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.\" dbus-launch manual page.
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.\" Copyright (C) 2003 Red Hat, Inc.
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dbus-launch \- Utility to start a message bus from a shell script
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.B dbus-launch [\-\-version] [\-\-sh-syntax] [\-\-csh-syntax] [\-\-auto-syntax] [\-\-exit-with-session] [\-\-autolaunch=MACHINEID] [\-\-config-file=FILENAME] [PROGRAM] [ARGS...]
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The \fIdbus-launch\fP command is used to start a session bus
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instance of \fIdbus-daemon\fP from a shell script.
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It would normally be called from a user's login
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scripts. Unlike the daemon itself, \fIdbus-launch\fP exits, so
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backticks or the $() construct can be used to read information from
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With no arguments, \fIdbus-launch\fP will launch a session bus
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instance and print the address and pid of that instance to standard
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You may specify a program to be run; in this case, \fIdbus-launch\fP
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will launch a session bus instance, set the appropriate environment
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variables so the specified program can find the bus, and then execute the
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specified program, with the specified arguments. See below for
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If you launch a program, \fIdbus-launch\fP will not print the
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information about the new bus to standard output.
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When \fIdbus-launch\fP prints bus information to standard output, by
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default it is in a simple key-value pairs format. However, you may
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request several alternate syntaxes using the \-\-sh-syntax, \-\-csh-syntax,
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\-\-auto-syntax options. Several of these cause \fIdbus-launch\fP to emit shell code
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to set up the environment.
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With the \-\-auto-syntax option, \fIdbus-launch\fP looks at the value
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of the SHELL environment variable to determine which shell syntax
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should be used. If SHELL ends in "csh", then csh-compatible code is
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emitted; otherwise Bourne shell code is emitted. Instead of passing
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\-\-auto-syntax, you may explicity specify a particular one by using
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\-\-sh-syntax for Bourne syntax, or \-\-csh-syntax for csh syntax.
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In scripts, it's more robust to avoid \-\-auto-syntax and you hopefully
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know which shell your script is written in.
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See http://www.freedesktop.org/software/dbus/ for more information
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about D-Bus. See also the man page for \fIdbus-daemon\fP.
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Here is an example of how to use \fIdbus-launch\fP with an
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sh-compatible shell to start the per-session bus daemon:
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## test for an existing bus daemon, just to be safe
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if test -z "$DBUS_SESSION_BUS_ADDRESS" ; then
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## if not found, launch a new one
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eval `dbus-launch --sh-syntax --exit-with-session`
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echo "D-Bus per-session daemon address is: $DBUS_SESSION_BUS_ADDRESS"
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You might run something like that in your login scripts.
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Another way to use \fIdbus-launch\fP is to run your main session
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dbus-launch gnome-session
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The above would likely be appropriate for ~/.xsession or ~/.Xclients.
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.SH AUTOMATIC LAUNCHING
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If DBUS_SESSION_BUS_ADDRESS is not set for a process that tries to use
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D-Bus, by default the process will attempt to invoke dbus-launch with
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the --autolaunch option to start up a new session bus or find the
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existing bus address on the X display or in a file in
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Whenever an autolaunch occurs, the application that had to
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start a new bus will be in its own little world; it can effectively
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end up starting a whole new session if it tries to use a lot of
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bus services. This can be suboptimal or even totally broken, depending
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on the app and what it tries to do.
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There are two common reasons for autolaunch. One is ssh to a remote
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machine. The ideal fix for that would be forwarding of
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DBUS_SESSION_BUS_ADDRESS in the same way that DISPLAY is forwarded.
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In the meantime, you can edit the session.conf config file to
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have your session bus listen on TCP, and manually set
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DBUS_SESSION_BUS_ADDRESS, if you like.
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The second common reason for autolaunch is an su to another user, and
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display of X applications running as the second user on the display
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belonging to the first user. Perhaps the ideal fix in this case
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would be to allow the second user to connect to the session bus of the
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first user, just as they can connect to the first user's display.
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However, a mechanism for that has not been coded.
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You can always avoid autolaunch by manually setting
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DBUS_SESSION_BUS_ADDRESS. Autolaunch happens because the default
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address if none is set is "autolaunch:", so if any other address is
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set there will be no autolaunch. You can however include autolaunch in
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an explicit session bus address as a fallback, for example
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DBUS_SESSION_BUS_ADDRESS="something:,autolaunch:" - in that case if
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the first address doesn't work, processes will autolaunch. (The bus
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address variable contains a comma-separated list of addresses to try.)
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The --autolaunch option is considered an internal implementation
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detail of libdbus, and in fact there are plans to change it. There's
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no real reason to use it outside of the libdbus implementation anyhow.
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The following options are supported:
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Choose \-\-csh-syntax or \-\-sh-syntax based on the SHELL environment variable.
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Write to stdout a nul-terminated bus address, then the bus PID as a
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binary integer of size sizeof(pid_t), then the bus X window ID as a
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binary integer of size sizeof(long). Integers are in the machine's
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byte order, not network byte order or any other canonical byte order.
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Close the standard error output stream before starting the D-Bus
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daemon. This is useful if you want to capture dbus-launch error
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messages but you don't want dbus-daemon to keep the stream open to
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.I "--config-file=FILENAME"
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Pass \-\-config-file=FILENAME to the bus daemon, instead of passing it
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the \-\-session argument. See the man page for dbus-daemon
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Emit csh compatible code to set up environment variables.
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.I "--exit-with-session"
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If this option is provided, a persistent "babysitter" process will be
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created that watches stdin for HUP and tries to connect to the X
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server. If this process gets a HUP on stdin or loses its X connection,
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it kills the message bus daemon.
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.I "--autolaunch=MACHINEID"
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This option implies that \fIdbus-launch\fP should scan for a
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previously-started session and reuse the values found there. If no
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session is found, it will start a new session. The
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\-\-exit-with-session option is implied if \-\-autolaunch is given.
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This option is for the exclusive use of libdbus, you do not want to
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use it manually. It may change in the future.
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Emit Bourne-shell compatible code to set up environment variables.
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Print the version of dbus-launch
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See http://www.freedesktop.org/software/dbus/doc/AUTHORS
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Please send bug reports to the D-Bus mailing list or bug tracker,
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see http://www.freedesktop.org/software/dbus/
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doc/dbus-launch.1
