Mac Prohibitory Symbol (Circle with Line) — Boot Volume Not Compatible

The Mac prohibitory symbol (circle with a line through it) during boot means the startup disk contains a macOS version that is not compatible with this Mac hardware. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: The prohibitory symbol replaces the old flashing question mark folder for some boot failures. Indicates the macOS on the startup disk is incompatible with the Mac's hardware. Can appear after macOS upgrade attempts, disk swaps, or migration from a different Mac model. The startup disk is found (unlike question mark folder) but the OS cannot run on this hardware. Common when moving a drive from a newer Mac to an older Mac. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: macOS version on disk requires newer hardware than available. Disk was migrated from a different Mac model with incompatible OS build. Failed macOS upgrade left an incomplete or incompatible installation. Boot volume file system corruption preventing OS verification. T2 or M-series security chip rejecting the OS installation. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Boot to Recovery Mode: Cmd+R (Intel) or hold Power button (M-series). In Recovery, open Disk Utility and run First Aid on the startup volume. Reinstall macOS from Recovery: this installs the latest compatible version for your hardware. If Recovery does not work, use Internet Recovery: Cmd+Option+R (installs latest compatible macOS). Create a bootable USB installer with the correct macOS version for your hardware. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our Mac Error Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.