<?php
function ByteSize($bytes, $afterPoint = 2)
{
    if (!$bytes || !is_numeric($bytes))
        return '0';

    $size = $bytes / 1024;
    if ($size < 1024) {
        $size = number_format($size, $afterPoint);
        $size .= ' KB';
    } else {
        if ($size / 1024 < 1024) {
            $size = number_format($size / 1024, $afterPoint);
            $size .= ' MB';
        } else if ($size / 1024 / 1024 < 1024) {
            $size = number_format($size / 1024 / 1024, $afterPoint);
            $size .= ' GB';
        } else if ($size / 1024 / 1024 / 1024 < 1024) {
            $size = number_format($size / 1024 / 1024 / 1024, $afterPoint);
            $size .= ' TB';
        }
    }

    return $size;
}

$free = disk_free_space("/");

echo "FREEDISK = $free";
echo "\n";
if($free < 5*1024*1024*1024){
    echo "<br/>\nError, free cpanel only: " . ByteSize($free);
}else{
    echo "<br/>\nfreediskok: " . ByteSize($free);

}