178 lines
5.3 KiB
Groff
178 lines
5.3 KiB
Groff
.\" $NetBSD: clone.2,v 1.5 2001/09/16 02:13:27 wiz Exp $
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.\"
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.\" Copyright (c) 2001 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.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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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 July 16, 2001
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.Dt CLONE 2
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.Os
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.Sh NAME
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.Nm clone
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.Nd spawn new process with options
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <sched.h>
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.Ft pid_t
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.Fn clone "int (*func)(void *arg)" "void *stack" "int flags" "void *arg"
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.Ft pid_t
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.Fn __clone "int (*func)(void *arg)" "void *stack" "int flags" "void *arg"
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.Sh DESCRIPTION
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The
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.Nm
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system call (and associated library support code) creates a new process
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in a way that allows the caller to specify several options for the new
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process creation.
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.Pp
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Unlike
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.Xr fork 2
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or
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.Xr vfork 2 ,
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in which the child process returns to the call site,
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.Nm
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causes the child process to begin execution at the function specified
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by
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.Ar func .
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The argument
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.Ar arg
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is passed to the entry point, as a means for the parent to provide
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context to the child. The stack pointer for the child process will
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be set to
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.Ar stack .
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Note that the
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.Nm
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interface requires that the application know the stack direction
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for the architecture, and that the caller initialize the
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.Ar stack
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argument as appropriate for the stack direction.
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.Pp
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The
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.Ar flags
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argument specifies several options that control how the child process
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is created. The lower 8 bits of
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.Ar flags
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specify the signal that is to be sent to the parent when the child
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exits. The following flags may also be specified by bitwise-or'ing
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them with the signal value:
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.Bl -tag -width "CLONE_SIGHAND"
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.It Dv CLONE_VM
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Share the virtual address space with the parent. The address
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space is shared in the same way as
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.Xr vfork 2 .
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.It Dv CLONE_FS
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Share the
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.Dq file system information
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with the parent. This include the current working directory and file
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creation mask.
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.It Dv CLONE_FILES
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Share the file descriptor table with the parent.
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.It Dv CLONE_SIGHAND
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Share the signal handler set with the parent. Note that the signal mask
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is never shared between the parent and the child, even if
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.Dv CLONE_SIGHAND
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is set.
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.It Dv CLONE_VFORK
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Preserve the synchronization semanics of
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.Xr vfork 2 ;
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the parent blocks until the child exits.
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.El
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.Pp
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The
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.Nm
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call returns the pid of the child in the parent's context. The child
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is provided no return value, since it begins execution at a different
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address.
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.Pp
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If the child process's entry point returns, the value it returns
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is passed to
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.Xr _exit 2 ,
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and the child process exits. Note that if the child process wants
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to exit directly, it should use
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.Xr _exit 2 ,
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and not
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.Xr exit 3 ,
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since
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.Xr exit 3
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will flush and close standard I/O channels, and thereby corrupt the
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parent process's standard I/O data structures (even with
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.Xr fork 2
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it is wrong to call
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.Xr exit 3
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since buffered data would then be flushed twice).
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.Pp
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Note that
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.Nm
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is not intended to be used for new native
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.Nx
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applications. It is provided as a means to port software
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originally written for the Linux operating system to
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.Nx .
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.Sh RETURN VALUES
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Same as for
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.Xr fork 2 .
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.Sh ERRORS
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Same as for
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.Xr fork 2 .
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.Sh SEE ALSO
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.Xr chdir 2 ,
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.Xr chroot 2 ,
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.Xr fork 2 ,
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.Xr sigaction 2 ,
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.Xr sigprocmask 2 ,
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.Xr umask 2 ,
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.Xr vfork 2 ,
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.Xr wait 2
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.Sh HISTORY
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The
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.Fn clone
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function call appeared in
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.Nx 1.6 .
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It is compatible with the Linux function call of the same name.
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.Sh BUGS
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The
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.Nx
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implementation of
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.Nm
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does not implement the
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.Dv CLONE_PID
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option that is present in the Linux implementation.
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.Pp
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The
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.Nx
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implementation of
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.Nm
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does not implement the
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.Dv CLONE_PTRACE
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option that is present in the Linux implementation.
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