<https://forums.FreeBSD.org/threads/why-are-usr-and-var-not-in-a-boot-environment.59844/>
<http://schema.org/articleBody>
"By default the file system structure was set up as is set up so that /usr and /var are not inside a boot environment dataset and have canmount set to off. \n\n$ zfs list -H -o name,mountpoint,canmount\nNAME             MOUNTPOINT  CANMOUNT..."
<https://forums.freebsd.org/threads/why-are-usr-and-var-not-in-a-boot-environment.59844/#post-343694>