apt-get update
apt-get upgrade -y
apt-get dist-upgrade -y

apt-get install update-manager-core
do-release-upgrade

reboot


.
if can’t pingout or ‘ifconfig’ show nothing.
or ‘reboot’ show
“Failed to connect to bus: No such file or directory”
“Failed to talk to init daemon.”

/etc/init.d/networking
apt-get install upstart 
apt-get install upstart-sysv
apt-get remove --purge --auto-remove systemd
apt-get clean

*https://www.claudiokuenzler.com/blog/634/ubuntu-16.04-xenial-container-on-14.04-trusty-lxc-host
.

#after reboot
cat /etc/issue
lsb_release -a
uname -a

share: How to upgrade Ubuntu 14.04 / 15.10 to 16.04 LTS