Quick Overview
There are a few common reasons why a Mac may not allow you to erase it:
- FileVault encryption is enabled
- The Mac is locked with a firmware password
- The startup disk is corrupted
- The Mac is enrolled in device management
Before erasing, it’s important to understand why the Mac is preventing erasure and address any underlying issues first. With the right troubleshooting, you can resolve any problems and erase the Mac fully.
What Does “Erase” Mean on a Mac?
On a Mac, erasing refers to deleting all data and settings on the startup disk and reinstalling a fresh copy of the Mac operating system. This restores the Mac to its factory settings.
When you erase a Mac, everything on the startup drive is deleted, including:
- User accounts and data
- Apps and program files
- System settings and preferences
- Operating system files
The Mac is wiped clean, with only the pre-installed operating system remaining.
Erasing is an option available in Disk Utility on Macs. It’s useful when selling, recycling or troubleshooting a Mac. But sometimes, the option to erase may be greyed out or unavailable.
Why Can’t I Erase My Mac?
There are four main reasons a Mac may not allow you to erase it:
1. FileVault Encryption is Enabled
FileVault is the Mac’s built-in full-disk encryption feature. When enabled, all data on the startup drive is encrypted.
To decrypt and erase an encrypted drive, you must first turn off FileVault. This requires the FileVault encryption password.
If you don’t have the password, you cannot decrypt the drive to erase it. Apple does not have a master password to decrypt FileVault.
To check if FileVault is enabled:
- Go to System Preferences > Security & Privacy
- Check if FileVault shows “Locked” under FileVault tab
To unlock FileVault:
- Click the lock icon and enter admin username and password
- Turn off FileVault and wait for decryption process to complete
- Enter FileVault password when prompted
Now with FileVault disabled, you can erase the Mac startup drive normally.
2. Firmware Password is Enabled
The firmware password prevents changing startup settings, including erasing. It stores a password in Mac firmware that must be entered to boot from another drive or access recovery mode.
If you don’t have the firmware password, you cannot alter startup settings to erase the Mac.
To check if firmware password is set:
- Restart Mac and hold Option key after startup chime
- If any drives show “Locked” icon, firmware password is enabled
To remove firmware password:
- Boot to Recovery Mode holding Command + R keys
- Select Utilities > Firmware Password Utility
- Enter firmware password to remove
With the firmware lock disabled, you can restart normally and erase the Mac.
3. Startup Disk is Corrupted
If the Mac startup disk is corrupted, damaged or unreadable, you may get errors when trying to erase it.
For example, you made encounter messages like:
- “Disk erase failed. Couldn’t unmount disk.”
- “Disk Erase failed with error: couldn’t open device”
Or see the erase button greyed out and unavailable.
In this case, don’t force erase the disk. First troubleshoot and repair any underlying disk errors.
To check for disk errors:
- Boot to Recovery Mode holding Command + R keys
- Select Disk Utility and run First Aid on affected disk
- If errors found, run Repair Disk to fix
With disk issues fixed, erasing should now be possible.
4. Mac is Enrolled in Device Management
If a Mac is enrolled in mobile device management (MDM), the administrator may have restrictions that prevent erasing.
For example, Macs owned by a business and managed via MDM cannot be erased without the admin removing MDM enrollment first.
Check System Preferences > Profiles to see if you have any MDM profiles installed. Contact the administrator to discuss removing enrollment so you can erase the device.
How to Erase a Mac If Unable to Erase Normally
If you cannot erase the Mac through the standard Disk Utility method, there are a couple recovery options:
1. Erase in macOS Recovery
To erase the startup disk using recovery mode:
- Boot to Recovery Mode holding Command + R keys
- Select Disk Utility from the Utilities menu
- Choose the startup disk and click Erase button
- Complete the erase process
This allows erasing the disk outside of the installed system.
2. Internet Recovery Erase
On newer Macs with Internet Recovery:
- Boot to Internet Recovery Mode holding Option + Command + R keys
- Select Disk Utility once booted to recovery screen
- Choose the startup disk and click Erase button
- Complete the erase process
Internet Recovery downloads fresh macOS files over the internet to erase and reinstall OS.
