1、关闭mysql服务
[root@node1 ~]# systemctl status mysql
[root@node1 ~]# systemctl stop mysql
尖叫提示：卸载用root用户
2、查看
[root@node1 ~]# rpm -qa | grep -i mysql
[root@node1 ~]# rpm -qa | grep -i mariadb
3、卸载全部查询出来的
[root@node1 ~]# yum -y remove mysql-* ……..
[root@node1 ~]# yum -y remove MySQL-client-5.7.21-1.el7.x86_64
[root@node1 ~]# yum -y remove MySQL-server-5.7.21-1.el7.x86_64
[root@node1 ~]# rpm -e --nodeps mariadb-libs-5.5.41-2.el7_0.x86_64
[root@node1 ~]# rpm -e --nodeps mysql-libs-5.1.73-7.el6.x86_64 ……….
尖叫提示：卸载的时候尽量别用“*”号，使用全称。
4、删除分散mysql文件夹,删除查询出来的
[root@node1 ~]# whereis mysql
[root@node1 ~]# rm -rf /usr/lib/mysql/
[root@node1 ~]# rm -rf /usr/share/mysql
[root@node1 ~]# rm -rf /etc/my.cnf
[root@node1 ~]# rm -rf /var/lib/mysql
[root@node1 ~]# rm -rf /root/.mysql_sercret …….
尖叫提示：rm -rf /var/lib/mysql(如果这个目录如果不删除，再重新安装之后，
密码还是之前的密码，不会重新初始化！)
[root@node1 ~]# find / -name mysql*
[root@node1 ~]# rm -rf ****
5、检查一下是否删除干净
[root@node1 ~]# rpm -qa | grep -i mysql
[root@node1 ~]# rpm -qa | grep -i mariadb
[root@node1 ~]# whereis mysql
[root@node1 ~]# find / -name mysql*
6、确定是不是真的卸载干净
(1)是看安装输出
如果没有卸载干净，安装server时输入只有两行
[root@node1 MySQL-5.7.21-rpm]# rpm -ivh MySQL-server-5.7.21-1.el7.x86_64.rpm
Preparing... ################################# [100%]
Updating / installing... MySQL-server-5.7.21-1.el7################################# [100%]
卸载干净了安装输入如下
[root@node1 MySQL-5.7.21-rpm]# rpm -ivh MySQL-server-5.7.21-1.el7.x86_64.rpm
Preparing... ################################# [100%]
Updating / installing...MySQL-server-5.7.21-1.el7################################# [100%]
2018-03-16 15:14:49 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2018-03-16 15:14:49 0 [Note] /usr/sbin/mysqld (mysqld 5.7.21) starting as process 5826 ...
2018-03-16 15:14:49 5826 [Note] InnoDB: Using atomics to ref count buffer pool pages
2018-03-16 15:14:49 5826 [Note] InnoDB: The InnoDB memory heap is disabled
2018-03-16 15:14:49 5826 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2018-03-16 15:14:49 5826 [Note] InnoDB: Memory barrier is not used
2018-03-16 15:14:49 5826 [Note] InnoDB: Compressed tables use zlib 1.2.3
2018-03-16 15:14:49 5826 [Note] InnoDB: Using Linux native AIO
2018-03-16 15:14:49 5826 [Note] InnoDB: Using CPU crc32 instructions
2018-03-16 15:14:49 5826 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2018-03-16 15:14:49 5826 [Note] InnoDB: Completed initialization of buffer pool
2018-03-16 15:14:49 5826 [Note] InnoDB: The first specified data file ./ibdata1 did not exist: a new database to be created!
2018-03-16 15:14:49 5826 [Note] InnoDB: Setting file ./ibdata1 size to 12 MB
2018-03-16 15:14:49 5826 [Note] InnoDB: Database physically writes the file full: wait...
