Machine check
mce=off disable machine check
+ 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 (number)
+ 0: always panic, 1: panic if deadlock possible,
+ 2: try to avoid panic, 3: never panic or exit (for testing)
+ default is 1
+ Can be also set using sysfs which is preferable.
nomce (for compatibility with i386): same as mce=off
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.
+
+ disable_8254_timer / enable_8254_timer
+ Enable interrupt 0 timer routing over the 8254 in addition to over
+ the IO-APIC. The kernel tries to set a sensible default.
+
Early Console
syntax: earlyprintk=vga
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
+ with not properly synchronized CPUs.
report_lost_ticks
Report when timer interrupts are lost because some code turned off
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] [, [w]arm | [c]old]
- bios Use the CPU reboto vector for warm reset
+ 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)
cpumask=MASK only use cpus with bits set in mask
+ additional_cpus=NUM Allow NUM more CPUs for hotplug
+ (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
+
NUMA
numa=off Only set up a single NUMA node spanning all memory.
numa=fake=X Fake X nodes and ignore NUMA setup of the actual machine.
+ numa=hotadd=percent
+ Only allow hotadd memory to preallocate page structures upto
+ percent of already available memory.
+ numa=hotadd=0 will disable hotadd memory.
+
ACPI
acpi=off Don't enable ACPI
IOMMU
iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
- [,forcesac][,fullflush][,nomerge][,noaperture]
+ [,forcesac][,fullflush][,nomerge][,noaperture][,calgary]
size set size of iommu (in bytes)
noagp don't initialize the AGP driver and use full aperture.
off don't use the IOMMU
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.
+ allowdac Allow DMA >4GB
+ When off all DMA over >4GB is forced through an IOMMU or bounce
+ buffering.
+ nodac Forbid DMA >4GB
+ panic Always panic when IOMMU overflows
+ calgary Use the Calgary IOMMU if it is available
swiotlb=pages[,force]
pages Prereserve that many 128K pages for the software IO bounce buffering.
force Force all IO through the software TLB.
+ calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
+ calgary=[translate_empty_slots]
+ calgary=[disable=<PCI bus number>]
+
+ 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
oops=panic Always panic on oopses. Default is to just kill the process,
kstack=N Print that many words from the kernel stack in oops dumps.
-Misc
+ pagefaulttrace Dump all page faults. Only useful for extreme debugging
+ and will create a lot of output.
- 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.
+ 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)
+
+ 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)
+
+Misc
+ noreplacement Don't replace instructions with more appropriate ones
+ for the CPU. This may be useful on asymmetric MP systems
+ where some CPU have less capabilities than the others.