Omnimount

Read/write access to filesystems macOS doesn't support natively — ext2/ext3/ext4 and NTFS — from a SwiftUI menu bar app and a CLI. Omnimount implements no drivers: it wraps existing open source tools (fuse2fs from e2fsprogs and ntfs-3g) over a FUSE layer (FUSE-T by default, kext-free; macFUSE as an alternative).

Built especially for retro-console SD cards (ArkOS, Batocera, ROCKNIX, muOS…), which mix FAT partitions with ext4 partitions invisible to macOS.

🌍 Versión en español · 🛒 Buy the ready-made build

• Requirements: macOS 13+, Apple Silicon (Intel should work, untested).
• License: GPL-3.0-or-later (fuse2fs and ntfs-3g are GPL).

Components

Component	What it is
omnimount (CLI)	Lists disks, detects filesystems by magic bytes, mounts/unmounts, formats, clones
Omnimount.app	Menu bar app: live disk detection (DiskArbitration), mount/eject/format, reveal in Finder
OmnimountHelper	Privileged daemon (SMAppService + XPC): password-free operations
OmnimountKit	Shared Swift library

Installation

1. FUSE layer

Recommended — FUSE-T (no kext, no Recovery, no reboots):

brew install --cask macos-fuse-t/cask/fuse-t

Trade-off: it's closed source (free of charge) and volumes mount as local NFS. Decisive advantage: zero install friction.

Fully open source alternative — macFUSE (kext):

brew install --cask macfuse

macFUSE uses a kernel extension, which macOS blocks by default:

1. Apple Silicon only (mandatory; without this the "Allow" button in step 2 never appears): shut the Mac down completely, hold the power button until "Loading startup options" → Options → menu Utilities → Startup Security Utility → select your disk → Security Policy… → Reduced Security + check Allow user management of kernel extensions from identified developers. Reboot. (Check the state with sudo bputil -d: it must say "3rd Party Kexts Status: Enabled".)
2. Back in macOS, go to System Settings → Privacy & Security: scroll to the notice about system software from "Benjamin Fleischer" — click Allow.
3. Reboot when prompted.

⚠️ FUSE-T and macFUSE don't coexist well: the FUSE-T installer overwrites macFUSE's libraries in /usr/local/lib. Pick one backend per system (or reinstall macFUSE to go back to it).

2. Filesystem tools

Build them from source against your FUSE layer (Homebrew is NOT needed — its e2fsprogs bottle lacks fuse2fs and its ntfs-3g links macFUSE):

make fuse2fs    # fuse2fs + static e2fsck, mke2fs, tune2fs (FUSE-T by default)
make ntfs3g     # ntfs-3g + mkntfs + ntfsfix, built against FUSE-T
BACKEND=macfuse make fuse2fs    # fuse2fs against macFUSE instead

Everything lands in vendor/bin/ and gets bundled into the app by make install. (The paid build ships all of this pre-built, signed and notarized.)

3. Omnimount

make install    # CLI at /opt/homebrew/bin/omnimount + app in /Applications

Check the state of everything:

omnimount doctor

4. Permissions (one-time)

Accessing /dev/diskXsY requires two distinct permissions:

1. root — device nodes belong to root:operator, mode 640.
2. Full Disk Access (TCC) — since macOS Catalina, opening raw devices returns Operation not permitted even as root unless the responsible app has Full Disk Access.

Recommended setup (app + helper, no password prompts):

1. Open Omnimount.app → click "Activate helper" → approve the background item in Settings → General → Login Items.
2. In Settings → Privacy & Security → Full Disk Access, add /Applications/Omnimount.app/Contents/MacOS/OmnimountHelper with + (Cmd+Shift+G to type the path).

To use the CLI with sudo, grant Full Disk Access to your terminal and to the omnimount binary as well.

⚠️ Developer note: TCC binds the permission to the binary's code signature. Build with a stable identity (the Makefile picks your first development identity) or you'll have to re-grant after every build.

CLI usage

omnimount list                  # external disks + detected filesystems
sudo omnimount detect disk4s2   # magic bytes (--verbose dumps the boot sector)
sudo omnimount mount disk4s2    # mounts with the right backend
omnimount unmount disk4s2       # clean unmount
sudo omnimount test disk4s2     # mount + write test + unmount + fsck

sudo omnimount clone disk4 backup.img        # clone whole disk (or partition)
sudo omnimount restore backup.img disk4      # restore (asks for confirmation)
sudo omnimount unhide disk4s3                # clear the "hidden" flag (FAT 0x1C, ArkOS)
sudo omnimount format disk4s3 ext4 --label EASYROMS   # format (strict confirmation)

Magic-byte detection:

• ext2/3/4 — superblock at offset 1024, magic 0xEF53; feature flags distinguish ext2/ext3/ext4 and the volume label is read too.
• NTFS — OEM ID NTFS at offset 3 of the boot sector.
• Also recognizes exFAT, FAT, Btrfs and Linux swap (without mounting them).

Menu bar app

• Lists external disks live (DiskArbitration); mount/eject/reveal in Finder per partition.
• Helper active → every operation without a password dialog (SMAppService + XPC; the helper verifies the client's code signature). Without the helper, the app falls back to the macOS admin dialog.
• Format from each partition's "⋯" menu: a sheet with warnings and two-step confirmation (ext2/3/4, NTFS, FAT32, exFAT; also updates the MBR type byte).
• 🎮 notice when the inserted card looks like a retro console's (ArkOS/EASYROMS, Batocera, ROCKNIX, muOS, RetroPie, Recalbox…).

Development

make build      # builds (scratch path at ~/.omnimount-build)
make test       # detector tests with synthetic images
make app        # signed dist/Omnimount.app

Layout:

Sources/OmnimountKit/     DiskLister, FilesystemDetector, Mounter, Cloner,
                          Formatter, RetroCards, ToolLocator, HelperProtocol
Sources/OmnimountCLI/     list, detect, mount, unmount, test, clone, restore,
                          unhide, format, doctor
Sources/OmnimountApp/     MenuBarExtra + DiskArbitration + XPC client
Sources/OmnimountHelper/  privileged daemon (SMAppService)
scripts/build-fuse2fs.sh  builds fuse2fs (BACKEND=fuse-t|macfuse)

Don't build inside synced folders (OneDrive/Dropbox/iCloud): the scripts use --scratch-path outside the repo for that reason.

Known limitations

• Volumes mounted by the helper/root don't show in the Finder sidebar (DiskArbitration doesn't publish them into the user session). The volume works normally at /Volumes/<name>; drag it to Favorites once if you want it handy.
• NTFS over FUSE-T is validated (mount, write, unmount, ntfsfix) using the bundled ntfs-3g built from source — avoid Homebrew's ntfs-3g-mac, which links against macFUSE's libraries.
• FUSE binaries aren't bundled with the open source build: they must be installed. (The paid build bundles everything.)
• Verification fsck is non-destructive (e2fsck -fn, ntfsfix -n): it reports, it doesn't repair.