10.3.3. Overriding or Augmenting Site Configuration Files

It can be useful to override site defaults for a specific mount point on a client system. For example, consider the following conditions:

Automounter maps are stored in NIS and the /etc/nsswitch.conf file has the following directive:
```
automount:    files nis
```
The auto.master file contains the following
```
+auto.master
```
The NIS auto.master map file contains the following:
```
/home auto.home
```

The NIS auto.home map contains the following:

beth        fileserver.example.com:/export/home/beth
joe        fileserver.example.com:/export/home/joe
*       fileserver.example.com:/export/home/&

The file map /etc/auto.home does not exist.

Given these conditions, let's assume that the client system needs to override the NIS map auto.home and mount home directories from a different server. In this case, the client will need to use the following /etc/auto.master map:

/home /etc/auto.home
+auto.master

And the /etc/auto.home map contains the entry:

*    labserver.example.com:/export/home/&

Because the automounter only processes the first occurrence of a mount point, /home will contain the contents of /etc/auto.home instead of the NIS auto.home map.

Alternatively, if you just want to augment the site-wide auto.home map with a few entries, create a /etc/auto.home file map, and in it put your new entries and at the end, include the NIS auto.home map. Then the /etc/auto.home file map might look similar to:

mydir someserver:/export/mydir
+auto.home

Given the NIS auto.home map listed above, ls /home would now output:

beth joe mydir

This last example works as expected because autofs knows not to include the contents of a file map of the same name as the one it is reading. As such, autofs moves on to the next map source in the nsswitch configuration.