February 05, 2019

Nicolas Dandrimont a.k.a olasd

It is complete!

(well, at least the front of it is)

After last week’s DebConf Video Team sprint (thanks again to Jasper @ Linux Belgium for hosting us), the missing components for the stage box turned up right as I was driving back to Paris, and I could take the time to assemble them tonight.

The final inventory of this 6U rack is, from top to bottom:

  • U1: 1 Shure UA844+SWB antenna and power distribution system
  • U2 and U3: 4 Shure BLX4R/S8 receivers
  • U4: 1 Numato Opsis, 1 Minnowboard Turbot, 1 Netgear Gigabit Ethernet Switch to do presenter laptop (HDMI) capture, all neatly packed in a rackmount case.
  • U5 and U6: 1 tray with 2 BLX1/S8 belt packs with MX153T earset microphones and 2 BLX2/SM58 handheld microphone assemblies

This combination of audio and video equipment is all the things that the DebConf Video Team needs to have near the stage to record presentations in one room.

The next step will be to get the back panel milled to properly mount connectors, so that we don’t have to take the back of the box apart to wire things up 🙂

You may see this equipment in action at one of Debian’s upcoming events.

by olasd at February 05, 2019 08:07 PM

December 23, 2018

Antoine Amarilli a.k.a a3nm

Trying out Wayland

I had been meaning for a long time to try out Wayland, which is designed as a modern replacement for the Linux graphical stack, the X Window System. The main selling point of Wayland for me is that it is better designed in terms of security: processes don't have access to each other's events, unlike X where any process can listen to all events that happen on the server. The lack of security in the design of X is a real problem: no matter which other kind of sandboxing you put in place (e.g., separate users, containers, etc.), you can't prevent a rogue process (e.g., malicious JavaScript using a browser security vulnerability) to access all events and, e.g., log all keystrokes that happen elsewhere in the session.

It is possible to sandbox processes in X by running an X server within the X server, e.g., Xnest, or more commonly Xpra. The way this works is that Xpra acts both as a client for the running X server, and as an X server in which you can run the process that you wish to sandbox: Xpra does not give the running process access to all events of the X server, but only gives it the events that it needs. This is what is done by Subuser, and it is what I did in my old setup to sandbox Skype. However, this is a rather ugly hack, and my experience the performance of the applications running inside Xpra has always been quite bad -- usable for Skype, but not really usable for something like a web browser. (I had tested this long ago by compiling the latest version of Xpra, and I just tested it again with the version packaged by Debian: video playback in a Web browser is not smooth.)

Another solution is what is done by QubesOS, which I haven't tested yet, but seems difficult to separate from the rest of their system (which looks interesting, but I'm not ready to migrate there yet). They are also thinking about using Wayland.

Anyway, Wayland looked like a reasonable solution to the problem, especially as the window manager that I use, i3, has been faithfully adapted to Wayland: sway. So I tried it out, and after some hours it seems to be fairly usable (using the Wayland packaged by Debian testing). This blogpost documents what I did.

Installing sway and its dependencies

Use apt-get to install all requisite dependencies for sway, and its dependency wlroots. The list of the packages that I installed for this is here. We will also need a recent version of libjson-c, because the one packaged by Debian is too old.

Essentially it should be something like:

mkdir ~/apps
cd apps

git clone 'https://github.com/json-c/json-c'
cd json-c
sh autogen.sh
sudo make install
cd ..

git clone 'https://github.com/swaywm/wlroots'
cd wlroots
meson build
ninja -C build
sudo ninja -C build install
cd ..

git clone 'https://github.com/swaywm/sway'
cd sway
meson build
ninja -C build
sudo ninja -C build install

You can then copy your i3 config to sway:

mkdir -p ~/.config/sway
cp ~/.config/{i3,sway}/config

And then you can try running sway in a TTY and see what happens. For me, everything almost worked out of the box: I document here what needs to be adapted. You can also have a look at my sway configuration, with only minimal changes relative to my i3 configuration,

For some reason the font in window titles and in the sway bar was wrong, but this was simply fixed by changing the font names in the config file to "Terminus". I think this is essentially the only change I had to make. When using sway there are some very small differences with i3 (e.g., the formatting of window title bars, or the precise behavior), but honestly the difference is hardly noticeable and I'm rather impressed at how close the adaptation is.

Fixing the keyboard layout

I have my custom keyboard which adapts the US Dvorak layout with some key combinations to write French accented characters. I used to load it with xkbcomp, but this no longer works with Wayland.

