shadow/man/passwd.1

195 lines
8.8 KiB
Groff

.\"$Id: passwd.1,v 1.17 2004/10/29 15:48:21 kloczek Exp $
.\" Copyright 1989 - 1994, Julianne Frances Haugh
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of Julianne F. Haugh nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.TH PASSWD 1
.SH NAME
passwd \- change user password
.SH SYNOPSIS
\fBpasswd\fR [\fB-f\fR|\fB-s\fR] [\fIname\fR]
.br
\fBpasswd\fR [\fB-g\fR] [\fB-r\fR|\fB-R\fR] \fIgroup\fR
.br
\fBpasswd\fR [\fB-x \fImax\fR] [\fB-n \fImin\fR]
[\fB-w \fIwarn\fR] [\fB-i \fIinact\fR] \fIlogin\fR
.br
\fBpasswd\fR {\fB-l\fR|\fB-u\fR|\fB-d\fR|\fB-S\fR|\fB-e\fR} \fIlogin\fR
.SH DESCRIPTION
\fBpasswd\fR changes passwords for user and group accounts. A normal user
may only change the password for his/her own account, the super user may
change the password for any account. The administrator of a group may change
the password for the group. \fBpasswd\fR also changes account information,
such as the full name of the user, user's login shell, or password expiry
date and interval.
.PP
The \fB-s\fR option makes passwd call chsh to change the user's shell. The
\fB-f\fR option makes passwd call chfn to change the user's gecos
information. These two options are only meant for compatiblity, since the
other programs can be called directly.
.SS Password Changes
The user is first prompted for his/her old password, if one is present. This
password is then encrypted and compared against the stored password. The
user has only one chance to enter the correct password. The super user is
permitted to bypass this step so that forgotten passwords may be changed.
.PP
After the password has been entered, password aging information is checked
to see if the user is permitted to change the password at this time. If not,
\fBpasswd\fR refuses to change the password and exits.
.PP
The user is then prompted for a replacement password. This password is
tested for complexity. As a general guideline, passwords should consist of 6
to 8 characters including one or more from each of following sets:
.IP "" .5i
Lower case alphabetics
.IP "" .5i
Upper case alphabetics
.IP "" .5i
Digits 0 thru 9
.IP "" .5i
Punctuation marks
.PP
Care must be taken not to include the system default erase or kill
characters. \fBpasswd\fR will reject any password which is not suitably
complex.
.PP
If the password is accepted, \fBpasswd\fR will prompt again and compare the
second entry against the first. Both entries are required to match in order
for the password to be changed.
.SS Group passwords
When the \fB-g\fR option is used, the password for the named group is
changed. The user must either be the super user, or a group administrator
for the named group. The current group password is not prompted for. The
\fB-r\fR option is used with the \fB-g\fR option to remove the current
password from the named group. This allows group access to all members. The
\fB-R\fR option is used with the \fB-g\fR option to restrict the named group
for all users.
.SS Password expiry information
The password aging information may be changed by the super user with the
\fB-x\fR, \fB-n\fR, \fB-w\fR, and \fB-i\fR options. The \fB-x\fR option is
used to set the maximum number of days a password remains valid. After
\fImax\fR days, the password is required to be changed. The \fB-n\fR option
is used to set the minimum number of days before a password may be changed.
The user will not be permitted to change the password until \fImin\fR days
have elapsed. The \fB-w\fR option is used to set the number of days of
warning the user will receive before his/her password will expire. The
warning occurs \fIwarn\fR days before the expiration, telling the user how
many days remain until the password is set to expire. The \fB-i\fR option is
used to disable an account after the password has been expired for a number
of days. After a user account has had an expired password for \fIinact\fR
days, the user may no longer sign on to the account.
.PP
If you wish to immediately expire an account's password, you can use the
\fB-e\fR option. This in effect can force a user to change his/her password at
the user's next login. You can also use the \fB-d\fR option to delete a user's
password (make it empty). Use caution with this option since it can make an
account not require a password at all to login, leaving your system open to
intruders.
.SS Account maintenance
User accounts may be locked and unlocked with the \fB-l\fR and \fB-u\fR
flags. The \fB-l\fR option disables an account by changing the password to
a value which matches no possible encrypted value. The \fB-u\fR option
re-enables an account by changing the password back to its previous value.
.PP
The account status may be given with the \fB-S\fR option. The status
information consists of 6 parts. The first part indicates if the user
account is locked (L), has no password (NP), or has a usable password (P).
The second part gives the date of the last password change. The next four
parts are the minimum age, maximum age, warning period, and inactivity
period for the password.
.SS Hints for user passwords
The security of a password depends upon the strength of the
encryption algorithm and the size of the key space.
The \fB\s-2UNIX\s+2\fR System encryption method is based on
the NBS DES algorithm and is very secure.
The size of the key space depends upon the randomness of the
password which is selected.
.PP
Compromises in password security normally result from careless
password selection or handling.
For this reason, you should not select a password which appears in
a dictionary or which must be written down.
The password should also not be a proper name, your license
number, birth date, or street address.
Any of these may be used as guesses to violate system security.
.PP
Your password must easily remembered so that you will not
be forced to write it on a piece of paper.
This can be accomplished by appending two small words together
and separating each with a special character or digit.
For example, Pass%word.
.PP
Other methods of construction involve selecting an easily
remembered phrase from literature and selecting the first
or last letter from each word.
An example of this is
.IP "" .5i
Ask not for whom the bell tolls.
.PP
which produces
.IP "" .5i
An4wtbt.
.PP
You may be reasonably sure few crackers will have included this in their
dictionaries. You should, however, select your own methods for constructing
passwords and not rely exclusively on the methods given here.
.SS Notes about group passwords
Group passwords are an inherent security problem since more than one person
is permitted to know the password. However, groups are a useful tool for
permitting co-operation between different users.
.SH CAVEATS
Not all options may be supported.
Password complexity checking may vary from site to site.
The user is urged to select a password as complex as he
feels comfortable with.
Users may not be able to change their password on a system if NIS
is enabled and they are not logged into the NIS server.
.SH FILES
\fI/etc/passwd\fR \- user account information
.br
\fI/etc/shadow\fR \- encrypted user passwords
.SH EXIT VALUES
.TP 2
The \fBpasswd\fR command exits with the following values:
\fB0\fR \- success
.br
\fB1\fR \- permission denied
.br
\fB2\fR \- invalid combination of options
.br
\fB3\fR \- unexpected failure, nothing done
.br
\fB4\fR \- unexpected failure, passwd file missing
.br
\fB5\fR \- passwd file busy, try again later
.br
\fB6\fR \- invalid argument to option
.SH "SEE ALSO"
.BR group (5),
.BR passwd (5)
.SH AUTHOR
Julianne Frances Haugh <jockgrrl@ix.netcom.com>