How to remove/delete a large file from commit history in the Git repository?

Question

I accidentally dropped a DVD-rip into a website project, then carelessly git commit -a -m ..., and, zap, the repo was bloated by 2.2 gigs. Next time I made some edits, deleted the video file, and committed everything, but the compressed file is still there in the repository, in history.

I know I can start branches from those commits and rebase one branch onto another. But what should I do to merge the 2 commits so that the big file doesn't show in the history and is cleaned in the garbage collection procedure?

Answer 1

Use the BFG Repo-Cleaner, a simpler, faster alternative to git-filter-branch specifically designed for removing unwanted files from Git history.

Carefully follow the usage instructions, the core part is just this:

$ java -jar bfg.jar --strip-blobs-bigger-than 100M my-repo.git 

Any files over 100MB in size (that aren't in your latest commit) will be removed from your Git repository's history. You can then use git gc to clean away the dead data:

$ git gc --prune=now --aggressive 

The BFG is typically at least 10-50x faster than running git-filter-branch, and generally easier to use.

Full disclosure: I'm the author of the BFG Repo-Cleaner.

Answer 2

What you want to do is highly disruptive if you have published history to other developers. See “Recovering From Upstream Rebase” in the git rebase documentation for the necessary steps after repairing your history.

You have at least two options: git filter-branch and an interactive rebase, both explained below.

Using git filter-branch

I had a similar problem with bulky binary test data from a Subversion import and wrote about removing data from a git repository.

Say your git history is:

$ git lola --name-status * f772d66 (HEAD, master) Login page | A     login.html * cb14efd Remove DVD-rip | D     oops.iso * ce36c98 Careless | A     oops.iso | A     other.html * 5af4522 Admin page | A     admin.html * e738b63 Index   A     index.html 

Note that git lola is a non-standard but highly useful alias. With the --name-status switch, we can see tree modifications associated with each commit.

In the “Careless” commit (whose SHA1 object name is ce36c98) the file oops.iso is the DVD-rip added by accident and removed in the next commit, cb14efd. Using the technique described in the aforementioned blog post, the command to execute is:

git filter-branch --prune-empty -d /dev/shm/scratch \   --index-filter "git rm --cached -f --ignore-unmatch oops.iso" \   --tag-name-filter cat -- --all 

Options:

• --prune-empty removes commits that become empty (i.e., do not change the tree) as a result of the filter operation. In the typical case, this option produces a cleaner history.
• -d names a temporary directory that does not yet exist to use for building the filtered history. If you are running on a modern Linux distribution, specifying a tree in /dev/shm will result in faster execution.
• --index-filter is the main event and runs against the index at each step in the history. You want to remove oops.iso wherever it is found, but it isn’t present in all commits. The command git rm --cached -f --ignore-unmatch oops.iso deletes the DVD-rip when it is present and does not fail otherwise.
• --tag-name-filter describes how to rewrite tag names. A filter of cat is the identity operation. Your repository, like the sample above, may not have any tags, but I included this option for full generality.
• -- specifies the end of options to git filter-branch
• --all following -- is shorthand for all refs. Your repository, like the sample above, may have only one ref (master), but I included this option for full generality.

After some churning, the history is now:

$ git lola --name-status * 8e0a11c (HEAD, master) Login page | A     login.html * e45ac59 Careless | A     other.html | | * f772d66 (refs/original/refs/heads/master) Login page | | A   login.html | * cb14efd Remove DVD-rip | | D   oops.iso | * ce36c98 Careless |/  A   oops.iso |   A   other.html | * 5af4522 Admin page | A     admin.html * e738b63 Index   A     index.html 

Notice that the new “Careless” commit adds only other.html and that the “Remove DVD-rip” commit is no longer on the master branch. The branch labeled refs/original/refs/heads/master contains your original commits in case you made a mistake. To remove it, follow the steps in “Checklist for Shrinking a Repository.”

$ git update-ref -d refs/original/refs/heads/master $ git reflog expire --expire=now --all $ git gc --prune=now 

For a simpler alternative, clone the repository to discard the unwanted bits.

$ cd ~/src $ mv repo repo.old $ git clone file:///home/user/src/repo.old repo 

Using a file:///... clone URL copies objects rather than creating hardlinks only.

Now your history is:

$ git lola --name-status * 8e0a11c (HEAD, master) Login page | A     login.html * e45ac59 Careless | A     other.html * 5af4522 Admin page | A     admin.html * e738b63 Index   A     index.html 

The SHA1 object names for the first two commits (“Index” and “Admin page”) stayed the same because the filter operation did not modify those commits. “Careless” lost oops.iso and “Login page” got a new parent, so their SHA1s did change.

Interactive rebase

With a history of:

$ git lola --name-status * f772d66 (HEAD, master) Login page | A     login.html * cb14efd Remove DVD-rip | D     oops.iso * ce36c98 Careless | A     oops.iso | A     other.html * 5af4522 Admin page | A     admin.html * e738b63 Index   A     index.html 

you want to remove oops.iso from “Careless” as though you never added it, and then “Remove DVD-rip” is useless to you. Thus, our plan going into an interactive rebase is to keep “Admin page,” edit “Careless,” and discard “Remove DVD-rip.”

Running $ git rebase -i 5af4522 starts an editor with the following contents.

pick ce36c98 Careless pick cb14efd Remove DVD-rip pick f772d66 Login page  # Rebase 5af4522..f772d66 onto 5af4522 # # Commands: #  p, pick = use commit #  r, reword = use commit, but edit the commit message #  e, edit = use commit, but stop for amending #  s, squash = use commit, but meld into previous commit #  f, fixup = like "squash", but discard this commit's log message #  x, exec = run command (the rest of the line) using shell # # If you remove a line here THAT COMMIT WILL BE LOST. # However, if you remove everything, the rebase will be aborted. # 

Executing our plan, we modify it to

edit ce36c98 Careless pick f772d66 Login page  # Rebase 5af4522..f772d66 onto 5af4522 # ... 

That is, we delete the line with “Remove DVD-rip” and change the operation on “Careless” to be edit rather than pick.

Save-quitting the editor drops us at a command prompt with the following message.

Stopped at ce36c98... Careless You can amend the commit now, with          git commit --amend  Once you are satisfied with your changes, run          git rebase --continue 

As the message tells us, we are on the “Careless” commit we want to edit, so we run two commands.

$ git rm --cached oops.iso $ git commit --amend -C HEAD $ git rebase --continue 

The first removes the offending file from the index. The second modifies or amends “Careless” to be the updated index and -C HEAD instructs git to reuse the old commit message. Finally, git rebase --continue goes ahead with the rest of the rebase operation.

This gives a history of:

$ git lola --name-status * 93174be (HEAD, master) Login page | A     login.html * a570198 Careless | A     other.html * 5af4522 Admin page | A     admin.html * e738b63 Index   A     index.html 

which is what you want.