㈠FTP main function
⑴ provide shared (computer program / data) file;
⑵ indirect support using a remote computer;
⑶ so that users are not due to differences in various types of host memory file system affected;
⑷ reliable and efficient data transmission.
㈡FTP control frame
FTP TELNET control frame refers to exchange of information, including TELNET commands and options.
However, most FTP control frames are simple ASCII text, it can be divided into FTP commands or FTP messages.
FTP FTP command message is a response, which is composed of a response code with explanatory text.
㈢FTP command table
| command | description |
| ABOR | Interrupt Data Connector |
| ACCT <account> | System privilege account |
| ALLO <bytes> | Bytes of memory allocated on the file server |
| APPE <filename> | Add files to the file server with the same name |
| CDUP <dir path> | Parent directory on the server change |
| CWD <dir path> | Change the working directory on the server |
| DELE <filename> | Delete the specified file on the server |
| HELP <command> | Returns the specified command information |
| LIST <name> | If the file name is listed in the file information, if it is listed in the directory file list |
| MODE <mode> | Transmission mode (S = streaming mode, B = block mode, C = compressed mode) |
| MKD <directory> | Establish specified directory on the server |
| NLST <directory> | Lists the contents of the specified directory |
| NOOP | No action, in addition to recognition from the server |
| PASS <password> | System password |
| PASV | Requests the server waits for a data connection |
| PORT <address> | IP address and port ID of two bytes |
| PWD | Displays the current working directory |
| QUIT | Log out from the FTP server |
| REIN | Log in to re-initialize the connection status |
| REST <offset> | Restart the specific offset file delivery |
| RETR <filename> | Retrieve (copy) files from the server |
| RMD <directory> | Deletes the specified directory on the server |
| RNFR <old path> | 对旧路径重命名 |
| RNTO <new path> | 对新路径重命名 |
| SITE <params> | 由服务器提供的站点特殊参数 |
| SMNT <pathname> | 挂载指定文件结构 |
| STAT <directory> | 在当前程序或目录上返回信息 |
| STOR <filename> | 储存（复制）文件到服务器上 |
| STOU <filename> | 储存文件到服务器名称上 |
| STRU <type> | 数据结构（F=文件，R=记录，P=页面） |
| SYST | 返回服务器使用的操作系统 |
| TYPE <data type> | 数据类型（A=ASCII，E=EBCDIC，I=binary） |
| USER <username>> | 系统登录的用户名 |
㈣FTP响应码
| 响应代码 | 解释说明 |
| 110 | 新文件指示器上的重启标记 |
| 120 | 服务器准备就绪的时间（分钟数） |
| 125 | 打开数据连接，开始传输 |
| 150 | 打开连接 |
| 200 | 成功 |
| 202 | 命令没有执行 |
| 211 | 系统状态回复 |
| 212 | 目录状态回复 |
| 213 | 文件状态回复 |
| 214 | 帮助信息回复 |
| 215 | 系统类型回复 |
| 220 | 服务就绪 |
| 221 | 退出网络 |
| 225 | 打开数据连接 |
| 226 | 结束数据连接 |
| 227 | 进入被动模式（IP 地址、ID 端口） |
| 230 | 登录因特网 |
| 250 | 文件行为完成 |
| 257 | 路径名建立 |
| 331 | 要求密码 |
| 332 | 要求帐号 |
| 350 | 文件行为暂停 |
| 421 | 服务关闭 |
| 425 | 无法打开数据连接 |
| 426 | 结束连接 |
| 450 | 文件不可用 |
| 451 | 遇到本地错误 |
| 452 | 磁盘空间不足 |
| 500 | 无效命令 |
| 501 | 错误参数 |
| 502 | 命令没有执行 |
| 503 | 错误指令序列 |
| 504 | 无效命令参数 |
| 530 | 未登录网络 |
| 532 | 存储文件需要帐号 |
| 550 | 文件不可用 |
| 551 | 不知道的页类型 |
| 552 | 超过存储分配 |
| 553 | 文件名不允许 |
参考：https://blog.csdn.net/unsv29/article/details/79468101