Автор: http://www.swissdelphicenter.ch

{
  In Linux it is possible to duplicate a process with fork. In the original
  process, fork will return the handle to the duplicated process. The
  duplicated process will return zero.
 }

program TestFork;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  Libc;

var
  ForkedProcessHandle: __pid_t;
  bForked: Boolean;

procedure ForkNow;
begin
  bForked := true;
  ForkedProcessHandle := fork;
end;

function IsForked: Boolean;
begin
  Result := (ForkedProcessHandle = 0) and bForked;
end;

var
  Lf: Integer;

begin
  sigignore(SIGCHLD);
  bForked := false;

  WriteLn('do some stuff');

  WriteLn('before fork');
  ForkNow;
  WriteLn('after fork - we have dublicated the process');

  if IsForked then
  begin
    WriteLn('do some stuff in forked process (wait 5s)');
    for Lf := 0 to 50 do
    begin
      Write('f');
      sleep(100);
    end;
  end
  else
  begin
    WriteLn('do stuff in original process (wait 10)');
    for Lf := 0 to 100 do
    begin
      Write('o');
      sleep(100);
    end;
  end;

  WriteLn;

  if IsForked then
    WriteLn('forked process end')
  else
    WriteLn('original process end');
end.

{
Output of this demo app:

do some stuff
before fork
after fork - we have dublicated the process
after fork - we have dublicated the process
do some stuff in forked process (wait 5s)
fdo stuff in original process (wait 10)
ooffooffooffooffooffooffooffooffooffooffooffooffooffooffooffooffooffooff
ooffooffooffooffooffooffooffoo
forked process end
ooooooooooooooooooooooooooooooooooooooooooooooooo
original process end
 }