login_name : password : uid : gid : comment : home_dir : login_shell
Fields are separated by a colon; entries, by a new-line. Comment lines (lines preceded by the # (hash) character) are not allowed in the /etc/passwd file.
/etc/passwd has general read permission on all systems, and can be used by routines that map numerical user IDs to names.
The passwd file can also have lines beginning with a + (plus sign) which means to incorporate entries from the Network Information Service (NIS). There are three styles of + entries in the passwd file: by itself, + means to insert the entire contents of the NIS password file at that point; +name means to insert the entry (if any) for name from the NIS service at that point; +@ netgroup means to insert the entries for all members of the network group netgroup at that point. If a + name entry has a non-null password, comment, home-dir, or login-shell field, the value of that field overrides what is contained in the NIS service. The uid and gid fields cannot be overridden.
The passwd file can also have lines beginning with a - (minus sign) which means to disallow entries from the NIS service. There are two styles of - entries in the passwd file: - name means to disallow any subsequent entries (if any) for name (in this file or in the NIS service); -@ netgroup means to disallow any subsequent entries for all members of the network group netgroup.
When the Network Information Service (NIS) is in use, the local /etc/passwd file is consulted first, then the NIS maps passwd.byname or passwd.byuid on the NIS server.
root:x:0:10:God:/:/bin/csh fred:x:508:10:& Fredericks:/usr2/fred:/bin/csh +john: +@documentation:no-login: +::::Guest
In this example, there are specific entries for users root and fred, to ensure that they can log in even when the system is running standalone. The user john will have his password entry in the NIS service incorporated without change; anyone in the netgroup documentation will have their password field disabled, and anyone else will be able to log in with their usual password, shell, and home directory, but with a comment field of Guest.