Debug mode in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of enabling debug mode in nginx?

Debug mode in nginx helps to log detailed information about requests and internal processing. This helps find and fix problems in configuration or performance.

beginner

How do you enable debug mode in nginx configuration?

Add the directive error_log /path/to/log debug; in the nginx configuration file to enable detailed debug logging.

beginner

Where does nginx write debug logs when debug mode is enabled?

Nginx writes debug logs to the file specified in the error_log directive with the debug level.

beginner

What is a common command to test nginx configuration before enabling debug mode?

Use nginx -t to test the configuration syntax and catch errors before restarting nginx with debug mode.

intermediate

Why should debug mode be used carefully in production?

Debug mode generates very detailed logs that can slow down nginx and fill disk space quickly. It is best used temporarily for troubleshooting.

Which directive enables debug logging in nginx?

A error_log /var/log/nginx/error.log debug;

B access_log /var/log/nginx/access.log debug;

C debug_mode on;

D log_level debug;

The error_log directive with the debug level enables debug logging in nginx.

What command checks nginx configuration syntax before enabling debug mode?

A nginx -t

B nginx -s reload

C nginx -v

D nginx -c

The nginx -t command tests the configuration syntax without starting nginx.

Where are debug logs written when debug mode is enabled?

A Access log file

B Error log file

C Standard output

D System journal

Debug logs are written to the error log file specified in the configuration.

Why should debug mode be disabled after troubleshooting?

A It disables nginx caching

B It disables SSL

C It slows down nginx and uses more disk space

D It blocks user requests

Debug mode creates detailed logs that can slow nginx and fill disk space quickly.

Which log level is required to see debug messages in nginx?

A info

B warn

C error

D debug

The debug log level enables detailed debug messages.

Explain how to enable and use debug mode in nginx for troubleshooting.

Think about the steps from configuration to checking logs and then turning off debug mode.

Describe the risks of leaving debug mode enabled in a production nginx server.

Consider what happens when too much logging is done on a live server.

Practice

1. What does enabling debug mode in nginx do?

easy

A. Shows detailed logs to help find problems

B. Stops nginx from running

C. Deletes all log files

D. Automatically fixes errors

Solution

1. Step 1: Understand debug mode purpose

   Debug mode is designed to provide detailed information about what nginx is doing internally.

2. Step 2: Identify effect of enabling debug mode

   It shows detailed logs that help find and fix problems in nginx configuration or operation.

3. Final Answer:

   Shows detailed logs to help find problems -> Option A

4. Quick Check:

   Debug mode = detailed logs [OK]

Hint: Debug mode means detailed logs for troubleshooting [OK]

Common Mistakes:

• Thinking debug mode stops nginx
• Believing debug mode deletes logs
• Assuming debug mode auto-fixes errors

2. Which is the correct syntax to enable debug mode in nginx's error log?

easy

A. error_log debug /var/log/nginx/error.log;

B. error_log /var/log/nginx/error.log info;

C. error_log /var/log/nginx/error.log debug;

D. error_log /var/log/nginx/error.log off;

Solution

1. Step 1: Recall error_log syntax

   The correct syntax is: error_log <file_path> <level>; where level can be debug, info, etc.

2. Step 2: Identify correct option

   error_log /var/log/nginx/error.log debug; uses correct order: file path first, then debug level.

3. Final Answer:

   error_log /var/log/nginx/error.log debug; -> Option C

4. Quick Check:

   error_log file_path debug; = error_log /var/log/nginx/error.log debug; [OK]

Hint: error_log path then level debug; is correct syntax [OK]

Common Mistakes:

• Swapping file path and level order
• Using info instead of debug for debug mode
• Setting level to off disables logging

3. Given this nginx config snippet:

error_log /var/log/nginx/error.log debug;
server {
  listen 80;
  server_name example.com;
}

What will happen when nginx receives a request?

medium

A. Detailed debug logs will be written to /var/log/nginx/error.log

B. No logs will be created

C. Only error messages will be logged

D. Nginx will refuse connections

Solution

1. Step 1: Analyze error_log level

   The error_log is set to debug level, which logs detailed info about requests.

2. Step 2: Understand effect on request handling

   When nginx receives a request, it logs detailed debug info to the specified file.

3. Final Answer:

   Detailed debug logs will be written to /var/log/nginx/error.log -> Option A

4. Quick Check:

   debug level logs detailed info [OK]

Hint: debug level logs detailed info on requests [OK]

Common Mistakes:

• Thinking debug disables logging
• Assuming only errors are logged
• Believing nginx refuses connections with debug

4. You set error_log /var/log/nginx/error.log debug; but see no debug logs. What is a likely cause?

medium

A. Debug mode disables logging

B. Nginx was not reloaded after config change

C. The log file path is missing

D. The debug level is misspelled

Solution

1. Step 1: Check if config changes are active

   After changing nginx config, you must reload nginx to apply changes.

2. Step 2: Identify why no debug logs appear

   If nginx is not reloaded, it uses old config without debug logging.

3. Final Answer:

   Nginx was not reloaded after config change -> Option B

4. Quick Check:

   Reload nginx after config change [OK]

Hint: Reload nginx after config changes to activate debug [OK]

Common Mistakes:

• Forgetting to reload nginx
• Thinking debug disables logs
• Misspelling debug level

5. You want to enable debug mode only temporarily to avoid large log files. Which is the best approach?

hard

A. Delete log files manually to reduce size

B. Permanently set debug mode in nginx.conf

C. Disable logging completely during debugging

D. Set error_log /var/log/nginx/error.log debug;, reload nginx, then revert after debugging

Solution

1. Step 1: Understand temporary debug enabling

   Temporarily enable debug by changing error_log level and reloading nginx.

2. Step 2: Revert changes after debugging

   To avoid large logs, revert error_log level back and reload nginx again.

3. Final Answer:

   Set error_log /var/log/nginx/error.log debug;, reload nginx, then revert after debugging -> Option D

4. Quick Check:

   Temporary debug = enable then revert [OK]

Hint: Enable debug, reload, then revert to avoid big logs [OK]

Common Mistakes:

• Leaving debug mode enabled permanently
• Deleting logs instead of controlling debug level
• Disabling logging disables debug info