WSL 2.9.11 lands with container restart support and Plan9 mount fixes
Microsoft's fast-moving pre-release stream adds a transactional restart method and resolves two DrvFs regressions.
Microsoft has released WSL 2.9.11, a small but targeted pre-release that lands just four days after its predecessor. The update, authored by WSL core maintainer Ben Hillis, brings a transactional container restart method to the WSLC runtime and patches two separate mount regressions tied to Plan9 shares.
WSL's release cadence has been relentless lately. The 2.9.10 version rolled out on September 4 with roughly 23 pull requests focused on CLI polish and docker parity. This new drop trims the scope down to three commits. If you've been running the WSLC beta, you've likely hit at least one of the issues this build addresses.
A proper restart loop
The headline here is the new Restart() operation on the IWSLCContainer COM interface. Bee Na Chauhan implemented it as a single atomic transaction. The method stops and starts the container without releasing host-scoped resources like ports and bind mounts in between.
That matters. You can now restart a container without manually tearing down port reservations, which previously required careful scripting to avoid conflicts. The implementation guards against race conditions with delete operations using a transaction lock, and introduces a new error code for containers that vanish mid-restart. Stop timeout validation also got moved to the top of the call path, fixing a corner case where invalid values slipped through.
The CLI wrapper for this feature lives in a separate pull request that didn't make the cut for this build. You won't see it at the command line just yet, but the underlying API is solid.
Fixing broken shares
Two regressions took up the other two slots, both handled by Feng Wang. The first untangles a read-only mount flag issue where the ;ro option was incorrectly passed to the Plan9 server. The server choked on it, throwing "Operation not supported" for mounts that should have just worked. Wang splits the handling: Plan9 shares now rely solely on the Linux MS_RDONLY flag, while VirtioFS shares keep their existing ro propagation.
The second fix addresses HCS-managed Plan9 shares failing to attach after a recent Windows update. It surfaces as E_FAIL during image builds or when plugins try to attach shares. Wang sidesteps the upstream issue by switching to WSL's existing per-user Plan9 server pattern. This preserves session user permissions on mounted shares, which the previous HCS path dropped.
These mount fixes touch on something many users run into but rarely complain about until they can't access their files. The Plan9 backend is the bridge for WSLC shares, so when it breaks, container operations stall. Hillis noted the team may roll back to inbox Plan9 once Microsoft patches the root cause upstream. A fix is already in progress.
The bigger picture
This release reinforces what we've seen all summer. Microsoft is pushing WSLC hard as a Docker alternative. The CLI commands for inspect, list, prune, and system info landed recently. The container restart API adds another parity point.
It's not ready for prime time yet. The release is strictly pre-release, and the CLI surface is still filling in. But the trajectory is clear. The wslc runtime is becoming a serious option for Linux container workloads on Windows, and the team isn't slowing down.
WSL 2.9.11 is available now. If you're testing the WSLC beta, updating resolves the Plan9 mount issues and adds a safer restart path. Head here to download the build.
