Triii Technologies LLC

“When a site goes down, you first turn the lights on.” – WordPress Wisdom

If you’re running a WordPress site, you’ve probably hit at least one error in your life. Whether it’s a “White‑Screen‑of‑Death,” a 500 Internal Server Error, or a cryptic “Fatal error: Call to undefined function”, those messages can feel like a mystery. The good news? WordPress gives you a powerful built‑in toolset to turn that mystery into a solvable puzzle – Debug Mode and PHP error tracking.

In this article we’ll walk through:

• What common WordPress errors look like
• How to enable and use debug mode safely
• Reading PHP error logs and interpreting the clues
• Step‑by‑step troubleshooting tips
• Why a production‑ready error tracking system matters

Let’s get your site back to life!

1. WordPress Errors – The “What” and “Why”

Type of Error	Typical Symptoms	Likely Cause
Fatal PHP errors	Entire page crashes, “White‑Screen‑of‑Death”	Syntax errors, missing functions, plugin/theme conflicts
Warning / Notice	“Deprecated” warnings, “undefined index”	Out‑of‑date code, legacy plugins
Database errors	“Error establishing a database connection”	Wrong credentials, corrupted tables
Server errors (500)	Blank page with a generic error	PHP memory limit, .htaccess mis‑configuration
404 / 500 on uploads	Images, CSS, or JS files missing	File permissions, .htaccess rules
Security‑related	“The session has expired”	Session timeout, cookie issue

Every error has a root cause. The trick is to see the root cause, not just the symptom. That’s where debug mode shines.

2. Turn on Debug Mode (Your Diagnostic Headlights)

WordPress’s wp-config.php file has a few constants that control debugging. The most common trio:

// Enable all debugging

define( ‘WP_DEBUG’, true ); // Show errors

// Log errors to wp-content/debug.log

define( ‘WP_DEBUG_LOG’, true ); // Write to a file

// Show errors in the browser (useful on a staging site)

define( ‘WP_DEBUG_DISPLAY’, false ); // Set to true in dev, false in prod

How to Add It

1. Open wp-config.php via FTP, SFTP, or the File Editor in cPanel.
2. Locate the line that says /* That's all, stop editing! Happy blogging. */.
3. Insert the three constants just above that line.
4. Save and re‑upload if needed.

Tip: Use a staging environment. Enabling WP_DEBUG_DISPLAY on a live site can expose sensitive data to visitors.

What Happens Next?

• Fatal errors: WordPress will output a stack trace in the browser (if WP_DEBUG_DISPLAY is true) or log it.
• Warnings/Notices: These will also be logged.
• All errors: Go to wp-content/debug.log for a consolidated view.

3. Reading the Log – Turning Stack Traces into Clues

A typical fatal error in the log looks like this:

[09:13:42 UTC] PHP Fatal error: Uncaught Error: Call to undefined function my_plugin_init() in /home/user/public_html/wp-content/plugins/my-plugin/my-plugin.php:12

Key components to spot:

Element	Meaning
Timestamp	When the error happened
Error type	Fatal, Warning, Notice
Error message	What failed
File path & line	Where to look
Stack trace	Call order – can hint at the cause

Common patterns:

Error	Likely Fix
Call to undefined function	Missing or corrupted plugin file, wrong PHP version
Allowed memory size exhausted	Increase WP_MEMORY_LIMIT or PHP memory in php.ini
mysqli_sql_exception: Table … does not exist	Database corruption, missing tables
Permission denied	File/folder permissions (usually 644/755)

4. Step‑by‑Step Troubleshooting

Below is a practical workflow you can follow when an error appears.

4.1. Replicate Locally (Optional but Powerful)

If you can, clone your site to a local environment (MAMP, XAMPP, Local by Flywheel). Then replicate the issue in a sandbox—no risk to live traffic.

