On Mon, Sep 23, 2019 at 2:12 AM Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > The pidfd_send_signal() system call allows the avoidance of race > conditions that occur when using traditional interfaces (such as > kill(2)) to signal a process. The problem is that the traditional > interfaces specify the target process via a process ID (PID), with > the result that the sender may accidentally send a signal to the > wrong process if the originally intended target process has termi‐ > nated and its PID has been recycled for another process. By con‐ > trast, a PID file descriptor is a stable reference to a specific > process; if that process terminates, then the file descriptor > ceases to be valid The file *descriptor* remains valid even after the process to which it refers exits. You can close(2) the file descriptor without getting EBADF. I'd say, instead, that "a PID file descriptor is a stable reference to a specific process; process-related operations on a PID file descriptor fail after that process exits".
