我在aws ec2服务器中使用单词按设置，而我正在努力突然错误建立数据库连接，我重新启动服务器它工作正常一段时间后再次关闭，错误日志如下所示，请帮我找到问题
(12)Cannot allocate memory: AH00159: fork: Unable to fork new process
(12)Cannot allocate memory: AH00159: fork: Unable to fork new process
(12)Cannot allocate memory: AH00159: fork: Unable to fork new process
(12)Cannot allocate memory: AH00159: fork: Unable to fork new process
PHP Warning: Module 'mysql' already loaded in Unknown on line 0
AH00163: Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.14 configured -- resuming normal operations
AH00094: Command line: '/usr/sbin/apache2'
AH00169: caught SIGTERM, shutting down`