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17 August 2020

Ian Jackson: Doctrinal obstructiveness in Free Software

Any software system has underlying design principles, and any software project has process rules. But I seem to be seeing more often, a pathological pattern where abstract and shakily-grounded broad principles, and even contrived and sophistic objections, are used to block sensible changes. Today I will go through an example in detail, before ending with a plea: PostgreSQL query planner, WITH [MATERIALIZED] optimisation fence Background history PostgreSQL has a sophisticated query planner which usually gets the right answer. For good reasons, the pgsql project has resisted providing lots of knobs to control query planning. But there are a few ways to influence the query planner, for when the programmer knows more than the planner. One of these is the use of a WITH common table expression. In pgsql versions prior to 12, the planner would first make a plan for the WITH clause; and then, it would make a plan for the second half, counting the WITH clause's likely output as a given. So WITH acts as an "optimisation fence". This was documented in the manual - not entirely clearly, but a careful reading of the docs reveals this behaviour:
The WITH query will generally be evaluated as written, without suppression of rows that the parent query might discard afterwards.
Users (authors of applications which use PostgreSQL) have been using this technique for a long time. New behaviour in PostgreSQL 12 In PostgreSQL 12 upstream were able to make the query planner more sophisticated. In particular, it is now often capable of looking "into" the WITH common table expression. Much of the time this will make things better and faster. But if WITH was being used for its side-effect as an optimisation fence, this change will break things: queries that ran very quickly in earlier versions might now run very slowly. Helpfully, pgsql 12 still has a way to specify an optimisation fence: specifying WITH ... AS MATERIALIZED in the query. So far so good. Upgrade path for existing users of WITH fence But what about the upgrade path for existing users of the WITH fence behaviour? Such users will have to update their queries to add AS MATERIALIZED. This is a small change. Having to update a query like this is part of routine software maintenance and not in itself very objectionable. However, this change cannnot be made in advance because pgsql versions prior to 12 will reject the new syntax. So the users are in a bit of a bind. The old query syntax can be unuseably slow with the new database and the new syntax is rejected by the old database. Upgrading both the database and the application, in lockstep, is a flag day upgrade, which every good sysadmin will want to avoid. A solution to this problem Colin Watson proposed a very simple solution: make the earlier PostgreSQL versions accept the new MATERIALIZED syntax. This is correct since the new syntax specifies precisely the actual behaviour of the old databases. It has no deleterious effect on any users of older pgsql versions. It makes it possible to add the new syntax to the application, before doing the database upgrade, decoupling the two upgrades. Colin Watson even provided an implementation of this proposal. The solution is rejected by upstream Unfortunately upstream did not accept this idea. You can read the whole thread yourself if you like. But in summary, the objections were (italic indicates literal quotes): I find these extremely unconvincing, even taken together. Many of them are very unattractive things to hear one's upstream saying. At best they are knee-jerk and inflexible application of very general principles. The authors of these objections seem to have lost sight of the fact that these principles have a purpose. When these kind of software principles work against their purposes, they should be revised, or exceptions made. At worst, it looks like a collective effort to find reasons - any reasons, no matter how bad - not to make this change. The OFFSET 0 trick One of the responses in the thread mentions OFFSET 0. As part of writing the queries in the Xen Project CI system, and preparing for our system upgrade, I had carefully read the relevant pgsql documentation. This OFFSET 0 trick was new to me. But, now that I know the answer, it is easy to provide the right search terms and find, for example, this answer on stackmumble. Apparently adding a no-op OFFSET 0 to the subquery defeats the pgsql 12 query planner's ability to see into the subquery.
I think OFFSET 0 is the better approach since it's more obviously a hack showing that something weird is going on, and it's unlikely we'll ever change the optimiser behaviour around OFFSET 0 ... wheras hopefully CTEs will become inlineable at some point CTEs became inlineable by default in PostgreSQL 12.
So in fact there is a syntax for an optimisation fence that is accepted by both earlier and later PostgreSQL versions. It's even recommended by pgsql devs. It's just not documented, and is described by pgsql developers as a "hack". Astonishingly, the fact that it is a "hack" is given as a reason to use it! Well, I have therefore deployed this "hack". No doubt it will stay in our codebase indefinitely. Please don't be like that! I could come up with a lot more examples of other projects that have exhibited similar arrogance. It is becoming a plague! But every example is contentious, and I don't really feel I need to annoy a dozen separate Free Software communities. So I won't make a laundry list of obstructiveness. If you are an upstream software developer, or a distributor of software to users (eg, a distro maintainer), you have a lot of practical power. In theory it is Free Software so your users could just change it themselves. But for a user or downstream, carrying a patch is often an unsustainable amount of work and risk. Most of us have patches we would love to be running, but which we haven't even written because simply running a nonstandard build is too difficult, no matter how technically excellent our delta. As an upstream, it is very easy to get into a mindset of defending your code's existing behaviour, and to turn your project's guidelines into inflexible rules. Constant exposure to users who make silly mistakes, and rudely ask for absurd changes, can lead to core project members feeling embattled. But there is no need for an upstream to feel embattled! You have the vast majority of the power over the software, and over your project communication fora. Use that power consciously, for good. I can't say that arrogance will hurt you in the short term. Users of software with obstructive upstreams do not have many good immediate options. But we do have longer-term choices: we can choose which software to use, and we can choose whether to try to help improve the software we use. After reading Colin's experience, I am less likely to try to help improve the experience of other PostgreSQL users by contributing upstream. It doesn't seem like there would be any point. Indeed, instead of helping the PostgreSQL community I am now using them as an example of bad practice. I'm only half sorry about that.

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Arnaud Rebillout: Modify Vim syntax files for your taste

In this short how-to, we'll see how to make small modifications to a Vim syntax file, in order to change how a particular file format is highlighted. We'll go for a simple use-case: modify the Markdown syntax file, so that H1 and H2 headings (titles and subtitles, if you prefer) are displayed in bold. Of course, this won't be exactly as easy as expected, but no worries, we'll succeed in the end. The calling Let's start with a screenshot: how Vim displays Markdown files for me, someone who use the GNOME terminal with the Solarized light theme. Vim - Markdown file with original highlighting I'm mostly happy with that, except for one or two little details. I'd like to have the titles displayed in bold, for example, so that they're easier to spot when I skim through a Markdown file. It seems like a simple thing to ask, so I hope there can be a simple solution. The first steps Let's learn the basics. In Vim world, the rules to highlight files formats are defined in the directory /usr/share/vim/vim82/syntax (I bet you'll have to adjust this path depending on the version of Vim that is installed on your system). And so, for the Markdown file format, the rules are defined in the file /usr/share/vim/vim82/syntax/markdown.vim. The first thing we could do is to have a look at this file, try to make sense of it, and maybe start to make some modifications. But wait a moment. You should know that modifying a system file is not a great idea. First because your changes will be lost as soon as an update kicks in and the package manager replaces this file by a new version. Second, because you will quickly forget what files you modified, and what were your modifications, and if you do that too much, you might experience what is called "maintenance headache" in the long run. So instead, maybe you DO NOT modify this file, and instead you copy it in your personal Vim folder, more precisely in ~/.vim/syntax. Create this directory if it does not exist:
mkdir -p ~/.vim/syntax
cp /usr/share/vim/vim82/syntax/markdown.vim ~/.vim/syntax
The file in your personal folder takes precedence over the system file of the same name in /usr/share/vim/vim82/syntax/, it is a replacement for the existing syntax files. And so from now on, Vim uses the file ~/.vim/syntax/markdown.vim, and this is where we can make our modifications. (And by the way, this is explained in the Vim faq-24.12) And so, it's already nice to know all of that, but wait, there's even better. There's is another location of interest, and it is ~/.vim/after/syntax. You can drop syntax files in this directory, and these files are treated as additions to the existing syntax. So if you only want to make slight modifications, that's the way to go. (And by the way, this is explained in the Vim faq-24.11) So let's forget about a syntax replacement in ~/.vim/syntax/markdown.vim, and instead let's go for some syntax additions in ~/.vim/after/syntax/markdown.vim.
mkdir -p ~/.vim/after/syntax
touch ~/.vim/after/syntax/markdown.vim
Now, let's answer the initial question: how do we modify the highlighting rules for Markdown files, so that the titles are displayed in bold? First, we have to understand where are the rules that define the highlighting for titles. Here there are, from the file /usr/share/vim/vim82/syntax/markdown.vim:
hi def link markdownH1 htmlH1
hi def link markdownH2 htmlH2
hi def link markdownH3 htmlH3
...
You should know that H1 means Heading 1, and so on, and so we want to make H1 and H2 bold. What we can see here is that the headings in the Markdown files are highlighted like the headings in HTML files, and this is obviously defined in the file /usr/share/vim/vim82/syntax/html.vim. So let's have a look into this file:
hi def link htmlH1 Title
hi def link htmlH2 htmlH1
hi def link htmlH3 htmlH2
...
Let's keep digging a bit. Where is Title defined? For those using the default color scheme like me, this is defined straight in the Vim source code, in the file src/highlight.c.
CENT("Title term=bold ctermfg=DarkMagenta",
     "Title term=bold ctermfg=DarkMagenta gui=bold guifg=Magenta"),
And for those using custom color schemes, it might be defined in a file under /usr/share/vim/vim82/colors/. Alright, so how do we override that? We can just define this kind of rules in our syntax additions file at ~/.vim/after/syntax/markdown.vim:
hi link markdownH1 markdownHxBold
hi link markdownH2 markdownHxBold
hi markdownHxBold  term=bold ctermfg=DarkMagenta gui=bold guifg=Magenta cterm=bold
As you can see, the only addition we made, compared to what's defined in src/highlight.c, is cterm=bold. And that's already enough to achieve the initial goal, make the titles (ie. H1 and H2) bold. The result can be seen in the following screenshot: Vim - Markdown file with modified highlighting The rabbit hole So we could stop right here, and life would be easy and good. However, with this solution there's still something that is not perfect. We use the color DarkMagenta as defined in the default color scheme. What I didn't mention however, is that this is applicable for a light background. If you have a dark background though, dark magenta won't be easy to read. Actually, if you look a bit more into src/highlight.c, you will see that the default color scheme comes in two variants, one for a light background, and one for a dark background. And so the definition for Title for a dark background is as follow:
CENT("Title term=bold ctermfg=LightMagenta",
     "Title term=bold ctermfg=LightMagenta gui=bold guifg=Magenta"),
Hmmm, so how do we do that in our syntax file? How can we support both light and dark background, so that the color is right in both cases? After a bit of research, and after looking at other syntax files, it seems that the solution is to check for the value of the background option, and so our syntax file becomes:
hi link markdownH1 markdownHxBold
hi link markdownH2 markdownHxBold
if &background == "light"
  hi markdownHxBold term=bold ctermfg=DarkMagenta gui=bold guifg=Magenta cterm=bold
else
  hi markdownHxBold term=bold ctermfg=LightMagenta gui=bold guifg=Magenta cterm=bold
endif
In case you wonder, in Vim script you prefix Vim options with &, and so you get the value of the background option by writing &background. You can learn this kind of things in the Vim scripting cheatsheet. And so, it's easy enough, except for one thing: it doesn't work. The headings always show up in DarkMagenta, even for a dark background. This is why I called this paragraph "the rabbit hole", by the way. So... Well after trying a few things, I noticed that in order to make it work, I would have to reload the syntax files with :syntax on. At this point, the most likely explanation is that the background option is not set yet when the syntax files are loaded at startup, hence it needs to be reloaded manually afterward. And after muuuuuuch research, I found out that it's actually possible to set a hook for when an option is modified. Meaning, it's possible to execute a function when the background option is modified. Quite cool actually. And so, there it goes in my ~/.vimrc:
" Reload syntax when the background changes 
autocmd OptionSet background if exists("g:syntax_on")   syntax on   endif
For humans, this line reads as:
  1. when the background option is modified -- autocmd OptionSet background
  2. check if the syntax is on -- if exists("g:syntax_on")
  3. if that's the case, reload it -- syntax on
With that in place, my Markdown syntax overrides work for both dark and light background. Champagne! The happy end To finish, let me share my actual additions to the markdown.vim syntax. It makes H1 and H2 bold, along with their delimiters, and it also colors the inline code and the code blocks.
" H1 and H2 headings -> bold
hi link markdownH1 markdownHxBold
hi link markdownH2 markdownHxBold
" Heading delimiters (eg '#') and rules (eg '----', '====') -> bold
hi link markdownHeadingDelimiter markdownHxBold
hi link markdownRule markdownHxBold
" Code blocks and inline code -> highlighted
hi link markdownCode htmlH1
" The following test requires this addition to your vimrc:
" autocmd OptionSet background if exists("g:syntax_on")   syntax on   endif
if &background == "light"
  hi markdownHxBold term=bold ctermfg=DarkMagenta gui=bold guifg=Magenta cterm=bold
else
  hi markdownHxBold term=bold ctermfg=LightMagenta gui=bold guifg=Magenta cterm=bold
endif
And here's how it looks like with a light background: Vim - Markdown file with final highlighting (light) And a dark background: Vim - Markdown file with final highlighting (dark) That's all, that's very little changes compared to the highlighting from the original syntax file, and now that we understand how it's supposed to be done, it's not much effort to achieve it. It's just that finding the workaround to make it work for both light and dark background took forever, and leaves the usual, unanswered question: bug or feature?

16 August 2020

Bits from Debian: Debian turns 27!

Today is Debian's 27th anniversary. We recently wrote about some ideas to celebrate the DebianDay, you can join the party or organise something yourselves :-) Today is also an opportunity for you to start or resume your contributions to Debian. For example, you can scratch your creative itch and suggest a wallpaper to be part of the artwork for the next release, have a look at the DebConf20 schedule and register to participate online (August 23rd to 29th, 2020), or put a Debian live image in a DVD or USB and give it to some person near you, who still didn't discover Debian. Our favorite operating system is the result of all the work we do together. Thanks to everybody who has contributed in these 27 years, and happy birthday Debian!

Andrej Shadura: Useful FFmpeg commands for video editing

As a response to Antonio Terceiro s blog post, I m publishing some FFmpeg commands I ve been using recently. Embedding subtitles Sometimes you have a video with subtitles in multiple languages and you don t want to clutter the directory with a lot of similarly-named files or maybe you want to be able to easily transfer the video and subtitles at once. In this case, it may be useful to embed to subtitles directly into the video container file.
ffmpeg -i video.mp4 -i video.eng.srt -map 0:v -map 0:a -c copy -map 1 \
        -c:s:0 mov_text -metadata:s:s:0 language="eng" video-out.mp4
This commands recodes the subtitle file into a format appropriate for the MP4 container and embeds it with a metadata element telling the video player what language it is in. You can add multiple subtitles at once, or you can also transcode the audio to AAC while doing so (I found that a lot of Android devices can t play Ogg Vorbis streams):
ffmpeg -i video.mp4 -i video.deu.srt -i video.eng.srt -map 0:v -map 0:a \
        -c:v copy -c:a aac -map 1 -c:s:0 mov_text -metadata:s:s:0 language="deu" \
                           -map 2 -c:s:1 mov_text -metadata:s:s:1 language="eng" video-out.mp4
Hard subtitles Sometimes you need to play the video with subtitles on devices not supporting them. In that case, it may be useful to hardcode the subtitles directly into the video stream:
ffmpeg -i video.mp4 -vf subtitles=video.eng.srt video-out.mp4
Unfortunately, if you also want to apply more transformations to the video, it starts getting tricky, the -vf option is no longer enough:
ffmpeg -i video.mp4 -i overlay.jpg -filter:a "volume=10" \
        -filter_complex '[0:v][1:v]overlay[outv];[outv]subtitles=video.eng.srt' \
                        video-out.mp4
This command adds an overlay to the video stream (in my case I overlaid a full frame over the original video offering some explanations), increases the volume ten times and adds hard subtitles. P.S. You can see the practical application of the above in this video with a head of one of the electoral commissions in Belarus forcing the members of the staff to manipulate the voting results. I transcribed the video in both Russian and English and encoded the English subtitles into the video.

