When I started the WordPress MU installation, I was very careful to step through the installation process outlined in the README file. I made sure MySQL was working. I made sure PHP was working. I stepped through the installation web page that you get. It seemed like I was doing everything exactly as I was supposed to do.
However, I was getting a completely blank page! Nothing at all. A 0-sized HTML page. And no PHP error logs. Nothing. I was completely and utterly confused and after spending the better part of a day trying to figure this all out was about ready to give up completely on WordPress MU. I posted to forums. I went on the #wmpu IRC channel. I bothered friends…. I believe it was ultimately someone in one of the Skype public groupchats I monitor that helped me out… I communicated with a ton of people that day!
In the end, it turned out to be one little command that was all that was needed:
# yum install php-mysql
You see, I was using a stock Fedora Linux installation and it had both PHP and MySQL installed, but did not have the package that glues them together installed. Oops.
One ‘yum’ command later and everything was working fine. The installation went ahead just as the README file said it should. All was good.
The good news out of all of this was that I learned an incredible amount about PHP and MySQL, both of which I had not really used in any serious way for a few years. I also became very good at doing a WPMU installation! (since I kept blowing away my installation to try it again!)
UPDATE 25 January 2008: In the comments to this post, Garth Roxburgh-Kidd has indicated that the command to do this update on Red Hat Enterprise Linux 4 (RHEL) is this:
# up2date php-mysql