>ESM is available through an Ubuntu Advantage for Infrastructure subscription for physical servers, virtual machines, containers and desktops, and is free for personal use.
Note that if you click through "personal use" means "up to 3 machines" and obviously doesn't apply to infrastructure. RHEL has free "personal use" subscriptions too, except they apply to up to 16 machines.
And also:
> Initially, free subscription is available for Ubuntu 14.04 LTS only.
>ESM is available through an Ubuntu Advantage for Infrastructure subscription for physical servers, virtual machines, containers and desktops, and is free for personal use.
https://ubuntu.com/security/esm
Note that if you click through "personal use" means "up to 3 machines" and obviously doesn't apply to infrastructure. RHEL has free "personal use" subscriptions too, except they apply to up to 16 machines.
And also:
> Initially, free subscription is available for Ubuntu 14.04 LTS only.