The FTP service commands are by far the most widely used commands in FTP.
They define all of the file transfer and navigation requests of the user.
The argument of a service command will normally be a pathname. The suggested
default handling is to use the last specified device, directory or file name, or the
default defined for the user. The commands may be
in any order except that a "rename from" command must be
followed by a "rename to" command and the restart command must
be followed by the interrupted service command (e.g., STOR or
RETR). The data, when transferred in response to FTP service
commands, shall always be sent over the data connection.
The following commands specify FTP service requests: