mark at woodstream.net wrote: > #./check_udp -H 10.10.10.17 -p 4000 This exact command works perfectly for me. My version is "check_udp (nagios-plugins 1.3.1) 1.4.2.1". What does "check_udp -V" return for you? What happens if you use a hostname instead of an address? :) Bjørnar