Serv-U FTP Server 错误代码详解
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.
211 System status, or system help reply.
212 Directory status.
213 File status.
214 Help message.On how to use the server or the meaning of a particular non-standard command. This reply is useful only to the human user.
215 NAME system type. Where NAME is an official system name from the list in the Assigned Numbers document.
220 Service ready for new user.
221 Service closing control connection.
225 Data connection open; no transfer in progress.
226 Closing data connection. Requested file action successful (for example, file transfer or file abort).
227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
230 User logged in, proceed. Logged out if appropriate.
250 Requested file action okay, completed.
257 "PATHNAME" created.
331 User name okay, need password.
332 Need account for login.
350 Requested file action pending further information
421 Service not available, closing control connection.This may be a reply to any command if the service knows it must shut down.
425 Can't open data connection.
426 Connection closed; transfer aborted.
450 Requested file action not taken.
451 Requested action aborted. Local error in processing.
452 Requested action not taken. Insufficient storage space in system.File unavailable (e.g., file busy).
500 Syntax error, command unrecognized. This may include errors such as command line too long.
501 Syntax error in parameters or arguments.
502 Command not implemented.
503 Bad sequence of commands.
504 Command not implemented for that parameter.
530 Not logged in.
532 Need account for storing files.
550 Requested action not taken. File unavailable (e.g., file not found, no access).
551 Requested action aborted. Page type unknown.
552 Requested file action aborted. Exceeded storage allocation (for current directory or dataset).
553 Requested action not taken. File name not allowed
110重新启动标记应答。在这种情况下文本是确定的，它必须是：MARK yyyy=mmmm，其中yyyy是用户进程数据流标记，mmmm是服务器标记。
120服务在nnn分钟内准备好
125数据连接已打开，准备传送
150文件状态良好，打开数据连接
200命令成功
202命令未实现
211系统状态或系统帮助响应
212目录状态
213文件状态
214帮助信息，信息仅对人类用户有用
215名字系统类型
220对新用户服务准备好
221服务关闭控制连接，可以退出登录
225数据连接打开，无传输正在进行
226关闭数据连接，请求的文件操作成功
227进入被动模式
230用户登录
250请求的文件操作完成
257创建"PATHNAME"
331用户名正确，需要口令
332登录时需要账户信息
350请求的文件操作需要进一步命令
421不能提供服务，关闭控制连接
425不能打开数据连接
426关闭连接，中止传输
450请求的文件操作未执行
451中止请求的操作：有本地错误
452未执行请求的操作：系统存储空间不足
500格式错误，命令不可识别
501参数语法错误
502命令未实现
503命令顺序错误
504此参数下的命令功能未实现
530未登录
532存储文件需要账户信息
550未执行请求的操作
551请求操作中止：页类型未知
552请求的文件操作中止，存储分配溢出
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.
211 System status, or system help reply.
212 Directory status.
213 File status.
214 Help message.On how to use the server or the meaning of a particular non-standard command. This reply is useful only to the human user.
215 NAME system type. Where NAME is an official system name from the list in the Assigned Numbers document.
220 Service ready for new user.
221 Service closing control connection.
225 Data connection open; no transfer in progress.
226 Closing data connection. Requested file action successful (for example, file transfer or file abort).
227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
230 User logged in, proceed. Logged out if appropriate.
250 Requested file action okay, completed.
257 "PATHNAME" created.
331 User name okay, need password.
332 Need account for login.
350 Requested file action pending further information
421 Service not available, closing control connection.This may be a reply to any command if the service knows it must shut down.
425 Can't open data connection.
426 Connection closed; transfer aborted.
450 Requested file action not taken.
451 Requested action aborted. Local error in processing.
452 Requested action not taken. Insufficient storage space in system.File unavailable (e.g., file busy).
500 Syntax error, command unrecognized. This may include errors such as command line too long.
501 Syntax error in parameters or arguments.
502 Command not implemented.
503 Bad sequence of commands.
504 Command not implemented for that parameter.
530 Not logged in.
532 Need account for storing files.
550 Requested action not taken. File unavailable (e.g., file not found, no access).
551 Requested action aborted. Page type unknown.
552 Requested file action aborted. Exceeded storage allocation (for current directory or dataset).
553 Requested action not taken. File name not allowed
110重新启动标记应答。在这种情况下文本是确定的，它必须是：MARK yyyy=mmmm，其中yyyy是用户进程数据流标记，mmmm是服务器标记。
120服务在nnn分钟内准备好
125数据连接已打开，准备传送
150文件状态良好，打开数据连接
200命令成功
202命令未实现
211系统状态或系统帮助响应
212目录状态
213文件状态
214帮助信息，信息仅对人类用户有用
215名字系统类型
220对新用户服务准备好
221服务关闭控制连接，可以退出登录
225数据连接打开，无传输正在进行
226关闭数据连接，请求的文件操作成功
227进入被动模式
230用户登录
250请求的文件操作完成
257创建"PATHNAME"
331用户名正确，需要口令
332登录时需要账户信息
350请求的文件操作需要进一步命令
421不能提供服务，关闭控制连接
425不能打开数据连接
426关闭连接，中止传输
450请求的文件操作未执行
451中止请求的操作：有本地错误
452未执行请求的操作：系统存储空间不足
500格式错误，命令不可识别
501参数语法错误
502命令未实现
503命令顺序错误
504此参数下的命令功能未实现
530未登录
532存储文件需要账户信息
550未执行请求的操作
551请求操作中止：页类型未知
552请求的文件操作中止，存储分配溢出
553未执行请求的操作：文件名不合法
最后，通过查看serv-u的日志也许可以找到原因！！！