Gunnar Wolf: DebConf20 talk recorded

Following Antonio Terceiro s post on tips for using ffmpeg for editing video, I will also share a bit of my experience producing my video for my session in DebConf20. I recorded my talk today. As Terceiro mentioned, even though I m used to speaking in front of my webcam (i.e. for my classes and some smaller conferences I ve worked on during the COVID lockdown), it does feel a bit weird to present a live talk to nobody :- OK, one step back. Why are we doing this? Because our hardworking friends of the DebConf20 video team recommended so. In order to minimize connecitvity issues from the variety of speakers throughout the world, we were requested to pre-record the exposition part of our talks, send them to the video team (deadline: today 2020-08-16, in case you still owe yours!), and make sure to be present at the end of the talk for the Q&A session. Of course, for a 45 minute talk, I prepared a 30 minute presentation, saving time for said Q&A session. Anyway, I used the excellent OBS studiolive video mixing/editing program (of course, Debian packages are available. This allowed me to set up several predefined views (combinations and layouts of the presentation, webcam, and maybe some other sources) and professionally and elegantly switch between them on the fly. I am still a newbie with OBS, but I surely see it becoming a part of my day to day streaming. Of course, my setup still was obvious (me looking right every now and then to see or control OBS, as I work on a dual-monitor setup ) Anyway, the experience was very good, much smoother and faster than what I usually have to do when editing video. But just as I was finishing thanking the (future) audience and closing the recording I had to tell the camera, oh, fuck! The button labeled Start Recording Had not been pressed. So, did I just lose 30 minutes of my life, plus a half-decent delivered talk? No, fortunately not. I had previously been playing with OBS, and configured some things. The button I did press was Start Streaming . So, my talk (swearing included, of course) was dutifully streamed over to my YouTube channel. It seems up to five people got a sneak preview as to what will my DebConf participation be (of course, I ve de-listed the video). I pulled it with the always-handy youtube-dl, edited out my curses using kdenlive, and pushed it to the DebConf video server. Oh, make sure you follow the advice for recording presentations. It has all the relevant advice, the settings you should use, and much more welcome information if you are new to this. So Next week, DebConf20! Be there or be square!

15 August 2020

Jelmer Vernooij: Debian Janitor: 8,200 landed changes landed so far

The Debian Janitor is an automated system that commits fixes for (minor) issues in Debian packages that can be fixed by software. It gradually started proposing merges in early December. The first set of changes sent out ran lintian-brush on sid packages maintained in Git. This post is part of a series about the progress of the Janitor. The bot has been submitting merge requests for about seven months now. The rollout has happened gradually across the Debian archive, and the bot is now enabled for all packages maintained on Salsa, GitLab, GitHub and Launchpad. There are currently over 1,000 open merge requests, and close to 3,400 merge requests have been merged so far. Direct pushes are enabled for a number of large Debian teams, with about 5,000 direct pushes to date. That covers about 11,000 lintian tags of varying severities (about 75 different varieties) fixed across Debian. Janitor pushes over time Janitor merges over time

For more information about the Janitor's lintian-fixes efforts, see the landing page

14 August 2020

Russell Coker: Jitsi on Debian

I ve just setup an instance of the Jitsi video-conference software for my local LUG. Here is an overview of how to set it up on Debian. Firstly create a new virtual machine to run it. Jitsi is complex and has lots of inter-dependencies. It s packages want to help you by dragging in other packages and configuring them. This is great if you have a blank slate to start with, but if you already have one component installed and running then it can break things. It wants to configure the Prosody Jabber server and a web server and my first attempt at an install failed when it tried to reconfigure the running instances of Prosody and Apache. Here s the upstream install docs [1]. They cover everything fairly well, but I ll document the configuration I wanted (basic public server with password required to create a meeting). Basic Installation The first thing to do is to get a short DNS name like j.example.com. People will type that every time they connect and will thank you for making it short. Using Certbot for certificates is best. It seems that you need them for j.example.com and auth.j.example.com.
apt install curl certbot
/usr/bin/letsencrypt certonly --standalone -d j.example.com,auth.j.example.com -m you@example.com
curl https://download.jitsi.org/jitsi-key.gpg.key   gpg --dearmor > /etc/apt/jitsi-keyring.gpg
echo "deb [signed-by=/etc/apt/jitsi-keyring.gpg] https://download.jitsi.org stable/" > /etc/apt/sources.list.d/jitsi-stable.list
apt-get update
apt-get -y install jitsi-meet
When apt installs jitsi-meet and it s dependencies you get asked many questions for configuring things. Most of it works well. If you get the nginx certificate wrong or don t have the full chain then phone clients will abort connections for no apparent reason, it seems that you need to edit /etc/nginx/sites-enabled/j.example.com.conf to use the following ssl configuration:
ssl_certificate /etc/letsencrypt/live/j.example.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/j.example.com/privkey.pem;
Then you have to edit /etc/prosody/conf.d/j.example.com.cfg.lua to use the following ssl configuration:
key = "/etc/letsencrypt/live/j.example.com/privkey.pem";
certificate = "/etc/letsencrypt/live/j.example.com/fullchain.pem";
It seems that you need to have an /etc/hosts entry with the public IP address of your server and the names j.example.com j auth.j.example.com . Jitsi also appears to use the names speakerstats.j.example.com conferenceduration.j.example.com lobby.j.example.com conference.j.example.com conference.j.example.com internal.auth.j.example.com but they aren t required for a basic setup, I guess you could add them to /etc/hosts to avoid the possibility of strange errors due to it not finding an internal host name. There are optional features of Jitsi which require some of these names, but so far I ve only used the basic functionality. Access Control This section describes how to restrict conference creation to authenticated users. The secure-domain document [2] shows how to restrict access, but I ll summarise the basics. Edit /etc/prosody/conf.avail/j.example.com.cfg.lua and use the following line in the main VirtualHost section:
        authentication = "internal_hashed"
Then add the following section:
VirtualHost "guest.j.example.com"
        authentication = "anonymous"
        c2s_require_encryption = false
        modules_enabled =  
            "turncredentials";
         
Edit /etc/jitsi/meet/j.example.com-config.js and add the following line:
        anonymousdomain: 'guest.j.example.com',
Edit /etc/jitsi/jicofo/sip-communicator.properties and add the following line:
org.jitsi.jicofo.auth.URL=XMPP:j.example.com
Then run commands like the following to create new users who can create rooms:
prosodyctl register admin j.example.com
Then restart most things (Prosody at least, maybe parts of Jitsi too), I rebooted the VM. Now only the accounts you created on the Prosody server will be able to create new meetings. You should be able to add, delete, and change passwords for users via prosodyctl while it s running once you have set this up. Conclusion Once I gave up on the idea of running Jitsi on the same server as anything else it wasn t particularly difficult to set up. Some bits were a little fiddly and hopefully this post will be a useful resource for people who have trouble understanding the documentation. Generally it s not difficult to install if it is the only thing running on a VM.

Markus Koschany: My Free Software Activities in July 2020

Welcome to gambaru.de. Here is my monthly report (+ the first week in August) that covers what I have been doing for Debian. If you re interested in Java, Games and LTS topics, this might be interesting for you. Debian Games
Debian Java Misc Debian LTS This was my 53. month as a paid contributor and I have been paid to work 15 hours on Debian LTS, a project started by Rapha l Hertzog. In that time I did the following: ELTS Extended Long Term Support (ELTS) is a project led by Freexian to further extend the lifetime of Debian releases. It is not an official Debian project but all Debian users benefit from it without cost. The current ELTS release is Debian 8 Jessie . This was my 26. month and I have been paid to work 13,25 hours on ELTS. Thanks for reading and see you next time.

Keith Packard: picolibc-news

Picolibc Updates I thought work on picolibc would slow down at some point, but I keep finding more things that need work. I spent a few weeks working in libm and then discovered some important memory allocation bugs in the last week that needed attention too. Cleaning up the Picolibc Math Library Picolibc uses the same math library sources as newlib, which includes code from a range of sources: The original SunPro math code had been split into two levels at some point:
  1. IEEE-754 functions. These offer pure IEEE-754 semantics, including return values and exceptions. They do not set the POSIX errno value. These are all prefixed with __ieee754_ and can be called directly by applications if desired.
  2. POSIX functions. These can offer POSIX semantics, including setting errno and returning expected values when errno is set.
New Code Sponsored by ARM Szabolcs Nagy and Wilco Dijkstra's work in the last few years has been to improve the performance of some of the core math functions, which is much appreciated. They've adopted a more modern coding style (C99) and written faster code at the expense of a larger memory foot print. One interesting choice was to use double computations for the float implementations of various functions. This makes these functions shorter and more accurate than versions done using float throughout. However, for machines which don't have HW double, this pulls in soft double code which adds considerable size to the resulting binary and slows down the computations, especially if the platform does support HW float. The new code also takes advantage of HW fused-multiply-add instructions. Those offer more precision than a sequence of primitive instructions, and so the new code can be much shorter as a result. The method used to detect whether the target machine supported fma operations was slightly broken on 32-bit ARM platforms, where those with 'float' fma acceleration but without 'double' fma acceleration would use the shorter code sequence, but with an emulated fma operation that used the less-precise sequence of operations, leading to significant reductions in the quality of the resulting math functions. I fixed the double fma detection and then also added float fma detection along with implementations of float and double fma for ARM and RISC-V. Now both of those platforms get fma-enhanced math functions where available. Errno Adventures I'd submitted patches to newlib a while ago that aliased the regular math library names to the __ieee754_ functions when the library was configured to not set errno, which is pretty common for embedded environments where a shared errno is a pain anyways. Note the use of the word can in remark about the old POSIX wrapper functions. That's because all of these functions are run-time switchable between _IEEE_ and _POSIX_ mode using the _LIB_VERSION global symbol. When left in the usual _IEEE_ mode, none of this extra code was ever executed, so these wrapper functions never did anything beyond what the underlying __ieee754_ functions did. The new code by Nagy and Dijkstra changed how functions are structured to eliminate the underlying IEEE-754 api. These new functions use tail calls to various __math_ error reporting functions. Those can be configured at library build time to set errno or not, centralizing those decisions in a few functions. The result of this combination of source material is that in the default configuration, some library functions (those written by Nagy and Dijkstra) would set errno and others (the old SunPro code) would not. To disable all errno references, the library would need to be compiled with a set of options, -D_IEEE_LIBM to disable errno in the SunPro code and -DWANT_ERRNO=0 to disable errno in the new code. To enable errno everywhere, you'd set -D_POSIX_MODE to make the default value for _LIB_VERSION be _POSIX_ instead of _IEEE_. To clean all of this up, I removed the run-time _LIB_VERSION variable and made that compile-time. In combination with the earlier work to alias the __ieee754_ functions to the regular POSIX names when _IEEE_LIBM was defined this means that the old SunPro POSIX functions now only get used when _IEEE_LIBM is not defined, and in that case the _LIB_VERSION tests always force use of the errno setting code. In addition, I made the value of WANT_ERRNO depend on whether _IEEE_LIBM was defined, so now a single definition (-D_IEEE_LIBM) causes all of the errno handling from libm to be removed, independent of which code is in use. As part of this work, I added a range of errno tests for the math functions to find places where the wrong errno value was being used. Exceptions As an alternative to errno, C also provides for IEEE-754 exceptions through the fenv functions. These have some significant advantages, including having independent bits for each exception type and having them accumulate instead of sharing errno with a huge range of other C library functions. Plus, they're generally implemented in hardware, so you get exceptions for both library functions and primitive operations. Well, you should get exceptions everywhere, except that the GCC soft float libraries don't support them at all. So, errno can still be useful if you need to know what happened in your library functions when using soft floats. Newlib has recently seen a spate of fenv support being added for various architectures, so I decided that it would be a good idea to add some tests. I added tests for both primitive operations, and then tests for library functions to check both exceptions and errno values. Oddly, this uncovered a range of minor mistakes in various math functions. Lots of these were mistakes in the SunPro POSIX wrapper functions where they modified the return values from the __ieee754_ implementations. Simply removing those value modifications fixed many of those errors. Fixing Memory Allocator bugs Picolibc inherits malloc code from newlib which offers two separate implementations, one big and fast, the other small and slow(er). Selecting between them is done while building the library, and as Picolibc is expected to be used on smaller systems, the small and slow one is the default. Contributed by someone from ARM back in 2012/2013, nano-mallocr reminds me of the old V7 memory allocator. A linked list, sorted in address order, holds discontiguous chunks of available memory. Allocation is done by searching for a large enough chunk in the list. The first one large enough is selected, and if it is large enough, a chunk is split off and left on the free list while the remainder is handed to the application. When the list doesn't have any chunk large enough, sbrk is called to get more memory. Free operations involve walking the list and inserting the chunk in the right location, merging the freed memory with any immediately adjacent chunks to reduce fragmentation. The size of each chunk is stored just before the first byte of memory used by the application, where it remains while the memory is in use and while on the free list. The free list is formed by pointers stored in the active area of the chunk, so the only overhead for chunks in use is the size field. Something Something Padding To deal with the vagaries of alignment, the original nano-mallocr code would allow for there to be 'padding' between the size field and the active memory area. The amount of padding could vary, depending on the alignment required for a particular chunk (in the case of memalign, that padding can be quite large). If present, nano-mallocr would store the padding value in the location immediately before the active area and distinguish that from a regular size field by a negative sign. The whole padding thing seems mysterious to me -- why would it ever be needed when the allocator could simply create chunks that were aligned to the required value and a multiple of that value in size. The only use I could think of was for memalign; adding this padding field would allow for less over-allocation to find a suitable chunk. I didn't feel like this one (infrequent) use case was worth the extra complexity; it certainly caused me difficulty in reading the code. A Few Bugs In reviewing the code, I found a couple of easy-to-fix bugs. Time For Testing Once I had uncovered a few bugs in this code, I decided that it would be good to write a few tests to exercise the API. With the tests running on four architectures in nearly 60 variants, it seemed like I'd be able to uncover at least a few more failures: These new tests did find bugs. But not where I expected them. Which is why I'm so fond of testing. GCC Optimizations One of my tests was to call calloc and make sure it returned a chunk of memory that appeared to work or failed with a reasonable value. To my surprise, on aarch64, that test never finished. It worked elsewhere, but on that architecture it hung in the middle of calloc itself. Which looked like this:
void * nano_calloc(malloc_size_t n, malloc_size_t elem)
 
    ptrdiff_t bytes;
    void * mem;
    if (__builtin_mul_overflow (n, elem, &bytes))
     
    RERRNO = ENOMEM;
    return NULL;
     
    mem = nano_malloc(bytes);
    if (mem != NULL) memset(mem, 0, bytes);
    return mem;
 
