Subject: [PATCH] lockfile: add case insensitive filesystem note

From: "Alan Da Costa via GitGitGadget" <[email-masked]>
Date: Mon, 22 Sep 2025 21:54:44 +0000

From: Alan Da Costa <[email-masked]>

* Add note of case insensitive client filesystems may error due to a lock
  on a case variant ref to more quickly identify failure in fetch/pull

Signed-off-by: Alan Da Costa <[email-masked]>
---
    lockfile: add case insensitive filesystem note
    
    When running git fetch or git pull on a case insensitive filesystem
    (e.g., default macOS), if multiple case variants of the same remote ref
    exist (often after a case-only rename), both variant locks map to the
    same on-disk path. When a local update is required, Git creates a lock
    for the first variant and then attempts to lock the second, which
    collides with the same lock file, so an “existing lock” error is
    reported. The underlying issue is mixed-case refs; resolve it by
    consolidating the remote to a single-case variant and update local refs
    accordingly.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2053%2Fadacosta%2Flockfile-add-case-insensitive-filesystem-note-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2053/adacosta/lockfile-add-case-insensitive-filesystem-note-v1
Pull-Request: https://github.com/git/git/pull/2053

 lockfile.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lockfile.c b/lockfile.c
index 1d5ed01682..99a470bd3d 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -156,7 +156,10 @@ void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
 		    "an editor opened by 'git commit'. Please make sure all processes\n"
 		    "are terminated then try again. If it still fails, a git process\n"
 		    "may have crashed in this repository earlier:\n"
-		    "remove the file manually to continue."),
+		    "remove the file manually to continue.\n\n"
+		    "On case insensitive client filesystems, multiple mixed-case refs will resolve\n"
+		    "to the same lock file, possibly causing this error. If so, ensure your remote\n"
+		    "refs have a single case variant."),
 			    absolute_path(path), strerror(err));
 	} else
 		strbuf_addf(buf, _("Unable to create '%s.lock': %s"),

base-commit: ab427cd991100e94792fce124b0934135abdea4b
-- 
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