Este comando:
sudo apt-get install ftp
instale um cliente ftp, não um servidor. Por isso, veja a saída de:
$apt-cache show ftp
Package: ftp
....
Description-en: classical file transfer client
This is the user interface to the ARPANET standard File Transfer Protocol.
The program allows a user to transfer files to and from a remote network
site.
Description-md5: ce93e483dfc5fef0655f73f364b3c01c
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Origin: Ubuntu
Supported: 5y
Task: standard, kubuntu-active, kubuntu-active