passwd - password file
The file /etc/passwd is a local source of information about users' accounts. The password file can be used in conjunction with other naming
sources, such as the NIS maps passwd.byname and passwd.bygid, data from the NIS+ passwd table, or password data stored on an LDAP server.
Programs use the getpwnam(3C) routines to access this information.
Each passwd entry is a single line of the form:
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 that resides in the /etc directory. Because the encrypted passwords on a secure system 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.
The password file can contain entries beginning with a `+' (plus sign) or '-' (minus sign) to selectively incorporate entries from another
naming service source, such as NIS, NIS+, or LDAP.
A line beginning with a '+' means to incorporate entries from the naming service source. There are three styles of the '+' entries in this
file. A single + means to insert all the entries from the alternate naming service source at that point, while a +name means to insert the
specific entry, if one exists, from the naming service source. A +@netgroup means to insert the entries for all members of the network
group netgroup from the alternate naming service. If a +name entry has a non-null password, gcos, home-dir, or login-shell field, the value
of that field overrides what is contained in the alternate naming service. The uid and gid fields cannot be overridden.
A line beginning with a `-' means to disallow entries from the alternate naming service. There are two styles of `-` entries in this file.
-name means to disallow any subsequent entries (if any) for name (in this file or in a naming service), and -@netgroup means to disallow
any subsequent entries for all members of the network group netgroup.
This is also 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 incor-
porating the entire contents of the naming service's passwd database or password-related information after the passwd file.
Note that in compat mode, for every /etc/passwd entry, there must be a corresponding entry in the /etc/shadow file.
Appropriate precautions must be taken to lock the /etc/passwd file against simultaneous changes if it is to be edited with a text editor;
vipw(1B) does the necessary locking.
Example 1: Sample passwd File
The following is a sample passwd file:
and the sample password entry from nsswitch.conf:
passwd: files ldap
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 whose password information is stored on an LDAP server will be able to login with their usual password, shell,
and home directory.
If the password file is:
and the password entry in nsswitch.conf is:
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. If the password entry in nsswitch.conf is:
then all password-related entries stored on the LDAP server will be incorporated after the entries for root and fred.
The following is a sample passwd file when shadow does not exist:
The following is a sample passwd file when shadow does exist:
In this example, there are specific entries for users root and fred, to assure that they can log in even when the system is running stand-
alone. The user john will have his password entry in the naming service source incorporated without change, anyone in the netgroup documen-
tation will have their password field disabled, and anyone else will be able to log in with their usual password, shell, and home direc-
tory, but with a gcos field of Guest
chgrp(1), chown(1), finger(1), groups(1), login(1), newgrp(1), nispasswd(1), passwd(1), sh(1), sort(1), domainname(1M), getent(1M),
in.ftpd(1M), passmgmt(1M), pwck(1M), pwconv(1M), su(1M), useradd(1M), userdel(1M), usermod(1M), a64l(3C), crypt(3C), getpw(3C), getpw-
nam(3C), getspnam(3C), putpwent(3C), group(4), hosts.equiv(4), nsswitch.conf(4), shadow(4), environ(5), unistd.h(3HEAD)
28 Jul 2004 passwd(4)