One of the more obscure features provided by Unix-domain sockets is the
ability to pass a file descriptor from one process to another.  This
feature is often used to provide access to a specific file or network
connection to a process running in a relatively unprivileged context.  But
what if the recipient doesn't <i>want</i> a new file descriptor?  A feature
added for the 6.16 release makes it possible to refuse that offer.