MSL release notes

What changed in each MSL release, newest first. Update to the latest release with msl --update. Changes that can break a script or a habit are marked Breaking. Each version links to its GitHub release, which has the downloads and checksums.

0.3.0

1 October 2026 · GitHub release · kernel kernel-6.18.15-msl-a1a22bd

Changed

• Breaking: MSL, its service and the VS Code extension are updated together, and the extension from MSL 0.2.0 or earlier can’t connect to MSL 0.3.0. After updating from 0.2.0, run msl --manage-ide --install once. From then on, msl --update also updates the extension in every IDE that has it. See Upgrade MSL.
• A command’s input and output go straight between msl and the VM instead of through msld (#57). Output through a pipe is about twice as fast (4 GiB in 4.8 s, was 8.2 s), and a slow or stuck command no longer slows down the others. msl --import, --export and --install move their tar streams the same way.
• Each distribution’s disk is attached to the VM when it starts and served by Virtualization.framework, so fsync inside a distribution reaches the SSD again: the durability caveat of 0.2.0 no longer applies. A disk that appears while the VM runs (an install, an import, a move to another volume, a resize) restarts the VM if no distribution is running, in about 1.5 s; otherwise it’s served more slowly until the VM next restarts. Up to 19 disks are attached at start, and a disk is no longer limited to 4 TB. See Manage disk space.
• An idle MSL wakes the Mac far less: the idle VM uses about 0.5% CPU, down from 2.5–3.5%.
• Forwarded ports and ~/.msl/distros are carried by two processes of their own, msl-portd and msl-fileviewd, like WSL’s wslrelay.exe, so msld no longer copies their data.
• MSL bundles VS Code extension 0.2.0.

Fixed

• msl --export <distro> - into a reader that stops early (| head) no longer crashes msl.

Removed

• MSL_DISK_SLOTS, with the disk slots it sized.

0.2.0

29 September 2026 · GitHub release · kernel kernel-6.18.15-msl-a1a22bd

Added

• MSL shuts down cleanly when you log out, restart or shut down the Mac (#52). Before, the VM died with msld: distributions got no warning, and writes not yet synced were lost. msld now stops the distributions, unmounts and flushes their disks, and powers the VM off. It runs as a LaunchAgent (~/Library/LaunchAgents/dev.msl.msld.plist) that launchd starts on demand and gives up to 30 seconds to do this. msl --uninstall removes it.
• Each new distribution gets its own disk, a sparse ext4.img in its install location, like WSL’s ext4.vhdx (#50). It’s 256 GB by default, or the size of the macOS disk if that’s smaller; msl --install --vhd-size and defaultVhdSize choose another size. The VM attaches disks through 16 disk slots, so a stopped distribution you haven’t used for a while can give its slot up. See Manage disk space.
• msl --manage --move, msl --manage --resize for one distribution, msl --export --vhd, msl --import --vhd and msl --import-in-place work as in WSL, with raw ext4 images instead of VHDX. msl --unregister deletes the distribution’s ext4.img, including one imported in place.
• nestedVirtualization in [msl2], as in .wslconfig (default true): /dev/kvm in the distributions on a Mac with an M3 chip or later; MSL’s kernel (6.18.15-msl-a1a22bd) has KVM built in, and uname -r now shows that release. msl --status shows whether it’s on.
• The VM keeps one machine identifier across boots, and its /etc/machine-id is that identifier’s UUID. Distributions keep their own.

Changed

• Breaking: msl --manage <distro> --resize grows that distribution’s disk (it must be stopped) rather than data.img for all of them. Distributions from earlier versions stay on data.img, and --resize still grows data.img for them, until you move them onto their own disk with msl --manage <distro> --move <folder>.
• Breaking: fsync inside a distribution on its own disk isn’t a durability point. Virtualization.framework passes no flushes to these disks, so writes are flushed to the SSD when a disk is detached and at msl --shutdown. A crash of MSL or the VM keeps what was written; a macOS crash or power loss can lose recent writes. See Durability.
• msl --status shows the distributions’ disks (Distribution disks), and the shared disk only while a distribution is still on it.
• The kernel and the VS Code extension moved to their own repositories, msl-kernel and msl-vscode-extension. MSL still bundles both.

