s6
Software
skarnet.org

The s6-fdholder-store program

s6-fdholder-store connects to a fd-holding daemon listening on a Unix domain socket, and gives it a copy of one of its open file descriptors for the daemon to hold.

Interface

     s6-fdholder-store [ -d fd ] [ -T fdtimeout ] [ -t timeout ] path id

• s6-fdholder-store connects to a s6-fdholderd server process listening on path.
• It attempts to pass a copy of its standard input, or of its descriptor fd, to the server, with identifier id.

Options

• -d fd : store descriptor number fd. By default, fd is 0 (i.e. the program's stdin will be stored).
• -T fdtimeout : the descriptor is stored with an expiration time of fdtimeout milliseconds, which means the s6-fdholderd daemon will close and get rid of the descriptor after that time. By default, fdtimeout is 0, which means infinite - no expiration time.
• -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).

Exit codes

• 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.

Usage example

   s6-ipcserver-socketbinder /tmp/mysocket s6-fdholder-store /service/fdholderd/s MYSOCKET

will open a Unix domain socket, bind it to /tmp/mysocket and listen to incoming connections, then give it to a s6-fdholderd instance listening on /service/fdholderd/s, with no expiration date, with the "MYSOCKET" identifier. Another program will be able to retrieve the socket later, using s6-fdholder-retrieve.