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. The old syslog
format is supported only.
-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.
-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.
-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. 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. 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 or iso. The first three formats are aliases of
the time-format-specific options. 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.
-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.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
