TUHS

tuhs@tuhs.org

31 participants
6541 discussions

by Douglas McIlroy

> Doug, if you insist on applying your superb editing skills on wiki material, we will never hear from you again! Thanks, Bill, for the wise advice. If I'm putting out stuff like this you shouldn't hear from me again. Apologies for again(!) posting to the wrong mailing list. Doug

3 years, 9 months

4.3BSD-Tahoe Restoration

by Henry Bent

Hello All, I am attempting to restore 4.3BSD-Tahoe to a usable state on the VAX. It appears, based on the work that I have done already, that this is possible. Starting with stock 4.3BSD I got a source tree into /usr/tahoe and using it I replaced all of /usr/include and /sys, recompiled and replaced /bin, /lib, and /etc, recompiled a GENERIC kernel, and from there I was able to successfully reboot using the new kernel. As far as I can tell (fingers crossed!) the hardest part is over and I'm in the process of working on /usr. My question is: how was this sort of thing done in the real world? If I was a site running stock 4.3BSD, would I have received (or been able to request) updated tapes at regular intervals? The replacement process that I have been using is fairly labor intensive and on a real VAX would have been very time intensive too. Fortunately two to three years' worth of changes were not so drastic that I ever found myself in a position where the existing tools were not able to compile pieces of Tahoe that I needed to proceed, but I could easily imagine finding myself in such a place. (This was, by the way, what I ran into when attempting to upgrade from 2.9BSD to 2.10BSD, despite a fully documented contemporary upgrade procedure). -Henry

3 years, 9 months

Groups origins

by norman＠oclsc.org

I can't speak to the evolution and use of specific groups; I suspect it was all ad-hoc early on. Groups appeared surprisingly late (given how familiar they seem now): they don't show up in the manual until the Sixth Edition. Before that, chown took only two arguments (filename and owner), and permission modes had three bits fewer. I forget how it came up, but the late Lee McMahon once told me an amusing story about their origin: Ken announced that he was adding groups. Lee asked what they were for. Ken replied with a shrug and `I dunno.' Norman Wilson Toronto ON

3 years, 9 months

Groups origins

by norman＠oclsc.org

Groups appeared surprisingly late (given how familiar they seem now): they don't show up in the manual until the Sixth Edition. Mea culpa; read too hastily. The change actually came with the Fourth Edition, at the same time as several other landmark system changes: -- Time changing from a 32-bit count of 60Hz clock ticks (which ran out so quickly that its epoch kept moving) to the modern 32 bits of whole seconds, based at 1970-01-01T00:00:00 GMT (which takes much longer to run out, though the horizon is now visible). -- The modern super-block. In 4/e, the super-block began at block 0, not 1 (so bootstrapping was rather more complicated); the free list was a bitmap rather than the later list of blocks containing lists of free block numbers. -- The super-block contained a bitmap of free i-numbers too. All told, the free block and free i-node map made up a 1024-byte super-block. -- I-numbers 1-40 were device files; the root directory was i-number 41. The only file-type indication in the mode word was a single bit to denote directory. It was already clear that the lifetime of the bitmaps was running out: the BUGS section says two blocks isn't enough for the bitmaps for a 20-megabyte RP02. Norman Wilson Toronto ON

3 years, 9 months

Groups origins

by Will Senn

Hi all, I was reading a recent thread, over on the FreeBSD forums about groups that quickly devolved into a discussion on the origin of the operator group: https://forums.freebsd.org/threads/groups-overview.82303/ I thought y’all would be the best place to ask the questions that arose in me during my read of the thread. Here they are in no special order: 1. Where did operator come from and what was it intended to solve? 2. How has it evolved. 3. What’s a good place to look/ref to read about groups, generally? I liked one respondent’s answer about using find, heir, and the files themselves to learn about groups being used in a running system, paying attention to the owner, Audi, etc along the way and this is how I do it now, but this approach doesn’t account for the history and evolution. Thanks! Willu Sent from my iPhone

