Multics vs Unix
by Lawrence D'Oliveiro
I’ve been reading the introductory “Multics Concepts and Utilization”
book
<http://bitsavers.trailing-edge.com/pdf/honeywell/multics/F01_multicsIntro...>
over at Bitsavers. Multics (the “MULTiplexed Information and Computing
Service”) was, for its time, an extremely ambitious operating system
project. It was first introduced in 1965, in the form of a series of
papers at the AFIPS Fall Joint Computer Conference of that year
<http://www.computer.org/csdl/proceedings/afips/1965/5066/00/index.html>.
Of course, it took far too long (7 years) to reach production quality.
In that time, a small group of researchers at AT&T Bell Labs grew tired
of waiting, and decided to create their own, less ambitious system,
which they called “UNIX” as a tongue-in-cheek homage to “Multics”. And
the rest, as they say, is history.
But, nevertheless, Multics remained an influential system. There are
even some present-day fans of it gathered at <http://multicians.org/>.
Apparently they have got the OS booting on an emulator of the original
GE 645 hardware. Though it was mostly written in a high-level language
(PL/I), Multics was never a portable OS; to support its advanced
virtual-memory and security features, it required special processor
hardware support which was not common in those days.
Even today, Multics has some features which can be considered
innovative and uncommon. It may be true that, for example, SELinux can
match all of its security capabilities and more. But some aspects of
its file-protection system seem, to me, to make sharing of data between
users a bit easier than your typical Linux/POSIX-type system.
For a start, there seems to be no concept of file “ownership” as such.
Or even of POSIX-style file protection modes (read/write/execute for
owner/group/world). Instead, all file and directory access is
controlled via access-control lists (ACLs). Directories have a
permission called “modify”, which effectively gives a matching entity
(user, group, process) owner-type rights over that directory; except
that more than one entity can have that permission at once. Thus, a
group of users working on a common project can all be given this
“modify” access to a shared directory for that project, allowing them
all to put data there, read it back again, control access to it, delete
it etc on a completely equal basis. Contrast this with POSIX/Linux,
where every file has to have exactly one owner; even if they create
that file in a shared directory, it still gives the creating user a
special status over that file, that others with write access to the
containing directory do not have.
(Multics also offers a separate “append” permission, that allows the
possessor to create an item in a directory, without having the ability
to remove an item once it’s there.)
One radical idea introduced in Unix was its profligate use of multiple
processes. Every new command you executed (except for the ones built
into the shell) required the creation of a new process, often several
processes. Other OSes tended to look askance at this; it seemed somehow
wasteful, perhaps even sinful to spawn so many processes so readily and
discard them so casually. The more conventional approach was to create
a single process at user login, and execute nearly all commands within
the context of that. There were special commands for explicitly
creating additional processes (e.g. for background command execution),
but such process creation did not simply happen as a matter of course.
Gradually, over time, the limitations of the single-process approach
became too much to ignore, and the versatility of the Unix approach won
over (nearly) everybody. Multics, however, is of the old school. More
than that, the process even preserves global state, including static
storage, in-between runs of programs, and this applies across different
programs, not just reruns of the same one. For example, in FORTRAN,
there is the concept of a “common block”. If you run two different
programs that both refer to the same common block, then the second one
will see values left in the block by the first one. To completely
reinitialize everything, you need to invoke the “new_proc” command,
which effectively deletes your process and gives you a fresh one.
One common irritation I find on POSIX/Linux systems is the convention
that every directory has to have an entry called “.”, pointing to
itself, and one called “..”, pointing to its parent. This way these
names can be used in relative pathnames to reach any point in the
directory hierarchy. But surely it is unnecessary to have explicit
entries for these names cluttering up every directory; why not just
build their recognition as a special case into the pathname-parsing
logic in the kernel, once and for all? That way, directory-traversal
routines in user programs don’t have to be specially coded to look for,
and skip these entries, every single time.
Multics doesn’t seem to have this problem. An absolute pathname begins
with “>” (which is the separator for pathname components, equivalent to
POSIX “/”), while a relative pathname doesn’t. Furthermore, a relative
pathname can begin with one or more “<” characters, indicating the
corresponding number of steps up from the current working directory.
Unlike POSIX “..”, you can’t have “<” characters in the middle of the
pathname, which is probably not a big loss.
It is interesting to see other features which are nearly, but not
quite, the same as, corresponding features in Unix. For example, there
is a search path for executables, to save you typing the entire
pathname to run the program. However, this does not seem as flexible as
the $PATH environment-variable convention observed by Unix/POSIX
shells. In particular, it does not seem possible to remove the current
directory from the search path, which we now know can be a security
risk.
Another one is the concept of “active functions” and “active strings”.
These allow you to perform substitutions of dynamically-computed values
into a command line. However, they are not as general as the Unix/POSIX
concept of “command substitution”, where an entire shell command can
supply its output to be interpolated into another command. Instead of
having a completely separate vocabulary of “active functions” which can
only be used for such substitutions, Unix/POSIX unifies this with the
standard set of commands, any of which can be used in this way.
There are other features of Multics that others more familiar with it
might want to see mentioned (the single-level store concept, where
“everything is a memory segment”, versus Unix “everything is a file”?
I/O redirection based on “switches”—symbolic references to files,
versus Unix integer “file descriptors”?). But then, this long-winded
essay would become even longer-winded :). So if you are interested in
this particular piece of computing history, feel free to follow up the
links above.
In summary, Multics is very much a museum piece, not something you
would want to use today for regular work—not in its original form. But
I think there are still one or two ideas there that we could usefully
copy and adapt to a present-day OS, particularly a versatile one like
Linux.
