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/.