but why?

My Ubuntu server (which has been working for a few years now) recently asked me in a full-screen prompt while updating something about GRUB. There was a list of partitions with just one element, which is the partition that GRUB os on. I was focused on something else so I just hit enter, but now I am really scared to reboot it. Is there any way to pull this back up or to double-check that everything is ok with the machine?