diff options
Diffstat (limited to 'sys-utils/dmesg.1')
| -rw-r--r-- | sys-utils/dmesg.1 | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/sys-utils/dmesg.1 b/sys-utils/dmesg.1 new file mode 100644 index 0000000..a93821a --- /dev/null +++ b/sys-utils/dmesg.1 @@ -0,0 +1,256 @@ +.\" 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 +[options] +.sp +.B dmesg \-\-clear +.br +.BR "dmesg \-\-read\-clear " [options] +.br +.BI "dmesg \-\-console\-level " level +.br +.B dmesg \-\-console\-on +.br +.B dmesg \-\-console\-off +.SH DESCRIPTION +.B dmesg +is used to examine or control the kernel ring buffer. +.PP +The default action is to display all messages from the kernel ring buffer. +.SH OPTIONS +The +.BR \-\-clear , +.BR \-\-read\-clear , +.BR \-\-console\-on , +.BR \-\-console\-off , +and +.B \-\-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 after first printing its contents. +.IP "\fB\-D\fR, \fB\-\-console\-off\fR" +Disable the printing of messages to the console. +.IP "\fB\-d\fR, \fB\-\-show\-delta\fR" +Display the timestamp and the 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\-\-console\-on\fR" +Enable printing messages to the console. +.IP "\fB\-e\fR, \fB\-\-reltime\fR" +Display the local time and the delta in human-readable format. Be aware that +conversion to the local time could be inaccurate (see \fB\-T\fR for more +details). +.IP "\fB\-F\fR, \fB\-\-file \fIfile\fR" +Read the syslog messages from the given +.IR file . +Note that \fB\-F\fR does not support messages in kmsg format. The old syslog format is supported only. +.IP "\fB\-f\fR, \fB\-\-facility \fIlist\fR" +Restrict output to the given (comma-separated) +.I list +of facilities. For example: +.PP +.RS 14 +.B dmesg \-\-facility=daemon +.RE +.IP +will print messages from system daemons only. For all supported facilities +see the +.B \-\-help +output. +.IP "\fB\-H\fR, \fB\-\-human\fR" +Enable human-readable output. See also \fB\-\-color\fR, \fB\-\-reltime\fR +and \fB\-\-nopager\fR. +.IP "\fB\-k\fR, \fB\-\-kernel\fR" +Print kernel messages. +.IP "\fB\-L\fR, \fB\-\-color\fR[=\fIwhen\fR]" +Colorize the output. The optional argument \fIwhen\fP +can be \fBauto\fR, \fBnever\fR or \fBalways\fR. If the \fIwhen\fR argument is omitted, +it defaults to \fBauto\fR. The colors can be disabled; for the current built-in default +see the \fB\-\-help\fR output. See also the \fBCOLORS\fR section below. +.IP "\fB\-l\fR, \fB\-\-level \fIlist\fR" +Restrict output to the given (comma-separated) +.I list +of levels. For example: +.PP +.RS 14 +.B dmesg \-\-level=err,warn +.RE +.IP +will print error and warning messages only. For all supported levels see the +.B \-\-help +output. +.IP "\fB\-n\fR, \fB\-\-console\-level \fIlevel\fR +Set the +.I level +at which printing 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 the +.B \-\-help +output. +.sp +For example, +.B \-n 1 +or +.B \-n emerg +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\-P\fR, \fB\-\-nopager\fR" +Do not pipe output into a pager. A pager is enabled by default for \fB\-\-human\fR output. +.IP "\fB\-p\fR, \fB\-\-force\-prefix\fR" +Add facility, level or timestamp information to each line of a multi-line message. +.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 the method how +.BR dmesg (1) +reads kernel messages. The /dev/kmsg device uses a different format than +.BR syslog (2). +For backward compatibility, +.BR dmesg (1) +returns data always in the +.BR syslog (2) +format. It is possible to read the real raw data from /dev/kmsg by, for example, +the command 'dd if=/dev/kmsg iflag=nonblock'. +.IP "\fB\-S\fR, \fB\-\-syslog\fR" +Force \fBdmesg\fR to use the +.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. +.IP +.B Be aware that the timestamp could be inaccurate! +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\-\-time\-format\fR \fIformat\fR" +Print timestamps using the given \fIformat\fR, which can be +.BR ctime , +.BR reltime , +.B delta +or +.BR iso . +The first three formats are aliases of the time-format-specific options. +The +.B iso +format is a +.B dmesg +implementation of the ISO-8601 timestamp format. The purpose of this format is +to make the comparing of timestamps between two systems, and any other parsing, +easy. The definition of the \fBiso\fR timestamp is: +YYYY-MM-DD<T>HH:MM:SS,<microseconds><-+><timezone offset from UTC>. +.IP +The +.B iso +format has the same issue as +.BR ctime : +the time may be inaccurate when a system is suspended and resumed. +.TP +.BR \-u , " \-\-userspace" +Print userspace messages. +.TP +.BR \-w , " \-\-follow" +Wait for new messages. This feature is supported only on systems with +a readable /dev/kmsg (since kernel 3.5.0). +.TP +.BR \-x , " \-\-decode" +Decode facility and level (priority) numbers to human-readable prefixes. +.TP +.BR \-V , " \-\-version" +Display version information and exit. +.TP +.BR \-h , " \-\-help" +Display help text and exit. +.SH COLORS +Implicit coloring can be disabled by an empty file \fI/etc/terminal-colors.d/dmesg.disable\fR. +See +.BR terminal-colors.d (5) +for more details about colorization configuration. +.PP +The logical color names supported by +.B dmesg +are: +.TP +.B subsys +The message sub-system prefix (e.g. "ACPI:"). +.TP +.B time +The message timestamp. +.TP +.B timebreak +The message timestamp in short ctime format in \fB\-\-reltime\fR +or \fB\-\-human\fR output. +.TP +.B alert +The text of the message with the alert log priority. +.TP +.B crit +The text of the message with the critical log priority. +.TP +.B err +The text of the message with the error log priority. +.TP +.B warn +The text of the message with the warning log priority. +.TP +.B segfault +The text of the message that inform about segmentation fault. +.SH EXIT STATUS +.B dmesg +can fail reporting permission denied error. This is usually caused by +.B dmesg_restrict +kernel setting, please see +.BR syslog (2) +for more details. +.SH SEE ALSO +.BR terminal-colors.d (5), +.BR syslogd (8) +.SH AUTHORS +.MT kzak@redhat.com +Karel Zak +.ME + +.br +.B dmesg +was originally written by +.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 https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/ +Linux Kernel Archive +.UE . |