sudo sed -i 's/archive.ubuntu.com/mirrors.ustc.edu.cn/g' /etc/apt/sources.list
sudo apt update
sudo apt install -y xfce4 xfce4-goodies
sudo apt install -y tightvncserver autocutsel

vagrant@ubuntu-focal:~$ vncserver

You will require a password to access your desktops.

Password:
Verify:
Would you like to enter a view-only password (y/n)?
xauth:  file /home/vagrant/.Xauthority does not exist

New 'X' desktop is ubuntu-focal:1

Creating default startup script /home/vagrant/.vnc/xstartup
Starting applications specified in /home/vagrant/.vnc/xstartup
Log file is /home/vagrant/.vnc/ubuntu-focal:1.log

vagrant@ubuntu-focal:~/.vnc$ vi ~/.vnc/xstartup

#!/bin/sh

xrdb $HOME/.Xresources
xsetroot -solid grey
#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
#x-window-manager &
# Fix to make GNOME work
export XKL_XMODMAP_DISABLE=1
/etc/X11/Xsession
startxfce4 &