1.Connected. Waiting for response.

220 Serv-U FTP Server v4.0 for WinSock ready...

USER anonymous

530 Sorry, no ANONYMOUS access allowed.

QUIT

这个就是不许匿名登录啦

2.Connected. Waiting for response.

220 Serv-U FTP Server v4.0 for WinSock ready...

USER test

331 User name okay, need password.

PASS xxxxxx

530 Not logged in.

QUIT

一般是密码输入错误时出现的信息，但对于Serv-U来说，如果没有这个帐号（test）存在，也会产生同样的出错信息。

3.Connecting to xxx.xxx.xxx.xxx, Port 21 (#1)

ERROR: Connection timed out

这个表明对方未开机，也可能是对方不在你能访问的范围内

4.Connecting to xxx.xxx.xxx.xxx Port 21 (#1)

ERROR: Connection refused

这个一般表明对方已开机，但未开启FTP服务（没有开Serv-U），也可能为对方不提供在这个端口上的服务

5.Connecting to xxx.xxx.xxx.xxx, Port 21 (#1)

Connected. Waiting for response.

Disconnected from server.

Connection attempt failed. Waiting for retry...

出现这个信息实在是很倒霉，你极有可能被对方Ban了。如果只是Ban几分钟or几小时or一天还好，不然只有和站长说说好话，让他给你解封吧。

6.Connecting to xxx.xxx.xxx.xxx, Port 21 (#1)

Connected. Waiting for response.

USER XXX

331 User name okay, need password

PASS xxxxxx

530 Not logged in, unauthorized IP address.

QUIT

这个有点麻烦，你的IP不在站长允许访问的IP范围内，只有和站长联系，让他把你的IP网段加入Allow Access列表里吧 。

7.Connected. Waiting for response.

220 Serv-U FTP Server v4.0 for WinSock ready...

USER user

421 Too many users - please try again later.

哈哈，这个很常见吧，用户太多，去过交大的都知道该怎么做

8.Connected. Waiting for response.

220 Serv-U FTP Server v4.0 for WinSock ready...

USER test

530 Not logged in, only one(也有可能是two or three) session from same IP allowed at a time.

QUIT

每个IP只能开一个(也有可能是two or three) 下载，就不要用多线程啦，小心Ban了你。

110 Restart marker reply. In this case, the text is exact and not left to the particular implementation; it must read: MARK yyyy = mmmm where yyyy is User-process data stream marker, and mmmm server's equivalent marker (note the spaces between markers and "=").

120 Service ready in nnn minutes.

125 Data connection already open; transfer starting.

150 File status okay; about to open data connection.

200 Command okay.

202 Command not implemented, superfluous at this site.