Merge tag 'efi-next' of git://git.kernel.org/pub/scm/linux/kernel/git/mfleming/efi...
[linux-2.6-block.git] / Documentation / kernel-parameters.txt
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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
1da177e4 3
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4The following is a consolidated list of the kernel parameters as
5implemented by the __setup(), core_param() and module_param() macros
6and sorted into English Dictionary order (defined as ignoring all
7punctuation and sorting digits before letters in a case insensitive
8manner), and with descriptions where known.
9
10The kernel parses parameters from the kernel command line up to "--";
11if it doesn't recognize a parameter and it doesn't contain a '.', the
12parameter gets passed to init: parameters with '=' go into init's
13environment, others are passed as command line arguments to init.
14Everything after "--" is passed as an argument to init.
15
16Module parameters can be specified in two ways: via the kernel command
17line with a module name prefix, or via modprobe, e.g.:
18
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
21
22Parameters for modules which are built into the kernel need to be
23specified on the kernel command line. modprobe looks through the
24kernel command line (/proc/cmdline) and collects module parameters
25when it loads a module, so the kernel command line can be used for
26loadable modules too.
1da177e4 27
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28Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30can also be entered as
31 log-buf-len=1M print_fatal_signals=1
32
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33Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
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36This document may not be entirely up to date and comprehensive. The command
37"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38module. Loadable modules, after being loaded into the running kernel, also
39reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40parameters may be changed at runtime by the command
41"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
42
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43The parameters listed below are only valid if certain kernel build options were
44enabled and if respective hardware is present. The text in square brackets at
45the beginning of each description states the restrictions within which a
46parameter is applicable:
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47
48 ACPI ACPI support is enabled.
c99c108a 49 AGP AGP (Accelerated Graphics Port) is enabled.
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50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
16290246 53 ARM ARM architecture is enabled.
e7ba176b 54 AVR32 AVR32 architecture is enabled.
1da177e4 55 AX25 Appropriate AX.25 support is enabled.
0ae53640 56 BLACKFIN Blackfin architecture is enabled.
1e435256 57 CLK Common clock infrastructure is enabled.
5c71d618 58 CMA Contiguous Memory Area support is enabled.
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59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
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61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
7102ebcd 64 EVM Extended Verification Module
1da177e4 65 FB The frame buffer device is enabled.
16290246 66 FTRACE Function tracing enabled.
2521f2c2 67 GCOV GCOV profiling is enabled.
1da177e4 68 HW Appropriate hardware is enabled.
1da177e4 69 IA-64 IA-64 architecture is enabled.
6146f0d5 70 IMA Integrity measurement architecture is enabled.
1da177e4 71 IOSCHED More than one I/O scheduler is enabled.
41e2e8be 72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
b0f83b28 73 IPV6 IPv6 support is enabled.
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74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
84c08fd6 77 KGDB Kernel debugger support is enabled.
fef07aae 78 KVM Kernel Virtual Machine support is enabled.
11ef697b 79 LIBATA Libata driver is enabled
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80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
1da177e4 85 MDA MDA console support is enabled.
16290246 86 MIPS MIPS architecture is enabled.
1da177e4 87 MOUSE Appropriate mouse support is enabled.
309e57df 88 MSI Message Signaled Interrupts (PCI).
c8facbb6 89 MTD MTD (Memory Technology Device) support is enabled.
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90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
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94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
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96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
7f785763 98 PCIE PCI Express support is enabled.
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99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
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107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
20510f2f 109 SECURITY Different security models are enabled.
1da177e4 110 SELINUX SELinux support is enabled.
c1c124e9 111 APPARMOR AppArmor support is enabled.
1da177e4 112 SERIAL Serial support is enabled.
e523d93c 113 SH SuperH architecture is enabled.
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114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
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116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
225a9be2 118 TPM TPM drivers are enabled.
1da177e4 119 TS Appropriate touchscreen support is enabled.
d4f373e5 120 UMS USB Mass Storage support is enabled.
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121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
81a054ce 124 VMMIO Driver for memory mapped virtio devices is enabled.
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125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
cd4f0ef7 129 X86-32 X86-32, aka i386 architecture is enabled.
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130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
71cced6e 132 Documentation/x86/x86_64/boot-options.txt .
16290246 133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
c1c5413a 134 XEN Xen support is enabled
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135
136In addition, the following text indicates that the option:
137
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
141
142Parameters denoted with BOOT are actually interpreted by the boot
143loader, and have no meaning to the kernel directly.
144Do not modify the syntax of boot loader parameters without extreme
954a8b81 145need or coordination with <Documentation/x86/boot.txt>.
1da177e4 146
5558870b 147There are also arch-specific kernel-parameters not documented here.
71cced6e 148See for example <Documentation/x86/x86_64/boot-options.txt>.
5558870b 149
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150Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151a trailing = on the name of any parameter states that that parameter will
152be entered as an environment variable, whereas its absence indicates that
153it will appear as a kernel argument readable via /proc/cmdline by programs
154running once the system is up.
155
9c4751fd 156The number of kernel parameters is not limited, but the length of the
157complete command line (parameters including spaces etc.) is limited to
158a fixed number of characters. This limit depends on the architecture
159and is between 256 and 4096 characters. It is defined in the file
160./include/asm/setup.h as COMMAND_LINE_SIZE.
161
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162Finally, the [KMG] suffix is commonly described after a number of kernel
163parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165bytes respectively. Such letter suffixes can also be entirely omitted.
166
9c4751fd 167
b10d79f7 168 acpi= [HW,ACPI,X86,ARM64]
03d926f8 169 Advanced Configuration and Power Interface
68ca4069 170 Format: { force | off | strict | noirq | rsdt }
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171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
a9913044 174 strict -- Be less tolerant of platforms that are not
1da177e4 175 strictly ACPI specification compliant.
237889bf 176 rsdt -- prefer RSDT over (default) XSDT
aa2110cb 177 copy_dsdt -- copy DSDT to memory
b10d79f7 178 For ARM64, ONLY "acpi=off" or "acpi=force" are available
1da177e4 179
395cf969 180 See also Documentation/power/runtime_pm.txt, pci=noacpi
1da177e4 181
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182 acpi_apic_instance= [ACPI, IOAPIC]
183 Format: <int>
184 2: use 2nd APIC table, if available
185 1,0: use 1st APIC table
4e381a4f 186 default: 0
a1fdcc0d 187
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188 acpi_backlight= [HW,ACPI]
189 acpi_backlight=vendor
190 acpi_backlight=video
191 If set to vendor, prefer vendor specific driver
192 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
193 of the ACPI video.ko driver.
194
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195 acpica_no_return_repair [HW, ACPI]
196 Disable AML predefined validation mechanism
197 This mechanism can repair the evaluation result to make
198 the return objects more ACPI specification compliant.
199 This option is useful for developers to identify the
200 root cause of an AML interpreter issue when the issue
201 has something to do with the repair mechanism.
202
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203 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
204 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
1da177e4 205 Format: <int>
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206 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
207 debug output. Bits in debug_layer correspond to a
208 _COMPONENT in an ACPI source file, e.g.,
209 #define _COMPONENT ACPI_PCI_COMPONENT
210 Bits in debug_level correspond to a level in
211 ACPI_DEBUG_PRINT statements, e.g.,
212 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
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213 The debug_level mask defaults to "info". See
214 Documentation/acpi/debug.txt for more information about
215 debug layers and levels.
a0d84a92 216
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217 Enable processor driver info messages:
218 acpi.debug_layer=0x20000000
219 Enable PCI/PCI interrupt routing info messages:
220 acpi.debug_layer=0x400000
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221 Enable AML "Debug" output, i.e., stores to the Debug
222 object while interpreting AML:
223 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
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224 Enable all messages related to ACPI hardware:
225 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
226
227 Some values produce so much output that the system is
228 unusable. The "log_buf_len" parameter may be useful
229 if you need to capture more output.
f989106c 230
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231 acpi_enforce_resources= [ACPI]
232 { strict | lax | no }
233 Check for resource conflicts between native drivers
234 and ACPI OperationRegions (SystemIO and SystemMemory
235 only). IO ports and memory declared in ACPI might be
236 used by the ACPI subsystem in arbitrary AML code and
237 can interfere with legacy drivers.
238 strict (default): access to resources claimed by ACPI
239 is denied; legacy drivers trying to access reserved
240 resources will fail to bind to device using them.
241 lax: access to resources claimed by ACPI is allowed;
242 legacy drivers trying to access reserved resources
243 will bind successfully but a warning message is logged.
244 no: ACPI OperationRegions are not marked as reserved,
245 no further checks are performed.
246
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247 acpi_force_table_verification [HW,ACPI]
248 Enable table checksum verification during early stage.
249 By default, this is disabled due to x86 early mapping
250 size limitation.
251
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252 acpi_irq_balance [HW,ACPI]
253 ACPI will balance active IRQs
254 default in APIC mode
255
256 acpi_irq_nobalance [HW,ACPI]
257 ACPI will not move active IRQs (default)
258 default in PIC mode
259
260 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
261 Format: <irq>,<irq>...
262
263 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
264 use by PCI
265 Format: <irq>,<irq>...
266
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267 acpi_no_auto_serialize [HW,ACPI]
268 Disable auto-serialization of AML methods
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269 AML control methods that contain the opcodes to create
270 named objects will be marked as "Serialized" by the
271 auto-serialization feature.
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272 This feature is enabled by default.
273 This option allows to turn off the feature.
22b5afce 274
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275 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
276 kernels.
277
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278 acpi_no_static_ssdt [HW,ACPI]
279 Disable installation of static SSDTs at early boot time
280 By default, SSDTs contained in the RSDT/XSDT will be
281 installed automatically and they will appear under
282 /sys/firmware/acpi/tables.
283 This option turns off this feature.
284 Note that specifying this option does not affect
285 dynamic table installation which will install SSDT
286 tables to /sys/firmware/acpi/tables/dynamic.
0cb55ad2 287
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288 acpi_rsdp= [ACPI,EFI,KEXEC]
289 Pass the RSDP address to the kernel, mostly used
290 on machines running EFI runtime service to boot the
291 second kernel for kdump.
4dde507f 292
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293 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
294 Format: To spoof as Windows 98: ="Microsoft Windows"
295
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296 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
297 of 2 which is mandated by ACPI 6) as the supported ACPI
298 specification revision (when using this switch, it may
299 be necessary to carry out a cold reboot _twice_ in a
300 row to make it take effect on the platform firmware).
301
0cb55ad2 302 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
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303 acpi_osi="string1" # add string1
304 acpi_osi="!string2" # remove string2
741d8128 305 acpi_osi=!* # remove all strings
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306 acpi_osi=! # disable all built-in OS vendor
307 strings
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308 acpi_osi= # disable all strings
309
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310 'acpi_osi=!' can be used in combination with single or
311 multiple 'acpi_osi="string1"' to support specific OS
312 vendor string(s). Note that such command can only
313 affect the default state of the OS vendor strings, thus
314 it cannot affect the default state of the feature group
315 strings and the current state of the OS vendor strings,
316 specifying it multiple times through kernel command line
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317 is meaningless. This command is useful when one do not
318 care about the state of the feature group strings which
319 should be controlled by the OSPM.
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320 Examples:
321 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
322 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
323 can make '_OSI("Windows 2000")' TRUE.
324
325 'acpi_osi=' cannot be used in combination with other
326 'acpi_osi=' command lines, the _OSI method will not
327 exist in the ACPI namespace. NOTE that such command can
328 only affect the _OSI support state, thus specifying it
329 multiple times through kernel command line is also
330 meaningless.
331 Examples:
332 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
333 FALSE.
334
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335 'acpi_osi=!*' can be used in combination with single or
336 multiple 'acpi_osi="string1"' to support specific
337 string(s). Note that such command can affect the
338 current state of both the OS vendor strings and the
339 feature group strings, thus specifying it multiple times
340 through kernel command line is meaningful. But it may
341 still not able to affect the final state of a string if
342 there are quirks related to this string. This command
343 is useful when one want to control the state of the
344 feature group strings to debug BIOS issues related to
345 the OSPM features.
346 Examples:
347 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
348 '_OSI("Module Device")' FALSE.
349 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
350 '_OSI("Module Device")' TRUE.
351 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
352 equivalent to
353 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
354 and
355 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
356 they all will make '_OSI("Windows 2000")' TRUE.
357
6cececfc 358 acpi_pm_good [X86]
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359 Override the pmtimer bug detection: force the kernel
360 to assume that this machine's pmtimer latches its value
361 and always returns good values.
362
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363 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
364 Format: { level | edge | high | low }
365
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366 acpi_skip_timer_override [HW,ACPI]
367 Recognize and ignore IRQ0/pin2 Interrupt Override.
368 For broken nForce2 BIOS resulting in XT-PIC timer.
369
370 acpi_sleep= [HW,ACPI] Sleep options
371 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
c3b0795c 372 old_ordering, nonvs, sci_force_enable }
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373 See Documentation/power/video.txt for information on
374 s3_bios and s3_mode.
375 s3_beep is for debugging; it makes the PC's speaker beep
376 as soon as the kernel's real-mode entry point is called.
377 s4_nohwsig prevents ACPI hardware signature from being
378 used during resume from hibernation.
379 old_ordering causes the ACPI 1.0 ordering of the _PTS
380 control method, with respect to putting devices into
381 low power states, to be enforced (the ACPI 2.0 ordering
382 of _PTS is used by default).
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383 nonvs prevents the kernel from saving/restoring the
384 ACPI NVS memory during suspend/hibernation and resume.
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385 sci_force_enable causes the kernel to set SCI_EN directly
386 on resume from S1/S3 (which is against the ACPI spec,
387 but some broken systems don't work without it).
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388
389 acpi_use_timer_override [HW,ACPI]
390 Use timer override. For some broken Nvidia NF5 boards
391 that require a timer override, but don't have HPET
392
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393 add_efi_memmap [EFI; X86] Include EFI memory map in
394 kernel's map of available physical RAM.
395
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396 agp= [AGP]
397 { off | try_unsupported }
398 off: disable AGP support
399 try_unsupported: try to drive unsupported chipsets
400 (may crash computer or cause data corruption)
401
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402 ALSA [HW,ALSA]
403 See Documentation/sound/alsa/alsa-parameters.txt
404
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405 alignment= [KNL,ARM]
406 Allow the default userspace alignment fault handler
407 behaviour to be specified. Bit 0 enables warnings,
408 bit 1 enables fixups, and bit 2 sends a segfault.
409
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410 align_va_addr= [X86-64]
411 Align virtual addresses by clearing slice [14:12] when
412 allocating a VMA at process creation time. This option
413 gives you up to 3% performance improvement on AMD F15h
414 machines (where it is enabled by default) for a
415 CPU-intensive style benchmark, and it can vary highly in
416 a microbenchmark depending on workload and compiler.
417
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418 32: only for 32-bit processes
419 64: only for 64-bit processes
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420 on: enable for both 32- and 64-bit processes
421 off: disable for both 32- and 64-bit processes
422
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423 alloc_snapshot [FTRACE]
424 Allocate the ftrace snapshot buffer on boot up when the
425 main buffer is allocated. This is handy if debugging
426 and you need to use tracing_snapshot() on boot up, and
427 do not want to use tracing_snapshot_alloc() as it needs
428 to be done where GFP_KERNEL allocations are allowed.
429
89e0b9a3 430 amd_iommu= [HW,X86-64]
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431 Pass parameters to the AMD IOMMU driver in the system.
432 Possible values are:
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433 fullflush - enable flushing of IO/TLB entries when
434 they are unmapped. Otherwise they are
435 flushed before they will be reused, which
436 is a lot of faster
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437 off - do not initialize any AMD IOMMU found in
438 the system
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439 force_isolation - Force device isolation for all
440 devices. The IOMMU driver is not
441 allowed anymore to lift isolation
442 requirements as needed. This option
443 does not override iommu=pt
afa9fdc2 444
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445 amd_iommu_dump= [HW,X86-64]
446 Enable AMD IOMMU driver option to dump the ACPI table
447 for AMD IOMMU. With this option enabled, AMD IOMMU
448 driver will print ACPI tables for AMD IOMMU during
449 IOMMU initialization.
450
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451 amijoy.map= [HW,JOY] Amiga joystick support
452 Map of devices attached to JOY0DAT and JOY1DAT
453 Format: <a>,<b>
395cf969 454 See also Documentation/input/joystick.txt
1da177e4
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455
456 analog.map= [HW,JOY] Analog joystick and gamepad support
457 Specifies type or capabilities of an analog joystick
458 connected to one of 16 gameports
459 Format: <type1>,<type2>,..<type16>
460
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461 apc= [HW,SPARC]
462 Power management functions (SPARCstation-4/5 + deriv.)
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463 Format: noidle
464 Disable APC CPU standby support. SPARCstation-Fox does
465 not play well with APC CPU idle - disable it if you have
466 APC and your system crashes randomly.
467
ca1eda2d 468 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
c8facbb6 469 Change the output verbosity whilst booting
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470 Format: { quiet (default) | verbose | debug }
471 Change the amount of debugging information output
472 when initialising the APIC and IO-APIC components.
a9913044 473
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474 autoconf= [IPV6]
475 See Documentation/networking/ipv6.txt.
476
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477 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
478 Limit apic dumping. The parameter defines the maximal
479 number of local apics being dumped. Also it is possible
480 to set it to "all" by meaning -- no limit here.
481 Format: { 1 (default) | 2 | ... | all }.
482 The parameter valid if only apic=debug or
483 apic=verbose is specified.
484 Example: apic=debug show_lapic=all
485
1da177e4 486 apm= [APM] Advanced Power Management
71f77055 487 See header of arch/x86/kernel/apm_32.c.
1da177e4 488
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489 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
490 Format: <io>,<irq>,<nodeID>
491
492 ataflop= [HW,M68k]
493
494 atarimouse= [HW,MOUSE] Atari Mouse
495
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496 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
497 EzKey and similar keyboards
498
499 atkbd.reset= [HW] Reset keyboard during initialization
500
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501 atkbd.set= [HW] Select keyboard code set
502 Format: <int> (2 = AT (default), 3 = PS/2)
1da177e4
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503
504 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
505 keyboards
506
507 atkbd.softraw= [HW] Choose between synthetic and real raw mode
508 Format: <bool> (0 = real, 1 = synthetic (default))
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509
510 atkbd.softrepeat= [HW]
511 Use software keyboard repeat
1da177e4 512
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513 audit= [KNL] Enable the audit sub-system
514 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
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515 0 - kernel audit is disabled and can not be enabled
516 until the next reboot
517 unset - kernel audit is initialized but disabled and
518 will be fully enabled by the userspace auditd.
519 1 - kernel audit is initialized and partially enabled,
520 storing at most audit_backlog_limit messages in
521 RAM until it is fully enabled by the userspace
522 auditd.
a106fb0c 523 Default: unset
f3411cb2 524
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525 audit_backlog_limit= [KNL] Set the audit queue size limit.
526 Format: <int> (must be >=0)
527 Default: 64
528
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529 baycom_epp= [HW,AX25]
530 Format: <io>,<mode>
a9913044 531
1da177e4
LT
532 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
533 Format: <io>,<mode>
534 See header of drivers/net/hamradio/baycom_par.c.
535
a9913044
RD
536 baycom_ser_fdx= [HW,AX25]
537 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
1da177e4
LT
538 Format: <io>,<irq>,<mode>[,<baud>]
539 See header of drivers/net/hamradio/baycom_ser_fdx.c.
540
a9913044
RD
541 baycom_ser_hdx= [HW,AX25]
542 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
1da177e4
LT
543 Format: <io>,<irq>,<mode>
544 See header of drivers/net/hamradio/baycom_ser_hdx.c.
545
080506ad
PG
546 blkdevparts= Manual partition parsing of block device(s) for
547 embedded devices based on command line input.
548 See Documentation/block/cmdline-partition.txt
549
bfe8df3d
RD
550 boot_delay= Milliseconds to delay each printk during boot.
551 Values larger than 10 seconds (10000) are changed to
552 no delay (0).
553 Format: integer
554
35fc908d
AH
555 bootmem_debug [KNL] Enable bootmem allocator debug messages.
556
1da177e4 557 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
a9913044
RD
558 bttv.radio= Most important insmod options are available as
559 kernel args too.
1da177e4 560 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
395cf969 561 bttv.tuner=
1da177e4 562
4e89a2d8
WS
563 bulk_remove=off [PPC] This parameter disables the use of the pSeries
564 firmware feature for flushing multiple hpte entries
565 at a time.
566
1da177e4
LT
567 c101= [NET] Moxa C101 synchronous serial card
568
cd4f0ef7 569 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
1da177e4
LT
570 Sometimes CPU hardware bugs make them report the cache
571 size incorrectly. The kernel will attempt work arounds
572 to fix known problems, but for some CPUs it is not
573 possible to determine what the correct size should be.
574 This option provides an override for these situations.
575
ffb70f61
DK
576 ca_keys= [KEYS] This parameter identifies a specific key(s) on
577 the system trusted keyring to be used for certificate
578 trust validation.
32c4741c 579 format: { id:<keyid> | builtin }
ffb70f61 580
fd1bb4c9
FF
581 cca= [MIPS] Override the kernel pages' cache coherency
582 algorithm. Accepted values range from 0 to 7
583 inclusive. See arch/mips/include/asm/pgtable-bits.h
584 for platform specific values (SB1, Loongson3 and
585 others).
