Failed to start The nginx HTTP and reverse proxy server.

There could be several reasons why nginx failed to start. Here are some troubleshooting steps you can try:

1. Check the nginx error log: The error log is usually located at /var/log/nginx/error.log. Check this log file for any error messages that might indicate why nginx failed to start.

2. Check the nginx configuration file: The configuration file is usually located at /etc/nginx/nginx.conf. Make sure that the configuration file is valid and does not contain any syntax errors. You can use the following command to check the syntax of the configuration file: `sudo nginx -t`.

3. Check if another process is already listening on the same port: Nginx listens on port 80 by default. If another process is already listening on this port, nginx will fail to start. You can use the following command to check if another process is listening on port 80: `sudo netstat -tlnp | grep :80`.

4. Check if nginx is already running: If nginx is already running, it will fail to start again. You can use the following command to check if nginx is already running: `sudo systemctl status nginx`.

5. Check if there is enough disk space: If there is not enough disk space, nginx may fail to start. You can use the following command to check the available disk space: `df -h`.

Once you have identified the cause of the problem, you can take the necessary steps to resolve it and start nginx.