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CentOS 7.0 - man page for dmesg (centos section 1)

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DMESG(1)				  User Commands 				 DMESG(1)

       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 read all messages from kernel ring buffer.

       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) mes-
	      sages, 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 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 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.


       Karel Zak <kzak@redhat.com>
       Theodore Ts'o <tytso@athena.mit.edu>

       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)

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