Set Up FTP on Ubuntu 16.04

sudo apt install vsftpd
Edit the config file:
write_enable=YES

local_umask=022
ssl_enable=YES

Then
sudo service vsftpd restart

Use FileZilla to connect to the FTP server

VirtualBox abort error

VirtualBox host: Macbook Pro macOS 10.12.2
VirtualBox guest: 16.04 Ubuntu
The guest Ubuntu system often had abort error.
It was caused by the Logitech software driver on the Mac system and the mouse M705 receiver.
It usually happens when I unplug the Logitech universal receiver, so the solution is to uninstall the Logitech software driver and use Mac's default driver. Also leave the universal receiver plugged in all the time.