So you want to roll your own distro?

This was supposed to be posted a week ago. So "today" in the text was actually about 10 days ago, give or take. Since then, all of us in the Fatdog team have migrated and are now eating our own dog food. But it doesn't change the essence of the post.




Today has been an exciting day for Fatdog64. For me at least, Fatdog64 800 has now entered the "eat own dogfood" phase. I have migrated my build machine to Fatdog64 800. In another word, Fatdog64 800 is now self-hosting. This is the the phase that we have always done since the early days of Fatdog - we use it ourselves first, internally, for actual day-to-day purposes, to make sure we weed out the most obvious and most annoying bugs. We suffer these bugs so you don't have to. Of course, some would still slip out; and that's why more testers means lesser bugs; and fortunately, there are now four of us in the Fatdog team, and we have helps from other pre-release testers too. We'll stay in this phase for as long as it is needed to polish it up.

It has been a long and winding road to get to this. For those people who aren't involved, they probably aren't aware of the effort that goes to a project like this. Some people says, a distro is just a collection of stuff, right, and you don't write that stuff - you just package them. What's so hard about it? To that, I could have replied "well if you think it's so easy then why don't you do it yourself" - but instead, I'd choose to explain what happens behind the scenes. Along the way, I can explain some key decisions that makes Fatdog what it is today.

Let's start.

Okay, so a distro is just a collection of "packages". That's correct, in general, but as in everything, the devil is in the details. First and foremost: where do these "packages" come from? You've two choices here: build your own, or use someone else's. If you use someone else's packages, then your distro effectively is a "derivative", even if you call it that way or not.

We don't want Fatdog to become a derivative, at least, not Fatdog64 (I have another stagnant project called Fatdog-Like which *is* a Fatdog derived from a parent distro - but it's not going anywhere at the moment due to lack of time and interest), and the reason is not because we simply don't like to be called as "derivative".

The reason is deeper: it's about management and control. Using someone else's packages means you don't have full-control over the decisions that goes into the making of that packages - from the simple things like "which version is available", to more complex things like what is the optional libraries linked to it (this determines overall size and functionality); where is the configuration data stored; what is the build-time configuration parameters, etc.

Okay, so we don't want to be derivative.

We want to strike it on our own. What's next?

Well, what's next is we need to build our own packages then. Before we build our own packages, there are a few things that we need to sort out. Firstly, the compiler. A compiler is special, because, a part of the compiler is always attached to the final program (=the run-time). If you use an existing compiler, whoever made that compiler already made a decision for you (at the very least - the version of the compiler), which will get carried on to all of your packages --- even if all those other packages are built by you. So, no, we cannot use an existing compiler, can we? We have to build our own compiler ourselves (more popularly known as the "toolchain" because a compiler is just one of the components that you need to build a program from source - there are also the linker, the libc, and others. I'd gloss over the problems that a correct functioning toolchain requires very specific combination of correct versions of its components).

Well, how to build a compiler then? It just another package, right? No. The compiler we build is special - the program it will build is not meant to run in the machine that the compiler is run; instead, that program is supposed to run in our brand new distro, which currently exists in the gleam of our eyes only. Building a compiler like this is what you call as "toolchain bootstrapping" (aka chicken-and-egg problem); and the compiler you produce this way is a cross-compiler. I'm not going to explain terms like this here - I will assume that if you're interested enough to read this, you have enough motivation to google for terms that you don't understand.

Ok, you've googled it - and as it turns out there are tons of tools to build a cross-compiler! There is "buildroot" from busybox team, and there is "crosstool-ng", and there are many others! Problem solved, no? Eh, the answer is still no. Most of these tools produce a cross-compiler all right, and they do it very beautifully. Only one problem - most of these tools are NOT capable of building a cross-compiler which can build a native compiler (that is, a compiler that will eventually run in the target system). Which means that we will forever be dependent on them to build packages for us. That is not good. We need a cross-compiler that can eventually build a native compiler so that we can use native compiler to build the rest of the packages.

