DMESG(1) User Commands DMESG(1)NAMEdmesg - print or control the kernel ring buffer
SYNOPSISdmesg [options]
dmesg--clear
dmesg--read-clear [options]
dmesg--console-level level
dmesg--console-on
dmesg--console-off
DESCRIPTIONdmesg 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, --file file
Read log from file.
-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 con‐
sole. 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 sys‐
logd(8) can still be used to control exactly where kernel mes‐
sages 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 inaccu‐
rate!
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 ALSOsyslogd(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/.
util-linux July 2011 DMESG(1)