binfalse

Again I installed a new kernel and again X isn’t able to start. Of course the last time I installed the proprietary NVIDIA driver I downloaded it to /tmp , and curiously it’s lost! The funny NVIDIA website is so damn incompatible, you need to have JavaScript or Flash or both to find your driver, no chance to get the driver with e.g. lynx from command line… So you need to have another running system to download the driver and secure copy it, or you need to reboot into the old kernel. (nonstop swearing at proprietary smut) Does this sound familiar? There is an alternative!

Once you have installed the driver, you’ve also installed a tool called nvidia-installer . This tool is able to find the newest driver at nvidia.com and to downloads it itself via FTP. Just type the following:

nvidia-installer --update

Even if you save your driver persistently, if you installed a new X version and your old driver is out of date you have to get a new driver! So this trick simplifies the world a lot ;-)

I frequently get asked about the error:

dpkg-query: warning: parsing file '/var/lib/dpkg/status' near line 5038 package 'linux-image-2.6.33-grml':
 error in Version string 'grml.02': version number does not start with digit
dpkg-query: warning: parsing file '/var/lib/dpkg/status' near line 21699 package 'linux-headers-2.6.33-grml':
 error in Version string 'grml.02': version number does not start with digit
dpkg-query: warning: parsing file '/var/lib/dpkg/status' near line 61359 package 'linux-doc-2.6.33-grml':
 error in Version string 'grml.02': version number does not start with digit

So this article is to answer all questions in a time.

I don’t know why, but that grml kernel has a version number of grml.02 (other kernel versions are also affected). This version string doesn’t meet the criteria for version numbers because it doesn’t start with a digit. So dpkg is correctly warning. This warning is not critical, you might ignore it without any consequences, or you can install a newer one. Kernel with corrected version numbers can be found in grml-testing , so add the following to your /etc/apt/sources.list.d/grml.list :

deb     http://deb.grml.org/ grml-testing main

and you’ll find for example the new 2.6.38 kernel. Just for those lazy guys:

aptitude install linux-image-2.6.38-grml linux-headers-2.6.38-grml

So, have fun with your new kernel :-P

I’m sure everyone of you got livid with the return value of the atan2 functions. Here is a fix.

public double arctan (double x, double y)
{
	double d = Math.atan2 (x, y) % (2 * Math.PI);
	if (d >= 0 && d <= Math.PI / 2)
		return Math.PI / 2 - d;
	else if (d < 0 && d >= -Math.PI)
		return Math.PI / 2 - d;
	else if (d > Math.PI / 2 && d <= Math.PI)
		return 2.5 * Math.PI - d;
	return d;
}

This is Java code, but easy to adapt for other languages. And since you are here, a little hint: Multiply the result with 180 / Math.PI to receive the angle in degrees.

I just installed Icinga, it was the right decision!

First of all respect to the Icinga guys, the compatibility to Nagios is great! Moving from Nagios to Icinga is mainly copy and paste. Syntax is the same, management structure also equals, you can even use all your previous installed Nagios plugins and the nagios-checker add on. Well done! Except for the web interface (looks much more professional) every feels like Nagios. So I can’t see any reason to stay with Nagios.

Here are some things I had to do:

• First of all I changed the credentials for the web interface:

  /etc/icinga % mv htpasswd.users htpasswd.users-org
  /etc/icinga % htpasswd -c -s htpasswd.users NewUser
  

• This new user needs also authorizations, so you need to edit /etc/icinga/cgi.cfg and replace icingaadmin with NewUser .
• The rights in /var/lib/icinga/rw/ were wrong, www-data wasn’t able to access the directory. So I wasn’t able to schedule manual checks via web. When I changed the permissions everything was fine:

  /etc/icinga % l /var/lib/icinga/rw/
  total 8.0K
  drwx------ 2 nagios www-data 4.0K Apr 18 01:02 .
  drwxr-xr-x 4 nagios nagios   4.0K Apr 18 01:02 ..
  prw-rw---- 1 nagios nagios      0 Apr 18 01:02 icinga.cmd
  /etc/icinga % chmod 750 /var/lib/icinga/rw/
  

• I added the following into the DirectoryMatch directive of /etc/icinga/apache2.conf , to force me to use SSL encryption:

  SSLOptions +StrictRequire
  SSLRequireSSL
  

• I shortened the mail subject of the notifications. By default the subject looks like:

  ** PROBLEM Service Alert: localhost/Aptitude-Updates is WARNING **
  

But I’m just interested in the important parts, so I changed the following in /etc/icinga/commands.cfg :

  [...] /usr/bin/mail -s "** $NOTIFICATIONTYPE$ Service Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" [...]
  

to:

  [...] /usr/bin/mail -s "** $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" [...]
  

the the notifications now come with a subject like this:

  ** localhost/Aptitude-Updates is WARNING **
  

All in all I’m glad that I gave Icinga this chance and recommend to test it if you are still using Nagios. Maybe I’ll test some further Icinga features and maybe we’ll migrate at the university..

The developers around you might know that there are some mechanism hooked when creating an object. Lets have a look at the order of these processes.

Even beginners should know about constructors. They are called if you create an object of a class, but there are some things running before. Here is an example class:

public class Initializing
{
	// static initializer
	static
	{
		System.out.println ("class loaded");
	}
	
	// instance initializer
	{
		System.out.println ("new instance");
	}
	
	// constructor
	public Initializing ()
	{
		System.out.println ("constructor");
	}
	
	public static void main (String [] args)
	{
		System.out.println ("first object");
		new Initializing ();
		System.out.println ("\\n\\nsecond object");
		new Initializing ();
	}
}

The output is:

class loaded
first object
new instance
constructor


second object
new instance
constructor

As you can see, first of all the static initializer is called. It’s also called exactly once, when the class is loaded. It’s clear that the class has to get loaded before the main () inside can be executed. The main () then prints a string to indicate the start of that routine and afterwards it creates the first object of the type Initializing . This calls the instance initializer before the constructor is executed. Also the creation of the second object calls first the instance initializer and then the constructor. That’s the workaround. At the first time a certain class is used the static initializer is executed, and each time an object of that class is created first the instance initializer is called and then the constructor. Btw. all of these routines are able to access members that are private, but notice that the static initializer can only access static fields.