Actually, any good cross-compiler can be used to build a native compiler. You just need to know how. And it's not easy. Even the process of building a corss-compiler itself is almost black magic - that's the reason why there are numerous tools that help you to do it. Fortunately, there is one project that aims to decipher all these gobbledy-gook into something that you can understand. That project guides you, step by step, through the process of making a cross-compiler, and how to build a native compiler. That project is the Linux From Scratch project (LFS). It is not a tool, it will not build a compiler for you, but it is a book, a guide, that will instruct you exactly how to do it, step by step, while explaining why certain things must be done in a certain way.

Fatdog64, since version 700, is based on LFS.

Once we've got the compiler, then we need to build the packages using it. The LFS is extremely helpful, it will guide you to build minimal set of packages that will enable you to build a minimal system that can boot to a console, in a bash shell. And that's when LFS ends. You end up with about 50 packages gives or take including the toolchain. But at least your target distro is now alive, with a native compiler in it that you configure it yourself (the LFS instructions are just a "guide", and you're welcome to vary it for your own needs once you know exactly what you're doing - so what you build is effectively your own compiler, not LFS'), that you can use for building the rest of the packages.

Ok. The rest of the packages. Where would they come from? Let say, ummm, you want to build a web browser. Firefox sounds good. Okay. How do build a Firefox web browser from scratch? Go to Mozilla website, spend a couple of hours digging in and out ... oh, I need to build a "desktop" first before I can even begin to build Firefox. And even with the desktop, there are these "libraries" that I need to have in order to build it. I also need tools - and certain tools must be very specific version (e.g. autoconf must be version 2.13 exactly and nothing older or newer). But how to build a "desktop"? A desktop is system of many components - quickly broken down to window managers, panel manager, file manager, system settings ... and then the basic graphics subsystem, of which you can choose between X desktop and Wayland as of today. X is more popular, so you decide to explore it - then you have X libraries, XCB libraries, input drivers, video drivers, and servers. And all those things needs supporting libraries before you can even build them - they need gzip libraries, XML libraries, etc down the rabbit hole we go. So how do we even start?

Well, within the umbrella of the LFS project (but run by different people), there is this project called BLFS - Beyond LFS. Its purpose is, you guess, to provide details about building packages which aren't part of LFS. For every package that it describes, it tells you: (a) where to get the source files, (b) what are the dependencies for that package (=what packages must be built and installed before you can build this one), (c) the commands to build it properly. BLFS is much larger in scope than LFS but even it does not cover everything. It will get going, though, as it says at the top of the book: "This book follows on from the Linux From Scratch book. It introduces and guides the reader through additions to the system including networking, graphical interfaces, sound support, and printer and scanner support." So it does get you going in the right direction. It even tells you how to build Firefox, and what exactly you need to build before you can do it (you're still going down the rabbit hole, but at least somebody holding a ladder so you can always climb back up).

Fatdog64, since version 700, uses parts of BLFS as the source of some of its packages.

But there is on major problem here. Both LFS and BLFS shows and guides you to build an operating system for yourself. It's like building a one-person distro. You cannot easily copy the resulting system into a distribution media, not without tainting it with your own personal information and machine-specific configurations. (the keyword is here "easily" - with enough effort surely you can do it - obviously WE are doing it for Fatdog64). No matter, you say. I'm just building a distro for one, for myself. So all is good, right? No. With the LFS (and BLFS), it is easy to add new packages into the system, but it is rather difficult to get rid of an installed package. All packages are installed to the target system as they're built, without any records of which files goes where; so it's difficult or even impossible to remove without breaking the system.

The ability to track installed packages, and thus remove them (in addition to installing one) is collectively known as "package management". Any decent distro has one. Package Management is not included in LFS/BLFS because it "gets in the way" of explaining how things works - which its main objective. It only goes as far as saying that a package management IS needed, and there are many possible ways to do it. Look it at LFS Chapter 6.3 if you're interested.

So, you need a package management. A package management has two parts - the "creator" that enables you to build a "bundled" package, and the package management proper that can install/uninstall/view installation of your "bundled" packages. The "creator" part must be used in conjunction with your build process; because it needs to keep track of the files produced by your build, collect all those files, and bundle them up in package.

Easy, you say. Just google it up, and you will find "porg". Or you can even use existing package management system. After all, many distros share the same system; it is unnecessary to invent a new package management system (yes, proper and correct package management system is HARD). Why don't I just take Debian's package management system (dpkg), or RedHat's one (rpm), or Slackware's one (tarball), or many other myriads ways that have been suggested?