3 years, 9 months

Re: [TUHS] Systematic approach to command-line interfaces

by Paul Ruizendaal

Greg wrote: > I guess pipe(2) kind of started this mess, [...] Maybe I'm > going to far with thinking pipe() could/should have just been a library > call that used open(2) internally, perhaps connecting the descriptors by > opening some kind of "cloning" device in the filesystem. At times I’ve been pondering this as well. All of creat/open/pipe could have been rolled into just open(). It is not clear to me why this synthesis did not happen around the time of 7th edition; although it seems the creat/open merger happened in BSD around that time. As to pipe(), the very first implementation returned just a single fd where writes echoed to reads. It was backed by a single disk buffer, so could only hold ~500 bytes, which was probably not enough in practice. Then it was reimplemented using an anonymous file as backing store and got the modern two fd system call. The latter probably arose as a convenient hack to store the two file pointers needed. It would have been possible to implement the anonymous file solution still using a single fd, and storing the second file pointer in the inode. Maybe this felt as a worse hack at the time (the conceptual split in vnode / inode was still a decade into the future.) With a single fd, it would also have been possible to have a cloning device for pipe’s as you suggest (e.g. /dev/pipe, somewhat analogous to the implementation of /dev/stdin in 10th edition). Arguably, in total code/data size this would not have been much different from pipe(). My guess is that from a 1975 perspective, creat/open/pipe was not perceived as something that needed fixing.

3 years, 9 months

Re: [TUHS] mmap origin (was Systematic approach to command-line interfaces)

by Paul Ruizendaal

Dan wrote: > 3BSD and I think 4.1BSD had vread() and vwrite(), which looked like > regular read() and write() but accessed pages only on demand. I was a > grad student at Berkeley at the time and remember their genesis. Bill > and I were eating lunch from Top Dog on the Etcheverry Hall plaza, and > were talking about memory-mapped I/O. I remember suggesting the actual > names, perhaps as a parallel to vfork(). I had used both TENEX and > Multics, which both had page mapping. Multics' memory-mapped segments > were quite fundamental, of course. I think we were looking for something > vaguely upward compatible from the existing system calls. We did not > leap to an mmap() right away just because it would have been a more > radical shift than continuing the stream orientation of UNIX. I did not > implement any of this: it was just a brainstorming session. Thank you for reminding me of these. On a substrate with a unified buffer cache and copy-on-write, vread/vwrite would have been very close to regular read/write and maybe could have been subsumed into them, using flags to open() as the differentiator. The user discernible effect would have been the alignment requirement on the buffer argument. John Reiser wrote that he "fretted” over adding a 6 argument system call. Perhaps he was considering something like the above as the alternative, I never asked. I looked at the archives and vread/vwrite were introduced with 3BSD, present in 4BSD but marked deprecated, and absent from 4.1BSD. This short lifetime suggests that using vread and vwrite wasn’t entirely satisfactory in 1980/81 practice. Maybe the issue was that there was no good way to deallocate the buffer after use.

3 years, 9 months

Systematic approach to command-line interfaces

by Michael Siegel

Hello, I've recently started to implement a set of helper functions and procedures for parsing Unix-like command-line interfaces (i.e., POSIX + GNU-style long options, in this case) in Ada. While doing that, I learned that there is a better way to approach this problem – beyond using getopt(s) (which never really made sense to me) and having to write case statements in loops every time: Define a grammar, let a pre-built parser do the work, and have the parser provide the results to the program. Now, defining such a grammar requires a thoroughly systematic approach to the design of command-line interfaces. One problem with that is whether that grammar should allow for sub-commands. And that leads to the question of how task-specific tool sets should be designed. These seem to be a relatively new phenomenon in Unix-like systems that POSIX doesn't say anything about, as far as I can see. So, I've prepared a bit of a write-up, pondering on the pros and cons of two different ways of having task-specific tool sets (non-hierarchical command sets vs. sub-commands) that is available at https://www.msiism.org/files/doc/unix-like_command-line_interfaces.html I tend to think the sub-command approach is better. But I'm neither a UI nor a Unix expert and have no formal training in computer things. So, I thought this would be a good place to ask for comment (and get some historical perspective). This is all just my pro-hobbyist attempt to make some people's lives easier, especially mine. I mean, currently, the "Unix" command line is quite a zoo, and not in a positive sense. Also, the number of well-thought-out command-line interfaces doesn't seem to be a growing one. But I guess that could be changed by providing truly easy ways to make good interfaces. -- Michael

3 years, 9 months

Re: [TUHS] Systematic approach to command-line interfaces

by Douglas McIlroy

> one other thing that SLS breaks, for data files, is the whole Unix 'pipe' > abstraction, which is at the heart of the whole Unix tools paradigm. Multics had an IO system with an inherent notion of redirectable data streams. Pipes could have--and eventually did (circa 1987)--fit into that framework. I presume a pipe DIM (device interface manager) was not hard to build once it was proposed and accepted. Doug

