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HuHa's VirtualBox Tips

Author: Stefan.Hundhammer@gmx.de

License: GNU Free Documentation License

Sharing Folders between Host and Guest System

Scenario:

I wanted to edit my checked-out source code on my host Linux and build the code in a Linux VM. I wanted to make two directory trees available from the host system to the guest VM just as if they were local directories inside the VM with the same permissions and everything.

I used the same user name and ID both in the host and in the guest VM (this makes things a bit easier).

Preparations

In the VirtualBox application, select the VM and open the settings details for that VM. Click on the Shared folders heading. In the pop-up dialog, add the desired folders that you want to share and give each one a name for use inside the VM:

work_src  /work/src
work_tmp  /work/tmp

work_src is the name that I chose, /work/src is the path on the host machine.

The Naive Approach

For each shared folder, also check the Auto-mount option.

Once you start the VM, the folders are instantly available.

Problem

The mount options are bizarre and completely useless. You basically don't have any reasonable access inside the guest VM; you can only use them as root (and then only with limitations).

You can add your normal user account inside the guest VM to the vboxsf user group in /etc/group:

vboxsf:x:463:myusername

But still, all shared files are owned by the root user and the vboxsf group, and all files have execute permissions.

The Correct Approach

Make sure to leave the Auto-mount option unchecked in the settings for the shared folders in the VirtualBox application. Instead, Mount the shared folders manually with the correct options.

The mount.vboxsf command uses those bizarre mount options by default!

Yes, it mounts everything with mount options uid=0,gid=0. It will only stop doing that when you explicitly specify different values for those options.

Manually Mounting the Shared Folders

Inside the guest VM:

sudo mount -t vboxsf -o uid=1000,gid=100 work_src /work/src
sudo mount -t vboxsf -o uid=1000,gid=100 work_tmp /work/tmp

This assumes that your user ID is 1000 and your group ID is 100 which is the default for modern Linux systems for the first user account that is created. For different IDs, use the correct numeric values accordingly.

Adding the Shared Folders to /etc/fstab

Inside the guest VM:

sudo vi /etc/fstab

Add those lines:

# VirtualBox shared folders

work_src  /work/src  vboxsf  uid=1000,gid=100  0  0
work_tmp  /work/tmp  vboxsf  uid=1000,gid=100  0  0

Apply the changes:

sudo mount -a

Check if it worked:

mount | grep vbox

or

df -x tmpfs -x devtmpfs

You should see your shared folders in both cases.

Enable Symlinks for Shared Folders

They disabled symbolic links for shared folders for security reasons. But that also makes shared folders pretty much unusable for most real uses, such as software development. Here is how to enable them:

On the host system (!), for each shared folder execute this command:

VBoxManage setextradata "$MY_VM_NAME" VBoxInternal2/SharedFoldersEnableSymlinksCreate/$SHARED_FOLDER_NAME 1

I.e. in the above example for shared folders work_src and work_tmp:

VBoxManage setextradata "MyVmName" VBoxInternal2/SharedFoldersEnableSymlinksCreate/work_src 1
VBoxManage setextradata "MyVmName" VBoxInternal2/SharedFoldersEnableSymlinksCreate/work_tmp 1

Notice that this will happily accept any random bullshit without any error.

Check:

VBoxManage getextradata "MyVmName" enumerate

Now shut down your guest VM and restart the VirtualBox application (!!) for the changes to take effect.

You should now be able to create symlinks in the guest VM in those shared folders.

No Graphics in Guest after VirtualBox Downgrade

This happened to me after going back to Xubuntu 18.04 LTS from 20.04 LTS because of constant NVidia / X11 crashes.

VirtualBox 6.x introduced a new setting for graphics card type and defaults to another one: VMSVGA instead of the old VBoxVGA. There is no way to set that in the VirtualBox GUI in older versions, so you have to manually edit the XML file for each affected virtual machine.

See also

https://superuser.com/questions/1403123/what-are-differences-between-vboxvga-vmsvga-and-vboxsvga-in-virtualbox

Go to your VirtualBox vms directory where the *.vbox XML files are and edit them.

  • Make sure to close the VirtualBox GUI, or it will overwrite your changes!

  • Look for lines like this:

      <Display controller="VMSVGA" VRAMSize="16" accelerate3D="true"/>

    and change them to look like this instead:

      <Display controller="VBoxVGA" VRAMSize="16" accelerate3D="true"/>

    There is one such line for every snapshot that the VM has, so make sure to edit all of them or at least the one for the most recent snapshot!

  • Or use this perl command to bulk-edit them all at once:

    cd /work/virtualbox/vms      # or wherever your VMs are

perl -p -i'*.bak' -e 's/VMSVGA/VBoxVGA/g' */*.vbox

    This leaves behind a .bak file for every changed file, so you can safely go back.

Starting such a VM or editing its settings may remove that <Display controller...> line entirely, leaving the defaults (which is VBoxVGA).

Newer VirtualBox (6.x) on older Ubuntu (18.04 LTS)

From some point on, the older VirtualBox 5.2 that comes with Ubuntu 18.04 LTS is no longer a viable option: A VM like Tumbleweed or Leap 15.3 boots fine, but when it starts X11, all you get is a black screen:

The VirtualBox 6.x guest additions in the VM are no longer compatible with the older VirtualBox 5.2 on the host. While this is clearly a bug, there is no fix in sight.

But you can install the official VirtualBox 6.x from https://www.virtualbox.org/ .

Add the VirtualBox APT Repo

See also https://tecadmin.net/install-virtualbox-on-ubuntu-18-04/

  • Import the repo's keys:

    wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add -
wget -q https://www.virtualbox.org/download/oracle_vbox.asc -O- | sudo apt-key add -

  • Add the repo. You could simply do this with sudo add-apt-repository ... as described in that (very good and very helpful) tecadmin.net article, but then it is added to all the other repos in /etc/apt/sources.list. For clarity and better organization, it is recommended to put this into a separate file:

    cd /etc/apt/sources.list.d
sudo vi virtualbox-org.list

    content of that file:

    deb [arch=amd64] http://download.virtualbox.org/virtualbox/debian bionic contrib
# deb-src http://download.virtualbox.org/virtualbox/debian bionic contrib

    Notice that the bionic part is about the Ubuntu version, in this case 18.04 LTS. For a different Ubuntu version, use that version's code name. If you don't know it, look it up in /etc/os-release:

    grep UBUNTU_CODENAME /etc/os-release

  • Whichever way you choose, make sure to add that [arch=amd64] part, or you will very likely get a warning

    Skipping acquire of configured file 'main/binary-i386/Packages' as repository 'xxx' doesn't support architecture 'i386'

    every time you do sudo apt update from now on which is very annoying, so tell apt that this repo only supports the amd64 architecture; that's what that [arch=amd64] is for .

    See the askubuntu.com article below for more background.

Install the Newer VirtualBox

  • Uninstall the old VirtualBox 5.2 packages that came with Ubuntu 18.04:

    sudo apt remove "virtualbox*"

  • Update the repo information, including the one we just added:

    sudo apt update

  • Check what newer versions are now available:

    sudo apt-search "virtualbox-6"

    Or, more generally, but with more irrelevant output:

    sudo apt-search virtualbox

  • Install the newer version. DO NOT install just any random version; be more specific by adding the version number:

    sudo apt install virtualbox-6.1

    Don't be surprised if that takes a while: It will have to compile a kernel module.

Reference