Somehow the NSS code must be told about the wishes of the user. For this reason there is the file /etc/nsswitch.conf. For each database this file contain a specification how the lookup process should work. The file could look like this:
# /etc/nsswitch.conf # # Name Service Switch configuration file. # passwd: db files nis shadow: files group: db files nis hosts: files nisplus nis dns networks: nisplus [NOTFOUND=return] files ethers: nisplus [NOTFOUND=return] db files protocols: nisplus [NOTFOUND=return] db files rpc: nisplus [NOTFOUND=return] db files services: nisplus [NOTFOUND=return] db files
The first column is the database as you can guess from the table above. The rest of the line specifies how the lookup process works. Please note that you specify the way it works for each database individually. This cannot be done with the old way of a monolithic implementation.
The configuration specification for each database can contain two different items: