1SD_BUS_DEFAULT(3)               sd_bus_default               SD_BUS_DEFAULT(3)
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NAME

6       sd_bus_default, sd_bus_default_user, sd_bus_default_system,
7       sd_bus_open, sd_bus_open_with_description, sd_bus_open_user,
8       sd_bus_open_user_with_description, sd_bus_open_user_machine,
9       sd_bus_open_system, sd_bus_open_system_with_description,
10       sd_bus_open_system_remote, sd_bus_open_system_machine - Acquire a
11       connection to a system or user bus
12

SYNOPSIS

14       #include <systemd/sd-bus.h>
15
16       int sd_bus_default(sd_bus **bus);
17
18       int sd_bus_default_user(sd_bus **bus);
19
20       int sd_bus_default_system(sd_bus **bus);
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22       int sd_bus_open(sd_bus **bus);
23
24       int sd_bus_open_with_description(sd_bus **bus,
25                                        const char *description);
26
27       int sd_bus_open_user(sd_bus **bus);
28
29       int sd_bus_open_user_with_description(sd_bus **bus,
30                                             const char *description);
31
32       int sd_bus_open_user_machine(sd_bus **bus, const char *machine);
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34       int sd_bus_open_system(sd_bus **bus);
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36       int sd_bus_open_system_with_description(sd_bus **bus,
37                                               const char *description);
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39       int sd_bus_open_system_remote(sd_bus **bus, const char *host);
40
41       int sd_bus_open_system_machine(sd_bus **bus, const char *machine);
42

DESCRIPTION

44       sd_bus_default() acquires a bus connection object to the user bus when
45       invoked in user context, or to the system bus otherwise. The connection
46       object is associated with the calling thread. Each time the function is
47       invoked from the same thread, the same object is returned, but its
48       reference count is increased by one, as long as at least one reference
49       is kept. When the last reference to the connection is dropped (using
50       the sd_bus_unref(3) call), the connection is terminated. Note that the
51       connection is not automatically terminated when the associated thread
52       ends. It is important to drop the last reference to the bus connection
53       explicitly before the thread ends, as otherwise, the connection will
54       leak. Also, queued but unread or unwritten messages keep the bus
55       referenced, see below.
56
57       sd_bus_default_user() returns a user bus connection object associated
58       with the calling thread.  sd_bus_default_system() is similar, but
59       connects to the system bus. Note that sd_bus_default() is identical to
60       these two calls, depending on the execution context.
61
62       sd_bus_open() creates a new, independent bus connection to the user bus
63       when invoked in user context, or the system bus otherwise.
64       sd_bus_open_user() is similar, but connects only to the user bus.
65       sd_bus_open_system() does the same, but connects to the system bus. In
66       contrast to sd_bus_default(), sd_bus_default_user(), and
67       sd_bus_default_system(), these calls return new, independent connection
68       objects that are not associated with the invoking thread and are not
69       shared between multiple invocations. It is recommended to share
70       connections per thread to efficiently make use the available resources.
71       Thus, it is recommended to use sd_bus_default(), sd_bus_default_user()
72       and sd_bus_default_system() to connect to the user or system buses.
73
74       sd_bus_open_with_description(), sd_bus_open_user_with_description(),
75       and sd_bus_open_system_with_description() are similar to sd_bus_open(),
76       sd_bus_open_user(), and sd_bus_open_system(), but allow a description
77       string to be set, see sd_bus_set_description(3).  description may be
78       NULL, in which case this function is equivalent to sd_bus_open(). This
79       description string is used in log messages about the bus object, and
80       including a "name" for the bus makes them easier to understand. Some
81       messages are emitted during bus initialization, hence using this
82       function is preferable to setting the description later with
83       sd_bus_open_with_description(). The argument is copied internally and
84       will not be referenced after the function returns.
85
86       If the $DBUS_SESSION_BUS_ADDRESS environment variable is set (cf.
87       environ(7)), it will be used as the address of the user bus. This
88       variable can contain multiple addresses separated by ";". If this
89       variable is not set, a suitable default for the default user D-Bus
90       instance will be used.
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92       If the $DBUS_SYSTEM_BUS_ADDRESS environment variable is set, it will be
93       used as the address of the system bus. This variable uses the same
94       syntax as $DBUS_SESSION_BUS_ADDRESS. If this variable is not set, a
95       suitable default for the default system D-Bus instance will be used.
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97       sd_bus_open_system_remote() connects to the system bus on the specified
98       host using ssh(1).  host consists of an optional user name followed by
99       the "@" symbol, and the hostname, optionally followed by a ":" and a
100       port, optionally followed by a "/" and a machine name. If the machine
101       name is given, a connection is created to the system bus in the
102       specified container on the remote machine, and otherwise a connection
103       to the system bus on the specified host is created.
104
105       Note that entering a container is a privileged operation, and will
106       likely only work for the root user on the remote machine.
107
108       sd_bus_open_system_machine() connects to the system bus in the
109       specified machine, where machine is the name of a local container,
110       possibly prefixed by a user name and a separating "@". If the container
111       name is specified as the special string ".host" the connection is made
112       to the local system. This is useful to connect to the local system bus
113       as specific user, e.g.  "foobar@.host" to connect to the local system
114       bus as local user "foobar". If the "@" syntax is used either the
115       left-hand side or the right-hand side may be omitted (but not both) in
116       which case the local user name or ".host" is implied. If the "@" syntax
117       is not used the connection is always made as root user. See
118       sd_bus_set_address(3) for a description of the address syntax, and
119       machinectl(1) for more information about the "machine" concept. Note
120       that connections into local containers are only available to privileged
121       processes at this time.
122
123       sd_bus_open_user_machine() is similar to sd_bus_open_system_machine(),
124       but connects to the user bus of the root user, or if the "@" syntax is
125       used, of the specified user.
126
127       These calls allocate a bus connection object and initiate the
128       connection to a well-known bus of some form. An alternative to using
129       these high-level calls is to create an unconnected bus object with
130       sd_bus_new(3) and to connect it with sd_bus_start(3).
131

