src/RpkUtils/Sysinfo/Server.php
public static function kernel()
    {
        if($os = static::os(true)){
            $os = explode(' ', $os);
            if('/' == DIRECTORY_SEPARATOR){
                $kernel = $os[2];
            }else{
                $kernel = $os[1];
            }
        }else{
            $kernel = '';
        }
        
        return $kernel;
    }
public static function kernel()
    {
        if($os = static::os(true)){
            $os = explode(' ', $os);
            if('/' == DIRECTORY_SEPARATOR){
                $kernel = $os[2];
            }else{
                $kernel = $os[1];
            }
        }else{
            $kernel = '';
        }
        
        return $kernel;
    }
Server kernel
@return string