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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"
ca1eda2d 35
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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
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170 Format: { force | off | strict | noirq | rsdt |
171 copy_dsdt }
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172 force -- enable ACPI if default was off
173 off -- disable ACPI if default was on
174 noirq -- do not use ACPI for IRQ routing
a9913044 175 strict -- Be less tolerant of platforms that are not
1da177e4 176 strictly ACPI specification compliant.
237889bf 177 rsdt -- prefer RSDT over (default) XSDT
aa2110cb 178 copy_dsdt -- copy DSDT to memory
b10d79f7 179 For ARM64, ONLY "acpi=off" or "acpi=force" are available
1da177e4 180
395cf969 181 See also Documentation/power/runtime_pm.txt, pci=noacpi
1da177e4 182
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183 acpi_apic_instance= [ACPI, IOAPIC]
184 Format: <int>
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
4e381a4f 187 default: 0
a1fdcc0d 188
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189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
191 acpi_backlight=video
192 If set to vendor, prefer vendor specific driver
193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
194 of the ACPI video.ko driver.
195
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196 acpica_no_return_repair [HW, ACPI]
197 Disable AML predefined validation mechanism
198 This mechanism can repair the evaluation result to make
199 the return objects more ACPI specification compliant.
200 This option is useful for developers to identify the
201 root cause of an AML interpreter issue when the issue
202 has something to do with the repair mechanism.
203
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204 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
205 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
1da177e4 206 Format: <int>
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207 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
208 debug output. Bits in debug_layer correspond to a
209 _COMPONENT in an ACPI source file, e.g.,
210 #define _COMPONENT ACPI_PCI_COMPONENT
211 Bits in debug_level correspond to a level in
212 ACPI_DEBUG_PRINT statements, e.g.,
213 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
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214 The debug_level mask defaults to "info". See
215 Documentation/acpi/debug.txt for more information about
216 debug layers and levels.
a0d84a92 217
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218 Enable processor driver info messages:
219 acpi.debug_layer=0x20000000
220 Enable PCI/PCI interrupt routing info messages:
221 acpi.debug_layer=0x400000
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222 Enable AML "Debug" output, i.e., stores to the Debug
223 object while interpreting AML:
224 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
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225 Enable all messages related to ACPI hardware:
226 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
227
228 Some values produce so much output that the system is
229 unusable. The "log_buf_len" parameter may be useful
230 if you need to capture more output.
f989106c 231
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232 acpi_enforce_resources= [ACPI]
233 { strict | lax | no }
234 Check for resource conflicts between native drivers
235 and ACPI OperationRegions (SystemIO and SystemMemory
236 only). IO ports and memory declared in ACPI might be
237 used by the ACPI subsystem in arbitrary AML code and
238 can interfere with legacy drivers.
239 strict (default): access to resources claimed by ACPI
240 is denied; legacy drivers trying to access reserved
241 resources will fail to bind to device using them.
242 lax: access to resources claimed by ACPI is allowed;
243 legacy drivers trying to access reserved resources
244 will bind successfully but a warning message is logged.
245 no: ACPI OperationRegions are not marked as reserved,
246 no further checks are performed.
247
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248 acpi_force_table_verification [HW,ACPI]
249 Enable table checksum verification during early stage.
250 By default, this is disabled due to x86 early mapping
251 size limitation.
252
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253 acpi_irq_balance [HW,ACPI]
254 ACPI will balance active IRQs
255 default in APIC mode
256
257 acpi_irq_nobalance [HW,ACPI]
258 ACPI will not move active IRQs (default)
259 default in PIC mode
260
261 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
262 Format: <irq>,<irq>...
263
264 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
265 use by PCI
266 Format: <irq>,<irq>...
267
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268 acpi_no_auto_serialize [HW,ACPI]
269 Disable auto-serialization of AML methods
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270 AML control methods that contain the opcodes to create
271 named objects will be marked as "Serialized" by the
272 auto-serialization feature.
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273 This feature is enabled by default.
274 This option allows to turn off the feature.
22b5afce 275
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276 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
277 kernels.
278
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279 acpi_no_static_ssdt [HW,ACPI]
280 Disable installation of static SSDTs at early boot time
281 By default, SSDTs contained in the RSDT/XSDT will be
282 installed automatically and they will appear under
283 /sys/firmware/acpi/tables.
284 This option turns off this feature.
285 Note that specifying this option does not affect
286 dynamic table installation which will install SSDT
287 tables to /sys/firmware/acpi/tables/dynamic.
0cb55ad2 288
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289 acpi_rsdp= [ACPI,EFI,KEXEC]
290 Pass the RSDP address to the kernel, mostly used
291 on machines running EFI runtime service to boot the
292 second kernel for kdump.
4dde507f 293
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294 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
295 Format: To spoof as Windows 98: ="Microsoft Windows"
296
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297 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
298 of 2 which is mandated by ACPI 6) as the supported ACPI
299 specification revision (when using this switch, it may
300 be necessary to carry out a cold reboot _twice_ in a
301 row to make it take effect on the platform firmware).
302
0cb55ad2 303 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
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304 acpi_osi="string1" # add string1
305 acpi_osi="!string2" # remove string2
741d8128 306 acpi_osi=!* # remove all strings
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307 acpi_osi=! # disable all built-in OS vendor
308 strings
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309 acpi_osi= # disable all strings
310
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311 'acpi_osi=!' can be used in combination with single or
312 multiple 'acpi_osi="string1"' to support specific OS
313 vendor string(s). Note that such command can only
314 affect the default state of the OS vendor strings, thus
315 it cannot affect the default state of the feature group
316 strings and the current state of the OS vendor strings,
317 specifying it multiple times through kernel command line
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318 is meaningless. This command is useful when one do not
319 care about the state of the feature group strings which
320 should be controlled by the OSPM.
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321 Examples:
322 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
323 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
324 can make '_OSI("Windows 2000")' TRUE.
325
326 'acpi_osi=' cannot be used in combination with other
327 'acpi_osi=' command lines, the _OSI method will not
328 exist in the ACPI namespace. NOTE that such command can
329 only affect the _OSI support state, thus specifying it
330 multiple times through kernel command line is also
331 meaningless.
332 Examples:
333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
334 FALSE.
335
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336 'acpi_osi=!*' can be used in combination with single or
337 multiple 'acpi_osi="string1"' to support specific
338 string(s). Note that such command can affect the
339 current state of both the OS vendor strings and the
340 feature group strings, thus specifying it multiple times
341 through kernel command line is meaningful. But it may
342 still not able to affect the final state of a string if
343 there are quirks related to this string. This command
344 is useful when one want to control the state of the
345 feature group strings to debug BIOS issues related to
346 the OSPM features.
347 Examples:
348 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
349 '_OSI("Module Device")' FALSE.
350 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
351 '_OSI("Module Device")' TRUE.
352 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
353 equivalent to
354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
355 and
356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
357 they all will make '_OSI("Windows 2000")' TRUE.
358
6cececfc 359 acpi_pm_good [X86]
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360 Override the pmtimer bug detection: force the kernel
361 to assume that this machine's pmtimer latches its value
362 and always returns good values.
363
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364 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
365 Format: { level | edge | high | low }
366
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367 acpi_skip_timer_override [HW,ACPI]
368 Recognize and ignore IRQ0/pin2 Interrupt Override.
369 For broken nForce2 BIOS resulting in XT-PIC timer.
370
371 acpi_sleep= [HW,ACPI] Sleep options
372 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
c3b0795c 373 old_ordering, nonvs, sci_force_enable }
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374 See Documentation/power/video.txt for information on
375 s3_bios and s3_mode.
376 s3_beep is for debugging; it makes the PC's speaker beep
377 as soon as the kernel's real-mode entry point is called.
378 s4_nohwsig prevents ACPI hardware signature from being
379 used during resume from hibernation.
380 old_ordering causes the ACPI 1.0 ordering of the _PTS
381 control method, with respect to putting devices into
382 low power states, to be enforced (the ACPI 2.0 ordering
383 of _PTS is used by default).
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384 nonvs prevents the kernel from saving/restoring the
385 ACPI NVS memory during suspend/hibernation and resume.
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386 sci_force_enable causes the kernel to set SCI_EN directly
387 on resume from S1/S3 (which is against the ACPI spec,
388 but some broken systems don't work without it).
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389
390 acpi_use_timer_override [HW,ACPI]
391 Use timer override. For some broken Nvidia NF5 boards
392 that require a timer override, but don't have HPET
393
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394 add_efi_memmap [EFI; X86] Include EFI memory map in
395 kernel's map of available physical RAM.
396
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397 agp= [AGP]
398 { off | try_unsupported }
399 off: disable AGP support
400 try_unsupported: try to drive unsupported chipsets
401 (may crash computer or cause data corruption)
402
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403 ALSA [HW,ALSA]
404 See Documentation/sound/alsa/alsa-parameters.txt
405
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406 alignment= [KNL,ARM]
407 Allow the default userspace alignment fault handler
408 behaviour to be specified. Bit 0 enables warnings,
409 bit 1 enables fixups, and bit 2 sends a segfault.
410
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411 align_va_addr= [X86-64]
412 Align virtual addresses by clearing slice [14:12] when
413 allocating a VMA at process creation time. This option
414 gives you up to 3% performance improvement on AMD F15h
415 machines (where it is enabled by default) for a
416 CPU-intensive style benchmark, and it can vary highly in
417 a microbenchmark depending on workload and compiler.
418
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419 32: only for 32-bit processes
420 64: only for 64-bit processes
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421 on: enable for both 32- and 64-bit processes
422 off: disable for both 32- and 64-bit processes
423
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424 alloc_snapshot [FTRACE]
425 Allocate the ftrace snapshot buffer on boot up when the
426 main buffer is allocated. This is handy if debugging
427 and you need to use tracing_snapshot() on boot up, and
428 do not want to use tracing_snapshot_alloc() as it needs
429 to be done where GFP_KERNEL allocations are allowed.
430
89e0b9a3 431 amd_iommu= [HW,X86-64]
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432 Pass parameters to the AMD IOMMU driver in the system.
433 Possible values are:
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434 fullflush - enable flushing of IO/TLB entries when
435 they are unmapped. Otherwise they are
436 flushed before they will be reused, which
437 is a lot of faster
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438 off - do not initialize any AMD IOMMU found in
439 the system
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440 force_isolation - Force device isolation for all
441 devices. The IOMMU driver is not
442 allowed anymore to lift isolation
443 requirements as needed. This option
444 does not override iommu=pt
afa9fdc2 445
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446 amd_iommu_dump= [HW,X86-64]
447 Enable AMD IOMMU driver option to dump the ACPI table
448 for AMD IOMMU. With this option enabled, AMD IOMMU
449 driver will print ACPI tables for AMD IOMMU during
450 IOMMU initialization.
451
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452 amijoy.map= [HW,JOY] Amiga joystick support
453 Map of devices attached to JOY0DAT and JOY1DAT
454 Format: <a>,<b>
395cf969 455 See also Documentation/input/joystick.txt
1da177e4
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456
457 analog.map= [HW,JOY] Analog joystick and gamepad support
458 Specifies type or capabilities of an analog joystick
459 connected to one of 16 gameports
460 Format: <type1>,<type2>,..<type16>
461
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462 apc= [HW,SPARC]
463 Power management functions (SPARCstation-4/5 + deriv.)
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464 Format: noidle
465 Disable APC CPU standby support. SPARCstation-Fox does
466 not play well with APC CPU idle - disable it if you have
467 APC and your system crashes randomly.
468
ca1eda2d 469 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
c8facbb6 470 Change the output verbosity whilst booting
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471 Format: { quiet (default) | verbose | debug }
472 Change the amount of debugging information output
473 when initialising the APIC and IO-APIC components.
a9913044 474
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475 apic_extnmi= [APIC,X86] External NMI delivery setting
476 Format: { bsp (default) | all | none }
477 bsp: External NMI is delivered only to CPU 0
478 all: External NMIs are broadcast to all CPUs as a
479 backup of CPU 0
480 none: External NMI is masked for all CPUs. This is
481 useful so that a dump capture kernel won't be
482 shot down by NMI
483
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484 autoconf= [IPV6]
485 See Documentation/networking/ipv6.txt.
486
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487 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
488 Limit apic dumping. The parameter defines the maximal
489 number of local apics being dumped. Also it is possible
490 to set it to "all" by meaning -- no limit here.
491 Format: { 1 (default) | 2 | ... | all }.
492 The parameter valid if only apic=debug or
493 apic=verbose is specified.
494 Example: apic=debug show_lapic=all
495
1da177e4 496 apm= [APM] Advanced Power Management
71f77055 497 See header of arch/x86/kernel/apm_32.c.
1da177e4 498
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499 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
500 Format: <io>,<irq>,<nodeID>
501
502 ataflop= [HW,M68k]
503
504 atarimouse= [HW,MOUSE] Atari Mouse
505
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506 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
507 EzKey and similar keyboards
508
509 atkbd.reset= [HW] Reset keyboard during initialization
510
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511 atkbd.set= [HW] Select keyboard code set
512 Format: <int> (2 = AT (default), 3 = PS/2)
1da177e4
LT
513
514 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
515 keyboards
516
517 atkbd.softraw= [HW] Choose between synthetic and real raw mode
518 Format: <bool> (0 = real, 1 = synthetic (default))
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519
520 atkbd.softrepeat= [HW]
521 Use software keyboard repeat
1da177e4 522
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523 audit= [KNL] Enable the audit sub-system
524 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
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EP
525 0 - kernel audit is disabled and can not be enabled
526 until the next reboot
527 unset - kernel audit is initialized but disabled and
528 will be fully enabled by the userspace auditd.
529 1 - kernel audit is initialized and partially enabled,
530 storing at most audit_backlog_limit messages in
531 RAM until it is fully enabled by the userspace
532 auditd.
a106fb0c 533 Default: unset
f3411cb2 534
f910fde7
RGB
535 audit_backlog_limit= [KNL] Set the audit queue size limit.
536 Format: <int> (must be >=0)
537 Default: 64
538
1da177e4
LT
539 baycom_epp= [HW,AX25]
540 Format: <io>,<mode>
a9913044 541
1da177e4
LT
542 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
543 Format: <io>,<mode>
544 See header of drivers/net/hamradio/baycom_par.c.
545
a9913044
RD
546 baycom_ser_fdx= [HW,AX25]
547 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
1da177e4
LT
548 Format: <io>,<irq>,<mode>[,<baud>]
549 See header of drivers/net/hamradio/baycom_ser_fdx.c.
550
a9913044
RD
551 baycom_ser_hdx= [HW,AX25]
552 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
1da177e4
LT
553 Format: <io>,<irq>,<mode>
554 See header of drivers/net/hamradio/baycom_ser_hdx.c.
555
080506ad
PG
556 blkdevparts= Manual partition parsing of block device(s) for
557 embedded devices based on command line input.
558 See Documentation/block/cmdline-partition.txt
559
bfe8df3d
RD
560 boot_delay= Milliseconds to delay each printk during boot.
561 Values larger than 10 seconds (10000) are changed to
562 no delay (0).
563 Format: integer
564
35fc908d
AH
565 bootmem_debug [KNL] Enable bootmem allocator debug messages.
566
1da177e4 567 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
a9913044
RD
568 bttv.radio= Most important insmod options are available as
569 kernel args too.
1da177e4 570 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
395cf969 571 bttv.tuner=
1da177e4 572
4e89a2d8
WS
573 bulk_remove=off [PPC] This parameter disables the use of the pSeries
574 firmware feature for flushing multiple hpte entries
575 at a time.
576
1da177e4
LT
577 c101= [NET] Moxa C101 synchronous serial card
578
cd4f0ef7 579 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
1da177e4
LT
580 Sometimes CPU hardware bugs make them report the cache
581 size incorrectly. The kernel will attempt work arounds
582 to fix known problems, but for some CPUs it is not
583 possible to determine what the correct size should be.
584 This option provides an override for these situations.
585
ffb70f61
DK
586 ca_keys= [KEYS] This parameter identifies a specific key(s) on
587 the system trusted keyring to be used for certificate
588 trust validation.
32c4741c 589 format: { id:<keyid> | builtin }
ffb70f61 590
fd1bb4c9
FF
591 cca= [MIPS] Override the kernel pages' cache coherency
592 algorithm. Accepted values range from 0 to 7
593 inclusive. See arch/mips/include/asm/pgtable-bits.h
594 for platform specific values (SB1, Loongson3 and
595 others).
596
14ff56bb
SO
597 ccw_timeout_log [S390]
598 See Documentation/s390/CommonIO for details.
1da177e4 599
8bab8dde
PM
600 cgroup_disable= [KNL] Disable a particular controller
601 Format: {name of the controller(s) to disable}
ca0bdbb5
QH
602 The effects of cgroup_disable=foo are:
603 - foo isn't auto-mounted if you mount all cgroups in
604 a single hierarchy
605 - foo isn't visible as an individually mountable
606 subsystem
607 {Currently only "memory" controller deal with this and
608 cut the overhead, others just disable the usage. So
609 only cgroup_disable=memory is actually worthy}
8bab8dde 610
1da177e4
LT
611 checkreqprot [SELINUX] Set initial checkreqprot flag value.
612 Format: { "0" | "1" }
613 See security/selinux/Kconfig help text.
a9913044
RD
614 0 -- check protection applied by kernel (includes
615 any implied execute protection).
1da177e4
LT
616 1 -- check protection requested by application.
617 Default value is set via a kernel config option.
a9913044
RD
618 Value can be changed at runtime via
619 /selinux/checkreqprot.
620
661ca0da
SO
621 cio_ignore= [S390]
622 See Documentation/s390/CommonIO for details.
1e435256
OJ
623 clk_ignore_unused
624 [CLK]
e156ee56
MT
625 Prevents the clock framework from automatically gating
626 clocks that have not been explicitly enabled by a Linux
627 device driver but are enabled in hardware at reset or
628 by the bootloader/firmware. Note that this does not
629 force such clocks to be always-on nor does it reserve
630 those clocks in any way. This parameter is useful for
631 debug and development, but should not be needed on a
632 platform with proper driver support. For more
633 information, see Documentation/clk.txt.
661ca0da 634
cd4f0ef7 635 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
734efb46 636 [Deprecated]
3f6dee9b 637 Forces specified clocksource (if available) to be used
734efb46 638 when calculating gettimeofday(). If specified
3f6dee9b 639 clocksource is not available, it defaults to PIT.
1da177e4
LT
640 Format: { pit | tsc | cyclone | pmtmr }
641
592913ec 642 clocksource= Override the default clocksource
3d6ac984
RD
643 Format: <string>
644 Override the default clocksource and use the clocksource
645 with the name specified.
646 Some clocksource names to choose from, depending on
647 the platform:
648 [all] jiffies (this is the base, fallback clocksource)
649 [ACPI] acpi_pm
650 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
651 pxa_timer,timer3,32k_counter,timer0_1
652 [AVR32] avr32
9863c90f 653 [X86-32] pit,hpet,tsc;
3d6ac984
RD
654 scx200_hrt on Geode; cyclone on IBM x440
655 [MIPS] MIPS
656 [PARISC] cr16
657 [S390] tod
658 [SH] SuperH
659 [SPARC64] tick
660 [X86-64] hpet,tsc
661
ac72e788
AK
662 clearcpuid=BITNUM [X86]
663 Disable CPUID feature X for the kernel. See
07983f0e
RD
664 arch/x86/include/asm/cpufeature.h for the valid bit
665 numbers. Note the Linux specific bits are not necessarily
ac72e788
AK
666 stable over kernel options, but the vendor specific
667 ones should be.
668 Also note that user programs calling CPUID directly
669 or using the feature without checking anything
670 will still see it. This just prevents it from
671 being used by the kernel or shown in /proc/cpuinfo.
672 Also note the kernel might malfunction if you disable
673 some critical bits.
674
5ea3b1b2
AM
675 cma=nn[MG]@[start[MG][-end[MG]]]
676 [ARM,X86,KNL]
677 Sets the size of kernel global memory area for
678 contiguous memory allocations and optionally the
679 placement constraint by the physical address range of
f0d6d1f6
JD
680 memory allocations. A value of 0 disables CMA
681 altogether. For more information, see
c64be2bb
MS
682 include/linux/dma-contiguous.h
683
14f966e7
RJ
684 cmo_free_hint= [PPC] Format: { yes | no }
685 Specify whether pages are marked as being inactive
686 when they are freed. This is used in CMO environments
687 to determine OS memory pressure for page stealing by
688 a hypervisor.
689 Default: yes
690
c7909509
MS
691 coherent_pool=nn[KMG] [ARM,KNL]
692 Sets the size of memory pool for coherent, atomic dma
e9da6e99 693 allocations, by default set to 256K.
c7909509 694
6cececfc 695 code_bytes [X86] How many bytes of object code to print
a25bd949 696 in an oops report.
86c41837
CE
697 Range: 0 - 8192
698 Default: 64
699
1da177e4 700 com20020= [HW,NET] ARCnet - COM20020 chipset
a9913044
RD
701 Format:
702 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
1da177e4
LT
703
704 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
705 Format: <io>[,<irq>]
706
a9913044
RD
707 com90xx= [HW,NET]
708 ARCnet - COM90xx chipset (memory-mapped buffers)
1da177e4
LT
709 Format: <io>[,<irq>[,<memstart>]]
710
711 condev= [HW,S390] console device
712 conmode=
a9913044 713
1da177e4
LT
714 console= [KNL] Output console device and options.
