VirtualBox 5.2.4 Shared clipboard not working in Ubuntu 16.04.3 LTS

I have tried this:

sudo apt-get install virtualbox-guest-dkms and enabling bidirectional shared clipboard.

VirtualBox 4.12 Shared clipboard not working in Ubuntu14.04

and various other things, now hard to collect, but nothing works so far.

How to fix it?

Update

When trying to insert guest additions CD image, I get this error:

From this question, Unable to Install Guest Additions CD Image on Virtual Box, I tried:

Tried also:

sudo apt-get upgrade
sudo apt-get install virtualbox-guest-additions-iso and this gives:

Restarting the virtual machine did not help, no errors.

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 encountered the "shared clipboard" bug in 6.1.4 while running on a Windows host. I know that it is, indeed, a not-yet-unresolved bug in this version of VirtualBox.

As others have suggested, I found that I could bypass the problem by reinstalling version 6.1.2 of the Guest Additions. I found the necessary Windows installer by going to "Older builds 6.0" on the VirtualBox website, then manually editing the URL from 6_0 to 6_1.

Then, after installing the Windows side of things (VirtualBox very graciously understands the idea of "downgrade"), you of course must then mount the CD image, and run the Linux-side ".run" file as root. (Exactly as you must do with any Guest Additions release ...) Then, restart the VirtualBox application on the host, and boot the virtual machine. (You must thereby update the software on both sides.)

Of course this problem is actively being discussed on the VirtualBox web site and it is a known, confirmed problem. ("Zed, we have a bug!") I'm quite sure that 6.1.5 will have a permanent solution.