Documentation/x86_64/boot-options.txt

AMD64 specific boot options

There are many others (usually documented in driver documentation), but 
only the AMD64 specific ones are listed here.

Machine check

(see the Opteron BIOS&Kernel manual for more details on the banks etc.)

   mce=off disable machine check
   mce=nok8 disable k8 specific features
   mce=disable<NUMBER> disable bank NUMBER
   mce=enable<NUMBER> enable bank number
   mce=device	Enable more machine check options in Northbridge. 
		Can be useful for device driver debugging.
   mce=NUMBER mcheck timer interval number seconds. 
   Can be also comma separated in a single mce=

   nomce (for compatibility with i386): same as mce=off

APICs

   nolocalapic   Don't use a local or IO-APIC. This should only
   		 be needed if you have a buggy BIOS. The newer
		 kernels already turn it off by default if the
		 BIOS didn't enable the local APIC, so it will
		 be hopefully not needed.
		 Note this code path is not very well tested, you are on
		 your own.
		
   apic		 Use IO-APIC. Default

   noapic	 Don't use the IO-APIC. 
		 Also only lightly tested. 

   pirq=...	 See Documentation/i386/IO-APIC.txt		 
    
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. Only useful with a SMP kernel

  report_lost_ticks
  Report when timer interrupts are lost because some code turned off
  interrupts for too long. 

  nmi_watchdog=NUMBER
  NUMBER can be: 
  0 don't use an NMI watchdog
  1 use the IO-APIC timer for the NMI watchdog
  2 use the local APIC for the NMI watchdog using a performance counter. Note
  This will use one performance counter and the local APIC's performance
  counter vector.

Idle loop

  idle=poll
  Don't do power saving in the idle loop using HLT, but poll for rescheduling 
  events. This will make the CPUs burn 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.

Rebooting

   reboot=b[ios] | t[riple] | k[bd] [, [w]arm | [c]old]
   bios	  Use the CPU reboto vector for warm reset
   warm   Don't set the cold reboot flag
   cold   Set the cold reboto flag
   triple Force a triple fault (init)
   kbd    Use the keyboard controller. cold reset (default)

   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.
   
Non Executable Mappings

  noexec=on|off

  on      Enable
  off     Disable
  noforce (default) Don't enable by default for heap/stack/data,
          but allow PROT_EXEC to be effective

  noexec32=opt{,opt} 

  Control the no exec default for 32bit processes. 
  Requires noexec=on or noexec=noforce to be effective.

  Valid options: 
     all,on    Heap,stack,data is non executable. 	
     off       (default) Heap,stack,data is executable
     stack     Stack is non executable, heap/data is.
     force     Don't imply PROT_EXEC for PROT_READ 
     compat    (default) Imply PROT_EXEC for PROT_READ
 
SMP 

  nosmp	Only use a single CPU

  maxcpus=NUMBER only use upto NUMBER CPUs

  cpumask=MASK   only use cpus with bits set in mask

NUMA

  numa=off	Only set up a single NUMA node spanning all memory.


ACPI 

  acpi=off	Don't enable ACPI
  
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 upto NUMBER busses, no matter what the mptable says.

IOMMU

  iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]]
   size  set size of iommu (in bytes) 
   noagp don't initialize the AGP driver and use full aperture.
   off   don't use the IOMMU
   leak  turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
   memaper[=order] allocate an own aperture over RAM with size 32MB^order.
   noforce don't force IOMMU usage. Default.
   force  Force IOMMU for all devices.