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 console.  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 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, 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 sys-
	      log(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 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.	The timestamp could be inaccurate!

	      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)