Running xfce on my new Lifebook, I was completely locked out after I ran xflock4 (which in turn calls gnome-screensaver-command –lock).
Back to the prompt I saw a lot of segfaults reported by the kernel like this one:
May 19 12:54:07 lulu kernel: [ 1166.757433] gnome-screensav[8313]:
segfault at 31 rip 7f8a51b1c8d4 rsp 7fff5b3d9a10 error 4
Fortunately using xscreensaver instead of gnome-screensaver is a work around.