Recovering lost commits with reflog in Git - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is git reflog used for?

git reflog shows a log of all recent changes to the HEAD, including commits, resets, and checkouts. It helps find lost commits.

beginner

How can you recover a lost commit using git reflog?

Find the commit hash in git reflog, then use git checkout <commit-hash> or git reset --hard <commit-hash> to restore it.

intermediate

What does the command git reset --hard <commit-hash> do?

It moves the current branch to the specified commit and resets the working directory and staging area to match that commit, discarding changes.

beginner

Why might commits become 'lost' in Git?

Commits can become lost after actions like git reset, git rebase, or branch deletion, but they still exist in reflog for a time.

intermediate

How long does Git keep reflog entries by default?

By default, reflog entries are kept for 90 days before they expire and are removed.

What command lists recent HEAD changes including lost commits?

A git reflog

B git log

C git status

D git branch

git reflog shows recent HEAD changes, helping find lost commits.

Which command restores your branch to a lost commit found in reflog?

A git clone <repo>

B git push origin main

C git merge <commit-hash>

D git checkout <commit-hash>

git checkout <commit-hash> lets you move to that commit to recover it.

What does git reset --hard <commit-hash> do?

A Creates a new commit

B Moves branch and resets files to that commit

C Deletes the commit permanently

D Shows commit details

This command moves the branch pointer and resets files to the specified commit.

Why might a commit be missing from git log but visible in git reflog?

A Because the commit is tagged

B Because the commit was pushed

C Because the branch was reset or changed

D Because the commit is merged

Resetting or changing branches can hide commits from git log but reflog still tracks them.

How long does Git keep reflog entries by default?

A 90 days

B 7 days

C Forever

D 30 days

Git keeps reflog entries for 90 days by default before cleaning them up.

Explain how to find and recover a lost commit using git reflog.

Think about how reflog tracks HEAD movements and how to move back to a commit.

Describe why commits might become lost and how reflog helps in recovery.

Consider what happens to commits after branch changes and how reflog records history.

Practice

1. What is the primary purpose of git reflog in Git?

easy

A. To show a log of where HEAD and branch references have been recently

B. To permanently delete commits from the repository

C. To merge two branches automatically

D. To push commits to a remote repository

Solution

1. Step 1: Understand what reflog tracks

   Git reflog records changes to HEAD and branch tips, showing recent commit movements.

2. Step 2: Identify reflog's main use

   It helps find lost commits by listing recent HEAD positions, not deleting or merging.

3. Final Answer:

   To show a log of where HEAD and branch references have been recently -> Option A

4. Quick Check:

   Reflog = recent HEAD changes [OK]

Hint: Reflog shows recent HEAD moves, not branch merges or deletions [OK]

Common Mistakes:

• Confusing reflog with git log
• Thinking reflog deletes commits
• Assuming reflog pushes commits

2. Which command correctly recovers a lost commit using its reflog hash abc1234 by creating a new branch named recovered?

easy

A. git branch recovered && git checkout abc1234

B. git reset --hard recovered abc1234

C. git reflog checkout abc1234 recovered

D. git checkout -b recovered abc1234

Solution

1. Step 1: Understand how to create a branch from a commit hash

   The command git checkout -b <branch> <commit> creates and switches to a new branch at that commit.

2. Step 2: Check each option's correctness

   git checkout -b recovered abc1234 uses correct syntax. git branch recovered && git checkout abc1234 creates branch but checks out commit separately (detached HEAD). git reflog checkout abc1234 recovered is invalid syntax. git reset --hard recovered abc1234 misuses reset.

3. Final Answer:

   git checkout -b recovered abc1234 -> Option D

4. Quick Check:

   Create branch from commit: checkout -b [OK]

Hint: Use 'git checkout -b branch commit' to recover lost commit [OK]

Common Mistakes:

• Using git reflog checkout (invalid command)
• Creating branch and checkout separately causing detached HEAD
• Misusing git reset syntax

3. Given the following reflog output snippet:

abc1234 HEAD@{0}: commit: Fix typo
def5678 HEAD@{1}: commit: Add feature
789abcd HEAD@{2}: commit: Initial commit

What command will restore the commit with message 'Add feature'?

medium

A. git checkout HEAD@{2}

B. git checkout 789abcd

C. git checkout def5678

D. git checkout abc1234

Solution

1. Step 1: Identify the commit hash for 'Add feature'

   From reflog, 'Add feature' commit hash is def5678 at HEAD@{1}.

2. Step 2: Use git checkout with the correct hash

   Checking out def5678 restores that commit state.

3. Final Answer:

   git checkout def5678 -> Option C

4. Quick Check:

   Checkout commit by hash = def5678 [OK]

Hint: Match commit message to hash, then checkout that hash [OK]

Common Mistakes:

• Choosing wrong commit hash
• Using HEAD@{2} which is 'Initial commit'
• Confusing latest commit with target commit

4. You ran git reflog and found a lost commit hash abc1234. You tried git checkout abc1234 but got a detached HEAD warning. How do you fix this to recover the commit safely?

medium

A. Create a new branch at that commit using git checkout -b recovered abc1234

B. Run git reset --hard abc1234 immediately

C. Delete the reflog entry and try again

D. Push the commit hash to remote

Solution

1. Step 1: Understand detached HEAD state

   Checking out a commit hash puts you in detached HEAD, which is risky for new work.

2. Step 2: Create a branch to save the commit safely

   Use git checkout -b recovered abc1234 to create a branch and avoid losing commits.

3. Final Answer:

   Create a new branch at that commit using git checkout -b recovered abc1234 -> Option A

4. Quick Check:

   Fix detached HEAD by creating branch [OK]

Hint: Always create a branch from lost commit to avoid detached HEAD [OK]

Common Mistakes:

• Ignoring detached HEAD and continuing work
• Deleting reflog entries mistakenly
• Trying to push without branch

5. You accidentally reset your branch to an older commit, losing recent commits. You run git reflog and see:

abc1234 HEAD@{0}: reset: moving to abc1234
def5678 HEAD@{1}: commit: Add new feature
789abcd HEAD@{2}: commit: Fix bug

How do you restore your branch to include the lost 'Add new feature' commit?

hard

A. Delete reflog entries before abc1234

B. Run git reset --hard def5678 to move branch back to lost commit

C. Run git checkout abc1234 to stay at reset point

D. Run git merge def5678 from abc1234

Solution

1. Step 1: Identify lost commit hash from reflog

   The lost commit 'Add new feature' is at def5678 (HEAD@{1}).

2. Step 2: Use git reset to move branch pointer back

   Running git reset --hard def5678 restores branch to that commit, recovering lost work.

3. Final Answer:

   Run git reset --hard def5678 to move branch back to lost commit -> Option B

4. Quick Check:

   Reset branch to lost commit hash [OK]

Hint: Use git reset --hard with reflog hash to recover lost commits [OK]

Common Mistakes:

• Checking out reset commit instead of resetting branch
• Deleting reflog entries unnecessarily
• Trying to merge without branch pointer