Note the naming here -- nano_mallocr uses nano_ prefixes in the code, but then uses #defines to change their names to those expected in the ABI. (No, I don't understand why either). However, GCC sees the real names and has some idea of what these functions are supposed to do. In particular, the pattern:
foo = malloc(n);
if (foo) memset(foo, '\0', n);
is converted into a shorter and semantically equivalent:
foo = calloc(n, 1);
Alas, GCC doesn't take into account that this optimization is occurring inside of the implementation of calloc. Another sequence of code looked like this:
chunk->size = foo
nano_free((char *) chunk + CHUNK_OFFSET);
Well, GCC knows that the content of memory passed to free cannot affect the operation of the application, and so it converted this into:
nano_free((char *) chunk + CHUNK_OFFSET);
Remember that nano_mallocr stores the size of the chunk just before the active memory. In this case, nano_mallocr was splitting a large chunk into two pieces, setting the size of the left-over part and placing that on the free list. Failing to set that size value left whatever was there before for the size and usually resulted in the free list becoming quite corrupted. Both of these problems can be corrected by compiling the code with a couple of GCC command-line switches (-fno-builtin-malloc and -fno-builtin-free). Reworking Malloc Having spent this much time reading through the nano_mallocr code, I decided to just go through it and make it easier for me to read today, hoping that other people (which includes 'future me') will also find it a bit easier to follow. I picked a couple of things to focus on:
  1. All newly allocated memory should be cleared. This reduces information disclosure between whatever code freed the memory and whatever code is about to use the memory. Plus, it reduces the effect of un-initialized allocations as they now consistently get zeroed memory. Yes, this masks bugs. Yes, this goes slower. This change is dedicated to Kees Cook, but please blame me for it not him.
  2. Get rid of the 'Padding' notion. Every time I read this code it made my brain hurt. I doubt I'll get any smarter in the future.
  3. Realloc could use some love, improving its efficiency in common cases to reduce memory usage.
  4. Reworking linked list walking. nano_mallocr uses a singly-linked free list and open-codes all list walking. Normally, I'd switch to a library implementation to avoid introducing my own bugs, but in this fairly simple case, I think it's a reasonable compromise to open-code the list operations using some patterns I learned while working at MIT from Bob Scheifler.
  5. Discover necessary values, like padding and the limits of the memory space, from the environment rather than having them hard-coded.
Padding To get rid of 'Padding' in malloc, I needed to make sure that every chunk was aligned and sized correctly. Remember that there is a header on every allocated chunk which is stored before the active memory which contains the size of the chunk. On 32-bit machines, that size is 4 bytes. If the machine requires allocations to be aligned on 8-byte boundaries (as might be the case for 'double' values), we're now going to force the alignment of the header to 8-bytes, wasting four bytes between the size field and the active memory. Well, the existing nano_mallocr code also wastes those four bytes to store the 'padding' value. Using a consistent alignment for chunk starting addresses and chunk sizes has made the code a lot simpler and easier to reason about while not using extra memory for normal allocation. Except for memalign, which I'll cover in the next section. realloc The original nano_realloc function was as simple as possible:
mem = nano_malloc(new_size);
if (mem)  
    memcpy(mem, old, MIN(old_size, new_size));
    nano_free(old);
 
return mem;
However, this really performs badly when the application is growing a buffer while accumulating data. A couple of simple optimizations occurred to me:
  1. If there's a free chunk just after the original location, it could be merged to the existing block and avoid copying the data.
  2. If the original chunk is at the end of the heap, call sbrk() to increase the size of the chunk.
The second one seems like the more important case; in a small system, the buffer will probably land at the end of the heap at some point, at which point growing it to the size of available memory becomes quite efficient. When shrinking the buffer, instead of allocating new space and copying, if there's enough space being freed for a new chunk, create one and add it to the free list. List Walking Walking singly-linked lists seem like one of the first things we see when learning pointer manipulation in C:
for (element = head; element; element = element->next)
    do stuff ...
However, this becomes pretty complicated when 'do stuff' includes removing something from the list:
prev = NULL;
for (element = head; element; element = element->next)
    ...
    if (found)
        break;
    ...
    prev = element
if (prev != NULL)
    prev->next = element->next;
else
    head = element->next;
An extra variable, and a test to figure out how to re-link the list. Bob showed me a simpler way, which I'm sure many people are familiar with:
for (ptr = &head; (element = *ptr); ptr = &(element->next))
    ...
    if (found)
        break;
*ptr = element->next;
Insertion is similar, as you would expect:
for (ptr = &head; (element = *ptr); ptr = &(element->next))
    if (found)
        break;
new_element->next = element;
*ptr = new_element;
In terms of memory operations, it's the same -- each 'next' pointer is fetched exactly once and the list is re-linked by performing a single store. In terms of reading the code, once you've seen this pattern, getting rid of the extra variable and the conditionals around the list update makes it shorter and less prone to errors. In the nano_mallocr code, instead of using 'prev = NULL', it actually used 'prev = free_list', and the test for updating the head was 'prev == element', which really caught me unawares. System Parameters Any malloc implementation needs to know a couple of things about the system it's running on:
  1. Address space. The maximum range of possible addresses sets the limit on how large a block of memory might be allocated, and hence the size of the 'size' field. Fortunately, we've got the 'size_t' type for this, so we can just use that.
  2. Alignment requirements. These derive from the alignment requirements of the basic machine types, including pointers, integers and floating point numbers which are formed from a combination of machine requirements (some systems will fault if attempting to use memory with the wrong alignment) along with a compromise between memory usage and memory system performance.
I decided to let the system tell me the alignment necessary using a special type declaration and the 'offsetof' operation:
typedef struct  
    char c;
    union  
    void *p;
    double d;
    long long ll;
    size_t s;
      u;
  align_t;
#define MALLOC_ALIGN        (offsetof(align_t, u))
Because C requires struct fields to be stored in order of declaration, the 'u' field would have to be after the 'c' field, and would have to be assigned an offset equal to the largest alignment necessary for any of its members. Testing on a range of machines yields the following alignment requirements:
Architecture Alignment
x86_64 8
RISC-V 8
aarch64 8
arm 8
x86 4
So, I guess I could have just used a constant value of '8' and not worried about it, but using the compiler-provided value means that running picolibc on older architectures might save a bit of memory at no real cost in the code. Now, the header containing the 'size' field can be aligned to this value, and all allocated blocks can be allocated in units of this value. memalign memalign, valloc and pvalloc all allocate memory with restrictions on the alignment of the base address and length. You'd think these would be simple -- allocate a large chunk, align within that chunk and return the address. However, they also all require that the address can be successfully passed to free. Which means that the allocator needs to do some tricks to make it all work. Essentially, you allocate 'lots' of memory and then arrange that any bytes at the head and tail of the allocation can be returned to the free list. The tail part is easy; if it's large enough to form a free chunk (which must contain the size and a 'next' pointer for the free list), it can be split off. Otherwise, it just sits at the end of the allocation being wasted space. The head part is a bit tricky when it's not large enough to form a free chunk. That's where the 'padding' business came in handy; that can be as small as a 'size_t' value, which (on 32-bit systems) is only four bytes. Now that we're giving up trying to reason about 'padding', any extra block at the start must be big enough to hold a free block, which includes the size and a next pointer. On 32-bit systems, that's just 8 bytes which (for most of our targets) is the same as the alignment value we're using. On 32-bit systems that can use 4-byte alignment, and on 64-bit systems, it's possible that the alignment required by the application for memalign and the alignment of a chunk returned by malloc might be off by too small an amount to create a free chunk. So, we just allocate a lot of extra space; enough so that we can create a block of size 'toosmall + align' at the start and create a free chunk of memory out of that. This works, and at least returns all of the unused memory back for other allocations. Sending Patches Back to Newlib I've sent the floating point fixes upstream to newlib where they've already landed on master. I've sent most of the malloc fixes, but I'm not sure they really care about seeing nano_mallocr refactored. If they do, I'll spend the time necessary to get the changes ported back to the newlib internal APIs and merged upstream.

13 August 2020

Sven Hoexter: An Average IT Org

Supply chain attacks are a known issue, and also lately there was a discussion around the relevance of reproducible builds. Looking in comparison at an average IT org doing something with the internet, I believe the pressing problem is neither supply chain attacks nor a lack of reproducible builds. The real problem is the amount of prefabricated binaries supplied by someone else, created in an unknown build environment with unknown tools, the average IT org requires to do anything. The Mess the World Runs on By chance I had an opportunity to look at what some other people I know use, and here is the list I could compile by scratching just at the surface: Of course there are also all the script language repos - Python, Ruby, Node/Typescript - around as well. Looking at myself, who's working in a different IT org but with a similar focus, I have the following lingering around on my for work laptop and retrieved it as a binary from a 3rd party: Yes some of that is even non-free and might contain spyw^telemetry. Takeway I By guessing based on Pareto Principle probably 80% of the software mentioned above is also open source software. But, and here we leave Pareto behind, close to none is build by the average IT org from source. Why should the average IT org care about advanced issues like supply chain attacks on source code and mitigations, when it already gets into very hot water the day DockerHub closes down, HashiCorp moves from open core to full proprietary or Elastic decides to no longer offer free binary builds? The reality out there seems to be that infrastructure of "modern" IT orgs is managed similar to the Windows 95 installation of my childhood. You just grab running binaries from somewhere and run them. The main difference seems to be that you no longer have the inconvenience of downloading a .xls from geocities you've to rename to .rar and that it's legal. Takeway II In the end the binary supply is like a drug for the user, and somehow the Debian project is also just another dealer / middle man in this setup. There are probably a lot of open questions to think about in that context. Are we the better dealer because we care about signed sources we retrieve from upstream and because we engage in reproducible build projects? Are our own means of distributing binaries any better than a binary download from github via https with a manual checksum verification, or the Debian repo at download.docker.com? Is the approach of the BSD/Gentoo ports, where you have to compile at least some software from source, the better one? Do I really want to know how some of the software is actually build? Or some more candid ones like is gnutls a good choice for the https support in apt and how solid is the gnupg code base? Update: Regarding apt there seems to be some movement.

Norbert Preining: Switching from KDE/Plasma to Gnome3 for one week

This guy is doing a great work, providing patches to improve kwin, and then tried Gnome3 for a week, 7 days. His verdict:
overall, after one week of using this, I can say it s f**king HORRIBLE!!! well, it s not as bad as I thought but yeah, it was overall a pretty unpleasant experience
I definitely have seen improvements, but the desktop is still not in shape. I mean, it s still not as usable as KDE is .
Honestly, I can t agree more. I have tried Gnome3 for over a year, again and again, and it feels like a block of concrete put onto the feet of dissidents by Italian mafia bosses. It drowns and kills you. Here are the links: Start, Day 1, Day 2, Day 3, Day 4, Day 5, Day 6, Day 7. Thanks a lot for these blog posts, incredibly informative and convincing!

12 August 2020

Michael Stapelberg: Linux distributions: Can we do without hooks and triggers?

Hooks are an extension feature provided by all package managers that are used in larger Linux distributions. For example, Debian uses apt, which has various maintainer scripts. Fedora uses rpm, which has scriptlets. Different package managers use different names for the concept, but all of them offer package maintainers the ability to run arbitrary code during package installation and upgrades. Example hook use cases include adding daemon user accounts to your system (e.g. postgres), or generating/updating cache files. Triggers are a kind of hook which run when other packages are installed. For example, on Debian, the man(1) package comes with a trigger which regenerates the search database index whenever any package installs a manpage. When, for example, the nginx(8) package is installed, a trigger provided by the man(1) package runs. Over the past few decades, Open Source software has become more and more uniform: instead of each piece of software defining its own rules, a small number of build systems are now widely adopted. Hence, I think it makes sense to revisit whether offering extension via hooks and triggers is a net win or net loss.

Hooks preclude concurrent package installation Package managers commonly can make very little assumptions about what hooks do, what preconditions they require, and which conflicts might be caused by running multiple package s hooks concurrently. Hence, package managers cannot concurrently install packages. At least the hook/trigger part of the installation needs to happen in sequence. While it seems technically feasible to retrofit package manager hooks with concurrency primitives such as locks for mutual exclusion between different hook processes, the required overhaul of all hooks seems like such a daunting task that it might be better to just get rid of the hooks instead. Only deleting code frees you from the burden of maintenance, automated testing and debugging. In Debian, there are 8620 non-generated maintainer scripts, as reported by find shard*/src/*/debian -regex ".*\(pre\ post\)\(inst\ rm\)$" on a Debian Code Search instance.

Triggers slow down installing/updating other packages Personally, I never use the apropos(1) command, so I don t appreciate the man(1) package s trigger which updates the database used by apropos(1). The process takes a long time and, because hooks and triggers must be executed serially (see previous section), blocks my installation or update. When I tell people this, they are often surprised to learn about the existance of the apropos(1) command. I suggest adopting an opt-in model.

Unnecessary work if programs are not used between updates Hooks run when packages are installed. If a package s contents are not used between two updates, running the hook in the first update could have been skipped. Running the hook lazily when the package contents are used reduces unnecessary work. As a welcome side-effect, lazy hook evaluation automatically makes the hook work in operating system images, such as live USB thumb drives or SD card images for the Raspberry Pi. Such images must not ship the same crypto keys (e.g. OpenSSH host keys) to all machines, but instead generate a different key on each machine. Why do users keep packages installed they don t use? It s extra work to remember and clean up those packages after use. Plus, users might not realize or value that having fewer packages installed has benefits such as faster updates. I can also imagine that there are people for whom the cost of re-installing packages incentivizes them to just keep packages installed you never know when you might need the program again

Implemented in an interpreted language While working on hermetic packages (more on that in another blog post), where the contained programs are started with modified environment variables (e.g. PATH) via a wrapper bash script, I noticed that the overhead of those wrapper bash scripts quickly becomes significant. For example, when using the excellent magit interface for Git in Emacs, I encountered second-long delays when using hermetic packages compared to standard packages. Re-implementing wrappers in a compiled language provided a significant speed-up. Similarly, getting rid of an extension point which mandates using shell scripts allows us to build an efficient and fast implementation of a predefined set of primitives, where you can reason about their effects and interactions. magit needs to run git a few times for displaying the full status, so small overhead quickly adds up.

Incentivizing more upstream standardization Hooks are an escape hatch for distribution maintainers to express anything which their packaging system cannot express. Distributions should only rely on well-established interfaces such as autoconf s classic ./configure && make && make install (including commonly used flags) to build a distribution package. Integrating upstream software into a distribution should not require custom hooks. For example, instead of requiring a hook which updates a cache of schema files, the library used to interact with those files should transparently (re-)generate the cache or fall back to a slower code path. Distribution maintainers are hard to come by, so we should value their time. In particular, there is a 1:n relationship of packages to distribution package maintainers (software is typically available in multiple Linux distributions), so it makes sense to spend the work in the 1 and have the n benefit.

Can we do without them? If we want to get rid of hooks, we need another mechanism to achieve what we currently achieve with hooks. If the hook is not specific to the package, it can be moved to the package manager. The desired system state should either be derived from the package contents (e.g. required system users can be discovered from systemd service files) or declaratively specified in the package build instructions more on that in another blog post. This turns hooks (arbitrary code) into configuration, which allows the package manager to collapse and sequence the required state changes. E.g., when 5 packages are installed which each need a new system user, the package manager could update /etc/passwd just once. If the hook is specific to the package, it should be moved into the package contents. This typically means moving the functionality into the program start (or the systemd service file if we are talking about a daemon). If (while?) upstream is not convinced, you can either wrap the program or patch it. Note that this case is relatively rare: I have worked with hundreds of packages and the only package-specific functionality I came across was automatically generating host keys before starting OpenSSH s sshd(8) . There is one exception where moving the hook doesn t work: packages which modify state outside of the system, such as bootloaders or kernel images. Even that can be moved out of a package-specific hook, as Fedora demonstrates.

Conclusion Global state modifications performed as part of package installation today use hooks, an overly expressive extension mechanism. Instead, all modifications should be driven by configuration. This is feasible because there are only a few different kinds of desired state modifications. This makes it possible for package managers to optimize package installation.

Michael Stapelberg: distri: 20x faster initramfs (initrd) from scratch

In case you are not yet familiar with why an initramfs (or initrd, or initial ramdisk) is typically used when starting Linux, let me quote the wikipedia definition: [ ] initrd is a scheme for loading a temporary root file system into memory, which may be used as part of the Linux startup process [ ] to make preparations before the real root file system can be mounted. Many Linux distributions do not compile all file system drivers into the kernel, but instead load them on-demand from an initramfs, which saves memory. Another common scenario, in which an initramfs is required, is full-disk encryption: the disk must be unlocked from userspace, but since userspace is encrypted, an initramfs is used.

Motivation Thus far, building a distri disk image was quite slow: This is on an AMD Ryzen 3900X 12-core processor (2019):
distri % time make cryptimage serial=1
80.29s user 13.56s system 186% cpu 50.419 total # 19s image, 31s initrd
Of these 50 seconds, dracut s initramfs generation accounts for 31 seconds (62%)! Initramfs generation time drops to 8.7 seconds once dracut no longer needs to use the single-threaded gzip(1) , but the multi-threaded replacement pigz(1) : This brings the total time to build a distri disk image down to:
distri % time make cryptimage serial=1
76.85s user 13.23s system 327% cpu 27.509 total # 19s image, 8.7s initrd
Clearly, when you use dracut on any modern computer, you should make pigz available. dracut should fail to compile unless one explicitly opts into the known-slower gzip. For more thoughts on optional dependencies, see Optional dependencies don t work . But why does it take 8.7 seconds still? Can we go faster? The answer is Yes! I recently built a distri-specific initramfs I m calling minitrd. I wrote both big parts from scratch:
  1. the initramfs generator program (distri initrd)
  2. a custom Go userland (cmd/minitrd), running as /init in the initramfs.
minitrd generates the initramfs image in 400ms, bringing the total time down to:
distri % time make cryptimage serial=1
50.09s user 8.80s system 314% cpu 18.739 total # 18s image, 400ms initrd
(The remaining time is spent in preparing the file system, then installing and configuring the distri system, i.e. preparing a disk image you can run on real hardware.) How can minitrd be 20 times faster than dracut? dracut is mainly written in shell, with a C helper program. It drives the generation process by spawning lots of external dependencies (e.g. ldd or the dracut-install helper program). I assume that the combination of using an interpreted language (shell) that spawns lots of processes and precludes a concurrent architecture is to blame for the poor performance. minitrd is written in Go, with speed as a goal. It leverages concurrency and uses no external dependencies; everything happens within a single process (but with enough threads to saturate modern hardware). Measuring early boot time using qemu, I measured the dracut-generated initramfs taking 588ms to display the full disk encryption passphrase prompt, whereas minitrd took only 195ms. The rest of this article dives deeper into how minitrd works.

