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Documentation / x86 / x86_64 / boot-options.txt

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Based on kernel version 3.13. Page generated on 2014-01-20 22:05 EST.

1	AMD64 specific boot options
3	There are many others (usually documented in driver documentation), but
4	only the AMD64 specific ones are listed here.
6	Machine check
8	   Please see Documentation/x86/x86_64/machinecheck for sysfs runtime tunables.
10	   mce=off
11			Disable machine check
12	   mce=no_cmci
13			Disable CMCI(Corrected Machine Check Interrupt) that
14			Intel processor supports.  Usually this disablement is
15			not recommended, but it might be handy if your hardware
16			is misbehaving.
17			Note that you'll get more problems without CMCI than with
18			due to the shared banks, i.e. you might get duplicated
19			error logs.
20	   mce=dont_log_ce
21			Don't make logs for corrected errors.  All events reported
22			as corrected are silently cleared by OS.
23			This option will be useful if you have no interest in any
24			of corrected errors.
25	   mce=ignore_ce
26			Disable features for corrected errors, e.g. polling timer
27			and CMCI.  All events reported as corrected are not cleared
28			by OS and remained in its error banks.
29			Usually this disablement is not recommended, however if
30			there is an agent checking/clearing corrected errors
31			(e.g. BIOS or hardware monitoring applications), conflicting
32			with OS's error handling, and you cannot deactivate the agent,
33			then this option will be a help.
34	   mce=bootlog
35			Enable logging of machine checks left over from booting.
36			Disabled by default on AMD because some BIOS leave bogus ones.
37			If your BIOS doesn't do that it's a good idea to enable though
38			to make sure you log even machine check events that result
39			in a reboot. On Intel systems it is enabled by default.
40	   mce=nobootlog
41			Disable boot machine check logging.
42	   mce=tolerancelevel[,monarchtimeout] (number,number)
43			tolerance levels:
44			0: always panic on uncorrected errors, log corrected errors
45			1: panic or SIGBUS on uncorrected errors, log corrected errors
46			2: SIGBUS or log uncorrected errors, log corrected errors
47			3: never panic or SIGBUS, log all errors (for testing only)
48			Default is 1
49			Can be also set using sysfs which is preferable.
50			monarchtimeout:
51			Sets the time in us to wait for other CPUs on machine checks. 0
52			to disable.
53	   mce=bios_cmci_threshold
54			Don't overwrite the bios-set CMCI threshold. This boot option
55			prevents Linux from overwriting the CMCI threshold set by the
56			bios. Without this option, Linux always sets the CMCI
57			threshold to 1. Enabling this may make memory predictive failure
58			analysis less effective if the bios sets thresholds for memory
59			errors since we will not see details for all errors.
61	   nomce (for compatibility with i386): same as mce=off
63	   Everything else is in sysfs now.
65	APICs
67	   apic		 Use IO-APIC. Default
69	   noapic	 Don't use the IO-APIC.
71	   disableapic	 Don't use the local APIC
73	   nolapic	 Don't use the local APIC (alias for i386 compatibility)
75	   pirq=...	 See Documentation/x86/i386/IO-APIC.txt
77	   noapictimer	 Don't set up the APIC timer
79	   no_timer_check Don't check the IO-APIC timer. This can work around
80			 problems with incorrect timer initialization on some boards.
82	   apicmaintimer Run time keeping from the local APIC timer instead
83	                 of using the PIT/HPET interrupt for this. This is useful
84	                 when the PIT/HPET interrupts are unreliable.
86	   noapicmaintimer  Don't do time keeping using the APIC timer.
87			 Useful when this option was auto selected, but doesn't work.
89	   apicpmtimer
90			 Do APIC timer calibration using the pmtimer. Implies
91			 apicmaintimer. Useful when your PIT timer is totally
92			 broken.
94	Timing
96	  notsc
97	  Don't use the CPU time stamp counter to read the wall time.
98	  This can be used to work around timing problems on multiprocessor systems
99	  with not properly synchronized CPUs.
