2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
138 lines
4.4 KiB
Groff
138 lines
4.4 KiB
Groff
.\" $NetBSD: fork.2,v 1.22 2004/06/25 15:29:25 wiz Exp $
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.\"
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.\" 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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.\" 3. 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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.\" @(#)fork.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd June 10, 2004
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.Dt FORK 2
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.Os
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.Sh NAME
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.Nm fork
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.Nd create a new process
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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 fork void
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.Sh DESCRIPTION
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.Fn fork
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causes creation of a new process.
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The new process (child process) is an exact copy of the
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calling process (parent process) except for the following:
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.Bl -bullet -offset indent
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.It
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The child process has a unique process ID.
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.It
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The child process has a different parent
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process ID (i.e., the process ID of the parent process).
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.It
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The child process has its own copy of the parent's descriptors.
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These descriptors reference the same underlying objects, so that,
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for instance, file pointers in file objects are shared between
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the child and the parent, so that an
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.Xr lseek 2
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on a descriptor in the child process can affect a subsequent
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.Xr read 2
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or
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.Xr write 2
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by the parent.
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This descriptor copying is also used by the shell to
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establish standard input and output for newly created processes
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as well as to set up pipes.
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.It
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The child process' resource utilizations
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are set to 0; see
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.Xr setrlimit 2 .
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.El
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.Pp
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In general, the child process should 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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Otherwise, any stdio buffers that exist both in the parent and child
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will be flushed twice.
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Similarly,
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.Xr _exit 2
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should be used to prevent
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.Xr atexit 3
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routines from being called twice (once in the parent and once in the child).
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.Pp
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In case of a threaded program, only the thread calling
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.Fn fork
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is still running in the child processes.
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.Pp
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Child processes of a threaded program have additional restrictions,
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a child must only call functions that are async-signal-safe.
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Very few functions are asynchronously safe and applications should
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make sure they call
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.Xr exec 3
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as soon as possible.
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn fork
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returns a value
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of 0 to the child process and returns the process ID of the child
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process to the parent process.
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Otherwise, a value of \-1 is returned to the parent process, no
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child process is created, and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn fork
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will fail and no child process will be created if:
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.Bl -tag -width [EAGAIN]
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.It Bq Er EAGAIN
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The system-imposed limit on the total
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number of processes under execution would be exceeded.
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This limit is configuration-dependent.
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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
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processes under execution by this user id would be exceeded.
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.It Bq Er ENOMEM
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There is insufficient swap space for the new process.
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.El
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.Sh SEE ALSO
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.Xr execve 2 ,
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.Xr setrlimit 2 ,
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.Xr vfork 2 ,
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.Xr wait 2 ,
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.Xr pthread_atfork 3
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.Sh STANDARDS
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The
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.Fn fork
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function conforms to
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.St -p1003.1-90 .
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.Sh HISTORY
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A
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.Fn fork
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system call appeared in
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.At v6 .
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