I figured out how to get apt-get to work again.

Edit gai.conf:

sudo vim /etc/gai.conf

change line ~54 to uncomment the following:

precedence ::ffff:0:0/96  100

write and quit:

後來強迫apt-key使用80 port才成功

apt-key adv --keyserver hkp://keyserver.ubuntu.com:80

安裝oracle java8要照下列步驟才會成功

sudo apt-get install software-properties-common

sudo add-apt-repository "deb http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main"

sudo apt-get update

sudo apt-get install oracle-java8-installer

ubuntu使用debian版本對照