What is NIS (yp)?

NIS (Network Information System) in the current name for what was once known as yp (Yellow Pages). The purpose of NIS is to allow many machines on a network to share configuration information, including password data. NIS is not designed to promote system security. If your system uses NIS you will have a very short /etc/passwd file that includes a line that looks like this:

+::0:0:::i

To view the real password file use this command `ypcat passwd`

NIS and NIS+ are being replaced by LDAP (Lightweight Directory Access Protocol).