Forking a Github repo to Bitbucket

github-to-bitbucket

Go to Bitbucket and create a new repository (its better to have an empty repo)
    git clone git@bitbucket.org:abc/myforkedrepo.git
    cd myforkedrepo

Now add Github repo as a new remote in Bitbucket called "sync"
    git remote add sync git@github.com:def/originalrepo.git

Verify what are the remotes currently being setup for "myforkedrepo". This following command should show "fetch" and "push" for two remotes i.e. "origin" and "sync"
    git remote -v

Now do a pull from the "master" branch in the "sync" remote 
    git pull sync master

Setup a local branch called "github"track the "sync" remote's "master" branch
    git branch --set-upstream github sync/master

Now push the local "master" branch to the "origin" remote in Bitbucket.
    git push -u origin master
    

Courtesy: http://stackoverflow.com/questions/8137997/forking-from-github-to-bitbucket

@Ralcon: One possible way I can think off is; you maintain two branches in your destination (e.g. Bitbucket) repo. One branch which you wish to own (let's call it "master") and modify(maybe) and another which is replica of source (e.g. github.com) and let's call it "source". Now you need to keep updating your "source" and there shouldn't be any merge conflicts as every-time it is syncing to the latest or source. Later you can decide to merge "source" to "master" as and when you need.

--set-upstream is no more supported use --track instead

Use: git branch --track github sync/master instead of git branch --set-upstream github sync/master

use git pull sync master --allow-unrelated-histories

Our local branch commit messages as it is only accepting certain format i.e []: message or else git push will fail,
as the upstream would have totally different commit message formats.

% git pull sync master

git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

If you run in to this, try connecting to the repo you want to fork with https instead of ssh. I hadn't set up keys on my system for git with ssh, so it complained.

If your main branch loses track of your origin (when it's not master, e.g. main), you can set it back with:

git branch --set-upstream-to=origin/main

Make sure that you were in the target branch, in the above example: main.