37abb66e2f
sigvec(2) references have been updated to sigaction(2), sigsetmask(2) and sigblock(2) to sigprocmask(2), sigpause(2) to sigsuspend(2). Some legacy man pages still refer to them, that is OK.
130 lines
3.6 KiB
Groff
130 lines
3.6 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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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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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)vfork.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd November 13, 2009
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.Dt VFORK 2
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.Os
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.Sh NAME
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.Nm vfork
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.Nd create a new process without copying the address space
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft pid_t
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.Fn vfork void
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.Sh DESCRIPTION
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The
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.Fn vfork
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system call
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can be used to create new processes without fully copying the address
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space of the old process, which is horrendously inefficient in a paged
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environment.
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It is useful when the purpose of
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.Xr fork 2
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would have been to create a new system context for an
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.Xr execve 2 .
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The
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.Fn vfork
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system call
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differs from
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.Xr fork 2
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in that the child borrows the parent's memory and thread of
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control until a call to
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.Xr execve 2
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or an exit (either by a call to
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.Xr _exit 2
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or abnormally).
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The parent process is suspended while the child is using its resources.
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.Pp
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The
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.Fn vfork
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system call
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returns 0 in the child's context and (later) the pid of the child in
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the parent's context.
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.Pp
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The
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.Fn vfork
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system call
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can normally be used just like
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.Xr fork 2 .
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It does not work, however, to return while running in the child's context
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from the procedure that called
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.Fn vfork
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since the eventual return from
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.Fn vfork
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would then return to a no longer existent stack frame.
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Be careful, also, to call
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.Xr _exit 2
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rather than
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.Xr exit 3
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if you cannot
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.Xr execve 2 ,
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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 mess up the
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parent processes standard I/O data structures.
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(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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.Sh RETURN VALUES
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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 execve 2 ,
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.Xr _exit 2 ,
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.Xr fork 2 ,
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.Xr rfork 2 ,
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.Xr sigaction 2 ,
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.Xr wait 2 ,
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.Xr exit 3
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.Sh HISTORY
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The
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.Fn vfork
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system call appeared in
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.Bx 2.9 .
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.Sh BUGS
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To avoid a possible deadlock situation,
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processes that are children in the middle
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of a
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.Fn vfork
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are never sent
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.Dv SIGTTOU
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or
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.Dv SIGTTIN
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signals; rather,
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output or
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.Xr ioctl 2
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calls
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are allowed
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and input attempts result in an end-of-file indication.
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