# Install VirtualBox guest additions onto Ubuntu server guests
Have tested these instructions successfully under an Ubuntu 16.04LTS guest with a VirtualBox 5.1 and 5.2 host.

- [Install steps](#install-steps)
- [Mount with guest/host permissions matched](#mount-with-guesthost-permissions-matched)
- [Reference](#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:

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

- After reboot:

	```sh
	$ sudo usermod --append --groups vboxsf USERNAME
	```

- 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.

## 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) is sub-optimal. To correct this behavior and 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 your host user.

	```sh
	$ 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:

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

- If all is good, we can now add an entry to our `/etc/fstab`:

	```
	SHARE_NAME /path/to/share vboxsf umask=UMASK,uid=UID,gid=GID 0 0
	```
	
- And remount all file systems

	```sh
	$ sudo mount -a
	```

- All done.

## 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