virtualbox.org

I have a virtual Ubuntu on my Windows laptop, and with guest additions, the virtual OS's display would be altered to fit the VBox window size. I made an update to my virtual Ubuntu, and now VBox displays Ubuntu through scroll bars instead of resizing it. I don't want to scroll up and down to use my virtual OS. The scroll bars aren't used if I set Ubuntu's resolution to 800x600, but then everything becomes really cramped. How can I fix this problem?

Install dkms on the ubuntu guest and then install the guest additions again.
See Chapter 4.2.2.1. Installing the Linux Guest Additions in your VirtualBox users manual.

Works now! Thanks!

It happened again. This is such a pain.

Okay, so I have updated Virtualbox, updated dkms, updated guest additions, but the largest screen resolution I can get is only 800x600.

The auto-resize of VirtualBox is done with the mouse click and drag, or the toggle keys of host+f for full screen.
Setting inside the guest is not suggested. Read the chapter I sent you on the guest additions.

Huh? Mouse click and drag? You mean resizing the VB window? Fullscreen? If the problem was that easy to solve I wouldn't be looking for help.The resolution remains just as small despite being in fullscreen mode. Below is what it looks like.

From the looks of it (if you are sure the guest additions are installed) the auto-resize is not working.
Try the host+g toggle to make sure it is turned on.

Oh. So it can be turned on and off. Okay. It works now. I'll just go and crawl into my hole of shame and stupidity now.

Well yes, that is the idea. A toggle switch is a two position switch. So the verb to toggle means to switch from one state to the other.