Well yes we can.

From version 700 onwards, Fatdog64 uses Slackware's package management system ("pkgtools"), fortified with slapt-get from jaos.org, modified for our use.

"pkgtools" is choosen because it's easy to create its packages, it's easy to host and publish the packages, it has tools that can extend it to support remote package management and dependency tracking (slapt-get), and the packages are basically tarballs that - in the worst case - you can always "untar" to install without needing special tools. No other package management tools comes even close.

Okay, once you choose a system then you need to hook it up with your build system so that the "creation" part of the package works, as I said above. I'd gloss over this fact and assume you can already do it. Let's move on.

Hang on, you said. We already bootstrap a system, have enough guides to build everything up to a web-browers and multimedia player (vlc), can install and uninstall packages, so what's next?

Ok, what's next? How about package updates. Software is being updated. What's new yesterday is old today and obsolete tomorrow. You need to keep building packages. These updates are not in the LFS/BLFS books, because they're published semi-annually. In between, if there is any updates, you must roll on your own sleeves and figure out how to do it yourself (it shouldn't be too hard now if you can follow BLFS guides this far). Ok, so updating is easy. *IF* you do this everyday. But if you don't - well, do you still remember how you built the previous version of the package? Do you remember the build-time flags you specified 3 months ago? Welcome to the club - you're not the only one.

You first response to the question is - I will make sure I keep a note of all the configurations, library dependencies, etc etc when I build the packages. Or, perhaps, even simpler, I will just stick to LFS/BLFS update cycles, so no need to write my own notes. I'm not that desperate to live in the bleeding edge anyway.

OK. If you decide to stick to BLFS, I have nothing else to say, but if you said you'd want to keep notes, then allow me to go a bit further. Rather than making a note, which you need to "translate" into your action when build the package, why don't you write them in the "scripting" language? So next time you can tell the computer to "read" your script for you and do the build too. Sound nice and too good to be true? It isn't, and it is actually the perfect solution. With a "build script", not only you know remember how to build a package, you also save time and (with exceptions) you have accomplished a "repeatable build" - which means that you can repeat the build many times and get a consistent result.

After a while, not only you want to record the build process, you may as well keep a record the location of the source package, perform the download, identify that the downloaded source package is correct (using checksum) before actually building it. You may even want to keep information about library dependencies there.

And if you're like me, after a while you will start to notice two things. (1) About half the content of the script is identical. It's always wget (or curl), then md5sum (or sha512sum), then extract, then apply patches, and build, then activate package-management-creator hooks, and then install and make package. The (2) point that you notice is that with the proliferation of build scripts, you need to manage them, and have the computer build them in the correct order (instead of you manually sorting out the build order).

Congratulations. You have recognised the need for a distro build infrastructure (shortened as "build system"). What we have been calling as "build scripts" are usually known as "build recipes"; once we take out the "scripting" out of them and move them into shared build infrastructure. Some people consider build infrastructure part of package management (because they can be very closely coupled) but they're actually separate systems.

Most major distros have their own distro build system, for example, Debian has "debuild", RedHat has "rpm", Arch Linux has "PKGBUILD", Slackware has SlackBuilds (for 3rd party packages only), etc. Each of these build systems have their own way to specify the "recipes" - some highly structured like debuild and rpm, some are rather loose like Arch PKGBUILD. You can use them, you don't have to re-invent the wheel. Of course, you can also come with your own if you wish.

Fatdog64 uses its own home-brewed build system conveniently named "Fatdog pkgbuild" (no relation to Arch Linux build system of the same name).

Simply because we found that none of the existing build systems have the features that we need (mainly simple enough to be understood and written but flexible enough to build complex packages). Fatdog64 build's system is more loosely defined (similar in spirit to Arch Linux) as opposed to the highly structured build system like rpm or debuild. It has proven itself enough to be able to build a customised firefox and libreoffice in a single-pass.

Ok. You have now gone a long way from building packages by hand manually and installing directly (./configure && make && make install). You are now the proud owner of a build system that can (re-)build the whole system in one command call. With some clever scripting you can even make install these packages into a chroot, and create an ISO file ready for distribution. Your job is done, you're now official an distro builder! Congratulations!

