[djm [at] demiurg ~]$ ssh -nNfS ~/ctl-sock-blah localhost
[djm [at] demiurg ~]$ ssh -S ~/ctl-sock-blah -O check localhost
Master running (pid=3517)
[djm [at] demiurg ~]$ ssh -S ~/ctl-sock-blah -O exit localhost
Exit request sent.
http://www.gossamer-threads.com/lists/openssh/dev/48040
By no means a new topic.