101	  nohpet
102	  Don't use the HPET timer.
104	Idle loop
106	  idle=poll
107	  Don't do power saving in the idle loop using HLT, but poll for rescheduling
108	  event. This will make the CPUs eat a lot more power, but may be useful
109	  to get slightly better performance in multiprocessor benchmarks. It also
110	  makes some profiling using performance counters more accurate.
111	  Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
112	  CPUs) this option has no performance advantage over the normal idle loop.
113	  It may also interact badly with hyperthreading.
115	Rebooting
117	   reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old]
118	   bios	  Use the CPU reboot vector for warm reset
119	   warm   Don't set the cold reboot flag
120	   cold   Set the cold reboot flag
121	   triple Force a triple fault (init)
122	   kbd    Use the keyboard controller. cold reset (default)
123	   acpi   Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
124	          ACPI reset does not work, the reboot path attempts the reset using
125	          the keyboard controller.
126	   efi    Use efi reset_system runtime service. If EFI is not configured or the
127	          EFI reset does not work, the reboot path attempts the reset using
128	          the keyboard controller.
130	   Using warm reset will be much faster especially on big memory
131	   systems because the BIOS will not go through the memory check.
132	   Disadvantage is that not all hardware will be completely reinitialized
133	   on reboot so there may be boot problems on some systems.
135	   reboot=force
137	   Don't stop other CPUs on reboot. This can make reboot more reliable
138	   in some cases.
140	Non Executable Mappings
142	  noexec=on|off
144	  on      Enable(default)
145	  off     Disable
147	SMP
149	  additional_cpus=NUM Allow NUM more CPUs for hotplug
150			 (defaults are specified by the BIOS, see Documentation/x86/x86_64/cpu-hotplug-spec)
152	NUMA
154	  numa=off	Only set up a single NUMA node spanning all memory.
156	  numa=noacpi   Don't parse the SRAT table for NUMA setup
158	  numa=fake=<size>[MG]
159			If given as a memory unit, fills all system RAM with nodes of
160			size interleaved over physical nodes.
162	  numa=fake=<N>
163			If given as an integer, fills all system RAM with N fake nodes
164			interleaved over physical nodes.
166	ACPI
168	  acpi=off	Don't enable ACPI
169	  acpi=ht	Use ACPI boot table parsing, but don't enable ACPI
170			interpreter
171	  acpi=force	Force ACPI on (currently not needed)
173	  acpi=strict   Disable out of spec ACPI workarounds.
175	  acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
177	  acpi=noirq	Don't route interrupts
179	  acpi=nocmcff	Disable firmware first mode for corrected errors. This
180			disables parsing the HEST CMC error source to check if
181			firmware has set the FF flag. This may result in
182			duplicate corrected error reports.
184	PCI
186	  pci=off		Don't use PCI
187	  pci=conf1		Use conf1 access.
188	  pci=conf2		Use conf2 access.
189	  pci=rom		Assign ROMs.
190	  pci=assign-busses	Assign busses
191	  pci=irqmask=MASK	Set PCI interrupt mask to MASK
192	  pci=lastbus=NUMBER	Scan up to NUMBER busses, no matter what the mptable says.
193	  pci=noacpi		Don't use ACPI to set up PCI interrupt routing.
195	IOMMU (input/output memory management unit)
197	 Currently four x86-64 PCI-DMA mapping implementations exist:
199	   1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
200	      (e.g. because you have < 3 GB memory).
201	      Kernel boot message: "PCI-DMA: Disabling IOMMU"
203	   2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
204	      Kernel boot message: "PCI-DMA: using GART IOMMU"
206	   3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
207	      e.g. if there is no hardware IOMMU in the system and it is need because
208	      you have >3GB memory or told the kernel to us it (iommu=soft))
209	      Kernel boot message: "PCI-DMA: Using software bounce buffering
210	      for IO (SWIOTLB)"
212	   4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
213	      pSeries and xSeries servers. This hardware IOMMU supports DMA address
214	      mapping with memory protection, etc.
