabled or L1D flush disabled.
2090 Disables SMT and enables the default
2091 hypervisor mitigation.
2093 SMT control and L1D flush control via the
2094 sysfs interface is still possible after
2095 boot. Hypervisors will issue a warning
2096 when the first VM is started in a
2097 potentially insecure configuration,
2098 i.e. SMT enabled or L1D flush disabled.
2101 Same as 'flush', but hypervisors will not
2102 warn when a VM is started in a potentially
2103 insecure configuration.
2106 Disables hypervisor mitigations and doesn't
2108 It also drops the swap size and available
2109 RAM limit restriction on both hypervisor and
2114 For details see: Documentation/hw-vuln/l1tf.rst
2120 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2123 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2124 value for LAPIC timer one-shot implementation. Default
2125 back to the programmable timer unit in the LAPIC.
2127 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2130 libata.dma= [LIBATA] DMA control
2131 libata.dma=0 Disable all PATA and SATA DMA
2132 libata.dma=1 PATA and SATA Disk DMA only
2133 libata.dma=2 ATAPI (CDROM) DMA only
2134 libata.dma=4 Compact Flash DMA only
2135 Combinations also work, so libata.dma=3 enables DMA
2136 for disks and CDROMs, but not CFs.
2138 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2139 libata.ignore_hpa=0 keep BIOS limits (default)
2140 libata.ignore_hpa=1 ignore limits, using full disk
2142 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2146 libata.force= [LIBATA] Force configurations. The format is comma
2147 separated list of "[ID:]VAL" where ID is
2148 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2149 matching port, link or device. Basically, it matches
2150 the ATA ID string printed on console by libata. If
2151 the whole ID part is omitted, the last PORT and DEVICE
2152 values are used. If ID hasn't been specified yet, the
2153 configuration applies to all ports, links and devices.
2155 If only DEVICE is omitted, the parameter applies to
2156 the port and all links and devices behind it. DEVICE
2157 number of 0 either selects the first device or the
2158 first fan-out link behind PMP device. It does not
2159 select the host link. DEVICE number of 15 selects the
2160 host link and device attached to it.
2162 The VAL specifies the configuration to force. As long
2163 as there's no ambiguity shortcut notation is allowed.
2164 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2165 The following configurations can be forced.
2167 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2168 Any ID with matching PORT is used.
2170 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2172 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2173 udma[/][16,25,33,44,66,100,133] notation is also
2176 * [no]ncq: Turn on or off NCQ.
2178 * [no]ncqtrim: Turn off queued DSM TRIM.
2180 * nohrst, nosrst, norst: suppress hard, soft
2183 * rstonce: only attempt one reset during
2184 hot-unplug link recovery
2186 * dump_id: dump IDENTIFY data.
2188 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2190 * disable: Disable this device.
2192 If there are multiple matching configurations changing
2193 the same attribute, the last one is used.
2195 memblock=debug [KNL] Enable memblock debug messages.
2197 load_ramdisk= [RAM] List of ramdisks to load from floppy
2198 See Documentation/blockdev/ramdisk.txt.
2200 lockd.nlm_grace_period=P [NFS] Assign grace period.
2203 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2206 lockd.nlm_timeout=T [NFS] Assign timeout value.
2209 lockd.nlm_udpport=M [NFS] Assign UDP port.
2212 locktorture.nreaders_stress= [KNL]
2213 Set the number of locking read-acquisition kthreads.
2214 Defaults to being automatically set based on the
2215 number of online CPUs.
2217 locktorture.nwriters_stress= [KNL]
2218 Set the number of locking write-acquisition kthreads.
2220 locktorture.onoff_holdoff= [KNL]
2221 Set time (s) after boot for CPU-hotplug testing.
2223 locktorture.onoff_interval= [KNL]
2224 Set time (s) between CPU-hotplug operations, or
2225 zero to disable CPU-hotplug testing.
2227 locktorture.shuffle_interval= [KNL]
2228 Set task-shuffle interval (jiffies). Shuffling
2229 tasks allows some CPUs to go into dyntick-idle
2230 mode during the locktorture test.
2232 locktorture.shutdown_secs= [KNL]
2233 Set time (s) after boot system shutdown. This
2234 is useful for hands-off automated testing.
2236 locktorture.stat_interval= [KNL]
2237 Time (s) between statistics printk()s.
2239 locktorture.stutter= [KNL]
2240 Time (s) to stutter testing, for example,
2241 specifying five seconds causes the test to run for
2242 five seconds, wait for five seconds, and so on.
2243 This tests the locking primitive's ability to
2244 transition abruptly to and from idle.
2246 locktorture.torture_runnable= [BOOT]
2247 Start locktorture running at boot time.
2249 locktorture.torture_type= [KNL]
2250 Specify the locking implementation to test.
2252 locktorture.verbose= [KNL]
2253 Enable additional printk() statements.
2255 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2258 loglevel= All Kernel Messages with a loglevel smaller than the
2259 console loglevel will be printed to the console. It can
2260 also be changed with klogd or other programs. The
2261 loglevels are defined as follows:
2263 0 (KERN_EMERG) system is unusable
2264 1 (KERN_ALERT) action must be taken immediately
2265 2 (KERN_CRIT) critical conditions
2266 3 (KERN_ERR) error conditions
2267 4 (KERN_WARNING) warning conditions
2268 5 (KERN_NOTICE) normal but significant condition
2269 6 (KERN_INFO) informational
2270 7 (KERN_DEBUG) debug-level messages
2272 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2273 in bytes. n must be a power of two and greater
2274 than the minimal size. The minimal size is defined
2275 by LOG_BUF_SHIFT kernel config parameter. There is
2276 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2277 that allows to increase the default size depending on
2278 the number of CPUs. See init/Kconfig for more details.
2280 logo.nologo [FB] Disables display of the built-in Linux logo.
2281 This may be used to provide more screen space for
2282 kernel log messages and is useful when debugging
2283 kernel boot problems.
2285 lp=0 [LP] Specify parallel ports to use, e.g,
2286 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2287 lp=reset first parallel port). 'lp=0' disables the
2288 lp=auto printer driver. 'lp=reset' (which can be
2289 specified in addition to the ports) causes
2290 attached printers to be reset. Using
2291 lp=port1,port2,... specifies the parallel ports
2292 to associate lp devices with, starting with
2293 lp0. A port specification may be 'none' to skip
2294 that lp device, or a parport name such as
2295 'parport0'. Specifying 'lp=auto' instead of a
2296 port specification list means that device IDs
2297 from each port should be examined, to see if
2298 an IEEE 1284-compliant printer is attached; if
2299 so, the driver will manage that printer.
2300 See also header of drivers/char/lp.c.
2303 Sets loops_per_jiffy to given constant, thus avoiding
2304 time-consuming boot-time autodetection (up to 250 ms per
2305 CPU). 0 enables autodetection (default). To determine
2306 the correct value for your kernel, boot with normal
2307 autodetection and see what value is printed. Note that
2308 on SMP systems the preset will be applied to all CPUs,
2309 which is likely to cause problems if your CPUs need
2310 significantly divergent settings. An incorrect value
2311 will cause delays in the kernel to be wrong, leading to
2312 unpredictable I/O errors and other breakage. Although
2313 unlikely, in the extreme case this might damage your
2317 Format: <io>,<irq>,<dma>
2319 machvec= [IA-64] Force the use of a particular machine-vector
2320 (machvec) in a generic kernel.
2321 Example: machvec=hpzx1_swiotlb
2323 machtype= [Loongson] Share the same kernel image file between different
2325 Example: machtype=lemote-yeeloong-2f-7inch
2327 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2328 than or equal to this physical address is ignored.
2330 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2331 will bring up during bootup. maxcpus=n : n >= 0 limits
2332 the kernel to bring up 'n' processors. Surely after
2333 bootup you can bring up the other plugged cpu by executing
2334 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2335 only takes effect during system bootup.
2336 While n=0 is a special case, it is equivalent to "nosmp",
2337 which also disables the IO APIC.
2339 max_loop= [LOOP] The number of loop block devices that get
2340 (loop.max_loop) unconditionally pre-created at init time. The default
2341 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2342 of statically allocating a predefined number, loop
2343 devices can be requested on-demand with the
2344 /dev/loop-control interface.
2346 mce [X86-32] Machine Check Exception
2348 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2350 md= [HW] RAID subsystems devices and level
2351 See Documentation/md.txt.
2354 Format: <first>,<last>
2355 Specifies range of consoles to be captured by the MDA.
2358 Control mitigation for the Micro-architectural Data
2359 Sampling (MDS) vulnerability.
2361 Certain CPUs are vulnerable to an exploit against CPU
2362 internal buffers which can forward information to a
2363 disclosure gadget under certain conditions.
2365 In vulnerable processors, the speculatively
2366 forwarded data can be used in a cache side channel
2367 attack, to access data to which the attacker does
2368 not have direct access.
2370 This parameter controls the MDS mitigation. The
2373 full - Enable MDS mitigation on vulnerable CPUs
2374 full,nosmt - Enable MDS mitigation and disable
2375 SMT on vulnerable CPUs
2376 off - Unconditionally disable MDS mitigation
2378 On TAA-affected machines, mds=off can be prevented by
2379 an active TAA mitigation as both vulnerabilities are
2380 mitigated with the same mechanism so in order to disable
2381 this mitigation, you need to specify tsx_async_abort=off
2384 Not specifying this option is equivalent to
2387 For details see: Documentation/hw-vuln/mds.rst
2389 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2390 Amount of memory to be used when the kernel is not able
2391 to see the whole system memory or for test.
2392 [X86] Work as limiting max address. Use together
2393 with memmap= to avoid physical address space collisions.
2394 Without memmap= PCI devices could be placed at addresses
2395 belonging to unused RAM.
2397 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2401 [KNL,SH] Allow user to override the default size for
2402 per-device physically contiguous DMA buffers.
2404 memhp_default_state=online/offline
2405 [KNL] Set the initial state for the memory hotplug
2406 onlining policy. If not specified, the default value is
2407 set according to the
2408 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2410 See Documentation/memory-hotplug.txt.
2412 memmap=exactmap [KNL,X86] Enable setting of an exact
2413 E820 memory map, as specified by the user.
2414 Such memmap=exactmap lines can be constructed based on
2415 BIOS output or other requirements. See the memmap=nn@ss
2418 memmap=nn[KMG]@ss[KMG]
2419 [KNL] Force usage of a specific region of memory.
2420 Region of memory to be used is from ss to ss+nn.
2422 memmap=nn[KMG]#ss[KMG]
2423 [KNL,ACPI] Mark specific memory as ACPI data.
2424 Region of memory to be marked is from ss to ss+nn.
2426 memmap=nn[KMG]$ss[KMG]
2427 [KNL,ACPI] Mark specific memory as reserved.
2428 Region of memory to be reserved is from ss to ss+nn.
2429 Example: Exclude memory from 0x18690000-0x1869ffff
2430 memmap=64K$0x18690000
2432 memmap=0x10000$0x18690000
2434 memmap=nn[KMG]!ss[KMG]
2435 [KNL,X86] Mark specific memory as protected.
2436 Region of memory to be used, from ss to ss+nn.
2437 The memory region may be marked as e820 type 12 (0xc)
2438 and is NVDIMM or ADR memory.
2440 memory_corruption_check=0/1 [X86]
2441 Some BIOSes seem to corrupt the first 64k of
2442 memory when doing things like suspend/resume.
2443 Setting this option will scan the memory
2444 looking for corruption. Enabling this will
2445 both detect corruption and prevent the kernel
2446 from using the memory being corrupted.
2447 However, its intended as a diagnostic tool; if
2448 repeatable BIOS-originated corruption always
2449 affects the same memory, you can use memmap=
2450 to prevent the kernel from using that memory.
2452 memory_corruption_check_size=size [X86]
2453 By default it checks for corruption in the low
2454 64k, making this memory unavailable for normal
2455 use. Use this parameter to scan for
2456 corruption in more or less memory.