715
716 tty<n> Use the virtual console device <n>.
717
718 ttyS<n>[,options]
f1a1c2dc 719 ttyUSB0[,options]
1da177e4 720 Use the specified serial port. The options are of
f1a1c2dc
RD
721 the form "bbbbpnf", where "bbbb" is the baud rate,
722 "p" is parity ("n", "o", or "e"), "n" is number of
723 bits, and "f" is flow control ("r" for RTS or
724 omit it). Default is "9600n8".
725
726 See Documentation/serial-console.txt for more
727 information. See
728 Documentation/networking/netconsole.txt for an
729 alternative.
1da177e4 730
18a8bd94
YL
731 uart[8250],io,<addr>[,options]
732 uart[8250],mmio,<addr>[,options]
ca782f16
PH
733 uart[8250],mmio32,<addr>[,options]
734 uart[8250],0x<addr>[,options]
1da177e4
LT
735 Start an early, polled-mode console on the 8250/16550
736 UART at the specified I/O port or MMIO address,
ca782f16
PH
737 switching to the matching ttyS device later.
738 MMIO inter-register address stride is either 8-bit
739 (mmio) or 32-bit (mmio32).
740 If none of [io|mmio|mmio32], <addr> is assumed to be
741 equivalent to 'mmio'. 'options' are specified in the
742 same format described for ttyS above; if unspecified,
743 the h/w is not re-initialized.
744
a2fd6419
KRW
745 hvc<n> Use the hypervisor console device <n>. This is for
746 both Xen and PowerPC hypervisors.
1da177e4 747
f7511d5f
ST
748 If the device connected to the port is not a TTY but a braille
749 device, prepend "brl," before the device type, for instance
750 console=brl,ttyS0
751 For now, only VisioBraille is supported.
752
f324edc8
DM
753 consoleblank= [KNL] The console blank (screen saver) timeout in
754 seconds. Defaults to 10*60 = 10mins. A value of 0
755 disables the blank timer.
756
4cb0e11b
HK
757 coredump_filter=
758 [KNL] Change the default value for
759 /proc/<pid>/coredump_filter.
760 See also Documentation/filesystems/proc.txt.
761
62027aea
LB
762 cpuidle.off=1 [CPU_IDLE]
763 disable the cpuidle sub-system
764
d68921f9
LB
765 cpu_init_udelay=N
766 [X86] Delay for N microsec between assert and de-assert
767 of APIC INIT to start processors. This delay occurs
768 on every CPU online, such as boot, and resume from suspend.
769 Default: 10000
770
1da177e4 771 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
a9913044
RD
772 Format:
773 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
1da177e4 774
6f21e646
AD
775 crashkernel=size[KMG][@offset[KMG]]
776 [KNL] Using kexec, Linux can switch to a 'crash kernel'
777 upon panic. This parameter reserves the physical
778 memory region [offset, offset + size] for that kernel
779 image. If '@offset' is omitted, then a suitable offset
780 is selected automatically. Check
781 Documentation/kdump/kdump.txt for further details.
dc009d92 782
fb391599
BW
783 crashkernel=range1:size1[,range2:size2,...][@offset]
784 [KNL] Same as above, but depends on the memory
785 in the running system. The syntax of range is
786 start-[end] where start and end are both
787 a memory unit (amount[KMG]). See also
6f21e646 788 Documentation/kdump/kdump.txt for an example.
fb391599 789
adbc742b 790 crashkernel=size[KMG],high
55a20ee7
YL
791 [KNL, x86_64] range could be above 4G. Allow kernel
792 to allocate physical memory region from top, so could
793 be above 4G if system have more than 4G ram installed.
794 Otherwise memory region will be allocated below 4G, if
795 available.
796 It will be ignored if crashkernel=X is specified.
adbc742b
YL
797 crashkernel=size[KMG],low
798 [KNL, x86_64] range under 4G. When crashkernel=X,high
799 is passed, kernel could allocate physical memory region
c729de8f
YL
800 above 4G, that cause second kernel crash on system
801 that require some amount of low memory, e.g. swiotlb
c6045031
BH
802 requires at least 64M+32K low memory, also enough extra
803 low memory is needed to make sure DMA buffers for 32-bit
804 devices won't run out. Kernel would try to allocate at
805 at least 256M below 4G automatically.
c729de8f
YL
806 This one let user to specify own low range under 4G
807 for second kernel instead.
808 0: to disable low allocation.
adbc742b 809 It will be ignored when crashkernel=X,high is not used
55a20ee7 810 or memory reserved is below 4G.
c729de8f 811
1da177e4
LT
812 cs89x0_dma= [HW,NET]
813 Format: <dma>
814
815 cs89x0_media= [HW,NET]
816 Format: { rj45 | aui | bnc }
a9913044 817
a9913044 818 dasd= [HW,NET]
1da177e4
LT
819 See header of drivers/s390/block/dasd_devmap.c.
820
821 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
822 (one device per port)
823 Format: <port#>,<type>
824 See also Documentation/input/joystick-parport.txt
825
a648ec05
TR
826 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
827 time. See Documentation/dynamic-debug-howto.txt for
29e36c9f 828 details. Deprecated, see dyndbg.
a648ec05 829
1da177e4
LT
830 debug [KNL] Enable kernel debugging (events log level).
831
cae2ed9a
IM
832 debug_locks_verbose=
833 [KNL] verbose self-tests
834 Format=<0|1>
835 Print debugging info while doing the locking API
836 self-tests.
837 We default to 0 (no extra messages), setting it to
838 1 will print _a lot_ more information - normally
839 only useful to kernel developers.
840
3ac7fe5a
TG
841 debug_objects [KNL] Enable object debugging
842
3e8ebb5c
KM
843 no_debug_objects
844 [KNL] Disable object debugging
845
c0a32fc5
SG
846 debug_guardpage_minorder=
847 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
848 parameter allows control of the order of pages that will
849 be intentionally kept free (and hence protected) by the
850 buddy allocator. Bigger value increase the probability
851 of catching random memory corruption, but reduce the
852 amount of memory for normal system use. The maximum
853 possible value is MAX_ORDER/2. Setting this parameter
854 to 1 or 2 should be enough to identify most random
855 memory corruption problems caused by bugs in kernel or
856 driver code when a CPU writes to (or reads from) a
857 random memory location. Note that there exists a class
858 of memory corruptions problems caused by buggy H/W or
859 F/W or by drivers badly programing DMA (basically when
860 memory is written at bus level and the CPU MMU is
861 bypassed) which are not detectable by
862 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
863 tracking down these problems.
864
031bc574
JK
865 debug_pagealloc=
866 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
867 parameter enables the feature at boot time. In
868 default, it is disabled. We can avoid allocating huge
869 chunk of memory for debug pagealloc if we don't enable
870 it at boot time and the system will work mostly same
871 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
872 on: enable the feature
873
d3af01f1
TG
874 debugpat [X86] Enable PAT debugging
875
2d27a966 876 decnet.addr= [HW,NET]
1da177e4
LT
877 Format: <area>[,<node>]
878 See also Documentation/networking/decnet.txt.
879
0cb55ad2
RD
880 default_hugepagesz=
881 [same as hugepagesz=] The size of the default
882 HugeTLB page size. This is the size represented by
883 the legacy /proc/ hugepages APIs, used for SHM, and
884 default size when mounting hugetlbfs filesystems.
885 Defaults to the default architecture's huge page size
886 if not specified.
55ff9780 887
1da177e4
LT
888 dhash_entries= [KNL]
889 Set number of hash buckets for dentry cache.
a9913044 890
b0f83b28
BH
891 disable= [IPV6]
892 See Documentation/networking/ipv6.txt.
893
151e0c7d
HD
894 disable_cpu_apicid= [X86,APIC,SMP]
895 Format: <int>
896 The number of initial APIC ID for the
897 corresponding CPU to be disabled at boot,
898 mostly used for the kdump 2nd kernel to
899 disable BSP to wake up multiple CPUs without
900 causing system reset or hang due to sending
901 INIT from AP to BSP.
902
4e8b0cf4
NA
903 disable_ddw [PPC/PSERIES]
904 Disable Dynamic DMA Window support. Use this if
905 to workaround buggy firmware.
906
b0f83b28
BH
907 disable_ipv6= [IPV6]
908 See Documentation/networking/ipv6.txt.
909
95ffa243 910 disable_mtrr_cleanup [X86]
95ffa243
YL
911 The kernel tries to adjust MTRR layout from continuous
912 to discrete, to make X server driver able to add WB
0cb55ad2 913 entry later. This parameter disables that.
95ffa243 914
093af8d7 915 disable_mtrr_trim [X86, Intel and AMD only]
99fc8d42
JB
916 By default the kernel will trim any uncacheable
917 memory out of your available memory pool based on
918 MTRR settings. This parameter disables that behavior,
919 possibly causing your machine to run very slowly.
920
6cececfc 921 disable_timer_pin_1 [X86]
0cb55ad2
RD
922 Disable PIN 1 of APIC timer
923 Can be useful to work around chipset bugs.
924
ce14c583
PB
925 dis_ucode_ldr [X86] Disable the microcode loader.
926
0cb55ad2
RD
927 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
928 this option disables the debugging code at boot.
929
930 dma_debug_entries=<number>
931 This option allows to tune the number of preallocated
932 entries for DMA-API debugging code. One entry is
933 required per DMA-API allocation. Use this if the
934 DMA-API debugging code disables itself because the
935 architectural default is too low.
936
1745de5e
JR
937 dma_debug_driver=<driver_name>
938 With this option the DMA-API debugging driver
939 filter feature can be enabled at boot time. Just
940 pass the driver to filter for as the parameter.
941 The filter can be disabled or changed to another
942 driver later using sysfs.
943
96206e29
BP
944 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
945 Broken monitors, graphic adapters, KVMs and EDIDless
946 panels may send no or incorrect EDID data sets.
947 This parameter allows to specify an EDID data sets
948 in the /lib/firmware directory that are used instead.
da0df92b
CE
949 Generic built-in EDID data sets are used, if one of
950 edid/1024x768.bin, edid/1280x1024.bin,
951 edid/1680x1050.bin, or edid/1920x1080.bin is given
952 and no file with the same name exists. Details and
953 instructions how to build your own EDID data are
954 available in Documentation/EDID/HOWTO.txt. An EDID
955 data set will only be used for a particular connector,
956 if its name and a colon are prepended to the EDID
96206e29
BP
957 name. Each connector may use a unique EDID data
958 set by separating the files with a comma. An EDID
959 data set with no connector name will be used for
960 any connectors not explicitly specified.
da0df92b 961
1da177e4
LT
962 dscc4.setup= [NET]
963
29e36c9f
JC
964 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
965 module.dyndbg[="val"]
966 Enable debug messages at boot time. See
967 Documentation/dynamic-debug-howto.txt for details.
968
8c3641e9
DH
969 nompx [X86] Disables Intel Memory Protection Extensions.
970 See Documentation/x86/intel_mpx.txt for more
971 information about the feature.
972
f29ba61d
BP
973 eagerfpu= [X86]
974 on enable eager fpu restore
975 off disable eager fpu restore
976 auto selects the default scheme, which automatically
977 enables eagerfpu restore for xsaveopt.
978
f2411da7
LR
979 module.async_probe [KNL]
980 Enable asynchronous probe on this module.
981
56aeeba8
MS
982 early_ioremap_debug [KNL]
983 Enable debug messages in early_ioremap support. This
984 is useful for tracking down temporary early mappings
985 which are not unmapped.
986
0cb55ad2 987 earlycon= [KNL] Output early console device and options.
0d3c673e 988
5664f764
SW
989 When used with no options, the early console is
990 determined by the stdout-path property in device
991 tree's chosen node.
992
6fa62fc4
MS
993 cdns,<addr>
994 Start an early, polled-mode console on a cadence serial
995 port at the specified address. The cadence serial port
996 must already be setup and configured. Options are not
997 yet supported.
998
0cb55ad2
RD
999 uart[8250],io,<addr>[,options]
1000 uart[8250],mmio,<addr>[,options]
1917ac76 1001 uart[8250],mmio32,<addr>[,options]
6e63be3f 1002 uart[8250],mmio32be,<addr>[,options]
ca782f16 1003 uart[8250],0x<addr>[,options]
0cb55ad2
RD
1004 Start an early, polled-mode console on the 8250/16550
1005 UART at the specified I/O port or MMIO address.
16290246 1006 MMIO inter-register address stride is either 8-bit
6e63be3f
NC
1007 (mmio) or 32-bit (mmio32 or mmio32be).
1008 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1009 to be equivalent to 'mmio'. 'options' are specified
1010 in the same format described for "console=ttyS<n>"; if
ca782f16 1011 unspecified, the h/w is not initialized.
0cb55ad2 1012
0d3c673e
RH
1013 pl011,<addr>
1014 Start an early, polled-mode console on a pl011 serial
1015 port at the specified address. The pl011 serial port
1016 must already be setup and configured. Options are not
1017 yet supported.
1018
0efe7296
SB
1019 msm_serial,<addr>
1020 Start an early, polled-mode console on an msm serial
1021 port at the specified address. The serial port
1022 must already be setup and configured. Options are not
1023 yet supported.
1024
1025 msm_serial_dm,<addr>
1026 Start an early, polled-mode console on an msm serial
1027 dm port at the specified address. The serial port
1028 must already be setup and configured. Options are not
1029 yet supported.
1030
d50d7269
RH
1031 smh Use ARM semihosting calls for early console.
1032
b94ba032
TF
1033 s3c2410,<addr>
1034 s3c2412,<addr>
1035 s3c2440,<addr>
1036 s3c6400,<addr>
1037 s5pv210,<addr>
1038 exynos4210,<addr>
1039 Use early console provided by serial driver available
1040 on Samsung SoCs, requires selecting proper type and
1041 a correct base address of the selected UART port. The
1042 serial port must already be setup and configured.
1043 Options are not yet supported.
1044
1d59b382
SA
1045 lpuart,<addr>
1046 lpuart32,<addr>
1047 Use early console provided by Freescale LP UART driver
1048 found on Freescale Vybrid and QorIQ LS1021A processors.
1049 A valid base address must be provided, and the serial
1050 port must already be setup and configured.
1051
7913ad1a 1052 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1da177e4 1053 earlyprintk=vga
72548e83 1054 earlyprintk=efi
2482a92e 1055 earlyprintk=xen
1da177e4 1056 earlyprintk=serial[,ttySn[,baudrate]]
147ea091 1057 earlyprintk=serial[,0x...[,baudrate]]
ea3acb19 1058 earlyprintk=ttySn[,baudrate]
9780bc41 1059 earlyprintk=dbgp[debugController#]
c43088e3 1060 earlyprintk=pciserial,bus:device.function[,baudrate]
1da177e4 1061
147ea091
DH
1062 earlyprintk is useful when the kernel crashes before
1063 the normal console is initialized. It is not enabled by
1064 default because it has some cosmetic problems.
1065
a9913044 1066 Append ",keep" to not disable it when the real console
1da177e4
LT
1067 takes over.
1068
72548e83
MF
1069 Only one of vga, efi, serial, or usb debug port can
1070 be used at a time.
1da177e4 1071
147ea091
DH
1072 Currently only ttyS0 and ttyS1 may be specified by
1073 name. Other I/O ports may be explicitly specified
1074 on some architectures (x86 and arm at least) by
1075 replacing ttySn with an I/O port address, like this:
1076 earlyprintk=serial,0x1008,115200
1077 You can find the port for a given device in
1078 /proc/tty/driver/serial:
1079 2: uart:ST16650V2 port:00001008 irq:18 ...
1da177e4
LT
1080
1081 Interaction with the standard serial driver is not
1082 very good.
1083
72548e83
MF
1084 The VGA and EFI output is eventually overwritten by
1085 the real console.
1da177e4 1086
2482a92e
KRW
1087 The xen output can only be used by Xen PV guests.
1088
c700f013
CG
1089 edac_report= [HW,EDAC] Control how to report EDAC event
1090 Format: {"on" | "off" | "force"}
1091 on: enable EDAC to report H/W event. May be overridden
1092 by other higher priority error reporting module.
1093 off: disable H/W event reporting through EDAC.
1094 force: enforce the use of EDAC to report H/W event.
1095 default: on.
1096
9731191f
JW
1097 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1098 ekgdboc=kbd
1099
25985edc 1100 This is designed to be used in conjunction with
9731191f
JW
1101 the boot argument: earlyprintk=vga
1102
1da177e4 1103 edd= [EDD]
8c4dd606 1104 Format: {"off" | "on" | "skip[mbr]"}
1da177e4 1105
d2f7cbe7 1106 efi= [EFI]
fed6cefe 1107 Format: { "old_map", "nochunk", "noruntime", "debug" }
d2f7cbe7
BP
1108 old_map [X86-64]: switch to the old ioremap-based EFI
1109 runtime services mapping. 32-bit still uses this one by
1110 default.
5a17dae4
MF
1111 nochunk: disable reading files in "chunks" in the EFI
1112 boot stub, as chunking can cause problems with some
1113 firmware implementations.
5ae3683c 1114 noruntime : disable EFI runtime services support
fed6cefe 1115 debug: enable misc debug output
d2f7cbe7 1116
8c58bf3e
RW
1117 efi_no_storage_paranoia [EFI; X86]
1118 Using this parameter you can use more than 50% of
1119 your efi variable storage. Use this parameter only if
1120 you are really sure that your UEFI does sane gc and
1121 fulfills the spec otherwise your board may brick.
1122
0f96a99d
TI
1123 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1124 Add arbitrary attribute to specific memory range by
1125 updating original EFI memory map.
1126 Region of memory which aa attribute is added to is
1127 from ss to ss+nn.
1128 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1129 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1130 attribute is added to range 0x100000000-0x180000000 and
1131 0x10a0000000-0x1120000000.
1132
1133 Using this parameter you can do debugging of EFI memmap
1134 related feature. For example, you can do debugging of
1135 Address Range Mirroring feature even if your box
1136 doesn't support it.
1137
1da177e4
LT
1138 eisa_irq_edge= [PARISC,HW]
1139 See header of drivers/parisc/eisa.c.
1140
cd4f0ef7 1141 elanfreq= [X86-32]
1da177e4 1142 See comment before function elanfreq_setup() in
71f77055 1143 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1da177e4
LT
1144
1145 elevator= [IOSCHED]
17a9e7bb 1146 Format: {"cfq" | "deadline" | "noop"}
395cf969 1147 See Documentation/block/cfq-iosched.txt and
a9913044
RD
1148 Documentation/block/deadline-iosched.txt for details.
1149
d3bf3795 1150 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
a9913044 1151 Specifies physical address of start of kernel core
d3bf3795
MH
1152 image elf header and optionally the size. Generally
1153 kexec loader will pass this option to capture kernel.
aac04b32 1154 See Documentation/kdump/kdump.txt for details.
1da177e4 1155
0cb55ad2
RD
1156 enable_mtrr_cleanup [X86]
1157 The kernel tries to adjust MTRR layout from continuous
1158 to discrete, to make X server driver able to add WB
1159 entry later. This parameter enables that.
1160
ca1eda2d 1161 enable_timer_pin_1 [X86]
0cb55ad2
RD
1162 Enable PIN 1 of APIC timer
1163 Can be useful to work around chipset bugs
1164 (in particular on some ATI chipsets).
1165 The kernel tries to set a reasonable default.
1166
1da177e4
LT
1167 enforcing [SELINUX] Set initial enforcing status.
1168 Format: {"0" | "1"}
1169 See security/selinux/Kconfig help text.
1170 0 -- permissive (log only, no denials).
1171 1 -- enforcing (deny and log).
1172 Default value is 0.
1173 Value can be changed at runtime via /selinux/enforce.
1174
a08f82d0
HY
1175 erst_disable [ACPI]
1176 Disable Error Record Serialization Table (ERST)
1177 support.
1178
1da177e4
LT
1179 ether= [HW,NET] Ethernet cards parameters
1180 This option is obsoleted by the "netdev=" option, which
1181 has equivalent usage. See its documentation for details.
1182
7102ebcd
MZ
1183 evm= [EVM]
1184 Format: { "fix" }
1185 Permit 'security.evm' to be updated regardless of
1186 current integrity status.
1187
de1ba09b
AM
1188 failslab=
1189 fail_page_alloc=
1190 fail_make_request=[KNL]
1191 General fault injection mechanism.
1192 Format: <interval>,<probability>,<space>,<times>
395cf969 1193 See also Documentation/fault-injection/.
de1ba09b 1194
1da177e4 1195 floppy= [HW]
31c00fc1 1196 See Documentation/blockdev/floppy.txt.
1da177e4 1197
f13ae30e
AC
1198 force_pal_cache_flush
1199 [IA-64] Avoid check_sal_cache_flush which may hang on
1200 buggy SAL_CACHE_FLUSH implementations. Using this
1201 parameter will force ia64_sal_cache_flush to call
1202 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1203
69f2366c
CB
1204 forcepae [X86-32]
1205 Forcefully enable Physical Address Extension (PAE).
1206 Many Pentium M systems disable PAE but may have a
1207 functionally usable PAE implementation.
1208 Warning: use of this parameter will taint the kernel
1209 and may cause unknown problems.
1210
d9e54076 1211 ftrace=[tracer]
2af15d6a 1212 [FTRACE] will set and start the specified tracer
d9e54076
PZ
1213 as early as possible in order to facilitate early
1214 boot debugging.