What works instead is to write a keyboard description like this and put it in ~/.xkb/symbols. Note that this includes some external files, some of which are in in the systemwide /usr/share/X11/xkb/symbols folder, and others are applying my customizations (see, e.g., this) and they should also go in ~/.xkb/symbols. For some reason, trying to load this keyboard description by running setxkbmap a3nm will not work. However, it works to load the keyboard description in sway, by running XKB_DEFAULT_LAYOUT=a3nm sway or editing the sway configuration file to add an input * block containing the xkb_layout a3nm directive, i.e.:

input * {
  repeat_delay 250
  repeat_rate 50
  xkb_layout a3nm

Note that this is also where I configure the keyboard repeat delay and rate.

Many thanks to ManDay for helping me figure this out on the #sway IRC channel.

Switching to apps with native support for Wayland

Most applications do not yet support Wayland, but there is a compatibility layer to run them on Wayland, called XWayland. The way this works is that, when you run an application with no Wayland support (or where Wayland support is not enabled), it will instead be run in an X server that will display in Wayland. For me this worked fine, with no noticeable lags or performance loss. However, all X applications run in XWayland share the same instance (for now), so in terms of security these applications are not better isolated from one another than with X.

So what matters is that applications manipulating sensitive information (e.g., for me, terminal emulators) should not be run in XWayland. This means switching to a Wayland-compatible terminal emulator. My current terminal emulator, rxvt-unicode, is not. For now I just went back to gnome-terminal, which works. Suggestions of terminals to try out (which I haven't tested yet) include:

  • Alacritty
  • Germinal
  • Kitty, which is packaged for Debian but the packaged version doesn't use Wayland (and I didn't find a way to convince it to do otherwise)
  • Termite

Again, thanks for ManDay for suggestions here.

As for other applications I don't care much except for the Web browser. Experimental support for Wayland just landed in Firefox Nightly, you can download it here, uncompress it, and then run it with GDK_BACKEND=wayland ./firefox. This is promising, however from my tests it's still not very stable: opening a second window often made it hang or at least fail to redraw the window that was being manipulated. I hope that this will improve and eventually be available in the normal Firefox releases.


Not a point to fix, but just a remark: one of the things that interested me in testing Wayland was that it is supposed to help reduce screen tearing. That said, it seems I'm no longer able to reproduce tearing on X either... Testing on some videos I didn't manage to see any noticeable difference between X and Wayland, so I can't really claim this as a benefit.

In terms of video playback: Debian's mpv in testing is able to use Wayland natively by running mpv --gpu-context=wayland. For me it worked fine but I couldn't see any difference with running it in XWayland. VLC, however, does not use Wayland (I couldn't figure out if there was a Wayland backend). In terms of performance (measured by CPU usage on the same file) for mpv and VLC:

  • VLC on Wayland (in XWayland) or in X, and mpv with hardware acceleration (--hwdec=auto) and with the native Wayland backend or in X, are the most efficient (around 8% CPU)
  • Running mpv with hardware acceleration and in XWayland is a bit worse (15% CPU)
  • Without hardware acceleration, mpv is much less efficient at around 45% CPU, both in X and in Wayland (both for XWayland and for the native backend).

Disclaimer: enabling hardware acceleration for mpv is discouraged.

Taking screenshots

I used to take screenshots with scrot, but it is an X utility, so it will fail silently. Instead, you can use grim, as suggested in the sway wiki.

cd ~/apps

git clone 'https://github.com/emersion/grim'
cd grim
meson build
ninja -C build

You cannot invoke grim without specifying an output file. I preferred scrot's way of automatically generating a filename based on date and time, so you just have to write a wrapper script, e.g., this.

Changing the screen locker

It seems that my previous screen locker (xtrlock) worked with Wayland, but I thought it safer to switch to the one supplied with sway, i.e., swaylock. I customized it to the way I like, e.g., I like to have the possibility of locking my session without hiding what's on the screen (e.g., to monitor stuff). The result is here.

Sandboxing a process

With sway in place, sandboxing a process is rather easy. Let's say that the process to sandbox uses X (not Wayland natively), and that it is running as user sandbox. In Wayland, you just need to issue xhost +si:localuser:sandbox (which will set the access controls for the XWayland server), and then run the process with sudo -u sandbox process as usual: the process will display while running in XWayland, and will be indistinguishable from other performances, in particular I didn't notice any performance problems. (For instance, playing a video on Youtube in Firefox is hungry in terms of CPU, using around 120-150%, but that's the same figure as running Firefox under X.) The sandboxed process will have access to all events in other X applications that use XWayland, but it is not able to access the events of native Wayland applications, and these applications cannot access the events of one another.