2458 memory_corruption_check_period=seconds [X86]
2459 By default it checks for corruption every 60
2460 seconds. Use this parameter to check at some
2461 other rate. 0 disables periodic checking.
2463 memtest= [KNL,X86,ARM] Enable memtest
2465 default : 0 <disable>
2466 Specifies the number of memtest passes to be
2467 performed. Each pass selects another test
2468 pattern from a given set of patterns. Memtest
2469 fills the memory with this pattern, validates
2470 memory contents and reserves bad memory
2471 regions that are detected.
2473 meye.*= [HW] Set MotionEye Camera parameters
2474 See Documentation/video4linux/meye.txt.
2476 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2477 Multi-Function General Purpose Timers on AMD Geode
2480 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2481 the BIOS has incorrectly applied a workaround. TinyBIOS
2482 version 0.98 is known to be affected, 0.99 fixes the
2483 problem by letting the user disable the workaround.
2487 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2488 physical address is ignored.
2490 mini2440= [ARM,HW,KNL]
2491 Format:[0..2][b][c][t]
2493 MINI2440 configuration specification:
2494 0 - The attached screen is the 3.5" TFT
2495 1 - The attached screen is the 7" TFT
2496 2 - The VGA Shield is attached (1024x768)
2497 Leaving out the screen size parameter will not load
2498 the TFT driver, and the framebuffer will be left
2500 b - Enable backlight. The TFT backlight pin will be
2501 linked to the kernel VESA blanking code and a GPIO
2502 LED. This parameter is not necessary when using the
2504 c - Enable the s3c camera interface.
2505 t - Reserved for enabling touchscreen support. The
2506 touchscreen support is not enabled in the mainstream
2507 kernel as of 2.6.30, a preliminary port can be found
2508 in the "bleeding edge" mini2440 support kernel at
2509 http://repo.or.cz/w/linux-2.6/mini2440.git
2512 [X86] Control optional mitigations for CPU
2513 vulnerabilities. This is a set of curated,
2514 arch-independent options, each of which is an
2515 aggregation of existing arch-specific options.
2518 Disable all optional CPU mitigations. This
2519 improves system performance, but it may also
2520 expose users to several CPU vulnerabilities.
2521 Equivalent to: nopti [X86]
2524 spectre_v2_user=off [X86]
2525 spec_store_bypass_disable=off [X86]
2528 tsx_async_abort=off [X86]
2529 kvm.nx_huge_pages=off [X86]
2530 no_entry_flush [PPC]
2531 no_uaccess_flush [PPC]
2534 This does not have any effect on
2535 kvm.nx_huge_pages when
2536 kvm.nx_huge_pages=force.
2539 Mitigate all CPU vulnerabilities, but leave SMT
2540 enabled, even if it's vulnerable. This is for
2541 users who don't want to be surprised by SMT
2542 getting disabled across kernel upgrades, or who
2543 have other ways of avoiding SMT-based attacks.
2544 Equivalent to: (default behavior)
2547 Mitigate all CPU vulnerabilities, disabling SMT
2548 if needed. This is for users who always want to
2549 be fully mitigated, even if it means losing SMT.
2550 Equivalent to: l1tf=flush,nosmt [X86]
2551 mds=full,nosmt [X86]
2552 tsx_async_abort=full,nosmt [X86]
2555 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2556 parameter allows control of the logging verbosity for
2557 the additional memory initialisation checks. A value
2558 of 0 disables mminit logging and a level of 4 will
2559 log everything. Information is printed at KERN_DEBUG
2560 so loglevel=8 may also need to be specified.
2563 [KNL] When CONFIG_MODULE_SIG is set, this means that
2564 modules without (valid) signatures will fail to load.
2565 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2566 is always true, so this option does nothing.
2568 module_blacklist= [KNL] Do not load a comma-separated list of
2569 modules. Useful for debugging problem modules.
2572 [MOUSE] Maximum time between finger touching and
2573 leaving touchpad surface for touch to be considered
2574 a tap and be reported as a left button click (for
2575 touchpads working in absolute mode only).
2577 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2578 reporting absolute coordinates, such as tablets
2579 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2580 reporting absolute coordinates, such as tablets
2582 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2583 is similar to kernelcore except it specifies the
2584 amount of memory used for migratable allocations.
2585 If both kernelcore and movablecore is specified,
2586 then kernelcore will be at *least* the specified
2587 value but may be more. If movablecore on its own
2588 is specified, the administrator must be careful
2589 that the amount of memory usable for all allocations
2592 movable_node [KNL,X86] Boot-time switch to enable the effects
2593 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2595 MTD_Partition= [MTD]
2596 Format: <name>,<region-number>,<size>,<offset>
2598 MTD_Region= [MTD] Format:
2599 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2602 See drivers/mtd/cmdlinepart.c.
2604 multitce=off [PPC] This parameter disables the use of the pSeries
2605 firmware feature for updating multiple TCE entries
2608 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2610 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2612 boundary - index of last SLC block on Flex-OneNAND.
2613 The remaining blocks are configured as MLC blocks.
2614 lock - Configure if Flex-OneNAND boundary should be locked.
2615 Once locked, the boundary cannot be changed.
2616 1 indicates lock status, 0 indicates unlock status.
2619 ARM/S3C2412 JIVE boot control
2621 See arch/arm/mach-s3c2412/mach-jive.c
2623 mtouchusb.raw_coordinates=
2624 [HW] Make the MicroTouch USB driver use raw coordinates
2625 ('y', default) or cooked coordinates ('n')
2627 mtrr_chunk_size=nn[KMG] [X86]
2628 used for mtrr cleanup. It is largest continuous chunk
2629 that could hold holes aka. UC entries.
2631 mtrr_gran_size=nn[KMG] [X86]
2632 Used for mtrr cleanup. It is granularity of mtrr block.
2634 Large value could prevent small alignment from
2637 mtrr_spare_reg_nr=n [X86]
2639 Range: 0,7 : spare reg number
2641 Used for mtrr cleanup. It is spare mtrr entries number.
2642 Set to 2 or more if your graphical card needs more.
2644 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2646 netdev= [NET] Network devices parameters
2647 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2648 Note that mem_start is often overloaded to mean
2649 something different and driver-specific.
2650 This usage is only documented in each driver source
2654 [NETFILTER] Enable connection tracking flow accounting
2655 0 to disable accounting
2656 1 to enable accounting
2659 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2660 See Documentation/filesystems/nfs/nfsroot.txt.
2662 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2663 See Documentation/filesystems/nfs/nfsroot.txt.
2665 nfsrootdebug [NFS] enable nfsroot debugging messages.
2666 See Documentation/filesystems/nfs/nfsroot.txt.
2668 nfs.callback_nr_threads=
2669 [NFSv4] set the total number of threads that the
2670 NFS client will assign to service NFSv4 callback
2673 nfs.callback_tcpport=
2674 [NFS] set the TCP port on which the NFSv4 callback
2675 channel should listen.
2678 [NFS] sets the pathname to the program which is used
2679 to update the NFS client cache entries.
2681 nfs.cache_getent_timeout=
2682 [NFS] sets the timeout after which an attempt to
2683 update a cache entry is deemed to have failed.
2685 nfs.idmap_cache_timeout=
2686 [NFS] set the maximum lifetime for idmapper cache
2690 [NFS] enable 64-bit inode numbers.
2691 If zero, the NFS client will fake up a 32-bit inode
2692 number for the readdir() and stat() syscalls instead
2693 of returning the full 64-bit number.
2694 The default is to return 64-bit inode numbers.
2696 nfs.max_session_cb_slots=
2697 [NFSv4.1] Sets the maximum number of session
2698 slots the client will assign to the callback
2699 channel. This determines the maximum number of
2700 callbacks the client will process in parallel for
2701 a particular server.
2703 nfs.max_session_slots=
2704 [NFSv4.1] Sets the maximum number of session slots
2705 the client will attempt to negotiate with the server.
2706 This limits the number of simultaneous RPC requests
2707 that the client can send to the NFSv4.1 server.
2708 Note that there is little point in setting this
2709 value higher than the max_tcp_slot_table_limit.
2711 nfs.nfs4_disable_idmapping=
2712 [NFSv4] When set to the default of '1', this option
2713 ensures that both the RPC level authentication
2714 scheme and the NFS level operations agree to use
2715 numeric uids/gids if the mount is using the
2716 'sec=sys' security flavour. In effect it is
2717 disabling idmapping, which can make migration from
2718 legacy NFSv2/v3 systems to NFSv4 easier.
2719 Servers that do not support this mode of operation
2720 will be autodetected by the client, and it will fall
2721 back to using the idmapper.
2722 To turn off this behaviour, set the value to '0'.
2724 [NFS4] Specify an additional fixed unique ident-
2725 ification string that NFSv4 clients can insert into
2726 their nfs_client_id4 string. This is typically a
2727 UUID that is generated at system install time.
2729 nfs.send_implementation_id =
2730 [NFSv4.1] Send client implementation identification
2731 information in exchange_id requests.
2732 If zero, no implementation identification information
2734 The default is to send the implementation identification
2737 nfs.recover_lost_locks =
2738 [NFSv4] Attempt to recover locks that were lost due
2739 to a lease timeout on the server. Please note that
2740 doing this risks data corruption, since there are
2741 no guarantees that the file will remain unchanged
2742 after the locks are lost.
2743 If you want to enable the kernel legacy behaviour of
2744 attempting to recover these locks, then set this
2746 The default parameter value of '0' causes the kernel
2747 not to attempt recovery of lost locks.
2749 nfs4.layoutstats_timer =
2750 [NFSv4.2] Change the rate at which the kernel sends
2751 layoutstats to the pNFS metadata server.
2753 Setting this to value to 0 causes the kernel to use
2754 whatever value is the default set by the layout
2755 driver. A non-zero value sets the minimum interval
2756 in seconds between layoutstats transmissions.
2758 nfsd.nfs4_disable_idmapping=
2759 [NFSv4] When set to the default of '1', the NFSv4
2760 server will return only numeric uids and gids to
2761 clients using auth_sys, and will accept numeric uids
2762 and gids from such clients. This is intended to ease
2763 migration from NFSv2/v3.
2765 objlayoutdriver.osd_login_prog=
2766 [NFS] [OBJLAYOUT] sets the pathname to the program which
2767 is used to automatically discover and login into new
2768 osd-targets. Please see:
2769 Documentation/filesystems/pnfs.txt for more explanations
2771 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2772 when a NMI is triggered.
2773 Format: [state][,regs][,debounce][,die]
2775 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2776 Format: [panic,][nopanic,][num]
2778 0 - turn hardlockup detector in nmi_watchdog off
2779 1 - turn hardlockup detector in nmi_watchdog on
2780 When panic is specified, panic when an NMI watchdog
2781 timeout occurs (or 'nopanic' to override the opposite
2782 default). To disable both hard and soft lockup detectors,
2783 please see 'nowatchdog'.
2784 This is useful when you use a panic=... timeout and
2785 need the box quickly up again.
2787 netpoll.carrier_timeout=
2788 [NET] Specifies amount of time (in seconds) that
2789 netpoll should wait for a carrier. By default netpoll
2792 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2793 emulation library even if a 387 maths coprocessor
2797 [HW] Never suspend the console
2798 Disable suspending of consoles during suspend and
2799 hibernate operations. Once disabled, debugging
2800 messages can reach various consoles while the rest
2801 of the system is being put to sleep (ie, while
2802 debugging driver suspend/resume hooks). This may
2803 not work reliably with all consoles, but is known
2804 to work with serial and VGA consoles.
2805 To facilitate more flexible debugging, we also add
2806 console_suspend, a printk module parameter to control
2807 it. Users could use console_suspend (usually
2808 /sys/module/printk/parameters/console_suspend) to
2809 turn on/off it dynamically.
2811 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2812 caches in the slab allocator. Saves per-node memory,
2813 but will impact performance.
2817 noaltinstr [S390] Disables alternative instructions patching
2818 (CPU alternatives feature).
2820 noapic [SMP,APIC] Tells the kernel to not make use of any
2821 IOAPICs that may be present in the system.
2823 noautogroup Disable scheduler automatic task group creation.