1215
cecbca96 1216 ftrace_dump_on_oops[=orig_cpu]
2af15d6a 1217 [FTRACE] will dump the trace buffers on oops.
cecbca96
FW
1218 If no parameter is passed, ftrace will dump
1219 buffers of all CPUs, but if you pass orig_cpu, it will
1220 dump only the buffer of the CPU that triggered the
1221 oops.
2af15d6a
SR
1222
1223 ftrace_filter=[function-list]
1224 [FTRACE] Limit the functions traced by the function
1225 tracer at boot up. function-list is a comma separated
1226 list of functions. This list can be changed at run
1227 time by the set_ftrace_filter file in the debugfs
16290246 1228 tracing directory.
2af15d6a
SR
1229
1230 ftrace_notrace=[function-list]
1231 [FTRACE] Do not trace the functions specified in
1232 function-list. This list can be changed at run time
1233 by the set_ftrace_notrace file in the debugfs
1234 tracing directory.
d9e54076 1235
369bc18f
SA
1236 ftrace_graph_filter=[function-list]
1237 [FTRACE] Limit the top level callers functions traced
1238 by the function graph tracer at boot up.
1239 function-list is a comma separated list of functions
1240 that can be changed at run time by the
1241 set_graph_function file in the debugfs tracing directory.
1242
0d7d9a16
NK
1243 ftrace_graph_notrace=[function-list]
1244 [FTRACE] Do not trace from the functions specified in
1245 function-list. This list is a comma separated list of
1246 functions that can be changed at run time by the
1247 set_graph_notrace file in the debugfs tracing directory.
1248
1da177e4
LT
1249 gamecon.map[2|3]=
1250 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1251 support via parallel port (up to 5 devices per port)
1252 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1253 See also Documentation/input/joystick-parport.txt
1254
1255 gamma= [HW,DRM]
1256
aaf23042
YL
1257 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1258 Format: off | on
1259 default: on
1260
2521f2c2
PO
1261 gcov_persist= [GCOV] When non-zero (default), profiling data for
1262 kernel modules is saved and remains accessible via
1263 debugfs, even when the module is unloaded/reloaded.
1264 When zero, profiling data is discarded and associated
1265 debugfs files are removed at module unload time.
1266
1da177e4 1267 gpt [EFI] Forces disk with valid GPT signature but
6c5de79b
DB
1268 invalid Protective MBR to be treated as GPT. If the
1269 primary GPT is corrupted, it enables the backup/alternate
1270 GPT to be used instead.
1da177e4 1271
6cec9b07
AL
1272 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1273 the "Enable 0" bit of the configuration register.
1274 Format: 0 | 1
1275 Default: 0
1276 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1277 the "Enable 0" bit of the configuration register.
1278 Format: 0 | 1
1279 Default: 0
1280 grcan.select= [HW] Select which physical interface to use.
1281 Format: 0 | 1
1282 Default: 0
1283 grcan.txsize= [HW] Sets the size of the tx buffer.
1284 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1285 Default: 1024
1286 grcan.rxsize= [HW] Sets the size of the rx buffer.
1287 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1288 Default: 1024
1289
55537871
JK
1290 hardlockup_all_cpu_backtrace=
1291 [KNL] Should the hard-lockup detector generate
1292 backtraces on all cpus.
1293 Format: <integer>
1294
1da177e4
LT
1295 hashdist= [KNL,NUMA] Large hashes allocated during boot
1296 are distributed across NUMA nodes. Defaults on
16290246 1297 for 64-bit NUMA, off otherwise.
a9913044 1298 Format: 0 | 1 (for off | on)
1da177e4
LT
1299
1300 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1301
1302 hd= [EIDE] (E)IDE hard drive subsystem geometry
1303 Format: <cyl>,<head>,<sect>
1304
ea8c071c
HY
1305 hest_disable [ACPI]
1306 Disable Hardware Error Source Table (HEST) support;
1307 corresponding firmware-first mode error processing
1308 logic will be disabled.
1309
1da177e4
LT
1310 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1311 size of <nn>. This works even on boxes that have no
1312 highmem otherwise. This also works to reduce highmem
1313 size on bigger boxes.
1314
54cdfdb4
TG
1315 highres= [KNL] Enable/disable high resolution timer mode.
1316 Valid parameters: "on", "off"
1317 Default: "on"
1318
1da177e4
LT
1319 hisax= [HW,ISDN]
1320 See Documentation/isdn/README.HiSax.
1321
0cb55ad2
RD
1322 hlt [BUGS=ARM,SH]
1323
1324 hpet= [X86-32,HPET] option to control HPET usage
1325 Format: { enable (default) | disable | force |
1326 verbose }
1327 disable: disable HPET and use PIT instead
1328 force: allow force enabled of undocumented chips (ICH4,
1329 VIA, nVidia)
1330 verbose: show contents of HPET registers during setup
1331
3d035f58
PB
1332 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1333 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1334
b4718e62
AK
1335 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1336 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
0d9ea754
JT
1337 On x86-64 and powerpc, this option can be specified
1338 multiple times interleaved with hugepages= to reserve
1339 huge pages of different sizes. Valid pages sizes on
1340 x86-64 are 2M (when the CPU supports "pse") and 1G
27ec26ec 1341 (when the CPU supports the "pdpe1gb" cpuinfo flag).
6902aa84 1342
555d61d6
HB
1343 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1344 terminal devices. Valid values: 0..8
431429ff
HB
1345 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1346 If specified, z/VM IUCV HVC accepts connections
1347 from listed z/VM user IDs only.
cef7125d 1348
fdabf525
JH
1349 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1350 hardware thread id mappings.
1351 Format: <cpu>:<hwthread>
1352
7bf69395
FDN
1353 keep_bootcon [KNL]
1354 Do not unregister boot console at start. This is only
1355 useful for debugging when something happens in the window
1356 between unregistering the boot console and initializing
1357 the real console.
1358
3a853fb9 1359 i2c_bus= [HW] Override the default board specific I2C bus speed
7954763b
JN
1360 or register an additional I2C bus that is not
1361 registered from board initialization code.
3a853fb9
JN
1362 Format:
1363 <bus_id>,<clkrate>
1364
36d95739 1365 i8042.debug [HW] Toggle i8042 debug mode
e1443d28
SCP
1366 i8042.unmask_kbd_data
1367 [HW] Enable printing of interrupt data from the KBD port
1368 (disabled by default, and as a pre-condition
1369 requires that i8042.debug=1 be enabled)
1da177e4 1370 i8042.direct [HW] Put keyboard port into non-translated mode
84eb8d06
ML
1371 i8042.dumbkbd [HW] Pretend that controller can only read data from
1372 keyboard and cannot control its state
1da177e4
LT
1373 (Don't attempt to blink the leds)
1374 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
945ef0d4 1375 i8042.nokbd [HW] Don't check/create keyboard port
75d08c78
JK
1376 i8042.noloop [HW] Disable the AUX Loopback command while probing
1377 for the AUX port
1da177e4 1378 i8042.nomux [HW] Don't check presence of an active multiplexing
e55a3366 1379 controller
1da177e4
LT
1380 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1381 controllers
24775d65 1382 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1da177e4
LT
1383 i8042.reset [HW] Reset the controller during init and cleanup
1384 i8042.unlock [HW] Unlock (ignore) the keylock
148e9a71 1385 i8042.kbdreset [HW] Reset device connected to KBD port
1da177e4
LT
1386
1387 i810= [HW,DRM]
1388
e70c9d5e
DT
1389 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1390 indicates that the driver is running on unsupported
1391 hardware.
1da177e4
LT
1392 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1393 does not match list of supported models.
1394 i8k.power_status
1395 [HW] Report power status in /proc/i8k
1396 (disabled by default)
1397 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1398 capability is set.
1399
4dca20ef 1400 i915.invert_brightness=
7bd90909
CE
1401 [DRM] Invert the sense of the variable that is used to
1402 set the brightness of the panel backlight. Normally a
4dca20ef
CE
1403 brightness value of 0 indicates backlight switched off,
1404 and the maximum of the brightness value sets the backlight
1405 to maximum brightness. If this parameter is set to 0
1406 (default) and the machine requires it, or this parameter
1407 is set to 1, a brightness value of 0 sets the backlight
1408 to maximum brightness, and the maximum of the brightness
1409 value switches the backlight off.
1410 -1 -- never invert brightness
1411 0 -- machine default
1412 1 -- force brightness inversion
7bd90909 1413
1da177e4
LT
1414 icn= [HW,ISDN]
1415 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1416
0af80c04
DF
1417 ide-core.nodma= [HW] (E)IDE subsystem
1418 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
075affcb
BZ
1419 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1420 .cdrom .chs .ignore_cable are additional options
1c10e938 1421 See Documentation/ide/ide.txt.
1da177e4 1422
0f8b7f5d
MR
1423 ide-generic.probe-mask= [HW] (E)IDE subsystem
1424 Format: <int>
1425 Probe mask for legacy ISA IDE ports. Depending on
1426 platform up to 6 ports are supported, enabled by
1427 setting corresponding bits in the mask to 1. The
1428 default value is 0x0, which has a special meaning.
1429 On systems that have PCI, it triggers scanning the
1430 PCI bus for the first and the second port, which
1431 are then probed. On systems without PCI the value
1432 of 0x0 enables probing the two first ports as if it
1433 was 0x3.
1434
0cb55ad2
RD
1435 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1436 Claim all unknown PCI IDE storage controllers.
1437
f039b754 1438 idle= [X86]
69fb3676 1439 Format: idle=poll, idle=halt, idle=nomwait
ada9cfdd
RD
1440 Poll forces a polling idle loop that can slightly
1441 improve the performance of waking up a idle CPU, but
1442 will use a lot of power and make the system run hot.
1443 Not recommended.
ada9cfdd 1444 idle=halt: Halt is forced to be used for CPU idle.
c1e3b377 1445 In such case C2/C3 won't be used again.
ada9cfdd 1446 idle=nomwait: Disable mwait for CPU C-states
a9913044 1447
79290822
IM
1448 ignore_loglevel [KNL]
1449 Ignore loglevel setting - this will print /all/
1450 kernel messages to the console. Useful for debugging.
0eca6b7c
YZ
1451 We also add it as printk module parameter, so users
1452 could change it dynamically, usually by
1453 /sys/module/printk/parameters/ignore_loglevel.
79290822 1454
1da177e4
LT
1455 ihash_entries= [KNL]
1456 Set number of hash buckets for inode cache.
1457
2fe5d6de 1458 ima_appraise= [IMA] appraise integrity measurements
2faa6ef3 1459 Format: { "off" | "enforce" | "fix" | "log" }
2fe5d6de
MZ
1460 default: "enforce"
1461
07f6a794
MZ
1462 ima_appraise_tcb [IMA]
1463 The builtin appraise policy appraises all files
1464 owned by uid=0.
1465
3323eec9 1466 ima_hash= [IMA]
e7a2ad7e
MZ
1467 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1468 | sha512 | ... }
3323eec9
MZ
1469 default: "sha1"
1470
e7a2ad7e
MZ
1471 The list of supported hash algorithms is defined
1472 in crypto/hash_info.h.
1473
24fd03c8
MZ
1474 ima_policy= [IMA]
1475 The builtin measurement policy to load during IMA
1476 setup. Specyfing "tcb" as the value, measures all
1477 programs exec'd, files mmap'd for exec, and all files
1478 opened with the read mode bit set by either the
1479 effective uid (euid=0) or uid=0.
1480 Format: "tcb"
1481
1482 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
5789ba3b
EP
1483 Load a policy which meets the needs of the Trusted
1484 Computing Base. This means IMA will measure all
1485 programs exec'd, files mmap'd for exec, and all files
1486 opened for read by uid=0.
1487
9b9d4ce5
RS
1488 ima_template= [IMA]
1489 Select one of defined IMA measurements template formats.
8265a2f8 1490 Formats: { "ima" | "ima-ng" | "ima-sig" }
9b9d4ce5
RS
1491 Default: "ima-ng"
1492
c2426d2a
RS
1493 ima_template_fmt=
1494 [IMA] Define a custom template format.
1495 Format: { "field1|...|fieldN" }
1496
3bcced39
DK
1497 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1498 Format: <min_file_size>
1499 Set the minimal file size for using asynchronous hash.
1500 If left unspecified, ahash usage is disabled.
1501
1502 ahash performance varies for different data sizes on
1503 different crypto accelerators. This option can be used
1504 to achieve the best performance for a particular HW.
1505
6edf7a89
DK
1506 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1507 Format: <bufsize>
1508 Set hashing buffer size. Default: 4k.
1509
1510 ahash performance varies for different chunk sizes on
1511 different crypto accelerators. This option can be used
1512 to achieve best performance for particular HW.
1513
1da177e4
LT
1514 init= [KNL]
1515 Format: <full_path>
1516 Run specified binary instead of /sbin/init as init
1517 process.
1518
1519 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1520 for working out where the kernel is dying during
1521 startup.
1522
7b0b73d7
PB
1523 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1524 initcall functions. Useful for debugging built-in
1525 modules and initcalls.
1526
1da177e4
LT
1527 initrd= [BOOT] Specify the location of the initial ramdisk
1528
1529 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1530 Format: <irq>
1531
6bb2ff84
FY
1532 int_pln_enable [x86] Enable power limit notification interrupt
1533
d726d8d7
MZ
1534 integrity_audit=[IMA]
1535 Format: { "0" | "1" }
1536 0 -- basic integrity auditing messages. (Default)
1537 1 -- additional integrity auditing messages.
1538
ba395927 1539 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
0cd5c3c8
KM
1540 on
1541 Enable intel iommu driver.
ba395927
KA
1542 off
1543 Disable intel iommu driver.
1544 igfx_off [Default Off]
1545 By default, gfx is mapped as normal device. If a gfx
1546 device has a dedicated DMAR unit, the DMAR unit is
1547 bypassed by not enabling DMAR with this option. In
1548 this case, gfx device will use physical address for
1549 DMA.
7d3b03ce
KA
1550 forcedac [x86_64]
1551 With this option iommu will not optimize to look
16290246 1552 for io virtual address below 32-bit forcing dual
7d3b03ce 1553 address cycle on pci bus for cards supporting greater
16290246
RD
1554 than 32-bit addressing. The default is to look
1555 for translation below 32-bit and if not available
7d3b03ce 1556 then look in the higher range.
5e0d2a6f 1557 strict [Default Off]
1558 With this option on every unmap_single operation will
1559 result in a hardware IOTLB flush operation as opposed
1560 to batching them for performance.
6dd9a7c7
YS
1561 sp_off [Default Off]
1562 By default, super page will be supported if Intel IOMMU
1563 has the capability. With this option, super page will
1564 not be supported.
c83b2f20
DW
1565 ecs_off [Default Off]
1566 By default, extended context tables will be supported if
1567 the hardware advertises that it has support both for the
1568 extended tables themselves, and also PASID support. With
1569 this option set, extended tables will not be used even
1570 on hardware which claims to support them.
2e92c7ad
MI
1571
1572 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1573 0 disables intel_idle and fall back on acpi_idle.
1574 1 to 6 specify maximum depth of C-state.
1575
6be26498
DB
1576 intel_pstate= [X86]
1577 disable
1578 Do not enable intel_pstate as the default
1579 scaling driver for the supported processors
aa4ea34d
EZ
1580 force
1581 Enable intel_pstate on systems that prohibit it by default
1582 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1583 instead of acpi-cpufreq may disable platform features, such
1584 as thermal controls and power capping, that rely on ACPI
1585 P-States information being indicated to OSPM and therefore
1586 should be used with caution. This option does not work with
1587 processors that aren't supported by the intel_pstate driver
1588 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2f86dc4c
DB
1589 no_hwp
1590 Do not enable hardware P state control (HWP)
1591 if available.
d64c3b0b
KCA
1592 hwp_only
1593 Only load intel_pstate on systems which support
1594 hardware P state control (HWP) if available.
6be26498 1595
d1423d56 1596 intremap= [X86-64, Intel-IOMMU]
d1423d56
CW
1597 on enable Interrupt Remapping (default)
1598 off disable Interrupt Remapping
1599 nosid disable Source ID checking
41750d31
SS
1600 no_x2apic_optout
1601 BIOS x2APIC opt-out request will be ignored
b7d20631 1602 nopost disable Interrupt Posting
d1423d56 1603
0cb55ad2
RD
1604 iomem= Disable strict checking of access to MMIO memory
1605 strict regions from userspace.
1606 relaxed
1607
1608 iommu= [x86]
1609 off
1610 force
1611 noforce
1612 biomerge
1613 panic
1614 nopanic
1615 merge
1616 nomerge
1617 forcesac
1618 soft
bcb71abe 1619 pt [x86, IA-64]
4e287840
TLSC
1620 nobypass [PPC/POWERNV]
1621 Disable IOMMU bypass, using IOMMU for PCI devices.
bcb71abe 1622
0cb55ad2
RD
1623
1624 io7= [HW] IO7 for Marvel based alpha systems
1625 See comment before marvel_specify_io7 in
1626 arch/alpha/kernel/core_marvel.c.
1627
6cececfc 1628 io_delay= [X86] I/O delay method
6e7c4025
IM
1629 0x80
1630 Standard port 0x80 based delay
1631 0xed
1632 Alternate port 0xed based delay (needed on some systems)
b02aae9c 1633 udelay
6e7c4025
IM
1634 Simple two microseconds delay
1635 none
1636 No delay
b02aae9c 1637
1da177e4 1638 ip= [IP_PNP]
dc7a0816 1639 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 1640
200803df
AC
1641 irqfixup [HW]
1642 When an interrupt is not handled search all handlers
1643 for it. Intended to get systems with badly broken
1644 firmware running.
1645
1646 irqpoll [HW]
1647 When an interrupt is not handled search all handlers
1648 for it. Also check all handlers each timer
1649 interrupt. Intended to get systems with badly broken
1650 firmware running.
1651
1da177e4 1652 isapnp= [ISAPNP]
a9913044 1653 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1da177e4
LT
1654
1655 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
22f2e280
DF
1656 Format:
1657 <cpu number>,...,<cpu number>
1658 or
b225d44e
LZ
1659 <cpu number>-<cpu number>
1660 (must be a positive range in ascending order)
22f2e280
DF
1661 or a mixture
1662 <cpu number>,...,<cpu number>-<cpu number>
b225d44e 1663
1da177e4
LT
1664 This option can be used to specify one or more CPUs
1665 to isolate from the general SMP balancing and scheduling
b225d44e
LZ
1666 algorithms. You can move a process onto or off an
1667 "isolated" CPU via the CPU affinity syscalls or cpuset.
1da177e4
LT
1668 <cpu number> begins at 0 and the maximum value is
1669 "number of CPUs in system - 1".
1670
1671 This option is the preferred way to isolate CPUs. The
a9913044
RD
1672 alternative -- manually setting the CPU mask of all
1673 tasks in the system -- can cause problems and
1674 suboptimal load balancer performance.
1da177e4 1675
a9913044 1676 iucv= [HW,NET]
1da177e4 1677
7d8bfa26
JR
1678 ivrs_ioapic [HW,X86_64]
1679 Provide an override to the IOAPIC-ID<->DEVICE-ID
1680 mapping provided in the IVRS ACPI table. For
1681 example, to map IOAPIC-ID decimal 10 to
1682 PCI device 00:14.0 write the parameter as:
1683 ivrs_ioapic[10]=00:14.0
1684
1685 ivrs_hpet [HW,X86_64]
1686 Provide an override to the HPET-ID<->DEVICE-ID
1687 mapping provided in the IVRS ACPI table. For
1688 example, to map HPET-ID decimal 0 to
1689 PCI device 00:14.0 write the parameter as:
1690 ivrs_hpet[0]=00:14.0
1691
1da177e4
LT
1692 js= [HW,JOY] Analog joystick
1693 See Documentation/input/joystick.txt.
1694
24f2e027
KC
1695 kaslr/nokaslr [X86]
1696 Enable/disable kernel and module base offset ASLR
1697 (Address Space Layout Randomization) if built into
1698 the kernel. When CONFIG_HIBERNATION is selected,
1699 kASLR is disabled by default. When kASLR is enabled,
1700 hibernation will be disabled.
1701
0cb55ad2
RD
1702 keepinitrd [HW,ARM]
1703
6cececfc 1704 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
ed7ed365
MG
1705 specifies the amount of memory usable by the kernel
1706 for non-movable allocations. The requested amount is
1707 spread evenly throughout all nodes in the system. The
1708 remaining memory in each node is used for Movable
1709 pages. In the event, a node is too small to have both
1710 kernelcore and Movable pages, kernelcore pages will
1711 take priority and other nodes will have a larger number
675217fd 1712 of Movable pages. The Movable zone is used for the
ed7ed365
MG
1713 allocation of pages that may be reclaimed or moved
1714 by the page migration subsystem. This means that
1715 HugeTLB pages may not be allocated from this zone.
1716 Note that allocations like PTEs-from-HighMem still
1717 use the HighMem zone if it exists, and the Normal
1718 zone if it does not.
1719
4fe1da4e
JW
1720 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1721 Format: <Controller#>[,poll interval]
1722 The controller # is the number of the ehci usb debug
1723 port as it is probed via PCI. The poll interval is
1724 optional and is the number seconds in between
1725 each poll cycle to the debug port in case you need
1726 the functionality for interrupting the kernel with
1727 gdb or control-c on the dbgp connection. When
1728 not using this parameter you use sysrq-g to break into
1729 the kernel debugger.
