systemd-cgls = show full hierarchy of control groups
systemd-cgtop = the same of systemd-cgls but ordered by CPU, memory and disk I/O load
systemctl kill apache = kill all processes associated with apache server
systemctl daemon-reload = reload a service configuration
systemctl list-unit-files = show a full list of installed unit along with their state
systemctl --failed = show failed units
systemctl isolate runlevel3.target = switch to run level 3. Run level 5 is named graphical.target
systemctl show --property=UnitPath = show all paths SystemD checks for unit files
systemctl list-unit-files -t target = list all unit files for the available target
systemctl get-default = show the current default system target
systemctl set-default target = set the default system target
systemctl rescue = start single-user rescue mode
systemctl reload service = reload the configuration files of service, without restarting the service itself
systemctl mask service = link the service unit file to /dev/null, practically disabling it, even if specifically started with systemctl start. It can be re-enabled with systemctl unmask service later
Journal
journalctl -o verbose = Enable verbose output for systemd’s journal
journalctl -e = Jumps directly at the end of the log (in conjuction with less)
Various
hostnamectl = get server hostname
hostnamectl set-hostname abc = set hostname to abc
localectl = get current locale, both on virtual console and X11
timedatctl = get info about time and timezone
Timers
systemctl list-timers --all = show a full list of timers, enabled or not
systemd-analyze calendar "Mon,Tue *-*-01..04 12:00:00" = check that the time specified in a timer unit is correct and when it will trigger the relative service