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Overview & Root Cause Summary: The error fatal: not a valid object name: 'HEAD@{1}' occurs when attempting to undo operations or restore commits using Git reflog references (such as git reset --hard HEAD@{1} or git checkout HEAD@{1}), but Git cannot find an entry at that index. The primary root causes are attempting reflog lookups in a freshly cloned repository that lacks local history, shell brace expansion in shells like Zsh or Bash mangling the curly braces, expired or pruned reflog entries (git gc), or disabled reflog logging in Git configuration.

Understanding the Root Causes

• No Prior Local State in Fresh Clones: Git reflogs are strictly local to your machine and are not transferred over the network. A freshly cloned repository has only a single entry (HEAD@{0}), meaning HEAD@{1} does not yet exist.
• Shell Expansion of Curly Braces: Modern shells like Zsh (the default on macOS) interpret curly braces {1} as brace expansion patterns or syntax tokens unless wrapped in quotation marks.
• Expired or Pruned Reflog Entries: Git’s automatic garbage collection (git gc --auto) purges unreachable reflog entries older than 30 days and reachable entries older than 90 days.
• Disabled Reflog Logging (core.logAllRefUpdates): Bare repositories or custom Git installations where ref tracking is disabled, preventing Git from recording state transitions under .git/logs/.

Step 1: Quick Fix (Quote Reflog Syntax & Inspect Commit SHAs)

Enclose the reflog identifier in quotes to prevent shell brace expansion, and inspect your real reflog history to target the commit hash directly.

# 1. Enclose the reference in quotes to prevent shell parsing errors:
git reset --hard "HEAD@{1}"
# (In Zsh / macOS):
git reset --hard 'HEAD@{1}'

# 2. View all available reflog entries for HEAD:
git reflog show HEAD -n 10

# 3. Use the exact commit SHA hash from the reflog output instead of relative indices:
# Example: git reset --hard 3a5b6c7
git reset --hard <commit_hash>

Step 2: Recovering Lost Commits via git fsck (Dangling Objects)

If the reflog entry was pruned or never recorded, locate orphaned commits directly inside Git’s object database.

# 1. Search for all dangling commits and objects in the repository:
git fsck --lost-found

# 2. Inspect the commit message and diff of any recovered dangling commit:
git show <dangling_commit_sha>

# 3. Create a recovery branch pointing directly to the recovered commit:
git branch recovery-branch <dangling_commit_sha>

# 4. Switch to the recovery branch to verify your restored files:
git switch recovery-branch

Step 3: Ensuring Reflog Logging is Permanently Enabled

Verify that your global Git configuration continuously logs all reference updates to protect against accidental future data loss.

# 1. Verify active reflog configuration:
git config --get core.logAllRefUpdates

# 2. Enable reference logging globally across all repositories:
git config --global core.logAllRefUpdates true

# 3. Confirm that the .git/logs directory exists in your project root:
ls -la .git/logs/HEAD

Verification & Testing Steps

Confirm that your branch pointer has been restored to the intended commit and verify repository health.

# 1. Confirm current HEAD commit hash and message:
git log --oneline -n 3

# 2. Check repository status:
git status

# 3. Verify that your reflog records the latest state transition:
git reflog -n 3

Summary Comparison Table

Recovery Approach	Applied Command	Target Identifier	Recommended Scenario
Quoted Reflog Specifier	git reset --hard 'HEAD@{1}'	Relative Reflog Index	Recent local operations blocked by Zsh/Bash brace expansion
Direct Commit Hash	git reset --hard <sha>	Explicit 40-char SHA	Reliable restoration after inspecting git reflog
Dangling Object Search	git fsck --lost-found	Unreachable Commit Blob	Expired reflogs, rebase drops, or deleted branches
Recovery Branch Creation	git branch recovery <sha>	New Branch Pointer	Safely inspecting recovered commits without modifying current branch