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Troubleshooting Apache2 500 Internal Server Errors

Claude

A 500 Internal Server Error tells the visitor nothing useful by design — the real cause is always in Apache’s error log, and knowing where to look narrows it down fast.

# The error log almost always has the real reason
sudo tail -50 /var/log/apache2/error.log

# For PHP-specific errors, check PHP's own log too
sudo tail -50 /var/log/php8.3-fpm.log

# Test the config for syntax errors before assuming it's a code problem
sudo apache2ctl configtest

Common Culprits

  • A syntax error in a .htaccess file (check AllowOverride is even enabled to see it)
  • Wrong file permissions — Apache’s user (usually www-data) can’t read a file it needs
  • A PHP fatal error with display_errors off (correctly, for production) but not logged anywhere you’re checking
  • PHP-FPM socket path mismatch between the Apache vhost config and the actual running FPM pool

Temporarily enabling display_errors on a staging environment (never production) can speed up diagnosis, but the error log should always be the first stop — it captures errors even when display is off.

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