1730
84c08fd6 1731 kgdboc= [KGDB,HW] kgdb over consoles.
ada64e4c
JW
1732 Requires a tty driver that supports console polling,
1733 or a supported polling keyboard driver (non-usb).
65b5ac14
JW
1734 Serial only format: <serial_device>[,baud]
1735 keyboard only format: kbd
1736 keyboard and serial format: kbd,<serial_device>[,baud]
1737 Optional Kernel mode setting:
1738 kms, kbd format: kms,kbd
1739 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
6cdf6e06 1740
84c08fd6
JW
1741 kgdbwait [KGDB] Stop kernel execution and enter the
1742 kernel debugger at the earliest opportunity.
1743
9bed90c6
FF
1744 kmac= [MIPS] korina ethernet MAC address.
1745 Configure the RouterBoard 532 series on-chip
1746 Ethernet adapter MAC address.
1747
04f70336
CM
1748 kmemleak= [KNL] Boot-time kmemleak enable/disable
1749 Valid arguments: on, off
1750 Default: on
47aeeddc
MI
1751 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1752 the default is off.
04f70336 1753
c3ac14b2
XQ
1754 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1755 Valid arguments: 0, 1, 2
1756 kmemcheck=0 (disabled)
1757 kmemcheck=1 (enabled)
1758 kmemcheck=2 (one-shot mode)
1759 Default: 2 (one-shot mode)
1760
6cececfc 1761 kstack=N [X86] Print N words from the kernel stack
0cb55ad2
RD
1762 in oops dumps.
1763
fef07aae
AP
1764 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1765 Default is 0 (don't ignore, but inject #GP)
1766
a182d873
XG
1767 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1768 KVM MMU at runtime.
fef07aae
AP
1769 Default is 0 (off)
1770
fef07aae 1771 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
8475f94a 1772 Default is 1 (enabled)
fef07aae
AP
1773
1774 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1775 for all guests.
16290246 1776 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
fef07aae 1777
fef07aae
AP
1778 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1779 (virtualized MMU) support on capable Intel chips.
1780 Default is 1 (enabled)
1781
1782 kvm-intel.emulate_invalid_guest_state=
1783 [KVM,Intel] Enable emulation of invalid guest states
1784 Default is 0 (disabled)
1785
1786 kvm-intel.flexpriority=
1787 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1788 Default is 1 (enabled)
1789
e1a72ae2
SL
1790 kvm-intel.nested=
1791 [KVM,Intel] Enable VMX nesting (nVMX).
1792 Default is 0 (disabled)
1793
fef07aae
AP
1794 kvm-intel.unrestricted_guest=
1795 [KVM,Intel] Disable unrestricted guest feature
1796 (virtualized real and unpaged mode) on capable
1797 Intel chips. Default is 1 (enabled)
1798
1799 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1800 feature (tagged TLBs) on capable Intel chips.
1801 Default is 1 (enabled)
1802
1da177e4
LT
1803 l2cr= [PPC]
1804
a78bfbfc
RB
1805 l3cr= [PPC]
1806
cd4f0ef7 1807 lapic [X86-32,APIC] Enable the local APIC even if BIOS
a9913044 1808 disabled it.
1da177e4 1809
279f1461
SS
1810 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1811 value for LAPIC timer one-shot implementation. Default
1812 back to the programmable timer unit in the LAPIC.
1813
6cececfc 1814 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
ada9cfdd 1815 in C2 power state.
e585bef8 1816
fcb71f6f
FC
1817 libata.dma= [LIBATA] DMA control
1818 libata.dma=0 Disable all PATA and SATA DMA
1819 libata.dma=1 PATA and SATA Disk DMA only
1820 libata.dma=2 ATAPI (CDROM) DMA only
16290246 1821 libata.dma=4 Compact Flash DMA only
fcb71f6f
FC
1822 Combinations also work, so libata.dma=3 enables DMA
1823 for disks and CDROMs, but not CFs.
16290246 1824
20308871
MP
1825 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1826 libata.ignore_hpa=0 keep BIOS limits (default)
1827 libata.ignore_hpa=1 ignore limits, using full disk
fcb71f6f 1828
78e70c23
DJ
1829 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1830 when set.
1831 Format: <int>
1832
33267325
TH
1833 libata.force= [LIBATA] Force configurations. The format is comma
1834 separated list of "[ID:]VAL" where ID is
4c44f309 1835 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
33267325
TH
1836 matching port, link or device. Basically, it matches
1837 the ATA ID string printed on console by libata. If
1838 the whole ID part is omitted, the last PORT and DEVICE
1839 values are used. If ID hasn't been specified yet, the
1840 configuration applies to all ports, links and devices.
1841
1842 If only DEVICE is omitted, the parameter applies to
1843 the port and all links and devices behind it. DEVICE
1844 number of 0 either selects the first device or the
1845 first fan-out link behind PMP device. It does not
1846 select the host link. DEVICE number of 15 selects the
1847 host link and device attached to it.
1848
1849 The VAL specifies the configuration to force. As long
1850 as there's no ambiguity shortcut notation is allowed.
1851 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1852 The following configurations can be forced.
1853
1854 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1855 Any ID with matching PORT is used.
1856
1857 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1858
1859 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1860 udma[/][16,25,33,44,66,100,133] notation is also
1861 allowed.
1862
1863 * [no]ncq: Turn on or off NCQ.
1864
d7b16e4f
MP
1865 * [no]ncqtrim: Turn off queued DSM TRIM.
1866
05944bdf
TH
1867 * nohrst, nosrst, norst: suppress hard, soft
1868 and both resets.
1869
ca6d43b0
DW
1870 * rstonce: only attempt one reset during
1871 hot-unplug link recovery
1872
43c9c591
TH
1873 * dump_id: dump IDENTIFY data.
1874
966fbe19
VP
1875 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1876
b8bd6dc3
RJ
1877 * disable: Disable this device.
1878
33267325
TH
1879 If there are multiple matching configurations changing
1880 the same attribute, the last one is used.
1881
95f72d1e 1882 memblock=debug [KNL] Enable memblock debug messages.
7c4be253 1883
1da177e4 1884 load_ramdisk= [RAM] List of ramdisks to load from floppy
31c00fc1 1885 See Documentation/blockdev/ramdisk.txt.
1da177e4 1886
a6b25b67
RD
1887 lockd.nlm_grace_period=P [NFS] Assign grace period.
1888 Format: <integer>
1da177e4 1889
a6b25b67
RD
1890 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1891 Format: <integer>
1892
1893 lockd.nlm_timeout=T [NFS] Assign timeout value.
1894 Format: <integer>
1895
1896 lockd.nlm_udpport=M [NFS] Assign UDP port.
1897 Format: <integer>
1da177e4 1898
ec4518aa
PM
1899 locktorture.nreaders_stress= [KNL]
1900 Set the number of locking read-acquisition kthreads.
1901 Defaults to being automatically set based on the
1902 number of online CPUs.
1903
1904 locktorture.nwriters_stress= [KNL]
1905 Set the number of locking write-acquisition kthreads.
1906
1907 locktorture.onoff_holdoff= [KNL]
1908 Set time (s) after boot for CPU-hotplug testing.
1909
1910 locktorture.onoff_interval= [KNL]
1911 Set time (s) between CPU-hotplug operations, or
1912 zero to disable CPU-hotplug testing.
1913
1914 locktorture.shuffle_interval= [KNL]
1915 Set task-shuffle interval (jiffies). Shuffling
1916 tasks allows some CPUs to go into dyntick-idle
1917 mode during the locktorture test.
1918
1919 locktorture.shutdown_secs= [KNL]
1920 Set time (s) after boot system shutdown. This
1921 is useful for hands-off automated testing.
1922
1923 locktorture.stat_interval= [KNL]
1924 Time (s) between statistics printk()s.
1925
1926 locktorture.stutter= [KNL]
1927 Time (s) to stutter testing, for example,
1928 specifying five seconds causes the test to run for
1929 five seconds, wait for five seconds, and so on.
1930 This tests the locking primitive's ability to
1931 transition abruptly to and from idle.
1932
1933 locktorture.torture_runnable= [BOOT]
1934 Start locktorture running at boot time.
1935
1936 locktorture.torture_type= [KNL]
1937 Specify the locking implementation to test.
1938
1939 locktorture.verbose= [KNL]
1940 Enable additional printk() statements.
1941
1da177e4
LT
1942 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1943 Format: <irq>
1944
1945 loglevel= All Kernel Messages with a loglevel smaller than the
1946 console loglevel will be printed to the console. It can
1947 also be changed with klogd or other programs. The
1948 loglevels are defined as follows:
1949
1950 0 (KERN_EMERG) system is unusable
1951 1 (KERN_ALERT) action must be taken immediately
1952 2 (KERN_CRIT) critical conditions
1953 3 (KERN_ERR) error conditions
1954 4 (KERN_WARNING) warning conditions
1955 5 (KERN_NOTICE) normal but significant condition
1956 6 (KERN_INFO) informational
1957 7 (KERN_DEBUG) debug-level messages
1958
c756d08a 1959 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
23b2899f
LR
1960 in bytes. n must be a power of two and greater
1961 than the minimal size. The minimal size is defined
1962 by LOG_BUF_SHIFT kernel config parameter. There is
1963 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1964 that allows to increase the default size depending on
1965 the number of CPUs. See init/Kconfig for more details.
1da177e4 1966
accaa24c
RD
1967 logo.nologo [FB] Disables display of the built-in Linux logo.
1968 This may be used to provide more screen space for
1969 kernel log messages and is useful when debugging
1970 kernel boot problems.
1971
1da177e4
LT
1972 lp=0 [LP] Specify parallel ports to use, e.g,
1973 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1974 lp=reset first parallel port). 'lp=0' disables the
1975 lp=auto printer driver. 'lp=reset' (which can be
1976 specified in addition to the ports) causes
1977 attached printers to be reset. Using
1978 lp=port1,port2,... specifies the parallel ports
1979 to associate lp devices with, starting with
1980 lp0. A port specification may be 'none' to skip
1981 that lp device, or a parport name such as
1982 'parport0'. Specifying 'lp=auto' instead of a
1983 port specification list means that device IDs
1984 from each port should be examined, to see if
1985 an IEEE 1284-compliant printer is attached; if
1986 so, the driver will manage that printer.
1987 See also header of drivers/char/lp.c.
1988
1989 lpj=n [KNL]
1990 Sets loops_per_jiffy to given constant, thus avoiding
1991 time-consuming boot-time autodetection (up to 250 ms per
1992 CPU). 0 enables autodetection (default). To determine
1993 the correct value for your kernel, boot with normal
1994 autodetection and see what value is printed. Note that
1995 on SMP systems the preset will be applied to all CPUs,
1996 which is likely to cause problems if your CPUs need
1997 significantly divergent settings. An incorrect value
1998 will cause delays in the kernel to be wrong, leading to
1999 unpredictable I/O errors and other breakage. Although
2000 unlikely, in the extreme case this might damage your
2001 hardware.
2002
2003 ltpc= [NET]
2004 Format: <io>,<irq>,<dma>
2005
16290246 2006 machvec= [IA-64] Force the use of a particular machine-vector
a9913044
RD
2007 (machvec) in a generic kernel.
2008 Example: machvec=hpzx1_swiotlb
1da177e4 2009
3209e70e
WZ
2010 machtype= [Loongson] Share the same kernel image file between different
2011 yeeloong laptop.
2012 Example: machtype=lemote-yeeloong-2f-7inch
2013
0cb55ad2
RD
2014 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2015 than or equal to this physical address is ignored.
1da177e4
LT
2016
2017 maxcpus= [SMP] Maximum number of processors that an SMP kernel
61ec7567
LB
2018 should make use of. maxcpus=n : n >= 0 limits the
2019 kernel to using 'n' processors. n=0 is a special case,
2020 it is equivalent to "nosmp", which also disables
2021 the IO APIC.
1da177e4 2022
d134b00b
KS
2023 max_loop= [LOOP] The number of loop block devices that get
2024 (loop.max_loop) unconditionally pre-created at init time. The default
2025 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2026 of statically allocating a predefined number, loop
2027 devices can be requested on-demand with the
2028 /dev/loop-control interface.
2b2c3750 2029
cd4f0ef7 2030 mce [X86-32] Machine Check Exception
1da177e4 2031
71cced6e 2032 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
909dd324 2033
1da177e4
LT
2034 md= [HW] RAID subsystems devices and level
2035 See Documentation/md.txt.
a9913044 2036
1da177e4
LT
2037 mdacon= [MDA]
2038 Format: <first>,<last>
2039 Specifies range of consoles to be captured by the MDA.
a9913044 2040
1da177e4
LT
2041 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2042 Amount of memory to be used when the kernel is not able
2043 to see the whole system memory or for test.
fbb97d87
WC
2044 [X86] Work as limiting max address. Use together
2045 with memmap= to avoid physical address space collisions.
2046 Without memmap= PCI devices could be placed at addresses
2047 belonging to unused RAM.
1da177e4 2048
cd4f0ef7 2049 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1da177e4
LT
2050 memory.
2051
6902aa84
PM
2052 memchunk=nn[KMG]
2053 [KNL,SH] Allow user to override the default size for
2054 per-device physically contiguous DMA buffers.
2055
6cececfc 2056 memmap=exactmap [KNL,X86] Enable setting of an exact
1da177e4
LT
2057 E820 memory map, as specified by the user.
2058 Such memmap=exactmap lines can be constructed based on
2059 BIOS output or other requirements. See the memmap=nn@ss
2060 option description.
2061
2062 memmap=nn[KMG]@ss[KMG]
277cba1d
RD
2063 [KNL] Force usage of a specific region of memory.
2064 Region of memory to be used is from ss to ss+nn.
1da177e4
LT
2065
2066 memmap=nn[KMG]#ss[KMG]
2067 [KNL,ACPI] Mark specific memory as ACPI data.
277cba1d 2068 Region of memory to be marked is from ss to ss+nn.
1da177e4
LT
2069
2070 memmap=nn[KMG]$ss[KMG]
2071 [KNL,ACPI] Mark specific memory as reserved.
277cba1d 2072 Region of memory to be reserved is from ss to ss+nn.
1312848e
PM
2073 Example: Exclude memory from 0x18690000-0x1869ffff
2074 memmap=64K$0x18690000
2075 or
2076 memmap=0x10000$0x18690000
1da177e4 2077
ec776ef6
CH
2078 memmap=nn[KMG]!ss[KMG]
2079 [KNL,X86] Mark specific memory as protected.
2080 Region of memory to be used, from ss to ss+nn.
2081 The memory region may be marked as e820 type 12 (0xc)
2082 and is NVDIMM or ADR memory.
2083
9f077871
JF
2084 memory_corruption_check=0/1 [X86]
2085 Some BIOSes seem to corrupt the first 64k of
2086 memory when doing things like suspend/resume.
2087 Setting this option will scan the memory
2088 looking for corruption. Enabling this will
2089 both detect corruption and prevent the kernel
2090 from using the memory being corrupted.
2091 However, its intended as a diagnostic tool; if
2092 repeatable BIOS-originated corruption always
2093 affects the same memory, you can use memmap=
2094 to prevent the kernel from using that memory.
2095
2096 memory_corruption_check_size=size [X86]
2097 By default it checks for corruption in the low
2098 64k, making this memory unavailable for normal
2099 use. Use this parameter to scan for
2100 corruption in more or less memory.
2101
2102 memory_corruption_check_period=seconds [X86]
2103 By default it checks for corruption every 60
2104 seconds. Use this parameter to check at some
2105 other rate. 0 disables periodic checking.
2106
e4b0db72 2107 memtest= [KNL,X86,ARM] Enable memtest
c64df707 2108 Format: <integer>
c64df707 2109 default : 0 <disable>
9e5f6cf5
AH
2110 Specifies the number of memtest passes to be
2111 performed. Each pass selects another test
2112 pattern from a given set of patterns. Memtest
2113 fills the memory with this pattern, validates
2114 memory contents and reserves bad memory
2115 regions that are detected.
c64df707 2116
1da177e4
LT
2117 meye.*= [HW] Set MotionEye Camera parameters
2118 See Documentation/video4linux/meye.txt.
2119
8f36881b
AS
2120 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2121 Multi-Function General Purpose Timers on AMD Geode
2122 platforms.
2123
e6c4dc6c
WT
2124 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2125 the BIOS has incorrectly applied a workaround. TinyBIOS
2126 version 0.98 is known to be affected, 0.99 fixes the
2127 problem by letting the user disable the workaround.
2128
1da177e4
LT
2129 mga= [HW,DRM]
2130
1c207f95
RD
2131 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2132 physical address is ignored.
2133
39f45d7b
MP
2134 mini2440= [ARM,HW,KNL]
2135 Format:[0..2][b][c][t]
2136 Default: "0tb"
2137 MINI2440 configuration specification:
2138 0 - The attached screen is the 3.5" TFT
2139 1 - The attached screen is the 7" TFT
2140 2 - The VGA Shield is attached (1024x768)
2141 Leaving out the screen size parameter will not load
2142 the TFT driver, and the framebuffer will be left
2143 unconfigured.
2144 b - Enable backlight. The TFT backlight pin will be
2145 linked to the kernel VESA blanking code and a GPIO
2146 LED. This parameter is not necessary when using the
2147 VGA shield.
2148 c - Enable the s3c camera interface.
2149 t - Reserved for enabling touchscreen support. The
2150 touchscreen support is not enabled in the mainstream
2151 kernel as of 2.6.30, a preliminary port can be found
2152 in the "bleeding edge" mini2440 support kernel at
2153 http://repo.or.cz/w/linux-2.6/mini2440.git
2154
6b74ab97
MG
2155 mminit_loglevel=
2156 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2157 parameter allows control of the logging verbosity for
2158 the additional memory initialisation checks. A value
2159 of 0 disables mminit logging and a level of 4 will
2160 log everything. Information is printed at KERN_DEBUG
2161 so loglevel=8 may also need to be specified.
2162
106a4ee2
RR
2163 module.sig_enforce
2164 [KNL] When CONFIG_MODULE_SIG is set, this means that
2165 modules without (valid) signatures will fail to load.
2a039be7 2166 Note that if CONFIG_MODULE_SIG_FORCE is set, that
106a4ee2
RR
2167 is always true, so this option does nothing.
2168
1da177e4
LT
2169 mousedev.tap_time=
2170 [MOUSE] Maximum time between finger touching and
2171 leaving touchpad surface for touch to be considered
2172 a tap and be reported as a left button click (for
2173 touchpads working in absolute mode only).
2174 Format: <msecs>
2175 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2176 reporting absolute coordinates, such as tablets
2177 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2178 reporting absolute coordinates, such as tablets
2179
6cececfc 2180 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
0cb55ad2
RD
2181 is similar to kernelcore except it specifies the
2182 amount of memory used for migratable allocations.
2183 If both kernelcore and movablecore is specified,
2184 then kernelcore will be at *least* the specified
2185 value but may be more. If movablecore on its own
2186 is specified, the administrator must be careful
2187 that the amount of memory usable for all allocations
2188 is not too small.
2189
c5320926
TC
2190 movable_node [KNL,X86] Boot-time switch to enable the effects
2191 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2192
1da177e4
LT
2193 MTD_Partition= [MTD]
2194 Format: <name>,<region-number>,<size>,<offset>
2195
a9913044
RD
2196 MTD_Region= [MTD] Format:
2197 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1da177e4
LT
2198
2199 mtdparts= [MTD]
c8facbb6 2200 See drivers/mtd/cmdlinepart.c.
1da177e4 2201
4e89a2d8
WS
2202 multitce=off [PPC] This parameter disables the use of the pSeries
2203 firmware feature for updating multiple TCE entries
2204 at a time.
2205
5988af23
RH
2206 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2207
2208 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2209
2210 boundary - index of last SLC block on Flex-OneNAND.
2211 The remaining blocks are configured as MLC blocks.
2212 lock - Configure if Flex-OneNAND boundary should be locked.
2213 Once locked, the boundary cannot be changed.
2214 1 indicates lock status, 0 indicates unlock status.
2215
9db829f4
BD
2216 mtdset= [ARM]
2217 ARM/S3C2412 JIVE boot control
2218
2219 See arch/arm/mach-s3c2412/mach-jive.c
2220
1da177e4 2221 mtouchusb.raw_coordinates=
a9913044
RD
2222 [HW] Make the MicroTouch USB driver use raw coordinates
2223 ('y', default) or cooked coordinates ('n')
1da177e4 2224
0cb55ad2 2225 mtrr_chunk_size=nn[KMG] [X86]
19f59460 2226 used for mtrr cleanup. It is largest continuous chunk
0cb55ad2
RD
2227 that could hold holes aka. UC entries.
2228
2229 mtrr_gran_size=nn[KMG] [X86]
2230 Used for mtrr cleanup. It is granularity of mtrr block.
2231 Default is 1.
2232 Large value could prevent small alignment from
2233 using up MTRRs.
