本次将在Linux下通过yum安装MySQL，安装的版本为MySQL 5.7，官网中是最新版本8.0，在网上查了下，发现最新版本的yum源也包含了旧版本，而我们，只需要在安装时启用 5.7 的安装即可。
本人环境：CentOS 7.3 64位
- 1.检查CentOS是否有系统自带的mysql
yum list installed | grep mysql
如果存在系统自带的mysql及依赖，则通过 yum remove 将其卸载
- 2.在官网中获取yum源
这里获取到的是最新版本的下载地址：https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm
- 3.CentOS中下载rpm包，并安装本地mysql源
下载rpm包：wget https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm --no-check-certificate
安装mysql源：yum localinstall mysql80-community-release-el7-3.noarch.rpm
通过 yum localinstall 安装mysql源，可以帮助我们解决本地rpm包的依赖问题。
最后，验证是否安装成功：yum repolist all | grep mysql
- 4.修改默认安装版本为5.7
从上面的图片，我们可以看到，默认是MySQL 8.0可用，我们若想安装MySQL 5.7，则需启用5.7。接下来通过直接修改配置文件来设置启用。
vim /etc/yum.repos.d/mysql-community.repo
输入上面的命令，在编辑界面，先输入 i 进入编辑模式，将8.0的 enabled 设置为0，将5.7的 enabled 设置为1，如下：
接着按 Esc 退出编辑模式，最后输入 :wq 保存并退出。
再次输入命令：yum repolist all | grep mysql ，可以看到8.0已被禁用，而5.7是启用的。
- 5.安装MySQL
yum install mysql-community-server
输入上面命令，进行安装即可。
[root@wintest mysql]# yum install mysql-community-server
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package mysql-community-server.x86_64 0:5.7.27-1.el7 will be installed
--> Processing Dependency: mysql-community-common(x86-64) = 5.7.27-1.el7 for package: mysql-community-server-5.7.27-1.el7.x86_64
--> Processing Dependency: mysql-community-client(x86-64) >= 5.7.9 for package: mysql-community-server-5.7.27-1.el7.x86_64
--> Processing Dependency: libaio.so.1(LIBAIO_0.4)(64bit) for package: mysql-community-server-5.7.27-1.el7.x86_64
--> Processing Dependency: libaio.so.1(LIBAIO_0.1)(64bit) for package: mysql-community-server-5.7.27-1.el7.x86_64
--> Processing Dependency: libaio.so.1()(64bit) for package: mysql-community-server-5.7.27-1.el7.x86_64
--> Running transaction check
---> Package libaio.x86_64 0:0.3.109-13.el7 will be installed
---> Package mysql-community-client.x86_64 0:5.7.27-1.el7 will be installed
--> Processing Dependency: mysql-community-libs(x86-64) >= 5.7.9 for package: mysql-community-client-5.7.27-1.el7.x86_64
---> Package mysql-community-common.x86_64 0:5.7.27-1.el7 will be installed
--> Running transaction check
---> Package mariadb-libs.x86_64 1:5.5.52-1.el7 will be obsoleted
--> Processing Dependency: libmysqlclient.so.18()(64bit) for package: 2:postfix-2.10.1-6.el7.x86_64
--> Processing Dependency: libmysqlclient.so.18(libmysqlclient_18)(64bit) for package: 2:postfix-2.10.1-6.el7.x86_64
---> Package mysql-community-libs.x86_64 0:5.7.27-1.el7 will be obsoleting
--> Running transaction check
---> Package mysql-community-libs-compat.x86_64 0:5.7.27-1.el7 will be obsoleting
---> Package postfix.x86_64 2:2.10.1-6.el7 will be updated
---> Package postfix.x86_64 2:2.10.1-7.el7 will be an update
--> Finished Dependency Resolution
Dependencies Resolved
====================================================================================
Package Arch Version Repository Size
====================================================================================
Installing:
mysql-community-libs x86_64 5.7.27-1.el7 mysql57-community 2.2 M
replacing mariadb-libs.x86_64 1:5.5.52-1.el7
mysql-community-libs-compat x86_64 5.7.27-1.el7 mysql57-community 2.0 M
replacing mariadb-libs.x86_64 1:5.5.52-1.el7
mysql-community-server x86_64 5.7.27-1.el7 mysql57-community 165 M
Installing for dependencies:
libaio x86_64 0.3.109-13.el7 base 24 k
mysql-community-client x86_64 5.7.27-1.el7 mysql57-community 24 M
mysql-community-common x86_64 5.7.27-1.el7 mysql57-community 275 k
Updating for dependencies:
postfix x86_64 2:2.10.1-7.el7 base 2.4 M
Transaction Summary
====================================================================================
Install 3 Packages (+3 Dependent packages)
Upgrade ( 1 Dependent package)
Total download size: 197 M
Is this ok [y/d/N]: y
Downloading packages:
Delta RPMs disabled because /usr/bin/applydeltarpm not installed.