0.1.11

28 September 2026 · GitHub release · kernel kernel-6.18.15-msl-21f0ec7

Fixed

• The VM no longer crashes when macOS runs short of memory (#48). With the 4 KiB-page kernel, every distribution could crash within seconds once macOS started compressing or swapping the VM’s memory, and a crash in the middle of a write could damage the data disk. The cause is Virtualization.framework’s handling of 4 KiB pages in the VM on the Mac’s 16 KiB pages. MSL’s kernel now uses 16 KiB pages, like the Mac (getconf PAGESIZE is 16384). Ubuntu 22.04 and 26.04, Debian 13, Fedora 44, AlmaLinux 9 and Kali were tested: every binary and library loads, and systemd and package managers work. Programs built to assume 4 KiB pages don’t run; see Troubleshooting.
• msl --install no longer hangs at the first setup prompt when its input is /dev/tty, as when install.sh runs it. On macOS, /dev/tty means the calling process’s controlling terminal, and msld has none. msl now passes msld the real terminal device.

0.1.10

26 September 2026 · GitHub release

Fixed

• MSL starts on macOS 26 again. 0.1.9 was built with Xcode 27, whose Swift runtime links libraries macOS 26 doesn’t have, so msld failed to start there. Releases are now built by CI with Xcode 26, the version that matches MSL’s minimum macOS. If you installed 0.1.9 on macOS 26, reinstall with the one-line installer; your distributions are kept.

0.1.9

25 September 2026 · GitHub release

Fixed

• Sessions get the distribution’s locale (LANG, LANGUAGE, LC_* from /etc/default/locale or /etc/locale.conf), as in WSL and login shells. Without it, VS Code’s terminal set LANG from VS Code’s own display language, and bash printed setlocale: cannot change locale (en_US.UTF-8) on distributions without that locale, such as Ubuntu with only C.UTF-8.

0.1.8

25 September 2026 · GitHub release

Fixed

• msl failed with “could not start /msld” when msld wasn’t already running, for example right after msl --update. It looked for msld next to argv[0], which is just msl when it runs from PATH. The same lookup set the install prefix for --update, --uninstall and --version --json, and the path recorded for the VS Code extension. msl now uses its real executable path.

Security

• Other local user accounts can no longer read or change your distributions through ~/.msl/distros (#1). The view is served through a Unix socket that only your user can open, instead of a 127.0.0.1 port, and msld checks every NFS call: only your user ID and the kernel’s get through, and only msld can mount the view. fileViewTransport = tcp in [msl2] brings back the port, with the same checks but weaker protection. See Security model.

0.1.7

25 September 2026 · GitHub release · kernel kernel-6.18.15-msl-76f230e

Added

• msl --manage <distro> --resize <size> grows the disk all distributions share (#3). Stop every distribution first with msl --shutdown. MSL restarts the VM, which checks and grows the filesystem before mounting it, in about 3 seconds for 256 GB. The disk can’t shrink, and can’t be larger than the macOS disk.
• defaultVhdSize in [msl2], as in .wslconfig, sets the disk’s size when it’s created. Without it, a new disk is 256 GB, but never more than the macOS disk.
• msl --status shows the disk: its maximum size, what it uses on macOS, and what’s free in the distributions and on macOS. It warns when macOS is nearly out of disk space, which the distributions can’t see.

Changed

• Breaking: macOS files are mounted at /mnt/macos in every distribution, not /mnt/mac (/macos with a custom [automount] root). The environment variables MSL_MAC_USER, MSL_MAC_HOME and MSL_MAC_VIEW are now MSL_MACOS_USER, MSL_MACOS_HOME and MSL_MACOS_VIEW, and msl --version --json reports macos instead of macOS. Update scripts, shell profiles and editor settings that use the old names; there’s no compatibility link.
• Messages say “macOS” throughout, instead of mixing “Mac” and “macOS”.
• msl --version and msld’s log show the commit a build came from, as 0.1.7+3af5916 (with .dirty for uncommitted changes). Update checks still compare the plain version.
• Kernel releases are tagged with a hash of their configuration instead of a counter, for example kernel-6.18.15-msl-76f230e. msl --version shows it.
• The kernel enables device-mapper and the NBD client. See Kernel release notes.
• The VM’s initial RAM disk carries static e2fsck and resize2fs from Debian’s e2fsprogs 1.47.2 (GPL-2.0), to check and grow the shared disk. Their source is attached to each release.

Fixed

• msl --shutdown leaves the shared disk clean. It used to power off with the filesystem still marked for journal recovery, which then ran at every boot (#45).

0.1.6

25 September 2026 · GitHub release

Changed

• Breaking: msl --manage <distro> --move fails with “not supported” instead of reporting success. It only recorded the location: every distribution lives on the shared disk, so nothing was moved.
• The VM section of ~/.mslconfig is now [msl2]. [wsl2] still works, so existing files and a copied .wslconfig need no change.

