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diff --git a/third_party/git/Documentation/howto/recover-corrupted-blob-object.txt b/third_party/git/Documentation/howto/recover-corrupted-blob-object.txt deleted file mode 100644 index 1b3b188d3c15..000000000000 --- a/third_party/git/Documentation/howto/recover-corrupted-blob-object.txt +++ /dev/null @@ -1,144 +0,0 @@ -Date: Fri, 9 Nov 2007 08:28:38 -0800 (PST) -From: Linus Torvalds <torvalds@linux-foundation.org> -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 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 -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). - -But since you don't seem to have backups right now, the good news is that -especially with a single blob being corrupt, these things *are* somewhat -debuggable. - -First off, move the corrupt object away, and *save* it. The most common -cause of corruption so far has been memory corruption, but even so, there -are people who would be interested in seeing the corruption - but it's -basically impossible to judge the corruption until we can also see the -original object, so right now the corrupt object is useless, but it's very -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 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 -at all interesting. But what remains is still very useful. In particular, -we now know which tree points to it! - -Now you can do - - git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 - -which will show something like - - 100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore - 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap - 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING - 100644 blob ee909f2cc49e54f0799a4739d24c4cb9151ae453 CREDITS - 040000 tree 0f5f709c17ad89e72bdbbef6ea221c69807009f6 Documentation - 100644 blob 1570d248ad9237e4fa6e4d079336b9da62d9ba32 Kbuild - 100644 blob 1c7c229a092665b11cd46a25dbd40feeb31661d9 MAINTAINERS - ... - -and you should now have a line that looks like - - 10064 blob 4b9458b3786228369c63936db65827de3cc06200 my-magic-file - -in the output. This already tells you a *lot* it tells you what file the -corrupt blob came from! - -Now, it doesn't tell you quite enough, though: it doesn't tell what -*version* of the file didn't get correctly written! You might be really -lucky, and it may be the version that you already have checked out in your -working tree, in which case fixing this problem is really simple, just do - - git hash-object -w my-magic-file - -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? - -The easiest way to do it is to do - - git log --raw --all --full-history -- subdirectory/my-magic-file - -and that will show you the whole log for that file (please realize that -the tree you had may not be the top-level tree, so you need to figure out -which subdirectory it was in on your own), and because you're asking for -raw output, you'll now get something like - - commit abc - Author: - Date: - .. - :100644 100644 4b9458b... newsha... M somedirectory/my-magic-file - - - commit xyz - Author: - Date: - - .. - :100644 100644 oldsha... 4b9458b... M somedirectory/my-magic-file - -and this actually tells you what the *previous* and *subsequent* versions -of that file were! So now you can look at those ("oldsha" and "newsha" -respectively), and hopefully you have done commits often, and can -re-create the missing my-magic-file version by looking at those older and -newer versions! - -If you can do that, you can now recreate the missing object with - - git hash-object -w <recreated-file> - -and your repository is good again! - -(Btw, you could have ignored the fsck, and started with doing a - - 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 -just missing one particular blob version. - -Trying to recreate trees and especially commits is *much* harder. So you -were lucky that it's a blob. It's quite possible that you can recreate the -thing. - - Linus |