122 lines
3.5 KiB
Groff
122 lines
3.5 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 2011" "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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.B dmesg \-\-clear
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.sp
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.B dmesg \-\-read-clear
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.RB [ options ]
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.sp
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.B dmesg \-\-console-level
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.I level
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.sp
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.B dmesg \-\-console-on
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.sp
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.B 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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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 --console-level
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options are mutually exclusive.
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.IP "\fB\-C, \-\-clear\fP"
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Clear the ring buffer.
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.IP "\fB\-c, \-\-read-clear\fP"
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Clear the ring buffer contents after printing.
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.IP "\fB\-D, \-\-console-off\fP"
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Disable printing messages to the console.
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.IP "\fB\-d, \-\-show-delta\fP"
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Display the timestamp and time delta spent between messages. If used together
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with --notime then only the time delta without the timestamp is printed.
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.IP "\fB\-E, \-\-console-on\fP"
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Enable printing messages to the console.
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.IP "\fB\-F, \-\-file \fIfile\fP"
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Read log from file.
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.IP "\fB\-f, \-\-facility \fIlist\fP"
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Restrict output to defined (comma separated) list of facilities. For example
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.sp
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dmesg --facility=daemon
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.sp
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will print messages from system daemons only. For all supported facilities see
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.B dmesg \-\-help
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output.
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.IP "\fB\-h, \-\-help\fP"
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Print a help text and exit.
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.IP "\fB\-k, \-\-kernel\fP"
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Print kernel messages.
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.IP "\fB\-l, \-\-level \fIlist\fP"
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Restrict output to defined (comma separated) list of levels. For example
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.sp
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dmesg --level=err,warn
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.sp
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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, \-\-console-level \fIlevel\fP
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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 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 the
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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
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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, \-\-raw\fP"
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Print the raw message buffer, i.e., don't strip the log level prefixes.
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.IP "\fB\-s, \-\-buffer-size \fIsize\fP
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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.
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(The default kernel syslog buffer size was 4096
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at first, 8192 since 1.3.54, 16384 since 2.1.113.)
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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, \-\-ctime\fP"
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Print human readable timestamps. The timestamp could be inaccurate!
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.B The time source used for the logs is not updated after system SUSPEND/RESUME.
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.IP "\fB\-t, \-\-notime\fP"
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Don't print kernel's timestampts.
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.IP "\fB\-u, \-\-userspace\fP"
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Print userspace messages.
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.IP "\fB\-V, \-\-version\fP"
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Output version information and exit.
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.IP "\fB\-x, \-\-decode\fP"
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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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.nf
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Karel Zak <kzak@redhat.com>
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Theodore Ts'o <tytso@athena.mit.edu>
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.fi
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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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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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