Log in as root beforehand (sudo -i)

Systemd Service Commands

systemctl stop service-name
systemd stop running service

systemctl start service-name
systemctl start service

systemctl restart service-name
systemd restart running service

e.g.
sudo systemctl restart network-manager.service

systemctl reload service-name
reloads all config files for service

systemctl status service-name
systemctl show if service is running

systemctl enable service-name
systemctl start service at boot

systemctl is-enabled service-name
check if a service is enabled on boot or not

systemctrl disable service-name
systemctl - disable service at boot

systemctl show service-name
show systemctl service info

systemctl -H target command service-name
(systemctl -H host status network)
run systemctl commands remotely

* * *

Systemd Information Commands
----------------------------
Systemd commands that show useful system information.

systemctl list-dependencies
show and units dependencies

systemctl list-sockets
systemd list sockets and activities

systemctl list-jobs
view active systemd jobs

systemctl list-unit-files
systemctl list unit files and their states

systemctl list-units
systemctl list default target (like run level)

systemctl --failed
list failed units

systemctl list-units -t service
list all active services

systemctl get-default
list default target (like run level)

* * *

Changing System State
systemd reboot, shutdown, default target etc

systemctl reboot
systemctl reboot the system

systemctl poweroff
systemctl shutdown (power off the system)

systemctl suspend
suspend the system (use "xscreensaver-command -lock" to lock beforehand)

systemctl emergency
Put in emergency mode

systemctl default
systemctl default mode

Systemctl Viewing Log Messages
------------------------------
journalctl
show all collected log messages

journalctl -u sshd.service
see sshd service messages

journalctl -f
follow messages as they appear

journalctl -k
show kernel messages only

* * *

Analyze
-------
boot process duration:
systemd-analyze
systemd-analyze time

print a list of all running units:
systemd-analyze blame