Documentation / x86 / x86_64 / boot-options.txt

Custom Search

Based on kernel version 3.9. Page generated on 2013-05-02 23:17 EST.

	AMD64 specific boot options
	
	There are many others (usually documented in driver documentation), but
	only the AMD64 specific ones are listed here.
	
	Machine check
	
	   Please see Documentation/x86/x86_64/machinecheck for sysfs runtime tunables.
	
	   mce=off
			Disable machine check
	   mce=no_cmci
			Disable CMCI(Corrected Machine Check Interrupt) that
			Intel processor supports.  Usually this disablement is
			not recommended, but it might be handy if your hardware
			is misbehaving.
			Note that you'll get more problems without CMCI than with
			due to the shared banks, i.e. you might get duplicated
			error logs.
	   mce=dont_log_ce
			Don't make logs for corrected errors.  All events reported
			as corrected are silently cleared by OS.
			This option will be useful if you have no interest in any
			of corrected errors.
	   mce=ignore_ce
			Disable features for corrected errors, e.g. polling timer
			and CMCI.  All events reported as corrected are not cleared
			by OS and remained in its error banks.
			Usually this disablement is not recommended, however if
			there is an agent checking/clearing corrected errors
			(e.g. BIOS or hardware monitoring applications), conflicting
			with OS's error handling, and you cannot deactivate the agent,
			then this option will be a help.
	   mce=bootlog
			Enable logging of machine checks left over from booting.
			Disabled by default on AMD because some BIOS leave bogus ones.
			If your BIOS doesn't do that it's a good idea to enable though
			to make sure you log even machine check events that result
			in a reboot. On Intel systems it is enabled by default.
	   mce=nobootlog
			Disable boot machine check logging.
	   mce=tolerancelevel[,monarchtimeout] (number,number)
			tolerance levels:
			0: always panic on uncorrected errors, log corrected errors
			1: panic or SIGBUS on uncorrected errors, log corrected errors
			2: SIGBUS or log uncorrected errors, log corrected errors
			3: never panic or SIGBUS, log all errors (for testing only)
			Default is 1
			Can be also set using sysfs which is preferable.
			monarchtimeout:
			Sets the time in us to wait for other CPUs on machine checks. 0
			to disable.
	   mce=bios_cmci_threshold
			Don't overwrite the bios-set CMCI threshold. This boot option
			prevents Linux from overwriting the CMCI threshold set by the
			bios. Without this option, Linux always sets the CMCI
			threshold to 1. Enabling this may make memory predictive failure
			analysis less effective if the bios sets thresholds for memory
			errors since we will not see details for all errors.
	
	   nomce (for compatibility with i386): same as mce=off
	
	   Everything else is in sysfs now.
	
	APICs
	
	   apic		 Use IO-APIC. Default
	
	   noapic	 Don't use the IO-APIC.
	
	   disableapic	 Don't use the local APIC
	
	   nolapic	 Don't use the local APIC (alias for i386 compatibility)
	
	   pirq=...	 See Documentation/x86/i386/IO-APIC.txt
	
	   noapictimer	 Don't set up the APIC timer
	
	   no_timer_check Don't check the IO-APIC timer. This can work around
			 problems with incorrect timer initialization on some boards.
	
	   apicmaintimer Run time keeping from the local APIC timer instead
	                 of using the PIT/HPET interrupt for this. This is useful
	                 when the PIT/HPET interrupts are unreliable.
	
	   noapicmaintimer  Don't do time keeping using the APIC timer.
			 Useful when this option was auto selected, but doesn't work.
	
	   apicpmtimer
			 Do APIC timer calibration using the pmtimer. Implies
			 apicmaintimer. Useful when your PIT timer is totally
			 broken.
	
	Early Console
	
	   syntax: earlyprintk=vga
	           earlyprintk=serial[,ttySn[,baudrate]]
	
	   The early console is useful when the kernel crashes before the
	   normal console is initialized. It is not enabled by
	   default because it has some cosmetic problems.
	   Append ,keep to not disable it when the real console takes over.
	   Only vga or serial at a time, not both.
	   Currently only ttyS0 and ttyS1 are supported.
	   Interaction with the standard serial driver is not very good.
	   The VGA output is eventually overwritten by the real console.
	
