If necessary, Nagios can even monitor itself: the included plugin,
check_nagios, tests, on the one hand, whether Nagios processes are running and, on the other hand, the age of the log file
nagios.log in the Nagios
var directory, for example,
Despite this, the question needs to be asked: if Nagios itself is not running, then the system simply cannot perform the plugin, which in turn cannot deliver an error message. The solution to this problem consists in having two Nagios servers, each of which addresses the locally installed plugin on the opposite server, with the help of NRPE (see Chapter 10 from page 213).
If you have just one Nagios server you can also run
check_nagios alone via cron and have ...