To add a swap file:

If your Hudson is really busy and it launches a lot of processes, in theory you could be temporarily running more than 2 instances of your application server.

There are many ways to check the usage of swap space, but I usually use the “top” command, which is available on most Unix systems.

This is a Unix-specific issue, as Windows launches child processes without forking.

If you know how to do this for OSes not listed here, please add it