Git repository corrupt (incorrect header check; loose object is corrupt)

Question

I experienced a power failure yesterday evening while writing a commit message. When I booted the machine back up I couldn't complete the commit. I ran git reset, added back the changed files, and tried again, and got this:

% git commit error: inflate: data stream error (incorrect header check) error: unable to unpack a94406345ac44982b00cf57b4b9660a35436637f header fatal: a94406345ac44982b00cf57b4b9660a35436637f is not a valid object 

git fsck reveals the following:

% git fsck --full Checking object directories: 100% (256/256), done. error: inflate: data stream error (incorrect header check) error: unable to unpack 4346883490a0990e68db0187241abc1642765a73 header error: inflate: data stream error (incorrect header check) fatal: loose object 4346883490a0990e68db0187241abc1642765a73 (stored in .git/objects/43/46883490a0990e68db0187241abc1642765a73) is corrupt 

I notice the messages are complaining about different objects.

I searched Stack Overflow and the Web and tried a few different things but to no avail.

• I don't have a recent backup copy.
• Cloning the repository into another directory doesn't help; the new repository exhibits the exact same problems.
• git stash gives the same message as git commit. All the other git commands seem to work normally.

How can I tell what is wrong and fix it?

git log output (just the first few lines):

% git log --oneline --decorate --all |head -n 8 253b086 (HEAD, new_tokenize) Normalized tokenizer interface slightly 0f2425a (master) Added procs to eval layer a4d4c22 Added procedures as a type d1e15ad (tag: v0.10) Added `if' form with tail call semantics f94a992 (tag: v0.9) Completed environments 031116e Fixed bug where # on a line by itself caused segfault 3d8b09f Added environments, define and set! 01cc624 Put symbol table implementation into types.c 

This is a small personal project; I usually just work in (master), but I was doing an experiment at the time (new_tokenize). 253b086 was the last successful commit before the power failure.

Answer 1

It appears that git created files in .git/objects for the new commit, but didn't successfully write to them. I solved it by deleting them one at a time and re-running git fsck --full to find the next one. I started with the one originally reported by git fsck:

% rm -f .git/objects/43/46883490a0990e68db0187241abc1642765a73 % git fsck --full Checking object directories: 100% (256/256), done. error: inflate: data stream error (incorrect header check) error: unable to unpack 86e7247af5865e857a3b61eed99986e2d9538df1 header error: inflate: data stream error (incorrect header check) fatal: loose object 86e7247af5865e857a3b61eed99986e2d9538df1 (stored in .git/objects/86/e7247af5865e857a3b61eed99986e2d9538df1) is corrupt % rm -f .git/objects/86/e7247af5865e857a3b61eed99986e2d9538df1 % git fsck --full Checking object directories: 100% (256/256), done. error: inflate: data stream error (incorrect header check) error: unable to unpack a94406345ac44982b00cf57b4b9660a35436637f header error: inflate: data stream error (incorrect header check) fatal: loose object a94406345ac44982b00cf57b4b9660a35436637f (stored in .git/objects/a9/4406345ac44982b00cf57b4b9660a35436637f) is corrupt 

And so on. I deleted five objects before git fsck came up clean, corresponding (as I suppose) to the five files in the commit I was trying to make. I guess that the file history was not corrupted at all.

Incidentally, I thought of another method that seems to work as well. git clone copies the bad objects, but git push does not. After backing up, I created a new empty repository (--bare, because otherwise you can't push to master), then unstaged my changes and pushed both branches into the new repository. Then it was just a matter of checking it out again and restoring the latest changes from my backups.

Still interested if anyone cares to shed light on the failure mechanism here.