Category Archives: Uncategorized

Why finalizers are really bad

It is more or less common knowledge that using finalize functions in java is bad. For one, you are depending on garbage collection for cleanup and there is no guarantee when the finalizer will be called. Further there is also no guarantee it will ever get called even if the appliction terminates nicely using System.exit().

However there is a far more important reason why finalizers are bad. Continue reading

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Encrypting an existing Centos install (2)

In a previous post, I described how to encrypt an existing Centos install that approach was based on find out how LUKS worked and then creating a storage logical volume that was encrypted with then logical volumes on top of that to contain the original data. The main disadvantage of that approach was that it was not possible to encrypt the root partition, and thus still potentially leaking confidential data.

Therefore, I looked at how a standard fully encrypted Centos install worked and basically that is quite simple. The basic setup of an encrypted Centos install is to have a simple partitioning setup with one small physical partition (e.g. /dev/sda1) with /boot on it (using typically ext4), and a second partition /dev/sda2 which is encrypted. On top of the encrypted /dev/sda2 device (e.g. /dev/mapper/luks) the previous logical volumes are based. This approach requires no power managements hacks nor special mount options in /etc/fstab.
Continue reading

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Why do developers write instead of reuse?

I am frequently amazed at the amount of software that is being written instead of simply looking around and reusing what’s already available. In practice I have seen a lot of reasons for this:

  • Our problems are unique: The misconception that “our problems are unique”. I really can’t recall how many times I have seen this but this is really occurring a lot.
  • Not looking for similar solutions: Simply forgetting to look for similar solutions on the internet to see what’s available (if only as an inspiration on how to best solve the problem). This is often also a side effect of thinking that this is a unique problem.
  • Underestimation of the problem: The misconception that it’s easy to write it yourself. In most cases, it is easy to come up with a first (half) working version that does approximately what you need. However, the work involved in making the same solution maintainable and with the correct feature set will make it much more expensive (the 80-20% rule).
  • Limited scope: A developer specialized in platform X (e.g. X = java) will typically only look for solutions in that area, whereas looking broader will reveal more solutions.
  • Coolness factor: It is cool to develop it yourself. Perhaps it involves an opportunity to do something cool with clustering or another chance to use one of your favorite frameworks. Perhaps you could use one of those cloud databases?
  • Overestimation of oneself: The idea that we can do something better in a few weeks time than what the industry or open source community has come up with using man years of development.
  • The desire for fame by writing reusable software: Paradoxically, the desire for reusable software can stimulate to roll your own. The problem is that writing reusable software (or calling it reusable) provides you with fame (even if it’s only in your local department). The reality is however that reuse can only exist through the willingness of people to use other people’s software. If there is one developer writing a reusable piece of software and 20 others using it, then clearly the willingness to use other’s software far outweighs writing it yourself.

I have seen these problems in companies of all sizes.

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Moving countdown

Yes folks! The countdown timer has been started again. This time it is counting down to the time when the move really starts and first boxes will be loaded onto a truck towards my new home.

Really looking forward to it…

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The last time I moved to a different city was 13 years ago. And before that time I had been moving every two years or so. So when I finally settled in 1998, I decided that I was going to stay in one place for a much longer time. It is time now however to move again, I got a new job in a new location and it makes a lot of sense to move. For one, I will have much better house (buying a house in the middle of the credit crunch), with a very nice garden, and it will reduce my traveling time to and from work considerably. Also, the environment is quite nice because my favorite mountainbiking locations are closer and there are also many more opportunities for mountainbiking close by.

One of the most important things when moving is of course…. my server. Of course, I am depending a lot on it. For one it is running my mail server and it also handles a number of mailing lists. It runs 4 web sites, and it is also my VCR (mythtv).

Therefore, it is important to me to minimize downtime of the server during the move. Luckily, I am already prepared for this since I am running the server as a virtual machine already. So as part of the move I will run this virtual machine on my laptop, which gives me plenty of time to disassemble the server rack and set it all up again at my new location. In fact as I am writing this, I am already running the server from my laptop. It is easy for me to do this because my regular server backups are bootable, see here.

Because of this setup, I can minimize the total down time of my web sites to the order of minutes and minimize mail down time to less than possibly one day in total (but no-one will notice that because mail servers retry sending mail).

Interestingly, I had quite a fight today to get things working again with my TVIX M-6500 which allows me to play movies hosted on the server (through NFS) on my TV. As it turns out there are subtle issues with network bridges on linux dropping UDP packages in some cases, see here.  As it turns out, the TVIX uses UDP for NFS, which can give problems with bridged network interfaces on virtual machines in some cases. Luckily, I managed to solve this by replacing the virtio network model on the machine by device emulation of a RTL8139 chipset. Anyway, all is  good now. The server VM is now fully functional again and I can watch movies, send/receive mail and all my websites are up. The only thing I cannot do is record at this time, but ok, this is only for the next 10 days or so. On the 16th of February I hope to be able to start the server again at its new location.

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