If you’d like to perform a clean install of macOS on your Mac, you’ll need to create a bootable USB installer. A clean install can be very helpful to clear your Mac of any unnecessary system files that may have piled up over time or to speed up your Mac.
Creating a bootable installer is very easy, and there are a variety of methods to do so. Follow the steps below to create a macOS bootable installer.
1. The first thing you’ll require for this guide is a 8GB (or larger) USB flash drive. It’s preferred that the flash drive be USB 3.0 to speed up the writing and installation process.
2. The macOS Mojave Installer file will be required as well. This can be downloaded directly from the Mac App Store. The installer is around 5.8GB in size, so you’ll need a fast Internet connection or some patience while it downloads.
Depending on your system, the App Store may either download the complete installer (6GB) or may download an incomplete installer (22MB). The installer will be downloaded into the “/Applications” folder where you can check the file size by right-clicking on the file, then clicking on “Get Info.” You’ll see the file size in the right corner like in the image below.
If the incomplete 22MB installer is downloaded, simply launch the installer – it should continue to complete the download. Once completed, quit the installer, and you should have the complete installer in your Applications folder.
Note: if you’re looking to create a bootable disk on a Mac that already has macOS Mojave installed, you may not be able to download the installer using the App Store, since macOS Mojave introduced software updates directly from System Preferences. In that case, use our third method detailed below to download and create a Mojave-bootable installer.
Format Your Disk
The first step to take before creating a bootable installer is to format your disk and change the drive format to “OS Extended.” You can do this with the following steps:
1. Open Disk Utility on your Mac from Spotlight or by navigating to “Applications -> Utilities -> Disk Utility.”
2. Select your USB drive from the pane on the left.
3. Click on Erase in the main panel.
4. Select the following options in the format menu:
- Name – enter “macOSInstaller” (without quotes) as the name. If you are going to use another name, you will have to make changes to the commands in the steps below.
- Format – select “OS X Extended (Journaled)” as the drive format.
Once you have selected these options, click on the “Erase” button to begin erasing the drive.
5. Your Mac should let you know when your drive is erased.
Use Terminal to Create a Bootable Installer
The first method we’ll cover uses Terminal to creating an installer. While entering code in Terminal may be a bit technical for normal users, this is Apple’s only officially-supported method to create a bootable installer. Follow the steps below to create an installer in Terminal:
1. Open Terminal on your Mac.
2. Paste the following command into Terminal:
3. Enter your admin password and press Enter to start the process. When prompted, press “Y” to agree to erase the volume.
Terminal may take a while to carry out the task, but it will keep on updating you with the progress of creating the installer. Once the entire process is done, Terminal will let you know. The drive will now be named as the original name of the installer, and you can now reboot your system and use the USB bootable installer to perform a clean install of macOS.
Using DiskMaker X
This is my personal favorite method to create a bootable installer, as it’s very simple and easy. Head over to Diskmaker’s website to download the app to create a bootable installer.
Once downloaded and installed, open Diskmaker X. (Note: if you’re already using macOS Mojave, macOS will ask you whether you’d like to allow DiskMaker to have access to System Events. Allow it to do so, which will open up the app.)
Simply point Diskmaker to the installer (if it doesn’t locate it by default), and select your USB drive. Diskmaker will start to make the installer and will do the rest for you.
Using dosdude Mojave (if you already have macOS Mojave installed on your system)
If you have macOS Mojave already installed on your system, you may have noticed that the App Store won’t let you download the macOS Mojave installer file. In this case, simply use dosdude Mojave to download and create a macOS Mojave bootable installer. Dosdude basically provides a patched version of macOS to allow installations on unsupported Mac hardware, but that’s not what we’re intending to do here. The downloaded installer is perfectly usable and works as expected, so this method can be used to create a bootable installer.
1. Download the dosdude Mojave installer tool by clicking on the Direct or Mirror link on their website.
2. Once downloaded, open the tool.
3. From the top menu in Tools, select “Download macOS Mojave.”
4. Select the location for the installer to save. (It’ll be a good idea to save it directly to the Applications folder to make creating the installer easy.)
5. The tool will start downloading the installer and will let you know once it’s done. Dosdude downloads the installer in different parts and compiles it in the end, so don’t worry if you find some unfamiliar names listed while it’s downloading.
In the end, just be sure to check the file size once completed to confirm that the entire installer has successfully downloaded.
6. Once the installer downloads, you can use the same app to create the USB bootable disk, or you can use the same installer and Diskmaker X (described above) to create the USB.
Once you’ve successfully create a bootable installer, you can easily do a clean install of macOS Mojave on your required system.