How To Boot With Installer Dmg On A Flash Drive

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Disk Images, or DMGs, are a common way to compress large files on Mac computers, including apps. Because these files can often be a few gigabytes in size, a USB flash drive is usually the fastest way. Sep 29, 2018  VirtualBox was not designed to boot from a USB, but what if you want to boot from a USB Flash Drive in Virtualbox? Well there is a easy way to boot.

If you're thinking about installing macOS Catalina, the first thing to consider is whether you want to install it directly onto your Mac or create a bootable drive. You can use a bootable drive on a hard drive partition for dual-software installation, to install on multiple Macs in your home, or as a bootable drive if you can't use the Internet Recovery partition.

Note: These instructions require the use of Terminal. If you don't feel comfortable making changes to your Mac with Terminal, you can create a bootable disk using the DiskMaker X program.

Before you start

Before you get started, make sure you have a thumb drive with at least 15GB of storage, or a spare external hard drive (one you aren't planning to use for anything else). You'll also need to download macOS Catalina and ensure that it's sitting in your Applications folder.

Note: After macOS Catalina has downloaded, it will automatically launch the installer to begin the installation process. Quit the installer when this happens.

And please: Don't forget to back up your Mac before you do anything.

How to format your external drive for macOS Catalina

You'll need to start with a clean thumb drive or external hard drive in order to make it a bootable drive.

  1. Plug the thumb drive or cable for your hard drive into the appropriate port on your Mac.
  2. Click on Finder in your Dock to open a Finder window.

  3. Select Applications from the list on the left side of the window.

  4. Scroll down and double-click on Utilities.

  5. Scroll down and double-click on Disk Utility.

  6. Select your thumb drive or external drive under External.

  7. Click on the Erase tab at the top of the window.

  8. Note the name of your external hard drive (probably 'Untitled') because you will need it when you create a bootable drive. If you have more than one external drive with the same name, you will need to rename the drive you are using as a bootable installer now.
  9. If your Mac is using AFS+, select Mac OS Extended (Journaled) from the format list. If your Mac is using APFS, select APFS from the list of options.
  10. If Scheme is available, select GUID Partition Map.
  11. Click Erase.
  12. Click Done when the process is complete.

  13. Close the Disk Utility window.

Your thumb drive or external hard drive is now ready.

How to put macOS Catalina onto your external drive

Important: You will need to use an administrator account on your Mac in order to run the Terminal commands to create a boot drive. You'll also need to ensure that macOS Catalina is in your Applications folder and you'll need to know the name of the external drive.

  1. Click on Finder in your Dock to open a Finder window.

  2. Select Applications from the list on the left side of the window.

  3. Scroll down and double-click on Utilities.

  4. Scroll down and double click on Terminal.

  5. Recall the name of your formatted external drivewhen entering the following text into Terminal. If it is not named 'Untitled,' you will need to change the command syntax for the pathname where it says: Volumes/MyVolume. The name of the drive can't have any spaces and it is case sensitive.

  6. Enter the following text into Terminal (Don't forget to change the name 'Untitled' in the text below to the actual name of your external drive. Names are case sensitive and can't have any spacing.):

    sudo /Applications/Install macOS Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

  7. Hit the enter/return key.

  8. Enter your administrator account password. This is the password you use to make changes on your Mac or log in. No text will appear in Terminal when you enter the password.

The process could take a very long time, depending on the drive. When it is done, the Terminal window will report 'Done.'

How to install macOS Catalina with a bootable installer drive

Once macOS Catalina is installed on your external drive, you can install it on any Mac with the drive plugged into it. You can use this installer to upgrade your operating system easily on multiple Macs or to help downgrade if you decide you want to go back to an earlier version of macOS.

If you're downgrading from macOS Catalina, please check out this guide instead.

If you're upgrading to macOS Catalina, follow the steps below.

  1. Turn off the Mac you want to install macOS Catalina with the bootable installer drive.
  2. Connect the external drive to your Mac via the USB port.
  3. Turn on your Mac.
  4. Hold down the Option key when it starts up.
  5. Select the external drive with macOS Catalina on it from the list of systems to start up your computer.
  6. Follow the installation process when prompted.

Questions?

Do you have any questions about how to create a bootable drive for the macOS Catalina installer? Let us know in the comments.

Updated September 2019: Updated for macOS Catalina.

macOS Catalina

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These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

Download macOS

Find the appropriate download link in the upgrade instructions for each macOS version:

How To Boot With Installer Dmg On A Flash Drive
  • macOS Catalina, macOS Mojave, and macOS High Sierra download directly to your Applications folder as an app named Install macOS Catalina, Install macOS Mojave, or Install macOS High Sierra. If the installer opens after downloading, quit it without continuing installation.
    To get the required installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
  • macOS Sierra downloads as a disk image that contains a file named InstallOS.pkg. Open this file and follow the onscreen instructions. It installs an app named Install macOS Sierra into your Applications folder.
  • OS X El Capitan downloads as a disk image that contains a file named InstallMacOSX.pkg. Open this file and follow the onscreen instructions. It installs an app named Install OS X El Capitan into your Applications folder.

Use the 'createinstallmedia' command in Terminal

  1. Connect the USB flash drive or other volume that you're using for the bootable installer. Make sure that it has at least 12GB of available storage and is formatted as Mac OS Extended.
  2. Open Terminal, which is in the Utilities folder of your Applications folder.
  3. Type or paste one of the following commands in Terminal. These assume that the installer is still in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume in these commands with the name of your volume.
    Catalina:*
    Mojave:*

    High Sierra:*
    Sierra:
    El Capitan:
  4. Press Return after typing the command.
  5. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
  6. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the bootable installer is created.
  7. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Catalina. You can now quit Terminal and eject the volume.

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument, similar to the way this argument is used in the commands for Sierra and El Capitan.

Flash

Use the bootable installer

After creating the bootable installer, follow these steps to use it:

  1. Plug the bootable installer into a compatible Mac.
  2. Use Startup Manager or Startup Disk preferences to select the bootable installer as the startup disk, then start up from it. Your Mac will start up to macOS Recovery.
    Learn about selecting a startup disk, including what to do if your Mac doesn't start up from it.
  3. Choose your language, if prompted.
  4. A bootable installer doesn't download macOS from the Internet, but it does require the Internet to get information specific to your Mac model, such as firmware updates. If you need to connect to a Wi-Fi network, use the Wi-Fi menu in the menu bar.
  5. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.
How To Boot With Installer Dmg On A Flash Drive

Learn more

For more information about the createinstallmedia command and the arguments that you can use with it, make sure that the macOS installer is in your Applications folder, then enter this path in Terminal:

Catalina:

Mojave:

High Sierra:

Sierra:

How To Boot With Installer Dmg On A Flash Drive Mac

El Capitan: