CentOS下MySQL默认安装在/var/lib/mysql目录下，但是随着存储数据的增多，所在的硬盘空间很快被占满，导致无法进行插入、建表等操作。

这时需要将MySQL数据存储文件夹移植到别的文件夹下，网上有很多教程，如http://www.cnblogs.com/5201351/p/4912614.html 是一篇很好的教程，但是在实际移植过程发现，只有MySQL的数据文件夹/var/lib/mysql被改为其他目录，无论如何修改/etc/my.cnf配置中的datadir和socket参数，都无法移动mysqld。

错误表现为，使用如下命令，启动mysql

systemctl start mysqld

会出现如下错误：

Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details.

如果使用如下命令查看

systemctl status mysqld

会得到如下错误信息

Redirecting to /bin/systemctl status  mysqld.service
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: failed (Result: start-limit) since Fri 2017-10-20 09:03:33 CST; 1min 11s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 5130 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=1/FAILURE)
  Process: 5108 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
 Main PID: 15110 (code=exited, status=0/SUCCESS)


Oct 20 09:03:33 bigdata-6 systemd[1]: Failed to start MySQL Server.
Oct 20 09:03:33 bigdata-6 systemd[1]: Unit mysqld.service entered failed state.
Oct 20 09:03:33 bigdata-6 systemd[1]: mysqld.service failed.
Oct 20 09:03:33 bigdata-6 systemd[1]: mysqld.service holdoff time over, scheduling restart.
Oct 20 09:03:33 bigdata-6 systemd[1]: start request repeated too quickly for mysqld.service
Oct 20 09:03:33 bigdata-6 systemd[1]: Failed to start MySQL Server.
Oct 20 09:03:33 bigdata-6 systemd[1]: Unit mysqld.service entered failed state.
Oct 20 09:03:33 bigdata-6 systemd[1]: mysqld.service failed.

一开始总以为是配置的问题，后来仔细查看一下msyql的日志文件：/var/log/mysqld.log

出现了几个Warning，说文件无法创建

120609 11:31:31 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
120609 11:35:12 mysqld_safe Starting mysqld daemon with databases from /mnt/hgfs/mysql_data
120609 11:35:13 [Warning] Can't create test file /home/mysql_data/data.lower-test
120609 11:35:13 [Warning] Can't create test file /home/mysql_data/data.lower-test
/usr/libexec/mysqld: Can't change dir to '/home/mysql_data/' (Errcode: 13)
120609 11:35:13 [ERROR] Aborting

120609 11:35:13 [Note] /usr/libexec/mysqld: Shutdown complete

120609 11:35:13 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended

解决方案：
关闭mysql:

systemctl stop mysqld

1、编辑/etc/selinux/config文件，将其中的SELINUX禁用，SELINUX=disabled，重新启动系统。
2、移动/var/lib/mysql到你需要的文件夹，mv /var/lib/mysql /home/mysql_data
3、在/var/lib下创建一个链接ln -s /home/mysql_data/mysql /var/lib/mysql（这种方法可以不用修改/etc/my.cnf配置）
4、启动mysql: systemctl start mysqld

记录一下