'Aloha! This might be common knowledge, but it was new to me, and took me quite a while to figure out, so i think I better share my experience. I have a not so small nagios installation, 1795 hosts and 3980 at this holy moment.... (nagios 3.2.0 on a linux/debian/etch box) Sometimes my nagios stopped working, and declaring everything to be down, with a message tomething like these log lines: Warning: Return code of 127 for check of host 'myhost' was out of bounds. Make sure the plugin you're trying to run actually exists. Warning: Return code of 127 for check of service 'myservice' on host 'myhost' was out of bounds. Make sure the plugin you're trying to run actually exists. I tracked it down to calls to the plugins were bloated with a huge set of environment variables, every plugin call where served something that looked like a big chunk of sibling hosts or services from the same hostgroup/servicegroup. The fix were easy, flip the config variable "enable_environment_macros" in nagios.cfg from 1 to 0. Reload an be happy.. (and I got a much better performance too) -- /Morten %-)