215	      Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
217	 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
218		[,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
219		[,noaperture][,calgary]
221	  General iommu options:
222	    off                Don't initialize and use any kind of IOMMU.
223	    noforce            Don't force hardware IOMMU usage when it is not needed.
224	                       (default).
225	    force              Force the use of the hardware IOMMU even when it is
226	                       not actually needed (e.g. because < 3 GB memory).
227	    soft               Use software bounce buffering (SWIOTLB) (default for
228	                       Intel machines). This can be used to prevent the usage
229	                       of an available hardware IOMMU.
231	  iommu options only relevant to the AMD GART hardware IOMMU:
232	    <size>             Set the size of the remapping area in bytes.
233	    allowed            Overwrite iommu off workarounds for specific chipsets.
234	    fullflush          Flush IOMMU on each allocation (default).
235	    nofullflush        Don't use IOMMU fullflush.
236	    leak               Turn on simple iommu leak tracing (only when
237	                       CONFIG_IOMMU_LEAK is on). Default number of leak pages
238	                       is 20.
239	    memaper[=<order>]  Allocate an own aperture over RAM with size 32MB<<order.
240	                       (default: order=1, i.e. 64MB)
241	    merge              Do scatter-gather (SG) merging. Implies "force"
242	                       (experimental).
243	    nomerge            Don't do scatter-gather (SG) merging.
244	    noaperture         Ask the IOMMU not to touch the aperture for AGP.
245	    forcesac           Force single-address cycle (SAC) mode for masks <40bits
246	                       (experimental).
247	    noagp              Don't initialize the AGP driver and use full aperture.
248	    allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
249	                       DAC is used with 32-bit PCI to push a 64-bit address in
250	                       two cycles. When off all DMA over >4GB is forced through
251	                       an IOMMU or software bounce buffering.
252	    nodac              Forbid DAC mode, i.e. DMA >4GB.
253	    panic              Always panic when IOMMU overflows.
254	    calgary            Use the Calgary IOMMU if it is available
256	  iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
257	  implementation:
258	    swiotlb=<pages>[,force]
259	    <pages>            Prereserve that many 128K pages for the software IO
260	                       bounce buffering.
261	    force              Force all IO through the software TLB.
263	  Settings for the IBM Calgary hardware IOMMU currently found in IBM
264	  pSeries and xSeries machines:
266	    calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
267	    calgary=[translate_empty_slots]
268	    calgary=[disable=<PCI bus number>]
269	    panic              Always panic when IOMMU overflows
271	    64k,...,8M - Set the size of each PCI slot's translation table
272	    when using the Calgary IOMMU. This is the size of the translation
273	    table itself in main memory. The smallest table, 64k, covers an IO
274	    space of 32MB; the largest, 8MB table, can cover an IO space of
275	    4GB. Normally the kernel will make the right choice by itself.
277	    translate_empty_slots - Enable translation even on slots that have
278	    no devices attached to them, in case a device will be hotplugged
279	    in the future.
281	    disable=<PCI bus number> - Disable translation on a given PHB. For
282	    example, the built-in graphics adapter resides on the first bridge
283	    (PCI bus number 0); if translation (isolation) is enabled on this
284	    bridge, X servers that access the hardware directly from user
285	    space might stop working. Use this option if you have devices that
286	    are accessed from userspace directly on some PCI host bridge.
288	Debugging
290	  kstack=N	Print N words from the kernel stack in oops dumps.
292	  pagefaulttrace  Dump all page faults. Only useful for extreme debugging
293			and will create a lot of output.
295	  call_trace=[old|both|newfallback|new]
296			old: use old inexact backtracer
297			new: use new exact dwarf2 unwinder
298	 		both: print entries from both
299			newfallback: use new unwinder but fall back to old if it gets
300				stuck (default)
302	Miscellaneous
304		nogbpages
305			Do not use GB pages for kernel direct mappings.
306		gbpages
307			Use GB pages for kernel direct mappings.
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