xfce: Prevent multiple instances of apps
What is really annoying in Ubuntu is that when some apps which don't need multiple instances such as 'appearance settings', a web browser, terminal window are loaded again when they are aready launched. For a browser or terminal I can still understand, although such apps have a 'new window' option. But for settings apps, multiple instances of e.g. 'Appearence' or 'Keyboard settings' are completely useless.
How do I prevent that the launcher launches an app (e.g. Firefox) again when it is already launched ?
I tried a shellscript called launch.sh:
#!/bin/sh
if ! pgrep $1 >/dev/null; then "$2" &
fiIn the xfce launcher for Firefox I set
launch.sh firefox /usr/bin/firefox
which does work (firefox is not launched when it is areay open), but for xfce4-appearance-settings it does not work, because pgrep xfce4-appearance-settings returns nothing while xfce4-appearance-settings is opened.
In macOS it works properly: such apps are launched only once and when clicking again on the app icon, it moves to the foreground rather than starting a new obsolete instance.
How can this be realized in Ubuntu ?
31 Answer
It is the application itself that controls that behavior.
A command, e.g. for firefox, that switches to a running window, and only launches the program if it is not running, looks like:
wmctrl -x -a firefox || firefoxIn bash, the command separator || means "OR". The first command, wmctrl, attempts to switch to a window of WM_CLASS "firefox". If that fails, firefox is executed.
The first instance firefox refers to the WM_CLASS of a firefox window. You can see the WM_CLASS of running windows in the output of wmctrl -lx.
To use this for a shortcut key, or in a .desktop launcher, use following command:
sh -c "wmctrl -x -a firefox || firefox"
