sosh

sosh is a lightweight command‑line client that implements the SOCKS protocol, primarily used to forward network connections through a SOCKS server. The program was originally developed for the NetBSD operating system and later made available for a variety of Unix‑like platforms, including FreeBSD, OpenBSD, and Linux. The source code is distributed under the BSD‑3 Clause license, which permits both free use and commercial modification.

The primary function of sosh is to act as an intermediary between a local application and a remote SOCKS server, allowing the local program to transparently communicate over the network as if it were directly connected. Sosh supports both SOCKS version 4 and version 5, and includes options for authentication, proxy chaining, and IPv6 address handling. Its design emphasizes small size and simplicity, making it suitable for embedded systems and environments where minimal dependencies are desired. Because it is a pure C implementation, sosh can be compiled on most POSIX systems without the need for external libraries beyond the C standard library and POSIX networking headers.

Typical usage patterns involve invoking sosh from a shell and redirecting standard input and output through the proxy. For example, one can forward a local port to a remote service by running:

```

sosh -L 8080:remotehost:80 -p 1080 localhost

```

or instruct a local program to use the proxy by setting the SOCKS5 proxy settings to localhost on port 1080. The daemon mode of sosh allows it to accept multiple incoming connections, acting as a local proxy that forwards traffic to a specified upstream SOCKS server.

Sosh has been incorporated into several larger networking projects as a lightweight dependency, and its straightforward API has led to its use in teaching networking concepts. Despite its age, sosh remains maintained by a small community of contributors and continues to function as a reliable component in proxy routing stacks.