2825 nobats [PPC] Do not use BATs for mapping kernel lowmem
2826 on "Classic" PPC cores.
2830 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2832 nodelayacct [KNL] Disable per-task delay accounting
2834 nodsp [SH] Disable hardware DSP at boot time.
2836 noefi Disable EFI runtime services support.
2838 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
2843 On X86-32 available only on PAE configured kernels.
2844 noexec=on: enable non-executable mappings (default)
2845 noexec=off: disable non-executable mappings
2848 Disable SMAP (Supervisor Mode Access Prevention)
2849 even if it is supported by processor.
2852 Disable SMEP (Supervisor Mode Execution Prevention)
2853 even if it is supported by processor.
2856 This affects only 32-bit executables.
2857 noexec32=on: enable non-executable mappings (default)
2858 read doesn't imply executable mappings
2859 noexec32=off: disable non-executable mappings
2860 read implies executable mappings
2862 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2864 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2865 register save and restore. The kernel will only save
2866 legacy floating-point registers on task switch.
2868 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2870 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2871 Equivalent to smt=1.
2873 [KNL,x86] Disable symmetric multithreading (SMT).
2874 nosmt=force: Force disable SMT, cannot be undone
2875 via the sysfs control file.
2877 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
2878 (bounds check bypass). With this option data leaks are
2879 possible in the system.
2881 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
2882 (indirect branch prediction) vulnerability. System may
2883 allow data leaks with this option, which is equivalent
2886 nospec_store_bypass_disable
2887 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2890 [PPC] Don't flush the L1-D cache after accessing user data.
2892 noxsave [BUGS=X86] Disables x86 extended register state save
2893 and restore using xsave. The kernel will fallback to
2894 enabling legacy floating-point and sse state.
2896 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2897 register states. The kernel will fall back to use
2898 xsave to save the states. By using this parameter,
2899 performance of saving the states is degraded because
2900 xsave doesn't support modified optimization while
2901 xsaveopt supports it on xsaveopt enabled systems.
2903 noxsaves [X86] Disables xsaves and xrstors used in saving and
2904 restoring x86 extended register state in compacted
2905 form of xsave area. The kernel will fall back to use
2906 xsaveopt and xrstor to save and restore the states
2907 in standard form of xsave area. By using this
2908 parameter, xsave area per process might occupy more
2909 memory on xsaves enabled systems.
2911 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2912 wfi(ARM) instruction doesn't work correctly and not to
2913 use it. This is also useful when using JTAG debugger.
2915 no_file_caps Tells the kernel not to honor file capabilities. The
2916 only way then for a file to be executed with privilege
2917 is to be setuid root or executed by root.
2919 nohalt [IA-64] Tells the kernel not to use the power saving
2920 function PAL_HALT_LIGHT when idle. This increases
2921 power-consumption. On the positive side, it reduces
2922 interrupt wake-up latency, which may improve performance
2923 in certain environments such as networked servers or
2926 nohibernate [HIBERNATION] Disable hibernation and resume.
2928 nohz= [KNL] Boottime enable/disable dynamic ticks
2929 Valid arguments: on, off
2932 nohz_full= [KNL,BOOT]
2933 The argument is a cpu list, as described above.
2934 In kernels built with CONFIG_NO_HZ_FULL=y, set
2935 the specified list of CPUs whose tick will be stopped
2936 whenever possible. The boot CPU will be forced outside
2937 the range to maintain the timekeeping.
2938 The CPUs in this range must also be included in the
2941 noiotrap [SH] Disables trapped I/O port accesses.
2943 noirqdebug [X86-32] Disables the code which attempts to detect and
2944 disable unhandled interrupt sources.
2946 no_timer_check [X86,APIC] Disables the code which tests for
2947 broken timer IRQ sources.
2949 noisapnp [ISAPNP] Disables ISA PnP code.
2951 noinitrd [RAM] Tells the kernel not to load any configured
2954 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2956 [Deprecated - use intremap=off]
2960 noinvpcid [X86] Disable the INVPCID cpu feature.
2962 nojitter [IA-64] Disables jitter checking for ITC timers.
2964 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2966 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2969 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2970 steal time is computed, but won't influence scheduler
2973 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2975 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2977 noltlbs [PPC] Do not use large page/tlb entries for kernel
2978 lowmem mapping on PPC40x and PPC8xx
2980 nomca [IA-64] Disable machine check abort handling
2982 nomce [X86-32] Disable Machine Check Exception
2984 nomfgpt [X86-32] Disable Multi-Function General Purpose
2985 Timer usage (for AMD Geode machines).
2987 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2988 shutdown the other cpus. Instead use the REBOOT_VECTOR
2991 nomodule Disable module load
2993 nopat [X86] Disable PAT (page attribute table extension of
2994 pagetables) support.
2996 nopcid [X86-64] Disable the PCID cpu feature.
2998 norandmaps Don't use address space randomization. Equivalent to
2999 echo 0 > /proc/sys/kernel/randomize_va_space
3001 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3002 with UP alternatives
3004 nordrand [X86] Disable kernel use of the RDRAND and
3005 RDSEED instructions even if they are supported
3006 by the processor. RDRAND and RDSEED are still
3007 available to user space applications.
3009 noresume [SWSUSP] Disables resume and restores original swap
3012 no-scroll [VGA] Disables scrollback.
3013 This is required for the Braillex ib80-piezo Braille
3014 reader made by F.H. Papenmeier (Germany).
3018 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3020 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3021 and disable the IO APIC. legacy for "maxcpus=0".
3023 nosoftlockup [KNL] Disable the soft-lockup detector.
3025 nosync [HW,M68K] Disables sync negotiation for all devices.
3027 notsc [BUGS=X86-32] Disable Time Stamp Counter
3029 nowatchdog [KNL] Disable both lockup detectors, i.e.
3030 soft-lockup and NMI watchdog (hard-lockup).
3034 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3036 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3037 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3038 Some features depend on CPU0. Known dependencies are:
3039 1. Resume from suspend/hibernate depends on CPU0.
3040 Suspend/hibernate will fail if CPU0 is offline and you
3041 need to online CPU0 before suspend/hibernate.
3042 2. PIC interrupts also depend on CPU0. CPU0 can't be
3043 removed if a PIC interrupt is detected.
3044 It's said poweroff/reboot may depend on CPU0 on some
3045 machines although I haven't seen such issues so far
3046 after CPU0 is offline on a few tested machines.
3047 If the dependencies are under your control, you can
3048 turn on cpu0_hotplug.
3050 nptcg= [IA-64] Override max number of concurrent global TLB
3051 purges which is reported from either PAL_VM_SUMMARY or
3054 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3055 could support. nr_cpus=n : n >= 1 limits the kernel to
3056 support 'n' processors. It could be larger than the
3057 number of already plugged CPU during bootup, later in
3058 runtime you can physically add extra cpu until it reaches
3059 n. So during boot up some boot time memory for per-cpu
3060 variables need be pre-allocated for later physical cpu
3063 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3065 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3066 Allowed values are enable and disable
3068 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3069 one of ['zone', 'node', 'default'] can be specified
3070 This can be set from sysctl after boot.
3071 See Documentation/sysctl/vm.txt for details.
3073 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3074 See Documentation/debugging-via-ohci1394.txt for more
3077 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3078 Rather than timing out after 20 ms if an EC
3079 command is not properly ACKed, override the length
3080 of the timeout. We have interrupts disabled while
3081 waiting for the ACK, so if this is set too high
3082 interrupts *may* be lost!
3084 omap_mux= [OMAP] Override bootloader pin multiplexing.
3085 Format: <mux_mode0.mode_name=value>...
3086 For example, to override I2C bus2:
3087 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3089 oprofile.timer= [HW]
3090 Use timer interrupt instead of performance counters
3092 oprofile.cpu_type= Force an oprofile cpu type
3093 This might be useful if you have an older oprofile
3094 userland or if you want common events.
3095 Format: { arch_perfmon }
3096 arch_perfmon: [X86] Force use of architectural
3097 perfmon on Intel CPUs instead of the
3098 CPU specific event set.
3099 timer: [X86] Force use of architectural NMI
3100 timer mode (see also oprofile.timer
3101 for generic hr timer mode)
3103 oops=panic Always panic on oopses. Default is to just kill the
3104 process, but there is a small probability of
3105 deadlocking the machine.
3106 This will also cause panics on machine check exceptions.
3107 Useful together with panic=30 to trigger a reboot.
3110 See Documentation/sound/oss/oss-parameters.txt
3112 page_owner= [KNL] Boot-time page_owner enabling option.
3113 Storage of the information about who allocated
3114 each page is disabled in default. With this switch,
3116 on: enable the feature
3118 page_poison= [KNL] Boot-time parameter changing the state of
3119 poisoning on the buddy allocator.
3120 off: turn off poisoning
3121 on: turn on poisoning
3123 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3124 timeout > 0: seconds before rebooting
3125 timeout = 0: wait forever
3126 timeout < 0: reboot immediately
3129 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3132 crash_kexec_post_notifiers
3133 Run kdump after running panic-notifiers and dumping
3134 kmsg. This only for the users who doubt kdump always
3135 succeeds in any situation.
3136 Note that this also increases risks of kdump failure,
3137 because some panic notifiers can make the crashed
3138 kernel more unstable.
3140 parkbd.port= [HW] Parallel port number the keyboard adapter is
3141 connected to, default is 0.
3143 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3144 0 for XT, 1 for AT (default is AT).
3147 parport= [HW,PPT] Specify parallel ports. 0 disables.
3148 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3149 Use 'auto' to force the driver to use any
3150 IRQ/DMA settings detected (the default is to
3151 ignore detected IRQ/DMA settings because of
3152 possible conflicts). You can specify the base
3153 address, IRQ, and DMA settings; IRQ and DMA
3154 should be numbers, or 'auto' (for using detected
3155 settings on that particular port), or 'nofifo'
3156 (to avoid using a FIFO even if it is detected).
3157 Parallel ports are assigned in the order they
3158 are specified on the command line, starting
3161 parport_init_mode= [HW,PPT]
3162 Configure VIA parallel port to operate in
3163 a specific mode. This is necessary on Pegasos
3164 computer where firmware has no options for setting
3165 up parallel port mode and sets it to spp.
3166 Currently this function knows 686a and 8231 chips.
3167 Format: [spp|ps2|epp|ecp|ecpepp]
3170 Halt all CPUs after the first oops has been printed for
3171 the specified number of seconds. This is to be used if
3172 your oopses keep scrolling off the screen.
3177 See header of drivers/block/paride/pcd.c.
3178 See also Documentation/blockdev/paride.txt.
3180 pci=option[,option...] [PCI] various PCI subsystem options:
3181 earlydump [X86] dump PCI config space before the kernel
3183 off [X86] don't probe for the PCI bus
3184 bios [X86-32] force use of PCI BIOS, don't access
3185 the hardware directly. Use this if your machine
3186 has a non-standard PCI host bridge.
3187 nobios [X86-32] disallow use of PCI BIOS, only direct
3188 hardware access methods are allowed. Use this
3189 if you experience crashes upon bootup and you
3190 suspect they are caused by the BIOS.
3191 conf1 [X86] Force use of PCI Configuration Access
3192 Mechanism 1 (config address in IO port 0xCF8,
3193 data in IO port 0xCFC, both 32-bit).
3194 conf2 [X86] Force use of PCI Configuration Access
3195 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3196 the function, IO port 0xCFA, also 8-bit, sets
3197 bus number. The config space is then accessed
3198 through ports 0xC000-0xCFFF).
3199 See http://wiki.osdev.org/PCI for more info
3200 on the configuration access mechanisms.
3201 noaer [PCIE] If the PCIEAER kernel config parameter is
3202 enabled, this kernel boot option can be used to
3203 disable the use of PCIE advanced error reporting.
3204 nodomains [PCI] Disable support for multiple PCI
3205 root domains (aka PCI segments, in ACPI-speak).
