Summary: This post introduces the meaning of the prohibitory symbol on Mac (also known as the sign of a circle with a line or a slash crossed). You'll know how to get rid of this symbol, so that you can boot up your MacBook Pro, MacBook Air, iMac, and Mac mini as usual.
The sign, a circle with a line through it, is one of the most common symbols you could see on Mac startup. But it's definitely not the bearer of good news. Its appearance indicates that your Mac has got a problem when booting up.
What does a circle with line through it mean at Mac startup?
When your Mac won't turn on but shows a circle with a line through it, it means that the Mac operating system on the selected startup disk can't be used by your Mac model.
This is a little different from the Mac folder with a question mark issue. In this case, Mac does detect an operating system in the startup disk, but it just doesn't work with your Mac machine. Apple has made it clear that "if you try to use an incompatible macOS, your Mac might not finish starting up, or it might behave unexpectedly."
Then, it makes sense why you see the circle with a slash sign on Mac boot. Computers like MacBook Pro often boot into the 'NO sign' or other boot problems after macOS update. So, it's better to check the system requirements before you jump to any later macOS update (e.g. macOS Big Sur).
But for users who have already run into this problem on Mac, how to get rid of this circle with slash symbol?
How to Fix the Prohibitory Symbol on Mac?
To help Mac boot past the prohibitory symbol, you can follow these steps.
Step 1. Boot the Mac into macOS Recovery mode
If you can't boot up Mac in a normal way because it's stuck on the prohibitory symbol screen, then you can try to boot Mac into macOS Recovery Mode. It is a local recovery system on your startup disk. Here is how to do this.
- 1. Force your Mac to shut down by holding the power button for 5 seconds around.
- 2. Restart the Mac and instantly hold Command + R key combinations.
- 3. Release these keys when you see the Apple logo or loading bar. Then you'll see the macOS Utilities, which means your Mac is in macOS Recovery mode.
Tips: If you can't boot into macOS Recovery mode by the guide above, you can replace the key combinations with Option + Command + R (or Shift+ Option + Command + R), and keep your Mac connecting to the Internet.
Step 2: Repair the startup disk with Disk Utility
Disk Utility can find and repair errors that lead to Mac's unexpected behaviors and that prevent your Mac from turning on. So, when your Mac won't boot past the sign of a circle with a line through it, simply check and verify the startup disk in macOS Recovery mode.
If Disk Utility succeeds in repairing the errors in the startup disk, you can quit Disk Utility and reboot your Mac as normal. If Disk Utility found no errors, continue with the next movement.
Step 3: Back up files from the Mac and reinstall macOS
If First Aid fails to repair the startup disk, then it should be the incompatible Mac operating system that causes the prohibitory symbol on Mac boot. Then, you can only reinstall a macOS that work with your Mac models.
However, you should know that macOS reinstallation could risk losing your data on the Mac. Your files could get lost or deleted sometimes, so make sure you have a backup of your data. If you don't, you can also get data off the Mac that won't turn on first.
After your files are retrieved from the Mac that boots to a prohibitory symbol, or if you don't worry about data loss, you can move to reinstall the macOS.
After all these steps, you can restart your Mac to see whether the annoying sign of a circle with a line through it has disappeared or not. Hopefully, you'll get rid of this prohibitory symbol when Mac is booting up.
But if the startup disk is not detected in Disk Utility or by the macOS reinstallation wizard, it means your hard drive has failed and needs to be replaced. Or, you may want to contact Apple support for help.