PDFORK(2)                 FreeBSD System Calls Manual                PDFORK(2)

NAME
     pdfork, pdgetpid, pdkill - System calls to manage process descriptors

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/procdesc.h>

     pid_t
     pdfork(int *fdp, int flags);

     int
     pdgetpid(int fd, pid_t *pidp);

     int
     pdkill(int fd, int signum);

DESCRIPTION
     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 cap_enter(2)).

     PD_CLOEXEC     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
     descriptors:

     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.

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

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

ERRORS
     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()).

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

HISTORY
     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.

AUTHORS
     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.

FreeBSD 13.1-RELEASE-p6        October 14, 2018        FreeBSD 13.1-RELEASE-p6