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GeezerVison is showing github.com — CYGWIN supports "/dev/fd" for listing the set of file descriptors open in a process. · Issue #148575 · python/cpython

CYGWIN supports "/dev/fd" for listing the set of file descriptors open in a process. #148575

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CYGWIN supports "/dev/fd" for listing the set of file descriptors open in a process.#148575
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OS-unsupportedextension-modulesC modules in the Modules dirC modules in the Modules dirtype-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

Description

@carlo-bramini
carlo-bramini
opened on Apr 14, 2026
Issue body actions

Bug report

Bug description:

While inspecting the code for finding the causes of the issues of my build for CYGWIN, I found this piece of code:

cpython/Modules/_posixsubprocess.c

Lines 66 to 70 in 5c3deca

#if defined(__FreeBSD__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__DragonFly__)
# define FD_DIR "/dev/fd"
#else
# define FD_DIR "/proc/self/fd"
#endif

CYGWIN supports /dev/fd and not /dev/self/fd as you can see here:

Image

so a tiny fix is needed for adding __CYGWIN__ to the list of platforms to support the rigth entry with the set of file descriptors open in a process.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

  • gh-148575: Use the right entry to read the set of file descriptors on CYGWIN #148576

Activity

  1. carlo-bramini
    added
    type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error
    on Apr 14, 2026
  2. carlo-bramini
    added a commit that references this issue on Apr 14, 2026

    pythongh-148575: Use the right entry to read the set of file descript…

    6b7bf01
  3. picnixz
    added
    OS-windows
    extension-modulesC modules in the Modules dirC modules in the Modules dir
    on Apr 15, 2026
  4. vstinner
    added a commit that references this issue on May 13, 2026

    gh-148575: Use /dev/fd/ to read the set of file descriptors on Cygwin (…

    b6854c5
  5. vstinner
    closed this as completedon May 13, 2026
  6. vstinner
    added a parent issue on May 15, 2026
    • Enhance Cygwin support #149879
  7. encukou
    added
    OS-unsupported
    and removed
    OS-windows
    on Jun 5, 2026
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