os.getlogin() fails with OSError: [Errno 34] for usernames > 9 characters

Bug report

Bug description:

import os
print(os.getlogin())

$ python3 -c "import os; print(os.getlogin())"

Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import os; print(os.getlogin())
                     ~~~~~~~~~~~^^
OSError: [Errno -34] Unknown error: -34

It appears that if Python is compiled in an environment without HAVE_MAXLOGNAME but with HAVE_UT_NAMESIZE, getlogin_r will return error 34 if username is >9 characters.

This appears to be a regression introduced in #132751:

https://github.com/duaneg/cpython/blob/675342cf59ffe53337d92af989b97dad687a10ea/configure.ac#L5434

The correct header file to search for is sys/param.h, not sys/params.h. As a result, HAVE_UT_NAMESIZE is satisfied (via utmp.h) but HAVE_MAXLOGNAME is not.

This was originally reported to Homebrew via Homebrew/homebrew-core#226857.

CPython versions tested on:

3.15

Operating systems tested on:

macOS

Linked PRs

@alebcay

@alebcay would you like to submit a PR with the fix?

Sure, I'd be happy to. ~~As far as processes go, should I also regenerate configure, and is there a particular command/script I should use for that?~~ I found https://devguide.python.org/contrib/workflows/regenerate/#regenerate-configure and will use that.

pythongh-135497: fix MAXLOGNAME detection in configure

gh-135497: fix `MAXLOGNAME` detection in `configure.ac` (#135508)

pythongh-135497: fix `MAXLOGNAME` detection in `configure.ac` (python…

[3.13] gh-135497: fix `MAXLOGNAME` detection in `configure.ac` (GH-13…

[3.14] gh-135497: fix `MAXLOGNAME` detection in `configure.ac` (GH-13…

Thank you for the report & the fix!

pythongh-135497: fix `MAXLOGNAME` detection in `configure.ac` (python…

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os.getlogin() fails with OSError: [Errno 34] for usernames > 9 characters #135497

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os.getlogin() fails with OSError: [Errno 34] for usernames > 9 characters #135497

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

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sobolevn commented on Jun 14, 2025

alebcay commented on Jun 14, 2025

picnixz commented on Jun 14, 2025

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