<?xml version="1.0" encoding="UTF-8"?>
<!--
   SPDX-FileCopyrightText: 1989 - 1990, Julianne Frances Haugh
   SPDX-FileCopyrightText: 2007 - 2009, Nicolas François
   SPDX-License-Identifier: BSD-3-Clause
-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!-- SHADOW-CONFIG-HERE -->
]>
<refentry id='shadow.5'>
  <!-- $Id$ -->
  <refentryinfo>
    <author>
      <firstname>Julianne Frances</firstname>
      <surname>Haugh</surname>
      <contrib>Creation, 1989</contrib>
    </author>
    <author>
      <firstname>Thomas</firstname>
      <surname>Kłoczko</surname>
      <email>kloczek@pld.org.pl</email>
      <contrib>shadow-utils maintainer, 2000 - 2007</contrib>
    </author>
    <author>
      <firstname>Nicolas</firstname>
      <surname>François</surname>
      <email>nicolas.francois@centraliens.net</email>
      <contrib>shadow-utils maintainer, 2007 - now</contrib>
    </author>
  </refentryinfo>
  <refmeta>
    <refentrytitle>shadow</refentrytitle>
    <manvolnum>5</manvolnum>
    <refmiscinfo class="sectdesc">File Formats and Configuration Files</refmiscinfo>
    <refmiscinfo class="source">shadow-utils</refmiscinfo>
    <refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
  </refmeta>
  <refnamediv id='name'>
    <refname>shadow</refname>
    <refpurpose>shadowed 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 exists on the system.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><emphasis role="bold">encrypted password</emphasis></term>
	<listitem>
	  <para>
	    If the password field is empty, the user can log in without a password.
	    However, some applications that read
	    the <filename>/etc/shadow</filename> file
	    might block access
	    if the password field is empty.
	  </para>
	  <para>
	    If the password field begins with an exclamation mark <emphasis>!</emphasis>,
	    the password is locked.
	    The remaining characters on the
	    line represent the password field before the password was
	    locked.
	  </para>
	  <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 a string that is not a valid
	    result of <citerefentry><refentrytitle>crypt</refentrytitle>
	    <manvolnum>3</manvolnum></citerefentry>, for instance ! or *,
	    the user cannot use a UNIX password to log in.
	    However, the user may log in the system by other means.
	  </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 1970-01-01 00:00:00 UTC.
	  </para>
	  <para>
	    The value 0 indicates that the user must change their password
	    the next time they log in to 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 must wait
	    before they can change their password again.
	  </para>
	  <para>
	    An empty field and value 0 mean that there is 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 must change their password.
	  </para>
	  <para>
	    After this number of days has elapsed, the password may still be valid.
	    The user is prompted to change their password at the next login.
	  </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 expires
	    (see the maximum password age above)
	    during which the user is warned.
	  </para>
	  <para>
	    An empty field and value 0 mean that there is 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 expires
	    (see the maximum password age above)
	    during which the password is still accepted,
	    and the user must update their password at the next login.
	  </para>
	  <para>
	    After the password expires and the password inactivity period elapses,
	    the user cannot log in and must contact their administrator.
	  </para>
	  <para>
	    An empty string means that no inactivity period is enforced.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <emphasis role="bold">account expiration date</emphasis>
	</term>
	<listitem>
	  <para>
	    The date when the account expires,
	    expressed as the number of days since 1970-01-01.
	  </para>
	  <para>
	    Note that account expiration differs from password expiration.
	    Account expiration prevents the user from logging in,
	    whereas password expiration only prevents users from logging in
	    with their password.
	  </para>
	  <para>
	    An empty field means that the account never expires.
	  </para>
	  <para>
	    The value 0 should not be used,
	    as it is interpreted either as an account with no expiration
	    or as an expiration date of 1970-01-01.
	  </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>
      <varlistentry>
	<term><filename>/etc/shadow-</filename></term>
	<listitem>
	  <para>Backup file for /etc/shadow.</para>
	  <para>
	    Note that this file is used by the tools of the shadow
	    toolsuite, but not by all user and password management tools.
	  </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>