How to permanently lose data with git (and then retrieve it again)

So I pushed some changes to github so Ondrej could help me debug the nseries tests, when I noticed that the changes that I pushed had some bad comments. So I decided to rebase. But git rebase -i told me that there was already a rebase in progress. I figured that I must have done it a long time ago and forgot to abort, so I ran git rebase –abort.

DON’T DO THAT.

I noticed my editor was telling me that an open file had changed. Then, I noticed that ALL of my uncommited changes were gone! And, being uncommited changes, git did not have them saved anywhere!

So now I started to panic. I had done a lot of work on dsolve that I hadn’t commited yet. Normally, I have hourly backups run by Time Machine, but I am on vacation and my backup drive is at home. So I started to see if I could retrieve it somewhere. grep quickly told me that it wasn’t in the hidden git directory, but it was still in my .pyc files. But a Google search told me that retrieving from that is not so easy, if not impossible with Python 2.6. So then, I decided to see if there was any lingering stuff in my virtual memory from my editor. So I ran grep on my harddrive and waited.

While I was waiting, though, I noticed when I scrolled up in my command history that my lost changes were in my Terminal. It turns out that I had just run git commit –interactive and had used * on my patches, so it gave me everything!

So I copied my Terminal history and will work on putting everything back tomorrow. It should be easy, assuming that git apply works for the format that git gives in commit –interactive.

So the lessons are: Don’t abort a rebase without commiting. Don’t start a rebase and then leave it there. Look in your Terminal history if you loose stuff. And it might be a good idea to make manual backups if you are away from your backup drive for a while.

This also highlights why it is important to try to recover data immediately after realizing that it is gone. If I had closed my Terminal session or filled it past the maximum number of lines, my data would be gone. Even if it were in my virtual memory, that wouldn’t last forever either.

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6 Responses to How to permanently lose data with git (and then retrieve it again)

  1. ulrik says:

    I’d say this is a very disturbing quirk in git; it’s happened to many, me included, but mostly I commit so often that I don’t lose anything. Still, that –abort calls reset –hard is very disturbing.

    The gitters just say.. commit often, commit everything, and use rebase -i to squash it back together really nice. But I hope this quirk is being resolved in future versions.

  2. It’s because you don’t color your prompt with the name of the branch (and the prompt also changes to something like “master|REBASE” if you rebase). See here how it looks like:

    http://code.google.com/p/sympy/wiki/GitTutorials

    so I very, very strongly suggest you use that.

    http://blog.ericgoodwin.com/2008/4/10/auto-completion-with-git

    e.g. here is my PS1 prompt:

    PS1=’${debian_chroot:+($debian_chroot)}\u@\h:\w\[33[31m\]$(__git_ps1 “(%s)”)\[33[00m\]\$ ‘

    if you use Mac, source the “contrib/completion/git-completion.bash” file (in the git repository for git), which contains the definition of the __git_ps1 and some documentation too (read it if you have troubles getting it work).

    Once you have the colored prompt, I am pretty sure it will never happen again.

  3. vks says:

    I think git should backup aborted local changes for 30 days, like it does with commits.

  4. andy says:

    Glad to see you got the lost data. A very important lesson, no matter what scm you use keeping things clean is very important. Usually I will just reclone somewhere else if I need to put in some quick changes.

  5. Chris Down says:

    You can also use `git reflog` to recover in such situations, even if you had closed your terminal. `man git reflog` should tell you everything you need.

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