Alternatives for Imaging a Mac Laptop

Last week, I wrote about how to forensically image the internal hard drive on a Mac laptop without needing to physically remove the drive. If your workspace doesn’t have the necessary tools to follow that tutorial (a firewire cable, a firewire port on the Mac you’re imaging, and a firewire port on a PC partitioned with BitCurator), we offer an alternative in this post.

The Mac laptop we wanted to forensically image.
The Mac laptop we wanted to forensically image.

Other Options for Imaging Mac Laptops

We recognize that you might not have the correct devices on hand to follow the instructions in the previous post. In that case, you may want to open the laptop to temporarily remove the hard drive for forensic imaging within the BitCurator environment, which means you’ll need a cable that connects a hard drive to your imaging computer (probably a SATA cable). You can also opt to make a forensics image outside BitCurator and then import the image into BitCurator for exploration.

Note that the issue complicating this imaging process is specific to Mac laptops; Linux and Windows laptops wouldn’t require target disk mode and the trouble that causes. Target disk mode works with other Macs (perhaps obviously) and Linux machines; I wasn’t able to get a Windows machine to recognize the Mac laptop in target disk mode. I’ve read that commercial software called MacDrive (currently about $50 for use on one PC) will let you connect the a Mac in target disk mode to a PC, but this would not make the Mac drive also available in the Windows computer’s BitCurator VM; unfortunately, VirtualBox is unable to take firewire input. It’s possible you could get around this issue by using other virtualization software, but VirtualBox is the best free/open-source option.

That leaves us with using either a Mac or Linux machine to create our backup of the Mac laptop; in our example, I used a Mac to create the backups. We’ll walk you through how to first lessen the risk of tampering with a laptop’s insides by securing a forensic image outside of BitCurator.

Why Backup?

Opening up the laptop, removing the drive, and later trying to put everything back risks the laptop refusing to start or otherwise being damaged: maybe you break something, or can’t get things to fit back together. If you don’t have another way to gather a forensics disk image packaged with metadata about the imaging, though, opening the laptop up can be an acceptable risk. All computers fail eventually, and we’d rather have a good forensics disk image of the laptop now, than more years with the laptop working but no forensics image preserved. We thus recommend you forensically image the laptop’s hard drive before opening it, or choose to create a forensics image with one of the non-BitCurator options discussed below and import the image into BitCurator. Opening up the computer is only necessary if none of these forensics imaging programs are right for you, your Mac laptop doesn’t have a firewire port, or if you prefer to do all your forensic work inside the BitCurator environment. For either method, you’ll need a firewire and another Mac (with a firewire port) on which to image the laptop.

Write Blocking

First, we need to protect the laptop from having the connected machine write back to it during the imaging process. This wasn’t a major concern in our example as Larsen’s laptop has already been explored by researchers at MITH—but it’s good practice nonetheless, especially if you use a command-line imaging method, where a simple is-typing could accidentally erase your device. Our WiebeTech Forensic ComboDock works well for most write-blocking purposes, but it doesn’t have the firewire input and output needed to work with a Mac in target disk mode. Tableau T9 Firewire Forensic Bridge is a hardware option that does accept both firewire input and output, but we didn’t have one on hand. We thus used software write-blocking instead, installing Aaron Burghardt’s Disk Arbitrator to protect the laptop.

Connecting the target old Mac laptop with the host new Mac laptop to image the old on the new.
Imaging time! Leaving the computers alone during imaging.

A Forensic Disk Image

Begin by putting the Mac laptop you want to image into target disk mode:

  1. The laptop to be imaged (e.g. our Larsen laptop) should be turned off.
  2. Hold down the t key and turn the laptop to be imaged on.
  3. Continue to hold down the t key until the target disk mode image appears on the screen (see photo below).
Old white Mac laptop opened to show screen in Target Display Mode
Old white Mac laptop opened to show screen in Target Disk Mode

You can now connect your firewire cable to both the laptop to be imaged and the Mac (or Linux computer) doing the imaging.

To create a forensics disk image, there are a variety of free and commercial programs that provide graphical interfaces for Mac and Linux, including MacOSXForensics Imager (Mac) and Guymager (Linux; note that Guymager is the imaging software BitCurator incorporates). Commercial options such as FTK Imager also exist. Almost any program that creates the image in an Encase (E01) or AFF forensic disk image format works, as these formats take a raw disk image and wrap metadata about the imaging around it. We haven’t formally evaluated the effectiveness of any programs outside the BitCurator suite, though, so you’ll want to check potential Mac forensic imaging software out yourself and explore the images they create within the BitCurator environment to make certain they captured your device correctly.

Alternatively, you can choose one of the following command line methods—but it’s of utmost importance that you use a write-blocker with these, as mis-typing could erase your device:

  1. If you’re very knowledgeable about using the command line, you may already know how to use dd or dcfldd.
  2. The ForensicsWiki has a detailed tutorial on “Acquiring a Mac OS System with Target Disk Mode” that uses dd and other commands to create a .dmg image, plus instructions on converting the .dmg to an Encase format.
  3. Macintosh Forensics: A Guide for the Forensically Sound Examination of a Macintosh Computer” by Ryan Kubasiak offers alternative instructions for using dd (use the hyperlinked table of contents to jump to the “Imaging a Target Macintosh” section starting on page 25).

Opening the Laptop to Remove the Hard Drive

After following these steps to make a forensic image of your laptop, you can either opt to import the forensic image into BitCurator and explore the image there, or choose to temporarily remove the hard drive in order to image it directly through BitCurator. If you choose the latter path, you’ll need to search for instructions like these that show how to open your particular model of Mac. If possible, use a guide with many photos to show you how to carefully open, remove, and replace the Mac laptop’s hard drive. I’ve found that sites dedicated to DIY fixing and making, such as iFixit and Instructables, offer good community-moderated tutorials on opening up computers.

