FTP 連線失敗時伺服器回傳三位數代碼，理解含義能快速定位問題。本文收錄完整代碼表，重點解析高頻錯誤。
| 代碼 | 含義 | 常見原因與對策 |
|---|---|---|
| 530 | Not logged in / unauthorized IP address | IP 被封禁、帳號密碼錯誤、帳號權限不足。聯繫管理員解封或核對帳密。 |
| 421 | Service not available | 伺服器關閉、維護中、達最大連線數。稍後重試。 |
| 425 | Can't open data connection | PASV/PORT 模式不匹配、防火牆封鎖資料埠。切換傳輸模式、開放防火牆高位埠。 |
| 550 | File unavailable | 檔案不存在、無讀取權限、磁碟配額滿。確認路徑、權限、空間。 |
| 553 | File name not allowed | 檔名含非法字元、超長、伺服器禁止該命名規則。更換檔名重試。 |
| 200 | Command okay | 指令執行成功（正常回應）。 |
| 226 | Closing data connection | 檔案傳輸/中止成功完成（正常回應）。 |
| 230 | User logged in | 登入成功（正常回應）。 |
110 Restart marker reply 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 211 System status / help reply 212 Directory status 213 File status 214 Help message 215 NAME system type 220 Service ready for new user 221 Service closing control connection 225 Data connection open; no transfer 226 Closing data connection. Requested file action successful 227 Entering Passive Mode (h1,h2,h3,h4,p1,p2) 230 User logged in, proceed 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 425 Can't open data connection 426 Connection closed; transfer aborted 450 Requested file action not taken 451 Requested action aborted. Local error 452 Requested action not taken. Insufficient storage 500 Syntax error, command unrecognized 501 Syntax error in parameters 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 551 Requested action aborted. Page type unknown 552 Requested file action aborted. Exceeded storage allocation 553 Requested action not taken. File name not allowed
遇到 530 錯誤切勿反覆嘗試（可能加重封禁），優先聯繫管理員確認 IP/帳號狀態。
