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What is D-Bus?

D-Bus is a message bus system, a simple way for applications to talk to one another. In addition to interprocess communication, D-Bus helps coordinate process lifecycle; it makes it simple and reliable to code a "single instance" application or daemon, and to launch applications and daemons on demand when their services are needed.

D-Bus supplies both a system daemon (for events such as "new hardware device added" or "printer queue changed") and a per-user-login-session daemon (for general IPC needs among user applications). Also, the message bus is built on top of a general one-to-one message passing framework, which can be used by any two apps to communicate directly (without going through the message bus daemon). Currently the communicating applications are on one computer, or through unencrypted TCP/IP suitable for use behind a firewall with shared NFS home directories. (Help wanted with better remote transports - the transport mechanism is well-abstracted and extensible.)

The D-Bus low-level API reference implementation and protocol have been heavily tested in the real world over several years, and are now "set in stone." Future changes will either be compatible or versioned appropriately.

The low-level libdbus reference implementation has no required dependencies; the bus daemon's only required dependency is an XML parser (expat). Higher-level bindings specific to particular frameworks (Qt, GLib, Java, C#, Python, etc.) add more dependencies, but can make more assumptions and are thus much simpler to use. The bindings evolve separately from the low-level libdbus, so some are more mature and ABI-stable than others; check the docs for the binding you plan to use.

There are also some reimplementations of the D-Bus protocol for languages such as C#, Java, and Ruby. These do not use the libdbus reference implementation.

It should be noted that the low-level implementation is not primarily designed for application authors to use. Rather, it is a basis for binding authors and a reference for reimplementations. If you are able to do so it is recommended that you use one of the higher level bindings or implementations. A list of these can be found on the bindings page.

The list of projects using D-Bus is growing and they provide a wealth of examples of using the various APIs to learn from.

D-Bus is very portable to any Linux or UNIX flavor, and a port to Windows is in progress.

If you have any trouble with D-Bus or suggestions for improvement, bug reports and comments are very welcome.

Get on D-Bus today!

Mailing List

All D-Bus discussion is currently on dbus@lists.freedesktop.org.

Reporting Bugs & Sending Patches

Please report bugs (and submit patches) through the freedesktop.org Bugzilla.

Ideally, include test suite coverage with your patch; or if you report a bug, it's good to add a test that fails even if you don't have a patch otherwise. You can see test coverage stats in the GNOME build bot results, at http://build.gnome.org:8080/coverage/dbus/lcov/ (note, coverage is understated since it counts the test code itself in the coverage, and the test suite does not test itself, in particular all the "test failed" codepaths are not covered).

Patches to improve test coverage are very welcome, though D-Bus is already among the best-covered codebases around.

Documentation

Some stuff from the doc/ subdirectory is prebuilt and browsable here. If you're new to D-Bus, the tutorial is probably the best place to start (even though it is very incomplete, the basics are covered).

Generic D-Bus protocol information:

Docs specific to the reference implementation:

Articles from around the web, including some tutorials:

Download

Reference Implementation (dbus-daemon and libdbus)

Released versions of D-Bus can be downloaded from the releases directory on dbus.freedesktop.org and are available in all major Linux distributions. If in doubt, use your distribution's packages.

The current stable branch is D-Bus 1.8.x. This is the recommended version for most purposes.

The current legacy branch is D-Bus 1.6.x. This is still supported, but only for security fixes: only use these versions when upgrading from older stable releases, or preparing security updates for frozen/stable distributions.

Older branches are unsupported and are unlikely to have any more releases, but distributors who still provide security support for an older version are invited to share backported patches via the older branches in the same git repository.

The current development branch is D-Bus 1.9.x, which will lead to a 1.10.x stable branch in future.

Bindings and Independent Implementations

Bindings and independent implementations are linked to from the Bindings Page.

A binding wraps libdbus (and thus automatically gets e.g. new authentication mechanisms and other additions to libdbus), while a reimplementation codes the protocol from scratch (and thus avoids a dependency on the libdbus C library, but has to be kept in sync with new features). We are working on a hybrid approach where libdbus can be used to set up connections but bindings don't use the message queue or message marshaling from libdbus.

Windows port

The Windows port from the windbus and dbus4win projects has been merged into the freedesktop dbus development branch and the spec has been updated with windows specific stuff. Many thanks to the people who worked on the windows port (in alphabetic order):

Marcus Brinkmann, Nguyễn Thái Ngọc Duy, Christian Ehrlicher, Peter Kümmel, Tor Lillqvist, Ralf Habacker, Frank Osterfeld, Marc Mutz, Romain Pokrzywka, Ole André Vadla Ravnås, Sebastian Sauer

The windows port is knowing to work on Windows XP, Windows Vista and Windows 7, supported compiler/sdk are MSVC 2010, mingw-w32/w64(gcc) and cygwin(gcc).

Everyone interested in having stable dbus on windows is invited to test the implementation, to reports bugs and/or to file patches.

Grab the Source

The core dbus code and the language bindings are under version control using Git. There is a nice tutorial for using git with freedesktop.org projects. There is also another tutorial at IBM Developerworks site.

All components of dbus are in the dbus/ subdirectory.

View the reference implementation in gitweb

Anonymous git for reference implementation: git://anongit.freedesktop.org/git/dbus/dbus

Developer git for reference implementation: ssh://git.freedesktop.org/git/dbus/dbus