586
14ff56bb
SO
587 ccw_timeout_log [S390]
588 See Documentation/s390/CommonIO for details.
1da177e4 589
8bab8dde
PM
590 cgroup_disable= [KNL] Disable a particular controller
591 Format: {name of the controller(s) to disable}
ca0bdbb5
QH
592 The effects of cgroup_disable=foo are:
593 - foo isn't auto-mounted if you mount all cgroups in
594 a single hierarchy
595 - foo isn't visible as an individually mountable
596 subsystem
597 {Currently only "memory" controller deal with this and
598 cut the overhead, others just disable the usage. So
599 only cgroup_disable=memory is actually worthy}
8bab8dde 600
1da177e4
LT
601 checkreqprot [SELINUX] Set initial checkreqprot flag value.
602 Format: { "0" | "1" }
603 See security/selinux/Kconfig help text.
a9913044
RD
604 0 -- check protection applied by kernel (includes
605 any implied execute protection).
1da177e4
LT
606 1 -- check protection requested by application.
607 Default value is set via a kernel config option.
a9913044
RD
608 Value can be changed at runtime via
609 /selinux/checkreqprot.
610
661ca0da
SO
611 cio_ignore= [S390]
612 See Documentation/s390/CommonIO for details.
1e435256
OJ
613 clk_ignore_unused
614 [CLK]
e156ee56
MT
615 Prevents the clock framework from automatically gating
616 clocks that have not been explicitly enabled by a Linux
617 device driver but are enabled in hardware at reset or
618 by the bootloader/firmware. Note that this does not
619 force such clocks to be always-on nor does it reserve
620 those clocks in any way. This parameter is useful for
621 debug and development, but should not be needed on a
622 platform with proper driver support. For more
623 information, see Documentation/clk.txt.
661ca0da 624
cd4f0ef7 625 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
734efb46 626 [Deprecated]
3f6dee9b 627 Forces specified clocksource (if available) to be used
734efb46 628 when calculating gettimeofday(). If specified
3f6dee9b 629 clocksource is not available, it defaults to PIT.
1da177e4
LT
630 Format: { pit | tsc | cyclone | pmtmr }
631
592913ec 632 clocksource= Override the default clocksource
3d6ac984
RD
633 Format: <string>
634 Override the default clocksource and use the clocksource
635 with the name specified.
636 Some clocksource names to choose from, depending on
637 the platform:
638 [all] jiffies (this is the base, fallback clocksource)
639 [ACPI] acpi_pm
640 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
641 pxa_timer,timer3,32k_counter,timer0_1
642 [AVR32] avr32
9863c90f 643 [X86-32] pit,hpet,tsc;
3d6ac984
RD
644 scx200_hrt on Geode; cyclone on IBM x440
645 [MIPS] MIPS
646 [PARISC] cr16
647 [S390] tod
648 [SH] SuperH
649 [SPARC64] tick
650 [X86-64] hpet,tsc
651
ac72e788
AK
652 clearcpuid=BITNUM [X86]
653 Disable CPUID feature X for the kernel. See
07983f0e
RD
654 arch/x86/include/asm/cpufeature.h for the valid bit
655 numbers. Note the Linux specific bits are not necessarily
ac72e788
AK
656 stable over kernel options, but the vendor specific
657 ones should be.
658 Also note that user programs calling CPUID directly
659 or using the feature without checking anything
660 will still see it. This just prevents it from
661 being used by the kernel or shown in /proc/cpuinfo.
662 Also note the kernel might malfunction if you disable
663 some critical bits.
664
5ea3b1b2
AM
665 cma=nn[MG]@[start[MG][-end[MG]]]
666 [ARM,X86,KNL]
667 Sets the size of kernel global memory area for
668 contiguous memory allocations and optionally the
669 placement constraint by the physical address range of
f0d6d1f6
JD
670 memory allocations. A value of 0 disables CMA
671 altogether. For more information, see
c64be2bb
MS
672 include/linux/dma-contiguous.h
673
14f966e7
RJ
674 cmo_free_hint= [PPC] Format: { yes | no }
675 Specify whether pages are marked as being inactive
676 when they are freed. This is used in CMO environments
677 to determine OS memory pressure for page stealing by
678 a hypervisor.
679 Default: yes
680
c7909509
MS
681 coherent_pool=nn[KMG] [ARM,KNL]
682 Sets the size of memory pool for coherent, atomic dma
e9da6e99 683 allocations, by default set to 256K.
c7909509 684
6cececfc 685 code_bytes [X86] How many bytes of object code to print
a25bd949 686 in an oops report.
86c41837
CE
687 Range: 0 - 8192
688 Default: 64
689
1da177e4 690 com20020= [HW,NET] ARCnet - COM20020 chipset
a9913044
RD
691 Format:
692 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
1da177e4
LT
693
694 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
695 Format: <io>[,<irq>]
696
a9913044
RD
697 com90xx= [HW,NET]
698 ARCnet - COM90xx chipset (memory-mapped buffers)
1da177e4
LT
699 Format: <io>[,<irq>[,<memstart>]]
700
701 condev= [HW,S390] console device
702 conmode=
a9913044 703
1da177e4
LT
704 console= [KNL] Output console device and options.
705
706 tty<n> Use the virtual console device <n>.
707
708 ttyS<n>[,options]
f1a1c2dc 709 ttyUSB0[,options]
1da177e4 710 Use the specified serial port. The options are of
f1a1c2dc
RD
711 the form "bbbbpnf", where "bbbb" is the baud rate,
712 "p" is parity ("n", "o", or "e"), "n" is number of
713 bits, and "f" is flow control ("r" for RTS or
714 omit it). Default is "9600n8".
715
716 See Documentation/serial-console.txt for more
717 information. See
718 Documentation/networking/netconsole.txt for an
719 alternative.
1da177e4 720
18a8bd94
YL
721 uart[8250],io,<addr>[,options]
722 uart[8250],mmio,<addr>[,options]
ca782f16
PH
723 uart[8250],mmio32,<addr>[,options]
724 uart[8250],0x<addr>[,options]
1da177e4
LT
725 Start an early, polled-mode console on the 8250/16550
726 UART at the specified I/O port or MMIO address,
ca782f16
PH
727 switching to the matching ttyS device later.
728 MMIO inter-register address stride is either 8-bit
729 (mmio) or 32-bit (mmio32).
730 If none of [io|mmio|mmio32], <addr> is assumed to be
731 equivalent to 'mmio'. 'options' are specified in the
732 same format described for ttyS above; if unspecified,
733 the h/w is not re-initialized.
734
a2fd6419
KRW
735 hvc<n> Use the hypervisor console device <n>. This is for
736 both Xen and PowerPC hypervisors.
1da177e4 737
f7511d5f
ST
738 If the device connected to the port is not a TTY but a braille
739 device, prepend "brl," before the device type, for instance
740 console=brl,ttyS0
741 For now, only VisioBraille is supported.
742
f324edc8
DM
743 consoleblank= [KNL] The console blank (screen saver) timeout in
744 seconds. Defaults to 10*60 = 10mins. A value of 0
745 disables the blank timer.
746
4cb0e11b
HK
747 coredump_filter=
748 [KNL] Change the default value for
749 /proc/<pid>/coredump_filter.
750 See also Documentation/filesystems/proc.txt.
751
62027aea
LB
752 cpuidle.off=1 [CPU_IDLE]
753 disable the cpuidle sub-system
754
d68921f9
LB
755 cpu_init_udelay=N
756 [X86] Delay for N microsec between assert and de-assert
757 of APIC INIT to start processors. This delay occurs
758 on every CPU online, such as boot, and resume from suspend.
759 Default: 10000
760
1da177e4 761 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
a9913044
RD
762 Format:
763 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
1da177e4 764
6f21e646
AD
765 crashkernel=size[KMG][@offset[KMG]]
766 [KNL] Using kexec, Linux can switch to a 'crash kernel'
767 upon panic. This parameter reserves the physical
768 memory region [offset, offset + size] for that kernel
769 image. If '@offset' is omitted, then a suitable offset
770 is selected automatically. Check
771 Documentation/kdump/kdump.txt for further details.
dc009d92 772
fb391599
BW
773 crashkernel=range1:size1[,range2:size2,...][@offset]
774 [KNL] Same as above, but depends on the memory
775 in the running system. The syntax of range is
776 start-[end] where start and end are both
777 a memory unit (amount[KMG]). See also
6f21e646 778 Documentation/kdump/kdump.txt for an example.
fb391599 779
adbc742b 780 crashkernel=size[KMG],high
55a20ee7
YL
781 [KNL, x86_64] range could be above 4G. Allow kernel
782 to allocate physical memory region from top, so could
783 be above 4G if system have more than 4G ram installed.
784 Otherwise memory region will be allocated below 4G, if
785 available.
786 It will be ignored if crashkernel=X is specified.
adbc742b
YL
787 crashkernel=size[KMG],low
788 [KNL, x86_64] range under 4G. When crashkernel=X,high
789 is passed, kernel could allocate physical memory region
c729de8f
YL
790 above 4G, that cause second kernel crash on system
791 that require some amount of low memory, e.g. swiotlb
792 requires at least 64M+32K low memory. Kernel would
793 try to allocate 72M below 4G automatically.
794 This one let user to specify own low range under 4G
795 for second kernel instead.
796 0: to disable low allocation.
adbc742b 797 It will be ignored when crashkernel=X,high is not used
55a20ee7 798 or memory reserved is below 4G.
c729de8f 799
1da177e4
LT
800 cs89x0_dma= [HW,NET]
801 Format: <dma>
802
803 cs89x0_media= [HW,NET]
804 Format: { rj45 | aui | bnc }
a9913044 805
a9913044 806 dasd= [HW,NET]
1da177e4
LT
807 See header of drivers/s390/block/dasd_devmap.c.
808
809 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
810 (one device per port)
811 Format: <port#>,<type>
812 See also Documentation/input/joystick-parport.txt
813
a648ec05
TR
814 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
815 time. See Documentation/dynamic-debug-howto.txt for
29e36c9f 816 details. Deprecated, see dyndbg.
a648ec05 817
1da177e4
LT
818 debug [KNL] Enable kernel debugging (events log level).
819
cae2ed9a
IM
820 debug_locks_verbose=
821 [KNL] verbose self-tests
822 Format=<0|1>
823 Print debugging info while doing the locking API
824 self-tests.
825 We default to 0 (no extra messages), setting it to
826 1 will print _a lot_ more information - normally
827 only useful to kernel developers.
828
3ac7fe5a
TG
829 debug_objects [KNL] Enable object debugging
830
3e8ebb5c
KM
831 no_debug_objects
832 [KNL] Disable object debugging
833
c0a32fc5
SG
834 debug_guardpage_minorder=
835 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
836 parameter allows control of the order of pages that will
837 be intentionally kept free (and hence protected) by the
838 buddy allocator. Bigger value increase the probability
839 of catching random memory corruption, but reduce the
840 amount of memory for normal system use. The maximum
841 possible value is MAX_ORDER/2. Setting this parameter
842 to 1 or 2 should be enough to identify most random
843 memory corruption problems caused by bugs in kernel or
844 driver code when a CPU writes to (or reads from) a
845 random memory location. Note that there exists a class
846 of memory corruptions problems caused by buggy H/W or
847 F/W or by drivers badly programing DMA (basically when
848 memory is written at bus level and the CPU MMU is
849 bypassed) which are not detectable by
850 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
851 tracking down these problems.
852
031bc574
JK
853 debug_pagealloc=
854 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
855 parameter enables the feature at boot time. In
856 default, it is disabled. We can avoid allocating huge
857 chunk of memory for debug pagealloc if we don't enable
858 it at boot time and the system will work mostly same
859 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
860 on: enable the feature
861
d3af01f1
TG
862 debugpat [X86] Enable PAT debugging
863
2d27a966 864 decnet.addr= [HW,NET]
1da177e4
LT
865 Format: <area>[,<node>]
866 See also Documentation/networking/decnet.txt.
867
0cb55ad2
RD
868 default_hugepagesz=
869 [same as hugepagesz=] The size of the default
870 HugeTLB page size. This is the size represented by
871 the legacy /proc/ hugepages APIs, used for SHM, and
872 default size when mounting hugetlbfs filesystems.
873 Defaults to the default architecture's huge page size
874 if not specified.
55ff9780 875
1da177e4
LT
876 dhash_entries= [KNL]
877 Set number of hash buckets for dentry cache.
a9913044 878
b0f83b28
BH
879 disable= [IPV6]
880 See Documentation/networking/ipv6.txt.
881
151e0c7d
HD
882 disable_cpu_apicid= [X86,APIC,SMP]
883 Format: <int>
884 The number of initial APIC ID for the
885 corresponding CPU to be disabled at boot,
886 mostly used for the kdump 2nd kernel to
887 disable BSP to wake up multiple CPUs without
888 causing system reset or hang due to sending
889 INIT from AP to BSP.
890
4e8b0cf4
NA
891 disable_ddw [PPC/PSERIES]
892 Disable Dynamic DMA Window support. Use this if
893 to workaround buggy firmware.
894
b0f83b28
BH
895 disable_ipv6= [IPV6]
896 See Documentation/networking/ipv6.txt.
897
95ffa243 898 disable_mtrr_cleanup [X86]
95ffa243
YL
899 The kernel tries to adjust MTRR layout from continuous
900 to discrete, to make X server driver able to add WB
0cb55ad2 901 entry later. This parameter disables that.
95ffa243 902
093af8d7 903 disable_mtrr_trim [X86, Intel and AMD only]
99fc8d42
JB
904 By default the kernel will trim any uncacheable
905 memory out of your available memory pool based on
906 MTRR settings. This parameter disables that behavior,
907 possibly causing your machine to run very slowly.
908
6cececfc 909 disable_timer_pin_1 [X86]
0cb55ad2
RD
910 Disable PIN 1 of APIC timer
911 Can be useful to work around chipset bugs.
912
ce14c583
PB
913 dis_ucode_ldr [X86] Disable the microcode loader.
914
0cb55ad2
RD
915 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
916 this option disables the debugging code at boot.
917
918 dma_debug_entries=<number>
919 This option allows to tune the number of preallocated
920 entries for DMA-API debugging code. One entry is
921 required per DMA-API allocation. Use this if the
922 DMA-API debugging code disables itself because the
923 architectural default is too low.
924
1745de5e
JR
925 dma_debug_driver=<driver_name>
926 With this option the DMA-API debugging driver
927 filter feature can be enabled at boot time. Just
928 pass the driver to filter for as the parameter.
929 The filter can be disabled or changed to another
930 driver later using sysfs.
931
da0df92b
CE
932 drm_kms_helper.edid_firmware=[<connector>:]<file>
933 Broken monitors, graphic adapters and KVMs may
934 send no or incorrect EDID data sets. This parameter
935 allows to specify an EDID data set in the
936 /lib/firmware directory that is used instead.
937 Generic built-in EDID data sets are used, if one of
938 edid/1024x768.bin, edid/1280x1024.bin,
939 edid/1680x1050.bin, or edid/1920x1080.bin is given
940 and no file with the same name exists. Details and
941 instructions how to build your own EDID data are
942 available in Documentation/EDID/HOWTO.txt. An EDID
943 data set will only be used for a particular connector,
944 if its name and a colon are prepended to the EDID
945 name.
946
1da177e4
LT
947 dscc4.setup= [NET]
948
29e36c9f
JC
949 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
950 module.dyndbg[="val"]
951 Enable debug messages at boot time. See
952 Documentation/dynamic-debug-howto.txt for details.
953
8c3641e9
DH
954 nompx [X86] Disables Intel Memory Protection Extensions.
955 See Documentation/x86/intel_mpx.txt for more
956 information about the feature.
957
f29ba61d
BP
958 eagerfpu= [X86]
959 on enable eager fpu restore
960 off disable eager fpu restore
961 auto selects the default scheme, which automatically
962 enables eagerfpu restore for xsaveopt.
963
f2411da7
LR
964 module.async_probe [KNL]
965 Enable asynchronous probe on this module.
966
56aeeba8
MS
967 early_ioremap_debug [KNL]
968 Enable debug messages in early_ioremap support. This
969 is useful for tracking down temporary early mappings
970 which are not unmapped.
971
0cb55ad2 972 earlycon= [KNL] Output early console device and options.
0d3c673e 973
6fa62fc4
MS
974 cdns,<addr>
975 Start an early, polled-mode console on a cadence serial
976 port at the specified address. The cadence serial port
977 must already be setup and configured. Options are not
978 yet supported.
979
0cb55ad2
RD
980 uart[8250],io,<addr>[,options]
981 uart[8250],mmio,<addr>[,options]
1917ac76 982 uart[8250],mmio32,<addr>[,options]
6e63be3f 983 uart[8250],mmio32be,<addr>[,options]
ca782f16 984 uart[8250],0x<addr>[,options]
0cb55ad2
RD
985 Start an early, polled-mode console on the 8250/16550
986 UART at the specified I/O port or MMIO address.
16290246 987 MMIO inter-register address stride is either 8-bit
6e63be3f
NC
988 (mmio) or 32-bit (mmio32 or mmio32be).
989 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
990 to be equivalent to 'mmio'. 'options' are specified
991 in the same format described for "console=ttyS<n>"; if
ca782f16 992 unspecified, the h/w is not initialized.
0cb55ad2 993
0d3c673e
RH
994 pl011,<addr>
995 Start an early, polled-mode console on a pl011 serial
996 port at the specified address. The pl011 serial port
997 must already be setup and configured. Options are not
998 yet supported.
999
0efe7296
SB
1000 msm_serial,<addr>
1001 Start an early, polled-mode console on an msm serial
1002 port at the specified address. The serial port
1003 must already be setup and configured. Options are not
1004 yet supported.
1005
1006 msm_serial_dm,<addr>
1007 Start an early, polled-mode console on an msm serial
1008 dm port at the specified address. The serial port
1009 must already be setup and configured. Options are not
1010 yet supported.
1011
d50d7269
RH
1012 smh Use ARM semihosting calls for early console.
1013
b94ba032
TF
1014 s3c2410,<addr>
1015 s3c2412,<addr>
1016 s3c2440,<addr>
1017 s3c6400,<addr>
1018 s5pv210,<addr>
1019 exynos4210,<addr>
1020 Use early console provided by serial driver available
1021 on Samsung SoCs, requires selecting proper type and
1022 a correct base address of the selected UART port. The
1023 serial port must already be setup and configured.
1024 Options are not yet supported.
1025
7913ad1a 1026 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1da177e4 1027 earlyprintk=vga
72548e83 1028 earlyprintk=efi
2482a92e 1029 earlyprintk=xen
1da177e4 1030 earlyprintk=serial[,ttySn[,baudrate]]
147ea091 1031 earlyprintk=serial[,0x...[,baudrate]]
ea3acb19 1032 earlyprintk=ttySn[,baudrate]
9780bc41 1033 earlyprintk=dbgp[debugController#]
c43088e3 1034 earlyprintk=pciserial,bus:device.function[,baudrate]
1da177e4 1035
147ea091
DH
1036 earlyprintk is useful when the kernel crashes before
1037 the normal console is initialized. It is not enabled by
1038 default because it has some cosmetic problems.
1039
a9913044 1040 Append ",keep" to not disable it when the real console
1da177e4
LT
1041 takes over.
1042
72548e83
MF
1043 Only one of vga, efi, serial, or usb debug port can
1044 be used at a time.
1da177e4 1045
147ea091
DH
1046 Currently only ttyS0 and ttyS1 may be specified by
1047 name. Other I/O ports may be explicitly specified
1048 on some architectures (x86 and arm at least) by
1049 replacing ttySn with an I/O port address, like this:
1050 earlyprintk=serial,0x1008,115200
1051 You can find the port for a given device in
1052 /proc/tty/driver/serial:
1053 2: uart:ST16650V2 port:00001008 irq:18 ...
1da177e4
LT
1054
1055 Interaction with the standard serial driver is not
1056 very good.
1057
72548e83
MF
1058 The VGA and EFI output is eventually overwritten by
1059 the real console.
1da177e4 1060
2482a92e
KRW
1061 The xen output can only be used by Xen PV guests.
1062
c700f013
CG
1063 edac_report= [HW,EDAC] Control how to report EDAC event
1064 Format: {"on" | "off" | "force"}
1065 on: enable EDAC to report H/W event. May be overridden
1066 by other higher priority error reporting module.
1067 off: disable H/W event reporting through EDAC.
1068 force: enforce the use of EDAC to report H/W event.
1069 default: on.
1070
9731191f
JW
1071 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1072 ekgdboc=kbd
1073
25985edc 1074 This is designed to be used in conjunction with
9731191f
JW
1075 the boot argument: earlyprintk=vga
1076
1da177e4 1077 edd= [EDD]
8c4dd606 1078 Format: {"off" | "on" | "skip[mbr]"}
1da177e4 1079
d2f7cbe7 1080 efi= [EFI]
fed6cefe 1081 Format: { "old_map", "nochunk", "noruntime", "debug" }
d2f7cbe7
BP
1082 old_map [X86-64]: switch to the old ioremap-based EFI
1083 runtime services mapping. 32-bit still uses this one by
1084 default.
5a17dae4
MF
1085 nochunk: disable reading files in "chunks" in the EFI
1086 boot stub, as chunking can cause problems with some
1087 firmware implementations.
5ae3683c 1088 noruntime : disable EFI runtime services support
fed6cefe 1089 debug: enable misc debug output
d2f7cbe7 1090
8c58bf3e
RW
1091 efi_no_storage_paranoia [EFI; X86]
1092 Using this parameter you can use more than 50% of
1093 your efi variable storage. Use this parameter only if
1094 you are really sure that your UEFI does sane gc and
1095 fulfills the spec otherwise your board may brick.
1096
0f96a99d
TI
1097 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1098 Add arbitrary attribute to specific memory range by
1099 updating original EFI memory map.
1100 Region of memory which aa attribute is added to is
1101 from ss to ss+nn.
1102 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1103 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1104 attribute is added to range 0x100000000-0x180000000 and
1105 0x10a0000000-0x1120000000.
