Nagios offers a very powerful mechanism to receive events and commands from external applications—the external commands pipe. This is a pipe file created on a filesystem that Nagios uses to receive incoming messages. The filename is rw/nagios.cmd, and it is located in the directory passed as the localstatedir option during compilation. If you have followed the compilation and installation instructions given in Chapter 2, Installing Nagios 4, the filename will be /var/nagios/rw/nagios.cmd.

The communication does not use any authentication or authorization. The only requirement is to have write access to the pipe file. An external command file is usually writable by the owner and the group; usually, the group used is nagioscmd. If you want a user to be able to send commands to the Nagios daemon, simply add that user to this group.

A small limitation of the command pipe is that there is no way to get any results, and so, it is not possible to send query commands to...