DearFTP/DearFTP/Connection/Commands/SystemCommand.cs

namespace DearFTP.Connection.Commands
{
    class SystemCommand : ICommand
    {
        public string[] Aliases { get; } = new string[]
        {
            "SYST"
        };

        public void Execute(Session session, FtpStream stream, string alias, string argument)
        {
            stream.Send(ResponseCode.NameSystemType, "UNIX Type: L8");
        }
    }
}