Nagios also offers plugins that monitor different network services. These include commands for checking FTP, DHCP protocol, and WWW servers. It is also possible for Nagios to monitor itself.
Nagios allows you to verify whether an FTP server is listening for connections using the
check_ftp command. This plugin is identical to
check_tcp, with the difference that the port is optional, and by default a valid FTP welcome message is expected:
check_ftp -H host -p port [-w <warning time>] [-c <critical time>] [-s <send string>] [-e <expect string>] [-q <quit string>][-m <maximum bytes>] [-d <delay>] [-t <timeout seconds>] [-r <refuse state>] [-M <mismatch state>] [-v] [-4|-6] [-j] [-D <warn days cert expire>[,<crit ...