Every so often, you may find yourself in a situation where you need to reinstall macOS Big Sur and everything is failing on you. Installing from macOS Recovery? Not working via the usual methods. Building a USB installer? Left the flash drive in your other pants. Using DFU mode and Apple Configurator on an Apple Silicon Mac? You need a second Mac to use this process and you just have the one Mac available.
For those situations, there’s one more option when you’ve exhausted all of the others. For more details, please see below the jump.
This method is referenced in the following Apple KBase article:
https://support.apple.com/HT211983
It involves the following:
- Wiping the drive that you intend to install macOS Big Sur onto.
- Creating the proper directory structure manually on the drive.
- Copying the Install macOS app available in macOS Recovery manually into the proper location on the drive
- Using the curl tool to download the needed installer files onto the drive
- Launching the Install macOS app
- Using the Install macOS app to install macOS Big Sur
To install macOS Big Sur using the methods described above, use the procedure below:
2. Erase your Mac’s startup drive using the correct procedure for your Mac model:
Macs with Intel processors: https://support.apple.com/HT208496
Apple Silicon Macs: https://support.apple.com/kb/HT212030
By default, an erased drive is named Untitled. We’ll be using that drive name for the examples shown in this post.
2. Once the drive is erased, open Safari and go to the following URL:
https://support.apple.com/HT211983
3. Scroll to the bottom of the KBase article and locate the Or use Terminal to reinstall section.
4. Copy the complete command which begins with curl. (This will save a lot of typing later.)
5. Quit Safari.
6. Open Terminal.
7. Run the following command to change to using the drive named Untitled:
cd "/Volumes/Untitled"
8. Run the following command to create a directory named private on the Untitled drive as well as a sub-directory inside of private which is named tmp:
mkdir -p private/tmp
9. Run the following command to copy the Install macOS Big Sur.app application from macOS Recovery to the /Volumes/Untitled/private/tmp directory.
cp -R "/Install macOS Big Sur.app" private/tmp
10. Run the following command to change to the /Volumes/Untitled/private/tmp/Install macOS Big Sur.app directory:
cd "private/tmp/Install macOS Big Sur.app"
11. Run the following command to create a directory named Contents on the Untitled drive as well as a sub-directory inside of Contents which is named SharedSupport:
mkdir Contents/SharedSupport
12. Paste the copied curl command and hit the enter key on your keyboard to have the macOS Big Sur installer files be downloaded into a file named SharedSupport.dmg. The SharedSupport.dmg will be located in /Volumes/Untitled/private/tmp/Install macOS Big Sur.app directory/Contents/SharedSupport.
curl -L -o Contents/SharedSupport/SharedSupport.dmg https://swcdn.apple.com/content/downloads/01/60/071-72781-A_CZ1D1FENMH/a09fvud3xxgih7qyau9a7lhtspho36mp0l/InstallAssistant.pkg
13. Once curl has finished downloading /Volumes/Untitled/private/tmp/Install macOS Big Sur.app directory/Contents/SharedSupport/SharedSupport.dmg, run the following command to launch the macOS Big Sur installer.
./Contents/MacOS/InstallAssistant_springboard
14. Follow the prompts to install macOS Big Sur.
