This howto describes how to install a minimal Ubuntu server on a Raspberry Pi 4. Everything is done as the root user in this howto.

Download from: https://ubuntu.com/download/raspberry-pi

Use Etcher or whatever to install the downloaded zip on a SD card.

Default user/pass is ubuntu/ubuntu. It take some minutes to be able to login.

apt update
apt upgrade -y

dpkg-reconfige tzdata

/etc/systemd/timesyncd.conf

[Time]
NTP=172.16.0.254
#FallbackNTP=0.debian.pool.ntp.org 1.debian.pool.ntp.org 2.debian.pool.ntp.org 3.debian.pool.ntp.org
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048