As long as no firmware lock is set, these recovery modes should allow erasing the Mac.
Before Erasing a Mac
Before committing to erasing your Mac, make sure to:
- Backup important data first
- Deauthorize iTunes and Adobe apps
- Sign out of iCloud account
- Unlink keychain data
Also confirm you have the correct login passwords, recovery key, and credentials required for reinstalling apps and services after erasing.
Having this information prepares you to cleanly erase the Mac and ensures critical data isn’t lost.
How to Erase and Reinstall macOS from Recovery
Once you’ve addressed any issues preventing erase, follow these steps to erase and reinstall macOS:
- Boot to Recovery Mode holding Command + R keys
- Select Disk Utility from the Utilities menu
- Click Continue to ignore any APFS conversion messages
- Select the Mac startup disk on the left sidebar
- Click Erase button at the top
- Choose APFS format
- Use GUID Partition Map scheme
- Click Erase to confirm disk erase
- This deletes all data and reformats the drive
- Quit Disk Utility when finished erasing
- Select Reinstall macOS option
- Follow prompts to install latest macOS version
The Mac will reboot during install. After 20-30 minutes, macOS will be freshly installed.
You can now set up the erased Mac, create a new user account, reinstall apps and restore data from backup.
Alternative Erase Options
Beyond fully erasing the startup disk, you have a few other options:
Erase Free Space Only
To delete leftover user files without losing programs and system files, erase free space only:
- Boot to Recovery Mode
- Open Disk Utility
- Select startup disk
- Click Erase button
- Choose “Erase Free Space” option only
This wipes unused space while retaining the OS, apps and user data.
Single Partition Erase
On drives with multiple partitions, you can selectively erase just one partition:
- Boot to Recovery Mode
- Open Disk Utility
- Select a partition from the left sidebar
- Click Erase button
- Choose a name and format for that partition
This erases one section without modifying other partitions.
Secure Erase Drives
To securely wipe a drive, using multiple pass erasing:
- Boot to Recovery Mode
- Open Disk Utility
- Select the physical drive on left
- Click Erase button
- Choose “Most Secure 3-Pass Erase” option
This overwrites all data to prevent forensic recovery.
Troubleshooting Mac Erase Problems
Some common erase issues and how to troubleshoot them:
“Erase process has failed” error
This points to an underlying disk issue. Run First Aid in Disk Utility to check and repair errors. Rerun erase after any fixes.
Greyed out or unavailable erase button
Check that FileVault, firmware lock and MDM restrictions are not preventing erase. Disable any security blocking erasure.
Stuck on erasing progress bar
Let the process run for at least 1 hour before interrupting it. An erase can take multiple hours. If still stuck after long wait, restart and erase again.
Drive doesn’t erase fully
Do a secure multi-pass erase or erase disk instead of just volume if traces of data remain after quick erase. This ensures thorough deletion.
FAQs and Common Questions
Here are answers to some frequently asked questions about erasing Macs:
Is erased data recoverable?
No. A standard erase overwrites all data on a drive so it cannot be recovered. For utmost security, do a 3-pass secure erase.
Can I reinstall the old macOS after erase?
No. Erasing removes the OS so you must reinstall a new macOS version after erase.
Is erasing bad for my drive?
No. Modern SSD and flash storage are designed for many erase cycles. Erasing doesn’t negatively impact drive hardware.
What will I lose when erasing?
Erasing deletes all user accounts, apps, files, system settings and the installed operating system. Only pre-installed software remains after erase.
Is there any risk of bricking from bad erase?
Extremely unlikely. Recovery mode provides a failsafe way to erase and reinstall the OS if the standard method fails.
Conclusion
Erasing and reinstalling macOS is a useful troubleshooting step if your Mac is acting up. By understanding what prevents erasure and following the right steps to securely wipe your drive, you can erase even encrypted or damaged Macs successfully. Just be sure to backup your data first and have all needed passwords on hand before committing to a full system erase.