Common error diagnosis in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does a 502 Bad Gateway error usually indicate in nginx?

It means nginx received an invalid response from the upstream server, often because the backend server is down or misconfigured.

beginner

How can you check nginx error logs to diagnose issues?

Use the command tail -f /var/log/nginx/error.log to view real-time error messages.

beginner

What does a 404 error mean in nginx?

It means the requested resource was not found on the server. This can happen if the URL is wrong or the file does not exist.

intermediate

Why might nginx fail to start after configuration changes?

Because of syntax errors in the config file. Running nginx -t checks the config for errors before restarting.

beginner

What is the purpose of the nginx -t command?

It tests the nginx configuration files for syntax errors without starting the server.

Which log file is most useful for diagnosing nginx errors?

A /var/log/nginx/error.log

B /var/log/nginx/access.log

C /etc/nginx/nginx.conf

D /var/log/syslog

The error.log file contains error messages that help diagnose nginx problems.

What does a 504 Gateway Timeout error mean in nginx?

A The requested page was not found

B The upstream server did not respond in time

C Nginx configuration syntax error

D Permission denied to access the file

A 504 error means nginx waited too long for the backend server to respond.

What command checks nginx configuration syntax without restarting?

A systemctl status nginx

B nginx -s reload

C nginx -v

D nginx -t

nginx -t tests the config files for syntax errors.

If nginx shows a 403 Forbidden error, what is a likely cause?

A File permissions prevent access

B The server is down

C The URL is incorrect

D Nginx configuration syntax error

403 means access is denied, often due to file or directory permissions.

What is the first step to diagnose nginx not starting after config change?

A Delete the config file

B Restart the server immediately

C Run <code>nginx -t</code> to check config syntax

D Check the access log

Checking config syntax helps find errors before restarting nginx.

Explain how to diagnose a 502 Bad Gateway error in nginx.

Think about what nginx means by 'Bad Gateway' and where to look for clues.

Describe the steps to safely apply changes to nginx configuration.

Testing config before reload prevents downtime.