<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="pam3">

  <refmeta>
    <refentrytitle>pam</refentrytitle>
    <manvolnum>3</manvolnum>
    <refmiscinfo class="source">Linux-PAM</refmiscinfo>
    <refmiscinfo class="manual">Linux-PAM Manual</refmiscinfo>
  </refmeta>

  <refnamediv xml:id="pam3-name">
    <refname>pam</refname>
    <refpurpose>Pluggable Authentication Modules Library</refpurpose>
  </refnamediv>

  <refsynopsisdiv xml:id="pam3-synopsis">
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;security/pam_appl.h&gt;</funcsynopsisinfo>
      <funcsynopsisinfo>#include &lt;security/pam_modules.h&gt;</funcsynopsisinfo>
      <funcsynopsisinfo>#include &lt;security/pam_ext.h&gt;</funcsynopsisinfo>
   </funcsynopsis>
  </refsynopsisdiv>

  <refsect1 xml:id="pam3-description">
    <title>DESCRIPTION</title>
    <para>
      <emphasis remap="B">PAM</emphasis> is a system of libraries
      that handle the authentication tasks of applications (services)
      on the system. The library provides a stable general interface
      (Application Programming Interface - API) that privilege granting
      programs (such as
      <citerefentry>
        <refentrytitle>login</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry> and <citerefentry>
        <refentrytitle>su</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry>)
      defer to to perform standard authentication tasks.
    </para>

    <refsect2 xml:id="pam3-initialization_and_cleanup">
      <title>Initialization and Cleanup</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_start</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> function creates the PAM context and initiates the
        PAM transaction. It is the first of the PAM functions that needs to
        be called by an application. The transaction state is contained
        entirely within the structure identified by this handle, so it is
        possible to have multiple transactions in parallel. But it is not
        possible to use the same handle for different transactions, a new
        one is needed for every new context.
      </para>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_end</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> function terminates the PAM transaction and is the last
        function an application should call in the PAM context. Upon return
        the handle pamh is no longer valid and all memory associated with it
        will be invalid. It can be called at any time to terminate a PAM
        transaction.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-authentication">
      <title>Authentication</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_authenticate</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        function is used to
        authenticate the user. The user is required to provide an
        authentication token depending upon the authentication service,
        usually this is a password, but could also be a finger print.
      </para>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_setcred</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        function manages the user's credentials.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-account_management">
      <title>Account Management</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_acct_mgmt</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> function is used to determine if the user's account is
        valid. It checks for authentication token and account expiration and
        verifies access restrictions. It is typically called after the user
        has been authenticated.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-password_management">
      <title>Password Management</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_chauthtok</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> function is used to change the authentication token
        for a given user on request or because the token has expired.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-session_management">
      <title>Session Management</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_open_session</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> function sets up a user session for a previously
        successful authenticated user. The session should later be terminated
        with a call to
        <citerefentry>
          <refentrytitle>pam_close_session</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-conversation">
      <title>Conversation</title>
      <para>
        The PAM library uses an application-defined callback to allow
        a direct communication between a loaded module and the application.
        This callback is specified by the
        <emphasis>struct pam_conv</emphasis> passed to
        <citerefentry>
          <refentrytitle>pam_start</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> at the start of the transaction. See
        <citerefentry>
          <refentrytitle>pam_conv</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        for details.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-data">
      <title>Data Objects</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_set_item</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        and
        <citerefentry>
          <refentrytitle>pam_get_item</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        functions allow applications and PAM service modules to set and
        retrieve PAM information.
      </para>
      <para>
         The
        <citerefentry>
          <refentrytitle>pam_get_user</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        function is the preferred method to obtain the username.
      </para>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_set_data</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        and
        <citerefentry>
          <refentrytitle>pam_get_data</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        function allows PAM service modules to set and retrieve free-form
        data from one invocation to another.
      </para>
    </refsect2>

    <refsect2 xml:id="pam3-miscellaneous">
    <title>Environment and Error Management</title>
      <para>
        The
        <citerefentry>
          <refentrytitle>pam_putenv</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>,
        <citerefentry>
          <refentrytitle>pam_getenv</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> and
        <citerefentry>
          <refentrytitle>pam_getenvlist</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry>
        functions are for maintaining a set of private environment variables.
      </para>

