Veja aqui: link Desloque-se para 6 "Gravação de Screencast".
Diz:
Unknown to many, Gnome Shell has a built-in screen recorder. At any point of time, you just have to press the shortcut key “Shift + Ctrl + Alt + R” to activate the screen recorder. Once activated, you will see a recording button at the bottom right corner. Press “Shift + Ctrl + Alt + R” again to stop the recording. It will then save itself with the filename “shell-date-string-counter.webm” in your Home folder.