.\" .\" This manual page is taken directly from Plan9, and modified to .\" describe the actual BSD implementation. Permission for .\" use of this page comes from Rob Pike . .\" .\" $FreeBSD: src/lib/libc/sys/rfork.2,v 1.11.2.11 2002/07/30 19:04:25 silby Exp $ .\" $DragonFly: src/lib/libcr/sys/Attic/rfork.2,v 1.2 2003/06/17 04:26:47 dillon Exp $ .\" .Dd January 12, 1996 .Dt RFORK 2 .Os .Sh NAME .Nm rfork .Nd manipulate process resources .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In unistd.h .Ft int .Fn rfork "int flags" .Sh DESCRIPTION Forking, vforking or rforking are the only ways new processes are created. The .Fa flags argument to .Fn 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 open file descriptor table (which, when shared, permits processes to open and close files for other processes), and open files. .Fa Flags is the logical OR of some subset of: .Bl -tag -width "RFCNAMEG" -compact -offset indent .It RFPROC If set a new process is created; otherwise changes affect the current process. The current implementation requires this flag to always be set. .It RFNOWAIT If set, the child process will be dissociated from the parent. Upon exit the child will not leave a status for the parent to collect. See .Xr wait 2 . .It RFFDG If set, the invoker's file descriptor table (see .Xr intro 2 ) is copied; otherwise the two processes share a single table. .It RFCFDG If set, the new process starts with a clean file descriptor table. Is mutually exclusive with .Dv RFFDG . .It RFMEM If set, the kernel will force sharing of the entire address space, typically by sharing the hardware page table directly. The child will thus inherit and share all the segments the parent process owns, whether they are normally shareable or not. The stack segment is not split (both the parent and child return on the same stack) and thus .Fn rfork with the RFMEM flag may not generally be called directly from high level languages including C. May be set only with .Dv RFPROC . A helper function is provided to assist with this problem and will cause the new process to run on the provided stack. See .Fn rfork_thread 3 for information. .It RFSIGSHARE If set, the kernel will force sharing the sigacts structure between the child and the parent. .It RFLINUXTHPN If set, the kernel will return SIGUSR1 instead of SIGCHILD upon thread exit for the child. This is intended to mimic certain Linux clone behaviour. .El .Pp File descriptors in a shared file descriptor table are kept open until either they are explicitly closed or all processes sharing the table exit. .Pp If .Dv 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 .Dv RFPROC , the return value is zero. Process id's range from 1 to the maximum integer .Ft ( int ) value. .Fn Rfork will sleep, if necessary, until required process resources are available. .Pp .Fn Fork can be implemented as a call to .Fn rfork "RFFDG | RFPROC" but isn't for backwards compatibility. .Sh RETURN VALUES Upon successful completion, .Fn rfork returns a value of 0 to the child process and returns the process ID of the child process to the parent process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable .Va errno is set to indicate the error. .Sh ERRORS .Fn Rfork will fail and no child process will be created if: .Bl -tag -width Er .It Bq Er EAGAIN The system-imposed limit on the total number of processes under execution would be exceeded. The limit is given by the .Xr sysctl 3 MIB variable .Dv KERN_MAXPROC . (The limit is actually ten less than this except for the super user). .It Bq Er EAGAIN The user is not the super user, and the system-imposed limit on the total number of processes under execution by a single user would be exceeded. The limit is given by the .Xr sysctl 3 MIB variable .Dv KERN_MAXPROCPERUID . .It Bq Er EAGAIN The user is not the super user, and the soft resource limit corresponding to the resource parameter .Dv RLIMIT_NOFILE would be exceeded (see .Xr getrlimit 2 ) . .It Bq Er EINVAL The RFPROC flag was not specified. .It Bq Er EINVAL Both the RFFDG and the RFCFDG flags were specified. .It Bq Er ENOMEM There is insufficient swap space for the new process. .El .Sh SEE ALSO .Xr fork 2 , .Xr intro 2 , .Xr minherit 2 , .Xr vfork 2 , .Xr rfork_thread 3 .Sh BUGS .Fx does not yet implement a native .Fn clone library call, and the current pthreads implementation does not use .Fn rfork with RFMEM. A native port of the linux threads library, .Pa /usr/ports/devel/linuxthreads , contains a working .Fn clone call that utilizes RFMEM. The .Fn rfork_thread library call can often be used instead of .Fn clone . .Sh HISTORY The .Fn rfork function call first appeared in Plan9.