Misleading error about WSLInterop

[slawekww]

Describe the bug

WSL 2.0, Ubuntu 24.04
az CLI version: 2.89.1

az login command reported misleading error that WSL interopt is disabled but it finally redirects to external browser and works as expected

Related command

az login

Errors

grep: /proc/sys/fs/binfmt_misc/WSLInterop: No such file or directory
WSL Interopability is disabled. Please enable it before using WSL.
grep: /proc/sys/fs/binfmt_misc/WSLInterop: No such file or directory
[error] WSL Interoperability is disabled. Please enable it before using WSL.

Issue script & Debug output

On WSL interopt is enabled and working:

$cat /etc/wsl.conf
[interop]
enabled=true
appendWindowsPath=false

$echo $WSL_INTEROP
/run/WSL/725_interopls 

$ls /proc/sys/fs/binfmt_misc
/proc/sys/fs/binfmt_misc/WSLInterop-late  python3.12  register  status

$cat /proc/sys/fs/binfmt_misc/WSLInterop-late
enabled
interpreter /init
flags: P
offset 0
magic 4d5a

Expected behavior

az login should work without misleading error and correctly detect WSL interop

Environment Summary

az cli: 2.89.1
WSL 2.0, Ubuntu 24.04

Additional context

No response

[yonzhan]

Thank you for opening this issue, we will look into it.

[x-engineering-agent]

Bug Analysis

On WSL, az login shells out to check /proc/sys/fs/binfmt_misc/WSLInterop to detect whether WSL interop is enabled, in order to decide whether it can launch a Windows browser for the interactive login flow. On newer WSL versions (WSL 2, Ubuntu 24.04+), the kernel exposes WSLInterop-late instead of WSLInterop when late interop registration is used, so the existing check finds no file, prints:

grep: /proc/sys/fs/binfmt_misc/WSLInterop: No such file or directory
WSL Interoperability is disabled. Please enable it before using WSL.

even though interop is actually enabled (confirmed by $WSL_INTEROP being set and WSLInterop-late present and enabled). The login still proceeds correctly with the external-browser fallback, so the message is only cosmetic/misleading, not a functional failure.

Suggested fix: update the WSL interop detection logic (likely in azure/cli/core/_profile.py or the WSL/browser-launch helper in azure-cli-core) to also check /proc/sys/fs/binfmt_misc/WSLInterop-late (and its enabled status) before falling back to the "disabled" warning, so the message is only shown when interop is genuinely unavailable. Add a unit test covering both WSLInterop and WSLInterop-late paths.

Use this EXACT PR title: [Profile] Fix #33931: az login: Fix misleading WSL interop error message

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Use this EXACT PR title (copy verbatim, do not reword):

[Profile] Fix #33931: `az login`: Fix misleading WSL interop error message

Keep the backticks around the command and the Fix #33931: prefix. You may only adjust the wording after the command (the final summary) if the fix changes; the [Profile] prefix, issue link, and backticked command must stay.

Description — follow the PR template and fill in:

• Link the issue — start the Description with a closing keyword so the PR auto-links and closes it: Fixes #33931.
• Related command — the az ... command this affects.
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