Boot environments and /var - what should be shared/unshared?

Arthur Chance freebsd at
Tue Jan 17 15:26:21 UTC 2017

I've been using beadm boot environments for a while now, but still
haven't seen a definitive reference for which parts of /var should be
shared across boot environments and which should be per environment. Is
there such a document, or is everybody still busking it?

Some top level directories in /var seem fairly obviously in need of
sharing, others less so, and /var/db seems to be a horrible mix of stuff
that could be shared across releases and stuff that might break horribly
if shared over major revisions. (That's "might" because I have no idea
if it would in practice.)

I doubt whether any of this would matter (except for space) if one
simply rolled forward monotonically, but a roll back because of
problems, or simply switching between development environments, could
lose necessary updates if the directory hadn't been shared when it
should have been.

By June 1949, people had begun to realize that it was not so easy to
get a program right as had at one time appeared. It was on one of my
journeys between the EDSAC room and the punching equipment that the
realization came over me with full force that a good part of the
remainder of my life was going to be spent in finding errors in my own

	-- Maurice Wilkes

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