1106
1107 Using this parameter you can do debugging of EFI memmap
1108 related feature. For example, you can do debugging of
1109 Address Range Mirroring feature even if your box
1110 doesn't support it.
1111
1da177e4
LT
1112 eisa_irq_edge= [PARISC,HW]
1113 See header of drivers/parisc/eisa.c.
1114
cd4f0ef7 1115 elanfreq= [X86-32]
1da177e4 1116 See comment before function elanfreq_setup() in
71f77055 1117 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1da177e4
LT
1118
1119 elevator= [IOSCHED]
17a9e7bb 1120 Format: {"cfq" | "deadline" | "noop"}
395cf969 1121 See Documentation/block/cfq-iosched.txt and
a9913044
RD
1122 Documentation/block/deadline-iosched.txt for details.
1123
d3bf3795 1124 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
a9913044 1125 Specifies physical address of start of kernel core
d3bf3795
MH
1126 image elf header and optionally the size. Generally
1127 kexec loader will pass this option to capture kernel.
aac04b32 1128 See Documentation/kdump/kdump.txt for details.
1da177e4 1129
0cb55ad2
RD
1130 enable_mtrr_cleanup [X86]
1131 The kernel tries to adjust MTRR layout from continuous
1132 to discrete, to make X server driver able to add WB
1133 entry later. This parameter enables that.
1134
ca1eda2d 1135 enable_timer_pin_1 [X86]
0cb55ad2
RD
1136 Enable PIN 1 of APIC timer
1137 Can be useful to work around chipset bugs
1138 (in particular on some ATI chipsets).
1139 The kernel tries to set a reasonable default.
1140
1da177e4
LT
1141 enforcing [SELINUX] Set initial enforcing status.
1142 Format: {"0" | "1"}
1143 See security/selinux/Kconfig help text.
1144 0 -- permissive (log only, no denials).
1145 1 -- enforcing (deny and log).
1146 Default value is 0.
1147 Value can be changed at runtime via /selinux/enforce.
1148
a08f82d0
HY
1149 erst_disable [ACPI]
1150 Disable Error Record Serialization Table (ERST)
1151 support.
1152
1da177e4
LT
1153 ether= [HW,NET] Ethernet cards parameters
1154 This option is obsoleted by the "netdev=" option, which
1155 has equivalent usage. See its documentation for details.
1156
7102ebcd
MZ
1157 evm= [EVM]
1158 Format: { "fix" }
1159 Permit 'security.evm' to be updated regardless of
1160 current integrity status.
1161
de1ba09b
AM
1162 failslab=
1163 fail_page_alloc=
1164 fail_make_request=[KNL]
1165 General fault injection mechanism.
1166 Format: <interval>,<probability>,<space>,<times>
395cf969 1167 See also Documentation/fault-injection/.
de1ba09b 1168
1da177e4 1169 floppy= [HW]
31c00fc1 1170 See Documentation/blockdev/floppy.txt.
1da177e4 1171
f13ae30e
AC
1172 force_pal_cache_flush
1173 [IA-64] Avoid check_sal_cache_flush which may hang on
1174 buggy SAL_CACHE_FLUSH implementations. Using this
1175 parameter will force ia64_sal_cache_flush to call
1176 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1177
69f2366c
CB
1178 forcepae [X86-32]
1179 Forcefully enable Physical Address Extension (PAE).
1180 Many Pentium M systems disable PAE but may have a
1181 functionally usable PAE implementation.
1182 Warning: use of this parameter will taint the kernel
1183 and may cause unknown problems.
1184
d9e54076 1185 ftrace=[tracer]
2af15d6a 1186 [FTRACE] will set and start the specified tracer
d9e54076
PZ
1187 as early as possible in order to facilitate early
1188 boot debugging.
1189
cecbca96 1190 ftrace_dump_on_oops[=orig_cpu]
2af15d6a 1191 [FTRACE] will dump the trace buffers on oops.
cecbca96
FW
1192 If no parameter is passed, ftrace will dump
1193 buffers of all CPUs, but if you pass orig_cpu, it will
1194 dump only the buffer of the CPU that triggered the
1195 oops.
2af15d6a
SR
1196
1197 ftrace_filter=[function-list]
1198 [FTRACE] Limit the functions traced by the function
1199 tracer at boot up. function-list is a comma separated
1200 list of functions. This list can be changed at run
1201 time by the set_ftrace_filter file in the debugfs
16290246 1202 tracing directory.
2af15d6a
SR
1203
1204 ftrace_notrace=[function-list]
1205 [FTRACE] Do not trace the functions specified in
1206 function-list. This list can be changed at run time
1207 by the set_ftrace_notrace file in the debugfs
1208 tracing directory.
d9e54076 1209
369bc18f
SA
1210 ftrace_graph_filter=[function-list]
1211 [FTRACE] Limit the top level callers functions traced
1212 by the function graph tracer at boot up.
1213 function-list is a comma separated list of functions
1214 that can be changed at run time by the
1215 set_graph_function file in the debugfs tracing directory.
1216
0d7d9a16
NK
1217 ftrace_graph_notrace=[function-list]
1218 [FTRACE] Do not trace from the functions specified in
1219 function-list. This list is a comma separated list of
1220 functions that can be changed at run time by the
1221 set_graph_notrace file in the debugfs tracing directory.
1222
1da177e4
LT
1223 gamecon.map[2|3]=
1224 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1225 support via parallel port (up to 5 devices per port)
1226 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1227 See also Documentation/input/joystick-parport.txt
1228
1229 gamma= [HW,DRM]
1230
aaf23042
YL
1231 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1232 Format: off | on
1233 default: on
1234
2521f2c2
PO
1235 gcov_persist= [GCOV] When non-zero (default), profiling data for
1236 kernel modules is saved and remains accessible via
1237 debugfs, even when the module is unloaded/reloaded.
1238 When zero, profiling data is discarded and associated
1239 debugfs files are removed at module unload time.
1240
1da177e4 1241 gpt [EFI] Forces disk with valid GPT signature but
6c5de79b
DB
1242 invalid Protective MBR to be treated as GPT. If the
1243 primary GPT is corrupted, it enables the backup/alternate
1244 GPT to be used instead.
1da177e4 1245
6cec9b07
AL
1246 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1247 the "Enable 0" bit of the configuration register.
1248 Format: 0 | 1
1249 Default: 0
1250 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1251 the "Enable 0" bit of the configuration register.
1252 Format: 0 | 1
1253 Default: 0
1254 grcan.select= [HW] Select which physical interface to use.
1255 Format: 0 | 1
1256 Default: 0
1257 grcan.txsize= [HW] Sets the size of the tx buffer.
1258 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1259 Default: 1024
1260 grcan.rxsize= [HW] Sets the size of the rx buffer.
1261 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1262 Default: 1024
1263
1da177e4
LT
1264 hashdist= [KNL,NUMA] Large hashes allocated during boot
1265 are distributed across NUMA nodes. Defaults on
16290246 1266 for 64-bit NUMA, off otherwise.
a9913044 1267 Format: 0 | 1 (for off | on)
1da177e4
LT
1268
1269 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1270
1271 hd= [EIDE] (E)IDE hard drive subsystem geometry
1272 Format: <cyl>,<head>,<sect>
1273
ea8c071c
HY
1274 hest_disable [ACPI]
1275 Disable Hardware Error Source Table (HEST) support;
1276 corresponding firmware-first mode error processing
1277 logic will be disabled.
1278
1da177e4
LT
1279 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1280 size of <nn>. This works even on boxes that have no
1281 highmem otherwise. This also works to reduce highmem
1282 size on bigger boxes.
1283
54cdfdb4
TG
1284 highres= [KNL] Enable/disable high resolution timer mode.
1285 Valid parameters: "on", "off"
1286 Default: "on"
1287
1da177e4
LT
1288 hisax= [HW,ISDN]
1289 See Documentation/isdn/README.HiSax.
1290
0cb55ad2
RD
1291 hlt [BUGS=ARM,SH]
1292
1293 hpet= [X86-32,HPET] option to control HPET usage
1294 Format: { enable (default) | disable | force |
1295 verbose }
1296 disable: disable HPET and use PIT instead
1297 force: allow force enabled of undocumented chips (ICH4,
1298 VIA, nVidia)
1299 verbose: show contents of HPET registers during setup
1300
3d035f58
PB
1301 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1302 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1303
b4718e62
AK
1304 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1305 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
0d9ea754
JT
1306 On x86-64 and powerpc, this option can be specified
1307 multiple times interleaved with hugepages= to reserve
1308 huge pages of different sizes. Valid pages sizes on
1309 x86-64 are 2M (when the CPU supports "pse") and 1G
27ec26ec 1310 (when the CPU supports the "pdpe1gb" cpuinfo flag).
6902aa84 1311
555d61d6
HB
1312 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1313 terminal devices. Valid values: 0..8
431429ff
HB
1314 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1315 If specified, z/VM IUCV HVC accepts connections
1316 from listed z/VM user IDs only.
cef7125d 1317
fdabf525
JH
1318 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1319 hardware thread id mappings.
1320 Format: <cpu>:<hwthread>
1321
7bf69395
FDN
1322 keep_bootcon [KNL]
1323 Do not unregister boot console at start. This is only
1324 useful for debugging when something happens in the window
1325 between unregistering the boot console and initializing
1326 the real console.
1327
3a853fb9 1328 i2c_bus= [HW] Override the default board specific I2C bus speed
7954763b
JN
1329 or register an additional I2C bus that is not
1330 registered from board initialization code.
3a853fb9
JN
1331 Format:
1332 <bus_id>,<clkrate>
1333
36d95739 1334 i8042.debug [HW] Toggle i8042 debug mode
e1443d28
SCP
1335 i8042.unmask_kbd_data
1336 [HW] Enable printing of interrupt data from the KBD port
1337 (disabled by default, and as a pre-condition
1338 requires that i8042.debug=1 be enabled)
1da177e4 1339 i8042.direct [HW] Put keyboard port into non-translated mode
84eb8d06
ML
1340 i8042.dumbkbd [HW] Pretend that controller can only read data from
1341 keyboard and cannot control its state
1da177e4
LT
1342 (Don't attempt to blink the leds)
1343 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
945ef0d4 1344 i8042.nokbd [HW] Don't check/create keyboard port
75d08c78
JK
1345 i8042.noloop [HW] Disable the AUX Loopback command while probing
1346 for the AUX port
1da177e4 1347 i8042.nomux [HW] Don't check presence of an active multiplexing
e55a3366 1348 controller
1da177e4
LT
1349 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1350 controllers
24775d65 1351 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1da177e4
LT
1352 i8042.reset [HW] Reset the controller during init and cleanup
1353 i8042.unlock [HW] Unlock (ignore) the keylock
148e9a71 1354 i8042.kbdreset [HW] Reset device connected to KBD port
1da177e4
LT
1355
1356 i810= [HW,DRM]
1357
e70c9d5e
DT
1358 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1359 indicates that the driver is running on unsupported
1360 hardware.
1da177e4
LT
1361 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1362 does not match list of supported models.
1363 i8k.power_status
1364 [HW] Report power status in /proc/i8k
1365 (disabled by default)
1366 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1367 capability is set.
1368
4dca20ef 1369 i915.invert_brightness=
7bd90909
CE
1370 [DRM] Invert the sense of the variable that is used to
1371 set the brightness of the panel backlight. Normally a
4dca20ef
CE
1372 brightness value of 0 indicates backlight switched off,
1373 and the maximum of the brightness value sets the backlight
1374 to maximum brightness. If this parameter is set to 0
1375 (default) and the machine requires it, or this parameter
1376 is set to 1, a brightness value of 0 sets the backlight
1377 to maximum brightness, and the maximum of the brightness
1378 value switches the backlight off.
1379 -1 -- never invert brightness
1380 0 -- machine default
1381 1 -- force brightness inversion
7bd90909 1382
1da177e4
LT
1383 icn= [HW,ISDN]
1384 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1385
0af80c04
DF
1386 ide-core.nodma= [HW] (E)IDE subsystem
1387 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
075affcb
BZ
1388 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1389 .cdrom .chs .ignore_cable are additional options
1c10e938 1390 See Documentation/ide/ide.txt.
1da177e4 1391
0f8b7f5d
MR
1392 ide-generic.probe-mask= [HW] (E)IDE subsystem
1393 Format: <int>
1394 Probe mask for legacy ISA IDE ports. Depending on
1395 platform up to 6 ports are supported, enabled by
1396 setting corresponding bits in the mask to 1. The
1397 default value is 0x0, which has a special meaning.
1398 On systems that have PCI, it triggers scanning the
1399 PCI bus for the first and the second port, which
1400 are then probed. On systems without PCI the value
1401 of 0x0 enables probing the two first ports as if it
1402 was 0x3.
1403
0cb55ad2
RD
1404 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1405 Claim all unknown PCI IDE storage controllers.
1406
f039b754 1407 idle= [X86]
69fb3676 1408 Format: idle=poll, idle=halt, idle=nomwait
ada9cfdd
RD
1409 Poll forces a polling idle loop that can slightly
1410 improve the performance of waking up a idle CPU, but
1411 will use a lot of power and make the system run hot.
1412 Not recommended.
ada9cfdd 1413 idle=halt: Halt is forced to be used for CPU idle.
c1e3b377 1414 In such case C2/C3 won't be used again.
ada9cfdd 1415 idle=nomwait: Disable mwait for CPU C-states
a9913044 1416
79290822
IM
1417 ignore_loglevel [KNL]
1418 Ignore loglevel setting - this will print /all/
1419 kernel messages to the console. Useful for debugging.
0eca6b7c
YZ
1420 We also add it as printk module parameter, so users
1421 could change it dynamically, usually by
1422 /sys/module/printk/parameters/ignore_loglevel.
79290822 1423
1da177e4
LT
1424 ihash_entries= [KNL]
1425 Set number of hash buckets for inode cache.
1426
2fe5d6de 1427 ima_appraise= [IMA] appraise integrity measurements
2faa6ef3 1428 Format: { "off" | "enforce" | "fix" | "log" }
2fe5d6de
MZ
1429 default: "enforce"
1430
07f6a794
MZ
1431 ima_appraise_tcb [IMA]
1432 The builtin appraise policy appraises all files
1433 owned by uid=0.
1434
3323eec9 1435 ima_hash= [IMA]
e7a2ad7e
MZ
1436 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1437 | sha512 | ... }
3323eec9
MZ
1438 default: "sha1"
1439
e7a2ad7e
MZ
1440 The list of supported hash algorithms is defined
1441 in crypto/hash_info.h.
1442
24fd03c8
MZ
1443 ima_policy= [IMA]
1444 The builtin measurement policy to load during IMA
1445 setup. Specyfing "tcb" as the value, measures all
1446 programs exec'd, files mmap'd for exec, and all files
1447 opened with the read mode bit set by either the
1448 effective uid (euid=0) or uid=0.
1449 Format: "tcb"
1450
1451 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
5789ba3b
EP
1452 Load a policy which meets the needs of the Trusted
1453 Computing Base. This means IMA will measure all
1454 programs exec'd, files mmap'd for exec, and all files
1455 opened for read by uid=0.
1456
9b9d4ce5
RS
1457 ima_template= [IMA]
1458 Select one of defined IMA measurements template formats.
8265a2f8 1459 Formats: { "ima" | "ima-ng" | "ima-sig" }
9b9d4ce5
RS
1460 Default: "ima-ng"
1461
c2426d2a
RS
1462 ima_template_fmt=
1463 [IMA] Define a custom template format.
1464 Format: { "field1|...|fieldN" }
1465
3bcced39
DK
1466 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1467 Format: <min_file_size>
1468 Set the minimal file size for using asynchronous hash.
1469 If left unspecified, ahash usage is disabled.
1470
1471 ahash performance varies for different data sizes on
1472 different crypto accelerators. This option can be used
1473 to achieve the best performance for a particular HW.
1474
6edf7a89
DK
1475 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1476 Format: <bufsize>
1477 Set hashing buffer size. Default: 4k.
1478
1479 ahash performance varies for different chunk sizes on
1480 different crypto accelerators. This option can be used
1481 to achieve best performance for particular HW.
1482
1da177e4
LT
1483 init= [KNL]
1484 Format: <full_path>
1485 Run specified binary instead of /sbin/init as init
1486 process.
1487
1488 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1489 for working out where the kernel is dying during
1490 startup.
1491
7b0b73d7
PB
1492 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1493 initcall functions. Useful for debugging built-in
1494 modules and initcalls.
1495
1da177e4
LT
1496 initrd= [BOOT] Specify the location of the initial ramdisk
1497
1498 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1499 Format: <irq>
1500
6bb2ff84
FY
1501 int_pln_enable [x86] Enable power limit notification interrupt
1502
d726d8d7
MZ
1503 integrity_audit=[IMA]
1504 Format: { "0" | "1" }
1505 0 -- basic integrity auditing messages. (Default)
1506 1 -- additional integrity auditing messages.
1507
ba395927 1508 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
0cd5c3c8
KM
1509 on
1510 Enable intel iommu driver.
ba395927
KA
1511 off
1512 Disable intel iommu driver.
1513 igfx_off [Default Off]
1514 By default, gfx is mapped as normal device. If a gfx
1515 device has a dedicated DMAR unit, the DMAR unit is
1516 bypassed by not enabling DMAR with this option. In
1517 this case, gfx device will use physical address for
1518 DMA.
7d3b03ce
KA
1519 forcedac [x86_64]
1520 With this option iommu will not optimize to look
16290246 1521 for io virtual address below 32-bit forcing dual
7d3b03ce 1522 address cycle on pci bus for cards supporting greater
16290246
RD
1523 than 32-bit addressing. The default is to look
1524 for translation below 32-bit and if not available
7d3b03ce 1525 then look in the higher range.
5e0d2a6f 1526 strict [Default Off]
1527 With this option on every unmap_single operation will
1528 result in a hardware IOTLB flush operation as opposed
1529 to batching them for performance.
6dd9a7c7
YS
1530 sp_off [Default Off]
1531 By default, super page will be supported if Intel IOMMU
1532 has the capability. With this option, super page will
1533 not be supported.
c83b2f20
DW
1534 ecs_off [Default Off]
1535 By default, extended context tables will be supported if
1536 the hardware advertises that it has support both for the
1537 extended tables themselves, and also PASID support. With
1538 this option set, extended tables will not be used even
1539 on hardware which claims to support them.
2e92c7ad
MI
1540
1541 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1542 0 disables intel_idle and fall back on acpi_idle.
1543 1 to 6 specify maximum depth of C-state.
1544
6be26498
DB
1545 intel_pstate= [X86]
1546 disable
1547 Do not enable intel_pstate as the default
1548 scaling driver for the supported processors
aa4ea34d
EZ
1549 force
1550 Enable intel_pstate on systems that prohibit it by default
1551 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1552 instead of acpi-cpufreq may disable platform features, such
1553 as thermal controls and power capping, that rely on ACPI
1554 P-States information being indicated to OSPM and therefore
1555 should be used with caution. This option does not work with
1556 processors that aren't supported by the intel_pstate driver
1557 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2f86dc4c
DB
1558 no_hwp
1559 Do not enable hardware P state control (HWP)
1560 if available.
d64c3b0b
KCA
1561 hwp_only
1562 Only load intel_pstate on systems which support
1563 hardware P state control (HWP) if available.
6be26498 1564
d1423d56 1565 intremap= [X86-64, Intel-IOMMU]
d1423d56
CW
1566 on enable Interrupt Remapping (default)
1567 off disable Interrupt Remapping
1568 nosid disable Source ID checking
41750d31
SS
1569 no_x2apic_optout
1570 BIOS x2APIC opt-out request will be ignored
d1423d56 1571
0cb55ad2
RD
1572 iomem= Disable strict checking of access to MMIO memory
1573 strict regions from userspace.
1574 relaxed
1575
1576 iommu= [x86]
1577 off
1578 force
1579 noforce
1580 biomerge
1581 panic
1582 nopanic
1583 merge
1584 nomerge
1585 forcesac
1586 soft
bcb71abe 1587 pt [x86, IA-64]
4e287840
TLSC
1588 nobypass [PPC/POWERNV]
1589 Disable IOMMU bypass, using IOMMU for PCI devices.
bcb71abe 1590
0cb55ad2
RD
1591
1592 io7= [HW] IO7 for Marvel based alpha systems
1593 See comment before marvel_specify_io7 in
1594 arch/alpha/kernel/core_marvel.c.
1595
6cececfc 1596 io_delay= [X86] I/O delay method
6e7c4025
IM
1597 0x80
1598 Standard port 0x80 based delay
1599 0xed
1600 Alternate port 0xed based delay (needed on some systems)
b02aae9c 1601 udelay
6e7c4025
IM
1602 Simple two microseconds delay
1603 none
1604 No delay
b02aae9c 1605
1da177e4 1606 ip= [IP_PNP]
dc7a0816 1607 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 1608
200803df
AC
1609 irqfixup [HW]
1610 When an interrupt is not handled search all handlers
1611 for it. Intended to get systems with badly broken
1612 firmware running.
1613
1614 irqpoll [HW]
1615 When an interrupt is not handled search all handlers
1616 for it. Also check all handlers each timer
1617 interrupt. Intended to get systems with badly broken
1618 firmware running.
1619
1da177e4 1620 isapnp= [ISAPNP]
a9913044 1621 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1da177e4
LT
1622
1623 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
22f2e280
DF
1624 Format:
1625 <cpu number>,...,<cpu number>
1626 or
b225d44e
LZ
1627 <cpu number>-<cpu number>
1628 (must be a positive range in ascending order)
22f2e280
DF
1629 or a mixture
1630 <cpu number>,...,<cpu number>-<cpu number>
b225d44e 1631
1da177e4
LT
1632 This option can be used to specify one or more CPUs
1633 to isolate from the general SMP balancing and scheduling
b225d44e
LZ
1634 algorithms. You can move a process onto or off an
1635 "isolated" CPU via the CPU affinity syscalls or cpuset.
