I use ControlMaster auto (along with ControlPath) in my ssh config and find it very handy. I have noticed an annoying behavior, though: it seems that if there is no existing master connection and ssh creates a new one, the master connection process that is started has its stderr left open. This has manifested itself in two ways so far: (1) When using ssh day-to-day, I may be doing some work and the text 'Shared connection to [servername] closed.' appears in my terminal. This happens when the remote server closes the connection after some amount of time (maybe hours or days). It's disruptive; I don't care about that connection and ssh will transparently open a new one the next time I ssh in. The text might appear while I'm inside vim or top and mess with that program. (2) Some software (I noticed it with Ansible[1]) waits for stderr/stdout of a process to be closed. In the case of Ansible it was because the communicate() method of Python's subprocess module[2] waits on stdout/stderr as well as wait()ing on the process itself. (This behavior seems strange to me, but it's indicative that openssh's behavior here is atypical, I think.) I haven't looked at the code yet, but I think the behavior I'd expect would be that when ssh creates the controlmaster process, it would set its stdin/stderr/stdout to /dev/null, or else some logfile. It's not useful to have that process writing to the terminal after its parent is long dead. Thanks for any information/feedback you can provide! -Caleb [1] http://www.ansibleworks.com/ [2] http://docs.python.org/2/library/subprocess.html#subprocess.Popen.communicate
