配置wordpress的时候突然提示我连接不上mysql。
首先使用了下面命令查了一下，发现进程中没有了mysql。确认出问题被关闭。
ps -ef | grep mysqld
尝试使用下面的命令启动mysql。提示错误：Starting MySQL.The server quit without updating PID file (/[FAILED]server/mysql/data/^).
service mysqld start
我擦，这是什么情况，按照错误提示消息去查百度，基本上是各式各样的问题，但是对我提示比较大的一点就是，要看mysql的错误日志文件。
打开错误日志文件（使用阿里云的一键安装包，这个log的位置找了半天，基本上是/alidata/server/log/mysql下），发现了很关键的一点（红字加粗部分）：
2016-06-07 22:11:09 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp ser
ver option (see documentation for more details).
2016-06-07 22:11:09 3563 [Note] Plugin 'FEDERATED' is disabled.
2016-06-07 22:11:09 3563 [Note] InnoDB: Using atomics to ref count buffer pool pages
2016-06-07 22:11:09 3563 [Note] InnoDB: The InnoDB memory heap is disabled
2016-06-07 22:11:09 3563 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2016-06-07 22:11:09 3563 [Note] InnoDB: Memory barrier is not used
2016-06-07 22:11:09 3563 [Note] InnoDB: Compressed tables use zlib 1.2.3
2016-06-07 22:11:09 3563 [Note] InnoDB: Using Linux native AIO
2016-06-07 22:11:09 3563 [Note] InnoDB: Using CPU crc32 instructions
2016-06-07 22:11:09 3563 [Note] InnoDB: Initializing buffer pool, size = 128.0M
InnoDB: mmap(137363456 bytes) failed; errno 12
2016-06-07 22:11:09 3563 [ERROR] InnoDB: Cannot allocate memory for the buffer pool
2016-06-07 22:11:09 3563 [ERROR] Plugin 'InnoDB' init function returned error.
2016-06-07 22:11:09 3563 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2016-06-07 22:11:09 3563 [ERROR] Unknown/unsupported storage engine: InnoDB
2016-06-07 22:11:09 3563 [ERROR] Aborting
这特么的，给狗一个大饼子，狗都知道内存不够用了。
拿这个关键字在搜搜吧，提示更改my.cnf文件，这个文件在mysql的安装目录下。
那个配置文件以前安装后没有更改过，基本上就改成下面就好了
------------------------------------原始是这样------------------------------------
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
------------------------------------原始是这样------------------------------------
------------------------------------改完是这样------------------------------------
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
innodb_buffer_pool_size = 16M
------------------------------------改完是这样------------------------------------
一句话，哥穷，128M的真心没有那么多内存，造成了mysql无法启动。改成这点儿后再启动就可以了。
service mysqld start
正常启动，表示如下：
Starting MySQL.. [ OK ]