Mac Error 69877 — APFS Operation Not Permitted on Signed Volume

Mac error 69877 occurs when trying to modify a Signed System Volume (SSV) in macOS Big Sur or later, as the system volume is now cryptographically verified. 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: Starting with macOS Big Sur, the system volume is a Signed System Volume (SSV). SSV is cryptographically verified at boot — any modification breaks the seal. Error 69877 appears when trying to mount the system volume as writable. SIP (System Integrity Protection) must also be disabled to modify system files. Even with SIP disabled, SSV prevents direct system volume modification. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Attempting to modify files on the sealed system volume. Legacy tools or scripts trying to write to /System or /usr (excluding /usr/local). Trying to mount the system volume as read-write. Older administration tools not compatible with SSV. Manual partition operations on the APFS system volume group. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Understand that modifying the system volume is intentionally blocked for security. Use the data volume (/System/Volumes/Data) for custom files instead. If absolutely necessary: disable SIP (csrutil disable in Recovery) then disable SSV (csrutil authenticated-root disable). After modifying system volume, re-seal it: sudo bless --folder /System/Library/CoreServices --bootefi --create-snapshot. Prefer synthetic firmlinks (/etc/synthetic.conf) for custom mount points instead of modifying system. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

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