It can be useful to have MacOS usb boot disk, eg. if need to erase the hard drive. After downloading MacOS disk image, follow this procedure to create a bootable usb drive.

Two options are described below. Use Option 1 to create a boot disk of a .dmg disk image and use Option 2 to make a boot disk of a Install MacOS [versionName].app.

Note: M1 Mac (Apple Silicon) and Intel i7 Mac have different processor architectures. Do not assume that the MacOS installer downloaded on an M1 will be compatible on an i7 mac.

Procedure

Option 1: Burning a .dmg

Insert a USB drive with minimum capacity 16GB

Open Balena Etcher imaging app which we will use to create a boot disk.

Applications > open Balena Etcher

Choose ‘Flash from file’ > select image file to burn

Select target destination drive

Option 2: Burning a Install\ Sequoia.app

The softwareupdate app downloads an installer application. This needs to be burned to boot disk with:

sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/[volname]

where volname is the name of your USB volume.

A non-empty storage disk will need to first be erased, which can be done with the Disk Utility app or on command line.

Troubleshooting

createinstallmedia hangs after erasing drive

If the createinstallmedia process does not progress after erasing the disk, it is likely that another app is monopolising the drive after it was remounted, preventing it from being written to by createinstallmedia. See which processes are using the drive:

sudo lsof +D /Volumes/[volname]

If it shows mds or mds_store, this is the Spotlight.app. Prevent Spotlight from reading the volume by opening:

System Preferences > Spotlight > Privacy and drag the /Volumes/[volname] folder from Finder into the box

Then reboot, and retry createinstallmedia.

References