dbus-launch(1) General Commands Manual dbus-launch(1)
dbus-launch - Utility to start a message bus from a shell script
dbus-launch [--version] [--sh-syntax] [--csh-syntax] [--auto-syntax]
[--exit-with-session] [--autolaunch=MACHINEID] [--config-file=FILENAME]
The dbus-launch command is used to start a session bus instance of
dbus-daemon from a shell script. It would normally be called from a
user's login scripts. Unlike the daemon itself, dbus-launch exits, so
backticks or the $() construct can be used to read information from
With no arguments, dbus-launch will launch a session bus instance and
print the address and pid of that instance to standard output.
You may specify a program to be run; in this case, dbus-launch will
launch a session bus instance, set the appropriate environment vari-
ables so the specified program can find the bus, and then execute the
specified program, with the specified arguments. See below for exam-
If you launch a program, dbus-launch will not print the information
about the new bus to standard output.
When dbus-launch prints bus information to standard output, by default
it is in a simple key-value pairs format. However, you may request sev-
eral alternate syntaxes using the --sh-syntax, --csh-syntax, --binary-
syntax, or --auto-syntax options. Several of these cause dbus-launch to
emit shell code to set up the environment.
With the --auto-syntax option, dbus-launch looks at the value of the
SHELL environment variable to determine which shell syntax should be
used. If SHELL ends in "csh", then csh-compatible code is emitted;
otherwise Bourne shell code is emitted. Instead of passing --auto-syn-
tax, you may explicity specify a particular one by using --sh-syntax
for Bourne syntax, or --csh-syntax for csh syntax. In scripts, it's
more robust to avoid --auto-syntax and you hopefully know which shell
your script is written in.
See http://www.freedesktop.org/software/dbus/ for more information
about D-Bus. See also the man page for dbus-daemon.
Here is an example of how to use dbus-launch with an sh-compatible
shell to start the per-session bus daemon:
## test for an existing bus daemon, just to be safe
if test -z "$DBUS_SESSION_BUS_ADDRESS" ; then
## if not found, launch a new one
eval `dbus-launch --sh-syntax --exit-with-session`
echo "D-Bus per-session daemon address is: $DBUS_SESSION_BUS_ADDRESS"
You might run something like that in your login scripts.
Another way to use dbus-launch is to run your main session program,
The above would likely be appropriate for ~/.xsession or ~/.Xclients.
If DBUS_SESSION_BUS_ADDRESS is not set for a process that tries to use
D-Bus, by default the process will attempt to invoke dbus-launch with
the --autolaunch option to start up a new session bus or find the
existing bus address on the X display or in a file in ~/.dbus/session-
Whenever an autolaunch occurs, the application that had to start a new
bus will be in its own little world; it can effectively end up starting
a whole new session if it tries to use a lot of bus services. This can
be suboptimal or even totally broken, depending on the app and what it
tries to do.
There are two common reasons for autolaunch. One is ssh to a remote
machine. The ideal fix for that would be forwarding of DBUS_SES-
SION_BUS_ADDRESS in the same way that DISPLAY is forwarded. In the
meantime, you can edit the session.conf config file to have your ses-
sion bus listen on TCP, and manually set DBUS_SESSION_BUS_ADDRESS, if
The second common reason for autolaunch is an su to another user, and
display of X applications running as the second user on the display
belonging to the first user. Perhaps the ideal fix in this case would
be to allow the second user to connect to the session bus of the first
user, just as they can connect to the first user's display. However, a
mechanism for that has not been coded.
You can always avoid autolaunch by manually setting DBUS_SES-
SION_BUS_ADDRESS. Autolaunch happens because the default address if
none is set is "autolaunch:", so if any other address is set there will
be no autolaunch. You can however include autolaunch in an explicit
session bus address as a fallback, for example DBUS_SES-
SION_BUS_ADDRESS="something:,autolaunch:" - in that case if the first
address doesn't work, processes will autolaunch. (The bus address vari-
able contains a comma-separated list of addresses to try.)
The --autolaunch option is considered an internal implementation detail
of libdbus, and in fact there are plans to change it. There's no real
reason to use it outside of the libdbus implementation anyhow.
The following options are supported:
Choose --csh-syntax or --sh-syntax based on the SHELL environ-
--binary-syntax Write to stdout a nul-terminated bus address,
then the bus PID as a binary integer of size sizeof(pid_t), then
the bus X window ID as a binary integer of size sizeof(long).
Integers are in the machine's byte order, not network byte order
or any other canonical byte order.
Close the standard error output stream before starting the D-Bus
daemon. This is useful if you want to capture dbus-launch error
messages but you don't want dbus-daemon to keep the stream open
to your application.
Pass --config-file=FILENAME to the bus daemon, instead of pass-
ing it the --session argument. See the man page for dbus-daemon
Emit csh compatible code to set up environment variables.
If this option is provided, a persistent "babysitter" process
will be created that watches stdin for HUP and tries to connect
to the X server. If this process gets a HUP on stdin or loses
its X connection, it kills the message bus daemon.
This option implies that dbus-launch should scan for a previ-
ously-started session and reuse the values found there. If no
session is found, it will start a new session. The --exit-with-
session option is implied if --autolaunch is given. This option
is for the exclusive use of libdbus, you do not want to use it
manually. It may change in the future.
Emit Bourne-shell compatible code to set up environment vari-
Print the version of dbus-launch
Please send bug reports to the D-Bus mailing list or bug tracker, see