首先停止MySQL

$ systemctl stop mysqld

打开/etc/my.cnf，加入skip_grant_tables：

[mysqld]
skip_grant_tables

重新启动MySQL：

$ systemctl start mysqld

在命令行内直接输入mysql，执行如下操作：

mysql> update mysql.user set authentication_string = '' where user = 'root';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

mysql> delete from mysql.user where user='root' and host='localhost';
Query OK, 1 row affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

mysql> create user 'root' identified by 'password';
Query OK, 0 rows affected (0.01 sec)

mysql> grant all privileges on *.* to 'root'@'%' with grant option;
Query OK, 0 rows affected (0.01 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

再次修改/etc/my.cnf文件，将skip_grant_tables删掉，重启mysqld，即可以重置后的新密码成功登入。