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)), 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 descriptor. Is mutually exclusive
with RFNAMEG.
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
parent, but if RFNOTEG is set (regardless of
RFPROC), the process becomes the first in a new
group, isolated from previous processes.
Page 1 Plan 9 (printed 12/21/24)
FORK(2) FORK(2)
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.
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 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|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 12/21/24)