This is a branch which knows which remote branch it is related to, and making this link allows us to take advantage of some neat git tricks. In particular:
git push or git pull without specifying remote or branch and it will use its tracking sister branch by defaultgit status command will include information about how far behind your tracking branch you are - useful to remind you that you haven't pushed your changes yet! It looks like this:$ git status
# On branch branch1
# Your branch is ahead of 'origin/branch1' by 1 commit.
# (use "git push" to publish your local commits)
#
nothing to commit, working directory clean
Let's start with getting a handle on what branches are currently tracking other branches, using git branch -vv
$ git branch -vv
branch1 c98bacf [origin/branch1] A random change of 24459 to ideas2.txt
experiment 09a0eb9 A random change of 16603 to list2.txt
* master 09a0eb9 [origin/master] A random change of 16603 to list2.txt
This shows three branches, two of them are tracking branches on another remote. It's common for the branches to have the same names on the various remotes but it's only a convention; you can actually call them anything you like (but beware of getting confused!)
git branch --unset-upstream
If you're pushing a branch (even if it exists in both places) to a remote location and you want to create the link:
$ git push -u origin feature
Counting objects: 9, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (5/5), done.
Writing objects: 100% (9/9), 746 bytes | 0 bytes/s, done.
Total 9 (delta 2), reused 0 (delta 0)
To /home/lorna/.../scripts/origin.git
* [new branch] feature -> feature
Branch feature set up to track remote branch feature from origin.
If you're creating a local version of an existing remote branch:
$ git fetch origin
remote: Counting objects: 9, done.
remote: Compressing objects: 100% (5/5), done.
remote: Total 9 (delta 2), reused 0 (delta 0)
Unpacking objects: 100% (9/9), done.
From /home/lorna/.../scripts/origin
* [new branch] feature -> origin/feature
Then:
$ git checkout feature
Branch feature set up to track remote branch feature from origin.
Switched to a new branch 'feature'
Addenda : If you have already an existing remote branch (upstream is the remote alias):
git checkout foo
git branch -u upstream/foo
or
git branch -u upstream/foo foo
This is an area of confusion because the defaults changed between versions of git. Take a look at your config (use git config --list) and find a setting called push.default. The usual default is simple which will only push/pull the branch to/from the branch you're currently on and the one it tracks. You can optionally set this to be matching (this was once the default) which will then push/pull all changes between all branches and their remote tracking sisters. Sometimes this second option is cumbersome if you have a branch that is not the one you're working on get into a state where it won't merge!