PASSWD(4) File Formats and Configurations 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 naming
sources, such as the NIS maps passwd.byname and passwd.bygid, 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:password:uid:
gid:gcos-field:home-dir:
login-shell


where

username
is the user's login name.

The login (login) and role (role) fields accept a string
of no more than 32 bytes consisting of characters from the
set of alphabetic characters, numeric characters, period
(.), underscore (_), and hyphen (-). The first character
should be alphabetic and the field should contain at least
one lower case alphabetic character. A warning message is
displayed if these restrictions are not met.

The login and role fields must contain at least one
character and must not contain a colon (:) or a newline
(\n).


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. (UIDs
from 0-99 inclusive are reserved by the operating system vendor for use
in future applications. Their use by end system users or vendors of
layered products is not supported and may cause security related issues
with future applications.)


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 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 incorporating
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.

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 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:


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


and the password entry in 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. If the password entry in nsswitch.conf is:


passwd_compat: ldap
passwd: compat


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:


root:q.mJzTnu8icf.:0:1:Super-User:/:/sbin/sh
fred:6k/7KCFRPNVXg:508:10:& Fredericks:/usr2/fred:/bin/csh
+john:
+@documentation:no-login:
+::::Guest


The following is a sample passwd file when shadow does exist:


root:##root:0:1:Super-User:/:/sbin/sh
fred:##fred: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
assure that they can log in even when the system is running standalone.
The user john will have his password entry in the naming service source
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 gcos
field of Guest


FILES


/etc/nsswitch.conf


/etc/passwd


/etc/shadow


SEE ALSO


chgrp(1), chown(1), finger(1), groups(1), login(1), newgrp(1), passwd(1),
sh(1), sort(1), domainname(1M), getent(1M), passmgmt(1M), pwck(1M),
pwconv(1M), su(1M), useradd(1M), userdel(1M), usermod(1M), a64l(3C),
crypt(3C), getpw(3C), getpwnam(3C), getspnam(3C), putpwent(3C), group(4),
hosts.equiv(4), nsswitch.conf(4), shadow(4), environ(5), unistd.h(3HEAD)


System Administration Guide: Basic Administration


February 25, 2017 PASSWD(4)