错误代码：
ERROR 1698 (28000): Access denied for user 'root'@'localhost
停止mysql服务
sudo service mysql stop
以安全模式启动MySQL
sudo mysqld_safe --skip-grant-tables &
MySQL启动之后就可以不用密码登陆了
~$ mysql -u root
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.10 MySQL Community Server (GPL)
查看一下user表，错误的起因就是在这里， root的[plugin](https://www.baidu.com/s?wd=plugin&tn=24004469_oem_dg&rsv_dl=gh_pl_sl_csd)被修改成了auth_socket，用密码登陆的plugin应该是mysql_native_password。
+-----------+-----------------------+
| user | plugin |
+-----------+-----------------------+
| root | auth_socket |
| mysql.sys | mysql_native_password |
| dev | mysql_native_password |
+-----------+-----------------------+
3 rows in set (0.01 sec)</pre>
mysql> update mysql.user set authentication_string=PASSWORD('newPwd'), plugin='mysql_native_password' where user='root';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 1
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
重启服务，问题就解决
~$ sudo service mysql stop
...
* MySQL Community Server 5.7.10 is stopped
~$ sudo service mysql start
..
* MySQL Community Server 5.7.10 is started
~$ mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.10 MySQL Community Server (GPL
