How to install OS X Lion on multiple Macs with only one download

Downloading Mac Lion to multiple computers will prove a headache for some Apple fans. Here's how to save bandwidth and time when downloading your own pride of Lions.

Nik Rawlinson
Nik Rawlinson has been writing about tech since Windows 95 was looking distinctly futuristic. He is a former Editor of MacUser magazine and one-time scribe for Personal Computer World. Nik is a freelance writer and is not an employee of CNET.
Nik Rawlinson
4 min read

Apple's decision to offer OS X Lion as download-only software, at least initially, has been well publicised, but that won't stop it causing headaches for some users.

The Lion installer is a 4GB download, which is roughly the same size as a high-definition movie. Those users who have a fast, all-you-can-eat broadband deal probably won't think twice before clicking the download button, but not everyone is so lucky. Moreover, if you're on a capped account with a 20GB limit, you only need download Lion to three Macs and you've already consumed more than half of your monthly allowance.

Apple suggests that those who can't, or would rather not, download the installer at home visit an Apple Store and download it there using the free, open Wi-Fi network. It's a neat idea, but not if you have to make several journeys to update more than one machine, or if your Mac is an iMac, Mac mini or Mac Pro, which aren't nearly so easy to use away from base.

What should you do then if you can neither travel nor afford the time or bandwidth hit involved in downloading Lion more than once?

App Store shopping

OS X's built-in Mac App Store has quickly established itself as the easiest, fastest way to buy software for your Mac. Browse the categories or use the search box to find the app you're after, and, with a single click, it'll be downloaded, installed and ready to use.

Better yet, you can download any apps you've bought to as many other Macs as you own, as long as they're all logged in through a single Apple ID. So, if you've already paid to install Lion on one machine, it'll appear in the App Store purchases tab on each of your other Macs. Clicking the 'install' button will download another copy to each of those machines.

Don't install right away

As we don't want to download the installer for each of our Macs, we need to take care of our initial download. The installer is a standard application package inside of which the company has bundled a full disk image. The installer mounts this as a virtual drive and, once the installation completes, deletes it and self-destructs, freeing up space on your drive, but giving you no chance of using the same installer on a second machine.

To avoid having to download the installer again, you need to save the package before you execute it, so, after downloading it to your first Mac, attach an external hard drive and copy it from your applications folder. Unmount and disconnect the drive, and connect it to the second machine on which you want to perform the upgrade. 

You can now launch the downloaded installer on your first machine.

Install a pride of Lions

Before performing any kind of operating system update, you should make a complete backup of your system, including all files, folders and user data. The easiest way to do this in OS X is to use Time Machine, via which you can also recover a corrupt install of Lion.

Force an immediate backup from the Time Machine menu-bar icon on your second machine and, when it completes, quit all of your applications, connect the external drive, and drag the installer to your applications folder, ensuring that you copy, rather than move, the file.

Double click on it to repeat the upgrade on your second machine.

Create your own boot disc

Burning the complete installer package to DVD makes it more portable than storing it on a drive, but, by digging a little deeper, it's possible to make it much more useful, too, as the disk image can be burned to a DVD.

As a standard compiled package, it's possible to view the installer's constituent parts by right clicking and selecting 'show package contents'.

Within the exposed directory structure, at Contents/SharedSupport, you'll find a file called InstallESD.dmg.

By dragging this onto your desktop and launching Disk Utility (found inside Applications/Utilities or through Spotlight), you can burn a copy of the installation code to optical media. After clicking 'burn' on the Disk Utility toolbar, you'll be asked to insert a DVD-R and locate the disk image you want to use, at which point you'd direct it to the image on your desktop.

While this time-saver has been widely publicised on various blogs and forums, it's not necessarily to be recommended as a long-term fix, since, over time, Apple will ship updated versions of Lion, incorporating fixes and security patches. Installing from an old disk image could leave you vulnerable to exploits that have been fixed in later versions.

Furthermore, while the licence agreement permits you to make 'one copy of the Apple software... in machine-readable form for backup purposes only', it's unclear whether a boot disc of this kind would constitute a backup.

Good things come to those who wait

If you'd rather not explore the components of the Lion installer package, then look ahead to August. Although Lion is currently available only as a download from the App Store, the company will start shipping it on a USB thumb drive roughly a month after its initial release.

The USB stick will be easier to store and transport than a DVD, as well as faster and more robust. At £55, though, it will be significantly more expensive than the download edition, most probably on account of the physical media and shipping involved. Apple hasn't yet announced any plans to release the operating system on optical media.