X: never before seen display strangeness

[Dave Feustel]

On Sat, Oct 11, 2008 at 06:24:13AM +0900, Slim Joe wrote:
> 2008/10/10, Dave Feustel <dfeustel at mindspring.com>:
> > As of two or three days ago, Windows of programs I kill disappear
> > from the screen, only to flash back upon the screen for an
> > instant before disappearing for good. I've never seen this
> > behavior in X before.
> 
> Hmm. This may be related to the problem I've been having. What kernel
> are you using? I've experienced something like this with Linux kernel
> 2.6.26 but not with 2.6.25. Maybe (wild, wild guess) it's an
> incompatibility between the xserver and kernel.

What command tells me what kernel is being used?