vagrantでmountエラーが出た時の対処

Failed to mount folders in Linux guest. This is usually because
the "vboxsf" file system is not available. Please verify that
the guest additions are properly installed in the guest and
can work properly. The command attempted was:

mount -t vboxsf -o uid=`id -u vagrant`,gid=`getent group vagrant | cut -d: -f3` vagrant_data /vagrant_data
mount -t vboxsf -o uid=`id -u vagrant`,gid=`id -g vagrant` vagrant_data /vagrant_data

The error output from the last command was:

mount: unknown filesystem type 'vboxsf'

が出た時には次のように対処します。

vagrant halt
vagrant plugin install vagrant-vbguest
vagrant up