This is the first time I am trying to write a plugin for Nagios. So please bear with me. We have an online testing system and I am writing a plugin to check how many users are actually taking a test. It is a module that is in built in the system and exported via http. So all I do is call that page and dump the number out. Nothing complicated. The code-block (perl) which dumps out is as follows: if ($content =~ m/<TD>Student Cache<\/TD><TD>(\d*)<\/TD>/) { if ($1>$critical) { if ($verbose) { print "CRITICAL: $1 Users Online > $critical Critical Status \t Critical ErrorLev 2 | UsersOnline=$1;0;0;\n"; } else { print "CRITICAL: $1 Users Online | UsersOnline=$1;0;0;\n"; } exit $ERRORS{'CRITICAL'}; } elsif ($1>$warning) { if ($verbose) { print "WARNING: $1 # Users Online > $warning Warning Status \t Critical ErrorLev 1 | UsersOnline=$1;0;0;\n"; } else { print "WARNING: $1 Users Online | UsersOnline=$1;0;0;\n";}; exit $ERRORS{'WARNING'}; } else { if ($verbose) { print "OK: $1 Users Online - Status normal \t Normal ErrorLev 0 | UsersOnline=$1;0;0;\n"; } else { print "OK: $1 Users Online | UsersOnline=$1;0;0;\n"; } exit $ERRORS{'OK'}; } } For e.g the output will look like: OK: 12 Users Online | UsersOnline=12;0;0; where -w is 150 and -c is 200. But nagios complains by saying "NRPE: Unable to read output". Is the format of the output wrong or am I missing any steps? --Turi