The server's initial response to the client must use code 220 or 421. However, servers must not do this. The BSD ftp program will treat the 120 as if it were a 220, causing a disastrous loss of synchronization with the server. RFC 959 does not impose any requirements on the text after 220.
Most servers use the text for a human-readable operating system name.
The rest of the line is a series of feature strings , in any order, each preceded by one space, terminated by a space and a dot at the end of the line. Feature strings do not contain spaces. The server supports pipelining . The server must use an empty string for y . The server must use an empty string for y .