Find out the application under the mouse

Using xdotool

First make sure xdotool is available on your system:

sudo apt-get install xdotool

The following command will print the process name of the window currently in focus:

cat "/proc/$(xdotool getwindowpid "$(xdotool getwindowfocus)")/comm"

To give yourself more time to focus the window / click on it you can prepend a small sleep duration:

sleep 5 && cat "/proc/$(xdotool getwindowpid "$(xdotool getwindowfocus)")/comm"

The process name should be displayed after a short amount of time.

Using wininfo

Wininfo is a graphical utility that displays various information on windows and their properties, including the PID (process ID) associated with the window:

image of PID in wininfo

wininfo should be available in the official repositories:

sudo apt-get install wininfo

Having determined the PID of the window you can then look up the process name associated with it. There are various ways to do this, e.g. by looking at /proc:

$ cat /proc/17002/comm

This would be the process name associated with the PID 17002.

A more elegant way that allows inspecting the process tree context, as suggested by @Rmano:

$ pstree -a -s -l -p -u 17002
      └─lightdm,3202 --session-child 12 19
          └─lxsession,3307,glutanimate -s LXDE -e LXDE
              └─openbox,3362 --config-file /home/glutanimate/.config/openbox/lxde-rc.xml
                      │   └─pstree,2484 -a -s -l -p -u 17002

Of course you can also combine pstree with the xdotool option above (thanks to @rubo77 for pointing this out!):

sleep 2; pstree -spaul $(xdotool getwindowpid "$(xdotool getwindowfocus)")


You can create a keyboard-shortcut with this command:

zenity --info --text $(xprop $win_id WM_CLASS | cut -d" " -f4-)

You can use xprop to get the Process ID of the clicked Window:

xprop $win_id _NET_WM_PID

then analyze it with pstree:

pstree -spaul $(xprop $win_id _NET_WM_PID | cut -d" " -f3-)

This you can redirected to a text-info window with

pstree -spaul $(xprop $win_id _NET_WM_PID | cut -d" " -f3-)|zenity --text-info --title "pstree of clicked Window"

I tried to create a keyboard-shortcut for this last command (if you need it regularely), but for some reason This doesn't work.