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<refentry id="sd_pid_get_session" conditional='HAVE_PAM'>

  <refentryinfo>
    <title>sd_pid_get_session</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_pid_get_session</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_pid_get_session</refname>
    <refname>sd_pid_get_unit</refname>
    <refname>sd_pid_get_user_unit</refname>
    <refname>sd_pid_get_owner_uid</refname>
    <refname>sd_pid_get_machine_name</refname>
    <refname>sd_pid_get_slice</refname>
    <refname>sd_peer_get_session</refname>
    <refname>sd_peer_get_unit</refname>
    <refname>sd_peer_get_user_unit</refname>
    <refname>sd_peer_get_owner_uid</refname>
    <refname>sd_peer_get_machine_name</refname>
    <refname>sd_peer_get_slice</refname>
    <refpurpose>Determine session, service, owner of a
    session, container/VM or slice of a specific
    PID or socket peer</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_session</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>session</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_unit</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>unit</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_user_unit</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>unit</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_owner_uid</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>uid_t *<parameter>uid</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_machine_name</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>name</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_slice</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>slice</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_session</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>session</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_unit</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>unit</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_user_unit</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>unit</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_owner_uid</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>uid_t *<parameter>uid</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_machine_name</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>name</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_slice</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>slice</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_pid_get_session()</function> may be used to
    determine the login session identifier of a process identified by
    the specified process identifier. The session identifier is a
    short string, suitable for usage in file system paths. Note that
    not all processes are part of a login session (e.g. system service
    processes, user processes that are shared between multiple
    sessions of the same user, or kernel threads). For processes not
    being part of a login session this function will fail with
    -ENXIO. The returned string needs to be freed with the libc
    <citerefentry
    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use.</para>

    <para><function>sd_pid_get_unit()</function> may be used to
    determine the systemd system unit (i.e. system service) identifier
    of a process identified by the specified PID. The unit name is a
    short string, suitable for usage in file system paths. Note that
    not all processes are part of a system unit/service (e.g. user
    processes, or kernel threads). For processes not being part of a
    systemd system unit this function will fail with -ENXIO (More
    specifically: this call will not work for processes that are part
    of user units, use <function>sd_pid_get_user_unit()</function> for
    that.) The returned string needs to be freed with the libc
    <citerefentry
    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use.</para>

    <para><function>sd_pid_get_user_unit()</function> may be used to
    determine the systemd user unit (i.e. user service) identifier of
    a process identified by the specified PID. This is similar to
    <function>sd_pid_get_unit()</function> but applies to user units
    instead of system units.</para>

    <para><function>sd_pid_get_owner_uid()</function> may be used to
    determine the Unix user identifier of the owner of the session of
    a process identified the specified PID. Note that this function
    will succeed for user processes which are shared between multiple
    login sessions of the same user, where
    <function>sd_pid_get_session()</function> will fail. For processes
    not being part of a login session and not being a shared process
    of a user this function will fail with -ENXIO.</para>

    <para><function>sd_pid_get_machine_name()</function> may be used
    to determine the name of the VM or container is a member of. The
    machine name is a short string, suitable for usage in file system
    paths. The returned string needs to be freed with the libc
    <citerefentry
    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use. For processes not part of a VM or containers this
    function fails with -ENXIO.</para>

    <para><function>sd_pid_get_slice()</function> may be used to
    determine the slice unit the process is a member of. See
    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for details about slices. The returned string needs to be freed
    with the libc
    <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use.</para>

    <para>If the <varname>pid</varname> parameter of any of these
    functions is passed as 0, the operation is executed for the
    calling process.</para>

    <para>The <function>sd_peer_get_session()</function>,
    <function>sd_peer_get_unit()</function>,
    <function>sd_peer_get_user_unit()</function>,
    <function>sd_peer_get_owner_uid()</function>,
    <function>sd_peer_get_machine_name()</function> and
    <function>sd_peer_get_slice()</function> calls operate similar to
    their PID counterparts, but operate on a connected AF_UNIX socket
    and retrieve information about the connected peer process.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On success, these calls return 0 or a positive integer. On
    failure, these calls return a negative errno-style error
    code.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para>Returned errors may indicate the following problems:</para>

    <variablelist>

      <varlistentry>
        <term><constant>-ENXIO</constant></term>

        <listitem><para>Given field is not specified for the described
        process or peer.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ESRCH</constant></term>

        <listitem><para>The specified PID does not refer to a running
        process.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ENOMEM</constant></term>

        <listitem><para>Memory allocation failed.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para>The <function>sd_pid_get_session()</function>,
    <function>sd_pid_get_unit()</function>,
    <function>sd_pid_get_user_unit()</function>,
    <function>sd_pid_get_owner_uid()</function>,
    <function>sd_pid_get_machine_name()</function>,
    <function>sd_pid_get_slice()</function>,
    <function>sd_peer_get_session()</function>,
    <function>sd_peer_get_unit()</function>,
    <function>sd_peer_get_user_unit()</function>,
    <function>sd_peer_get_owner_uid()</function>,
    <function>sd_peer_get_machine_name()</function> and
    <function>sd_peer_get_slice()</function> interfaces are
    available as a shared library, which can be compiled
    and linked to with the
    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    file.</para>

    <para>Note that the login session identifier as
    returned by <function>sd_pid_get_session()</function>
    is completely unrelated to the process session
    identifier as returned by
    <citerefentry><refentrytitle>getsid</refentrytitle><manvolnum>2</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>getsid</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
