Install VirtualBox guest additions onto Ubuntu server guests

Have tested these steps successfully with Ubuntu guest of:

• 22.04LTS
• 18.04LTS
• 16.04LTS

using VirtualBox editions of 6.1, 6.0, 5.2 and 5.1 as host.

• Install steps
• Mount with guest/host permissions matched
• Allow symlink creation for shared folders
• Reference

Install steps

• Create Ubuntu server instance under VirtualBox (obviously).

• Start VM, goto Devices - Insert Guest Additions CD image to mount the ISO image.

• From the terminal, run the following commands:

   $ sudo su
   $ apt install gcc make
   $ mkdir --parents /media/cdrom
   $ mount /dev/cdrom /media/cdrom
   $ /media/cdrom/VBoxLinuxAdditions.run
   $ reboot

• After reboot:

   $ modinfo vboxguest
   $ sudo usermod --append --groups vboxsf -- "$USER"
   $ cat /etc/group | grep "$USER"

• Host shares should now be mounted in Ubuntu guest under /media via the installed VBoxService service, set to start on system boot-up.

• All done.

Note: the above steps can be repeated on an existing VM image for guest addition upgrades, VBoxLinuxAdditions.run will handle the uninstall and reinstall process automatically.

Mount with guest/host permissions matched

By default with auto mounted shares, VirtualBox will set an interesting set of ownership and file/directory permissions for the guest which (for me at least) is sub-optimal.

To correct this behavior and correctly mirror permissions between host and guest we can do the following:

• Shut down the guest (if not already) and ensure "Auto-mount" is disabled.

• Restart the guest.

• From the shell, determine the umask and uid/gid of the host user:

   $ umask
   0022
   $ id
   uid=1000(USERNAME) gid=1000(USERNAME) groups=1000(USERNAME),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),110(lxd),115(lpadmin),116(sambashare)

• Now mount the share as follows, inserting UMASK, UID, GID and SHARE_NAME:

   $ mkdir --parents /path/to/share
   $ sudo mount.vboxsf -o umask=UMASK,uid=UID,gid=GID SHARE_NAME /path/to/share

• If this works, we can now add a permanent entry to /etc/fstab, again inserting UMASK, UID, GID and SHARE_NAME:

   SHARE_NAME /path/to/share vboxsf umask=UMASK,uid=UID,gid=GID 0 0
  

• Remount all file systems

   $ sudo mount -a

• All done.

Allow symlink creation for shared folders

By default symlink creation by a VirtualBox guest against a shared/host filesystem is not allowed. To unlock run the following:

$ vboxmanage setextradata VBOX_GUID VBoxInternal2/SharedFoldersEnableSymlinksCreate/SHARED_FOLDER_NAME 1

A list of active/valid VBOX_GUID's can be returned via:

$ vboxmanage list vms

Reference

• https://askubuntu.com/questions/123025/what-is-the-correct-way-to-share-directories-in-mac-and-ubuntu-with-correct-perm/123156#123156
• https://askubuntu.com/questions/252853/how-to-mount-a-virtualbox-shared-folder-at-startup/252865#252865