1da177e4
LT
1636 <cpu number> begins at 0 and the maximum value is
1637 "number of CPUs in system - 1".
1638
1639 This option is the preferred way to isolate CPUs. The
a9913044
RD
1640 alternative -- manually setting the CPU mask of all
1641 tasks in the system -- can cause problems and
1642 suboptimal load balancer performance.
1da177e4 1643
a9913044 1644 iucv= [HW,NET]
1da177e4 1645
7d8bfa26
JR
1646 ivrs_ioapic [HW,X86_64]
1647 Provide an override to the IOAPIC-ID<->DEVICE-ID
1648 mapping provided in the IVRS ACPI table. For
1649 example, to map IOAPIC-ID decimal 10 to
1650 PCI device 00:14.0 write the parameter as:
1651 ivrs_ioapic[10]=00:14.0
1652
1653 ivrs_hpet [HW,X86_64]
1654 Provide an override to the HPET-ID<->DEVICE-ID
1655 mapping provided in the IVRS ACPI table. For
1656 example, to map HPET-ID decimal 0 to
1657 PCI device 00:14.0 write the parameter as:
1658 ivrs_hpet[0]=00:14.0
1659
1da177e4
LT
1660 js= [HW,JOY] Analog joystick
1661 See Documentation/input/joystick.txt.
1662
24f2e027
KC
1663 kaslr/nokaslr [X86]
1664 Enable/disable kernel and module base offset ASLR
1665 (Address Space Layout Randomization) if built into
1666 the kernel. When CONFIG_HIBERNATION is selected,
1667 kASLR is disabled by default. When kASLR is enabled,
1668 hibernation will be disabled.
1669
0cb55ad2
RD
1670 keepinitrd [HW,ARM]
1671
6cececfc 1672 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
ed7ed365
MG
1673 specifies the amount of memory usable by the kernel
1674 for non-movable allocations. The requested amount is
1675 spread evenly throughout all nodes in the system. The
1676 remaining memory in each node is used for Movable
1677 pages. In the event, a node is too small to have both
1678 kernelcore and Movable pages, kernelcore pages will
1679 take priority and other nodes will have a larger number
675217fd 1680 of Movable pages. The Movable zone is used for the
ed7ed365
MG
1681 allocation of pages that may be reclaimed or moved
1682 by the page migration subsystem. This means that
1683 HugeTLB pages may not be allocated from this zone.
1684 Note that allocations like PTEs-from-HighMem still
1685 use the HighMem zone if it exists, and the Normal
1686 zone if it does not.
1687
4fe1da4e
JW
1688 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1689 Format: <Controller#>[,poll interval]
1690 The controller # is the number of the ehci usb debug
1691 port as it is probed via PCI. The poll interval is
1692 optional and is the number seconds in between
1693 each poll cycle to the debug port in case you need
1694 the functionality for interrupting the kernel with
1695 gdb or control-c on the dbgp connection. When
1696 not using this parameter you use sysrq-g to break into
1697 the kernel debugger.
1698
84c08fd6 1699 kgdboc= [KGDB,HW] kgdb over consoles.
ada64e4c
JW
1700 Requires a tty driver that supports console polling,
1701 or a supported polling keyboard driver (non-usb).
65b5ac14
JW
1702 Serial only format: <serial_device>[,baud]
1703 keyboard only format: kbd
1704 keyboard and serial format: kbd,<serial_device>[,baud]
1705 Optional Kernel mode setting:
1706 kms, kbd format: kms,kbd
1707 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
6cdf6e06 1708
84c08fd6
JW
1709 kgdbwait [KGDB] Stop kernel execution and enter the
1710 kernel debugger at the earliest opportunity.
1711
9bed90c6
FF
1712 kmac= [MIPS] korina ethernet MAC address.
1713 Configure the RouterBoard 532 series on-chip
1714 Ethernet adapter MAC address.
1715
04f70336
CM
1716 kmemleak= [KNL] Boot-time kmemleak enable/disable
1717 Valid arguments: on, off
1718 Default: on
47aeeddc
MI
1719 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1720 the default is off.
04f70336 1721
c3ac14b2
XQ
1722 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1723 Valid arguments: 0, 1, 2
1724 kmemcheck=0 (disabled)
1725 kmemcheck=1 (enabled)
1726 kmemcheck=2 (one-shot mode)
1727 Default: 2 (one-shot mode)
1728
6cececfc 1729 kstack=N [X86] Print N words from the kernel stack
0cb55ad2
RD
1730 in oops dumps.
1731
fef07aae
AP
1732 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1733 Default is 0 (don't ignore, but inject #GP)
1734
a182d873
XG
1735 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1736 KVM MMU at runtime.
fef07aae
AP
1737 Default is 0 (off)
1738
fef07aae 1739 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
8475f94a 1740 Default is 1 (enabled)
fef07aae
AP
1741
1742 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1743 for all guests.
16290246 1744 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
fef07aae 1745
fef07aae
AP
1746 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1747 (virtualized MMU) support on capable Intel chips.
1748 Default is 1 (enabled)
1749
1750 kvm-intel.emulate_invalid_guest_state=
1751 [KVM,Intel] Enable emulation of invalid guest states
1752 Default is 0 (disabled)
1753
1754 kvm-intel.flexpriority=
1755 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1756 Default is 1 (enabled)
1757
e1a72ae2
SL
1758 kvm-intel.nested=
1759 [KVM,Intel] Enable VMX nesting (nVMX).
1760 Default is 0 (disabled)
1761
fef07aae
AP
1762 kvm-intel.unrestricted_guest=
1763 [KVM,Intel] Disable unrestricted guest feature
1764 (virtualized real and unpaged mode) on capable
1765 Intel chips. Default is 1 (enabled)
1766
1767 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1768 feature (tagged TLBs) on capable Intel chips.
1769 Default is 1 (enabled)
1770
1da177e4
LT
1771 l2cr= [PPC]
1772
a78bfbfc
RB
1773 l3cr= [PPC]
1774
cd4f0ef7 1775 lapic [X86-32,APIC] Enable the local APIC even if BIOS
a9913044 1776 disabled it.
1da177e4 1777
279f1461
SS
1778 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1779 value for LAPIC timer one-shot implementation. Default
1780 back to the programmable timer unit in the LAPIC.
1781
6cececfc 1782 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
ada9cfdd 1783 in C2 power state.
e585bef8 1784
fcb71f6f
FC
1785 libata.dma= [LIBATA] DMA control
1786 libata.dma=0 Disable all PATA and SATA DMA
1787 libata.dma=1 PATA and SATA Disk DMA only
1788 libata.dma=2 ATAPI (CDROM) DMA only
16290246 1789 libata.dma=4 Compact Flash DMA only
fcb71f6f
FC
1790 Combinations also work, so libata.dma=3 enables DMA
1791 for disks and CDROMs, but not CFs.
16290246 1792
20308871
MP
1793 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1794 libata.ignore_hpa=0 keep BIOS limits (default)
1795 libata.ignore_hpa=1 ignore limits, using full disk
fcb71f6f 1796
78e70c23
DJ
1797 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1798 when set.
1799 Format: <int>
1800
33267325
TH
1801 libata.force= [LIBATA] Force configurations. The format is comma
1802 separated list of "[ID:]VAL" where ID is
4c44f309 1803 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
33267325
TH
1804 matching port, link or device. Basically, it matches
1805 the ATA ID string printed on console by libata. If
1806 the whole ID part is omitted, the last PORT and DEVICE
1807 values are used. If ID hasn't been specified yet, the
1808 configuration applies to all ports, links and devices.
1809
1810 If only DEVICE is omitted, the parameter applies to
1811 the port and all links and devices behind it. DEVICE
1812 number of 0 either selects the first device or the
1813 first fan-out link behind PMP device. It does not
1814 select the host link. DEVICE number of 15 selects the
1815 host link and device attached to it.
1816
1817 The VAL specifies the configuration to force. As long
1818 as there's no ambiguity shortcut notation is allowed.
1819 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1820 The following configurations can be forced.
1821
1822 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1823 Any ID with matching PORT is used.
1824
1825 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1826
1827 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1828 udma[/][16,25,33,44,66,100,133] notation is also
1829 allowed.
1830
1831 * [no]ncq: Turn on or off NCQ.
1832
d7b16e4f
MP
1833 * [no]ncqtrim: Turn off queued DSM TRIM.
1834
05944bdf
TH
1835 * nohrst, nosrst, norst: suppress hard, soft
1836 and both resets.
1837
ca6d43b0
DW
1838 * rstonce: only attempt one reset during
1839 hot-unplug link recovery
1840
43c9c591
TH
1841 * dump_id: dump IDENTIFY data.
1842
966fbe19
VP
1843 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1844
b8bd6dc3
RJ
1845 * disable: Disable this device.
1846
33267325
TH
1847 If there are multiple matching configurations changing
1848 the same attribute, the last one is used.
1849
95f72d1e 1850 memblock=debug [KNL] Enable memblock debug messages.
7c4be253 1851
1da177e4 1852 load_ramdisk= [RAM] List of ramdisks to load from floppy
31c00fc1 1853 See Documentation/blockdev/ramdisk.txt.
1da177e4 1854
a6b25b67
RD
1855 lockd.nlm_grace_period=P [NFS] Assign grace period.
1856 Format: <integer>
1da177e4 1857
a6b25b67
RD
1858 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1859 Format: <integer>
1860
1861 lockd.nlm_timeout=T [NFS] Assign timeout value.
1862 Format: <integer>
1863
1864 lockd.nlm_udpport=M [NFS] Assign UDP port.
1865 Format: <integer>
1da177e4 1866
ec4518aa
PM
1867 locktorture.nreaders_stress= [KNL]
1868 Set the number of locking read-acquisition kthreads.
1869 Defaults to being automatically set based on the
1870 number of online CPUs.
1871
1872 locktorture.nwriters_stress= [KNL]
1873 Set the number of locking write-acquisition kthreads.
1874
1875 locktorture.onoff_holdoff= [KNL]
1876 Set time (s) after boot for CPU-hotplug testing.
1877
1878 locktorture.onoff_interval= [KNL]
1879 Set time (s) between CPU-hotplug operations, or
1880 zero to disable CPU-hotplug testing.
1881
1882 locktorture.shuffle_interval= [KNL]
1883 Set task-shuffle interval (jiffies). Shuffling
1884 tasks allows some CPUs to go into dyntick-idle
1885 mode during the locktorture test.
1886
1887 locktorture.shutdown_secs= [KNL]
1888 Set time (s) after boot system shutdown. This
1889 is useful for hands-off automated testing.
1890
1891 locktorture.stat_interval= [KNL]
1892 Time (s) between statistics printk()s.
1893
1894 locktorture.stutter= [KNL]
1895 Time (s) to stutter testing, for example,
1896 specifying five seconds causes the test to run for
1897 five seconds, wait for five seconds, and so on.
1898 This tests the locking primitive's ability to
1899 transition abruptly to and from idle.
1900
1901 locktorture.torture_runnable= [BOOT]
1902 Start locktorture running at boot time.
1903
1904 locktorture.torture_type= [KNL]
1905 Specify the locking implementation to test.
1906
1907 locktorture.verbose= [KNL]
1908 Enable additional printk() statements.
1909
1da177e4
LT
1910 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1911 Format: <irq>
1912
1913 loglevel= All Kernel Messages with a loglevel smaller than the
1914 console loglevel will be printed to the console. It can
1915 also be changed with klogd or other programs. The
1916 loglevels are defined as follows:
1917
1918 0 (KERN_EMERG) system is unusable
1919 1 (KERN_ALERT) action must be taken immediately
1920 2 (KERN_CRIT) critical conditions
1921 3 (KERN_ERR) error conditions
1922 4 (KERN_WARNING) warning conditions
1923 5 (KERN_NOTICE) normal but significant condition
1924 6 (KERN_INFO) informational
1925 7 (KERN_DEBUG) debug-level messages
1926
c756d08a 1927 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
23b2899f
LR
1928 in bytes. n must be a power of two and greater
1929 than the minimal size. The minimal size is defined
1930 by LOG_BUF_SHIFT kernel config parameter. There is
1931 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1932 that allows to increase the default size depending on
1933 the number of CPUs. See init/Kconfig for more details.
1da177e4 1934
accaa24c
RD
1935 logo.nologo [FB] Disables display of the built-in Linux logo.
1936 This may be used to provide more screen space for
1937 kernel log messages and is useful when debugging
1938 kernel boot problems.
1939
1da177e4
LT
1940 lp=0 [LP] Specify parallel ports to use, e.g,
1941 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1942 lp=reset first parallel port). 'lp=0' disables the
1943 lp=auto printer driver. 'lp=reset' (which can be
1944 specified in addition to the ports) causes
1945 attached printers to be reset. Using
1946 lp=port1,port2,... specifies the parallel ports
1947 to associate lp devices with, starting with
1948 lp0. A port specification may be 'none' to skip
1949 that lp device, or a parport name such as
1950 'parport0'. Specifying 'lp=auto' instead of a
1951 port specification list means that device IDs
1952 from each port should be examined, to see if
1953 an IEEE 1284-compliant printer is attached; if
1954 so, the driver will manage that printer.
1955 See also header of drivers/char/lp.c.
1956
1957 lpj=n [KNL]
1958 Sets loops_per_jiffy to given constant, thus avoiding
1959 time-consuming boot-time autodetection (up to 250 ms per
1960 CPU). 0 enables autodetection (default). To determine
1961 the correct value for your kernel, boot with normal
1962 autodetection and see what value is printed. Note that
1963 on SMP systems the preset will be applied to all CPUs,
1964 which is likely to cause problems if your CPUs need
1965 significantly divergent settings. An incorrect value
1966 will cause delays in the kernel to be wrong, leading to
1967 unpredictable I/O errors and other breakage. Although
1968 unlikely, in the extreme case this might damage your
1969 hardware.
1970
1971 ltpc= [NET]
1972 Format: <io>,<irq>,<dma>
1973
16290246 1974 machvec= [IA-64] Force the use of a particular machine-vector
a9913044
RD
1975 (machvec) in a generic kernel.
1976 Example: machvec=hpzx1_swiotlb
1da177e4 1977
3209e70e
WZ
1978 machtype= [Loongson] Share the same kernel image file between different
1979 yeeloong laptop.
1980 Example: machtype=lemote-yeeloong-2f-7inch
1981
0cb55ad2
RD
1982 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1983 than or equal to this physical address is ignored.
1da177e4
LT
1984
1985 maxcpus= [SMP] Maximum number of processors that an SMP kernel
61ec7567
LB
1986 should make use of. maxcpus=n : n >= 0 limits the
1987 kernel to using 'n' processors. n=0 is a special case,
1988 it is equivalent to "nosmp", which also disables
1989 the IO APIC.
1da177e4 1990
d134b00b
KS
1991 max_loop= [LOOP] The number of loop block devices that get
1992 (loop.max_loop) unconditionally pre-created at init time. The default
1993 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1994 of statically allocating a predefined number, loop
1995 devices can be requested on-demand with the
1996 /dev/loop-control interface.
2b2c3750 1997
cd4f0ef7 1998 mce [X86-32] Machine Check Exception
1da177e4 1999
71cced6e 2000 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
909dd324 2001
1da177e4
LT
2002 md= [HW] RAID subsystems devices and level
2003 See Documentation/md.txt.
a9913044 2004
1da177e4
LT
2005 mdacon= [MDA]
2006 Format: <first>,<last>
2007 Specifies range of consoles to be captured by the MDA.
a9913044 2008
1da177e4
LT
2009 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2010 Amount of memory to be used when the kernel is not able
2011 to see the whole system memory or for test.
fbb97d87
WC
2012 [X86] Work as limiting max address. Use together
2013 with memmap= to avoid physical address space collisions.
2014 Without memmap= PCI devices could be placed at addresses
2015 belonging to unused RAM.
1da177e4 2016
cd4f0ef7 2017 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1da177e4
LT
2018 memory.
2019
6902aa84
PM
2020 memchunk=nn[KMG]
2021 [KNL,SH] Allow user to override the default size for
2022 per-device physically contiguous DMA buffers.
2023
6cececfc 2024 memmap=exactmap [KNL,X86] Enable setting of an exact
1da177e4
LT
2025 E820 memory map, as specified by the user.
2026 Such memmap=exactmap lines can be constructed based on
2027 BIOS output or other requirements. See the memmap=nn@ss
2028 option description.
2029
2030 memmap=nn[KMG]@ss[KMG]
277cba1d
RD
2031 [KNL] Force usage of a specific region of memory.
2032 Region of memory to be used is from ss to ss+nn.
1da177e4
LT
2033
2034 memmap=nn[KMG]#ss[KMG]
2035 [KNL,ACPI] Mark specific memory as ACPI data.
277cba1d 2036 Region of memory to be marked is from ss to ss+nn.
1da177e4
LT
2037
2038 memmap=nn[KMG]$ss[KMG]
2039 [KNL,ACPI] Mark specific memory as reserved.
277cba1d 2040 Region of memory to be reserved is from ss to ss+nn.
1312848e
PM
2041 Example: Exclude memory from 0x18690000-0x1869ffff
2042 memmap=64K$0x18690000
2043 or
2044 memmap=0x10000$0x18690000
1da177e4 2045
ec776ef6
CH
2046 memmap=nn[KMG]!ss[KMG]
2047 [KNL,X86] Mark specific memory as protected.
2048 Region of memory to be used, from ss to ss+nn.
2049 The memory region may be marked as e820 type 12 (0xc)
2050 and is NVDIMM or ADR memory.
2051
9f077871
JF
2052 memory_corruption_check=0/1 [X86]
2053 Some BIOSes seem to corrupt the first 64k of
2054 memory when doing things like suspend/resume.
2055 Setting this option will scan the memory
2056 looking for corruption. Enabling this will
2057 both detect corruption and prevent the kernel
2058 from using the memory being corrupted.
2059 However, its intended as a diagnostic tool; if
2060 repeatable BIOS-originated corruption always
2061 affects the same memory, you can use memmap=
2062 to prevent the kernel from using that memory.
2063
2064 memory_corruption_check_size=size [X86]
2065 By default it checks for corruption in the low
2066 64k, making this memory unavailable for normal
2067 use. Use this parameter to scan for
2068 corruption in more or less memory.
2069
2070 memory_corruption_check_period=seconds [X86]
2071 By default it checks for corruption every 60
2072 seconds. Use this parameter to check at some
2073 other rate. 0 disables periodic checking.
2074
e4b0db72 2075 memtest= [KNL,X86,ARM] Enable memtest
c64df707 2076 Format: <integer>
c64df707 2077 default : 0 <disable>
9e5f6cf5
AH
2078 Specifies the number of memtest passes to be
2079 performed. Each pass selects another test
2080 pattern from a given set of patterns. Memtest
2081 fills the memory with this pattern, validates
2082 memory contents and reserves bad memory
2083 regions that are detected.
c64df707 2084
1da177e4
LT
2085 meye.*= [HW] Set MotionEye Camera parameters
2086 See Documentation/video4linux/meye.txt.
2087
8f36881b
AS
2088 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2089 Multi-Function General Purpose Timers on AMD Geode
2090 platforms.
2091
e6c4dc6c
WT
2092 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2093 the BIOS has incorrectly applied a workaround. TinyBIOS
2094 version 0.98 is known to be affected, 0.99 fixes the
2095 problem by letting the user disable the workaround.
2096
1da177e4
LT
2097 mga= [HW,DRM]
2098
1c207f95
RD
2099 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2100 physical address is ignored.
2101
39f45d7b
MP
2102 mini2440= [ARM,HW,KNL]
2103 Format:[0..2][b][c][t]
2104 Default: "0tb"
2105 MINI2440 configuration specification:
2106 0 - The attached screen is the 3.5" TFT
2107 1 - The attached screen is the 7" TFT
2108 2 - The VGA Shield is attached (1024x768)
2109 Leaving out the screen size parameter will not load
2110 the TFT driver, and the framebuffer will be left
2111 unconfigured.
2112 b - Enable backlight. The TFT backlight pin will be
2113 linked to the kernel VESA blanking code and a GPIO
2114 LED. This parameter is not necessary when using the
2115 VGA shield.
2116 c - Enable the s3c camera interface.
2117 t - Reserved for enabling touchscreen support. The
2118 touchscreen support is not enabled in the mainstream
2119 kernel as of 2.6.30, a preliminary port can be found
2120 in the "bleeding edge" mini2440 support kernel at
2121 http://repo.or.cz/w/linux-2.6/mini2440.git
2122
6b74ab97
MG
2123 mminit_loglevel=
2124 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2125 parameter allows control of the logging verbosity for
2126 the additional memory initialisation checks. A value
2127 of 0 disables mminit logging and a level of 4 will
2128 log everything. Information is printed at KERN_DEBUG
2129 so loglevel=8 may also need to be specified.
2130
106a4ee2
RR
2131 module.sig_enforce
2132 [KNL] When CONFIG_MODULE_SIG is set, this means that
2133 modules without (valid) signatures will fail to load.
2a039be7 2134 Note that if CONFIG_MODULE_SIG_FORCE is set, that
106a4ee2
RR
2135 is always true, so this option does nothing.
2136
1da177e4
LT
2137 mousedev.tap_time=
2138 [MOUSE] Maximum time between finger touching and
2139 leaving touchpad surface for touch to be considered
2140 a tap and be reported as a left button click (for
2141 touchpads working in absolute mode only).
