I have installed mysql: installed successfully

Then I have run mysql_install_db: successful

Then
skm@skmpc:~$ sudo /etc/init.d/mysql start
* Starting MySQL database server mysqld [ OK ]
skm@skmpc:~$


Then
skm@skmpc:~$ mysql -u root
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

In the last step I am facing problem, and can't login to mysql.

What to do?