Ubuntu – VirtualBox 4.12 Shared clipboard not working in Ubuntu14.04

virtualbox-guest-dkms's version in Ubuntu 16.04.3 is 5.0.40-dfsg-0ubuntu1.16.04.2, which is the version of VirtualBox in Ubuntu's repository rather than 5.2.4. This might be causing your issue.

Try the following to install the proper version of Guest Additions:

1. Start the virtual machine
2. In the VirtualBox Devices menu, choose Insert Guest Additions CD image...
3. Open a terminal by pressing Ctrl+Alt+T
4. Run sudo apt purge virtualbox-guest-dkms
5. Run sudo /media/$USER/VBox_GAs_5.2.4/VBoxLinuxAdditions.run
6. Reboot

Except for step 4, it's a good idea to do this every time there's a new version of VirtualBox (step 5 should be changed to the proper path, of course).

I have just got the same problem with Ubuntu MATE 18.10 guest.

The solution is to install two packages linux-headers and build tools:

sudo apt-get install linux-headers-generic build-essential

then reinstall VirtualBox Guest Additions from ISO and then reboot. The clipboard works after reboot.

The complete list of VirtualBox services will look like below:

$ ps ax | grep VBox
  514 ?        I<     0:00 [iprt-VBoxWQueue]
  803 ?        Sl     0:00 /usr/sbin/VBoxService --pidfile /var/run/vboxadd-service.sh
 1320 ?        S      0:00 /usr/bin/VBoxClient --clipboard
 1321 ?        Sl     0:00 /usr/bin/VBoxClient --clipboard
 1330 ?        S      0:00 /usr/bin/VBoxClient --display
 1331 ?        S      0:00 /usr/bin/VBoxClient --display
 1340 ?        S      0:00 /usr/bin/VBoxClient --seamless
 1341 ?        Sl     0:00 /usr/bin/VBoxClient --seamless
 1349 ?        S      0:00 /usr/bin/VBoxClient --draganddrop
 1350 ?        Sl     0:00 /usr/bin/VBoxClient --draganddrop
 1938 pts/0    S+     0:00 grep --color=auto VBox