Scenario 4 — Recover Lost Commits with Reflog

# Scenario 4 — Recover Lost Commits ## The brief Deliberately "lose" commits via reset and rebase, then recover them using reflog. Build the muscle memory for the safety net. ## Step 1: Setup (5 min) ```bash mkdir reflog-drill && cd reflog-drill git init echo "v1" > app.py && git add . && git commit -m "Initial" echo "v2" > app.py && git commit -am "Improve" echo "v3" > app.py && git commit -am "Add feature" echo "v4" > app.py && git commit -am "Refactor" echo "v5" > app.py && git commit -am "Polish" git log --oneline # abc1 Polish # abc2 Refactor # abc3 Add feature # abc4 Improve # abc5 Initial ``` ## Step 2: Lose via reset --hard (10 min) ```bash git reset --hard HEAD~3 # Lost: Polish, Refactor, Add feature # HEAD now at abc4 Improve git log --oneline # abc4 Improve # abc5 Initial cat app.py # v2 ``` The last 3 commits and the v3-v5 content seem gone. But: ```bash git reflog # abc4 HEAD@{0}: reset: moving to HEAD~3 # abc1 HEAD@{1}: commit: Polish # abc2 HEAD@{2}: commit: Refactor # abc3 HEAD@{3}: commit: Add feature # abc4 HEAD@{4}: commit: Improve # abc5 HEAD@{5}: commit (initial): Initial ``` Each operation logged. Restore: ```bash git reset --hard abc1 # the Polish commit # OR git reset --hard HEAD@{1} # same effect git log --oneline # abc1 Polish # abc2 Refactor # abc3 Add feature # abc4 Improve # abc5 Initial cat app.py # v5 ``` Recovered. ## Step 3: Lose via interactive rebase mistake (10 min) ```bash git rebase -i HEAD~3 ``` Mark all as drop (mistake!): ``` drop abc1 Polish drop abc2 Refactor drop abc3 Add feature ``` Save. Git executes; commits gone: ```bash git log --oneline # abc4 Improve # abc5 Initial ``` Recover via reflog: ```bash git reflog # Look for: rebase (start): checkout abc4 (pre-rebase state) # Or: the SHA of where you were before rebase git reset --hard # Or: git reset --hard ORIG_HEAD (Git sets ORIG_HEAD before destructive ops) ``` `ORIG_HEAD` is a convenient shortcut for the position before the last "big" operation. ## Step 4: Recover a deleted branch (5 min) ```bash git switch -c feature echo "feature work" > feature.txt git add . && git commit -m "Feature commit" git switch main git branch -D feature # Deleted branch feature (was abc7). git branch # Only main shown; feature gone ``` But the commit still exists: ```bash git reflog # abc7 HEAD@{2}: commit: Feature commit # ... git branch feature abc7 # recreate branch at that commit git switch feature cat feature.txt # feature work ``` ## Step 5: Use fsck for truly lost commits Simulate an old loss (in real life, after reflog expired): ```bash git fsck --lost-found # dangling commit abc8 ... ``` These are commits not referenced by any branch or in reflog. Investigate: ```bash git show abc8 # See its diff and message git branch recovered abc8 ``` ## Step 6: Reflog scope ```bash git reflog # HEAD's reflog git reflog main # main branch's reflog git reflog --all # all refs' reflog ``` Branches have their own reflog. If you reset `main` and want history of main specifically: ```bash git reflog main # Specifically tracks main's tip history ``` ## Deliverables **Submission contract:** upload `RECOVERY.md` (reflog retention, `ORIG_HEAD`, `fsck --lost-found`, what can't be recovered). **100-pt rubric:** reset --hard recovery (25) / rebase-mistake recovery via reflog/ORIG_HEAD (25) / deleted-branch recovery (20) / fsck dangling-commit recovery (15) / RECOVERY.md documents limits (15). upload `RECOVERY.md` (reflog retention, `ORIG_HEAD`, `fsck --lost-found`, what can't be recovered). reset --hard recovery (25) / rebase-mistake recovery via reflog/ORIG_HEAD (25) / deleted-branch recovery (20) / fsck dangling-commit recovery (15) / RECOVERY.md documents limits (15). upload `RECOVERY.md` (reflog retention, `ORIG_HEAD`, `fsck --lost-found`, what can't be recovered). reset --hard recovery (25) / rebase-mistake recovery via reflog/ORIG_HEAD (25) / deleted-branch recovery (20) / fsck dangling-commit recovery (15) / RECOVERY.md documents limits (15). - A demonstrated recovery from each scenario: reset --hard, rebase mistake, deleted branch. - A `RECOVERY.md` documenting: - How reflog records every HEAD movement. - The 90-day default retention. - `ORIG_HEAD` shortcut. - `git fsck --lost-found` for ancient losses. - What CAN'T be recovered (uncommitted/untracked work). ## What you'll learn - Reflog as the universal safety net. - `git reset --hard ` to restore any prior state. - `ORIG_HEAD` after destructive operations. - Branch reflog vs HEAD reflog. - `git fsck --lost-found` for last-resort recovery. - Why frequent commits make recovery easier. ## Stretch - Set reflog retention: `git config gc.reflogExpire 365.days` (1 year). - Experiment with `git gc --prune=now` to see what truly gets deleted (CAUTION: irreversible). - Build a script that creates a daily snapshot tag for extra safety.