I needed to add a custom System Request (Sys Req or SysRq) to a linux kernel some time ago. While doing so, I dug deep into how it works and I thought I’d make a quick post about it. Here is a good SuperUser answer about what a SysRq is. You may also know about SysRq via REISUB. This post has three parts: how to raise a SysRq, how SysRq works (looking into kernel code), and how to add your own SysRq.
  • @[email protected]English
    9•6 months ago

    I love abusing sigusr1 and 2. Absolutely no confusion or shooting myself in the foot in 3 months when I forget what I did… No sir

  • @[email protected]
    7•6 months ago

    Huh, I never actually gave any thought to how the SysRq key works. Interesting thing to learn after all these decades, heh

    • @[email protected]English
      6•6 months ago

      https://lwn.net/Articles/296738/

      Unix internals is a great book! If you haven’t had an occasion to read it, I can’t recommend it highly enough. Similar to design of the BSD operating system, it goes into the internal data structures, but most importantly the rationale

      • @[email protected]
        2•6 months ago

        I actually don’t know nearly enough about OS design, and I’ve been toying with the idea of learning more for like 20 years now but never manage to get around to it. How’s that book hold up, considering it was (apparently?) published in '96? I’d assume a lot of the basics are still the same, and since it’s a book about the “evolution” of UNIX the historical parts will still be interesting in any case

        • @[email protected]English
          4•6 months ago

          The design of the BSD operating system is more narrative friendly, easier to read just for fun

          Unix internals keeps getting updates, but is far more technically applied. And probably easier to become outdated.

          From a philosophy perspective both books are great but if you could only read one I would recommend the BSD book. I know the Linux kernel and the BSD kernel have divergent development, but as far as posix structures are concerned they’re pretty similar

          • @[email protected]
            1•6 months ago

            The BSD book does seem interesting from a historical perspective, BSD is one of Ye Olden UN*X distros after all. Thanks for the recommendations! I think I’ll try to get my hands on a dead trees version of the BSD book.

            Oh and did you specifically mean “The Design and Implementation of the 4.4BSD Operating System”? Looks like there’s one for FreeBSD as well

            • A Basil Plant
              4•6 months ago

              Operating Systems: Three Easy Pieces by Remzi H. Arpaci-Dusseau & Andrea C. Arpaci-Dusseau (University of Wisconsin-Madison) is an excellent book and used by many universities worldwide. Extremely well written and it’s one of the only textbooks I’ve ever completed from start to end.

              It’s also completely free: https://pages.cs.wisc.edu/~remzi/OSTEP/

              • @[email protected]
                2•6 months ago

                Ooo nice, thank you for the tip.

                I wonder where I could get a physical version. Somewhere other than Amazon that is, they do have it but I’d like to avoid them if at all possible because, well, Amazon. I searched Adlibris which is a Nordic online bookstore but they didn’t have it, unfortunately.

                I’m a fan of physical books nowadays. I read e-books for a few years but I felt like I didn’t remember what I read nearly as well as I do if I read an actual paper book, and apparently there’s actually some empirical evidence for this being a wider phenomenon

                • @[email protected]English
                  3•6 months ago

                  100% I’m in the same boat.

                  I looked into various print on demand services with binding, but they always were more hassle than just printing everything at home

            • @[email protected]English
              3•6 months ago

              Yes that’s the book, though I read a older version initially.

              I haven’t read the free BSD version, I wonder if there’s a Linux version? That would be interesting too