Fix UseSystemd() silently failing with ProtectProc=invisible by CybCorv · Pull Request #125520 · dotnet/runtime

CybCorv · 2026-03-13T14:32:42Z

Summary

UseSystemd() silently fails when the service is configured with ProtectProc=invisible (recommended by systemd.exec(5) for most services).

GetIsSystemdService() reads /proc/{ppid}/comm to check whether the parent process is named systemd. Under ProtectProc=invisible, this file is hidden for processes owned by other users, causing an exception that is silently swallowed — the method returns false, no IHostLifetime is registered, READY=1 is never sent, and systemd times out waiting for the service to become ready.

Fix

Use $SYSTEMD_EXEC_PID (introduced in systemd v248) as the primary detection method. systemd sets this variable to the PID of the main service process; comparing it to Environment.ProcessId is reliable and unaffected by ProtectProc.

The existing /proc/{ppid}/comm check is kept as a fallback for older systemd versions still in use on maintained distributions (Ubuntu 20.04 ships systemd 245, Debian 10 ships systemd 241).

Out of scope

Two related issues are deferred to separate PRs to keep this change focused and easy to review:

SystemdNotifier never unsets NOTIFY_SOCKET after capturing it
SystemdConsoleFormatter should use $JOURNAL_STREAM + fstat instead of unconditionally writing journal-formatted output

Testing

Tests use RemoteExecutor to isolate the static cache in SystemdHelpers._isSystemdService.

Partially addresses #88660
See #125368

GetIsSystemdService() used to read /proc/{ppid}/comm to verify the parent process is named "systemd". This file is hidden when the service runs with ProtectProc=invisible (recommended by systemd.exec(5)), causing the check to silently return false. As a result, no IHostLifetime is registered and READY=1 is never sent, leading to a systemd start timeout. Fix this by using the SYSTEMD_EXEC_PID environment variable (systemd v248+), which is set to the PID of the main service process. Comparing it to the current PID is reliable and unaffected by ProtectProc=invisible. The /proc fallback is kept for compatibility with older systemd versions (e.g. Ubuntu 20.04 / systemd 245, Debian 10 / systemd 241). Partially addresses dotnet#88660 See dotnet#125368

dotnet-policy-service · 2026-03-13T14:33:55Z

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Copilot

Pull request overview

Updates Microsoft.Extensions.Hosting.Systemd systemd-service detection so UseSystemd() works when /proc access is restricted by ProtectProc=invisible, and adds tests for the new detection behavior.

Changes:

Prefer $SYSTEMD_EXEC_PID (systemd v248+) to detect whether the current process is the main systemd service process.
Keep the existing /proc/{ppid}/comm check as a legacy fallback for older systemd versions.
Add Linux-only RemoteExecutor tests covering $SYSTEMD_EXEC_PID matching/mismatching/missing/malformed and the existing static caching behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Adds `$SYSTEMD_EXEC_PID`-based detection before the legacy `/proc` fallback.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs	New `RemoteExecutor` tests for detection behavior and caching.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/Microsoft.Extensions.Hosting.Systemd.Tests.csproj	Enables `RemoteExecutor` support for the test project and fixes a trailing space in the `ProjectReference`.

src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs

CybCorv · 2026-03-13T14:41:14Z

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Fixes UseSystemd() incorrectly not detecting systemd services when /proc/{ppid}/comm is inaccessible under ProtectProc=invisible, by switching to $SYSTEMD_EXEC_PID (systemd v248+) as the primary detection signal while keeping the /proc parent-name check as a legacy fallback.

Changes:

Add $SYSTEMD_EXEC_PID-based detection to SystemdHelpers.GetIsSystemdService() with legacy fallback retained.
Add Linux-only RemoteExecutor tests covering env-var detection and caching behavior.
Update the test project to include RemoteExecutor infrastructure and fix a malformed ProjectReference.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs	Adds `RemoteExecutor`-isolated tests validating `SYSTEMD_EXEC_PID` behavior and caching.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/Microsoft.Extensions.Hosting.Systemd.Tests.csproj	Enables `RemoteExecutor` support and fixes `ProjectReference` formatting.
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Uses `SYSTEMD_EXEC_PID` as the primary systemd detection method; retains `/proc` fallback.

CybCorv · 2026-03-16T08:46:00Z

src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs

+using Microsoft.Extensions.Hosting.Systemd;
+using Xunit;
+
+namespace Microsoft.Extensions.Hosting


Keeping Microsoft.Extensions.Hosting to match the existing convention in this test project.
See UseSystemdTests.cs.

Copilot

Pull request overview

This PR fixes UseSystemd() incorrectly detecting “not running under systemd” when ProtectProc=invisible prevents reading /proc/<ppid>/comm, by preferring the SYSTEMD_EXEC_PID environment variable (systemd v248+) for detection and keeping the legacy /proc check as a fallback.