What does an initramfs do? Ultimately, the job of an initramfs is to make the root file system available and continue booting the system from there. Depending on the system setup, this involves the following 5 steps:

1. Load kernel modules to access the block devices with the root file system Depending on the system, the block devices with the root file system might already be present when the initramfs runs, or some kernel modules might need to be loaded first. On my Dell XPS 9360 laptop, the NVMe system disk is already present when the initramfs starts, whereas in qemu, we need to load the virtio_pci module, followed by the virtio_scsi module. How will our userland program know which kernel modules to load? Linux kernel modules declare patterns for their supported hardware as an alias, e.g.:
initrd# grep virtio_pci lib/modules/5.4.6/modules.alias
alias pci:v00001AF4d*sv*sd*bc*sc*i* virtio_pci
Devices in sysfs have a modalias file whose content can be matched against these declarations to identify the module to load:
initrd# cat /sys/devices/pci0000:00/*/modalias
pci:v00001AF4d00001005sv00001AF4sd00000004bc00scFFi00
pci:v00001AF4d00001004sv00001AF4sd00000008bc01sc00i00
[ ]
Hence, for the initial round of module loading, it is sufficient to locate all modalias files within sysfs and load the responsible modules. Loading a kernel module can result in new devices appearing. When that happens, the kernel sends a uevent, which the uevent consumer in userspace receives via a netlink socket. Typically, this consumer is udev(7) , but in our case, it s minitrd. For each uevent messages that comes with a MODALIAS variable, minitrd will load the relevant kernel module(s). When loading a kernel module, its dependencies need to be loaded first. Dependency information is stored in the modules.dep file in a Makefile-like syntax:
initrd# grep virtio_pci lib/modules/5.4.6/modules.dep
kernel/drivers/virtio/virtio_pci.ko: kernel/drivers/virtio/virtio_ring.ko kernel/drivers/virtio/virtio.ko
To load a module, we can open its file and then call the Linux-specific finit_module(2) system call. Some modules are expected to return an error code, e.g. ENODEV or ENOENT when some hardware device is not actually present. Side note: next to the textual versions, there are also binary versions of the modules.alias and modules.dep files. Presumably, those can be queried more quickly, but for simplicitly, I have not (yet?) implemented support in minitrd.

2. Console settings: font, keyboard layout Setting a legible font is necessary for hi-dpi displays. On my Dell XPS 9360 (3200 x 1800 QHD+ display), the following works well:
initrd# setfont latarcyrheb-sun32
Setting the user s keyboard layout is necessary for entering the LUKS full-disk encryption passphrase in their preferred keyboard layout. I use the NEO layout:
initrd# loadkeys neo

3. Block device identification In the Linux kernel, block device enumeration order is not necessarily the same on each boot. Even if it was deterministic, device order could still be changed when users modify their computer s device topology (e.g. connect a new disk to a formerly unused port). Hence, it is good style to refer to disks and their partitions with stable identifiers. This also applies to boot loader configuration, and so most distributions will set a kernel parameter such as root=UUID=1fa04de7-30a9-4183-93e9-1b0061567121. Identifying the block device or partition with the specified UUID is the initramfs s job. Depending on what the device contains, the UUID comes from a different place. For example, ext4 file systems have a UUID field in their file system superblock, whereas LUKS volumes have a UUID in their LUKS header. Canonically, probing a device to extract the UUID is done by libblkid from the util-linux package, but the logic can easily be re-implemented in other languages and changes rarely. minitrd comes with its own implementation to avoid cgo or running the blkid(8) program.

4. LUKS full-disk encryption unlocking (only on encrypted systems) Unlocking a LUKS-encrypted volume is done in userspace. The kernel handles the crypto, but reading the metadata, obtaining the passphrase (or e.g. key material from a file) and setting up the device mapper table entries are done in user space.
initrd# modprobe algif_skcipher
initrd# cryptsetup luksOpen /dev/sda4 cryptroot1
After the user entered their passphrase, the root file system can be mounted:
initrd# mount /dev/dm-0 /mnt

5. Continuing the boot process (switch_root) Now that everything is set up, we need to pass execution to the init program on the root file system with a careful sequence of chdir(2) , mount(2) , chroot(2) , chdir(2) and execve(2) system calls that is explained in this busybox switch_root comment.
initrd# mount -t devtmpfs dev /mnt/dev
initrd# exec switch_root -c /dev/console /mnt /init
To conserve RAM, the files in the temporary file system to which the initramfs archive is extracted are typically deleted.

How is an initramfs generated? An initramfs image (more accurately: archive) is a compressed cpio archive. Typically, gzip compression is used, but the kernel supports a bunch of different algorithms and distributions such as Ubuntu are switching to lz4. Generators typically prepare a temporary directory and feed it to the cpio(1) program. In minitrd, we read the files into memory and generate the cpio archive using the go-cpio package. We use the pgzip package for parallel gzip compression. The following files need to go into the cpio archive:

minitrd Go userland The minitrd binary is copied into the cpio archive as /init and will be run by the kernel after extracting the archive. Like the rest of distri, minitrd is built statically without cgo, which means it can be copied as-is into the cpio archive.

Linux kernel modules Aside from the modules.alias and modules.dep metadata files, the kernel modules themselves reside in e.g. /lib/modules/5.4.6/kernel and need to be copied into the cpio archive. Copying all modules results in a 80 MiB archive, so it is common to only copy modules that are relevant to the initramfs s features. This reduces archive size to 24 MiB. The filtering relies on hard-coded patterns and module names. For example, disk encryption related modules are all kernel modules underneath kernel/crypto, plus kernel/drivers/md/dm-crypt.ko. When generating a host-only initramfs (works on precisely the computer that generated it), some initramfs generators look at the currently loaded modules and just copy those.

Console Fonts and Keymaps The kbd package s setfont(8) and loadkeys(1) programs load console fonts and keymaps from /usr/share/consolefonts and /usr/share/keymaps, respectively. Hence, these directories need to be copied into the cpio archive. Depending on whether the initramfs should be generic (work on many computers) or host-only (works on precisely the computer/settings that generated it), the entire directories are copied, or only the required font/keymap.

cryptsetup, setfont, loadkeys These programs are (currently) required because minitrd does not implement their functionality. As they are dynamically linked, not only the programs themselves need to be copied, but also the ELF dynamic linking loader (path stored in the .interp ELF section) and any ELF library dependencies. For example, cryptsetup in distri declares the ELF interpreter /ro/glibc-amd64-2.27-3/out/lib/ld-linux-x86-64.so.2 and declares dependencies on shared libraries libcryptsetup.so.12, libblkid.so.1 and others. Luckily, in distri, packages contain a lib subdirectory containing symbolic links to the resolved shared library paths (hermetic packaging), so it is sufficient to mirror the lib directory into the cpio archive, recursing into shared library dependencies of shared libraries. cryptsetup also requires the GCC runtime library libgcc_s.so.1 to be present at runtime, and will abort with an error message about not being able to call pthread_cancel(3) if it is unavailable.

time zone data To print log messages in the correct time zone, we copy /etc/localtime from the host into the cpio archive.

minitrd outside of distri? I currently have no desire to make minitrd available outside of distri. While the technical challenges (such as extending the generator to not rely on distri s hermetic packages) are surmountable, I don t want to support people s initramfs remotely. Also, I think that people s efforts should in general be spent on rallying behind dracut and making it work faster, thereby benefiting all Linux distributions that use dracut (increasingly more). With minitrd, I have demonstrated that significant speed-ups are achievable.

Conclusion It was interesting to dive into how an initramfs really works. I had been working with the concept for many years, from small tasks such as debug why the encrypted root file system is not unlocked to more complicated tasks such as set up a root file system on DRBD for a high-availability setup . But even with that sort of experience, I didn t know all the details, until I was forced to implement every little thing. As I suspected going into this exercise, dracut is much slower than it needs to be. Re-implementing its generation stage in a modern language instead of shell helps a lot. Of course, my minitrd does a bit less than dracut, but not drastically so. The overall architecture is the same. I hope my effort helps with two things:
  1. As a teaching implementation: instead of wading through the various components that make up a modern initramfs (udev, systemd, various shell scripts, ), people can learn about how an initramfs works in a single place.
  2. I hope the significant time difference motivates people to improve dracut.

Appendix: qemu development environment Before writing any Go code, I did some manual prototyping. Learning how other people prototype is often immensely useful to me, so I m sharing my notes here. First, I copied all kernel modules and a statically built busybox binary:
% mkdir -p lib/modules/5.4.6
% cp -Lr /ro/lib/modules/5.4.6/* lib/modules/5.4.6/
% cp ~/busybox-1.22.0-amd64/busybox sh
To generate an initramfs from the current directory, I used:
% find .   cpio -o -H newc   pigz > /tmp/initrd
In distri s Makefile, I append these flags to the QEMU invocation:
-kernel /tmp/kernel \
-initrd /tmp/initrd \
-append "root=/dev/mapper/cryptroot1 rdinit=/sh ro console=ttyS0,115200 rd.luks=1 rd.luks.uuid=63051f8a-54b9-4996-b94f-3cf105af2900 rd.luks.name=63051f8a-54b9-4996-b94f-3cf105af2900=cryptroot1 rd.vconsole.keymap=neo rd.vconsole.font=latarcyrheb-sun32 init=/init systemd.setenv=PATH=/bin rw vga=836"
The vga= mode parameter is required for loading font latarcyrheb-sun32. Once in the busybox shell, I manually prepared the required mount points and kernel modules:
ln -s sh mount
ln -s sh lsmod
mkdir /proc /sys /run /mnt
mount -t proc proc /proc
mount -t sysfs sys /sys
mount -t devtmpfs dev /dev
modprobe virtio_pci
modprobe virtio_scsi
As a next step, I copied cryptsetup and dependencies into the initramfs directory:
% for f in /ro/cryptsetup-amd64-2.0.4-6/lib/*; do full=$(readlink -f $f); rel=$(echo $full   sed 's,^/,,g'); mkdir -p $(dirname $rel); install $full $rel; done
% ln -s ld-2.27.so ro/glibc-amd64-2.27-3/out/lib/ld-linux-x86-64.so.2
% cp /ro/glibc-amd64-2.27-3/out/lib/ld-2.27.so ro/glibc-amd64-2.27-3/out/lib/ld-2.27.so
% cp -r /ro/cryptsetup-amd64-2.0.4-6/lib ro/cryptsetup-amd64-2.0.4-6/
% mkdir -p ro/gcc-libs-amd64-8.2.0-3/out/lib64/
% cp /ro/gcc-libs-amd64-8.2.0-3/out/lib64/libgcc_s.so.1 ro/gcc-libs-amd64-8.2.0-3/out/lib64/libgcc_s.so.1
% ln -s /ro/gcc-libs-amd64-8.2.0-3/out/lib64/libgcc_s.so.1 ro/cryptsetup-amd64-2.0.4-6/lib
% cp -r /ro/lvm2-amd64-2.03.00-6/lib ro/lvm2-amd64-2.03.00-6/
In busybox, I used the following commands to unlock the root file system:
modprobe algif_skcipher
./cryptsetup luksOpen /dev/sda4 cryptroot1
mount /dev/dm-0 /mnt

Michael Stapelberg: Hermetic packages (in distri)

In distri, packages (e.g. emacs) are hermetic. By hermetic, I mean that the dependencies a package uses (e.g. libusb) don t change, even when newer versions are installed. For example, if package libusb-amd64-1.0.22-7 is available at build time, the package will always use that same version, even after the newer libusb-amd64-1.0.23-8 will be installed into the package store. Another way of saying the same thing is: packages in distri are always co-installable. This makes the package store more robust: additions to it will not break the system. On a technical level, the package store is implemented as a directory containing distri SquashFS images and metadata files, into which packages are installed in an atomic way.

Out of scope: plugins are not hermetic by design One exception where hermeticity is not desired are plugin mechanisms: optionally loading out-of-tree code at runtime obviously is not hermetic. As an example, consider glibc s Name Service Switch (NSS) mechanism. Page 29.4.1 Adding another Service to NSS describes how glibc searches $prefix/lib for shared libraries at runtime. Debian ships about a dozen NSS libraries for a variety of purposes, and enterprise setups might add their own into the mix. systemd (as of v245) accounts for 4 NSS libraries, e.g. nss-systemd for user/group name resolution for users allocated through systemd s DynamicUser= option. Having packages be as hermetic as possible remains a worthwhile goal despite any exceptions: I will gladly use a 99% hermetic system over a 0% hermetic system any day. Side note: Xorg s driver model (which can be characterized as a plugin mechanism) does not fall under this category because of its tight API/ABI coupling! For this case, where drivers are only guaranteed to work with precisely the Xorg version for which they were compiled, distri uses per-package exchange directories.

Implementation of hermetic packages in distri On a technical level, the requirement is: all paths used by the program must always result in the same contents. This is implemented in distri via the read-only package store mounted at /ro, e.g. files underneath /ro/emacs-amd64-26.3-15 never change. To change all paths used by a program, in practice, three strategies cover most paths:

ELF interpreter and dynamic libraries Programs on Linux use the ELF file format, which contains two kinds of references: First, the ELF interpreter (PT_INTERP segment), which is used to start the program. For dynamically linked programs on 64-bit systems, this is typically ld.so(8). Many distributions use system-global paths such as /lib64/ld-linux-x86-64.so.2, but distri compiles programs with -Wl,--dynamic-linker=/ro/glibc-amd64-2.31-4/out/lib/ld-linux-x86-64.so.2 so that the full path ends up in the binary. The ELF interpreter is shown by file(1), but you can also use readelf -a $BINARY grep 'program interpreter' to display it. And secondly, the rpath, a run-time search path for dynamic libraries. Instead of storing full references to all dynamic libraries, we set the rpath so that ld.so(8) will find the correct dynamic libraries. Originally, we used to just set a long rpath, containing one entry for each dynamic library dependency. However, we have since switched to using a single lib subdirectory per package as its rpath, and placing symlinks with full path references into that lib directory, e.g. using -Wl,-rpath=/ro/grep-amd64-3.4-4/lib. This is better for performance, as ld.so uses a per-directory cache. Note that program load times are significantly influenced by how quickly you can locate the dynamic libraries. distri uses a FUSE file system to load programs from, so getting proper -ENOENT caching into place drastically sped up program load times. Instead of compiling software with the -Wl,--dynamic-linker and -Wl,-rpath flags, one can also modify these fields after the fact using patchelf(1). For closed-source programs, this is the only possibility. The rpath can be inspected by using e.g. readelf -a $BINARY grep RPATH.

Environment variable setup wrapper programs Many programs are influenced by environment variables: to start another program, said program is often found by checking each directory in the PATH environment variable. Such search paths are prevalent in scripting languages, too, to find modules. Python has PYTHONPATH, Perl has PERL5LIB, and so on. To set up these search path environment variables at run time, distri employs an indirection. Instead of e.g. teensy-loader-cli, you run a small wrapper program that calls precisely one execve system call with the desired environment variables. Initially, I used shell scripts as wrapper programs because they are easily inspectable. This turned out to be too slow, so I switched to compiled programs. I m linking them statically for fast startup, and I m linking them against musl libc for significantly smaller file sizes than glibc (per-executable overhead adds up quickly in a distribution!). Note that the wrapper programs prepend to the PATH environment variable, they don t replace it in its entirely. This is important so that users have a way to extend the PATH (and other variables) if they so choose. This doesn t hurt hermeticity because it is only relevant for programs that were not present at build time, i.e. plugin mechanisms which, by design, cannot be hermetic.

Shebang interpreter patching The Shebang of scripts contains a path, too, and hence needs to be changed. We don t do this in distri yet (the number of packaged scripts is small), but we should.

Performance requirements The performance improvements in the previous sections are not just good to have, but practically required when many processes are involved: without them, you ll encounter second-long delays in magit which spawns many git processes under the covers, or in dracut, which spawns one cp(1) process per file.

Downside: rebuild of packages required to pick up changes Linux distributions such as Debian consider it an advantage to roll out security fixes to the entire system by updating a single shared library package (e.g. openssl). The flip side of that coin is that changes to a single critical package can break the entire system. With hermetic packages, all reverse dependencies must be rebuilt when a library s changes should be picked up by the whole system. E.g., when openssl changes, curl must be rebuilt to pick up the new version of openssl. This approach trades off using more bandwidth and more disk space (temporarily) against reducing the blast radius of any individual package update.

