Dear Debian os-prober maintainers, I would like to report what appears to be a locale-dependent bug in os-prober affecting Windows Boot Manager detection. System ------ Distribution: Debian 13 (Trixie) Package: os-prober 1.83 Locale: tr_TR.UTF-8 Boot mode: UEFI Disk layout: - EFI System Partition (FAT32) - Windows Boot Manager - Debian GNU/Linux Problem ------- Running: sudo update-grub does not detect the existing Windows Boot Manager. The generated GRUB configuration only contains Linux entries. However, running: sudo LC_ALL=C update-grub correctly reports: Found Windows Boot Manager on /dev/nvme0n1p2@/EFI/Microsoft/Boot/bootmgfw.efi and Windows is added to the GRUB menu. Investigation ------------- The EFI System Partition was verified to be correct. The following all succeed: - EFI partition mounts correctly. - /boot/efi/EFI exists. - /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi exists. - efibootmgr shows Windows Boot Manager. - The Microsoft probe: /usr/lib/os-probes/mounted/efi/20microsoft /boot/efi/EFI correctly detects Windows. Tracing os-prober using: sh -x /usr/bin/os-prober showed that it executes: /usr/lib/os-probes/mounted/05efi Tracing that script further shows that it exits with: /boot/efi does not have /EFI directory even though the directory exists. The relevant helper function is: item_in_dir() defined in: /usr/share/os-prober/common.sh which performs: ls -1 "$2" | grep -i "^$1$" Additional testing showed: Under tr_TR.UTF-8: ls -1 /boot/efi | grep -i '^efi$' returns no output. Under the C locale: LC_ALL=C sh -c 'ls -1 /boot/efi | grep -i "^efi$"' correctly returns: EFI This strongly suggests that the failure is locale-dependent. Expected behaviour ------------------ Windows Boot Manager should be detected regardless of the user's locale. Workaround ---------- Running: sudo LC_ALL=C update-grub correctly detects Windows and generates the expected GRUB entry. Possible cause -------------- The failure appears to be related to locale-sensitive case-insensitive matching inside item_in_dir(). The helper should ideally perform the comparison in a locale-independent manner. Investigation performed by: Erol Saner ChatGPT (OpenAI) Thank you for maintaining Debian and for your time reviewing this report.
Hi Erol, Am 26. Juli 2026 02:23:34 MESZ schrieb Erol SANER <erolsaner@gmail.com>: Thanks for your exact analysis. Subject to another/better ideas, and until a final fix arrives, my proposal would be, to add "LC_ALL=C" to the command for now. Thoughts/objections anyone? Holger
That's exactly the right thing, yeah.
Hi,
Erol SANER <erolsaner@gmail.com> (2026-07-26):
This would:
echo EFI | grep -i '^efı$'
with the final character before the anchor on the right being:
U+0131 LATIN SMALL LETTER DOTLESS I
And this would:
echo EFİ | grep -i '^efi$'
with the final character in the echo being:
U+0130 LATIN CAPITAL LETTER I WITH DOT ABOVE
The presence/absence of the dot being significant in Turkish:
https://en.wikipedia.org/wiki/Turkish_alphabet
And yes, as Steve hinted, setting LC_ALL=C is the way to go: we don't
want to have to know about (or be exposed to) locale-dependent fun here.
Cheers,
Hi, Steve McIntyre <steve@einval.com> wrote (Thu, 30 Jul 2026 11:35:04 +0100): Pushed to git. Holger
We believe that the bug you reported is fixed in the latest version of
os-prober, which is due to be installed in the Debian FTP archive.
A summary of the changes between this version and the previous one is
attached.
Thank you for reporting the bug, which will now be closed. If you
have further comments please address them to 1142788@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.
Debian distribution maintenance software
pp.
Holger Wansing <hwansing@mailbox.org> (supplier of updated os-prober package)
(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Thu, 30 Jul 2026 14:26:34 +0200
Source: os-prober
Architecture: source
Version: 1.85
Distribution: unstable
Urgency: medium
Maintainer: Debian Install System Team <debian-boot@lists.debian.org>
Changed-By: Holger Wansing <hwansing@mailbox.org>
Closes: 1142788
Changes:
os-prober (1.85) unstable; urgency=medium
.
* Team upload
.
* Make sure, that the grep call for finding /boot/efi/EFI is locale-
independent (add "LC_ALL=C"). Closes: #1142788.
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