參考網址：
https://blog.51cto.com/dreamway/1045610
關鍵的幾個：
CWD：允許切換目錄
DELE：允許刪除文件
MKD：允許新建目錄
PNFR、PNTO：允許重命名
STOR：允許上傳
SITE：允許修改權限 （指windows資源管理器，右擊屬性改權限）
ABOR - abort a file transfer
CWD - change working directory
DELE - delete a remote file
LIST - list remote files
MDTM - return the modification time of a file
MKD - make a remote directory
NLST - name list of remote directory
PASS - send password
PASV - enter passive mode
PORT - open a data port
PWD - print working directory
QUIT - terminate the connection
RETR - retrieve a remote file
RMD - remove a remote directory
RNFR - rename from
RNTO - rename to
SITE - site-specific commands
SIZE - return the size of a file
STOR - store a file on the remote host
TYPE - set transfer type
USER - send username
ACCT - send account information
APPE - append to a remote file
CDUP - CWD to the parent of the current directory
HELP - return help on using the server
MODE - set transfer mode
NOOP - do nothing
REIN - reinitialize the connection
STAT - return server status
STOU - store a file uniquely
STRU - set file transfer structure
SYST - return system type