This guide deals with 3 ways of making a boot disk from macOS, the first one is the fastest and is done via the Terminal from a command in macOS called createinstallmedia, the other 2 are older ways are done with a mixture of finder using Disk Utility and command line.
Download the macOS version you need but don’t install.
Attach your USB stick/drive.
Launch the Terminal from /Applications/Utilities and enter the command below and then your password when prompted, be sure to change the ‘Untitled‘ name in the below command to your external disk name:
Let it do its thing and there you have it, one bootable macOS drive.
This really is a super simple way – however if using the Terminal fills you with fear and dread, there are some GUI apps that can get the job done namely DiskMakerX and a new imaging tool that can clone a new disk very quickly – AutoDMG, although AutoDMG can not work with macOS Big Sur
Alternative Ways of building a Bootable macOS Disk.
An alternative way to make a boot disk of macOS (but not macOS Big Sur), first of all, get the app or download via the App store, if downloaded it will file in the folder Applications.
The example below uses OSX Mavericks.
Control / Left click Options, Show in Finder to get to the app, don’t install at this stage.
Located in the Applications Folder
Finding the InstallESD.dmg
To find the actual InstallESD.dmg file, control/left click the ‘Install macOS’ app and choose show contents – then navigate to Shared Support folder.
Control/Right click to show contents
Navigate to Shared Support folder to see the InstallESD.dmg file
Mount InstallESD.dmg
Double click to mount the image.
Make Invisible Files Visible
We need to see the BaseSystem.dmg inside the InstallESD.dmg
This will show all invisible files have a look inside the mounted InstallESD.dmg
Mount an External Disk
Attach a USB/external drive – this guide uses the external drive name called BootDisk, you need to make sure the format is correct, it needs to be Mac OSX Extended Journaled – if it’s not you can format that in Disk Utility.
Launch Disk Utility
Launch Disk Utility as found in Applications/Utilities and go to the Restore tab.
Drag BaseSystem.dmg to the Source field and your external disk to the Destination and click Restore.
This will mount your new macOS external disk and name it OSX Base System – but we need to add the packages.
Fix the Packages
Couple of things to fix in the newly created boot disk, remove the Packagealias at System/Installation/ folder
Now from the previously mounted InstallESD.dmg copy over the Packages folder to the same location where we just removed the alias above.
Will take a while as it holds all the install packages.
Job done now you can boot from the OSX 10.9 disk.
Make the Visible back to Invisible
If you want all to return back to normal and hide the system files run a couple more commands in the Terminal
This puts you back in the Finder in front of the newly mounted InstallESD.dmg, go back to Terminal and clone the BaseSystem.dmg to the remote USB drive
And there it is! – to eject the new bootable USB OSX Mavericks 10.9 disk ‘cd’ to home and eject
cd ~/
hdiutil eject /Volumes/OS\ X\ Base\ System/
Now you can boot up from your newly bootable disk and either Install OSX10.9 on another device or use the Terminal/Disk Utility or Firmware Password Utilities on another device.
