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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 AT redhat.com>
       Theodore Ts'o <tytso AT athena.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)