..then you may end up with an unusable system. I have about 25 sites, including some pretty high-traffic sites, running in a shared environment on a dedicated box (Ubuntu 6.06LTS, Apache2.0.55, MySql 4.1.15.)

It is not clear to me that the 5.5 upgrade was the entire problem, since I also (stupidly) updated PEAR at the same time) - but, for the last 12 hours all of these sites were oddly 'read-mostly' - the only tables which Drupal could write into were the logs. I was not able to take the sites into maintenance mode, for example, or post comments.

Finally I removed PHP4 and PEAR (and all the config files), and installed PHP5, and reinstalled PEAR. At long last, my sites are back, and I have been able to run update.php to get everything up to present standard..

Just thought you'd like to know. I suspect that if you are running PHP4.x you will also have problems.

[ Edited by: VeryMisunderstood; Removed use of ALL CAPS in title. ]