FORK(2) FORK(2)
NAME
fork, rfork - manipulate process resources
SYNOPSIS
#include <u.h>
#include <libc.h>
int fork(void)
int rfork(int flags)
DESCRIPTION
Forking is the only way new processes are created. The
flags argument to rfork selects which resources of the
invoking process (parent) are shared by the new process
(child) or initialized to their default values. The
resources include the file name space, the open file
descriptor table (which, when shared, permits processes to
open and close files for other processes), the set of envi-
ronment variables (see env(3)), the note group (the set of
processes that receive notes written to a member's notepg
file; see proc(3)), the set of rendezvous tags (see
rendezvous(2)); and open files. Flags is the logical OR of
some subset of
RFPROC If set a new process is created; otherwise changes
affect the current process.
RFNOWAIT If set, the child process will be dissociated from
the parent. Upon exit the child will leave no
Waitmsg (see wait(2)) for the parent to collect.
RFNAMEG If set, the new process inherits a copy of the
parent's name space; otherwise the new process
shares the parent's name space. Is mutually
exclusive with RFCNAMEG.
RFCNAMEG If set, the new process starts with a clean name
space. A new name space must be built from a mount
of an open file descriptor. Is mutually exclusive
with RFNAMEG.
RFNOMNT If set, subsequent mounts into the new namespace
and dereferencing of pathnames starting with # are
disallowed.
RFENVG If set, the environment variables are copied; oth-
erwise the two processes share environment vari-
ables. Is mutually exclusive with RFCENVG.
RFCENVG If set, the new process starts with an empty envi-
ronment. Is mutually exclusive with RFENVG.
RFNOTEG Each process is a member of a group of processes
that all receive notes when a note is written to
any of their notepg files (see proc(3)). The group
of a new process is by default the same as its
Page 1 Plan 9 (printed 11/22/24)
FORK(2) FORK(2)
parent, but if RFNOTEG is set (regardless of
RFPROC), the process becomes the first in a new
group, isolated from previous processes.
RFFDG If set, the invoker's file descriptor table (see
intro(2)) is copied; otherwise the two processes
share a single table.
RFCFDG If set, the new process starts with a clean file
descriptor table. Is mutually exclusive with
RFFDG.
RFREND If set, the process will be unable to
rendezvous(2) with any of its ancestors; its chil-
dren will, however, be able to rendezvous with it.
In effect, RFREND makes the process the first in a
group of processes that share a space for
rendezvous tags.
RFMEM If set, the child and the parent will share data
and bss segments. Otherwise, the child inherits a
copy of those segments. Other segment types, in
particular stack segments, will be unaffected.
May be set only with RFPROC.
File descriptors in a shared file descriptor table are kept
open until either they are explicitly closed or all pro-
cesses sharing the table exit.
If RFPROC is set, the value returned in the parent process
is the process id of the child process; the value returned
in the child is zero. Without RFPROC, the return value is
zero. Process ids range from 1 to the maximum integer (int)
value. Rfork will sleep, if necessary, until required pro-
cess resources are available.
Fork is just a call of rfork(RFFDG|RFREND|RFPROC).
SOURCE
/sys/src/libc/9syscall
/sys/src/libc/9sys/fork.c
SEE ALSO
intro(2), proc(3),
DIAGNOSTICS
These functions set errstr.
Page 2 Plan 9 (printed 11/22/24)