A function, returning an array of process ids of children (and their children, ...) of a process

get_proc_children.php

<?php
function get_proc_children($pid, $tree=null) {
  $tree=array();
  $ret=array();

  // build process tree in $tree
  if($tree==null) {
    $p=popen("ps eo pid,ppid", "r");
    while($r=fgets($p)) {
      if(preg_match("/^\s*([0-9]+)\s+([0-9]+)/", $r, $m)) {
        if(!isset($tree[$m[2]]))
          $tree[$m[2]]=array();

        $tree[$m[2]][]=$m[1];
      }
    }
  }

  // no children? return
  if(!isset($tree[$pid]))
    return array();

  // add grand children
  foreach($tree[$pid] as $child) {
    $ret=array_merge($ret, get_proc_children($child, &$tree));
  }

  return array_merge($ret, $tree[$pid]);
}