[9fans] Re: Free Plan 9 "shell" accounts?

[Jim Choate <ravage@einstein.ssz.com>]

On Sun, 18 May 2003, Dan Cross wrote:

> I don't understand what this means; doesn't the ability to start a
> process on a remote machine (``process pool'') mean you can start a
> shell on it?

Yes, if you want to look at it by the 'process tied to machine' viewpoint.
Plan 9 means much more. The concept of 'starting a shell on it' is a
rather non-distributed way of thinking about Plan 9 though. An archaic
viewpoint if you will.

Plan 9 has per process namespace, and there is really nothing that says
the namespace that a particular process is running on a particular piece
of hardware are shared. In other words the resources for a given shell
don't necessarily have to reside on that machine. In other words the
process server doesn't have to share any of its kfs resources into the
namespace of the process). The namespace doesn't even have to come from a
single machine. So, if you've got a process that has it's I/O connected to
your machine, and various namespaces transitively mounted from machines
other than the process server executing the job, can you really say the
shell is running on 'that machine'?

I'd say "No".

If you have a process server executing a job that spawns multiple
processes, Tower of Hanoi or a factorial might be a job that would do for
an example, and those processes are running on different machines; can
you say that the program runs on 'that machine'?

I'd say "No",

You're running a 'shell on a machine' and that machine hiccups, with
traditional operating systems the only result is to throw an error
condition and halt. On Plan 9 it's possible that in cases that if a
machine were to die the namespace resources (which we'll assume aren't on
the process server native) are saved and the machine that started the
process would simply re-init that job on another processer, without the
user even knowing about it. Is that running that program 'on a machine'?

I'd say "No".

There are many other examples I could think of, you will too; eventually.

Plan 9 has the unique advantage of being able to create a distributed
virtual machine. This means that where the job runs is irrelevant, and
where the resources of the namespace exist is irrelevant. Plan 9 is not so
much 'where' but 'how to impliment'.

To worry about the specific machine is a pretty archaic viewpoint that is
not really compatible with understanding what one can get out of Plan 9.

Plan 9 is a -distributed- operating system. This means that you have to
think of 'process clouds' and many resources clustered together to form a
namespace. The fact the namespace is -per process- is what takes it a step
above the 'run a shell on a machine' perspective.

You have to get past thinking of Plan 9 as a OS 'on a machine' and think
of it as a OS -across machines-. Note the plural in that, it's critical to
understanding the true power of the OS from the perspective of the user.
[1]

If you really want to have an OS on -a machine- then Plan 9 will bring you
nothing of interest. Stick with traditional operating systems. If you want
to join a -community of resources- then look into Plan 9, it will surpise
you. [2]

Hope that helps clear up your confusion...;)


[1] This goes right to the heart of one of my issues with the Plan 9
community here with regard to lack of understanding of 'user' space as
compared to looking at everything as a 'developer' space issue. Such is
the flaw of having a goal of keeping a technology limited to a niche (ie
research OS).

[2] I've mentioned this distinction many times in the past, and it amazes
me that many long time users of Plan 9 still don't 'get it'.


 --
    ____________________________________________________________________

      We are all interested in the future for that is where you and I
      are going to spend the rest of our lives.

                              Criswell, "Plan 9 from Outer Space"

      ravage@ssz.com                            jchoate@open-forge.org
      www.ssz.com                               www.open-forge.org
    --------------------------------------------------------------------