VirtualBox Ubuntu 14.04 - vboxclient the virtualbox kernel service is not running

This usually happens when you update the Guest's Linux Kernel.
After each update, you need to do:

• For Host (installing server)

  sudo /etc/init.d/vboxdrv setup
  

• For Guest (installing additions)

  sudo /etc/init.d/vboxadd setup
  

The reason why inserting the VBox addition disk again works is because that's one of the things the installation procedure does as well.

Try eject the VBOXADDITIONS cd image on ubuntu and "insert" it again from Vbox menu. I was just having this same problem and doing this fixed it.

I'm running Ubuntu 15.04 on Virtualbox 5.02. The same notification went away after I selected two "restricted drivers" from Virtualbox.

More specifically, from Software & Updates > Additional Drivers tab, there are two drivers previously not selected: Using x86 virtualization solution - X11 guest utilities from virtualbox-guest-x11 and Using x86 virtualization solution - guest addition module source for dkms from virtualbox-guest-dkms. The notification was gone after I selected to use these two proprietary drivers.

Update: one of these two drivers seem to cause a repository inconsistency when I run apt-get update. I chose to use the package maintainer's version to solve the inconsistency, and haven't run into any further problem.