path: root/modules/pam_unix/pam_unix.8.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
	"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">

<refentry id="pam_unix">

  <refmeta>
    <refentrytitle>pam_unix</refentrytitle>
    <manvolnum>8</manvolnum>
    <refmiscinfo class="sectdesc">Linux-PAM Manual</refmiscinfo>
  </refmeta>

  <refnamediv id="pam_unix-name">
    <refname>pam_unix</refname>
    <refpurpose>Module for traditional password authentication</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis id="pam_unix-cmdsynopsis">
      <command>pam_unix.so</command>
      <arg choice="opt">
        ...
      </arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1 id="pam_unix-description">

    <title>DESCRIPTION</title>

    <para>
      This is the standard Unix authentication module. It uses standard
      calls from the system's libraries to retrieve and set account
      information as well as authentication. Usually this is obtained
      from the /etc/passwd and the /etc/shadow file as well if shadow is
      enabled.
    </para>

    <para>
      The account component performs the task of establishing the status
      of the user's account and password based on the following
      <emphasis>shadow</emphasis> elements: expire, last_change, max_change,
      min_change, warn_change. In the case of the latter, it may offer advice
      to the user on changing their password or, through the
      <emphasis remap='B'>PAM_AUTHTOKEN_REQD</emphasis> return, delay
      giving service to the user until they have established a new password.
      The entries listed above are documented in the <citerefentry>
      <refentrytitle>shadow</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry> manual page. Should the user's record not contain
      one or more of these entries, the corresponding
      <emphasis>shadow</emphasis> check is not performed.
    </para>

    <para>
      The authentication component performs the task of checking the
      users credentials (password). The default action of this module
      is to not permit the user access to a service if their official
      password is blank.
    </para>

    <para>
      A helper binary, <citerefentry>
      <refentrytitle>unix_chkpwd</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>, is provided
      to check the user's password when it is stored in a read
      protected database. This binary is very simple and will only
      check the password of the user invoking it. It is called
      transparently on behalf of the user by the authenticating
      component of this module. In this way it is possible
      for applications like <citerefentry>
      <refentrytitle>xlock</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry> to work without
      being setuid-root. The module, by default, will temporarily turn
      off SIGCHLD handling for the duration of execution of the helper
      binary. This is generally the right thing to do, as many applications
      are not prepared to handle this signal from a child they didn't know
      was <function>fork()</function>d. The <option>noreap</option> module
      argument can be used to suppress this temporary shielding and may be
      needed for use with certain applications.
    </para>

    <para>
      The maximum length of a password supported by the pam_unix module
      via the helper binary is <emphasis>PAM_MAX_RESP_SIZE</emphasis>
      - currently 512 bytes. The rest of the password provided by the
      conversation function to the module will be ignored.
    </para>

    <para>
      The password component of this module performs the task of updating
      the user's password. The default encryption hash is taken from the
      <emphasis remap='B'>ENCRYPT_METHOD</emphasis> variable from
      <emphasis>/etc/login.defs</emphasis>
    </para>

    <para>
      The session component of this module logs when a user logins
      or leave the system.
    </para>

    <para>
      Remaining arguments, supported by others functions of this
      module, are silently ignored. Other arguments are logged as
      errors through <citerefentry>
      <refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>.
    </para>
  </refsect1>

