fwknop command not found

Introduction

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

fwknop: command not found

or when using sudo you get the following error message

sudo: fwknop: command not found

Solutions to fwknop: command not found

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

In Ubuntu fwknop is provided by fwknop-client package.

fwknop-client is:

The FireWall KNock OPerator implements an authorization scheme called Single Packet Authorization (SPA), based on Netfilter and libpcap.

Its main application is to protect services such as OpenSSH with an additional layer of security in order to make the exploitation of vulnerabilities (both 0-day and unpatched code) much more difficult.

This is the client program responsible for accepting password input from the user, constructing SPA packets that conform to the fwknop packet format, and encrypting packet data.

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

sudo apt-get -y install fwknop-client

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

You can also use apt command to install fwknop-client.

sudo apt -y install fwknop-client

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

sudo aptitude install fwknop-client

Summary

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