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)), 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.
The tag space for rendezvous(2) is considered part of the 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.
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.
RFMEM If set, the kernel will mark segments of type data and bss as
shared. The child will then inherit all the shared segments the
parent process owns. Other segment types will be unaffected.
Subsequent forks by the parent will then propagate the shared
data and bss between children. The stack segment is always
split. 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|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)