在CentOS安裝MySQL5.7。

1. 使用el 8源不能成功安装

安装步骤如下¹：

1. 添加MySQL仓库源
   在dev.mysql.com/downloads/repo/yum/查看相应系统版本的下载链接。当前CentOS 8对应的链接是：mysql80-community-release-el8-1.noarch.rpm，使用wget下载：

$ wget https://dev.mysql.com/get/mysql80-community-release-el8-1.noarch.rpm

添加yum源：

sudo yum localinstall mysql80-community-release-el8-1.noarch.rpm

查看可用的MySQL源：

yum repolist enabled | grep "mysql.*-community.*"
...
mysql80-community                    MySQL 8.0 Community Server              41

显示源已经被成功添加，目前可用的是8.0版本。

2. 选择MySQL版本
   查看所有的版本：

$ yum repolist all | grep mysql
...
mysql80-community                  MySQL 8.0 Community Server     enabled:    41
mysql80-community-source           MySQL 8.0 Community Server - S disabled

但是发现添加的源并没有包含5.7版本，网上有讨论同样的问题：installing-mysql-5-7-on-centos-8，需要使用其它方法安装。

2. 使用el 7源成功安装

安装步骤如下²：

1. 禁止默认的MySQL源

$ sudo dnf remove @mysql
$ sudo dnf module reset mysql && sudo dnf module disable mysql

2. 使用el 7的源，修改mysql源文件

sudo vi /etc/yum.repos.d/mysql-community.repo

添加如下内容：

[mysql57-community]
name=MySQL 5.7 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.7-community/el/7/basearch/
enabled=1
gpgcheck=0

[mysql-connectors-community]
name=MySQL Connectors Community
baseurl=http://repo.mysql.com/yum/mysql-connectors-community/el/7/basearch/
enabled=1
gpgcheck=0

[mysql-tools-community]
name=MySQL Tools Community
baseurl=http://repo.mysql.com/yum/mysql-tools-community/el/7/$basearch/
enabled=1
gpgcheck=0

3. 更新源并再次查看可用的版本，5.7版本出现

$ sudo dnf update
$ yum repolist all | grep mysql
...
mysql57-community                  MySQL 5.7 Community Server     enabled:   424
mysql80-community-source           MySQL 8.0 Community Server - S disabled

4. 安装5.7版本

$ sudo dnf --enablerepo=mysql57-community install mysql-community-server

3. 设置MySQL

1. 启动MySQL

$ sudo systemctl start mysqld.service

2. 可以检查是否开机启动：

$ systemctl is-enabled mysqld.service
enabled

3. 查看初始root密码

 sudo grep 'temporary password' /var/log/mysqld.log

4. 进行安全设置

$ mysql_secure_installation

Securing the MySQL server deployment.

Enter password for user root:

The existing password for the user account root has expired. Please set a new password.

New password:

Re-enter new password:
The 'validate_password' plugin is installed on the server.
The subsequent steps will run with the existing configuration
of the plugin.
Using existing password for root.

Estimated strength of the password: 100
Change the password for root ? ((Press y|Y for Yes, any other key for No) : y

New password:

Re-enter new password:

Estimated strength of the password: 100
Do you wish to continue with the password provided?(Press y|Y for Yes, any other key for No) : y
By default, a MySQL installation has an anonymous user,
allowing anyone to log into MySQL without having to have
a user account created for them. This is intended only for
testing, and to make the installation go a bit smoother.
You should remove them before moving into a production
environment.

Remove anonymous users? (Press y|Y for Yes, any other key for No) : y
Success.


Normally, root should only be allowed to connect from
'localhost'. This ensures that someone cannot guess at
the root password from the network.

Disallow root login remotely? (Press y|Y for Yes, any other key for No) : n

 ... skipping.
By default, MySQL comes with a database named 'test' that
anyone can access. This is also intended only for testing,
and should be removed before moving into a production
environment.


Remove test database and access to it? (Press y|Y for Yes, any other key for No) : y
 - Dropping test database...
Success.

 - Removing privileges on test database...
Success.

Reloading the privilege tables will ensure that all changes
made so far will take effect immediately.

Reload privilege tables now? (Press y|Y for Yes, any other key for No) : y
Success.

All done!

至此MySQL5.7安装完毕，可以进一步做如远程链接等其它设置。