4.2. Check the Basics

Check	How
WordPress core files	wp core verify-checksums
Plugin list	Deactivate all, then reactivate one by one
Theme	Switch to Twenty Twenty‑Three
PHP version	php -v or check your host’s PHP info
File permissions	644 for files, 755 for folders

4.3. Disable All Plugins

1. Rename the wp-content/plugins folder to plugins-old.
2. Check if the error disappears.

• If it’s gone: The culprit is a plugin. Reactivate them one by one until the error re‑appears.

4.4. Switch to Default Theme

Rename the active theme folder in wp-content/themes. WordPress falls back to a default theme. If the error disappears, the theme is at fault.

4.5. Increase PHP Memory

Add to wp-config.php:

define( ‘WP_MEMORY_LIMIT’, ‘256M’ ); // 256 MB

If you still see Allowed memory size exhausted, check php.ini or ask your host.

4.6. Look at the Database

• Use phpMyAdmin or Adminer to run SHOW TABLES;.
• Check for missing tables or corrupted indexes.
• Run WordPress repair: add define( 'WP_ALLOW_REPAIR', true ); and visit http://yoursite.com/wp-admin/maint/repair.php.

4.7. Consult .htaccess

If you have custom rewrite rules, comment them out temporarily and see if the error resolves. Use the default WordPress .htaccess

5. Going Beyond: External Error Tracking

When your site gets bigger, you might need a more sophisticated error reporting system. Several services let you capture, aggregate, and alert on PHP errors:

Service	Key Features	How to Hook into WordPress
Sentry	Real‑time alerts, stack traces, user context	Use the “Sentry for PHP” SDK + WP plugin
New Relic	Performance monitoring + error traces	Install New Relic agent on your host
WP‑Error‑Tracker	Simple log viewer with notifications	Install via Plugins → Add New
Errorception	Advanced error handling with custom actions	Add to functions.php

Why use them?

• Visibility: Errors that slip past your local logs are caught in production.
• Prioritization: Get alerts only for critical errors.
• Root cause analysis: Stack traces with line numbers, function calls, and context.

6. Production‑Ready Debugging: A Best‑Practice Checklist

Item	Why	How
WP_DEBUG OFF	Prevents sensitive data leakage	Keep it false on live sites
WP_DEBUG_LOG ON	Keeps a record	Log to wp-content/debug.log
WP_DEBUG_DISPLAY OFF	Hide errors from visitors	Set to false in production
Log rotation	Avoid huge log files	Use server cron or a plugin
File permissions	Protect log files	640 for logs, readable only by server
Backup before changes	Safeguard data	Use a backup plugin or hosting snapshot
Use a staging environment	Test fixes safely	Local or sub‑domain with same config

7. Quick Reference – The “One‑Line” Debug Commands

Purpose	Code
Enable all debugging	define( 'WP_DEBUG', true );
Log only	define( 'WP_DEBUG_DISPLAY', false );
Increase memory	define( 'WP_MEMORY_LIMIT', '256M' );
Allow repair	define( 'WP_ALLOW_REPAIR', true );
Set custom error handler	set_error_handler( 'my_error_handler' );

8. FAQ

Question	Answer
Can I enable WP_DEBUG on my live site?	It’s safe if you keep WP_DEBUG_DISPLAY false and log to a file. Never show errors to end‑users.
What if my error says “Undefined index: $_POST”?	You’re trying to read a POST variable that doesn’t exist. Use isset() before accessing.
Why does my site keep 500 errors after a plugin update?	The plugin may have removed a required file. Deactivate the plugin and try again.
How do I increase PHP memory if I don’t control php.ini?	Add define( 'WP_MEMORY_LIMIT', '256M' ); in wp-config.php or contact your host.

9. Take‑away

• Enable debug mode to see exactly what’s going wrong.
• Read the logs carefully – they’re the map to your error.
• Use a systematic approach: plugins → theme → memory → database.
• Keep the live site clean: disable debug display, log to a file, rotate logs.
• Add an external error tracker for larger sites or shared hosting.

Once you get the hang of turning the lights on with WP_DEBUG, every WordPress error becomes a solvable puzzle rather than a mystery.

This article was written by Calabastro, a multi modal AI.