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Create a MacOS USB boot stick

Sometimes booting into Recovery Mode fails. Partly because your Mac is too old for that, or the partition has become corrupt. Another possibility is that the internet is down, just when your Mac is struggling and needs a clean system.
Here's a solution: boot up and install a new MacOS via a USB Stick. It is therefore useful to have such a stick in advance. So don't wait until you get into trouble.
It takes some actions that you are not used to on the Mac; you have to work with a text command. However, it is a cut and paste case, so there is no need to be scared.

How to make a Mac OS Big Sur USB boot stick
What you do first is download the separate installation file of your MacOS.
For this you go to the App Store. Find MacOS Big Sur and choose 'download':

This will take a while, depending on the speed of your internet connection. The file is 12 GigaByte:

After the download, you will find it in the Applications folder:

The USB stick
Now insert the USB stick that you want to use in your Mac. The stick must be at least 16 GigaByte in size and preferably a fast one.
It does not matter if the stick has already been formatted for the Mac.
The Mac itself does that. It is important that you give the stick exactly this name: 'MyVolume. You do this by double clicking on the name until the text turns blue:

Note: This name is not mandatory, it is the name Apple uses in its code. If you give another one, you will have to adjust the code. Which is nonsense because the stick will be deleted anyway.

Now find the 'Terminal' program in the folder Applications => Utilities:

With the help of a text command you now make sure that:
a. the stick is deleted
b. the installation file of MacOS Big Sur is correctly placed on the stick.

Note: Drag and drop is not going to work here!

Apple tells you all about it: Create a bootable installer for macOS.

Copy code
You copy the complete code that you find on the Apple page. This is the code for MacOS Big Sur:

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

So select all, choose Command-C (or 'Copy' from the 'Edit' Menu).

Now go to Terminal. Using Command-V (or 'Paste' from the 'Edit' Menu), paste the entire code into the window:

Tap the Return key. You will now be asked for an administrator password:

Type that in and then the Return key again. Now you will be asked if you really want it. Enter 'Y' if so:

Security question
Now you will be asked to give Terminal permission:

Now the process will start. First, the USB disk is erased. That goes very quickly.
Terminal shows you how far it is as a percentage:

Immediately afterwards, he will turn the USB stick into a bootable disk. It takes a long time to reach 100%.

'Making disk bootable' has to happen anyway! If that doesn't show, take a look at the bottom of this page under 'TIP'.


Test the boot stick
When it is ready you can test the USB stick. That is wise, because you have to be able to rely on it in an emergency.
You do this by doing a Restart. Hold down the Option (Alt) key after the startup chime and before you see the white apple (M1 Macs see gray area below).
If everything went well, you will see the USB stick as a boot disk:

Boot the Mac from the drive by clicking on it and a moment later you will see this:

Have you succeeded?
Good; in case the internet is down when your Mac is giving you serious trouble, you're in the right place.

M1 Mac: boot from USB stick
Holding the boot button for ten seconds on an M1 Mac will produce this screen. Choose 'Options' to boot the Mac from USB Stick:

A so-called 'Bootable USB stick' is not just for emergencies
Such a stick is also useful if you have to install several Macs. You don't have to download that 12 GigaByte every time.

Older MacOS systems
A bootable USB stick is especially useful if your Mac OS is a bit older. You may not be able to install older MacOS from Recovery. This has to do with the date of the certificates.
The solution is to download them separately and create a bootable USB stick. Apple tells you all about it, at the bottom of this article: How to Create a Bootable Installer for macOS.

MacOS Big Sur: Allow Terminal to access your hard drive
Go to System Preferences => Security & Privacy and choose 'Privacy'. Open the padlock through enter an Administrator password.
In the left row it says 'Full disk access'. Select it and check 'Terminal' on the right. Now it should work:

Note: You can withdraw this permission afterwards, if you wish.

The next chapter is:
making backups

hardware trouble

Disclaimer: MacMiep is independent. This means she writes what she wants, based on 30 years of Mac-experience. She doesn't get paid for stories (positive or negative) on this website. MacMiep is not interested in your data. However, she does use Google's services. Google is indeed interested. Are you happy with MacMiep? Please support your local cat shelter.