.TH FORK 2 
.SH NAME
fork \- spawn new process
.SH SYNOPSIS
.B fork( )
.SH DESCRIPTION
.I Fork
and
.IR vfork (2)
are the only ways new processes are created.
With
.I fork ,
the new process's core image is a copy of
that of the caller of
.IR fork .
The only distinction
is the fact
that the value returned in the old (parent) process
contains the process ID
of the new (child) process,
while the value returned in the child is 0.
Process ID's range from 1 to 30,000.
This process ID is used by
.IR wait (2).
.PP
Files open before the fork
are shared, and have a common read-write pointer.
In particular,
this is the way that standard input and output
files are passed and also how
pipes are set up.
.PP
.I Vfork
is the most efficient way of creating a new process
when the fork is to be followed shortly by an exec,
but is not suitable when the fork is not to be followed
by an exec.
.SH "SEE ALSO"
wait(2), exec(2), vfork(2)
.SH DIAGNOSTICS
Returns \-1 and fails to create a process if:
there is inadequate swap space,
the user is not super-user and has too many processes,
or the system's process table is full.
Only the super-user can take the last process-table slot.
.SH "ASSEMBLER (PDP-11)"
(fork = 2.)
.br
.B sys fork
.br
(new process return)
.br
(old process return, new process ID in r0)
.PP
The return locations in the old and new process
differ by one word.
The C-bit is set in the old process if a new
process could not be created.