How do I use 'git reset --hard HEAD' to revert to a previous commit?

Question

I know that Git tracks changes I make to my application, and it holds on to them until I commit the changes, but here's where I'm hung up:

When I want to revert to a previous commit I use:

git reset --hard HEAD

And Git returns:

HEAD is now at 820f417 micro

How do I then revert the files on my hard drive back to that previous commit?

My next steps were:

git add .
git commit -m "revert"

But none of the files have changed on my hard drive...

What am I doing right/wrong?

Answer 1

First, it's always worth noting that git reset --hard is a potentially dangerous command, since it throws away all your uncommitted changes. For safety, you should always check that the output of git status is clean (that is, empty) before using it.

Initially you say the following:

So I know that Git tracks changes I make to my application, and it holds on to them until I commit the changes, but here's where I'm hung up:

That's incorrect. Git only records the state of the files when you stage them (with git add) or when you create a commit. Once you've created a commit which has your project files in a particular state, they're very safe, but until then Git's not really "tracking changes" to your files. (for example, even if you do git add to stage a new version of the file, that overwrites the previously staged version of that file in the staging area.)

In your question you then go on to ask the following:

When I want to revert to a previous commit I use: git reset --hard HEAD And git returns: HEAD is now at 820f417 micro

How do I then revert the files on my hard drive back to that previous commit?

If you do git reset --hard <SOME-COMMIT> then Git will:

• Make your current branch (typically master) back to point at <SOME-COMMIT>.
• Then make the files in your working tree and the index ("staging area") the same as the versions committed in <SOME-COMMIT>.

HEAD points to your current branch (or current commit), so all that git reset --hard HEAD will do is to throw away any uncommitted changes you have.

So, suppose the good commit that you want to go back to is f414f31. (You can find that via git log or any history browser.) You then have a few different options depending on exactly what you want to do:

• Change your current branch to point to the older commit instead. You could do that with git reset --hard f414f31. However, this is rewriting the history of your branch, so you should avoid it if you've shared this branch with anyone. Also, the commits you did after f414f31 will no longer be in the history of your master branch.

• Create a new commit that represents exactly the same state of the project as f414f31, but just adds that on to the history, so you don't lose any history. You can do that using the steps suggested in this answer - something like:

  git reset --hard f414f31
  git reset --soft HEAD@{1}
  git commit -m "Reverting to the state of the project at f414f31"