A completely different approach is to make check_by_ssh perform multiple tests and report them directly to Nagios over the external command pipe. This way, the results are sent to Nagios as passive check results. So, specified services need to accept passive check results.

The reason for this approach is that SSH protocol negotiations introduce a lot of overhead related to the protocol itself. For hosts with heavy load, it is more efficient to log in once and run all the checks instead of performing a complete login for each check.

A drawback of doing multiple checks is that it is not trivial to schedule these directly from Nagios. The typical approach to passive checks is to schedule checks from an external application such as cron (http://man.linuxquestions.org/index.php?query=cron).

An alternate approach is to create a dummy service that will launch passive checks in the background. The actual result for this service would also be to check whether running the...