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DMESG(1)                         User CommandsDMESG(1)NAME       dmesg - print or control the kernel ring bufferSYNOPSIS       dmesg [options]       dmesg --clear       dmesg --read-clear [options]       dmesg --console-level level       dmesg --console-on       dmesg --console-offDESCRIPTION       dmesg is used to examine or control the kernel ring buffer.       The default action is to display all messages from the kernel ring buf-       fer.OPTIONS       The --clear,  --read-clear,  --console-on,  --console-off,  and  --con-       sole-level options are mutually exclusive.       -C, --clear              Clear the ring buffer.       -c, --read-clear              Clear the ring buffer after first printing its contents.       -D, --console-off              Disable the printing of messages to the console.       -d, --show-delta              Display the timestamp and the time delta spent between messages.              If used together with --notime then only the time delta  without              the timestamp is printed.       -E, --console-on              Enable printing messages to the console.       -e, --reltime              Display  the  local time and the delta in human-readable format.              Be aware that conversion to the local time could  be  inaccurate              (see -T for more details).       -F, --file file              Read the syslog messages from the given file.  Note that -F does              not support messages in kmsg format. The old  syslog  format  is              supported only.       -f, --facility list              Restrict  output  to the given (comma-separated) list of facili-              ties.  For example:                     dmesg --facility=daemon              will print messages from system daemons only.  For all supported              facilities see the --help output.       -H, --human              Enable  human-readable  output.  See also --color, --reltime and              --nopager.       -k, --kernel              Print kernel messages.       -L, --color[=when]              Colorize the output.  The optional argument when  can  be  auto,              never  or  always.  If the when argument is omitted, it defaults              to auto.  The colors can be disabled; for the  current  built-in              default  see the --help output.  See also the COLORS section be-              low.       -l, --level list              Restrict output to the given (comma-separated) list  of  levels.              For example:                     dmesg --level=err,warn              will  print  error and warning messages only.  For all supported              levels see the --help output.       -n, --console-level level              Set the level at which printing of messages is done to the  con-              sole.   The level is a level number or abbreviation of the level              name.  For all supported levels see the --help output.              For example, -n 1 or -n  emerg  prevents  all  messages,  except              emergency  (panic) messages, from appearing on the console.  All              levels of messages are still  written  to  /proc/kmsg,  so  sys-logd(8)  can  still be used to control exactly where kernel mes-              sages appear.  When the -n option is used, dmesg will not  print              or clear the kernel ring buffer.       -P, --nopager              Do  not pipe output into a pager.  A pager is enabled by default              for --human output.       -p, --force-prefix              Add facility, level or timestamp information to each line  of  a              multi-line message.       -r, --raw              Print  the  raw  message buffer, i.e. do not strip the log-level              prefixes.              Note that the real raw format depends on the method howdmesg(1)              reads  kernel  messages.   The /dev/kmsg device uses a different              format thansyslog(2).  For backward compatibility,dmesg(1) re-              turns  data  always  in thesyslog(2) format.  It is possible to              read the real raw data from /dev/kmsg by, for example, the  com-              mand 'dd if=/dev/kmsg iflag=nonblock'.       -S, --syslog              Force dmesg to use thesyslog(2) kernel interface to read kernel              messages.  The default is to use /dev/kmsg rather thansyslog(2)              since kernel 3.5.0.       -s, --buffer-size size              Use  a  buffer of size to query the kernel ring buffer.  This is              16392 by default.  (The default kernel syslog  buffer  size  was              4096  at first, 8192 since 1.3.54, 16384 since 2.1.113.)  If you              have set the kernel buffer to be larger than the  default,  then              this option can be used to view the entire buffer.       -T, --ctime              Print human-readable timestamps.              Be  aware  that  the  timestamp  could  be inaccurate!  The time              source used for the logs is not updated after system SUSPEND/RE-              SUME.       -t, --notime              Do not print kernel's timestamps.       --time-format format              Print  timestamps  using  the  given format, which can be ctime,              reltime, delta or iso.  The first three formats are  aliases  of              the time-format-specific options.  The iso format is a dmesg im-              plementation of the ISO-8601 timestamp format.  The  purpose  of              this  format  is to make the comparing of timestamps between two              systems, and any other parsing, easy.  The definition of the iso              timestamp  is: YYYY-MM-DD<T>HH:MM:SS,<microseconds><-+><timezone              offset from UTC>.              The iso format has the same issue as ctime: the time may be  in-              accurate when a system is suspended and resumed.       -u, --userspace              Print userspace messages.       -w, --follow              Wait  for  new messages.  This feature is supported only on sys-              tems with a readable /dev/kmsg (since kernel 3.5.0).       -x, --decode              Decode facility and level (priority) numbers  to  human-readable              prefixes.       -V, --version              Display version information and exit.       -h, --help              Display help text and exit.COLORS       Implicit  coloring  can be disabled by an empty file /etc/terminal-col-       ors.d/dmesg.disable.  Seeterminal-colors.d(5) for more  details  about       colorization configuration.       The logical color names supported by dmesg are:       subsys The message sub-system prefix (e.g. "ACPI:").       time   The message timestamp.       timebreak              The  message  timestamp  in  short  ctime format in --reltime or              --human output.       alert  The text of the message with the alert log priority.       crit   The text of the message with the critical log priority.       err    The text of the message with the error log priority.       warn   The text of the message with the warning log priority.       segfault              The text of the message that inform about segmentation fault.EXIT STATUS       dmesg can fail reporting permission  denied  error.   This  is  usually       caused  by dmesg_restrict kernel setting, please seesyslog(2) for more       details.SEE ALSOterminal-colors.d(5),syslogd(8)AUTHORS       Karel Zak <kzak@redhat.com>       dmesg was originally written by Theodore Ts'o <tytso@athena.mit.edu>AVAILABILITY       The dmesg command is part of the util-linux package  and  is  available       from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-       linux/>.util-linux                         July 2012DMESG(1)