3206 nommconf [X86] Disable use of MMCONFIG for PCI
3208 check_enable_amd_mmconf [X86] check for and enable
3209 properly configured MMIO access to PCI
3210 config space on AMD family 10h CPU
3211 nomsi [MSI] If the PCI_MSI kernel config parameter is
3212 enabled, this kernel boot option can be used to
3213 disable the use of MSI interrupts system-wide.
3214 noioapicquirk [APIC] Disable all boot interrupt quirks.
3215 Safety option to keep boot IRQs enabled. This
3216 should never be necessary.
3217 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3218 primary IO-APIC for bridges that cannot disable
3219 boot IRQs. This fixes a source of spurious IRQs
3220 when the system masks IRQs.
3221 noioapicreroute [APIC] Disable workaround that uses the
3222 boot IRQ equivalent of an IRQ that connects to
3223 a chipset where boot IRQs cannot be disabled.
3224 The opposite of ioapicreroute.
3225 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3226 routing table. These calls are known to be buggy
3227 on several machines and they hang the machine
3228 when used, but on other computers it's the only
3229 way to get the interrupt routing table. Try
3230 this option if the kernel is unable to allocate
3231 IRQs or discover secondary PCI buses on your
3233 rom [X86] Assign address space to expansion ROMs.
3234 Use with caution as certain devices share
3235 address decoders between ROMs and other
3237 norom [X86] Do not assign address space to
3238 expansion ROMs that do not already have
3239 BIOS assigned address ranges.
3240 nobar [X86] Do not assign address space to the
3241 BARs that weren't assigned by the BIOS.
3242 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3243 assigned automatically to PCI devices. You can
3244 make the kernel exclude IRQs of your ISA cards
3246 pirqaddr=0xAAAAA [X86] Specify the physical address
3247 of the PIRQ table (normally generated
3248 by the BIOS) if it is outside the
3249 F0000h-100000h range.
3250 lastbus=N [X86] Scan all buses thru bus #N. Can be
3251 useful if the kernel is unable to find your
3252 secondary buses and you want to tell it
3253 explicitly which ones they are.
3254 assign-busses [X86] Always assign all PCI bus
3255 numbers ourselves, overriding
3256 whatever the firmware may have done.
3257 usepirqmask [X86] Honor the possible IRQ mask stored
3258 in the BIOS $PIR table. This is needed on
3259 some systems with broken BIOSes, notably
3260 some HP Pavilion N5400 and Omnibook XE3
3261 notebooks. This will have no effect if ACPI
3262 IRQ routing is enabled.
3263 noacpi [X86] Do not use ACPI for IRQ routing
3264 or for PCI scanning.
3265 use_crs [X86] Use PCI host bridge window information
3266 from ACPI. On BIOSes from 2008 or later, this
3267 is enabled by default. If you need to use this,
3268 please report a bug.
3269 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3270 If you need to use this, please report a bug.
3271 routeirq Do IRQ routing for all PCI devices.
3272 This is normally done in pci_enable_device(),
3273 so this option is a temporary workaround
3274 for broken drivers that don't call it.
3275 skip_isa_align [X86] do not align io start addr, so can
3276 handle more pci cards
3277 noearly [X86] Don't do any early type 1 scanning.
3278 This might help on some broken boards which
3279 machine check when some devices' config space
3280 is read. But various workarounds are disabled
3281 and some IOMMU drivers will not work.
3282 bfsort Sort PCI devices into breadth-first order.
3283 This sorting is done to get a device
3284 order compatible with older (<= 2.4) kernels.
3285 nobfsort Don't sort PCI devices into breadth-first order.
3286 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3287 tuning and use the BIOS-configured MPS defaults.
3288 pcie_bus_safe Set every device's MPS to the largest value
3289 supported by all devices below the root complex.
3290 pcie_bus_perf Set device MPS to the largest allowable MPS
3291 based on its parent bus. Also set MRRS (Max
3292 Read Request Size) to the largest supported
3293 value (no larger than the MPS that the device
3294 or bus can support) for best performance.
3295 pcie_bus_peer2peer Set every device's MPS to 128B, which
3296 every device is guaranteed to support. This
3297 configuration allows peer-to-peer DMA between
3298 any pair of devices, possibly at the cost of
3299 reduced performance. This also guarantees
3300 that hot-added devices will work.
3301 cbiosize=nn[KMG] The fixed amount of bus space which is
3302 reserved for the CardBus bridge's IO window.
3303 The default value is 256 bytes.
3304 cbmemsize=nn[KMG] The fixed amount of bus space which is
3305 reserved for the CardBus bridge's memory
3306 window. The default value is 64 megabytes.
3309 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3310 [<order of align>@]pci:<vendor>:<device>\
3311 [:<subvendor>:<subdevice>][; ...]
3312 Specifies alignment and device to reassign
3313 aligned memory resources.
3314 If <order of align> is not specified,
3315 PAGE_SIZE is used as alignment.
3316 PCI-PCI bridge can be specified, if resource
3317 windows need to be expanded.
3318 To specify the alignment for several
3319 instances of a device, the PCI vendor,
3320 device, subvendor, and subdevice may be
3321 specified, e.g., 4096@pci:8086:9c22:103c:198f
3322 ecrc= Enable/disable PCIe ECRC (transaction layer
3323 end-to-end CRC checking).
3324 bios: Use BIOS/firmware settings. This is the
3328 hpiosize=nn[KMG] The fixed amount of bus space which is
3329 reserved for hotplug bridge's IO window.
3330 Default size is 256 bytes.
3331 hpmemsize=nn[KMG] The fixed amount of bus space which is
3332 reserved for hotplug bridge's memory window.
3333 Default size is 2 megabytes.
3334 hpbussize=nn The minimum amount of additional bus numbers
3335 reserved for buses below a hotplug bridge.
3337 realloc= Enable/disable reallocating PCI bridge resources
3338 if allocations done by BIOS are too small to
3339 accommodate resources required by all child
3341 off: Turn realloc off
3343 realloc same as realloc=on
3344 noari do not use PCIe ARI.
3345 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3346 only look for one device below a PCIe downstream
3349 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3352 force Enable ASPM even on devices that claim not to support it.
3353 WARNING: Forcing ASPM on may cause system lockups.
3355 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3356 nomsi Do not use MSI for PCI Express Native Hotplug (this
3357 makes all PCIe ports use INTx for hotplug services).
3359 pcie_ports= [PCIE] PCIe ports handling:
3360 auto Ask the BIOS whether or not to use native PCIe services
3361 associated with PCIe ports (PME, hot-plug, AER). Use
3362 them only if that is allowed by the BIOS.
3363 native Use native PCIe services associated with PCIe ports
3365 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3368 pcie_port_pm= [PCIE] PCIe port power management handling:
3369 off Disable power management of all PCIe ports
3370 force Forcibly enable power management of all PCIe ports
3372 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3373 nomsi Do not use MSI for native PCIe PME signaling (this makes
3374 all PCIe root ports use INTx for all services).
3376 pcmv= [HW,PCMCIA] BadgePAD 4
3380 Keep all power-domains already enabled by bootloader on,
3381 even if no driver has claimed them. This is useful
3382 for debug and development, but should not be
3383 needed on a platform with proper driver support.
3386 See Documentation/blockdev/paride.txt.
3388 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3391 See arch/parisc/kernel/pdc_chassis.c
3393 percpu_alloc= Select which percpu first chunk allocator to use.
3394 Currently supported values are "embed" and "page".
3395 Archs may support subset or none of the selections.
3396 See comments in mm/percpu.c for details on each
3397 allocator. This parameter is primarily for debugging
3398 and performance comparison.
3401 See Documentation/blockdev/paride.txt.
3404 See Documentation/blockdev/paride.txt.
3406 pirq= [SMP,APIC] Manual mp-table setup
3407 See Documentation/x86/i386/IO-APIC.txt.
3409 plip= [PPT,NET] Parallel port network link
3410 Format: { parport<nr> | timid | 0 }
3411 See also Documentation/parport.txt.
3413 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3414 Override pmtimer IOPort with a hex value.
3418 Enable PNP debug messages (depends on the
3419 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3420 via /sys/module/pnp/parameters/debug. We always show
3421 current resource usage; turning this on also shows
3422 possible settings and some assignment information.
3428 { on | off | curr | res | no-curr | no-res }
3431 [ISAPNP] Exclude IRQs for the autoconfiguration
3434 [ISAPNP] Exclude DMAs for the autoconfiguration
3436 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3437 Ranges are in pairs (I/O port base and size).
3440 [ISAPNP] Exclude memory regions for the
3442 Ranges are in pairs (memory base and size).
3444 ports= [IP_VS_FTP] IPVS ftp helper module
3446 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3448 Format: <port>,<port>....
3450 ppc_strict_facility_enable
3451 [PPC] This option catches any kernel floating point,
3452 Altivec, VSX and SPE outside of regions specifically
3453 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3454 There is some performance impact when enabling this.
3456 print-fatal-signals=
3457 [KNL] debug: print fatal signals
3459 If enabled, warn about various signal handling
3460 related application anomalies: too many signals,
3461 too many POSIX.1 timers, fatal signals causing a
3464 If you hit the warning due to signal overflow,
3465 you might want to try "ulimit -i unlimited".
3469 printk.always_kmsg_dump=
3470 Trigger kmsg_dump for cases other than kernel oops or
3472 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3475 printk.devkmsg={on,off,ratelimit}
3476 Control writing to /dev/kmsg.
3477 on - unlimited logging to /dev/kmsg from userspace
3478 off - logging to /dev/kmsg disabled
3479 ratelimit - ratelimit the logging
3482 printk.time= Show timing data prefixed to each printk message line
3483 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3485 processor.max_cstate= [HW,ACPI]
3486 Limit processor to maximum C-state
3487 max_cstate=9 overrides any DMI blacklist limit.
3489 processor.nocst [HW,ACPI]
3490 Ignore the _CST method to determine C-states,
3491 instead using the legacy FADT method
3493 profile= [KNL] Enable kernel profiling via /proc/profile
3494 Format: [schedule,]<number>
3495 Param: "schedule" - profile schedule points.
3496 Param: <number> - step/bucket size as a power of 2 for
3497 statistical time based profiling.
3498 Param: "sleep" - profile D-state sleeping (millisecs).
3499 Requires CONFIG_SCHEDSTATS
3500 Param: "kvm" - profile VM exits.
3502 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3504 See Documentation/blockdev/ramdisk.txt.
3506 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3507 probe for; one of (bare|imps|exps|lifebook|any).
3508 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3510 psmouse.resetafter= [HW,MOUSE]
3511 Try to reset the device after so many bad packets
3514 [HW,MOUSE] Set desired mouse resolution, in dpi.
3515 psmouse.smartscroll=
3516 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3517 0 = disabled, 1 = enabled (default).
3519 pstore.backend= Specify the name of the pstore backend to use
3522 See Documentation/blockdev/paride.txt.
3524 pti= [X86_64] Control Page Table Isolation of user and
3525 kernel address spaces. Disabling this feature
3526 removes hardening, but improves performance of
3527 system calls and interrupts.
3529 on - unconditionally enable
3530 off - unconditionally disable
3531 auto - kernel detects whether your CPU model is
3532 vulnerable to issues that PTI mitigates
3534 Not specifying this option is equivalent to pti=auto.
3537 Equivalent to pti=off
3540 [KNL] Number of legacy pty's. Overwrites compiled-in
3543 quiet [KNL] Disable most log messages
3548 See Documentation/md.txt.
3550 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3551 See Documentation/blockdev/ramdisk.txt.
3554 The argument is a cpu list, as described above.
3556 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3557 the specified list of CPUs to be no-callback CPUs.
3558 Invocation of these CPUs' RCU callbacks will
3559 be offloaded to "rcuox/N" kthreads created for
3560 that purpose, where "x" is "b" for RCU-bh, "p"
3561 for RCU-preempt, and "s" for RCU-sched, and "N"
3562 is the CPU number. This reduces OS jitter on the
3563 offloaded CPUs, which can be useful for HPC and
3564 real-time workloads. It can also improve energy
3565 efficiency for asymmetric multiprocessors.
