.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" May be distributed under the GNU General Public License
.TH DMESG 1 "July 2011" "util-linux" "User Commands"
.SH NAME
dmesg \- print or control the kernel ring buffer
.SH SYNOPSIS
.B dmesg
.RB [ options ]
.sp
.B dmesg \-\-clear
.sp
.B dmesg \-\-read-clear
.RB [ options ]
.sp
.B dmesg \-\-console-level
.I level
.sp
.B dmesg \-\-console-on
.sp
.B dmesg \-\-console-off
.SH DESCRIPTION
.B dmesg
is used to examine or control the kernel ring buffer.

The default action is to read all messages from kernel ring buffer.

.SH OPTIONS
The --clear, --read-clear, --console-on, --console-off and --console-level
options are mutually exclusive.

.IP "\fB\-C, \-\-clear\fP"
Clear the ring buffer.
.IP "\fB\-c, \-\-read-clear\fP"
Clear the ring buffer contents after printing.
.IP "\fB\-D, \-\-console-off\fP"
Disable printing messages to the console.
.IP "\fB\-d, \-\-show-delta\fP"
Display the timestamp and time delta spent between messages. If used together
with --notime then only the time delta without the timestamp is printed.
.IP "\fB\-E, \-\-console-on\fP"
Enable printing messages to the console.
.IP "\fB\-f, \-\-facility \fIlist\fP"
Restrict output to defined (comma separated) list of facilities. For example
.sp
  dmesg --facility=daemon
.sp
will print messages from system daemons only. For all supported facilities see
.B dmesg \-\-help
output.
.IP "\fB\-h, \-\-help\fP"
Print a help text and exit.
.IP "\fB\-k, \-\-kernel\fP"
Print kernel messages.
.IP "\fB\-l, \-\-level \fIlist\fP"
Restrict output to defined (comma separated) list of levels. For example
.sp
  dmesg --level=err,warn
.sp
will print error and warning messages only. For all supported levels see
.B dmesg \-\-help
output.
.IP "\fB\-n, \-\-console-level \fIlevel\fP
Set the
.I level
at which logging of messages is done to the console. The 
.I level
is a level number or abbreviation of the level name. For all supported levels see
.B dmesg \-\-help
output.
.sp
For example,
.B \-n 1
or
.B \-n alert
prevents all messages, except emergency (panic) messages, from appearing on the
console.  All levels of messages are still written to
.IR /proc/kmsg ,
so
.BR syslogd (8)
can still be used to control exactly where kernel messages appear.  When
the
.B \-n
option is used,
.B dmesg
will
.I not
print or clear the kernel ring buffer.
.IP "\fB\-r, \-\-raw\fP"
Print the raw message buffer, i.e., don't strip the log level prefixes.
.IP "\fB\-s, \-\-buffer-size \fIsize\fP
Use a buffer of
.I 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.
.IP "\fB\-T, \-\-ctime\fP"
Print human readable timestamps. The timestamp could be inaccurate!

.B The time source used for the logs is not updated after system SUSPEND/RESUME.
.IP "\fB\-t, \-\-notime\fP"
Don't print kernel's timestampts.
.IP "\fB\-u, \-\-userspace\fP"
Print userspace messages.
.IP "\fB\-V, \-\-version\fP"
Output version information and exit.
.IP "\fB\-x, \-\-decode\fP"
Decode facility and level (priority) number to human readable prefixes.
.SH SEE ALSO
.BR syslogd (8)
.SH AUTHORS
.nf
Karel Zak <kzak@redhat.com>
Theodore Ts'o <tytso@athena.mit.edu>
.fi
.SH AVAILABILITY
The dmesg command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.