Working with Linux log files

Linux has several log files that are useful in determining the health of your system. The four most important are:

• /VAR/ADM/SYSLOG
• /VAR/ADMMESSAGES
• /VAR/ADM/KERNEL
• /VAR/LOG

In Linux the LOG, the <SYSLOG>{+ } command will redirect where your logging entries are stored. Command information is stored in the MESSAGES log, although in Red Hat Linux the documentation tells you that these entries appear in the /VAR/LOG/XFERLOG file. When you use the LOG command, you'll find information in the /VAR/XFERLOG that documents what files were logged.

You can use the LOG [<TYPELIST>] command to create a log of the specific commands a user has executed. The TYPELIST is a list of anonymous, guest, and real users separated by commas. Two other related commands, LOG SECURITY [<TYPELIST>] and LOG TRANSFERS [<TYPELIST> <DIRECTIONS>], log security violations for these three user types and log all files transferred to and from a server.

It's a good idea to examine these files on a regular basis, save them in secure locations, and restrict access to these files to only those people with a need to know. These log files should never be in the root directory ( / ) where they can be hacked more easily.

Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.