1<?xml version='1.0'?>
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="sd_bus_default" xmlns:xi="http://www.w3.org/2001/XInclude">
7
8  <refentryinfo>
9    <title>sd_bus_default</title>
10    <productname>systemd</productname>
11  </refentryinfo>
12
13  <refmeta>
14    <refentrytitle>sd_bus_default</refentrytitle>
15    <manvolnum>3</manvolnum>
16  </refmeta>
17
18  <refnamediv>
19    <refname>sd_bus_default</refname>
20    <refname>sd_bus_default_user</refname>
21    <refname>sd_bus_default_system</refname>
22
23    <refname>sd_bus_open</refname>
24    <refname>sd_bus_open_with_description</refname>
25    <refname>sd_bus_open_user</refname>
26    <refname>sd_bus_open_user_with_description</refname>
27    <refname>sd_bus_open_user_machine</refname>
28    <refname>sd_bus_open_system</refname>
29    <refname>sd_bus_open_system_with_description</refname>
30    <refname>sd_bus_open_system_remote</refname>
31    <refname>sd_bus_open_system_machine</refname>
32
33    <refpurpose>Acquire a connection to a system or user bus</refpurpose>
34  </refnamediv>
35
36  <refsynopsisdiv>
37    <funcsynopsis>
38      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
39
40      <funcprototype>
41        <funcdef>int <function>sd_bus_default</function></funcdef>
42        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
43      </funcprototype>
44
45      <funcprototype>
46        <funcdef>int <function>sd_bus_default_user</function></funcdef>
47        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
48      </funcprototype>
49
50      <funcprototype>
51        <funcdef>int <function>sd_bus_default_system</function></funcdef>
52        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
53      </funcprototype>
54
55      <funcprototype>
56        <funcdef>int <function>sd_bus_open</function></funcdef>
57        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
58      </funcprototype>
59
60      <funcprototype>
61        <funcdef>int <function>sd_bus_open_with_description</function></funcdef>
62        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
63        <paramdef>const char *<parameter>description</parameter></paramdef>
64      </funcprototype>
65
66      <funcprototype>
67        <funcdef>int <function>sd_bus_open_user</function></funcdef>
68        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
69      </funcprototype>
70
71      <funcprototype>
72        <funcdef>int <function>sd_bus_open_user_with_description</function></funcdef>
73        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
74        <paramdef>const char *<parameter>description</parameter></paramdef>
75      </funcprototype>
76
77      <funcprototype>
78        <funcdef>int <function>sd_bus_open_user_machine</function></funcdef>
79        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
80        <paramdef>const char *<parameter>machine</parameter></paramdef>
81      </funcprototype>
82
83      <funcprototype>
84        <funcdef>int <function>sd_bus_open_system</function></funcdef>
85        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
86      </funcprototype>
87
88      <funcprototype>
89        <funcdef>int <function>sd_bus_open_system_with_description</function></funcdef>
90        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
91        <paramdef>const char *<parameter>description</parameter></paramdef>
92      </funcprototype>
93
94      <funcprototype>
95        <funcdef>int <function>sd_bus_open_system_remote</function></funcdef>
96        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
97        <paramdef>const char *<parameter>host</parameter></paramdef>
98      </funcprototype>
99
100      <funcprototype>
101        <funcdef>int <function>sd_bus_open_system_machine</function></funcdef>
102        <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
103        <paramdef>const char *<parameter>machine</parameter></paramdef>
104      </funcprototype>
105
106    </funcsynopsis>
107  </refsynopsisdiv>
108
109  <refsect1>
110    <title>Description</title>
111
112    <para><function>sd_bus_default()</function> acquires a bus
113    connection object to the user bus when invoked in user context, or
114    to the system bus otherwise. The connection object is associated
115    with the calling thread. Each time the function is invoked from
116    the same thread, the same object is returned, but its reference
117    count is increased by one, as long as at least one reference is
118    kept. When the last reference to the connection is dropped (using
119    the
120    <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
121    call), the connection is terminated. Note that the connection is
122    not automatically terminated when the associated thread ends. It
123    is important to drop the last reference to the bus connection
124    explicitly before the thread ends, as otherwise, the connection will
125    leak. Also, queued but unread or unwritten messages keep the
126    bus referenced, see below.</para>
127
128    <para><function>sd_bus_default_user()</function> returns a user
129    bus connection object associated with the calling thread.
130    <function>sd_bus_default_system()</function> is similar, but
131    connects to the system bus. Note that
132    <function>sd_bus_default()</function> is identical to these two
133    calls, depending on the execution context.</para>
134
135    <para><function>sd_bus_open()</function> creates a new,
136    independent bus connection to the user bus when invoked in user
137    context, or the system bus
138    otherwise. <function>sd_bus_open_user()</function> is similar, but
139    connects only to the user bus.
