git revert merge commit — how to undo a merge safely

Q: What `-m 1` means

-m 1 tells Git to keep parent 1, which is usually the branch you were on when you ran git merge . The merged-in branch changes are undone. ``` # Most common case git revert -m 1 ```

Quick Answer

# 1. Find the merge commit hash
git log --oneline --graph

# 2. Revert the merge commit
git revert -m 1 <merge-commit-hash>

# 3. Push the new revert commit
git push origin main

When this happens

You already merged a branch and pushed it, but now need to undo that merge without rewriting shared history.

error: commit abc1234 is a merge but no -m option was given.
fatal: revert failed

Merge commits have more than one parent, so git revert needs the -m option to know which parent should be kept as the mainline.

Details

What `-m 1` means

-m 1 tells Git to keep parent 1, which is usually the branch you were on when you ran git merge. The merged-in branch changes are undone.

# Most common case
git revert -m 1 <merge-commit-hash>

Inspect the parents before reverting

git show --summary <merge-commit-hash>

# Or list parents directly
git rev-list --parents -n 1 <merge-commit-hash>

If conflicts happen during the revert

# Resolve conflicts in the files
git status
git add .
git revert --continue

# Or abandon the revert
git revert --abort

Do not use reset on shared branches

If the merge commit is already pushed to a shared branch, prefer git revert over git reset. Reset rewrites history and usually requires a force-push.

# Safer on shared branches
git revert -m 1 <merge-commit-hash>

# Risky on shared branches
git reset --hard <commit-before-merge>