shadow/man/shadow.5.xml

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<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>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 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>
      <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>