This document is intended to help you through frequently encountered weird technical failure scenarios (WTFS) in Git. It will be populated as questions arise.

HEAD detached at [...] ??

$ git status
HEAD detached at 1193e06
Untracked files:
  (use "git add <file>..." to include in what will be commited)

        ../seitan/

nothing added to commit but untracked files preset (use "git add" to track)

Chances are, you've probably used the git checkout command without specifying a file (or a directory). That's OK! If you haven't made any changes, you can fix this by using the command git checkout master. If everything is ok, you should a message similar to this:

$ git checkout master
Previous HEAD position was b405852... added tofu recipes
Switched to branch 'master'

If you have made some changes (i.e. using the command git status tells you that you have modified some file(s) like the image below), there are a few more steps to take.

$ git status
HEAD detached at 1193e06
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified: kung_pao_tofu.txt

Untracked files:
  (use "git add <file>..." to include in what will be commited)

        ../seitan/

no changes added to commit (use "git add" and/or "git commit -a")

First, use the command git stash. Your modifications may have magically disappeared! Dont worry - we'll be able to retrieve them in a second!

$ git stash
Saved working directory and index state WIP on (no branch): 1193e06 added tofu recipes
HEAD is now at 1193e06 added tofu recipes

$ git status
HEAD detached at 1193e06
Untracked files:
  (use "git add <file>..." to include in what will be commited)

        ../seitan/

nothing added to commit but untracked files preset (use "git add" to track)

From here, use the command git checkout master. You should see the all clear message from before:

$ git checkout master
Previous HEAD position was b405852... added tofu recipes
Switched to branch 'master'

Almost done! Let's go get our changes. Use git stash pop. But wait, we've got a conflict!

$ git stash pop
Auto-merging tofu/kung_pao_tofu.txt
CONFLICT (content): Merge conflict in tofu/kung_pao_tofu.txt

$ git status
On branch master
Unmerged paths:
  (use "git reset HEAD <file>..." to unstage)
  (use "git add <file>..." to mark resolution)

        both modified: kung_pao_tofu.txt

Untracked files:
  (use "git add <file>..." to include in what will be committed)

        ../seitan/

no changes added to commit (use "git add" and/or "git commit -a")

Now use git stash drop:

$ git stash drop
Dropped refs/stash@{0} (57f0ac5c5480964cdf29a94ed6b87e38da823488)<Paste>

Now we've got to fix this merge conflict. To learn how, take a look here!

Error: failed to push some refs??

Sometimes when working with others, you'll get a message like this when you push:

$ git push origin master
To https://github.com/gilbertghang/recipes.git
 ! [rejected]     master -> master (non-fast-forward)
error: failed to push some refs to 'https://github.com/gilbertghang/recipes.git"
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

What has happened here is that your remote (i.e. your online Github repository) contains commits that your local repository does not have. Luckily, Git is very good about telling you how to fix these errors: if you read the error message carefully, you'll see that is suggests that you git pull. Do that, fix any merge conflicts, and push. Done!

What are all these >>>> symbols in my code??

Sometimes when you pull from a repository, you'll get a message like this when you pull:

$ git pull origin master
From github.com:Berkeley-CS61B/course-materials-sp16
 * branch            master     -> FETCH_HEAD
Auto-merging proj/proj0/solution/canonical/Planet.java
CONFLICT (content): Merge conflict in proj/proj0/solution/canonical/Planet.java
Automatic merge failed; fix conflicts and then commit the result.

The problem here is that the code on your computer had a conflict with the code in the remote repository you're pulling from, and Git couldn't figure out how to resolve it. Since it is unsure, Git refuses to overwrite your local code.

However, when you open your Planet.java, you see some kind of crazy garbage like:

    public Planet(Planet p) {
<<<<<<< HEAD
        this.xPos = p.xPos;
        this.yPos = p.yPos;
=======
        this.xxPos = p.xxPos;
        this.yyPos = p.yyPos;
>>>>>>> 27ddd0c71515e5cfc7f58a43bcf0e2144c127aed

This is a good thing! Everything between <<<<<<< HEAD and ======= is what was on your computer, and everything between ======= and 27ddd0c71515e5cfc7f58a43bcf0e2144c127aed is what was on the remote server.

Your job is to look for these and resolve the merge conflict yourself. In this case, the remote repository is right, so we simply delete out everything between <<<<<<< HEAD and =======, and also delete the >>>>>>> 27ddd0c71515e5cfc7f58a43bcf0e2144c127aed marker, leaving:

public Planet(Planet p) {
    this.xxPos = p.xxPos;
    this.yyPos = p.yyPos;

Once you've resolved all of your merge conflicts, add all the files you manually edited, and commit them as usual, e.g.

git add Planet.java
git commit -m "resolved merge conflict"
git push origin master