Every time I installed phpmyadmin in my ubuntu desktop, navigating to http://localhost/phpmyadmin simply displays a 404 message. This is how I fix everytime -

$ sudo ln -s /usr/share/phpmyadmin /var/www

Fixing AllowNoPassword

I don’t use any password for mysql in my development invironment. But by default phpmyadmin doesn’t allow you to login without a password. You can overcome it by editing the /etc/phpmyadmin/config.inc.php. Open the file with root previledge -

$ sudo gedit /etc/phpmyadmin/config.inc.php

And uncomment this line

$cfg['Servers'][$i]['AllowNoPassword'] = TRUE;