Many people seem to run into problems when they want to share folders in their virtualbox windows. So let's help you out here: In this manual I assume you installed the latest version of Virtualbox AND that you installed the VirtualBox Extension Pack. If not: hurry to the virtualbox.org website ;-) and see you in a sec! To write this manual and re-create the following steps to be sure all steps were in the right order, I used a laptop with Ubuntu 16.04 64bit (OS), Virtualbox 5.1.14 (for Ubuntu), Expansion pack 5.1.14, and Windows 7 64bit (virtual).
1/ in VIRTUALBOX :
select (highlight) the OS you installed (for Example Win7)
click the 'SETTINGS' button en choose 'STORAGE'.
Add OPTICAL DRIVE (right-click at 'Controller:IDE')
Choose 'LEAVE EMPTY' at the question 'Cancel - Choose disk - leave Empty'
Check the boxes 'Live CD/DVD' on highlighted 'Empty'
2/ in your Virtual OS :
Boot up the virtual machine (for Example Win7)
In the VirtualBox menu (top of the screen), click on Devices - Insert Guest Additions CD image (at the bottom in the drop-down list)
Be patient! After a short while a box will pop up asking you about the VirtualBox Guest Additions CD.
You will see and should click 'Run VboxWindowsAdditions.exe'
Click 'Yes' in the box that pops up
Now you will enter the 'setup wizard'
Click Next and don't forget to accept each license agreement that follows
Next you'll see the install location part
Click Next - to accept the default location
Now you'll see the component selection part
Don't enable 3D hardware acceleration unless this was your target in the first place
Now click Install.
During the installation you will receive several device driver installation dialogs
Click Install for each and every one of them
Click Finish (and reboot the OS)
Guest Additions should be installed
3/ in your Virtual OS :
Select in VirtualBox the Windows 7 virtual machine
Click the 'SETTINGS' button
Choose the "Shared Folders" entry
Click on the little folder icon with a plus (+) on it, which you will find on the right and so add a new shared folder
A dialog 'ADD SHARE' appears
Click the arrow on the 'Folder Path' field
Select 'Other' and search for folder that you want to share with the Win7 virtual machine
You'll see the full path to that folder you want to share
Give it a new name or leave it as it is
Click OK to close the dialog
The folder will now be visible in the 'Shared Folders' section
Click 'OK' to close the settings dialog
Next start the Win7 virtual machine
When Windows is fully loaded open 'My Computer' and click on the 'Map network drive' button
Select a drive letter on the 'Drive' field
Now type \\vboxsrv\ followed by the name of your shared folder in the 'Folder'
Check the 'Connect using different credentials'
Click the 'Finish' button
You will be prompted to insert the user name and password of your Linux machine
Check the 'Remember my credentials' option and click 'OK'
Now you can see the shared folder in the 'My Computer' window, right under the Network location section