But wait. I don't have to go through all these processes. There are already "distro build system" out there, complete with fully populated recipes for every software under the sun and the moon! There is one called T2-SDE, for example. "buildroot" from busybox can actually build an entire distro's worth of packages by itself, all nicely packaged into tarballs too. Or you can start with debootstrap from Debian and start working your way up - Debian publishes every single one of their recipes, from every version ever released. And wait, they're not the only one. You have openwrt, you have ptx-dist, you have open-embedded, you have gentoo, you have yocto, and many others that I've forgotten. (You can even include android in the list - yes AOSP is a distro build system). Why not just use them?

Well, why not. If you like them, then by all means use them. Just remember this: every single build system released out there, is released to serve a purpose. Investigate that purpose is, and see if it is aligned with what you want to do. Also, all those build system (and recipes) are maintained by others, and they follow different objectives and schedules than you. This may or may not be important for you.

Fatdog64 500 and Fatdog64 600 were originally build using T2-SDE. T2-SDE was the build system used to build packages for earlier Puppy Linux builds too (version 4.x - the Dingo series). The reason why we drop T2-SDE is again because of management and control. Having T2-SDE is great because we don't have to bother about recipes and upgrades anymore, someone else is taking care of that for us. But it also means that version updates etc depends on the maintainer. Adding new packages (new recipes) depends on the maintainer. Etc. We can of course update the recipes on our own (once we understand the format), but then it means we to start keeping track of these recipes ourselves. The more we have to change, the more we have to maintain ourselves. Some packages' changes only affect themselves, some affect others (e.g. library updates more often than not introduces incompatibilities, which means that all packages that uses this updated library will now also have to be updated themselves, causing an avalanche of recipe updates), so before you know it, you basically have "forked" your build system from the original maintainer. This is even more true if you find "bugs" in the build system which the maintainer won't fix for whatever reasons, and you ends up fixing it yourself. Congratulations, you're now maintaining a distro build system that you don't fully understand and was created by someone else for objectives that may or may not align with yours.

So, okay, you decide to start a build system on your own. At least, this is your system, you know it upside down and you can debug it with your eyes closed. You write this exactly to your own needs - nothing less, nothing more. Then you start to populate this system with recipes.

You can initially source the recipes from BLFS, and then you can start writing your own, or even use recipes from Debian, RedHat, OpenSuse, Arch, or wherever else you can find them. Lots of time spent in experimenting to make sure that the right combination of packages and libraries all work well together and produce the best outcome that you want (in terms of feature, performance/speed and size). If you use only one source (e.g. BLFS) this is not important - the tuning is already done for you. But if you mix recipes from many sources, they have have assumptions that is no longer true when you apply them in your system (e.g. assuming a library is installed when it is not, etc); you will find out when you get a build failure (or worse: a run-time failure) so you have to tinker and adjust. Imagine, then: at the very near end of the building, you've got a compilation failure. You've got to troubleshoot this, figure out why it fails, what's the probably fix, and try to build again. And it fails again. So you investigate again, and try fixing up again. And then rebuild. This cycle continues until you finally get a working recipe that builds correctly, or until you give up. But if this is a very important library which is used by many other packages, "giving up" is not an option (unless you want to give up building the distro altogether). Now imagine this trial-and-error cycles, for a large package like libreoffice which can easily take a few hours to build. A single, big, and yet important recalcitrant package can easily delay progress by days.

Of course you're not always on your own. I don't want to make it sound more difficult than what it is. stackoverflow.com is here to help. You can also ask linuxquestions.org or similar places, and if you're lucky, you're not the first one to encounter the problem, so google is your friend. But once a while you do get unlucky and the problem you need to solve is truly yours only.

Anyway, let's move on. After spending countless, sleepless and thankless hours building your distro, finally come to the period of testing (which is where we are at, now, for Fatdog64 800). This is where the proof meets the pudding - see if those recipes get us a good cake. And then only way to know whether the food is good is to eat it, so the mantra "eat your own dog food". After an eternity of testing, you finally come to the conclusion that you're going to have to publish this distro or it will be obsolete before it is released.

