NSS means Name Service Switch. There is a good description of NSS here: http://www.gnu.org/software/libc/manual/html_node/Name-Service-Switch.html
What is important to know about NSS from an application packaging perspective is:
- There are functions such as:
- translation a uid to a user name and back
- translation a gid to a group name and back
- translation a hostname to an IP addresses and back
- and more
- The behavior of those functions is configured in the NSS Configuration File
- Depending on the configuration in /etc/nsswitch.conf different NSS shared libraries can be loaded and used by an application, like libnss_files.so.2, libnss_dns.so.2, etc.
- Those libraries aren't detected by ldd, so if the application uses them the --with-nss option should be specified.