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, --console-on
              Enable printing messages to the console.

       -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, --help
              Print a help text and exit.

       -k, --kernel
              Print kernel 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.

       -r, --raw
              Print the raw message buffer, i.e., don't strip the log level prefixes.

       -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
              Don't print kernel's timestampts.

       -u, --userspace
              Print userspace messages.

       -V, --version
              Output version information and exit.

       -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 ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
 

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