The macOS 10.14 Mojave public beta dropped yesterday and while some of you will go crazy and install it as your main OS, it is preferable to install it on an external drive for testing purposes only. While you can just download the installer as a developer or public beta tester and proceed to install it directly, creating an installation drive (e.g. on a pendrive) has its benefits, especially if you foresee the need to install Mojave more than once.

Requirements

macOS Mojave requires one of the following Macs:

• MacBook (early 2015 or newer),
• MacBook Air (mid 2012 or newer),
• MacBook Pro (mid 2012 or newer),
• Mac mini (late 2012 or newer),
• iMac (late 2012 or newer),
• iMac Pro (2017 or newer),
• Mac Pro (late 2013 or newer; mid 2010 and mid 2012 are supported when equipped with RX 560 or RX 580 GPUs).

You will also need:

• a pendrive, external SSD/HDD or a spare internal drive (Mac Pro),
• the administrator password.

Download

After you download the installer it will launch automatically. Close it and locate the file in your /Applications/ folder — it will be called Install macOS Mojave beta — just to make sure it’s there.

Prepare Your Drive

1. Connect your pendrive/drive to your Mac via USB.
2. Launch Disk Utility.
3. Find your drive in the list on the left. Double and triple check that you have the right drive!
4. Click on Erase in the toolbar.
5. Call your drive Mojave or whatever else you prefer. If you choose a different name, make sure to modify the Terminal command below appropriately.
6. Select Mac OS Extended (Journaled) and GUID Partition Map in the dialogue box.
7. Click Erase and wait for it to finish.
8. You can close Disk Utility after your drive is ready.

Create the Installer

1. Launch Terminal — you will find it in /Applications/Utilities (or just use Spotlight).
2. Enter the following command into Terminal, remembering to replace /Volumes/Mojave with whatever you named your drive:

   sudo /Applications/Install\ macOS\ Mojave\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Mojave --nointeraction --downloadassets

3. Press Enter.
4. Enter your admin password and press Enter again.

Wait until the process finishes — it could take over 30 minutes, depending on the speed of your drive.

Booting From the Installer

1. Connect the drive via USB to your Mac (if not already connected).
2. Restart your Mac.
3. As soon as the screen lights up, press and hold ⌥ on the keyboard.
4. You should be able to choose which drive you want to boot from — choose Install macOS Mojave beta.

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If you decide to install macOS Mojave over High Sierra, you will not lose your data (unless there is some sort of catastrophic failure; make sure to have a backup or three). Consider installing the new OS on a clean, external drive, to keep your existing installation intact — you will need to erase your SSD/HDD if you wish to downgrade to High Sierra.