passwd - password file, pwd.h
/etc/passwd contains the following information for each user:
+ login name
+ encrypted password
+ numerical user ID
+ numerical group ID
+ reserved gecos ID
+ initial working directory
+ program to use as shell
This is an ASCII file. Each field within each user's entry is
separated from the next by a colon. Each user is separated from the
next by a newline. This file resides in the /etc directory. It can
and does have general read permission and can be used, for example, to
map numerical user IDs to names.
getpwent(3C) returns a pointer to a user's entry passwd structure
declared in <<<<pwd.h>>>>
The login name must begin with an alpha character and may only contain
alphanumeric and underscore characters. If the login directory is
null the user will be placed in / by default. If the login shell is
null, /usr/bin/sh is used.
It is suggested that the range 0-99 not be used for user and group IDs
so that IDs that might be assigned for system software do not
The gecos field may contain the following identification: user's full
name, office location, extension, and home phone. The gecos field can
be set by use of the chfn command and is displayed by the finger
command (see chfn(1) and finger(1)). These two commands assume the
information in this field is in the order listed above. A portion of
the user's real name can be represented in the gecos field by an &&&&
character, which some utilities (including finger) expand by
substituting the login name for it and shifting the first letter of
the login name to uppercase.
The following description of the password field applies only to a
standard system. For a trusted system see the SECURITY FEATURES
If the password field is null there is no password and no password is
demanded on login. Otherwise this field consists of an encrypted
password with an optional password aging subfield.
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The encrypted password consists of 13 characters chosen from a 64-
character set of "digits" described below, Login can be prevented by
entering in the password field a character that is not part of the set
of digits (such as *).
The characters used to represent "digits" are . for 0, / for 1, 0
through 9 for 2 through 11, A through Z for 12 through 37, and a
through z for 38 through 63.
Password aging is put in effect for a particular user if his encrypted
password in the password file is followed by a comma and a non-null
string of characters from the above alphabet. (Such a string must be
introduced in the first instance by a superuser.) This string defines
the "age" needed to implement password aging.
UNIX keeps internal time stamps in a format with a base date of
Thursday January 1, 1970. Because of this, passwd considers the
beginning of a week to be 00:00 GMT Thursday.
The first character of the age, M, denotes the maximum number of weeks
for which a password is valid. A user who attempts to login after his
password has expired is forced to supply a new one. The next
character, m, denotes the minimum period in weeks that must expire
before the password can be changed. The remaining two characters
define the week when the password was last changed (a null string is
equivalent to zero). M and m have numerical values in the range 0
through 63 that correspond to the 64-character set of "digits" shown
If m = M = 0 (derived from the string . or ..), the user is forced to
change his password next time he logs in (and the "age" disappears
from his entry in the password file). If m > M (signified, for
example, by the string ./), then only a superuser (not the user) can
change the password. Not allowing the user to ever change the
password is discouraged.
This section applies only to trusted systems. On a trusted system the
password field always contains * by default. Password and aging
information are instead part of the Protected Password Database.
On trusted systems, the encrypted password for each user is stored in
the file /tcb/files/auth/c/user_name (where c is the first letter in
user_name). Password information files are not accessible to the
public. The encrypted password can be longer than 13 characters. For
example, the password file for user david is stored in
/tcb/files/auth/d/david. In addition to the password, the user
profile in /tcb/files/auth/c/user_name also has many other fields,
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+ numerical audit ID
+ numerical audit flag
Like /etc/passwd, this file is an ASCII file. Fields within each
user's entry are separated by colons. Refer to authcap(4) and
prpwd(4) for details. The passwords contained in /tcb/files/auth/c/*
take precedence over those contained in the encrypted password field
of /etc/passwd. User authentication is done using the encrypted
passwords in this file. The password aging mechanism described in
passwd(1), under the section called SECURITY FEATURES, applies to this
For more information on converting to trusted system and on password,
see Managing Systems and Workgroups and sam(1M).
The passwd file can have entries that begin with a plus (+) or minus
(-) sign in the first column. Such lines are used to access the
Network Information System network database. A line beginning with a
plus (+) is used to incorporate entries from the Network Information
System. There are three styles of + entries:
+ Insert the entire contents of the Network Information
System password file at that point;
+name Insert the entry (if any) for name from the Network
Information System at that point
+@name Insert the entries for all members of the network
group name at that point.
If a + entry has a non-null password, directory, gecos, or shell
field, they override what is contained in the Network Information
System. The numerical user ID and group ID fields cannot be
The passwd file can also have lines beginning with a minus (-), which
disallow entries from the Network Information System. There are two
styles of - entries:
-name Disallow any subsequent entries (if any) for name.
-@name Disallow any subsequent entries for all members of
the network group name.
The plus (+) and minus (-) features are NIS functionality; therefore,
if NIS is not installed, they do not work. Also, these features work
only with /etc/passwd, but not with a system that has been converted
to a trusted system. When the system has been converted to a trusted
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system, the encrypted passwords can be accessed only from the
protected password database, /tcb/files/auth/*/*. Any user entry in
the Network Information System database also must have an entry in the
protected password database.
The uid of -2 is reserved for remote root access by means of NFS. The
user name usually given to this uid is nobody. Since uids are stored
as signed values, the following define is included in <<<<pwd.h>>>> to match
the user nobody.
The login shell for the root user (uid 0) must be /sbin/sh to
guarantee it can always boot. Other shells such as sh, ksh, and csh
are all located under the /usr directory which may not be mounted
during earlier stages of the bootup process. Changing the login shell
of the root user to a value other than /sbin/sh is allowed but may
result in a non-functional system.
The information kept in the gecos field may conflict with unsupported
or future uses of this field. Use of the gecos field for keeping user
identification information has not been formalized within any of the
industry standards. The current use of this field is derived from its
use within the Berkeley Software Distribution. Future standards may
define this field for other purposes.
The following fields have size limitations as noted:
+ Login name field can be no longer than 8 characters;
+ Initial working directory field can be no longer than 63
+ Program field can be no longer than 44 characters.
+ Results are unpredictable if these fields are longer than the
limits specified above.
The following fields have numerical limitations as noted:
+ The user ID is an integer value between 0 and UID_MAX-1
inclusive. As a special case -2 maybe present.
+ The group ID is an integer value between 0 and UID_MAX-1
inclusive. As a special case -2 maybe present.
+ If either of these values are out of range, the getpwent(3C)
functions reset the ID value to (UID_MAX).
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Here is a sample /etc/passwd file:
joe:r4hRJr4GJ4CqE:100:50:Joe User,Post 4A,12345:/home/joe:/usr/bin/ksh
In this example, there are specific entries for users root and joe, in
case the Network Information System are out of order.
+ User john's password entry in the Network Information System
is incorporated without change.
+ Any subsequent entries for user bob are ignored.
+ The password field for anyone in the netgroup documentation
+ Users in netgroup marketing are not returned by getpwent(3C)
and thus are not allowed to log in.
+ Anyone else can log in with their usual password, shell, and
home directory, but with a gecos field of Guest.
/tcb/files/auth/*/* Protected password database used when
system is converted to trusted system.
/etc/passwd Standard password file used by HP-UX.
chfn(1), chsh(1), finger(1), login(1), passwd(1), pwck(1),
useradd(1M), a64l(3C), crypt(3C), getpass(3C), getpwent(3C),
getprpwent(3), authcap(4), limits(5).
passwd: SVID2, SVID3, XPG2
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