ftp服务器设计成为一个守护进程，程序接受三个参数start,stop,restart。程序捕获SIGHUP、SIGQUIT、SIGCHLD、SIGPIPE信号并做相应处理，实现FTP所以命令列表。-ftp server designed as a daemon, the program to accept three arguments start, stop, restart. Program to capture SIGHUP, SIGQUIT, SIGCHLD, SIGPIPE sign