You can use xinput test (running in XWayland) to see the events that are communicated to the XWayland X server. In fact, this is the easiest way I found to test if a window was running natively in Wayland or in XWayland.

Remaining issues

To me the main issues that remain with the setup are:

  • General perceived sluggishness. It's hard to explain why but I get the impression that some things are less smooth in Wayland, in particular moving windows around (while in tiling mode), but even displaying text in a terminal emulator just feels a tiny bit slower. I'm not sure if I'm just imagining this, or I'll stop noticing this after a while, or if there's a way to improve performance, or if it will improve over time as the code of sway, wlroots, etc., improves. For now it's just a rather mild annoyance. We'll see whether I stick with Wayland nevertheless or if I get fed up with it and give up.
  • Having to install programs (sway and dependencies) that are not packaged for Debian yet. That said, there has been some interest in packaging sway for Debian, and hopefully it will happen once sway reaches version 1.0, which doesn't seem so far away.
  • Lack of native apps for Wayland, in particular having to go back to gnome-terminal or to try more experimental terminals.
  • The realization that X applications are not isolated from one another as they are all running with the same XWayland server.
  • I did not try using a projector yet. With X you use xrandr (see my guide here), but this doesn't work on Wayland. It looks like you should configure it instead with sway by specifying the coordinates of the various outputs. However, I don't know whether projectors would work fine, given that the list of modes that they support is often pretty erratic, whereas with my laptop's screen, for instance, sway only shows one available mode. Also, there is no support yet for showing the same content on two monitors, e.g., on the screen and on the projector.
  • There is no support for the nm-applet icon to configure NetworkManager, see this issue.

A more subtle point is that there is no discernible benefit to the user in running Wayland: at best it works just like X. For me the main benefit is security, but this is a pretty hard benefit to notice...

Thanks to linkmauve for proofreading and suggestions.

by a3nm at December 23, 2018 09:49 PM

November 08, 2018

Nicolas Dandrimont a.k.a olasd

Record number of uploads of a Debian package in an arbitrary 24-hour window

Since Dimitri has given me the SQL virus I have a hard time avoiding opportunities for twisting my brain.

Seeing the latest post from Chris Lamb made me wonder: how hard would it be to do better? Splitting by date is rather arbitrary (the split may even depend on the timezone you’re using when you’re doing the query), so let’s try to find out the maximum number of uploads that happened for each package in any 24 hour window.

First, for each upload, we get how many uploads of the same package happened in the subsequent 24 hours.

      upload_history AS other_upload
      other_upload.source = first_upload.source
      AND other_upload.date >= first_upload.date
      AND other_upload.date < first_upload.date + '24 hours') AS count
    upload_history AS first_upload

For each source package, we want the maximum count of uploads in a 24 hour window.


We can then join both queries together, to get the 24-hour window in which the most uploads of a given source package has happened.

WITH upload_counts AS (
        upload_history AS other_upload
        other_upload.source = first_upload.source
        AND other_upload.date >= first_upload.date
        AND other_upload.date < first_upload.date + '24 hours') AS count
      upload_history AS first_upload
    max(count) AS max_uploads
  ) AS m
  USING (source)
  count = max_uploads
  AND max_uploads >= 9
  max_uploads DESC,
  date ASC;

The results are almost the ones Chris has found, but cl-sql and live-config now have one more upload than live-boot.

       source       |          date          | count 
 cl-sql             | 2004-04-17 03:34:52+00 |    14
 live-config        | 2010-07-15 17:19:11+00 |    14
 live-boot          | 2010-07-15 17:17:07+00 |    13
 zutils             | 2010-12-30 17:33:45+00 |    11
 belocs-locales-bin | 2005-03-20 21:05:44+00 |    10
 openerp-web        | 2010-12-30 17:32:07+00 |    10
 debconf            | 1999-09-25 18:52:37+00 |     9
 gretl              | 2000-06-16 18:53:11+00 |     9
 posh               | 2002-07-24 17:04:46+00 |     9
 module-assistant   | 2003-09-11 05:53:18+00 |     9
 live-helper        | 2007-04-20 18:16:38+00 |     9
 dxvk               | 2018-11-06 00:04:02+00 |     9
(12 lines)

Thanks to Adrian and Chris for the involuntary challenge!

by olasd at November 08, 2018 10:56 PM

August 24, 2018

Antoine Amarilli a.k.a a3nm

What's wrong with academia?

I have just finished writing up a long document that tries to give a comprehensive list of problems affecting academic research.

