I upgraded one of my last remaining Tiger servers to Leopard this morning, and ran into a very odd problem. Every time it got to the install screen, as it appeared to be determining what to show in the progress bar, it semi-crashed. A message would pop up, and the entire window would disappear, leaving an unresponsive menu. (I could choose items from the menus, but they didn’t do anything—not even “Quit”.)

The error dialog disappeared so quickly that I couldn’t read it; it said something about “DVD”. I was considering getting a camera to film it so that I could freeze frame on the error message, when I remembered that OS X installs can be done on the command line. If I could start the installation from the command line, that ought to show me the error message.

I booted back into Tiger and opened Safari, and wrote down these commands from Apple’s command-line manual:

1. Show available volume names: /usr/sbin/installer -pkg /System/Installations/Packages/OSInstall.mpkg -volinfo
2. Install the OS: /usr/sbin/installer -pkg /System/Installations/Packages/OSInstall.mpkg -target /Volumes/drivename -verbose

Sure enough, it started the installation process… and then continued right on through where the error should have shown up. That wasn’t exactly what I wanted—I don’t like to force installs when there’s an error, I prefer to fix the error—but the installation went fine. Whatever error was being displayed in the window, this bypassed it entirely.