git - How to push a shallow clone to a new repo?

Question

I wish to get rid of a lot of my repo's old history, so I did a shallow clone to get the last 50 commits only:

git clone --depth=50 https://my.repo

That worked OK, but when I create a new Gitlab repo and try to push it I get an error:

git remote remove origin
git remote add origin https://my.repo
git push -u origin --all
[...]
 ! [remote rejected] master -> master (shallow update not allowed)

But I only want these 50 commits to be in my new repo's history. How can I tell git that it should just treat these 50 commits as the only commits in the new repo?

Answer 1

Here's what I ended up doing - it worked perfectly. Note that I was moving from my old host (Bitbucket) to my new one (Gitlab). My comments are above the commands:

# First, shallow-clone the old repo to the depth we want to keep
git clone --depth=50 https://...@bitbucket.org/....git

# Go into the directory of the clone
cd clonedrepo

# Once in the clone's repo directory, remove the old origin
git remote remove origin

# Store the hash of the oldest commit (ie. in this case, the 50th) in a var
START_COMMIT=$(git rev-list master|tail -n 1)

# Checkout the oldest commit; detached HEAD
git checkout $START_COMMIT

# Create a new orphaned branch, which will be temporary
git checkout --orphan temp_branch

# Commit the initial commit for our new truncated history; it will be the state of the tree at the time of the oldest commit (the 50th)
git commit -m "Initial commit"

# Now that we have that initial commit, we're ready to replay all the other commits on top of it, in order, so rebase master onto it, except for the oldest commit whose parents don't exist in the shallow clone... it has been replaced by our 'initial commit'
git rebase --onto temp_branch $START_COMMIT master

# We're now ready to push this to the new remote repo... add the remote...
git remote add origin https://gitlab.com/....git

# ... and push.  We don't need to push the temp branch, only master, the beginning of whose commit chain will be our 'initial commit'
git push -u origin master

After that, I did a fresh clone of the new repo and I got just the master branch with the 50 most recent commits - exactly what I wanted! :-) Commit history has gone from 250MB to 50MB. Woot.