knock command not found

Introduction

When you run more command in linux terminal / console, you get the following error message

knock: command not found

or when using sudo you get the following error message

sudo: knock: command not found

Solutions to knock: command not found

How To Fix knock: command not found in Ubuntu / Debian / Kali Linux / Raspbian

In Ubuntu knock is provided by knockd package.

knockd is:

A port-knock server that listens to all traffic on a given network interface (only Ethernet and PPP are currently supported), looking for a special “knock” sequences of port-hits. A remote system makes these port-hits by sending a TCP (or UDP) packet to a port on the server. When the server detects a specific sequence of port-hits, it runs a command defined in its configuration file. This can be used to open up holes in a firewall for quick access.

To fix this problem, we can install more using the command below.

sudo apt-get -y install knockd

This command might take some time to finish depending on your machine internet connection.

You can also use apt command to install knockd.

sudo apt -y install knockd

Or if you have aptitude installed you can use the following command.

sudo aptitude install knockd

Summary

In this tutorial we learn how to fix knock command not found error in Ubuntu / Debian / Kali Linux or Raspbian distribution.