shadow/man/passwd.1.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
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<refentry id='passwd.1'>
  <!--  $Id: passwd.1.xml,v 1.8 2005/05/09 10:14:39 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>    
      <group choice='opt'>
        <arg choice='plain'>-f </arg><arg choice='plain'>-s </arg>
      </group>
      <arg choice='opt'>
        <replaceable>name</replaceable>
      </arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>passwd</command>
      <arg choice='opt'>-g </arg>
      <group choice='opt'>
        <arg choice='plain'>-r </arg>
	<arg choice='plain'>-R </arg>
      </group>
      <arg choice='plain'>
        <replaceable>group</replaceable>
      </arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>passwd</command>
      <arg choice='opt'>-x <replaceable>max</replaceable></arg>
      <arg choice='opt'>-n <replaceable>min</replaceable></arg>
      <arg choice='opt'>-w <replaceable>warn</replaceable></arg>
      <arg choice='opt'>-i <replaceable>inact</replaceable></arg>
      <arg choice='plain'><replaceable>login</replaceable>
      </arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>passwd</command>    
      <group choice='opt'>
        <arg choice='plain'>-l </arg>
	<arg choice='plain'>-u </arg>
	<arg choice='plain'>-d </arg>
        <arg choice='plain'>-S </arg>
	<arg choice='plain'>-e </arg>
      </group>
      <arg choice='plain'><replaceable>login</replaceable></arg>
    </cmdsynopsis>
  </refsynopsisdiv>
  
  <refsect1 id='description'>
    <title>DESCRIPTION</title>
    <para>
      <command>passwd</command> 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.
      <command>passwd</command> also changes account information, such as
      the full name of the user, user's login shell, or password expiry date
      and interval.
    </para>
    
    <para>The <option>-s</option> option makes <command>passwd</command>
      call <command>chsh</coamand> to change the user's shell.  The
      <option>-f</option> option makes <command>passwd</command> call
      <command>chfn</command> to change the user's gecos information. These
      two options are only meant for compatiblity, since the other programs
      can be called directly.
    </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 super user 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 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:
      </para>
      
      <para>Lower case alphabetics</para>
      
      <para>Upper case alphabetics</para>
      
      <para>Digits 0 thru 9</para>
      
      <para>Punctuation marks</para>
      
      <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>
      
      <para>If the password is accepted, <command>passwd</command> 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.
      </para>
    </refsect2>
    
    <refsect2 id='group_passwords'>
      <title>Group passwords</title>
      <para>
        When the <option>-g</option> 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 <option>-r</option> option is used with the
        <option>-g</option> option to remove the current password from the
        named group. This allows group access to all members. The
        <option>-R</option> option is used with the <option>-g</option>
        option to restrict the named group for all users.
      </para>
    </refsect2>
    
    <refsect2 id='password_expiry_information'>
      <title>Password expiry information</title>
      <para>The password aging information may be changed by the super user
        with the <option>-x</option>, <option>-n</option>,
        <option>-w</option>, and <option>-i</option> options. The
        <option>-x</option> option is used to set the maximum number of days
        a password remains valid. After <emphasis remap='I'>max</emphasis>
        days, the password is required to be changed. The
        <option>-n</option> 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 <emphasis remap='I'>min</emphasis> days
        have elapsed. The <option>-w</option> option is used to set the
        number of days of warning the user will receive before his/her
        password will expire. The warning occurs <emphasis
        remap='I'>warn</emphasis> days before the expiration, telling the
        user how many days remain until the password is set to expire. The
        <option>-i</option> 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 <emphasis remap='I'>inact</emphasis>
        days, the user may no longer sign on to the account.
      </para>
      
      <para>If you wish to immediately expire an account's password, you can
        use the <option>-e</option> option. This in effect can force a user
        to change his/her password at the user's next login. You can also
        use the <option>-d</option> 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.
      </para>
    </refsect2>
    
    <refsect2 id='account_maintenance'>
      <title>Account maintenance</title>
      <para> User accounts may be locked and unlocked with the
        <option>-l</option> and <option>-u</option> flags. The
        <option>-l</option> option disables an account by changing the
        password to a value which matches no possible encrypted value. The
        <option>-u</option> option re-enables an account by changing the
        password back to its previous value.
      </para>
      
      <para>The account status may be viewed with the <option>-S</option>
        option. 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. See <emphasis remap='B'>Password expiry
        information</emphasis> above for a discussion of these fields.
      </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
        remap='B'>\s-2UNIX</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 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>
      
      <para>Ask not for whom the bell tolls.</para>
      
      <para>which produces</para>
      
      <para>An4wtbt.</para>
      
      <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>
    
    <refsect2 id='notes_about_group_passwords'>
      <title>Notes about group passwords</title>
      <para>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.
      </para>
    </refsect2>
  </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 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>user account information</listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>/etc/shadow</filename></term>
        <listitem>secure user account information</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
  
  <refsect1 id='exit_values'>
    <title>EXIT VALUES</title>
    <variablelist remap='TP'>
      <varlistentry>
        <term>
          The <command>passwd</command> command exits with the
          following values:
        </term>
        <listitem>
          <para>
            <literal>0</literal>	- success
            <!-- .br -->
            <literal>1</literal>	- permission denied
            <!-- .br -->
            <literal>2</literal>	- invalid combination of options
            <!-- .br -->
            <literal>3</literal>	- unexpected failure, nothing done
            <!-- .br -->
            <literal>4</literal>	- unexpected failure, passwd file
            missing
            <!-- .br -->
            <literal>5</literal>	- passwd file busy, try again
            later                        <!-- .br -->
            <literal>6</literal>	- invalid argument to option
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
  </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>
  
  <refsect1 id='author'>
    <title>AUTHOR</title>
    <para>Julianne Frances Haugh &lt;jockgrrl@ix.netcom.com&gt;</para>
  </refsect1>
</refentry>