util-linux-ng-2.17.2/sys-utils/dmesg.1

.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" May be distributed under the GNU General Public License
.TH DMESG 1
.SH NAME
dmesg \- print or control the kernel ring buffer
.SH SYNOPSIS
.B dmesg
.RB [ \-c ]
.RB [ \-r ]
.RB [ \-n
.IR level ]
.RB [ \-s
.IR bufsize ]
.SH DESCRIPTION
.B dmesg
is used to examine or control the kernel ring buffer.

The program helps users to print out their bootup messages.  Instead of
copying the messages by hand, the user need only:
.RS
dmesg > boot.messages
.RE
and mail the
.I boot.messages
file to whoever can debug their problem.
.SH OPTIONS
.TP
.B \-c
Clear the ring buffer contents after printing.
.TP
.B \-r
Print the raw message buffer, i.e., don't strip the log level prefixes.
.TP
.BI \-s " bufsize"
Use a buffer of size
.I bufsize
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.
.TP
.BI \-n " level"
Set the
.I level
at which logging of messages is done to the console.  For example,
.B \-n 1
prevents all messages, except 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.

When both options are used, only the last option on the command line will
have an effect.
.SH SEE ALSO
.BR syslogd (8)
.\" .SH AUTHOR
.\" Theodore Ts'o (tytso@athena.mit.edu)
.SH AVAILABILITY
The dmesg command is part of the util-linux-ng package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.