Tips – Page 14 – Guy Rutenberg

Upgrading All KDE Related Packages in Gentoo

Yesterday, Gentoo marked KDE 3.5.10 as stable on amd64. I looked for a way to upgrade all of the KDE related packages, without manually specifying each one of them. Normally one could do

emerge -avu world

but I encountered some nasty conflicts that I didn’t have time, nor will, to resolve at that time. So I’ve looked for a different solution. To my rescue came qlist for the great app-portage/portage-utils package. This package provides a set of very fast utilities to query portage. I’ve used qlist to list all of my installed packages, grep‘ed the list and piped the result as arguments to emerge using xargs.
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Installing Lighttpd-1.4.22 on Ubuntu 8.04

I had some problems with the lighttpd-1.4.19 that comes with Ubuntu 8.04, mainly it’s problems of handling the HTTP header Expect: 100-continue (which older versions of Lighttpd return error 417). The problem was fixed in Lighttpd-1.4.21, but 1.4.22 is the newest version so I’ve decided to install it.

As I mentioned before, Ubuntu doesn’t have lighttpd-1.4.22 for 8.04, and it’s also not available in the updates or backports repositories. Fortunately, I’ve found that the package is available from Debuian Sid (unstable). Here are some instructions on how to install it.
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Re-distilling PDFs to Reduce Size

I decided to finally learn QT and started to read the “C++ GUI Programming with Qt 4” (first edition) which is available online. The book comes in a zip file that unzips to a huge, 51MB, pdf file. Even when considering the book is quite long (556 pages), the file size is very large compared to what one is used to except. The huge file size made reading the PDF less convinient, as one notices a considerable delay when opening it (especially if the PDF resides on some portable storage), so I’ve decided to play a little and see what I can do about it.
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Displaying Non-Builtin Math Macros in LyX

I believe LyX is a great tool for writing LaTeX document. It makes writing formulas very easy and it allows you to see the formula as you are writing, as opposed to seeing only LaTeX code. However LyX doesn’t support every LaTeX package and the macros it defines. Sure it doesn’t stop you from using these macros in your formulas, but it doesn’t display nicely, you see the name of the macro instead of a schematic preview.

While LyX doesn’t support many of the great packages out there like mathtools (which I really hope it will someday), you can add some support to your documents. At the beginning of the document insert a comment, via Insert->Note->Comment. Inside the newly created comment insert a math-macro via Insert->Math->Macro. In the name part, put the name of the command you want to add support for. In the second box (caption LyX), use existing LyX commands to mimic how the macro will look like. For example, this is what it looks like for the \coloneqq macro (from the great mathtools package):
$math-macro$

After adding the math macro in the comment, when you will use the macro inside formulas it will display nicely:
$math-macro2$

A little explanation how things work. When you define a math macro in LyX, LyX does two things:

Inserts LaTeX code to create the macro.
Displays the macro nicely when editing the document.

While the latter is desirable, the former is problematic. If LyX inserts LaTeX code to define the existing macro, it will cause errors. So when you put the LyX macro in the comment environment, the code LyX generates gets ignored and only the second, desirable, outcome is achieved.

Convert `int` to `string` (As Well As Almost Anything)

This is a little code snippet from Open Yahtzee‘s code base that converts all the built-in types and many custom classes (ones that override the << operator) to string.

template <class T> inline std::string stringify(T x)
{
	std::ostringstream o;
	o << x;
	return o.str();
}

I first wrote it to convert ints to string, but later I templatized it so it would work with other types as well. It’s a clean elegant snippet that I thought other might find useful too.

RTL Tiddlers in TiddlyWiki

Update – For TiddlyWiki 5 see RTL Tiddlers in TiddlyWiki 5.

I’ve been using TiddlyWiki for a while now, and it became a very useful tool for me. Today, I’ve decided to organize my various recipes (somehow cooking and especially making deserts has turned into an hobby of mine), and as you can expect I’ve decided to use TiddlyWiki for the tasks.

There was a slight problem as some of the recipes are in Hebrew, and it seems TiddlyWiki doesn’t have built-in support for RTL (right-to-left) tiddlers. However, such support can be added via custom stylesheets and the tiddlers’ tags. The idea for this method is taken from this TiddlyWiki.

Create a new tiddler called “StyleSheet” (without the quotes). This is a special tiddler (a shadow tiddler) that lets you add additional CSS code for your wiki. Insert the following code into the newly created tiddler:

/*{{{*/
div[tags~="RTL"].tiddler {
    direction: rtl;
}
div[tags~="RTL"].tiddler .subtitle {
    direction: ltr;
}
div[tags~="RTL"].tiddler .tagged {
    direction: ltr;
    float: left;
}
/*}}}*/

Now for every tiddler you want to be in RTL direction just add RTL to its list of tags. After you do it, the tiddler will appear correctly. Here is an example of what in RTL looks like after the fix:

Iptables Cheatsheet

From time to time I find myself having to go through man pages and googling for some simple iptable rules. This post is meant as a cheatsheet for me, so I can concentrate here various rules and remarks.

I hope others will benefit from this cheatsheet as well. Intend to expand it over time as I gather more rules and tips, so bookmarking the post might be a good idea. Last but not least, if you have some useful iptables rules I’ve missed please send them using the comments.
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Starting `tracd` without Root Privileges at Startup

I use Trac for the Open Yahtzee website. I’ve decided to use tracd for serving the requests (due to a configuration issue I didn’t want to mess with), which required starting it each time the server restarts. I’ve already written one solution for it, in the form of an init.d script for tracd. However, it bothered me that the tracd runs with root privileges which it doesn’t really requires.

After searching a bit I’ve found out that cron can run tasks on startup using the special @reboot keyword instead of the normal time fields. So edit your crontab and add the following line:

@reboot /usr/bin/tracd --daemonize --pidfile=~/run/tracd.pid --port=PORT --hostname=HOSTNAME -s TRAC_ENV

Just replace PORT, HOSTNAME and TRAC_ENV with the appropriate values for your environment, and make sure you got a run/ sub-directory in your home folder (or change the pidfile value).

To stop the server just do:

kill `cat ~/run/tracd.pid`

While there is no straight way to restart the server (like /etc/init.d/tracd restart), it’s a good compromise for dropping root privileges.

Amarok Sleep – Stop Playback After Specified Amount of Time

Amarok is my favourite music player. I like to listen to music when I go a sleep, but I don’t want the music to keep playing all night long. This is why I’ve added a sleep feature to radio.py. Unfortunately Amarok doesn’t have a built-in sleep functionality, but the Amarok developers left open door for us to implement it with ease by means of interfaces allowing to control amarok from the command line.
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Configuring Lighttpd for CakePHP

I tried a few days ago to install a CakePHP project of mine on a lighttpd web-server. As expected, its clean URLs didn’t work, so I set out to find a solution.

One possible solution is the one outlined in the CakePHP manual. The solution uses the mod_magnet module (which basically runs a Lua script to do the rewriting), and I found it an overkill. I was looking for a simple solution based only on mod_rewrite, something like the solution for WordPress.
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