prohibite error during macOS boot: causes and fixes

What the Prohibited Symbol Error Means

The prohibited symbol error (⛔) is a common issue when booting macOS. It appears as a yellow circle with a prohibition symbol on the screen instead of the usual Apple logo. The system cannot continue booting due to the detection of an incompatible or corrupted kernel extension (kext). This error usually occurs after installing third-party software, updating the system, or a power failure.

The full error text may vary, but the key message is "Prohibited symbol." In more serious cases, a kernel panic message may also appear, which also halts the boot process.

The prohibited symbol error is critical because it completely blocks the use of the Mac until it is resolved.

Common Causes

1. Third-party kernel extensions (kext files). Some programs for macOS (e.g., hardware drivers, antiviruses, virtualization utilities) install kernel extensions. If they are incompatible with the current version of macOS or are corrupted, the system blocks the boot process.
2. Corrupted system files. Failures during a macOS update, an improper shutdown, or a disk failure can damage critical files necessary for booting.
3. Hardware issues. Faulty RAM or a solid-state drive (SSD) can cause errors when reading system data, leading to the prohibited symbol.
4. Extension version conflicts. After a macOS update, older kext files may become incompatible if the developer has not released an update.
5. System Integrity Protection (SIP) enabled while attempting to modify system files. Although SIP usually prevents such issues, disabling it and subsequently installing incompatible software can lead to this error.

Solutions

Solution 1: Boot in Safe Mode

Safe Mode boots macOS with a minimal set of kernel extensions and runs a disk check. This helps determine if the error is caused by third-party software.

Steps:

1. Shut down your Mac.
2. Turn on your Mac and immediately hold the Shift key. Continue holding it until you see the login window. "Safe Mode" will be indicated in the top-right corner.
3. Log in. Your Mac will boot slower as it performs checks.
4. If your Mac boots successfully, restart it normally (without holding keys) to exit Safe Mode.
5. If the prohibited symbol error does not appear after a normal boot, the problem is a kernel extension. Proceed to the next solution to remove problematic extensions.

Note: On Macs with Apple Silicon (M1, M2, etc.), Safe Mode is enabled differently: shut down the Mac, hold the power button until the startup options appear, select "Start up in Safe Mode."

Solution 2: Manually Remove Kernel Extensions

If Safe Mode worked, you need to remove the incompatible kernel extensions.

Steps in Safe Mode:

1. Open Finder.
2. Press Cmd+Shift+G, enter the path /Library/Extensions/, and press Enter.
3. This folder contains all third-party kernel extensions (files with the .kext extension). Sort by modification date to find recently installed ones.
4. Move suspicious files to the Trash. If you are unsure which ones caused the problem, temporarily move all third-party kext files (do not remove Apple's built-in ones).
5. Restart your Mac normally.
6. If the error disappears, one of the removed folders was the cause. To identify which one, return the extensions one by one and restart until the error reappears.

Alternatively, via Terminal:

# Show a list of loaded kernel extensions
kextstat | grep -v com.apple

This command will output only third-party extensions. Note their identifiers to find the corresponding files in /Library/Extensions/.

Solution 3: Reset NVRAM and SMC

Resetting NVRAM (non-volatile RAM) and SMC (System Management Controller) can resolve boot configuration and power management issues that sometimes cause the prohibited symbol.

Reset NVRAM:

1. Shut down your Mac.
2. Turn it on and immediately hold Option+Command+P+R.
3. Hold for about 20 seconds (on Macs with Apple Silicon, release when you see the second Apple logo).
4. Your Mac will reboot. NVRAM settings (like the startup disk selection) will be reset.

Reset SMC:

• For Macs with an Intel processor:
  • Shut down your Mac.
  • Wait 10 seconds.
  • Hold Shift+Control+Option (left side) and the power button simultaneously for 10 seconds.
  • Release all keys and the power button, then turn on your Mac.
• For Macs with Apple Silicon: Simply shut down the Mac, wait 30 seconds, and turn it back on. The SMC resets automatically.

Solution 4: Recovery Mode and Disk Check

Recovery Mode provides utilities for diagnosing and fixing system issues.

Steps:

1. Shut down your Mac.
2. Turn it on and immediately hold Command+R (on Apple Silicon: hold the power button until startup options appear, then select "Options" → "Recovery").
3. Wait for the recovery utilities to load.
4. Launch Disk Utility.
5. Select your system disk (usually "Macintosh HD") and click "First Aid".
6. If Disk Utility finds and repairs errors, try restarting your Mac.
7. You can also restore your Mac from a Time Machine backup in Recovery Mode if one is available.

Note: If Disk Utility cannot repair the disk, the drive may need to be replaced.

Solution 5: Reinstall macOS

If the previous methods did not help, reinstalling macOS can replace corrupted system files while preserving your data.

Steps:

1. Boot into Recovery Mode (Command+R).
2. Select "Reinstall macOS".
3. Follow the on-screen instructions. The process will take from 30 minutes to several hours, depending on your internet speed and disk.
4. After reinstalling, you can restore data from a Time Machine backup or from the "Users" folder on your disk if you did not erase it.
5. Important: Before reinstalling, ensure you have a current backup. Although user data is usually preserved, there is still a risk of loss.

For Macs with Apple Silicon: The process is similar, but booting into Recovery Mode is different.

Solution 6: Hardware Check (Apple Diagnostics)

If the prohibited symbol error persists after all software fixes, the problem may be hardware-related.

Running Apple Diagnostics:

1. Shut down your Mac.
2. Turn it on and immediately hold the D key.
3. Follow the on-screen instructions. The diagnostic will take a few minutes.
4. If errors are found, note the provided codes (e.g., "PPM001").
5. With these codes, you can contact Apple Support or an authorized service provider.

What is checked: RAM, logic board, storage drive, and other components.

Prevention

To avoid a recurrence of the prohibited symbol error, follow these simple guidelines:

1. Install kernel extensions only from trusted sources. Before installing any software that requires kernel-level permissions (e.g., printer drivers, antiviruses), check reviews and compatibility with your macOS version.
2. Regularly update macOS and your applications. Apple frequently releases updates that fix compatibility and security issues.
3. Create backups using Time Machine. This allows you to quickly restore your system in case of serious failures.
4. Do not disable System Integrity Protection (SIP) unless required for specific tasks. Disabled SIP makes the system vulnerable to incompatible software.
5. Avoid interrupting a macOS update. Ensure your Mac is connected to power and does not go to sleep during the update.
6. Periodically check disk health using Disk Utility's First Aid.

Following these recommendations will significantly reduce the risk of boot errors.