The `s6-fdholder-setdump` program

s6-fdholder-setdump connects to a fd-holding daemon listening on a Unix domain socket, and dumps a set of file descriptors into that daemon.

Interface

     s6-fdholder-setdump [ -t timeout ] path

s6-fdholder-setdump executes into s6-ipcclient path s6-fdholder-setdumpc id. It does nothing else: it is just a convenience program. The s6-ipcclient program connects to a Unix socket at path, and the s6-fdholder-setdumpc program transmits the file descriptors over the socket.
It should be used to connect to a s6-fdholderd daemon, which will store the set of file descriptors.

-t timeout : if the operation cannot be processed in timeout milliseconds, then fail with an error message. Communications with the server should be near-instant, so this option is only here to protect users against programming errors (connecting to the wrong socket, for instance).

The file descriptors to transmit to the server should of course be already open in the s6-fdholder-setdump program; also, s6-fdholder-setdump should have certain environment variables that describe that set of file descriptors. The format of the environment is the same as the one set by s6-fdholder-getdumpc.
Getting the whole state of a s6-fdholderd daemon requires specific privileges. Make sure you properly configure the s6-fdholderd access rights so your client can perform that operation.