Error 500 after migration solved only by manual version/mode toggle

abs_yav · April 22, 2026, 10:08pm

SYSTEM INFORMATION
OS type and version	Debian 13
Webmin version	2.630
Virtualmin version	8.1.0 GPL
Webserver version	Apache/2.4.66
Related packages	PHP 5.6, 7.0, 7.4, and 8.4

Hello,

I have encountered an issue that occurs after migrating web project contents or performing a major OS upgrade (e.g. Debian 9->12). Some websites start returning “500 Internal Server Error”.

The current workaround is to manually go to Server Configuration → PHP Versions and toggle between different PHP versions or execution modes (e.g., switching from FPM to FCGI and then back to FPM). This resolves the issue most of the time.

I would appreciate any insights on how to ensure the configuration is correctly applied during migrations/upgrades.

DrCarsonBeckett · April 23, 2026, 7:37am

Did you preinstall the needed packages for the PHP versions in question and did you check the logfile in question?

abs_yav · April 23, 2026, 1:20pm

PHP packages were installed manually on a clean machine. There are no errors in logs corresponding to PHP/Apache

Ilia · May 12, 2026, 9:20am

Yes, this is the best solution for now after a major distro upgrade. The issue happens because default PHP versions change between major releases, so we can’t easily automate it.

More details and further discussion are available here.

github.com/virtualmin/virtualmin-gpl

HTTP 503 error, PHP-FPM, no Pool files.

opened 07:45PM - 04 May 26 UTC

chris001

PHP was updated to 8.5 when this Ubuntu server was upgraded to 26.04, and PHP-FP…M started using 8.5. However, the monitoring tool notified that websites were failing with 503 Service Unavailable due to downtime or maintenance backed error, and as it turns out, this 503 was due to PHP-FPM failing to respond to Apache front end web server. Browsing the Virtualmin PHP Options page for the virtual server, you see this error at the top of the page: ``` Warning! PHP-FPM configuration error found : No listen directive found in FPM config Click Save button below to update the PHP-FPM configuration and correct this error " ``` <img width="903" height="348" alt="Image" src="https://github.com/user-attachments/assets/3142445c-2654-4e46-9d70-7402b6106824" /> As it turns out, the PHP-FPM pool files (one per virtual server) are completely missing missing from the new PHP version's pool directory `/etc/php/8.5/fpm/pool.d/`. Click Save and Virtualmin correctly generates the pool file, the 503 error is gone and this one website is now online. Switch to next virtual server, click Save, and repeat for all virtual servers. For less website downtime, it would be nice to have either an obvious notification, or better yet, after an upgrade that triggers this issue, to do a self-check, and when the issue with the missing Listen directive is detected, because the website's pool file is missing, the system automatically generates the pool files, and in doing so, prevents website downtime.