-.\" Copyright (c) 1993 Michael Haardt (michael@moria.de), Fri Apr 2 11:32:09 MET DST 1993
+.\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
+.\" Fri Apr 2 11:32:09 MET DST 1993
.\"
+.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
-.\" License along with this manual; if not, write to the Free
-.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
-.\" USA.
+.\" License along with this manual; if not, see
+.\" <http://www.gnu.org/licenses/>.
+.\" %%%LICENSE_END
.\"
.\" Modified Sun Jul 25 10:46:28 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Sun Aug 21 18:12:27 1994 by Rik Faith (faith@cs.unc.edu)
.\" Modified Sun Jun 18 01:53:57 1995 by Andries Brouwer (aeb@cwi.nl)
.\" Modified Mon Jan 5 20:24:40 MET 1998 by Michael Haardt
.\" (michael@cantor.informatik.rwth-aachen.de)
-.TH PASSWD 5 1998-01-05 "Linux" "Linux Programmer's Manual"
+.TH PASSWD 5 2015-02-01 "Linux" "Linux Programmer's Manual"
.SH NAME
passwd \- password file
.SH DESCRIPTION
-.B Passwd
-is a text file, that contains a list of the system's accounts,
-giving for each account some useful information like user ID,
-group ID, home directory, shell, etc.
-Often, it also contains the encrypted passwords for each account.
-It should have general read permission (many utilities, like
+The
+.IR /etc/passwd
+file is a text file that describes user login accounts for the system.
+It should have read permission allowed for all users (many utilities, like
.BR ls (1)
-use it to map user IDs to user names), but write access only for the
+use it to map user IDs to usernames), but write access only for the
superuser.
.PP
In the good old days there was no great problem with this general
read permission.
Everybody could read the encrypted passwords, but the
-hardware was too slow to crack a well-chosen password, and moreover, the
+hardware was too slow to crack a well-chosen password, and moreover the
basic assumption used to be that of a friendly user-community.
These days many people run some version of the shadow password suite, where
.I /etc/passwd
-has asterisks (*) instead of encrypted passwords,
+has an \(aqx\(aq character in the password field,
and the encrypted passwords are in
-.I /etc/shadow
+.IR /etc/shadow ,
which is readable by the superuser only.
.PP
-Regardless of whether shadow passwords are used, many sysadmins
-use an asterisk in the encrypted password field to make sure
+If the encrypted password, whether in
+.I /etc/passwd
+or in
+.IR /etc/shadow ,
+is an empty string, login is allowed without even asking for a password.
+Note that this functionality may be intentionally disabled in applications,
+or configurable (for example using the "nullok" or "nonull" arguments to
+pam_unix.so).
+.PP
+If the encrypted password in
+.I /etc/passwd
+is "\fI*NP*\fP" (without the quotes),
+the shadow record should be obtained from an NIS+ server.
+.PP
+Regardless of whether shadow passwords are used, many system administrators
+use an asterisk (*) in the encrypted password field to make sure
that this user can not authenticate him- or herself using a
-password. (But see the Notes below.)
+password.
+(But see NOTES below.)
.PP
-If you create a new login, first put an asterisk in the password field,
+If you create a new login, first put an asterisk (*) in the password field,
then use
.BR passwd (1)
to set it.
.PP
-There is one entry per line, and each line has the format:
+Each line of the file describes a single user,
+and contains seven colon-separated fields:
.sp
.RS
-account:password:UID:GID:GECOS:directory:shell
+name:password:UID:GID:GECOS:directory:shell
.RE
.sp
-The field descriptions are:
-.RS
-.TP 1.0in
-.I account
-the name of the user on the system.
+The field are as follows:
+.TP 12
+.I name
+This is the user's login name.
It should not contain capital letters.
.TP
.I password
-the encrypted user password, an asterisk (*), or the letter \'x\'.
+This is either the encrypted user password,
+an asterisk (*), or the letter \(aqx\(aq.
(See
.BR pwconv (8)
-for an explanation of \'x\'.)
+for an explanation of \(aqx\(aq.)
.TP
.I UID
-the numerical user ID.
+The privileged
+.I root
+login account (superuser) has the user ID 0.
.TP
.I GID
-the numerical primary group ID for this user.
+This is the numeric primary group ID for this user.
+(Additional groups for the user are defined in the system group file; see
+.BR group (5)).
.TP
.I GECOS
-This field is optional and only used for informational purposes.
-Usually, it contains the full user name.
-GECOS means General Electric
-Comprehensive Operating System, which has been renamed to GCOS when
+This field (sometimes called the "comment field")
+is optional and used only for informational purposes.
+Usually, it contains the full username.
+Some programs (for example,
+.BR finger (1))
+display information from this field.
+.IP
+GECOS stands for "General Electric Comprehensive Operating System",
+which was renamed to GCOS when
GE's large systems division was sold to Honeywell.
Dennis Ritchie has reported: "Sometimes we sent printer output or
batch jobs to the GCOS machine.
Not elegant."
.TP
.I directory
-the user's
-.B $HOME
-directory.
+This is the user's home directory:
+the initial directory where the user is placed after logging in.
+The value in this field is used to set the
+.B HOME
+environment variable.
.TP
.I shell
-the program to run at login (if empty, use
+This is the program to run at login (if empty, use
.IR /bin/sh ).
-If set to a non-existing executable, the user will be unable to login
+If set to a nonexistent executable, the user will be unable to login
through
.BR login (1).
-.RE
+The value in this field is used to set the
+.B SHELL
+environment variable.
.SH FILES
.I /etc/passwd
.SH NOTES
-If you want to create
-user groups, their GIDs must be equal and there must be an entry in
-\fI/etc/group\fP, or no group will exist.
+If you want to create user groups, there must be an entry in
+.IR /etc/group ,
+or no group will exist.
.PP
-If the encrypted password is set to an asterisk, the user will be unable
+If the encrypted password is set to an asterisk (*), the user will be unable
to login using
.BR login (1),
but may still login using
Trying to lock an account by simply changing the
shell field yields the same result and additionally allows the use of
.BR su (1).
-.SH "SEE ALSO"
+.SH SEE ALSO
+.BR chfn (1),
+.BR chsh (1),
.BR login (1),
.BR passwd (1),
.BR su (1),
+.BR crypt (3),
+.BR getpwent (3),
+.BR getpwnam (3),
.BR group (5),
.BR shadow (5)
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