Downside: long env variables are cumbersome to deal with This can be partially mitigated by removing empty directories at build time, which will result in shorter variables. In general, there is no getting around this. One little trick is to use tr : '\n', e.g.:
distri0# echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/ro/openssh-amd64-8.2p1-11/out/bin
distri0# echo $PATH   tr : '\n'
/usr/bin
/bin
/usr/sbin
/sbin
/ro/openssh-amd64-8.2p1-11/out/bin

Edge cases The implementation outlined above works well in hundreds of packages, and only a small handful exhibited problems of any kind. Here are some issues I encountered:

Issue: accidental ABI breakage in plugin mechanisms NSS libraries built against glibc 2.28 and newer cannot be loaded by glibc 2.27. In all likelihood, such changes do not happen too often, but it does illustrate that glibc s published interface spec is not sufficient for forwards and backwards compatibility. In distri, we could likely use a per-package exchange directory for glibc s NSS mechanism to prevent the above problem from happening in the future.

Issue: wrapper bypass when a program re-executes itself Some programs try to arrange for themselves to be re-executed outside of their current process tree. For example, consider building a program with the meson build system:
  1. When meson first configures the build, it generates ninja files (think Makefiles) which contain command lines that run the meson --internal helper.
  2. Once meson returns, ninja is called as a separate process, so it will not have the environment which the meson wrapper sets up. ninja then runs the previously persisted meson command line. Since the command line uses the full path to meson (not to its wrapper), it bypasses the wrapper.
Luckily, not many programs try to arrange for other process trees to run them. Here is a table summarizing how affected programs might try to arrange for re-execution, whether the technique results in a wrapper bypass, and what we do about it in distri:
technique to execute itself uses wrapper mitigation
run-time: find own basename in PATH yes wrapper program
compile-time: embed expected path no; bypass! configure or patch
run-time: argv[0] or /proc/self/exe no; bypass! patch
One might think that setting argv[0] to the wrapper location seems like a way to side-step this problem. We tried doing this in distri, but had to revert and go the other way.

Misc smaller issues

Appendix: Could other distributions adopt hermetic packages? At a very high level, adopting hermetic packages will require two steps:
  1. Using fully qualified paths whose contents don t change (e.g. /ro/emacs-amd64-26.3-15) generally requires rebuilding programs, e.g. with --prefix set.
  2. Once you use fully qualified paths you need to make the packages able to exchange data. distri solves this with exchange directories, implemented in the /ro file system which is backed by a FUSE daemon.
The first step is pretty simple, whereas the second step is where I expect controversy around any suggested mechanism.

Appendix: demo (in distri) This appendix contains commands and their outputs, run on upcoming distri version supersilverhaze, but verified to work on older versions, too. Large outputs have been collapsed and can be expanded by clicking on the output. The /bin directory contains symlinks for the union of all package s bin subdirectories:
distri0# readlink -f /bin/teensy_loader_cli
/ro/teensy-loader-cli-amd64-2.1+g20180927-7/bin/teensy_loader_cli
The wrapper program in the bin subdirectory is small:
distri0# ls -lh $(readlink -f /bin/teensy_loader_cli)
-rwxr-xr-x 1 root root 46K Apr 21 21:56 /ro/teensy-loader-cli-amd64-2.1+g20180927-7/bin/teensy_loader_cli
Wrapper programs execute quickly:
distri0# strace -fvy /bin/teensy_loader_cli & head cat -n
     1  execve("/bin/teensy_loader_cli", ["/bin/teensy_loader_cli"], ["USER=root", "LOGNAME=root", "HOME=/root", "PATH=/ro/bash-amd64-5.0-4/bin:/r"..., "SHELL=/bin/zsh", "TERM=screen.xterm-256color", "XDG_SESSION_ID=c1", "XDG_RUNTIME_DIR=/run/user/0", "DBUS_SESSION_BUS_ADDRESS=unix:pa"..., "XDG_SESSION_TYPE=tty", "XDG_SESSION_CLASS=user", "SSH_CLIENT=10.0.2.2 42556 22", "SSH_CONNECTION=10.0.2.2 42556 10"..., "SSHTTY=/dev/pts/0", "SHLVL=1", "PWD=/root", "OLDPWD=/root", "=/usr/bin/strace", "LD_LIBRARY_PATH=/ro/bash-amd64-5"..., "PERL5LIB=/ro/bash-amd64-5.0-4/ou"..., "PYTHONPATH=/ro/bash-amd64-5.b0-4/"...]) = 0
     2  arch_prctl(ARCH_SET_FS, 0x40c878)       = 0
     3  set_tid_address(0x40ca9c)               = 715
     4  brk(NULL)                               = 0x15b9000
     5  brk(0x15ba000)                          = 0x15ba000
     6  brk(0x15bb000)                          = 0x15bb000
     7  brk(0x15bd000)                          = 0x15bd000
     8  brk(0x15bf000)                          = 0x15bf000
     9  brk(0x15c1000)                          = 0x15c1000
    10  execve("/ro/teensy-loader-cli-amd64-2.1+g20180927-7/out/bin/teensy_loader_cli", ["/ro/teensy-loader-cli-amd64-2.1+"...], ["USER=root", "LOGNAME=root", "HOME=/root", "PATH=/ro/bash-amd64-5.0-4/bin:/r"..., "SHELL=/bin/zsh", "TERM=screen.xterm-256color", "XDG_SESSION_ID=c1", "XDG_RUNTIME_DIR=/run/user/0", "DBUS_SESSION_BUS_ADDRESS=unix:pa"..., "XDG_SESSION_TYPE=tty", "XDG_SESSION_CLASS=user", "SSH_CLIENT=10.0.2.2 42556 22", "SSH_CONNECTION=10.0.2.2 42556 10"..., "SSHTTY=/dev/pts/0", "SHLVL=1", "PWD=/root", "OLDPWD=/root", "=/usr/bin/strace", "LD_LIBRARY_PATH=/ro/bash-amd64-5"..., "PERL5LIB=/ro/bash-amd64-5.0-4/ou"..., "PYTHONPATH=/ro/bash-amd64-5.0-4/"...]) = 0
Confirm which ELF interpreter is set for a binary using readelf(1):
distri0# readelf -a /ro/teensy-loader-cli-amd64-2.1+g20180927-7/out/bin/teensy_loader_cli grep 'program interpreter'
[Requesting program interpreter: /ro/glibc-amd64-2.31-4/out/lib/ld-linux-x86-64.so.2]
Confirm the rpath is set to the package s lib subdirectory using readelf(1):
distri0# readelf -a /ro/teensy-loader-cli-amd64-2.1+g20180927-7/out/bin/teensy_loader_cli grep RPATH
 0x000000000000000f (RPATH)              Library rpath: [/ro/teensy-loader-cli-amd64-2.1+g20180927-7/lib]
and verify the lib subdirectory has the expected symlinks and target versions:
distri0# find /ro/teensy-loader-cli-amd64-*/lib -type f -printf '%P -> %l\n'
libc.so.6 -> /ro/glibc-amd64-2.31-4/out/lib/libc-2.31.so
libpthread.so.0 -> /ro/glibc-amd64-2.31-4/out/lib/libpthread-2.31.so
librt.so.1 -> /ro/glibc-amd64-2.31-4/out/lib/librt-2.31.so
libudev.so.1 -> /ro/libudev-amd64-245-11/out/lib/libudev.so.1.6.17
libusb-0.1.so.4 -> /ro/libusb-compat-amd64-0.1.5-7/out/lib/libusb-0.1.so.4.4.4
libusb-1.0.so.0 -> /ro/libusb-amd64-1.0.23-8/out/lib/libusb-1.0.so.0.2.0
To verify the correct libraries are actually loaded, you can set the LD_DEBUG environment variable for ld.so(8):
distri0# LD_DEBUG=libs teensy_loader_cli
[ ]
       678:     find library=libc.so.6 [0]; searching
       678:      search path=/ro/teensy-loader-cli-amd64-2.1+g20180927-7/lib            (RPATH from file /ro/teensy-loader-cli-amd64-2.1+g20180927-7/out/bin/teensy_loader_cli)
       678:       trying file=/ro/teensy-loader-cli-amd64-2.1+g20180927-7/lib/libc.so.6
       678:
[ ]
NSS libraries that distri ships:
find /lib/ -name "libnss_*.so.2" -type f -printf '%P -> %l\n'
libnss_myhostname.so.2 -> ../systemd-amd64-245-11/out/lib/libnss_myhostname.so.2
libnss_mymachines.so.2 -> ../systemd-amd64-245-11/out/lib/libnss_mymachines.so.2
libnss_resolve.so.2 -> ../systemd-amd64-245-11/out/lib/libnss_resolve.so.2
libnss_systemd.so.2 -> ../systemd-amd64-245-11/out/lib/libnss_systemd.so.2
libnss_compat.so.2 -> ../glibc-amd64-2.31-4/out/lib/libnss_compat.so.2
libnss_db.so.2 -> ../glibc-amd64-2.31-4/out/lib/libnss_db.so.2
libnss_dns.so.2 -> ../glibc-amd64-2.31-4/out/lib/libnss_dns.so.2
libnss_files.so.2 -> ../glibc-amd64-2.31-4/out/lib/libnss_files.so.2
libnss_hesiod.so.2 -> ../glibc-amd64-2.31-4/out/lib/libnss_hesiod.so.2

11 August 2020

Jonathan Carter: GameMode in Debian

What is GameMode, what does it do? About two years ago, I ran into some bugs running a game on Debian, so installed Windows 10 on a spare computer and ran it on there. I learned that when you launch a game in Windows 10, it automatically disables notifications, screensaver, reduces power saving measures and gives the game maximum priority. I thought Oh, that s actually quite nice, but we probably won t see that kind of integration on Linux any time soon . The very next week, I read the initial announcement of GameMode, a tool from Feral Interactive that does a bunch of tricks to maximise performance for games running on Linux. When GameMode is invoked it:

How GameMode is invoked Some newer games (proprietary games like Rise of the Tomb Raider , Total War Saga: Thrones of Britannia , Total War: WARHAMMER II , DiRT 4 and Total War: Three Kingdoms ) will automatically invoke GameMode if it s installed. For games that don t, you can manually evoke it using the gamemoderun command. Lutris is a tool that makes it easy to install and run games on Linux, and it also integrates with GameMode. (Lutris is currently being packaged for Debian, hopefully it will make it in on time for Bullseye).

Screenshot of Lutris, a tool that makes it easy to install your non-Linux games, which also integrates with GameMode.

GameMode in Debian The latest GameMode is packaged in Debian (Stephan Lachnit and I maintain it in the Debian Games Team) and it s also available for Debian 10 (Buster) via buster-backports. All you need to do to get up and running with GameMode is to install the gamemode package. GameMode in Debian supports 64 bit and 32 bit mode, so running it with older games (and many proprietary games) still work. Some distributions (like Arch Linux), have dropped 32 bit support, so 32 bit games on such systems lose any kind of integration with GameMode even if you can get those games running via other wrappers on such systems. We also include a binary called gamemode-simulate-game (installed under /usr/games/). This is a minimalistic program that will invoke gamemode automatically for 10 seconds and then exit without an error if it was successful. Its source code might be useful if you d like to add GameMode support to your game, or patch a game in Debian to automatically invoke it. In Debian we install Gamemode s example config file to /etc/gamemode.ini where a user can customise their system-wide preferences, or alternatively they can place a copy of that in ~/.gamemode.ini with their personal preferences. In this config file, you can also choose to explicitly allow or deny games. GameMode might also be useful for many pieces of software that aren t games. I haven t done any benchmarks on such software yet, but it might be great for users who use CAD programs or use a combination of their CPU/GPU to crunch a large amount of data. I ve also packaged an extension for GNOME called gamemode-extension. The Debian package is called gnome-shell-extension-gamemode . You ll need to enable it using gnome-tweaks after installation, it will then display a green controller in your notification area whenever GameMode is active. It s only in testing/bullseye since it relies on a newer gnome-shell than what s available in buster.

Running gamemode-simulate-game, with the shell extension showing that it s activated in the top left corner.

