SD_BUS_DEFAULT(3)              sd_bus_default              SD_BUS_DEFAULT(3)

NAME         top

       sd_bus_default, sd_bus_default_user, sd_bus_default_system,
       sd_bus_open, sd_bus_open_user, sd_bus_open_system,
       sd_bus_open_system_remote, sd_bus_open_system_machine - Acquire a
       connection to a system or user bus

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       int sd_bus_default(sd_bus **bus);

       int sd_bus_default_user(sd_bus **bus);

       int sd_bus_default_system(sd_bus **bus);

       int sd_bus_open(sd_bus **bus);

       int sd_bus_open_user(sd_bus **bus);

       int sd_bus_open_system(sd_bus **bus);

       int sd_bus_open_system_remote(sd_bus **bus, const char *host);

       int sd_bus_open_system_machine(sd_bus **bus, const char *machine);

DESCRIPTION         top

       sd_bus_default() acquires a bus connection object to the user bus
       when invoked in user context, or to the system bus otherwise. The
       connection object is associated with the calling thread. Each time
       the function is invoked from the same thread, the same object is
       returned, but its reference count is increased by one, as long as at
       least one reference is kept. When the last reference to the
       connection is dropped (using the sd_bus_unref(3) call), the
       connection is terminated. Note that the connection is not
       automatically terminated when the associated thread ends. It is
       important to drop the last reference to the bus connection explicitly
       before the thread ends, as otherwise, the connection will leak. Also,
       queued but unread or unwritten messages keep the bus referenced, see

       sd_bus_default_user() returns a user bus connection object associated
       with the calling thread.  sd_bus_default_system() is similar, but
       connects to the system bus. Note that sd_bus_default() is identical
       to these two calls, depending on the execution context.

       sd_bus_open() creates a new, independent bus connection to the user
       bus when invoked in user context, or the system bus otherwise.
       sd_bus_open_user() is similar, but connects only to the user bus.
       sd_bus_open_system() does the same, but connects to the system bus.
       In contrast to sd_bus_default(), sd_bus_default_user(), and
       sd_bus_default_system(), these calls return new, independent
       connection objects that are not associated with the invoking thread
       and are not shared between multiple invocations. It is recommended to
       share connections per thread to efficiently make use the available
       resources. Thus, it is recommended to use sd_bus_default(),
       sd_bus_default_user() and sd_bus_default_system() to connect to the
       user or system buses.

       If the $DBUS_SESSION_BUS_ADDRESS environment variable is set (cf.
       environ(7)), it will be used as the address of the user bus. This
       variable can contain multiple addresses separated by ";". If this
       variable is not set, a suitable default for the default user D-Bus
       instance will be used.

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

       sd_bus_open_system_remote() connects to the system bus on the
       specified host using ssh(1).  host consists of an optional user name
       followed by the "@" symbol, and the hostname.

       sd_bus_open_system_machine() connects to the system bus in the
       specified machine, where machine is the name of a local container.
       See machinectl(1) for more information about the "machine" concept.
       Note that connections into local containers are only available to
       privileged processes at this time.

       These calls allocate a bus connection object and initiate the
       connection to a well-known bus of some form. An alternative to using
       these high-level calls is to create an unconnected bus object with
       sd_bus_new(3) and to connect it with sd_bus_start(3).


       The functions sd_bus_open(), sd_bus_open_user(),
       sd_bus_open_system(), sd_bus_open_system_remote(), and
       sd_bus_open_system_machine() return a new connection object and the
       caller owns the sole reference. When not needed anymore, this
       reference should be destroyed with sd_bus_unref(3).

       The functions sd_bus_default(), sd_bus_default_user() and
       sd_bus_default_system() do not necessarily create a new object, but
       increase the connection reference of an existing connection object by
       one. Use sd_bus_unref(3) to drop the reference.

       Queued but unwritten/unread messages also keep a reference to their
       bus connection object. For this reason, even if an application
       dropped all references to a bus connection, it might not get
       destroyed right away. Until all incoming queued messages are read,
       and until all outgoing unwritten messages are written, the bus object
       will stay alive.  sd_bus_flush() may be used to write all outgoing
       queued messages so they drop their references. To flush the unread
       incoming messages, use sd_bus_close(), which will also close the bus
       connection. When using the default bus logic, it is a good idea to
       first invoke sd_bus_flush() followed by sd_bus_close() when a thread
       or process terminates, and thus its bus connection object should be

       The life cycle of the default bus connection should be the
       responsibility of the code that creates/owns the thread the default
       bus connection object is associated with. Library code should neither
       call sd_bus_flush() nor sd_bus_close() on default bus objects unless
       it does so in its own private, self-allocated thread. Library code
       should not use the default bus object in other threads unless it is
       clear that the program using it will life cycle the bus connection
       object and flush and close it before exiting from the thread. In
       libraries where it is not clear that the calling program will life
       cycle the bus connection object, it is hence recommended to use
       sd_bus_open_system() instead of sd_bus_default_system() and related

RETURN VALUE         top

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

ERRORS         top

       Returned errors may indicate the following problems:

           The specified parameters are invalid.

           Memory allocation failed.

           The protocol version required to connect to the selected bus is
           not supported.

       In addition, any further connection-related errors may be by
       returned. See sd_bus_send(3).

NOTES         top

       sd_bus_open_user() and the other functions described here are
       available as a shared library, which can be compiled and linked to
       with the libsystemd pkg-config(1) file.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_new(3), sd_bus_ref(3), sd_bus_unref(3),
       ssh(1), systemd-machined.service(8), machinectl(1)

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2019-07-28.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2019-07-27.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

systemd 234                                                SD_BUS_DEFAULT(3)

Pages that refer to this page: sd-bus(3)sd_bus_negotiate_fds(3)sd_bus_new(3)systemd.directives(7)systemd.index(7)