Changes:

Update systemd-service detection to use SYSTEMD_EXEC_PID (v248+) as the primary signal.
Keep the existing /proc/<ppid>/comm parent-name check as a legacy fallback path.
Add Linux-only unit tests (using RemoteExecutor) to cover the new detection logic and the static caching behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Prefer `SYSTEMD_EXEC_PID`-based detection to avoid `/proc` access failures under `ProtectProc=invisible`, with legacy fallback retained.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs	Adds `RemoteExecutor`-isolated tests for `SYSTEMD_EXEC_PID` match/mismatch/absent/malformed and caching behavior.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/Microsoft.Extensions.Hosting.Systemd.Tests.csproj	Enables `RemoteExecutor` usage for the new tests and fixes the project reference formatting.

Copilot

Pull request overview

Updates Microsoft.Extensions.Hosting.Systemd’s systemd-service detection so UseSystemd() doesn’t silently no-op when /proc access is restricted (e.g., ProtectProc=invisible), and adds focused unit tests for the new detection behavior.

Changes:

Prefer $SYSTEMD_EXEC_PID (systemd v248+) to detect running under systemd without relying on /proc.
Retain existing /proc/<ppid>/comm parent-name check as a fallback for older systemd versions.
Add RemoteExecutor-based tests to validate SYSTEMD_EXEC_PID handling and static caching; enable RemoteExecutor in the test project.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/libraries/Microsoft.Extensions.Hosting.Systemd/src/SystemdHelpers.cs	Adds `$SYSTEMD_EXEC_PID`-based detection with legacy `/proc` fallback.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs	New RemoteExecutor tests covering matching/mismatching/absent/malformed values and caching.
src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/Microsoft.Extensions.Hosting.Systemd.Tests.csproj	Enables RemoteExecutor; fixes a stray space in the ProjectReference include.

CybCorv · 2026-03-18T11:15:43Z

Manual integration testing

I've validated the fix against a full test matrix using a dedicated test harness: https://github.com/CybCorv/systemd-dotnet-hosting-tests

Scenario	.NET	ProtectProc	IsSystemdService	Result
System service + notify	10 (unfixed)	Yes	False	❌ timeout
System service + notify	11 (this PR)	Yes	True	✅ Started
System service + notify	10/11	No	True	✅ Started
User service + notify	10/11	Yes*	True	✅ Started
Podman + --sdnotify=container	10/11	Yes*	True (PID=1)	✅ Started
Docker + notify	10/11	Yes/No	True (PID=1)	⚠️ timeout†

ProtectProc has no effect in user-scoped services (systemd limitation).
Docker timeout is a pre-existing issue -NOTIFY_SOCKET is not proxied to the notifier socket.

Copilot AI review requested due to automatic review settings March 13, 2026 14:32

github-actions bot added the area-Extensions-Hosting label Mar 13, 2026

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Mar 13, 2026

Copilot started reviewing on behalf of CybCorv March 13, 2026 14:33 View session

Copilot AI reviewed Mar 13, 2026

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src/libraries/Microsoft.Extensions.Hosting.Systemd/tests/SystemdHelpersTests.cs Outdated Show resolved Hide resolved

Remove unused variable in Test

db71c71

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings March 13, 2026 14:45

Copilot AI reviewed Mar 13, 2026

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This was referenced Mar 13, 2026

System.Net.WebSockets.Client.Tests: Assertion failed: !_hasWaiter #121157

Open

iOS.Device test WorkItemExecutions #122874

Open

XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

Open

CybCorv added 2 commits March 16, 2026 09:55

Merge branch 'main' into fix/systemd-protect-proc-invisible

87a6fd5

Merge branch 'dotnet:main' into fix/systemd-protect-proc-invisible

83c25dd

Copilot AI review requested due to automatic review settings March 17, 2026 13:38

Copilot started reviewing on behalf of CybCorv March 17, 2026 13:39 View session

Copilot AI reviewed Mar 17, 2026

View reviewed changes

Add SYSTEMD_EXEC_PID constant and refactor comments in SystemdHelpers

8d3278f

cincuranet requested a review from tmds March 18, 2026 07:37

cincuranet self-assigned this Mar 18, 2026

cincuranet self-requested a review March 18, 2026 07:38

CybCorv marked this pull request as ready for review March 18, 2026 11:11

Copilot AI review requested due to automatic review settings March 18, 2026 11:11

Copilot started reviewing on behalf of CybCorv March 18, 2026 11:12 View session

Copilot AI reviewed Mar 18, 2026

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This was referenced Mar 18, 2026

slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

Open

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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This was referenced Mar 18, 2026

[wasm] OpenQA.Selenium.WebDriverTimeoutException: timeout: Timed out receiving message from renderer #117486

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[android-arm64] The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#6408

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Fix UseSystemd() silently failing with ProtectProc=invisible#125520

Fix UseSystemd() silently failing with ProtectProc=invisible#125520
CybCorv wants to merge 5 commits intodotnet:mainfrom
CybCorv:fix/systemd-protect-proc-invisible

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CybCorv commented Mar 18, 2026 •

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CybCorv commented Mar 13, 2026

Summary

Fix

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Testing

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CybCorv commented Mar 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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CybCorv commented Mar 18, 2026 •

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