      <para>
        The
        <citerefentry>
          <refentrytitle>pam_strerror</refentrytitle><manvolnum>3</manvolnum>
        </citerefentry> function returns a pointer to a string describing the
        given PAM error code.
      </para>
    </refsect2>
  </refsect1>

  <refsect1 xml:id="pam3-return_values">
    <title>RETURN VALUES</title>
    <para>
      The following return codes are known by PAM:
    </para>
    <variablelist>
      <varlistentry>
        <term>PAM_ABORT</term>
        <listitem>
          <para>Critical error, immediate abort.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_ACCT_EXPIRED</term>
        <listitem>
          <para>User account has expired.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTHINFO_UNAVAIL</term>
        <listitem>
          <para>
            Authentication service cannot retrieve authentication info.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTHTOK_DISABLE_AGING</term>
        <listitem>
          <para>Authentication token aging disabled.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTHTOK_ERR</term>
        <listitem>
          <para>Authentication token manipulation error.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTHTOK_EXPIRED</term>
        <listitem>
          <para>Authentication token expired.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTHTOK_LOCK_BUSY</term>
        <listitem>
          <para>Authentication token lock busy.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTHTOK_RECOVERY_ERR</term>
        <listitem>
          <para>Authentication information cannot be recovered.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_AUTH_ERR</term>
        <listitem>
          <para>Authentication failure.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_BUF_ERR</term>
        <listitem>
          <para>Memory buffer error.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_CONV_ERR</term>
        <listitem>
          <para>Conversation failure.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_CRED_ERR</term>
        <listitem>
          <para>Failure setting user credentials.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_CRED_EXPIRED</term>
        <listitem>
          <para>User credentials expired.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_CRED_INSUFFICIENT</term>
        <listitem>
          <para>Insufficient credentials to access authentication data.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_CRED_UNAVAIL</term>
        <listitem>
          <para>Authentication service cannot retrieve user credentials.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_IGNORE</term>
        <listitem>
          <para>The return value should be ignored by PAM dispatch.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_MAXTRIES</term>
        <listitem>
          <para>Have exhausted maximum number of retries for service.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_MODULE_UNKNOWN</term>
        <listitem>
          <para>Module is unknown.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_NEW_AUTHTOK_REQD</term>
        <listitem>
          <para>
            Authentication token is no longer valid; new one required.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_NO_MODULE_DATA</term>
        <listitem>
          <para>No module specific data is present.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_OPEN_ERR</term>
        <listitem>
          <para>Failed to load module.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_PERM_DENIED</term>
        <listitem>
          <para>Permission denied.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_SERVICE_ERR</term>
        <listitem>
          <para>Error in service module.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_SESSION_ERR</term>
        <listitem>
          <para>Cannot make/remove an entry for the specified session.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_SUCCESS</term>
        <listitem>
          <para>Success.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_SYMBOL_ERR</term>
        <listitem>
          <para>Symbol not found.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_SYSTEM_ERR</term>
        <listitem>
          <para>System error.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_TRY_AGAIN</term>
        <listitem>
          <para>Failed preliminary check by password service.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>PAM_USER_UNKNOWN</term>
        <listitem>
          <para>User not known to the underlying authentication module.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 xml:id="see_also"><title>SEE ALSO</title>
    <para>
      <citerefentry>
        <refentrytitle>pam_acct_mgmt</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_authenticate</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_chauthtok</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_close_session</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_conv</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_end</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_get_data</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_getenv</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_getenvlist</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_get_item</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_get_user</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_open_session</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_putenv</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_set_data</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_set_item</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_setcred</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_start</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>, <citerefentry>
        <refentrytitle>pam_strerror</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry>
    </para>
  </refsect1>
  <refsect1 xml:id="pam3-notes"><title>NOTES</title>
    <para>
      The <emphasis>libpam</emphasis> interfaces are only thread-safe if each
      thread within the multithreaded application uses its own PAM handle.
    </para>
  </refsect1>
</refentry>