Problem(s) Encountered:

VNC screen stalled around 3:40am.  Since that,  x11vnc -nomodtweak -display :0” is not working anymore.

Unfortunately, there is no one at the 2.4m. We do not have remote control on the system, so it is not possible to stop telescope from our side.

Telescope is now on tracking a target which meridian time is  around 7 AM.


Solution:

Not really sure what went wrong.  I logged into mdm13ws2 from home this morning, reboot McGraw to free up processes (TCS, xmis2…), then brought enough tasks online to stow the telescope and close the dome.  Once on the mountain, checked mdm13ws1 and found the pesky continuous ‘r’ key enter in the IRAF terminal.  Still don’t know why this would cause issues.  Also found that I could not close Owl.  It weas simply frozen on the desktop.  Did a ps -aux and there was no associated process.  Weird.  
I went ahead and reboot McGraw once more as well as mdmarc2 and mdm13ws1.  Then I brought everything back online and verified I could vnc from the 2.4m.  Everything should be working ok.  Don’t really know what to say on this one.

From Halpern: The pesky continuous 'r' key is indeed a persistent problem, one that will freeze theworkstation, and force you to exit vnc.  On some nights I've had this problem 3-4 times.The 'r' key is used frequently in 'imexam', an iraf command that interacts with the ds9 to measure properties of the image.It's this interaction among vnc, iraf imexam, 'r', and ds9 that somehow causes the freeze, not the 'r' key per se.  I think it would take a real computer geek to explain this.But this is the first time I've heard that it kills vnc permanently.  That brings the danger to a higher level.