A strange black square appears at the top-left side of the screen. I log in, it does not appear until I open Whisker menu, but whenever I open it, it simply appears and stays at the top of all application windows.

It is not a functional problem but it is getting annoying. This is the screenshot while Whisker menu is open:

It might sometimes imitate the wallpaper, ss:

  • Could it be a tool tip of some sort?
    – Minix
    Sep 1 '15 at 7:48
  • It does not seem so, will not fade out while I'm busy with other applications. It stays black, but can change color in time like this: i.hizliresim.com/EqAv0v.png . This is actually color of the wallpaper, I don't know why this happens.
    – Eray Erdin
    Sep 3 '15 at 14:44
  • Are you using Thunar as your file manager?
    – Minix
    Sep 4 '15 at 16:42
  • Yes. I use Thunar.
    – Eray Erdin
    Sep 4 '15 at 20:33
  • this happened to me on Ubuntu 19.10, Zac's solution fixed the problem
    – Pafnucy
    May 16 '20 at 8:45

Xubuntu 12.04.5 user here, I launched xwininfo command from a shell, and point to the black rectangle, it says:

xwininfo: Window id: 0x240007d (has no name)

launching command xkill -id 0x240007d did close the black rectange.

The window id is not the same every time: this time wininfo shows an id of 0x360007b.

Moreover, I played an openGL game and the rectangle is no more black, but shows a bit of game graphics.

  • Does window id change on each reboot?
    – Eray Erdin
    Dec 1 '15 at 19:28
  • This worked for me in Linux Mint 20 with MATE desktop. Clipit seems not to play well with MATE...?
    – RBV
    Oct 9 '20 at 9:19

Try in a terminal

xfconf-query -c xfwm4 -p /general/use_compositing -t bool -s false
xfconf-query -c xfwm4 -p /general/use_compositing -t bool -s true

The square disappears, but you need to do after each reboot of the computer.

I found this solution on another forum. I don't understand why that works.

  • Thanks... ^^ However, I found another permanent solution.
    – Eray Erdin
    Oct 11 '15 at 18:31

There's another permanent solution to this issue.

If you install another Ubuntu with desktop environment (like Kubuntu) and then install Xubuntu and completely uninstall the old environment, the black square will not appear.

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