PDFORK(2)                    BSD System Calls Manual                   PDFORK(2)

     pdfork, pdgetpid, pdkill — System calls to manage process descriptors

     Standard C Library (libc, -lc)

     #include <sys/procdesc.h>

     pdfork(int *fdp, int flags);

     pdgetpid(int fd, pid_t *pidp);

     pdkill(int fd, int signum);

     Process descriptors are special file descriptors that represent processes,
     and are created using pdfork(), a variant of fork(2), which, if successful,
     returns a process descriptor in the integer pointed to by fdp.  Processes
     created via pdfork() will not cause SIGCHLD on termination.  pdfork() can
     accept the flags:

     PD_DAEMON  Instead of the default terminate-on-close behaviour, allow the
                process to live until it is explicitly killed with kill(2).

                This option is not permitted in capsicum(4) capability mode (see

                Set close-on-exec on process descriptor.

     pdgetpid() queries the process ID (PID) in the process descriptor fd.

     pdkill() is functionally identical to kill(2), except that it accepts a
     process descriptor, fd, rather than a PID.

     The following system calls also have effects specific to process

     fstat(2) queries status of a process descriptor; currently only the
     st_mode, st_birthtime, st_atime, st_ctime and st_mtime fields are defined.
     If the owner read, write, and execute bits are set then the process
     represented by the process descriptor is still alive.

     poll(2) and select(2) allow waiting for process state transitions;
     currently only POLLHUP is defined, and will be raised when the process
     dies.  Process state transitions can also be monitored using kqueue(2)
     filter EVFILT_PROCDESC; currently only NOTE_EXIT is implemented.

     close(2) will close the process descriptor unless PD_DAEMON is set; if the
     process is still alive and this is the last reference to the process
     descriptor, the process will be terminated with the signal SIGKILL.

     pdfork() returns a PID, 0 or -1, as fork(2) does.

     pdgetpid() and pdkill() return 0 on success and -1 on failure.

     These functions may return the same error numbers as their PID-based
     equivalents (e.g.  pdfork() may return the same error numbers as fork(2)),
     with the following additions:

     [EINVAL]           The signal number given to pdkill() is invalid.

     [ENOTCAPABLE]      The process descriptor being operated on has
                        insufficient rights (e.g.  CAP_PDKILL for pdkill()).

     close(2), fork(2), fstat(2), kill(2), poll(2), kqueue(2), wait4(2),
     capsicum(4), procdesc(4)

     The pdfork(), pdgetpid(), and pdkill() system calls first appeared in
     FreeBSD 9.0.

     Support for process descriptors mode was developed as part of the
     TrustedBSD Project.

     These functions and the capability facility were created by Robert N. M.
     Watson <rwatson@FreeBSD.org> and Jonathan Anderson <jonathan@FreeBSD.org>
     at the University of Cambridge Computer Laboratory with support from a
     grant from Google, Inc.

BSD                             October 14, 2018                             BSD