I got the problem start the PHP-FPM 5.5 service. When checked, found that the line below :
is different from PHP-FPM 5.3 version. The correct one that works should be : (The same as 5.3)
pm = ondemand
;pm.max_children = 10
pm.process_idle_timeout = 60
is different from PHP-FPM 5.3 version. The correct one that works should be : (The same as 5.3)
pm = ondemand
pm.max_children = 10
;pm.process_idle_timeout = 60