Fixed

• Names that are CNAME aliases, such as deb.debian.org, cdn.kernel.org and www.apple.com, resolve in distributions again (#42). 0.1.5’s DNS fix made macOS report the CNAME record as well, and msld then answered with the alias alone or with records glibc rejects, so apt and curl couldn’t reach those hosts.

0.1.5

25 September 2026 · GitHub release

Fixed

• DNS lookups no longer stall for 5 to 10 seconds when a name has an IPv4 address but no IPv6 one, as github.com does (#41). msld now passes on macOS’s “no such record” answer instead of waiting for a timeout. Tools that look up both address families, such as curl, git and VS Code’s extension host, used to hit connect timeouts; VS Code timed out connecting to api.github.com while cloning.

0.1.4

25 September 2026 · GitHub release

Added

• msl --manage-ide [--ide <vscode|vscode-insiders|vscode-oss|cursor|all>] [--install|--uninstall] sets up the VS Code extension (#35). It installs the bundled extension and enables its proposed API in the IDE’s argv.json, keeping comments and other keys. Without options, it lists the IDEs it finds and asks what to do. The installer runs it for the IDEs it finds (--no-ide skips this), and msl --uninstall undoes it.
• A preview VS Code extension that opens folders inside a distribution, with no SSH and no network port on macOS. See Get started with VS Code and the VS Code extension release notes.
• msld’s connect socket, connect.sock, which the extension uses to open byte streams into a distribution (#32).

Changed

• Breaking: distribution files on macOS moved from ~/MSL/<distro> to ~/.msl/distros/<distro>, so they no longer add a visible folder to your home directory. Each distribution still appears in Finder under Locations with its logo. On start, msld unmounts old ~/MSL mounts and removes ~/MSL if it’s empty. MSL_VIEW_DIR still overrides the location.
• x86_64-only distributions (Arch Linux, SUSE Linux Enterprise, eLxr) are no longer offered by msl --list --online, and msl --install refuses them (#40). --install --from-file still accepts x86_64 images.
• Releases no longer include a .pkg. install.sh is the way to install MSL, and the only one that sets up IDEs.
• The VS Code extension has its own releases, vscode-<version>, like the kernel. Each MSL release bundles the published one.

Fixed

• msl --help lists every command msl accepts, adding --debug-shell, --mount and --unmount, --update, --uninstall, --manage, --set-version, --set-default-version and --list --online.
• msld removes its VM bridge sockets when the VM stops, so stale sockets no longer pile up.

0.1.3

25 September 2026 · GitHub release

Added

• --json for the query commands: --list and its variants, --list --online, --status and --version. Errors go to stderr as JSON, with wsl.exe’s exit codes.

0.1.2

24 September 2026 · GitHub release

Fixed

• Stopping a distribution (--terminate, the idle timeout, --shutdown) shuts it down cleanly instead of killing it (#19). systemd distributions power off, and other distributions’ processes get SIGTERM. Anything still running after 10 seconds is killed. Previously journald reported “corrupted or uncleanly shut down” journals, and services could lose unflushed data.
• The network interface stays eth0, as in WSL (#20). systemd 259, in Ubuntu 26.04, treats the distribution as a container, so it ignored net.ifnames=0 and renamed the interface to enp0s1.

0.1.1

24 September 2026 · GitHub release · kernel kernel-6.18.15-msl.1

The first release. (0.1.0 was withdrawn before it was announced; 0.1.1 replaces it.)

• The wsl.exe command line on macOS, with the same arguments, behaviour and messages: install, import, export and unregister; list, set the default, terminate and shut down; --status, --manage, --mount and --unmount; --debug-shell, --update, --uninstall and --version.
• Unmodified arm64 WSL distribution images, from Microsoft’s distribution list or a .wsl file, in one lightweight Virtualization.framework VM. Each distribution gets its own init and can run systemd.
• Integration with macOS: the macOS filesystem in every distribution, with msl starting in your current macOS directory; MSLENV and mslpath; localhost forwarding and DNS through macOS; each distribution’s files in Finder, with the distribution’s logo.
• ~/.mslconfig (the .wslconfig equivalent), /etc/wsl.conf and /etc/msl.conf, idle timeouts, and MSL’s own first-run setup for Debian.
• An interactive installer, install.sh, and self-update with msl --update.
• PGP-signed release checksums: install.sh verifies the signature when gpg is installed and a signature is published.
• Releases include the full licence texts of all dependencies, and the GPL source of BusyBox and the kernel.
• Licensed under Apache-2.0.