git-upload-pack

git upload-pack <directory>

<directory>
    The path to the Git repository on the server that git-upload-pack should serve objects from. This is usually an absolute or relative path to a bare repository's .git directory or the repository itself.

git-upload-pack is a "plumbing" command, meaning it's an internal Git command not typically invoked directly by end-users. Its primary function is to serve Git objects (commits, trees, blobs, tags) from a remote repository to a client. When you run git fetch, git pull, or git clone, the client-side Git process communicates with a remote server. On the server, git-upload-pack is executed.

It reads "want" and "have" lines from the client's standard input, identifies which objects the client needs, and then sends a packfile containing those objects to the client's standard output. This command forms the core of Git's "smart" protocol for transferring data efficiently over network connections like SSH, HTTP(S), or the native Git protocol (git://). It ensures only necessary data is transferred, optimizing bandwidth usage and facilitating the distributed nature of Git repositories.

git-upload-pack is an internal command and should generally not be executed directly by users. It relies on specific Git protocol messages exchanged via standard input/output. Incorrect direct usage or exposing it without proper security mechanisms (e.g., via a misconfigured git-daemon or SSH setup) can lead to security vulnerabilities or unexpected behavior. It is designed to be invoked by higher-level Git commands or services like SSH or git-daemon.

git-upload-pack is typically invoked by a server-side process handling various Git protocols:

SSH: When you clone or fetch via SSH (e.g., git clone user@host:/path/to/repo.git), the SSH daemon on the server executes git-upload-pack within the context of the requested repository. The SSH connection acts as the transparent channel for stdin/stdout.

Smart HTTP(S): For HTTP(S) access, a web server (like Apache or Nginx) or a Git hosting service routes requests to a CGI script or an application that executes git-upload-pack. This setup often involves git-http-backend which acts as the intermediary.

Git Protocol (git://): The git-daemon service listens for incoming Git protocol connections and, upon request, forks git-upload-pack to handle the object transfer for public, read-only access.

git-upload-pack has been a fundamental component of Git's network transfer capabilities since its early days, essential for enabling the distributed nature of Git. It was designed by Linus Torvalds and the early Git developers to provide an efficient and stateless mechanism for clients to request and receive repository objects from a server, forming the basis of the "smart" protocol. Its core functionality has remained largely consistent, evolving with performance optimizations and protocol enhancements over time.

git-fetch(1), git-pull(1), git-clone(1), git-receive-pack(1), git-daemon(1)