最近需要使用 ftp 工具，所以借此机会来进行整理以下具体的内容：
具体什么是ftp, ftp 能干什么？
请参考：
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/s1-ftp
http://cn.linux.vbird.org/linux_server/0410vsftpd.php
重点理解：主动联机 与 被动联机 两种模式中，端口的选择。
主动连接
active mode
Active mode is the original method used by the
FTP protocol for transferring data to the client application. When an active-mode data transfer is initiated by the FTP client, the server opens a connection from port 20 on the server to the IP address and a random, unprivileged port (greater than 1024) specified by the client. This arrangement means that the client machine must be allowed to accept connections over any port above 1024. With the growth of insecure networks, such as the Internet, the use of firewalls for protecting client machines is now prevalent. Because these client-side firewalls often deny incoming connections from active-mode FTP servers, passive mode was devised. 
被动连接
passive mode
Passive mode, like active mode, is initiated by the
FTP client application. When requesting data from the server, the FTP client indicates it wants to access the data in passive mode and the server provides the IP address and a random, unprivileged port (greater than 1024) on the server. The client then connects to that port on the server to download the requested information. While passive mode does resolve issues for client-side firewall interference with data connections, it can complicate administration of the server-side firewall. You can reduce the number of open ports on a server by limiting the range of unprivileged ports on the
FTP server. This also simplifies the process of configuring firewall rules for the server.安装vsftpd 软件：
➜ Desktop yum search vsftpd Last metadata expiration check: 5 days, 21:35:37 ago on Tue 26 Jun 2018 04:58:21 PM CST. ================================================== Name Exactly Matched: vsftpd ================================================== vsftpd.x86_64 : Very Secure Ftp Daemon
vsftpd 全称为: Very Secure Ftp Daemon
vsftpd 配置文件：我们可以使用 man 5 vsftpd.conf 命令，来查找vsftpd 的配置说明。
FTP 连接与命令：
1. 登录
[root@dhcp-65-15 ~]# ftp localhost Trying ::1... Connected to localhost (::1). 220 Welcome to blah FTP service. Name (localhost:root): yaowen 331 Please specify the password. Password: 230 Login successful. Remote system type is UNIX. Using binary mode to transfer files. ftp> ls 229 Entering Extended Passive Mode (|||60063|) 150 Here comes the directory listing. drwxr-xr-x 4 1000 1000 4096 Jun 26 08:50 Desktop drwxr-xr-x 2 1000 1000 4096 Jun 27 2017 Documents drwxr-xr-x 2 1000 1000 4096 May 29 02:09 Downloads drwxrwxr-x 3 36 36 4096 Jun 27 02:59 ISO drwxr-xr-x 4 36 36 4096 Jun 25 08:41 NFS4 drwxr-xr-x 2 1000 1000 4096 Jun 27 2017 Pictures drwxr-xr-x 2 1000 1000 4096 Jun 27 2017 Public drwxr-xr-x 2 1000 1000 4096 Jun 27 2017 Templates drwxr-xr-x 2 1000 1000 4096 Jun 27 2017 Videos 226 Directory send OK. ftp>
2. 如果没有ftp 命令，则进行安装
[root@yaowenxu Desktop]# yum install ftp
3. ftp 支持的命令
使用 help 或者 ？ 来进行查看当前服务所支持的命令
ftp> ? Commands may be abbreviated. Commands are: ! debug mdir sendport site $ dir mget put size account disconnect mkdir pwd status append exit mls quit struct ascii form mode quote system bell get modtime recv sunique binary glob mput reget tenex bye hash newer rstatus tick case help nmap rhelp trace cd idle nlist rename type cdup image ntrans reset user chmod lcd open restart umask close ls prompt rmdir verbose cr macdef passive runique ? delete mdelete proxy send
我们可以使用 ftp 利用交互式的方式来进行与 ftpd 服务器来进行交互。
我们 可以使用 get 下载文件，使用 put 上传文件；
使用 lcd 确定本地文件夹，使用pwd 确定服务器文件夹。
保持更新，转载请注明出处。