Writing this document is something that I had been meaning to do for a very long time, almost since I got started in academia in 2012 with my master's internship. Many academic practices did not make any sense to me already at the time, e.g., hiding research articles behind paywalls rather than simply hosting them online. I tried to ignore these concerns for a while, and did my PhD without questioning too much the order of things: for some practices I eventually saw a justification, but for many others I did not, and they made me more and more uneasy. So I thought that I should eventually come back to these problems, to re-examine my beliefs about the way academia works. Hence this long list of all the problems that annoy me, which I will try to keep up-to-date as time passes and my experience evolves.

Of course, complaining is always easy, so I have also tried to give some thought in the document about ways to fix these problems. The document does not mention my own initiatives in this direction (e.g., refusing to review for closed-access venues), which I will eventually write up separately.

So I encourage you to have a look at the document, What's wrong with academia?, and share with me any feedback that you may have!

by a3nm at August 24, 2018 09:51 AM

August 14, 2018

Antoine Amarilli a.k.a a3nm

Finding the members of the theoretical database community with DBLP

The DBLP service is a great bibliographical tool for computer science research. In this post, I explain how to use it to prepare the list of members of a research community. I will be using the theoretical database community, whose two conferences are PODS and ICDT.

The list of publications for one edition of a conference can be found on DBLP as XML, e.g., for ICDT'18. It is then easy to use xmlstarlet to find the list of people who have published at that conference:

curl -s 'https://dblp.uni-trier.de/db/conf/icdt/icdt2018.xml' |
  xmlstarlet sel -T -t -m "//inproceedings/author" -m . -c '.' -n |
  sort | uniq

For each person in the list, we can obtain detailed XML information, including its homepage, ORCID, etc., using the DBLP API again. (This also gives us a canonical form for the name, which may appear in different ways in various inproceedings entries.) This is just a bit more complicated than it should, because of a limitation of the DBLP search API: when queried with a name, sometimes the API inexplicably favors non-exact matches even in some cases where an exact match exist. So we must filter the matches ourselves to use an exact match if one exists, and a non-exact match otherwise. Of course, independently from this problem, you may be getting the wrong author, in particular because of homonyms, so these results should be taken with a grain of salt.

NAME="Antoine Amarilli"
ENAME=$(echo "$NAME" | sed 's/ /%20/g')
curl -s "https://dblp.org/search/author/api?h=1000&q=$ENAME" > matches.xml
URL=$(xmlstarlet sel -T -t -m "/result/hits/hit/info[author='$NAME']" \
    -c url -n < matches.xml | head -1)
if [[ -z "$URL" ]]
  URL=$(xmlstarlet sel -T -t -m /result/hits/hit/info/url \
      -c . -n < matches.xml | head -1)
curl -L "${URL}.xml"

From there, we can use this to prepare a list of community members. Of course, any criterion for inclusion is completely arbitrary... My criterion to get a list of "active community members" is to select the who have published on three different years, with one publication in 2015 or later. Which gives:

Corrected one error in this list caused by the DBLP search API limitation

Click to see the list...

Another inclusion criterion for a "historical" list would be the list of people who are not necessarily still active but have published over a long period, say, 10 different (not necessarily contiguous) years. Here is the resulting list, sorted by the year where the person has last published in ICDT or PODS.

Click to see the list...

Another kind of statistics that can be computed in this way is the "neighboring" conferences, i.e., the other conferences where members of the community have published. Here is the list of the top neighboring conferences of PODS and ICDT, sorted by the number of active community members who have published at least once there since 2015 (with hyperlinks and descriptions added manually):

  • 38: SIGMOD Conference, the practical database conference held jointly with PODS
  • 34: AMW, the database theory workshop held in honor of Alberto O. Mendelzon (whom you may remember from the previous list)
  • 29: IJCAI, an AI conference
  • 28: ICALP, a theoretical CS conference on logics and automata
  • 26: LICS, another theoretical CS conference about logics
  • 20: SODA, a theoretical CS conference on algorithms
  • 19: AAAI, another AI conference
  • 19: EDBT, the practical database conference held jointly with ICDT
  • 18: WWW, a conference about the World Wide Web
  • 15: Description Logics, the workshop on description logics
  • 15: ICDE, a practical data management conference
  • 13: CIKM, an information and knowledge management conference
  • 12: SEBD, the Italian conference on databases
  • 12: STOC, a general-purpose theoretical computer science conference
  • 11: KR, a conference on knowledge representation and reasoning
  • 11: FOCS, another general-purpose theoretical computer science conference

It would be interesting to visualize this data differently, e.g., visualize a world map with the community members, but sadly the affiliation information in DBLP is too sparse for this to work.

by a3nm at August 14, 2018 11:23 PM