How to maintain a persistent SSH connection?

[Phil Pennock]

On 2017-11-15 at 14:08 +0100, martin f krafft wrote:
> What does not work fine, however, is the server-side. If the
> connection goes down, sshd(8) lingers on the remote, bound to the
> port that I need to forward back across the link. As a result, new
> connections can't bind the port.
> 
> The sshd(8) process stays around for an unspecified time (>90min)
> after the connection went down.
> 
> I realise I could use ClientAliveInterval on the server-side, but
> there seems to be no way to specify this per-connection, and
> there simply won't be a server-wide policy change in this case.

So, instead of running no command server side, would a suitable
workaround be to run 'while sleep 1; do echo .; done' as the server
command and discard stdout from ssh on the client side?  That way, the
server side should detect the dropped link sooner, leading to sshd exit
and port release.

-Phil