Problem

When building OpenCV-3.1.0 in Ubuntu 14.04 installed inside VirtualBox 5.0.16 (in Win7 host), I encountered the following error:

cmake_symlink_library: System Error: Read-only file system

Both the OpenCV source folder and build folder locate in a shared folder that resides outside the VirtualBox’s virtual hard disk (in my Win7 host drive). And I created a symbolic link inside the Ubuntu home folder

~/project/ -> /media/sf_D_DRIVE/project/

I have full access to the share folder (I can read and write without any issue).

Solution

After Google, I found several web pages with similar problem, which appears to be a well-known issue for VirtualBox existing for a while.

I solved the issue according to this:

1. Shut down the VirtualBox

2. Open CMD.exe:

   cd C:/Program Files/Oracle/VirtualBox
   VBoxManage setextradata VM_NAME VBoxInternal2/SharedFoldersEnableSymlinksCreate/SHARE_NAME 1
   

   where VM_NAME=ubuntu14 and SHARE_NAME=D_DRIVE (Yes, remove the “sf_” prefix) in my case.

3. Open VirtualBox as Administrator, and start the ubuntu, rebuild OpenCV, everything works fine now!