I was just programming as a normal user (not root) when Xemacs(ESS) hung up because of lots of output - Xemacs did not react to stop button or ESC-ESC and I could not activate any other window.
Waited a minute or two and tried an ordinary reboot from within X/KDE with the result that now X does not start. I get:
(II) Loading /usr/lib64/xorg/modules//extensions/libdri.so (II) Module dri: vendor="X.Org Foundation" compiled for 1.5.2, module version = 1.0.0 ABI class: X.Org Server Extension, version 1.1 (II) Loading extension XFree86-DRI Backtrace: 0: X(xf86SigHandler+0x65) [0x489be5] 1: /lib64/libc.so.6 [0x7fb7dc7d46e0] 2: X(InitOutput+0x508) [0x467858] 3: X(main+0x286) [0x4324c6] 4: /lib64/libc.so.6(__libc_start_main+0xe6) [0x7fb7dc7c0586] 5: X [0x431a79] Fatal server error: Caught signal 11. Server aborting