REFERENCE OWNERSHIP

133       The functions sd_bus_open(), sd_bus_open_user(),
134       sd_bus_open_user_machine(), sd_bus_open_system(),
135       sd_bus_open_system_remote(), and sd_bus_open_system_machine() return a
136       new connection object and the caller owns the sole reference. When not
137       needed anymore, this reference should be destroyed with
138       sd_bus_unref(3).
139
140       The functions sd_bus_default(), sd_bus_default_user() and
141       sd_bus_default_system() do not necessarily create a new object, but
142       increase the connection reference of an existing connection object by
143       one. Use sd_bus_unref(3) to drop the reference.
144
145       Queued but unwritten/unread messages keep a reference to their bus
146       connection object. For this reason, even if an application dropped all
147       references to a bus connection, it might not get destroyed right away.
148       Until all incoming queued messages are read, and until all outgoing
149       unwritten messages are written, the bus object will stay alive.
150       sd_bus_flush() may be used to write all outgoing queued messages so
151       they drop their references. To flush the unread incoming messages, use
152       sd_bus_close(), which will also close the bus connection. When using
153       the default bus logic, it is a good idea to first invoke sd_bus_flush()
154       followed by sd_bus_close() when a thread or process terminates, and
155       thus its bus connection object should be freed.
156
157       Normally, slot objects (as created by sd_bus_add_match(3) and similar
158       calls) keep a reference to their bus connection object, too. Thus, as
159       long as a bus slot object remains referenced its bus object will remain
160       allocated too. Optionally, bus slot objects may be placed in "floating"
161       mode. When in floating mode the life cycle of the bus slot object is
162       bound to the bus object, i.e. when the bus object is freed the bus slot
163       object is automatically unreferenced too. The floating state of a slot
164       object may be controlled explicitly with sd_bus_slot_set_floating(3),
165       though usually floating bus slot objects are created by passing NULL as
166       the slot parameter of sd_bus_add_match() and related calls, thus
167       indicating that the caller is not directly interested in referencing
168       and managing the bus slot object.
169
170       The life cycle of the default bus connection should be the
171       responsibility of the code that creates/owns the thread the default bus
172       connection object is associated with. Library code should neither call
173       sd_bus_flush() nor sd_bus_close() on default bus objects unless it does
174       so in its own private, self-allocated thread. Library code should not
175       use the default bus object in other threads unless it is clear that the
176       program using it will life cycle the bus connection object and flush
177       and close it before exiting from the thread. In libraries where it is
178       not clear that the calling program will life cycle the bus connection
179       object, it is hence recommended to use sd_bus_open_system() instead of
180       sd_bus_default_system() and related calls.
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RETURN VALUE

183       On success, these calls return 0 or a positive integer. On failure,
184       these calls return a negative errno-style error code.
185
186   Errors
187       Returned errors may indicate the following problems:
188
189       -EINVAL
190           The specified parameters are invalid.
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192       -ENOMEDIUM
193           The requested bus type is not available because of invalid
194           environment (for example the user session bus is not available
195           because $XDG_RUNTIME_DIR is not set).
196
197       -ENOMEM
198           Memory allocation failed.
199
200       -ESOCKTNOSUPPORT
201           The protocol version required to connect to the selected bus is not
202           supported.
203
204       In addition, other connection-related errors may be returned. See
205       sd_bus_send(3).
206

NOTES

208       These APIs are implemented as a shared library, which can be compiled
209       and linked to with the libsystemd pkg-config(1) file.
210

SEE ALSO

212       systemd(1), sd-bus(3), sd_bus_new(3), sd_bus_ref(3), sd_bus_unref(3),
213       sd_bus_close(3), ssh(1), systemd-machined.service(8), machinectl(1)
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217systemd 251                                                  SD_BUS_DEFAULT(3)
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