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 connects to a s6-fdholderd server process listening on path.
It attempts to pass a complete state - i.e. a set of file descriptors with identifiers and expiration dates - to the server.

-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).

0: success.
1: the server denied the operation. The meaning of the error messages is explained here.
100: wrong usage.
111: system call failed - that includes attempting to connect to a nonexistent socket, or one where no s6-fdholderd daemon is listening.

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-getdump.
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.