Must every git commit be an ancestor of a branch?

Given this git tree:

A <--- B <--- C (HEAD, master)

is it possible to put the tree into this state:

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  • A <--- B (HEAD, master) <--- C
    

    (There are no branches or tags other than master.) In other words, can a commit (C) exist without either being a commit pointed to by a branch (or tag) or the ancestor of a commit pointed to by a branch (or tag)?

    (This question is purely theoretical to help me understand better how git branches works.)

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  • 2 Solutions collect form web for “Must every git commit be an ancestor of a branch?”

    Sure,

    git checkout -b tmp
    touch whatever.txt
    git add -A
    git commit -m "committed!"
    git checkout master
    git branch -D tmp
    

    The commit whose predecessor is the current HEAD of master is now still available, but no name is pointing to it. You can still get to it e.g. with the reflog commands.

    Another possibility, given that C already exists:

    git checkout -b tmp
    git checkout master
    git reset --hard HEAD-1
    git branch -D tmp
    

    ps, cannot find the tilde key on this kb…

    Commit C can exist temporarily (as a dangling commit); once a GC occurs it will be reclaimed.

    Use:

    git fsck --unreachable
    

    to see dangling commits and blobs. Note that because git has a notion of reflog what you’ve described won’t create a dangling commit right away, C will stay in the reflog for a while. git maintains the reflog just in case you’ve made a mistake and need to recover something.

    Git Baby is a git and github fan, let's start git clone.