On Thu, Nov 22, 2018 at 06:21:01PM +0000, Roger Leigh wrote:
>
> It would be possible to share the ports tree on a FreeBSD system, since it's
> mostly self-contained, so long as it's read-only (it has unshared data in
> /var including the package database, so can't be read-write). But this is
> not reasonable with dpkg, by design. The packages are putting data in / and
> /usr, as well as /var. You cannot just export /usr without getting into an
> inconsistent and incoherent mess.

The only way I can see for BSD to have a package system with a separate
and shared /usr is
(1) to absolutely forbid any dependencies from anything on /usr from
anything in the root file system,
(2) No package to have files in both /usr and the root file system
(3) Split the package data base so that packages in /usr are tracked in
/usr and that packages in the root file system are tracked in the root
file system.
(4) Make sure that you don't need anything in /usr to to packaage
maintenance on the root file system.

Then upgrading the root file system can be done independently of
upgrading /usr.

I suspect that this may be too severe a set of restrictions for BSD to
tolerate, and as you mention, for Debian that ship has sailed long ago.

-- hendrik