	Timing
	
	  notsc
	  Don't use the CPU time stamp counter to read the wall time.
	  This can be used to work around timing problems on multiprocessor systems
	  with not properly synchronized CPUs.
	
	  nohpet
	  Don't use the HPET timer.
	
	Idle loop
	
	  idle=poll
	  Don't do power saving in the idle loop using HLT, but poll for rescheduling
	  event. This will make the CPUs eat a lot more power, but may be useful
	  to get slightly better performance in multiprocessor benchmarks. It also
	  makes some profiling using performance counters more accurate.
	  Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
	  CPUs) this option has no performance advantage over the normal idle loop.
	  It may also interact badly with hyperthreading.
	
	Rebooting
	
	   reboot=b[ios] | t[riple] | k[bd] | a[cpi] | e[fi] [, [w]arm | [c]old]
	   bios	  Use the CPU reboot vector for warm reset
	   warm   Don't set the cold reboot flag
	   cold   Set the cold reboot flag
	   triple Force a triple fault (init)
	   kbd    Use the keyboard controller. cold reset (default)
	   acpi   Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the
	          ACPI reset does not work, the reboot path attempts the reset using
	          the keyboard controller.
	   efi    Use efi reset_system runtime service. If EFI is not configured or the
	          EFI reset does not work, the reboot path attempts the reset using
	          the keyboard controller.
	
	   Using warm reset will be much faster especially on big memory
	   systems because the BIOS will not go through the memory check.
	   Disadvantage is that not all hardware will be completely reinitialized
	   on reboot so there may be boot problems on some systems.
	
	   reboot=force
	
	   Don't stop other CPUs on reboot. This can make reboot more reliable
	   in some cases.
	
	Non Executable Mappings
	
	  noexec=on|off
	
	  on      Enable(default)
	  off     Disable
	
	SMP
	
	  additional_cpus=NUM Allow NUM more CPUs for hotplug
			 (defaults are specified by the BIOS, see Documentation/x86/x86_64/cpu-hotplug-spec)
	
	NUMA
	
	  numa=off	Only set up a single NUMA node spanning all memory.
	
	  numa=noacpi   Don't parse the SRAT table for NUMA setup
	
	  numa=fake=<size>[MG]
			If given as a memory unit, fills all system RAM with nodes of
			size interleaved over physical nodes.
	
	  numa=fake=<N>
			If given as an integer, fills all system RAM with N fake nodes
			interleaved over physical nodes.
	
	ACPI
	
	  acpi=off	Don't enable ACPI
	  acpi=ht	Use ACPI boot table parsing, but don't enable ACPI
			interpreter
	  acpi=force	Force ACPI on (currently not needed)
	
	  acpi=strict   Disable out of spec ACPI workarounds.
	
	  acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
	
	  acpi=noirq	Don't route interrupts
	
	PCI
	
	  pci=off		Don't use PCI
	  pci=conf1		Use conf1 access.
	  pci=conf2		Use conf2 access.
	  pci=rom		Assign ROMs.
	  pci=assign-busses	Assign busses
	  pci=irqmask=MASK	Set PCI interrupt mask to MASK
	  pci=lastbus=NUMBER	Scan up to NUMBER busses, no matter what the mptable says.
	  pci=noacpi		Don't use ACPI to set up PCI interrupt routing.
	
	IOMMU (input/output memory management unit)
	
	 Currently four x86-64 PCI-DMA mapping implementations exist:
	
	   1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
	      (e.g. because you have < 3 GB memory).
	      Kernel boot message: "PCI-DMA: Disabling IOMMU"
	
	   2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
	      Kernel boot message: "PCI-DMA: using GART IOMMU"
	
	   3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
	      e.g. if there is no hardware IOMMU in the system and it is need because
	      you have >3GB memory or told the kernel to us it (iommu=soft))
	      Kernel boot message: "PCI-DMA: Using software bounce buffering
	      for IO (SWIOTLB)"
	
