160 lines
5.0 KiB
Groff
160 lines
5.0 KiB
Groff
.\" $NetBSD: fork1.9,v 1.14 2008/04/30 13:10:58 martin Exp $
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.\"
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.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
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.\" NASA Ames Research Center.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd January 4, 2008
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.Dt FORK1 9
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.Os
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.Sh NAME
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.Nm fork1
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.Nd create a new process
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/proc.h
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.Ft int
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.Fn "fork1" "struct lwp *l1" "int flags" "int exitsig" "void *stack" "size_t stacksize" "void (*func)(void *)" "void *arg" "register_t *retval" "struct proc **rnewprocp"
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.Sh DESCRIPTION
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.Fn fork1
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creates a new process out of the process behind
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.Ar l1 ,
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which is assumed to be the current lwp.
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This function is used primarily to implement the
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.Xr fork 2
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and
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.Xr vfork 2
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system calls, but is versatile enough to be used as a backend for
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e.g. the
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.Xr __clone 2
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call.
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.Pp
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The
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.Ar flags
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argument controls the semantics of the fork operation, and is made up of
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the bitwise-OR of the following values:
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.Bl -tag -width FORK_SHAREFILES
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.It FORK_PPWAIT
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The parent process will sleep until the child process successfully calls
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.Xr execve 2
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or exits (either by a call to
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.Xr _exit 2
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or abnormally).
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.It FORK_SHAREVM
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The child process will share the parent's virtual address space.
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If this flag is not specified, the child will get a copy-on-write
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snapshot of the parent's address space.
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.It FORK_SHARECWD
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The child process will share the parent's current directory, root directory,
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and file creation mask.
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.It FORK_SHAREFILES
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The child process will share the parent's file descriptors.
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.It FORK_SHARESIGS
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The child process will share the parent's signal actions.
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.It FORK_NOWAIT
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The child process will at creation time be inherited by the init process.
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.It FORK_CLEANFILES
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The child process will not copy or share the parent's descriptors, but
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rather will start out with a clean set.
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.El
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.Pp
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A
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.Ar flags
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value of 0 indicates a standard fork operation.
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.Pp
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The
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.Ar exitsig
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argument controls the signal sent to the parent on child death.
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If normal operation desired, SIGCHLD should be supplied.
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.Pp
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It is possible to specify the child userspace stack location and size
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by using the
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.Ar stack
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and
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.Ar stacksize
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arguments, respectively.
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Values
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.Dv NULL
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and 0, respectively, will give the child the default values
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for the machine architecture in question.
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.Pp
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The arguments
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.Ar func
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and
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.Ar arg
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can be used to specify a kernel function to be called when the child process
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returns instead of
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.Fn child_return .
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These are used for example in starting the init process and creating kernel
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threads.
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.Pp
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The
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.Ar retval
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argument is provided for the use of system call stubs.
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If
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.Ar retval
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is not NULL, it will hold the following values after successful completion
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of the fork operation:
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.Bl -tag -width retval[0]
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.It Ar retval[0]
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This will contain the pid of the child process.
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.It Ar retval[1]
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In the parent process, this will contain the value 0.
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In the child process, this will contain 1.
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.El
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.Pp
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User level system call stubs typically subtract 1 from
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.Ar retval[1]
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and bitwise-AND it with
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.Ar retval[0] ,
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thus returning the pid to the parent process and 0 to the child.
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.Pp
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If
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.Ar rnewprocp
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is not NULL,
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.Ar *rnewprocp
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will point to the newly created process upon successful completion of
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the fork operation.
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.Sh RETURN VALUES
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Upon successful completion of the fork operation,
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.Fn fork1
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returns 0.
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Otherwise, the following error values are returned:
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.Bl -tag -width [EAGAIN]
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.It Bq Er EAGAIN
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The limit on the total number of system processes would be exceeded.
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.It Bq Er EAGAIN
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The limit
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.Dv RLIMIT_NPROC
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on the total number of processes under execution by this
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user id would be exceeded.
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.El
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.Sh SEE ALSO
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.Xr execve 2 ,
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.Xr fork 2 ,
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.Xr vfork 2
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