dmesg - phpMan

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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 AT>
       Theodore Ts'o <tytso AT>

       The  dmesg  command  is  part of the util-linux package and is available from Linux Kernel
       Archive <>.

util-linux                                  July 2012                                    DMESG(1)

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