Understand recoveryOS
Apple’s separate recovery operating system (recoveryOS) has been a vital part of troubleshooting your Mac since it first appeared about a decade ago. It’s also where you go when you need to make changes to certain low-level and security settings that can’t be modified while macOS is running.
Restart in recoveryOS
To enter recoveryOS on your M-series Mac:
Choose Apple > Shut Down.
When you see your Mac has powered down, hold down the power button until you see a prompt that says “Loading startup options.”
One or more drives appear along with a gear icon labeled Options. To continue down the path of using apps like Disk Utility or reinstalling macOS, select Options and click Continue.
recoveryOS prompts you to “Select a user you know the password for” (Figure 18). Choose a user from the list, and click Next.
Figure 18: Select an account and then enter its password. Enter the password for that account and click Continue.
A screen appears on which you can click to select from among four tasks or choose other options from the Utilities or Apple menu.
If you reach step 4 above and have somehow forgotten the passwords for all accounts that are valid to start up your Mac, click the “Forgot all passwords?” link. You’re then taken through a series of possibilities to unlock the computer. This starts with entering the Apple ID (partially revealed) and password associated with the active account. If you don’t know that, you can click “Forgot Apple ID or password?” Ultimately, you have to remember something.
Fallback To Move Forward
You may be fascinated to discover that recoveryOS has a doppelgänger: there’s not just one recoveryOS, but two of them. The primary one works as expected and is booted into as above. But Apple has hidden a second fallback recoveryOS, that’s a failsafe in case something goes wrong with the primary system.
In an ideal world, you should never need to trigger fallback recoveryOS: either you never need it, or it will automatically boot if it detects a problem with the primary recoveryOS.
The main difference between the two is that you can’t apply security policy changes using the fallback version as described in Modify Startup Security with a Utility. Instead, you can reinstall macOS, which will fix the original recoveryOS.
To restart purposely into fallback recoveryOS, in step 2 above, double-press and hold the power button instead of pressing down and holding it. This press/release/hold sequence triggers the emergency backup.
The fallback recoveryOS coupled with the firmware revive and restore process I explain later in this chapter, in Revive or Restore a Startup Volume, replaces and expands on the Internet Recovery feature that’s built into the boot ROM (read-only memory silicon chip) of an Intel Mac.
An Intel Mac’s Internet Recovery feature is a last-ditch option that can be triggered by holding down ⌘-Option-R, and which downloads and installs the recoveryOS via an internet connection. In contrast, fallback recoveryOS is part of a disk-based installation, and can fail if the SSD fails or the macOS Data volume is corrupted. There’s no recovery option built into ROM.
However, the revive and restore operations described later rely on a special mode you can invoke in M-series Macs (and Intel Macs with a T2 chip) that let you connect to the internet to repair firmware required for booting up, or overwrite it if it can’t be repaired. This is a bit more complicated than plain Internet Recovery, but provides more nuance for fixing a problem, too.
Share Within recoveryOS
As part of enhanced protections on M-series Macs, Apple no longer allows the simple option of restarting your Mac and holding down the T key to enable Target Disk Mode and have the Mac mounted on another Mac as a volume.
Instead, you have to follow these steps to share a volume, which makes it appear as a networked volume on the other Mac:
Restart in recoveryOS as noted above in Restart in recoveryOS.
Choose Utilities > Share Disk.
Select the disk to share, and click Start Sharing (Figure 19).
Figure 19: Sharing your M-series Mac as a disk requires using a special recovery mode. Connect your Mac to another one via a USB data cable (with Type-A or USB-C plugs on either or both ends) or a Thunderbolt 3 cable.
On the other Mac in the Finder, click the Network link in the sidebar to view the shared Mac’s volume.
Click the Mac in the main window, click Connect As in the upper-right corner, select Guest as the user, and click Connect.
You can now transfer files between the two computers. When complete, eject the mounted Mac volume by selecting it and dragging it to the Eject icon in the Dock or pressing ⌘-E.
Master the Ins and Outs of Recovery
recoveryOS includes several other features, presented as apps, some of which are labeled macOS Recovery:
Restore from Time Machine: Use this option to restore the Data volume of a backup.
Reinstall macOS Big Sur/Monterey/Ventura: This allows you to reinstall macOS on the internal or on an external volume.
Safari: You can access Safari via a sort of guest account that lets you browse, but doesn’t let you launch other apps or store permanent settings.
Disk Utility: Sometimes you need to run operations against the internal or other volumes without being booted into macOS.
Utilities > Startup Security Utility: To learn more about the Startup Security Utility, see Modify Startup Security with a Utility.
Utilities > Terminal: Launch Terminal to perform command-line actions while in recoveryOS.
Apple > Startup Disk: Startup Disk is an app of sorts instead of a preference pane in recoveryOS. To learn more about setting the startup volume, see Make a Bootable Clone.
Some of the above options require internet access. recoveryOS retains previous selections and passwords for Wi-Fi networks you’ve already connected to. If you don’t see an active connection, however, click the Wi-Fi 
icon, select a network, and enter its password if it has one.