2142 Format: <msecs>
2143 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2144 reporting absolute coordinates, such as tablets
2145 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2146 reporting absolute coordinates, such as tablets
2147
6cececfc 2148 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
0cb55ad2
RD
2149 is similar to kernelcore except it specifies the
2150 amount of memory used for migratable allocations.
2151 If both kernelcore and movablecore is specified,
2152 then kernelcore will be at *least* the specified
2153 value but may be more. If movablecore on its own
2154 is specified, the administrator must be careful
2155 that the amount of memory usable for all allocations
2156 is not too small.
2157
c5320926
TC
2158 movable_node [KNL,X86] Boot-time switch to enable the effects
2159 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2160
1da177e4
LT
2161 MTD_Partition= [MTD]
2162 Format: <name>,<region-number>,<size>,<offset>
2163
a9913044
RD
2164 MTD_Region= [MTD] Format:
2165 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1da177e4
LT
2166
2167 mtdparts= [MTD]
c8facbb6 2168 See drivers/mtd/cmdlinepart.c.
1da177e4 2169
4e89a2d8
WS
2170 multitce=off [PPC] This parameter disables the use of the pSeries
2171 firmware feature for updating multiple TCE entries
2172 at a time.
2173
5988af23
RH
2174 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2175
2176 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2177
2178 boundary - index of last SLC block on Flex-OneNAND.
2179 The remaining blocks are configured as MLC blocks.
2180 lock - Configure if Flex-OneNAND boundary should be locked.
2181 Once locked, the boundary cannot be changed.
2182 1 indicates lock status, 0 indicates unlock status.
2183
9db829f4
BD
2184 mtdset= [ARM]
2185 ARM/S3C2412 JIVE boot control
2186
2187 See arch/arm/mach-s3c2412/mach-jive.c
2188
1da177e4 2189 mtouchusb.raw_coordinates=
a9913044
RD
2190 [HW] Make the MicroTouch USB driver use raw coordinates
2191 ('y', default) or cooked coordinates ('n')
1da177e4 2192
0cb55ad2 2193 mtrr_chunk_size=nn[KMG] [X86]
19f59460 2194 used for mtrr cleanup. It is largest continuous chunk
0cb55ad2
RD
2195 that could hold holes aka. UC entries.
2196
2197 mtrr_gran_size=nn[KMG] [X86]
2198 Used for mtrr cleanup. It is granularity of mtrr block.
2199 Default is 1.
2200 Large value could prevent small alignment from
2201 using up MTRRs.
2202
2203 mtrr_spare_reg_nr=n [X86]
2204 Format: <integer>
2205 Range: 0,7 : spare reg number
2206 Default : 1
2207 Used for mtrr cleanup. It is spare mtrr entries number.
2208 Set to 2 or more if your graphical card needs more.
2209
1da177e4
LT
2210 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2211
1da177e4
LT
2212 netdev= [NET] Network devices parameters
2213 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2214 Note that mem_start is often overloaded to mean
2215 something different and driver-specific.
a9913044
RD
2216 This usage is only documented in each driver source
2217 file if at all.
2218
58401572
KPO
2219 nf_conntrack.acct=
2220 [NETFILTER] Enable connection tracking flow accounting
2221 0 to disable accounting
2222 1 to enable accounting
d70a011d 2223 Default value is 0.
58401572 2224
306a0753 2225 nfsaddrs= [NFS] Deprecated. Use ip= instead.
dc7a0816 2226 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
2227
2228 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
dc7a0816 2229 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 2230
306a0753
CL
2231 nfsrootdebug [NFS] enable nfsroot debugging messages.
2232 See Documentation/filesystems/nfs/nfsroot.txt.
2233
a72b4422
TM
2234 nfs.callback_tcpport=
2235 [NFS] set the TCP port on which the NFSv4 callback
2236 channel should listen.
2237
e571cbf1
TM
2238 nfs.cache_getent=
2239 [NFS] sets the pathname to the program which is used
2240 to update the NFS client cache entries.
2241
2242 nfs.cache_getent_timeout=
2243 [NFS] sets the timeout after which an attempt to
2244 update a cache entry is deemed to have failed.
2245
58df095b
TM
2246 nfs.idmap_cache_timeout=
2247 [NFS] set the maximum lifetime for idmapper cache
2248 entries.
2249
f43bf0be
TM
2250 nfs.enable_ino64=
2251 [NFS] enable 64-bit inode numbers.
2252 If zero, the NFS client will fake up a 32-bit inode
2253 number for the readdir() and stat() syscalls instead
2254 of returning the full 64-bit number.
2255 The default is to return 64-bit inode numbers.
2256
ef159e91
TM
2257 nfs.max_session_slots=
2258 [NFSv4.1] Sets the maximum number of session slots
2259 the client will attempt to negotiate with the server.
2260 This limits the number of simultaneous RPC requests
2261 that the client can send to the NFSv4.1 server.
2262 Note that there is little point in setting this
2263 value higher than the max_tcp_slot_table_limit.
2264
b064eca2 2265 nfs.nfs4_disable_idmapping=
074b1d12
TM
2266 [NFSv4] When set to the default of '1', this option
2267 ensures that both the RPC level authentication
2268 scheme and the NFS level operations agree to use
2269 numeric uids/gids if the mount is using the
2270 'sec=sys' security flavour. In effect it is
2271 disabling idmapping, which can make migration from
2272 legacy NFSv2/v3 systems to NFSv4 easier.
2273 Servers that do not support this mode of operation
2274 will be autodetected by the client, and it will fall
2275 back to using the idmapper.
2276 To turn off this behaviour, set the value to '0'.
6f2ea7f2
CL
2277 nfs.nfs4_unique_id=
2278 [NFS4] Specify an additional fixed unique ident-
2279 ification string that NFSv4 clients can insert into
2280 their nfs_client_id4 string. This is typically a
2281 UUID that is generated at system install time.
b064eca2 2282
db8ac8ba
WAA
2283 nfs.send_implementation_id =
2284 [NFSv4.1] Send client implementation identification
2285 information in exchange_id requests.
2286 If zero, no implementation identification information
2287 will be sent.
2288 The default is to send the implementation identification
2289 information.
f6de7a39
TM
2290
2291 nfs.recover_lost_locks =
2292 [NFSv4] Attempt to recover locks that were lost due
2293 to a lease timeout on the server. Please note that
2294 doing this risks data corruption, since there are
2295 no guarantees that the file will remain unchanged
2296 after the locks are lost.
2297 If you want to enable the kernel legacy behaviour of
2298 attempting to recover these locks, then set this
2299 parameter to '1'.
2300 The default parameter value of '0' causes the kernel
2301 not to attempt recovery of lost locks.
db8ac8ba 2302
bbf58bf3
TM
2303 nfs4.layoutstats_timer =
2304 [NFSv4.2] Change the rate at which the kernel sends
2305 layoutstats to the pNFS metadata server.
2306
2307 Setting this to value to 0 causes the kernel to use
2308 whatever value is the default set by the layout
2309 driver. A non-zero value sets the minimum interval
2310 in seconds between layoutstats transmissions.
2311
e9541ce8
BF
2312 nfsd.nfs4_disable_idmapping=
2313 [NFSv4] When set to the default of '1', the NFSv4
2314 server will return only numeric uids and gids to
2315 clients using auth_sys, and will accept numeric uids
2316 and gids from such clients. This is intended to ease
2317 migration from NFSv2/v3.
db8ac8ba 2318
18d98f6c
SB
2319 objlayoutdriver.osd_login_prog=
2320 [NFS] [OBJLAYOUT] sets the pathname to the program which
2321 is used to automatically discover and login into new
2322 osd-targets. Please see:
2323 Documentation/filesystems/pnfs.txt for more explanations
2324
1e1030dc 2325 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
e7ba176b
HS
2326 when a NMI is triggered.
2327 Format: [state][,regs][,debounce][,die]
2328
6cececfc 2329 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
fef2c9bc 2330 Format: [panic,][nopanic,][num]
195daf66 2331 Valid num: 0 or 1
5b9a0e14 2332 0 - turn nmi_watchdog off
195daf66 2333 1 - turn nmi_watchdog on
0cb55ad2 2334 When panic is specified, panic when an NMI watchdog
fef2c9bc
DZ
2335 timeout occurs (or 'nopanic' to override the opposite
2336 default).
0cb55ad2
RD
2337 This is useful when you use a panic=... timeout and
2338 need the box quickly up again.
1da177e4 2339
bff38771
AV
2340 netpoll.carrier_timeout=
2341 [NET] Specifies amount of time (in seconds) that
2342 netpoll should wait for a carrier. By default netpoll
2343 waits 4 seconds.
2344
cd4f0ef7 2345 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1da177e4
LT
2346 emulation library even if a 387 maths coprocessor
2347 is present.
2348
0cb55ad2
RD
2349 no_console_suspend
2350 [HW] Never suspend the console
2351 Disable suspending of consoles during suspend and
2352 hibernate operations. Once disabled, debugging
2353 messages can reach various consoles while the rest
2354 of the system is being put to sleep (ie, while
2355 debugging driver suspend/resume hooks). This may
2356 not work reliably with all consoles, but is known
2357 to work with serial and VGA consoles.
134620f7
YZ
2358 To facilitate more flexible debugging, we also add
2359 console_suspend, a printk module parameter to control
2360 it. Users could use console_suspend (usually
2361 /sys/module/printk/parameters/console_suspend) to
2362 turn on/off it dynamically.
0cb55ad2 2363
c1aee215
CL
2364 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2365 caches in the slab allocator. Saves per-node memory,
2366 but will impact performance.
3395ee05 2367
a9913044
RD
2368 noalign [KNL,ARM]
2369
1da177e4
LT
2370 noapic [SMP,APIC] Tells the kernel to not make use of any
2371 IOAPICs that may be present in the system.
2372
5091faa4
MG
2373 noautogroup Disable scheduler automatic task group creation.
2374
1da177e4
LT
2375 nobats [PPC] Do not use BATs for mapping kernel lowmem
2376 on "Classic" PPC cores.
2377
2378 nocache [ARM]
a9913044 2379
0cb55ad2
RD
2380 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2381
163ecdff
SN
2382 nodelayacct [KNL] Disable per-task delay accounting
2383
1da177e4
LT
2384 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2385
6902aa84
PM
2386 nodsp [SH] Disable hardware DSP at boot time.
2387
b2e0a54a 2388 noefi Disable EFI runtime services support.
8b2cb7a8 2389
1da177e4
LT
2390 noexec [IA-64]
2391
6cececfc 2392 noexec [X86]
f5a1b191 2393 On X86-32 available only on PAE configured kernels.
1da177e4 2394 noexec=on: enable non-executable mappings (default)
f5a1b191
JS
2395 noexec=off: disable non-executable mappings
2396
52b6179a
PA
2397 nosmap [X86]
2398 Disable SMAP (Supervisor Mode Access Prevention)
2399 even if it is supported by processor.
2400
de5397ad 2401 nosmep [X86]
52b6179a 2402 Disable SMEP (Supervisor Mode Execution Prevention)
de5397ad
FY
2403 even if it is supported by processor.
2404
f5a1b191
JS
2405 noexec32 [X86-64]
2406 This affects only 32-bit executables.
2407 noexec32=on: enable non-executable mappings (default)
2408 read doesn't imply executable mappings
2409 noexec32=off: disable non-executable mappings
2410 read implies executable mappings
1da177e4 2411
fab43ef4 2412 nofpu [MIPS,SH] Disable hardware FPU at boot time.
6902aa84 2413
cd4f0ef7 2414 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4f886511
CE
2415 register save and restore. The kernel will only save
2416 legacy floating-point registers on task switch.
1da177e4 2417
0ddab1d2
TK
2418 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2419
0c752a93
SS
2420 noxsave [BUGS=X86] Disables x86 extended register state save
2421 and restore using xsave. The kernel will fallback to
2422 enabling legacy floating-point and sse state.
2423
b6f42a4a
FY
2424 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2425 register states. The kernel will fall back to use
2426 xsave to save the states. By using this parameter,
2427 performance of saving the states is degraded because
2428 xsave doesn't support modified optimization while
2429 xsaveopt supports it on xsaveopt enabled systems.
2430
2431 noxsaves [X86] Disables xsaves and xrstors used in saving and
2432 restoring x86 extended register state in compacted
2433 form of xsave area. The kernel will fall back to use
2434 xsaveopt and xrstor to save and restore the states
2435 in standard form of xsave area. By using this
2436 parameter, xsave area per process might occupy more
2437 memory on xsaves enabled systems.
2438
01a24d2b
PZ
2439 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2440 wfi(ARM) instruction doesn't work correctly and not to
2441 use it. This is also useful when using JTAG debugger.
a9913044 2442
1f29fae2
SH
2443 no_file_caps Tells the kernel not to honor file capabilities. The
2444 only way then for a file to be executed with privilege
2445 is to be setuid root or executed by root.
2446
1da177e4
LT
2447 nohalt [IA-64] Tells the kernel not to use the power saving
2448 function PAL_HALT_LIGHT when idle. This increases
2449 power-consumption. On the positive side, it reduces
2450 interrupt wake-up latency, which may improve performance
2451 in certain environments such as networked servers or
2452 real-time systems.
2453
a6e15a39
KC
2454 nohibernate [HIBERNATION] Disable hibernation and resume.
2455
79bf2bb3
TG
2456 nohz= [KNL] Boottime enable/disable dynamic ticks
2457 Valid arguments: on, off
2458 Default: on
2459
c5bfece2
FW
2460 nohz_full= [KNL,BOOT]
2461 In kernels built with CONFIG_NO_HZ_FULL=y, set
a831881b 2462 the specified list of CPUs whose tick will be stopped
0453b435
FW
2463 whenever possible. The boot CPU will be forced outside
2464 the range to maintain the timekeeping.
d1e43fa5
FW
2465 The CPUs in this range must also be included in the
2466 rcu_nocbs= set.
a831881b 2467
eeee7853
PM
2468 noiotrap [SH] Disables trapped I/O port accesses.
2469
cd4f0ef7 2470 noirqdebug [X86-32] Disables the code which attempts to detect and
1da177e4
LT
2471 disable unhandled interrupt sources.
2472
6cececfc 2473 no_timer_check [X86,APIC] Disables the code which tests for
8542b200
ZA
2474 broken timer IRQ sources.
2475
1da177e4
LT
2476 noisapnp [ISAPNP] Disables ISA PnP code.
2477
2478 noinitrd [RAM] Tells the kernel not to load any configured
2479 initial RAM disk.
2480
03ea8155
WH
2481 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2482 remapping.
d1423d56 2483 [Deprecated - use intremap=off]
03ea8155 2484
1da177e4
LT
2485 nointroute [IA-64]
2486
16290246 2487 nojitter [IA-64] Disables jitter checking for ITC timers.
0aa366f3 2488
9cf4c4fc
JK
2489 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2490
fd10cde9
GN
2491 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2492 fault handling.
2493
d910f5c1
GC
2494 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2495 steal time is computed, but won't influence scheduler
2496 behaviour
2497
cd4f0ef7 2498 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1da177e4 2499
cd4f0ef7 2500 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
ad62ca2b 2501
1da177e4
LT
2502 noltlbs [PPC] Do not use large page/tlb entries for kernel
2503 lowmem mapping on PPC40x.
2504
312f1f01
H
2505 nomca [IA-64] Disable machine check abort handling
2506
13696e0a 2507 nomce [X86-32] Disable Machine Check Exception
abe37e5a 2508
83d7384f
AS
2509 nomfgpt [X86-32] Disable Multi-Function General Purpose
2510 Timer usage (for AMD Geode machines).
2511
bda62633
DZ
2512 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2513 shutdown the other cpus. Instead use the REBOOT_VECTOR
2514 irq.
2515
02608bef
DY
2516 nomodule Disable module load
2517
016ddd9b
JK
2518 nopat [X86] Disable PAT (page attribute table extension of
2519 pagetables) support.
2520
0cb55ad2
RD
2521 norandmaps Don't use address space randomization. Equivalent to
2522 echo 0 > /proc/sys/kernel/randomize_va_space
2523
bbff2168 2524 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
959b4fdf 2525
cd4f0ef7 2526 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
b7fb4af0
JF
2527 with UP alternatives
2528
7a5091d5
PA
2529 nordrand [X86] Disable kernel use of the RDRAND and
2530 RDSEED instructions even if they are supported
2531 by the processor. RDRAND and RDSEED are still
2532 available to user space applications.
49d859d7 2533
a9913044
RD
2534 noresume [SWSUSP] Disables resume and restores original swap
2535 space.
2536
1da177e4
LT
2537 no-scroll [VGA] Disables scrollback.
2538 This is required for the Braillex ib80-piezo Braille
2539 reader made by F.H. Papenmeier (Germany).
2540
2541 nosbagart [IA-64]
2542
cd4f0ef7 2543 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
4f886511 2544
61ec7567
LB
2545 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2546 and disable the IO APIC. legacy for "maxcpus=0".
1da177e4 2547
97842216
DJ
2548 nosoftlockup [KNL] Disable the soft-lockup detector.
2549
1da177e4
LT
2550 nosync [HW,M68K] Disables sync negotiation for all devices.
2551
cd4f0ef7 2552 notsc [BUGS=X86-32] Disable Time Stamp Counter
1da177e4
LT
2553
2554 nousb [USB] Disable the USB subsystem
2555
195daf66
UO
2556 nowatchdog [KNL] Disable both lockup detectors, i.e.
2557 soft-lockup and NMI watchdog (hard-lockup).
58687acb 2558
1da177e4 2559 nowb [ARM]
a9913044 2560
2b2fd87a
WH
2561 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2562
f78cff48
FY
2563 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2564 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2565 Some features depend on CPU0. Known dependencies are:
2566 1. Resume from suspend/hibernate depends on CPU0.
2567 Suspend/hibernate will fail if CPU0 is offline and you
2568 need to online CPU0 before suspend/hibernate.
2569 2. PIC interrupts also depend on CPU0. CPU0 can't be
2570 removed if a PIC interrupt is detected.
2571 It's said poweroff/reboot may depend on CPU0 on some
2572 machines although I haven't seen such issues so far
2573 after CPU0 is offline on a few tested machines.
2574 If the dependencies are under your control, you can
2575 turn on cpu0_hotplug.
2576
16290246 2577 nptcg= [IA-64] Override max number of concurrent global TLB
a6c75b86
FY
2578 purges which is reported from either PAL_VM_SUMMARY or
2579 SAL PALO.
2580
2b633e3f
YL
2581 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2582 could support. nr_cpus=n : n >= 1 limits the kernel to
2583 supporting 'n' processors. Later in runtime you can not
2584 use hotplug cpu feature to put more cpu back to online.
2585 just like you compile the kernel NR_CPUS=n
2586
0cb55ad2
RD
2587 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2588
1a687c2e
MG
2589 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2590 Allowed values are enable and disable
2591
f0c0b2b8
KH
2592 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2593 one of ['zone', 'node', 'default'] can be specified
2594 This can be set from sysctl after boot.
2595 See Documentation/sysctl/vm.txt for details.
2596
7c4be253
RD
2597 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2598 See Documentation/debugging-via-ohci1394.txt for more
2599 info.
2600
3ef0e1f8
AS
2601 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2602 Rather than timing out after 20 ms if an EC
2603 command is not properly ACKed, override the length
2604 of the timeout. We have interrupts disabled while
2605 waiting for the ACK, so if this is set too high
2606 interrupts *may* be lost!
2607
15ac7afe
TL
2608 omap_mux= [OMAP] Override bootloader pin multiplexing.
2609 Format: <mux_mode0.mode_name=value>...
2610 For example, to override I2C bus2:
2611 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2612
1da177e4
LT
2613 oprofile.timer= [HW]
2614 Use timer interrupt instead of performance counters
2615
7e4e0bd5
RR
2616 oprofile.cpu_type= Force an oprofile cpu type
2617 This might be useful if you have an older oprofile
2618 userland or if you want common events.
8d7ff4f2
RR
2619 Format: { arch_perfmon }
2620 arch_perfmon: [X86] Force use of architectural
7e4e0bd5
RR
2621 perfmon on Intel CPUs instead of the
2622 CPU specific event set.
159a80b2
RR
2623 timer: [X86] Force use of architectural NMI
2624 timer mode (see also oprofile.timer
2625 for generic hr timer mode)
dd3c4670
AK
2626 [s390] Force legacy basic mode sampling
2627 (report cpu_type "timer")
1dcdb5a9 2628
44a4dcf7
RD
2629 oops=panic Always panic on oopses. Default is to just kill the
2630 process, but there is a small probability of
2631 deadlocking the machine.
d404ab0a
OH
2632 This will also cause panics on machine check exceptions.
2633 Useful together with panic=30 to trigger a reboot.
2634
bcfde334
RD
2635 OSS [HW,OSS]
2636 See Documentation/sound/oss/oss-parameters.txt
2637
48c96a36
JK
2638 page_owner= [KNL] Boot-time page_owner enabling option.
2639 Storage of the information about who allocated
2640 each page is disabled in default. With this switch,
2641 we can turn it on.
2642 on: enable the feature
2643
44a4dcf7 2644 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4302fbc8
HD
2645 timeout > 0: seconds before rebooting
2646 timeout = 0: wait forever
2647 timeout < 0: reboot immediately
1da177e4
LT
2648 Format: <timeout>
2649
9e3961a0
PB
2650 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2651 on a WARN().
2652
f06e5153
MH
2653 crash_kexec_post_notifiers
2654 Run kdump after running panic-notifiers and dumping
2655 kmsg. This only for the users who doubt kdump always
2656 succeeds in any situation.
2657 Note that this also increases risks of kdump failure,
2658 because some panic notifiers can make the crashed
2659 kernel more unstable.
