Intro

My machine had disk problems. I lost quite a bit of data and it seems I lost one of my git repositories as well.

git log | head
error: Could not read 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc
fatal: Failed to traverse parents of commit 92a2c1a74048cf8caec7ddd27f943652fab147ac

Analyzing the damage

The ref log apparently is still intact:

$ tail -n 3 .git/logs/refs/heads/master
ba6111ef1ebafac3346f816f36c01bc4af6c2734 03c6b33d82e9e9ec1ecea4985fbe1cca994f44e2 Dirk Tilger  1299783879 +0400 commit: Virgin mono-basic checkin
03c6b33d82e9e9ec1ecea4985fbe1cca994f44e2 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc Dirk Tilger  1300007389 +0400 commit: Missing efreet dependency
2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc 92a2c1a74048cf8caec7ddd27f943652fab147ac Dirk Tilger  1300007427 +0400 commit: Missing edje dependency

In the list above the first ID is the commit ID, the second ID is the tree ID. The most recent commit is the last one. The commit object 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc seems damaged:

git log 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc
fatal: bad object 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc

The tree object 92a2c1a74048cf8caec7ddd27f943652fab147ac seems intact:

git ls-tree 92a2c1a74048cf8caec7ddd27f943652fab147ac
040000 tree a82504d023fe31e3ed093e58fc4872e5ccd7a4d9    app-portage
040000 tree 0a52ed4638173345b769ec17091db2285849c789    app-text
040000 tree febb17823eb11421f76188d9900c94d6528a6401    app-vim
040000 tree 466e19ae9676334eba999f20e51e6bbea5570933    dev-lang
040000 tree 78dd40b37ebc0cb9ccd59877b08658024416feab    dev-libs
040000 tree 1d60e8774bd1ba9a2170c5507d5357bcfe7bd11d    media-libs
040000 tree 29b1bb0b660a7a7006d2482a9c5703237e2c273f    media-video
040000 tree 5da17094d77e36eb216074117b1fc869aa80b0ce    www-plugins

The commit object 03c6b33d82e9e9ec1ecea4985fbe1cca994f44e2 seems not damaged:

git log --oneline 03c6b33d82e9e9ec1ecea4985fbe1cca994f44e2 | head
03c6b33 Virgin mono-basic checkin
ba6111e Renamed mono ebuild to 9999 version
1fe38af Mono ebuild from the main tree
4835a15 Rename to git ebuild
7ca911f Moonlight ebuild from the main tree
ef843f2 Added odf-converter ebuild from https://bugs.gentoo.org/show_bug.cgi?id=171182
3dce387 g-pypi from my modified pythonhead
1c0ffb8 Compiler plugin for PyLint ( http://www.logilab.org/projects/pylint/ ), a style checking tool for Python.
283897d Awesome. Completion with manual. :
fa38747 vim tasklist greps out TODO and FIXME

The tree object 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc is damaged:

git ls-tree 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc
fatal: not a tree object

So to repair this repository all we have to do is to recreate commit 2e3f651d6fdd1ca7604df1f3b1424a4c67095ccc by using the working tree object 92a2c1a74048cf8caec7ddd27f943652fab147ac.

Repairing

What has been lost is one commit object. In theory we might be able to look for a tree object that is not referenced either by another tree object or a commit object. However, as in my case the last two commits actually had been accepted upstream, all I really need to do is to change the tip of my branch to before the damaged commit.

git branch -l before-efreet 03c6b33d82e9e9ec1ecea4985fbe1cca994f44e2

When I now checkout, I still get an error, because it tries to see what needs merging and so on:

git checkout before-efreet
fatal: unable to read tree 78dd40b37ebc0cb9ccd59877b08658024416feab

This can be fixed by forcing the checkout and with having made a backup of everything just before, nothing will get lost.

git checkout -f before-efreet