- Plesk for Linux
If Plesk has a significant time for Apache restart interval, website is not accessible after switching from PHP-FPM to FastCGI:
Service Temporarily Unavailable
The following error can be found in domains
ERROR: An another FPM instance seems to already listen on /var/www/vhosts/system/example.com/php-fpm.sock
ERROR: FPM initialization failed
This is Plesk bug with ID #PPPM-6028 which will be fixed in future Plesk updates.
As a workaround, set Apache restart interval at Home > Tools & Settings > Apache Web Server Settings to 0 and enable graceful restart.