Miscellaneous failure No principal in keytab matches desired name

I was getting this error in the server logs when trying to ssh into a kerberos enabled box and although my ssh client was getting a principal for the machine host/machine.ox.ac.uk@OX.AC.UK I wasn't getting logged in. Now looking on the net it seemed that it was likely that I didn't have the matching principal in the keytab file. But a klist -k /etc/krb5.keytab showed all the correct keys. The next thing I checked was that the DNS records matched host machine.ox.ac.uk and host 192.0.2.0. After running round in circles I checked /etc/hosts to find the line 192.0.2.0 machine and because my machine used the hosts file before DNS it was looking for the principal host/machine@OX.AC.UK which of course didn't exist.

This whole saga would have been much easier to debug if the error message had just included the principal that wasn't present in the keytab file. The machine was a server Ubuntu 6.10 install. Strangely it seems that my desktop Ubuntu machine has the machine name only associated with 127.0.0.1 and not the external IP, although this machine uses DHCP to get its IP.

pam_env, /etc/environment and expansion

Rather than setting environment variables for a system in shell startup files (/etc/profile) you can use pam_env to set them (both ssh and login by default use pam_env). By default on Ubuntu this appears to be where the path is set, now to add something extra to the path I wanted to define a new value (JAVA_HOME) and then include $JAVA_HOME/bin in the path. To start with I edited /etc/environment but it seems that expansion doesn't occur in this file. However you can edit /etc/security/pam_env.conf to set the PATH and expansion does happen here. This is what I ended up adding to /etc/security/pam_env.conf : JAVA_HOME DEFAULT="/opt/jdk1.5.0_11" PATH DEFAULT="/usr/local/sbin:/usr/local/bin:/usr/sbin:\ /usr/bin:/sbin:/bin:/usr/bin/X11:/usr/games:${JAVA_HOME}/bin"

Firebug and Net View

It seems that Firebug has a nice little bug. This caught me out when using it to monitor if some of our files were getting cached. Basically it seems that firebug doesn't notice when some files come from the cache and reports them as being downloaded again.

Microsoft, Patnets and BlueJ (Java IDE)

Through Planet Eclipse I found a post detailing how Microsoft first stole and then patented an idea from a Educational Java IDE called BlueJ developed by Deakin University and the University of Kent. Although this may have been done unintentionally I hope this blows up into a bit of a PR disaster for them as their behavior in this matter doesn't seem very good.

ProxyUserDirectoryProvider

As part of the work I have been doing with Sakai and Bodington I needed to allow Sakai to access the user details that are stored in Bodington. The normal way to do this would be to write a UserDirectoryProvider (UDP) that sits in the components folder. The problem is that I didn't want to put the whole of Bodington into the components classloader and tomcat was going to load Bodington anyway as a webapp. The solution was to create a proxy that could be injected with the real Bodington UDP when Bodington started up. This needed to be an API that extended the standard UDP:

public interface ProxyUserDirectoryProvider extends UserDirectoryProvider {
UserDirectoryProvider getUdp();
void setUdp(UserDirectoryProvider udp);
}


This ProxyUserDirectoryProvider could then be requested from the component manager at Bodington startup and setUdp() called with the full implementation of the Bodington UDP. The proxy I created is currently sitting in https://svn.oucs.ox.ac.uk/projects/vle/sakai/user-proxy/trunk/.

element.getAttribute("class")

Why are even the simple things sometimes hard? Attempting to get a element attribute. Here is a table of what the various browsers return when trying to get the class attribute having already found an element:

var element = document.getElementById("theSpan");

in a document containing the HTML:

<span id="theSpan" class="something">

Browser	element. getAttribute( "class" );	element. getAttribute( "CLASS" );	element. getAttribute( "className" );	element. attributes[ "class" ];	element. className;
Firefox 2.0	something	something	null	[object Attr]	something
Opera 9.0	something	something	null	[object Attr]	something
Safari 1.3.2	something	something	null	undefined	something
IE 5.5 (Mac)	null	null	something	something	something
IE 7.0	null	null	something	[object]	something

Updated: Thanks to anonymous for pointing out that you can just use element.className to get the class name used and it seems to work correctly across all browsers I tested.

It seems that there is no simple way to get the class attribute across browsers. The solution seems to be to get the class attribute and if it undefined try the className attribute. Most other attributes should work fine, it is just that IE doesn't like the class attribute that throws the spanner in the works. Here is the quick testing page.

Label Based Feeds

When I was at the Sakai conference I was asked if I wanted my blog added to Sakai Planet, the thing is that I blog about more than just Sakai and so only the posts for Sakai should end up in the planet. After a little googling I discovered you can have feeds for labels and it seems that my sakai feed works. I wonder why Google don't make this the default RSS feed when viewing all the posts for a tag?