2234
2235 mtrr_spare_reg_nr=n [X86]
2236 Format: <integer>
2237 Range: 0,7 : spare reg number
2238 Default : 1
2239 Used for mtrr cleanup. It is spare mtrr entries number.
2240 Set to 2 or more if your graphical card needs more.
2241
1da177e4
LT
2242 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2243
1da177e4
LT
2244 netdev= [NET] Network devices parameters
2245 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2246 Note that mem_start is often overloaded to mean
2247 something different and driver-specific.
a9913044
RD
2248 This usage is only documented in each driver source
2249 file if at all.
2250
58401572
KPO
2251 nf_conntrack.acct=
2252 [NETFILTER] Enable connection tracking flow accounting
2253 0 to disable accounting
2254 1 to enable accounting
d70a011d 2255 Default value is 0.
58401572 2256
306a0753 2257 nfsaddrs= [NFS] Deprecated. Use ip= instead.
dc7a0816 2258 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
2259
2260 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
dc7a0816 2261 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 2262
306a0753
CL
2263 nfsrootdebug [NFS] enable nfsroot debugging messages.
2264 See Documentation/filesystems/nfs/nfsroot.txt.
2265
a72b4422
TM
2266 nfs.callback_tcpport=
2267 [NFS] set the TCP port on which the NFSv4 callback
2268 channel should listen.
2269
e571cbf1
TM
2270 nfs.cache_getent=
2271 [NFS] sets the pathname to the program which is used
2272 to update the NFS client cache entries.
2273
2274 nfs.cache_getent_timeout=
2275 [NFS] sets the timeout after which an attempt to
2276 update a cache entry is deemed to have failed.
2277
58df095b
TM
2278 nfs.idmap_cache_timeout=
2279 [NFS] set the maximum lifetime for idmapper cache
2280 entries.
2281
f43bf0be
TM
2282 nfs.enable_ino64=
2283 [NFS] enable 64-bit inode numbers.
2284 If zero, the NFS client will fake up a 32-bit inode
2285 number for the readdir() and stat() syscalls instead
2286 of returning the full 64-bit number.
2287 The default is to return 64-bit inode numbers.
2288
ef159e91
TM
2289 nfs.max_session_slots=
2290 [NFSv4.1] Sets the maximum number of session slots
2291 the client will attempt to negotiate with the server.
2292 This limits the number of simultaneous RPC requests
2293 that the client can send to the NFSv4.1 server.
2294 Note that there is little point in setting this
2295 value higher than the max_tcp_slot_table_limit.
2296
b064eca2 2297 nfs.nfs4_disable_idmapping=
074b1d12
TM
2298 [NFSv4] When set to the default of '1', this option
2299 ensures that both the RPC level authentication
2300 scheme and the NFS level operations agree to use
2301 numeric uids/gids if the mount is using the
2302 'sec=sys' security flavour. In effect it is
2303 disabling idmapping, which can make migration from
2304 legacy NFSv2/v3 systems to NFSv4 easier.
2305 Servers that do not support this mode of operation
2306 will be autodetected by the client, and it will fall
2307 back to using the idmapper.
2308 To turn off this behaviour, set the value to '0'.
6f2ea7f2
CL
2309 nfs.nfs4_unique_id=
2310 [NFS4] Specify an additional fixed unique ident-
2311 ification string that NFSv4 clients can insert into
2312 their nfs_client_id4 string. This is typically a
2313 UUID that is generated at system install time.
b064eca2 2314
db8ac8ba
WAA
2315 nfs.send_implementation_id =
2316 [NFSv4.1] Send client implementation identification
2317 information in exchange_id requests.
2318 If zero, no implementation identification information
2319 will be sent.
2320 The default is to send the implementation identification
2321 information.
f6de7a39
TM
2322
2323 nfs.recover_lost_locks =
2324 [NFSv4] Attempt to recover locks that were lost due
2325 to a lease timeout on the server. Please note that
2326 doing this risks data corruption, since there are
2327 no guarantees that the file will remain unchanged
2328 after the locks are lost.
2329 If you want to enable the kernel legacy behaviour of
2330 attempting to recover these locks, then set this
2331 parameter to '1'.
2332 The default parameter value of '0' causes the kernel
2333 not to attempt recovery of lost locks.
db8ac8ba 2334
bbf58bf3
TM
2335 nfs4.layoutstats_timer =
2336 [NFSv4.2] Change the rate at which the kernel sends
2337 layoutstats to the pNFS metadata server.
2338
2339 Setting this to value to 0 causes the kernel to use
2340 whatever value is the default set by the layout
2341 driver. A non-zero value sets the minimum interval
2342 in seconds between layoutstats transmissions.
2343
e9541ce8
BF
2344 nfsd.nfs4_disable_idmapping=
2345 [NFSv4] When set to the default of '1', the NFSv4
2346 server will return only numeric uids and gids to
2347 clients using auth_sys, and will accept numeric uids
2348 and gids from such clients. This is intended to ease
2349 migration from NFSv2/v3.
db8ac8ba 2350
18d98f6c
SB
2351 objlayoutdriver.osd_login_prog=
2352 [NFS] [OBJLAYOUT] sets the pathname to the program which
2353 is used to automatically discover and login into new
2354 osd-targets. Please see:
2355 Documentation/filesystems/pnfs.txt for more explanations
2356
1e1030dc 2357 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
e7ba176b
HS
2358 when a NMI is triggered.
2359 Format: [state][,regs][,debounce][,die]
2360
6cececfc 2361 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
fef2c9bc 2362 Format: [panic,][nopanic,][num]
195daf66 2363 Valid num: 0 or 1
334bb79c
PK
2364 0 - turn hardlockup detector in nmi_watchdog off
2365 1 - turn hardlockup detector in nmi_watchdog on
0cb55ad2 2366 When panic is specified, panic when an NMI watchdog
fef2c9bc 2367 timeout occurs (or 'nopanic' to override the opposite
334bb79c
PK
2368 default). To disable both hard and soft lockup detectors,
2369 please see 'nowatchdog'.
0cb55ad2
RD
2370 This is useful when you use a panic=... timeout and
2371 need the box quickly up again.
1da177e4 2372
bff38771
AV
2373 netpoll.carrier_timeout=
2374 [NET] Specifies amount of time (in seconds) that
2375 netpoll should wait for a carrier. By default netpoll
2376 waits 4 seconds.
2377
cd4f0ef7 2378 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1da177e4
LT
2379 emulation library even if a 387 maths coprocessor
2380 is present.
2381
0cb55ad2
RD
2382 no_console_suspend
2383 [HW] Never suspend the console
2384 Disable suspending of consoles during suspend and
2385 hibernate operations. Once disabled, debugging
2386 messages can reach various consoles while the rest
2387 of the system is being put to sleep (ie, while
2388 debugging driver suspend/resume hooks). This may
2389 not work reliably with all consoles, but is known
2390 to work with serial and VGA consoles.
134620f7
YZ
2391 To facilitate more flexible debugging, we also add
2392 console_suspend, a printk module parameter to control
2393 it. Users could use console_suspend (usually
2394 /sys/module/printk/parameters/console_suspend) to
2395 turn on/off it dynamically.
0cb55ad2 2396
c1aee215
CL
2397 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2398 caches in the slab allocator. Saves per-node memory,
2399 but will impact performance.
3395ee05 2400
a9913044
RD
2401 noalign [KNL,ARM]
2402
1da177e4
LT
2403 noapic [SMP,APIC] Tells the kernel to not make use of any
2404 IOAPICs that may be present in the system.
2405
5091faa4
MG
2406 noautogroup Disable scheduler automatic task group creation.
2407
1da177e4
LT
2408 nobats [PPC] Do not use BATs for mapping kernel lowmem
2409 on "Classic" PPC cores.
2410
2411 nocache [ARM]
a9913044 2412
0cb55ad2
RD
2413 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2414
163ecdff
SN
2415 nodelayacct [KNL] Disable per-task delay accounting
2416
1da177e4
LT
2417 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2418
6902aa84
PM
2419 nodsp [SH] Disable hardware DSP at boot time.
2420
b2e0a54a 2421 noefi Disable EFI runtime services support.
8b2cb7a8 2422
1da177e4
LT
2423 noexec [IA-64]
2424
6cececfc 2425 noexec [X86]
f5a1b191 2426 On X86-32 available only on PAE configured kernels.
1da177e4 2427 noexec=on: enable non-executable mappings (default)
f5a1b191
JS
2428 noexec=off: disable non-executable mappings
2429
52b6179a
PA
2430 nosmap [X86]
2431 Disable SMAP (Supervisor Mode Access Prevention)
2432 even if it is supported by processor.
2433
de5397ad 2434 nosmep [X86]
52b6179a 2435 Disable SMEP (Supervisor Mode Execution Prevention)
de5397ad
FY
2436 even if it is supported by processor.
2437
f5a1b191
JS
2438 noexec32 [X86-64]
2439 This affects only 32-bit executables.
2440 noexec32=on: enable non-executable mappings (default)
2441 read doesn't imply executable mappings
2442 noexec32=off: disable non-executable mappings
2443 read implies executable mappings
1da177e4 2444
fab43ef4 2445 nofpu [MIPS,SH] Disable hardware FPU at boot time.
6902aa84 2446
cd4f0ef7 2447 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4f886511
CE
2448 register save and restore. The kernel will only save
2449 legacy floating-point registers on task switch.
1da177e4 2450
0ddab1d2
TK
2451 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2452
0c752a93
SS
2453 noxsave [BUGS=X86] Disables x86 extended register state save
2454 and restore using xsave. The kernel will fallback to
2455 enabling legacy floating-point and sse state.
2456
b6f42a4a
FY
2457 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2458 register states. The kernel will fall back to use
2459 xsave to save the states. By using this parameter,
2460 performance of saving the states is degraded because
2461 xsave doesn't support modified optimization while
2462 xsaveopt supports it on xsaveopt enabled systems.
2463
2464 noxsaves [X86] Disables xsaves and xrstors used in saving and
2465 restoring x86 extended register state in compacted
2466 form of xsave area. The kernel will fall back to use
2467 xsaveopt and xrstor to save and restore the states
2468 in standard form of xsave area. By using this
2469 parameter, xsave area per process might occupy more
2470 memory on xsaves enabled systems.
2471
01a24d2b
PZ
2472 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2473 wfi(ARM) instruction doesn't work correctly and not to
2474 use it. This is also useful when using JTAG debugger.
a9913044 2475
1f29fae2
SH
2476 no_file_caps Tells the kernel not to honor file capabilities. The
2477 only way then for a file to be executed with privilege
2478 is to be setuid root or executed by root.
2479
1da177e4
LT
2480 nohalt [IA-64] Tells the kernel not to use the power saving
2481 function PAL_HALT_LIGHT when idle. This increases
2482 power-consumption. On the positive side, it reduces
2483 interrupt wake-up latency, which may improve performance
2484 in certain environments such as networked servers or
2485 real-time systems.
2486
a6e15a39
KC
2487 nohibernate [HIBERNATION] Disable hibernation and resume.
2488
79bf2bb3
TG
2489 nohz= [KNL] Boottime enable/disable dynamic ticks
2490 Valid arguments: on, off
2491 Default: on
2492
c5bfece2
FW
2493 nohz_full= [KNL,BOOT]
2494 In kernels built with CONFIG_NO_HZ_FULL=y, set
a831881b 2495 the specified list of CPUs whose tick will be stopped
0453b435
FW
2496 whenever possible. The boot CPU will be forced outside
2497 the range to maintain the timekeeping.
d1e43fa5
FW
2498 The CPUs in this range must also be included in the
2499 rcu_nocbs= set.
a831881b 2500
eeee7853
PM
2501 noiotrap [SH] Disables trapped I/O port accesses.
2502
cd4f0ef7 2503 noirqdebug [X86-32] Disables the code which attempts to detect and
1da177e4
LT
2504 disable unhandled interrupt sources.
2505
6cececfc 2506 no_timer_check [X86,APIC] Disables the code which tests for
8542b200
ZA
2507 broken timer IRQ sources.
2508
1da177e4
LT
2509 noisapnp [ISAPNP] Disables ISA PnP code.
2510
2511 noinitrd [RAM] Tells the kernel not to load any configured
2512 initial RAM disk.
2513
03ea8155
WH
2514 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2515 remapping.
d1423d56 2516 [Deprecated - use intremap=off]
03ea8155 2517
1da177e4
LT
2518 nointroute [IA-64]
2519
16290246 2520 nojitter [IA-64] Disables jitter checking for ITC timers.
0aa366f3 2521
9cf4c4fc
JK
2522 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2523
fd10cde9
GN
2524 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2525 fault handling.
2526
d910f5c1
GC
2527 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2528 steal time is computed, but won't influence scheduler
2529 behaviour
2530
cd4f0ef7 2531 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1da177e4 2532
cd4f0ef7 2533 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
ad62ca2b 2534
1da177e4
LT
2535 noltlbs [PPC] Do not use large page/tlb entries for kernel
2536 lowmem mapping on PPC40x.
2537
312f1f01
H
2538 nomca [IA-64] Disable machine check abort handling
2539
13696e0a 2540 nomce [X86-32] Disable Machine Check Exception
abe37e5a 2541
83d7384f
AS
2542 nomfgpt [X86-32] Disable Multi-Function General Purpose
2543 Timer usage (for AMD Geode machines).
2544
bda62633
DZ
2545 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2546 shutdown the other cpus. Instead use the REBOOT_VECTOR
2547 irq.
2548
02608bef
DY
2549 nomodule Disable module load
2550
016ddd9b
JK
2551 nopat [X86] Disable PAT (page attribute table extension of
2552 pagetables) support.
2553
0cb55ad2
RD
2554 norandmaps Don't use address space randomization. Equivalent to
2555 echo 0 > /proc/sys/kernel/randomize_va_space
2556
bbff2168 2557 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
959b4fdf 2558
cd4f0ef7 2559 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
b7fb4af0
JF
2560 with UP alternatives
2561
7a5091d5
PA
2562 nordrand [X86] Disable kernel use of the RDRAND and
2563 RDSEED instructions even if they are supported
2564 by the processor. RDRAND and RDSEED are still
2565 available to user space applications.
49d859d7 2566
a9913044
RD
2567 noresume [SWSUSP] Disables resume and restores original swap
2568 space.
2569
1da177e4
LT
2570 no-scroll [VGA] Disables scrollback.
2571 This is required for the Braillex ib80-piezo Braille
2572 reader made by F.H. Papenmeier (Germany).
2573
2574 nosbagart [IA-64]
2575
cd4f0ef7 2576 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
4f886511 2577
61ec7567
LB
2578 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2579 and disable the IO APIC. legacy for "maxcpus=0".
1da177e4 2580
97842216
DJ
2581 nosoftlockup [KNL] Disable the soft-lockup detector.
2582
1da177e4
LT
2583 nosync [HW,M68K] Disables sync negotiation for all devices.
2584
cd4f0ef7 2585 notsc [BUGS=X86-32] Disable Time Stamp Counter
1da177e4
LT
2586
2587 nousb [USB] Disable the USB subsystem
2588
195daf66
UO
2589 nowatchdog [KNL] Disable both lockup detectors, i.e.
2590 soft-lockup and NMI watchdog (hard-lockup).
58687acb 2591
1da177e4 2592 nowb [ARM]
a9913044 2593
2b2fd87a
WH
2594 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2595
f78cff48
FY
2596 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2597 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2598 Some features depend on CPU0. Known dependencies are:
2599 1. Resume from suspend/hibernate depends on CPU0.
2600 Suspend/hibernate will fail if CPU0 is offline and you
2601 need to online CPU0 before suspend/hibernate.
2602 2. PIC interrupts also depend on CPU0. CPU0 can't be
2603 removed if a PIC interrupt is detected.
2604 It's said poweroff/reboot may depend on CPU0 on some
2605 machines although I haven't seen such issues so far
2606 after CPU0 is offline on a few tested machines.
2607 If the dependencies are under your control, you can
2608 turn on cpu0_hotplug.
2609
16290246 2610 nptcg= [IA-64] Override max number of concurrent global TLB
a6c75b86
FY
2611 purges which is reported from either PAL_VM_SUMMARY or
2612 SAL PALO.
2613
2b633e3f
YL
2614 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2615 could support. nr_cpus=n : n >= 1 limits the kernel to
2616 supporting 'n' processors. Later in runtime you can not
2617 use hotplug cpu feature to put more cpu back to online.
2618 just like you compile the kernel NR_CPUS=n
2619
0cb55ad2
RD
2620 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2621
1a687c2e
MG
2622 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2623 Allowed values are enable and disable
2624
f0c0b2b8
KH
2625 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2626 one of ['zone', 'node', 'default'] can be specified
2627 This can be set from sysctl after boot.
2628 See Documentation/sysctl/vm.txt for details.
2629
7c4be253
RD
2630 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2631 See Documentation/debugging-via-ohci1394.txt for more
2632 info.
2633
3ef0e1f8
AS
2634 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2635 Rather than timing out after 20 ms if an EC
2636 command is not properly ACKed, override the length
2637 of the timeout. We have interrupts disabled while
2638 waiting for the ACK, so if this is set too high
2639 interrupts *may* be lost!
2640
15ac7afe
TL
2641 omap_mux= [OMAP] Override bootloader pin multiplexing.
2642 Format: <mux_mode0.mode_name=value>...
2643 For example, to override I2C bus2:
2644 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2645
1da177e4
LT
2646 oprofile.timer= [HW]
2647 Use timer interrupt instead of performance counters
2648
7e4e0bd5
RR
2649 oprofile.cpu_type= Force an oprofile cpu type
2650 This might be useful if you have an older oprofile
2651 userland or if you want common events.
8d7ff4f2
RR
2652 Format: { arch_perfmon }
2653 arch_perfmon: [X86] Force use of architectural
7e4e0bd5
RR
2654 perfmon on Intel CPUs instead of the
2655 CPU specific event set.
159a80b2
RR
2656 timer: [X86] Force use of architectural NMI
2657 timer mode (see also oprofile.timer
2658 for generic hr timer mode)
dd3c4670
AK
2659 [s390] Force legacy basic mode sampling
2660 (report cpu_type "timer")
1dcdb5a9 2661
44a4dcf7
RD
2662 oops=panic Always panic on oopses. Default is to just kill the
2663 process, but there is a small probability of
2664 deadlocking the machine.
d404ab0a
OH
2665 This will also cause panics on machine check exceptions.
2666 Useful together with panic=30 to trigger a reboot.
2667
bcfde334
RD
2668 OSS [HW,OSS]
2669 See Documentation/sound/oss/oss-parameters.txt
2670
48c96a36
JK
2671 page_owner= [KNL] Boot-time page_owner enabling option.
2672 Storage of the information about who allocated
2673 each page is disabled in default. With this switch,
2674 we can turn it on.
2675 on: enable the feature
2676
44a4dcf7 2677 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4302fbc8
HD
2678 timeout > 0: seconds before rebooting
2679 timeout = 0: wait forever
2680 timeout < 0: reboot immediately
1da177e4
LT
2681 Format: <timeout>
2682
9e3961a0
PB
2683 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2684 on a WARN().
2685
f06e5153
MH
2686 crash_kexec_post_notifiers
2687 Run kdump after running panic-notifiers and dumping
2688 kmsg. This only for the users who doubt kdump always
2689 succeeds in any situation.
2690 Note that this also increases risks of kdump failure,
2691 because some panic notifiers can make the crashed
2692 kernel more unstable.
2693
1da177e4
LT
2694 parkbd.port= [HW] Parallel port number the keyboard adapter is
2695 connected to, default is 0.
2696 Format: <parport#>
2697 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2698 0 for XT, 1 for AT (default is AT).
a9913044
RD
2699 Format: <mode>
2700
2701 parport= [HW,PPT] Specify parallel ports. 0 disables.
2702 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2703 Use 'auto' to force the driver to use any
2704 IRQ/DMA settings detected (the default is to
2705 ignore detected IRQ/DMA settings because of
2706 possible conflicts). You can specify the base
2707 address, IRQ, and DMA settings; IRQ and DMA
2708 should be numbers, or 'auto' (for using detected
2709 settings on that particular port), or 'nofifo'
2710 (to avoid using a FIFO even if it is detected).
2711 Parallel ports are assigned in the order they
2712 are specified on the command line, starting
2713 with parport0.
2714
2715 parport_init_mode= [HW,PPT]
2716 Configure VIA parallel port to operate in
2717 a specific mode. This is necessary on Pegasos
2718 computer where firmware has no options for setting
2719 up parallel port mode and sets it to spp.
2720 Currently this function knows 686a and 8231 chips.
1da177e4
LT
2721 Format: [spp|ps2|epp|ecp|ecpepp]
2722
dd287796
AM
2723 pause_on_oops=
2724 Halt all CPUs after the first oops has been printed for
2725 the specified number of seconds. This is to be used if
2726 your oopses keep scrolling off the screen.
2727
1da177e4
LT
2728 pcbit= [HW,ISDN]
2729
2730 pcd. [PARIDE]
2731 See header of drivers/block/paride/pcd.c.
31c00fc1 2732 See also Documentation/blockdev/paride.txt.
1da177e4 2733
a9913044 2734 pci=option[,option...] [PCI] various PCI subsystem options:
1cc0ca26
BH
2735 earlydump [X86] dump PCI config space before the kernel
2736 changes anything
c0115606 2737 off [X86] don't probe for the PCI bus
cd4f0ef7 2738 bios [X86-32] force use of PCI BIOS, don't access
a9913044
RD
2739 the hardware directly. Use this if your machine
2740 has a non-standard PCI host bridge.
cd4f0ef7 2741 nobios [X86-32] disallow use of PCI BIOS, only direct
a9913044
RD
2742 hardware access methods are allowed. Use this
2743 if you experience crashes upon bootup and you
2744 suspect they are caused by the BIOS.
c0115606 2745 conf1 [X86] Force use of PCI Configuration
a9913044 2746 Mechanism 1.
c0115606 2747 conf2 [X86] Force use of PCI Configuration
a9913044 2748 Mechanism 2.
