At times, the error logs say
2017/05/15 11:37:01 [notice] 22229#0: signal process started
2017/05/15 11:37:02 [alert] 22030#0: sendmsg() failed (32: Broken pipe)
2017/05/15 11:37:02 [alert] 22030#0: sendmsg() failed (32: Broken pipe)
2017/05/15 11:37:04 [alert] 22030#0: sendmsg() failed (9: Bad file descriptor)
2017/05/15 11:37:04 [alert] 22030#0: sendmsg() failed (32: Broken pipe)
2017/05/15 11:37:04 [alert] 22030#0: sendmsg() failed (9: Bad file descriptor)
2017/05/15 11:37:04 [alert] 22030#0: sendmsg() failed (32: Broken pipe)