November 2010 Archive

Sometimes, I want to install and test bleeding-edge-software, like snapshots of ECL in the days when it didnt support gray-streams in the stable version. Always creating a new Package and installing it is a lot of work, especially when having to compile multiple times. Maintaining several paths of different versions of software can also be a pain, but installing them on a central place can cause problems, for example it can be non-trivial to remove them again.

A very good solution for that problem seems to be stow and xstow. It can be used to create symlinks from a directory to /usr/local, and remove them again afterwards.

Lets say you want to install Mizar. Well, this project is not open source, nor does it come in a really useful format. So firstly, after downloading and expanding, I am creating a directory /usr/local/stow/mizar. Then I run the installer to install it into this directory

$ sudo ./install.sh
 
Installation of Mizar System Version 7.9.03 (Linux/FPC) (MML 4.110.1033)
 
Enter the path for installing Mizar executables
[default is /usr/local/bin]
/usr/local/stow/mizar/bin
Unpacking to /usr/local/stow/mizar/bin
 
Enter the path for installing Mizar shared files
[default is /usr/local/share/mizar]
/usr/local/stow/mizar/share/mizar
Unpacking to /usr/local/stow/mizar/share/mizar
 
It may take some time...
 
Enter the path for installing Mizar documentation
[default is /usr/local/doc/mizar]
/usr/local/stow/mizar/doc/mizar
Unpacking to /usr/local/stow/mizar/doc/mizar
 
The installation process of the Mizar system is completed.
 (...)

That being done, lets go to xstow:

$ cd /usr/local/stow
$ sudo xstow mizar
$ which mizf
/usr/local/bin/mizf

That worked well so far. Of course, we have to change the MIZFILES environment variable properly, but anyway, now mizar is sort of installed.

To uninstall it again:

$ cd /usr/local/stow
$ sudo xstow -D mizar
$ which mizf

It is not installed anymore (well, the files are still in /usr/local/stow/mizar, but not in any default directory). This is very helpful, especially for software like mizar, which is not really cooperative with the system.

Under Windows, there has already been a driver for mounting Virtualbox VDIs under Windows, called ImDisk (which I have never tried). For Linux, there was a default method using losetup (which I also didnt try, because it sounded like these hacky solutions that often fail and break your whole virtual disk).

Anyway, meanwhile, Ubuntu has a package named virtualbox-ose-fuse, containing a tool called "vdfuse", which creates a fuse filesystem containing a file that can be loopmounted (the partitions are added, but I prefer kpartx).

The command is self-explaining and trivial to use, a little bit of configuration for fuse is necessary, but thats all. A pretty useful tool.

Da das automatische Ausfüllen von Form-Data in Browsern gefährlich ist, weil man sie mit diversen exploits möglicherweise unbemerkt auslesen kann, wird hier das addon Secure Login für Firefox empfohlen. Sehr gut! Das war nämlich ein Feature von Opera, das ich vermisst habe.

I hate encodings. I dont understand why not everybody just uses utf-8, at least for data exchange. I really like Textonly-Software, running in an Xterm, but as soon as run into trouble with encodings, it is almost impossible to use it.

I tried Finch, CenterIM and Irssi+Bitlbee which I liked most and did best with encoding-problems, but all of them are sort of convenient, when you got used to them. But all of them have problems when special characters are sent.

All of them have settings for encodings, but I always run into trouble with them when using different terminal emulators. Its not just a few characters appearing in a strange way, it can lead to disappearing parts of the UI and make the terminal emulator not respond anymore to keystrokes.

Maybe the right way of handling encoding shit is not to try to do it right, but to try to do it good enough to work with it. For example, I would mostly be satisfied when I could at least tell them to just display everything as quoted printable, so at least the UI wouldnt be disturbed. Any maybe have a mode to display single characters as ascii-art.

Hallo.

BASIC, the Beginner's All-Purpose Symbol Instruction Code, may not be the best tribe of programming languages, but it has brought a few programming languages that were quite nice for scriptkiddies.

