Книга: Fedora™ Unleashed, 2008 edition

The /etc/nsswitch.conf File

The /etc/nsswitch.conf File

The file /etc/nsswitch.conf is the system databases and name service switch configuration file. It contains methods for many types of lookups, but here we are concerned with DNS resolution, so the line we are interested in is the hosts line. This line defines the methods to be used for resolving hostnames and the order in which to apply them. The methods used are the following:

? db — Local database files (*.db)

? files — Use the local file /etc/hosts

? dns — Use BIND

? nis — Use Sun's NIS

? nisplus — Use Sun's NIS+

The default line with Fedora is this:

hosts: files dns

With this default, the same methods and order are specified as in the default /etc/host.conf. First /etc/hosts is searched, and then DNS is used.

Another example is as follows:

hosts: files dns nisplus nis

In this example, name searches that fail in /etc/hosts and with DNS continue to the NIS services (nisplus and nis). NIS included with Fedora is the ypserv daemon.

When you are testing your configuration, you might want to halt name searching at a specific point. You can use the entry [NOTFOUND=return]. For example, to stop searching after looking in /etc/hosts, you would use the following line:

hosts: files [NOTFOUND=return] dns nisplus nis

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