NAME¶
mcelog - Decode kernel machine check log on x86 machines
SYNOPSIS¶
mcelog [options] [device]
mcelog [options] --daemon
mcelog [options] --client
mcelog [options] --ascii
mcelog [options] --is-cpu-supported
mcelog --version
DESCRIPTION¶
X86 CPUs report errors detected by the CPU as
machine check events
(MCEs). These can be data corruption detected in the CPU caches, in main
memory by an integrated memory controller, data transfer errors on the front
side bus or CPU interconnect or other internal errors. Possible causes can be
cosmic radiation, instable power supplies, cooling problems, broken hardware,
running systems out of specification, or bad luck.
Most errors can be corrected by the CPU by internal error correction mechanisms.
Uncorrected errors cause machine check exceptions which may kill processes or
panic the machine. A small number of corrected errors is usually not a cause
for worry, but a large number can indicate future failure.
When a corrected or recovered error happens the x86 kernel writes a record
describing the MCE into a internal ring buffer available through the
/dev/mcelog device
mcelog retrieves errors from
/dev/mcelog, decodes them into a human readable format and prints them
on the standard output or optionally into the system log.
Optionally it can also take more options like keeping statistics or triggering
shell scripts on specific events. By default mcelog supports offlining memory
pages with persistent corrected errors, offlining CPU cores if they developed
cache problems, and otherwise logging specific events to the system log after
they crossed a threshold.
The normal operating modi for mcelog are running as a regular cron job
(traditional way, deprecated), running as a trigger directly executed by the
kernel, or running as a daemon with the
--daemon option.
When an uncorrected machine check error happens that the kernel cannot recover
from then it will usually panic the system. In this case when there was a warm
reset after the panic mcelog should pick up the machine check errors after
reboot. This is not possible after a cold reset.
In addition mcelog can be used on the command line to decode the kernel output
for a fatal machine check panic in text format using the
--ascii
option. This is typically used to decode the panic console output of a fatal
machine check, if the system was power cycled or mcelog didn't run immediately
after reboot.
When the panic triggers a kdump kexec crash kernel the crash kernel boot up
script should log the machine checks to disk, otherwise they might be lost.
Note that after mcelog retrieves an error the kernel doesn't store it anymore
(different from
dmesg(1)), so the output should be always saved
somewhere and mcelog not run in uncontrolled ways.
When invoked with the
--is-cpu-supported option mcelog exits with code 0
if the current CPU is supported, 1 otherwise.
OPTIONS¶
When the
--syslog option is specified redirect output to system log. The
--syslog-error option causes the normal machine checks to be logged as
LOG_ERR (implies
--syslog ). Normally only fatal errors or high
level remarks are logged with error level. High level one line summaries of
specific errors are also logged to the syslog by default unless mcelog
operates in
--ascii mode.
When the
--logfile=file option is specified append log output to the
specified file. With the
--no-syslog option mcelog will never log
anything to the syslog.
When the
--cpu=cputype option is specified set the to be decoded CPU to
cputype. See
mcelog --help for a list of valid CPUs. Note that
specifying an incorrect CPU can lead to incorrect decoding output. Default is
either the CPU of the machine that reported the machine check (needs a newer
kernel version) or the CPU of the machine mcelog is running on, so normally
this option doesn't have to be used. Older versions of mcelog had separate
options for different CPU types. These are still implemented, but deprecated
and undocumented now.
With the
--dmi option mcelog will look up the DIMMs reported in machine
checks in the
SMBIOS/DMI tables of the BIOS and map the DIMMs to board
identifiers. This only works when the BIOS reports the identifiers correctly.
Unfortunately often the information reported by the BIOS is either subtly or
obviously wrong or useless. This option requires that mcelog has read access
to /dev/mem (normally requires root) and runs on the same machine in the same
hardware configuration as when the machine check event happened.
When
--ignorenodev is specified then mcelog will exit silently when the
device cannot be opened. This is useful in virtualized environment with
limited devices.
When
--filter is specified
mcelog will filter out known broken
machine check events (default on). When the
--no-filter option is
specified mcelog does not filter events.
When
--raw is specified
mcelog will not decode, but just dump the
mcelog in a raw hex format. This can be useful for automatic post processing.
When a device is specified the machine check logs are read from device instead
of the default
/dev/mcelog.
With the
--ascii option mcelog decodes a fatal machine check panic
generated by the kernel ("CPU n: Machine Check Exception ...") in
ASCII from standard input and exits afterwards. Note that when the panic comes
from a different machine than where mcelog is running on you might need to
specify the correct cputype on older kernels. On newer kernels which output
the
PROCESSOR field this is not needed anymore.
When the
--file filename option is specified
mcelog --ascii will
read the ASCII machine check record from input file
filename instead of
standard input.
With the
--config-file file option mcelog reads the specified config
file. Default is
/etc/mcelog/mcelog.conf See also
CONFIG FILE
below.
With the
--daemon option mcelog will run in the background. This gives
the fastest reaction time and is the recommended operating mode. If an output
option isn't selected (
--logfile or
--syslog or
--syslog-error ), this option implies
--logfile=/var/log/mcelog.
Important messages will be logged as one-liner summaries to syslog unless
--no-syslog is given. The option
--foreground will prevent
mcelog from giving up the terminal in daemon mode. This is intended for
debugging.
With the
--client option mcelog will query a running daemon for
accumulated errors.
With the
--cpumhz=mhz option assume the CPU has
mhz frequency for
decoding the time of the event using the CPU time stamp counter. This also
forces decoding. Note this can be unreliable. on some systems with CPU
frequency scaling or deep C states, where the CPU time stamp counter does not
increase linearly. By default the frequency of the current CPU is used when
mcelog determines it is safe to use. Newer kernels report the time directly in
the event and don't need this anymore.
The
--pidfile file option writes the process id of the daemon into file
file. Only valid in daemon mode.
Mcelog will enable extended error reporting from the memory controller on
processors that support it unless you tell it not to with the
--no-imc-log option. You might need this option when decoding old logs
from a system where this mode was not enabled.
--version displays the version of mcelog and exits.
CONFIG FILE¶
mcelog supports a config file to set defaults. Command line options override the
config file. By default the config file is read from
/etc/mcelog/mcelog.conf unless overridden with the
--config-file
option.
The general format is
optionname = value White space is not allowed in
value currently, except at the end where it is dropped Comments start with #.
All command line options that are not commands can be specified in the config
file. For example t to enable the
--no-syslog option use
no-syslog =
yes (or no to disable). When the option has a argument use
logfile =
/tmp/logfile
For more information on the config file please see
mcelog.conf(5).
NOTES¶
The kernel prefers old messages over new. If the log buffer overflows only old
ones will be kept.
The exact output in the log file depends on the CPU, unless the --raw option is
used.
mcelog will report serious errors to the syslog during decoding.
SIGNALS¶
When
mcelog runs in daemon mode and receives a
SIGUSR1 it will
close and reopen the log files. This can be used to rotate logs without
restarting the daemon.
FILES¶
/dev/mcelog (char 10, minor 227)
/etc/mcelog/mcelog.conf
/var/log/mcelog
/var/run/mcelog.pid
SEE ALSO¶
mcelog.conf(5), mcelog.triggers(5)
http://www.mcelog.org
AMD x86-64 architecture programmer's manual, Volume 2, System programming
Intel 64 and IA32 Architectures Software Developer's manual, Volume 3, System
programming guide Chapter 15 and 16.
http://www.intel.com/sdm
Datasheet of your CPU.