1. Check Web Server Status:
   • Connect to the Linux server using SSH.
   • Use the command: systemctl status apache2 (replace “apache2” with the name of your web server, e.g., “nginx” or “httpd”).
   • If the service is inactive or failed, start it using: sudo systemctl start apache2.
2. Examine Web Server Logs:
   • Inspect the web server error logs for any issues. Common log locations are /var/log/apache2/error.log for Apache or /var/log/nginx/error.log for Nginx.
   • Use the tail command to view the last few lines of the log: sudo tail -n 20 /var/log/apache2/error.log.
3. Check Port Availability:
   • Ensure that the web server is listening on the correct port (usually port 80 for HTTP or 443 for HTTPS).
   • Use the command: sudo netstat -tulpn | grep LISTEN to check for open ports and the processes listening on them.
4. Firewall Inspection:
   • Verify that the firewall allows traffic on the web server port.
   • For example, if using UFW: sudo ufw allow 80 (replace “80” with your web server port).
5. Network Connectivity:
   • Check the server’s network connectivity. Ensure the server has a valid IP address and is reachable from the network.
   • Use the command: ping server_ip to check network connectivity.
6. Resource Usage:
   • Verify server resource usage (CPU, memory) to ensure there are no resource constraints impacting the web server.
   • Use the command: top or htop to view resource usage.
7. Service Configuration:
   • Confirm the web server’s configuration files for any syntax errors or misconfigurations.
   • For Apache: sudo apachectl configtest.
   • For Nginx: sudo nginx -t.
8. Restart Services:
   • After making any changes, restart the web server service: sudo systemctl restart apache2 (or the appropriate command for your web server).

By systematically checking these steps, you can identify and resolve common issues affecting the accessibility of a web server on a Linux machine.