10 August 2020

Arnaud Rebillout: GoAccess 1.4, a detailed tutorial

GoAccess v1.4 was just released a few weeks ago! Let's take this chance to write a loooong tutorial. We'll go over every steps to install and operate GoAccess. This is a tutorial aimed at those who don't play sysadmin every day, and that's why it's so long, I did my best to provide thorough explanations all along, so that it's more than just a "copy-and-paste" kind of tutorial. And for those who do play sysadmin everyday: please try not to fall asleep while reading, and don't hesitate to drop me an e-mail if you spot anything inaccurate in here. Thanks! Introduction So what's GoAccess already? GoAccess is a web log analyzer, and it allows you to visualize the traffic for your website, and get to know a bit more about your visitors: how many visitors and hits, for which pages, coming from where (geolocation, operating system, web browser...), etc... It does so by parsing the access logs from your web server, be it Apache, NGINX or whatever. GoAccess gives you different options to display the statistics, and in this tutorial we'll focus on producing a HTML report. Meaning that you can see the statistics for your website straight in your web browser, under the form of a single HTML page. For an example, you can have a look at the stats of my blog here: http://goaccess.arnaudr.io. GoAccess is written in C, it has very few dependencies, it had been around for about 10 years, and it's distributed under the MIT license. Assumptions This tutorial is about installing and configuring, so I'll assume that all the commands are run as root. I won't prefix each of them with sudo. I use the Apache web server, running on a Debian system. I don't think it matters so much for this tutorial though. If you're using NGINX it's fine, you can keep reading. Also, I will just use the name SITE for the name of the website that we want to analyze with GoAccess. Just replace that with the real name of your site. I also assume the following locations for your stuff: If you have your stuff in /srv/SITE/ log,www instead, no worries, just adjust the paths accordingly, I bet you can do it. Installation The latest version of GoAccess is v1.4, and it's not yet available in the Debian repositories. So for this part, you can follow the instructions from the official GoAccess download page. Install steps are explained in details, so there's nothing left for me to say :) When this is done, let's get started with the basics. We're talking about the latest version v1.4 here, let's make sure:
$ goaccess --version
GoAccess - 1.4.
...
Now let's try to create a HTML report. I assume that you already have a website up and running. GoAccess needs to parse the access logs. These logs are optional, they might or might not be created by your web server, depending on how it's configured. Usually, these log files are named access.log, unsurprisingly. You can check if those logs exist on your system by running this command:
find /var/log -name access.log
Another important thing to know is that these logs can be in different formats. In this tutorial we'll assume that we work with the combined log format, because it seems to be the most common default. To check what kind of access logs your web server produces, you must look at the configuration for your site. For an Apache web server, you should have such a line in the file /etc/apache2/sites-enabled/SITE.conf:
CustomLog $ APACHE_LOG_DIR /SITE/access.log combined
For NGINX, it's quite similar. The configuration file would be something like /etc/nginx/sites-enabled/SITE, and the line to enable access logs would be something like:
access_log /var/log/nginx/SITE/access.log
Note that NGINX writes the access logs in the combined format by default, that's why you don't see the word combined anywhere in the line above: it's implicit. Alright, so from now on we assume that yes, you have access log files available, and yes, they are in the combined log format. If that's the case, then you can already run GoAccess and generate a report, for example for the log file /var/log/apache2/access.log
goaccess \
    --log-format COMBINED \
    --output /tmp/report.html \
    /var/log/apache2/access.log
It's possible to give GoAccess more than one log files to process, so if you have for example the file access.log.1 around, you can use it as well:
goaccess \
    --log-format COMBINED \
    --output /tmp/report.html \
    /var/log/apache2/access.log \
    /var/log/apache2/access.log.1
If GoAccess succeeds (and it should), you're on the right track! All is left to do to complete this test is to have a look at the HTML report created. It's a single HTML page, so you can easily scp it to your machine, or just move it to the document root of your site, and then open it in your web browser. Looks good? So let's move on to more interesting things. Web server configuration This part is very short, because in terms of configuration of the web server, there's very little to do. As I said above, the only thing you want from the web server is to create access log files. Then you want to be sure that GoAccess and your web server agree on the format for these files. In the part above we used the combined log format, but GoAccess supports many other common log formats out of the box, and even allows you to parse custom log formats. For more details, refer to the option --log-format in the GoAccess manual page. Another common log format is named, well, common. It even has its own Wikipedia page. But compared to combined, the common log format contains less information, it doesn't include the referrer and user-agent values, meaning that you won't have it in the GoAccess report. So at this point you should understand that, unsurprisingly, GoAccess can only tell you about what's in the access logs, no more no less. And that's all in term of web server configuration. Configuration to run GoAccess unprivileged Now we're going to create a user and group for GoAccess, so that we don't have to run it as root. The reason is that, well, for everything running unattended on your server, the less code runs as root, the better. It's good practice and common sense. In this case, GoAccess is simply a log analyzer. So it just needs to read the logs files from your web server, and there is no need to be root for that, an unprivileged user can do the job just as well, assuming it has read permissions on /var/log/apache2 or /var/log/nginx. The log files of the web server are usually part of the adm group (though it might depend on your distro, I'm not sure). This is something you can check easily with the following command:
ls -l /var/log   grep -e apache2 -e nginx
As a result you should get something like that:
drwxr-x--- 2 root adm 20480 Jul 22 00:00 /var/log/apache2/
And as you can see, the directory apache2 belongs to the group adm. It means that you don't need to be root to read the logs, instead any unprivileged user that belongs to the group adm can do it. So, let's create the goaccess user, and add it to the adm group:
adduser --system --group --no-create-home goaccess
addgroup goaccess adm
And now, let's run GoAccess unprivileged, and verify that it can still read the log files:
setpriv \
    --reuid=goaccess --regid=goaccess \
    --init-groups --inh-caps=-all \
    -- \
    goaccess \
    --log-format COMBINED \
    --output /tmp/report2.html \
    /var/log/apache2/access.log
setpriv is the command used to drop privileges. The syntax is quite verbose, it's not super friendly for tutorials, but don't be scared and read the manual page to learn what it does. In any case, this command should work, and at this point, it means that you have a goaccess user ready, and we'll use it to run GoAccess unprivileged. Integration, option A - Run GoAccess once a day, from a logrotate hook In this part we wire things together, so that GoAccess processes the log files once a day, adds the new logs to its internal database, and generates a report from all that aggregated data. The result will be a single HTML page. Introducing logrotate In order to do that, we'll use a logrotate hook. logrotate is a little tool that should already be installed on your server, and that runs once a day, and that is in charge of rotating the log files. "Rotating the logs" means moving access.log to access.log.1 and so on. With logrotate, a new log file is created every day, and log files that are too old are deleted. That's what prevents your logs from filling up your disk basically :) You can check that logrotate is indeed installed and enabled with this command (assuming that your init system is systemd):
systemctl status logrotate.timer
What's interesting for us is that logrotate allows you to run scripts before and after the rotation is performed, so it's an ideal place from where to run GoAccess. In short, we want to run GoAccess just before the logs are rotated away, in the prerotate hook. But let's do things in order. At first, we need to write a little wrapper script that will be in charge of running GoAccess with the right arguments, and that will process all of your sites. The wrapper script This wrapper is made to process more than one site, but if you have only one site it works just as well, of course. So let me just drop it on you like that, and I'll explain afterward. Here's my wrapper script:
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#!/bin/bash
# Process log files /var/www/apache2/SITE/access.log,
# only if /var/lib/goaccess-db/SITE exists.
# Create HTML reports in $1, a directory that must exist.
set -eu
OUTDIR=
LOGDIR=/var/log/apache2
DBDIR=/var/lib/goaccess-db
fail()   echo >&2 "$@"; exit 1;  
[ $# -eq 1 ]   fail "Usage: $(basename $0) OUTPUT_DIRECTORY"
OUTDIR=$1
[ -d "$OUTDIR" ]   fail "'$OUTDIR' is not a directory"
[ -d "$LOGDIR" ]   fail "'$LOGDIR' is not a directory"
[ -d "$DBDIR"  ]   fail "'$DBDIR' is not a directory"
for d in $(find "$LOGDIR" -mindepth 1 -maxdepth 1 -type d); do
    site=$(basename "$sitedir")
    dbdir=$DBDIR/$site
    logfile=$d/access.log
    outfile=$OUTDIR/$site.html
    if [ ! -d "$dbdir" ]   [ ! -e "$logfile" ]; then
        echo "  Skipping site '$site'"
        continue
    else
        echo "  Processing site '$site'"
    fi
    setpriv \
        --reuid=goaccess --regid=goaccess \
        --init-groups --inh-caps=-all \
        -- \
    goaccess \
        --agent-list \
        --anonymize-ip \
        --persist \
        --restore \
        --config-file /etc/goaccess/goaccess.conf \
        --db-path "$dbdir" \
        --log-format "COMBINED" \
        --output "$outfile" \
        "$logfile"
done
So you'd install this script at /usr/local/bin/goaccess-wrapper for example, and make it executable:
chmod +x /usr/local/bin/goaccess-wrapper
A few things to note: As is, the script makes the assumption that the logs for your site are logged in a sub-directory /var/log/apache2/SITE/. If it's not the case, adjust that in the wrapper accordingly. The name of this sub-directory is then used to find the GoAccess database directory /var/lib/goaccess-db/SITE/. This directory is expected to exist, meaning that if you don't create it yourself, the wrapper won't process this particular site. It's a simple way to control which sites are processed by this GoAccess wrapper, and which sites are not. So if you want goaccess-wrapper to process the site SITE, just create a directory with the name of this site under /var/lib/goaccess-db:
mkdir -p /var/lib/goaccess-db/SITE
chown goaccess:goaccess /var/lib/goaccess-db/SITE
Now let's create an output directory:
mkdir /tmp/goaccess-reports
chown goaccess:goaccess /tmp/goaccess-reports
And let's give a try to the wrapper script:
goaccess-wrapper /tmp/goaccess-reports
ls /tmp/goaccess-reports
Which should give you:
SITE.html
At the same time, you can check that GoAccess populated the database with a bunch of files:
ls /var/lib/goaccess-db/SITE
Setting up the logrotate prerotate hook At this point, we have the wrapper in place. Let's now add a pre-rotate hook so that goaccess-wrapper runs once a day, just before the logs are rotated away. The logrotate config file for Apache2 is located at /etc/logrotate.d/apache2, and for NGINX it's at /etc/logrotate.d/nginx. Among the many things you'll see in this file, here's what is of interest for us: In the config file, there is also this snippet:
prerotate
    if [ -d /etc/logrotate.d/httpd-prerotate ]; then \
        run-parts /etc/logrotate.d/httpd-prerotate; \
    fi; \
endscript
It indicates that scripts in the directory /etc/logrotate.d/httpd-prerotate/ will be executed before the rotation takes place. Refer to the man page run-parts(8) for more details... Putting all of that together, it means that logs from the web server are rotated once a day, and if we want to run scripts just before the rotation, we can just drop them in the httpd-prerotate directory. Simple, right? Let's first create this directory if it doesn't exist:
mkdir -p /etc/logrotate.d/httpd-prerotate/
And let's create a tiny script at /etc/logrotate.d/httpd-prerotate/goaccess:
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#!/bin/sh
exec goaccess-wrapper /tmp/goaccess-reports
Don't forget to make it executable:
chmod +x /etc/logrotate.d/httpd-prerotate/goaccess
As you can see, the only thing that this script does is to invoke the wrapper with the right argument, ie. the output directory for the HTML reports that are generated. And that's all. Now you can just come back tomorrow, check the logs, and make sure that the hook was executed and succeeded. For example, this kind of command will tell you quickly if it worked:
journalctl   grep logrotate
Integration, option B - Run GoAccess once a day, from a systemd service OK so we've just seen how to use a logrotate hook. One downside with that is that we have to drop privileges in the wrapper script, because logrotate runs as root, and we don't want to run GoAccess as root. Hence the rather convoluted syntax with setpriv. Rather than embedding this kind of thing in a wrapper script, we can instead run the wrapper script from a [systemd][] service, and define which user runs the wrapper straight in the systemd service file. Introducing systemd niceties So we can create a systemd service, along with a systemd timer that fires daily. We can then set the user and group that execute the script straight in the systemd service, and there's no need for setpriv anymore. It's a bit more streamlined. We can even go a bit further, and use systemd parameterized units (also called templates), so that we have one service per site (instead of one service that process all of our sites). That will simplify the wrapper script a lot, and it also looks nicer in the logs. With this approach however, it seems that we can't really run exactly before the logs are rotated away, like we did in the section above. But that's OK. What we'll do is that we'll run once a day, no matter the time, and we'll just make sure to process both log files access.log and access.log.1 (ie. the current logs and the logs from yesterday). This way, we're sure not to miss any line from the logs. Note that GoAccess is smart enough to only consider newer entries from the log files, and discard entries that are already in the database. In other words, it's safe to parse the same log file more than once, GoAccess will do the right thing. For more details see "INCREMENTAL LOG PROCESSING" from man goaccess. systemd]: https://freedesktop.org/wiki/Software/systemd/ Implementation And here's how it all looks like. First, a little wrapper script for GoAccess:
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#!/bin/bash
# Usage: $0 SITE DBDIR LOGDIR OUTDIR
set -eu
SITE=$1
DBDIR=$2
LOGDIR=$3
OUTDIR=$4
LOGFILES=()
for ext in log log.1; do
    logfile="$LOGDIR/access.$ext"
    [ -e "$logfile" ] && LOGFILES+=("$logfile")
done
if [ $ #LOGFILES[@]  -eq 0 ]; then
    echo "No log files in '$LOGDIR'"
    exit 0
fi
goaccess \
    --agent-list \
    --anonymize-ip \
    --persist \
    --restore \
    --config-file /etc/goaccess/goaccess.conf \
    --db-path "$DBDIR" \
    --log-format "COMBINED" \
    --output "$OUTDIR/$SITE.html" \
    "$ LOGFILES[@] "
This wrapper does very little. Actually, the only thing it does is to check for the existence of the two log files access.log and access.log.1, to be sure that we don't ask GoAccess to process a file that does not exist (GoAccess would not be happy about that). Save this file under /usr/local/bin/goaccess-wrapper, don't forget to make it executable:
chmod +x /usr/local/bin/goaccess-wrapper
Then, create a systemd parameterized unit file, so that we can run this wrapper as a systemd service. Save it under /etc/systemd/system/goaccess@.service:
[Unit]
Description=Update GoAccess report - %i
ConditionPathIsDirectory=/var/lib/goaccess-db/%i
ConditionPathIsDirectory=/var/log/apache2/%i
ConditionPathIsDirectory=/tmp/goaccess-reports
PartOf=goaccess.service
[Service]
Type=oneshot
User=goaccess
Group=goaccess
Nice=19
ExecStart=/usr/local/bin/goaccess-wrapper \
 %i \
 /var/lib/goaccess-db/%i \
 /var/log/apache2/%i \
 /tmp/goaccess-reports
So, what is a systemd parameterized unit? It's a service to which you can pass an argument when you enable it. The %i in the unit definition will be replaced by this argument. In our case, the argument will be the name of the site that we want to process. As you can see, we use the directive ConditionPathIsDirectory= extensively, so that if ever one of the required directories does not exist, the unit will just be skipped (and marked as such in the logs). It's a graceful way to fail. We run the wrapper as the user and group goaccess, thanks to User= and Group=. We also use Nice= to give a low priority to the process. At this point, it's already possible to test. Just make sure that you created a directory for the GoAccess database:
mkdir -p /var/lib/goaccess-db/SITE
chown goaccess:goaccess /var/lib/goaccess-db/SITE
Also make sure that the output directory exists:
mkdir /tmp/goaccess-reports
chown goaccess:goaccess /tmp/goaccess-reports
Then reload systemd and fire the unit to see if it works:
systemctl daemon-reload
systemctl start goaccess@SITE.service
journalctl   tail
And that should work already. As you can see, the argument, SITE, is passed in the systemctl start command. We just append it after the @, in the name of the unit. Now, let's create another GoAccess service file, which sole purpose is to group all the parameterized units together, so that we can start them all in one go. Note that we don't use a systemd target for that, because ultimately we want to run it once a day, and that would not be possible with a target. So instead we use a dummy oneshot service. So here it is, saved under /etc/systemd/system/goaccess.service:
[Unit]
Description=Update GoAccess reports
Requires= \
 goaccess@SITE1.service \
 goaccess@SITE2.service
[Service]
Type=oneshot
ExecStart=true
As you can see, we simply list the sites that we want to process in the Requires= directive. In this example we have two sites named SITE1 and SITE2. Let's ensure that everything is still good:
systemctl daemon-reload
systemctl start goaccess.service
journalctl   tail
Check the logs, both sites SITE1 and SITE2 should have been processed. And finally, let's create a timer, so that systemd runs goaccess.service once a day. Save it under /etc/systemd/system/goaccess.timer.
[Unit]
Description=Daily update of GoAccess reports
[Timer]
OnCalendar=daily
RandomizedDelaySec=1h
Persistent=true
[Install]
WantedBy=timers.target
Finally, enable the timer:
systemctl daemon-reload
systemctl enable --now goaccess.timer
At this point, everything should be OK. Just come back tomorrow and check the logs with something like:
journalctl   grep goaccess
Last word: if you have only one site to process, of course you can simplify, for example you can hardcode all the paths in the file goaccess.service instead of using a parameterized unit. Up to you. Daily operations So in this part, we assume that you have GoAccess all setup and running, once a day or so. Let's just go over a few things worth noting. Serve your report Up to now in this tutorial, we created the reports in /tmp/goaccess-reports, but that was just for the sake of the example. You will probably want to save your reports in a directory that is served by your web server, so that, well, you can actually look at it in your web browser, that was the point, right? So how to do that is a bit out of scope here, and I guess that if you want to monitor your website, you already have a website, so you will have no trouble serving the GoAccess HTML report. However there's an important detail to be aware of: GoAccess shows all the IP addresses of your visitors in the report. As long as the report is private it's OK, but if ever you make your GoAccess report public, then you should definitely invoke GoAccess with the option --anonymize-ip. Keep an eye on the logs In this tutorial, the reports we create, along with the GoAccess databases, will grow bigger every day, forever. It also means that the GoAccess processing time will grow a bit each day. So maybe the first thing to do is to keep an eye on the logs, to see how long it takes to GoAccess to do its job every day. Also, maybe you'd like to keep an eye on the size of the GoAccess database with:
du -sh /var/lib/goaccess-db/SITE
If your site has few visitors, I suspect it won't be a problem though. You could also be a bit pro-active in preventing this problem in the future, and for example you could break the reports into, say, monthly reports. Meaning that every month, you would create a new database in a new directory, and also start a new HTML report. This way you'd have monthly reports, and you make sure to limit the GoAccess processing time, by limiting the database size to a month. This can be achieved very easily, by including something like YEAR-MONTH in the database directory, and in the HTML report. You can handle that automatically in the wrapper script, for example:
sfx=$(date +'%Y-%m')
mkdir -p $DBDIR/$sfx
goaccess \
    --db-path $DBDIR/$sfx \
    --output "$OUTDIR/$SITE-$sfx.html" \
    ...
You get the idea. Further notes Migration from older versions With the --persist option, GoAccess keeps all the information from the logs in a database, so that it can re-use it later. In prior versions, GoAccess used the Tokyo Cabinet key-value store for that. However starting from v1.4, GoAccess dropped this dependency and now uses its own database format. As a result, the previous database can't be used anymore, you will have to remove it and restart from zero. At the moment there is no way to convert the data from the old database to the new one. If you're interested, this is discussed upstream at [#1783][bug-1783]. Another thing that changed with this new version is the name for some of the command-line options. For example, --load-from-disk was dropped in favor of --restore, and --keep-db-files became --persist. So you'll have to look at the documentation a bit, and update your script(s) accordingly. Other ways to use GoAccess It's also possible to do it completely differently. You could keep GoAccess running, pretty much like a daemon, with the --real-time-html option, and have it process the logs continuously, rather than calling it on a regular basis. It's also possible to see the GoAccess report straight in the terminal, thanks to libncurses, rather than creating a HTML report. And much more, GoAccess is packed with features. Conclusion I hope that this tutorial helped some of you folks. Feel free to drop an e-mail for comments.