3 years, 9 months

Re: [TUHS] Systematic approach to command-line interfaces

by jnc＠mercury.lcs.mit.edu

> From: Larry McVoy > If you read(2) a page and mmap()ed it and then did a write(2) to the > page, the mapped page is the same physical memory as the write()ed > page. Zero coherency issues. Now I'm confused; read() and write() semantically include a copy operation (so there are then two copies of that data chunk, and possible consistency issues between them), and the copied item is not necessarily page-sized (so you can't ensure consistency between the original+copy by mapping it in). So when one does a read(file, &buffer, 1), one gets a _copy of just that byte_ in the process' address space (and similar for write()). Yes, there's no coherency issue between the contents of an mmap()'d page, and the system's idea of what's in that page of the file, but that's a _different_ coherency issue. Or am I confused? PS: > From: "Greg A. Woods" > I now struggle with liking the the Unix concept of "everything is a > file" -- especially with respect to actual data files. Multics also got > it right to use single-level storage -- that's the right abstraction Oh, one other thing that SLS breaks, for data files, is the whole Unix 'pipe' abstraction, which is at the heart of the whole Unix tools paradigm. So no more 'cmd | wc' et al. And since SLS doesn't have the 'make a copy' semantics of pipe output, it would be hard to trivially work around it. Yes, one could build up a similar framework, but each command would have to specify an input file and an output file (no more 'standard in' and 'out'), and then the command interpreter would have to i) take command A's output file and feed it to command B, and ii) delete A's output file when the whole works was done. Yes, the user could do it manually, but compare: cmd aaa | wc and cmd aaa bbb wc bbb rm bbb If bbb is huge, one might run out of room, but with today's 'light my cigar with disk blocks' life, not a problem - but it would involve more disk traffic, as bbb would have to be written out in its entirety, not just have a mall piece kept in the disk cache as with a pipe. Noel

3 years, 9 months

Re: [TUHS] Systematic approach to command-line interfaces

by jnc＠mercury.lcs.mit.edu

> From: "Greg A. Woods" > the elegance of fork() is incredible! That's because in PDP-11 Unix, they didn't have the _room_ to create a huge mess. Try reading the exec() code in V6 or so. (I'm in a bit of a foul mood today; my laptop sorta locked up when a _single_ Edge browser window process grew to almost _2GB_ in size. Are you effing kidding me? If I had any idea what today would look like, back when I was 20 - especially the massive excrement pile that the Internet has turned into - I never would have gone into computers - cabinetwork, or something, would have been an infinitely superior career choice.) > I now struggle with liking the the Unix concept of "everything is a > file" -- especially with respect to actual data files. Multics also got > it right to use single-level storage -- that's the right abstraction Well, files a la Unix, instead of the SLS, are OK for a _lot_ of data storage - pretty much everything except less-common cases like concurrent access to a shared database, etc. Where the SLS really shines is _code_ - being able to just do a subroutine call to interact with something else has incredible bang/buck ratio - although I concede doing it all securely is hard (although they did make a lot of progress there). Noel

3 years, 9 months

Thompson trojan put into practice

by Douglas McIlroy

>> > It's part of my academic project to work on provable compiler security. >> > I tried to do it according to the "Reflections on Trusting Trust" by Ken >> > Thompson, not only to show a compiler Trojan horse but also to prove that >> > we can discover it. >> >> Of course it can be discovered if you look for it. What was impressive about >> the folks who got Thompson's compiler at PWB is that they found the horse >> even though they weren't looking for it. > I had not heard this story. Can you elaborate, please? My impression from having > read the paper (a long time ago now) is that Ken did the experiment locally only. Ken did it locally, but a vigilant person at PWB noticed there was an experimental compiler on the research machine and grabbed it. While they weren't looking for hidden stuff, they probably were trying to find what was new in the compiler. Ken may know details about what they had in the way of source and binary. Doug

3 years, 10 months

Thompson trojan put into practice

by Douglas McIlroy

> It's part of my academic project to work on provable compiler security. > I tried to do it according to the "Reflections on Trusting Trust" by Ken > Thompson, not only to show a compiler Trojan horse but also to prove that > we can discover it. Of course it can be discovered if you look for it. What was impressive about the folks who got Thompson's compiler at PWB is that they found the horse even though they weren't looking for it. Then there was the first time Jim Reeds and I turned on integrity control in IX, our multilevel-security version of Research Unix. When it reported a security violation during startup we were sure it was a bug. But no, it had snagged Tom Duff's virus in the act of replication. It surprised Tom as much as it did us, because he thought he'd eradicated it. Doug

