NAME¶

dmesg - print or control the kernel ring buffer

SYNOPSIS¶

dmesg [options] dmesg --clear dmesg --read-clear [options] dmesg --console-level level dmesg --console-on dmesg --console-off

DESCRIPTION¶

dmesg is used to examine or control the kernel ring buffer. The default action is to read all messages from kernel ring buffer.

OPTIONS¶

The --clear, --read-clear, --console-on, --console-off and --console-level options are mutually exclusive.

-C, --clear

Clear the ring buffer.

-c, --read-clear

Clear the ring buffer contents after printing.

-D, --console-off

Disable printing messages to the console.

-d, --show-delta

Display the timestamp and time delta spent between messages. If used together with --notime then only the time delta without the timestamp is printed.

-E, --console-on

Enable printing messages to the console.

-f, --facility list

Restrict output to defined (comma separated) list of facilities. For example

 

dmesg --facility=daemon

 

will print messages from system daemons only. For all supported facilities see dmesg --help output.

-h, --help

Print a help text and exit.

-k, --kernel

Print kernel messages.

-l, --level list

Restrict output to defined (comma separated) list of levels. For example

 

dmesg --level=err,warn

 

will print error and warning messages only. For all supported levels see dmesg --help output.

-n, --console-level level

Set the level at which logging of messages is done to the console. The level is a level number or abbreviation of the level name. For all supported levels see dmesg --help output.

 

For example, -n 1 or -n alert prevents all messages, except emergency (panic) messages, from appearing on the console. All levels of messages are still written to /proc/kmsg, so syslogd(8) can still be used to control exactly where kernel messages appear. When the -n option is used, dmesg will not print or clear the kernel ring buffer.

-r, --raw

Print the raw message buffer, i.e., don't strip the log level prefixes.

-s, --buffer-size size

Use a buffer of 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.

-T, --ctime

Print human readable timestamps. The timestamp could be inaccurate!

 

The time source used for the logs is not updated after system SUSPEND/RESUME.

-t, --notime

Don't print kernel's timestampts.

-u, --userspace

Print userspace messages.

-V, --version

Output version information and exit.

-x, --decode

Decode facility and level (priority) number to human readable prefixes.

SEE ALSO¶

syslogd(8)

AUTHORS¶

Karel Zak <kzak@redhat.com>
Theodore Ts'o <tytso@athena.mit.edu>

AVAILABILITY¶

The dmesg command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.