This seems to be bug of kernel 4.19.0-5 according to this bug report. Upgrade to debian 10.1 or 10.2 solve the problem.
devel@master:/opt/VBoxGuestAdditions-6.1.2/init$ sudo ./vboxadd setup
update-initramfs: Generating /boot/initrd.img-4.19.0-5-amd64
update-initramfs: Generating /boot/initrd.img-4.19.0-6-amd64
VirtualBox Guest Additions: Starting.
VirtualBox Guest Additions: Building the VirtualBox Guest Additions kernel
modules. This may take a while.
VirtualBox Guest Additions: To build modules for other installed kernels, run
VirtualBox Guest Additions: /sbin/rcvboxadd quicksetup <version>
VirtualBox Guest Additions: or
VirtualBox Guest Additions: /sbin/rcvboxadd quicksetup all
VirtualBox Guest Additions: Building the modules for kernel 4.19.0-5-amd64.
update-initramfs: Generating /boot/initrd.img-4.19.0-5-amd64
modprobe vboxguest failed
The log file /var/log/vboxadd-setup.log may contain further information.
Get errors:
Vagrant was unable to mount VirtualBox shared folders. This is usually
because the filesystem "vboxsf" is not available. This filesystem is
made available via the VirtualBox Guest Additions and kernel module.
Please verify that these guest additions are properly installed in the
guest. This is not a bug in Vagrant and is usually caused by a faulty
Vagrant box. For context, the command attempted was:
mount -t vboxsf -o uid=1000,gid=1000 work /work
The error output from the command was:
mount: /work: unknown filesystem type 'vboxsf'.
May be caused by Linux kernal bug as found on Debian 10?
Get error messages like:
Initramfs unpacking failed: write error
rngd.service: Failed to execute command
rngd.service: Failed at step EXEC spawn
error creating /var/lib/lldpad/lldpad.conf
failed to initialize configuration file
Failed to connect to lldpad