Bye sidux - welcome aptosid!

I just dist-upgraded to aptosid, sidux is gone.

Yesterday the sidux team announced that sidux is dead, but the good news just followed:

As I am sure you are all aware, there have been interesting times for sidux recently. The bad news is that the sidux project is dead. The good news is that aptosid has been aptly born like a phoenix from the ashes and will provide a smooth upgrade for sidux systems. In many ways nothing has changed but our name.

After a long period of silence I already change the OS on my notebook from sidux to grml. It’s a very good alternative, but I decided to wait for an official announcement before deleting my main OS.

Now, the official announce is released, I upgraded my system to aptosid. First of all I created a aptosid.list in my /etc/apt/sources.list.d/ containing:

deb http://debian.tu-bs.de/project/aptosid/debian/ sid main fix.main contrib fix.contrib non-free fix.non-free vdr
deb-src http://debian.tu-bs.de/project/aptosid/debian/ sid main fix.main contrib fix.contrib non-free fix.non-free vdr

deb ftp://ftp.spline.de/pub/aptosid/debian/ sid main fix.main contrib fix.contrib non-free fix.non-free vdr
deb-src ftp://ftp.spline.de/pub/aptosid/debian/ sid main fix.main contrib fix.contrib non-free fix.non-free vdr

After wards calling aptitude update to reread the package listings. It notifies me that the new servers couldn’t be verified, I had to install the new keyring:

aptitude install aptosid-archive-keyring

It’s time to upgrade:

aptitude update
aptitude dist-upgrade

That fails at the first time:

Running update-initramfs.
update-initramfs: Generating /boot/initrd.img-2.6.35-4.slh.9-aptosid-amd64
initrd.img(/boot/initrd.img-2.6.35-4.slh.9-aptosid-amd64
) points to /boot/initrd.img-2.6.35-4.slh.9-aptosid-amd64
 (/boot/initrd.img-2.6.35-4.slh.9-aptosid-amd64) -- doing nothing at /var/lib/dpkg/info/linux-image-2.6.35-4.slh.9-aptosid-amd64.postinst line 348.
vmlinuz(/boot/vmlinuz-2.6.35-4.slh.9-aptosid-amd64
) points to /boot/vmlinuz-2.6.35-4.slh.9-aptosid-amd64
 (/boot/vmlinuz-2.6.35-4.slh.9-aptosid-amd64) -- doing nothing at /var/lib/dpkg/info/linux-image-2.6.35-4.slh.9-aptosid-amd64.postinst line 348.
Running /usr/sbin/update-grub.
Can't exec "/usr/sbin/update-grub": No such file or directory at /var/lib/dpkg/info/linux-image-2.6.35-4.slh.9-aptosid-amd64.postinst line 770.
User postinst hook script [/usr/sbin/update-grub] failed to execute: No such file or directory
dpkg: error processing linux-image-2.6.35-4.slh.9-aptosid-amd64 (--configure):
 subprocess installed post-installation script returned error exit status 255

As you see, /usr/sbin/update-grub wasn’t found. It is in grub-pc , but I have no idea why there isn’t a dependency so that grub-pc is installed by default!? Not fine but doesn’t matter, just install it:

aptitude install grub-pc
aptitude dist-upgrade

If this is done, just reboot and join the new kernel version 2.6.35 (slh is the greatest!!).

~ % uname -r
2.6.35-4.slh.9-aptosid-amd64

Jabber meets Twitter

This evening I implemented a XMPP bridge to twitter. So I’ll get all news via IM and can update my status by sending an IM to a bot.

Nothing new, I don’t like the twitter web interface. Neither to read, nor to write messages. So I developed some scripts to tweet from command line. These tools are still working, but not that comfortable as preferred.

Today I had a great thought. At Gajim I’m online at least 24/7, talking with people, getting news etc. So the comparison with twitter is obvious.

After some research how to connect to twitter and jabber I decided to implement the bot in Perl. I still worked a little bit with Net::Twitter, so one side of the connection is almost done. For the other side I used the module Net::Jabber::Bot to implement a bot listening for messages or commands and sending twitter news via IM to my jabber account. The call for the jabber bot looks like:

my $bot = Net::Jabber::Bot->new ({
	server => $j_serv
	, port => $j_port
	, username => $j_user
	, password => $j_pass
	, alias => $j_user
	, message_function => \\&messageCheck
	, background_function => \\&updateCheck
	, loop_sleep_time => 40
	, process_timeout => 5
	, forums_and_responses => {}
	, ignore_server_messages => 1
	, ignore_self_messages => 1
	, out_messages_per_second => 20
	, max_message_size => 1000
	, max_messages_per_hour => 1000});

$bot->SendPersonalMessage($j_auth_user, "hey i'm back again!");
$bot->Start();

Most of it should be clear, the function messageCheck is called when a new message arrives the bot’s jabber account. There I parse the text whether it starts with ! (then it’s a command) otherwise the bot schould take the message to update the twitter status. updateCheck is the background function, it’s called when the bot idles. Here is time to check for news at twitter. It is called loop_sleep_time secs.