3 years, 10 months

Re: [TUHS] Thompson trojan put into practice

by jnc＠mercury.lcs.mit.edu

https://googlethatforyou.com/?q=Tom%20Duff%20Virus Noel

3 years, 10 months

Thompson trojan put into practice

by arnold＠skeeve.com

This is FYI. No comment on whether it was a good idea or not. :-) Arnold > From: Niklas Rosencrantz <niklasro(a)gmail.com> > Date: Sun, 19 Sep 2021 17:10:24 +0200 > To: tinycc-devel(a)nongnu.org > Subject: Re: [Tinycc-devel] Can tcc compile itself with Apple M1? > > > Hello! > > For demonstration purpose I put my experiment with a compiler backdoor in a > public repository > https://github.com/montao/ddc-tinyc/blob/857d927363e9c9aaa713bb20adbe99ded7… > > It's part of my academic project to work on provable compiler security. > I tried to do it according to the "Reflections on Trusting Trust" by Ken > Thompson, not only to show a compiler Trojan horse but also to prove that > we can discover it. > What it does is inject arbitrary code to the next version of the compiler > and so on. > > Regards \n

3 years, 10 months

ATC/OSDI'21 joint keynote: It's Time for Operating Systems to Rediscover Hardware (Timothy Roscoe)

by Dan Cross

One of the things I really appreciate about participating in this community and studying Unix history (and the history of other systems) is that it gives one firm intellectual ground from which to evaluate where one is going: without understanding where one is and where one has been, it's difficult to assert that one isn't going sideways or completely backwards. Maybe either of those outcomes is appropriate at times (paradigms shift; we make mistakes; etc) but generally we want to be moving mostly forward. The danger when immersing ourselves in history, where we must consider and appreciate the set of problems that created the evolutionary paths leading to the systems we are studying, is that our thinking can become calcified in assuming that those systems continue to meet the needs of the problems of today. It is therefore always important to reevaluate our base assumptions in light of either disconfirming evidence or (in our specific case) changing environments. To that end, I found Timothy Roscoe's (ETH) joint keynote address at ATC/OSDI'21 particularly compelling. He argues that what we consider the "operating system" is only controlling a fraction of a modern computer these days, and that in many ways our models for what we consider "the computer" are outdated and incomplete, resulting in systems that are artificially constrained, insecure, and with separate components that do not consider each other and therefore frequently conflict. Further, hardware is ossifying around the need to present a system interface that can be controlled by something like Linux (used as a proxy more generally for a Unix-like operating system), simultaneously broadening the divide and making it ever more entrenched. Another theme in the presentation is that, to the limited extent the broader systems research community is actually approaching OS topics at all, it is focusing almost exclusively on Linux in lieu of new, novel systems; where non-Linux systems are featured (something like 3 accepted papers between SOSP and OSDI in the last two years out of $n$), the described systems are largely Linux-like. Here the presentation reminded me of Rob Pike's "Systems Software Research is Irrelevant" talk (slides of which are available in various places, though I know of no recording of that talk). Roscoe's challenge is that all of this should be seen as both a challenge and an opportunity for new research into operating systems specifically: what would it look like to take a holistic approach towards the hardware when architecting a new system to drive all this hardware? We have new tools that can make this tractable, so why don't we do it? Part of it is bias, but part of it is that we've lost sight of the larger picture. My own question is, have we become entrenched in the world of systems that are "good enough"? Things he does NOT mention are system interfaces to userspace software; he doesn't seem to have any quibbles with, say, the Linux system call interface, the process model, etc. He's mostly talking about taking into account the hardware. Also, in fairness, his highlighting a "small" portion of the system and saying, "that's what the OS drives!" sort of reminds me of the US voter maps that show vast tracts of largely unpopulated land colored a certain shade as having voted for a particular candidate, without normalizing for population (land doesn't vote, people do, though in the US there is a relationship between how these things impact the overall election for, say, the presidency). I'm curious about other peoples' thoughts on the talk and the overall topic? https://www.youtube.com/watch?v=36myc8wQhLo - Dan C.

