What does the circle with a line through it mean on Mac startup?

The short answer

The prohibitory symbol (a circle with a line through it) means your Mac found a startup disk but the macOS version on it isn’t compatible or is corrupted.

Why does this happen?

Your Mac checks its startup disk every time it turns on. If it finds a macOS installation that it can’t use, it shows this symbol instead of booting normally. Common causes include:

  • Incompatible macOS version — the installed macOS is too old or too new for your Mac hardware
  • Corrupted system files — a failed update, unexpected shutdown, or disk error damaged key files
  • Wrong startup disk selected — your Mac is trying to boot from an external drive or partition with an incompatible system
  • Hard drive or SSD failing — the disk itself may be physically damaged

How to fix it

Try these steps in order:

  1. Reset NVRAM — shut down your Mac, then turn it on while holding Option + Command + P + R for about 20 seconds. This resets the startup disk selection.
  2. Choose the right startup disk — restart and hold the Option key to see available disks. Select your main macOS drive.
  3. Boot into macOS Recovery — restart and hold Command + R. From there:
    • Run Disk Utility to check and repair your disk
    • Reinstall macOS if the disk checks out fine but the system is corrupted
  4. Use Internet Recovery — if regular Recovery doesn’t work, restart while holding Option + Command + R to reinstall the latest compatible macOS over the internet

For Apple Silicon Macs (M1/M2/M3/M4)

Instead of holding key combinations, press and hold the power button until you see “Loading startup options,” then follow the on-screen prompts to access recovery tools.

When should you worry?

If a simple NVRAM reset or startup disk reselection fixes it, you’re fine — it was likely a one-time glitch. But if the symbol keeps appearing:

  • Your disk may be failing — back up your data immediately using Recovery mode and consider replacing the drive
  • Your macOS installation may be beyond repair — a clean reinstall from Recovery is your best option
  • If nothing works, contact Apple Support or visit an Apple Store, as it could be a hardware issue