There was a thread posted here suggesting to use this environment variable
to disable the cook dialog and allow ESC to interrupt cooks.

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=12375&highlight=houdinienablelinuxthreadedui [sidefx.com]

if you set this env variable, you can be sure that the pyqt cookbook example
will fail. It also appears that its no longer needed anway… It was an incredible
pain to find the root of our pyqt troubles… and it all boiled down to this hidden,
undocumented env variables set in some dark corner of our pipeline. Evidently
as of 9.5.139 this env variable is no longer used!

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=59329 [sidefx.com]