Things to do after install Ubuntu 18.04

Change your repository into local for better download.

deb http://kambing.ui.ac.id/ubuntu/ bionic main restricted
deb http://kambing.ui.ac.id/ubuntu/ bionic-updates main restricted
deb http://kambing.ui.ac.id/ubuntu/ bionic universe
deb http://kambing.ui.ac.id/ubuntu/ bionic-updates universe
deb http://kambing.ui.ac.id/ubuntu/ bionic multiverse
deb http://kambing.ui.ac.id/ubuntu/ bionic-updates multiverse
deb http://kambing.ui.ac.id/ubuntu/ bionic-backports main restricted universe multiverse
deb http://kambing.ui.ac.id/ubuntu/ bionic-security main restricted
deb http://kambing.ui.ac.id/ubuntu/ bionic-security universe
deb http://kambing.ui.ac.id/ubuntu/ bionic-security multiverse