2660
1da177e4
LT
2661 parkbd.port= [HW] Parallel port number the keyboard adapter is
2662 connected to, default is 0.
2663 Format: <parport#>
2664 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2665 0 for XT, 1 for AT (default is AT).
a9913044
RD
2666 Format: <mode>
2667
2668 parport= [HW,PPT] Specify parallel ports. 0 disables.
2669 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2670 Use 'auto' to force the driver to use any
2671 IRQ/DMA settings detected (the default is to
2672 ignore detected IRQ/DMA settings because of
2673 possible conflicts). You can specify the base
2674 address, IRQ, and DMA settings; IRQ and DMA
2675 should be numbers, or 'auto' (for using detected
2676 settings on that particular port), or 'nofifo'
2677 (to avoid using a FIFO even if it is detected).
2678 Parallel ports are assigned in the order they
2679 are specified on the command line, starting
2680 with parport0.
2681
2682 parport_init_mode= [HW,PPT]
2683 Configure VIA parallel port to operate in
2684 a specific mode. This is necessary on Pegasos
2685 computer where firmware has no options for setting
2686 up parallel port mode and sets it to spp.
2687 Currently this function knows 686a and 8231 chips.
1da177e4
LT
2688 Format: [spp|ps2|epp|ecp|ecpepp]
2689
dd287796
AM
2690 pause_on_oops=
2691 Halt all CPUs after the first oops has been printed for
2692 the specified number of seconds. This is to be used if
2693 your oopses keep scrolling off the screen.
2694
1da177e4
LT
2695 pcbit= [HW,ISDN]
2696
2697 pcd. [PARIDE]
2698 See header of drivers/block/paride/pcd.c.
31c00fc1 2699 See also Documentation/blockdev/paride.txt.
1da177e4 2700
a9913044 2701 pci=option[,option...] [PCI] various PCI subsystem options:
1cc0ca26
BH
2702 earlydump [X86] dump PCI config space before the kernel
2703 changes anything
c0115606 2704 off [X86] don't probe for the PCI bus
cd4f0ef7 2705 bios [X86-32] force use of PCI BIOS, don't access
a9913044
RD
2706 the hardware directly. Use this if your machine
2707 has a non-standard PCI host bridge.
cd4f0ef7 2708 nobios [X86-32] disallow use of PCI BIOS, only direct
a9913044
RD
2709 hardware access methods are allowed. Use this
2710 if you experience crashes upon bootup and you
2711 suspect they are caused by the BIOS.
c0115606 2712 conf1 [X86] Force use of PCI Configuration
a9913044 2713 Mechanism 1.
c0115606 2714 conf2 [X86] Force use of PCI Configuration
a9913044 2715 Mechanism 2.
7f785763
RD
2716 noaer [PCIE] If the PCIEAER kernel config parameter is
2717 enabled, this kernel boot option can be used to
2718 disable the use of PCIE advanced error reporting.
32a2eea7
JG
2719 nodomains [PCI] Disable support for multiple PCI
2720 root domains (aka PCI segments, in ACPI-speak).
6cececfc 2721 nommconf [X86] Disable use of MMCONFIG for PCI
61be6d66 2722 Configuration
12983077
AH
2723 check_enable_amd_mmconf [X86] check for and enable
2724 properly configured MMIO access to PCI
2725 config space on AMD family 10h CPU
309e57df
MW
2726 nomsi [MSI] If the PCI_MSI kernel config parameter is
2727 enabled, this kernel boot option can be used to
2728 disable the use of MSI interrupts system-wide.
a9322f64
SA
2729 noioapicquirk [APIC] Disable all boot interrupt quirks.
2730 Safety option to keep boot IRQs enabled. This
2731 should never be necessary.
9197979b
SA
2732 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2733 primary IO-APIC for bridges that cannot disable
2734 boot IRQs. This fixes a source of spurious IRQs
2735 when the system masks IRQs.
41b9eb26
SA
2736 noioapicreroute [APIC] Disable workaround that uses the
2737 boot IRQ equivalent of an IRQ that connects to
2738 a chipset where boot IRQs cannot be disabled.
2739 The opposite of ioapicreroute.
cd4f0ef7 2740 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
a9913044
RD
2741 routing table. These calls are known to be buggy
2742 on several machines and they hang the machine
2743 when used, but on other computers it's the only
2744 way to get the interrupt routing table. Try
2745 this option if the kernel is unable to allocate
2746 IRQs or discover secondary PCI buses on your
2747 motherboard.
c0115606 2748 rom [X86] Assign address space to expansion ROMs.
a9913044
RD
2749 Use with caution as certain devices share
2750 address decoders between ROMs and other
2751 resources.
c0115606 2752 norom [X86] Do not assign address space to
bb71ad88
GH
2753 expansion ROMs that do not already have
2754 BIOS assigned address ranges.
7bd1c365
MH
2755 nobar [X86] Do not assign address space to the
2756 BARs that weren't assigned by the BIOS.
c0115606 2757 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
a9913044
RD
2758 assigned automatically to PCI devices. You can
2759 make the kernel exclude IRQs of your ISA cards
2760 this way.
c0115606 2761 pirqaddr=0xAAAAA [X86] Specify the physical address
a9913044
RD
2762 of the PIRQ table (normally generated
2763 by the BIOS) if it is outside the
2764 F0000h-100000h range.
c0115606 2765 lastbus=N [X86] Scan all buses thru bus #N. Can be
a9913044
RD
2766 useful if the kernel is unable to find your
2767 secondary buses and you want to tell it
2768 explicitly which ones they are.
c0115606 2769 assign-busses [X86] Always assign all PCI bus
a9913044
RD
2770 numbers ourselves, overriding
2771 whatever the firmware may have done.
c0115606 2772 usepirqmask [X86] Honor the possible IRQ mask stored
a9913044
RD
2773 in the BIOS $PIR table. This is needed on
2774 some systems with broken BIOSes, notably
2775 some HP Pavilion N5400 and Omnibook XE3
2776 notebooks. This will have no effect if ACPI
2777 IRQ routing is enabled.
c0115606 2778 noacpi [X86] Do not use ACPI for IRQ routing
a9913044 2779 or for PCI scanning.
7bc5e3f2
BH
2780 use_crs [X86] Use PCI host bridge window information
2781 from ACPI. On BIOSes from 2008 or later, this
2782 is enabled by default. If you need to use this,
2783 please report a bug.
2784 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2785 If you need to use this, please report a bug.
a9913044
RD
2786 routeirq Do IRQ routing for all PCI devices.
2787 This is normally done in pci_enable_device(),
2788 so this option is a temporary workaround
2789 for broken drivers that don't call it.
13a6ddb0
YL
2790 skip_isa_align [X86] do not align io start addr, so can
2791 handle more pci cards
a9913044
RD
2792 firmware [ARM] Do not re-enumerate the bus but instead
2793 just use the configuration from the
2794 bootloader. This is currently used on
2795 IXP2000 systems where the bus has to be
2796 configured a certain way for adjunct CPUs.
0637a70a
AK
2797 noearly [X86] Don't do any early type 1 scanning.
2798 This might help on some broken boards which
2799 machine check when some devices' config space
2800 is read. But various workarounds are disabled
2801 and some IOMMU drivers will not work.
6b4b78fe
MD
2802 bfsort Sort PCI devices into breadth-first order.
2803 This sorting is done to get a device
2804 order compatible with older (<= 2.4) kernels.
2805 nobfsort Don't sort PCI devices into breadth-first order.
fa238712
YW
2806 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2807 tuning and use the BIOS-configured MPS defaults.
2808 pcie_bus_safe Set every device's MPS to the largest value
2809 supported by all devices below the root complex.
2810 pcie_bus_perf Set device MPS to the largest allowable MPS
2811 based on its parent bus. Also set MRRS (Max
2812 Read Request Size) to the largest supported
2813 value (no larger than the MPS that the device
2814 or bus can support) for best performance.
2815 pcie_bus_peer2peer Set every device's MPS to 128B, which
2816 every device is guaranteed to support. This
2817 configuration allows peer-to-peer DMA between
2818 any pair of devices, possibly at the cost of
2819 reduced performance. This also guarantees
2820 that hot-added devices will work.
4516a618
AN
2821 cbiosize=nn[KMG] The fixed amount of bus space which is
2822 reserved for the CardBus bridge's IO window.
2823 The default value is 256 bytes.
2824 cbmemsize=nn[KMG] The fixed amount of bus space which is
2825 reserved for the CardBus bridge's memory
2826 window. The default value is 64 megabytes.
32a9a682
YS
2827 resource_alignment=
2828 Format:
2829 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2830 Specifies alignment and device to reassign
2831 aligned memory resources.
2832 If <order of align> is not specified,
2833 PAGE_SIZE is used as alignment.
2834 PCI-PCI bridge can be specified, if resource
2835 windows need to be expanded.
43c16408
AP
2836 ecrc= Enable/disable PCIe ECRC (transaction layer
2837 end-to-end CRC checking).
2838 bios: Use BIOS/firmware settings. This is the
2839 the default.
2840 off: Turn ECRC off
2841 on: Turn ECRC on.
8c8803c5
YW
2842 hpiosize=nn[KMG] The fixed amount of bus space which is
2843 reserved for hotplug bridge's IO window.
2844 Default size is 256 bytes.
2845 hpmemsize=nn[KMG] The fixed amount of bus space which is
2846 reserved for hotplug bridge's memory window.
2847 Default size is 2 megabytes.
b55438fd
YL
2848 realloc= Enable/disable reallocating PCI bridge resources
2849 if allocations done by BIOS are too small to
2850 accommodate resources required by all child
2851 devices.
2852 off: Turn realloc off
2853 on: Turn realloc on
2854 realloc same as realloc=on
6748dcc2 2855 noari do not use PCIe ARI.
284f5f9d
BH
2856 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2857 only look for one device below a PCIe downstream
2858 port.
6b4b78fe 2859
e5665a45
CE
2860 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2861 Management.
2862 off Disable ASPM.
2863 force Enable ASPM even on devices that claim not to support it.
2864 WARNING: Forcing ASPM on may cause system lockups.
2865
7570a333
MT
2866 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2867 nomsi Do not use MSI for PCI Express Native Hotplug (this
2868 makes all PCIe ports use INTx for hotplug services).
2869
79dd9182 2870 pcie_ports= [PCIE] PCIe ports handling:
28eb5f27
RW
2871 auto Ask the BIOS whether or not to use native PCIe services
2872 associated with PCIe ports (PME, hot-plug, AER). Use
2873 them only if that is allowed by the BIOS.
2874 native Use native PCIe services associated with PCIe ports
2875 unconditionally.
79dd9182
RW
2876 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2877 ports driver.
2878
c7f48656 2879 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
c39fae14 2880 nomsi Do not use MSI for native PCIe PME signaling (this makes
28eb5f27 2881 all PCIe root ports use INTx for all services).
c7f48656 2882
1da177e4
LT
2883 pcmv= [HW,PCMCIA] BadgePAD 4
2884
39ac5ba5
TB
2885 pd_ignore_unused
2886 [PM]
2887 Keep all power-domains already enabled by bootloader on,
2888 even if no driver has claimed them. This is useful
2889 for debug and development, but should not be
2890 needed on a platform with proper driver support.
2891
1da177e4 2892 pd. [PARIDE]
31c00fc1 2893 See Documentation/blockdev/paride.txt.
1da177e4
LT
2894
2895 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2896 boot time.
2897 Format: { 0 | 1 }
2898 See arch/parisc/kernel/pdc_chassis.c
2899
f58dc01b 2900 percpu_alloc= Select which percpu first chunk allocator to use.
e933a73f
TH
2901 Currently supported values are "embed" and "page".
2902 Archs may support subset or none of the selections.
2903 See comments in mm/percpu.c for details on each
2904 allocator. This parameter is primarily for debugging
2905 and performance comparison.
fa8a7094 2906
1da177e4 2907 pf. [PARIDE]
31c00fc1 2908 See Documentation/blockdev/paride.txt.
1da177e4
LT
2909
2910 pg. [PARIDE]
31c00fc1 2911 See Documentation/blockdev/paride.txt.
1da177e4
LT
2912
2913 pirq= [SMP,APIC] Manual mp-table setup
71cced6e 2914 See Documentation/x86/i386/IO-APIC.txt.
1da177e4
LT
2915
2916 plip= [PPT,NET] Parallel port network link
2917 Format: { parport<nr> | timid | 0 }
2918 See also Documentation/parport.txt.
2919
16290246 2920 pmtmr= [X86] Manual setup of pmtmr I/O Port.
de32a243
TG
2921 Override pmtimer IOPort with a hex value.
2922 e.g. pmtmr=0x508
2923
96242116
BH
2924 pnp.debug=1 [PNP]
2925 Enable PNP debug messages (depends on the
2926 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2927 via /sys/module/pnp/parameters/debug. We always show
2928 current resource usage; turning this on also shows
2929 possible settings and some assignment information.
97ef062b 2930
1da177e4
LT
2931 pnpacpi= [ACPI]
2932 { off }
2933
2934 pnpbios= [ISAPNP]
2935 { on | off | curr | res | no-curr | no-res }
2936
2937 pnp_reserve_irq=
2938 [ISAPNP] Exclude IRQs for the autoconfiguration
2939
2940 pnp_reserve_dma=
2941 [ISAPNP] Exclude DMAs for the autoconfiguration
2942
2943 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
a9913044 2944 Ranges are in pairs (I/O port base and size).
1da177e4
LT
2945
2946 pnp_reserve_mem=
a9913044
RD
2947 [ISAPNP] Exclude memory regions for the
2948 autoconfiguration.
1da177e4
LT
2949 Ranges are in pairs (memory base and size).
2950
4af94f39
RD
2951 ports= [IP_VS_FTP] IPVS ftp helper module
2952 Default is 21.
2953 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2954 may be specified.
2955 Format: <port>,<port>....
2956
45807a1d
IM
2957 print-fatal-signals=
2958 [KNL] debug: print fatal signals
f84d49b2
NO
2959
2960 If enabled, warn about various signal handling
2961 related application anomalies: too many signals,
2962 too many POSIX.1 timers, fatal signals causing a
2963 coredump - etc.
2964
2965 If you hit the warning due to signal overflow,
2966 you might want to try "ulimit -i unlimited".
2967
45807a1d
IM
2968 default: off.
2969
c22ab332
MG
2970 printk.always_kmsg_dump=
2971 Trigger kmsg_dump for cases other than kernel oops or
2972 panics
2973 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2974 default: disabled
2975
e84845c4
RD
2976 printk.time= Show timing data prefixed to each printk message line
2977 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2978
0cb55ad2
RD
2979 processor.max_cstate= [HW,ACPI]
2980 Limit processor to maximum C-state
2981 max_cstate=9 overrides any DMI blacklist limit.
2982
2983 processor.nocst [HW,ACPI]
2984 Ignore the _CST method to determine C-states,
2985 instead using the legacy FADT method
2986
1da177e4 2987 profile= [KNL] Enable kernel profiling via /proc/profile
a9913044
RD
2988 Format: [schedule,]<number>
2989 Param: "schedule" - profile schedule points.
2990 Param: <number> - step/bucket size as a power of 2 for
2991 statistical time based profiling.
b3da2a73
MG
2992 Param: "sleep" - profile D-state sleeping (millisecs).
2993 Requires CONFIG_SCHEDSTATS
c0fe2e69 2994 Param: "kvm" - profile VM exits.
1da177e4 2995
1da177e4
LT
2996 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2997 before loading.
31c00fc1 2998 See Documentation/blockdev/ramdisk.txt.
1da177e4 2999
a9913044
RD
3000 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3001 probe for; one of (bare|imps|exps|lifebook|any).
1da177e4
LT
3002 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3003 per second.
a9913044
RD
3004 psmouse.resetafter= [HW,MOUSE]
3005 Try to reset the device after so many bad packets
1da177e4
LT
3006 (0 = never).
3007 psmouse.resolution=
3008 [HW,MOUSE] Set desired mouse resolution, in dpi.
3009 psmouse.smartscroll=
a9913044 3010 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1da177e4
LT
3011 0 = disabled, 1 = enabled (default).
3012
dee28e72
MG
3013 pstore.backend= Specify the name of the pstore backend to use
3014
1da177e4 3015 pt. [PARIDE]
31c00fc1 3016 See Documentation/blockdev/paride.txt.
1da177e4 3017
dc8c8587
KS
3018 pty.legacy_count=
3019 [KNL] Number of legacy pty's. Overwrites compiled-in
3020 default number.
3021
7d2c502f 3022 quiet [KNL] Disable most log messages
a9913044 3023
1da177e4
LT
3024 r128= [HW,DRM]
3025
3026 raid= [HW,RAID]
3027 See Documentation/md.txt.
3028
a9913044 3029 ramdisk_blocksize= [RAM]
31c00fc1 3030 See Documentation/blockdev/ramdisk.txt.
a9913044 3031
1da177e4 3032 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
31c00fc1 3033 See Documentation/blockdev/ramdisk.txt.
1da177e4 3034
4102adab 3035 rcu_nocbs= [KNL]
3fbfbf7a
PM
3036 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3037 the specified list of CPUs to be no-callback CPUs.
3038 Invocation of these CPUs' RCU callbacks will
a4889858
PM
3039 be offloaded to "rcuox/N" kthreads created for
3040 that purpose, where "x" is "b" for RCU-bh, "p"
3041 for RCU-preempt, and "s" for RCU-sched, and "N"
3042 is the CPU number. This reduces OS jitter on the
3fbfbf7a
PM
3043 offloaded CPUs, which can be useful for HPC and
3044 real-time workloads. It can also improve energy
3045 efficiency for asymmetric multiprocessors.
3046
4102adab 3047 rcu_nocb_poll [KNL]
3fbfbf7a
PM
3048 Rather than requiring that offloaded CPUs
3049 (specified by rcu_nocbs= above) explicitly
3050 awaken the corresponding "rcuoN" kthreads,
3051 make these kthreads poll for callbacks.
3052 This improves the real-time response for the
3053 offloaded CPUs by relieving them of the need to
3054 wake up the corresponding kthread, but degrades
3055 energy efficiency by requiring that the kthreads
3056 periodically wake up to do the polling.
3057
4102adab 3058 rcutree.blimit= [KNL]
97e63f0c
PM
3059 Set maximum number of finished RCU callbacks to
3060 process in one batch.
21a1ea9e 3061
a3dc2948
PM
3062 rcutree.dump_tree= [KNL]
3063 Dump the structure of the rcu_node combining tree
3064 out at early boot. This is used for diagnostic
3065 purposes, to verify correct tree setup.
3066
0f41c0dd
PM
3067 rcutree.gp_cleanup_delay= [KNL]
3068 Set the number of jiffies to delay each step of
3069 RCU grace-period cleanup. This only has effect
3070 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3071
37745d28
PM
3072 rcutree.gp_init_delay= [KNL]
3073 Set the number of jiffies to delay each step of
3074 RCU grace-period initialization. This only has
0f41c0dd
PM
3075 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3076 is set.
3077
3078 rcutree.gp_preinit_delay= [KNL]
3079 Set the number of jiffies to delay each step of
3080 RCU grace-period pre-initialization, that is,
3081 the propagation of recent CPU-hotplug changes up
3082 the rcu_node combining tree. This only has effect
3083 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
37745d28 3084
7fa27001
PM
3085 rcutree.rcu_fanout_exact= [KNL]
3086 Disable autobalancing of the rcu_node combining
3087 tree. This is used by rcutorture, and might
3088 possibly be useful for architectures having high
3089 cache-to-cache transfer latencies.
37745d28 3090
4102adab 3091 rcutree.rcu_fanout_leaf= [KNL]
f885b7f2
PM
3092 Increase the number of CPUs assigned to each
3093 leaf rcu_node structure. Useful for very large
3094 systems.
3095
4a81e832
PM
3096 rcutree.jiffies_till_sched_qs= [KNL]
3097 Set required age in jiffies for a
3098 given grace period before RCU starts
3099 soliciting quiescent-state help from
3100 rcu_note_context_switch().
3101
4102adab 3102 rcutree.jiffies_till_first_fqs= [KNL]
c0f4dfd4
PM
3103 Set delay from grace-period initialization to
3104 first attempt to force quiescent states.
3105 Units are jiffies, minimum value is zero,
3106 and maximum value is HZ.
3107
4102adab 3108 rcutree.jiffies_till_next_fqs= [KNL]
c0f4dfd4
PM
3109 Set delay between subsequent attempts to force
3110 quiescent states. Units are jiffies, minimum
3111 value is one, and maximum value is HZ.
3112
21871d7e 3113 rcutree.kthread_prio= [KNL,BOOT]
d2af1ad7
PM
3114 Set the SCHED_FIFO priority of the RCU per-CPU
3115 kthreads (rcuc/N). This value is also used for
3116 the priority of the RCU boost threads (rcub/N)
3117 and for the RCU grace-period kthreads (rcu_bh,
3118 rcu_preempt, and rcu_sched). If RCU_BOOST is
3119 set, valid values are 1-99 and the default is 1
3120 (the least-favored priority). Otherwise, when
3121 RCU_BOOST is not set, valid values are 0-99 and
3122 the default is zero (non-realtime operation).
21871d7e 3123
fbce7497
PM
3124 rcutree.rcu_nocb_leader_stride= [KNL]
3125 Set the number of NOCB kthread groups, which
3126 defaults to the square root of the number of
3127 CPUs. Larger numbers reduces the wakeup overhead
3128 on the per-CPU grace-period kthreads, but increases
3129 that same overhead on each group's leader.
3130
4102adab 3131 rcutree.qhimark= [KNL]
97e63f0c
PM
3132 Set threshold of queued RCU callbacks beyond which
3133 batch limiting is disabled.
