sd_bus_open_with_description(3)

1SD_BUS_DEFAULT(3)               sd_bus_default               SD_BUS_DEFAULT(3)
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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_system,
9       sd_bus_open_system_with_description, sd_bus_open_system_remote,
10       sd_bus_open_system_machine - Acquire a connection to a system or user
11       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);
21
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_system(sd_bus **bus);
33
34       int sd_bus_open_system_with_description(sd_bus **bus,
35                                               const char *description);
36
37       int sd_bus_open_system_remote(sd_bus **bus, const char *host);
38
39       int sd_bus_open_system_machine(sd_bus **bus, const char *machine);
40

DESCRIPTION

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

REFERENCE OWNERSHIP

118       The functions sd_bus_open(), sd_bus_open_user(), sd_bus_open_system(),
119       sd_bus_open_system_remote(), and sd_bus_open_system_machine() return a
120       new connection object and the caller owns the sole reference. When not
121       needed anymore, this reference should be destroyed with
122       sd_bus_unref(3).
123
124       The functions sd_bus_default(), sd_bus_default_user() and
125       sd_bus_default_system() do not necessarily create a new object, but
126       increase the connection reference of an existing connection object by
127       one. Use sd_bus_unref(3) to drop the reference.
128
129       Queued but unwritten/unread messages keep a reference to their bus
130       connection object. For this reason, even if an application dropped all
131       references to a bus connection, it might not get destroyed right away.
132       Until all incoming queued messages are read, and until all outgoing
133       unwritten messages are written, the bus object will stay alive.
134       sd_bus_flush() may be used to write all outgoing queued messages so
135       they drop their references. To flush the unread incoming messages, use
136       sd_bus_close(), which will also close the bus connection. When using
137       the default bus logic, it is a good idea to first invoke sd_bus_flush()
138       followed by sd_bus_close() when a thread or process terminates, and
139       thus its bus connection object should be freed.
140
141       Normally, slot objects (as created by sd_bus_add_match(3) and similar
142       calls) keep a reference to their bus connection object, too. Thus, as
143       long as a bus slot object remains referenced its bus object will remain
144       allocated too. Optionally, bus slot objects may be placed in "floating"
145       mode. When in floating mode the life cycle of the bus slot object is
146       bound to the bus object, i.e. when the bus object is freed the bus slot
147       object is automatically unreferenced too. The floating state of a slot
148       object may be controlled explicitly with sd_bus_slot_set_floating(3),
149       though usually floating bus slot objects are created by passing NULL as
150       the slot parameter of sd_bus_add_match() and related calls, thus
151       indicating that the caller is not directly interested in referencing
152       and managing the bus slot object.
153
154       The life cycle of the default bus connection should be the
155       responsibility of the code that creates/owns the thread the default bus
156       connection object is associated with. Library code should neither call
157       sd_bus_flush() nor sd_bus_close() on default bus objects unless it does
158       so in its own private, self-allocated thread. Library code should not
159       use the default bus object in other threads unless it is clear that the
160       program using it will life cycle the bus connection object and flush
161       and close it before exiting from the thread. In libraries where it is
162       not clear that the calling program will life cycle the bus connection
163       object, it is hence recommended to use sd_bus_open_system() instead of
164       sd_bus_default_system() and related calls.
165

RETURN VALUE

167       On success, these calls return 0 or a positive integer. On failure,
168       these calls return a negative errno-style error code.
169

ERRORS

171       Returned errors may indicate the following problems:
172
173       -EINVAL
174           The specified parameters are invalid.
175
176       -ENOMEM
177           Memory allocation failed.
178
179       -ESOCKTNOSUPPORT
180           The protocol version required to connect to the selected bus is not
181           supported.
182
183       In addition, any further connection-related errors may be by returned.
184       See sd_bus_send(3).
185

NOTES

187       These APIs are implemented as a shared library, which can be compiled
188       and linked to with the libsystemd pkg-config(1) file.
189