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Posted in Misc | Leave a comment

Setting up up a deep learning box

After doing a number of courses on machine learning I now have some overview of what is available and how it all works. So now it is getting time to start doing some work from start to finish myself. To do some of the more interesting things you definitely need access to a system with a good GPU and the systems I have at home are not really suitable for this:

  • My work laptop has an Nvidia GT Quadro 1000M which has compute capability 2.1
  • My private laptop has a GPU (Nvidia GT 330M) which has compute capability 1.2
  • My server which does not have a GPU and so has compute capability 0

On the other hand popular frameworks like Tensorflow require, as of this writing, compute capability 3.0. This effectively rules out the use of my private and work laptops.

As alternatives, I considered starting of in the cloud by using Google or Amazon GPU offerings. But then the workflow there is also always to first setup some work at home and then do the same in the cloud. Also, costs can add up quite quickly if you go that way. Then another alternative is to get a new laptop or a new PC with a fast GPU. That seems nice since it opens up some more opportunities for gaming as well, but then I am not really a gamer, and it also feels like a bit of a shame to get another laptop/PC when my current one is still working fine (A Sony Vaio F11 laptop with 1.6GHz CPU). My current laptop is running linux most of the time and really still performs quite well.

Then I started looking at another possibility which is to add a GPU to my server. In fact, this turns out to be possible since my server has a free PCIe 2.0 x16 slot. Looking on the internet it seems that PCIe 3.0 cards should work without problems in PCI 2.0 so that makes it possible. Also, there is a way to setup a VM on KVM so that GPU accelerated computing can be used inside a VM, see for instance server world. This is preferred over running natively. The idea will be to do a lot of (long running) experiments locally and if I really want to do something big ‘rent’ some capacity in the cloud.

To do all this, I first had to upgrade my server which is now running Centos 6 on the virtual host to Centos 7. Well “upgrade” is a big word. It involved installing Centos 7 side by side to Centos 6 and getting everything to work again. Now that part is done. The next step is to get a nice graphics card (e.g. Nvidia GTX 1080 or 1070) and set that up in the server.  This will be interesting.

Posted in Fun, Server/LAN, Software | Leave a comment

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

Posted in Uncategorized | Leave a comment

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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Encrypting an existing Centos install

Edit: Meanwhile I have found a better way to migrate an existing centos unencrypted install to a fully encrypted install with /boot as the only unencrypted disk space. This solution is much preferred over the one described in this post. The new approach is here.

Inspired by yet another incident in the news of a laptop with sensitive information getting stolen, you start imagining what would happen if someone would get hold of your laptop. How much sensitive data would be on it and what would the consequences be. A small investigation revealed that the consequences could be quite big. There are various personal document stored, version control systems and IDEs with insecure password storage and of course various browser history files and cookies. That made me a bit nervous.

Therefore, I set out the investigate how to make this laptop more secure. The setup is an extension of setups I found on the internet where typically LUKS over LVM or LVM over LUKS is used. The current setup will in effect be LVM over LUKS over LVM.
Continue reading

Posted in Java, Server/LAN, Software | 1 Comment

Creating a USB install for Centos 6.4

The days of rotating disks for storing information and in particular for installing OSes are nearing their end. Why rely on something with rotating parts for storing data in the 21st century? Unfortunately, not every software vendor has caught up with this so in some cases special measures must be taken for installing an OS from a USB disk. One example of this is Centos/RHEL which does not come with a USB install by default. There is procedure from Red Hat that can be used, but that procedure is limited to starting an installation when you already have the installation media available somewhere (e.g. on a hard drive).

One common method to create such a USB install is to use the livecd-iso-to-disk script. Unfortunately that did not appear to work and I have tried it many times. After reading the interesting discussion on, I tried to give it another shot and this time it worked.

What I did was the following on a laptop running Centos 6.4:

  • Insert the USB stick: Find out the device name (e.g. using dmesg). Make sure the stick is unmounted as it could be automounted.
  • Partitioning: Make sure the disk is partitioned to contain one single primary partition (e.g. /dev/sdb1) using for example cfdisk. For now I will assume that /dev/sdb is the USB stick. Make sure to substitute this for the correct device in the next instructions.
  • File system: Create an ext3 filesystem on /dev/sdb1
    mkfs.ext3 /dev/sdb1

    I did not try ext2 and ext4 but these could also work. You can also optionally do a

    tune2fs -m0 /dev/sdb1

    to increase the available space by removing reserved blocks for the kernel (these are not needed anyway).

  • Install livecd tools: Install using yum:
    yum install livecd-tools
  • Transfer the ISO to the USB stick: Transfer disk 1 of the Centos 6.4 installation to the USB stick:
    livecd-iso-to-disk  CentOS-6.4-x86_64-bin-DVD1.iso  /dev/sdb1

    Note that it is important to specify /dev/sdb1 here and not /dev/sdb.



After this step, the USB stick can be tested locally using qemu-kvm.

To simply verify the the USB stick is found and the boot menu is recognized, bootup a virtual machine with only the USB disk:

/usr/libexec/qemu-kvm -hda /dev/sdb -m 256 -vga std

And use a VNC viewer (e.g. vncviewer from tigervnc) to view the VM. This should show a boot menu and should allow you to start the installation until the point that the installation procedure cannot continue anymore.

If you want to test a full installation, create a disk using logical volume management

lvcreate -L 10g -n bladibla vg_mylaptop

where vg_mylaptop is a volume group where you have at least 10GB of space left, and start qemu-kvm with the created logical volume as disk hdb and give it a bit more memory:

/usr/libexec/qemu-kvm -boot c -hda /dev/sdb -hdb /dev/vg_mylaptop/bladibla -m 2048 -vga std

After the install is completed, start the VM again without the USB stick

/usr/libexec/qemu-kvm -boot c  -hda /dev/vg_mylaptop/bladibla -m 2048 -vga std

The VM should now start up successfully. The USB boot stick is also recognized by my laptop natively and I it looks like I can install a full OS also there (at least the upgrade, which did nothing of course in my case, worked completely).

Disclaimer: As mentioned in the discussion at the link above, the whole procedure might give different results based on the USB stick you might use. I tested this procedure on a Dell Latitude M4700 laptop using a Kingston GT160 8GB memory stick.

Posted in Server/LAN, Software | 4 Comments