In a wild burst of enthusiasm, I updated our other two Macs to Leopard yesterday.

These were both upgrades rather than clean installs, and I did fall foul of another glitch which can affect upgrades. It's easy to fix once you know what's happening, but ironically it manifests itself as an unresponsive "blue screen", which appears when the system first boots after the OS installation and so can be a little worrying!

The issue is a third-party subsystem called 'Application Enhancer' ('APE') which you may never knowingly have installed but which is distributed as part of a few popular utilities and so may be on your system. It doesn't work under Leopard, which is fine, but unfortunately, early versions of APE will cause the Leopard login window to crash. If you do an Upgrade installation of Leopard, which doesn't remove such things from your system, you never get a chance to log in to your shiny new OS!

Some argue that this isn't really Apple's fault, because APE puts hooks into the OS in ways that weren't really intended, and is installed, like the Abomination of Desolation, in a place where it ought not to be. On the other hand, APE's creator, Unsanity, point out that you have to be using a pretty elderly version of their library for this to be an issue.

Fortunately, there are various easy ways to make sure this doesn't happen to you:

  • Check, before you install, whether you have any of the following files on your machine and delete them if so: 
    /System/Library/SystemConfiguration/ApplicationEnhancer.bundle
    (that's the important one) 
    /Library/Frameworks/ApplicationEnhancer.framework
/Library/PreferencePanes/Application\ Enhancer.prefpane
/Library/Preferences/com.unsanity.ape.plist
  • or, install the latest version of APE before beginning
  • or, install Leopard by doing an 'archive and install' rather than an 'upgrade'
  • or, if you find you're already in this situation, you can fix it by booting into single-user mode and running a couple of commands as described in Apple's article on the problem.
So, perhaps because I'm a somewhat unusual user, two out of our three Macs hit issues on the Leopard install. This is bad. On the other hand, they were the most common issues others have faced too, and were quickly resolved by Googling. I can't comment on the long-term stability of Leopard yet, but I'm very pleased with how well everything seems to be working now it's up and running. I was expecting a lot more pain, or at least inconvenience. There was a nasty moment when I thought that one of my network printers wasn't supported, but everything went much better after I went into the next room and discovered that it wasn't actually turned on!