Reinstall with the Personalization Error
If you erase the volume group on the startup volume, and potentially in some other rare circumstances, you might attempt to reinstall macOS from recoveryOS and receive the error, “An error occurred while preparing the update. Failed to personalize the software update. Please try again.”
Something went wrong that prevented recoveryOS from creating the specific installation for your Mac required by an M-series chip’s baseline security as described in Modify Startup Security with a Utility. You can opt to use the steps below in Revive or Restore a Startup Volume, but there’s a simple way to try first.
It requires that you navigate to a hidden Recovery Assistant that guides you through a more rigorous scrubbing of the previous macOS installation.
Here’s how it works:
Restart in recoveryOS by following the steps in Restart in recoveryOS until you see menus and the window with four options.
The following sub-steps, 2a through 2g, must be followed twice:
Choose Utilities > Terminal.
At the command-line prompt, type
resetpasswordand press Return. This launches an app.Select the window labeled Reset Password.
Choose Recovery Assistant > Erase Mac.
Pick a language if prompted.
You may also be prompted that macOS needs to be reinstalled. If so, click macOS Utilities, and wait for activation, which requires an internet connection.
Once Recovery Assistant says that macOS is now activated, click Exit to Recovery Utilities.
Now return to step 2a and perform steps 2a through 2g once more.
On your second exit to Recovery Utilities, click Reinstall macOS Big Sur/Monterey/Ventura, and follow the installation steps.
Revive or Restore a Startup Volume
Your Mac might become unresponsive and not start up properly in either macOS or recoveryOS in rare circumstances. If recoveryOS won’t startup normally or with the automatic fallback recoveryOS, and you can’t trigger fallback recoveryOS manually as discussed in the previous section, you may have a problem with your Mac’s firmware that handles startup and some aspects of encryption.
Apple offers two special operations—revive and restore—accessible through a piece of free software it makes available largely for system administrators called Apple Configurator 2.
Here’s the difference between the two operations:
Revive fixes the firmware and other problems without erasing any of your data. You may have to reinstall macOS afterwards, but your files will be retained.
Restore is a last-ditch effort to get your Mac to boot again. It performs a full reset that blasts the firmware, dumping anything stored in the Secure Enclave, and also erases your drive en route to reinstalling macOS. None of your data is retained.
You also need a USB-C cable that supports just USB 3—that is, it has USB-C on both ends and isn’t a Thunderbolt 3/4 cable. If it’s a high-wattage charging cable, it must also support data, which includes the USB-C cable Apple ships with Apple laptops to connect to an AC adapter. (Read my article on determining which kind of USB-C cable you have.)
The steps are quite complicated, and Apple offers an extensive support document with illustrations that will help. The article has even more details, along with some graphics, than what follows if you need additional steps.
Here’s what to do:
Install Configurator 2 on the Mac that will be reviving or restoring the M-series one. (It requires Catalina or later.)
Plug the restoring Mac into power if it’s a laptop, and make sure it has an active internet connection.
Connect the USB-C cable between the restoring Mac and the appropriate port on the unresponsive M-series Mac:
On a Mac mini or iMac with two USB-C ports, that’s the left of the two Thunderbolt 3 ports on the back.
On an iMac or Studio Mac, it’s the farthest right of the USB-C ports on the back.
On the laptop models, it’s the left of the two Thunderbolt 3 ports on the left-hand side.
Launch Configurator 2 on the restoring Mac.
Make sure your Mac is in a fully powered down state and then get it into the correct state by model type:
With a Mac mini, iMac, or Mac Studio, make sure a monitor is plugged in to watch progress in step 6. Disconnect the Mac from power for at least 10 seconds. Hold down the power button, reconnect power, and release the power button. Its status light should be amber. It will also appear as a selectable item in Configurator 2.
With a Mac laptop, press the power button and then keep holding it down while also pressing three keys: the right Shift key, the left Option key, and the left Control key. Release the modifier keys after about 10 seconds, but keep holding down the power button until you see your unresponsive Mac appear as an available selection in Configurator 2.
To revive, in Configurator 2, select the Mac in the device window, and then choose Actions > Advanced > Revive Device and click Revive Device. The Apple logo will intermittently appear and disappear on the Mac that’s being revived, and then the Mac will reboot. You may be prompted to reinstall macOS, but this will be a non-destructive operation.
If your Mac functions normally at this point, you can unplug cables and stop.
If your Mac is not functioning correctly, proceed as follows:
Restart at step 5 above to get your Mac back in its special mode and appearing as a selection in Configurator 2.
In Configurator 2, select the Mac and then choose Actions > Advanced >Restore and click Restore. As with revive, the Apple logo will intermittently appear and disappear.
If the restoration was successful, your Mac restarts with the macOS Setup Assistant. Unplug cables and proceed.
At this point, if you can’t use your Mac, it’s time to call Apple Support to get additional help, as it may require a repair or replacement.