How do I fix the prohibitory symbol on my Mac?

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How do I fix the prohibitory symbol on my Mac

What is the prohibitory symbol?

The prohibitory symbol is a circular icon with a diagonal slash through it that appears when you attempt to start up your Mac. This symbol indicates that your Mac is unable to read the startup drive or locate the system software it needs to boot up (1).

Specifically, the prohibitory symbol appears because the Mac’s boot loader cannot find a valid system folder or boot partition on the startup drive. This is usually caused by corruption or damage to the drive that prevents the operating system from starting up properly (2).

If the prohibitory symbol shows up, your Mac will get stuck at the gray screen and won’t finish starting up. The symbol serves as a warning that there is an underlying problem with the startup disk that needs to be addressed before you can use your Mac again.

References:

(1) https://support.apple.com/en-us/101666

(2) https://iboysoft.com/mac-data-recovery/mac-circle-with-line-through-it.html

Common causes of the prohibitory symbol

The prohibitory symbol typically appears due to three main issues with your Mac:

Corrupt system files or operating system – This is one of the most common reasons for the prohibitory symbol. If your Mac’s system files or OS get corrupted or damaged, it can prevent your Mac from being able to start up properly.1 Reinstalling or repairing your Mac’s operating system can often fix this issue.

Hardware failure – Faulty or failed hardware components like the hard drive, RAM, logic board, etc. can also lead to the prohibitory symbol appearing on startup. If repairing your software does not resolve the issue, it may be caused by a hardware problem that requires replacement of the damaged hardware component.2

Attempted unauthorized startup – If you try to start up your Mac from an unauthorized startup disk, like an external drive without a valid system on it, the prohibitory symbol will appear to indicate that the startup disk cannot be used. This is a security measure to prevent unauthorized access to your Mac.1

Run Apple Diagnostics

Apple Diagnostics is a built-in tool on Macs that can help identify hardware issues that may be causing the prohibitory symbol. To access Apple Diagnostics:

  1. Restart your Mac and immediately press and hold the D key on your keyboard.
  2. Keep holding the D key until you see the Apple Diagnostics screen appear.
  3. Follow the on-screen instructions and your Mac will check essential components such as the memory, storage, and CPU for issues.

Apple Diagnostics runs through a quick series of tests and provides error codes if any hardware issues are detected. Make a note of any error codes as these can help identify specifically which component is faulty. The diagnostic process may take 5-10 minutes to fully complete.

If Apple Diagnostics finds no hardware issues, it’s likely another software problem causing the prohibitory symbol. But if it detects and reports hardware errors, you may need to get those components repaired or replaced to properly fix your Mac. Using Apple Diagnostics is a quick and easy first step in troubleshooting the prohibitory symbol on a Mac.

For more details on using Apple Diagnostics, Apple provides technical documentation here: https://support.apple.com/en-us/HT202731

Reset NVRAM

NVRAM (non-volatile random-access memory) stores certain settings and information that macOS uses during startup. This can include display resolution, volume settings, startup drive selection, and more. Over time, corrupted NVRAM settings may lead to startup issues like the prohibitory symbol. Resetting the NVRAM can clear out these settings and potentially resolve the issue.

To reset the NVRAM on a Mac (1):

  1. Shut down your Mac.
  2. Turn it back on and immediately press and hold Command + Option + P + R.
  3. Keep holding down the four keys until you hear the startup chime a second time.
  4. Release the keys and let your Mac finish starting up.

This will reset the NVRAM and clear any corrupted settings that may be causing the prohibitory symbol at startup. Be sure to test starting up your Mac afterwards to see if the issue is resolved.

Reset SMC

The System Management Controller (SMC) is a chip inside your Mac that controls functions like power management, battery charging, and temperature control. Resetting the SMC can help resolve issues like the prohibitory symbol appearing on startup. To reset SMC on a MacBook Pro or MacBook Air:

  1. Shut down your Mac completely
  2. Press and hold the Shift, Control, and Option keys on the left side of the built-in keyboard, then press and hold the power button at the same time. Hold these keys and the power button for 10 seconds.
  3. Release all keys.
  4. Press the power button again to turn on your Mac.

Resetting SMC will reset various settings like the time and date, but it often resolves issues like the prohibitory symbol on startup. For more details, see this Apple Support article: How to reset the System Management Controller (SMC) on your Mac.

Boot into Safe Mode

Safe Mode is a special way to start up your Mac that only loads essential macOS components and services. Booting into Safe Mode can help troubleshoot issues caused by software conflicts or startup items.

