How to Create a Bootable MacOS Catalina Installer Drive

Jul 14, 2020 - 18 Comments

How to make a MacOS Catalina beta bootable install drive

Some Mac users may wish to create a bootable MacOS Catalina installer drive, typically using a USB flash drive or with another similar small boot disk.

Bootable USB installers offer an easy way to upgrade multiple Macs to macOS Catalina, to perform clean installs of MacOS Catalina, to perform maintenance from a boot disk like formatting disks, modifying disk partitions, and performing restorations, and much more.

We’ll walk through how to create a boot USB install drive for MacOS Catalina 10.15.

Requirements to Create a Bootable macOS Catalina USB Install Drive

The following prerequisites are necessary to make a bootable installer drive for macOS Catalina:

The Mac will also need to be online so that it can download the MacOS Catalina installer, if that hasn’t already be accomplished.

How to Make a Bootable macOS Catalina 10.15 Beta USB Installer Drive

This process requires using the command line, if you are not comfortable using the Terminal than it is better to avoid this process. Mistakes with syntax can lead to permanent data loss, or the erasure and formatting of the wrong disk, so proceed at your own risk.

  1. Connect the USB flash drive to the Mac if you haven’t done so already, name the drive “UNTITLED”
  2. Open the “Terminal” application, it’s found in the Utilities folder and you can also launch it from hitting Command+Spacebar typing Terminal and hitting return
  3. Enter the following command at the Terminal command line, assuming “UNTITLED” is the name of the USB flash drive you want to make into the Mac Catalina installer boot disk:
  4. sudo /Applications/Install\ macOS\ --volume /Volumes/UNTITLED

  5. If the syntax is correct, hit the Enter/Return key and authenticate with the admin password as necessitated by sudo
  6. Let the creation process build the boot installer disk and complete, it may take a little while

After the MacOS Catalina 10.15 USB boot installer drive has been created, it will be mounted on the Mac. At this point it can be used like any other boot disk or installation disk.

The MacOS Catalina boot disk can be used with any MacOS Catalina compatible Mac.

* If you see a “command not found” error message in the terminal, it’s likely because there was a typo or syntax error, or because the “Install macOS” application file was not found in the /Applications/ folder where it is expected to be.

How to Boot with macOS Catalina USB Install Drive

To boot from the MacOS Catalina boot disk, connect it to a Mac, then reboot the computer and hold down the OPTION key to boot into the boot menu, where you will be able to choose the MacOS Catalina installer drive as a boot option.

  1. Connect the macOS Catalina install drive to the target Mac
  2. Reboot the Mac as usual
  3. Hold down the OPTION key upon system boot, and continue holding Option until you see the Mac boot menu
  4. Choose the macOS Catalina installer volume to boot from

The MacOS Catalina boot disk will allow you to install MacOS Catalina as an upgrade, and also to perform clean installations of macOS Catalina if desired. You can also access the regular bootable installer utilities, including Disk Utility for formatting and partitioning drives, and Time Machine recovery tools for restoring from backups.

Were you successful in making a MacOS Catalina bootable install drive? Did you use another method? Let us know in the comments whatever your experience has been.


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Posted by: Paul Horowitz in Mac OS, Tips & Tricks


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  1. Mimi says:

    This is the 3rd time I make a bootable drive. Withvery one of the 3 usb thumb drives that I used I got the same error message telling me that Catalina could not be installed because the copy of the install application is damaged. I downloaded Catalina from the Apple store! I also tried to install from the network but the install never ends, it goes into some sort of loop where the Apple logo keeps appearing and disappearing. The thing was running all night and never finished. When I plugged the Macbook air in Target mode to my MBP I saw that I had three drives! I erased all, started all over but going nowhere. Several times. Nothing works. I cannot even re-install the original system (Mavericks)

  2. Craig Reynolds says:

    THis seems like what I need, but it is not working quite right.

    I am trying to do this for an old (circa 2012 ) Mac that is running OS X Catalina.

    I downloaded the Catalina app to the applications folder on a second Mac running Big Sur. (Side note, the download tried to install too, which scared the hell out of me, but the install seemed to abort before going far enough to do any damage,

    I then ran the sudo command as directed, and everything SEEMED to work until the last step. It erased the disk (thumb drive), copied the file to the drive, and gave some sort of message about completion sucess, but the thumb drive kept flashing like something was going on. I left it like that for 45 minutes and it kept flashing. So I went back to finder and tried to eject. And it would not let me eject. I had to do a force eject. Seemed like a bad sign.

    So I tried to use it to reboot the old Mac. I got to the point where I could select the drive, and it gave me the circle with a line (do not enter) symbol for about 30 seconds and then just shut off.

    Repeated attempts had the same impact. Help?

    • Paul says:

      If the Mac is booting into a screen with a circle with a line through it, that typically means the version of macOS on the boot volume is not compatible with that Mac.

      It’s possible that the Mac you are trying to use the USB installer on is therefore not compatible with Catalina (or Big Sur for that matter).

      Putting aside the USB installer drive for a moment, you might try booting the Mac directly into Recovery Mode, or Internet Recovery Mode, by rebooting and holding down Command+R to enter into Recovery Mode. Once in Recovery Mode, use Disk Utility to repair the startup disk, and, if there is no working operating system, trying to reinstall MacOS from there. It will attempt to install whatever version of Mac OS came on the computer. (Make sure you have a backup of the important data just to be sure, before updating/installing any system software)

      Do you know what version of Mac OS X is actively on the Mac? If the iMac is definitely currently running Catalina, but won’t boot with a Catalina boot disk, perhaps Catalina was installed with one of the unofficial utilities (like DosDude) that allows to install macOS versions on unsupported Macs?

