libnss-pgsql - Name Service Switch module for use with PostgreSQL
Chapter 3 Name Service Switch Setup

WARNING: You can do serious damage to your system if you do not know what you are doing! If you are trying changes in the Name Service Switch for the very first time, consider doing that in a chroot environment or a test machine. Have at least an editor with /etc/nsswitch.conf open to revert your changes easily. You have been warned!

Setting up the Name Service Switch is fairly easy, given a working installation of the libnss-pgsql module. Just add an entry pgsql the passwd and group lines of /etc/nsswitch.conf. You can tune the behaviour with options between the entries to get a fully working system. Useful lines in /etc/nsswitch.conf would look like these:

     passwd:         compat [SUCCESS=continue] pgsql
     group:          compat [SUCCESS=continue] pgsql

This will make your libc look into the standard passwd and group files first, then lookup names via NIS (that is integrated in the libnss-compat modules) and then use libnss-pgsql. The option [SUCCESS=continue] ensures that all accounts or groups are retrieved when using the iteration functions getpwent(3) and getgrent(3).