[PLUG] What Controls Mouse Clipboard in X Window?

[Rich Shepard]

   Does anyone know the library or tool that controls cutting and pasting
using the mouse when the X Window System is running? I suspect that it's not
xclipboard because that is a text-based terminal application that can be
used to cut and paste, but I'm interested in what is used when the left
mouse button is used to highlight text and the middle button used to paste
it in another vt or application window.

   The past couple of weeks I've had this fail sporatically. A couple of days
not at all, some days once, or twice, and a couple of days multiple times.
Killing the X server and restarting it restores the capability but it can
again silently disappear.

   Tomorrow night I'll run memtest86 all night to see if the new DIMMs are
responsible, and after that I'll exchange hard drives to eliminate that
potential source of hardware error. In the meantime I'm interested in
learning what else it might be. This has not happened before so I've no idea
what might cause it.

TIA,

Rich