Update To Mac OS X Lion Without Losing Your Current Installation

Despite our initial scepticism, there are some pretty compelling features in Mac OS X Lion. That said, it's still a beta and running it as your primary OS is a little risky for several reasons. If you want to give it a shot without the risk, you don't have to give up your current OS X installation or even boot from an external drive. Here's how.

This process requires a couple of things: first, that you've got a copy of OS X Lion, and second, that you're mildly comfortable with using the Terminal in OS X. If you are, this should be pretty easy. What we're going to do is create a live partition on your disk and install OS X Lion onto that so you can dual boot. We'll then look at linking important files from your old, non-Lion partition so you can use them in Lion without having to create duplicates and waste disk space. It'll be like you've updated to Lion without having to worry about downgrading if you don't like it. Interested? Just follow the steps below.

By the way, if you don't have a copy of the Mac OS X Lion beta, you can easily get one by signing up for a Mac OS X developer account. It costs $US99 and gives you access to betas for the whole year. There are, of course, less reputable ways to get yourself a copy of OS X betas but we recommend going the honourable route.

Install and Update Mac OS X Lion

Before you can install, you need to create a partition on your existing disk so you can install OS X Lion there rather than updating your existing system. This way we can switch between your current stable installation of OS X and Lion just by restarting. Just follow these steps to get everything set up:

  1. Create a partition on your disk of 12.5GB. You do not have to erase your disk to do this if you're running a recent version of Mac OS X. Just open Disk Utility and add a new partition to your disk. Note: This will take a lot longer and is more likely to fail if you're adjusting the current startup disk. You'll save yourself some time and trouble by booting to another disk (like the Mac OS X Lion Installer) and then resizing the partition. It works better and goes faster when the disk being live-partitioned can be unmounted.
  2. Install Mac OS X Lion on your new 12.5GB (or greater) partition.
  3. Lion will automatically boot when the installation has finished. Set up your computer like you normally would, but do not transfer your user accounts, applications, or other files and documents. You can transfer over global system settings, but that's it. DO NOT transfer over anything else. You will be wasting time and causing problems later by doing so.
  4. Once you've finished with the setup assistant, run Software Update to get any new updates for Lion. It's still accessible from the Apple menu like you'd expect.

Link Your Systems

Now that you've finished the installation, set it up, and updated anything and everything that requires an update, we can start linking your old system with your new one so you can share files between partitions. Because Mac OS X's Setup Assistant is sort of an all-or-nothing affair and doesn't provide enough fine-grained control to transfer a select number of settings and other files, we'll have to do that manually as well. Just follow these steps to transfer over all your information and link your old system with the new one:

  1. First things first: one thing you may notice about OS X Lion is that it hides the Library in your home folder. This is really annoying if you want to make changes, but fortunately we can fix this problem with a terminal command. So, open Terminal (Hard Drive —> Applications —> Utilities —> Terminal) and type chflags nohidden /Users/[Username] /Library (changing [Username]to your username). Now you'll be able to see your user Library in your home folder.
  2. You'll need to open two windows. First, open one window with your old Mac OS X user library. In the second, open up your new Mac OS X Lion user library. (I like to put old on the left and new on the right so it's easy to know which is which). Now copy any preferences, preference panes, and other relevant settings you want to transfer over. You'll also want to copy over files from Application Support if you plan on running any of those apps in Lion. As an alternative, you may prefer to create symlinks to folders within Application Support (not the Application Support folder itself) so the data is up to date regardless of what partition you're booting from, but we'll talk more about symlinks in the next step. And don't worry about forgetting anything — you can always go back for it later!
  3. You don't want to copy files and folders over to your new partition or you're going to have a bunch of duplicates, so the best way around that is to create symbolic links (symlinks) to items on the old Mac OS X partition so they're easily accessible on the new one. This is a little different than creating an alias even though a symbolic link will appear identical when you see it in the Finder. To create a symlink, just use the following command in the terminal:

    ln -s [Path to Old Partition Folder][Path to New Partition Folder]

    You, of course, want to replace [Path to Old Partition Folder] with a path to whatever folder you want to link to. You also want to replace [Path to New Partition Folder] with the path to where you want to save your symlink.

Once you're done copying over preferences and making your symlinks, you should have Mac OS X Lion running pretty similarly to your old setup without keeping any of the actual files on the new partition. You'll probably need to still set a few settings manually and re-install some applications, but for the most part you should be all set to go. Now you can play around with Lion like it's your primary OS while always being able to go right back to your older version of Mac OS X if you want to.


    or much easier and a little riskier… In Terminal:

    cd ~
    sudo mv ~ ~.lion.homedir
    sudo ln -s [pre-lion-home-dir-path] ~

    Logout of Lion and back in, or reboot. Now you have a single shared home directory for Lion and Snow Leopard and didn't need to copy any files.

    The question I'm trying to get answered now - before I do this, is what happens to the files that get opened in Lion - such as iTunes preference files, address book files, iCal files, Mail.app files etc?

    Can these files in my Home User still be opened normally in Snow Leopard after being opened in 10.7, or are they permanently changed to the new Lion file type making it impossible to "downgrade" back to 10.6?

    I would think anyone wanting to try this would want to know the answer to this before jumping in ;)

    Liked the article, but I think you need to be extremely careful about what you link together, as going back to Snow Leopard may not be possible if Lion ends up changing critical files (so be very conservative -- i.e. don't share the home directory, etc.). Usually, I'll use CCC to clone a new drive from the old one and then install the new version of the OS on the copied (usually larger) drive. Then, swap the drives physically (if necessary). Once I've done this, in practice, I find I seldom go back to the old OS. My Tiger system was last booted up maybe two years ago? I suppose I should recycle that drive for other things ;-)

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