В логе php-fpm сообщения вот такого вида:
[10-Aug-2015 11:42:05] WARNING: [pool www] child 1627 exited on signal 11 (SIGSEGV) after 0.944585 seconds from start
[10-Aug-2015 11:42:05] NOTICE: [pool www] child 1629 started
[10-Aug-2015 11:42:05] WARNING: [pool www] child 1628 exited on signal 11 (SIGSEGV) after 1.275092 seconds from start
[10-Aug-2015 11:42:05] NOTICE: [pool www] child 1631 started
[10-Aug-2015 11:42:05] WARNING: [pool www] child 1629 exited on signal 11 (SIGSEGV) after 0.484413 seconds from start
[10-Aug-2015 11:42:05] NOTICE: [pool www] child 1632 started