So, you have a pet project in a private repository. It turns out that the project could work as an open source project. When you looked into its history, you find some stuff that must not go public. You want to delete those early commits and keep recent commits.

Note that this article uses master as the default branch name. Recent repositories might use main for it.

Note that the instructions provided in this document might destroy your working repository. Be warned.

Let’s imagine our repository state like this:

master: O-----X--------H
  • O is original first commit
  • X is the commit you want to be as the new first commit
  • H is the head, i.e., latest commit

Note: I recommend to delete all but master branch before we start the operation.

We will need to get the commits

  • ORev is the commit of O – use the command git rev-list --max-parents=0 HEAD
  • XRev is the commit of X. You will need to use git log or a Git GUI to find the commit.
$ git checkout -b reroot <XRev>
$ git reset --soft <ORev>
$ git commit --amend -m "My new initial commit"

The above commands do the following:

  • First, it checks out X into a new branch named reroot
  • Resets the original commit without reseting the files and index
  • Creates a new commit with files from commit X

After running above commands, we are not at the following state.

master: O-----X--------H
reroot:       R--------I

We are now at branch reroot and at commit R.

Next step is to get RRev, which is the commit R – use the command git rev-list --max-parents=0 HEAD. Yes, the same command we used to obtain ORev. We use the same command because we are now at commit R, so, the first commit will be R.

$ git checkout master
$ git replace <XRev> <RRev>
$ git filter-branch master
$ rm -rf .git/refs/original .git/refs/replace
$ git branch -d reroot

They do the following:

  • First, it checks out the default branch (master in this case)
  • Replaces the reference to XRev with RRev
  • Rewrites the history
  • Removes temporary references
  • Deletes the now unused reroot branch

End result will look like this:

master:       R--------I

Please note that at the end of the process, the history is practically rewritten. The new head commit will not be the same as the old head commit and, no, you can’t have the same head commit after re-root as it is logically impossible.