如果您安装了pcntl extension,它将是：

function detached_exec($cmd) {
    $pid = pcntl_fork();
    switch($pid) {
         // fork errror
         case -1 : return false
 
         // this code runs in child process
         case 0 :
             // obtain a new process group
             posix_setsid();
             // exec the command
             exec($cmd);
             break;
 
         // return the child pid in father
         default: 
             return $pid;
    }
}

这样叫：

$pid = detached_exec($cmd);
if($pid === FALSE) {
    echo 'exec Failed';
}
 
// do some work
 
// kill child
posix_kill($pid,SIGINT);
waitpid($pid,$status);
 
echo 'Child exited with ' . $status;