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>
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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);
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24       int sd_bus_open_with_description(sd_bus **bus,
25                                        const char *description);
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27       int sd_bus_open_user(sd_bus **bus);
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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 from within a user slice (any session under "user-*.slice",
46       e.g.: "user@1000.service"), or to the system bus otherwise. The
47       connection object is associated with the calling thread. Each time the
48       function is invoked from the same thread, the same object is returned,
49       but its reference count is increased by one, as long as at least one
50       reference is kept. When the last reference to the connection is dropped
51       (using the sd_bus_unref(3) call), the connection is terminated. Note
52       that the connection is not automatically terminated when the associated
53       thread ends. It is important to drop the last reference to the bus
54       connection explicitly before the thread ends, as otherwise, the
55       connection will leak. Also, queued but unread or unwritten messages
56       keep the bus referenced, see below.
57
58       sd_bus_default_user() returns a user bus connection object associated
59       with the calling thread.  sd_bus_default_system() is similar, but
60       connects to the system bus. Note that sd_bus_default() is identical to
61       these two calls, depending on the execution context.
62
63       sd_bus_open() creates a new, independent bus connection to the user bus
64       when invoked in user context, or the system bus otherwise.
65       sd_bus_open_user() is similar, but connects only to the user bus.
66       sd_bus_open_system() does the same, but connects to the system bus. In
67       contrast to sd_bus_default(), sd_bus_default_user(), and
68       sd_bus_default_system(), these calls return new, independent connection
69       objects that are not associated with the invoking thread and are not
70       shared between multiple invocations. It is recommended to share
71       connections per thread to efficiently make use the available resources.
72       Thus, it is recommended to use sd_bus_default(), sd_bus_default_user()
73       and sd_bus_default_system() to connect to the user or system buses.
74
75       sd_bus_open_with_description(), sd_bus_open_user_with_description(),
76       and sd_bus_open_system_with_description() are similar to sd_bus_open(),
77       sd_bus_open_user(), and sd_bus_open_system(), but allow a description
78       string to be set, see sd_bus_set_description(3).  description may be
79       NULL, in which case this function is equivalent to sd_bus_open(). This
80       description string is used in log messages about the bus object, and
81       including a "name" for the bus makes them easier to understand. Some
82       messages are emitted during bus initialization, hence using this
83       function is preferable to setting the description later with
84       sd_bus_open_with_description(). The argument is copied internally and
85       will not be referenced after the function returns.
86
87       If the $DBUS_SESSION_BUS_ADDRESS environment variable is set (cf.
88       environ(7)), it will be used as the address of the user bus. This
89       variable can contain multiple addresses separated by ";". If this
90       variable is not set, a suitable default for the default user D-Bus
91       instance will be used.
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93       If the $DBUS_SYSTEM_BUS_ADDRESS environment variable is set, it will be
94       used as the address of the system bus. This variable uses the same
95       syntax as $DBUS_SESSION_BUS_ADDRESS. If this variable is not set, a
96       suitable default for the default system D-Bus instance will be used.
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98       sd_bus_open_system_remote() connects to the system bus on the specified
99       host using ssh(1).  host consists of an optional user name followed by
100       the "@" symbol, and the hostname, optionally followed by a ":" and a
101       port, optionally followed by a "/" and a machine name. If the machine
102       name is given, a connection is created to the system bus in the
103       specified container on the remote machine, and otherwise a connection
104       to the system bus on the specified host is created.
105
106       Note that entering a container is a privileged operation, and will
107       likely only work for the root user on the remote machine.
108
109       sd_bus_open_system_machine() connects to the system bus in the
110       specified machine, where machine is the name of a local container,
111       possibly prefixed by a user name and a separating "@". If the container
112       name is specified as the special string ".host" the connection is made
113       to the local system. This is useful to connect to the local system bus
114       as specific user, e.g.  "foobar@.host" to connect to the local system
115       bus as local user "foobar". If the "@" syntax is used either the
116       left-hand side or the right-hand side may be omitted (but not both) in
117       which case the local user name or ".host" is implied. If the "@" syntax
118       is not used the connection is always made as root user. See
119       sd_bus_set_address(3) for a description of the address syntax, and
120       machinectl(1) for more information about the "machine" concept. Note
121       that connections into local containers are only available to privileged
122       processes at this time.
123
124       sd_bus_open_user_machine() is similar to sd_bus_open_system_machine(),
125       but connects to the user bus of the root user, or if the "@" syntax is
126       used, of the specified user.
127
128       These calls allocate a bus connection object and initiate the
129       connection to a well-known bus of some form. An alternative to using
130       these high-level calls is to create an unconnected bus object with
131       sd_bus_new(3) and to connect it with sd_bus_start(3).
132

REFERENCE OWNERSHIP

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

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

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

213       systemd(1), sd-bus(3), sd_bus_new(3), sd_bus_ref(3), sd_bus_unref(3),
214       sd_bus_close(3), ssh(1), systemd-machined.service(8), machinectl(1)
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218systemd 253                                                  SD_BUS_DEFAULT(3)
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