Files
WSL/doc/docs/technical-documentation/relay.md
Ben Hillis 8c220dc083 Fix grammar, typos, and formatting in docs and source (#14286)
* Fix localization text, Intune capitalization, ADMX indentation, unused import

- distributions/validate.py: Remove unused 'import base64'
- en-US/en-GB Resources.resw: Fix word order 'the list distribution' -> 'the distribution list' in MessageCouldFetchDistributionList
- en-US/en-GB Resources.resw: Remove trailing space from MessageCorruptedDistroRegistration value
- intune/en-US/WSL.adml: Fix 'For Linux' -> 'for Linux' capitalization (5 occurrences) to match official product name
- intune/WSL.admx: Fix inconsistent 3-space indent to 4-space on AllowWSL1 and CustomKernelUserSettingConfigurable policies

* Fix grammar, typos, and formatting in docs and source code

- WmiService.h: Fix duplicated word 'of of' -> 'is of' in WQL comment
- drvfs.md: Fix 'which tell' -> 'which tells' (subject-verb agreement), double space, second 'tell' -> 'tells'
- systemd.md: Fix 'tries synchronizes' -> 'tries to synchronize'
- wslhost.exe.md: Fix 'processes terminates' -> 'process terminates'
- boot-process.md: Add missing 'in' preposition, fix C:/ -> C:\, fix lowercase 'linux' to 'Linux' (4 occurrences), fix misplaced parenthesis
- init.md: Fix double space before hvsocket backtick
- session-leader.md: Fix heading level ## -> ### to match sibling section
- CONTRIBUTING.md: Fix double period after bold security notice
- debugging.md: Fix missing word 'be' in 'can enabled', fix 'process' -> 'processes'
- index.md: Add missing period at end of sentence
- technical-documentation/index.md: Fix 'API's' -> 'APIs' (remove incorrect apostrophe)
- relay.md: Fix lowercase 'linux' to 'Linux' (3 occurrences)
- localhost.md: Fix lowercase 'linux' to 'Linux'
- plan9.md: Fix lowercase 'linux' to 'Linux'

* update errormessages testcase

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Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com>
2026-03-03 18:13:59 -08:00

924 B

Relay

Relay is a WSL2 Linux process created by a session leader. Its job is to create a Linux process on behalf of the user, and relay its output back to Windows.

Creating a user process

A relay is created when a LxInitMessageCreateProcessUtilityVm message is sent to a session leader. Once created, the relay creates multiple hvsocket channels with wslservice.exe.

These channels are used to:

  • Relay standard file descriptors (stdin, stdout, stderr)
  • Relay information about the terminal (for instance when the terminal window is resized from Windows)
  • Notify Windows when the Linux process exits

Once those channels are configured, the relay forks() into two processes:

  • The parent, which will read & write to the child's standard file descriptors and relay it to Windows
  • The child, which calls exec() and starts the user process