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boot-options.txt
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AMD64 specific boot options
There are many others (usually documented in driver documentation), but
only the AMD64 specific ones are listed here.
Machine check
mce=off disable machine check
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/i386/IO-APIC.txt
noapictimer Don't set up the APIC timer
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[,panic]
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
vector.
When panic is specified panic when an NMI watchdog timeout occurs.
This is useful when you use a panic=... timeout and need the box
quickly up again.
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.
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 reboot 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.
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
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.
numa=noacpi Don't parse the SRAT table for NUMA setup
numa=fake=X Fake X nodes and ignore NUMA setup of the actual machine.
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 upto NUMBER busses, no matter what the mptable says.
pci=noacpi Don't use ACPI to set up PCI interrupt routing.
IOMMU
iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
[,forcesac][,fullflush][,nomerge][,noaperture]
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.
merge Do SG merging. Implies force (experimental)
nomerge Don't do SG merging.
forcesac For SAC mode for masks <40bits (experimental)
fullflush Flush IOMMU on each allocation (default)
nofullflush Don't use IOMMU fullflush
allowed overwrite iommu off workarounds for specific chipsets.
soft Use software bounce buffering (default for Intel machines)
noaperture Don't touch the aperture for AGP.
swiotlb=pages[,force]
pages Prereserve that many 128K pages for the software IO bounce buffering.
force Force all IO through the software TLB.
Debugging
oops=panic Always panic on oopses. Default is to just kill the process,
but there is a small probability of deadlocking the machine.
This will also cause panics on machine check exceptions.
Useful together with panic=30 to trigger a reboot.
kstack=N Print that many words from the kernel stack in oops dumps.
Misc
noreplacement Don't replace instructions with more appropiate ones
for the CPU. This may be useful on asymmetric MP systems
where some CPU have less capabilities than the others.