git fsck

Find dangling and broken objects.

🎯 What & why

git fsck (file system check) verifies the integrity of the object database: hashes match, refs point to real objects, no corruption. Run it when something feels wrong, or proactively on critical repos.

🧠 Mental model

Think fsck for your .git directory. It walks every object, every ref, every reflog entry and reports anything that does not add up - dangling, unreachable, broken, missing.

🛠️ Synopsis

git fsck [--tags] [--root] [--unreachable] [--cache] [--no-reflogs]
              [--full] [--strict] [--verbose] [--lost-found]
              [--connectivity-only] [--name-objects] [<object>...]

🎚️ Switches & options

Flag	What it does
`--full`	Check all object directories including alternates (default in modern Git)
`--strict`	Stricter checks - flags trees with bad permissions, etc.
`--unreachable`	Report objects not reachable from any ref or reflog
`--dangling`	Report objects no other object refers to (default: on)
`--lost-found`	Write dangling objects into .git/lost-found/ for recovery
`--no-reflogs`	Treat reflogs as not a source of reachability
`--connectivity-only`	Skip hash verification - faster, only checks the graph

💡 Use cases

After a power loss, disk error, or kill -9 during a git operation
Recovering objects from a deleted branch via lost-found
Diagnosing 'object file is empty' or 'invalid sha1' errors
Pre-flight check before a critical push or release tag

🧪 Examples

Standard check

git fsck

Aggressive check

git fsck --full --strict

Recover lost commits

git fsck --lost-found

Fast graph-only check

git fsck --connectivity-only

🎓 Recommendations

Dangling objects are usually benign - they are just commits/blobs no ref points to. Do not panic.
Run with --lost-found when you deleted a branch and want the commits back.
If fsck reports actual corruption, stop writing to the repo and clone fresh from a known-good copy.

🪤 Common pitfalls

'dangling commit' messages alarm people but are normal after rebases and amends.
--unreachable plus aggressive gc can permanently delete recovery candidates - back up first.
fsck does not fix anything; it only reports. Repair is manual.

🔗 Related modules

📝 Quiz

Hit each option, then Check answers. Score is recorded; Next is always open.