For reference, I was trying to pull from a remote branch and got the error message:

Pull is not possible because you have unmerged files.

A google search revealed this commit (d38a30df7dd54c5c6883) to the git source on January 12, 2010.

The error messages have been updated to be much clearer. Before, you’d get “needs merge” or “error building trees” errors, which didn’t really mean much.

In this case, I was pulling in many commits and had a conflict partway through. I just needed to resolve the files, add/delete them, commit the result and then continue with the pull.

$ git push origin master
...
warning: updating the current branch
warning: Updating the currently checked out branch may cause confusion,
warning: as the index and work tree do not reflect changes that are in HEAD.
warning: As a result, you may see the changes you just pushed into it
warning: reverted when you run 'git diff' over there, and you may want
warning: to run 'git reset --hard' before starting to work to recover.
warning:
warning: You can set 'receive.denyCurrentBranch' configuration variable to
warning: 'refuse' in the remote repository to forbid pushing into its
warning: current branch.
warning: To allow pushing into the current branch, you can set it to 'ignore';
warning: but this is not recommended unless you arranged to update its work
warning: tree to match what you pushed in some other way.
warning:
warning: To squelch this message, you can set it to 'warn'.
warning:
warning: Note that the default will change in a future version of git
warning: to refuse updating the current branch unless you have the
warning: configuration variable set to either 'ignore' or 'warn'.

Woah! After some research, this is because I didn’t set up my remote folder as “bare”. A non-bare repository has a working copy attached to it, and this warning is telling you that said working copy exists and is currently checked out to the branch you’re trying to push to.

This is bad, because if you were pushing to a co-worker’s machine, then when they go to commit or run a diff, things will go awry. In this case, I just didn’t set up the repository correctly (it was the first one I’d done!) so I wasn’t in danger of losing anything.

The fix is to use --bare:
git init --bare or git clone --bare

fatal: unable to create '.git/index.lock': File exists

The fix:
Got to your project’s shared/cached-copy/.git folder and delete index.lock . It shouldn’t ever get hung up like that, but it happened to me.

You asked me to pull without telling me which branch you
want to merge with, and 'branch.master.merge' in
your configuration file does not tell me either.

To fix, I added this to .git/config:

git push origin master
error: failed to push some refs to origin

Most likely, there are changes in the remote repo that you need to pull first:

git pull origin master

Resolve any conflicts, then you can push to the remote git repo.

I’m not sure why “failed to push some refs” couldn’t include “(do you need to pull?)”

Every once in a while, I want to poke back the history. git ships with a graphical repository viewer, but I like gitx better.

git makes branching off to try something super easy, which is quickly becoming one of my favorite features. I can create a branch quickly, try something out, switch away and come back later if I want.

Using gitx to view my repository history, I can quickly find where branches diverged and it’s just kinda neat to look at.