DBUS-LAUNCH(1) User Commands DBUS-LAUNCH(1)
NAME
dbus-launch - Utility to start a message bus from a shell script
SYNOPSIS
dbus-launch [--version] [--help] [--sh-syntax] [--csh-syntax]
[--auto-syntax] [--binary-syntax] [--close-stderr]
[--exit-with-session] [--exit-with-x11]
[--autolaunch=
MACHINEID] [--config-file=
FILENAME]
[
PROGRAM] [
ARGS...]
DESCRIPTION
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
dbus-launch.
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
examples.
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.
EXAMPLES
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"
fi
Note that in this case, dbus-launch will exit, and dbus-daemon will
not be terminated automatically on logout.
AUTOMATIC LAUNCHING
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-bus/
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.
OPTIONS
The following options are supported:
--auto-syntax Choose --csh-syntax or --sh-syntax based on the SHELL environment
variable.
--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-stderr 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.
--config-file=FILENAME Pass --config-file=FILENAME to the bus daemon, instead of passing
it the --session argument. See the man page for dbus-daemon
--csh-syntax Emit csh compatible code to set up environment variables.
--exit-with-x11 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.
--exit-with-session 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.
--autolaunch=MACHINEID 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.
--sh-syntax Emit Bourne-shell compatible code to set up environment
variables.
--version Print the version of dbus-launch
--help Print the help info of dbus-launch
NOTES
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.
AUTHOR
See
http://www.freedesktop.org/software/dbus/doc/AUTHORSBUGS
Please send bug reports to the D-Bus mailing list or bug tracker, see
http://www.freedesktop.org/software/dbus/D-Bus 1.12.28 01/10/2025 DBUS-LAUNCH(1)
