Adding a service permanently
systemctl enable name-of-the-service
To use Samba as an example
systemctl enable smb.service systemctl enable nmb.service systemctl start smb.service systemctl start nmb.service
All that the first command does is create a symlink
ln -s ‘/usr/lib/systemd/system/smb.service’ ‘/etc/systemd/system/multi-user.target.wants/smb.service’
Thus /etc/systemd/system/multi-user.target.wants contains all services that need to start automatically.