A PHP upgrade is great—until WordPress throws a blank screen or a 500. This flow helps you isolate whether the problem is a plugin, theme, or config so you can fix it quickly.
Identify the failure type
- 500 error (server-side)
- White screen (often a fatal PHP error)
- Admin loads, but certain pages crash
Fast isolation steps
- Check Apache error log:
/var/log/apache2/error.log - Check PHP-FPM logs (location depends on version/config)
- Temporarily disable plugins (rename the plugin folder) to isolate offenders
- Switch to a default theme if needed
Common causes
- Plugins using deprecated or removed PHP behavior
- Composer/autoloader mismatch inside a plugin
- Mixed PHP versions across sites or pools
FAQ
Why does WordPress break after a PHP upgrade?
Core is usually compatible; plugins and themes often rely on deprecated features or assume an older PHP version. See why PHP upgrades break WordPress for more detail.
What’s the fastest way to get the site back online?
Disable plugins via the filesystem (rename wp-content/plugins or the specific plugin folder) or use WP-CLI if you have shell access. Then re-enable one by one to find the culprit.
Related
- Apache + PHP-FPM stability basics — baseline checks
- Safer plugin updates on production — reduce future risk