如何防止在分离的HEAD中提交

Question

Why does git allow you to commit to a detached head? Is there any pre commit hook that can disable it? What is the purpose? Many new developers do this and I'd like to find a way to disable it.

Answer 1

This can be only prevented by a local git pre-commit hook, so developers would need to create it. Add the your-local-project/.git/hooks/pre-commit file with the following contents:

#!/bin/sh

if ! git symbolic-ref HEAD &> /dev/null; then
  echo "You are in a detached head state! Commit has been blocked. (Use --no-verify to bypass this check.)"
  exit 1
fi

Make sure it's executable. Credits go to svachalek

Why should git prevent commiting in detached HEAD? Detached HEAD means only that there is no pointer to the repository state you are working on. It assumes that you know what you are doing.

I would rather investigate why many developers in your team enter this state? Maybe they apply some weird worklow?

Answer 2

git checkout $commit-sha1 can lead to a detached HEAD. So does git checkout FETCH_HEAD . A detached HEAD could be considered as a branch without a name. If it does not confuse you, you could just ignore it. As @fracz said, you could prevent it by pre-commit . You could also make it a branch with a name with git checkout -b some_name . A post-checkout hook may help you to detect the detached HEAD state and make it a branch.

Answer 3

Git uses this internally for many operations. The detached HEAD mode simply gets you on the (one, single, special) anonymous branch, and the anonymous branch can be given a name later.

This is, for instance, how git rebase manages to copy the commits from their original chain to a new chain. First it checks out the --onto target commit ( --onto defaults to the <upstream> ) using this detached HEAD mode. Then, for each commit that is to be copied, it copies that commit (with git cherry-pick or something equivalent: the details vary depending on interactive vs non-interactive rebase, and if interactive, many more details). Last, it moves the existing branch label so that it points to the final copied commit.