One of OS X’s most versatile utilities is Disk Utility—a tool not only used for formatting and managing a variety of storage devices, but also employed for fixing damaged volumes and performing the ever-so-common “permissions fix” routine. While these features are relatively apparent, the program does have some often overlooked options that can be useful.
The first of these is the hidden checksumming routines for verifying disk image files. If you have an image, especially an older one, you might wish to verify its integrity before opening it. This is usually done when the image is opened, but you can also do it manually by adding an image to Disk Utility, selecting it, and choosing Images > Checksum > CRC-32 image checksum. This is fine, but often developers (including Apple) will issue updates and other software in disk images and include an SHA or MD5 checksum that you can use to verify the image’s integrity before opening it. However, these options are hidden in Disk Utility by default. To enable them, follow these steps:
After performing these steps, the Images > Checksum menu will have a number of additional options for verifying image checksums. Leaving these options exposed does no harm, but if you’d like to restore the menu to its default state, just follow the first two steps above and use this command in step 3:
One useful feature of Disk Utility is its ability to create a disk image from the contents of a folder, where, like compressing the folder into a zip archive, you can use the resulting image to easily transfer the items to an online disk or other location that doesn’t accept folders. The benefits of this are that you can not only use disk image compression to help save space, but can also take advantage of Apple’s robust AES-128 or AES-256 encryption for the disk image.
While you can access this feature using the File > New > Disk Image from Folder command, a quicker way is to simply drag your desired folder to the Disk Utility icon, which can be even more convenient if you have Disk Utility in your Dock. When you do this, a save dialogue box will appear that allows you to save the folder as an image immediately. Within this dialog box you can additionally configure compression and encryption settings.
Manage hidden volumes on your Mac
While Disk Utility will allow you to partition, repair, erase, and manage drives that you’ve attached and mounted on your Mac, it can also show those that are attached but currently not mounted. This can be useful for checking that a drive is connected and “seen” by your Mac, determining how it’s partitioned, and ensuring there aren’t obvious problems with the drive (for instance, you thought it had only one partition but two or more appear). You can additionally force-mount some volumes that are configured to remain hidden and then access their contents in the Finder.
To enable this feature you must expose Disk Utility’s Debug menu, which Apple uses for testing the app’s features during development. Here’s how:
With this menu enabled, choose the Show every partition command near the bottom and any hidden partitions will appear. You’ll see, for example, an EFI partition appear on bootable drives and a Recovery HD partition for those drives that hold one. To undo this option, first deselect the Show every partition command, repeat the procedure above, and then run the following command in step 3:
This last tip is a matter of quick convenience, particularly if you regularly check drives for errors. To verify a drive you’d normally ensure that Disk Utility’s First Aid tab was selected, choose an individual drive, and click the Verify Disk button in the bottom-right of the window. You’d then move on to another disk and repeat these steps. However, to speed things up you can verify more than one drive at a time, including all drives at once, if you wish.
To do this, simply hold down the Command key and, in the sidebar, select the volumes and disks that you want to verify (or press Command-A to select them all). Note that Select All means exactly what it says; you’ll select mounted disk images and optical disks along with your drives, so be sure to deselect any you don’t want to check by Command-clicking on them. With the desired devices selected you can then click Verify Disk. Disk Utility will then act on them in sequence.