Log files
From Linux 101, The beginner's guide to all things Linux.
Log files for the system are mostly stored in /var/log and are produced by system loggers. Depending on what your system runs, you will see logs for various things:
- Kernel
- XFree/Xorg
- Login managers (SSH/KDM/XDM/GDM)
- Printing (CUPS)
- Windows network logging (Samba)
- Daemon logging (Apache, SQL servers, etc.)
These can be crucial to review what is happening on your system. Also if your computer freezes (not an often problem) this can possibly help you to track down what made it fail.

