Update: The below was tested on Parallels Desktop 6. Commenters have reported that it doesn’t work on Parallels Desktop 7, which is indeed a drag. When I have some time I’ll take a closer look.

Yesterday, I explained how to install Snow Leopard as a guest in Parallels (or presumably another virtualization product for Mac) if you have a Snow Leopard Server DVD. Here, I explain how to do it without the Server DVD. You will need a blank (or erasable) 8 GB flash drive and a Mac which natively supports Snow Leopard (i.e. not the 2011 versions of the MacBook Air and Mac mini).

The same disclaimers apply: I’m not recommending this, I’m writing this as Ivan Drucker and not as part of IvanExpert, I’m not responsible for anything that happens, etc.

1. Download Ubuntu Linux. (We will only be booting from this, not installing it.)
2. With Parallels not running, insert an 8 GB flash drive.
3. Open /Applications/Utilities/Disk Utility, click the flash drive on the left, click Partition, select “1 Partition” under Partition Layout, click Options, choose GUID Partition Table, set Name to “SL”, and click Apply.
4. Install Snow Leopard to the flash drive.
5. When it’s done, your Mac will restart; pull out the USB flash drive so it doesn’t boot from there.
6. When your Mac has rebooted, reinsert the USB flash drive.
7. Open Terminal (in the Utilities folder of the Applications folder), and type this line followed by return: touch /Volumes/SL/System/Library/CoreServices/ServerVersion.plist
8. Unmount (eject) the flash drive, and remove it.
9. Create a new Parallels VM. Choose “Continue Without Disc” and then choose “Ubuntu Linux” as the type of virtual machine, and select “Customize Settings Before Installation”.
10. Click on CD/DVD 1 and select the Ubuntu .iso file you just downloaded to use it.
11. If “USB Controller” is not listed, add a virtual USB controller.
12. Click OK and start the VM. Ubuntu Linux will start up.
13. When asked, click “Try Ubuntu”.
14. At the Ubuntu desktop, choose Applications -> Accessories -> Terminal
15. Insert the flash drive. When asked, choose the Ubuntu VM for it to be used with.
16. Type: sudo dd if=/dev/sdb of=/dev/sda bs=16384
17. The Snow Leopard installation on the flash drive will be copied to the Parallels virtual HD. You’ll see nothing happening until it completes, when it will show you the the number of bytes copied and return you to the Terminal prompt.
18. Remove the flash drive, and type sudo shutdown -h now
19. The Parallels VM will turn off.
20. Configure the virtual machine, and add another hard drive. This will be your working drive, so make sure it is a capacity that works for you.
21. Turn on the VM, and Snow Leopard will boot. However, you only have 8 GB of total capacity, which is probably not enough; plus there may be issues with your partition table.
22. Get Carbon Copy Cloner or a similar utility to copy the drive “SL” to the drive “Macintosh HD”.
23. When it is complete, shut down the VM, and go back to Configure. Remove the 8 GB virtual HD, but keep the files, for reasons explained below.
24. Restart your VM, and you’ve got Snow Leopard up and running.

As explained yesterday: One thing to be aware of is that the presence of the file /System/Library/CoreServices/ServerVersion.plist causes at least two side effects: A) Software Update won’t offer you many updates that it is supposed to, and B) the Sharing system preference pane hides many of its settings.

So before using either, you should remove that file, but be sure to put it back when you’re done, or the VM won’t start up. If you do find yourself in that situation, add the original 8 GB Snow Leopard drive back to your VM and boot from that, then typing the command in line 7, substituting “Macintosh HD” or whatever you renamed your drive to for “SL”.  This blog post also suggests a script which takes care of creating and deleting it automatically; I haven’t (yet) tried it.