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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_pid_get_user_slice</refname>
    <refname>sd_pid_get_cgroup</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>
    <refname>sd_peer_get_user_slice</refname>
    <refname>sd_peer_get_cgroup</refname>
    <refpurpose>Determine session, unit, 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_pid_get_user_slice</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>slice</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_pid_get_cgroup</function></funcdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>char **<parameter>cgroup</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>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_user_slice</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>slice</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_peer_get_cgroup</function></funcdef>
        <paramdef>int <parameter>fd</parameter></paramdef>
        <paramdef>char **<parameter>cgroup</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
    -ENODATA. 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 or scope
    unit) 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 -ENODATA. (More specifically, this call will not
    work for kernel threads.) 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 or scope unit)
    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 UID (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, whereas
    <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 -ENODATA.</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 -ENODATA.</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>Similarly, <function>sd_pid_get_user_slice()</function>
    returns the user slice (as managed by the user's systemd instance)
    of a process.</para>

    <para><function>sd_pid_get_cgroup()</function> returns the control
    group path of the specified process, relative to the root of the
    hierarchy. Returns the path without trailing slash, except for
    processes located in the root control group, where "/" is
    returned. To find the actual control group path in the file system,
    the returned path needs to be prefixed with
    <filename>/sys/fs/cgroup/</filename> (if the unified control group
    setup is used), or
    <filename>/sys/fs/cgroup/<replaceable>HIERARCHY</replaceable>/</filename>
    (if the legacy multi-hierarchy control group setup is used).</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>,
    <function>sd_peer_get_slice()</function>,
    <function>sd_peer_get_user_slice()</function> and
    <function>sd_peer_get_cgroup()</function> calls operate similar to
    their PID counterparts, but operate on a connected AF_UNIX socket
    and retrieve information about the connected peer process. Note
    that these fields are retrieved via <filename>/proc</filename>,
    and hence are not suitable for authorization purposes, as they are
    subject to races.</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>-ESRCH</constant></term>

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

      <varlistentry>
        <term><constant>-BADF</constant></term>

        <listitem><para>The specified socket file descriptor was
        invalid.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ENODATA</constant></term>

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

      <varlistentry>
        <term><constant>-EINVAL</constant></term>

        <listitem><para>An input parameter was invalid (out of range,
        or NULL, where that is not accepted).</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_pid_get_user_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>,
    <function>sd_peer_get_slice()</function> and
    <function>sd_peer_get_user_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>