The rest is merely a matter of form. News from twitter are jabber’ed, IM’s from the authorized user are twitter’ed. Cool, isn’t it!?

Just download the tool, create a new jabber account for the bot (you’ll get one for example from jabber.ccc.de) and update the jmt.conf file with your credentials. Of course you need the additional Perl modules, if you also experience various problems with Net::Jabber::Bot try to use the latest code from git://github.com/toddr/perl-net-jabber-bot.git.

The bot could simply be launched by running the Perl script. Send !help to the bot to get some information about known commands. Just start it at any server/PC that has a network connection.

What comes next? If anyone would provide a server I would like to implement a multiuser tool, maybe with database connectivity!?

Download: Perl: jmt.tgz please see GitHub for the latest version (Please take a look at the man-page. Browse bugs and feature requests.)

Advanced searching via Z-Algorithm

I’m actually learning some stuff related to algorithms on sequences. The naive search for a pattern in a long string is of course very slow and comes with a lot of unintelligent compares. The Z-Algorithm improves the searching by preprocessing the pattern.

Naive searching

A simple search algorithm written in java may look like

public void search (String needle, String haystack)
{
	for (int off = 0; off < haystack.length () - needle.length () + 1; off++)
	{
		boolean found = true;
		for (int p = 0; p < needle.length (); p++)
			if (needle.charAt (p) != haystack.charAt (off + p))
			{
				found = false;
				break;
			}
		if (found) System.out.println ("Fount pattern at position " + off);
	}
}

This code reliably finds any existence of needle in haystack in , with length of needle and length of haystack. That screams for improvements ;)

Definitions

The first algorithm that I want to present in this series is called Z-Algorithm. First of all we need some definitions.

Definition 1: In the following we denote as the substring of beginning at position and ending at position . We can also leave one of the limits clear, so that is the substring and means .

Definition 2: So is the length of the longest prefix of the suffix that is also prefix of itself. To abbreviate is further on mentioned as .

Definition 3: The set for a is called Z-Box at position .

Definition 4: is the set of limits of all Z-Box’es that start at the left-handed side of . Consider .

Definition 5: If and , defines the rightest Z-Box that starts before respectively at position . Consider .

Algorithm

In the following will denote the actual position we are looking for, and describe the current respectively last found of a Z-Box. First of all we set the values and to zero because we haven’t found any Z-Box yet. of our text is according to Definition 2 the length of the longest prefix of that is also prefix of itself. If we found a first Z-Box and update the limits to and .

Now we have to run through the word , so with defines the length of .

Case 1: Let’s assume position is outside of the last found Z-Box or we didn’t find any Z-Box yet (). We find by comparing the prefixes of and . If we’ve found a new Z-Box and need to update the limits to and .

Case 2: If the current position is inside of a current Z-Box () we try to find the equivalent position at the beginning of . The position we are searching for is steps off the beginning of (we are steps behind and has the same prefix as ). Case 2a: If we don’t break out of the current Z-Box by creating another Z-Box with the length of the box at position (, so position is not behind position ), we can simply apply this Z-Box to the current position and . Case 2b: Otherwise, if we would leave the actual Z-Box () we have to recheck the prefix conditions of and . We know that equals , so we only have to find the length of the longest prefix of that equals the prefix of . Now we can apply the new Z-Box such that and of course we update the Z-Box limits to and .

If we reached the end of all Z-Boxes are found in .

Pseudo code

l = r = 0
Z[2] = prefix (S, S[2 ..]).length
if Z[2] > 0 then
	l = 2
	r = 2 + Z[2] - 1

for i = 3..|S| do
	if i > r then 										'(case 1)'
		Z[i] = prefix (S, S[i ..]).length
		if Z[i] > 0 then
			l = i
			r = i + Z[i] - 1

	else 												'(case 2)'
		k = i - l + 1
		if Z[k] < r - i + 1 then 						'(case 2a)'
			Z[i] = Z[k]

		else											'(case 2b)'
			p = prefix (S[r - i + 2 ..], S[r + 1 ..]).length
			Z[i] = r - i + 1 + p
			l = i
			r = i + Z[i] - 1

Example

Let me demonstrate the algorithm with a small example. Let’s take the word . First we start with and at position 2. is the length of the shared prefix of () and (). Easy to see the prefix is with a length of 1. So , and . At the beginning of our for-loop the program’s status is:

$$T$$aabaaab
$$i$$12
$$Z_i$$1
$$l$$2
$$r$$2

At the first round in the loop , so because . So we meet case 1 and have to find the length of the prefix of () and (). Of course it’s zero, nothing to do.

$$T$$aabaaab
$$i$$123
$$Z_i$$10
$$l$$22
$$r$$22

Next round, we’re at position 4 and again (case 1). So we have to compare and . The longest prefix of both words is with a length of 2. So we start a new Z-Box at 4 with a size of 2, so and .

