macFUSE
File system integration made easy

Announcing macFUSE 5.5.0 Posted on 17 Oct 2026

Download macFUSE 5.5.0 macOS 12 or later Apple Silicon or Intel SHA-256: 92c21ef2db4199bcf5bddc8e6efb57b23ecb9715f74ab38cba2c77ab226d3830

Release Notes

General

• Update the build process to use Xcode 27.1 (macOS 27.0 SDK)

• Build user-space components for arm64e in addition to arm64 and x86_64 to support Xcode’s enhanced security build settings

FSModule (FSKit Backend)

• Fix Disk Arbitration integration for volumes mounted with the local option so they appear as local volumes in Finder and can be unmounted through Finder

• Fix mounting on paths containing spaces and other non-ASCII characters. This addresses macfuse/macfuse#1198.

• Add support for read-only mounts on macOS 26.4 and later. This addresses macfuse/macfuse#1208.

• Add support for file preallocation through FUSE_FALLOCATE, using the same allocation flags as the kernel backend

• Fix extended attribute removal by sending FUSE_REMOVEXATTR instead of setting the attribute to an empty value. This addresses macfuse/macfuse#1213.

• Send FUSE_FLUSH when closing a file. This addresses macfuse/macfuse#1214.

  FSKit does not expose a per-file fsync(2) callback. On macOS 27, its close callback cannot return errors, so flush failures are logged but cannot be reported to the application through close(2).

• Mitigate a data corruption issue in FSKit on macOS 26 and 27 by rejecting empty FUSE_READ replies with EIO and clearing unused buffer tails after short reads

  This workaround can cause read errors when a file’s size changes remotely. This addresses macfuse/macfuse#1188.

• Add support for the daemon_timeout option and improve request cancellation by tracking FUSE_INTERRUPT requests, retrying interrupts after EAGAIN, and disconnecting unresponsive file system servers when interruption times out

• Improve item reclamation on macOS 27 by protecting items until FSKit has registered returned references, coordinating reclamation with concurrent lookups, and balancing lookup references and file handles on error paths

• Improve stability by validating incoming FUSE and XPC messages, checking buffer alignment, preventing request identifier collisions, and fixing races in request completion, cancellation, and timeout handling

• Improve concurrency and add fast paths for uncontended locks and semaphores

• Avoid repeated requests for access checks, flushes, preallocation, and file or directory synchronization when the file system server does not implement the corresponding callbacks

• Keep named pipes metadata-only and reject stream operations, size changes, and preallocation locally

• Fix a crash when mounting volumes using unsigned file system binaries on Intel Macs. This addresses macfuse/macfuse#1205.

Kernel Extension (Kernel Backend)

• Update the kernel extension version to 5.5.0

• Add support for remote POSIX and BSD advisory locking, allowing file system servers to coordinate fcntl(2) and flock(2) locks across clients

  POSIX and BSD locking are negotiated independently. Local advisory locking remains available when neither capability is enabled. If only one family is enabled, requests for the other return ENOTSUP. Timed locks and PID-filtered lock queries are unsupported when remote locking is enabled.

  File system servers must track lock ownership using fi->lock_owner independently of fi->fh, because multiple lock owners can share a FUSE file handle. Close-time unlocks are sent explicitly instead of being inferred from flush or release requests.

• Add native I/O support for named pipes and character and block devices through macOS fifofs and specfs, while retaining FUSE namespace and metadata handling. This addresses macfuse/macfuse#1212

• Default kernel backend mounts to nodev to disable device access

  Mounting with -o dev requires root privileges. Named pipes are unaffected by nodev.

• Harden extended attribute reply handling by validating reply sizes before allocation and enforcing the advertised extended attribute size limit

• Validate file types, sizes, block counts, timestamps, and cache timeouts before updating vnode state

• Prevent duplicate request identifiers during concurrent allocation

• Preserve request timeout deadlines across signal interruptions so repeated signals cannot extend waits indefinitely, and protect the FUSE_INIT handshake from signal interruption

• Improve node locking by making attribute-refresh waits consistently uninterruptible

MFMount.framework

• Verify the mount service’s code signature when processing its reply and authenticate the FSKit channel peer before decoding its first message

• Reject additional XPC channel connections to prevent other peers from injecting requests into the receive queue or invalidating the active channel

• Improve XPC mount connection cleanup and cancel connections after mount requests complete

• Avoid logging expected ENOENT errors when replies arrive after their requests have been interrupted or the volume has been unmounted

• Please note that parts of the public MFMount.framework API may still change in future releases.

libfuse

• Preserve POSIX lock ownership by skipping synthetic unlocks during FUSE_FLUSH on macOS, where close-time unlocks are sent explicitly

• Forward BSD advisory locking through the threadid and volicon modules so stacking these modules preserves the underlying file system’s locking support

• Fix source builds with newer Autoconf and Gettext versions by allowing autopoint to install config.rpath on macOS

libfuse3

• Update libfuse3 to version 3.18.3

• Preserve POSIX lock ownership by skipping synthetic unlocks during FUSE_FLUSH on macOS, where close-time unlocks are sent explicitly

• Include upstream fixes for multithreaded loop teardown, allocation failure handling, resource leaks, and iconv initialization

• Disable fuse_session_custom_io() by default as part of the upstream security changes

  The function returns -ENOTSUP unless the library is built with -Denable-custom-io=true. Custom I/O peers must validate protocol messages because libfuse relies on validation normally performed by the kernel.

Sponsor

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