mariadb-libs-5.5.52-1.el7.x86_64
rpm -qa|grep mariadb
rpm -e --nodeps mariadb-libs

rpm -ivh mysql-community-common-5.7.21-1.el7.x86_64.rpm
 rpm -ivh mysql-community-libs-5.7.21-1.el7.x86_64.rpm 
rpm -ivh mysql-community-devel-5.7.21-1.el7.x86_64.rpm 
rpm -ivh mysql-community-libs-compat-5.7.21-1.el7.x86_64.rpm 
rpm -ivh mysql-community-client-5.7.21-1.el7.x86_64.rpm
 rpm -ivh mysql-community-server-5.7.21-1.el7.x86_64.rpm

# Disabling symbolic-links is recommended to prevent assorted security risks
skip-grant-tables   #添加这句话，这时候登入mysql就不需要密码
symbolic-links=0

mysql> set password for root@localhost = password('123456');
ERROR 1290 (HY000): The MySQL server is running with the --skip-grant-tables option so it cannot execute this statement
mysql> flush privileges; #更新权限
Query OK, 0 rows affected (0.00 sec)
mysql> set password for root@localhost = password('123456'); 
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql>flush privileges; #更新权限
mysql>quit; #退出
service mysqld stop # 停止mysql服务, 恢复mysql配置
vim /etc/my.cnf   #修改配置文件
# Disabling symbolic-links is recommended to prevent assorted security risks
# skip-grant-tables # 注释掉这句话
symbolic-links=0
service mysqld start # 启动mysql服务
mysql -uroot -p # 输入新密码登录