kernelbuffer/dmesg

NAME

kernelbuffer, 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. ## kernelbuffer/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. kernelbuffer 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. It's now Oct 2000 and I did implement that. ##

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)