OK, I was doing some debugging with Xorg, and thought I had to use the Magic SysRq key to kill it. But when I had pressed Alt-SysRq-R to give the keyboard control from Xorg back to the kernel, it turned out that I not longer needed to do another SysRq because my Xorg magically worked again… 😉 Unfortunately now, everytime I pressed Alt-F4 to close a window, I found myself on tty4… rather poor. So I needed some way to tell Xorg to grab the keyboard again, and there it is: Just open an xterm and execute
sudo kbd_mode -s
I had to debug a machine that was behind a DSL-2000 connection, and had about 20 KB/s of upstream. For that, I needed to see what was going on on the X screen, but due to the low bandwidth (and a screen resolution of 1920×1080), VNC was about as fast as 2 frames per minute.
But I found a comparable replacement: The ImageMagick suite has a program called import that allows you to dump the contents of the X screen to a image file. So I took a few screen shots from the console via DISPLAY=:0 import -window root foo.png and then copied the files to my machine.