Ubuntu – “Protocol error” mounting VirtualBox shared folders in an Ubuntu guest


I have Ubuntu 10 as the guest OS on a Windows 7 machine. I have been trying to setup shares through VirtualBox, but nothing is working. First, I create the share in VirtualBox and point it to a Windows folder. Then I try to mount the drive in Linux, but I keep getting

/sbin/mount.vboxsf: mounting failed with the error: Protocol error

I have read so many solutions to this, but none seem to work. I have tried:

  • Using the mount.vboxsf syntax
  • Reinstalling VBox additions
  • Rebooting
  • Enabling and trying as root account

I made a share called "Test" in VBox Shared folders. Then I made a directory in ubuntu named "test2". Then I tried to execute this command:

sudo mount -t vboxsf Test /mnt/test2

Any other ideas?

Best Answer

In order to use shared folder functionality few prerequisites need to be met:

  • Make sure that Guest Additions are properly installed on the guest OS.
  • Users in a guest Ubuntu must be in the group vboxsf to be able to access shares.
  • Define a directory on the host that will be used in the virtual machine using the settings dialogue of Virtual Box.

Depending on host or guest OS the following may also be needed:

  • Do not share personal folders like /home/username or My Documents
  • Avoid special characters or empty spaces in the path to the shared folder, especially if the host or VM is a Windows machine
  • Use different names for share and mountpoint
  • Create a mountpoint on the guest OS (best in your HOME directory).

Testing shared folders functionality can be done by creating a shared directory on the host (e.g. C:\myshare), define this as a shared folder for your guest system in Virtual Box settings (e.g. share), create a mount point in your guest os (e.g. mkdir /home/username/host) and mount this in the guest OS with the command:

sudo mount -t vboxsf -o uid=1000,gid=1000 share /home/username/host

where the option -o makes sure that you will have access to the mount (that will otherwise be owned by root).

For further information on shared folders see also the Virtual Box User Manual.

Files or directories can also be shared over the network by using Samba on the host and the guest.

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