# Mirroring and taking upstream updates from an existing repository

## Definitions

`a-repository` is the repository we'd like to mirror and `b-repository` is the mirroring repository. `b-repository` will mirror the `a-repository` and take any future updates going into `a-repository`.

## Mirror the repository

Follow the steps in the article [Duplicating a repository](https://help.github.com/en/articles/duplicating-a-repository) but change the names as follows: `old-repository` corresponds to `a-repository` and `new-repository` corresponds to `b-repository`.

## Check the remote urls

Check the current remote urls for `b-repository`:
```
cd b-repository
git remote show origin
```

and the output should start with:
```
* remote origin
  Fetch URL: git@github.com:<username>/b-repository.git
  Push  URL: git@github.com:<username>/b-repository.git
```

## Add `a-repository` as remote upstream for `b-repository`

The following connects the `b-repository` to fetch updates from `a-repository` as `a`:
```
cd b-repository
git remote add a git@github.com:<username>/a-repository.git
```

## Check that the `a-repository` was added as remote upstream

Doing the following:
```
git remote show -v
```
Should now starts with:
```
a	git@github.com:<username>/a-repository.git (fetch)
a	git@github.com:<username>/a-repository.git (push)
origin	git@github.com:<username>/b-repository.git (fetch)
origin	git@github.com:<username>/b-repository.git (push)
```

## Use your `b-repository` to fetch and push

Now you may do the usual:
```
cd b-repository
git pull # pulls from git@github.com:<username>/b-repository.git
...
git push origin master # pushes changes to git@github.com:<username>/b-repository.git
```

## Pull changes from `a-repository` into the `b-repository`

Remember that we labelled the `a-repository` as `a`:
```
cd b-repository
git pull a master # can use any other branch than master
```