Warning: shell_exec() has been disabled for security reasons

$folder = $_SERVER['DOCUMENT_ROOT'].'/projects/charli/dashboard/';
$folder = escapeshellcmd($folder);

if( ! is_dir($folder) )
{
        echo "$folder is not a folder.<br />";
}
else
{
        $output = `du -s $folder`;

        if( preg_match('/([0-9]+)(\t.*)/',$output,$match) )
        {
                $size = $match[1];

                echo "Folder $folder is $size bytes<br />";
        }
        else
        {
                echo "Error fetching folder size, are you on Linux? and can you execute commands?<br />";
        }
}