140    <function>sd_bus_open_system()</function> does the same, but
141    connects to the system bus. In contrast to
142    <function>sd_bus_default()</function>,
143    <function>sd_bus_default_user()</function>, and
144    <function>sd_bus_default_system()</function>, these calls return
145    new, independent connection objects that are not associated with
146    the invoking thread and are not shared between multiple
147    invocations. It is recommended to share connections per thread to
148    efficiently make use the available resources. Thus, it is
149    recommended to use <function>sd_bus_default()</function>,
150    <function>sd_bus_default_user()</function> and
151    <function>sd_bus_default_system()</function> to connect to the
152    user or system buses.</para>
153
154    <para><function>sd_bus_open_with_description()</function>,
155    <function>sd_bus_open_user_with_description()</function>, and
156    <function>sd_bus_open_system_with_description()</function> are similar to
157    <function>sd_bus_open()</function>, <function>sd_bus_open_user()</function>, and
158    <function>sd_bus_open_system()</function>, but allow a description string to be set, see
159    <citerefentry><refentrytitle>sd_bus_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
160    <parameter>description</parameter> may be <constant>NULL</constant>, in which case this function
161    is equivalent to <function>sd_bus_open()</function>. This description string is used in log
162    messages about the bus object, and including a "name" for the bus makes them easier to
163    understand. Some messages are emitted during bus initialization, hence using this function is
164    preferable to setting the description later with
165    <function>sd_bus_open_with_description()</function>. The argument is copied internally and will
166    not be referenced after the function returns.</para>
167
168    <para>If the <varname>$DBUS_SESSION_BUS_ADDRESS</varname> environment
169    variable is set
170    (cf. <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
171    it will be used as the address of the user bus. This variable can
172    contain multiple addresses separated by <literal>;</literal>. If
173    this variable is not set, a suitable default for the default user
174    D-Bus instance will be used.</para>
175
176    <para>If the <varname>$DBUS_SYSTEM_BUS_ADDRESS</varname>
177    environment variable is set, it will be used as the address of the
178    system bus. This variable uses the same syntax as
179    <varname>$DBUS_SESSION_BUS_ADDRESS</varname>. If this variable is
180    not set, a suitable default for the default system D-Bus instance
181    will be used.</para>
182
183    <para><function>sd_bus_open_system_remote()</function> connects to the system bus on
184    the specified host using
185    <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
186    <parameter>host</parameter> consists of an optional user name followed by the
187    <literal>@</literal> symbol, and the hostname, optionally followed by a
188    <literal>:</literal> and a port, optionally followed by a
189    <literal>/</literal> and a machine name. If the machine name is given, a connection
190    is created to the system bus in the specified container on the remote machine, and
191    otherwise a connection to the system bus on the specified host is created.</para>
192
193    <para>Note that entering a container is a privileged operation, and will likely only
194    work for the root user on the remote machine.</para>
195
196    <para><function>sd_bus_open_system_machine()</function> connects to the system bus in the specified
197    <parameter>machine</parameter>, where <parameter>machine</parameter> is the name of a local container,
198    possibly prefixed by a user name and a separating <literal>@</literal>. If the container name is
199    specified as the special string <literal>.host</literal> the connection is made to the local system. This
200    is useful to connect to the local system bus as specific user, e.g. <literal>foobar@.host</literal> to
201    connect to the local system bus as local user <literal>foobar</literal>. If the <literal>@</literal>
202    syntax is used either the left-hand side or the right-hand side may be omitted (but not both) in which
203    case the local user name or <literal>.host</literal> is implied. If the <literal>@</literal> syntax is
204    not used the connection is always made as root user. See
205    <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
206    for a description of the address syntax, and
207    <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for more
208    information about the "machine" concept. Note that connections into local containers are only available
209    to privileged processes at this time.</para>
210
211    <para><function>sd_bus_open_user_machine()</function> is similar to
212    <function>sd_bus_open_system_machine()</function>, but connects to the user bus of the root user, or if
213    the <literal>@</literal> syntax is used, of the specified user.</para>
214
215    <para>These calls allocate a bus connection object and initiate
216    the connection to a well-known bus of some form. An alternative to
217    using these high-level calls is to create an unconnected bus
218    object with
219    <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
220    and to connect it with
221    <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
222    </para>
223
224  </refsect1>
225
226  <refsect1>
227    <title>Reference ownership</title>
228    <para>The functions <function>sd_bus_open()</function>,
229    <function>sd_bus_open_user()</function>,
230    <function>sd_bus_open_user_machine()</function>,
231    <function>sd_bus_open_system()</function>,
232    <function>sd_bus_open_system_remote()</function>, and
233    <function>sd_bus_open_system_machine()</function> return a new
