MySQL 可以正常运行数周或数天，然后突然且没有任何用户操作，所有连接尝试都开始失败。这是/var/log/mysqld.log：
160916 14:42:01 [Note] /usr/libexec/mysql55/mysqld: ready for connections.
Version: '5.5.51' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL)
160930 03:05:51 mysqld_safe Number of processes running now: 0
160930 03:05:52 mysqld_safe mysqld restarted
160930 3:05:53 [Note] /usr/libexec/mysql55/mysqld (mysqld 5.5.51) starting as process 8961 ...
160930 3:05:53 [Note] Plugin 'FEDERATED' is disabled.
160930 3:05:54 InnoDB: The InnoDB memory heap is disabled
160930 3:05:54 InnoDB: Mutexes and rw_locks use GCC atomic builtins
160930 3:05:54 InnoDB: Compressed tables use zlib 1.2.8 …