Alpine Virtual Box shared folder setup

install_vboxsf.sh

apk update 
apk add virtualbox-guest-additions virtualbox-guest-modules-virthardened 

# auto load vboxsf kernel module
echo vboxsf > /etc/modules-load.d/vboxsf.conf

reboot

setup_mount.sh

# enable local service in openrc
rc-update add local default

# create mount point folder
mkdir /mnt/outside 

# auto mount after reboot
echo mount -t vboxsf vbox_shared_folder_name /mnt/outside > /etc/local.d/outside.start
chmod +x /etc/local.d/outside.start

reboot

according to a currently visible todo notice on the top on https://wiki.alpinelinux.org/wiki/VirtualBox_shared_folders "Need to update this article. I think the virtualbox-guest-modules-virt package has been obsoleted by linux-virt on 3.11 and later" it worked for me like that (alpine 3.17):

echo "create a shared folder via the gui and name it 'vbox_shared'"
mkdir -p /mnt/outside
apk add virtualbox-guest-additions linux-virt
reboot
modprobe -a vboxsf 
mount -t vboxsf vbox_shared /mnt/outside