2018-03-16 15:14:49 5826 [Note] InnoDB: Setting log file ./ib_logfile101 size to 48 MB
2018-03-16 15:14:49 5826 [Note] InnoDB: Setting log file ./ib_logfile1 size to 48 MB
2018-03-16 15:14:50 5826 [Note] InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0
2018-03-16 15:14:50 5826 [Warning] InnoDB: New log files created, LSN=45781
2018-03-16 15:14:50 5826 [Note] InnoDB: Doublewrite buffer not found: creating new
2018-03-16 15:14:50 5826 [Note] InnoDB: Doublewrite buffer created
2018-03-16 15:14:50 5826 [Note] InnoDB: 128 rollback segment(s) are active.
2018-03-16 15:14:50 5826 [Warning] InnoDB: Creating foreign key constraint system tables.
2018-03-16 15:14:50 5826 [Note] InnoDB: Foreign key constraint system tables created
2018-03-16 15:14:50 5826 [Note] InnoDB: Creating tablespace and datafile system tables.
2018-03-16 15:14:50 5826 [Note] InnoDB: Tablespace and datafile system tables created.
2018-03-16 15:14:50 5826 [Note] InnoDB: Waiting for purge to start
2018-03-16 15:14:50 5826 [Note] InnoDB: 5.7.21 started; log sequence number 0
A random root password has been set. You will find it in '/root/.mysql_secret'.
2018-03-16 15:14:50 5826 [Note] Binlog end
2018-03-16 15:14:50 5826 [Note] InnoDB: FTS optimize thread exiting.
2018-03-16 15:14:50 5826 [Note] InnoDB: Starting shutdown...
2018-03-16 15:14:52 5826 [Note] InnoDB: Shutdown completed; log sequence number 1625977
2018-03-16 15:14:52 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2018-03-16 15:14:52 0 [Note] /usr/sbin/mysqld (mysqld 5.7.21) starting as process 5848 ...
2018-03-16 15:14:52 5848 [Note] InnoDB: Using atomics to ref count buffer pool pages
2018-03-16 15:14:52 5848 [Note] InnoDB: The InnoDB memory heap is disabled
2018-03-16 15:14:52 5848 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2018-03-16 15:14:52 5848 [Note] InnoDB: Memory barrier is not used
2018-03-16 15:14:52 5848 [Note] InnoDB: Compressed tables use zlib 1.2.3
2018-03-16 15:14:52 5848 [Note] InnoDB: Using Linux native AIO
2018-03-16 15:14:52 5848 [Note] InnoDB: Using CPU crc32 instructions
2018-03-16 15:14:52 5848 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2018-03-16 15:14:52 5848 [Note] InnoDB: Completed initialization of buffer pool
2018-03-16 15:14:52 5848 [Note] InnoDB: Highest supported file format is Barracuda.
2018-03-16 15:14:52 5848 [Note] InnoDB: 128 rollback segment(s) are active.
2018-03-16 15:14:52 5848 [Note] InnoDB: Waiting for purge to start
2018-03-16 15:14:52 5848 [Note] InnoDB: 5.7.21 started; log sequence number 1625977
2018-03-16 15:14:52 5848 [Note] Binlog end
2018-03-16 15:14:52 5848 [Note] InnoDB: FTS optimize thread exiting.
2018-03-16 15:14:52 5848 [Note] InnoDB: Starting shutdown...
2018-03-16 15:14:54 5848 [Note] InnoDB: Shutdown completed; log sequence number 1625987
A RANDOM PASSWORD HAS BEEN SET FOR THE MySQL root USER !
You will find that password in '/root/.mysql_secret'.
You must change that password on your first connect,
no other statement but 'SET PASSWORD' will be accepted.
See the manual for the semantics of the 'password expired' flag.
Also, the account for the anonymous user has been removed.
In addition, you can run:
/usr/bin/mysql_secure_installation
which will also give you the option of removing the test database.
This is strongly recommended for production servers.
See the manual for more instructions.
Please report any problems at http://bugs.mysql.com/
The latest information about MySQL is available on the web at
http://www.mysql.com
Support MySQL by buying support/licenses at http://shop.mysql.com
New default config file was created as /usr/my.cnf and
will be used by default by the server when you start it.
You may edit this file to change server settings
最后一段中提示了重要信息。
(2)就是安装完成，启动服务之后
使用命令：”mysql -uroot –p”输入你之前安装后设置的密码，看能不能登录，如果还可以登录，说明没有卸载干净！
