$ vim /etc/my.cnf

[mysqld]
skip-grant-tables=1
#添加这一行，跳过密码输入

$ systemctl restart mysqld

$ mysql -u root -p
Enter password:        #直接回车

> ALTER USER 'root'@'localhost' IDENTIFIED BY 'Redhat123..';
ERROR 1290 (HY000): The MySQL server is running with the --skip-grant-tables option so it cannot execute this statement
#跳过密码的方式不能用这种方式修改 root 密码

> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed

> update user set authentication_string = password('Redhat123..'),password_last_changed=now() where user='root';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 1

$ vim /etc/my.cnf

[mysqld]
skip-grant-tables=1
#注释掉这一行,不跳过密码登录

$ systemctl restart mysqld

$ mysql -u root -p
Enter password:  #输入修改好的密码即可登录