147 lines
3.9 KiB
Groff
147 lines
3.9 KiB
Groff
.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\" May be distributed under the GNU General Public License
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.TH DMESG "1" "July 2012" "util-linux" "User Commands"
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.SH NAME
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dmesg \- print or control the kernel ring buffer
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.SH SYNOPSIS
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.B dmesg
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.RB [ options ]
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.sp
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dmesg \-\-clear
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.br
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dmesg \-\-read-clear [options]
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.br
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dmesg \-\-console-level level
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.br
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dmesg \-\-console-on
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.br
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dmesg \-\-console-off
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.SH DESCRIPTION
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.B dmesg
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is used to examine or control the kernel ring buffer.
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.PP
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The default action is to read all messages from kernel ring buffer.
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.SH OPTIONS
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The \-\-clear, \-\-read-clear, \-\-console-on, \-\-console-off and
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\-\-console-level options are mutually exclusive.
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.PP
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.IP "\fB\-C\fR, \fB\-\-clear\fR"
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Clear the ring buffer.
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.IP "\fB\-c\fR, \fB\-\-read-clear\fR"
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Clear the ring buffer contents after printing.
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.IP "\fB\-D\fR, \fB\-\-console-off\fR"
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Disable printing messages to the console.
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.IP "\fB\-d\fR, \fB\-\-show-delta\fR"
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Display the timestamp and time delta spent between messages. If used
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together with
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.B \-\-notime
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then only the time delta without the timestamp is printed.
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.IP "\fB\-E\fR, \fB\-\-console-on\fR"
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Enable printing messages to the console.
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.IP "\fB\-F\fR, \fB\-\-file \fIfile\fR"
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Read log from
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.IR file .
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.IP "\fB\-f\fR, \fB\-\-facility \fIlist\fR"
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Restrict output to defined (comma separated)
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.I list
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of facilities. For example
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.PP
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.RS 14
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dmesg \-\-facility=daemon
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.RE
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.IP
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will print messages from system daemons only. For all supported facilities
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see
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.B dmesg \-\-help
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output.
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.IP "\fB\-h\fR, \fB\-\-help\fR"
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Print a help text and exit.
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.IP "\fB\-k\fR, \fB\-\-kernel\fR"
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Print kernel messages.
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.IP "\fB\-l\fR, \fB\-\-level \fIlist\fR"
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Restrict output to defined (comma separated)
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.I list
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of levels. For example
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.PP
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.RS 14
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dmesg \-\-level=err,warn
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.RE
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.IP
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will print error and warning messages only. For all supported levels see
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.B dmesg \-\-help
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output.
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.IP "\fB\-n\fR, \fB\-\-console-level \fIlevel\fR
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Set the
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.I level
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at which logging of messages is done to the console. The
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.I level
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is a level number or abbreviation of the level name. For all supported
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levels see
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.B dmesg \-\-help
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output.
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.sp
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For example,
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.B \-n 1
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or
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.B \-n alert
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prevents all messages, except emergency (panic) messages, from appearing on
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the console. All levels of messages are still written to
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.IR /proc/kmsg ,
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so
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.BR syslogd (8)
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can still be used to control exactly where kernel messages appear. When the
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.B \-n
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option is used,
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.B dmesg
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will
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.I not
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print or clear the kernel ring buffer.
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.IP "\fB\-r\fR, \fB\-\-raw\fR"
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Print the raw message buffer, i.e., do not strip the log level prefixes.
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.IP "\fB\-S\fR, \fB\-\-syslog\fR"
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Force to use
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.BR syslog(2)
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kernel interface to read kernel messages. The default is to use /dev/kmsg rather
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than
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.BR syslog(2)
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since kernel 3.5.0.
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.IP "\fB\-s\fR, \fB\-\-buffer-size \fIsize\fR
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Use a buffer of
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.I size
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to query the kernel ring buffer. This is 16392 by default. (The default
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kernel syslog buffer size was 4096 at first, 8192 since 1.3.54, 16384 since
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2.1.113.) If you have set the kernel buffer to be larger than the default
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then this option can be used to view the entire buffer.
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.IP "\fB\-T\fR, \fB\-\-ctime\fR"
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Print human readable timestamps. The timestamp could be inaccurate!
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.IP
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The
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.B time
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source used for the logs is
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.B not updated after
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system
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.BR SUSPEND / RESUME .
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.IP "\fB\-t\fR, \fB\-\-notime\fR"
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Do not print kernel's timestamps.
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.IP "\fB\-u\fR, \fB\-\-userspace\fR"
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Print userspace messages.
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.IP "\fB\-V\fR, \fB\-\-version\fR"
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Output version information and exit.
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.IP "\fB\-x\fR, \fB\-\-decode\fR"
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Decode facility and level (priority) number to human readable prefixes.
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.SH SEE ALSO
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.BR syslogd (8)
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.SH AUTHORS
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.MT kzak@redhat.com
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Karel Zak
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.ME
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.br
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.MT tytso@athena.mit.edu
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Theodore Ts'o
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.ME
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.SH AVAILABILITY
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The dmesg command is part of the util-linux package and is available from
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.UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
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Linux Kernel Archive
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.UE .
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