Stop MySQL:

Debian/Ubuntu:

# /etc/init.d/mysql stop

Redhat/CentOS:

# /etc/init.d/mysqld stop

Start MySQL without password:

# mysqld_safe --skip-grant-tables &

Login to MySQL:

# mysql -u root

Reset the password:

mysql> UPDATE mysql.user SET password=PASSWORD("NewRootPassword") where User='root';
mysql> flush privileges;
mysql> quit

Stop MySQL:

Debian/Ubuntu:

# /etc/init.d/mysql stop

Redhat/CentOS:

# /etc/init.d/mysqld stop

Start MySQL:

Debian/Ubuntu:

# /etc/init.d/mysql start

Redhat/CentOS:

# /etc/init.d/mysqld start

Login with the new password:

# mysql -u root -pNewRootPassword