Checking the boot messages on Debian

Sometimes when a machine is booting up with Linux Operating System, some errors appears on the console while booting up, but they just pass too fast for one to read them. Therefore you need look at those messages somewhere else.

If you are using Debian, you can enable boot logging so all the messages send to console while booting will also be sent to a file that you can later examine.

Note for Ubuntu: Since Feisty, it seems that do not include bootlogd anymore, and the boot messages are now copied to: //var/log/dmesg from kernel's ring buffer, the script that does this is: /etc/init.d/bootmisc.sh

To enable this behavior which is off by default edit the file:

/etc/default/bootlogd

The default content of this file is:

# Run bootlogd at startup ?
BOOTLOGD_ENABLE=No

just change the No to Yes and the bootlogd command will start sending all messages to a file, which by default is: /var/log/boot.

You can also check /var/log/dmesg on Debian, or use the dmesg command, when using this command use also grep, to filter the output.