What is /etc/nsswitch.conf?

An idea whose time has come (it came to Ultrix a few years
ago). You can control which of the "resolver" services are
read from NIS (formerly YP), which from NIS+, which from the
files in /etc, and which are from DNS (but only "hosts" can
come from DNS).

A common example would be:

hosts: nis files

which means ask NIS for host info and, if it's not found, try
the local machine's host table as a fallback.

Advice: if you're not using NIS or DNS, SunInstall probably put
the right version in. If you are, ensure that hosts and passwd
come from the network. However, many of the other services
seldom if ever change. When was that last time you
added a line in /etc/protocols? If your workstation has a local
disk, it may be better to have programs on your machine look up
these services locally, so use "files".

Terminology: Sun worried over the term "resolver", which
technically means any "get info" routine (getpwent(3),
gethostbyname(3), etc), but is also specifically attached to
the DNS resolver. Therefore they used the term "source" to
mean the things after the colon (files/DNS/NIS/NIS+) and
"database" to mean the thing before the colon
(passwd/group/hosts/services/netgroup etc).

A complete discussion can be found in nsswitch.conf(4).

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