Yenya's World

Mon, 29 Oct 2007

Presentation style

I have already discussed problems with creating a presentation in Beamer. When we have talked about the presentation style, Mirka has told me about an interesting approach to the slides-based presentation:

Some people use a simple rule: one word per slide. It may seem too little, but seeing some YouTube videos has proved otherwise. There is even a (Japanese-based :-) term for those short talks: Pecha Kucha. Also, I have found a very interesting presentation (by its style, not only by its contents): look at Dick Hardt's OSCON 2005 keynote (warning: probably not suitable for epileptics; thanks to Mirka for showing this to me :-)

For conference talks, it may help. While I did not use such style for my XXXI. EurOpen slides, I have much shortened the text, and made an additional dynamics by using covered parts of the slides, changing colors (red-emphasized words in some phases of the frame), and pictures which were only vaguely related to the topic. I wonder how the evaluation marks from EurOpen will look like (as of this writing it is not published yet).

I also wonder whether such presentation style could be used for regular university lectures, which should sometimes have to be more in-depth.

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Sun, 28 Oct 2007

Non-ASCII Basic Authentication

We use a HTTP basic autentication for authenticating users to IS MU. It is most widely supported in clients, and it does not have some security problems which cookies have. Recently, while implementing a better method for storing passwords in IS MU, which would allow passwords of an arbitrary length, I have discovered the following problem:

I wanted to use this change to not only allow passwords of arbitrary length, but also to allow non-ASCII characters in passwords. However, reading the HTTP specification, I have not found in which charset is the Authorization: HTTP header supposed to be sent. Experiments showed that for example MSIE sends the password in the client's native encoding (windows-1250 in this part of the world), regardless of the charset of the previous 401 page.

What is worse, my Galeon (so probably all Gecko-based browsers too) mangle the password into something totally unreadable: for example, when I tried to send an user name "kas" and a password "asděščřžýáíé", the Authorization: header from Galeon contained the base64-encoded string "a2FzOmFzZBthDVl+/eHt6Q==" (decoded to bytes it is 6b 61 73 3a 61 73 64 1b 61 0d 59 7e fd e1 ed e9). Total crap, even with a newline! It looks like these bytes are the lowest bytes of the Unicode codepoint number of the character in the password. No UTF-8 or something, just codepoints truncated to 8 bits.

So we will stay with ASCII-only passwords, as we do not want to affect the accessibility of IS from various devices. By the way, did you know that Apache has its own proprietary algorithm for MD5-based password hashing? Talk about reinventing the wheel.

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Sat, 27 Oct 2007

EurOpen 2007

XXXI. EurOpen is over. I think the conference was quite interesting. My presentation was in the "Operating systems and desktops" section.

There was a presentation on OpenSolaris with some interesting points, altough they still mostly repeat their old "ZFS-Dtrace-Zones-WeAreStableWhileLinuxIsNot" mantra. The FreeBSD presentation was quite sad: they apparently do not even have working software RAID-5 in their new device-mapper alike, and the author seemed to be disappointed with the state of FreeBSD as an operating system.

Altough the section was originally meant to summarize the state of desktop support in modern kernels, only my own paper was on topic (I talked about things like udev, HAL, inotify, etc.). In my talk I have said that server kernels are generally less interesting, because the desktops have usually more varied usage than (most) servers, which often only run a single application like Oracle or Postfix for their whole lifetime. Interestingly enough authors of both OpenSolaris and FreeBSD presentation explicitly declined to talk about desktops, but still declared that Linux is unstable while their OS is stable. Oh well.

Anyway, here is my paper and slides, and also slides for my other talk The Linux Kernel in the Last Few Years (I have prepared this talk instead of Jirka Kosina, who could not attend the conference).

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Fri, 26 Oct 2007


In EurOpen, my roommate had a GPS and was into this Geocaching thing. So we have tried to find some nearby caches. During one afternoon we have found five caches, and I've got a Geocoin[?].

It was quite interesting, we have visited places which we would not normally visit. However, the weather was quite bad (fog, rain and snow), so we could not appreciate the landscape views. I hope I get my own GPS soon, and maybe I will even try geocaching myself.