7f785763
RD
2749 noaer [PCIE] If the PCIEAER kernel config parameter is
2750 enabled, this kernel boot option can be used to
2751 disable the use of PCIE advanced error reporting.
32a2eea7
JG
2752 nodomains [PCI] Disable support for multiple PCI
2753 root domains (aka PCI segments, in ACPI-speak).
6cececfc 2754 nommconf [X86] Disable use of MMCONFIG for PCI
61be6d66 2755 Configuration
12983077
AH
2756 check_enable_amd_mmconf [X86] check for and enable
2757 properly configured MMIO access to PCI
2758 config space on AMD family 10h CPU
309e57df
MW
2759 nomsi [MSI] If the PCI_MSI kernel config parameter is
2760 enabled, this kernel boot option can be used to
2761 disable the use of MSI interrupts system-wide.
a9322f64
SA
2762 noioapicquirk [APIC] Disable all boot interrupt quirks.
2763 Safety option to keep boot IRQs enabled. This
2764 should never be necessary.
9197979b
SA
2765 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2766 primary IO-APIC for bridges that cannot disable
2767 boot IRQs. This fixes a source of spurious IRQs
2768 when the system masks IRQs.
41b9eb26
SA
2769 noioapicreroute [APIC] Disable workaround that uses the
2770 boot IRQ equivalent of an IRQ that connects to
2771 a chipset where boot IRQs cannot be disabled.
2772 The opposite of ioapicreroute.
cd4f0ef7 2773 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
a9913044
RD
2774 routing table. These calls are known to be buggy
2775 on several machines and they hang the machine
2776 when used, but on other computers it's the only
2777 way to get the interrupt routing table. Try
2778 this option if the kernel is unable to allocate
2779 IRQs or discover secondary PCI buses on your
2780 motherboard.
c0115606 2781 rom [X86] Assign address space to expansion ROMs.
a9913044
RD
2782 Use with caution as certain devices share
2783 address decoders between ROMs and other
2784 resources.
c0115606 2785 norom [X86] Do not assign address space to
bb71ad88
GH
2786 expansion ROMs that do not already have
2787 BIOS assigned address ranges.
7bd1c365
MH
2788 nobar [X86] Do not assign address space to the
2789 BARs that weren't assigned by the BIOS.
c0115606 2790 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
a9913044
RD
2791 assigned automatically to PCI devices. You can
2792 make the kernel exclude IRQs of your ISA cards
2793 this way.
c0115606 2794 pirqaddr=0xAAAAA [X86] Specify the physical address
a9913044
RD
2795 of the PIRQ table (normally generated
2796 by the BIOS) if it is outside the
2797 F0000h-100000h range.
c0115606 2798 lastbus=N [X86] Scan all buses thru bus #N. Can be
a9913044
RD
2799 useful if the kernel is unable to find your
2800 secondary buses and you want to tell it
2801 explicitly which ones they are.
c0115606 2802 assign-busses [X86] Always assign all PCI bus
a9913044
RD
2803 numbers ourselves, overriding
2804 whatever the firmware may have done.
c0115606 2805 usepirqmask [X86] Honor the possible IRQ mask stored
a9913044
RD
2806 in the BIOS $PIR table. This is needed on
2807 some systems with broken BIOSes, notably
2808 some HP Pavilion N5400 and Omnibook XE3
2809 notebooks. This will have no effect if ACPI
2810 IRQ routing is enabled.
c0115606 2811 noacpi [X86] Do not use ACPI for IRQ routing
a9913044 2812 or for PCI scanning.
7bc5e3f2
BH
2813 use_crs [X86] Use PCI host bridge window information
2814 from ACPI. On BIOSes from 2008 or later, this
2815 is enabled by default. If you need to use this,
2816 please report a bug.
2817 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2818 If you need to use this, please report a bug.
a9913044
RD
2819 routeirq Do IRQ routing for all PCI devices.
2820 This is normally done in pci_enable_device(),
2821 so this option is a temporary workaround
2822 for broken drivers that don't call it.
13a6ddb0
YL
2823 skip_isa_align [X86] do not align io start addr, so can
2824 handle more pci cards
a9913044
RD
2825 firmware [ARM] Do not re-enumerate the bus but instead
2826 just use the configuration from the
2827 bootloader. This is currently used on
2828 IXP2000 systems where the bus has to be
2829 configured a certain way for adjunct CPUs.
0637a70a
AK
2830 noearly [X86] Don't do any early type 1 scanning.
2831 This might help on some broken boards which
2832 machine check when some devices' config space
2833 is read. But various workarounds are disabled
2834 and some IOMMU drivers will not work.
6b4b78fe
MD
2835 bfsort Sort PCI devices into breadth-first order.
2836 This sorting is done to get a device
2837 order compatible with older (<= 2.4) kernels.
2838 nobfsort Don't sort PCI devices into breadth-first order.
fa238712
YW
2839 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2840 tuning and use the BIOS-configured MPS defaults.
2841 pcie_bus_safe Set every device's MPS to the largest value
2842 supported by all devices below the root complex.
2843 pcie_bus_perf Set device MPS to the largest allowable MPS
2844 based on its parent bus. Also set MRRS (Max
2845 Read Request Size) to the largest supported
2846 value (no larger than the MPS that the device
2847 or bus can support) for best performance.
2848 pcie_bus_peer2peer Set every device's MPS to 128B, which
2849 every device is guaranteed to support. This
2850 configuration allows peer-to-peer DMA between
2851 any pair of devices, possibly at the cost of
2852 reduced performance. This also guarantees
2853 that hot-added devices will work.
4516a618
AN
2854 cbiosize=nn[KMG] The fixed amount of bus space which is
2855 reserved for the CardBus bridge's IO window.
2856 The default value is 256 bytes.
2857 cbmemsize=nn[KMG] The fixed amount of bus space which is
2858 reserved for the CardBus bridge's memory
2859 window. The default value is 64 megabytes.
32a9a682
YS
2860 resource_alignment=
2861 Format:
2862 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2863 Specifies alignment and device to reassign
2864 aligned memory resources.
2865 If <order of align> is not specified,
2866 PAGE_SIZE is used as alignment.
2867 PCI-PCI bridge can be specified, if resource
2868 windows need to be expanded.
43c16408
AP
2869 ecrc= Enable/disable PCIe ECRC (transaction layer
2870 end-to-end CRC checking).
2871 bios: Use BIOS/firmware settings. This is the
2872 the default.
2873 off: Turn ECRC off
2874 on: Turn ECRC on.
8c8803c5
YW
2875 hpiosize=nn[KMG] The fixed amount of bus space which is
2876 reserved for hotplug bridge's IO window.
2877 Default size is 256 bytes.
2878 hpmemsize=nn[KMG] The fixed amount of bus space which is
2879 reserved for hotplug bridge's memory window.
2880 Default size is 2 megabytes.
b55438fd
YL
2881 realloc= Enable/disable reallocating PCI bridge resources
2882 if allocations done by BIOS are too small to
2883 accommodate resources required by all child
2884 devices.
2885 off: Turn realloc off
2886 on: Turn realloc on
2887 realloc same as realloc=on
6748dcc2 2888 noari do not use PCIe ARI.
284f5f9d
BH
2889 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2890 only look for one device below a PCIe downstream
2891 port.
6b4b78fe 2892
e5665a45
CE
2893 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2894 Management.
2895 off Disable ASPM.
2896 force Enable ASPM even on devices that claim not to support it.
2897 WARNING: Forcing ASPM on may cause system lockups.
2898
7570a333
MT
2899 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2900 nomsi Do not use MSI for PCI Express Native Hotplug (this
2901 makes all PCIe ports use INTx for hotplug services).
2902
79dd9182 2903 pcie_ports= [PCIE] PCIe ports handling:
28eb5f27
RW
2904 auto Ask the BIOS whether or not to use native PCIe services
2905 associated with PCIe ports (PME, hot-plug, AER). Use
2906 them only if that is allowed by the BIOS.
2907 native Use native PCIe services associated with PCIe ports
2908 unconditionally.
79dd9182
RW
2909 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2910 ports driver.
2911
c7f48656 2912 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
c39fae14 2913 nomsi Do not use MSI for native PCIe PME signaling (this makes
28eb5f27 2914 all PCIe root ports use INTx for all services).
c7f48656 2915
1da177e4
LT
2916 pcmv= [HW,PCMCIA] BadgePAD 4
2917
39ac5ba5
TB
2918 pd_ignore_unused
2919 [PM]
2920 Keep all power-domains already enabled by bootloader on,
2921 even if no driver has claimed them. This is useful
2922 for debug and development, but should not be
2923 needed on a platform with proper driver support.
2924
1da177e4 2925 pd. [PARIDE]
31c00fc1 2926 See Documentation/blockdev/paride.txt.
1da177e4
LT
2927
2928 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2929 boot time.
2930 Format: { 0 | 1 }
2931 See arch/parisc/kernel/pdc_chassis.c
2932
f58dc01b 2933 percpu_alloc= Select which percpu first chunk allocator to use.
e933a73f
TH
2934 Currently supported values are "embed" and "page".
2935 Archs may support subset or none of the selections.
2936 See comments in mm/percpu.c for details on each
2937 allocator. This parameter is primarily for debugging
2938 and performance comparison.
fa8a7094 2939
1da177e4 2940 pf. [PARIDE]
31c00fc1 2941 See Documentation/blockdev/paride.txt.
1da177e4
LT
2942
2943 pg. [PARIDE]
31c00fc1 2944 See Documentation/blockdev/paride.txt.
1da177e4
LT
2945
2946 pirq= [SMP,APIC] Manual mp-table setup
71cced6e 2947 See Documentation/x86/i386/IO-APIC.txt.
1da177e4
LT
2948
2949 plip= [PPT,NET] Parallel port network link
2950 Format: { parport<nr> | timid | 0 }
2951 See also Documentation/parport.txt.
2952
16290246 2953 pmtmr= [X86] Manual setup of pmtmr I/O Port.
de32a243
TG
2954 Override pmtimer IOPort with a hex value.
2955 e.g. pmtmr=0x508
2956
96242116
BH
2957 pnp.debug=1 [PNP]
2958 Enable PNP debug messages (depends on the
2959 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2960 via /sys/module/pnp/parameters/debug. We always show
2961 current resource usage; turning this on also shows
2962 possible settings and some assignment information.
97ef062b 2963
1da177e4
LT
2964 pnpacpi= [ACPI]
2965 { off }
2966
2967 pnpbios= [ISAPNP]
2968 { on | off | curr | res | no-curr | no-res }
2969
2970 pnp_reserve_irq=
2971 [ISAPNP] Exclude IRQs for the autoconfiguration
2972
2973 pnp_reserve_dma=
2974 [ISAPNP] Exclude DMAs for the autoconfiguration
2975
2976 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
a9913044 2977 Ranges are in pairs (I/O port base and size).
1da177e4
LT
2978
2979 pnp_reserve_mem=
a9913044
RD
2980 [ISAPNP] Exclude memory regions for the
2981 autoconfiguration.
1da177e4
LT
2982 Ranges are in pairs (memory base and size).
2983
4af94f39
RD
2984 ports= [IP_VS_FTP] IPVS ftp helper module
2985 Default is 21.
2986 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2987 may be specified.
2988 Format: <port>,<port>....
2989
45807a1d
IM
2990 print-fatal-signals=
2991 [KNL] debug: print fatal signals
f84d49b2
NO
2992
2993 If enabled, warn about various signal handling
2994 related application anomalies: too many signals,
2995 too many POSIX.1 timers, fatal signals causing a
2996 coredump - etc.
2997
2998 If you hit the warning due to signal overflow,
2999 you might want to try "ulimit -i unlimited".
3000
45807a1d
IM
3001 default: off.
3002
c22ab332
MG
3003 printk.always_kmsg_dump=
3004 Trigger kmsg_dump for cases other than kernel oops or
3005 panics
3006 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3007 default: disabled
3008
e84845c4
RD
3009 printk.time= Show timing data prefixed to each printk message line
3010 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3011
0cb55ad2
RD
3012 processor.max_cstate= [HW,ACPI]
3013 Limit processor to maximum C-state
3014 max_cstate=9 overrides any DMI blacklist limit.
3015
3016 processor.nocst [HW,ACPI]
3017 Ignore the _CST method to determine C-states,
3018 instead using the legacy FADT method
3019
1da177e4 3020 profile= [KNL] Enable kernel profiling via /proc/profile
a9913044
RD
3021 Format: [schedule,]<number>
3022 Param: "schedule" - profile schedule points.
3023 Param: <number> - step/bucket size as a power of 2 for
3024 statistical time based profiling.
b3da2a73
MG
3025 Param: "sleep" - profile D-state sleeping (millisecs).
3026 Requires CONFIG_SCHEDSTATS
c0fe2e69 3027 Param: "kvm" - profile VM exits.
1da177e4 3028
1da177e4
LT
3029 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3030 before loading.
31c00fc1 3031 See Documentation/blockdev/ramdisk.txt.
1da177e4 3032
a9913044
RD
3033 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3034 probe for; one of (bare|imps|exps|lifebook|any).
1da177e4
LT
3035 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3036 per second.
a9913044
RD
3037 psmouse.resetafter= [HW,MOUSE]
3038 Try to reset the device after so many bad packets
1da177e4
LT
3039 (0 = never).
3040 psmouse.resolution=
3041 [HW,MOUSE] Set desired mouse resolution, in dpi.
3042 psmouse.smartscroll=
a9913044 3043 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1da177e4
LT
3044 0 = disabled, 1 = enabled (default).
3045
dee28e72
MG
3046 pstore.backend= Specify the name of the pstore backend to use
3047
1da177e4 3048 pt. [PARIDE]
31c00fc1 3049 See Documentation/blockdev/paride.txt.
1da177e4 3050
dc8c8587
KS
3051 pty.legacy_count=
3052 [KNL] Number of legacy pty's. Overwrites compiled-in
3053 default number.
3054
7d2c502f 3055 quiet [KNL] Disable most log messages
a9913044 3056
1da177e4
LT
3057 r128= [HW,DRM]
3058
3059 raid= [HW,RAID]
3060 See Documentation/md.txt.
3061
a9913044 3062 ramdisk_blocksize= [RAM]
31c00fc1 3063 See Documentation/blockdev/ramdisk.txt.
a9913044 3064
1da177e4 3065 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
31c00fc1 3066 See Documentation/blockdev/ramdisk.txt.
1da177e4 3067
4102adab 3068 rcu_nocbs= [KNL]
3fbfbf7a
PM
3069 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3070 the specified list of CPUs to be no-callback CPUs.
3071 Invocation of these CPUs' RCU callbacks will
a4889858
PM
3072 be offloaded to "rcuox/N" kthreads created for
3073 that purpose, where "x" is "b" for RCU-bh, "p"
3074 for RCU-preempt, and "s" for RCU-sched, and "N"
3075 is the CPU number. This reduces OS jitter on the
3fbfbf7a
PM
3076 offloaded CPUs, which can be useful for HPC and
3077 real-time workloads. It can also improve energy
3078 efficiency for asymmetric multiprocessors.
3079
4102adab 3080 rcu_nocb_poll [KNL]
3fbfbf7a
PM
3081 Rather than requiring that offloaded CPUs
3082 (specified by rcu_nocbs= above) explicitly
3083 awaken the corresponding "rcuoN" kthreads,
3084 make these kthreads poll for callbacks.
3085 This improves the real-time response for the
3086 offloaded CPUs by relieving them of the need to
3087 wake up the corresponding kthread, but degrades
3088 energy efficiency by requiring that the kthreads
3089 periodically wake up to do the polling.
3090
4102adab 3091 rcutree.blimit= [KNL]
97e63f0c
PM
3092 Set maximum number of finished RCU callbacks to
3093 process in one batch.
21a1ea9e 3094
a3dc2948
PM
3095 rcutree.dump_tree= [KNL]
3096 Dump the structure of the rcu_node combining tree
3097 out at early boot. This is used for diagnostic
3098 purposes, to verify correct tree setup.
3099
0f41c0dd
PM
3100 rcutree.gp_cleanup_delay= [KNL]
3101 Set the number of jiffies to delay each step of
3102 RCU grace-period cleanup. This only has effect
3103 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3104
37745d28
PM
3105 rcutree.gp_init_delay= [KNL]
3106 Set the number of jiffies to delay each step of
3107 RCU grace-period initialization. This only has
0f41c0dd
PM
3108 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3109 is set.
3110
3111 rcutree.gp_preinit_delay= [KNL]
3112 Set the number of jiffies to delay each step of
3113 RCU grace-period pre-initialization, that is,
3114 the propagation of recent CPU-hotplug changes up
3115 the rcu_node combining tree. This only has effect
3116 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
37745d28 3117
7fa27001
PM
3118 rcutree.rcu_fanout_exact= [KNL]
3119 Disable autobalancing of the rcu_node combining
3120 tree. This is used by rcutorture, and might
3121 possibly be useful for architectures having high
3122 cache-to-cache transfer latencies.
37745d28 3123
4102adab 3124 rcutree.rcu_fanout_leaf= [KNL]
ee968ac6
PM
3125 Change the number of CPUs assigned to each
3126 leaf rcu_node structure. Useful for very
3127 large systems, which will choose the value 64,
3128 and for NUMA systems with large remote-access
3129 latencies, which will choose a value aligned
3130 with the appropriate hardware boundaries.
f885b7f2 3131
4a81e832
PM
3132 rcutree.jiffies_till_sched_qs= [KNL]
3133 Set required age in jiffies for a
3134 given grace period before RCU starts
3135 soliciting quiescent-state help from
3136 rcu_note_context_switch().
3137
4102adab 3138 rcutree.jiffies_till_first_fqs= [KNL]
c0f4dfd4
PM
3139 Set delay from grace-period initialization to
3140 first attempt to force quiescent states.
3141 Units are jiffies, minimum value is zero,
3142 and maximum value is HZ.
3143
4102adab 3144 rcutree.jiffies_till_next_fqs= [KNL]
c0f4dfd4
PM
3145 Set delay between subsequent attempts to force
3146 quiescent states. Units are jiffies, minimum
3147 value is one, and maximum value is HZ.
3148
21871d7e 3149 rcutree.kthread_prio= [KNL,BOOT]
d2af1ad7
PM
3150 Set the SCHED_FIFO priority of the RCU per-CPU
3151 kthreads (rcuc/N). This value is also used for
3152 the priority of the RCU boost threads (rcub/N)
3153 and for the RCU grace-period kthreads (rcu_bh,
3154 rcu_preempt, and rcu_sched). If RCU_BOOST is
3155 set, valid values are 1-99 and the default is 1
3156 (the least-favored priority). Otherwise, when
3157 RCU_BOOST is not set, valid values are 0-99 and
3158 the default is zero (non-realtime operation).
21871d7e 3159
fbce7497
PM
3160 rcutree.rcu_nocb_leader_stride= [KNL]
3161 Set the number of NOCB kthread groups, which
3162 defaults to the square root of the number of
3163 CPUs. Larger numbers reduces the wakeup overhead
3164 on the per-CPU grace-period kthreads, but increases
3165 that same overhead on each group's leader.
3166
4102adab 3167 rcutree.qhimark= [KNL]
97e63f0c
PM
3168 Set threshold of queued RCU callbacks beyond which
3169 batch limiting is disabled.
21a1ea9e 3170
4102adab 3171 rcutree.qlowmark= [KNL]
24aaef8d
RD
3172 Set threshold of queued RCU callbacks below which
3173 batch limiting is re-enabled.
21a1ea9e 3174
4102adab 3175 rcutree.rcu_idle_gp_delay= [KNL]
c0f4dfd4
PM
3176 Set wakeup interval for idle CPUs that have
3177 RCU callbacks (RCU_FAST_NO_HZ=y).
d40011f6 3178
4102adab 3179 rcutree.rcu_idle_lazy_gp_delay= [KNL]
c0f4dfd4
PM
3180 Set wakeup interval for idle CPUs that have
3181 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3182 Lazy RCU callbacks are those which RCU can
3183 prove do nothing more than free memory.
d40011f6 3184
38706bc5
PM
3185 rcutorture.cbflood_inter_holdoff= [KNL]
3186 Set holdoff time (jiffies) between successive
3187 callback-flood tests.
3188
3189 rcutorture.cbflood_intra_holdoff= [KNL]
3190 Set holdoff time (jiffies) between successive
3191 bursts of callbacks within a given callback-flood
3192 test.
3193
3194 rcutorture.cbflood_n_burst= [KNL]
3195 Set the number of bursts making up a given
3196 callback-flood test. Set this to zero to
3197 disable callback-flood testing.
3198
3199 rcutorture.cbflood_n_per_burst= [KNL]
3200 Set the number of callbacks to be registered
3201 in a given burst of a callback-flood test.