(1/7): libaio-0.3.109-13.el7.x86_64.rpm | 24 kB 00:00:00
warning: /var/cache/yum/x86_64/7/mysql57-community/packages/mysql-community-common-5.7.27-1.el7.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY
Public key for mysql-community-common-5.7.27-1.el7.x86_64.rpm is not installed
(2/7): mysql-community-common-5.7.27-1.el7.x86_64.rpm | 275 kB 00:00:01
(3/7): mysql-community-libs-5.7.27-1.el7.x86_64.rpm | 2.2 MB 00:00:01
(4/7): mysql-community-libs-compat-5.7.27-1.el7.x86_64.rpm | 2.0 MB 00:00:01
(5/7): postfix-2.10.1-7.el7.x86_64.rpm | 2.4 MB 00:00:00
(6/7): mysql-community-client-5.7.27-1.el7.x86_64.rpm | 24 MB 00:00:34
(7/7): mysql-community-server-5.7.27-1.el7.x86_64.rpm | 165 MB 00:00:52
------------------------------------------------------------------------------------
Total 3.5 MB/s | 197 MB 00:56
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
Importing GPG key 0x5072E1F5:
Userid : "MySQL Release Engineering <mysql-build@oss.oracle.com>"
Fingerprint: a4a9 4068 76fc bd3c 4567 70c8 8c71 8d3b 5072 e1f5
Package : mysql80-community-release-el7-3.noarch (installed)
From : /etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
Is this ok [y/N]: y
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : mysql-community-common-5.7.27-1.el7.x86_64 1/9
Installing : mysql-community-libs-5.7.27-1.el7.x86_64 2/9
Installing : mysql-community-libs-compat-5.7.27-1.el7.x86_64 3/9
Installing : mysql-community-client-5.7.27-1.el7.x86_64 4/9
Installing : libaio-0.3.109-13.el7.x86_64 5/9
Installing : mysql-community-server-5.7.27-1.el7.x86_64 6/9
Updating : 2:postfix-2.10.1-7.el7.x86_64 7/9
Cleanup : 2:postfix-2.10.1-6.el7.x86_64 8/9
Erasing : 1:mariadb-libs-5.5.52-1.el7.x86_64 9/9
Verifying : mysql-community-libs-compat-5.7.27-1.el7.x86_64 1/9
Verifying : mysql-community-common-5.7.27-1.el7.x86_64 2/9
Verifying : mysql-community-libs-5.7.27-1.el7.x86_64 3/9
Verifying : 2:postfix-2.10.1-7.el7.x86_64 4/9
Verifying : mysql-community-server-5.7.27-1.el7.x86_64 5/9
Verifying : mysql-community-client-5.7.27-1.el7.x86_64 6/9
Verifying : libaio-0.3.109-13.el7.x86_64 7/9
Verifying : 1:mariadb-libs-5.5.52-1.el7.x86_64 8/9
Verifying : 2:postfix-2.10.1-6.el7.x86_64 9/9
Installed:
mysql-community-libs.x86_64 0:5.7.27-1.el7
mysql-community-libs-compat.x86_64 0:5.7.27-1.el7
mysql-community-server.x86_64 0:5.7.27-1.el7
Dependency Installed:
libaio.x86_64 0:0.3.109-13.el7
mysql-community-client.x86_64 0:5.7.27-1.el7
mysql-community-common.x86_64 0:5.7.27-1.el7
Dependency Updated:
postfix.x86_64 2:2.10.1-7.el7
Replaced:
mariadb-libs.x86_64 1:5.5.52-1.el7
Complete!
- 6.启用MySQL
在CentOS 6中，我们一般通过 service mysqld start 来启动mysql，在CentOS 7中，如果直接输入 service mysqld start ，则会出现以下信息：
这是因为 CentOS 7 下重启服务不再通过 service 操作，而是通过 systemctl 操作，因此我们可以输入命令：
启动mysql：systemctl start mysqld.service
查看mysql状态：systemctl status mysqld.service
- 7.登录mysql
mysql -u root -p
在要求输入密码时，因为mysql 5.7的初始密码不是空，直接按回车键不能成功登录，因此需先找到初始密码，才能登录。
grep 'temporary password' /var/log/mysqld.log
如上，最后的内容就是初始密码。
再次登录，输入初始密码，即可成功登录。
第一次登录成功后，发现不能执行操作，同时提示让修改密码。
- 8.修改登录密码
alter user root@localhost identified by '新密码'
这里，我想设置新密码为 123456，但出现了报错，这里的报错是mysql的密码策略问题，输入命令：show variables like 'validate_password%'，查看 mysql 初始的密码策略，发现密码的最小长度为8，密码的验证强度等级为MEDIUM，可以修改一下密码策略：
设置密码的验证强度等级：set global validate_password_policy=LOW
设置密码的最小长度：set global validate_password_length=6
好了，这时我们再次执行修改密码的sql，便不会报错了。
最后通过 flush privileges 刷新权限，使当前操作立即生效，就大功告成了。
注意：最后这里，也可以不修改密码策略，只要自己设置的密码满足MySQL的原密码策略即可。