Unix Domain Sockets

SCM_RIGHTS Transfers Open File Descriptions Across Process Boundaries

SCM_RIGHTS lets one process send a reference to an open file through a Unix domain socket. The receiver obtains a file descriptor in its own descriptor table, but the transfer does not reopen the pathname or copy the kernel object. On Linux, the resulting reference has semantics equivalent to duplicating the sender’s descriptor into the receiving process. That distinction matters whenever a process boundary is also an authority boundary. A supervisor can open a socket, file, pipe, device, or other descriptor-backed object and pass the established reference to a worker. The worker receives access to the already-open object, including open-file state that can remain shared with the sender.