Questions[xprop](ubuntu)

I'm using a window manager and compositor in Ubuntu. I have blur enabled for transparent windows, which means that when I take a screenshot with gnome-screenshot, the content I'm trying to take a picture of is blurred. With xprop, or some other tool, how do I identify the class of the screenshot window so that I can add it to my blur-exclude rule in my compositor config?

When I start xprop, then take a screenshot and click on the screenshot window, I'm prompted with the following, which doesn't give me any information about the class of the window:

$ xprop WM_CLASS

X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  20 (X_GetProperty)
  Resource id in failed request:  0x4001a3
  Serial number of failed request:  33
  Current serial number in output stream:  33

Hello I'm new to the Linux system and would like to know if there is a code or application which opens a terminal that will tell me the lines of code being used. For example, If I were to open a folder or directory I would like to know the lines of code associated with it.

I know that

xprop | awk '/PID/ {print $3}' | xargs ps

and

xprop | awk '/COMMAND/ {print $4}' | xargs which

work great with GUI applications which are deb-packaged, AppImage'd or Snap'd.

But this method does not give executable file-name for application which is packaged as FlatPak.
See example below:

$ flatpak run org.libretro.RetroArch

$ xprop 
_NET_WM_VISIBLE_NAME(UTF8_STRING) = "RetroArch   (as superuser)"
WM_NAME(STRING) = "RetroArch  "
_NET_WM_ICON_GEOMETRY(CARDINAL) = 446, 744, 207, 24
WM_PROTOCOLS(ATOM): protocols  WM_DELETE_WINDOW
XKLAVIER_STATE(INTEGER) = 0, -180379392
_NET_WM_STATE(ATOM) = 
WM_STATE(WM_STATE):
      window state: Normal
      icon window: 0x0
_NET_FRAME_EXTENTS(CARDINAL) = 3, 3, 23, 3
_NET_WM_DESKTOP(CARDINAL) = 0
_NET_WM_ALLOWED_ACTIONS(ATOM) = _NET_WM_ACTION_MOVE, _NET_WM_ACTION_RESIZE, _NET_WM_ACTION_FULLSCREEN, _NET_WM_ACTION_MINIMIZE, _NET_WM_ACTION_SHADE, _NET_WM_ACTION_MAXIMIZE_HORZ, _NET_WM_ACTION_MAXIMIZE_VERT, _NET_WM_ACTION_CHANGE_DESKTOP, _NET_WM_ACTION_CLOSE, _NET_WM_ACTION_ABOVE, _NET_WM_ACTION_BELOW
WM_CLIENT_MACHINE(STRING) = "norbert-UX32A"
_NET_WM_PID(CARDINAL) = 2
WM_CLASS(STRING) = "retroarch", "retroarch"
_NET_WM_ICON(CARDINAL) =  Icon (16 x 16):
                  
    ▓▓▓▓▓▓▓▓▓▓▓   
   ▓▓▓▓▓▓▓▓▓▓▓▓▓  
   ▓▓▓▓▓▓▓▓▓▓▓▓▓  
   ▓▓▓ ▓▓▓▓▓ ▓▓▓  
   ▓ ▓▓ ▓▓▓ ▓▓ ▓  
   ▓ ▓       ▓ ▓  
   ▓   ▓   ▓   ▓  
   ▓           ▓  
   ▓▓         ▓▓  
   ▓▓▓ ▓▓▓▓▓ ▓▓▓  
   ▓▓ ▓▓▓▓▓▓▓ ▓▓  
   ▓▓▓▓▓▓▓▓▓▓▓▓▓  
   ▓▓▓▓▓▓▓▓▓▓▓▓▓  
    ▓▓▓▓▓▓▓▓▓▓▓   
                  

So I do not see PID- or COMMAND-related lines in xprop output. But of course it is launched:

$ flatpak ps
Instance  PID   Application            Runtime
752290322 23857 org.libretro.RetroArch org.kde.Platform

How can I get PID of window created by FlatPak application while using xprop, wmctrl or something similar?

I have a bash script that moves my windows from the left screen to right screen in dual-screen setup. Currently the way it works is cycling through the window ids that are given by xdotool search --onlyvisible --maxdepth 2 --class "" and then moves them to the right by the screen width. It already works... unless the window in question is maximises or minimised.

So what is needed is a way to check the current status of the window. I have found an answer that provides the way to add and remove those bits, but where is the way to check if they are set already?

If it is not possible to do via xdotool, it should be possible to reuse the window id provided by the command mentioned above.

I followed all the steps in this answer: https://askubuntu.com/a/975230/719469

However when I run xprop WM_CLASS in Terminal and click on my application's window, it gives me: WM_CLASS: not found. What should I do to get a single icon of the app on the Ubuntu Dock?

The application I am talking about is Recoll, installed using apt-get install recoll. I am using Ubuntu 18.04 (Xorg).

The contents of .desktop file in /usr/share/applications:

[Desktop Entry]
Categories=Utility;Filesystem;Database;
Comment=Find documents by specifying search terms
Exec=recoll
GenericName=Local Text Search
Icon=recoll
Name=Recoll
Terminal=false
Type=Application
Keywords=Search;Full Text;

Edit:

I tried changing the .desktop file lines by making these changes

Exec=recoll --class CustomClassName

and then adding the line

StartupWMClass=CustomClassName

After doing this, the app fails to launch from its icon and I still get WM_CLASS: not found. in the terminal