[ Thanks to linuxaria for this link.
“Installation: Knockd it’s available in the repository of the
major distributions, i’m using it on Ubuntu/Debian where the
package it’s available.
“Configuration: knockd reads all knock/event sets from a
configuration file. Each knock/event begins with a title marker, in
the form [name], where name is the name of the event that will
appear in the log. A special marker, [options], is used to define