3 years, 10 months

RegExp decision for meta characters: Circumflex

by Douglas McIlroy

> Maybe there existed RE notations that were simply copied ... Ed was derived from Ken's earlier qed. Qed's descendant in Multics was described in a 1969 GE document: http://www.bitsavers.org/pdf/honeywell/multics/swenson/6906.multics-condens…. Unfortunately it describes regular expressions only sketchily by example. However, alternation, symbolized by | with grouping by parentheses, was supported in qed, whereas alternation was omitted from ed. The GE document does not mention character classes; an example shows how to use alternation for the same purpose. Beginning-of-line is specified by a logical-negation symbol. In apparent contradiction, the v1 manual says the meanings of [ and ^ are the same in ed and (an unspecified version of) qed. My guess about the discrepancies is no better than yours. (I am amused by the title "condensed guide" for a manual in which each qed request gets a full page of explanation. It exemplifies how Unix split from Multics in matters of taste.) Doug

3 years, 10 months

Re: [TUHS] Unix for PDP11/20 w/o mmu or paging option

by jnc＠mercury.lcs.mit.edu

> From: Roland Huisman > I have a PDP11/20 and I would love to run an early Unix version on > it. ... But it seems that the earliest versions of Unix do not need the > extra memory. Does anyone have RK05 disk images for these early Unix > versions? Although the _kernel_ source for V1 is available: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V1 most of the rest is missing; only 'init' and 'sh' are available. So one would have to write almost _everything_ else. Some commands are available in PDP-11 assembler in later versions, and might be movable without _too_ much work - but one would have to start with the assembler itself, which is luckily in assembler. If I were trying to run 'UNIX' on an -11/20, I think the only reasonable choice would be MINI-UNIX: https://gunkies.org/wiki/MINI-UNIX It's basically V6 UNIX with all use of the PDP-11 memory management removed. The advantage of going MINI-UNIX is that almost all V6 source (applications, drivers, etc) will run on it 'as is'. It does need ~56KB of main memory. If you don't have that much on the -11/20, LSX (links in the above) would be an option; it's very similar to MINI-UNIX, but is trimmed down some, to allow its use on systems with less main memory. I'm not sure if MINI-UNIX has been run on the -11/20, but it _should_ run there; it runs on the -11/05, and the only differences between the /20 and the /05 are that the /20 does not have the RTT instruction (and I just checked, and MINI-UNIX doesn't use RTT), and SWAB doesn't clear the V condition code bit. (There are other minor differences, such as OP Rn, (Rn)+ are different on the -11/20, but that shouldn't be an issue.) Step 1 would be to get MINI-UNIX running on an -11/20 under a simulator; links in the above to get you there. Noel

3 years, 10 months

Re: [TUHS] Unix for PDP11/20 w/o mmu or paging option

by jnc＠mercury.lcs.mit.edu

> From: Clem Cole > The KS11 MMU for the 11/20 was built by CSS ... I think Noel has done > more investigation than I have. I got a very rough description of how it worked, but that was about it. > I'm not sure if the KS11 code is still there. I did not think so. No, the KS11 was long gone by later Vn. Also,I think not all of the -11/20 UNIX machines had it, just some. > The V1 work was for a PDP-7 Actually, there is a PDP-11 version prior to V2, canonically called V1. The PDP-7 version seems to be called 'PDP-7 UNIX' or 'V0'. > I'm fairly sure that the RK05, used the RK11-D controller. Normally, yes. I have the impression that one could finagle RK03's to work on the RK11-D, and vice versa for RK05's on the RK11-C, but I don't recall the details. The main difference between the RK11-C and -D (other then the implementation) was that i) the RK11-C used one line per drive for drive selection (the -D used binary encoding on 3 lines), and ii) it had the 'maintenance' capability and register (al omitted from the -D). > The difference seems to have been in drive performance. Yes, but it wasn't major. They both did 1500RPM, so since they used the same pack format, the rotational delay, transfer rate, etc were identical. The one peformance difference was in seeks; the average on the RK01 was quoted as 70 msec, and 50 msec on the RK05. > Love to see the {KT11-B prints] and if you know where you found them. They were sold on eBait along with an -11/20 that allegedly had a KT11-B. (It didn't; it was an RK11-C.) I managed to get them scanned, and they and the minimal manual are now in Bitsavers. I started working on a Tech Manual for it, but gave up with it about half-way done. > I wonder if [our V1 source] had the KS-11 stuff in it. No; I had that idea a while back, looked carefully, our V1 listings pre-date the KS11. > From: Roland Huisman > There is a KT11B paging option that makes the PDP11/20 a 18 bit > machine. Well, it allows 2^18 bytes of main memory, but the address space of the CPU is still2^16 bytes. > It looks a bit like the TC11 DECtape controller. IITC, it's two backplanes high, the TC11 is one. So more like the RK11-C... :-) > I have no idea how it compares to the later MMU units from the > software perspective. Totally different; it's real paging (with page tables stored in masin memory). The KT11-B provides up to 128 pages of 512 bytes each, in both Exec and User mode. The KT11-C, -D etc are all segmentation, with all the info stored in registers in the unit. > I wonder is there is some compatibility with the KT11-B [from the KS11] I got the impression that the KS11 was more a 'base and bounds' kind of thing. Noel

