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

       mcelog -	Decode kernel machine check log	on x86 machines

       mcelog [options]	[device]
       mcelog [options]	--daemon
       mcelog [options]	--client
       mcelog [options]	--ascii
       mcelog [options]	--is-cpu-supported
       mcelog --version

       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.	  Pos-
       sible  causes can be cosmic radiation, instable power supplies, cooling
       problems, broken	hardware, running systems out of specification,	or bad

       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  fu-
       ture 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, de-
       codes 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  modes for mcelog	are: running as	a regular cron
       job (traditional	way, deprecated), running as a trigger	directly  exe-
       cuted 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 ma-
       chine check errors after	reboot.	 This is not possible after a cold re-

       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.

       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 sum-
       maries of specific errors are also logged to the	syslog by default  un-
       less 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  any-
       thing 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	speci-
       fying  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  pro-

       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 gen-
       erated  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 accumu-
       lated errors.

       With  the  --cpumhz=mhz option assume the CPU has mhz frequency for de-
       coding 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 any-

       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.

       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  op-

       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).

       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.

       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.

       /dev/mcelog (char 10, minor 227)




       mcelog.conf(5), mcelog.triggers(5)

       AMD x86-64 architecture programmer's manual, Volume 2, System  program-

       Intel  64 and IA32 Architectures	Software Developer's manual, Volume 3,
       System programming guide	Chapter	15 and 16.

       Datasheet of your CPU.

				   Mar 2015			     MCELOG(8)


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