How to fix fatal: Not a valid object name abc1234 in Git

First, verify that your repository actually has commits:

git log --oneline

If you see "does not have any commits yet", you need to make your first commit before you can reference branches:

git add .
git commit -m "Initial commit"

After the first commit, 'master' or 'main' will exist.

Check what branches, tags, and references exist in your repository:

# List all local branches
git branch

# List all remote-tracking branches
git branch -r

# List all tags
git tag

# List all references
git show-ref

Make sure the name you're trying to use appears in one of these lists.

If you're trying to reference a remote branch like 'origin/main', you need to fetch it first:

# Fetch all branches from origin
git fetch origin

# Or fetch a specific branch
git fetch origin main

After fetching, 'origin/main' will be available as a valid object name.

Git object names are case-sensitive. Verify you're using the correct spelling:

# Check if a partial SHA exists
git rev-parse --verify abc1234

# Search for similar branch names
git branch --list '*main*'
git branch --list '*master*'

Common mistakes include 'Main' vs 'main', 'master' vs 'main', or truncated SHAs that are too short to be unique.

If you cloned with --depth, older commits may be missing:

# Check if this is a shallow clone
git rev-parse --is-shallow-repository

# If true, fetch full history
git fetch --unshallow

# Or fetch more commits
git fetch --depth=100

This is common in CI/CD pipelines that use shallow clones for speed.

In GitHub Actions, GitLab CI, or other CI systems, you often need to explicitly fetch branches:

# GitHub Actions example
- uses: actions/checkout@v4
  with:
    fetch-depth: 0  # Fetch all history

# Or manually fetch the base branch
- run: git fetch origin main

For tools like Nx that compare against a base branch, ensure that branch is available:

git fetch origin main:main

If the object should exist but Git can't find it, the repository may be corrupted:

# Verify repository integrity
git fsck --full

# Check for missing objects
git fsck --lost-found

If objects are missing, you may need to re-clone the repository or restore from a backup.