To boot into Safe Mode on your Mac with the prohibitory symbol:

  1. Restart your Mac and immediately press and hold the Shift key after you hear the startup sound. The Shift key should be held down until you see the login window.
  2. If you have FileVault enabled, you may need to log in twice.
  3. Test if the issue persists when booted in Safe Mode.
  4. Once logged in, run Apple Diagnostics and try other troubleshooting steps like resetting NVRAM before restarting back into normal startup.

If the prohibitory symbol disappears in Safe Mode, it indicates startup items or system extensions may be causing the problem. You can troubleshoot by removing startup items or perform a clean reinstall of macOS (Source).

Reinstall Mac OS

Sometimes a prohibitory symbol appears because of corrupted system files or issues with the Mac OS installation itself. Reinstalling the Mac operating system can often fix these types of problems and get your Mac working again. Here are the steps to reinstall Mac OS:

  1. First, backup your Mac data to an external hard drive or cloud storage to avoid data loss.
  2. Then, boot your Mac into Recovery Mode by restarting your computer and holding down the Command + R keys.
  3. When the Recovery screen appears, click on Reinstall macOS (or Reinstall OS X depending on your version).
  4. Follow the onscreen prompts to reinstall the latest macOS your computer shipped with.
  5. After installation completes, migrate your data back from the backup.

Reinstalling the Mac operating system replaces all of the main system files and drivers, clearing out any underlying corruption that could be preventing your Mac from booting properly. This process often resolves many software-related causes of the prohibitory symbol. Just be sure to backup your data first!

Repair Startup Disk

One of the most common fixes for the prohibitory symbol is to repair your Mac’s startup disk using Disk Utility’s First Aid feature. The startup disk contains important system files and applications necessary for your Mac to boot up properly. If these files become damaged or corrupted, it can prevent your Mac from starting up and cause the prohibitory symbol to appear.

To repair the startup disk:

  1. Restart your Mac and hold down the Command and R keys simultaneously after you hear the startup chime. This will boot your Mac into Recovery Mode.
  2. Once in Recovery Mode, click on “Disk Utility” in the macOS Utilities window.
  3. Select your startup disk (usually named “Macintosh HD”) in the sidebar of Disk Utility.
  4. Click on the “First Aid” tab and then click “Run.” This will check the disk for errors and attempt to repair any issues it finds.
  5. When finished, quit Disk Utility and restart your Mac normally.

Running First Aid can fix disk permission errors, reattach corrupt directories, and repair other common disk problems that can cause startup issues like the prohibitory symbol. This straightforward process often resolves the issue and allows your Mac to boot up properly again. If First Aid is unable to repair the disk, it may indicate a deeper hardware problem.

Hardware Repair/Replacement

If none of the software troubleshooting steps work, it’s possible there is an issue with the Mac’s hardware that requires professional repair or replacement. Some signs indicating hardware issues that may cause the prohibitory symbol include:

  • Hearing unusual sounds like clicks, beeps or fans spinning loudly at startup
  • Seeing visual artifacts or distortions on the screen
  • Experiencing overheating issues
  • Mac repeatedly freezing during use, even after reinstalling the OS

Hardware components that commonly fail and lead to the prohibitory symbol include the hard drive, RAM and logic board. If you’ve exhausted all software-based fixes, it’s best to take the Mac to an Apple Store or Apple Authorized Service Provider for diagnosis and repair. Technicians will run Apple diagnostics to pinpoint the faulty hardware.

In some cases, certain components like the hard drive or RAM can be replaced, but issues with the logic board often require replacing the entire Mac. You can discuss repair costs with the Apple technician and determine if replacement is a better option for you. Apple offers out-of-warranty replacements through its Flat Rate Repair program.

Bringing the Mac to Apple is the best way to resolve hardware-related prohibitory symbols, as their technicians have the proper tools, diagnostics, parts and expertise to accurately troubleshoot and fix Mac hardware issues.

Summary

If you see a prohibitory symbol when trying to start up your Mac, there are several steps you can take to try and resolve the issue:

First, run Apple Diagnostics to see if it detects any hardware issues. If no issues are found, try resetting the NVRAM and SMC, as corrupted settings files can sometimes cause the prohibitory symbol.

Booting into Safe Mode starts your Mac with only the essential system software loaded, which can help isolate software issues causing the symbol. Reinstalling or repairing your Mac’s system software using Recovery Mode is another option if system file corruption is suspected.

If none of these steps resolve the prohibitory symbol, then a hardware issue like failed RAM or storage drive may be the culprit, requiring professional repair or replacement of the component.

Following this standard troubleshooting sequence can help identify and resolve many common causes of the prohibitory symbol. If the symbol persists after trying all of these steps, further diagnosis may be needed to pinpoint the exact issue.