How to delete the old git history?

Question

I have git repository with many, many (2000+) commits, for example:

                 l-- m -- n   
                /
a -- b -- c -- d -- e -- f -- g -- h -- i --         


        

Answer 1

For those who get alot of merge conflicts (and broken results) with rebase --onto I'd like recommend this script which uses git filter-branch:

#!/bin/sh

cut_sha="$1"
branch="$2"

git filter-branch \
  --parent-filter "sed -e 's/-p $cut_sha[0-9a-f]*//'" \
  --prune-empty \
  -- $branch

git for-each-ref --format='%(refname)' refs/original | \
  while read ref
  do
    git update-ref -d "$ref"
  done

git reflog expire --expire=0 --all
git repack -ad
git prune

Source: https://github.com/adrienthebo/git-tools/blob/master/git-truncate

Instructions:

1. Save the script above to local repository root (maybe as git-truncate.sh).
2. Check out the branch you'd like to truncate (maybe master).
3. Go down history and find the first (newest) commit SHA you want to cut off (assume it's 2c75a32) AND ensure the commit has no branches in parallel!
4. Run it like this: $ ./git-truncate.sh 2c75a32 master.
5. (Push force, if any remote is present.)

IMPORTANT: The SHA must be "part" of the branch and it must be the first commit you want to delete. Don't pass the first commit you want to keep (the new "beginning of repository" commit)!