4 years, 6 months
Official, Customized Raspberry Pi Versions Coming Soon
by Peter Reutemann
"The immensely popular Raspberry Pi will soon be offered in customized
versions, through an exclusive arrangement between Raspberry Pi
Trading and Element14. According to the companies' announcement,
Element14 will provide design and manufacturing services to OEM
customers to create 'bespoke designs' based upon the Raspberry Pi
technology platform. That's weird U.K. English for saying that
contracts for creating customized Raspberry Pi SBCs will entail
substantial NRE fees and 3,000 to 5,000 unit orders, depending on the
nature of the customization. The tweaked Pi's are likely to have
revised board layouts, additional or alternative functions,
interfaces, connectors, and memory configurations, and more. A handful
of unsanctioned Raspberry Pi knock-offs have already appeared over the
past couple of years, including various Orange Pi and Banana Pi
flavors, which certainly didn't involve any 'bespeaking.' More info is
at Element14's CustomPi page."
-- source: http://hardware.slashdot.org/story/15/10/27/1211234
Cheers, Peter
--
Peter Reutemann
Dept. of Computer Science
University of Waikato, NZ
+64 (7) 858-5174
http://www.cms.waikato.ac.nz/~fracpete/
http://www.data-mining.co.nz/
4 years, 7 months
Intel Develops Linux 'Software GPU' That's ~29-51x Faster
by Peter Reutemann
"Intel is open-sourcing their work on creating a high-performance
graphics software rasterizer that originally was developed for
scientific visualizations. Intel is planning to integrate this new
OpenSWR project with Mesa to deploy it on the Linux desktop as a
faster software rasterizer than what's currently available (LLVMpipe).
OpenSWR should be ideal for cases where there isn't a discrete GPU
available or the drivers fail to function. This software rasterizer
implements OpenGL 3.2 on Intel/AMD CPUs supporting AVX(2) (Sandy
Bridge / Bulldozer and newer) while being 29~51x faster than LLVMpipe
and the code is MIT licensed. The code prior to being integrated in
Mesa is offered on GitHub."
-- source: http://news.slashdot.org/story/15/10/20/2213215
Cheers, Peter
--
Peter Reutemann
Dept. of Computer Science
University of Waikato, NZ
+64 (7) 858-5174
http://www.cms.waikato.ac.nz/~fracpete/
http://www.data-mining.co.nz/
4 years, 7 months
Microsoft Publishes OpenSSH For Windows Code
by Peter Reutemann
"Microsoft has published early source code for its OpenSSH-for-Windows
port for developers to pick apart and improve. In a blog post on
Monday, Steve Lee – the PowerShell team's principal software engineer
manager – said Redmond has finished early work on a Windows port of
OpenSSH 7.1, built in a joint-effort with NoMachine. Their rough
roadmap from here: 1) Leverage Windows crypto APIs instead of
OpenSSL/LibreSSL and run as Windows Service. 2) Address POSIX
compatibility concerns. 3) Stabilize the code and address reported
issues. 4) Production quality release."
-- source: http://news.slashdot.org/story/15/10/20/1925226
Cheers, Peter
--
Peter Reutemann
Dept. of Computer Science
University of Waikato, NZ
+64 (7) 858-5174
http://www.cms.waikato.ac.nz/~fracpete/
http://www.data-mining.co.nz/
4 years, 7 months
AGM?
by Peter Reutemann
Hi everyone
I'm proposing this year's AGM to take place on November 23rd, usual
place at uni, MS4.G.02.
Agenda:
- President's Report
- Treasurer's Report
- Election of 2016 Committee
- Consumption of pizza
Any comments or things to add to the agenda?
Cheers, Peter
--
Peter Reutemann
Dept. of Computer Science
University of Waikato, NZ
+64 (7) 858-5174
http://www.cms.waikato.ac.nz/~fracpete/
http://www.data-mining.co.nz/
4 years, 7 months
Fwd: [NZLUG] Linux Lite banned from TradeMe
by Peter Reutemann
Apologies, if you've received this already.
Cheers, Peter
---------- Forwarded message ----------
From: philip
Date: Tue, Oct 20, 2015 at 12:09 AM
Subject: Re: [NZLUG] Linux Lite banned from TradeMe
To: nzlug(a)lists.nzoss.org.nz
On Wed, 2015-10-14 at 08:32 +1300, Volker Kuhlmann wrote:
> In Europe there is a good chance that it would be recognised that a
> business like trademe is practically a monopoly, and anti-competitive
> behaviour does not go down well with authorities with company
> policies
> not carrying much weight. E.g. google is permanently under
> investigation
> for something.
>
> In New Zealand trademe is essentially a monopoly, and they are
> hindering
> legitimate local businesses. (Isn't Johnny keen on local business, or
> is
> that only when overseas companies grease him up first?) You could try
> complaining on those grounds, but the commerce commission is not
> often
> useful.
>
> Until things change use a better trading platform than tardme, and
> don't
> waste your time discussing anything with them, their back pockets are
> far too fat to need to pay attention to you.
>
> Volker
>From Jerry.
Got a call from TradeMe today and they are happy to allow linux
distributions to be listed again. This of course goes hand in hand
with a pending policy wording review/change.
Phil.
_______________________________________________
NZLUG mailing list
NZLUG(a)lists.nzoss.org.nz
http://lists.nzoss.org.nz/mailman/listinfo/nzlug
--
Peter Reutemann
Dept. of Computer Science
University of Waikato, NZ
+64 (7) 858-5174
http://www.cms.waikato.ac.nz/~fracpete/
http://www.data-mining.co.nz/
4 years, 7 months
