Figure 2: Meanings of digits 1 and 2 of reply codes

First digit:

1 Positive Preliminary: more to come, do not send command
2 Positive Completion: done, send next command
3 Positive Intermediate: request for more data, send
command completing request
4 Transient Negative Completion: command not accepted, try
again at beginning of
command sequence
5 Permanent Negative Completion: command not accepted, do
not try exact same command
again

Second digit:

0 Syntax: syntax error; command not implemented; message
not fitting in other categories
1 Information: status or help data
2 Connections: control and data connection
3 Authentication: login
4 not specified
5 File system: status of server file system for a given request