I run Ubuntu as Guest OS in a Windows VirtualBox VM Host. In the existing, up-to-date VB, I have just moved from 17.04 to 18.04 by creating a new VM/
.vdi from scratch (including Guest Additions).
Previously, whatever I resized the whole VM/desktop window to was remembered across reboots, which is obviously desirable.
Under 18.04 (which, remember is now using GNOME instead of Unity, if that is relevant) this does not happen. The resizing is fine, but when I reboot it reverts to some small-ish size.
I imagine this is a Guest Ubuntu issue, not a Host VirtualBox one, so I don't think trying to ask the VB people will help any. Obviously I have installed Guest Additions, and do have View > Auto-resize Guest Display enabled.
Is this happening to other VirtualBox+18.04 users? Am I missing some setting to tell Ubuntu/GNOME to restore window/desktop size?