September 2015 - wlug - list.wlug.org.nz

Multics vs Unix
by Lawrence D'Oliveiro 12 Nov '15

12 Nov '15

I’ve been reading the introductory “Multics Concepts and Utilization” book <http://bitsavers.trailing-edge.com/pdf/honeywell/multics/F01_multicsIntroCo…> 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.

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Ditch Linux For Windows 10 On Your Raspberry Pi With Microsoft's IoT Kit
by Peter Reutemann 29 Sep '15

29 Sep '15

'Partnering with Adafruit, Microsoft has announced the Windows IoT Core Starter Kit. The $75 kit comes comes with an SD card preloaded with Windows 10 IoT. According to the Raspberry Pi blog: "The pack is available with a Pi 2 for people who are are new to Raspberry Pi or who'd like a dedicated device for their projects, or without one for those who'll be using a Pi they already own. The box contains an SD card with Windows 10 Core and a case, power supply, wifi module and Ethernet cable for your Pi; a breadboard, jumper wires and components including LEDs, potentiometers and switches; and sensors for light, colour, temperature and pressure. There's everything you need to start building."' -- source: http://hardware.slashdot.org/story/15/09/28/1949211 Looks like it wasn't vaporware after all. But I'm not gonna replace the Linux on my RPis. Especially not since I can have a full-blown Linux OS on it rather than some stripped down Windows version. :-) 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/

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The Life And Death Of A Laptop Battery
by Lawrence D'Oliveiro 27 Sep '15

27 Sep '15

<http://people.skolelinux.org/pere/blog/The_life_and_death_of_a_laptop_batte…> “Why are my laptop batteries always dying in a year or two, while the batteries of space probes and satellites keep working year after year. If we are to believe Battery University, the cause is me charging the battery whenever I have a chance, and the fix is to not charge the Lithium-ion batteries to 100% all the time, but to stay below 90% of full charge most of the time.” ... “Is there a good and generic way with Linux to tell the battery to stop charging at 80%, unless requested to charge to 100% once in preparation for a longer trip?”

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LibreSSL Gets Rid Of SSL
by Lawrence D'Oliveiro 25 Sep '15

25 Sep '15

LibreSSL (a fork of OpenSSL created after the security scandals over the latter) has now got rid of all versions of the protocol called “SSL” (“Secure Sockets Layer”) <http://phoronix.com/scan.php?page=news_item&px=LibreSSL-2.3-Released>. The official name of current versions of the protocol used for secure HTTP connections (among other things) is “TLS” (“Transport Layer Security”).

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Why Ad Blockers Could Be A Good Thing
by Lawrence D'Oliveiro 25 Sep '15

25 Sep '15

A posting <https://freedom-to-tinker.com/blog/golden/has-apple-doomed-ads-on-the-web-w…> on “Freedom To Tinker”, which is part of my regular reading, talks about the potential implications of more widespread use of ad-blocker plugins in Web browsers. Not quite triggering an “arms race” of ad-blocker-blockers, and so on: If the use of these plugins becomes ubiquitous, only one thing would have to change – the publishers would have to insert the line of code in some way on the server side, and the ad would just look as though it came with the rest of the page. At that point, the browser plugin is useless. What would be the knock-on effects of this? The ad companies no longer have any way to track users as they move around the web. Absent some way on the ad companies’ part to implement a cross-site evercookie (which would be considered unethical and would quickly be blocked by browser authors if discovered), the ad companies will no longer have a way to connect users on one site to users on another. The ads you’d see on a given site could be based solely on the interactions you’ve had with that one site – which would be a boon to privacy. So rather than becoming worse, the ads would actually take on a less creepy form.

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PatchSee Ethernet Cables
by Lawrence D'Oliveiro 23 Sep '15

23 Sep '15

The unique selling point is the special LED tool that, when plugged in to one end, lights up the other end. So you can tell where your cables run without having to colour-code or label them. But is it worth the cost? <https://www.youtube.com/watch?v=PETJpmxiyOY>

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Copying from a pdf, removing EOL and spaces
by Roderick Aldridge 23 Sep '15

23 Sep '15

Hi everyone I want to copy an extract from a .pdf file. When I select some text to copy and paste it puts each word followed by two spaces on a separate line. Do you know a better way to extract some text from a .pdf? Alternatively what is an easy way to remove the space and EOL to reformat the text in a readable format? I am sure there are several, but I would appreciate a really easy one. TIA Roderick

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WLUG meeting next Monday
by Peter Reutemann 22 Sep '15

22 Sep '15

Hi everyone We have a WLUG meeting coming up next Monday: "Hieu Trinh will talk about how to use a Raspberry Pi for sorting fruit." More details: http://www.meetup.com/WaikatoLinuxUsersGroup/events/223612685/ According to Hieu, his presentation will be a short one, so if you have something else from the world of Linux/Open Source, then please let me know and I'll add it. 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/

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Keith Packard On X11
by Lawrence D'Oliveiro 19 Sep '15

19 Sep '15

A half-hour talk from “Mr X11” himself, Keith Packard <http://phoronix.com/scan.php?page=news_item&px=KeithP-Sustaining-X>. Notable points: * The original MIT X Consortium was dominated by the proprietary UNIX workstation vendors, who were all trying to lock in their own customers into their own ways of doing things. These “UNIX Wars” led to the whole workstation market imploding, letting Microsoft take over with Windows NT. * XFree86 was, in the beginning, like a “rebel alliance”, trying to bring X11 to commodity PC hardware. They were shunned for many years by the X Consortium. Of course this changed after all the UNIX vendors went under. Later, the revitalized X Consortium became a home for the X11 developer community which left the inflexibilities of the XFree86 corporate organization behind. * Over the last decade, the X server has become less and less of an operating system in its own right. Hardware-specific graphics drivers have been moved into the Linux kernel, leaving the X userland code to focus on the hardware-independent implementation layers. * Programs written to work with X11 nearly thirty years ago still work today. Even with all the reorganization and rewrites, X11 still remains fully backward-compatible. Which is more than Microsoft Windows can manage. * Keith made it clear he prefers GPL-style (copyleft/sharealike) licences to MIT/BSD style ones. Net contributors of code tend to prefer the former, while net consumers of code (those who don’t want to give back to the community) tend to favour the latter. In other words, freeloaders.

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Microsoft Linux
by Lawrence D'Oliveiro 18 Sep '15

18 Sep '15

Microsoft’s “Azure Cloud Switch” is a “a cross-platform modular operating system for data center networking built on Linux”. <http://www.theregister.co.uk/2015/09/18/microsoft_has_developed_its_own_lin…>

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