This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
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 $
|
|
.\"
|
|
.\" Copyright (c) 1980, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)fork.2 8.1 (Berkeley) 6/4/93
|
|
.\"
|
|
.Dd June 10, 2004
|
|
.Dt FORK 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm fork
|
|
.Nd create a new process
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In unistd.h
|
|
.Ft pid_t
|
|
.Fn fork void
|
|
.Sh DESCRIPTION
|
|
.Fn fork
|
|
causes creation of a new process.
|
|
The new process (child process) is an exact copy of the
|
|
calling process (parent process) except for the following:
|
|
.Bl -bullet -offset indent
|
|
.It
|
|
The child process has a unique process ID.
|
|
.It
|
|
The child process has a different parent
|
|
process ID (i.e., the process ID of the parent process).
|
|
.It
|
|
The child process has its own copy of the parent's descriptors.
|
|
These descriptors reference the same underlying objects, so that,
|
|
for instance, file pointers in file objects are shared between
|
|
the child and the parent, so that an
|
|
.Xr lseek 2
|
|
on a descriptor in the child process can affect a subsequent
|
|
.Xr read 2
|
|
or
|
|
.Xr write 2
|
|
by the parent.
|
|
This descriptor copying is also used by the shell to
|
|
establish standard input and output for newly created processes
|
|
as well as to set up pipes.
|
|
.It
|
|
The child process' resource utilizations
|
|
are set to 0; see
|
|
.Xr setrlimit 2 .
|
|
.El
|
|
.Pp
|
|
In general, the child process should call
|
|
.Xr _exit 2
|
|
rather than
|
|
.Xr exit 3 .
|
|
Otherwise, any stdio buffers that exist both in the parent and child
|
|
will be flushed twice.
|
|
Similarly,
|
|
.Xr _exit 2
|
|
should be used to prevent
|
|
.Xr atexit 3
|
|
routines from being called twice (once in the parent and once in the child).
|
|
.Pp
|
|
In case of a threaded program, only the thread calling
|
|
.Fn fork
|
|
is still running in the child processes.
|
|
.Pp
|
|
Child processes of a threaded program have additional restrictions,
|
|
a child must only call functions that are async-signal-safe.
|
|
Very few functions are asynchronously safe and applications should
|
|
make sure they call
|
|
.Xr exec 3
|
|
as soon as possible.
|
|
.Sh RETURN VALUES
|
|
Upon successful completion,
|
|
.Fn fork
|
|
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 fork
|
|
will fail and no child process will be created if:
|
|
.Bl -tag -width [EAGAIN]
|
|
.It Bq Er EAGAIN
|
|
The system-imposed limit on the total
|
|
number of processes under execution would be exceeded.
|
|
This limit is configuration-dependent.
|
|
.It Bq Er EAGAIN
|
|
The limit
|
|
.Dv RLIMIT_NPROC
|
|
on the total number of
|
|
processes under execution by this user id would be exceeded.
|
|
.It Bq Er ENOMEM
|
|
There is insufficient swap space for the new process.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr execve 2 ,
|
|
.Xr setrlimit 2 ,
|
|
.Xr vfork 2 ,
|
|
.Xr wait 2 ,
|
|
.Xr pthread_atfork 3
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn fork
|
|
function conforms to
|
|
.St -p1003.1-90 .
|
|
.Sh HISTORY
|
|
A
|
|
.Fn fork
|
|
system call appeared in
|
|
.At v6 .
|