For me, the main reason for using a computer was that I wanted to learn programming. And DOS had a QuickBasic-Interpreter, called QBasic. This interpreter had an excellent documentation, documenting most of the calls. This was perfect for me, since I didnt have to buy any book and could learn it myself by searching through the documentation, and could do my own experiments, and get my own expierience.

And it had a few example programs, like a Snake-game named "Nibbles", from which it was easy to "steal" code.

Though, it had a few drawbacks. For example, there are ASCII-Characters which couldnt be printed by its "Print"-Command. And there was no possibility to use the mouse. Later, I got a book about x86-assembler, which hat a table of MS-Dos-Interrupts. And I got a newer version, QuickBasic 4.5, which also had a compiler, and hat an instruction named Call Interrupt, which could be used to call MS-Dos-Interrupts. With that, I could write my own Print-Command that supported all characters, and could use the mouse. Later, when I finally got an internet connection, I found a lot of stuff, like the 3d-Game "Return To Marchfeld".

Still, there seem to be many people who like QBasic. Thats not surprising. Its a simple language with a lot of things the usual child wants to have. Many software and code can be found under my favourite site for that topic, QBasic.de (which is german, but should be quite understandable through google translate).

Well, meanwhile, all of this is not that interesting anymore. It is trivial to use the mouse, it is trivial to print every unicode-character, it is trivial to create 3d-images. But at that time, this was new to me. It was a nice world to explore, and I am not sure if such a thing still exists today, because most languages simply have default libraries for everything that can be done without further reading. And Basic seems dead to me, anyway - seems like some people still use Visual Basic, or VB Script, but the last time I saw it it was not even comparable to what QBasic was, at least in my opinion.

Ich stelle gerade mit erschrecken fest, dass das Wohnhaus in dem ich wohne in Google Street View unkenntlich gemacht ist. Naja, ist ein großes Wohnhaus, und es reicht vermutlich ein Idiot besorgter Bewohner aus, damit es verpixelt werden musste.

Ist schon irgendwie peinlich, in einem solchen Haus zu wohnen. Üblicherweise gibt es keinen triftigen Grund, denn es ist nichts, was man nicht auch sehen könnte, wenn man einfach so auf der Straße vorbeifährt. Ein unkenntlich gemachtes Haus zeigt für mich also ziemlich deutlich, dass es in so einem Haus Personen gibt, die als Hauptinformationsquelle die Bild nutzen.

Ich warte schon auf die ersten Wertminderungen von Häusern, weil niemand in ein solches Haus ziehen will, wenn erstmal die Moralpanik vorbei ist.

As I am using bitlbee and quite a few autojoined irc-channels, irssi can get a lot less handy because of its many windows.

There are M-0 to M-9 to quickly navigate through the first 10 windows. M-a gets you to what irssi thinks that is the active window, but I want to control this myself. "/window 27" is a long command, that takes long to type.

So I decided to add a few aliases. I didnt want to write an irssi-script for it, and since I never had more than 100 windows, I just typed

$ i=0; while [[ $i -le 100 ]]; do echo /alias $i /window $i; ((i++)); done

in bash and pasted the output into irssi. Now I can acces windows via /<window_number>, i.e. /1, /27, /100. Nice.

Ich erhielt jetzt ein paar mal die Kritik, dass die Anzahl meiner deutschen Beiträge hier langsam aber sicher abnimmt. Das hat verschiedene Gründe.

Zum Einen nimmt die Anzahl meiner Beiträge ohnehin gerade mangels Zeit ab. Ich komme nur noch selten zum Bloggen, und wenn, dann habe ich meistens keine Themen, die interessant genug wären, als dass ich sie veröffentlichen würde.

Und die meisten davon sind momentan Softwareverwandt. Und wer sich mit Software beschäftigt, sollte ohnehin Englisch können. Ansonsten schreibe ich auf deutsch eigentlich meistens Beiträge, die eher für Deutsche interessant sind. Es fällt mir persönlich auch erheblich leichter, auf deutsch zu schreiben, und mein Englisch ist durchaus verbesserungsbedürftig. Andererseits ist es doch relativ verständlich, wie man mir bestätigte.

