The above example file mentions five different services: files,
db, dns, nis, and nisplus. This does not
mean these
services are available on all sites and neither does it mean these are
all the services which will ever be available.
In fact, these names are simply strings which the NSS code uses to find the implicitly addressed functions. The internal interface will be described later. Visible to the user are the modules which implement an individual service.
Assume the service name shall be used for a lookup. The code for this service is implemented in a module called libnss_name. On a system supporting shared libraries this is in fact a shared library with the name (for example) libnss_name.so.2. The number at the end is the currently used version of the interface which will not change frequently. Normally the user should not have to be cognizant of these files since they should be placed in a directory where they are found automatically. Only the names of all available services are important.
Lastly, some system software may make use of the NSS configuration file
to store their own configuration for similar purposes. Examples of this
include the automount service which is used by autofs.