3202
4102adab 3203 rcutorture.fqs_duration= [KNL]
21b05de4
PM
3204 Set duration of force_quiescent_state bursts
3205 in microseconds.
dabb8aa9 3206
4102adab 3207 rcutorture.fqs_holdoff= [KNL]
21b05de4
PM
3208 Set holdoff time within force_quiescent_state bursts
3209 in microseconds.
dabb8aa9 3210
4102adab 3211 rcutorture.fqs_stutter= [KNL]
21b05de4
PM
3212 Set wait time between force_quiescent_state bursts
3213 in seconds.
3214
3215 rcutorture.gp_cond= [KNL]
3216 Use conditional/asynchronous update-side
3217 primitives, if available.
dabb8aa9 3218
4102adab 3219 rcutorture.gp_exp= [KNL]
21b05de4 3220 Use expedited update-side primitives, if available.
4102adab
PM
3221
3222 rcutorture.gp_normal= [KNL]
21b05de4
PM
3223 Use normal (non-expedited) asynchronous
3224 update-side primitives, if available.
3225
3226 rcutorture.gp_sync= [KNL]
3227 Use normal (non-expedited) synchronous
3228 update-side primitives, if available. If all
3229 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3230 rcutorture.gp_normal=, and rcutorture.gp_sync=
3231 are zero, rcutorture acts as if is interpreted
3232 they are all non-zero.
dabb8aa9 3233
4102adab 3234 rcutorture.n_barrier_cbs= [KNL]
dabb8aa9
PM
3235 Set callbacks/threads for rcu_barrier() testing.
3236
4102adab 3237 rcutorture.nfakewriters= [KNL]
dabb8aa9
PM
3238 Set number of concurrent RCU writers. These just
3239 stress RCU, they don't participate in the actual
3240 test, hence the "fake".
3241
4102adab 3242 rcutorture.nreaders= [KNL]
3838cc18
PM
3243 Set number of RCU readers. The value -1 selects
3244 N-1, where N is the number of CPUs. A value
3245 "n" less than -1 selects N-n-2, where N is again
3246 the number of CPUs. For example, -2 selects N
3247 (the number of CPUs), -3 selects N+1, and so on.
dabb8aa9 3248
4102adab
PM
3249 rcutorture.object_debug= [KNL]
3250 Enable debug-object double-call_rcu() testing.
3251
3252 rcutorture.onoff_holdoff= [KNL]
dabb8aa9
PM
3253 Set time (s) after boot for CPU-hotplug testing.
3254
4102adab 3255 rcutorture.onoff_interval= [KNL]
dabb8aa9
PM
3256 Set time (s) between CPU-hotplug operations, or
3257 zero to disable CPU-hotplug testing.
3258
4102adab 3259 rcutorture.shuffle_interval= [KNL]
dabb8aa9
PM
3260 Set task-shuffle interval (s). Shuffling tasks
3261 allows some CPUs to go into dyntick-idle mode
3262 during the rcutorture test.
3263
4102adab 3264 rcutorture.shutdown_secs= [KNL]
dabb8aa9
PM
3265 Set time (s) after boot system shutdown. This
3266 is useful for hands-off automated testing.
3267
4102adab 3268 rcutorture.stall_cpu= [KNL]
dabb8aa9
PM
3269 Duration of CPU stall (s) to test RCU CPU stall
3270 warnings, zero to disable.
3271
4102adab 3272 rcutorture.stall_cpu_holdoff= [KNL]
dabb8aa9
PM
3273 Time to wait (s) after boot before inducing stall.
3274
4102adab 3275 rcutorture.stat_interval= [KNL]
dabb8aa9
PM
3276 Time (s) between statistics printk()s.
3277
4102adab 3278 rcutorture.stutter= [KNL]
dabb8aa9
PM
3279 Time (s) to stutter testing, for example, specifying
3280 five seconds causes the test to run for five seconds,
3281 wait for five seconds, and so on. This tests RCU's
3282 ability to transition abruptly to and from idle.
3283
4102adab 3284 rcutorture.test_boost= [KNL]
dabb8aa9
PM
3285 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3286 "Maybe" means test if the RCU implementation
3287 under test support RCU priority boosting.
3288
4102adab 3289 rcutorture.test_boost_duration= [KNL]
dabb8aa9
PM
3290 Duration (s) of each individual boost test.
3291
4102adab 3292 rcutorture.test_boost_interval= [KNL]
dabb8aa9
PM
3293 Interval (s) between each boost test.
3294
4102adab 3295 rcutorture.test_no_idle_hz= [KNL]
dabb8aa9
PM
3296 Test RCU's dyntick-idle handling. See also the
3297 rcutorture.shuffle_interval parameter.
3298
21b05de4
PM
3299 rcutorture.torture_runnable= [BOOT]
3300 Start rcutorture running at boot time.
3301
4102adab 3302 rcutorture.torture_type= [KNL]
dabb8aa9
PM
3303 Specify the RCU implementation to test.
3304
4102adab 3305 rcutorture.verbose= [KNL]
dabb8aa9
PM
3306 Enable additional printk() statements.
3307
5a9be7c6
PM
3308 rcupdate.rcu_cpu_stall_suppress= [KNL]
3309 Suppress RCU CPU stall warning messages.
3310
3311 rcupdate.rcu_cpu_stall_timeout= [KNL]
3312 Set timeout for RCU CPU stall warning messages.
3313
4102adab
PM
3314 rcupdate.rcu_expedited= [KNL]
3315 Use expedited grace-period primitives, for
3316 example, synchronize_rcu_expedited() instead
3317 of synchronize_rcu(). This reduces latency,
3318 but can increase CPU utilization, degrade
3319 real-time latency, and degrade energy efficiency.
79cfea02 3320 No effect on CONFIG_TINY_RCU kernels.
4102adab 3321
5a9be7c6
PM
3322 rcupdate.rcu_normal= [KNL]
3323 Use only normal grace-period primitives,
3324 for example, synchronize_rcu() instead of
3325 synchronize_rcu_expedited(). This improves
79cfea02
PM
3326 real-time latency, CPU utilization, and
3327 energy efficiency, but can expose users to
3328 increased grace-period latency. This parameter
3329 overrides rcupdate.rcu_expedited. No effect on
3330 CONFIG_TINY_RCU kernels.
4102adab 3331
3e42ec1a
PM
3332 rcupdate.rcu_normal_after_boot= [KNL]
3333 Once boot has completed (that is, after
3334 rcu_end_inkernel_boot() has been invoked), use
79cfea02
PM
3335 only normal grace-period primitives. No effect
3336 on CONFIG_TINY_RCU kernels.
3e42ec1a 3337
52db30ab
PM
3338 rcupdate.rcu_task_stall_timeout= [KNL]
3339 Set timeout in jiffies for RCU task stall warning
3340 messages. Disable with a value less than or equal
3341 to zero.
3342
74860fee
PK
3343 rcupdate.rcu_self_test= [KNL]
3344 Run the RCU early boot self tests
3345
3346 rcupdate.rcu_self_test_bh= [KNL]
3347 Run the RCU bh early boot self tests
3348
3349 rcupdate.rcu_self_test_sched= [KNL]
3350 Run the RCU sched early boot self tests
3351
ffdfc409
OJ
3352 rdinit= [KNL]
3353 Format: <full_path>
3354 Run specified binary instead of /init from the ramdisk,
3355 used for early userspace startup. See initrd.
3356
1b3a5d02
RH
3357 reboot= [KNL]
3358 Format (x86 or x86_64):
3359 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3360 [[,]s[mp]#### \
3361 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3362 [[,]f[orce]
3363 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3364 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3365 reboot_force is either force or not specified,
3366 reboot_cpu is s[mp]#### with #### being the processor
3367 to be used for rebooting.
1da177e4 3368
46b6d94e
PJ
3369 relax_domain_level=
3370 [KNL, SMP] Set scheduler's default relax_domain_level.
21acb9ca 3371 See Documentation/cgroups/cpusets.txt.
46b6d94e 3372
0399d4db
RW
3373 relative_sleep_states=
3374 [SUSPEND] Use sleep state labeling where the deepest
3375 state available other than hibernation is always "mem".
3376 Format: { "0" | "1" }
3377 0 -- Traditional sleep state labels.
3378 1 -- Relative sleep state labels.
3379
1da177e4
LT
3380 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3381
cd4f0ef7 3382 reservetop= [X86-32]
461a9aff
ZA
3383 Format: nn[KMG]
3384 Reserves a hole at the top of the kernel virtual
3385 address space.
3386
9ea77bdb
PA
3387 reservelow= [X86]
3388 Format: nn[K]
3389 Set the amount of memory to reserve for BIOS at
3390 the bottom of the address space.
3391
7e96287d
VG
3392 reset_devices [KNL] Force drivers to reset the underlying device
3393 during initialization.
3394
a9913044
RD
3395 resume= [SWSUSP]
3396 Specify the partition device for software suspend
2df83fa4
MB
3397 Format:
3398 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
1da177e4 3399
ecbd0da1
RW
3400 resume_offset= [SWSUSP]
3401 Specify the offset from the beginning of the partition
3402 given by "resume=" at which the swap header is located,
3403 in <PAGE_SIZE> units (needed only for swap files).
3404 See Documentation/power/swsusp-and-swap-files.txt
3405
f126f733
BS
3406 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3407 read the resume files
3408
6f8d7022
BS
3409 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3410 Useful for devices that are detected asynchronously
3411 (e.g. USB and MMC devices).
3412
f996fc96
BS
3413 hibernate= [HIBERNATION]
3414 noresume Don't check if there's a hibernation image
3415 present during boot.
3416 nocompress Don't compress/decompress hibernation images.
a6e15a39 3417 no Disable hibernation and resume.
f996fc96 3418
0a7b35cb
MN
3419 retain_initrd [RAM] Keep initrd memory after extraction
3420
0efbb786
AC
3421 rfkill.default_state=
3422 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3423 etc. communication is blocked by default.
3424 1 Unblocked.
3425
3426 rfkill.master_switch_mode=
3427 0 The "airplane mode" button does nothing.
3428 1 The "airplane mode" button toggles between everything
3429 blocked and the previous configuration.
3430 2 The "airplane mode" button toggles between everything
3431 blocked and everything unblocked.
3432
1da177e4
LT
3433 rhash_entries= [KNL,NET]
3434 Set number of hash buckets for route cache
3435
1da177e4
LT
3436 ro [KNL] Mount root device read-only on boot
3437
3438 root= [KNL] Root filesystem
f2d34fd9 3439 See name_to_dev_t comment in init/do_mounts.c.
1da177e4
LT
3440
3441 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3442 mount the root filesystem
3443
3444 rootflags= [KNL] Set root filesystem mount option string
3445
3446 rootfstype= [KNL] Set root filesystem type
3447
cc1ed754
PO
3448 rootwait [KNL] Wait (indefinitely) for root device to show up.
3449 Useful for devices that are detected asynchronously
3450 (e.g. USB and MMC devices).
3451
5c71d618
RT
3452 rproc_mem=nn[KMG][@address]
3453 [KNL,ARM,CMA] Remoteproc physical memory block.
3454 Memory area to be used by remote processor image,
3455 managed by CMA.
3456
1da177e4
LT
3457 rw [KNL] Mount root device read-write on boot
3458
3459 S [KNL] Run init in single mode
3460
c60d1ae4
GS
3461 s390_iommu= [HW,S390]
3462 Set s390 IOTLB flushing mode
3463 strict
3464 With strict flushing every unmap operation will result in
3465 an IOTLB flush. Default is lazy flushing before reuse,
3466 which is faster.
3467
1da177e4
LT
3468 sa1100ir [NET]
3469 See drivers/net/irda/sa1100_ir.c.
3470
1da177e4 3471 sbni= [NET] Granch SBNI12 leased line adapter
a9913044 3472
f6630114
MT
3473 sched_debug [KNL] Enables verbose scheduler debug messages.
3474
5307c955
MG
3475 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3476 xtime_lock contention on larger systems, and/or RCU lock
3477 contention on all systems with CONFIG_MAXSMP set.
3478 Format: { "0" | "1" }
3479 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3480 1 -- enable.
3481 Note: increases power consumption, thus should only be
3482 enabled if running jitter sensitive (HPC/RT) workloads.
3483
0cb55ad2
RD
3484 security= [SECURITY] Choose a security module to enable at boot.
3485 If this boot parameter is not specified, only the first
3486 security module asking for security registration will be
3487 loaded. An invalid security module name will be treated
3488 as if no module has been chosen.
3489
3490 selinux= [SELINUX] Disable or enable SELinux at boot time.
1da177e4
LT
3491 Format: { "0" | "1" }
3492 See security/selinux/Kconfig help text.
3493 0 -- disable.
3494 1 -- enable.
3495 Default value is set via kernel config option.
3496 If enabled at boot time, /selinux/disable can be used
3497 later to disable prior to initial policy load.
3498
c1c124e9
JJ
3499 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3500 Format: { "0" | "1" }
3501 See security/apparmor/Kconfig help text
3502 0 -- disable.
3503 1 -- enable.
3504 Default value is set via kernel config option.
3505
cd4f0ef7 3506 serialnumber [BUGS=X86-32]
1da177e4 3507
1da177e4
LT
3508 shapers= [NET]
3509 Maximal number of shapers.
a9913044 3510
b05f78f5
YL
3511 show_msr= [x86] show boot-time MSR settings
3512 Format: { <integer> }
3513 Show boot-time (BIOS-initialized) MSR settings.
3514 The parameter means the number of CPUs to show,
3515 for example 1 means boot CPU only.
3516
1da177e4
LT
3517 simeth= [IA-64]
3518 simscsi=
a9913044 3519
1da177e4
LT
3520 slram= [HW,MTD]
3521
423c929c
JK
3522 slab_nomerge [MM]
3523 Disable merging of slabs with similar size. May be
3524 necessary if there is some reason to distinguish
3525 allocs to different slabs. Debug options disable
3526 merging on their own.
3527 For more information see Documentation/vm/slub.txt.
3528
3df1cccd
DR
3529 slab_max_order= [MM, SLAB]
3530 Determines the maximum allowed order for slabs.
3531 A high setting may cause OOMs due to memory
3532 fragmentation. Defaults to 1 for systems with
3533 more than 32MB of RAM, 0 otherwise.
3534
f0630fff
CL
3535 slub_debug[=options[,slabs]] [MM, SLUB]
3536 Enabling slub_debug allows one to determine the
3537 culprit if slab objects become corrupted. Enabling
3538 slub_debug can create guard zones around objects and
3539 may poison objects when not in use. Also tracks the
3540 last alloc / free. For more information see
3541 Documentation/vm/slub.txt.
c1aee215
CL
3542
3543 slub_max_order= [MM, SLUB]
f0630fff
CL
3544 Determines the maximum allowed order for slabs.
3545 A high setting may cause OOMs due to memory
3546 fragmentation. For more information see
3547 Documentation/vm/slub.txt.
c1aee215
CL
3548
3549 slub_min_objects= [MM, SLUB]
f0630fff
CL
3550 The minimum number of objects per slab. SLUB will
3551 increase the slab order up to slub_max_order to
3552 generate a sufficiently large slab able to contain
3553 the number of objects indicated. The higher the number
3554 of objects the smaller the overhead of tracking slabs
3555 and the less frequently locks need to be acquired.
c1aee215
CL
3556 For more information see Documentation/vm/slub.txt.
3557
3558 slub_min_order= [MM, SLUB]
24775d65 3559 Determines the minimum page order for slabs. Must be
f0630fff 3560 lower than slub_max_order.
c1aee215
CL
3561 For more information see Documentation/vm/slub.txt.
3562
3563 slub_nomerge [MM, SLUB]
423c929c
JK
3564 Same with slab_nomerge. This is supported for legacy.
3565 See slab_nomerge for more information.
c1aee215 3566
1da177e4
LT
3567 smart2= [HW]
3568 Format: <io1>[,<io2>[,...,<io8>]]
3569
d0d4f69b
BH
3570 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3571 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3572 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3573 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3574 smsc-ircc2.ircc_irq= [HW] IRQ line
3575 smsc-ircc2.ircc_dma= [HW] DMA channel
3576 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3577 0: Toshiba Satellite 1800 (GP data pin select)
3578 1: Fast pin select (default)
3579 2: ATC IRMode
3580
9c44bc03
IM
3581 softlockup_panic=
3582 [KNL] Should the soft-lockup detector generate panics.
44a4dcf7 3583 Format: <integer>
9c44bc03 3584
ed235875
AT
3585 softlockup_all_cpu_backtrace=
3586 [KNL] Should the soft-lockup detector generate
3587 backtraces on all cpus.
3588 Format: <integer>
3589
1da177e4 3590 sonypi.*= [HW] Sony Programmable I/O Control Device driver
395cf969 3591 See Documentation/laptops/sonypi.txt
1da177e4 3592
1da177e4
LT
3593 spia_io_base= [HW,MTD]
3594 spia_fio_base=
3595 spia_pedr=
3596 spia_peddr=
3597
f38f1d2a
SR
3598 stacktrace [FTRACE]
3599 Enabled the stack tracer on boot up.
3600
762e1207
SR
3601 stacktrace_filter=[function-list]
3602 [FTRACE] Limit the functions that the stack tracer
3603 will trace at boot up. function-list is a comma separated
3604 list of functions. This list can be changed at run
3605 time by the stack_trace_filter file in the debugfs
3606 tracing directory. Note, this enables stack tracing
3607 and the stacktrace above is not needed.
3608
1da177e4
LT
3609 sti= [PARISC,HW]
3610 Format: <num>
3611 Set the STI (builtin display/keyboard on the HP-PARISC
3612 machines) console (graphic card) which should be used
3613 as the initial boot-console.
3614 See also comment in drivers/video/console/sticore.c.
3615
3616 sti_font= [HW]
3617 See comment in drivers/video/console/sticore.c.
3618
3619 stifb= [HW]
3620 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3621
cbf11071
TM
3622 sunrpc.min_resvport=
3623 sunrpc.max_resvport=
3624 [NFS,SUNRPC]
3625 SunRPC servers often require that client requests
3626 originate from a privileged port (i.e. a port in the
3627 range 0 < portnr < 1024).
3628 An administrator who wishes to reserve some of these
3629 ports for other uses may adjust the range that the
3630 kernel's sunrpc client considers to be privileged
3631 using these two parameters to set the minimum and
3632 maximum port values.
3633
42a7fc4a
GB
3634 sunrpc.pool_mode=
3635 [NFS]
3636 Control how the NFS server code allocates CPUs to
3637 service thread pools. Depending on how many NICs
3638 you have and where their interrupts are bound, this
3639 option will affect which CPUs will do NFS serving.
3640 Note: this parameter cannot be changed while the
3641 NFS server is running.
3642
3643 auto the server chooses an appropriate mode
3644 automatically using heuristics
3645 global a single global pool contains all CPUs
3646 percpu one pool for each CPU
3647 pernode one pool for each NUMA node (equivalent
3648 to global on non-NUMA machines)
3649
cbf11071
TM
3650 sunrpc.tcp_slot_table_entries=
3651 sunrpc.udp_slot_table_entries=
3652 [NFS,SUNRPC]
3653 Sets the upper limit on the number of simultaneous
3654 RPC calls that can be sent from the client to a
3655 server. Increasing these values may allow you to
3656 improve throughput, but will also increase the
3657 amount of memory reserved for use by the client.
3658
1d4a9c17
BN
3659 suspend.pm_test_delay=
3660 [SUSPEND]
3661 Sets the number of seconds to remain in a suspend test
3662 mode before resuming the system (see
3663 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3664 is set. Default value is 5.
3665
07555ac1 3666 swapaccount=[0|1]
a42c390c
MH
3667 [KNL] Enable accounting of swap in memory resource
3668 controller if no parameter or 1 is given or disable
3669 it if 0 is given (See Documentation/cgroups/memory.txt)
3670
91fec0f5
JK
3671 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3672 Format: { <int> | force }
3673 <int> -- Number of I/O TLB slabs
3674 force -- force using of bounce buffers even if they
3675 wouldn't be automatically used by the kernel
a9913044 3676
1da177e4
LT
3677 switches= [HW,M68k]
3678
e52eec13
AK
3679 sysfs.deprecated=0|1 [KNL]
3680 Enable/disable old style sysfs layout for old udev
3681 on older distributions. When this option is enabled
3682 very new udev will not work anymore. When this option
3683 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3684 in older udev will not work anymore.
3685 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3686 the kernel configuration.
3687
5d6f647f
IM
3688 sysrq_always_enabled
3689 [KNL]
3690 Ignore sysrq setting - this boot parameter will
3691 neutralize any effect of /proc/sys/kernel/sysrq.
3692 Useful for debugging.
3693
747029a5
FF
3694 tcpmhash_entries= [KNL,NET]
3695 Set the number of tcp_metrics_hash slots.
3696 Default value is 8192 or 16384 depending on total
3697 ram pages. This is used to specify the TCP metrics
3698 cache size. See Documentation/networking/ip-sysctl.txt
3699 "tcp_no_metrics_save" section for more details.
3700
1da177e4
LT
3701 tdfx= [HW,DRM]
3702
acc82342 3703 test_suspend= [SUSPEND][,N]
77437fd4 3704 Specify "mem" (for Suspend-to-RAM) or "standby" (for
acc82342
SP
3705 standby suspend) or "freeze" (for suspend type freeze)
3706 as the system sleep state during system startup with
3707 the optional capability to repeat N number of times.
3708 The system is woken from this state using a
3709 wakeup-capable RTC alarm.
