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21.3.3. autofs Common Tasks 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, assuming that the automounter maps are stored in NIS and the /etc/nsswitch.conf file has the following directive:
automount:  files nis
and the NIS auto.master map file contains the following:
/home auto.home
Also assume the NIS auto.home map contains the following:
and the file map /etc/auto.home does not exist.
For the above example, lets assume that the client system needs to 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.home2
And the /etc/auto.home2 map contains the entry:
Because only the first occurrence of a mount point is processed, /home will contain the contents of /etc/auto.home2 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
Given the NIS auto.home map listed above, an ls of /home would now give:
~]$ ls /home
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 and so moves on to the next map source in the nsswitch configuration.