Identify the Version of Mac OS on the Recovery Partition

When Apple released OS X Lion in 2010, it included a hidden partition known as the Recovery HD on the Mac's startup drive. It is a special partition that is used for troubleshooting a Mac, fixing common startup problems, or—if worse comes to worst—reinstalling macOS or OS X.

Competing computing systems offer similar capabilities, but one thing that sets the Mac's Recovery HD system apart from others is that the operating system is installed using the internet to download a fresh install of macOS or OS X when needed.

Which Version of the OS Does Recovery HD Install?

When you buy a new Mac, it has the most current version of the operating system installed on it, and that's what is tied to the Recovery HD. If you need to reinstall the system using Recovery HD, it installs the same version of the operating system as is on your new computer.

If you didn't buy a new Mac recently, you probably updated the operating system when Apple made an upgrade available, perhaps several times.

So, what if your Mac had OS X Mountain Lion (10.8) when you bought it, and then you updated to OS X Mavericks (10.9) or OS X Yosemite (10.10)? Is the Recovery HD volume updated to the newer OS, or do you end up back with OS X Lion?

When you perform a major upgrade, the Recovery HD or macOS Recovery partition is also upgraded to the same version of macOS or OS X. So, an upgrade from a Mac running Mountain Lion results in a Recovery HD linked to OS X Mountain Lion. Likewise, if you skip upgrading to Mavericks and then upgrade to OS X Yosemite, the Recovery HD partition reflects the change and is linked to OS X Yosemite.

Copies of the Recovery HD

As a troubleshooting tactic, Mac users are encouraged to make a copy of the Recovery HD on at least one bootable device—an external drive, a second internal drive for Macs that support multiple drives, or a USB flash drive.

The idea is a simple one; you can't have too many working recovery HD volumes, should you ever need to make use of one. This becomes apparent when you encounter startup problems with your Mac's drive, only to discover that the Recovery HD also isn't working because it's part of the same startup drive.

So, now you have multiple Recovery HD partitions on various bootable volumes. Which one do you use, and how can you tell which version of the Mac OS will be installed, should you need to reinstall the OS?

Identifying the OS Version Linked to a Recovery HD

The easiest way to find out which version of the Mac OS is tied to a Recovery HD partition is to reboot your Mac using the Startup Manager.

Connect any external drive or USB flash drive that contains a Recovery HD partition and hold down the Option key while you power on or restart your Mac. This brings up the Startup Manager, which displays all the bootable devices connected to your Mac, including your Recovery HD partitions.

The Recovery HD partitions are displayed in the format Recovery-xx.xx.xx, where the xx's are replaced with the version number of the Mac operating system associated with the Recovery HD partition. For example, the Startup Manager may show this:

CaseyTNG   Recovery-10.13.2  Recovery-10.12.6   Recovery-10.11

There are four bootable devices on the list. CaseyTNG is the current startup drive, and the three Recovery HD partitions each display a different associated Mac OS version. Select the Recovery HD partition you want to use from this list.

It's best to use the Recovery HD partition that's associated with the version of OS X running on the startup device that's having problems. If that's not possible, use the closest match you have available.