passwd(4)
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passwd File Format
password file
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SYNTAX
/etc/passwd
DESCRIPTION
The passwd file contains for each user the following information:
name User's login name. Contains no uppercase characters and
must not be greater than USR_NAME (see limits(4))
characters long.
password encrypted password.
numerical user id
This is the user's id in the system and it must be
unique. Otherwise, users with the same uid will be
able to access each other's files.
numerical group id
This is the number of the group that the user belongs
to.
user's real name
Some system administrators use this field to contain
the user's office, extension, home phone, and so on.
For historical reasons this field is called the GCOS
field.
initial working directory
The directory that the user is positioned in when they
log in - this is also known as the home directory.
shell program to use as shell when the user logs in.
The user's real name field may contain "&", meaning to insert the
login name.
The password file 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 new-line. If the password field is
null, no password is demanded; if the shell field is null,
/bin/sh is used.
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passwd(4)
This file resides in directory /etc. Because of the encrypted
passwords, it has general read permission. It can be used, for
example to map numerical user IDs to names.
The encrypted password consists of 13 characters chosen from a
64-character alphabet ( . , / , 0-9 , A-Z , a-z ), except when
the password is null. In that case, the encrypted password is
also null. Password aging is affected for a particular user if
the user's 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 first be introduced by the
superuser).
The first character of the age denotes the maximum number of
weeks for which a password is valid. If you try to login after
your password has expired, you must supply a new one. The next
character denotes the minimum period in weeks that must elapse
before the password may be changed. The remaining characters
define the week (counted from the beginning of 1970) when the
password was last changed ( a null string is equivalent to zero).
The first and second characters have numerical values in the
range 0-63 that correspond to the 64-character alphabet shown
above (i.e., / = 1 week; z = 63 weeks). If both characters are
equal to zero (derived from the string "." or ".."), you must
change your password the next time you login. The age will
disappear from your entry in the password file. If the second
character is greater than the first (signified, e.g., by the
string "./"), then only the superuser will be able to change the
password.
The passwd file can also have lines beginning with a plus (+),
which means to incorporate entries from the Yellow Pages.
NOTE:
You must be using the Network File System (NFS) to use this
feature.
There are three styles of + entries: all by itself, + means to
insert the entire contents of the Yellow Pages password file at
that point; +name means to insert the entry (if any) for name
from the Yellow Pages at that point; +@name means to insert the
entries for all members of the network group name at that point.
If a + entry has a non-null password, directory, user's real
name, or shell field, they will override what is contained in the
Yellow Pages. The numerical user ID and group ID fields cannot
be overridden.
Entries beginning with a minus sign (-) are also allowed. They
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passwd(4)
have two formats: -name and -@name. The meaning of these formats
is the same as for +name and +@name, respectively, except that
the action is reversed; all members matched are considered to be
excluded from the password file, regardless of subsequent
entries. Minus entries can be used to exclude specific entries
from the Yellow Pages.
EXAMPLE
Here is a sample /etc/passwd file:
root:q.mJzTnu8icF.:0:10:God:/:/bin/csh
tut:6k/7KCFRPNVXg:508:10:Bill Tuthill:/usr/tut:/bin/csh
+john:
-@documentation:no-login:
+:::Guest
john::605:20:John Smith:/usr/john:
In this example, there are specific entries for users root and
tut, in case the Yellow Pages are not running. (See The Network
File System on Your DG/UX System.) The user john will have his
password entry in the Yellow Pages incorporated without change;
anyone in the netgroup documentation will have their password
field disabled, and anyone else will be able to login with their
usual password, shell, and home directory, but with a GCOS field
of Guest.
The second entry for john in this example will not be used if the
Yellow Pages are running; the first entry for a given user name
will be used if multiple entries exist.
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(1M) does the necessary locking. The password
file can be scanned for inconsistencies using pwck(1M).
FILES
/etc/passwd
SEE ALSO
getpwent(3C), login(1), crypt(3C), passwd(1), group(4), vipw(1M),
adduser(8), pwck(1M), limits(4)
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