You have not concluded your merge (MERGE_HEAD exists)
OK. The problem is your previous pull failed to merge automatically and went to conflict state. And the conflict wasn't resolved properly before the next pull.
Undo the merge and pull again.
To undo a merge:
git merge --abort [Since git version 1.7.4]
git reset --merge [prior git versions]
Resolve the conflict.
Don't forget to add and commit the merge.
git pull now should work fine.
How to resolve merge conflicts in Git?
Try: git mergetool
It opens a GUI that steps you through each conflict, and you get to choose how to merge. Sometimes it requires a bit of hand editing afterwards, but usually it's enough by itself. It is much better than doing the whole thing by hand certainly.
As per @JoshGlover comment:
The command doesn't necessarily open a GUI unless you install one. Running git mergetool for me resulted in vimdiff being used. You can install one of the following tools to use it instead: meld, opendiff, kdiff3, tkdiff, xxdiff, tortoisemerge, gvimdiff, diffuse, ecmerge, p4merge, araxis, vimdiff, emerge.
Below is the sample procedure to use vimdiff for resolve merge conflicts. Based on this link
Step 1: Run following commands in your terminal
git config merge.tool vimdiff
git config merge.conflictstyle diff3
git config mergetool.prompt false
This will set vimdiff as the default merge tool.
Step 2: Run following command in terminal
git mergetool
Step 3: You will see a vimdiff display in following format
+----------------------+
| | | |
|LOCAL |BASE |REMOTE |
| | | |
+----------------------+
| MERGED |
| |
+----------------------+
These 4 views are
LOCAL – this is file from the current branch
BASE – common ancestor, how file looked before both changes
REMOTE – file you are merging into your branch
MERGED – merge result, this is what gets saved in the repo
You can navigate among these views using ctrl+w. You can directly reach MERGED view using ctrl+w followed by j.
More info about vimdiff navigation here and here
Step 4. You could edit the MERGED view the following way
If you want to get changes from REMOTE
:diffg RE
If you want to get changes from BASE
:diffg BA
If you want to get changes from LOCAL
:diffg LO
Step 5. Save, Exit, Commit and Clean up
:wqa save and exit from vi
git commit -m "message"
git clean Remove extra files (e.g. *.orig) created by diff tool.
https://stackoverflow.com/questions/11646107/you-have-not-concluded-your-merge-merge-head-exists