DMESG(1)			 User Commands			      DMESG(1)



NAME
       dmesg - print or control the kernel ring buffer

SYNOPSIS
       dmesg [options]

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

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

       The default action is to read all messages from kernel ring buffer.

OPTIONS
       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 contents after printing.

       -D, --console-off
	      Disable printing messages to the console.

       -d, --show-delta
	      Display the timestamp and time delta spent between messages.  If
	      used together with --notime then only the time delta without the
	      timestamp is printed.

       -e, --reltime
	      Display the local time and delta in human readable format.

       -E, --console-on
	      Enable printing messages to the console.

       -F, --file file
	      Read log from file.

       -f, --facility list
	      Restrict output to defined (comma separated) list of facilities.
	      For example

		     dmesg --facility=daemon

	      will print messages from system daemons only.  For all supported
	      facilities see dmesg --help output.

       -H, --human
	      Enable human readable output.  See also --color,	--reltime  and
	      --nopager.

       -h, --help
	      Print a help text and exit.

       -k, --kernel
	      Print kernel messages.

       -L, --color
	      Colorize important messages.

       -l, --level list
	      Restrict	output	to  defined  (comma separated) list of levels.
	      For example

		     dmesg --level=err,warn

	      will print error and warning messages only.  For	all  supported
	      levels see dmesg --help output.

       -n, --console-level level
	      Set  the	level at which logging 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 dmesg --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 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,  the  pager  is  enabled  for
	      --human output.

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

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

       -S, --syslog
	      Force to use syslog(2) kernel interface to read kernel messages.
	      The default is to use /dev/kmsg rather than syslog(2) since ker-
	      nel 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.	The timestamp could be inaccu-
	      rate!

	      The time source used for the logs is not	updated	 after	system
	      SUSPEND/RESUME.

       -t, --notime
	      Do not print kernel's timestamps.

       -u, --userspace
	      Print userspace messages.

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

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

       -x, --decode
	      Decode facility and level (priority) number  to  human  readable
	      prefixes.

SEE ALSO
       syslogd(8)

AUTHORS
       Karel Zak <kzak@redhat.com>
       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  <ftp://ftp.kernel.org/pub/linux/utils/util-
       linux/>.



util-linux			   July 2012			      DMESG(1)