I ran into this very cryptic one while setting up Nagios at Joyent. I copied my plugins from one nrpe client to a new server. Three of my checks used check_procs which all failed with a message like this:
check_procs System call sent warnings to stderr: pst3: This program can only be run by the root user!
To make this even more annoying, sudo did not fix it. The same error message was displayed. What was the problem? File permissions! The error message should say “This program must be owned by the root user!” The fix:
sudo chmod root:root pst3
