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

These times, my virtualisation needs are being well served by VirtualBox 2.2. It may be the closed source variant but I have no complaints about it. Along with a number Windows VM’s, I also have one running Ubuntu 9.04 and, for the first time, I seem to have VirtualBox’s Guest Additions playing with a Linux guest as they should. Even the Shared Folders functionality is working.

However, I did get one problem when I tried out the last feature for the first time. The procedure is to issue a command like the following in a terminal session after creating the requisite directory in the file system and adding a host directory as a shared folder:

sudo mount -t vboxsf Music /mnt/host_music/

Above, Music is the name of the folder in the VirtualBox manager and /mnt/host_music in the directory in the guest file system. However, this returned the message at the head of this post at that first attempt:

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

The solution thankfully turns out to be an easy one: reinstalling the Guest Additions and that certainly did the trick for me. The cause would appear to have been an update to Ubuntu and 9.04 is understandably in a state of flux at the moment (I suspect kernel upgrades because of my previous experiences). Regardless of this, it is good to know that it’s a problem with a simple fix and I am seeing the niceties of a larger virtual screen system together automatic grabbing and releasing of the mouse cursor too. There may be a chance to explore the availability of these sorts of features to other Linux guests but I have other things that I should be doing and there’s sunshine outside to be enjoyed.


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There is a simple solution which solved my problem on Open Solaris with an Ubuntu 9 guest. Instead of using mount -t vboxsf Public /home/andrius/Public, type this this one: mount.vboxsf Public /home/andrius/Public. It works!

Thanks Andrius. I too have used mount.vboxsf with some success. It looks as if mount -t vboxsf is its alias in more customary syntax.

Thanks Andrius! I’ve been searching the web for the past 1 hour to find a solution to this. What you suggested did the trick for me (Running Ubuntu 9.04 virtualized on WinXP).

Hi all

I’ve found this solution:

For example:

mount -t vboxsf vshare /home/paulsiu/vshare

The problem is when you tried this, you get the following error:

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

If you look at syslog, you’ll see the following error:

Nov 8 19:28:09 wxbuilder kernel: vboxvfs: sf_glob_alloc: vboxCallMapFolder failed rc=-102
Nov 8 19:28:09 wxbuilder kernel: sf_read_super_aux err=-71

Apparently, you’ll only get this error if you use the default sharename. When you create a new shared folder, Virtualbox will ask where your shared directory is on the host. When you select the shared directory, the sharename will default to that directory. If I create a shared folder at “/home/paulsiu/vshare”, virtualbox will generate a sharename of “vshare”. Unfortunately, if you use this default sharename, you will get a protocol error, so you should rename the sharename to something other than default, such as “vboxshare” for example. I have no idea why, but that appears to be what’s happening.


Had the same problem. Windows 7 host, Ubuntu 9.10 guest. Windows D drive shared with share name of DRIVE_D, created sharepoint /media/shared/. Whether mount or /sbin/mount.vboxsf, everything I tried elicited the protocol error.

Finally, I changed the share name from the default DRIVE_D to shared and it worked. Played around with changing the share name, eventually changing it back to the VirtualBox default DRIVE_D and it still worked.

This would appear to be a VirtualBox bug. Solution: don’t use the default share name.


Haha, same for me! (I actually unchecked accidentally the Make Permanent option in the shared folder) Luckily I read your post before I reinstalled the guest additions! Thanks!

Hi i tried giving mount.vboxsf also tried changing the shared folder name but still its not working for me..The error is mount.vboxsf: mounting failed with the error: Protocol error.. Im using windows7 as my host and openSUSE as my guest os…

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