1、查看路径
mysql> show variables like '%dir%';
+-----------------------------------------+----------------------------------------+
| Variable_name                           | Value                                  |
+-----------------------------------------+----------------------------------------+
| basedir                                 | /usr/local/mysql/                      |
| binlog_direct_non_transactional_updates | OFF                                    |
| character_sets_dir                      | /usr/local/mysql/share/mysql/charsets/ |
| datadir                                 | /usr/local/mysql/var/                  |
| innodb_data_home_dir                    |                                        |
| innodb_log_group_home_dir               | ./                                     |
| innodb_max_dirty_pages_pct              | 90                                     |
| plugin_dir                              | /usr/local/mysql/lib/mysql/plugin      |
| slave_load_tmpdir                       | /tmp                                   |
| tmpdir                                  | /tmp                                   |
+-----------------------------------------+----------------------------------------+
10 rows in set

2、查看配置文件
[root@RHEL var]# mysql --verbose --help | grep -A 1 'Default options'
Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf
[root@RHEL var]#

如果my.cnf文件的[mysqld]段下没有 datadir=/var/lib/mysql ，新增即可。

3、关闭服务
service mysqld stop

4、将mysql文件夹移动/复制到新的文件夹
cd /usr/local/mysql/
mv var /var/lib/mysql
或复制：一定要加 -a 参数
cp -a var /var/lib/mysql

5、启动服务
service mysqld start

6、再查看路径，已经移动到新文件夹
mysql> show variables like '%dir%';
+-----------------------------------------+----------------------------------------+
| Variable_name                           | Value                                  |
+-----------------------------------------+----------------------------------------+
| basedir                                 | /usr/local/mysql/                      |
| binlog_direct_non_transactional_updates | OFF                                    |
| character_sets_dir                      | /usr/local/mysql/share/mysql/charsets/ |
| datadir                                 | /var/lib/mysql/                        |
| innodb_data_home_dir                    |                                        |
| innodb_log_group_home_dir               | ./                                     |
| innodb_max_dirty_pages_pct              | 90                                     |
| plugin_dir                              | /usr/local/mysql/lib/mysql/plugin      |
| slave_load_tmpdir                       | /tmp                                   |
| tmpdir                                  | /tmp                                   |
+-----------------------------------------+----------------------------------------+
10 rows in set