Congratulations! It's release time! (We're not there yet for Fatdog64 800 - but we have been through this many times with earlier versions - you can refer to all our previous releases in Fatdog History site). To be on the safe side, you don't immediately claim for the Final release (aka "Gold" release), but you call is a "test" release and call it using Greek alphabet to make it cooler (alpha release, beta release etc - but normally it stops at beta because "gamma" sounds very bad for your health - after all gamma radiation is what turns Bruce Banner into Hulk, remember?).

And then the silence is deafening. Nobody (in their right mind) will touch a test release within a 10-feet pole (unless they're dedicated testers, and thankfully, over the years we have managed to attract some of them - so the silence is not usually deafening for Fatdog release. But others don't fare as well). Oh well, after a few weeks of test release, we think we've squashed all the bugs we can find (and willing to, and able to fix). It is now finally the time for the Grand release, aka Final, the Gold.

Drum rolls please!

As soon as we made the final announcement, comes the news that the kernel we included in the final release has a severe CVE problem (privilege escalation). Or that the openssl version that we use has CVE reports about remote exploits. Or the install scripts corrupts the user's hard disk. Or there is yet one more bug that we missed earlier in the test release. This is not including people whose only sorry life's existence depends on trolling people (Again: this paragraph, like the the rest of this post, is illustration only. We don't usually get it so bad - in fact we've evaded the worst and fared quite well in our releases so far). So what can you do? Depending on the severity of the problem, you can: (a) ignore it, or (b) fix it and issue a minor version update, or (c) pull out the release completely until you can work the problem out. Oh, and just ignore the trolls.

But the life of a distro doesn't end here, unless you're fine doing just doing one-trick pony. Software gets updated, bugs got found, more CVEs got reported, so you've got to update your releases too. Sounds familiar isn't it. But you've got your build system! You've got your recipes! So no problem, right?

You update your recipes, (re-)build them in your build system, spending more countless hours fixing breakage caused by the updated recipes, etc. And then you issue an update - this can be package update, or build a new ISO and issue a minor revision release, etc. Generally it's quite manageable unless you're trying to "live in the edge" and wants to always be on the latest version on everything (note of warning: bleeding edge is not wise. Newer versions comes with fixes but also comes with new bugs too).

But updates doesn't last forever. There are components of the system that you can't update. "libc" for example. It is part of the toolchain. It is part of every software in your distro. To update it, firstly you need build a new toolchain. Secondly it means either (1) you need to rebuild all the packages with the new toolchain - this is the proper way of doing it, or (2) just drop the old libc and put in a new one - this is the improper way of doing it and has great risks of introducing unpredictable crashes. In other words, unreliablity.

So, eventually, you have to do the proper way (1) above. This is what in Fatdog64 parlance is what we call as "updating the base". It is what comprises a major release, in Fatdogs. All minor version updates have the same base - same compiler, same libc. For example 600, 601, 602, 610, 611, 620, 621, 630, 631 releases all use the same toolchain and same toolchain libraries. When we move to 700 series, we have a new toolchain - "the base". Fatdog64 800 is one such major release - we're moving from gcc 4.8.3 and glibc 2.19 in 710 series to gcc 7.3.0 and glibc 2.27 in Fatdog64 800.

Naturally, when we have to rebuild all of the packages, we may as well update them as we go. So, not only we're updating the toolchain, but we're updating every single one of the packages that we have build previously. The fact that we've sourced some of our packages from LFS and BLFS doesn't help - we still have to review and update (all of) our recipes; and we still have to build it. Again, we while we borrow and use recipes from many sources (including writing our own as needed), the environment and the combination of packages that we build and use is completely unique to us, so basically we have to repeat the countless, sleepless, and thankless hours of tuning the updated recipes (=all of them) again and again, waiting for a package to build just to see the compiler spits out cryptic error messages because (a) new gcc now uses new c++ standards which considers previously accepted language construct as an error unless you know certain magic incantations that will bring its understanding of "ancient wisdom" back - but sometimes even such incantation doesn't work as advertised and you need to patch it (b) openssl has a new ABI that makes all other openssl-using packages to fail and must be patched (c) poppler changes some of the method signature for no good reason and causes undecipherable error messages to some, but not all, packages that uses it, (=me spending hours convincing scribus to build) or (d) Qt goes yet again for another re-factoring spree that breaks all except the latest of the software; whose fix is easy just insert #include <QStyle> but of course you must know that this is the solution (and on which file you need to insert it) (e) original website goes dead, need to confirm if this is the latest/final version of the software or if anyone picks up the debris and start a fork (f) change of source code hosting - we have been in the business long enough to see migrations sourceforge to googlecode to github and now to gitlab with pieces left along the way - so we need to confirm which hosting contains the latest (g) and many other fine gotchas in similar vein.

