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/etc/passwd is a local source of information about users’ accounts. The password file can be used in conjunction with other password sources, including the NIS maps passwd.byname and passwd.bygid and the NIS + table passwd. Programs use the getpwnam(3C) routines to access this information.
Each passwd entry is a single line of the form:
username:password:uid:gid:gcos-field:home-dir:login-shell
where
- username
- is the user’s login name. It is recommended that this field conform to the checks performed by pwck(1M) .
- password
- is an empty field; The encrypted password for the user is in the corresponding entry in the /etc/shadow file. pwconv(1M) relies on a special value of ’x’ in the password field of /etc/passwd. If this value of ’x’ exists in the password field of /etc/passwd, this indicates that the password for the user is already in /etc/shadow and should not be modified.
- uid
- is the user’s unique numerical ID for the system.
- gid
- is the unique numerical ID of the group that the user belongs to.
- gcos-field
- is the user’s real name, along with information to pass along in a mail-message heading. (It is called the gcos-field for historical reasons.) A ‘‘&’’ (ampersand) in this field stands for the login name (in cases where the login name appears in a user’s real name).
- home-dir
- is the pathname to the directory in which the user is initially positioned upon logging in.
- login-shell
- is the user’s initial shell program. If this field is empty, the default shell is /usr/bin/sh.
The maximum value of the uid and gid fields is 2147483647. To maximize interoperability and compatibility, administrators are recommended to assign users a range of UID s and GID s below 60000 where possible.
The password file is an ASCII file. Because the encrypted passwords are always kept in the shadow file, /etc/passwd has general read permission on all systems, and can be used by routines that map between numerical user IDs and user names.
Previous releases used a password entry beginning with a ‘+’ (plus
sign) or ‘-’ (minus sign) to selectively incorporate entries from NIS
maps
for password. If still required, this is supported by specifying ‘‘passwd
: compat’’ in nsswitch.conf(4)
. The ‘‘compat’’ source may not be supported in future
releases. The preferred sources are, ‘‘files’’ followed by ‘‘nisplus’’. This has
the effect of incorporating the entire contents of the NIS
+ passwd table
after the password file.
root:q.mJzTnu8icF.:0:10:God:/:/bin/csh fred:6k/7KCFRPNVXg:508:10:% Fredericks:/usr2/fred:/bin/csh
and the sample password entry from nsswitch.conf:
passwd: files nisplus
In this example, there are specific entries for users root and fred to assure that they can login even when the system is running single-user. In addition, anyone in the NIS + table passwd will be able to login with their usual password, shell and home directory.
If the password file is:
root:q.mJzTnu8icF.:0:10:God:/:/bin/csh fred:6k/7KCFRPNVXg:508:10:% Fredericks:/usr2/fred:/bin/csh +
and the password entry from nsswitch.conf:
passwd: compat
all the entries listed in the NIS passwd.byuid and passwd.byname maps will be effectively incorporated after the entries for root and fred.