首先CentOS7 已经不支持mysql，因为收费了你懂得，所以内部集成了mariadb，而安装mysql的话会和mariadb的文件冲突，所以需要先卸载掉mariadb，以下为卸载mariadb，安装mysql的步骤。
#列出所有被安装的rpm package
rpm -qa | grep mariadb
#卸载
rpm -e mariadb-libs-5.5.37-1.el7_0.x86_64
错误：依赖检测失败：
libmysqlclient.so.18()(64bit) 被 (已安裝) postfix-2:2.10.1-6.el7.x86_64 需要
libmysqlclient.so.18(libmysqlclient_18)(64bit) 被 (已安裝) postfix-2:2.10.1-6.el7.x86_64 需要
#强制卸载，因为没有--nodeps
rpm -e --nodeps mariadb-libs-5.5.37-1.el7_0.x86_64
#安装mysql依赖
yum install vim libaio net-tools
其他情况：
1、centos下yum暂时没有mysql-server直接安装包；
MariaDB是MySQL社区开发的分支，也是一个增强型的替代品;
2、安装MariaDB
yum -y install mariadb-server mariadb mariadb-devel
systemctl start mariadb
systemctl enable mariadb
mysql_secure_installation
firewall-cmd --permanent --add-service mysql
systemctl restart firewalld.service
iptables -L -n|grep 3306
In order to log into MariaDB to secure it, we\'ll need the current
password for the root user. If you\'ve just installed MariaDB, and
you haven\'t set the root password yet, the password will be blank,
so you should just press enter here.
Enter current password for root (enter for none):
ERROR 1045 (28000): Access denied for user \'root\'@\'localhost\' (using password: YES)
此处可以设置mysql的密码
Setting the root password ensures that nobody can log into the MariaDB
root user without the proper authorisation.
Set root password? [Y/n] Y
New password:
Re-enter new password:
Password updated successfully!
Reloading privilege tables..
... Success!
By default, a MariaDB installation has an anonymous user, allowing anyone
to log into MariaDB 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? [Y/n] 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? [Y/n] n
... skipping.
By default, MariaDB 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? [Y/n] 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? [Y/n] Y
... Success!
Cleaning up...
All done! If you\'ve completed all of the above steps, your MariaDB
installation should now be secure.
Thanks for using MariaDB!
跟着上面的设置，注意remote login这里设置为n.
1. 下载mysql的repo源
$ wget http://repo.mysql.com/mysql-community-release-el7-5.noarch.rpm
2. 安装mysql-community-release-el7-5.noarch.rpm包
$ sudo rpm -ivh mysql-community-release-el7-5.noarch.rpm
安装这个包后，会获得两个mysql的yum repo源：/etc/yum.repos.d/mysql-community.repo，/etc/yum.repos.d/mysql-community-source.repo。
3. 安装mysql
$ sudo yum install mysql-server
根据步骤安装就可以了。
修改mysql的默认字符集
cat /etc/my.cnf
添加
character-set-server=utf8
default-character-set=utf8
好了，下一步
[root@nicknailo ~]# /usr/bin/mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 11
输入上面的设置密码
进入mysql客户端之后，show databases;
启动mysql服务：
1、使用 service 启动：service mysqld start
2、使用 mysqld 脚本启动：/etc/inint.d/mysqld start
持久化启动mysql cd /usr/bin/,
pm2 start mysql
[PM2] Starting /usr/bin/mysql in fork_mode (1 instance)
[PM2] Done.
┌──────────┬────┬──────┬───────┬────────┬─────────┬────────┬─────┬───────────┬──────┬──────────┐
│ App name │ id │ mode │ pid │ status │ restart │ uptime │ cpu │ mem │ user │ watching │
├──────────┼────┼──────┼───────┼────────┼─────────┼────────┼─────┼───────────┼──────┼──────────┤
│ app │ 1 │ fork │ 2330 │ online │ 0 │ 95m │ 0% │ 37.3 MB │ root │ disabled │
│ app │ 3 │ fork │ 3498 │ online │ 0 │ 82m │ 0% │ 25.2 MB │ root │ disabled │
│ mongo │ 0 │ fork │ 2104 │ online │ 0 │ 104m │ 0% │ 11.5 MB │ root │ disabled │
│ mysql │ 5 │ fork │ 11449 │ online │ 0 │ 0s │ 0% │ 2.0 MB │ root │ disabled │
└──────────┴────┴──────┴───────┴────────┴─────────┴────────┴─────┴───────────┴──────┴──────────┘
Use `pm2 show <id|name>` to get more details about an app