How do I make clipboard and shared folder in Virtualboxed Ubuntu working

I'm using Ubuntu 16 server as guest OS in VirtualBox, Ubuntu 18.04 as host OS. VirtualBox version 5.2.38.

I'm trying to setup shared folders and clipboard from host machine to guest one and all my attempts are vain. After installation of Virtual box guest additions I enabled bidirectional clipboard and added shared folder, but it didn't work out.

I tried:

• added guest user to vboxsf user group
• reinstalled Guest additions
• deleted and restored shared folders
• enabled and disabled clipboard
• reinstalled VirtualBox to 5.2.38

with no effect.

Please, help.