Instead of replacing your existing macOS Sierra installation with macOS High Sierra, you can dual boot both versions of the operating system. This way, you can keep your existing installation safe while testing out the new beta version of macOS 10.13 High Sierra.
Before starting, please note the following:
- Backup your data using Time Machine to an external drive, to avoid any data loss.
- Make sure that your Mac is compatible with macOS. Check the compatibility list here.
- Download the latest version of macOS High Sierra. At the time of writing this guide, only the first developer preview is out while a public beta is expected later this month.
- Use a fast USB flash drive, at least 8 GB in storage size. We will use this to create a bootable USB drive for High Sierra.
Dual boot macOS High Sierra with macOS Sierra
- Download macOS High Sierra from the Mac App Store and make sure that it shows up in your Applications folder. Follow our guide here to download it.
- Plugin your USB drive and name it macOS drive or something easy to remember with.
- Open Terminal in macOS and enter the following command to create a bootable macOS USB drive:
sudo /Applications/Install\ macOS\ 10.13\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/macOS--applicationpath /Applications/Install\ macOS\ 10.13\ Beta.app --nointeraction &&say Ready
- After your bootable USB is created, we will re-partition the disk in your Mac to make space for High Sierra. Open Disk Utility, select your drive and click Partition in the toolbar. You should see a menu as shown below. Resize the new partition with the format macOS Extended (Journaled) and select the size. Note that the size that you enter here is the size of the current partition. So, entering 70 GB would mean that your Sierra partition would be resized to 70 GB and the rest will be reserved for your High Sierra installation.
- Now starts the last step and most important step. We have the partition ready as well as the bootable USB drive. Reboot your Mac and press and hold the Option key while it boots. You will see the startup manager. Select your USB drive here as the boot device and it will load the installer.
- During the installation process, make sure that you select the new partition you created i step 4, so that you can dual boot both operating systems. Make sure to select the ‘Upgrade Macintosh HD to APFS’ option in the installer. This is a non-destructive upgrade and will take some time but you will end up using Apple’s new file system, which is one of the headline features of High Sierra.
If you run into any issues while following the above guide, let us know in the comments below and we would be glad to help.