systemd

systemctl
systemctl enable late_command.service
systemctl disable late_command.service
systemctl status late_command.service
journalctl -f
systemd-analyze verify

Example
wget -q --no-check-certificate https://raw.githubusercontent.com/panticz/preseed/master/late_command.service -O /etc/systemd/system/late_command.service && \
systemctl enable late_command.service

[Unit]
Description=preseed late_command script
After=network.target

[Service]
StandardOutput=tty
ExecStartPre=/usr/bin/wget -q --no-check-certificate https://raw.githubusercontent.com/panticz/preseed/master/late_command.sh -O /tmp/late_command.sh
ExecStart=/bin/bash /tmp/late_command.sh
ExecStartPost=/bin/systemctl disable late_command.service

[Install]
WantedBy=multi-user.target

# test
[Unit]
After=getty.target

[Service]
TTYPath=/dev/tty1

# test
journalctl -xn
systemctl list-unit-files --all

# timesynchronization
https://feeding.cloud.geek.nz/posts/time-synchronization-with-ntp-and-systemd/

# cat /etc/systemd/timesyncd.conf
[Time]
FallbackNTP=ntp.ubuntu.com

# apt purge ntp ntpdate
# systemctl restart systemd-timesyncd.service
# timedatectl set-ntp true
# systemctl status systemd-timesyncd.service
# timedatectl status

# resolv
systemd-resolve --status

Links
https://wiki.ubuntuusers.de/systemd/
https://wiki.ubuntuusers.de/systemd/Service_Units/
http://www.freedesktop.org/software/systemd/man/systemd.service.html
https://wiki.archlinux.org/index.php/Systemd_FAQ
https://wiki.ubuntu.com/SystemdForUpstartUsers
http://www.freedesktop.org/software/systemd/man/systemd.special.html