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<refentry id="sd_bus_open_user" conditional="ENABLE_KDBUS">

  <refentryinfo>
    <title>sd_bus_open_user</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>A monkey with a typewriter</contrib>
        <firstname>Zbigniew</firstname>
        <surname>Jędrzejewski-Szmek</surname>
        <email>zbyszek@in.waw.pl</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_open_user</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_open_user</refname>
    <refname>sd_bus_open_system</refname>
    <refname>sd_bus_open_system_remote</refname>
    <refname>sd_bus_open_system_container</refname>

    <refname>sd_bus_default_user</refname>
    <refname>sd_bus_default_system</refname>

    <refpurpose>Open a connection to the system or user bus</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_open_user</function></funcdef>
        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_open_system</function></funcdef>
        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_open_system_remote</function></funcdef>
        <paramdef>const char *<parameter>host</parameter></paramdef>
        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_open_system_container</function></funcdef>
        <paramdef>const char *<parameter>machine</parameter></paramdef>
        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_default_user</function></funcdef>
        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_default_system</function></funcdef>
        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_open_user()</function> creates a new bus
    object and opens a connection to the user bus.
    <function>sd_bus_open_system()</function> does the same, but
    connects to the system bus.</para>

    <para>If the <varname>$DBUS_SESSION_BUS_ADDRESS</varname> environment
    variable is set
    (cf. <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
    it will be used as the address of the user bus. This variable can
    contain multiple addresses separated by <literal>;</literal>. If
    this variable is not set, a suitable default for the default user
    D-Bus instance will be used.</para>

    <para>If the <varname>$DBUS_SYSTEM_BUS_ADDRESS</varname> environment
    variable is set, it will be used as the address of the system
    bus. This variable uses the same syntax as
    <varname>$DBUS_SESSION_BUS_ADDRESS</varname>/. If this variable is
    not set, a suitable default for the default system D-Bus instance
    will be used.</para>

    <para><function>sd_bus_open_system_remote()</function> connects to
    the system bus on the specified <parameter>host</parameter> using
    SSH. <parameter>host</parameter> consists of an optional user name
    followed by the <literal>@</literal> symbol, and the hostname.
    </para>

    <para><function>sd_bus_open_system_remote()</function> connects to
    the system bus in the specified <parameter>machine</parameter>,
    where <parameter>machine</parameter> is the name of a container.
    See
    <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    for more information about "machines".</para>

    <para><function>sd_bus_default_user()</function> returns a bus
    object connected to the user bus. Each thread has its own object, but it
    may be passed around. It is created on the first invocation of
    <function>sd_bus_default_user()</function>, and subsequent
    invocations returns a reference to the same object.</para>

    <para><function>sd_bus_default_system()</function> is similar to
    <function>sd_bus_default_user()</function>, but connects to the
    system bus.</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>Reference ownership</title>
    <para>Functions <function>sd_bus_open_user()</function>,
    <function>sd_bus_open_system()</function>,
    <function>sd_bus_open_system_remote()</function>, and
    <function>sd_bus_open_system_machine()</function> return a new
    object and the caller owns the sole reference. When not needed
    anymore, this reference should be destroyed with
    <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    </para>

    <para>The functions <function>sd_bus_default_user()</function> and
    <function>sd_bus_default_system()</function> do not create a new
    reference.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

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

    <variablelist>

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

        <listitem><para>Specified parameter is invalid
        (<constant>NULL</constant> in case of output
        parameters).</para></listitem>
      </varlistentry>

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

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

      <para>In addition, any further connection-related errors may be
      by returned. See <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para><function>sd_bus_open_user()</function> and other functions
    described here 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>
  </refsect1>

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

    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
