term% cat index.txt FORK(2) System Calls Manual 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 val‐
ues. The resources include the file name space, the open file descrip‐
tor table (which, when shared, permits processes to open and close
files for other processes), the set of environment variables (see
env(3)), the note group (the set of processes that receive notes writ‐
ten 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 descrip‐
tor. Is mutually exclusive with RFNAMEG.
RFNOMNT
If set, subsequent mounts into the new name space and derefer‐
encing of pathnames starting with # are disallowed.
RFENVG If set, the environment variables are copied; otherwise the two
processes share environment variables. Is mutually exclusive
with RFCENVG.
RFCENVG
If set, the new process starts with an empty environment. Is
mutually exclusive with RFENVG.
RFNOTEG
Each process is a member of a group of processes that all re‐
ceive 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 parent, but if RFNOTEG is set (regardless of RF‐
PROC), 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 ta‐
ble. Is mutually exclusive with RFFDG.
RFREND If set, the process will be unable to rendezvous(2) with any of
its ancestors; its children 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 seg‐
ments. Otherwise, the child inherits a copy of those segments.
Other segment types, in particular stack segments, will be unaf‐
fected. 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 processes 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 neces‐
sary, until required process 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.
FORK(2)