I went ahead and tested this by installing Ubuntu 17.10 with a separate /var partition and then filled it up with junk. I did receive an error message indicating that the upgrade aborted because /var needed a total of 506 M free. So it seems all good.
I went ahead and tested this by installing Ubuntu 17.10 with a separate /var partition and then filled it up with junk. I did receive an error message indicating that the upgrade aborted because /var needed a total of 506 M free. So it seems all good.