Open Stack

Rather than cloning the entire OpenStack docs repo again, I thought I would
follow the instructions[1], went to the local copy I cloned a few weeks ago
and issued the commands below - which ultimately failed:

[bbausch at ceres openstack-manuals]$ git remote update
Fetching origin
remote: Counting objects: 4911, done.
remote: Compressing objects: 100% (1577/1577), done.
remote: Total 3727 (delta 2581), reused 2715 (delta 1648)
Receiving objects: 100% (3727/3727), 5.16 MiB | 625.00 KiB/s, done.
Resolving deltas: 100% (2581/2581), completed with 351 local objects.
>From https://git.openstack.org/openstack/openstack-manuals
   c251097..e6f7e32  master     -> origin/master
   a7ac312..b5ba71b  stable/mitaka -> origin/stable/mitaka
   306f430..0940625  stable/newton -> origin/stable/newton
Fetching gerrit
>From ssh://review.openstack.org:29418/openstack/openstack-manuals
   c251097..e6f7e32  master     -> gerrit/master
   a7ac312..b5ba71b  stable/mitaka -> gerrit/stable/mitaka
   306f430..0940625  stable/newton -> gerrit/stable/newton

This looks good!

[bbausch at ceres openstack-manuals]$ git checkout master
Already on 'master'
Your branch and 'origin/master' have diverged,
and have 1 and 434 different commits each, respectively.
  (use "git pull" to merge the remote branch into yours)

Yes, the instructions do talk about doing a pull.

[bbausch at ceres openstack-manuals]$ git pull --ff-only origin master
remote: Counting objects: 24, done.
remote: Compressing objects: 100% (11/11), done.
remote: Total 13 (delta 11), reused 3 (delta 2)
Unpacking objects: 100% (13/13), done.
>From https://git.openstack.org/openstack/openstack-manuals
 * branch            master     -> FETCH_HEAD
   e6f7e32..d7ad707  master     -> origin/master
fatal: Not possible to fast-forward, aborting.

That's an error, right? Unfortunately, it doesn't tell me what's wrong. 

Admittedly, to me Git continues to be black magic. All I can do is
copy-paste magical incantations. Without access to a fellow shaman, I am
stuck if they don't work.
Apart from just cloning the whole 700MB or so of openstack-docs, are there
any suggestions how to tackle this error?

This is not a showstopper, but would be nice to know.

Bernd

[1]
https://docs.openstack.org/infra/manual/developers.html#starting-a-change