The thing is that spawned processed do not give a damn about already opened file descriptors (except for stdio). But the standard is broken for historical reaso

The thing is that spawned processed do not give a damn about already opened file descriptors (except for stdio). But the standard is broken for historical reasons, very unfortunately. It would be nice to have more detail here, at least why this is "historical" and "unfortunate". A whole slew of programs wouldn't be possible and capabilities wouldn't exist without this, both older and modern. Two examples are inetd's wait functionality (letting the spawned program accept(2) further connections on the inherited listening socket) and systemd's, ahem, socket activation. main program sens[sic] commands to remote location and closes the socket If you intend the socket connection to be ended, you should be calling shutdown(2) on it, not close(2). close(2) only asserts that the calling process is done with it. The child process would end up with a dead socket fd (although, there are bugs related to improperly handling this, here's one that bit me: https://github.com/brianmario/mysql2/issues/516 https://github.com/brianmario/mysql2/issues/516 ). This is why the failure cases on syscalls should always be examined and there should be a sane, default failure case. In an ideal world, the leaked file descriptor would merely be just that, and a properly written program would ignore (or close) any file descriptors it wasn't explicitly designed/meant to use.