System Administration: Maximizing Linux Security: Part 2

Last month's installment covered many aspects of password protection. This month's installment goes on to explain several other aspects of system security.
Probing Network Vulnerabilities

The network should be examined for potential security problems on a regular basis just like the local system. The once notorious Satan program provides one way of doing so. Satan is designed to look for network vulnerabilities from the outside in. It looks for a variety of problems, including:

  • The availability of notoriously insecure network services, such as rexd and old versions of sendmail.

  • The setup of any ftp and/or tftp facilities.

  • A variety of NFS vulnerabilities.

  • X server vulnerabilities.

  • Unprotected modems.

For those concerned about the misuse of such a powerful tool, the Gabriel and Courtney packages attempt to detect suspicious uses of Satan itself.

Don't Despair

We've covered a wide variety of threats to system security in this article. Don't let the sheer number of them overwhelm you. All you can do is protect your system as well as is currently possible and make frequent backups so that you can recover quickly in the event that your best efforts are not enough. Remember that system security is an ongoing process, not something you can take care of once and then forget about. And as in all of life, there are no guarantees.

See sidebars for security resources or more information about system security.

Æleen Frisch ( manages a very heterogeneous network of Linux and other UNIX systems and PCs. Having recently finished second editions of two books, she looks forward to pursuing her true calling: pulling the string for her cats, Daphne and Sarah.