0. Environment
Ubuntu 12.04 x64 server
MySQL 5.5.29
1. Steps
1.1 Modify your MySQL's "my.cnf" file, and add a line in "[mysqld]" session:
skip-grant-tables
1.2 Restart MySQL
1.3 Log in MySQL without password
$ bin/mysql -u root -p
press enter when the command shows "Enter password:"
1.4 Select database
mysql> use mysql;
1.5 Updata password
mysql> update user set password = password('mypass') where user = 'root';
1.6 Refresh tables related with system permissionmysql> flush privileges;
1.7 Modify your MySQL's "my.cnf" file to original version, delete the following line in "[mysqld]" session:skip-grant-tables
1.8 Restart MySQL