I have finished most of the upgrade to Fedora Core 4 from Red Hat 9. This was relatively successful, as you are reading this now.
I did encounter some problems with this upgrade, and I am going to attempt to document them. My notes may not be that clear, as I only got 4 hours of sleep in the past two days, because of this upgrade.
Fedora Core 4 includes PHP5. This mainly worked for the scripts that I run, but I did have to do some modification in order to get pLog to work. It appears that when pLog is run within PHP5, it uses more than the 8Mb of memory allocated to scripts. While in PHP4, this was not a problem. I increased it to 16Mb and the problem went away most of the time. I am still seeing it periodically.
Also PHP5 is more strict on php syntax, so there are a lot of notices in the logs. I am working through these warnings now, and I hope to check something in soon.
Also, It looks like the version of php that is included with Fedora Core 4, does not include GD. To get gd, you should run "yum install php-gd".
This took me the longest to get working. I had been using cryus previously for my imap server, so I was assuming that the upgrade would be seamless. It looks like the db4 database format changed sometime between RH9 and FC4. I used the steps on this page to get the imap folders working correctly. This was a pain for my account, as I have a lot of nested folders. In fact, I haven't finished this step yet
I couldn't figure out why my mail wasn't being filtered anymore. It turns out that there is a new bytecode format for the sieve scripts. It seems that sieveshell creates the bytecode when uploading the scripts, so I had to manually re-upload the scripts again, even though nothing in the scripts change, to get the filtering to work.
After the upgrade, webmin was not offering to do ssl encrypted connections. Once I installed the Net::SSLeay perl module, this worked correctly.
The installed location of awstats changed from the rpm that was available on their Sourceforge site, and the one that is included in FC4. I needed to use the //etc/cron.hourly/awstats.rpmnew instead of the old /etc/cron.hourly/awstats file
Also, since I had been using GeoIPFree to map the ip address, I needed to reinstall the Geo::IPfree and Geo::IP::PurePerl perl modules.
Authenticated smtpd connections
After the upgrade I was not able to send email through Postfix with my password. I was able to fix this by replacing the /usr/lib/sasl2/smtpd.conf file with the /usr/lib/sasl2/smtpd.conf.rpmnew file.