方法1： 用SET PASSWORD命令
```
mysql -u root

mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD('newpass');
```
方法2：用mysqladmin
```
mysqladmin -u root password "newpass"
```
如果root已经设置过密码，采用如下方法
```
mysqladmin -u root password oldpass "newpass"
```
方法3： 用UPDATE直接编辑user表
```
mysql -u root

mysql> use mysql;

mysql> UPDATE user SET Password = PASSWORD('newpass') WHERE user = 'root';

mysql> FLUSH PRIVILEGES;
```
在丢失root密码的时候，可以这样
```
mysqld_safe --skip-grant-tables&

mysql -u root mysql

mysql> UPDATE user SET password=PASSWORD("new password") WHERE user='root';

mysql> FLUSH PRIVILEGES;
```