一、卸载MySql

卸载之前关闭所有mysql服务

systemctl stop mysqld

查看进程,还存在的话，直接kill掉

ps -ef | grep mysql

rpm -qa | grep -i mysql

[root@iZwz9dev0583p7pppda7ymZ ~]# rpm -qa | grep -i mysqlmysql-community-common-5.7.35-1.el7.x86_64mysql-community-server-5.7.35-1.el7.x86_64mysql-community-client-5.7.35-1.el7.x86_64mysql80-community-release-el7-3.noarchmysql-community-libs-5.7.35-1.el7.x86_64

rpm -e mysql-community-common-5.7.35-1.el7.x86_64rpm -e mysql-community-server-5.7.35-1.el7.x86_64rpm -e mysql-community-client-5.7.35-1.el7.x86_64rpm -e mysql-community-libs-5.7.35-1.el7.x86_64

mysql80-community-release-el7-3.noarch这是yum库的rpm包，如果版本符合，可以不卸载

注意：官网的mysql80-community-release-el8-1.noarch内只包含了mysql8.0以上版本，如果需要安装mysql5.7，需要使用mysql80-community-release-el7-3.noarch，el7表示操作系统版本linux7。

3. 卸载其他相关文件

1⃣️查找出来后使用rm -rf命令逐个删除

find / -name mysql

2⃣️或者直接使用如下命令删除

find / -name mysql -exec rm -rf {} \;

centOS8中的yum库默认的是mariaDB，我们需要下载mysql80-community-release-el7-3.noarch，里面包含了5.6，5.7，8.0等版本。官网

wget 

安装mysql的rmp

rpm -ivh mysql80-community-release-el7-3.noarch.rpm

查看将要安装的mysql相关文件

yum repolist all | grep mysql

[root@iZwz9dev0583p7pppda7ymZ ~]# yum repolist all | grep mysqlRepository epel is listed more than once in the configurationmysql-cluster-7.5-community        MySQL Cluster 7.5 Community              禁用mysql-cluster-7.5-community-source MySQL Cluster 7.5 Community - Source     禁用mysql-cluster-7.6-community        MySQL Cluster 7.6 Community              禁用mysql-cluster-7.6-community-source MySQL Cluster 7.6 Community - Source     禁用mysql-cluster-8.0-community        MySQL Cluster 8.0 Community              禁用mysql-cluster-8.0-community-source MySQL Cluster 8.0 Community - Source     禁用mysql-connectors-community         MySQL Connectors Community               启用mysql-connectors-community-source  MySQL Connectors Community - Source      禁用mysql-tools-community              MySQL Tools Community                    启用mysql-tools-community-source       MySQL Tools Community - Source           禁用mysql-tools-preview                MySQL Tools Preview                      禁用mysql-tools-preview-source         MySQL Tools Preview - Source             禁用mysql55-community                  MySQL 5.5 Community Server               禁用mysql55-community-source           MySQL 5.5 Community Server - Source      禁用mysql56-community                  MySQL 5.6 Community Server               禁用mysql56-community-source           MySQL 5.6 Community Server - Source      禁用mysql57-community                  MySQL 5.7 Community Server               启用mysql57-community-source           MySQL 5.7 Community Server - Source      禁用mysql80-community                  MySQL 8.0 Community Server               禁用mysql80-community-source           MySQL 8.0 Community Server - Source      禁用

默认情况下mysql80-community是启用的，mysql57-community是禁用的，用以下命令改变将要安装的版本

yum-config-manager --disable mysql80-communityyum-config-manager --enable mysql57-community

如果出现yum-config-manager: command not found,安装yum的utils工具即可

yum -y install yum-utils

安装完再执行上一步

2.安装MySql

yum -y install mysql-community-server

如果遇到Error: Unable to find a match: mysql-community-server

先执行以下命令，关闭当前的MariaDB，再执行上面的安装命令

yum module disable mysql 

安装完毕，查看MySql版本

[root@iZwz9dev0583p7pppda7ymZ ~]# mysql --versionmysql  Ver 14.14 Distrib 5.7.35, for Linux (x86_64) using  EditLine wrapper

启动MySql

systemctl start mysqld

查看MySql状态

[root@iZwz9dev0583p7pppda7ymZ ~]# systemctl status mysqld● mysqld.service - MySQL Server   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)   Active: active (running) since Sat 2021-07-31 16:51:39 CST; 5h 57min ago     Docs: man:mysqld(8)             Process: 1585 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)  Process: 1563 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS) Main PID: 1587 (mysqld)    Tasks: 30 (limit: 23683)   Memory: 228.7M   CGroup: /system.slice/mysqld.service           └─1587 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid7月 31 16:51:37 iZwz9dev0583p7pppda7ymZ systemd[1]: mysqld.service: Succeeded.7月 31 16:51:37 iZwz9dev0583p7pppda7ymZ systemd[1]: Stopped MySQL Server.7月 31 16:51:37 iZwz9dev0583p7pppda7ymZ systemd[1]: Starting MySQL Server...7月 31 16:51:39 iZwz9dev0583p7pppda7ymZ systemd[1]: Started MySQL Server.

接下来是进入数据库，先查看数据库root用户的初始密码

grep "password" /var/log/mysqld.log

最后面冒号后的就是DNDcewvug3.-

[root@iZwz9dev0583p7pppda7ymZ ~]# grep "password" /var/log/mysqld.log2021-07-31T08:26:01.664775Z 1 [Note] A temporary password is generated for root@localhost: DNDcewvug3.-

如果提示没有/var/log/mysqld.log或者sock之类的文件，重启服务器即可

通过以下命令进入数据库

mysql -uroot -p

更改root用户密码（不改的话无法进行其他操作）

ALTER USER USER() IDENTIFIED BY 'root';

密码设置太简单有可能出现ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

查看密码规则

SHOW VARIABLES LIKE 'validate_password%';

mysql> SHOW VARIABLES LIKE 'validate_password%';+--------------------------------------+-------+| Variable_name                        | Value |+--------------------------------------+-------+| validate_password_check_user_name    | OFF   || validate_password_dictionary_file    |       || validate_password_length             | 6     |#默认情况下这里是8| validate_password_mixed_case_count   | 1     || validate_password_number_count       | 1     || validate_password_policy             | LOW   |#默认情况下这里是MEDIUM| validate_password_special_char_count | 1     |+--------------------------------------+-------+7 rows in set (0.00 sec)

如果想要设置简单密码，可以更改规则中的长度和验证策略

set global validate_password_length=4;set global validate_password_policy=0;

密码规则如下图

最后，就可以创建数据库了

create database testDB