HOWTO Fix Fatal error: Call to undefined function: mysql_connect()

Hi, I want to share this with all of you, today my server suddenly start showing this.

Fatal error: Call to undefined function: mysql_connect()

Googling I found the solution here.

http://www.idealog.us/2005/01/howto_fix_fatal.html

What I had to do is
First,

apt-get install php4-mysql

after that

dpkg-reconfigure php4-mysql

and finaly.

/etc/init.d/mysql restart
and.
/etc/init.d/apache2 restart

I don't know why if it was working before, suddenly stop working, my PHP application (like this one) but it did.