stdbuf: use exec instead of forking by Ecordonnier · Pull Request #9495 · uutils/coreutils

Ecordonnier · 2025-11-26T23:04:13Z

forking creates a new PID and it not compatible with GNU coreutils implementation.

use Command::exec() instead of Command::spawn() which forks
add stdbuf test verifying that no fork happens

github-actions · 2025-11-26T23:18:55Z

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

github-actions · 2025-12-01T13:51:20Z

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

codspeed-hq · 2025-12-03T13:07:37Z

Merging this PR will not alter performance

✅ 141 untouched benchmarks
⏩ 38 skipped benchmarks¹

_{Comparing Ecordonnier:eco/stdbuf-exec-instead-of-fork (548a5e9) with main (0d403a4)}

38 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

github-actions · 2025-12-03T13:10:39Z

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

github-actions · 2025-12-03T13:35:59Z

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

Ecordonnier · 2025-12-03T14:53:49Z

This is ready for review. I don't intend to work on this branch any more.

Ecordonnier · 2025-12-09T00:03:21Z

I've just seen #9013 (comment) which is also relevant for my PR. I'll check if Command::exec() can be used instead of Command::status().

github-actions · 2025-12-09T10:43:05Z

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

github-actions · 2025-12-09T11:30:40Z

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

Ecordonnier · 2025-12-09T12:23:18Z

The PR is ready for review.

github-actions · 2025-12-09T21:13:12Z

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

github-actions · 2025-12-09T21:40:10Z

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

github-actions · 2025-12-10T10:02:18Z

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

github-actions · 2025-12-17T09:53:51Z

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/inotify-dir-recreate is now passing!

github-actions · 2026-01-06T17:46:22Z

GNU testsuite comparison:

GNU test failed: tests/shuf/shuf-reservoir. tests/shuf/shuf-reservoir is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/sort/sort-stale-thread-mem. tests/sort/sort-stale-thread-mem is passing on 'main'. Maybe you have to rebase?

Forking creates a new PID and it not compatible with GNU coreutils implementation. - use exec instead of forking - add test verifying that execvp is used Fixes uutils#9066 Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>

github-actions · 2026-01-06T21:35:26Z

GNU testsuite comparison:

Congrats! The gnu test tests/shuf/shuf-reservoir is no longer failing!
Congrats! The gnu test tests/sort/sort-stale-thread-mem is no longer failing!

Copilot

Pull request overview

This PR replaces the fork+spawn implementation in stdbuf with a direct exec() call, making it compatible with GNU coreutils. The previous implementation broke signal handling and PR_SET_PDEATHSIG because it created a new PID through forking. With exec(), the stdbuf process is replaced by the target command, preserving the PID and allowing signals to propagate correctly.

Changes:

Replaced Command::spawn() with Command::exec() to avoid forking
Simplified error handling by removing wait/signal logic (no longer needed with exec)
Added comprehensive test to verify no fork occurs by checking /proc cmdline

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/uu/stdbuf/src/stdbuf.rs	Replaces spawn+wait with exec, updates imports, simplifies error handling to match exec-only flow
tests/by-util/test_stdbuf.rs	Adds Linux-specific regression test that validates exec behavior by polling /proc to ensure process replacement occurs

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src/uu/stdbuf/src/stdbuf.rs

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Ecordonnier · 2026-01-14T15:23:18Z

@cakebaker can you please review this PR?

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Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from de2b66c to 0110357 Compare December 1, 2025 12:50

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 0d7529b to 4c557bf Compare December 3, 2025 13:21

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 4c557bf to 9afe842 Compare December 9, 2025 10:27

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 9afe842 to af3957e Compare December 9, 2025 11:13

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from af3957e to 197203c Compare December 9, 2025 20:54

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 197203c to 8ae82a8 Compare December 9, 2025 21:23

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 8ae82a8 to 11a9c80 Compare December 10, 2025 09:46

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 11a9c80 to 7963769 Compare December 17, 2025 09:35

ChrisDryden mentioned this pull request Dec 19, 2025

GNU coreutils 9.9: Detailed Test report 12/19 #9729

Closed

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 8534afe to 964753c Compare January 6, 2026 17:27

stdbuf: use exec instead of forking

a235f1a

Forking creates a new PID and it not compatible with GNU coreutils implementation. - use exec instead of forking - add test verifying that execvp is used Fixes uutils#9066 Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>

Ecordonnier force-pushed the eco/stdbuf-exec-instead-of-fork branch from 964753c to a235f1a Compare January 6, 2026 21:24

Ecordonnier requested a review from Copilot January 11, 2026 20:18

Copilot started reviewing on behalf of Ecordonnier January 11, 2026 20:18 View session

Copilot AI reviewed Jan 11, 2026

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Update src/uu/stdbuf/src/stdbuf.rs

548a5e9

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

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sylvestre merged commit c66be8c into uutils:main Jan 17, 2026
132 checks passed

Ecordonnier deleted the eco/stdbuf-exec-instead-of-fork branch January 17, 2026 09:32

mattsu2020 pushed a commit to mattsu2020/coreutils that referenced this pull request Jan 23, 2026

stdbuf: use exec instead of forking (uutils#9495)

7433f88

moonfruit mentioned this pull request Feb 3, 2026

uutils-selected 0.6.0 moonfruit/homebrew-tap#453

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Merging this PR will not alter performance

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Ecordonnier commented Jan 14, 2026

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Ecordonnier commented Nov 26, 2025 •

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