In a future post, I’ll discuss what I found while exploring the Larsen laptop disk image using BitCurator. Send us your suggestions for other difficult-to-image use cases, and we’ll cover them in future posts!

Amanda Visconti is a MITH graduate research assistant on the BitCurator project, where she creates user-friendly technical documentation, develops and designs for the web, and researches software usability. As a Literature Ph.D. candidate, she blogs about her digital humanities work regularly at LiteratureGeek.com.

Forensically Imaging a Mac Laptop for BitCurator Exploration

Let’s say a digital beauty like this makes its way into your collection:

Lid of the old white Mac Larsen laptop, covered in flower and lace doily decals
The lid of the Larsen laptop is covered in flower and lace doily decals.

This is a laptop donated to us by electronic literature author, educator, and collector Deena Larsen. Larsen used the laptop as an everyday work machine, and as such it’s an important digital artifact: everything from the lid decals to the desktop icon layout to the file system can give us important insight into how an e-lit author worked.

BitCurator can aid us in such investigations by freeing Larsen’s laptop data from its storage media (which will fail eventually), capturing important contextual details about Larsen’s original work environment, and helping to ensure the authenticity and integrity of files during forensic processing (see this page on how BitCurator fits into existing archival workflows, or this page on how the individual tools making up the BitCurator suite address particular archival concerns, for more information on what BitCurator can do).

To use BitCurator, we’ll need to figure out how to connect the laptop’s hard drive to the BitCurator environment; this post will explore how you can similarly image your Mac laptop for digital forensic work.

Why is it difficult to image an internal Mac laptop drive?

Old white Mac laptop opened to show screen in Target Display Mode
Old white Mac laptop opened to show screen in Target Disk Mode

You can get to work quickly with BitCurator if you’ve got a digital device ready to be connected to your computer: an external hard drive or removed internal hard drive, a floppy disk port, a USB stick, or other devices and the cables to attach them to your host machine.

With a Mac laptop, however, the device isn’t as easy to get at. If it’s a working, explorable laptop, as with Larsen’s, there’s a risk to that working status associated with temporarily physically removing the drive for imaging via a SATA cable—so we’d like to avoid opening the laptop up if possible, and find some other way of imaging the drive.

Imaging the laptop hard drive by connecting one of its exterior ports (e.g. USB) seems like the way to go, but Macs are finicky about showing up as drives on other computers.

If you want to see your Mac laptop as a drive mounted on another computer (and thus be able to image it), you’ll need to set the laptop to something called Target Disk Mode:

Target Disk Mode Steps

  1. The laptop to be imaged (e.g. our Larsen laptop) should be turned off.
  2. Hold down the t key and turn the laptop to be imaged on.
  3. Continue to hold down the t key until the target disk mode image appears on the screen (see photo example).
  4. You can now attach the target disk via firewire cable to a machine with BitCurator running in a partition, and the Mac laptop should show up as a connected drive like any other connected device.

Unfortunately, target disk mode can only transfer data over a firewire; using other ports/cables such as USB will not work. This presents three problems:

  1. Both your laptop and the machine running BitCurator must have firewire ports to allow for the firewire
  2. You’ll need to be running BitCurator on a partition and not as a virtual machine, as VirtualBox can’t handle firewire input
  3. If you want to use a hardware write-blocker, it will need to have both firewire input and output

This use case is Mac plus laptop-specific: that is, desktop Macs don’t use the compact unibody design of the laptop, so it’s far easier to open the case and connect the hard drive to a machine running BitCurator (thus there is no need to adopt Target Disk Mode). And non-Mac laptops will show up as image-able drives on other machines automatically, without the special needs of the Mac Target Disk Mode.

Our Choice: Imaging with BitCurator on a Partition

Imaging the Larsen Mac laptop using a firewire and PC partitioned with the BitCurator Ubuntu.
Imaging the Larsen Mac laptop using a firewire and PC partitioned with the BitCurator Ubuntu.

Why? We had the necessary components to let BitCurator recognize the Mac laptop as a drive: a firewire cable, a firewire port on the Larsen Mac, and a firewire port on a PC partitioned with BitCurator.

WiebeTech Forensic ComboDock used for write-blocking devices while they're being imaged
Our hardware write-blocker (WiebeTech Forensic ComboDock), used to protect devices from being written to while we’re imaging them.

We weren’t able to use our usual hardware write-blocker, as it only takes firewire input but doesn’t output it; BitCurator incorporates a feature that can mount devices safely, however, so we were still able to protect the device from being written back to.

Using BitCurator's default software write-blocker to protect the laptop.
Using BitCurator’s default software write-blocker to protect the laptop.

Follow these instructions to safely mount devices in BitCurator.

The software write-blocker safely mounts the laptop as a drive.
The software write-blocker safely mounts the laptop as a drive.

Next, we used BitCurator’s bundled Guymager software to forensically image the laptop (see these instructions or this video for steps to use Guymager yourself.) This produced a forensic image of the laptop, which we’ll be further exploring with BitCurator in a future post.

Using BitCurator's Guymager instance to forensically image the laptop.
Using BitCurator’s Guymager instance to forensically image the laptop.

In another future post, I’ll discuss an alternative approach for those of you who couldn’t follow these instructions (e.g. no firewire port, no BitCurator running on a partition).

Send us your suggestions for other difficult-to-image use cases and we’ll cover them in future posts!

Amanda Visconti is a MITH graduate research assistant on the BitCurator project, where she creates user-friendly technical documentation, develops and designs for the web, and researches software usability. As a Literature Ph.D. candidate, she blogs about her digital humanities work regularly at LiteratureGeek.com.