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110重新啟動標記應答。在這種情況下文本是確定的，它必須是：MARK yyyy=mmmm，其中yyyy是用戶進程數據流標記，mmmm是服務器標記。
120服務在nnn分鐘內準備好
125數據連接已打開，準備傳送
150文件狀態良好，打開數據連接
200命令成功
202命令未實現
211系統狀態或系統幫助響應
212目錄狀態
213文件狀態
214幫助信息，信息僅對人類用戶有用
215名字系統類型
220對新用戶服務準備好
221服務關閉控制連接，可以退出登錄
225數據連接打開，無傳輸正在進行
226關閉數據連接，請求的文件操作成功
227進入被動模式
230用戶登錄
250請求的文件操作完成
257創建"PATHNAME"
331用戶名正確，需要口令
332登錄時需要賬戶信息
350請求的文件操作需要進一步命令
421不能提供服務，關閉控制連接
425不能打開數據連接
426關閉連接，中止傳輸
450請求的文件操作未執行
451中止請求的操作：有本地錯誤
452未執行請求的操作：系統存儲空間不足
500格式錯誤，命令不可識別
501參數語法錯誤
502命令未實現
503命令順序錯誤
504此參數下的命令功能未實現
530未登錄
532存儲文件需要賬戶信息
550未執行請求的操作
551請求操作中止：頁類型未知
552請求的文件操作中止，存儲分配溢出
553未執行請求的操作：文件名不合法
=============================================
1.Connected. Waiting for response.
220 Serv-U FTP Server v4.0 for WinSock ready...
USER anonymous
530 Sorry, no ANONYMOUS access allowed.
QUIT
這個就是不許匿名登錄啦
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
一般是密碼輸入錯誤時出現的信息，但對于Serv-U來說，如果沒有這個帳號（test）存在，也會產生同樣的出錯信息。
3.Connecting to xxx.xxx.xxx.xxx, Port 21 (#1)
ERROR: Connection timed out
這個表明對方未開機，也可能是對方不在你能訪問的范圍內
4.Connecting to xxx.xxx.xxx.xxx Port 21 (#1)
ERROR: Connection refused
這個一般表明對方已開機，但未開啟FTP服務（沒有開Serv-U），也可能為對方不提供在這個端口上的服務
5.Connecting to xxx.xxx.xxx.xxx, Port 21 (#1)
Connected. Waiting for response.
Disconnected from server.
Connection attempt failed. Waiting for retry...
出現這個信息實在是很倒霉，你極有可能被對方Ban了。如果只是Ban幾分鐘or幾小時or一天還好，不然只有和站長說說好話，讓他給你解封吧。
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
這個有點麻煩，你的IP不在站長允許訪問的IP范圍內，只有和站長聯系，讓他把你的IP網段加入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，這個很常見吧，用戶太多，去過交大的都知道該怎么做
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
每個IP只能開一個(也有可能是two or three) 下載，就不要用多線程啦，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

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