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A number of autossh connections are already left open for port-forwarding Munin ports; autossh starts the connections and ensures that they are automatically restarted if they are severed. However, this represents a missed opportunity. Nagios's monitoring uses a large number of SSH connections to the remote hosts to run commands on them; each of these connections requires doing a complete SSH handshake and authentication, which can have non-trivial network latency, particularly for hosts which may be located far away, in a network topology sense (up to 1s for a no-op command!). Use OpenSSH's ability to multiplex multiple connections over a single socket, to reuse the already-established connection. We leave an explicit `ControlMaster no` in the general configuration, and not `auto`, as we do not wish any of the short-lived Nagios connections to get promoted to being a control socket if the autossh is not running for some reason. We enable protocol-level keepalives, to give a better chance of the socket being kept open.