centos上mysql安装操作

卸载mysql8的方法：
	1.查看mysql安装文件：
	rpm -qa |grep -i mysql

	2.卸载安装文件
	yum remove  mysql-community-libs-8.0.21-1.el7.x86_64
	yum remove mysql-community-libs-compat-8.0.21-1.el7.x86_64
	yum remove mysql80-community-release-el7-3.noarch
	yum remove mysql-community-common-8.0.21-1.el7.x86_64
	yum remove mysql-community-server-8.0.21-1.el7.x86_64

	3.查看是否卸载完成：
	rpm -qa |grep -i mysql

	4.查找mysql相关目录
	find / -name mysql

	5.删除相关目录
	rm -rf

	6.删除配置
	rm -rf /etc/my.cnf

	7.删除/var/log/mysqld.log
	rm -rf /var/log/mysqld.log

安装5.7mysql：
	1.下载rpm源
	 rpm -ivh https://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
	2.添加mysql仓库
	yum repolist all | grep mysql | grep enabled
	3.安装mysql
	yum -y install mysql-community-server
	4.service mysqld start  //启动
	5.service mysqld status  查看启动状态
	6.cat /var/log/mysqld.log | grep -i 'temporary password'   查看默认密码并打印
	7.mysql -u root -p  登入
	8.打开防火墙：
		1).iptables -L -n    查看防火墙开发端口
		2). 安装firewall插件：yum install firewalld firewalld-config
		3).配置文件：/etc/firewalld/
		  详细信息：开启防火墙：systemctl start firewalld 
					关闭防火墙：systemctl stop firewalld
					设置开机启动：systemctl enable firewalld
					停止并禁用开机启动：sytemctl disable firewalld
					查看指定区域所有开启的端口号  firewall-cmd --zone=public --list-ports
					在指定区域开启端口(如80端口号，命令方式)  firewall-cmd --zone=public --add-port=80/tcp --permanent
					重新启动防火墙  firewall-cmd --reload
	9.SET PASSWORD = PASSWORD('123456');
	10.重新登入，use mysql
	11.select host,user from user， update user set host = '%' where user = 'root';
　　　　 12.flush privileges;  重新刷新权限