[TUHS] environments/universes (was: Unix v6 problem with /tmp)

[Sven Mascheck]

On Wed, Jul 27, 2016 at 04:57:47PM -0400, Clem Cole wrote:
> I created Conditionally Dependant Symlinks (CDSL) which I think only showed
> up in Masscomp's RTU, Stellix and Tru64.   The were not only late binding,
> but added the concept of a user settable context.   Very handy when trying
> to create a "single system image" from multiple system.

How did you implement it?

> Also, around the same time that Dennis added symlinks, Apollo's Aegis (aka
> Domain) guys came up with a cool idea where you can run application code
> from a link - extensible types.    I remember talking to Dennis and Ken
> about them at a SOSP IIRC, and toyed with putting them into one of the
> Locus UNIX Kernels.   We proposed it for HP-UX and Tru64, but never got
> funded to try it, although I think / believe others did some where else.

I just wonder if and how the following are related to the above two.

Sequent Dynix "universes" (idea picked up by Siemens Sinix) puts several
targets in one symlink. Example:

  ln -c ucb=.bin att=/usr/att/bin   /bin

and the actual resolving (and usage of different default PATHs)
is controlled by an environment variable, as far as I know
(s.a. http://www.in-ulm.de/~mascheck/various/universes/)

HP-UX 9 "context dependent files" (as early alternative to NFS) make use of
the set uid bit on directories and work like this,

  # mkdir /etc/inittab
  # chmod +H /etc/inittab
  # touch /etc/inittab+/node1 /etc/inittab+/default

By accessing /etc/inittab, node1 will see the file node1, other systems
will see default (s.a. http://www.in-ulm.de/~mascheck/various/permissions/)


> [...]
> You are right the BSD 4.2 made the world know about them but like
> a number of things in BSD (such as networking) it was in some
> cases a (better) integration of ideas others had played with before.

F.i. #! also got widely known in 4.2BSD but was suggested by DMR before 8th ed.

-Sven