The Nagios plugin package provides two plugins to monitor the classic Internet services FTP and HTTP (including HTTPS):
check_ http. When many users from a network are using Web services, a proxy is usually used in addition. To monitor this, you could also use
check_http, but with the
check_squid.pl plugin, The Nagios Exchange has a better tool available.
check_ftp is, like the plugins for POP and IMAP, a symbolic link to the generic plugin
check_tcp, so that it also has the same options. They are described in detail in 6.7.1 Testing TCP ports in page 132.
The generic plugin sets the following parameters if it is called with the name
--port=21 --expect="220" ...