Branch from a previous commit using Git

If I have n commits, how can I branch from the n-3 commit?

I can see the hash of every commit.

You can create the branch via a hash:

git branch branchname <sha1-of-commit>

Or by using a symbolic reference:

git branch branchname HEAD~3

To checkout the branch when creating it, use

git checkout -b branchname <sha1-of-commit or HEAD~3>

To do this on github.com:

1. Go to your project.
2. Click on the "Commits".
3. Click on the <> ("Browse the repository at this point in the history") on the commit you want to branch from.
4. Click on the "tree: xxxxxx" up in the upper left. Just below the language statistics bar, you'll get the option to "Find or Create Branch" (just type in a new branch name there)

The magic can be done by git reset.

1. Create a new branch and switch to it (so all of your latest commits are stored here)

   git checkout -b your_new_branch
   

2. Switch back to your previous working branch (assume it's master)

   git checkout master
   

3. Remove the latest x commits, keep master clean

   git reset --hard HEAD~x    # in your case, x = 3
   

From this moment on, all the latest x commits are only in the new branch, not in your previous working branch (master) any more.

If you are not sure which commit you want to branch from in advance you can check commits out and examine their code (see source, compile, test) by

git checkout <sha1-of-commit>

once you find the commit you want to branch from you can do that from within the commit (i.e. without going back to the master first) just by creating a branch in the usual way:

git checkout -b <branch_name>