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), poll(2), kqueue(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.

Debian                                          October 14, 2018                                       PDFORK(2)