libsdsock

November 3, 2023 · View on GitHub

Description

libsdsock is an LD_PRELOAD hack that allows (or at least tries to...) many pieces of software that listen for network connections to be started on demand via systemd’s “Socket Activation” feature. TCP, UDP, Unix stream sockets are supported.

The motivating use case was to have SSH dynamic port forwarding that starts (and restarts) on demand. Examples (jump.socket, jump.service and jump.sh) are provided for that, though the tool is generic.

Getting Started

Dependencies

libsystemd development files
libdl development files
gcc

Installation

git clone https://github.com/ryancdotorg/libsdsock.git
cd libsdsock
make
make install

Run as root (sudo make install) to install system-wide.

Usage

Create systemd .socket and .service files as required (see examples)
Use systemctl enable on the .socket unit - this is not required for the corresponding .service unit.
Use systemctl start on the .socket unit - again, this is not required for the corresponding .service unit.

Debugging

Run make debug to build libsdsock-debug.so version, it will print debug infomation to stderr.

Help

You can file an issue on GitHub, however I may not respond. This software is being provided without warranty in the hopes that it may be useful.

Security

This software has not been independently audited and may contain bugs. That said, the exposure surface of the code is minimal, and no untrusted data is processed. The only functions shimmed are bind, listen, close, closefrom and close_range.