Beyond Linux® From Scratch (System V Edition) - Version 2021-04-13

Chapter 12. System Utilities

dbus-1.12.20

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).

This package is known to build and work properly using an LFS-10.1 platform.

Package Information

D-Bus Dependencies

Recommended

Xorg Libraries (for dbus-launch program) and elogind-246.10 (These are circular dependencies. First build without them, and then again after both packages are installed.)

Optional

For the tests: dbus-glib-0.112, D-Bus Python-1.2.16, PyGObject-3.40.1, and Valgrind-3.17.0; for documentation: Doxygen-1.9.1, xmlto-0.0.28, Ducktype, and Yelp Tools

User Notes: http://wiki.linuxfromscratch.org/blfs/wiki/dbus

Installation of D-Bus

Install D-Bus by running the following commands (you may wish to review the output from ./configure --help first and add any desired parameters to the configure command shown below): 

./configure --prefix=/usr                        \
            --sysconfdir=/etc                    \
            --localstatedir=/var                 \
            --enable-user-session                \
            --disable-doxygen-docs               \
            --disable-xml-docs                   \
            --disable-static                     \
            --with-systemduserunitdir=no         \
            --with-systemdsystemunitdir=no       \
            --docdir=/usr/share/doc/dbus-1.12.20 \
            --with-console-auth-dir=/run/console \
            --with-system-pid-file=/run/dbus/pid \
            --with-system-socket=/run/dbus/system_bus_socket &&
make

See below for test instructions.

Now, as the root user: 

make install

The shared library needs to be moved to /lib, and as a result the .so file in /usr/lib will need to be recreated. Run the following command as the root user: 

mv -v /usr/lib/libdbus-1.so.* /lib &&
ln -sfv ../../lib/$(readlink /usr/lib/libdbus-1.so) /usr/lib/libdbus-1.so

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-246.10, create a symlink to the /var/lib/dbus/machine-id file: 

ln -sv /var/lib/dbus/machine-id /etc

The dbus tests cannot be run until after dbus-glib-0.112 has been installed. They must be run as an unprivileged user from a local session with bus address. To run the standard tests issue make check.

If you want to run the unit regression tests, configure 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): 

make distclean                                    &&
PYTHON=python3 ./configure --enable-tests         \
                           --enable-asserts       \
                           --disable-doxygen-docs \
                           --disable-xml-docs     &&
make                                              &&
make check

There have been reports that the tests may fail if running inside a Midnight Commander shell. You may get out-of-memory error messages when running the tests. These are normal and can be safely ignored.

Command Explanations

--disable-doxygen-docs: This switch disables doxygen documentation build and install, if you have doxygen installed. If doxygen is installed, and you wish to build them, remove this parameter.

--disable-xml-docs: This switch disables html documentation build and install, if you have xmlto installed. If xmlto is installed, and you wish to build them, remove this parameter.

--disable-static: This switch prevents installation of static versions of the libraries.

--enable-user-session: This parameter enables per-user DBus sessions with elogind.

--with-systemd{user,system}unitdir=no: These switches disable installation of systemd units on elogind based systems.

--with-console-auth-dir=/run/console: This parameter specifies the directory to check for console ownership.

--with-system-pid-file=/run/dbus/pid: This parameter specifies the location of the PID file.

--with-system-socket=/run/dbus/system_bus_socket: This parameter specifies the location of the system bus socket.

--enable-tests: Builds extra parts of the code to support all tests. Do not use on a production build.

--enable-embedded-tests: Builds extra parts of the code to support only unit tests. Do not use on a production build.

--enable-asserts: Enables debugging code to run assertions for statements normally assumed to be true. This prevents a warning that '--enable-tests' 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-20210110 package. 

make install-dbus

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-session 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

Contents

Installed Programs: dbus-cleanup-sockets, dbus-daemon, dbus-launch, dbus-monitor, dbus-run-session, dbus-send, dbus-test-tool, dbus-update-activation-environment, and dbus-uuidgen
Installed Library: libdbus-1.so
Installed Directories: /etc/dbus-1, /usr/{include,lib}/dbus-1.0, /usr/lib/cmake/DBus1, /usr/share/dbus-1, /usr/share/xml/dbus-1, /usr/share/doc/dbus-1.12.20, and /var/{lib,run}/dbus

Short Descriptions

dbus-cleanup-sockets

is used to clean up leftover sockets in a directory

dbus-daemon

is the D-Bus message bus daemon

dbus-launch

is used to start dbus-daemon from a shell script. It would normally be called from a user's login scripts

dbus-monitor

is used to monitor messages going through a D-Bus message bus

dbus-run-session

starts a process as a new D-Bus session

dbus-send

is used to send a message to a D-Bus message bus

dbus-test-tool

is a D-Bus traffic generator and test tool; it is a multi-purpose tool for debugging and profiling D-Bus

dbus-update-activation-environment

is used to update the environment used for D-Bus session services; it updates the list of environment variables used by dbus-daemon --session when it activates session services without using systemd

dbus-uuidgen

is used to generate a universally unique ID

libdbus-1.so

contains the API functions used by the D-Bus message daemon. D-Bus is first a library that provides one-to-one communication between any two applications; dbus-daemon is an application that uses this library to implement a message bus daemon

Last updated on 2021-02-20 19:41:49 -0600