1.vi /etc/my.cnf

2.在[mysqld]中新增

skip-grant-tables

例如：

[mysqld]
skip-grant-tables
datadir=/var/lib/MySQL
socket=/var/lib/mysql/mysql.sock

3.重啟mysql

service mysql restart

4.使用者無密碼登入

mysql -uroot -p (直接點選回車，密碼為空)

5.選擇資料庫

use mysql;

6.修改root密碼

update user set authentication_string=password('123456') where user='root';

7.執行

 flush privileges;

8.退出

exit;

9.刪除

skip-grant-tables

10.重啟mysql

service mysql restart

其它版本

2．修改MySQL的登入設定： 
# vim /etc/my.cnf 
在[mysqld]的段中加上一句：skip-grant-tables 
例如： 
[mysqld] 
datadir=/var/lib/mysql 
socket=/var/lib/mysql/mysql.sock 
skip-grant-tables 
儲存並且退出vi。

3．重新啟動mysqld 
# service mysqld restart 
Stopping MySQL: [ OK ] 
Starting MySQL: [ OK ]

4．登入並修改MySQL的root密碼 
# mysql 
Welcome to the MySQL monitor. Commands end with ; or \g. 
Your MySQL connection id is 3 to server version: 3.23.56 
Type 'help;' or '\h' for help. Type '\c' to clear the buffer. 
mysql> USE mysql ; 
Database changed 
mysql> UPDATE user SET Password = password ( 'new-password'

5．將MySQL的登入設定修改回來 
# vim /etc/my.cnf 
將剛才在[mysqld]的段中加上的skip-grant-tables刪除 
儲存並且退出vim

6．重新啟動mysqld 
# service mysqld restart 
Stopping MySQL: [ OK ] 
Starting MySQL: [ OK ]