The s6-fdholder-retrieve program
s6-fdholder-retrieve connects to a
fd-holding daemon listening on a
Unix domain socket, and retrieves a file descriptor from that
daemon, then executes a program with that file descriptor as the
program's standard input.
s6-fdholder-retrieve [ -D ] [ -t timeout ] path id prog...
- s6-fdholder-retrieve executes into s6-ipcclient path
s6-fdholder-retrievec id prog....
It does nothing else: it is just a convenience program.
The s6-ipcclient program connects
to a Unix socket at path, and the
gets the file descriptor identified by id over the socket.
- It should be used to connect to a
s6-fdholderd daemon, which will pass the
file descriptor to the client over the path socket.
- It executes into prog... with the retrieved file
descriptor as prog...'s standard input.
- -D : delete the file descriptor from the server's
storage after retrieval. This option requires writing rights over the
given identifier as well as reading rights: check the server's
- -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).
s6-fdholder-retrieve /service/fdholderd/s MYSOCKET s6-ipcserverd cat
will retrieve a file descriptor stored under the MYSOCKET identifier in
the s6-fdholderd daemon listening on the /service/fdholderd/s
socket, and execute into s6-ipcserverd cat with that file
descriptor as stdin. In this case, if MYSOCKET referred to a Unix domain
socket, s6-ipcserverd will then accept
client connections on it and spawn a cat program for every
- s6-fdholder-retrieve really executes into s6-ipcclient
6 fdclose 7 prog..., so that prog... does not
have a connection with the fd-holding daemon anymore. If you want to
keep the server connection open for prog..., use
s6-ipcclient s6-fdholder-retrievec manually.
- To execute prog with the newly retrieved file descriptor
as number n while preserving stdin, use the following construct:
fdmove n 0 s6-fdholder-retrieve path id
0 n prog.... Be aware that n
cannot be 6 or 7, internally used by s6-fdholder-retrieve.