git fsck complains about error: refs/tags/.cyg000000000559e25517156b51cf219f51/libgcj-2.95.0: badRefName: invalid refname format?!

[Jon Turney]

On 31/01/2026 18:42, Dan Shelton via Cygwin wrote:
> Hello, on Cygwin 3.6.6-1.x86_64 on CYGWIN_NT-10.0-19045/Win10 I get
> these errors from git fsck when working on a clean clone of the
> gcc.git repro:
> 
> git fsck
> error: refs/tags/.cyg000000000559e25517156b51cf219f51/libgcj-2.95.1:
> badRefName: invalid refname format
> error: refs/tags/.cyg000000000559e25517156b51cf219f51/libgcj-2.95.0:
> badRefName: invalid refname format
> error: refs/tags/.cyg000000000559e25817156b51cf219f51/libf2c-0.5.22:
> badRefName: invalid refname format
> error: refs/tags/.cyg000000000559e25817156b51cf219f51/libf2c-0.5.21:
> badRefName: invalid refname format
> 
> git fsck then exits with error code 8, breaking our scripts.
> 
> Is this a Cygwin bug or feature running wild?
Yes.

These .cygXXX files are made by the cygwin DLL (I think it's something 
like a hardlink to the running executable so we can fork even if it's 
deleted, but I might well be misremembering the details) and are 
supposed to get automatically removed.

Obviously, 'git fsck' objects to their presence, but it is safe to 
remove them.