Linux System Administration

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Chapter 4: An Initial Internet-Ready Environment

If you get an “-ERR Unknown AUTHORIZATION state command”

error message when trying to fetch your mail via POP3, you have

probably forgotten to activate SSL/TLS encryption. Reconfigure your

email client, activate POP3-over-SSL, and try again.

Safeguarding a Linux Web Server

In today’s business environment, unexpected events often occur. Ill-intentioned indi-

viduals scan IP addresses looking for exploits. They use sophisticated password dic-

tionaries to attempt to gain root access to servers so they can relay spam, viruses,

and worms. The situations system administrators face arise from a unique combina-

tion of shifting factors that cannot be controlled with precision or certainty. Conse-

quently, administrators need to learn to adapt quickly to new (often hostile)

situations.

There are two ways to adapt. First, if you have enough awareness to understand a sit-

uation in advance, you can take precautions. We’ll call this anticipation.

At other times, however, you’ll have to adapt to the situation on the spur of the

moment, without time for preparation. This involves improvisation. To be fully

adaptable, you must be able to both anticipate and improvise.

The Role of a Daemon-Monitoring Daemon

No matter how rigorously you work at safeguarding your Internet server, for some

unknown combination of reasons, something on your system could fail. In