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Fri, 19 Oct 2007


Next Tuesday I will have a presentation in the XXXI. EurOpen.CZ conference. I took this event as an opportunity to learn a new presentation software. In the past I have used several presentation software tools. From plain TeX (presented using xdvi(1), or later evince), to MagicPoint.

The candidates were's Impress, and Beamer. Since I would like to be able to enter and edit text using vim(1) or at least with vi-like keyboard shortcuts, I have decided to try Beamer. So far it looks nice and configurable (and their manual even had some interesting presentation tips!). There are only two drawbacks:

The first one is that it is TeX-based, so the ugliness and unorthogonality of the TeX command set sometimes cannot be hidden (I am speaking about \begin{frame}[fragile], or the fact that you cannot use \pause in some environments - like matrices in math).

And the second one is, that it is LaTeX-based, and LaTeX, as we all know, is even more disgusting than - say - XML. For example, look at the following code which describes a single frame for MagicPoint:

My first slide

The things I want to talk about:
	This one
	That one
	and also those over there

... and now the equivalent in Beamer:

	\frametitle{My first slide}
	The things I want to talk about:
		\item This one
		\item That one
		\item and also those over there

Hope you see the difference. It is about 80 characters more on each slide. Since the Beamer output looks quite good, I am thinking about writing a conversion tool from the MagicPoint syntax to those verbose LaTeX environments.

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Thu, 18 Oct 2007

Another Time Eater

Do not click on the following link: The Impossible Quiz. You have been warned.

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Wed, 10 Oct 2007

Spam Volume Decline

This month was the first in at least last two years when I had less than 10,000 spam messages per month.

Spam statistics

In the above graph there is a number of messages which ended in my spambox per month since January 2006 (which is the first bar) to September 2007 (which is the bar number 21).

The peak was in the last December, when I had 113,477 spam messages. Since then we have deployed greylisting on most systems (the last one around March 2007), but nevertheless, the volume of spam has been decreasing even after that time. Can anybody explain this? Is spam becoming too expensive for spammers?

I don't have a hard data, but it looks like the other people in our domain have a similar decrease in spam volume like me.

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Wed, 03 Oct 2007

Tree in a Pot: Part Two

It has been almost two years since I bought my first bonsai tree. It was Serissa foetida ("A Tree of a Thousand Stars"). Looking back at this time I am quite surprised that I am still as interested in bonsai as I was two years ago.

serissa 2007

As you can see, my Serissa is still alive :-). It has grown up a bit, so I have decided to grow another level of branches - I have removed most of the apic, keeping only two main branches of the original apic, and another one which I plan to use as a new apic.

serissa flower

The tree has grown many flowers in the last month or so (probably in response to heavier pruning in the apic).

Serissa is not hard to maintain, but it requires a lot of time - without monthly (or tri-weekly) backpruning the apical growth makes the tree proportions out of balance, and (even though I keep my Serissa near the southern window) leafs get more than twice as big on the unpruned twigs than on the backpruned ones.

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Tue, 02 Oct 2007

Bicycle Rim

A while ago I wrote about my trouble with a new paint for my bicycle frame. I have already solved this problem (people at Aluservis have removed the old paint, and the paintshop Pavel Oršula painted the frame). Today I want to add another complaint to RockRoad.CZ, a shop which did the original paint, and some other repairs of my bicycle:

I bought a new rim for my front wheel there. I used to have 20-622 tyre, and they recommended a suitable new rim, which I have bought. However, yesterday I rode the bicycle and had a quite serious puncture (destroying not only the tube, but also the tyre). I went to another repair shop, which is near to the place where I work, to buy a new tyre and tube. They were quite unhappy with my new rim, and said that 20 milimeters wide tyre is too narrow for this rim, and that they are not surprised that I had a puncture with such a narrow tyre on that relatively wide rim.

So I bought a 23-622 tyre instead (they said even this is probably too narrow for that rim). Meanwhile, I have discovered a new development in bicycle tyres: the new tyre has beads with kevlar cords, which is not only lighter than the tyre with steel cords, but the tyre can also be folded to a small package(!) - just like the inner tube is folded to a small package. Anyway, stay away from RockRoad.CZ.

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