Troubleshooting OS X can be accomplished in a myriad of different ways. Given how resilient the OS is, most of the time, tasks take place directly from the startup drive itself, with little to no worry of data loss or corruption.
Since OS X Lion, installations create a recovery partition to assist in resolving deeper issues that could prevent computers from booting into OS X successfully or otherwise limit access to data.
However, what do you do when the disk itself — not just a system file or partition — is the problem? How do you troubleshoot the computer when the recovery partition isn't accessible or simply doesn't exist?
The solution is to boot the computer from an external device that has a full installation of OS X. Similar to booting from a USB flash drive to install a fresh copy of OS X, the method outlined below actually takes it a step further by creating a live, fully functioning OS X environment that can be used to boot from, further allowing sys admins to perform troubleshooting, run applications, access precious data, or backup a failing device.
Before you install OS X, let's review the requirements needed to create an emergency disk:
- Apple OS X Installer App (10.7+) from the Mac App Store
- Apple computer
- External media with at least 8 GB of storage space available* (USB flash drive, SD card, or external hard drive)
* Note: According to Apple's OS X Yosemite minimum requirements, only 8 GB of available storage are required in theory — but in practice, due to the way gigabytes are converted mathematically, you may encounter an insufficient space error when attempting to install OS X on your media. It's advisable to use a higher capacity drive whenever possible, especially if you wish to be able to install applications on the drive and/or backup/recover data. Common uses such as those will certainly require additional free storage space and should be accounted for prior to purchasing a spare drive.
With the necessary hardware/software in place, follow the steps below to create your emergency boot drive.
- If you've already formatted the drive for OS X, skip down to step #6. If not, launch Disk Utility.app from Applications | Utilities (Figure A).
- Select the Partition tab, and select 1 Partition from the Partition Layout drop-down window.
- Select OS X Extended (Journaled) from the Format drop-down menu — and optionally, give the drive a Name (Figure B).
- Click the Options button, and select GUID Partition Table, then click the OK button to return to the previous screen (Figure C).
- Clicking the Apply button will prompt you to confirm the changes. Click the Partition button to begin the partitioning process (Figure D).
- Depending on the size of the media, the process could take several minutes, though it's generally a very quick procedure (Figure E).
- Once the partition has been created, close Disk Utility.
- Launch the OS X Installer.app and the welcome screen will greet you. Click Continue to begin (Figure F).
- On the next page, click Agree if you agree with Apple's software license agreement (Figure G).
- You will be prompted to click the Agree button once more time to confirm (Figure H).
- At the install page, only locally installed hard disks will appear by default (Figure I).
- However, by clicking Show All Disks... externally connected media and drives will be shown. Select the device you wish to install OS X onto, and then click Install to proceed with the process (Figure J).
- If you're prompted to authenticate as an administrator, enter the administrator-level credentials and click the OK button to authenticate (Figure K).
- The installer will prepare the destination drive momentarily and then restart the computer to perform the remainder of the operation (Figure L).
Once the computer reboots, it will install OS X onto the destination drive/media as it normally would on any other hard drive or SSD. The speed at which the installation occurs will vary greatly on the media/drive used. Typically, external hard drives have a faster read/write speed than, say, the average USB 2.0 flash drive. Using the fastest media or external drive connections available to you will cut the installation time dramatically. A USB 3.0 or Thunderbolt drive would be several times faster than a professional-class SDHC card, though an SD card is much more portable and takes up less space in your troubleshooting kit than an external drive — even a 2.5" one.
Upon the final reboot, the Mac will boot to the newly installed media/drive and initiate the post-install procedures, which consist of connecting to Wi-Fi, creating a user account, and setting the time/date. Once that's been completed, the computer will boot into the desktop of the newly installed emergency boot drive.
As with any computing environment, the emergency boot drive will need maintenance and upkeep from time to time. System updates are just as crucial as on a production node, especially since the last thing you'd want is for your emergency disk to fail when you need it the most. Additionally, applications, scripts, or any other troubleshooting tricks you've come to rely on may be copied and/or installed on this drive to aide in future troubleshooting sessions, as needed.
Stay focused on addressing the basic needs of a potentially failed device when creating a drive like this. Especially if storage space is minimal, common sense should indicate that including the most recent combo update or installing a data recovery application would better utilize the limited space than including versions of common apps, such as Adobe Flash or Google Chrome, which update too frequently and require administrative overhead. Ultimately, your time is better spent on getting production machines back online and communicating again.
If you've created an emergency boot drive for OS X on external media, what tips would you include to make this process as smooth as possible? Share your experience in the discussion thread below.
Jesus Vigo is a Network Administrator by day and owner of Mac|Jesus, LLC, specializing in Mac and Windows integration and providing solutions to small- and medium-size businesses. He brings 19 years of experience and multiple certifications from several vendors, including Apple and CompTIA.