	   4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
	      pSeries and xSeries servers. This hardware IOMMU supports DMA address
	      mapping with memory protection, etc.
	      Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
	
	 iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
		[,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
		[,noaperture][,calgary]
	
	  General iommu options:
	    off                Don't initialize and use any kind of IOMMU.
	    noforce            Don't force hardware IOMMU usage when it is not needed.
	                       (default).
	    force              Force the use of the hardware IOMMU even when it is
	                       not actually needed (e.g. because < 3 GB memory).
	    soft               Use software bounce buffering (SWIOTLB) (default for
	                       Intel machines). This can be used to prevent the usage
	                       of an available hardware IOMMU.
	
	  iommu options only relevant to the AMD GART hardware IOMMU:
	    <size>             Set the size of the remapping area in bytes.
	    allowed            Overwrite iommu off workarounds for specific chipsets.
	    fullflush          Flush IOMMU on each allocation (default).
	    nofullflush        Don't use IOMMU fullflush.
	    leak               Turn on simple iommu leak tracing (only when
	                       CONFIG_IOMMU_LEAK is on). Default number of leak pages
	                       is 20.
	    memaper[=<order>]  Allocate an own aperture over RAM with size 32MB<<order.
	                       (default: order=1, i.e. 64MB)
	    merge              Do scatter-gather (SG) merging. Implies "force"
	                       (experimental).
	    nomerge            Don't do scatter-gather (SG) merging.
	    noaperture         Ask the IOMMU not to touch the aperture for AGP.
	    forcesac           Force single-address cycle (SAC) mode for masks <40bits
	                       (experimental).
	    noagp              Don't initialize the AGP driver and use full aperture.
	    allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
	                       DAC is used with 32-bit PCI to push a 64-bit address in
	                       two cycles. When off all DMA over >4GB is forced through
	                       an IOMMU or software bounce buffering.
	    nodac              Forbid DAC mode, i.e. DMA >4GB.
	    panic              Always panic when IOMMU overflows.
	    calgary            Use the Calgary IOMMU if it is available
	
	  iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
	  implementation:
	    swiotlb=<pages>[,force]
	    <pages>            Prereserve that many 128K pages for the software IO
	                       bounce buffering.
	    force              Force all IO through the software TLB.
	
	  Settings for the IBM Calgary hardware IOMMU currently found in IBM
	  pSeries and xSeries machines:
	
	    calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
	    calgary=[translate_empty_slots]
	    calgary=[disable=<PCI bus number>]
	    panic              Always panic when IOMMU overflows
	
	    64k,...,8M - Set the size of each PCI slot's translation table
	    when using the Calgary IOMMU. This is the size of the translation
	    table itself in main memory. The smallest table, 64k, covers an IO
	    space of 32MB; the largest, 8MB table, can cover an IO space of
	    4GB. Normally the kernel will make the right choice by itself.
	
	    translate_empty_slots - Enable translation even on slots that have
	    no devices attached to them, in case a device will be hotplugged
	    in the future.
	
	    disable=<PCI bus number> - Disable translation on a given PHB. For
	    example, the built-in graphics adapter resides on the first bridge
	    (PCI bus number 0); if translation (isolation) is enabled on this
	    bridge, X servers that access the hardware directly from user
	    space might stop working. Use this option if you have devices that
	    are accessed from userspace directly on some PCI host bridge.
	
	Debugging
	
	  kstack=N	Print N words from the kernel stack in oops dumps.
	
	  pagefaulttrace  Dump all page faults. Only useful for extreme debugging
			and will create a lot of output.
	
	  call_trace=[old|both|newfallback|new]
			old: use old inexact backtracer
			new: use new exact dwarf2 unwinder
	 		both: print entries from both
			newfallback: use new unwinder but fall back to old if it gets
				stuck (default)
	
	Miscellaneous
	
		nogbpages
			Do not use GB pages for kernel direct mappings.
		gbpages
			Use GB pages for kernel direct mappings.

• [ x86_64 ]
• 00-INDEX
• boot-options.txt
• cpu-hotplug-spec
• fake-numa-for-cpusets
• kernel-stacks
• machinecheck
• mm.txt
• uefi.txt
•