System Administration Guide: Naming and Directory Services (NIS+)

NIS+ and Login Passwords in /etc/passwd File

Your NIS+ password is stored in the NIS+ passwd table. Your user login password may be stored in NIS+ passwd table or in your /etc/passwd file. (Your user password and NIS+ password can be the same or different.) To change a password in an /etc/passwd file, you must run the passwd command with the nsswitch.conf file set to files or with the -r files flag.

The nsswitch.conf file specifies which password is used for which purpose. If the nsswitch.conf file is directing system queries to the wrong location, you will get password and permission errors.