实现了ftp服务器端的功能



（1）FTP服务器运行FTPd守护进程，等待用户的FTP请求。



（2）用户运行FTP命令,请求FTP服务器为其服务。



（3）FTPd守护进程收到用户的FTP请求后，派生出子进程FTP与用户进程FTP交互，建立文件传输控制连接



（4）用户输入FTP子命令，服务器接收子命令，如果命令正确，双方各派生一个数据传输进程FTP-DATA,建立数据连接，进行数据传输。



（5）本次子命令的数据传输完，拆除数据连接，结束FTP-DATA进程。



（6）用户继续输入FTP子命令，重复（4）、（5）的过程，直至用户输入quit命令，双方拆除控制连接，结束文件传输，结束FTP进程。-realized the ftp server functions (1) run-FTPd FTP server daemon, FTP user request. (2) users running FTP, FTP server requests for services. (3) - FTPd Daemon FTP users received a request, derived from the process-the process of FTP and FTP user interaction, file transfer control to establish connection (4) User input FTP subcommands, the server receiving subcommand, if correct order, both parties have a data transmission process FTP-DATA, set up a data link for data transmission. (5) The second son of orders data transmission End, the demolition of data connectivity, the end of the FTP-DATA process. (6) users to import FTP subcommands, repeat (4), (5) the process until the user input quit order to remove control of linking the two sides, the end of file transfer, FTP end of the process.