Master Reset an iMac: Full Step-by-Step Guide

To master reset an iMac, start it in macOS Recovery, erase Macintosh HD with Disk Utility, and then reinstall macOS. A master reset permanently removes your accounts, settings, apps, and personal files, so back up anything you need before beginning.

What does a master reset do to an iMac?

A master reset, also called a factory reset, erases the iMac’s startup disk and returns the computer to a fresh macOS installation. It removes user accounts, locally stored documents, installed apps, saved passwords, network settings, and other personal data.

A normal restart only turns the iMac off and on again; it does not erase files or settings. An NVRAM reset clears a small group of hardware-related settings on certain Intel-based iMac models, such as startup-disk selection or sound volume. It is not a factory reset and does not remove personal data.

Files already synchronized with iCloud or another online service are not deleted from that service merely because the iMac is erased. However, files stored only on the iMac will be lost. If the computer is being transferred to someone else, do not restore your backup after resetting it.

What should you do before master resetting an iMac?

1. Back up your files with Time Machine or copy important documents, photos, and other data to external storage. Confirm that you can open the backup before erasing the iMac.

2. Allow any pending iCloud synchronization to finish. A file that has not finished uploading may exist only on the iMac.

3. Sign out of iCloud from System Settings or System Preferences when possible. If you are giving the iMac to another person, also sign out of services such as Messages and remove the iMac from your account as directed by Apple.

4. Write down the Apple Account email address and password associated with the iMac. Apple Account is the current name for what was previously called an Apple ID. The credentials may be required for activation or reinstalling macOS.

5. Have the Wi-Fi network name and password ready. Recovery, activation, and macOS installation normally require an internet connection.

6. Connect a wired keyboard and mouse if available. Erasing can disconnect Bluetooth accessories, and startup key combinations are more reliable with a wired keyboard.

How do you master reset an iMac step by step?

The correct recovery startup method depends on whether the iMac has Apple silicon or an Intel processor. In macOS, open the Apple menu and choose About This Mac if you need to identify the processor before starting.

1. Shut down the iMac completely.

2. On an Apple silicon iMac, press and continue holding the power button until the startup volumes and Options appear. Select Options, then Continue. On an Intel-based iMac, press the power button and immediately hold Command-R until the Apple logo or another startup screen appears.

3. If requested, choose an administrator account, enter its password, and connect to Wi-Fi.

4. In the Recovery utilities window, select Disk Utility and choose Continue.

5. Select Macintosh HD under Internal in the sidebar. Do not select an external backup drive. If the sidebar is unclear, choose View, then Show All Devices, and locate the internal startup volume carefully.

6. Select Erase. Use Macintosh HD as the name and APFS as the format when offered. If Disk Utility recommends Mac OS Extended for an older Intel iMac, use the format it recommends.

7. Select Erase Volume Group if that button appears; otherwise, select Erase. Enter the Apple Account information if requested. On some models, the iMac restarts and must connect to the internet for activation.

8. Quit Disk Utility to return to the Recovery utilities window.

9. Select Reinstall macOS, choose Continue, and follow the prompts. Select Macintosh HD as the installation destination. Keep the iMac powered on and connected to the internet while installation completes.

If the iMac displays Setup Assistant after installation, the master reset is complete. If another person will use the iMac, stop at the initial setup screen instead of entering your information.

What should you do if the iMac will not boot into Recovery?

• For an Apple silicon iMac, shut it down, wait until the screen is fully black, and then hold the power button continuously until startup options appear. A quick press will start the computer normally.

• For an Intel iMac, restart and immediately hold Command-R. If the shortcut is ignored, try a wired Apple-compatible keyboard and disconnect unnecessary accessories.

• If built-in Recovery does not load on an Intel iMac, use Internet Recovery. Hold Option-Command-R at startup to request the newest compatible macOS, or Shift-Option-Command-R to request the original macOS version or the closest version still available.

• If a firmware lock appears, the firmware password is required before startup shortcuts can work.

• If Macintosh HD does not appear in Disk Utility, shut down, unplug nonessential devices, and try Recovery again. If the internal disk remains missing or cannot be erased, stop rather than erasing another listed device and contact Apple Support.

What should you do after resetting an iMac?

1. Select the country or region, language, Wi-Fi network, and accessibility options in Setup Assistant.

2. Sign in with the Apple Account that you want to use. Complete activation or account verification if prompted.

3. Create the local administrator account and choose privacy, location, and analytics settings.

4. Restore files through Setup Assistant from a Time Machine backup, or set up the iMac as new and copy back only the files you need.

5. Open Software Update after reaching the desktop and install compatible macOS updates.

6. Sign back in to iCloud, Messages, email, and other authorized services. Some apps may require activation again because the reset removed their local credentials.

How do you get further help with an iMac reset?

Open {site} and choose the Mac support area to contact official Apple Support. Describe whether the iMac uses Apple silicon or Intel, which recovery method you tried, and the exact message shown on screen.

Seek official help if the startup disk is absent, Disk Utility repeatedly fails, activation cannot be completed, or you do not know a requested firmware or Apple Account password. Do not repeatedly erase unfamiliar disks, because one may contain the only available backup.