错误日志：
$ tail -n 100 /var/log/mysql/error.log | head -n 20 #或者 tail -n 20 /var/log/mysql/error.log
最近的错误信息：
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
151009 21:54:03 InnoDB: Unable to open the first data file
InnoDB: Error in opening ./ibdata1
151009 21:54:03 InnoDB: Operating system error number 11 in a file operation.
InnoDB: Error number 11 means 'Resource temporarily unavailable'.
InnoDB: Some operating system error numbers are described at
错误已经很明确了：存在其它的mysql数据库服务进程
$ ps aux | grep mysql
找到mysqld进程ID，kill
mysql 6821 0.0 1.1 484456 47276 ? Ssl 22:15 0:00 /usr/sbin/mysqld
$ sudo kill 6821 #这里的数字是mysqld的进程ID
$ sudo /etc/init.d/mysql start
Linux下查看MySQL的安装路径：http://www.linuxdiyf.com/linux/14760.html
ubuntu15.04手动安装MySQL5.6.27数据库：http://www.linuxdiyf.com/linux/14699.html
Ununtu 15.04安装MySql（Django连接Mysql）：http://www.linuxdiyf.com/linux/13783.html
Ubuntu15.04下MySQL5.6安装过程：http://www.linuxdiyf.com/linux/13250.html
Ubuntu 15.04安装配置Apache和mysql的方法：http://www.linuxdiyf.com/linux/13074.html