Unit nginx.service could not be found.

This error message usually occurs when trying to start or enable the nginx service on a system where nginx is not installed or has been removed.

To fix this issue, you will need to install nginx on your system. Here are the steps to install nginx on Ubuntu:

1. Update your system's package index:

   sudo apt update

2. Install nginx:

   sudo apt install nginx

3. Once the installation is complete, start the nginx service:

   sudo systemctl start nginx

You can also enable the service to start automatically at boot time by running:

   sudo systemctl enable nginx

After completing these steps, you should be able to run the nginx service without encountering the "Unit nginx.service could not be found" error.