$$T$$aabaaab
$$i$$1234
$$Z_i$$102
$$l$$224
$$r$$225

With and we reach case 2 for the first time. so our similar position at the beginning of is position 2. and so we are in case 2b and have to find the shared prefix of () and (). It’s , so and . and .

$$T$$aabaaab
$$i$$12345
$$Z_i$$1023
$$l$$2245
$$r$$2257

Next round brings us , therefor we’re in case 2. Equivalent position is again , but now and we’re in case 2a and can just set .

$$T$$aabaaab
$$i$$123456
$$Z_i$$10231
$$l$$22455
$$r$$22577

The last round we have to process is , case 2. Equivalent position is and , so case 2a and .

$$T$$aabaaab
$$i$$1234567
$$Z_i$$102310
$$l$$224555
$$r$$225777

That’s it. The Z-Box’es we’ve found are visualized in the image.

Searching

To search for a pattern in a text just calculate the Z-Boxes of with . These calculations are done in . For any : If means is prefix of , so is found at position in .

Code

Of course I’m providing an implementation, see attachment.

Download: Java: Zbox.java (Please take a look at the man-page. Browse bugs and feature requests.)

SSH escape sequences

Such as telnet the SSH protocol also has a control character, it’s the tilde (~).

If you for example want to kill a hanging SSH session just type ~. . With ~^Z you can suspend a running session and get back to your local machine. To reactivate it just type fg (yes, the SSH session is also just a job). All supported escape sequences will be listed with ~? :

me@remote ~ % ~?
Supported escape sequences:
  ~.  - terminate connection (and any multiplexed sessions)
  ~B  - send a BREAK to the remote system
  ~C  - open a command line
  ~R  - Request rekey (SSH protocol 2 only)
  ~^Z - suspend ssh
  ~#  - list forwarded connections
  ~&  - background ssh (when waiting for connections to terminate)
  ~?  - this message
  ~~  - send the escape character by typing it twice
(Note that escapes are only recognized immediately after newline.)

All sequences are of course only understood after a newline ;)

First HTML5 experiences

Although I have too much to do it’s in the nick of time to try some stuff with HTML5.

You should all have heard about HTML5, next generation of web ;) I still saw a lot of new features, some are still not supported in many browsers but all in all I’m looking forward.

Here I played a little bit with the canvas stuff and created a binary clock:

Wasn’t that difficult, just created an HTML element of type canvas with enough space in it to draw the clock:

<canvas id="clock" width="250" height="100"></canvas>

and via JavaScript I draw the clock in it:

/* JS binary clock by Martin Scharm <http://binfalse.de> */
function init()
{
	clock();
	setInterval(clock,1000);
}
function draw (ctx, x, y, stroke)
{
	ctx.beginPath(); 
	ctx.arc(x, y, 9, 0, Math.PI*2,true);
	if (stroke) ctx.stroke();
	else ctx.fill ();
}
function clock ()
{
	var canvas = document.getElementById("clock");  
	if (canvas.getContext)
	{  
		var offset = 60;
		var ctx = canvas.getContext("2d");
		ctx.save();
		ctx.clearRect(0,0,300,300); 
		var now = new Date();
		var sec = now.getSeconds();  
		var min = now.getMinutes(); 
		var hr  = now.getHours(); 
		for (var i = 0; i < 3; i++)
			for (var x = 0; x < 2; x++)
				for (var y = 0; y < 3; y++)
				{
					draw (ctx, i*offset + x*20 + 20, y*20 + 20, true);
				}
				for (var x = 1; x < 3; x++)
					for (var y = 2; y < 4; y++)
					{
						ctx.beginPath();
						ctx.arc(x * offset, y * 20, 4, 0, Math.PI*2,true);
						ctx.fill ();
					}
					for (var x = 0; x < 2; x++)
						for (var y = 0; y < 3; y++)
						{
							if (sec & Math.pow (2, (1 - x) * 3 + 2 - y)) draw (ctx, 2*offset + x*20 + 20, y*20 + 20, false);
							if (min & Math.pow (2, (1 - x) * 3 + 2 - y)) draw (ctx, 1*offset + x*20 + 20, y*20 + 20, false);
							if (hr & Math.pow (2, (1 - x) * 3 + 2 - y)) draw (ctx, x*20 + 20, y*20 + 20, false);
						}
						ctx.fillText(hr + ":" + min + ":" + sec, 70, 80);
					ctx.restore();
	}
}

After wards just called init (); , that calls clock(); once a second to draw the clock. Please tell me whether it works in your browser ;)

If anybody is interested, here is the code: html5_clock. If you also want to deal with it, Mozilla has a good tutorial.

I hope this new age of web will delete all the flash trash out there!

Download: Javascript: html5_clock.js (Please take a look at the man-page. Browse bugs and feature requests.)


Martin Scharm

stuff. just for the records.