Heckroth Industries

New site

It's been a while since I've last had any spare time to work on the site, but I've finally found some time to work on it. It's changed a bit and as usual I'm using it to experiment with different ways of tackling an issue. So what's changed? Well, I've dropped WordPress and moved to a static site. I've moved the contents into JSON files which are rendered via a project I've been working on, renderJsonAsHtml. I've made it available via npm and the source is available on GitLab

The styling of the site is built on top of another project I've finally released, CoopersCoreCSS. This is the core set of CSS that I normally start from when developing a website and build the rest of the site's CSS on top. I've also made this available via GitLab.

HTML5 CSS JSON
Jason — 2017-01-26

Access denied, but I'm the Administrator!

Recently my HTPC, Windows Media Center (WMC) running under Windows 7, started to exhibit an odd issue. One or two of the recordings couldn't be deleted from within WMC. So I tried falling back to closing down WMC and deleting the files from the Recorded TV directory, only to receive an "Access Denied" error message. Ok, let's run a shell (cmd) as the administrator user change to the Recorded TV directory and use del to delete the files. Still I got the "Access Denied" error message.

Looking at the files properties showed even more odd results, they weren't owned by anyone. When I tried to change the owner to the administrator account I go the same error message. This was the point that I decided to fall back to basics, if the file system is behaving oddly then check the disk, so I ran

chkdsk c: /R

It replied that it couldn't check it now but would I like to check it on the next restart, which of course I said yes to and then immediately restarted the machine. 20 minutes later, after a full disk check, windows reappeared and I could delete the files. My current assumption is that windows had lost some of the ntfs details for the files and that the chkdsk reset them.

Windows
Jason — 2015-01-06

Launching screen only if the current terminal isn't already in a screen instance

If you like to use screen then this is a useful piece of code to add to the end of your .bashrc file. It will launch screen, but only if it isn't currently in an instance of screen. The great thing about this is that it works across machines so you can put it in your .bashrc on all the machines you like and then when you ssh into the first one you get a new screen session, but ssh into a second machine from within that screen session and the second machine won't launch another session of screen.

command_exists () {
    type "$1" &> /dev/null ;
}

# If we are in a ssh tty and not already running screen and screen exists then think about starting it
if [ $SSH_TTY ] && [ ! $WINDOW ] && [ "$TERM" != "screen.linux" ] && command_exists screen; then
    # If we don't have any attached screen sessions run screen and attach to the first dettached session
    SCREENLIST=`screen -ls | grep 'Attached'`
    if [ $? -eq "0" ]; then
        echo -e "Screen is already running and attached:\n ${SCREENLIST}"
    else
        screen -U -R
    fi
fi
Linux bash
Jason — 2013-12-03

IPv6 Routing issue

Recently I have been noticing an issue with my IPv6 networking. Everything was working fine locally but if I connected from outside the network then connections would lock up when they got busy.

It took a bit of investigating but I discovered that the IPv6 MTU size wasn't being detected correctly by some devices. The reason it would work locally was that the local network's MTU was 1500, but for IPv6 packets leaving the network the routing goes through an IPv4 tunnel, which results in it having a lower MTU size.

The solution was to add a line to the radvd.conf file (used by the daemon that handle the router advertisements). The line that I added was

AdvLinkMTU 1280;

Which results in those devices that configure their IPv6 details from the router advertisement setting their MTU to 1280 which is the minimum datagram size for IPv6.

IPv6 Networking
Jason — 2013-04-24

Extending the number of post parameters supported by Tomcat5 on RedHat Enterprise Linux 5

I have just had to work around a weird limit to the number of post parameters in Tomcat5 on RedHat Enterprise Linux 5 install. Specifically the error was

org.apache.catalina.connector.Request parseParameters WARNING: Exception thrown whilst processing POSTed parameters

java.lang.IllegalStateException: Parameter count exceeded allowed maximum: 512

A quick Google lead me to solution editing the catalina.properties file, but that can get overwritten by a yum update. The adapted solution is to edit your /etc/syconfig/tomcat5.conf file and extend the JAVA_OPTs variable to include this parameter change.

-Dorg.apache.tomcat.util.http.Parameters.MAX_COUNT=10000
Tomcat
Jason — 2012-06-18

Linux or GNU/Linux

Yet again an old argument discussion has reared its head and so I have decided to voice my opinion The discussion in question is "should it be called Linux or GNU Linux?"

To me the idea that I should call the operating system GNU Linux is wrong. The operating system is Linux, the Kernel is Linux. Yes I run a lot of GNU software on Linux, but I run a lot of GNU software on my Windows machines and no-one tells me I should refer to it as GNU Windows.

