bootmessage/dmesg
NAME
bootmessage, dmesg - print or control the kernel message ring buffer
SYNOPSIS
dmesg [ -c ] [ -n level ] [ -s bufsize ]
DESCRIPTION
dmesg
is used to examine or control the kernel ring buffer. ## bootmessage/dmesg's
most common interactive
use is to read the system boot messages. It is the simplest place to see if your
ethernet card is supported, for example.
bootmessage displays the last 4k of the kernel's
text buffer, which usually contains the boot messages, but those will get clobbered
by
syslog'ed
messages too. In cLIeNUX that will include messages
about mounting unchecked filesystems, unless you rearrange the init process.
As I'm writing this
it occurs to me that a
/boot/messages file might be a handy thing to have
init generate.
##
OPTIONS
-nlevel
set the
level
at which logging of messages is done to the console. For example,
-n 1
prevents all messages, expect 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.
When both options are used, only the last option on the command line will
have an effect.
- -c
-
clear the ring buffer contents after printing.
- -sbufsize
-
use a buffer of bufsize to query the kernel ring buffer. This is
8196 by default (this matches the default kernel syslog buffer size in
2.0.33 and 2.1.103). If you have set the kernel buffer to larger than
the default then this option can be used to view the entire buffer.
SEE ALSO
syslogd(8)
## GRIPE
I just now noticed that dmesg controls console logging level. This is kind of
a funny place for it, and might well be a separate command, at least in name.
##
AUTHOR
Theodore Ts'o (tytso@athena.mit.edu)