3568 Rather than requiring that offloaded CPUs
3569 (specified by rcu_nocbs= above) explicitly
3570 awaken the corresponding "rcuoN" kthreads,
3571 make these kthreads poll for callbacks.
3572 This improves the real-time response for the
3573 offloaded CPUs by relieving them of the need to
3574 wake up the corresponding kthread, but degrades
3575 energy efficiency by requiring that the kthreads
3576 periodically wake up to do the polling.
3578 rcutree.blimit= [KNL]
3579 Set maximum number of finished RCU callbacks to
3580 process in one batch.
3582 rcutree.dump_tree= [KNL]
3583 Dump the structure of the rcu_node combining tree
3584 out at early boot. This is used for diagnostic
3585 purposes, to verify correct tree setup.
3587 rcutree.gp_cleanup_delay= [KNL]
3588 Set the number of jiffies to delay each step of
3589 RCU grace-period cleanup. This only has effect
3590 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3592 rcutree.gp_init_delay= [KNL]
3593 Set the number of jiffies to delay each step of
3594 RCU grace-period initialization. This only has
3595 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3598 rcutree.gp_preinit_delay= [KNL]
3599 Set the number of jiffies to delay each step of
3600 RCU grace-period pre-initialization, that is,
3601 the propagation of recent CPU-hotplug changes up
3602 the rcu_node combining tree. This only has effect
3603 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3605 rcutree.rcu_fanout_exact= [KNL]
3606 Disable autobalancing of the rcu_node combining
3607 tree. This is used by rcutorture, and might
3608 possibly be useful for architectures having high
3609 cache-to-cache transfer latencies.
3611 rcutree.rcu_fanout_leaf= [KNL]
3612 Change the number of CPUs assigned to each
3613 leaf rcu_node structure. Useful for very
3614 large systems, which will choose the value 64,
3615 and for NUMA systems with large remote-access
3616 latencies, which will choose a value aligned
3617 with the appropriate hardware boundaries.
3619 rcutree.jiffies_till_sched_qs= [KNL]
3620 Set required age in jiffies for a
3621 given grace period before RCU starts
3622 soliciting quiescent-state help from
3623 rcu_note_context_switch().
3625 rcutree.jiffies_till_first_fqs= [KNL]
3626 Set delay from grace-period initialization to
3627 first attempt to force quiescent states.
3628 Units are jiffies, minimum value is zero,
3629 and maximum value is HZ.
3631 rcutree.jiffies_till_next_fqs= [KNL]
3632 Set delay between subsequent attempts to force
3633 quiescent states. Units are jiffies, minimum
3634 value is one, and maximum value is HZ.
3636 rcutree.kthread_prio= [KNL,BOOT]
3637 Set the SCHED_FIFO priority of the RCU per-CPU
3638 kthreads (rcuc/N). This value is also used for
3639 the priority of the RCU boost threads (rcub/N)
3640 and for the RCU grace-period kthreads (rcu_bh,
3641 rcu_preempt, and rcu_sched). If RCU_BOOST is
3642 set, valid values are 1-99 and the default is 1
3643 (the least-favored priority). Otherwise, when
3644 RCU_BOOST is not set, valid values are 0-99 and
3645 the default is zero (non-realtime operation).
3647 rcutree.rcu_nocb_leader_stride= [KNL]
3648 Set the number of NOCB kthread groups, which
3649 defaults to the square root of the number of
3650 CPUs. Larger numbers reduces the wakeup overhead
3651 on the per-CPU grace-period kthreads, but increases
3652 that same overhead on each group's leader.
3654 rcutree.qhimark= [KNL]
3655 Set threshold of queued RCU callbacks beyond which
3656 batch limiting is disabled.
3658 rcutree.qlowmark= [KNL]
3659 Set threshold of queued RCU callbacks below which
3660 batch limiting is re-enabled.
3662 rcutree.rcu_idle_gp_delay= [KNL]
3663 Set wakeup interval for idle CPUs that have
3664 RCU callbacks (RCU_FAST_NO_HZ=y).
3666 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3667 Set wakeup interval for idle CPUs that have
3668 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3669 Lazy RCU callbacks are those which RCU can
3670 prove do nothing more than free memory.
3672 rcuperf.gp_exp= [KNL]
3673 Measure performance of expedited synchronous
3674 grace-period primitives.
3676 rcuperf.holdoff= [KNL]
3677 Set test-start holdoff period. The purpose of
3678 this parameter is to delay the start of the
3679 test until boot completes in order to avoid
3682 rcuperf.nreaders= [KNL]
3683 Set number of RCU readers. The value -1 selects
3684 N, where N is the number of CPUs. A value
3685 "n" less than -1 selects N-n+1, where N is again
3686 the number of CPUs. For example, -2 selects N
3687 (the number of CPUs), -3 selects N+1, and so on.
3688 A value of "n" less than or equal to -N selects
3691 rcuperf.nwriters= [KNL]
3692 Set number of RCU writers. The values operate
3693 the same as for rcuperf.nreaders.
3694 N, where N is the number of CPUs
3696 rcuperf.perf_runnable= [BOOT]
3697 Start rcuperf running at boot time.
3699 rcuperf.shutdown= [KNL]
3700 Shut the system down after performance tests
3701 complete. This is useful for hands-off automated
3704 rcuperf.perf_type= [KNL]
3705 Specify the RCU implementation to test.
3707 rcuperf.verbose= [KNL]
3708 Enable additional printk() statements.
3710 rcutorture.cbflood_inter_holdoff= [KNL]
3711 Set holdoff time (jiffies) between successive
3712 callback-flood tests.
3714 rcutorture.cbflood_intra_holdoff= [KNL]
3715 Set holdoff time (jiffies) between successive
3716 bursts of callbacks within a given callback-flood
3719 rcutorture.cbflood_n_burst= [KNL]
3720 Set the number of bursts making up a given
3721 callback-flood test. Set this to zero to
3722 disable callback-flood testing.
3724 rcutorture.cbflood_n_per_burst= [KNL]
3725 Set the number of callbacks to be registered
3726 in a given burst of a callback-flood test.
3728 rcutorture.fqs_duration= [KNL]
3729 Set duration of force_quiescent_state bursts
3732 rcutorture.fqs_holdoff= [KNL]
3733 Set holdoff time within force_quiescent_state bursts
3736 rcutorture.fqs_stutter= [KNL]
3737 Set wait time between force_quiescent_state bursts
3740 rcutorture.gp_cond= [KNL]
3741 Use conditional/asynchronous update-side
3742 primitives, if available.
3744 rcutorture.gp_exp= [KNL]
3745 Use expedited update-side primitives, if available.
3747 rcutorture.gp_normal= [KNL]
3748 Use normal (non-expedited) asynchronous
3749 update-side primitives, if available.
3751 rcutorture.gp_sync= [KNL]
3752 Use normal (non-expedited) synchronous
3753 update-side primitives, if available. If all
3754 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3755 rcutorture.gp_normal=, and rcutorture.gp_sync=
3756 are zero, rcutorture acts as if is interpreted
3757 they are all non-zero.
3759 rcutorture.n_barrier_cbs= [KNL]
3760 Set callbacks/threads for rcu_barrier() testing.
3762 rcutorture.nfakewriters= [KNL]
3763 Set number of concurrent RCU writers. These just
3764 stress RCU, they don't participate in the actual
3765 test, hence the "fake".
3767 rcutorture.nreaders= [KNL]
3768 Set number of RCU readers. The value -1 selects
3769 N-1, where N is the number of CPUs. A value
3770 "n" less than -1 selects N-n-2, where N is again
3771 the number of CPUs. For example, -2 selects N
3772 (the number of CPUs), -3 selects N+1, and so on.
3774 rcutorture.object_debug= [KNL]
3775 Enable debug-object double-call_rcu() testing.
3777 rcutorture.onoff_holdoff= [KNL]
3778 Set time (s) after boot for CPU-hotplug testing.
3780 rcutorture.onoff_interval= [KNL]
3781 Set time (s) between CPU-hotplug operations, or
3782 zero to disable CPU-hotplug testing.
3784 rcutorture.shuffle_interval= [KNL]
3785 Set task-shuffle interval (s). Shuffling tasks
3786 allows some CPUs to go into dyntick-idle mode
3787 during the rcutorture test.
3789 rcutorture.shutdown_secs= [KNL]
3790 Set time (s) after boot system shutdown. This
3791 is useful for hands-off automated testing.
3793 rcutorture.stall_cpu= [KNL]
3794 Duration of CPU stall (s) to test RCU CPU stall
3795 warnings, zero to disable.
3797 rcutorture.stall_cpu_holdoff= [KNL]
3798 Time to wait (s) after boot before inducing stall.
3800 rcutorture.stat_interval= [KNL]
3801 Time (s) between statistics printk()s.
3803 rcutorture.stutter= [KNL]
3804 Time (s) to stutter testing, for example, specifying
3805 five seconds causes the test to run for five seconds,
3806 wait for five seconds, and so on. This tests RCU's
3807 ability to transition abruptly to and from idle.
3809 rcutorture.test_boost= [KNL]
3810 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3811 "Maybe" means test if the RCU implementation
3812 under test support RCU priority boosting.
3814 rcutorture.test_boost_duration= [KNL]
3815 Duration (s) of each individual boost test.
3817 rcutorture.test_boost_interval= [KNL]
3818 Interval (s) between each boost test.
3820 rcutorture.test_no_idle_hz= [KNL]
3821 Test RCU's dyntick-idle handling. See also the
3822 rcutorture.shuffle_interval parameter.
3824 rcutorture.torture_runnable= [BOOT]
3825 Start rcutorture running at boot time.
3827 rcutorture.torture_type= [KNL]
3828 Specify the RCU implementation to test.
3830 rcutorture.verbose= [KNL]
3831 Enable additional printk() statements.
3833 rcupdate.rcu_cpu_stall_suppress= [KNL]
3834 Suppress RCU CPU stall warning messages.
3836 rcupdate.rcu_cpu_stall_timeout= [KNL]
3837 Set timeout for RCU CPU stall warning messages.
3839 rcupdate.rcu_expedited= [KNL]
3840 Use expedited grace-period primitives, for
3841 example, synchronize_rcu_expedited() instead
3842 of synchronize_rcu(). This reduces latency,
3843 but can increase CPU utilization, degrade
3844 real-time latency, and degrade energy efficiency.
3845 No effect on CONFIG_TINY_RCU kernels.
3847 rcupdate.rcu_normal= [KNL]
3848 Use only normal grace-period primitives,
3849 for example, synchronize_rcu() instead of
3850 synchronize_rcu_expedited(). This improves
3851 real-time latency, CPU utilization, and
3852 energy efficiency, but can expose users to
3853 increased grace-period latency. This parameter
3854 overrides rcupdate.rcu_expedited. No effect on
3855 CONFIG_TINY_RCU kernels.
3857 rcupdate.rcu_normal_after_boot= [KNL]
3858 Once boot has completed (that is, after
3859 rcu_end_inkernel_boot() has been invoked), use
3860 only normal grace-period primitives. No effect
3861 on CONFIG_TINY_RCU kernels.
3863 rcupdate.rcu_task_stall_timeout= [KNL]
3864 Set timeout in jiffies for RCU task stall warning
3865 messages. Disable with a value less than or equal
3868 rcupdate.rcu_self_test= [KNL]
3869 Run the RCU early boot self tests
3871 rcupdate.rcu_self_test_bh= [KNL]
3872 Run the RCU bh early boot self tests
3874 rcupdate.rcu_self_test_sched= [KNL]
3875 Run the RCU sched early boot self tests
3879 Run specified binary instead of /init from the ramdisk,
3880 used for early userspace startup. See initrd.
3883 force - Override the decision by the kernel to hide the
3884 advertisement of RDRAND support (this affects
3885 certain AMD processors because of buggy BIOS
3886 support, specifically around the suspend/resume
3890 Format (x86 or x86_64):
3891 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3893 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3895 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3896 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3897 reboot_force is either force or not specified,
3898 reboot_cpu is s[mp]#### with #### being the processor
3899 to be used for rebooting.
3902 [KNL, SMP] Set scheduler's default relax_domain_level.