77437fd4 3710
1da177e4
LT
3711 thash_entries= [KNL,NET]
3712 Set number of hash buckets for TCP connection
3713
f8707ec9
LB
3714 thermal.act= [HW,ACPI]
3715 -1: disable all active trip points in all thermal zones
3716 <degrees C>: override all lowest active trip points
3717
c52a7419
LB
3718 thermal.crt= [HW,ACPI]
3719 -1: disable all critical trip points in all thermal zones
22a94d79 3720 <degrees C>: override all critical trip points
c52a7419 3721
f5487145
LB
3722 thermal.nocrt= [HW,ACPI]
3723 Set to disable actions on ACPI thermal zone
3724 critical and hot trip points.
3725
72b33ef8
LB
3726 thermal.off= [HW,ACPI]
3727 1: disable ACPI thermal control
3728
a70cdc52
LB
3729 thermal.psv= [HW,ACPI]
3730 -1: disable all passive trip points
ada9cfdd
RD
3731 <degrees C>: override all passive trip points to this
3732 value
a70cdc52 3733
730ff34d
LB
3734 thermal.tzp= [HW,ACPI]
3735 Specify global default ACPI thermal zone polling rate
3736 <deci-seconds>: poll all this frequency
3737 0: no polling (default)
3738
8d32a307
TG
3739 threadirqs [KNL]
3740 Force threading of all interrupt handlers except those
24775d65 3741 marked explicitly IRQF_NO_THREAD.
8d32a307 3742
2ca62b04
KRW
3743 tmem [KNL,XEN]
3744 Enable the Transcendent memory driver if built-in.
3745
3746 tmem.cleancache=0|1 [KNL, XEN]
3747 Default is on (1). Disable the usage of the cleancache
3748 API to send anonymous pages to the hypervisor.
3749
3750 tmem.frontswap=0|1 [KNL, XEN]
3751 Default is on (1). Disable the usage of the frontswap
37d46e15
KRW
3752 API to send swap pages to the hypervisor. If disabled
3753 the selfballooning and selfshrinking are force disabled.
2ca62b04
KRW
3754
3755 tmem.selfballooning=0|1 [KNL, XEN]
3756 Default is on (1). Disable the driving of swap pages
3757 to the hypervisor.
3758
3759 tmem.selfshrinking=0|1 [KNL, XEN]
3760 Default is on (1). Partial swapoff that immediately
3761 transfers pages from Xen hypervisor back to the
3762 kernel based on different criteria.
3763
2b1a61f0
HC
3764 topology= [S390]
3765 Format: {off | on}
3766 Specify if the kernel should make use of the cpu
f65e51d7
SL
3767 topology information if the hardware supports this.
3768 The scheduler will make use of this information and
2b1a61f0 3769 e.g. base its process migration decisions on it.
c9af3fa9 3770 Default is on.
2b1a61f0 3771
2d73bae1
NA
3772 topology_updates= [KNL, PPC, NUMA]
3773 Format: {off}
3774 Specify if the kernel should ignore (off)
3775 topology updates sent by the hypervisor to this
3776 LPAR.
3777
1da177e4
LT
3778 tp720= [HW,PS2]
3779
225a9be2
RA
3780 tpm_suspend_pcr=[HW,TPM]
3781 Format: integer pcr id
3782 Specify that at suspend time, the tpm driver
3783 should extend the specified pcr with zeros,
3784 as a workaround for some chips which fail to
3785 flush the last written pcr on TPM_SaveState.
3786 This will guarantee that all the other pcrs
3787 are saved.
3788
9d612bef 3789 trace_buf_size=nn[KMG]
3e6fb8e9 3790 [FTRACE] will set tracing buffer size on each cpu.
631595fb 3791
020e5f85
LZ
3792 trace_event=[event-list]
3793 [FTRACE] Set and start specified trace events in order
3794 to facilitate early boot debugging.
3795 See also Documentation/trace/events.txt
3796
7bcfaf54
SR
3797 trace_options=[option-list]
3798 [FTRACE] Enable or disable tracer options at boot.
3799 The option-list is a comma delimited list of options
3800 that can be enabled or disabled just as if you were
3801 to echo the option name into
3802
3803 /sys/kernel/debug/tracing/trace_options
3804
3805 For example, to enable stacktrace option (to dump the
3806 stack trace of each event), add to the command line:
3807
3808 trace_options=stacktrace
3809
3810 See also Documentation/trace/ftrace.txt "trace options"
3811 section.
3812
0daa2302
SRRH
3813 tp_printk[FTRACE]
3814 Have the tracepoints sent to printk as well as the
3815 tracing ring buffer. This is useful for early boot up
3816 where the system hangs or reboots and does not give the
3817 option for reading the tracing buffer or performing a
3818 ftrace_dump_on_oops.
3819
3820 To turn off having tracepoints sent to printk,
3821 echo 0 > /proc/sys/kernel/tracepoint_printk
3822 Note, echoing 1 into this file without the
3823 tracepoint_printk kernel cmdline option has no effect.
3824
3825 ** CAUTION **
3826
3827 Having tracepoints sent to printk() and activating high
3828 frequency tracepoints such as irq or sched, can cause
3829 the system to live lock.
3830
de7edd31
SRRH
3831 traceoff_on_warning
3832 [FTRACE] enable this option to disable tracing when a
3833 warning is hit. This turns off "tracing_on". Tracing can
3834 be enabled again by echoing '1' into the "tracing_on"
3835 file located in /sys/kernel/debug/tracing/
3836
3837 This option is useful, as it disables the trace before
3838 the WARNING dump is called, which prevents the trace to
3839 be filled with content caused by the warning output.
3840
3841 This option can also be set at run time via the sysctl
3842 option: kernel/traceoff_on_warning
3843
fcf4d821
JK
3844 transparent_hugepage=
3845 [KNL]
3846 Format: [always|madvise|never]
3847 Can be used to control the default behavior of the system
3848 with respect to transparent hugepages.
3849 See Documentation/vm/transhuge.txt for more details.
3850
d3b8f889 3851 tsc= Disable clocksource stability checks for TSC.
395628ef
AK
3852 Format: <string>
3853 [x86] reliable: mark tsc clocksource as reliable, this
d3b8f889
JS
3854 disables clocksource verification at runtime, as well
3855 as the stability checks done at bootup. Used to enable
3856 high-resolution timer mode on older hardware, and in
3857 virtualized environment.
e82b8e4e
VP
3858 [x86] noirqtime: Do not use TSC to do irq accounting.
3859 Used to run time disable IRQ_TIME_ACCOUNTING on any
3860 platforms where RDTSC is slow and this accounting
3861 can add overhead.
395628ef 3862
a9913044
RD
3863 turbografx.map[2|3]= [HW,JOY]
3864 TurboGraFX parallel port interface
3865 Format:
3866 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
1da177e4
LT
3867 See also Documentation/input/joystick-parport.txt
3868
b6935f8c
CK
3869 udbg-immortal [PPC] When debugging early kernel crashes that
3870 happen after console_init() and before a proper
3871 console driver takes over, this boot options might
3872 help "seeing" what's going on.
3873
f86dcc5a
ED
3874 uhash_entries= [KNL,NET]
3875 Set number of hash buckets for UDP/UDP-Lite connections
3876
5f8364b7
AS
3877 uhci-hcd.ignore_oc=
3878 [USB] Ignore overcurrent events (default N).
3879 Some badly-designed motherboards generate lots of
3880 bogus events, for ports that aren't wired to
3881 anything. Set this parameter to avoid log spamming.
3882 Note that genuine overcurrent events won't be
3883 reported either.
3884
e3a61b0a 3885 unknown_nmi_panic
44a4dcf7 3886 [X86] Cause panic on unknown NMI.
e3a61b0a 3887
c4fc2342
CDH
3888 usbcore.authorized_default=
3889 [USB] Default USB device authorization:
3890 (default -1 = authorized except for wireless USB,
3891 0 = not authorized, 1 = authorized)
3892
b5e795f8
AS
3893 usbcore.autosuspend=
3894 [USB] The autosuspend time delay (in seconds) used
3895 for newly-detected USB devices (default 2). This
3896 is the time required before an idle device will be
3897 autosuspended. Devices for which the delay is set
eaafbc3a 3898 to a negative value won't be autosuspended at all.
b5e795f8 3899
fd7c519d
JK
3900 usbcore.usbfs_snoop=
3901 [USB] Set to log all usbfs traffic (default 0 = off).
3902
3903 usbcore.blinkenlights=
3904 [USB] Set to cycle leds on hubs (default 0 = off).
3905
3906 usbcore.old_scheme_first=
3907 [USB] Start with the old device initialization
3908 scheme (default 0 = off).
3909
3f5eb8d5
AS
3910 usbcore.usbfs_memory_mb=
3911 [USB] Memory limit (in MB) for buffers allocated by
3912 usbfs (default = 16, 0 = max = 2047).
3913
fd7c519d
JK
3914 usbcore.use_both_schemes=
3915 [USB] Try the other device initialization scheme
3916 if the first one fails (default 1 = enabled).
3917
3918 usbcore.initial_descriptor_timeout=
3919 [USB] Specifies timeout for the initial 64-byte
3920 USB_REQ_GET_DESCRIPTOR request in milliseconds
3921 (default 5000 = 5.0 seconds).
3922
1da177e4
LT
3923 usbhid.mousepoll=
3924 [USBHID] The interval which mice are to be polled at.
a9913044 3925
d4f373e5
AS
3926 usb-storage.delay_use=
3927 [UMS] The delay in seconds before a new device is
19101954 3928 scanned for Logical Units (default 1).
d4f373e5
AS
3929
3930 usb-storage.quirks=
3931 [UMS] A list of quirks entries to supplement or
3932 override the built-in unusual_devs list. List
3933 entries are separated by commas. Each entry has
3934 the form VID:PID:Flags where VID and PID are Vendor
3935 and Product ID values (4-digit hex numbers) and
3936 Flags is a set of characters, each corresponding
3937 to a common usb-storage quirk flag as follows:
c838ea46
AS
3938 a = SANE_SENSE (collect more than 18 bytes
3939 of sense data);
a0bb1081
AS
3940 b = BAD_SENSE (don't collect more than 18
3941 bytes of sense data);
d4f373e5
AS
3942 c = FIX_CAPACITY (decrease the reported
3943 device capacity by one sector);
5116901d
KR
3944 d = NO_READ_DISC_INFO (don't use
3945 READ_DISC_INFO command);
3946 e = NO_READ_CAPACITY_16 (don't use
3947 READ_CAPACITY_16 command);
734016b0
HG
3948 f = NO_REPORT_OPCODES (don't use report opcodes
3949 command, uas only);
ee136af4
HG
3950 g = MAX_SECTORS_240 (don't transfer more than
3951 240 sectors at a time, uas only);
c838ea46
AS
3952 h = CAPACITY_HEURISTICS (decrease the
3953 reported device capacity by one
3954 sector if the number is odd);
d4f373e5
AS
3955 i = IGNORE_DEVICE (don't bind to this
3956 device);
3957 l = NOT_LOCKABLE (don't try to lock and
3958 unlock ejectable media);
3959 m = MAX_SECTORS_64 (don't transfer more
3960 than 64 sectors = 32 KB at a time);
21c13a4f
AS
3961 n = INITIAL_READ10 (force a retry of the
3962 initial READ(10) command);
c838ea46
AS
3963 o = CAPACITY_OK (accept the capacity
3964 reported by the device);
eaa05dfc
NJ
3965 p = WRITE_CACHE (the device cache is ON
3966 by default);
d4f373e5
AS
3967 r = IGNORE_RESIDUE (the device reports
3968 bogus residue values);
3969 s = SINGLE_LUN (the device has only one
3970 Logical Unit);
59307852
HG
3971 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3972 commands, uas only);
b6089f19 3973 u = IGNORE_UAS (don't bind to the uas driver);
d4f373e5
AS
3974 w = NO_WP_DETECT (don't test whether the
3975 medium is write-protected).
3976 Example: quirks=0419:aaf5:rl,0421:0433:rc
3977
ac1667db
SB
3978 user_debug= [KNL,ARM]
3979 Format: <int>
3980 See arch/arm/Kconfig.debug help text.
3981 1 - undefined instruction events
3982 2 - system calls
3983 4 - invalid data aborts
3984 8 - SIGSEGV faults
3985 16 - SIGBUS faults
3986 Example: user_debug=31
3987
14315592
IC
3988 userpte=
3989 [X86] Flags controlling user PTE allocations.
3990
3991 nohigh = do not allocate PTE pages in
3992 HIGHMEM regardless of setting
3993 of CONFIG_HIGHPTE.
3994
6cececfc 3995 vdso= [X86,SH]
b0b49f26
AL
3996 On X86_32, this is an alias for vdso32=. Otherwise:
3997
3998 vdso=1: enable VDSO (the default)
e6e5494c
IM
3999 vdso=0: disable VDSO mapping
4000
b0b49f26
AL
4001 vdso32= [X86] Control the 32-bit vDSO
4002 vdso32=1: enable 32-bit VDSO
4003 vdso32=0 or vdso32=2: disable 32-bit VDSO
4004
4005 See the help text for CONFIG_COMPAT_VDSO for more
4006 details. If CONFIG_COMPAT_VDSO is set, the default is
4007 vdso32=0; otherwise, the default is vdso32=1.
4008
4009 For compatibility with older kernels, vdso32=2 is an
4010 alias for vdso32=0.
4011
4012 Try vdso32=0 if you encounter an error that says:
4013 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
af65d648 4014
d080d397
YI
4015 vector= [IA-64,SMP]
4016 vector=percpu: enable percpu vector domain
4017
1da177e4
LT
4018 video= [FB] Frame buffer configuration
4019 See Documentation/fb/modedb.txt.
4020
3afe6dab
AL
4021 video.brightness_switch_enabled= [0,1]
4022 If set to 1, on receiving an ACPI notify event
4023 generated by hotkey, video driver will adjust brightness
4024 level and then send out the event to user space through
4025 the allocated input device; If set to 0, video driver
4026 will only send out the event without touching backlight
4027 brightness level.
2843768b 4028 default: 1
3afe6dab 4029
81a054ce
PM
4030 virtio_mmio.device=
4031 [VMMIO] Memory mapped virtio (platform) device.
4032
4033 <size>@<baseaddr>:<irq>[:<id>]
4034 where:
4035 <size> := size (can use standard suffixes
4036 like K, M and G)
4037 <baseaddr> := physical base address
4038 <irq> := interrupt number (as passed to
4039 request_irq())
4040 <id> := (optional) platform device id
4041 example:
4042 virtio_mmio.device=1K@0x100b0000:48:7
4043
4044 Can be used multiple times for multiple devices.
4045
cd4f0ef7 4046 vga= [BOOT,X86-32] Select a particular video mode
954a8b81 4047 See Documentation/x86/boot.txt and
a9913044 4048 Documentation/svga.txt.
1da177e4
LT
4049 Use vga=ask for menu.
4050 This is actually a boot loader parameter; the value is
4051 passed to the kernel using a special protocol.
4052
a9913044 4053 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
1da177e4
LT
4054 size of <nn>. This can be used to increase the
4055 minimum size (128MB on x86). It can also be used to
4056 decrease the size and leave more room for directly
4057 mapped kernel RAM.
4058
585c3047
PO
4059 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4060 Format: <command>
1da177e4 4061
585c3047
PO
4062 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4063 Format: <command>
4064
4065 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4066 Format: <command>
a9913044 4067
3ae36655
AL
4068 vsyscall= [X86-64]
4069 Controls the behavior of vsyscalls (i.e. calls to
4070 fixed addresses of 0xffffffffff600x00 from legacy
4071 code). Most statically-linked binaries and older
4072 versions of glibc use these calls. Because these
4073 functions are at fixed addresses, they make nice
4074 targets for exploits that can control RIP.
4075
2e57ae05
AL
4076 emulate [default] Vsyscalls turn into traps and are
4077 emulated reasonably safely.
3ae36655 4078
2e57ae05 4079 native Vsyscalls are native syscall instructions.
3ae36655
AL
4080 This is a little bit faster than trapping
4081 and makes a few dynamic recompilers work
4082 better than they would in emulation mode.
4083 It also makes exploits much easier to write.
4084
4085 none Vsyscalls don't work at all. This makes
4086 them quite hard to use for exploits but
4087 might break your system.
4088
3855ae1c
CL
4089 vt.color= [VT] Default text color.
4090 Format: 0xYX, X = foreground, Y = background.
4091 Default: 0x07 = light gray on black.
4092
9ea9a886
CL
4093 vt.cur_default= [VT] Default cursor shape.
4094 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4095 the parameters of the <Esc>[?A;B;Cc escape sequence;
4096 see VGA-softcursor.txt. Default: 2 = underline.
4097
0cb55ad2
RD
4098 vt.default_blu= [VT]
4099 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4100 Change the default blue palette of the console.
4101 This is a 16-member array composed of values
4102 ranging from 0-255.
4103
4104 vt.default_grn= [VT]
4105 Format: <green0>,<green1>,<green2>,...,<green15>
4106 Change the default green palette of the console.
4107 This is a 16-member array composed of values
4108 ranging from 0-255.
4109
4110 vt.default_red= [VT]
4111 Format: <red0>,<red1>,<red2>,...,<red15>
4112 Change the default red palette of the console.
4113 This is a 16-member array composed of values
4114 ranging from 0-255.
4115
4116 vt.default_utf8=
4117 [VT]
4118 Format=<0|1>
4119 Set system-wide default UTF-8 mode for all tty's.
4120 Default is 1, i.e. UTF-8 mode is enabled for all
4121 newly opened terminals.
4122
f6c06b68
MG
4123 vt.global_cursor_default=
4124 [VT]
4125 Format=<-1|0|1>
4126 Set system-wide default for whether a cursor
4127 is shown on new VTs. Default is -1,
4128 i.e. cursors will be created by default unless
4129 overridden by individual drivers. 0 will hide
4130 cursors, 1 will display them.
4131
3855ae1c
CL
4132 vt.italic= [VT] Default color for italic text; 0-15.
4133 Default: 2 = green.
4134
4135 vt.underline= [VT] Default color for underlined text; 0-15.
4136 Default: 3 = cyan.
4137
4724ba57
RD
4138 watchdog timers [HW,WDT] For information on watchdog timers,
4139 see Documentation/watchdog/watchdog-parameters.txt
4140 or other driver-specific files in the
4141 Documentation/watchdog/ directory.
1da177e4 4142
d55262c4
TH
4143 workqueue.disable_numa
4144 By default, all work items queued to unbound
4145 workqueues are affine to the NUMA nodes they're
4146 issued on, which results in better behavior in
4147 general. If NUMA affinity needs to be disabled for
4148 whatever reason, this option can be used. Note
4149 that this also can be controlled per-workqueue for
4150 workqueues visible under /sys/bus/workqueue/.
4151
cee22a15
VK
4152 workqueue.power_efficient
4153 Per-cpu workqueues are generally preferred because
4154 they show better performance thanks to cache
4155 locality; unfortunately, per-cpu workqueues tend to
4156 be more power hungry than unbound workqueues.
4157
4158 Enabling this makes the per-cpu workqueues which
4159 were observed to contribute significantly to power
4160 consumption unbound, leading to measurably lower
4161 power usage at the cost of small performance
4162 overhead.
4163
4164 The default value of this parameter is determined by
4165 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4166
0cb55ad2
RD
4167 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4168 default x2apic cluster mode on platforms
4169 supporting x2apic.
4170
712b6aa8
KS
4171 x86_intel_mid_timer= [X86-32,APBT]
4172 Choose timer option for x86 Intel MID platform.
bb24c471
JP
4173 Two valid options are apbt timer only and lapic timer
4174 plus one apbt timer for broadcast timer.
712b6aa8 4175 x86_intel_mid_timer=apbt_only | lapic_and_apbt
bb24c471 4176
c70727a5
JG
4177 xen_512gb_limit [KNL,X86-64,XEN]
4178 Restricts the kernel running paravirtualized under Xen
4179 to use only up to 512 GB of RAM. The reason to do so is
4180 crash analysis tools and Xen tools for doing domain
4181 save/restore/migration must be enabled to handle larger
4182 domains.
4183
c1c5413a
SS
4184 xen_emul_unplug= [HW,X86,XEN]
4185 Unplug Xen emulated devices
4186 Format: [unplug0,][unplug1]
4187 ide-disks -- unplug primary master IDE devices
4188 aux-ide-disks -- unplug non-primary-master IDE devices
4189 nics -- unplug network devices
4190 all -- unplug all emulated devices (NICs and IDE disks)
1dc7ce99
IC
4191 unnecessary -- unplugging emulated devices is
4192 unnecessary even if the host did not respond to
4193 the unplug protocol
c93a4dfb 4194 never -- do not unplug even if version check succeeds
c1c5413a 4195
15a3eac0
KRW
4196 xen_nopvspin [X86,XEN]
4197 Disables the ticketlock slowpath using Xen PV
4198 optimizations.
4199
8d693b91
KRW
4200 xen_nopv [X86]
4201 Disables the PV optimizations forcing the HVM guest to
4202 run as generic HVM guest with no PV drivers.
4203
1da177e4 4204 xirc2ps_cs= [NET,PCMCIA]
a9913044
RD
4205 Format:
4206 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
1da177e4 4207
a9913044 4208______________________________________________________________________
1da177e4
LT
4209
4210TODO:
4211
1da177e4 4212 Add more DRM drivers.