[cygwin] openssh connection sharing fails: "mux_client_request_session: read from master failed: Connection reset by peer"

[Jason Pyeron]

> -----Original Message-----
> From: Adam Dinwoodie
> Sent: Monday, January 17, 2022 11:30 AM
> 
> The SSH connection sharing function in Cygwin's openssh release, using
> `ssh -M` or the ssh_config.5 ControlMaster configuration, doesn't appear
> to work.  Setting up a master connection seems fine, but subsequent SSH

Sadly, it is a known issue.

https://stackoverflow.com/questions/20959792/is-ssh-controlmaster-with-cygwin-on-windows-actually-possible/21439862#21439862

We would be happy to thrown some $ or beer at it.

> sessions that should reuse master connection instead set up their own
> session, with an error stating "mux_client_request_session: read from
> master failed: Connection reset by peer".
> 
> Simple testcase attached, which creates a master connection, starts a
> long sleep in a second SSH session, then terminates the master
> connection.  When I run this on one of my Debian boxes, the script takes
> about 6s to run, as tearing down the master connection terminates the
> long-running command.  When run from Cygwin, however, the script takes
> about 64s, as the second SSH session creates an independent connection
> that's unaffected by the master connection terminating.
> 
> On Debian:
> 
> ```
> $ time bash test.sh adam@192.168.1.131
> Master running (pid=7008)
> 
> Exit request sent.
> 
> real    0m6.048s
> user    0m0.083s
> sys     0m0.111s
> ```
> 
> On Cygwin:
> 
> ```
> $ time bash test.sh adam@192.168.1.131
> Master running (pid=5079)
> mux_client_request_session: read from master failed: Connection reset by peer
> 
> Exit request sent.
> finishing
> 
> real    1m4.071s
> user    0m0.106s
> sys     0m0.540s
> ```
> 
> Slightly redacted `cygcheck -srv` output also attached.
> 
> Adam


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