A number of macros contain values that were not defined within the Nagios configuration or defined by Nagios itself, but which originate from external programs. These include macros that record the plugin output (
$HOSTPERFDATA$), and the corresponding macros for services. Via the Web interface, the administrator can pass on values to Nagios through acknowledgments, which can be read out from the macros
$HOSTACKCOMMENT$, and the equivalent service macros.
To guard against the possibility that these macros might contain damaging code, which might trigger a buffer overflow or enable other mischievous things, Nagios removes "dangerous" lines. What these are ...