Ubuntu’s built-in error logs to help diagnose any unseen faults

Ubuntu has a command that enables you to see detailed messages that are output directly by the operating system: the dmesg command, which is commonly used with the grep command to filter output. The dmesg command takes its output directly from the /var/log/messages file, so you can choose to either run dmesg directly or enter less /var/log/messages instead. The output is fairly detailed.

You might find it easier to generate a file with the dmesg output by using the following command:

dmesg > dmesg.txt

This takes the output from the dmesg command and stores it in a new text file called dmesg.txt. You can then browse it at your leisure using your choice of text editor such as vi or emacs. You can even use the less command, like so:

less dmesg.txt

You might find what appear to be errors at first glance, but some errors are not really problems (for example, if a piece of hardware is configured but not present on your system).

Thanks to Google, troubleshooting is no longer the slow process it used to be. You can simply copy and paste error messages into Google and click Find to bring up a whole selection of results similar to the problem you face. Remember, Google is your friend, especially http://www.google.com/linux, which provides a specialized search engine for Linux. You can also try http://marc.info, which browses newsgroup and mailing list archives. Either way, you are likely to come across people who have had the same problem as you.

Reference: Ubuntu Unleashed 2008 Edition