An easy way to mount ext4, btrfs or in fact any linux-supported filesystem on a Mac. With full write support, based on the libkrun microVM hypervisor and NFS. Doesn't require installing any kernel extensions or lowering system security.

• mounts any filesystem supported by Linux
• supports LUKS-encrypted drives
• supports LVM (even volume groups spanning multiple drives)
• supports LVM on LUKS (i.e. encrypted LVM)
• works with both external and internal drives
• supports disks with GPT, MBR or no partition table (single filesystem or LVM/LUKS container)
• NFS share by default only reachable from localhost but can be shared across network too

brew tap nohajc/anylinuxfs
brew install anylinuxfs

Mounting 3rd-party filesystems on macOS has always been tricky. There's official support for reading NTFS but otherwise we've mainly used solutions based on macFUSE. We've got NTFS-3g which is a pretty mature driver but for Linux filesystems there's only a couple of experimental solutions like fuse-ext2 or ext4fuse.

If you want a reliable solution with write access, you need to run a Linux virtual machine with physical disk access and take care of exposing the mounted filesystem to the host. This is exactly what anylinuxfs does and it streamlines it so that it's as easy as running one command in terminal.

You pick a drive, mount it with anylinuxfs and it appears as a NFS share on localhost. This spins up a microVM in the background which uses the real linux drivers, so you can access anything from ext* to btrfs. Any mount options on the command-line will be forwarded to the linux mount command, so you can mount read-only, read-write, pick btrfs subvolumes, etc. Then you simply eject the drive in Finder or use umount in terminal and the virtual machine will be turned off.

This all sounds like a lot of work but it's actually very fast. Not like a traditional virtual machine which takes a while to boot. This one is just a stripped down version of Linux, there's not even a UEFI firmware. Practically, it takes only a couple of seconds before the drive is mounted and ready to use.

sudo anylinuxfs list

Possible output

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   5:                       ext4 BOOT                    1.0 GB     disk0s5
   6:                      btrfs fedora                  144.2 GB   disk0s6

/dev/disk7 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *30.8 GB    disk7
   1:                LVM2_member                         30.8 GB    disk7s1

/dev/disk8 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.2 GB     disk8
   1:                LVM2_member                         4.2 GB     disk8s1

/dev/disk9 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                crypto_LUKS                        *8.1 GB     disk9

lvm:vg1 (volume group):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                LVM2_scheme                        +35.0 GB    vg1
                                 Physical Store disk7s1
                                                disk8s1
   1:                       ext4 lvol0                   15.4 GB    vg1:disk7s1:lvol0
   2:                        xfs lvol1                   7.7 GB     vg1:disk7s1:lvol1
   3:                      btrfs lvol2                   11.9 GB    vg1:disk7s1:disk8s1:lvol2

sudo anylinuxfs /dev/disk0s6

sudo anylinuxfs /dev/disk0s6 -o ro

sudo anylinuxfs lvm:vg1:disk7s1:lvol0

sudo anylinuxfs lvm:vg1:disk7s1:disk8s1:lvol2

sudo anylinuxfs list -d /dev/disk9

Output will show the encrypted partition filesystem and label

...
/dev/disk9 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:          crypto_LUKS: ext4 enc-ext4               *8.1 GB     disk9
...

sudo anylinuxfs list -d all

sudo anylinuxfs /dev/disk9

sudo anylinuxfs /dev/disk0s6 -b 0.0.0.0

# by server, we mean the device which is sharing the mounted filesystem
sudo anylinuxfs /dev/disk0s6 -b <YOUR_SERVER_IP>

anylinuxfs status

anylinuxfs stop

• When you first run anylinuxfs to mount a drive, it will download the alpine Linux image from Docker hub and unpack it to your user profile (~/.anylinuxfs/alpine). Then it will spin up a VM so it can install dependencies and do the initial environment setup. After that, the Linux root filesystem will be reused for every mount operation. You can also run anylinuxfs init to download a fresh copy of alpine:latest and reinitialize the environment at any time.
• It is needed to run mount commands with sudo otherwise we're not allowed direct access to /dev/disk* files. However, the virtual machine itself will in fact run under the regular user who invoked sudo in the first place (i.e. all unnecessary permissions are dropped after the disk is opened)
• When you mount a LUKS-encrypted drive, the microVM requires at least 2.5 GiB RAM for cryptsetup to work properly. If your VM is configured with a lower amount of memory, you'll get a warning about it and the RAM configuration will be adjusted automatically. If you don't want to see the warning, set your default RAM to match this requirement (anylinuxfs config -r <size-in-MiB>)
• Configured amount of RAM is the maximum that can be allocated. The actual amount of memory consumed by the VM can be lower.

• Only one drive can be mounted at a time (this might be improved in the future)
• Only Apple Silicon Macs are supported (libkrun limitation)

• Check your mount flags (e.g. the subvol flag from demo is specific to btrfs, make sure you don't use it with other filesystems)
• Check file owner and permissions with ls -l and adjust accordingly. Typically, your macOS user won't have write access to your drive out of the box so you need to write files as root or first prepare a target directory writable by everyone (chmod 777).
• If you get fcopyfile failed: Operation not permitted, it can actually mean the file you're trying to copy has the quarantine attribute set (can be removed with xattr -d com.apple.quarantine <filename>)
• Accessing disks might require Full Disk Access permission (although you should get pop-ups that let you allow access case-by-case)

This project was made possible by

• libkrun the microVM hypervisor for Linux anc Mac
• libkrunfw - Linux kernel bundled for libkrun as a dynamic library
• gvproxy - user space networking for virtual machines (also used by podman)
• docker-nfs-server - launcher for NFS server in a container

Thank you all for your great work!