Practical UNIX and Internet Security, 3rd Edition

Backing Up System Files

In addition to performing routine backups of your entire computer system, you may wish to make separate backup copies of system-critical files on a regular basis. These backups can serve several functions:

• They can help you quickly recover if a vital configuration file is unexpectedly erased or modified.

• They can help you detect unauthorized modifications to critical files, as well as monitor legitimate modifications.

• They make installing a new version of your operating system dramatically easier (especially if you do not wish to use your vendor’s “upgrade” facility) by isolating all site-dependent configuration files in a single place.

Ideally, you should back up every file that contains vital system configuration or account information.

Setting up an automatic system for backing up your system files is not difficult. You might, for instance, simply have a shell script that makes a tar file of the /etc directory on a regular basis. Or you might have a more sophisticated system, in which a particular workstation gathers all of the configuration files for every computer on a network, archives them in a directory, and sends you email each day that describes any modifications. The choice is up to you and your needs.

Which Files to Back Up?

If you are constructing a system for backing up system files on a regular basis, you should carefully consider which files you wish to archive and what you want to do with them.

By comparing a copy of the password file with /etc/passwd ...