How to create a macOS 10.15 Catalina USB installer

This guide will show you how to make an install drive from the macOS Catalina 10.15 application. Having an install drive allows for deployment to multiple computers without re-downloading, performing clean installs, and booting to the installer’s built-in recovery tools for troubleshooting.

To get started you’ll need the Install macOS Catalina application and an external storage drive larger than 8GB. A USB thumb drive is usually best for this, but you could also use an SD card or an external hard drive partition.

How to create a macOS Catalina installer

1) Download the Install macOS Catalina application from the Mac App Store.

If you want to download a Beta version instead, the process is slightly different:

Paid developers can download the Beta Access Utility from the Apple Developer portal downloads section. Once installed on your computer, it will begin downloading the Developer Beta.

Other users can join the Public Beta for free. You will then be provided with a different version of the Beta Access Utility. Once installed on your computer, it will begin downloading the Public Beta.

2) Once the download is finished, your Mac will launch the installer app. Quit it, open your /Applications folder and find the installer there. Don’t rename the file or move it out of /Applications.

3) Format your >8GB drive to GUID Partition Map and Mac OS Extended (Journaled); this can be done from the Disk Utility application. This will wipe the drive completely.

Erase drive

4) Name the formatted USB drive USB.

5) Now open up Terminal and paste in this command:

sudo /Applications/Install\ macOS\ --volume /Volumes/USB --nointeraction

If you are creating an install USB from a Beta version of Catalina, you’ll need to update the command to list the correct name of the installer in your Applications folder. For example, if the installer is called Install macOS Catalina Public Beta, you would use this command instead:

sudo /Applications/Install\ macOS\ Catalina\ Public\ --volume /Volumes/USB --nointeraction

Be sure to update the command based on what the installer is called, and not just blindly use the command above for all situations.

  • If you want to be asked for confirmation before erasing the drive, remove “–nointeraction” from the command.
  • The “–downloadassets” flag was introduced with macOS Mojave. It downloads assets which may be required during installation. This is presumably helpful for faster or offline installations, though I haven’t noticed any difference. I wouldn’t bother with it personally, but feel free. The command works fine without the flag.
  • Older versions of macOS used an “–applicationpath” flag in this command, but this is now deprecated and will cause an error if used. Use the command we have provided above, instead of the old command mentioned in guides which were written for previous versions of macOS.

6) Hit Enter to issue the command, and put in your password when prompted. Terminal will inform you when the drive has been successfully created, and it will appear on the desktop entitled Install macOS Catalina.

How to use the macOS Catalina USB installer

1) Shut down your computer and insert the USB drive.

2) Start the computer whilst holding down the Option (⌥) key.

3) The Startup Manager will show a list of available drives. Select Install macOS Catalina to boot from the USB drive.

4) You can now install macOS Catalina as you like. The installer allows you to reformat your startup drive and other storage disks too. Tools such as Terminal, Startup Disk, and Firmware Password Utility are accessible from the top-bar menus.

Enjoy trying out Apple’s newest offering! Remember to back up your data before performing an upgrade to a new OS, particularly if you are testing out a beta version of Catalina.

Your USB install drive can be used to troubleshoot your Mac if it becomes corrupted and can’t make use of its own Recovery partition. The ability to reinstall the operating system or use Terminal from the drive is extremely useful. You can also use it to install Catalina to other computers without having to re-download the installer each time.

Need help with this guide? Ask your questions below!