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On rare occasions, an Apple computer may fail to start due to a corrupted file system. This may happen after an attempted macOS upgrade. The usual recovery options recommended by Apple may not work. A possible alternative for recovery is to create a bootable installation USB device. This process requires a working Apple computer of similar model year and same processor (Intel or Apple M1).

STEP #1 — Save Your Files

With an Apple Mac computer that won’t start up normally, you will hopefully be able to use Target Mode by holding the letter “T” on the keyboard while starting the computer. This temporarily turns your computer into an external hard drive. With a USB cable or Thunderbolt cable you should be able to plug into a working computer and read the files from the non-working computer.

Ideally, you would have a solid state drive to copy your files onto. At a minimum, you would want to get your Desktop, Documents, Downloads, Pictures, and other folders copied.

Keep in mind that this won’t copy over any locally saved data such as notes, calendar, contacts, or other items saved to the Mac. Hopefully you don’t rely on local storage, but instead use your Apple iCloud account to sync data from your iCloud compatible Mac apps. If you have an Apple Time Machine backup of your files, then this copying process is just an additional measure of security.

STEP #2 — Clone Your Drive

In Step #1 above, we just copied the basic documents from your home folder to an external drive using a working computer to complete the process.

Here in Step #2, we want to copy the entire drive. Making an exact duplicate clone image is very important. You can use this copy of your drive later to recover all of your files, photos, settings, programs, and other data. If you have an Apple Time Machine backup of your files, then this copying process is just an additional measure of security.

With newer Apple Mac computers, removal of the internal drive is difficult or impossible. So you can’t just pull out the drive and use a dock or enclosure to help in this process. Instead, to make the copy, do the following:

  1. Have the problematic computer running in Target Mode, as explained in Step #1.
  2. On the working computer being used for this process, you will want to have Carbon Copy Cloner installed. [Learn More] This software will allow you to make a duplicate of the problematic drive.
  3. Use a new empty solid state drive as a target drive. It will get erased in the process.
  4. Run Carbon Copy Cloner and instruct the software to duplicate your problematic drive to the USB solid state drive.

You might be wondering what benefit there is in having a duplicate of a non-bootable drive. Despite the problem of failing to start, the file system is likely still usable. That will be explained in more detail below.

STEP #3 — Create a Bootable USB Drive

Using a computer of similar vintage to your non-working computer, follow the instructions outlined in the support document “How to create a bootable installer for macOS.” [View]

In those instructions, you’ll see options for creating different bootable versions of macOS on USB. You will need to choose a version that’s not too much newer or older than what’s compatible with your computer.

If you try creating a bootable USB, but choose a version of macOS that is too old, you will be told, “This version of the operating system is not compatible with this computer.” The same will happen if you choose a version of macOS that is too new. This will depend on what model of working computer you are using for this process.

Good choices might be macOS 10.13 High Sierra or macOS 10.15 Catalina.

You will download these from the App Store as instructed. The “Install macOS _____” utility program will show up alphabetically in your list of Applications, with the version of the OS named.

You won’t use the installation utility directly. Instead, you will follow the instructions to copy and paste the appropriate command in the Terminal interface, replacing the words MyVolume with the name of the USB device you have. This part may seem a bit confusing and foreign if you’ve not performed a process like this before.

For this part of the process, you need to open the Terminal program (found in Applications > Utilities), then paste in the correct command line (using command+v for paste) as described in the support document. At the end of that command line, replace MyVolume with whatever name your USB has. To make things easier, you may want to rename your USB drive to be something like “install” (without the quotes). At the end of that command line you copied and pasted, replace MyVolume with the word install.

If the process goes smoothly, the installation media will be created on your USB drive and it will be given a new name like “Install macOS Catalina.” This will all be done on the available working computer that you are using for this recovery process.

STEP #4 — macOS Installation and Recovery

Using the bootable USB installation media created in Step #3, insert the media into an available USB port on the non-working computer with the computer turned off.

Turn on the computer while holding down the option key. When given a choice of drive to startup with, choose the installation USB from the list. You may need to use the trackpad, mouse, or arrows to select the correct startup drive.

After starting, you should see a list of options. Choose the option to reinstall the operating system.

At some point during the reinstallation process, you should be given an option to recover your data from a “From a Mac, Time Machine backup or Startup disk.” This is the Migration Assistant which can be run separately later, or during the system installation and recovery. [Learn More]

For purposes of this process, we will choose this option and use the Startup disk copy/clone that was created in Step #2.

This is where the magic starts to happen. The working bootable new macOS that’s been installed, need not import the corrupted failing files from your old drive. The data to be copied will be the programs and files you had.

When this works properly, you’ll end up with a functioning Mac computer that can start and operate properly again.

STEP #5 — Updates

From the instructions above, you may have created a bootable installation USB with an older version of the operating system. You will want to go to the App Store to update to the most current macOS compatible with your computer. This may also be under System Preferences > Software Update.

If you have a newer Apple computer, then you should be able to upgrade to macOS 12.4 Monterey, which is current as of mid-2022 and should have the latest features and security available.

Other Scenarios and Considerations

These are some possible scenarios and considerations.

  • USER ACCOUNT RETAINED — In some situations, when you perform what seems to be a fresh installation of macOS from a bootable USB, you will be surprised to discover that the computer has your old login, and old user account, and all your old files. In other words, the macOS installation process in some situations will overwrite the operating system, but not the user home folder.
  • REPEATED TRIES — It’s possible the process described on this page will fail for some reason. You may try the entire process again and have luck the second or third time through.
  • ERASING DRIVE — Using the recovery media, as you startup, among the options will be the Disk Utility software. You can use that software to erase the computer’s drive. This will remove all your files, making Step #1 and Step#2 more important. Be very careful not to erase your files if you don’t have a backup copy of them.
  • FULL DRIVE — It’s possible that your computer was malfunctioning because the drive was full. If that happened, then the recovery steps on this page may not work since the data being restored exceeds the drive capacity. Restoring to a different computer with more capacity may work. Or, if you’re able to, consider removing one or a few really large files from the drive clone image created in Step #2 after making sure you have copies stored safely elsewhere.

Having some help from a tech savvy friend or computer support person can help.