ControlMaster auto and stderr

[Caleb Spare]

A small correction: when I referred to text appearing in my terminal
in (1), the message is actually (for example):

Connection to github.com closed by remote host.

On Tue, Jan 14, 2014 at 5:42 PM, Caleb Spare <cespare at gmail.com> wrote:
> 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