Share first ssh connection to user@host opportunisitically using ControlMaster

Solution 1:

From the ssh_config man page:

ControlMaster
    ...
    Two additional options allow for opportunistic multiplexing: try
    to use a master connection but fall back to creating a new one if
    one does not already exist.  These options are: “auto” and
    “autoask”.  The latter requires confirmation like the “ask”
    option.

So if you configure ssh with ControlMaster auto, it will attempt to connect to use an existing SSH session, falling back to creating a new master connection if that fails.

So a configuration like the following is probably what you're after:

ControlMaster auto
ControlPath ~/.ssh/control/%r@%h:%p