> bectl and this manual page were derived from beadm(8).

* https://man.freebsd.org/cgi/man.cgi?query=bectl#end

> beadm(1M) originally appeared in Solaris.

* https://man.freebsd.org/cgi/man.cgi?query=beadm#end

Solaris Live Upgrade BEs worked with (mirrored) UFS root:

* https://docs.oracle.com/cd/E18752_01/html/821-1910/chapter-5...

* https://www.filibeto.org/sun/lib/solaris8-docs/_solaris8_2_0...

It allowed/s for migration from UFS to ZFS root:

* https://docs.oracle.com/cd/E23823_01/html/E23801/ggavn.html