Linux disks on the Mac,
read and written.
Plug in a USB drive or the SD card from a Raspberry Pi and it shows up in the Finder like any other disk — ext2, ext3 and ext4, no Terminal, no kernel extension. Writing to ext4 goes through the disk's own journal, the way Linux does it.
Free to read · writing $3.99 one-time · macOS 27 or later · Apple silicon
A Linux disk that behaves like a disk.
Extent is a file system extension built on FSKit, the framework Apple ships for exactly this. Nothing to allow in Recovery, nothing running as root, nothing left behind when you remove the app.
Every ext there is
ext4, ext3 and ext2 as Ubuntu, Debian, Fedora and Raspberry Pi OS format them: checksums, 64-bit, extents, indexed directories, extended attributes, symbolic links and permissions.
Mounts itself
Plug the disk in and it is in the Finder and in every app, with the files where Linux left them. Disk images open too — drop an .img on the window.
Writing with the journal
Create, change, rename and delete on ext4. Every change travels through the disk's journal, as on Linux, so a disk pulled out mid-write comes back consistent.
A card straight from the Pi
A disk that left Linux without being ejected reads as Linux itself will see it once it finishes its journal. Nothing to repair first, nothing to mount by hand.
Off until you say so
Writing stays off, disk by disk. A disk carrying damage that Linux recorded stays read-only until it has been checked there — and Extent tells you that's why.
Says why, in words
When a disk stays read-only or won't mount at all, the reason is a sentence with the next step in it, not an error code. Help › Copy Diagnostics gathers the details.
Where your files go.
Extent runs on your Mac as an FSKit extension, outside the kernel. It tells macOS where each file lives on the disk, and the files themselves travel straight between the disk and macOS.
What you actually see
The disks, what each one allows, and what Extent says when a disk can’t be read — light or dark, as your Mac is.
The part everything else gets wrong.
Writing to ext4 is where a driver either respects the file system's journal or quietly damages it. Extent writes the way the kernel does: changes gather into a transaction, the transaction commits to the journal, and only then does the disk itself change.
- Tested by pulling the cable mid-write: every file that had been saved was intact and the disk came back clean
- Checked against Linux — what Extent writes passes
e2fsck -fn, and Linux reads it back exactly - ext4 with a journal and extents; ext2, ext3 and features Extent can't write yet stay read-only
- A disk with recorded damage is never written to
Three things, once.
A file system extension is something macOS wants you to turn on yourself. After that, disks simply appear.
Open Extent
The window lists the Linux disks it knows — the ones connected now and the ones it has seen before.
Turn the extension on
System Settings › General › Login Items & Extensions › File System Extensions. The window has a button that opens that pane for you.
Plug the disk in
It mounts for reading. Turn writing on for the disks you mean to change, then reconnect them.
Read for free. Write once, pay once.
No subscription, no account, no upgrade prompts. Reading every disk Extent supports stays free.
Unlocks writing on all your disks, on every Mac signed in to your Apple Account. Family Sharing included.
US price. The App Store sets the price for each country, so yours may differ.
- Reading ext2, ext3 and ext4 — free, with or without the purchase
- Writing to ext4 disks with a journal, through that journal
- A switch per disk, so a disk you only read can't be written by accident
- Fully offline: nothing about your disks ever leaves the Mac
From the maker of Preview3D, PreviewMD and PreviewSVG.
Questions about Extent
Which disks can Extent read?
ext2, ext3 and ext4, as Ubuntu, Debian, Fedora and Raspberry Pi OS create them — on external drives, SD cards and disk images, as a whole disk or as a partition in a GPT or MBR layout. Other Linux file systems such as Btrfs or XFS aren't supported, and neither are volumes inside LVM, software RAID or LUKS encryption. Which disks open, device by device.
Which disks can it write to?
ext4 with a journal and extents, which is how Linux formats a disk as ext4 unless told otherwise. ext2, ext3, ext4 without a journal, and disks that use a feature Extent can't write yet — such as inline data, case-insensitive folders or quotas — mount read-only.
Is it safe to write to my Linux disks?
Writing stays off until you turn it on, disk by disk. Once it's on, every change goes through the disk's journal, the way Linux writes ext4, so a disk that loses its cable mid-write comes back consistent. Writing is tested against Linux itself: what Extent writes passes e2fsck -fn, and the Linux kernel reads it back exactly. A disk on which Linux has recorded damage is never written to.
Why do I have to turn on an extension in System Settings?
Extent reaches the Finder through a file system extension, and macOS leaves switching those on to you — once, in System Settings › General › Login Items & Extensions › File System Extensions. Until then, Extent's window says so and has a button that opens that pane. It isn't a kernel extension: Extent is built on FSKit, Apple's framework for file systems that run outside the kernel, so there's nothing to allow in Recovery — unlike macFUSE or a kernel extension. One catch on macOS 27: reach that switch through the File System Extensions row, not through Extent’s own row in the Extensions list — that one can refuse to turn on.
I connected a disk and Extent doesn't show it. Why?
Since version 1.0.2, Extent lists every Linux partition it can't open, with the reason. The usual one: the disk was connected before the file system extension was on, or while the Mac was starting up — macOS doesn't offer it to Extent again, so eject the disk and connect it once more. Partitions inside LVM, LUKS encryption or software RAID, and other Linux file systems such as Btrfs or XFS, can't be opened; a damaged ext file system wants e2fsck on Linux first – which disks open, and which don't. If macOS said “The disk you attached was not readable by this computer”, here's what that means.
I bought writing. Why is my disk still read-only?
Writing is also a switch on each disk, off until you turn it on in that disk's details, and it takes effect the next time the disk is connected. If it's on and the disk still mounts read-only, Extent's window says why in a sentence: an ext2 or ext3 disk, a feature Extent can't write yet, or damage Linux recorded, which needs a check there first.
What happens if I unplug a disk without ejecting it?
Eject first when you can. If the cable does come out mid-write, everything already committed to the journal is there the next time you connect the disk, and the file system is consistent — no repair needed. Only the changes still on their way at that moment are lost, the same as on Linux. Extent was tested exactly like this.
Can I read the SD card from my Raspberry Pi?
Yes — it's one of the disks Extent is made for. The card's small boot partition is FAT, which macOS mounts by itself; Extent mounts the ext4 partition that holds the system and your files. A card pulled out without shutting the Pi down reads too: Extent replays its journal as it reads, so you see the files the way Linux will. Step by step: a Raspberry Pi card on a Mac.
Who owns the files I create on the disk?
A new file or folder takes the owner and group of the folder it's created in, so on Linux it belongs to the same user as the files around it — not to a user ID that exists only on your Mac.
Can Extent format or repair a disk?
No. Create ext4 disks with mkfs.ext4 – it works from a Mac too – and repair damaged ones on Linux with e2fsck. When a disk needs a check, Extent says so and gives you the command to copy.
What does it cost?
Reading is free, with no time limit. Writing is a one-time in-app purchase, not a subscription: it unlocks writing on every Mac signed in to your Apple Account and is shared through Family Sharing. No other account, and no internet needed afterwards — the purchase is checked against the copy the App Store keeps on your Mac. In the app it's under Extent › Unlock Writing…, and in the window until writing is unlocked.
Which Macs does it run on?
Macs with Apple silicon, running macOS 27 or later. On an older Mac, other apps and tools read ext4 — every way, compared.