The `s6-ipcserver-socketbinder` program

s6-ipcserver-socketbinder binds a Unix domain socket, then executes a program.

Interface

     s6-ipcserver-socketbinder [ -d | -D ] [ -b backlog ] path prog...

s6-ipcserver-socketbinder creates a Unix domain socket of type SOCK_STREAM and binds it to path. It prepares the socket to accept connections by calling listen().
It then execs into prog... with the open socket as its standard input.

-d : allow instant rebinding to the same path even if it has been used not long ago - this is the SO_REUSEADDR flag to setsockopt() and is generally used with server programs. This is the default. Note that path will be deleted if it already exists at program start time.
-D : disallow instant rebinding to the same path.
-b backlog : set a maximum of backlog backlog connections on the socket. Extra connection attempts will rejected by the kernel.

s6-ipcserver-socketbinder is part of a set of basic blocks used to build a flexible Unix super-server. It normally should be given a command line crafted to make it execute into s6-ipcserverd to accept connections from clients, or into a program such as s6-applyuidgid to drop privileges before doing so.
The s6-ipcserver program does exactly this. It implements a full Unix super-server by building a command line starting with s6-ipcserver-socketbinder and ending with s6-ipcserverd followed by the application program, and executing into it.