How to fix fatal: invalid upstream 'origin/main' in Git

First, fetch all remote branches to ensure your local repository knows about all available branches:

git fetch --all

This downloads references to all branches from all configured remotes. If you only want to fetch from a specific remote:

git fetch origin

List all branches (local and remote) to confirm the branch name is correct:

git branch -a

Look for the branch you want to use. Remote branches appear as remotes/origin/main or similar. If the branch is not listed, it may have been renamed or deleted.

If the branch has been renamed (common with master to main migrations), use the correct name:

# If main doesn't exist but master does
git rebase origin/master

# Or if master doesn't exist but main does
git rebase origin/main

You can also check what the default branch is for the remote:

git remote show origin

If the remote branch exists but you cannot reference it directly, create a local branch that tracks it:

git checkout -b main origin/main
git checkout your-feature-branch
git rebase main

This creates a local main branch tracking origin/main, which can then be used for rebasing.

If you are trying to rebase onto a branch from an upstream repository (such as the original repo of a fork), you may need to add the remote first:

git remote add upstream https://github.com/original-owner/repo.git
git fetch upstream
git rebase upstream/main

If using just the remote name in commands, ensure the default branch is configured:

git remote set-head origin --auto

This automatically sets the default branch for the remote based on what the remote repository has configured.