21a1ea9e 3134
4102adab 3135 rcutree.qlowmark= [KNL]
24aaef8d
RD
3136 Set threshold of queued RCU callbacks below which
3137 batch limiting is re-enabled.
21a1ea9e 3138
4102adab 3139 rcutree.rcu_idle_gp_delay= [KNL]
c0f4dfd4
PM
3140 Set wakeup interval for idle CPUs that have
3141 RCU callbacks (RCU_FAST_NO_HZ=y).
d40011f6 3142
4102adab 3143 rcutree.rcu_idle_lazy_gp_delay= [KNL]
c0f4dfd4
PM
3144 Set wakeup interval for idle CPUs that have
3145 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3146 Lazy RCU callbacks are those which RCU can
3147 prove do nothing more than free memory.
d40011f6 3148
38706bc5
PM
3149 rcutorture.cbflood_inter_holdoff= [KNL]
3150 Set holdoff time (jiffies) between successive
3151 callback-flood tests.
3152
3153 rcutorture.cbflood_intra_holdoff= [KNL]
3154 Set holdoff time (jiffies) between successive
3155 bursts of callbacks within a given callback-flood
3156 test.
3157
3158 rcutorture.cbflood_n_burst= [KNL]
3159 Set the number of bursts making up a given
3160 callback-flood test. Set this to zero to
3161 disable callback-flood testing.
3162
3163 rcutorture.cbflood_n_per_burst= [KNL]
3164 Set the number of callbacks to be registered
3165 in a given burst of a callback-flood test.
3166
4102adab 3167 rcutorture.fqs_duration= [KNL]
21b05de4
PM
3168 Set duration of force_quiescent_state bursts
3169 in microseconds.
dabb8aa9 3170
4102adab 3171 rcutorture.fqs_holdoff= [KNL]
21b05de4
PM
3172 Set holdoff time within force_quiescent_state bursts
3173 in microseconds.
dabb8aa9 3174
4102adab 3175 rcutorture.fqs_stutter= [KNL]
21b05de4
PM
3176 Set wait time between force_quiescent_state bursts
3177 in seconds.
3178
3179 rcutorture.gp_cond= [KNL]
3180 Use conditional/asynchronous update-side
3181 primitives, if available.
dabb8aa9 3182
4102adab 3183 rcutorture.gp_exp= [KNL]
21b05de4 3184 Use expedited update-side primitives, if available.
4102adab
PM
3185
3186 rcutorture.gp_normal= [KNL]
21b05de4
PM
3187 Use normal (non-expedited) asynchronous
3188 update-side primitives, if available.
3189
3190 rcutorture.gp_sync= [KNL]
3191 Use normal (non-expedited) synchronous
3192 update-side primitives, if available. If all
3193 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3194 rcutorture.gp_normal=, and rcutorture.gp_sync=
3195 are zero, rcutorture acts as if is interpreted
3196 they are all non-zero.
dabb8aa9 3197
4102adab 3198 rcutorture.n_barrier_cbs= [KNL]
dabb8aa9
PM
3199 Set callbacks/threads for rcu_barrier() testing.
3200
4102adab 3201 rcutorture.nfakewriters= [KNL]
dabb8aa9
PM
3202 Set number of concurrent RCU writers. These just
3203 stress RCU, they don't participate in the actual
3204 test, hence the "fake".
3205
4102adab 3206 rcutorture.nreaders= [KNL]
3838cc18
PM
3207 Set number of RCU readers. The value -1 selects
3208 N-1, where N is the number of CPUs. A value
3209 "n" less than -1 selects N-n-2, where N is again
3210 the number of CPUs. For example, -2 selects N
3211 (the number of CPUs), -3 selects N+1, and so on.
dabb8aa9 3212
4102adab
PM
3213 rcutorture.object_debug= [KNL]
3214 Enable debug-object double-call_rcu() testing.
3215
3216 rcutorture.onoff_holdoff= [KNL]
dabb8aa9
PM
3217 Set time (s) after boot for CPU-hotplug testing.
3218
4102adab 3219 rcutorture.onoff_interval= [KNL]
dabb8aa9
PM
3220 Set time (s) between CPU-hotplug operations, or
3221 zero to disable CPU-hotplug testing.
3222
4102adab 3223 rcutorture.shuffle_interval= [KNL]
dabb8aa9
PM
3224 Set task-shuffle interval (s). Shuffling tasks
3225 allows some CPUs to go into dyntick-idle mode
3226 during the rcutorture test.
3227
4102adab 3228 rcutorture.shutdown_secs= [KNL]
dabb8aa9
PM
3229 Set time (s) after boot system shutdown. This
3230 is useful for hands-off automated testing.
3231
4102adab 3232 rcutorture.stall_cpu= [KNL]
dabb8aa9
PM
3233 Duration of CPU stall (s) to test RCU CPU stall
3234 warnings, zero to disable.
3235
4102adab 3236 rcutorture.stall_cpu_holdoff= [KNL]
dabb8aa9
PM
3237 Time to wait (s) after boot before inducing stall.
3238
4102adab 3239 rcutorture.stat_interval= [KNL]
dabb8aa9
PM
3240 Time (s) between statistics printk()s.
3241
4102adab 3242 rcutorture.stutter= [KNL]
dabb8aa9
PM
3243 Time (s) to stutter testing, for example, specifying
3244 five seconds causes the test to run for five seconds,
3245 wait for five seconds, and so on. This tests RCU's
3246 ability to transition abruptly to and from idle.
3247
4102adab 3248 rcutorture.test_boost= [KNL]
dabb8aa9
PM
3249 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3250 "Maybe" means test if the RCU implementation
3251 under test support RCU priority boosting.
3252
4102adab 3253 rcutorture.test_boost_duration= [KNL]
dabb8aa9
PM
3254 Duration (s) of each individual boost test.
3255
4102adab 3256 rcutorture.test_boost_interval= [KNL]
dabb8aa9
PM
3257 Interval (s) between each boost test.
3258
4102adab 3259 rcutorture.test_no_idle_hz= [KNL]
dabb8aa9
PM
3260 Test RCU's dyntick-idle handling. See also the
3261 rcutorture.shuffle_interval parameter.
3262
21b05de4
PM
3263 rcutorture.torture_runnable= [BOOT]
3264 Start rcutorture running at boot time.
3265
4102adab 3266 rcutorture.torture_type= [KNL]
dabb8aa9
PM
3267 Specify the RCU implementation to test.
3268
4102adab 3269 rcutorture.verbose= [KNL]
dabb8aa9
PM
3270 Enable additional printk() statements.
3271
4102adab
PM
3272 rcupdate.rcu_expedited= [KNL]
3273 Use expedited grace-period primitives, for
3274 example, synchronize_rcu_expedited() instead
3275 of synchronize_rcu(). This reduces latency,
3276 but can increase CPU utilization, degrade
3277 real-time latency, and degrade energy efficiency.
3278
3279 rcupdate.rcu_cpu_stall_suppress= [KNL]
3280 Suppress RCU CPU stall warning messages.
3281
3282 rcupdate.rcu_cpu_stall_timeout= [KNL]
3283 Set timeout for RCU CPU stall warning messages.
3284
52db30ab
PM
3285 rcupdate.rcu_task_stall_timeout= [KNL]
3286 Set timeout in jiffies for RCU task stall warning
3287 messages. Disable with a value less than or equal
3288 to zero.
3289
74860fee
PK
3290 rcupdate.rcu_self_test= [KNL]
3291 Run the RCU early boot self tests
3292
3293 rcupdate.rcu_self_test_bh= [KNL]
3294 Run the RCU bh early boot self tests
3295
3296 rcupdate.rcu_self_test_sched= [KNL]
3297 Run the RCU sched early boot self tests
3298
ffdfc409
OJ
3299 rdinit= [KNL]
3300 Format: <full_path>
3301 Run specified binary instead of /init from the ramdisk,
3302 used for early userspace startup. See initrd.
3303
1b3a5d02
RH
3304 reboot= [KNL]
3305 Format (x86 or x86_64):
3306 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3307 [[,]s[mp]#### \
3308 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3309 [[,]f[orce]
3310 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3311 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3312 reboot_force is either force or not specified,
3313 reboot_cpu is s[mp]#### with #### being the processor
3314 to be used for rebooting.
1da177e4 3315
46b6d94e
PJ
3316 relax_domain_level=
3317 [KNL, SMP] Set scheduler's default relax_domain_level.
21acb9ca 3318 See Documentation/cgroups/cpusets.txt.
46b6d94e 3319
0399d4db
RW
3320 relative_sleep_states=
3321 [SUSPEND] Use sleep state labeling where the deepest
3322 state available other than hibernation is always "mem".
3323 Format: { "0" | "1" }
3324 0 -- Traditional sleep state labels.
3325 1 -- Relative sleep state labels.
3326
1da177e4
LT
3327 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3328
cd4f0ef7 3329 reservetop= [X86-32]
461a9aff
ZA
3330 Format: nn[KMG]
3331 Reserves a hole at the top of the kernel virtual
3332 address space.
3333
9ea77bdb
PA
3334 reservelow= [X86]
3335 Format: nn[K]
3336 Set the amount of memory to reserve for BIOS at
3337 the bottom of the address space.
3338
7e96287d
VG
3339 reset_devices [KNL] Force drivers to reset the underlying device
3340 during initialization.
3341
a9913044
RD
3342 resume= [SWSUSP]
3343 Specify the partition device for software suspend
2df83fa4
MB
3344 Format:
3345 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
1da177e4 3346
ecbd0da1
RW
3347 resume_offset= [SWSUSP]
3348 Specify the offset from the beginning of the partition
3349 given by "resume=" at which the swap header is located,
3350 in <PAGE_SIZE> units (needed only for swap files).
3351 See Documentation/power/swsusp-and-swap-files.txt
3352
f126f733
BS
3353 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3354 read the resume files
3355
6f8d7022
BS
3356 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3357 Useful for devices that are detected asynchronously
3358 (e.g. USB and MMC devices).
3359
f996fc96
BS
3360 hibernate= [HIBERNATION]
3361 noresume Don't check if there's a hibernation image
3362 present during boot.
3363 nocompress Don't compress/decompress hibernation images.
a6e15a39 3364 no Disable hibernation and resume.
f996fc96 3365
0a7b35cb
MN
3366 retain_initrd [RAM] Keep initrd memory after extraction
3367
0efbb786
AC
3368 rfkill.default_state=
3369 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3370 etc. communication is blocked by default.
3371 1 Unblocked.
3372
3373 rfkill.master_switch_mode=
3374 0 The "airplane mode" button does nothing.
3375 1 The "airplane mode" button toggles between everything
3376 blocked and the previous configuration.
3377 2 The "airplane mode" button toggles between everything
3378 blocked and everything unblocked.
3379
1da177e4
LT
3380 rhash_entries= [KNL,NET]
3381 Set number of hash buckets for route cache
3382
1da177e4
LT
3383 ro [KNL] Mount root device read-only on boot
3384
3385 root= [KNL] Root filesystem
f2d34fd9 3386 See name_to_dev_t comment in init/do_mounts.c.
1da177e4
LT
3387
3388 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3389 mount the root filesystem
3390
3391 rootflags= [KNL] Set root filesystem mount option string
3392
3393 rootfstype= [KNL] Set root filesystem type
3394
cc1ed754
PO
3395 rootwait [KNL] Wait (indefinitely) for root device to show up.
3396 Useful for devices that are detected asynchronously
3397 (e.g. USB and MMC devices).
3398
5c71d618
RT
3399 rproc_mem=nn[KMG][@address]
3400 [KNL,ARM,CMA] Remoteproc physical memory block.
3401 Memory area to be used by remote processor image,
3402 managed by CMA.
3403
1da177e4
LT
3404 rw [KNL] Mount root device read-write on boot
3405
3406 S [KNL] Run init in single mode
3407
c60d1ae4
GS
3408 s390_iommu= [HW,S390]
3409 Set s390 IOTLB flushing mode
3410 strict
3411 With strict flushing every unmap operation will result in
3412 an IOTLB flush. Default is lazy flushing before reuse,
3413 which is faster.
3414
1da177e4
LT
3415 sa1100ir [NET]
3416 See drivers/net/irda/sa1100_ir.c.
3417
1da177e4 3418 sbni= [NET] Granch SBNI12 leased line adapter
a9913044 3419
f6630114
MT
3420 sched_debug [KNL] Enables verbose scheduler debug messages.
3421
5307c955
MG
3422 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3423 xtime_lock contention on larger systems, and/or RCU lock
3424 contention on all systems with CONFIG_MAXSMP set.
3425 Format: { "0" | "1" }
3426 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3427 1 -- enable.
3428 Note: increases power consumption, thus should only be
3429 enabled if running jitter sensitive (HPC/RT) workloads.
3430
0cb55ad2
RD
3431 security= [SECURITY] Choose a security module to enable at boot.
3432 If this boot parameter is not specified, only the first
3433 security module asking for security registration will be
3434 loaded. An invalid security module name will be treated
3435 as if no module has been chosen.
3436
3437 selinux= [SELINUX] Disable or enable SELinux at boot time.
1da177e4
LT
3438 Format: { "0" | "1" }
3439 See security/selinux/Kconfig help text.
3440 0 -- disable.
3441 1 -- enable.
3442 Default value is set via kernel config option.
3443 If enabled at boot time, /selinux/disable can be used
3444 later to disable prior to initial policy load.
3445
c1c124e9
JJ
3446 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3447 Format: { "0" | "1" }
3448 See security/apparmor/Kconfig help text
3449 0 -- disable.
3450 1 -- enable.
3451 Default value is set via kernel config option.
3452
cd4f0ef7 3453 serialnumber [BUGS=X86-32]
1da177e4 3454
1da177e4
LT
3455 shapers= [NET]
3456 Maximal number of shapers.
a9913044 3457
b05f78f5
YL
3458 show_msr= [x86] show boot-time MSR settings
3459 Format: { <integer> }
3460 Show boot-time (BIOS-initialized) MSR settings.
3461 The parameter means the number of CPUs to show,
3462 for example 1 means boot CPU only.
3463
1da177e4
LT
3464 simeth= [IA-64]
3465 simscsi=
a9913044 3466
1da177e4
LT
3467 slram= [HW,MTD]
3468
423c929c
JK
3469 slab_nomerge [MM]
3470 Disable merging of slabs with similar size. May be
3471 necessary if there is some reason to distinguish
3472 allocs to different slabs. Debug options disable
3473 merging on their own.
3474 For more information see Documentation/vm/slub.txt.
3475
3df1cccd
DR
3476 slab_max_order= [MM, SLAB]
3477 Determines the maximum allowed order for slabs.
3478 A high setting may cause OOMs due to memory
3479 fragmentation. Defaults to 1 for systems with
3480 more than 32MB of RAM, 0 otherwise.
3481
f0630fff
CL
3482 slub_debug[=options[,slabs]] [MM, SLUB]
3483 Enabling slub_debug allows one to determine the
3484 culprit if slab objects become corrupted. Enabling
3485 slub_debug can create guard zones around objects and
3486 may poison objects when not in use. Also tracks the
3487 last alloc / free. For more information see
3488 Documentation/vm/slub.txt.
c1aee215
CL
3489
3490 slub_max_order= [MM, SLUB]
f0630fff
CL
3491 Determines the maximum allowed order for slabs.
3492 A high setting may cause OOMs due to memory
3493 fragmentation. For more information see
3494 Documentation/vm/slub.txt.
c1aee215
CL
3495
3496 slub_min_objects= [MM, SLUB]
f0630fff
CL
3497 The minimum number of objects per slab. SLUB will
3498 increase the slab order up to slub_max_order to
3499 generate a sufficiently large slab able to contain
3500 the number of objects indicated. The higher the number
3501 of objects the smaller the overhead of tracking slabs
3502 and the less frequently locks need to be acquired.
c1aee215
CL
3503 For more information see Documentation/vm/slub.txt.
3504
3505 slub_min_order= [MM, SLUB]
24775d65 3506 Determines the minimum page order for slabs. Must be
f0630fff 3507 lower than slub_max_order.
c1aee215
CL
3508 For more information see Documentation/vm/slub.txt.
3509
3510 slub_nomerge [MM, SLUB]
423c929c
JK
3511 Same with slab_nomerge. This is supported for legacy.
3512 See slab_nomerge for more information.
c1aee215 3513
1da177e4
LT
3514 smart2= [HW]
3515 Format: <io1>[,<io2>[,...,<io8>]]
3516
d0d4f69b
BH
3517 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3518 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3519 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3520 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3521 smsc-ircc2.ircc_irq= [HW] IRQ line
3522 smsc-ircc2.ircc_dma= [HW] DMA channel
3523 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3524 0: Toshiba Satellite 1800 (GP data pin select)
3525 1: Fast pin select (default)
3526 2: ATC IRMode
3527
9c44bc03
IM
3528 softlockup_panic=
3529 [KNL] Should the soft-lockup detector generate panics.
44a4dcf7 3530 Format: <integer>
9c44bc03 3531
ed235875
AT
3532 softlockup_all_cpu_backtrace=
3533 [KNL] Should the soft-lockup detector generate
3534 backtraces on all cpus.
3535 Format: <integer>
3536
1da177e4 3537 sonypi.*= [HW] Sony Programmable I/O Control Device driver
395cf969 3538 See Documentation/laptops/sonypi.txt
1da177e4 3539
1da177e4
LT
3540 spia_io_base= [HW,MTD]
3541 spia_fio_base=
3542 spia_pedr=
3543 spia_peddr=
3544
f38f1d2a
SR
3545 stacktrace [FTRACE]
3546 Enabled the stack tracer on boot up.
3547
762e1207
SR
3548 stacktrace_filter=[function-list]
3549 [FTRACE] Limit the functions that the stack tracer
3550 will trace at boot up. function-list is a comma separated
3551 list of functions. This list can be changed at run
3552 time by the stack_trace_filter file in the debugfs
3553 tracing directory. Note, this enables stack tracing
3554 and the stacktrace above is not needed.
3555
1da177e4
LT
3556 sti= [PARISC,HW]
3557 Format: <num>
3558 Set the STI (builtin display/keyboard on the HP-PARISC
3559 machines) console (graphic card) which should be used
3560 as the initial boot-console.
3561 See also comment in drivers/video/console/sticore.c.
3562
3563 sti_font= [HW]
3564 See comment in drivers/video/console/sticore.c.
3565
3566 stifb= [HW]
3567 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3568
cbf11071
TM
3569 sunrpc.min_resvport=
3570 sunrpc.max_resvport=
3571 [NFS,SUNRPC]
3572 SunRPC servers often require that client requests
3573 originate from a privileged port (i.e. a port in the
3574 range 0 < portnr < 1024).
3575 An administrator who wishes to reserve some of these
3576 ports for other uses may adjust the range that the
3577 kernel's sunrpc client considers to be privileged
3578 using these two parameters to set the minimum and
3579 maximum port values.
3580
42a7fc4a
GB
3581 sunrpc.pool_mode=
3582 [NFS]
3583 Control how the NFS server code allocates CPUs to
3584 service thread pools. Depending on how many NICs
3585 you have and where their interrupts are bound, this
3586 option will affect which CPUs will do NFS serving.
3587 Note: this parameter cannot be changed while the
3588 NFS server is running.
3589
3590 auto the server chooses an appropriate mode
3591 automatically using heuristics
3592 global a single global pool contains all CPUs
3593 percpu one pool for each CPU
3594 pernode one pool for each NUMA node (equivalent
3595 to global on non-NUMA machines)
3596
cbf11071
TM
3597 sunrpc.tcp_slot_table_entries=
3598 sunrpc.udp_slot_table_entries=
3599 [NFS,SUNRPC]
3600 Sets the upper limit on the number of simultaneous
3601 RPC calls that can be sent from the client to a
3602 server. Increasing these values may allow you to
3603 improve throughput, but will also increase the
3604 amount of memory reserved for use by the client.
3605
1d4a9c17
BN
3606 suspend.pm_test_delay=
3607 [SUSPEND]
3608 Sets the number of seconds to remain in a suspend test
3609 mode before resuming the system (see
3610 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3611 is set. Default value is 5.
3612
07555ac1 3613 swapaccount=[0|1]
a42c390c
MH
3614 [KNL] Enable accounting of swap in memory resource
3615 controller if no parameter or 1 is given or disable
3616 it if 0 is given (See Documentation/cgroups/memory.txt)
3617
91fec0f5
JK
3618 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3619 Format: { <int> | force }
3620 <int> -- Number of I/O TLB slabs
3621 force -- force using of bounce buffers even if they
3622 wouldn't be automatically used by the kernel
a9913044 3623
1da177e4
LT
3624 switches= [HW,M68k]
3625
e52eec13
AK
3626 sysfs.deprecated=0|1 [KNL]
3627 Enable/disable old style sysfs layout for old udev
3628 on older distributions. When this option is enabled
3629 very new udev will not work anymore. When this option
3630 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3631 in older udev will not work anymore.
3632 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3633 the kernel configuration.
3634
5d6f647f
IM
3635 sysrq_always_enabled
3636 [KNL]
3637 Ignore sysrq setting - this boot parameter will
3638 neutralize any effect of /proc/sys/kernel/sysrq.
3639 Useful for debugging.
3640
747029a5
FF
3641 tcpmhash_entries= [KNL,NET]
3642 Set the number of tcp_metrics_hash slots.
3643 Default value is 8192 or 16384 depending on total
3644 ram pages. This is used to specify the TCP metrics
3645 cache size. See Documentation/networking/ip-sysctl.txt
3646 "tcp_no_metrics_save" section for more details.
