RFORK(2) BSD Programmer's Manual RFORK(2)
rfork - control new processes
#include <sys/param.h>
#include <unistd.h>
int
rfork(int flags);
The fork functions (fork(2), vfork(2), and rfork()) create new processes.
The new process (child process) is an exact copy of the calling process
(parent process), except as outlined in the fork(2) manual page. rfork()
is used to manipulate the resources of the parent process and the child
process.
Operations currently supported include whether to copy or share the file
descriptor table between the two processes, whether to share the address
space, and whether the parent should wait(2) for the child process to
_exit(2). rfork() takes a single argument, flags, which controls which of
these resources should be manipulated. They are defined in the header
file <sys/param.h> and are the logical OR of one or more of the follow-
ing:
RFFDG Copy the parent's file descriptor table. If this flag is unset,
the parent and child will share the parent's file descriptor
table. Descriptors will remain in existence until they are
closed by all child processes using the table copies as well as
by the parent process. May not be used in conjunction with
RFCFDG.
RFPROC Create a new process. The current implementation requires this
flag to always be set.
RFMEM Force sharing of the entire address space between the parent
and child processes. The child will then inherit all the shared
segments the parent process owns. Subsequent forks by the
parent will then propagate the shared data and BSS segments
among children.
RFNOWAIT Child processes will have their resources reaped immediately
and implicitly when they terminate instead of turning into zom-
bies, so the parent process may not call wait(2) to collect
their exit statuses and have their resources released explicit-
ly.
RFCFDG Zero the child's file descriptor table (i.e. start with a blank
file descriptor table). May not be used in conjunction with
RFFDG.
fork(2) can be implemented as a call to rfork() using "RFFDG|RFPROC", but
isn't for backwards compatibility. If a process has file descriptor table
sharing active, setuid or setgid programs will not execve(2) with extra
privileges.
The parent process returns the process ID (PID) of the child process. The
child process returns 0. The range of the process ID is defined in
<sys/proc.h> and is currently between 1 and 32766, inclusive.
rfork() will fail and no child process will be created if:
[ENOMEM] Cannot allocate memory. The new process image required more
memory than was allowed by the hardware or by system-
imposed memory management constraints. A lack of swap space
is normally temporary; however, a lack of core is not. Soft
limits may be increased to their corresponding hard limits.
[EINVAL] Invalid argument. Some invalid argument was supplied.
[EAGAIN] Resource temporarily unavailable. The system-imposed limit
on the total number of processes under execution would be
exceeded. This limit is configuration-dependent.
[EAGAIN] Resource temporarily unavailable. The system-imposed limit
MAXUPRC on the total number of processes under execution by
a single user would be exceeded. MAXUPRC is currently de-
fined in <sys/param.h> as CHILD_MAX, which is currently de-
fined as 80 in <sys/syslimits.h>.
_exit(2), execve(2), fork(2), intro(2), vfork(2)
The rfork() function first appeared in Plan 9.
MirBSD #10-current June 17, 2003 1