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, --filefile
Read the syslog messages from the given file. Note that -F does not support messages in kmsg format.
See -K instead.
-f, --facilitylist
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-filefile
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, --levellist
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-levellevel
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, -n1 or -nemerg 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-sizesize
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.
Beawarethatthetimestampcouldbeinaccurate! The time source used for the logs is notupdatedafter system SUSPEND/RESUME. Timestamps are adjusted according to current delta between boottime and
monotonic clocks, this works only for messages printed after last resume.
--sincetime
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.
--untiltime
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-formatformat
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
Print version and exit.
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