3 years, 10 months

Unix for PDP11/20 w/o mmu or paging option

by Roland

Hello Unix fanatics, I have a PDP11/20 and I would love to run an early Unix version on it. I've been working on the hardware for a while and I'm getting more and more of the pieces back online again. The configuration will be two RK05 hard disks, TU56H tape, PC11 paper tape reader/puncher and a RX01 floppy drive. Unfortunately I don't have a MMU or paging option. But it seems that the earliest versions of Unix do not need the extra memory. Does anyone have RK05 disk images for these early Unix versions? That would be a great help. Otherwise it would be great to have some input about how to create a bootable Unix pack for this machine. A bit about the hardware restoring is on the vcfed forum:https://www.vcfed.org/forum/forum/genres/dec/78961-rk05-disk-drive-ve… Booting RT11 from RK05https://youtu.be/k0tiUcRBPQATU56H tape drive back onlinehttps://youtu.be/_ZJK3QP9gRA Thanks in advance!Roland Huisman

3 years, 10 months

RegExp decision for meta characters: Circumflex

by markus schnalke

Hoi, I'm interested in the early design decisions for meta characters in REs, mainly regarding Ken's RE implementation in ed. Two questions: 1) Circumflex As far as I see, the circumflex (^) is the only meta character that has two different special meanings in REs: First being the beginning of line anchor and second inverting a character class. Why was it chosen for the second one? Why not the exclamation mark in that case? (Sure, C didn't exist by then, but the bang probably was used to negate in other languages of the time, I think.) 2) Symbol for the end of line anchor What is the reason that the beginning of line and end of line anchors are different symbols? Is there a reason why not only one symbol, say the circumflex, was chosen to represent both? I currently see no disadvantages of such a design. (Circumflexes aren't likely to end lines of text, neither.) I would appreciate if you could help me understand these design decisions better. Maybe there existed RE notations that were simply copied ... meillo

3 years, 10 months

Re: [TUHS] desiderata

by Douglas McIlroy

You can check the Computer History Museum's holdings on line. If they don't have the documents already, they would probably like them. The Living Computer Museum in Seattle had a working blit on display. If they don't already have the manual, I'm sure they would love to have one. Alas, their website says they've "suspended all operations for now", a result of the double whammy of Covid and the death of their principal angel, Paul Allen.

3 years, 10 months

desiderata

by Andrew Hume

more garage cleaning this last weekend. i came across some memorabilia from my time at Bell Labs, including a lovely article titled The Electrical Properties of Infants Infants have long been known to grow into adults. Recent experiments show they are useful in applications such as high power circuit breakers. Not to mention a lovely article from the “Medical Aspects of Human Sexuality” (July 1991) titled “Scrotum Self-Repair”. the two items are 1) “Documents for UNIX Volume 1” by Dolotta, Olson and Petrucelli (jan 1981)” 2) The complete manual for the Blit. this comes in a blue Teletype binder and includes the full manual (including man pages) and circuit diagrams. i’d prefer to have them go to some archival place, but send me a private email if you interested and we’ll see what we can do. andrew

