<code bash>
systemctl -t help

systemctl list-unit-files

systemctl list-units

systemctl start name.service

systemctl stop name.service

systemctl status name.service
systemctl status name.service -l

systemctl enable name.service

systemctl disable name.service

systemctl cat name.service

systemctl show

systemctl edit

systemctl daemon-reload

systemctl list-dependecies name.target 

systemctl start name.target

systemctl isolate name.target 

systemctl get-default 

systemctl set-default name.target 


multi-user.target

graphical.target

emergency.target

[root@ip-10-0-1-205 system]# cat /etc/systemd/system/target.service 
[Unit] 
Description=Log when default target reached
After=cloud-final.service 

[Service] 
Type=oneshot        
RemainAfterExit=yes   
ExecStart=/bin/echo "--->  Reached default.target"
ExecStart=/usr/bin/ls -l /etc/systemd/system/default.target 

[Install]  
WantedBy=default.target 

</code>
====== Referencias ======
  * https://wiki.debian.org/UnattendedUpgrades
  * https://www.linux.com/tutorials/setting-timer-systemd-linux/
  * https://wiki.archlinux.org/index.php/Systemd-resolved
  * https://www.linuxuprising.com/2019/07/how-to-flush-dns-cache-on-linux-for.html
  *