dmesg only shows you messages generated during and after your last boot, most of them read from
/var/log/messages and filtered by date ant time.
What you need to do is look at
/var/log/messages for errors and warnings when you reboot after a failure. For example:
Code:
sudo cat /var/log/messages | gawk 'BEGIN {IGNORECASE=1;}/error/{print;};/warning/{print;}'
will print all errors and warnings in your
message file.
Most of such errors and warnings are of no importance, but you may get a clue by looking at them.
If you're interested, here's a few lines of what I get on my system, none of any significance:
Code:
$ sudo cat /var/log/messages | gawk 'BEGIN {IGNORECASE=1;}/error/{print;};/warning/{print;}' | tail
Jan 11 17:32:57 localhost nmbd[1766]: Error was Cannot assign requested address
Jan 11 17:32:57 localhost nmbd[1766]: ERROR: Failed when creating subnet lists. Exiting.
Jan 11 20:33:41 localhost NetworkManager: <WARNING> nm_signal_handler (): Caught signal 15, shutting down normally.
Jan 12 05:31:43 localhost nmbd[1768]: Error = Cannot assign requested address
Jan 12 05:31:45 localhost nmbd[1768]: Error was Cannot assign requested address
Jan 12 05:31:46 localhost nmbd[1768]: ERROR: Failed when creating subnet lists. Exiting.
Jan 12 07:18:59 localhost NetworkManager: <WARNING> nm_signal_handler (): Caught signal 15, shutting down normally.
Jan 12 12:20:11 localhost nmbd[1760]: Error = Cannot assign requested address
Jan 12 12:20:13 localhost nmbd[1760]: Error was Cannot assign requested address
Jan 12 12:20:13 localhost nmbd[1760]: ERROR: Failed when creating subnet lists. Exiting.
(Actually, of some significance - the
samba nmb service is failing to start because of a configuration error. But I'm not using
samba now, so it can wait. And the
NetworkManager message is from a normal shutdown of my laptop.)