123 lines
4.1 KiB
Groff
123 lines
4.1 KiB
Groff
.\" 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. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. 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 4, 1993
|
|
.Dt FORK 2
|
|
.Os BSD 4
|
|
.Sh NAME
|
|
.Nm fork
|
|
.Nd create a new process
|
|
.Sh SYNOPSIS
|
|
.Fd #include <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 processes resource utilizations
|
|
are set to 0; see
|
|
.Xr setrlimit 2 .
|
|
.El
|
|
.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.
|
|
The limit is given by the
|
|
.Xr sysctl 3
|
|
MIB variable
|
|
.Dv KERN_MAXPROC .
|
|
(The limit is actually one less than this
|
|
except for the super user).
|
|
.It Bq Er EAGAIN
|
|
The user is not the super user, and
|
|
the system-imposed limit
|
|
on the total number of
|
|
processes under execution by a single user would be exceeded.
|
|
The limit is given by the
|
|
.Xr sysctl 3
|
|
MIB variable
|
|
.Dv KERN_MAXPROCPERUID .
|
|
.It Bq Er EAGAIN
|
|
The user is not the super user, and
|
|
the soft resource limit corresponding to the resource parameter
|
|
.Dv RLIMIT_NOFILE
|
|
would be exceeded (see
|
|
.Xr getrlimit 2 ) .
|
|
.It Bq Er ENOMEM
|
|
There is insufficient swap space for the new process.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr execve 2 ,
|
|
.Xr wait 2
|
|
.Sh HISTORY
|
|
A
|
|
.Fn fork 2
|
|
function call appeared in
|
|
.At v6 .
|