master branch and 'origin/master' have diverged, how to 'undiverge' branches'?

I had this and am mystified as to what has caused it, even after reading the above responses. My solution was to do

git reset --hard origin/master

Then that just resets my (local) copy of master (which I assume is screwed up) to the correct point, as represented by (remote) origin/master.

WARNING: You will lose all changes not yet pushed to origin/master.

You can review the differences with a:

git log HEAD..origin/master

before pulling it (fetch + merge) (see also "How do you get git to always pull from a specific branch?")

---

When you have a message like:

"Your branch and 'origin/master' have diverged, # and have 1 and 1 different commit(s) each, respectively."

, check if you need to update origin. If origin is up-to-date, then some commits have been pushed to origin from another repo while you made your own commits locally.

... o ---- o ---- A ---- B  origin/master (upstream work)
                   \
                    C  master (your work)

You based commit C on commit A because that was the latest work you had fetched from upstream at the time.

However, before you tried to push back to origin, someone else pushed commit B.
Development history has diverged into separate paths.

You can then merge or rebase. See Pro Git: Git Branching - Rebasing for details.

Merge

Use the git merge command:

$ git merge origin/master

This tells Git to integrate the changes from origin/master into your work and create a merge commit.
The graph of history now looks like this:

... o ---- o ---- A ---- B  origin/master (upstream work)
                   \      \
                    C ---- M  master (your work)

The new merge, commit M, has two parents, each representing one path of development that led to the content stored in that commit.

Note that the history behind M is now non-linear.

Rebase

Use the git rebase command:

$ git rebase origin/master

This tells Git to replay commit C (your work) as if you had based it on commit B instead of A.
CVS and Subversion users routinely rebase their local changes on top of upstream work when they update before commit.
Git just adds explicit separation between the commit and rebase steps.

The graph of history now looks like this:

... o ---- o ---- A ---- B  origin/master (upstream work)
                          \
                           C'  master (your work)

Commit C' is a new commit created by the git rebase command.
It is different from C in two ways:

1. It has a different history: B instead of A.
2. Its content accounts for changes in both B and C; it is the same as M from the merge example.

Note that the history behind C' is still linear.
We have chosen (for now) to allow only linear history in cmake.org/cmake.git.
This approach preserves the CVS-based workflow used previously and may ease the transition.
An attempt to push C' into our repository will work (assuming you have permissions and no one has pushed while you were rebasing).

The git pull command provides a shorthand way to fetch from origin and rebase local work on it:

$ git pull --rebase

This combines the above fetch and rebase steps into one command.