After upgrading VirtualBox to 5.1.24, Vagrant 1.9.7 didn't know how to install the corresponding vbox guest additions on the guest boxes because the installer blocked on standard input:
Installing Virtualbox Guest Additions 5.1.24 - guest version is 5.0.14 Verifying archive integrity... All good. Uncompressing VirtualBox 5.1.24 Guest Additions for Linux........... VirtualBox Guest Additions installer This system appears to have a version of the VirtualBox Guest Additions already installed. If it is part of the operating system and kept up-to-date, there is most likely no need to replace it. If it is not up-to-date, you should get a notification when you start the system. If you wish to replace it with this version, please do not continue with this installation now, but instead remove the current version first, following the instructions for the operating system.
If your system simply has the remains of a version of the Additions you could not remove you should probably continue now, and these will be removed during installation.
Do you wish to continue? [yes or no]
Cancelling installation.
An error occurred during installation of VirtualBox Guest Additions 5.1.24. Some functionality may not work as intended. In most cases it is OK that the "Window System drivers" installation failed.
Since it uninstalled the previous version before installing the new one, vboxsf was obviously gone:
mount: unknown filesystem type 'vboxsf'
If you run into this, it's real easy to just install it on the guest yourself:
vagrant ssh
curl -0 http://download.virtualbox.org/virtualbox/5.1.24/VBoxGuestAdditions_5.1.24.iso > /tmp/vboxguest.iso
sudo mount -o loop /tmp/vboxguest.iso /mnt
yes yes | sudo /mnt/VBoxLinuxAdditions.run
exit
vagrant reload
@bdero
I had same problem.
I have solved the problem.
Thanks.