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 display all messages from the 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 after first printing its contents.

       -D, --console-off
	   Disable the printing of messages to the console.

       -d, --show-delta
	   Display the timestamp and the 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.

       -e, --reltime
	   Display the local time and the delta in human-readable format. Be
	   aware that conversion to the local time could be inaccurate (see -T
	   for more details).

       -F, --file file
	   Read the syslog messages from the given file. Note that -F does not
	   support messages in kmsg format. See -K instead.

       -f, --facility list
	   Restrict output to the given (comma-separated) list of facilities.
	   For example:

	   dmesg --facility=daemon

	   will print messages from system daemons only. For all supported
	   facilities see the --help output.

       -H, --human
	   Enable human-readable output. See also --color, --reltime and
	   --nopager.

       -J, --json
	   Use JSON output format. The time output format is in "sec.usec"
	   format only, log priority level is not decoded by default (use
	   --decode to split into facility and priority), the other options to
	   control the output format or time format are silently ignored.

       -K, --kmsg-file file
	   Read the /dev/kmsg messages from the given file. Different record
	   as expected to be separated by a NULL byte.

       -k, --kernel
	   Print kernel messages.

       -L, --color[=when]
	   Colorize the output. The optional argument when can be auto, never
	   or always. If the when argument is omitted, it defaults to auto.
	   The colors can be disabled; for the current built-in default see
	   the --help output. See also the COLORS section below.

       -l, --level list
	   Restrict output to the given (comma-separated) list of levels. For
	   example:

	   dmesg --level=err,warn

	   will print error and warning messages only. For all supported
	   levels see the --help output.

	   Appending a plus + to a level name also includes all higher levels.
	   For example:

	   dmesg --level=err+

	   will print levels err, crit, alert and emerg.

	   Prepending it will include all lower levels.

       -n, --console-level level
	   Set the level at which printing of messages is done to the console.
	   The level is a level number or abbreviation of the level name. For
	   all supported levels see the --help output.

	   For example, -n 1 or -n emerg 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.

       --noescape
	   The unprintable and potentially unsafe characters (e.g., broken
	   multi-byte sequences, terminal controlling chars, etc.) are escaped
	   in format \x<hex> for security reason by default. This option
	   disables this feature at all. It’s usable for example for debugging
	   purpose together with --raw. Be careful and don’t use it by
	   default.

       -P, --nopager
	   Do not pipe output into a pager. A pager is enabled by default for
	   --human output.

       -p, --force-prefix
	   Add facility, level or timestamp information to each line of a
	   multi-line message.

       -r, --raw
	   Print the raw message buffer, i.e., do not strip the log-level
	   prefixes, but all unprintable characters are still escaped (see
	   also --noescape).

	   Note that the real raw format depends on the method how dmesg reads
	   kernel messages. The /dev/kmsg device uses a different format than
	   syslog(2). For backward compatibility, dmesg returns data always in
	   the syslog(2) format. It is possible to read the real raw data from
	   /dev/kmsg by, for example, the command 'dd if=/dev/kmsg
	   iflag=nonblock'.

       -S, --syslog
	   Force dmesg to use the 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.

	   Be aware that the timestamp could be inaccurate! The time source
	   used for the logs is not updated after system SUSPEND/RESUME.
	   Timestamps are adjusted according to current delta between boottime
	   and monotonic clocks, this works only for messages printed after
	   last resume.

       --since time
	   Display record since the specified time. Supported is the subsecond
	   granularity. The time is possible to specify in absolute way as
	   well as by relative notation (e.g. '1 hour ago'). Be aware that the
	   timestamp could be inaccurate and see --ctime for more details.

       --until time
	   Display record until the specified time. Supported is the subsecond
	   granularity. The time is possible to specify in absolute way as
	   well as by relative notation (e.g. '1 hour ago'). Be aware that the
	   timestamp could be inaccurate and see --ctime for more details.

       -t, --notime
	   Do not print kernel’s timestamps.

       --time-format format
	   Print timestamps using the given format, which can be ctime,
	   reltime, delta, iso or raw. The first three formats are aliases of
	   the time-format-specific options. The raw format uses the default
	   timestamp format showing seconds since boot. The iso format is a
	   dmesg implementation of the ISO-8601 timestamp format. The purpose
	   of this format is to make the comparing of timestamps between two
	   systems, and any other parsing, easy. The definition of the iso
	   timestamp is: YYYY-MM-DD<T>HH:MM:SS,<microseconds>←+><timezone
	   offset from UTC>.

	   The iso format has the same issue as ctime: the time may be
	   inaccurate when a system is suspended and resumed.

	   --time-format may be used multiple times with different values for
	   format to output each specified format.

	   The delta always follows ctime or raw if specified together.

       -u, --userspace
	   Print userspace messages.

       -w, --follow
	   Wait for new messages. This feature is supported only on systems
	   with a readable /dev/kmsg (since kernel 3.5.0).

       -W, --follow-new
	   Wait and print only new messages.

       -x, --decode
	   Decode facility and level (priority) numbers to human-readable
	   prefixes.

       -h, --help
	   Display help text and exit.

       -V, --version
	   Display version and exit.

COLORS
       The output colorization is implemented by terminal-colors.d(5)
       functionality.  Implicit coloring can be disabled by an empty file

	  /etc/terminal-colors.d/dmesg.disable

       for the dmesg command or for all tools by

	  /etc/terminal-colors.d/disable

       Since version 2.41, the $NO_COLOR environment variable is also
       supported to disable output colorization unless explicitly enabled by a
       command-line option.

       The user-specific $XDG_CONFIG_HOME/terminal-colors.d or
       $HOME/.config/terminal-colors.d overrides the global setting.

       Note that the output colorization may be enabled by default, and in
       this case terminal-colors.d directories do not have to exist yet.

       The logical color names supported by dmesg are:

       subsys
	   The message sub-system prefix (e.g., "ACPI:").

       time
	   The message timestamp.

       timebreak
	   The message timestamp in short ctime format in --reltime or --human
	   output.

       alert
	   The text of the message with the alert log priority.

       crit
	   The text of the message with the critical log priority.

       err
	   The text of the message with the error log priority.

       warn
	   The text of the message with the warning log priority.

       segfault
	   The text of the message that inform about segmentation fault.

EXIT STATUS
       dmesg can fail reporting permission denied error. This is usually
       caused by dmesg_restrict kernel setting, please see syslog(2) for more
       details.

AUTHORS
       Karel Zak <kzak@redhat.com>

       dmesg was originally written by Theodore Ts’o <tytso@athena.mit.edu>.

SEE ALSO
       terminal-colors.d(5), syslogd(8)

REPORTING BUGS
       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY
       The dmesg command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41.2		  2025-09-22			      DMESG(1)