[root@localhost ~]# mysql -uroot -p
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

[root@localhost ~]# mysql -uroot -p
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

[root@localhost ~]# service mysqld stop
Stopping mysqld:                      [ OK ]

skip-grant-tables  //跳过授权直接进入数据库

[root@localhost ~]# service mysqld start
[root@localhost ~]# mysql -uroot -p  
mysql> 

mysql> use mysql //密码存放在MySQL中，需要进入
mysql> desc user; //查看user表中的字段
密码一般存在password表中
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Field     | Type        | Null | Key | Default    | Extra |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Host     | char(60)       | NO | PRI |      |  |
| User     | char(16)       | NO | PRI |      |  |
| Password    | char(41)       | NO |  |      |  |

mysql> update user set password=password('passw0rd') where user="root"; //设置密码为passw0rd
mysql> flush privileges; //刷新

[root@localhost ~]# mysql -uroot -ppassw0rd
mysql>