I also think that it is detrimental for GNU when people refer to Linux as GNU Linux. It sets up people to only think of GNU software if they are looking for software on Linux, when in fact there is GNU software available for most OS's.

So in conclusion, its going to be called Linux by me for the foreseeable future. (Though it looks like my CMS has decided to call it GNU Linux via its tag ordering)

GNU Linux
Jason — 2012-05-11

Using libcurl with wxDev-C++

Just had to do some C++ development on a Windows 7 machine so I downloaded and installed wxDev-C++ on my machine and download the required packages for libcurl and added the -lcurl to the linker options for the project.

The problem came when I tried to compile to code, I got the following errors

[Linker Error] undefined reference to `_imp__curl_easy_init'
[Linker Error] undefined reference to `_imp__curl_easy_setopt'
[Linker Error] undefined reference to `_imp__curl_easy_perform'
[Linker Error] undefined reference to `_imp__curl_easy_cleanup'
[Linker Error] undefined reference to `_imp__curl_easy_init'
[Linker Error] undefined reference to `_imp__curl_easy_init'
[Linker Error] undefined reference to `_imp__curl_easy_setopt'
[Linker Error] undefined reference to `_imp__curl_easy_setopt'
[Linker Error] undefined reference to `_imp__curl_easy_setopt'

They all looked like I was missing the curl library, but it was in the linker options. After looking through the libraries available I discovered that there was a second libcurl library, libcurldll.a, so I changed the linker options to include

-lcurl -lcurldll

Having added in the extra library I could recompiled the code without any problems.

C++
Jason — 2012-01-12

Time for a new battery

Recently my eeePc 900's battery has been struggling, so I figured it was time to actually test how dead it is. I charged it up fully and ran a script to log the battery's charge every 15 seconds. I then unplugged the power and left it downloading files over a wireless network. 36 minutes later it ran out of power.

I then plugged in the power turned it back on and once it had booted up I ran the same script to log the battery levels as it charged up. Turns out it took about 90 minutes to charge up again.

As it now only last half an hour I decided that a new battery was due. So I replaced it with the same spec battery and reran the tests. With the new battery it can run for 3 hours, though it does still take a long time to charge.

As I had the data to hand I decided to run it through gnuplot to produce a nice graph to visualise the differences.

Hardware
Jason — 2011-12-13

Please don't truncate error messages

This morning I have spent 10 minutes trying to figure out what an error message was referring to. Cryptic error messages are one thing that you get used to dealing with, but this time it was different. The error message made sense but left you thinking that you had to add some more space to something but didn't say what.

It turns out that the error message was from the underlying Oracle database, but that the software running the SQL against Oracle had truncated the error message. After reading through Oracles logs I discovered the end of the message which detailed which tablespace was in need of expanding. A couple of minutes later the tablespace was extended and it all started working

So if you output error messages from an underlying system, please don't truncate them.

Programming
Jason — 2011-11-28

Augmenting LDAP

Recently I needed to augment an LDAP service so that we could authenticate users against an Active Directory or an another internal system. This initially looked like a very time consuming task which would get very messy, that was until I stumbled across the ability for OpenLDAP to use a Perl Module for processing LDAP requests.

The documentation for the actual Perl Module side of this is not very good, the best thing to do is to play with the example module to get an understanding of how it all fits together.

Any sticking points? yes, if you are using Red Hat Enterprise Linux (Version 5 in my case) then you have to get the stable version of OpenLDAP and manually compile and install it (remembering to specify –enable-perl when configuring). The version being used by Red Hat doesn't include the perl backend part of OpenLDAP and even if you install their source and try to compile it as a module it fails.

If you require the option to accept a search filter with sAMAccountName in it then you will need to create a file with the other OpenLDAP schema containing

attributetype ( 1.2.840.113556.1.4.221
NAME 'sAMAccountName'
EQUALITY caseIgnoreMatch
SYNTAX '1.3.6.1.4.1.1466.115.121.1.15'
SINGLE-VALUE )

and in your slapd.conf add an include line to include the schema file.

The bind method wasn't present in the Perl example module I started from and while some people say you shouldn't do the bind in Perl but I couldn't get it started without it. Here is an extract of the bind method I used.

sub bind {
    print {*STDERR} "==== bind start ====\n";
    my ($this,$dn,$pass)=@_;
    print {*STDERR} "DN=$dn\n";
    #print {*STDERR} "Pass=$pass\n";

    my $retval=1;

    # Code here to set $retval to 0 if the distinguised name and password are valid
    print {*STDERR} "==== bind end ====\n";
    return $retval;
}

If you don't require a method then simply return the value 53, which is an "unwilling to perform" error.

LDAP Perl
Jason — 2011-09-13
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