So. Having a build system makes maintenance oh so much easier. But when it comes to major updates like this, there is always serious work involved behind it. It is almost like re-starting everything from scratch again (because it actually is). Fatdog64 is relatively small, we have only about 1500 packages (not including the contributed packages), but even this takes considerable amount of time to maintain and especially to perform major update. To give you an idea, Fatdog64 800 work was seriously started not long after LFS 8.2 is released, in March (our based is based on LFS 8.2 - we started ours major cycle update around late May). At the time of this writing, LFS 8.3 has been been released, and we're still in internal testing phase.

Oh, one more thing. Even though we use LFS as the base, it is not purely LFS. LFS is not multi-lib aware. As early as Fatdog64 700 (which uses LFS 7.5), we've tried to build it in away that is 64-bit clean - that is, all 64-bit libs goes for "lib64". This we can tack on 32-bit compatibily libraries in "lib", using libraries we took from other 32-bit distros (mainly from Puppy Linux variants). In Fatdog64 710 we upped the ante and build a full multilib version - which means that both the build system now builds both 64-bit and 32-bit packages directly. One of the key parameter of success is the ability to build wine - which requires both 64-bit and 32-bit infrastucture to work. LFS is not multilib aware, does not support multilib, and does not plan to do it, because, doing so, will just obscure the points (same reason why package management is not included). And I fully agree.

To that end, in 710 our base was actually shifted to CLFS 3.0.0. CLFS - Cross-LFS is an extension of CLFS that builds Linux distros for target platform which is not identical to the original host platform (LFS requires that host and target platform to be the same - if you start on 32-bit system, you end up with 32-bit distro), and in addition, it supports multilib too. But in term of the age of the packages, CLFS 3.0.0 was very close to LFS 7.5 so that they're virtually identical (same glibc versions, gcc only differs in revision numbers, etc) so aside from the build infrastructure changes, CLFS-based Fatdog64 710 is identical to LFS-based Fatdog64 700.

The point is, we don't just take and use LFS/BLFS recipes (or any other 3rd party recipes) verbatim. We need to convert them into multilib-compatible recipes, we need to create the 32-bit version of the recipes, and lastly we need to test them that they build, and that they work. There is serious amount of work going behind the scenes that people rarely see.

And lastly - all those packages you build, you need to publish it somewhere, right? Debian users uses apt-get to install new packages. RedHat/Centos uses "yum". Arch uses pacman. What will your distro use? Where will you publish the packages? How to maintain and ensure that this "software repository" / "package repository" ("repo" for short) of yours is up-to-date? If you have a non-traditional delivery system like Fatdog64, whose entire operating system files are kept in the "initrd", how can you deliver updates? These are important non-rhetorical questions which I leave as an exercise for the reader.

So, do you still want to start and maintain your own "personal" distro?

Sure, writing and programming a software as complex as libreoffice is difficult and hard, especially always playing catch up to moving goalpost of "MS compatibility". Sure, writing and programming a web browser as complex as Chromium is hard - especially playing catch up to the "Living Standard". But building and maintaining a distro with over 1000 independent moving components created by different groups of people who may or may not be aware of each other is not exactly a walk in the park either.

It's fun, though. If you just have the right mindset. Which is why I'm still here, and will still be here for foreseeable future, ceteris paribus.


Posted on 9 Oct 2018, 02:13 - Categories: Fatdog64 Linux
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Comments:

Posted on 17 Nov 2018, 03:03 by step
"Nice article"
Nice article. It does give a sense of the hard work, learning and fun that involved in rolling a "private" distro. Thanks.
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