git send-pack

What 'push' invokes to ship a pack to the remote.

🎯 What & why

git send-pack is the client half of push — it negotiates with the remote's receive-pack, builds a pack of objects the remote lacks, and sends update lines of the form 'old-sha new-sha refname'.

🧠 Mental model

Imagine a three-step handshake: receive ref advertisement, compute which refs to update with which old/new SHAs, ship the pack plus the update commands. The remote applies them atomically per-ref (or all-or-nothing with --atomic).

🛠️ Synopsis

git send-pack [--all] [--mirror] [--dry-run] [--force]
              [--receive-pack=<git-receive-pack>] [--verbose] [--thin]
              [--atomic] [--[no-]signed | --signed=(true|false|if-asked)]
              [--push-option=<string>] [--stdin]
              [<host>:]<directory> [<ref>...]

🎚️ Switches & options

Flag	What it does
`--all`	Push every local branch
`--mirror`	Push every ref under refs/ and delete remote refs that no longer exist locally
`--dry-run`	Negotiate but do not actually update remote refs
`--force`	⚠️ Allow non-fast-forward updates — overwrites remote history
`--receive-pack=<path>`	Override the path to git-receive-pack on the remote
`--verbose`	Emit detailed progress to stderr
`--thin`	Send a thin pack — smaller wire size, fattened on the receiver
`--atomic`	Either all ref updates succeed or none do
`--signed`	GPG-sign the push certificate so the server can verify the pusher
`--push-option=<string>`	Pass an arbitrary string to server-side hooks (repeatable)
`--stdin`	Read refspecs from standard input instead of arguments

💡 Use cases

Script bulk pushes that pipe refspecs from another tool via --stdin
Exercise atomic multi-ref updates in CI release jobs
Mirror a repo to a backup remote with --mirror
Pass deployment metadata to server-side hooks via --push-option

🧪 Examples

Dry-run a push to a local daemon

git send-pack --dry-run --verbose git://127.0.0.1/repo.git refs/heads/main

Atomic push of two refs

git send-pack --atomic origin refs/heads/main refs/heads/release

Mirror to a backup remote

git send-pack --mirror backup-mirror

Pipe refspecs from a script

printf 'refs/heads/main\nrefs/tags/v1.0\n' | git send-pack --stdin origin

🎓 Recommendations

Use 'git push' for daily work; send-pack is for tooling and protocol-level debugging
Pair --atomic with multi-ref releases so a partial push never leaves the remote in a half-state
Sign pushes with --signed when the remote enforces receive.certNonceSeed for accountability

🪤 Common pitfalls

--force on a shared branch silently destroys other people's commits — prefer --force-with-lease in everyday push
--mirror also deletes remote refs you no longer have locally — easy way to wipe a backup mirror
send-pack does not update remote-tracking refs the way 'git push' does — your local view of the remote will lag

🔗 Related modules

📝 Quiz

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