      Is it possible the iMac is a 2011 or earlier model, a year that is not compatible with Catalina? 2012 and later iMac models should be compatible with Catalina, they’re on the supported devices list:

      Other things potentially worth considering:
      – booting a different compatible Mac with the boot disk
      – trying a different USB thumb drive
      – trying a different USB port
      – using an earlier compatible macOS USB installer (macOS Mojave) then upgrading to Catalina manually
      – the internal Mac hard drive may be failing (but this would not explain the failure to boot from the USB bootable installer)

      Hope this helps, or offers some insight!

  3. Marina says:

    Oh boy, this really saved my MacBook, thank you! I tried installing Big Sur and, despite enough room, it crashed multiple times, rendering my drive unreachable.

    Using my iMac I performed every step (including reformatting the USB drive and erasing/remounting my MacBook drive) and have restored Catalina, this was brilliant!

  4. axel says:

    Worked for me! Going to be swapping the SSD on my 2015 MBP soon and plan on installing via USB.

  5. David says:

    Nov 17, 2020: Tried using these instructions and get an error in Terminal just after I type admin password:
    “/Applications/Install macOS does not appear to be a valid OS installer application.”

    To note: The “Install macOS Catalina” I downloaded from the app store is not a full version of Catalina, it is only 19.1 MB. Is that normal? I tried downloading multiple times with the same result.
    I’m currently running High Sierra 10.13.6

    • David says:

      UPDATE: I was able to get the full version throught the app store by using a friend’s laptop that is currently running Catalina.

  6. Mark Hennon says:

    Worked Great! Especially liked the Terminal download, which overcomes the “corrupt” message when trying to use previously-downloaded “aged” versions of macOS installers.

    Outstanding article–best method of all the many I’ve done in the past. THANK YOU!!!


  7. David says:

    Not sure why, but had to manually cd to the Resources folder. The command typed as provided from the default Terminal prompt failed as command “createinstallmedia” not found, however when the full string command “sudo …UNTITLED” was run from within the Resources folder worked a charm.

  8. Armando says:

    I cut and copied the terminal instruction replacing UNTITLED with my volume name.
    Terminal keeps asking me for a password. I provided the one I use to unlock the iMac (I have no other dealing with the Mac) but I keep on getting an erro

    • Paul says:

      Creating the bootable installer requires an admin password to use sudo, when requested enter the admin password for the current user account and then hit enter. The password doesn’t display as it’s being typed in Terminal as a security measure.

  9. Bill Turini says:

    Like a lot of the instructions on the site, it doesn’t work.

    You comment “assuming you have the installer application in the Applications directory …” Well, if it crashes because you don’t have the app, how do you get the app?

    • Paul says:

      Yes this does work Bill. Why didn’t you read the article? It covers specifically how MacOS Catalina bootable installer drives are made and what the requirements are to make them.

      It sounds like you don’t have the installer application which is obviously why you are not able to get it to work. Therefore the fault lies in something you are doing, not the technical process as written. If you want assistance you can be specific about what issue you are experiencing, but don’t make blanket false statements or disparaging claims about this site, our work, and our tutorials.

    • ebert says:

      Bill, download the Mac Catalina installer from App Store, then connect your formatted USB flash key and call it UNTITLED, then run this command in Terminal

      sudo /Applications/Install\ macOS\ --volume /Volumes/UNTITLED

      It definitely works, just made one!

      And thanks to Osxdaily for the guides, always amongst the best resources on the Apple web!

  10. Garth Fletcher says:

    Terminal instructions do not work.
    Tried them while booted to 10.15.15 for:
    Similar error in each case. Showing the 10.15.6 attempt:
    MacMini-X14:~ garth$ softwareupdate –fetch-full-installer –full-installer-version 10.15.6
    Downloading and installing 10.15.6 installer
    SUPreferenceManager: Failed to set object of class: __NSCFConstantString for key: LastRecommendedMajorOSBundleIdentifier with error: Error Domain=SUPreferenceManagerErrorDomain Code=1 “(null)”
    Installing: 54.0%
    Installing: 84.0%SUPreferenceManager: Failed to set object of class: __NSCFConstantString for key: LastRecommendedMajorOSBundleIdentifier with error: Error Domain=SUPreferenceManagerErrorDomain Code=1 “(null)”

    • Paul says:

      Garth, assuming you have the installer application in the Applications directory the only Terminal command you should need to make the bootable MacOS Catalina installer is as follows:

      sudo /Applications/Install\ macOS\ --volume /Volumes/UNTITLED

      replacing “UNTITLED” with the name of the volume to make into the boot installer.

      The download command (not necessary for creating the boot installer with the installer app already downloaded) may be failing because you’re not using two dashes — for the flags. Be sure the syntax is correct:

      softwareupdate --fetch-full-installer --full-installer-version 10.15.6

  11. Ian says:

    Previously, when I’m creating one of these boot drives using your instructions, I’ve always copied and pasted your command line entry as then I won’t have any entry mistakes. I’m sure probably everyone else does this also.

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