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+.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
+.\" May be distributed under the GNU General Public License
+.TH DMESG "1" "July 2012" "util-linux" "User Commands"
+.SH NAME
+dmesg \- print or control the kernel ring buffer
+.SH SYNOPSIS
+.B dmesg
+.RB [ options ]
+.sp
+dmesg \-\-clear
+.br
+dmesg \-\-read-clear [options]
+.br
+dmesg \-\-console-level level
+.br
+dmesg \-\-console-on
+.br
+dmesg \-\-console-off
+.SH DESCRIPTION
+.B dmesg
+is used to examine or control the kernel ring buffer.
+.PP
+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.
+.PP
+.IP "\fB\-C\fR, \fB\-\-clear\fR"
+Clear the ring buffer.
+.IP "\fB\-c\fR, \fB\-\-read-clear\fR"
+Clear the ring buffer contents after printing.
+.IP "\fB\-D\fR, \fB\-\-console-off\fR"
+Disable printing messages to the console.
+.IP "\fB\-d\fR, \fB\-\-show-delta\fR"
+Display the timestamp and time delta spent between messages.  If used
+together with
+.B \-\-notime
+then only the time delta without the timestamp is printed.
+.IP "\fB\-e\fR, \fB\-\-reltime\fR"
+Display the local time and delta in human readable format.
+.IP "\fB\-E\fR, \fB\-\-console-on\fR"
+Enable printing messages to the console.
+.IP "\fB\-F\fR, \fB\-\-file \fIfile\fR"
+Read log from
+.IR file .
+.IP "\fB\-f\fR, \fB\-\-facility \fIlist\fR"
+Restrict output to defined (comma separated)
+.I list
+of facilities.  For example
+.PP
+.RS 14
+dmesg \-\-facility=daemon
+.RE
+.IP
+will print messages from system daemons only.  For all supported facilities
+see
+.B dmesg \-\-help
+output.
+.IP "\fB\-h\fR, \fB\-\-help\fR"
+Print a help text and exit.
+.IP "\fB\-k\fR, \fB\-\-kernel\fR"
+Print kernel messages.
+.IP  "\fB\-l\fR, \fB\-\-level \fIlist\fR"
+Restrict output to defined (comma separated)
+.I list
+of levels.  For example
+.PP
+.RS 14
+dmesg \-\-level=err,warn
+.RE
+.IP
+will print error and warning messages only.  For all supported levels see
+.B dmesg \-\-help
+output.
+.IP "\fB\-n\fR, \fB\-\-console-level \fIlevel\fR
+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\fR, \fB\-\-raw\fR"
+Print the raw message buffer, i.e., do not strip the log level prefixes.
+
+Note that the real raw format depends on method how
+.BR dmesg (1)
+reads kernel messages. The /dev/kmsg uses different format than
+.BR syslog (2) .
+For backward compatibility
+.BR dmesg (1)
+returns data always in
+.BR syslog (2)
+format. The real raw data from /dev/kmsg is possible to read for example by
+command 'dd if=/dev/kmsg iflag=nonblock'.
+.IP "\fB\-S\fR, \fB\-\-syslog\fR"
+Force to use
+.BR syslog (2)
+kernel interface to read kernel messages. The default is to use /dev/kmsg rather
+than
+.BR syslog (2)
+since kernel 3.5.0.
+.IP "\fB\-s\fR, \fB\-\-buffer-size \fIsize\fR
+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\fR, \fB\-\-ctime\fR"
+Print human readable timestamps.  The timestamp could be inaccurate!
+.IP
+The
+.B time
+source used for the logs is
+.B not updated after
+system
+.BR SUSPEND / RESUME .
+.IP "\fB\-t\fR, \fB\-\-notime\fR"
+Do not print kernel's timestamps.
+.IP "\fB\-u\fR, \fB\-\-userspace\fR"
+Print userspace messages.
+.IP "\fB\-V\fR, \fB\-\-version\fR"
+Output version information and exit.
+.IP "\fB\-w\fR, \fB\-\-follow\fR"
+Wait for new messages. This feature is supported on systems with readable
+/dev/kmsg only (since kernel 3.5.0).
+.IP "\fB\-x\fR, \fB\-\-decode\fR"
+Decode facility and level (priority) number to human readable prefixes.
+.SH SEE ALSO
+.BR syslogd (8)
+.SH AUTHORS
+.MT kzak@redhat.com
+Karel Zak
+.ME
+.br
+.MT tytso@athena.mit.edu
+Theodore Ts'o
+.ME
+.SH AVAILABILITY
+The dmesg command is part of the util-linux package and is available from
+.UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
+Linux Kernel Archive
+.UE .