<?xml version="1.0" encoding="UTF-8"?>
<!--
Copyright (c) 1989 - 1990, Julianne Frances Haugh
Copyright (c) 2007 - 2009, Nicolas François
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. The name of the copyright holders or contributors may not be used to
endorse or promote products derived from this software without
specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 THE COPYRIGHT
HOLDERS 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.
-->
<refentry id='shadow.5'>
<!-- $Id$ -->
<refmeta>
<refentrytitle>shadow</refentrytitle>
<manvolnum>5</manvolnum>
<refmiscinfo class="sectdesc">File Formats and Conversions</refmiscinfo>
</refmeta>
<refnamediv id='name'>
<refname>shadow</refname>
<refpurpose>encrypted password file</refpurpose>
</refnamediv>
<refsect1 id='description'>
<title>DESCRIPTION</title>
<para>
<filename>shadow</filename> is a file which contains the password
information for the system's accounts and optional aging
information.
</para>
<para>
This file must not be readable by regular users if password security
is to be maintained.
</para>
<para>
Each line of this file contains 9 fields, separated by colons
(<quote>:</quote>), in the following order:
</para>
<variablelist>
<varlistentry>
<term><emphasis role="bold">login name</emphasis></term>
<listitem>
<para>
It must be a valid account name, which exist on the system.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">encrypted password</emphasis></term>
<listitem>
<para>
Refer to <citerefentry><refentrytitle>crypt</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> for details on how
this string is interpreted.
</para>
<para>
If the password field contains some string that is not a valid
result of <citerefentry><refentrytitle>crypt</refentrytitle>
<manvolnum>3</manvolnum></citerefentry>, for instance ! or *,
the user will not be able to use a unix password to log in
(but the user may log in the system by other means).
</para>
<para>
This field may be empty, in which case no passwords are
required to authenticate as the specified login name.
However, some applications which read the
<filename>/etc/shadow</filename> file may decide not to permit
any access at all if the password field is empty.
</para>
<para>
A password field which starts with a exclamation mark means
that the password is locked. The remaining characters on the
line represent the password field before the password was
locked.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<emphasis role="bold">date of last password change</emphasis>
</term>
<listitem>
<para>
The date of the last password change, expressed as the number
of days since Jan 1, 1970.
</para>
<para>
The value 0 has a special meaning, which is that the user
should change her pasword the next time she will log in the
system.
</para>
<para>
An empty field means that password aging features are
disabled.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">minimum password age</emphasis></term>
<listitem>
<para>
The minimum password age is the number of days the user will
have to wait before she will be allowed to change her password
again.
</para>
<para>
An empty field and value 0 mean that there are no minimum
password age.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">maximum password age</emphasis></term>
<listitem>
<para>
The maximum password age is the number of days after which the
user will have to change her password.
</para>
<para>
After this number of days is elapsed, the password may still
be valid. The user should be asked to change her password the
next time she will log in.
</para>
<para>
An empty field means that there are no maximum password age,
no password warning period, and no password inactivity period
(see below).
</para>
<para>
If the maximum password age is lower than the minimum password
age, the user cannot change her password.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<emphasis role="bold">password warning period</emphasis>
</term>
<listitem>
<para>
The number of days before a password is going to expire (see
the maximum password age above) during which the user should
be warned.
</para>
<para>
An empty field and value 0 mean that there are no password
warning period.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<emphasis role="bold">password inactivity period</emphasis>
</term>
<listitem>
<para>
The number of days after a password has expired (see the
maximum password age above) during which the password should
still be accepted (and the user should update her password
during the next login).
</para>
<para>
After expiration of the password and this expiration period is
elapsed, no login is possible using the current user's
password. The user should contact her administrator.
</para>
<para>
An empty field means that there are no enforcement of an
inactivity period.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<emphasis role="bold">account expiration date</emphasis>
</term>
<listitem>
<para>
The date of expiration of the account, expressed as the number
of days since Jan 1, 1970.
</para>
<para>
Note that an account expiration differs from a password
expiration. In case of an acount expiration, the user shall
not be allowed to login. In case of a password expiration,
the user is not allowed to login using her password.
</para>
<para>
An empty field means that the account will never expire.
</para>
<para>
The value 0 should not be used as it is interpreted as either
an account with no expiration, or as an expiration on Jan 1,
1970.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">reserved field</emphasis></term>
<listitem>
<para>This field is reserved for future use.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id='files'>
<title>FILES</title>
<variablelist>
<varlistentry>
<term><filename>/etc/passwd</filename></term>
<listitem>
<para>User account information.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/etc/shadow</filename></term>
<listitem>
<para>Secure user account information.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id='see_also'>
<title>SEE ALSO</title>
<para>
<citerefentry>
<refentrytitle>chage</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>login</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>passwd</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>pwck</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>pwconv</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>pwunconv</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>su</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>sulogin</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>.
</para>
</refsect1>
</refentry>