How to close a program that has frozen the environment 

Although Linux is a really stable platform, there will be some times that a program will freeze your GUI environment.
There is an option suitable at cases, when the most common methods will not save you, simply because they are not applicable.

Sometimes, mostly at games, more specifically at Microsoft Windows games played via Wine but not only, the entire graphical interface freezes.
Ctrl-Alt-Del and Ctrl-Alt-Backspace are not options, as you want to kill only the faulty game/processes, and at the same time not to lose other running applications/processes.

The steps to kill the faulty process are:

  1. Open another TTY console of your choice – Press one of Ctrl-Alt-F2 through Ctrl-Alt-F6 sequence;
  2. Login at the console;
  3. Navigate the processes by issuing the command ps -ef | less and find the frozen processes;
  4. Escape from less and kill these processes with the command kill pid1 pid2 ... pidN , substituting the correct values for the PIDs;
  5. Switch and finally return to the original graphical screen by pressing Ctrl-Alt-F7.

Enjoy.