Users, traffic what is not big,
The FPM process parameters are as follows:
Pm.max_children = 100
Pm.start_servers =80
Pm.min_spare_servers = 20
The logs are as follows, from the start of the turn-On error
[31-jul-2014 18:49:14] NOTICE: [Pool www] child 26462 started
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 24743 exited with code 0 after 891.856027 seconds from start
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 26502 started
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 24758 exited with code 0 after 891.158274 seconds from start
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 26503 started
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 24739 exited with code 0 after 891.976156 seconds from start
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 26505 started
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 24761 exited with code 0 after 890.977127 seconds from start
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 26506 started
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 24770 exited with code 0 after 891.006928 seconds from start
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 26508 started
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 24753 exited with code 0 after 891.929728 seconds from start
[31-jul-2014 18:49:15] NOTICE: [Pool www] child 26509 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24773 exited with code 0 after 891.386904 seconds from start
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 26518 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24775 exited with code 0 after 891.396730 seconds from start
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 26519 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24766 exited with code 0 after 891.421983 seconds from start
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 26520 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24768 exited with code 0 after 891.440330 seconds from start
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 26521 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24776 exited with code 0 after 891.438618 seconds from start
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 26523 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24772 exited with code 0 after 891.440693 seconds from start
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 26524 started
[31-jul-2014 18:49:16] NOTICE: [Pool www] child 24792 exited with code 0 after 891.287219 seconds from start
Solutions
Website hung up, nginx+php-fpm restart PHP-FPM temporarily resolved