The named.boot file is generally very small and contains little else but pointers to master files containing zone information, and pointers to other name servers. Comments in the boot file start with a semicolon and extend to the next newline. Before we discuss the format of named.boot in more detail, we will take a look at the sample file for vlager given in figure .
Figure: The named.boot file for vlager.
The cache and primary commands shown in this example load information into named. This information is taken from the master files specified in the second argument. They contain textual representations of DNS resource records, which we will look at below.
In this example, we configured named as the primary name server for three domains, as indicated by the primary statements at the end of the file. The first of these lines, for instance, instructs named to act as a primary server for vbrew.com, taking the zone data from the file named.hosts. The directory keyword tells it that all zone files are located in /var/named.
The cache entry is very special and should be present on virtually all machines running a name server. Its function is two-fold: it instructs named to enable its cache, and to load the root name server hints from the cache file specified (named.ca in our example). We will come back to the name server hints below.
Here's a list of the most important options you can use in named.boot:
There are two options which we will not describe here, being sortlist and domain. Additionally, there are two directives that may be used inside the zone database files. These are $INCLUDE and $ORIGIN. Since they are rarely needed, we will not describe them here, either.