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PDFORK(2)		       System Calls Manual		       PDFORK(2)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/procdesc.h>

     pid_t
     pdfork(int *fdp, int pdflags);

     pid_t
     pdrfork(int *fdp, int pdflags, int rfflags);

     int
     pdgetpid(int fd, pid_t *pidp);

     int
     pdkill(int fd, int signum);

     int
     pdwait(int fd, int *status, int options, struct __wrusage *wrusage,
	 struct __siginfo *info);

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 pdflags:

     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.

     The pdrfork() system call is a variant of	pdfork()  that	also  takes  the
     rfflags argument to control sharing of process resources between the caller
     and  the  new  process.  Like pdfork(), the function writes the process de-
     scriptor referencing the created process into the location  pointed  to  by
     the  fdp  argument.   See rfork(2) for a description of the possible rfflag
     flags.  The pdrfork()  system  call  requires  that  both	the  RFPROC  and
     RFPROCDESC flags, or RFSPAWN flag are specified.

     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 pdwait() system call allows the calling thread to wait and retrieve the
     status information on the process referenced by the fd process  descriptor.
     See  the  description  of the wait6 system call for the behavior specifica-
     tion.

     The following system calls also have effects specific to  process	descrip-
     tors:

     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 repre-
     sented by the process descriptor is still alive.

     poll(2) and select(2) allow waiting for  process  state  transitions;  cur-
     rently  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  de-
     scriptor,	the process will be terminated with the signal SIGKILL.  The PID
     of the referenced process is not reused until  the  process  descriptor  is
     closed,  whether or not the zombie process is reaped by pdwait(), wait6, or
     similar system calls.

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

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

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

     [EFAULT]		The  copyout  of  the resulting file descriptor value to
			the memory pointed to by fdp failed.

			Note that the child process  was  already  created  when
			this condition is detected, and the child continues exe-
			cution,  same as the parent.  If this error must be han-
			dled, it is advisable to memoize the getpid() result be-
			fore the call to pdfork() or pdrfork(), and  compare  it
			to  the value returned by getpid() after, to see if code
			is executing in parent or child.

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

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

SEE ALSO
     close(2),	fork(2),  fstat(2),  kill(2), kqueue(2), poll(2), wait4(2), cap-
     sicum(4), procdesc(4)

HISTORY
     The pdfork(), pdgetpid(), and  pdkill()  system  calls  first  appeared  in
     FreeBSD  9.0.   The  pdrfork()  and pdwait() system calls first appeared in
     FreeBSD 15.1.

     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.  The pdrfork() and pdwait() functions  were  devel-
     oped  by  Konstantin Belousov <kib@FreeBSD.org> with input from Alan Somers
     <asomers@FreeBSD.org>.

FreeBSD ports 15.quarterly	 April 19, 2026 		       PDFORK(2)

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