passwd(4) (man pages section 4: File Formats)

man pages section 4: File Formats

passwd(4)

NAME

passwd– password file

SYNOPSIS

/etc/passwd

DESCRIPTION

The file /etc/passwd is a local source of information about users' accounts. The password file can be used in conjunction with other password sources, such as 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.) An ``&'' (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 UIDs and GIDs 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.

Blank lines are treated as malformed entries in the passwd file and cause consumers of the file , such as getpwnam(3C), to fail.

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 might not be supported in future releases. The preferred sources are files followed by the identifier of a name service, such as nis or ldap. This has the effect of incorporating the entire contents of the name service's passwd database after the passwd file.

EXAMPLES

Example 1 Sample passwd file

The following is a sample passwd file:

root:x:0:1:Super-User:/:/sbin/sh
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:x:0:1:Super-User:/:/sbin/sh
fred:6k/7KCFRPNVXg:508:10:& Fredericks:/usr2/fred:/bin/csh
+

and the password entry from nsswitch.conf is:

passwd: compat

then all the entries listed in the NIS passwd.byuid and passwd.byname maps will be effectively incorporated after the entries for root and fred.

FILES

/etc/nsswitch.conf
/etc/passwd
/etc/shadow