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Restore the logic to re-create the WSL binfmt_misc entry if it's overriden by systemd-binfmt - #41780
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ExecStopPostappears malformed in two ways: (1)$$SERVICE_RESULT… · NewExecStop=(empty) which… · New\n, while earlier in the same testcmd.exeoutput is… · New
What changed in this PR
Restores WSL’s protection of its binfmt_misc entry when systemd-managed binfmt services override it, and adds coverage to validate interop remains functional across systemd-binfmt lifecycle events.
Changes:
- Add a Windows unit test that exercises systemd-binfmt overrides/restarts and validates
WSLInteropis restored. - Reintroduce/initiate generation of systemd override drop-ins to re-register WSL’s binfmt handler when it’s replaced.
- Gate the behavior behind
wsl.confoptions (boot.protectBinfmtand interop enablement).
| File | Description |
|---|---|
| test/windows/UnitTests.cpp | Adds a new test validating binfmt restoration and interop stability across systemd-binfmt events. |
| src/linux/init/init.cpp | Adds config parsing and generates systemd drop-in overrides to restore WSL’s binfmt registration. |
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| [Service] | ||
| ExecStop= | ||
| ExecStartPost=/bin/sh -c '{0}' | ||
| ExecStopPost=/bin/sh -c 'if [ "$$SERVICE_RESULT" != "success" ]; then {0}; fi')", |
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Ben Hillis (benhillis)
approved these changes
Oct 2, 2026
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Summary of the Pull Request
This change is a partial revert of https://github.com/microsoft/WSL/pull/40621/changes, to restore the logic to re-create our binfmt_misc entry if something like mono overrides it.
While working on this, I noticed that the read-only mount actually causes the systemd-binfmt unit to fail to start, but that's a pre-existing issue so we can investigate that in a separate change
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