Host machine (Ubuntu)
- shared folder: /home/username/Downloads
- virtualbox share name: shared
Guest machine (Centos)
- mount share as /mnt/hostfolder
Step 1: Install Virtualbox Guest Additions.
Read the manual.
Step 2: Apply the shared folder for Virtualbox
Open the virtualmachine (guest) and go to Devices ->Shared Folders
Click on "Add Shared Folders", its a plus sign. Enter the following values
Folder path: /home/username/Downloads
Folder name (no white spaces): shared
Step 3: Mount the shared folder
Reboot the guest machine and mount with following command (use root/administrator);
mount -t vboxsf shared /mnt/hostfolder
Then apply the required permissions to the folder.