1.修改配置文件：進入/etc/mysql/mysql.conf.d/ ，在配置文件mysqld.cnf下添加 skip-grant-tables
2.在終端輸入命令：sudo service mysql restart來重新啟動mysql服務
3.輸入:mysql -u root -p，回車進入mysql（此時不需要密碼即可直接進入）
4.輸入：use mysql；
5.輸入:update user set authentication_string='' where user='root';,將authentication_string 置空;
6.輸入：alter user 'root'@'localhost' identified by 'newpassword'；，newpassword為要修改的新密碼；
此時提示錯誤：ERROR 1290 (HY000): The MySQL server is running with the --skip-grant-tables option so it cannot execute this statement
輸入：FLUSH PRIVILEGES;
再重新alter user 'root'@'localhost' identified by 'newpassword'；
此時錯誤提示為：ERROR 1524 (HY000): Plugin 'auth_socket' is not loaded
，
輸入select user,plugin from mysql.user;來查看plugin
這里輸入update user set plugin='mysql_native_password' where user='root';將plugin改為以前版本的密碼認證方式
然后輸入：FLUSH PRIVILEGES;
再重試alter user 'root'@'localhost' identified by 'newpassword'；即可修改密碼
7.修改完成后輸入FLUSH PRIVILEGES;
8. 將第一步的skip-grant-tables注釋掉；
9.輸入service mysql restart重啟mysql