Subject: corrupt object on git-gc
Abstract: Some tricks to reconstruct blob objects in order to fix
a corrupted repository.
+Content-type: text/asciidoc
+How to recover a corrupted blob object
+======================================
+
+-----------------------------------------------------------
On Fri, 9 Nov 2007, Yossi Leybovich wrote:
>
> Did not help still the repository look for this object?
> Any one know how can I track this object and understand which file is it
+-----------------------------------------------------------
-So exactly *because* the SHA1 hash is cryptographically secure, the hash
+So exactly *because* the SHA-1 hash is cryptographically secure, the hash
itself doesn't actually tell you anything, in order to fix a corrupt
object you basically have to find the "original source" for it.
The easiest way to do that is almost always to have backups, and find the
-same object somewhere else. Backups really are a good idea, and git makes
+same object somewhere else. Backups really are a good idea, and Git makes
it pretty easy (if nothing else, just clone the repository somewhere else,
and make sure that you do *not* use a hard-linked clone, and preferably
not the same disk/machine).
interesting for the future, in the hope that you can re-create a
non-corrupt version.
+-----------------------------------------------------------
So:
> ib]$ mv .git/objects/4b/9458b3786228369c63936db65827de3cc06200 ../
+-----------------------------------------------------------
This is the right thing to do, although it's usually best to save it under
-it's full SHA1 name (you just dropped the "4b" from the result ;).
+it's full SHA-1 name (you just dropped the "4b" from the result ;).
Let's see what that tells us:
+-----------------------------------------------------------
> ib]$ git-fsck --full
> broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
> to blob 4b9458b3786228369c63936db65827de3cc06200
> missing blob 4b9458b3786228369c63936db65827de3cc06200
+-----------------------------------------------------------
Ok, I removed the "dangling commit" messages, because they are just
messages about the fact that you probably have rebased etc, so they're not
git hash-object -w my-magic-file
-again, and if it outputs the missing SHA1 (4b945..) you're now all done!
+again, and if it outputs the missing SHA-1 (4b945..) you're now all done!
But that's the really lucky case, so let's assume that it was some older
version that was broken. How do you tell which version it was?
git log --raw --all
and just looked for the sha of the missing object (4b9458b..) in that
-whole thing. It's up to you - git does *have* a lot of information, it is
+whole thing. It's up to you - Git does *have* a lot of information, it is
just missing one particular blob version.
Trying to recreate trees and especially commits is *much* harder. So you