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 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 sys‐
              log(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 buf‐
              fer 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)