When I get saddled with an unfamiliar server, the first thing I do is look for the previous sysadmin’s documentation. When I discover there isn’t any, I study the /etc directory because it contains the basic configuration for a Unix-like system. The fastest way to go from a junior sysadmin to a midgrade one is to read /etc and the associated man pages—all of the documentation. Yes, that’s a lot of reading.

Once you understand /etc, you understand how the system hangs together. You must learn all this anyhow, but you might as well take the easier route and learn it up front rather than in an unscheduled series of desperate troubleshooting sessions. (I’ve already discussed many /etc files in earlier chapters where relevant, such as /etc/fstab in Chapter 8 and /etc/services in Chapter 11.)

Some files that you’ll find in /etc are of only historical interest or are gradually dying out. I’ll discuss briefly what they do, but I won’t spend much time on obsolete files. I also won’t spend much time on files useful only in edge cases (where they relate to software that’s not used too often or only in very peculiar circumstances). On the other hand, I will dive deeply into important /etc files that haven’t already found a place elsewhere in this book.