.\" 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 2012-02-14 "Linux" "Linux Programmer's Manual"
+.TH PASSWD 5 2012-05-03 "Linux" "Linux Programmer's Manual"
.SH NAME
passwd \- password file
.SH DESCRIPTION
.IR /etc/shadow ,
which is readable by the superuser only.
.PP
+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
.BR passwd (1)
to set it.
.PP
-Each line of the file describes a single user, and has the following 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 are as follows:
.TP 12
-.I account
-the name of the user on the system.
+.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 \(aqx\(aq.
+This is either the encrypted user password,
+an asterisk (*), or the letter \(aqx\(aq.
(See
.BR pwconv (8)
for an explanation of \(aqx\(aq.)
.TP
.I UID
-the numeric user ID.
+The privileged
+.I root
+login account (superuser) has the user ID 0.
.TP
.I GID
-the numeric 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 used only for informational purposes.
+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.
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 nonexistent executable, the user will be unable to login
through
.BR login (1).
+The value in this field is used to set the
+.B SHELL
+environment variable.
.SH FILES
.I /etc/passwd
.SH NOTES
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 login (1),
.BR passwd (1),
.BR su (1),
.BR getpwent (3),
.BR getpwnam (3),
+.BR crypt (3),
.BR group (5),
.BR shadow (5)
OSDN Git Service
