Introduction to D-Bus
D-Bus is a message bus system, a
simple way for applications to talk to one another. 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 applications to communicate directly (without going through
the message bus daemon).
![[Note]](../images/note.png)
Note
Development versions of BLFS may not build or run some packages
properly if LFS or dependencies have been updated since the most
recent stable versions of the books.
Package Information
D-Bus Dependencies
Recommended
Xorg
Libraries (for dbus-launch program)
Optional
For the tests: D-Bus
Python-1.4.0, PyGObject-3.52.3, and Valgrind-3.26.0; for
documentation: Doxygen-1.15.0, xmlto-0.0.29,
Ducktype, and
Yelp Tools
Installation of D-Bus
Install D-Bus by running the
following commands (you may wish to review the meson_options.txt
file first and add any additional desired options to the meson
setup line below):
mkdir build &&
cd build &&
meson setup --prefix=/usr \
--buildtype=release \
--wrap-mode=nofallback \
-D systemd=disabled \
.. &&
ninja
See below for test instructions.
Now, as the root user:
ninja install
If you are using a DESTDIR install, dbus-daemon-launch-helper needs
to be fixed afterwards. Issue, as root user:
chown -v root:messagebus /usr/libexec/dbus-daemon-launch-helper &&
chmod -v 4750 /usr/libexec/dbus-daemon-launch-helper
If you are still building your system in chroot or you did not
start the daemon yet, but you want to compile some packages that
require D-Bus, generate the
D-Bus UUID to avoid warnings when
compiling some packages with the following command as the
root user:
dbus-uuidgen --ensure
If using elogind-255.17, create a symlink to the
/var/lib/dbus/machine-id file:
ln -sfv /var/lib/dbus/machine-id /etc
Finally, still as the root user,
rename the documentation directory (it only exists if the optional
dependencies are satisfied for at least one documentation format)
to make it versioned:
if [ -e /usr/share/doc/dbus ]; then
rm -rf /usr/share/doc/dbus-1.16.2 &&
mv -v /usr/share/doc/dbus{,-1.16.2}
fi
Many tests are disabled unless both D-Bus
Python-1.4.0 and PyGObject-3.52.3 have been installed. They
must be run as an unprivileged user from a local session with bus
address. To run the standard tests issue ninja test.
If you want to run the unit regression tests, meson requires
additional parameters which expose additional functionality in the
binaries that are not intended to be used in a production build of
D-Bus. If you would like to run
the tests, issue the following commands (for the tests, you don't
need to build the docs):
meson configure -D asserts=true -D intrusive_tests=true &&
ninja test
Command Explanations
--wrap-mode=nofallback:
This switch prevents meson from using subproject
fallbacks for any dependency declarations in the build files,
preventing it from downloading any optional dependencies which are
not installed on the system.
-D systemd=disabled: Don't
install systemd support files even if libsystemd exists (i.e. the elogind-255.17
package is installed).
-D intrusive_tests=true:
Builds extra parts of the code to support all tests. Do not use on
a production build.
-D asserts=true: Enables
debugging code to run assertions for statements normally assumed to
be true. This prevents a warning that '-D asserts=true' on its own is only
useful for profiling and might not give true results for all tests,
but adds its own NOTE that this should not be used in a production
build.
Configuring D-Bus
Config Files
/etc/dbus-1/session.conf,
/etc/dbus-1/system.conf and
/etc/dbus-1/system.d/*
Configuration Information
The configuration files listed above should probably not be
modified. If changes are required, you should create /etc/dbus-1/session-local.conf and/or
/etc/dbus-1/system-local.conf and
make any desired changes to these files.
If any packages install a D-Bus
.service file outside of the
standard /usr/share/dbus-1/services
directory, that directory should be added to the local session
configuration. For instance, /usr/local/share/dbus-1/services can be added
by performing the following commands as the root user:
cat > /etc/dbus-1/session-local.conf << "EOF"
<!DOCTYPE busconfig PUBLIC
"-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
"http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
<!-- Search for .service files in /usr/local -->
<servicedir>/usr/local/share/dbus-1/services</servicedir>
</busconfig>
EOF
D-Bus Session Daemon
To automatically start dbus-daemon when the system is
rebooted, install the /etc/rc.d/init.d/dbus bootscript from the
blfs-bootscripts-20250225 package.
make install-dbus
If this is the first time to install D-Bus on the system and you are not
operating in a chroot environment, you can immediately start
dbus-daemon without
rebooting the system:
/etc/init.d/dbus start
Note that this boot script only starts the system-wide
D-Bus daemon. Each user
requiring access to D-Bus
services will also need to run a session daemon as well. There
are many methods you can use to start a session daemon using the
dbus-launch
command. Review the dbus-launch man page for
details about the available parameters and options. Here are some
suggestions and examples:
-
Add dbus-launch to the line
in the ~/.xinitrc file that
starts your graphical desktop environment.
-
If you use gdm or some other display
manager that calls the ~/.xsession file, you can add
dbus-launch
to the line in your ~/.xsession file that starts your
graphical desktop environment. The syntax would be similar
to the example in the ~/.xinitrc file.
-
The examples shown previously use dbus-launch to specify a
program to be run. This has the benefit (when also using
the --exit-with-x11
parameter) of stopping the session daemon when the
specified program is stopped. You can also start the
session daemon in your system or personal startup scripts
by adding the following lines:
# Start the D-Bus session daemon
eval `dbus-launch`
export DBUS_SESSION_BUS_ADDRESS
This method will not stop the session daemon when you exit
your shell, therefore you should add the following line to
your ~/.bash_logout file:
# Kill the D-Bus session daemon
kill $DBUS_SESSION_BUS_PID