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MCELOG(8)               Linux's Administrator's Manual               MCELOG(8)



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
       mcelog --supported

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 nor-
       mal 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 use-
       ful 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  ker-
       nels. 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 fre-
       quency 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.

       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.

       --supported returns 0 if the system has processors which support MCE, and 1 otherwise.


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.



                                   Mar 2015                          MCELOG(8)