3903 See Documentation/cgroup-v1/cpusets.txt.
3905 relative_sleep_states=
3906 [SUSPEND] Use sleep state labeling where the deepest
3907 state available other than hibernation is always "mem".
3908 Format: { "0" | "1" }
3909 0 -- Traditional sleep state labels.
3910 1 -- Relative sleep state labels.
3912 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3914 reservetop= [X86-32]
3916 Reserves a hole at the top of the kernel virtual
3921 Set the amount of memory to reserve for BIOS at
3922 the bottom of the address space.
3924 reset_devices [KNL] Force drivers to reset the underlying device
3925 during initialization.
3928 Specify the partition device for software suspend
3930 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3932 resume_offset= [SWSUSP]
3933 Specify the offset from the beginning of the partition
3934 given by "resume=" at which the swap header is located,
3935 in <PAGE_SIZE> units (needed only for swap files).
3936 See Documentation/power/swsusp-and-swap-files.txt
3938 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3939 read the resume files
3941 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3942 Useful for devices that are detected asynchronously
3943 (e.g. USB and MMC devices).
3945 hibernate= [HIBERNATION]
3946 noresume Don't check if there's a hibernation image
3947 present during boot.
3948 nocompress Don't compress/decompress hibernation images.
3949 no Disable hibernation and resume.
3950 protect_image Turn on image protection during restoration
3951 (that will set all pages holding image data
3952 during restoration read-only).
3954 retain_initrd [RAM] Keep initrd memory after extraction
3956 rfkill.default_state=
3957 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3958 etc. communication is blocked by default.
3961 rfkill.master_switch_mode=
3962 0 The "airplane mode" button does nothing.
3963 1 The "airplane mode" button toggles between everything
3964 blocked and the previous configuration.
3965 2 The "airplane mode" button toggles between everything
3966 blocked and everything unblocked.
3968 rhash_entries= [KNL,NET]
3969 Set number of hash buckets for route cache
3971 ro [KNL] Mount root device read-only on boot
3974 on Mark read-only kernel memory as read-only (default).
3975 off Leave read-only kernel memory writable for debugging.
3978 Enable the uart passthrough on the designated usb port
3979 on Rockchip SoCs. When active, the signals of the
3980 debug-uart get routed to the D+ and D- pins of the usb
3981 port and the regular usb controller gets disabled.
3983 root= [KNL] Root filesystem
3984 See name_to_dev_t comment in init/do_mounts.c.
3986 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3987 mount the root filesystem
3989 rootflags= [KNL] Set root filesystem mount option string
3991 rootfstype= [KNL] Set root filesystem type
3993 rootwait [KNL] Wait (indefinitely) for root device to show up.
3994 Useful for devices that are detected asynchronously
3995 (e.g. USB and MMC devices).
3997 rproc_mem=nn[KMG][@address]
3998 [KNL,ARM,CMA] Remoteproc physical memory block.
3999 Memory area to be used by remote processor image,
4002 rw [KNL] Mount root device read-write on boot
4004 S [KNL] Run init in single mode
4006 s390_iommu= [HW,S390]
4007 Set s390 IOTLB flushing mode
4009 With strict flushing every unmap operation will result in
4010 an IOTLB flush. Default is lazy flushing before reuse,
4014 See drivers/net/irda/sa1100_ir.c.
4016 sbni= [NET] Granch SBNI12 leased line adapter
4018 sched_debug [KNL] Enables verbose scheduler debug messages.
4020 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4021 Allowed values are enable and disable. This feature
4022 incurs a small amount of overhead in the scheduler
4023 but is useful for debugging and performance tuning.
4025 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4026 xtime_lock contention on larger systems, and/or RCU lock
4027 contention on all systems with CONFIG_MAXSMP set.
4028 Format: { "0" | "1" }
4029 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4031 Note: increases power consumption, thus should only be
4032 enabled if running jitter sensitive (HPC/RT) workloads.
4034 security= [SECURITY] Choose a security module to enable at boot.
4035 If this boot parameter is not specified, only the first
4036 security module asking for security registration will be
4037 loaded. An invalid security module name will be treated
4038 as if no module has been chosen.
4040 selinux= [SELINUX] Disable or enable SELinux at boot time.
4041 Format: { "0" | "1" }
4042 See security/selinux/Kconfig help text.
4045 Default value is set via kernel config option.
4046 If enabled at boot time, /selinux/disable can be used
4047 later to disable prior to initial policy load.
4049 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4050 Format: { "0" | "1" }
4051 See security/apparmor/Kconfig help text
4054 Default value is set via kernel config option.
4056 serialnumber [BUGS=X86-32]
4059 Maximal number of shapers.
4061 show_msr= [x86] show boot-time MSR settings
4062 Format: { <integer> }
4063 Show boot-time (BIOS-initialized) MSR settings.
4064 The parameter means the number of CPUs to show,
4065 for example 1 means boot CPU only.
4073 Disable merging of slabs with similar size. May be
4074 necessary if there is some reason to distinguish
4075 allocs to different slabs. Debug options disable
4076 merging on their own.
4077 For more information see Documentation/vm/slub.txt.
4079 slab_max_order= [MM, SLAB]
4080 Determines the maximum allowed order for slabs.
4081 A high setting may cause OOMs due to memory
4082 fragmentation. Defaults to 1 for systems with
4083 more than 32MB of RAM, 0 otherwise.
4085 slub_debug[=options[,slabs]] [MM, SLUB]
4086 Enabling slub_debug allows one to determine the
4087 culprit if slab objects become corrupted. Enabling
4088 slub_debug can create guard zones around objects and
4089 may poison objects when not in use. Also tracks the
4090 last alloc / free. For more information see
4091 Documentation/vm/slub.txt.
4093 slub_max_order= [MM, SLUB]
4094 Determines the maximum allowed order for slabs.
4095 A high setting may cause OOMs due to memory
4096 fragmentation. For more information see
4097 Documentation/vm/slub.txt.
4099 slub_min_objects= [MM, SLUB]
4100 The minimum number of objects per slab. SLUB will
4101 increase the slab order up to slub_max_order to
4102 generate a sufficiently large slab able to contain
4103 the number of objects indicated. The higher the number
4104 of objects the smaller the overhead of tracking slabs
4105 and the less frequently locks need to be acquired.
4106 For more information see Documentation/vm/slub.txt.
4108 slub_min_order= [MM, SLUB]
4109 Determines the minimum page order for slabs. Must be
4110 lower than slub_max_order.
4111 For more information see Documentation/vm/slub.txt.
4113 slub_nomerge [MM, SLUB]
4114 Same with slab_nomerge. This is supported for legacy.
4115 See slab_nomerge for more information.
4118 Format: <io1>[,<io2>[,...,<io8>]]
4120 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4121 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4122 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4123 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4124 smsc-ircc2.ircc_irq= [HW] IRQ line
4125 smsc-ircc2.ircc_dma= [HW] DMA channel
4126 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4127 0: Toshiba Satellite 1800 (GP data pin select)
4128 1: Fast pin select (default)
4131 smt [KNL,S390] Set the maximum number of threads (logical
4132 CPUs) to use per physical CPU on systems capable of
4133 symmetric multithreading (SMT). Will be capped to the
4134 actual hardware limit.
4136 Default: -1 (no limit)
4139 [KNL] Should the soft-lockup detector generate panics.
4142 softlockup_all_cpu_backtrace=
4143 [KNL] Should the soft-lockup detector generate
4144 backtraces on all cpus.
4147 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4148 See Documentation/laptops/sonypi.txt
4150 spectre_v2= [X86] Control mitigation of Spectre variant 2
4151 (indirect branch speculation) vulnerability.
4152 The default operation protects the kernel from
4155 on - unconditionally enable, implies
4157 off - unconditionally disable, implies
4159 auto - kernel detects whether your CPU model is
4162 Selecting 'on' will, and 'auto' may, choose a
4163 mitigation method at run time according to the
4164 CPU, the available microcode, the setting of the
4165 CONFIG_RETPOLINE configuration option, and the
4166 compiler with which the kernel was built.
4168 Selecting 'on' will also enable the mitigation
4169 against user space to user space task attacks.
4171 Selecting 'off' will disable both the kernel and
4172 the user space protections.
4174 Specific mitigations can also be selected manually:
4176 retpoline - replace indirect branches
4177 retpoline,generic - google's original retpoline
4178 retpoline,amd - AMD-specific minimal thunk
4180 Not specifying this option is equivalent to
4184 [X86] Control mitigation of Spectre variant 2
4185 (indirect branch speculation) vulnerability between
4188 on - Unconditionally enable mitigations. Is
4189 enforced by spectre_v2=on
4191 off - Unconditionally disable mitigations. Is
4192 enforced by spectre_v2=off
4194 prctl - Indirect branch speculation is enabled,
4195 but mitigation can be enabled via prctl
4196 per thread. The mitigation control state
4197 is inherited on fork.
4200 - Like "prctl" above, but only STIBP is
4201 controlled per thread. IBPB is issued
4202 always when switching between different user
4206 - Same as "prctl" above, but all seccomp
4207 threads will enable the mitigation unless
4208 they explicitly opt out.
4211 - Like "seccomp" above, but only STIBP is
4212 controlled per thread. IBPB is issued
4213 always when switching between different
4214 user space processes.
4216 auto - Kernel selects the mitigation depending on
4217 the available CPU features and vulnerability.
4220 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4222 Not specifying this option is equivalent to
4223 spectre_v2_user=auto.
4225 spec_store_bypass_disable=
4226 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4227 (Speculative Store Bypass vulnerability)
4229 Certain CPUs are vulnerable to an exploit against a
4230 a common industry wide performance optimization known
4231 as "Speculative Store Bypass" in which recent stores
4232 to the same memory location may not be observed by
4233 later loads during speculative execution. The idea
4234 is that such stores are unlikely and that they can
4235 be detected prior to instruction retirement at the
4236 end of a particular speculation execution window.
4238 In vulnerable processors, the speculatively forwarded
4239 store can be used in a cache side channel attack, for
4240 example to read memory to which the attacker does not
4241 directly have access (e.g. inside sandboxed code).
4243 This parameter controls whether the Speculative Store
4244 Bypass optimization is used.
4246 on - Unconditionally disable Speculative Store Bypass
4247 off - Unconditionally enable Speculative Store Bypass
4248 auto - Kernel detects whether the CPU model contains an
4249 implementation of Speculative Store Bypass and
4250 picks the most appropriate mitigation. If the
4251 CPU is not vulnerable, "off" is selected. If the
4252 CPU is vulnerable the default mitigation is
4253 architecture and Kconfig dependent. See below.
4254 prctl - Control Speculative Store Bypass per thread
4255 via prctl. Speculative Store Bypass is enabled
4256 for a process by default. The state of the control
4257 is inherited on fork.
4258 seccomp - Same as "prctl" above, but all seccomp threads
4259 will disable SSB unless they explicitly opt out.
4261 Not specifying this option is equivalent to
4262 spec_store_bypass_disable=auto.
4264 Default mitigations:
4265 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4267 spia_io_base= [HW,MTD]
4273 Control the Special Register Buffer Data Sampling
4276 Certain CPUs are vulnerable to an MDS-like
4277 exploit which can leak bits from the random
4280 By default, this issue is mitigated by
4281 microcode. However, the microcode fix can cause
4282 the RDRAND and RDSEED instructions to become
4283 much slower. Among other effects, this will
4284 result in reduced throughput from /dev/urandom.
4286 The microcode mitigation can be disabled with
4287 the following option:
4289 off: Disable mitigation and remove
4290 performance impact to RDRAND and RDSEED
4293 Speculative Store Bypass Disable control
4295 On CPUs that are vulnerable to the Speculative
4296 Store Bypass vulnerability and offer a
4297 firmware based mitigation, this parameter
4298 indicates how the mitigation should be used:
4300 force-on: Unconditionally enable mitigation for
4301 for both kernel and userspace
4302 force-off: Unconditionally disable mitigation for
4303 for both kernel and userspace
4304 kernel: Always enable mitigation in the
4305 kernel, and offer a prctl interface
4306 to allow userspace to register its
4307 interest in being mitigated too.