3647
1da177e4
LT
3648 tdfx= [HW,DRM]
3649
acc82342 3650 test_suspend= [SUSPEND][,N]
77437fd4 3651 Specify "mem" (for Suspend-to-RAM) or "standby" (for
acc82342
SP
3652 standby suspend) or "freeze" (for suspend type freeze)
3653 as the system sleep state during system startup with
3654 the optional capability to repeat N number of times.
3655 The system is woken from this state using a
3656 wakeup-capable RTC alarm.
77437fd4 3657
1da177e4
LT
3658 thash_entries= [KNL,NET]
3659 Set number of hash buckets for TCP connection
3660
f8707ec9
LB
3661 thermal.act= [HW,ACPI]
3662 -1: disable all active trip points in all thermal zones
3663 <degrees C>: override all lowest active trip points
3664
c52a7419
LB
3665 thermal.crt= [HW,ACPI]
3666 -1: disable all critical trip points in all thermal zones
22a94d79 3667 <degrees C>: override all critical trip points
c52a7419 3668
f5487145
LB
3669 thermal.nocrt= [HW,ACPI]
3670 Set to disable actions on ACPI thermal zone
3671 critical and hot trip points.
3672
72b33ef8
LB
3673 thermal.off= [HW,ACPI]
3674 1: disable ACPI thermal control
3675
a70cdc52
LB
3676 thermal.psv= [HW,ACPI]
3677 -1: disable all passive trip points
ada9cfdd
RD
3678 <degrees C>: override all passive trip points to this
3679 value
a70cdc52 3680
730ff34d
LB
3681 thermal.tzp= [HW,ACPI]
3682 Specify global default ACPI thermal zone polling rate
3683 <deci-seconds>: poll all this frequency
3684 0: no polling (default)
3685
8d32a307
TG
3686 threadirqs [KNL]
3687 Force threading of all interrupt handlers except those
24775d65 3688 marked explicitly IRQF_NO_THREAD.
8d32a307 3689
2ca62b04
KRW
3690 tmem [KNL,XEN]
3691 Enable the Transcendent memory driver if built-in.
3692
3693 tmem.cleancache=0|1 [KNL, XEN]
3694 Default is on (1). Disable the usage of the cleancache
3695 API to send anonymous pages to the hypervisor.
3696
3697 tmem.frontswap=0|1 [KNL, XEN]
3698 Default is on (1). Disable the usage of the frontswap
37d46e15
KRW
3699 API to send swap pages to the hypervisor. If disabled
3700 the selfballooning and selfshrinking are force disabled.
2ca62b04
KRW
3701
3702 tmem.selfballooning=0|1 [KNL, XEN]
3703 Default is on (1). Disable the driving of swap pages
3704 to the hypervisor.
3705
3706 tmem.selfshrinking=0|1 [KNL, XEN]
3707 Default is on (1). Partial swapoff that immediately
3708 transfers pages from Xen hypervisor back to the
3709 kernel based on different criteria.
3710
2b1a61f0
HC
3711 topology= [S390]
3712 Format: {off | on}
3713 Specify if the kernel should make use of the cpu
f65e51d7
SL
3714 topology information if the hardware supports this.
3715 The scheduler will make use of this information and
2b1a61f0 3716 e.g. base its process migration decisions on it.
c9af3fa9 3717 Default is on.
2b1a61f0 3718
2d73bae1
NA
3719 topology_updates= [KNL, PPC, NUMA]
3720 Format: {off}
3721 Specify if the kernel should ignore (off)
3722 topology updates sent by the hypervisor to this
3723 LPAR.
3724
1da177e4
LT
3725 tp720= [HW,PS2]
3726
225a9be2
RA
3727 tpm_suspend_pcr=[HW,TPM]
3728 Format: integer pcr id
3729 Specify that at suspend time, the tpm driver
3730 should extend the specified pcr with zeros,
3731 as a workaround for some chips which fail to
3732 flush the last written pcr on TPM_SaveState.
3733 This will guarantee that all the other pcrs
3734 are saved.
3735
9d612bef 3736 trace_buf_size=nn[KMG]
3e6fb8e9 3737 [FTRACE] will set tracing buffer size on each cpu.
631595fb 3738
020e5f85
LZ
3739 trace_event=[event-list]
3740 [FTRACE] Set and start specified trace events in order
3741 to facilitate early boot debugging.
3742 See also Documentation/trace/events.txt
3743
7bcfaf54
SR
3744 trace_options=[option-list]
3745 [FTRACE] Enable or disable tracer options at boot.
3746 The option-list is a comma delimited list of options
3747 that can be enabled or disabled just as if you were
3748 to echo the option name into
3749
3750 /sys/kernel/debug/tracing/trace_options
3751
3752 For example, to enable stacktrace option (to dump the
3753 stack trace of each event), add to the command line:
3754
3755 trace_options=stacktrace
3756
3757 See also Documentation/trace/ftrace.txt "trace options"
3758 section.
3759
0daa2302
SRRH
3760 tp_printk[FTRACE]
3761 Have the tracepoints sent to printk as well as the
3762 tracing ring buffer. This is useful for early boot up
3763 where the system hangs or reboots and does not give the
3764 option for reading the tracing buffer or performing a
3765 ftrace_dump_on_oops.
3766
3767 To turn off having tracepoints sent to printk,
3768 echo 0 > /proc/sys/kernel/tracepoint_printk
3769 Note, echoing 1 into this file without the
3770 tracepoint_printk kernel cmdline option has no effect.
3771
3772 ** CAUTION **
3773
3774 Having tracepoints sent to printk() and activating high
3775 frequency tracepoints such as irq or sched, can cause
3776 the system to live lock.
3777
de7edd31
SRRH
3778 traceoff_on_warning
3779 [FTRACE] enable this option to disable tracing when a
3780 warning is hit. This turns off "tracing_on". Tracing can
3781 be enabled again by echoing '1' into the "tracing_on"
3782 file located in /sys/kernel/debug/tracing/
3783
3784 This option is useful, as it disables the trace before
3785 the WARNING dump is called, which prevents the trace to
3786 be filled with content caused by the warning output.
3787
3788 This option can also be set at run time via the sysctl
3789 option: kernel/traceoff_on_warning
3790
fcf4d821
JK
3791 transparent_hugepage=
3792 [KNL]
3793 Format: [always|madvise|never]
3794 Can be used to control the default behavior of the system
3795 with respect to transparent hugepages.
3796 See Documentation/vm/transhuge.txt for more details.
3797
d3b8f889 3798 tsc= Disable clocksource stability checks for TSC.
395628ef
AK
3799 Format: <string>
3800 [x86] reliable: mark tsc clocksource as reliable, this
d3b8f889 3801 disables clocksource verification at runtime, as well
3802 as the stability checks done at bootup. Used to enable
3803 high-resolution timer mode on older hardware, and in
3804 virtualized environment.
e82b8e4e
VP
3805 [x86] noirqtime: Do not use TSC to do irq accounting.
3806 Used to run time disable IRQ_TIME_ACCOUNTING on any
3807 platforms where RDTSC is slow and this accounting
3808 can add overhead.
395628ef 3809
a9913044
RD
3810 turbografx.map[2|3]= [HW,JOY]
3811 TurboGraFX parallel port interface
3812 Format:
3813 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
1da177e4
LT
3814 See also Documentation/input/joystick-parport.txt
3815
b6935f8c
CK
3816 udbg-immortal [PPC] When debugging early kernel crashes that
3817 happen after console_init() and before a proper
3818 console driver takes over, this boot options might
3819 help "seeing" what's going on.
3820
f86dcc5a
ED
3821 uhash_entries= [KNL,NET]
3822 Set number of hash buckets for UDP/UDP-Lite connections
3823
5f8364b7
AS
3824 uhci-hcd.ignore_oc=
3825 [USB] Ignore overcurrent events (default N).
3826 Some badly-designed motherboards generate lots of
3827 bogus events, for ports that aren't wired to
3828 anything. Set this parameter to avoid log spamming.
3829 Note that genuine overcurrent events won't be
3830 reported either.
3831
e3a61b0a 3832 unknown_nmi_panic
44a4dcf7 3833 [X86] Cause panic on unknown NMI.
e3a61b0a 3834
c4fc2342
CDH
3835 usbcore.authorized_default=
3836 [USB] Default USB device authorization:
3837 (default -1 = authorized except for wireless USB,
3838 0 = not authorized, 1 = authorized)
3839
b5e795f8
AS
3840 usbcore.autosuspend=
3841 [USB] The autosuspend time delay (in seconds) used
3842 for newly-detected USB devices (default 2). This
3843 is the time required before an idle device will be
3844 autosuspended. Devices for which the delay is set
eaafbc3a 3845 to a negative value won't be autosuspended at all.
b5e795f8 3846
fd7c519d
JK
3847 usbcore.usbfs_snoop=
3848 [USB] Set to log all usbfs traffic (default 0 = off).
3849
3850 usbcore.blinkenlights=
3851 [USB] Set to cycle leds on hubs (default 0 = off).
3852
3853 usbcore.old_scheme_first=
3854 [USB] Start with the old device initialization
3855 scheme (default 0 = off).
3856
3f5eb8d5
AS
3857 usbcore.usbfs_memory_mb=
3858 [USB] Memory limit (in MB) for buffers allocated by
3859 usbfs (default = 16, 0 = max = 2047).
3860
fd7c519d
JK
3861 usbcore.use_both_schemes=
3862 [USB] Try the other device initialization scheme
3863 if the first one fails (default 1 = enabled).
3864
3865 usbcore.initial_descriptor_timeout=
3866 [USB] Specifies timeout for the initial 64-byte
3867 USB_REQ_GET_DESCRIPTOR request in milliseconds
3868 (default 5000 = 5.0 seconds).
3869
1da177e4
LT
3870 usbhid.mousepoll=
3871 [USBHID] The interval which mice are to be polled at.
a9913044 3872
d4f373e5
AS
3873 usb-storage.delay_use=
3874 [UMS] The delay in seconds before a new device is
19101954 3875 scanned for Logical Units (default 1).
d4f373e5
AS
3876
3877 usb-storage.quirks=
3878 [UMS] A list of quirks entries to supplement or
3879 override the built-in unusual_devs list. List
3880 entries are separated by commas. Each entry has
3881 the form VID:PID:Flags where VID and PID are Vendor
3882 and Product ID values (4-digit hex numbers) and
3883 Flags is a set of characters, each corresponding
3884 to a common usb-storage quirk flag as follows:
c838ea46
AS
3885 a = SANE_SENSE (collect more than 18 bytes
3886 of sense data);
a0bb1081
AS
3887 b = BAD_SENSE (don't collect more than 18
3888 bytes of sense data);
d4f373e5
AS
3889 c = FIX_CAPACITY (decrease the reported
3890 device capacity by one sector);
5116901d
KR
3891 d = NO_READ_DISC_INFO (don't use
3892 READ_DISC_INFO command);
3893 e = NO_READ_CAPACITY_16 (don't use
3894 READ_CAPACITY_16 command);
734016b0
HG
3895 f = NO_REPORT_OPCODES (don't use report opcodes
3896 command, uas only);
ee136af4
HG
3897 g = MAX_SECTORS_240 (don't transfer more than
3898 240 sectors at a time, uas only);
c838ea46
AS
3899 h = CAPACITY_HEURISTICS (decrease the
3900 reported device capacity by one
3901 sector if the number is odd);
d4f373e5
AS
3902 i = IGNORE_DEVICE (don't bind to this
3903 device);
3904 l = NOT_LOCKABLE (don't try to lock and
3905 unlock ejectable media);
3906 m = MAX_SECTORS_64 (don't transfer more
3907 than 64 sectors = 32 KB at a time);
21c13a4f
AS
3908 n = INITIAL_READ10 (force a retry of the
3909 initial READ(10) command);
c838ea46
AS
3910 o = CAPACITY_OK (accept the capacity
3911 reported by the device);
eaa05dfc
NJ
3912 p = WRITE_CACHE (the device cache is ON
3913 by default);
d4f373e5
AS
3914 r = IGNORE_RESIDUE (the device reports
3915 bogus residue values);
3916 s = SINGLE_LUN (the device has only one
3917 Logical Unit);
59307852
HG
3918 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3919 commands, uas only);
b6089f19 3920 u = IGNORE_UAS (don't bind to the uas driver);
d4f373e5
AS
3921 w = NO_WP_DETECT (don't test whether the
3922 medium is write-protected).
3923 Example: quirks=0419:aaf5:rl,0421:0433:rc
3924
ac1667db
SB
3925 user_debug= [KNL,ARM]
3926 Format: <int>
3927 See arch/arm/Kconfig.debug help text.
3928 1 - undefined instruction events
3929 2 - system calls
3930 4 - invalid data aborts
3931 8 - SIGSEGV faults
3932 16 - SIGBUS faults
3933 Example: user_debug=31
3934
14315592
IC
3935 userpte=
3936 [X86] Flags controlling user PTE allocations.
3937
3938 nohigh = do not allocate PTE pages in
3939 HIGHMEM regardless of setting
3940 of CONFIG_HIGHPTE.
3941
6cececfc 3942 vdso= [X86,SH]
b0b49f26
AL
3943 On X86_32, this is an alias for vdso32=. Otherwise:
3944
3945 vdso=1: enable VDSO (the default)
e6e5494c
IM
3946 vdso=0: disable VDSO mapping
3947
b0b49f26
AL
3948 vdso32= [X86] Control the 32-bit vDSO
3949 vdso32=1: enable 32-bit VDSO
3950 vdso32=0 or vdso32=2: disable 32-bit VDSO
3951
3952 See the help text for CONFIG_COMPAT_VDSO for more
3953 details. If CONFIG_COMPAT_VDSO is set, the default is
3954 vdso32=0; otherwise, the default is vdso32=1.
3955
3956 For compatibility with older kernels, vdso32=2 is an
3957 alias for vdso32=0.
3958
3959 Try vdso32=0 if you encounter an error that says:
3960 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
af65d648 3961
d080d397
YI
3962 vector= [IA-64,SMP]
3963 vector=percpu: enable percpu vector domain
3964
1da177e4
LT
3965 video= [FB] Frame buffer configuration
3966 See Documentation/fb/modedb.txt.
3967
3afe6dab
AL
3968 video.brightness_switch_enabled= [0,1]
3969 If set to 1, on receiving an ACPI notify event
3970 generated by hotkey, video driver will adjust brightness
3971 level and then send out the event to user space through
3972 the allocated input device; If set to 0, video driver
3973 will only send out the event without touching backlight
3974 brightness level.
2843768b 3975 default: 1
3afe6dab 3976
81a054ce
PM
3977 virtio_mmio.device=
3978 [VMMIO] Memory mapped virtio (platform) device.
3979
3980 <size>@<baseaddr>:<irq>[:<id>]
3981 where:
3982 <size> := size (can use standard suffixes
3983 like K, M and G)
3984 <baseaddr> := physical base address
3985 <irq> := interrupt number (as passed to
3986 request_irq())
3987 <id> := (optional) platform device id
3988 example:
3989 virtio_mmio.device=1K@0x100b0000:48:7
3990
3991 Can be used multiple times for multiple devices.
3992
cd4f0ef7 3993 vga= [BOOT,X86-32] Select a particular video mode
954a8b81 3994 See Documentation/x86/boot.txt and
a9913044 3995 Documentation/svga.txt.
1da177e4
LT
3996 Use vga=ask for menu.
3997 This is actually a boot loader parameter; the value is
3998 passed to the kernel using a special protocol.
3999
a9913044 4000 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
1da177e4
LT
4001 size of <nn>. This can be used to increase the
4002 minimum size (128MB on x86). It can also be used to
4003 decrease the size and leave more room for directly
4004 mapped kernel RAM.
4005
585c3047
PO
4006 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4007 Format: <command>
1da177e4 4008
585c3047
PO
4009 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4010 Format: <command>
4011
4012 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4013 Format: <command>
a9913044 4014
3ae36655
AL
4015 vsyscall= [X86-64]
4016 Controls the behavior of vsyscalls (i.e. calls to
4017 fixed addresses of 0xffffffffff600x00 from legacy
4018 code). Most statically-linked binaries and older
4019 versions of glibc use these calls. Because these
4020 functions are at fixed addresses, they make nice
4021 targets for exploits that can control RIP.
4022
2e57ae05
AL
4023 emulate [default] Vsyscalls turn into traps and are
4024 emulated reasonably safely.
3ae36655 4025
2e57ae05 4026 native Vsyscalls are native syscall instructions.
3ae36655
AL
4027 This is a little bit faster than trapping
4028 and makes a few dynamic recompilers work
4029 better than they would in emulation mode.
4030 It also makes exploits much easier to write.
4031
4032 none Vsyscalls don't work at all. This makes
4033 them quite hard to use for exploits but
4034 might break your system.
4035
3855ae1c
CL
4036 vt.color= [VT] Default text color.
4037 Format: 0xYX, X = foreground, Y = background.
4038 Default: 0x07 = light gray on black.
4039
9ea9a886
CL
4040 vt.cur_default= [VT] Default cursor shape.
4041 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4042 the parameters of the <Esc>[?A;B;Cc escape sequence;
4043 see VGA-softcursor.txt. Default: 2 = underline.
4044
0cb55ad2
RD
4045 vt.default_blu= [VT]
4046 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4047 Change the default blue palette of the console.
4048 This is a 16-member array composed of values
4049 ranging from 0-255.
4050
4051 vt.default_grn= [VT]
4052 Format: <green0>,<green1>,<green2>,...,<green15>
4053 Change the default green palette of the console.
4054 This is a 16-member array composed of values
4055 ranging from 0-255.
4056
4057 vt.default_red= [VT]
4058 Format: <red0>,<red1>,<red2>,...,<red15>
4059 Change the default red palette of the console.
4060 This is a 16-member array composed of values
4061 ranging from 0-255.
4062
4063 vt.default_utf8=
4064 [VT]
4065 Format=<0|1>
4066 Set system-wide default UTF-8 mode for all tty's.
4067 Default is 1, i.e. UTF-8 mode is enabled for all
4068 newly opened terminals.
4069
f6c06b68
MG
4070 vt.global_cursor_default=
4071 [VT]
4072 Format=<-1|0|1>
4073 Set system-wide default for whether a cursor
4074 is shown on new VTs. Default is -1,
4075 i.e. cursors will be created by default unless
4076 overridden by individual drivers. 0 will hide
4077 cursors, 1 will display them.
4078
3855ae1c
CL
4079 vt.italic= [VT] Default color for italic text; 0-15.
4080 Default: 2 = green.
4081
4082 vt.underline= [VT] Default color for underlined text; 0-15.
4083 Default: 3 = cyan.
4084
4724ba57
RD
4085 watchdog timers [HW,WDT] For information on watchdog timers,
4086 see Documentation/watchdog/watchdog-parameters.txt
4087 or other driver-specific files in the
4088 Documentation/watchdog/ directory.
1da177e4 4089
d55262c4
TH
4090 workqueue.disable_numa
4091 By default, all work items queued to unbound
4092 workqueues are affine to the NUMA nodes they're
4093 issued on, which results in better behavior in
4094 general. If NUMA affinity needs to be disabled for
4095 whatever reason, this option can be used. Note
4096 that this also can be controlled per-workqueue for
4097 workqueues visible under /sys/bus/workqueue/.
4098
cee22a15
VK
4099 workqueue.power_efficient
4100 Per-cpu workqueues are generally preferred because
4101 they show better performance thanks to cache
4102 locality; unfortunately, per-cpu workqueues tend to
4103 be more power hungry than unbound workqueues.
4104
4105 Enabling this makes the per-cpu workqueues which
4106 were observed to contribute significantly to power
4107 consumption unbound, leading to measurably lower
4108 power usage at the cost of small performance
4109 overhead.
4110
4111 The default value of this parameter is determined by
4112 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4113
0cb55ad2
RD
4114 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4115 default x2apic cluster mode on platforms
4116 supporting x2apic.
4117
712b6aa8
KS
4118 x86_intel_mid_timer= [X86-32,APBT]
4119 Choose timer option for x86 Intel MID platform.
bb24c471
JP
4120 Two valid options are apbt timer only and lapic timer
4121 plus one apbt timer for broadcast timer.
712b6aa8 4122 x86_intel_mid_timer=apbt_only | lapic_and_apbt
bb24c471 4123
c70727a5
JG
4124 xen_512gb_limit [KNL,X86-64,XEN]
4125 Restricts the kernel running paravirtualized under Xen
4126 to use only up to 512 GB of RAM. The reason to do so is
4127 crash analysis tools and Xen tools for doing domain
4128 save/restore/migration must be enabled to handle larger
4129 domains.
4130
c1c5413a
SS
4131 xen_emul_unplug= [HW,X86,XEN]
4132 Unplug Xen emulated devices
4133 Format: [unplug0,][unplug1]
4134 ide-disks -- unplug primary master IDE devices
4135 aux-ide-disks -- unplug non-primary-master IDE devices
4136 nics -- unplug network devices
4137 all -- unplug all emulated devices (NICs and IDE disks)
1dc7ce99
IC
4138 unnecessary -- unplugging emulated devices is
4139 unnecessary even if the host did not respond to
4140 the unplug protocol
c93a4dfb 4141 never -- do not unplug even if version check succeeds
c1c5413a 4142
15a3eac0
KRW
4143 xen_nopvspin [X86,XEN]
4144 Disables the ticketlock slowpath using Xen PV
4145 optimizations.
4146
8d693b91
KRW
4147 xen_nopv [X86]
4148 Disables the PV optimizations forcing the HVM guest to
4149 run as generic HVM guest with no PV drivers.
4150
1da177e4 4151 xirc2ps_cs= [NET,PCMCIA]
a9913044
RD
4152 Format:
4153 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
1da177e4 4154
a9913044 4155______________________________________________________________________
1da177e4
LT
4156
4157TODO:
4158
1da177e4 4159 Add more DRM drivers.