234    connection object and the caller owns the sole reference. When not
235    needed anymore, this reference should be destroyed with
236    <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
237    </para>
238
239    <para>The functions <function>sd_bus_default()</function>,
240    <function>sd_bus_default_user()</function> and
241    <function>sd_bus_default_system()</function> do not necessarily
242    create a new object, but increase the connection reference of an
243    existing connection object by one. Use
244    <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
245    to drop the reference.</para>
246
247    <para>Queued but unwritten/unread messages keep a reference to their bus connection object. For this reason, even
248    if an application dropped all references to a bus connection, it might not get destroyed right away. Until all
249    incoming queued messages are read, and until all outgoing unwritten messages are written, the bus object will stay
250    alive. <function>sd_bus_flush()</function> may be used to write all outgoing queued messages so they drop their
251    references. To flush the unread incoming messages, use <function>sd_bus_close()</function>, which will also close
252    the bus connection. When using the default bus logic, it is a good idea to first invoke
253    <function>sd_bus_flush()</function> followed by <function>sd_bus_close()</function> when a thread or process
254    terminates, and thus its bus connection object should be freed.</para>
255
256    <para>Normally, slot objects (as created by
257    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> and similar
258    calls) keep a reference to their bus connection object, too. Thus, as long as a bus slot object remains referenced
259    its bus object will remain allocated too. Optionally, bus slot objects may be placed in "floating" mode. When in
260    floating mode the life cycle of the bus slot object is bound to the bus object, i.e. when the bus object is freed
261    the bus slot object is automatically unreferenced too. The floating state of a slot object may be controlled
262    explicitly with
263    <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
264    though usually floating bus slot objects are created by passing <constant>NULL</constant> as the
265    <parameter>slot</parameter> parameter of <function>sd_bus_add_match()</function> and related calls, thus indicating
266    that the caller is not directly interested in referencing and managing the bus slot object.</para>
267
268    <para>The life cycle of the default bus connection should be the
269    responsibility of the code that creates/owns the thread the
270    default bus connection object is associated with. Library code
271    should neither call <function>sd_bus_flush()</function> nor
272    <function>sd_bus_close()</function> on default bus objects unless
273    it does so in its own private, self-allocated thread. Library code
274    should not use the default bus object in other threads unless it
275    is clear that the program using it will life cycle the bus
276    connection object and flush and close it before exiting from the
277    thread. In libraries where it is not clear that the calling
278    program will life cycle the bus connection object, it is hence
279    recommended to use <function>sd_bus_open_system()</function>
280    instead of <function>sd_bus_default_system()</function> and
281    related calls.</para>
282  </refsect1>
283
284  <refsect1>
285    <title>Return Value</title>
286
287    <para>On success, these calls return 0 or a positive
288    integer. On failure, these calls return a negative
289    errno-style error code.</para>
290
291    <refsect2>
292      <title>Errors</title>
293
294      <para>Returned errors may indicate the following problems:</para>
295
296      <variablelist>
297        <varlistentry>
298          <term><constant>-EINVAL</constant></term>
299
300          <listitem><para>The specified parameters are invalid.</para></listitem>
301        </varlistentry>
302
303        <varlistentry>
304          <term><constant>-ENOMEDIUM</constant></term>
305
306          <listitem><para>The requested bus type is not available because of invalid environment (for example
307          the user session bus is not available because <varname>$XDG_RUNTIME_DIR</varname> is not set).
308          </para></listitem>
309        </varlistentry>
310
311        <varlistentry>
312          <term><constant>-ENOMEM</constant></term>
313
314          <listitem><para>Memory allocation failed.</para></listitem>
315        </varlistentry>
316
317        <varlistentry>
318          <term><constant>-ESOCKTNOSUPPORT</constant></term>
319
320          <listitem><para>The protocol version required to connect to the selected bus is not
321          supported.</para></listitem>
322        </varlistentry>
323      </variablelist>
324
325      <para>In addition, other connection-related errors may be returned. See
326      <citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
327    </refsect2>
328  </refsect1>
329
330  <xi:include href="libsystemd-pkgconfig.xml" />
331
332  <refsect1>
333    <title>See Also</title>
334
335    <para>
336      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
337      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
338      <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
339      <citerefentry><refentrytitle>sd_bus_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
340      <citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
341      <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
342      <citerefentry project='die-net'><refentrytitle>ssh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
343      <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
344      <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
345    </para>
346  </refsect1>
347
348</refentry>
349