4309 stack_guard_gap= [MM]
4310 override the default stack gap protection. The value
4311 is in page units and it defines how many pages prior
4312 to (for stacks growing down) resp. after (for stacks
4313 growing up) the main stack are reserved for no other
4314 mapping. Default value is 256 pages.
4317 Enabled the stack tracer on boot up.
4319 stacktrace_filter=[function-list]
4320 [FTRACE] Limit the functions that the stack tracer
4321 will trace at boot up. function-list is a comma separated
4322 list of functions. This list can be changed at run
4323 time by the stack_trace_filter file in the debugfs
4324 tracing directory. Note, this enables stack tracing
4325 and the stacktrace above is not needed.
4329 Set the STI (builtin display/keyboard on the HP-PARISC
4330 machines) console (graphic card) which should be used
4331 as the initial boot-console.
4332 See also comment in drivers/video/console/sticore.c.
4335 See comment in drivers/video/console/sticore.c.
4338 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4340 sunrpc.min_resvport=
4341 sunrpc.max_resvport=
4343 SunRPC servers often require that client requests
4344 originate from a privileged port (i.e. a port in the
4345 range 0 < portnr < 1024).
4346 An administrator who wishes to reserve some of these
4347 ports for other uses may adjust the range that the
4348 kernel's sunrpc client considers to be privileged
4349 using these two parameters to set the minimum and
4350 maximum port values.
4352 sunrpc.svc_rpc_per_connection_limit=
4354 Limit the number of requests that the server will
4355 process in parallel from a single connection.
4356 The default value is 0 (no limit).
4360 Control how the NFS server code allocates CPUs to
4361 service thread pools. Depending on how many NICs
4362 you have and where their interrupts are bound, this
4363 option will affect which CPUs will do NFS serving.
4364 Note: this parameter cannot be changed while the
4365 NFS server is running.
4367 auto the server chooses an appropriate mode
4368 automatically using heuristics
4369 global a single global pool contains all CPUs
4370 percpu one pool for each CPU
4371 pernode one pool for each NUMA node (equivalent
4372 to global on non-NUMA machines)
4374 sunrpc.tcp_slot_table_entries=
4375 sunrpc.udp_slot_table_entries=
4377 Sets the upper limit on the number of simultaneous
4378 RPC calls that can be sent from the client to a
4379 server. Increasing these values may allow you to
4380 improve throughput, but will also increase the
4381 amount of memory reserved for use by the client.
4383 suspend.pm_test_delay=
4385 Sets the number of seconds to remain in a suspend test
4386 mode before resuming the system (see
4387 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4388 is set. Default value is 5.
4391 [KNL] Enable accounting of swap in memory resource
4392 controller if no parameter or 1 is given or disable
4393 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4395 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4396 Format: { <int> | force | noforce }
4397 <int> -- Number of I/O TLB slabs
4398 force -- force using of bounce buffers even if they
4399 wouldn't be automatically used by the kernel
4400 noforce -- Never use bounce buffers (for debugging)
4404 sysfs.deprecated=0|1 [KNL]
4405 Enable/disable old style sysfs layout for old udev
4406 on older distributions. When this option is enabled
4407 very new udev will not work anymore. When this option
4408 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4409 in older udev will not work anymore.
4410 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4411 the kernel configuration.
4413 sysrq_always_enabled
4415 Ignore sysrq setting - this boot parameter will
4416 neutralize any effect of /proc/sys/kernel/sysrq.
4417 Useful for debugging.
4419 tcpmhash_entries= [KNL,NET]
4420 Set the number of tcp_metrics_hash slots.
4421 Default value is 8192 or 16384 depending on total
4422 ram pages. This is used to specify the TCP metrics
4423 cache size. See Documentation/networking/ip-sysctl.txt
4424 "tcp_no_metrics_save" section for more details.
4428 test_suspend= [SUSPEND][,N]
4429 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4430 standby suspend) or "freeze" (for suspend type freeze)
4431 as the system sleep state during system startup with
4432 the optional capability to repeat N number of times.
4433 The system is woken from this state using a
4434 wakeup-capable RTC alarm.
4436 thash_entries= [KNL,NET]
4437 Set number of hash buckets for TCP connection
4439 thermal.act= [HW,ACPI]
4440 -1: disable all active trip points in all thermal zones
4441 <degrees C>: override all lowest active trip points
4443 thermal.crt= [HW,ACPI]
4444 -1: disable all critical trip points in all thermal zones
4445 <degrees C>: override all critical trip points
4447 thermal.nocrt= [HW,ACPI]
4448 Set to disable actions on ACPI thermal zone
4449 critical and hot trip points.
4451 thermal.off= [HW,ACPI]
4452 1: disable ACPI thermal control
4454 thermal.psv= [HW,ACPI]
4455 -1: disable all passive trip points
4456 <degrees C>: override all passive trip points to this
4459 thermal.tzp= [HW,ACPI]
4460 Specify global default ACPI thermal zone polling rate
4461 <deci-seconds>: poll all this frequency
4462 0: no polling (default)
4465 Force threading of all interrupt handlers except those
4466 marked explicitly IRQF_NO_THREAD.
4469 Enable the Transcendent memory driver if built-in.
4471 tmem.cleancache=0|1 [KNL, XEN]
4472 Default is on (1). Disable the usage of the cleancache
4473 API to send anonymous pages to the hypervisor.
4475 tmem.frontswap=0|1 [KNL, XEN]
4476 Default is on (1). Disable the usage of the frontswap
4477 API to send swap pages to the hypervisor. If disabled
4478 the selfballooning and selfshrinking are force disabled.
4480 tmem.selfballooning=0|1 [KNL, XEN]
4481 Default is on (1). Disable the driving of swap pages
4484 tmem.selfshrinking=0|1 [KNL, XEN]
4485 Default is on (1). Partial swapoff that immediately
4486 transfers pages from Xen hypervisor back to the
4487 kernel based on different criteria.
4491 Specify if the kernel should make use of the cpu
4492 topology information if the hardware supports this.
4493 The scheduler will make use of this information and
4494 e.g. base its process migration decisions on it.
4497 topology_updates= [KNL, PPC, NUMA]
4499 Specify if the kernel should ignore (off)
4500 topology updates sent by the hypervisor to this
4505 tpm_suspend_pcr=[HW,TPM]
4506 Format: integer pcr id
4507 Specify that at suspend time, the tpm driver
4508 should extend the specified pcr with zeros,
4509 as a workaround for some chips which fail to
4510 flush the last written pcr on TPM_SaveState.
4511 This will guarantee that all the other pcrs
4514 trace_buf_size=nn[KMG]
4515 [FTRACE] will set tracing buffer size on each cpu.
4517 trace_event=[event-list]
4518 [FTRACE] Set and start specified trace events in order
4519 to facilitate early boot debugging. The event-list is a
4520 comma separated list of trace events to enable. See
4521 also Documentation/trace/events.txt
4523 trace_options=[option-list]
4524 [FTRACE] Enable or disable tracer options at boot.
4525 The option-list is a comma delimited list of options
4526 that can be enabled or disabled just as if you were
4527 to echo the option name into
4529 /sys/kernel/debug/tracing/trace_options
4531 For example, to enable stacktrace option (to dump the
4532 stack trace of each event), add to the command line:
4534 trace_options=stacktrace
4536 See also Documentation/trace/ftrace.txt "trace options"
4540 Have the tracepoints sent to printk as well as the
4541 tracing ring buffer. This is useful for early boot up
4542 where the system hangs or reboots and does not give the
4543 option for reading the tracing buffer or performing a
4544 ftrace_dump_on_oops.
4546 To turn off having tracepoints sent to printk,
4547 echo 0 > /proc/sys/kernel/tracepoint_printk
4548 Note, echoing 1 into this file without the
4549 tracepoint_printk kernel cmdline option has no effect.
4553 Having tracepoints sent to printk() and activating high
4554 frequency tracepoints such as irq or sched, can cause
4555 the system to live lock.
4558 [FTRACE] enable this option to disable tracing when a
4559 warning is hit. This turns off "tracing_on". Tracing can
4560 be enabled again by echoing '1' into the "tracing_on"
4561 file located in /sys/kernel/debug/tracing/
4563 This option is useful, as it disables the trace before
4564 the WARNING dump is called, which prevents the trace to
4565 be filled with content caused by the warning output.
4567 This option can also be set at run time via the sysctl
4568 option: kernel/traceoff_on_warning
4570 transparent_hugepage=
4572 Format: [always|madvise|never]
4573 Can be used to control the default behavior of the system
4574 with respect to transparent hugepages.
4575 See Documentation/vm/transhuge.txt for more details.
4577 tsc= Disable clocksource stability checks for TSC.
4579 [x86] reliable: mark tsc clocksource as reliable, this
4580 disables clocksource verification at runtime, as well
4581 as the stability checks done at bootup. Used to enable
4582 high-resolution timer mode on older hardware, and in
4583 virtualized environment.
4584 [x86] noirqtime: Do not use TSC to do irq accounting.
4585 Used to run time disable IRQ_TIME_ACCOUNTING on any
4586 platforms where RDTSC is slow and this accounting
4589 tsx= [X86] Control Transactional Synchronization
4590 Extensions (TSX) feature in Intel processors that
4591 support TSX control.
4593 This parameter controls the TSX feature. The options are:
4595 on - Enable TSX on the system. Although there are
4596 mitigations for all known security vulnerabilities,
4597 TSX has been known to be an accelerator for
4598 several previous speculation-related CVEs, and
4599 so there may be unknown security risks associated
4600 with leaving it enabled.
4602 off - Disable TSX on the system. (Note that this
4603 option takes effect only on newer CPUs which are
4604 not vulnerable to MDS, i.e., have
4605 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4606 the new IA32_TSX_CTRL MSR through a microcode
4607 update. This new MSR allows for the reliable
4608 deactivation of the TSX functionality.)
4610 auto - Disable TSX if X86_BUG_TAA is present,
4611 otherwise enable TSX on the system.
4613 Not specifying this option is equivalent to tsx=off.
4615 See Documentation/hw-vuln/tsx_async_abort.rst
4618 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4619 Abort (TAA) vulnerability.
4621 Similar to Micro-architectural Data Sampling (MDS)
4622 certain CPUs that support Transactional
4623 Synchronization Extensions (TSX) are vulnerable to an
4624 exploit against CPU internal buffers which can forward
4625 information to a disclosure gadget under certain
4628 In vulnerable processors, the speculatively forwarded
4629 data can be used in a cache side channel attack, to
4630 access data to which the attacker does not have direct
4633 This parameter controls the TAA mitigation. The
4636 full - Enable TAA mitigation on vulnerable CPUs
4639 full,nosmt - Enable TAA mitigation and disable SMT on
4640 vulnerable CPUs. If TSX is disabled, SMT
4641 is not disabled because CPU is not
4642 vulnerable to cross-thread TAA attacks.
4643 off - Unconditionally disable TAA mitigation
4645 On MDS-affected machines, tsx_async_abort=off can be
4646 prevented by an active MDS mitigation as both vulnerabilities
4647 are mitigated with the same mechanism so in order to disable
4648 this mitigation, you need to specify mds=off too.
4650 Not specifying this option is equivalent to
4651 tsx_async_abort=full. On CPUs which are MDS affected
4652 and deploy MDS mitigation, TAA mitigation is not
4653 required and doesn't provide any additional
4657 Documentation/hw-vuln/tsx_async_abort.rst
4659 turbografx.map[2|3]= [HW,JOY]
4660 TurboGraFX parallel port interface
4662 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4663 See also Documentation/input/joystick-parport.txt
4665 udbg-immortal [PPC] When debugging early kernel crashes that
4666 happen after console_init() and before a proper
4667 console driver takes over, this boot options might
4668 help "seeing" what's going on.
4670 uhash_entries= [KNL,NET]
4671 Set number of hash buckets for UDP/UDP-Lite connections
4674 [USB] Ignore overcurrent events (default N).