Jedenfalls ist das Problem, dass ich da momentan kaum noch interessante Themen finde. Die Politik trollt fröhlich vor sich hin, die Leute werden nicht schlauer aber auch nicht erheblich dümmer, und auch ansonsten passiert eigentlich nichts was nicht mindestens auf Fefe verlinkt wird, und trotzdem irgendwie interessant wäre.

Im Moment habe ich jedenfalls andere Prioritäten als den Blog. Ich hab ne lange Liste von Sachen die ich mal schreiben könnte, da ist auch einiges dabei, was deutsch ist. Behold!

There are quite a lot of things that have to work together properly, to make a PXE-Boot-System work. If you really want a fully-qualified operating system, you will have to export a filesystem, for example via nfs, have a special kernel that can use this filesystem, and act as a dhcp-Server and NAT. It can be complicated to configure all this.

In a large network, you may want to have a fine-grained configuration of all of this. But usually, you are in a situation where some computer chooses to strike and you cant get any bootable medium. Well, surprisingly, still, the most safe way to get something to boot at least somehow is - besides burning a CD - to boot it via PXE-Boot, as far as I see. Maybe because this is some standard that most computers support (I am afraid that this will change as soon as the first routers that dont support IPv4 anymore will spread). So it would be desirable to have some software-package, that allows you to manually turn on an administrative dhcp-server on one of your ethernet-devices, with a linux-live-system that can install itself, such that you only have to plug in the computer you want to boot and then get a system to work with, and maybe to install directly.

There is a package that does something similar, namely ltsp-server-standalone, which create an LTSP-Architecture - but thats still not what I want. I want a bunch of servers and their configuration which I only have to turn on when I want it, and then "just work", passing a live-system (like on the ubuntu livecd) to all computers doing netboot, and routing internet connections.

It should be comparably easy to create such a thing (maybe it would take long to make it stable). In the end, there are a lot of howtos to achieve a Netboot-Livesystem. The parts are there, they only have to be put together.

There is a lot of software I really dont like. And I often write about it. So I thought, maybe I should start writing about software I like. And well, there is actually plenty of it.

Well, one piece of software I really do like is Xvfb. It is an X-Server, drawing on a virtual framebuffer. X-Servers like Xvnc and Xrdp are basing on it, the pgo-compilation of Firefox I was using used it to run Firefox in a virutal X-Server, and it should be much more versatile, but maybe its too unknown.

To start it, like most X-Servers, just do

$ Xvfb -ac :1 &

Then lets start a Window-Manager and an Xterm

$ fvwm -display :1 &
$ xterm -display :1 &

Now we have a twm running with an xterm. W00t. But we cannot see anything yet. So lets kill the server again and restart it with a few more arguments:

$ Xvfb -ac :1 -shmem -fbdir /tmp/fbdir &
$ fvwm -display :1 &
$ xterm -display :1 &


Now, lets get a screenshot:

$ cp /tmp/fbdir/Xvfb_screen0 ./screenshot.xwd
$ convert screenshot.xwd screenshot.png
$ rm screenshot.xwd

we get a file "screenshot.png" looking like



which looks like what we wanted to have. A fvwm with an xterm. Unfortunately, we cannot type anything inside it. And we cannot move the mouse. We have to use a trick here, and use the XTEST-Extension for Xvfb.

That is, kill Xvfb again, and run it with the XTEST-Extension:

$ Xvfb -ac :1 -shmem -fbdir /tmp/fbdir +extension XTEST &
$ fvwm -display :1 &
$ xterm -display :1 &

First, lets move the mouse on top of our xterm, since that is how to get the focus under fvwm in its default configuration, and then we can type in:

$ DISPLAY=:1 xdotool mousemove 100 100
$ DISPLAY=:1 xdotool type "apt-get moo"
$ DISPLAY=:1 xdotool key Return

And now lets get a screenshot like before

$ cp /tmp/fbdir/Xvfb_screen0 ./screenshot2.xwd
$ convert screenshot2.xwd screenshot2.png
$ rm screenshot2.xwd

Now our screenshot is



Well, its a bit more complicated than one would maybe want it. But compared to some other X11-Stuff, it is easy. And its very nice to have such a thing.