#image of /dev/sd5 in sd5.img
sudo dd if=/dev/sda5 of=/home/sda5.img
#install grub in sdb
grub-install /dev/sdb
update-grub
#make a disk bootable
sudo umount /dev/sdX
sudo dd if=/path/to/ubuntu.iso of=/dev/sdX bs=4M && sync
#set a partition to boot
parted -s /dev/sda set 2 boot on

# increase virtual size of vbox machine
VBoxManage modifyhd --resize 25000 /Volumes/Transcend/VirtualBox\ VMs/Buildozer/Buildozer.vdi

# Know the distribution installed for linux
lsb_release -a