3 years, 10 months

desiderata

by Paul Ruizendaal

I’d be interested in a scan of the Blit schematics, and it seems that a few others might be as well: https://minnie.tuhs.org/pipermail/tuhs/2019-December/thread.html#19652 https://github.com/aiju/fpga-blit (for clarity: I’m not ‘aiju') Paul > Message: 1 > Date: Wed, 8 Sep 2021 01:29:13 -0700 > From: Andrew Hume <andrew(a)humeweb.com> > To: The Eunuchs Hysterical Society <tuhs(a)tuhs.org> > Subject: [TUHS] desiderata > Message-ID: <34E984D3-AD92-402D-9A9C-E84B6362DF77(a)humeweb.com> > Content-Type: text/plain; charset=utf-8 > > more garage cleaning this last weekend. [...] > 2) The complete manual for the Blit. this comes in a blue Teletype binder and includes > the full manual (including man pages) and circuit diagrams. > > i’d prefer to have them go to some archival place, but send me a private email > if you interested and we’ll see what we can do. > > andrew

3 years, 10 months

Is it time to resurrect the original dsw (delete with switches)?

by Jon Steinhart

I recently upgraded my machines to fc34. I just did a stock uncomplicated installation using the defaults and it failed miserably. Fc34 uses btrfs as the default filesystem so I thought that I'd give it a try. I was especially interested in the automatic checksumming because the majority of my storage is large media files and I worry about bit rot in seldom used files. I have been keeping a separate database of file hashes and in theory btrfs would make that automatic and transparent. I have 32T of disk on my system, so it took a long time to convert everything over. A few weeks after I did this I went to unload my camera and couldn't because the filesystem that holds my photos was mounted read-only. WTF? I didn't do that. After a bit of poking around I discovered that btrfs SILENTLY remounted the filesystem because it had errors. Sure, it put something in a log file, but I don't spend all day surfing logs for things that shouldn't be going wrong. Maybe my expectation that filesystems just work is antiquated. This was on a brand new 16T drive, so I didn't think that it was worth the month that it would take to run the badblocks program which doesn't really scale to modern disk sizes. Besides, SMART said that it was fine. Although it's been discredited by some, I'm still a believer in "stop and fsck" policing of disk drives. Unmounted the filesystem and ran fsck to discover that btrfs had to do its own thing. No idea why; I guess some think that incompatibility is a good thing. Ran "btrfs check" which reported errors in the filesystem but was otherwise useless BECAUSE IT DIDN'T FIX ANYTHING. What good is knowing that the filesystem has errors if you can't fix them? Near the top of the manual page it says: Warning Do not use --repair unless you are advised to do so by a developer or an experienced user, and then only after having accepted that no fsck successfully repair all types of filesystem corruption. Eg. some other software or hardware bugs can fatally damage a volume. Whoa! I'm sure that operators are standing by, call 1-800-FIX-BTRFS. Really? Is a ploy by the developers to form a support business? Later on, the manual page says: DANGEROUS OPTIONS --repair enable the repair mode and attempt to fix problems where possible Note there’s a warning and 10 second delay when this option is run without --force to give users a chance to think twice before running repair, the warnings in documentation have shown to be insufficient Since when is it dangerous to repair a filesystem? That's a new one to me. Having no option other than not being able to use the disk, I ran btrfs check with the --repair option. It crashed. Lesson so far is that trusting my data to an unreliable unrepairable filesystem is not a good idea. Since this was one of my media disks I just rebuilt it using ext4. Last week I was working away and tried to write out a file to discover that /home and /root had become read-only. Charming. Tried rebooting, but couldn't since btrfs filesystems aren't checked and repaired. Plugged in a flash drive with a live version, managed to successfully run --repair, and rebooted. Lasted about 15 minutes before flipping back to read only with the same error. Time to suck it up and revert. Started a clean reinstall. Got stuck because it crashed during disk setup with anaconda giving me a completely useless big python stack trace. Eventually figured out that it was unable to delete the btrfs filesystem that had errors so it just crashed instead. Wiped it using dd; nice that some reliable tools still survive. Finished the installation and am back up and running. Any of the rest of you have any experiences with btrfs? I'm sure that it works fine at large companies that can afford a team of disk babysitters. What benefits does btrfs provide that other filesystem formats such as ext4 and ZFS don't? Is it just a continuation of the "we have to do everything ourselves and under no circumstances use anything that came from the BSD world" mentality? So what's the future for filesystem repair? Does it look like the past? Is Ken's original need for dsw going to rise from the dead? In my limited experience btrfs is a BiTteR FileSystem to swallow. Or, as Saturday Night Live might put it: And now, linux, starring the not ready for prime time filesystem. Seems like something that's been under development for around 15 years should be in better shape. Jon

3 years, 10 months

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