  <refsect1 id="pam_unix-options">

    <title>OPTIONS</title>
    <variablelist>
      <varlistentry>
        <term>
          <option>debug</option>
        </term>
        <listitem>
          <para>
	    Turns on debugging via
            <citerefentry>
              <refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>
          <option>audit</option>
        </term>
        <listitem>
          <para>
            A little more extreme than debug.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>
          <option>quiet</option>
        </term>
        <listitem>
          <para>
	    Turns off informational messages namely messages about
	    session open and close via
            <citerefentry>
              <refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>
          <option>nullok</option>
        </term>
        <listitem>
          <para>
            The default action of this module is to not permit the
            user access to a service if their official password is blank.
            The <option>nullok</option> argument overrides this default.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>nullresetok</option>
        </term>
        <listitem>
          <para>
            Allow users to authenticate with blank password if password reset
            is enforced even if <option>nullok</option> is not set. If password
            reset is not required and <option>nullok</option> is not set the
            authentication with blank password will be denied.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>try_first_pass</option>
        </term>
        <listitem>
          <para>
            Before prompting the user for their password, the module first
            tries the previous stacked module's password in case that
            satisfies this module as well.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>use_first_pass</option>
        </term>
        <listitem>
          <para>
            The argument <option>use_first_pass</option> forces the module
            to use a previous stacked modules password and will never prompt
            the user - if no password is available or the password is not
            appropriate, the user will be denied access.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>nodelay</option>
        </term>
        <listitem>
          <para>
            This argument can be used to discourage the authentication
            component from requesting a delay should the authentication
            as a whole fail. The default action is for the module to
            request a delay-on-failure of the order of two second.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>use_authtok</option>
        </term>
        <listitem>
          <para>
            When password changing enforce the module to set the new
            password to the one provided by a previously stacked
            <option>password</option> module (this is used in the
            example of the stacking of the <command>pam_cracklib</command>
            module documented below).
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>authtok_type=<replaceable>type</replaceable></option>
        </term>
        <listitem>
          <para>
            This argument can be used to modify the password prompt
            when changing passwords to include the type of the password.
            Empty by default.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>nis</option>
        </term>
        <listitem>
          <para>
            NIS RPC is used for setting new passwords.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>remember=<replaceable>n</replaceable></option>
        </term>
        <listitem>
          <para>
            The last <replaceable>n</replaceable> passwords for each
            user are saved in <filename>/etc/security/opasswd</filename>
            in order to force password change history and keep the user
            from alternating between the same password too frequently.
            The MD5 password hash algorithm is used for storing the
            old passwords.
            Instead of this option the <command>pam_pwhistory</command>
            module should be used.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>shadow</option>
        </term>
        <listitem>
          <para>
            Try to maintain a shadow based system.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>md5</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next, encrypt
            it with the MD5 algorithm.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>bigcrypt</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next,
            encrypt it with the DEC C2 algorithm.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>sha256</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next,
            encrypt it with the SHA256 algorithm. The
            SHA256 algorithm must be supported by the <citerefentry>
	    <refentrytitle>crypt</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry> function.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>sha512</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next,
            encrypt it with the SHA512 algorithm. The
            SHA512 algorithm must be supported by the <citerefentry>
	    <refentrytitle>crypt</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry> function.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>blowfish</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next,
            encrypt it with the blowfish algorithm. The
            blowfish algorithm must be supported by the <citerefentry>
	    <refentrytitle>crypt</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry> function.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>gost_yescrypt</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next,
            encrypt it with the gost-yescrypt algorithm. The
            gost-yescrypt algorithm must be supported by the <citerefentry>
	    <refentrytitle>crypt</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry> function.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>yescrypt</option>
        </term>
        <listitem>
          <para>
            When a user changes their password next,
            encrypt it with the yescrypt algorithm. The
            yescrypt algorithm must be supported by the <citerefentry>
	    <refentrytitle>crypt</refentrytitle><manvolnum>3</manvolnum>
            </citerefentry> function.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>rounds=<replaceable>n</replaceable></option>
        </term>
        <listitem>
          <para>
            Set the optional number of rounds of the SHA256, SHA512,
            blowfish, gost-yescrypt, and yescrypt password hashing
            algorithms to
            <replaceable>n</replaceable>.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>broken_shadow</option>
        </term>
        <listitem>
          <para>
            Ignore errors reading shadow information for
            users in the account management module.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>minlen=<replaceable>n</replaceable></option>
        </term>
        <listitem>
          <para>
            Set a minimum password length of <replaceable>n</replaceable>
            characters. The max. for DES crypt based passwords are 8
            characters.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <option>no_pass_expiry</option>
        </term>
        <listitem>
          <para>
            When set ignore password expiration as defined by the
            <emphasis>shadow</emphasis> entry of the user. The option has an
            effect only in case <emphasis>pam_unix</emphasis> was not used
            for the authentication or it returned authentication failure
            meaning that other authentication source or method succeeded.
            The example can be public key authentication in
            <emphasis>sshd</emphasis>. The module will return
            <emphasis remap='B'>PAM_SUCCESS</emphasis> instead of eventual
            <emphasis remap='B'>PAM_NEW_AUTHTOK_REQD</emphasis> or
            <emphasis remap='B'>PAM_AUTHTOK_EXPIRED</emphasis>.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
    <para>
      Invalid arguments are logged with  <citerefentry>
      <refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>.
    </para>
  </refsect1>

  <refsect1 id="pam_unix-types">
    <title>MODULE TYPES PROVIDED</title>
    <para>
      All module types (<option>account</option>, <option>auth</option>,
      <option>password</option> and <option>session</option>) are provided.
    </para>
  </refsect1>

  <refsect1 id='pam_unix-return_values'>
    <title>RETURN VALUES</title>
    <variablelist>
      <varlistentry>
        <term>PAM_IGNORE</term>
        <listitem>
          <para>
            Ignore this module.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
     </refsect1>

  <refsect1 id='pam_unix-examples'>
    <title>EXAMPLES</title>
    <para>
      An example usage for <filename>/etc/pam.d/login</filename>
      would be:
      <programlisting>
# Authenticate the user
auth       required   pam_unix.so
# Ensure users account and password are still active
account    required   pam_unix.so
# Change the user's password, but at first check the strength
# with pam_cracklib(8)
password   required   pam_cracklib.so retry=3 minlen=6 difok=3
password   required   pam_unix.so use_authtok nullok yescrypt
session    required   pam_unix.so
      </programlisting>
    </para>
  </refsect1>

  <refsect1 id='pam_unix-see_also'>
    <title>SEE ALSO</title>
    <para>
      <citerefentry>
	<refentrytitle>login.defs</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>
    </para>
  </refsect1>

  <refsect1 id='pam_unix-author'>
    <title>AUTHOR</title>
      <para>
        pam_unix was written by various people.
      </para>
  </refsect1>

</refentry>