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DBUS-LAUNCH(1) User Commands DBUS-LAUNCH(1)
dbus-launch - Utility to start a message bus from a shell script
dbus-launch [--version] [--help] [--sh-syntax] [--csh-syntax]
[--auto-syntax] [--binary-syntax] [--close-stderr]
[--autolaunch=MACHINEID] [--config-file=FILENAME] [PROGRAM]
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
variables so the specified program can find the bus, and then execute
the specified program, with the specified arguments. See below for
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
several 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-syntax, you may explicitly 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.
Distributions running dbus-launch as part of a standard X session
should run dbus-launch --exit-with-session after the X server has
started and become available, as a wrapper around the "main" X client
(typically a session manager or window manager), as in these examples:
dbus-launch --exit-with-session gnome-session
dbus-launch --exit-with-session openbox
dbus-launch --exit-with-session ~/.xsession
If your distribution does not do this, you can achieve similar results
by running your session or window manager in the same way in a script
run by your X session, such as ~/.xsession, ~/.xinitrc or ~/.Xclients.
To start a D-Bus session within a text-mode session, do not use
dbus-launch. Instead, see dbus-run-session(1).
## 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`
echo "D-Bus per-session daemon address is: $DBUS_SESSION_BUS_ADDRESS"
Note that in this case, dbus-launch will exit, and dbus-daemon will not
be terminated automatically on logout.
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
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_SESSION_BUS_ADDRESS in the same way that DISPLAY is forwarded. In
the meantime, you can edit the session.conf config file to have your
session bus listen on TCP, and manually set DBUS_SESSION_BUS_ADDRESS,
if you like.
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_SESSION_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_SESSION_BUS_ADDRESS="something:,autolaunch:" - in that case if the
first address doesn't work, processes will autolaunch. (The bus address
variable 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 environment
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
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
Pass --config-file=FILENAME to the bus daemon, instead of passing
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, and will connect to the X server. If it cannot do so,
launching fails. If the "babysitter" process loses its X
connection, it kills the message bus daemon, disconnecting all of
its clients (which should exit in response). This avoids having
leftover daemon processes from a user X session, after the X
session has ended.
If this option is provided, a persistent "babysitter" process will
be created, as if for --exit-with-x11. If it cannot connect to the
X server, it will monitor the terminal from which dbus-launch was
started instead, and if it gets a HUP on stdin, the message bus
daemon will be killed. This option is not recommended, since it
will consume input from the terminal where it was started; it is
mainly provided for backwards compatibility.
This option implies that dbus-launch should scan for a
previously-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 variables.
Print the version of dbus-launch
Print the help info of dbus-launch
If you run dbus-launch myapp (with any other options), dbus-daemon will
not exit when myapp terminates: this is because myapp is assumed to be
part of a larger session, rather than a session in its own right.
Please send bug reports to the D-Bus mailing list or bug tracker, see
D-Bus 1.14.4 12/24/2022 DBUS-LAUNCH(1)