Using Plesk 12.0.18 and CentOS 6.6, I installed PHP 5.6 through the Plesk Updates menu. After that, the new version was not automatically selectable inside Plesk Panel. I added it using php_handler. However, when selecting PHP 5.6 for a website, I only get a 500 server error. Trying to troubleshoot, I ran "/opt/plesk/php/5.6/bin/php-cgi -v", which also resulted in an error: Fatal Error Unable to allocate shared memory segment of 67108864 bytes: mmap: Cannot allocate memory (12) The same kind of error is logged in the error_log for the website I switched to 5.6. I have found some guides how to fix this, but in none of them, the error also occurs when calling "php-cgi -v" directly in the command line. The same error occured when I tried the same thing with PHP 5.5. How can this issue be fixed?