Nagios allows you to verify whether an FTP server is listening for connections by using the
check_ftp command. This plugin is identical to
check_tcp, with the difference that the port is optional. 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>] [-A] [-m <maximum bytes>] [-d <delay>] [-t <timeout seconds>] [-r <refuse state>] [-M <mismatch state>] [-v] [-4|-6] [-j] [-D <days to cert expiry>] [-S] [-E]
The port argument can be omitted and defaults to 21, or 990 for SSL-based connections. A sample command definition for...