Arnaud Rebillout: GoAccess 1.4, a detailed tutorial

GoAccess v1.4 was just released a few weeks ago! Let's take this chance to write a loooong tutorial. We'll go over every steps to install and operate GoAccess. This is a tutorial aimed at those who don't play sysadmin every day, and that's why it's so long, I did my best to provide thorough explanations all along, so that it's more than just a "copy-and-paste" kind of tutorial. And for those who do play sysadmin everyday: please try not to fall asleep while reading, and don't hesitate to drop me an e-mail if you spot anything inaccurate in here. Thanks! Introduction So what's GoAccess already? GoAccess is a web log analyzer, and it allows you to visualize the traffic for your website, and get to know a bit more about your visitors: how many visitors and hits, for which pages, coming from where (geolocation, operating system, web browser...), etc... It does so by parsing the access logs from your web server, be it Apache, NGINX or whatever. GoAccess gives you different options to display the statistics, and in this tutorial we'll focus on producing a HTML report. Meaning that you can see the statistics for your website straight in your web browser, under the form of a single HTML page. For an example, you can have a look at the stats of my blog here: https://goaccess.arnaudr.io. GoAccess is written in C, it has very few dependencies, it had been around for about 10 years, and it's distributed under the MIT license. Assumptions This tutorial is about installing and configuring, so I'll assume that all the commands are run as root. I won't prefix each of them with sudo. I use the Apache web server, running on a Debian system. I don't think it matters so much for this tutorial though. If you're using NGINX it's fine, you can keep reading. Also, I will just use the name SITE for the name of the website that we want to analyze with GoAccess. Just replace that with the real name of your site. I also assume the following locations for your stuff: If you have your stuff in /srv/SITE/ log,www instead, no worries, just adjust the paths accordingly, I bet you can do it. Installation The latest version of GoAccess is v1.4, and it's not yet available in the Debian repositories. So for this part, you can follow the instructions from the official GoAccess download page. Install steps are explained in details, so there's nothing left for me to say :) When this is done, let's get started with the basics. We're talking about the latest version v1.4 here, let's make sure:
$ goaccess --version
GoAccess - 1.4.
...
Now let's try to create a HTML report. I assume that you already have a website up and running. GoAccess needs to parse the access logs. These logs are optional, they might or might not be created by your web server, depending on how it's configured. Usually, these log files are named access.log, unsurprisingly. You can check if those logs exist on your system by running this command:
find /var/log -name access.log
Another important thing to know is that these logs can be in different formats. In this tutorial we'll assume that we work with the combined log format, because it seems to be the most common default. To check what kind of access logs your web server produces, you must look at the configuration for your site. For an Apache web server, you should have such a line in the file /etc/apache2/sites-enabled/SITE.conf:
CustomLog $ APACHE_LOG_DIR /SITE/access.log combined
For NGINX, it's quite similar. The configuration file would be something like /etc/nginx/sites-enabled/SITE, and the line to enable access logs would be something like:
access_log /var/log/nginx/SITE/access.log
Note that NGINX writes the access logs in the combined format by default, that's why you don't see the word combined anywhere in the line above: it's implicit. Alright, so from now on we assume that yes, you have access log files available, and yes, they are in the combined log format. If that's the case, then you can already run GoAccess and generate a report, for example for the log file /var/log/apache2/access.log
goaccess \
    --log-format COMBINED \
    --output /tmp/report.html \
    /var/log/apache2/access.log
It's possible to give GoAccess more than one log files to process, so if you have for example the file access.log.1 around, you can use it as well:
goaccess \
    --log-format COMBINED \
    --output /tmp/report.html \
    /var/log/apache2/access.log \
    /var/log/apache2/access.log.1
If GoAccess succeeds (and it should), you're on the right track! All is left to do to complete this test is to have a look at the HTML report created. It's a single HTML page, so you can easily scp it to your machine, or just move it to the document root of your site, and then open it in your web browser. Looks good? So let's move on to more interesting things. Web server configuration This part is very short, because in terms of configuration of the web server, there's very little to do. As I said above, the only thing you want from the web server is to create access log files. Then you want to be sure that GoAccess and your web server agree on the format for these files. In the part above we used the combined log format, but GoAccess supports many other common log formats out of the box, and even allows you to parse custom log formats. For more details, refer to the option --log-format in the GoAccess manual page. Another common log format is named, well, common. It even has its own Wikipedia page. But compared to combined, the common log format contains less information, it doesn't include the referrer and user-agent values, meaning that you won't have it in the GoAccess report. So at this point you should understand that, unsurprisingly, GoAccess can only tell you about what's in the access logs, no more no less. And that's all in term of web server configuration. Configuration to run GoAccess unprivileged Now we're going to create a user and group for GoAccess, so that we don't have to run it as root. The reason is that, well, for everything running unattended on your server, the less code runs as root, the better. It's good practice and common sense. In this case, GoAccess is simply a log analyzer. So it just needs to read the logs files from your web server, and there is no need to be root for that, an unprivileged user can do the job just as well, assuming it has read permissions on /var/log/apache2 or /var/log/nginx. The log files of the web server are usually part of the adm group (though it might depend on your distro, I'm not sure). This is something you can check easily with the following command:
ls -l /var/log   grep -e apache2 -e nginx
As a result you should get something like that:
drwxr-x--- 2 root adm 20480 Jul 22 00:00 /var/log/apache2/
And as you can see, the directory apache2 belongs to the group adm. It means that you don't need to be root to read the logs, instead any unprivileged user that belongs to the group adm can do it. So, let's create the goaccess user, and add it to the adm group:
adduser --system --group --no-create-home goaccess
addgroup goaccess adm
And now, let's run GoAccess unprivileged, and verify that it can still read the log files:
setpriv \
    --reuid=goaccess --regid=goaccess \
    --init-groups --inh-caps=-all \
    -- \
    goaccess \
    --log-format COMBINED \
    --output /tmp/report2.html \
    /var/log/apache2/access.log
setpriv is the command used to drop privileges. The syntax is quite verbose, it's not super friendly for tutorials, but don't be scared and read the manual page to learn what it does. In any case, this command should work, and at this point, it means that you have a goaccess user ready, and we'll use it to run GoAccess unprivileged. Integration, option A - Run GoAccess once a day, from a logrotate hook In this part we wire things together, so that GoAccess processes the log files once a day, adds the new logs to its internal database, and generates a report from all that aggregated data. The result will be a single HTML page. Introducing logrotate In order to do that, we'll use a logrotate hook. logrotate is a little tool that should already be installed on your server, and that runs once a day, and that is in charge of rotating the log files. "Rotating the logs" means moving access.log to access.log.1 and so on. With logrotate, a new log file is created every day, and log files that are too old are deleted. That's what prevents your logs from filling up your disk basically :) You can check that logrotate is indeed installed and enabled with this command (assuming that your init system is systemd):
systemctl status logrotate.timer
What's interesting for us is that logrotate allows you to run scripts before and after the rotation is performed, so it's an ideal place from where to run GoAccess. In short, we want to run GoAccess just before the logs are rotated away, in the prerotate hook. But let's do things in order. At first, we need to write a little wrapper script that will be in charge of running GoAccess with the right arguments, and that will process all of your sites. The wrapper script This wrapper is made to process more than one site, but if you have only one site it works just as well, of course. So let me just drop it on you like that, and I'll explain afterward. Here's my wrapper script:
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#!/bin/bash
# Process log files /var/www/apache2/SITE/access.log,
# only if /var/lib/goaccess-db/SITE exists.
# Create HTML reports in $1, a directory that must exist.
set -eu
OUTDIR=
LOGDIR=/var/log/apache2
DBDIR=/var/lib/goaccess-db
fail()   echo >&2 "$@"; exit 1;  
[ $# -eq 1 ]   fail "Usage: $(basename $0) OUTPUT_DIRECTORY"
OUTDIR=$1
[ -d "$OUTDIR" ]   fail "'$OUTDIR' is not a directory"
[ -d "$LOGDIR" ]   fail "'$LOGDIR' is not a directory"
[ -d "$DBDIR"  ]   fail "'$DBDIR' is not a directory"
for d in $(find "$LOGDIR" -mindepth 1 -maxdepth 1 -type d); do
    site=$(basename "$sitedir")
    dbdir=$DBDIR/$site
    logfile=$d/access.log
    outfile=$OUTDIR/$site.html
    if [ ! -d "$dbdir" ]   [ ! -e "$logfile" ]; then
        echo "  Skipping site '$site'"
        continue
    else
        echo "  Processing site '$site'"
    fi
    setpriv \
        --reuid=goaccess --regid=goaccess \
        --init-groups --inh-caps=-all \
        -- \
    goaccess \
        --agent-list \
        --anonymize-ip \
        --persist \
        --restore \
        --config-file /etc/goaccess/goaccess.conf \
        --db-path "$dbdir" \
        --log-format "COMBINED" \
        --output "$outfile" \
        "$logfile"
done
So you'd install this script at /usr/local/bin/goaccess-wrapper for example, and make it executable:
chmod +x /usr/local/bin/goaccess-wrapper
A few things to note: As is, the script makes the assumption that the logs for your site are logged in a sub-directory /var/log/apache2/SITE/. If it's not the case, adjust that in the wrapper accordingly. The name of this sub-directory is then used to find the GoAccess database directory /var/lib/goaccess-db/SITE/. This directory is expected to exist, meaning that if you don't create it yourself, the wrapper won't process this particular site. It's a simple way to control which sites are processed by this GoAccess wrapper, and which sites are not. So if you want goaccess-wrapper to process the site SITE, just create a directory with the name of this site under /var/lib/goaccess-db:
mkdir -p /var/lib/goaccess-db/SITE
chown goaccess:goaccess /var/lib/goaccess-db/SITE
Now let's create an output directory:
mkdir /tmp/goaccess-reports
chown goaccess:goaccess /tmp/goaccess-reports
And let's give a try to the wrapper script:
goaccess-wrapper /tmp/goaccess-reports
ls /tmp/goaccess-reports
Which should give you:
SITE.html
At the same time, you can check that GoAccess populated the database with a bunch of files:
ls /var/lib/goaccess-db/SITE
Setting up the logrotate prerotate hook At this point, we have the wrapper in place. Let's now add a pre-rotate hook so that goaccess-wrapper runs once a day, just before the logs are rotated away. The logrotate config file for Apache2 is located at /etc/logrotate.d/apache2, and for NGINX it's at /etc/logrotate.d/nginx. Among the many things you'll see in this file, here's what is of interest for us: In the config file, there is also this snippet:
prerotate
    if [ -d /etc/logrotate.d/httpd-prerotate ]; then \
        run-parts /etc/logrotate.d/httpd-prerotate; \
    fi; \
endscript
It indicates that scripts in the directory /etc/logrotate.d/httpd-prerotate/ will be executed before the rotation takes place. Refer to the man page run-parts(8) for more details... Putting all of that together, it means that logs from the web server are rotated once a day, and if we want to run scripts just before the rotation, we can just drop them in the httpd-prerotate directory. Simple, right? Let's first create this directory if it doesn't exist:
mkdir -p /etc/logrotate.d/httpd-prerotate/
And let's create a tiny script at /etc/logrotate.d/httpd-prerotate/goaccess:
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#!/bin/sh
exec goaccess-wrapper /tmp/goaccess-reports
Don't forget to make it executable:
chmod +x /etc/logrotate.d/httpd-prerotate/goaccess
As you can see, the only thing that this script does is to invoke the wrapper with the right argument, ie. the output directory for the HTML reports that are generated. And that's all. Now you can just come back tomorrow, check the logs, and make sure that the hook was executed and succeeded. For example, this kind of command will tell you quickly if it worked:
journalctl   grep logrotate
Integration, option B - Run GoAccess once a day, from a systemd service OK so we've just seen how to use a logrotate hook. One downside with that is that we have to drop privileges in the wrapper script, because logrotate runs as root, and we don't want to run GoAccess as root. Hence the rather convoluted syntax with setpriv. Rather than embedding this kind of thing in a wrapper script, we can instead run the wrapper script from a [systemd][] service, and define which user runs the wrapper straight in the systemd service file. Introducing systemd niceties So we can create a systemd service, along with a systemd timer that fires daily. We can then set the user and group that execute the script straight in the systemd service, and there's no need for setpriv anymore. It's a bit more streamlined. We can even go a bit further, and use systemd parameterized units (also called templates), so that we have one service per site (instead of one service that process all of our sites). That will simplify the wrapper script a lot, and it also looks nicer in the logs. With this approach however, it seems that we can't really run exactly before the logs are rotated away, like we did in the section above. But that's OK. What we'll do is that we'll run once a day, no matter the time, and we'll just make sure to process both log files access.log and access.log.1 (ie. the current logs and the logs from yesterday). This way, we're sure not to miss any line from the logs. Note that GoAccess is smart enough to only consider newer entries from the log files, and discard entries that are already in the database. In other words, it's safe to parse the same log file more than once, GoAccess will do the right thing. For more details see "INCREMENTAL LOG PROCESSING" from man goaccess. systemd]: https://freedesktop.org/wiki/Software/systemd/ Implementation And here's how it all looks like. First, a little wrapper script for GoAccess:
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#!/bin/bash
# Usage: $0 SITE DBDIR LOGDIR OUTDIR
set -eu
SITE=$1
DBDIR=$2
LOGDIR=$3
OUTDIR=$4
LOGFILES=()
for ext in log log.1; do
    logfile="$LOGDIR/access.$ext"
    [ -e "$logfile" ] && LOGFILES+=("$logfile")
done
if [ $ #LOGFILES[@]  -eq 0 ]; then
    echo "No log files in '$LOGDIR'"
    exit 0
fi
goaccess \
    --agent-list \
    --anonymize-ip \
    --persist \
    --restore \
    --config-file /etc/goaccess/goaccess.conf \
    --db-path "$DBDIR" \
    --log-format "COMBINED" \
    --output "$OUTDIR/$SITE.html" \
    "$ LOGFILES[@] "
This wrapper does very little. Actually, the only thing it does is to check for the existence of the two log files access.log and access.log.1, to be sure that we don't ask GoAccess to process a file that does not exist (GoAccess would not be happy about that). Save this file under /usr/local/bin/goaccess-wrapper, don't forget to make it executable:
chmod +x /usr/local/bin/goaccess-wrapper
Then, create a systemd parameterized unit file, so that we can run this wrapper as a systemd service. Save it under /etc/systemd/system/goaccess@.service:
[Unit]
Description=Update GoAccess report - %i
ConditionPathIsDirectory=/var/lib/goaccess-db/%i
ConditionPathIsDirectory=/var/log/apache2/%i
ConditionPathIsDirectory=/tmp/goaccess-reports
PartOf=goaccess.service
[Service]
Type=oneshot
User=goaccess
Group=goaccess
Nice=19
ExecStart=/usr/local/bin/goaccess-wrapper \
 %i \
 /var/lib/goaccess-db/%i \
 /var/log/apache2/%i \
 /tmp/goaccess-reports
So, what is a systemd parameterized unit? It's a service to which you can pass an argument when you enable it. The %i in the unit definition will be replaced by this argument. In our case, the argument will be the name of the site that we want to process. As you can see, we use the directive ConditionPathIsDirectory= extensively, so that if ever one of the required directories does not exist, the unit will just be skipped (and marked as such in the logs). It's a graceful way to fail. We run the wrapper as the user and group goaccess, thanks to User= and Group=. We also use Nice= to give a low priority to the process. At this point, it's already possible to test. Just make sure that you created a directory for the GoAccess database:
mkdir -p /var/lib/goaccess-db/SITE
chown goaccess:goaccess /var/lib/goaccess-db/SITE
Also make sure that the output directory exists:
mkdir /tmp/goaccess-reports
chown goaccess:goaccess /tmp/goaccess-reports
Then reload systemd and fire the unit to see if it works:
systemctl daemon-reload
systemctl start goaccess@SITE.service
journalctl   tail
And that should work already. As you can see, the argument, SITE, is passed in the systemctl start command. We just append it after the @, in the name of the unit. Now, let's create another GoAccess service file, which sole purpose is to group all the parameterized units together, so that we can start them all in one go. Note that we don't use a systemd target for that, because ultimately we want to run it once a day, and that would not be possible with a target. So instead we use a dummy oneshot service. So here it is, saved under /etc/systemd/system/goaccess.service:
[Unit]
Description=Update GoAccess reports
Requires= \
 goaccess@SITE1.service \
 goaccess@SITE2.service
[Service]
Type=oneshot
ExecStart=true
As you can see, we simply list the sites that we want to process in the Requires= directive. In this example we have two sites named SITE1 and SITE2. Let's ensure that everything is still good:
systemctl daemon-reload
systemctl start goaccess.service
journalctl   tail
Check the logs, both sites SITE1 and SITE2 should have been processed. And finally, let's create a timer, so that systemd runs goaccess.service once a day. Save it under /etc/systemd/system/goaccess.timer.
[Unit]
Description=Daily update of GoAccess reports
[Timer]
OnCalendar=daily
RandomizedDelaySec=1h
Persistent=true
[Install]
WantedBy=timers.target
Finally, enable the timer:
systemctl daemon-reload
systemctl enable --now goaccess.timer
At this point, everything should be OK. Just come back tomorrow and check the logs with something like:
journalctl   grep goaccess
Last word: if you have only one site to process, of course you can simplify, for example you can hardcode all the paths in the file goaccess.service instead of using a parameterized unit. Up to you. Daily operations So in this part, we assume that you have GoAccess all setup and running, once a day or so. Let's just go over a few things worth noting. Serve your report Up to now in this tutorial, we created the reports in /tmp/goaccess-reports, but that was just for the sake of the example. You will probably want to save your reports in a directory that is served by your web server, so that, well, you can actually look at it in your web browser, that was the point, right? So how to do that is a bit out of scope here, and I guess that if you want to monitor your website, you already have a website, so you will have no trouble serving the GoAccess HTML report. However there's an important detail to be aware of: GoAccess shows all the IP addresses of your visitors in the report. As long as the report is private it's OK, but if ever you make your GoAccess report public, then you should definitely invoke GoAccess with the option --anonymize-ip. Keep an eye on the logs In this tutorial, the reports we create, along with the GoAccess databases, will grow bigger every day, forever. It also means that the GoAccess processing time will grow a bit each day. So maybe the first thing to do is to keep an eye on the logs, to see how long it takes to GoAccess to do its job every day. Also, maybe you'd like to keep an eye on the size of the GoAccess database with:
du -sh /var/lib/goaccess-db/SITE
If your site has few visitors, I suspect it won't be a problem though. You could also be a bit pro-active in preventing this problem in the future, and for example you could break the reports into, say, monthly reports. Meaning that every month, you would create a new database in a new directory, and also start a new HTML report. This way you'd have monthly reports, and you make sure to limit the GoAccess processing time, by limiting the database size to a month. This can be achieved very easily, by including something like YEAR-MONTH in the database directory, and in the HTML report. You can handle that automatically in the wrapper script, for example:
sfx=$(date +'%Y-%m')
mkdir -p $DBDIR/$sfx
goaccess \
    --db-path $DBDIR/$sfx \
    --output "$OUTDIR/$SITE-$sfx.html" \
    ...
You get the idea. Further notes Migration from older versions With the --persist option, GoAccess keeps all the information from the logs in a database, so that it can re-use it later. In prior versions, GoAccess used the Tokyo Cabinet key-value store for that. However starting from v1.4, GoAccess dropped this dependency and now uses its own database format. As a result, the previous database can't be used anymore, you will have to remove it and restart from zero. At the moment there is no way to convert the data from the old database to the new one. If you're interested, this is discussed upstream at [#1783][bug-1783]. Another thing that changed with this new version is the name for some of the command-line options. For example, --load-from-disk was dropped in favor of --restore, and --keep-db-files became --persist. So you'll have to look at the documentation a bit, and update your script(s) accordingly. Other ways to use GoAccess It's also possible to do it completely differently. You could keep GoAccess running, pretty much like a daemon, with the --real-time-html option, and have it process the logs continuously, rather than calling it on a regular basis. It's also possible to see the GoAccess report straight in the terminal, thanks to libncurses, rather than creating a HTML report. And much more, GoAccess is packed with features. Conclusion I hope that this tutorial helped some of you folks. Feel free to drop an e-mail for comments.

