shadow/man/passwd.1.xml

<?xml version="1.0" encoding="UTF-8"?>
<refentry id='passwd.1'>
  <!--  $Id: passwd.1.xml,v 1.36 2006/11/12 19:20:34 kloczek Exp $ -->
  <refmeta>
    <refentrytitle>passwd</refentrytitle>
    <manvolnum>1</manvolnum>
    <refmiscinfo class="sectdesc">User Commands</refmiscinfo>
  </refmeta>
  <refnamediv id='name'>
    <refname>passwd</refname>
    <refpurpose>change user password</refpurpose>
  </refnamediv>

  <refsynopsisdiv id='synopsis'>
    <cmdsynopsis>
      <command>passwd</command>
      <arg choice='opt'>
	<replaceable>options</replaceable>
      </arg>
      <arg choice='opt'>
        <replaceable>LOGIN</replaceable>
      </arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1 id='description'>
    <title>DESCRIPTION</title>
    <para>
      The <command>passwd</command> command changes passwords for user accounts.
      A normal user may only change the password for his/her own account, while
      the superuser may change the password for any account.
      <command>passwd</command> also changes account information, such as
      the full name of the user, the user's login shell, or his/her password
      expiry date and interval.
    </para>

    <refsect2 id='password_changes'>
      <title>Password Changes</title>
      <para>
	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 superuser is permitted to bypass this step so that
	forgotten passwords may be changed.
      </para>

      <para>
	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, <command>passwd</command> refuses to change the
	password and exits.
      </para>

      <para>
	The user is then prompted twice for a replacement password. The
	second entry is compared against the first and both are required to
	match in order for the password to be changed.
      </para>

      <para>
	Then, the password is tested for complexity. As a general guideline,
	passwords should consist of 6 to 8 characters including one or more
	characters from each of the following sets:
      </para>

      <itemizedlist mark='bullet'>
	<listitem>
	  <para>lower case alphabetics</para>
	</listitem>
	<listitem>
	  <para>digits 0 thru 9</para>
	</listitem>
	<listitem>
	  <para>punctuation marks</para>
	</listitem>
      </itemizedlist>

      <para>
	Care must be taken not to include the system default erase or kill
	characters. <command>passwd</command> will reject any password which
	is not suitably complex.
      </para>

    </refsect2>

    <refsect2 id='hints_for_user_passwords'>
      <title>Hints for user passwords</title>
      <para>
	The security of a password depends upon the strength of the
	encryption algorithm and the size of the key space. The
	<emphasis>UNIX</emphasis> 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.
      </para>

      <para>
	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.
      </para>

      <para>
	Your password must be 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.
      </para>

      <para>
	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:
      </para>

      <itemizedlist mark='bullet'>
	<listitem>
	  <para>Ask not for whom the bell tolls</para>
	</listitem>
	<listitem>
	  <para>which produces</para>
	</listitem>
	<listitem>
	  <para>An4wtbt</para>
	</listitem>
      </itemizedlist>

      <para>
	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.
      </para>
    </refsect2>
  </refsect1>

  <refsect1 id='options'>
    <title>OPTIONS</title>
    <para>
      The options which apply to the <command>passwd</command> command are:
    </para>
    <variablelist remap='IP'>
      <varlistentry>
	<term>
	  <option>-a</option>, <option>--all</option>
	</term>
	<listitem>
	  <para>
	    This option can be used only with <option>-S</option> and causes show
	    status for all users.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-d</option>, <option>--delete</option>
	</term>
	<listitem>
	  <para>
	    Delete a user's password (make it empty). This is a quick way
	    to disable a password for an account. It will set the named
	    account passwordless.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-e</option>, <option>--expire</option>
	</term>
	<listitem>
	  <para>
	    Immediately expire an account's password. This in effect can
	    force a user to change his/her password at the user's next login.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><option>-h</option>, <option>--help</option></term>
	<listitem>
	  <para>Display help message and exit.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-i</option>, <option>--inactive</option> <replaceable>INACTIVE</replaceable>
	</term>
	<listitem>
	  <para>
	    This 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 <replaceable>INACTIVE</replaceable>
	    days, the user may no longer sign on to the account.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-k</option>, <option>--keep-tokens</option>
	</term>
	<listitem>
	  <para>
	    Indicate password change should be performed only for expired
	    authentication tokens (passwords). The user wishes to keep their
	    non-expired tokens as before.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-l</option>, <option>--lock</option>
	</term>
	<listitem>
	  <para>
	    Lock the named account. This option disables an account by changing
	    the password to a value which matches no possible encrypted value.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-m</option>, <option>--mindays</option> <replaceable>MIN_DAYS</replaceable>
	</term>
	<listitem>
	  <para>
	    Set the minimum number of days between password changes to
	    <replaceable>MIN_DAYS</replaceable>. A value of zero for this field
	    indicates that the user may change his/her password at any time.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-q</option>, <option>--quiet</option>
	</term>
	<listitem>
	  <para>
	    Quiet mode.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-r</option>, <option>--repository</option> <replaceable>REPOSITORY</replaceable>
	</term>
	<listitem>
	  <para>
	    change password in <replaceable>REPOSITORY</replaceable> repository
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-S</option>, <option>--status</option>
	</term>
	<listitem>
	  <para>
	    Display account status information. The status information
	    consists of 7 fields. The first field is the user's login name. 
	    The second field indicates if the user account is locked (L),
	    has no password (NP), or has a usable password (P). The third
	    field gives the date of the last password change. The next four
	    fields are the minimum age, maximum age, warning period, and
	    inactivity period for the password. These ages are expressed in
	    days.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-u</option>, <option>--unlock</option>
	</term>
	<listitem>
	  <para>
	    Unlock the named account. This option re-enables an account by
	    changing the password back to its previous value (to value before
	    using <option>-l</option> option).
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-w</option>, <option>--warndays</option> <replaceable>WARN_DAYS</replaceable>
	</term>
	<listitem>
	  <para>
	    Set the number of days of warning before a password change is
	    required. The <replaceable>WARN_DAYS</replaceable> option is
	    the number of days prior to the password expiring that a user
	    will be warned that his/her password is about to expire.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-x</option>, <option>--maxdays</option> <replaceable>MAX_DAYS</replaceable>
	</term>
	<listitem>
	  <para>
	    Set the maximum number of days a password remains valid. After
	    <replaceable>MAX_DAYS</replaceable>, the password is required
	    to be changed.
	  </para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id='caveats'>
    <title>CAVEATS</title>
    <para>
      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 or she 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.
    </para>
  </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='exit_values'>
    <title>EXIT VALUES</title>
    <para>
      The <command>passwd</command> command exits with the following values:
      <variablelist>
	<varlistentry>
	  <term><replaceable>0</replaceable></term>
	  <listitem>
	    <para>success</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>1</replaceable></term>
	  <listitem>
	    <para>permission denied</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>2</replaceable></term>
	  <listitem>
	    <para>invalid combination of options</para>
	    </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>3</replaceable></term>
	  <listitem>
	    <para>unexpected failure, nothing done</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>4</replaceable></term>
	  <listitem>
	    <para>unexpected failure, <filename>passwd</filename> file missing</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>5</replaceable></term>
	  <listitem>
	    <para><filename>passwd</filename> file busy, try again</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>6</replaceable></term>
	  <listitem>
	    <para>invalid argument to option</para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </para>
  </refsect1>

  <refsect1 id='see_also'>
    <title>SEE ALSO</title>
    <para>
      <citerefentry>
	<refentrytitle>group</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>shadow</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>.
    </para>
  </refsect1>
</refentry>