WhatWeb is an open-source reconnaissance tool used for web scanning and fingerprinting. It is designed to identify and gather information about a target website by analyzing its HTTP response headers, HTML content, and other relevant data. WhatWeb helps in understanding the technologies, frameworks, and software components used by a website.

It's worth noting that while WhatWeb can provide valuable information, it should be used responsibly and within legal and ethical boundaries. Always ensure you have the necessary permissions and adhere to applicable laws and regulations when performing any form of website scanning or reconnaissance. To install WhatWeb on Ubuntu you can follow these steps:

1. Open a terminal: Press Ctrl + Alt + T to open a new terminal window or search for "Terminal" in the Ubuntu Dash.

2. Update the package repository: Run the following command to update the package repository on your Ubuntu system:

   sudo apt update

3. Install the required dependencies for WhatWeb:

   sudo apt install ruby ruby-dev libcurl4-openssl-dev liblzma-dev zlib1g-dev

4. Install the "WhatWeb" tool manually using Git:

   git clone https://github.com/urbanadventurer/WhatWeb.git
   cd WhatWeb
   sudo gem install bundler
   bundle install

   This will clone the WhatWeb repository from GitHub and install the necessary gems using Bundler.

5. Verify the installation by running the following command:

   ​whatweb --version

If WhatWeb is installed properly, you should see the version number displayed in the terminal.

Congratulations! You have successfully installed WhatWeb on your Ubuntu system. You can now start using WhatWeb for website analysis and reconnaissance purposes by running the whatweb command followed by the URL of the website you want to analyze.

Please note that WhatWeb requires a working internet connection to perform web scanning and gather information from the target website.