4675 Some badly-designed motherboards generate lots of
4676 bogus events, for ports that aren't wired to
4677 anything. Set this parameter to avoid log spamming.
4678 Note that genuine overcurrent events won't be
4682 [X86] Cause panic on unknown NMI.
4684 usbcore.authorized_default=
4685 [USB] Default USB device authorization:
4686 (default -1 = authorized except for wireless USB,
4687 0 = not authorized, 1 = authorized)
4689 usbcore.autosuspend=
4690 [USB] The autosuspend time delay (in seconds) used
4691 for newly-detected USB devices (default 2). This
4692 is the time required before an idle device will be
4693 autosuspended. Devices for which the delay is set
4694 to a negative value won't be autosuspended at all.
4696 usbcore.usbfs_snoop=
4697 [USB] Set to log all usbfs traffic (default 0 = off).
4699 usbcore.usbfs_snoop_max=
4700 [USB] Maximum number of bytes to snoop in each URB
4703 usbcore.blinkenlights=
4704 [USB] Set to cycle leds on hubs (default 0 = off).
4706 usbcore.old_scheme_first=
4707 [USB] Start with the old device initialization
4708 scheme (default 0 = off).
4710 usbcore.usbfs_memory_mb=
4711 [USB] Memory limit (in MB) for buffers allocated by
4712 usbfs (default = 16, 0 = max = 2047).
4714 usbcore.use_both_schemes=
4715 [USB] Try the other device initialization scheme
4716 if the first one fails (default 1 = enabled).
4718 usbcore.initial_descriptor_timeout=
4719 [USB] Specifies timeout for the initial 64-byte
4720 USB_REQ_GET_DESCRIPTOR request in milliseconds
4721 (default 5000 = 5.0 seconds).
4723 usbcore.nousb [USB] Disable the USB subsystem
4726 [USBHID] The interval which mice are to be polled at.
4728 usb-storage.delay_use=
4729 [UMS] The delay in seconds before a new device is
4730 scanned for Logical Units (default 1).
4733 [UMS] A list of quirks entries to supplement or
4734 override the built-in unusual_devs list. List
4735 entries are separated by commas. Each entry has
4736 the form VID:PID:Flags where VID and PID are Vendor
4737 and Product ID values (4-digit hex numbers) and
4738 Flags is a set of characters, each corresponding
4739 to a common usb-storage quirk flag as follows:
4740 a = SANE_SENSE (collect more than 18 bytes
4742 b = BAD_SENSE (don't collect more than 18
4743 bytes of sense data);
4744 c = FIX_CAPACITY (decrease the reported
4745 device capacity by one sector);
4746 d = NO_READ_DISC_INFO (don't use
4747 READ_DISC_INFO command);
4748 e = NO_READ_CAPACITY_16 (don't use
4749 READ_CAPACITY_16 command);
4750 f = NO_REPORT_OPCODES (don't use report opcodes
4752 g = MAX_SECTORS_240 (don't transfer more than
4753 240 sectors at a time, uas only);
4754 h = CAPACITY_HEURISTICS (decrease the
4755 reported device capacity by one
4756 sector if the number is odd);
4757 i = IGNORE_DEVICE (don't bind to this
4759 j = NO_REPORT_LUNS (don't use report luns
4761 l = NOT_LOCKABLE (don't try to lock and
4762 unlock ejectable media);
4763 m = MAX_SECTORS_64 (don't transfer more
4764 than 64 sectors = 32 KB at a time);
4765 n = INITIAL_READ10 (force a retry of the
4766 initial READ(10) command);
4767 o = CAPACITY_OK (accept the capacity
4768 reported by the device);
4769 p = WRITE_CACHE (the device cache is ON
4771 r = IGNORE_RESIDUE (the device reports
4772 bogus residue values);
4773 s = SINGLE_LUN (the device has only one
4775 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4776 commands, uas only);
4777 u = IGNORE_UAS (don't bind to the uas driver);
4778 w = NO_WP_DETECT (don't test whether the
4779 medium is write-protected).
4780 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4781 even if the device claims no cache)
4782 Example: quirks=0419:aaf5:rl,0421:0433:rc
4784 user_debug= [KNL,ARM]
4786 See arch/arm/Kconfig.debug help text.
4787 1 - undefined instruction events
4789 4 - invalid data aborts
4792 Example: user_debug=31
4795 [X86] Flags controlling user PTE allocations.
4797 nohigh = do not allocate PTE pages in
4798 HIGHMEM regardless of setting
4802 On X86_32, this is an alias for vdso32=. Otherwise:
4804 vdso=1: enable VDSO (the default)
4805 vdso=0: disable VDSO mapping
4807 vdso32= [X86] Control the 32-bit vDSO
4808 vdso32=1: enable 32-bit VDSO
4809 vdso32=0 or vdso32=2: disable 32-bit VDSO
4811 See the help text for CONFIG_COMPAT_VDSO for more
4812 details. If CONFIG_COMPAT_VDSO is set, the default is
4813 vdso32=0; otherwise, the default is vdso32=1.
4815 For compatibility with older kernels, vdso32=2 is an
4818 Try vdso32=0 if you encounter an error that says:
4819 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4822 vector=percpu: enable percpu vector domain
4824 video= [FB] Frame buffer configuration
4825 See Documentation/fb/modedb.txt.
4827 video.brightness_switch_enabled= [0,1]
4828 If set to 1, on receiving an ACPI notify event
4829 generated by hotkey, video driver will adjust brightness
4830 level and then send out the event to user space through
4831 the allocated input device; If set to 0, video driver
4832 will only send out the event without touching backlight
4837 [VMMIO] Memory mapped virtio (platform) device.
4839 <size>@<baseaddr>:<irq>[:<id>]
4841 <size> := size (can use standard suffixes
4843 <baseaddr> := physical base address
4844 <irq> := interrupt number (as passed to
4846 <id> := (optional) platform device id
4848 virtio_mmio.device=1K@0x100b0000:48:7
4850 Can be used multiple times for multiple devices.
4852 vga= [BOOT,X86-32] Select a particular video mode
4853 See Documentation/x86/boot.txt and
4854 Documentation/svga.txt.
4855 Use vga=ask for menu.
4856 This is actually a boot loader parameter; the value is
4857 passed to the kernel using a special protocol.
4859 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4860 size of <nn>. This can be used to increase the
4861 minimum size (128MB on x86). It can also be used to
4862 decrease the size and leave more room for directly
4865 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4868 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4871 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4875 Controls the behavior of vsyscalls (i.e. calls to
4876 fixed addresses of 0xffffffffff600x00 from legacy
4877 code). Most statically-linked binaries and older
4878 versions of glibc use these calls. Because these
4879 functions are at fixed addresses, they make nice
4880 targets for exploits that can control RIP.
4882 emulate [default] Vsyscalls turn into traps and are
4883 emulated reasonably safely.
4885 native Vsyscalls are native syscall instructions.
4886 This is a little bit faster than trapping
4887 and makes a few dynamic recompilers work
4888 better than they would in emulation mode.
4889 It also makes exploits much easier to write.
4891 none Vsyscalls don't work at all. This makes
4892 them quite hard to use for exploits but
4893 might break your system.
4895 vt.color= [VT] Default text color.
4896 Format: 0xYX, X = foreground, Y = background.
4897 Default: 0x07 = light gray on black.
4899 vt.cur_default= [VT] Default cursor shape.
4900 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4901 the parameters of the <Esc>[?A;B;Cc escape sequence;
4902 see VGA-softcursor.txt. Default: 2 = underline.
4904 vt.default_blu= [VT]
4905 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4906 Change the default blue palette of the console.
4907 This is a 16-member array composed of values
4910 vt.default_grn= [VT]
4911 Format: <green0>,<green1>,<green2>,...,<green15>
4912 Change the default green palette of the console.
4913 This is a 16-member array composed of values
4916 vt.default_red= [VT]
4917 Format: <red0>,<red1>,<red2>,...,<red15>
4918 Change the default red palette of the console.
4919 This is a 16-member array composed of values
4925 Set system-wide default UTF-8 mode for all tty's.
4926 Default is 1, i.e. UTF-8 mode is enabled for all
4927 newly opened terminals.
4929 vt.global_cursor_default=
4932 Set system-wide default for whether a cursor
4933 is shown on new VTs. Default is -1,
4934 i.e. cursors will be created by default unless
4935 overridden by individual drivers. 0 will hide
4936 cursors, 1 will display them.
4938 vt.italic= [VT] Default color for italic text; 0-15.
4941 vt.underline= [VT] Default color for underlined text; 0-15.
4944 watchdog timers [HW,WDT] For information on watchdog timers,
4945 see Documentation/watchdog/watchdog-parameters.txt
4946 or other driver-specific files in the
4947 Documentation/watchdog/ directory.
4949 workqueue.watchdog_thresh=
4950 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4951 warn stall conditions and dump internal state to
4952 help debugging. 0 disables workqueue stall
4953 detection; otherwise, it's the stall threshold
4954 duration in seconds. The default value is 30 and
4955 it can be updated at runtime by writing to the
4956 corresponding sysfs file.
4958 workqueue.disable_numa
4959 By default, all work items queued to unbound
4960 workqueues are affine to the NUMA nodes they're
4961 issued on, which results in better behavior in
4962 general. If NUMA affinity needs to be disabled for
4963 whatever reason, this option can be used. Note
4964 that this also can be controlled per-workqueue for
4965 workqueues visible under /sys/bus/workqueue/.
4967 workqueue.power_efficient
4968 Per-cpu workqueues are generally preferred because
4969 they show better performance thanks to cache
4970 locality; unfortunately, per-cpu workqueues tend to
4971 be more power hungry than unbound workqueues.
4973 Enabling this makes the per-cpu workqueues which
4974 were observed to contribute significantly to power
4975 consumption unbound, leading to measurably lower
4976 power usage at the cost of small performance
4979 The default value of this parameter is determined by
4980 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4982 workqueue.debug_force_rr_cpu
4983 Workqueue used to implicitly guarantee that work
4984 items queued without explicit CPU specified are put
4985 on the local CPU. This guarantee is no longer true
4986 and while local CPU is still preferred work items
4987 may be put on foreign CPUs. This debug option
4988 forces round-robin CPU selection to flush out
4989 usages which depend on the now broken guarantee.
4990 When enabled, memory and cache locality will be
4993 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4994 default x2apic cluster mode on platforms
4997 x86_intel_mid_timer= [X86-32,APBT]
4998 Choose timer option for x86 Intel MID platform.
4999 Two valid options are apbt timer only and lapic timer
5000 plus one apbt timer for broadcast timer.
5001 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5003 xen_512gb_limit [KNL,X86-64,XEN]
5004 Restricts the kernel running paravirtualized under Xen
5005 to use only up to 512 GB of RAM. The reason to do so is
5006 crash analysis tools and Xen tools for doing domain
5007 save/restore/migration must be enabled to handle larger
5010 xen_emul_unplug= [HW,X86,XEN]
5011 Unplug Xen emulated devices
5012 Format: [unplug0,][unplug1]
5013 ide-disks -- unplug primary master IDE devices
5014 aux-ide-disks -- unplug non-primary-master IDE devices
5015 nics -- unplug network devices
5016 all -- unplug all emulated devices (NICs and IDE disks)
5017 unnecessary -- unplugging emulated devices is
5018 unnecessary even if the host did not respond to
5020 never -- do not unplug even if version check succeeds
5022 xen_nopvspin [X86,XEN]
5023 Disables the ticketlock slowpath using Xen PV
5027 Disables the PV optimizations forcing the HVM guest to
5028 run as generic HVM guest with no PV drivers.
5030 xen.event_eoi_delay= [XEN]
5031 How long to delay EOI handling in case of event
5032 storms (jiffies). Default is 10.
5034 xen.event_loop_timeout= [XEN]
5035 After which time (jiffies) the event handling loop
5036 should start to delay EOI handling. Default is 2.
5038 xirc2ps_cs= [NET,PCMCIA]
5040 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5042 ______________________________________________________________________
5046 Add more DRM drivers.
projects / releases.git / blob