How do you automate enabling a service on a debian filesystem without booting into it?
Solution 1:
What systemctl enable does is creates a symlink for the service you specify from the /lib/systemd/system folder to /etc/systemd/multi-user.target.wants, so you can simply do:
ln -s '/lib/systemd/system/myservice.service' '/etc/systemd/multi-user.target.wants/myservice.service'