Provided by: util-linux_2.27.1-6ubuntu2_i386 bug


       dmesg - print or control the kernel ring buffer


       dmesg [options]

       dmesg --clear
       dmesg --read-clear [options]
       dmesg --console-level level
       dmesg --console-on
       dmesg --console-off


       dmesg is used to examine or control the kernel ring buffer.

       The  default  action  is  to  display all messages from the kernel ring


       The   --clear,   --read-clear,   --console-on,    --console-off,    and
       --console-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 messages from the given file.

       -f, --facility list
              Restrict   output   to   the  given  (comma-separated)  list  of
              facilities.  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

       -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 --help output. See also the COLORS section.

       -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
              console.  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 alert prevents all messages, except
              emergency (panic) messages, from appearing on the console.   All
              levels   of   messages  are  still  written  to  /proc/kmsg,  so
              syslogd(8) can still be used to  control  exactly  where  kernel
              messages  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.

       -r, --raw
              Print  the  raw  message buffer, i.e. do not strip the log-level

              Note that the real raw format depends on the method how dmesg(1)
              reads  kernel  messages.   The /dev/kmsg device uses a different
              format than syslog(2).   For  backward  compatibility,  dmesg(1)
              returns  data always in the syslog(2) format.  It is possible to
              read the real raw data  from  /dev/kmsg  by,  for  example,  the
              command 'dd if=/dev/kmsg iflag=nonblock'.

       -S, --syslog
              Force dmesg to use the syslog(2) kernel interface to read kernel
              messages.  The default is to use /dev/kmsg rather than syslog(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

       -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
              implementation 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
              inaccurate when a system is suspended and resumed.

       -u, --userspace
              Print userspace messages.

       -w, --follow
              Wait  for  new  messages.   This  feature  is  supported only on
              systems with a readable /dev/kmsg (since kernel 3.5.0).

       -x, --decode
              Decode facility and level (priority) numbers  to  human-readable

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.


       Implicit  coloring  can  be  disabled  by  an empty file /etc/terminal-
       colors.d/dmesg.disable.   See  terminal-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.

              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.

              The text of the message that inform about segmentation fault.


       syslogd(8) terminal-colors.d(5)


       Karel Zak ⟨kzak@redhat.comdmesg was originally written by Theodore Ts'o ⟨


       The dmesg command is part of the util-linux package  and  is  available
       from  Linux  Kernel Archive ⟨