9 August 2020

Junichi Uekawa: Started writing some golang code.

Started writing some golang code. Trying to rewrite some of the tools as a daily driver for machine management tool. It's easier than rust in that having a good rust compiler is a hassle though golang preinstalled on systems can build and run. go run is simple enough to invoke on most Debian systems.

8 August 2020

Holger Levsen: 20200808-debconf8

DebConf8 This tshirt is 12 years old and from DebConf8. DebConf8 was my 6th DebConf and took place in Mar de la Plata, Argentina. Also this is my 6th post in this series of posts about DebConfs and for the last two days for the first time I failed my plan to do one post per day. And while two days ago I still planned to catch up on this by doing more than one post in a day, I have now decided to give in to realities, which mostly translates to sudden fantastic weather in Hamburg and other summer related changes in life. So yeah, I still plan to do short posts about all the DebConfs I was lucky to attend, but there might be days without a blog post. Anyhow, Mar de la Plata. When we held DebConf in Argentina it was winter there, meaning locals and other folks would wear jackets, scarfs, probably gloves, while many Debian folks not so much. Andreas Tille freaked out and/or amazed local people by going swimming in the sea every morning. And when I told Stephen Gran that even I would find it a bit cold with just a tshirt he replied "na, the weather is fine, just like british summer", while it was 14 celcius and mildly raining. DebConf8 was the first time I've met Valessio Brito, who I had worked together since at least DebConf6. That meeting was really super nice, Valessio is such a lovely person. Back in 2008 however, there was just one problem: his spoken English was worse than his written one, and that was already hard to parse sometimes. Fast forward eleven years to Curitiba last year and boom, Valessio speaks really nice English now. And, you might wonder why I'm telling this, especially if you were exposed to my Spanish back then and also now. So my point in telling this story about Valessio is to illustrate two things: a.) one can contribute to Debian without speaking/writing much English, Valessio did lots of great artwork since DebConf6 and b.) one can learn English by doing Debian stuff. It worked for me too! During set up of the conference there was one very memorable moment, some time after the openssl maintainer, Kurt Roeckx arrived at the venue: Shortly before DebConf8 Luciano Bello, from Argentina no less, had found CVE-2008-0166 which basically compromised the security of sshd of all Debian and Ubuntu installations done in the last 4 years (IIRC two Debian releases were affected) and which was commented heavily and noticed everywhere. So poor Kurt arrived and wondered whether we would all hate him, how many toilets he would have to clean and what not... And then, someone rather quickly noticed this, approached some people and suddenly a bunch of people at DebConf were group-hugging Kurt and then we were all smiling and continuing doing set up of the conference. That moment is one of my most joyful memories of all DebConfs and partly explains why I remember little about the conference itself, everything else pales in comparison and most things pale over the years anyway. As I remember it, the conference ran very smoothly in the end, despite quite some organisational problems right before the start. But as usual, once the geeks arrive and are happily geeking, things start to run smooth, also because Debian people are kind and smart and give hands and brain were needed. And like other DebConfs, Mar de la Plata also had moments which I want to share but I will only hint about, so it's up to you to imagine the special leaves which were brought to that cheese and wine party! ;-) Update: added another xkcd link, spelled out Kurt's name after talking to him and added a link to a video of the group hug.

Reproducible Builds: Reproducible Builds in July 2020

Welcome to the July 2020 report from the Reproducible Builds project. In these monthly reports, we round-up the things that we have been up to over the past month. As a brief refresher, the motivation behind the Reproducible Builds effort is to ensure no flaws have been introduced from the original free software source code to the pre-compiled binaries we install on our systems. (If you re interested in contributing to the project, please visit our main website.)

General news At the upcoming DebConf20 conference (now being held online), Holger Levsen will present a talk on Thursday 27th August about Reproducing Bullseye in practice , focusing on independently verifying that the binaries distributed from ftp.debian.org were made from their claimed sources. Tavis Ormandy published a blog post making the provocative claim that You don t need reproducible builds , asserting elsewhere that the many attacks that have been extensively reported in our previous reports are fantasy threat models . A number of rebuttals have been made, including one from long-time contributor Reproducible Builds contributor Bernhard Wiedemann. On our mailing list this month, Debian Developer Graham Inggs posted to our list asking for ideas why the openorienteering-mapper Debian package was failing to build on the Reproducible Builds testing framework. Chris Lamb remarked from the build logs that the package may be missing a build dependency, although Graham then used our own diffoscope tool to show that the resulting package remains unchanged with or without it. Later, Nico Tyni noticed that the build failure may be due to the relationship between the FILE C preprocessor macro and the -ffile-prefix-map GCC flag. An issue in Zephyr, a small-footprint kernel designed for use on resource-constrained systems, around .a library files not being reproducible was closed after it was noticed that a key part of their toolchain was updated that now calls --enable-deterministic-archives by default. Reproducible Builds developer kpcyrd commented on a pull request against the libsodium cryptographic library wrapper for Rust, arguing against the testing of CPU features at compile-time. He noted that:
I ve accidentally shipped broken updates to users in the past because the build system was feature-tested and the final binary assumed the instructions would be present without further runtime checks
David Kleuker also asked a question on our mailing list about using SOURCE_DATE_EPOCH with the install(1) tool from GNU coreutils. When comparing two installed packages he noticed that the filesystem birth times differed between them. Chris Lamb replied, realising that this was actually a consequence of using an outdated version of diffoscope and that a fix was in diffoscope version 146 released in May 2020. Later in July, John Scott posted asking for clarification regarding on the Javascript files on our website to add metadata for LibreJS, the browser extension that blocks non-free Javascript scripts from executing. Chris Lamb investigated the issue and realised that we could drop a number of unused Javascript files [ ][ ][ ] and added unminified versions of Bootstrap and jQuery [ ].

Development work

Website On our website this month, Chris Lamb updated the main Reproducible Builds website and documentation to drop a number of unused Javascript files [ ][ ][ ] and added unminified versions of Bootstrap and jQuery [ ]. He also fixed a number of broken URLs [ ][ ]. Gonzalo Bulnes Guilpain made a large number of grammatical improvements [ ][ ][ ][ ][ ] as well as some misspellings, case and whitespace changes too [ ][ ][ ]. Lastly, Holger Levsen updated the README file [ ], marked the Alpine Linux continuous integration tests as currently disabled [ ] and linked the Arch Linux Reproducible Status page from our projects page [ ].

diffoscope diffoscope is our in-depth and content-aware diff utility that can not only locate and diagnose reproducibility issues, it provides human-readable diffs of all kinds. In July, Chris Lamb made the following changes to diffoscope, including releasing versions 150, 151, 152, 153 & 154:
  • New features:
    • Add support for flash-optimised F2FS filesystems. (#207)
    • Don t require zipnote(1) to determine differences in a .zip file as we can use libarchive. [ ]
    • Allow --profile as a synonym for --profile=-, ie. write profiling data to standard output. [ ]
    • Increase the minimum length of the output of strings(1) to eight characters to avoid unnecessary diff noise. [ ]
    • Drop some legacy argument styles: --exclude-directory-metadata and --no-exclude-directory-metadata have been replaced with --exclude-directory-metadata= yes,no . [ ]
  • Bug fixes:
    • Pass the absolute path when extracting members from SquashFS images as we run the command with working directory in a temporary directory. (#189)
    • Correct adding a comment when we cannot extract a filesystem due to missing libguestfs module. [ ]
    • Don t crash when listing entries in archives if they don t have a listed size such as hardlinks in ISO images. (#188)
  • Output improvements:
    • Strip off the file offset prefix from xxd(1) and show bytes in groups of 4. [ ]
    • Don t emit javap not found in path if it is available in the path but it did not result in an actual difference. [ ]
    • Fix ... not available in path messages when looking for Java decompilers that used the Python class name instead of the command. [ ]
  • Logging improvements:
    • Add a bit more debugging info when launching libguestfs. [ ]
    • Reduce the --debug log noise by truncating the has_some_content messages. [ ]
    • Fix the compare_files log message when the file does not have a literal name. [ ]
  • Codebase improvements:
    • Rewrite and rename exit_if_paths_do_not_exist to not check files multiple times. [ ][ ]
    • Add an add_comment helper method; don t mess with our internal list directly. [ ]
    • Replace some simple usages of str.format with Python f-strings [ ] and make it easier to navigate to the main.py entry point [ ].
    • In the RData comparator, always explicitly return None in the failure case as we return a non-None value in the success one. [ ]
    • Tidy some imports [ ][ ][ ] and don t alias a variable when we do not use it. [ ]
    • Clarify the use of a separate NullChanges quasi-file to represent missing data in the Debian package comparator [ ] and clarify use of a null diff in order to remember an exit code. [ ]
  • Other changes:
    • Profile the launch of libguestfs filesystems. [ ]
    • Clarify and correct our contributing info. [ ][ ][ ][ ][ ][ ]
Jean-Romain Garnier also made the following changes:
  • Allow passing a file with a list of arguments via diffoscope @args.txt. (!62)
  • Improve the output of side-by-side diffs by detecting added lines better. (!64)
  • Remove offsets before instructions in objdump [ ][ ] and remove raw instructions from ELF tests [ ].

Other tools strip-nondeterminism is our tool to remove specific non-deterministic results from a completed build. It is used automatically in most Debian package builds. In July, Chris Lamb ensured that we did not install the internal handler documentation generated from Perl POD documents [ ] and fixed a trivial typo [ ]. Marc Herbert added a --verbose-level warning when the Archive::Cpio Perl module is missing. (!6) reprotest is our end-user tool to build same source code twice in widely differing environments and then checks the binaries produced by each build for any differences. This month, Vagrant Cascadian made a number of changes to support diffoscope version 153 which had removed the (deprecated) --exclude-directory-metadata and --no-exclude-directory-metadata command-line arguments, and updated the testing configuration to also test under Python version 3.8 [ ].

Distributions

Debian In June 2020, Timo R hling filed a wishlist bug against the debhelper build tool impacting the reproducibility status of hundreds of packages that use the CMake build system. This month however, Niels Thykier uploaded debhelper version 13.2 that passes the -DCMAKE_SKIP_RPATH=ON and -DBUILD_RPATH_USE_ORIGIN=ON arguments to CMake when using the (currently-experimental) Debhelper compatibility level 14. According to Niels, this change:
should fix some reproducibility issues, but may cause breakage if packages run binaries directly from the build directory.
34 reviews of Debian packages were added, 14 were updated and 20 were removed this month adding to our knowledge about identified issues. Chris Lamb added and categorised the nondeterministic_order_of_debhelper_snippets_added_by_dh_fortran_mod [ ] and gem2deb_install_mkmf_log [ ] toolchain issues. Lastly, Holger Levsen filed two more wishlist bugs against the debrebuild Debian package rebuilder tool [ ][ ].

openSUSE In openSUSE, Bernhard M. Wiedemann published his monthly Reproducible Builds status update. Bernhard also published the results of performing 12,235 verification builds of packages from openSUSE Leap version 15.2 and, as a result, created three pull requests against the openSUSE Build Result Compare Script [ ][ ][ ].

Other distributions In Arch Linux, there was a mass rebuild of old packages in an attempt to make them reproducible. This was performed because building with a previous release of the pacman package manager caused file ordering and size calculation issues when using the btrfs filesystem. A system was also implemented for Arch Linux packagers to receive notifications if/when their package becomes unreproducible, and packagers now have access to a dashboard where they can all see all their unreproducible packages (more info). Paul Spooren sent two versions of a patch for the OpenWrt embedded distribution for adding a build system revision to the packages manifest so that all external feeds can be rebuilt and verified. [ ][ ]

Upstream patches The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where appropriate. This month, we wrote a large number of these patches, including: Vagrant Cascadian also reported two issues, the first regarding a regression in u-boot boot loader reproducibility for a particular target [ ] and a non-deterministic segmentation fault in the guile-ssh test suite [ ]. Lastly, Jelle van der Waa filed a bug against the MeiliSearch search API to report that it embeds the current build date.

Testing framework We operate a large and many-featured Jenkins-based testing framework that powers tests.reproducible-builds.org. This month, Holger Levsen made the following changes:
  • Debian-related changes:
    • Tweak the rescheduling of various architecture and suite combinations. [ ][ ]
    • Fix links for 404 and not for us icons. (#959363)
    • Further work on a rebuilder prototype, for example correctly processing the sbuild exit code. [ ][ ]
    • Update the sudo configuration file to allow the node health job to work correctly. [ ]
    • Add php-horde packages back to the pkg-php-pear package set for the bullseye distribution. [ ]
    • Update the version of debrebuild. [ ]
  • System health check development:
    • Add checks for broken SSH [ ], logrotate [ ], pbuilder [ ], NetBSD [ ], unkillable processes [ ], unresponsive nodes [ ][ ][ ][ ], proxy connection failures [ ], too many installed kernels [ ], etc.
    • Automatically fix some failed systemd units. [ ]
    • Add notes explaining all the issues that hosts are experiencing [ ] and handle zipped job log files correctly [ ].
    • Separate nodes which have been automatically marked as down [ ] and show status icons for jobs with issues [ ].
  • Misc:
    • Disable all Alpine Linux jobs until they are or Alpine is fixed. [ ]
    • Perform some general upkeep of build nodes hosted by OSUOSL. [ ][ ][ ][ ]
In addition, Mattia Rizzolo updated the init_node script to suggest using sudo instead of explicit logout and logins [ ][ ] and the usual build node maintenance was performed by Holger Levsen [ ][ ][ ][ ][ ][ ], Mattia Rizzolo [ ][ ] and Vagrant Cascadian [ ][ ][ ][ ].

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