I often met issues when installing new Ubuntu Linux machine or upgrade current Ubuntu Linux. Most issues are fixable but one has kept me crazy many times, the desktop resolution mode. In many online solutions, people often suggest “xrandr” to get resolution, followed by many different protocols (different from online solutions) to fix the resolution issue. The problem is none of them works to my case.
Now, I finally got a very simple solution (although I have no idea why it works) by modifying /etc/default/grub. In /etc/default/grub, change “GRUB_GFXMODE=640×480” to “GRUB_GFXMODE=1920×1080” (if 1920 x 1080 is the target resolution) and restart the linux. The resolution issue is gone. Amazing.