Beyond Linux® From Scratch - Version 7.4

Chapter 12. System Utilities

D-Bus-1.6.14

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-7.4 platform.

Package Information

D-Bus Dependencies

Required

expat-2.1.0 or libxml2-2.9.1

Recommended

Xorg Libraries (for dbus-launch program)

Optional

dbus-glib-0.100.2 (to run tests), Python-2.7.5 (to run tests) and Doxygen-1.8.5 (to generate the API documentation)

Note that the configure script will look for xmlto-0.0.25 but it does nothing as the XML/HTML documentation is already shipped in the source tree.

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

Installation of D-Bus

As the root user, create a system user and group to handle the system message bus activity: 

groupadd -g 18 messagebus &&
useradd -c "D-Bus Message Daemon User" -d /var/run/dbus \
        -u 18 -g messagebus -s /bin/false messagebus

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           \
            --libexecdir=/usr/lib/dbus-1.0 \
            --with-console-auth-dir=/run/console/ \
            --without-systemdsystemunitdir \
            --disable-systemd              \
            --disable-static &&
make

See below for test instructions.

Now, as the root user: 

make install &&
mv -v /usr/share/doc/dbus /usr/share/doc/dbus-1.6.14

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 D-Bus UUID to avoid warnings when compiling some packages with the following command as the root user: 

dbus-uuidgen --ensure

The dbus tests cannot be run until after dbus-glib-0.100.2 has been installed. The tests require passing additional parameters to configure and exposing additional functionality in the binaries. These interfaces are not intended to be used in a production build of D-Bus. If you would like to run the unit tests, issue the following commands: 

make distclean                              &&
./configure --enable-tests --enable-asserts &&
make                                        &&
make check                                  &&
make distclean

Note there has been a report 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

--with-console-auth-dir=/run/console/: This parameter specifies location of the ConsoleKit auth dir.

--without-systemdsystemunitdir: This switch prevents installation of systemd unit files.

--disable-systemd: This switch disables systemd support in D-Bus

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

--enable-tests: Build extra parts of the code to support testing. Configure will end with a NOTE warning about this.

--enable-asserts: Enable 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 dbus

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

Boot Script

To automatically start dbus-daemon when the system is rebooted, install the /etc/rc.d/init.d/dbus bootscript from the blfs-bootscripts-20130908 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 xdm 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

  • A hint has been written that provides ways to start scripts using the KDM session manager of KDE. The concepts in this hint could possibly be used with other session managers as well. The hint is located at http://www.linuxfromscratch.org/hints/downloads/files/execute-session-scripts-using-kdm.txt.

Contents

Installed Programs: dbus-cleanup-sockets, dbus-daemon, dbus-launch, dbus-monitor, dbus-send and dbus-uuidgen
Installed Library: libdbus-1.so
Installed Directories: /etc/dbus-1, /usr/include/dbus-1.0, /usr/lib/dbus-1.0, /usr/share/dbus-1, /usr/share/doc/dbus-1.6.14 and /var/lib/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-send

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

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 2013-09-09 14:35:19 -0700