"Warning: session_start(): Failed to read session data" after upgrading from PHP 7.4 to PHP 8.0

Question

After upgrading a stable Joomla 3.10.11 website from PHP 7.4 to PHP 8.0, the following error is displayed on the front end and back end of the website:

Warning: session_start(): Failed to read session data: user (path: /tmp) in /home/xxxxxxxx/public_html/libraries/joomla/session/handler/native.php on line 260

I have already checked that the appropriate PHP extensions (such as mysqli) are enabled in cPanel -> Select PHP Version -> Extensions for PHP 8.0.

I am also seeing the same issue on some of my Joomla 4 websites.

Answer 1

Check and manually update any Addhandler directives in the .htaccess file if necessary.

For example, you may need to update:

This: AddHandler application/x-httpd-php74 .php

To this: AddHandler application/x-httpd-php80 .php

It seems that cPanel may not update .htaccess if the website is a subdomain or in a subdirectory.