xx@xxx.com [~/public_html/xxx]# ls > ls2.out 2>&1 &
[1] 15205

$run = "ls > ls2.out 2>&1 &";
$return = exec($run, $output, $return_var);
echo '=====', PHP_EOL;
echo var_dump($run);
echo var_dump($return);
echo print_r($output);
echo print_r($return_var);
echo '=====', PHP_EOL;

=====
string(19) "ls > ls2.out 2>&1 &"
string(0) ""
Array
(
)
101=====