dbus-launch - Utility to start a message bus from a shell script
[--version] [--help] [--sh-syntax] [--csh-syntax] [--auto-syntax]
[--binary-syntax] [--close-stderr] [--exit-with-session] [--exit-with-x11]
] [ ARGS
command is used to start a session bus instance of
from a shell script. It would normally be called from a
user's login scripts. Unlike the daemon itself, dbus-launch
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
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.
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.
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
. Instead, see dbus-run-session
## 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 ~/.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.
The following options are supported:
Choose --csh-syntax or --sh-syntax based on
the SHELL environment variable.
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 your
Pass --config-file=FILENAME to the bus daemon,
instead of passing it the --session argument. See the man page for
Emit csh compatible code to set up environment
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
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
Emit Bourne-shell compatible code to set up
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
exit when myapp
terminates: this is because myapp
assumed to be part of a larger session, rather than a session in its own
Please send bug reports to the D-Bus mailing list or bug tracker, see