Author Archives: Brock Tice

Migrating to new server

I’ve just updated the DNS entries for VirtuallyShocking.com to point to the new web server. Everything seems to be working, but let me know if you see something amiss.

Getting a Linux Kernel changelog using git

I am setting up my new webserver (which, incidentally, this post is being written on), and had some trouble with the version of the Linux kernel I was using. I wanted to see whether my problem had been fixed between my kernel version and the current one, but couldn’t find an easy way to do that. User Octayn in ##linux on freenode IRC suggested I use git with tags. A little googling suppiled the right command-line magic.

First, I cloned the linux-stable git:


git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

Then, after changing into the linux-stable directory, I checked the tag names available:


git tag -l | less

That showed me the formatting of the tags, namely v. So then the command to get the full changelog was:


git log --decorate v3.0.9..v3.0.32

I did find some commits that might have fixed my problem. I upgraded and so far, so good. Only time will tell.

This is here as much for my own reference as it is for yours, but I hope it helps you!

delayacct and iotop in Ubuntu 10.04 Lucid Lynx

I was trying to use iotop yesterday on my workstation and it was complaining that “CONFIG_TASK_DELAY_ACCT” was not enabled in the kernel. “OK,” I thought, “I can rebuild the kernel, no problem.” So I went to rebuild the kernel and discovered that CONFIG_TASK_DELAY_ACCT was already enabled along with the associated config options needed for iotop, so I was confused.

After a little spelunking of old mailing list entries (which I am trying to spare you with this post, dear reader), I discovered that the Ubuntu folks flipped around how the “nodelayacct” kernel boot parameter works for various arcane reasons. Here’s the short version of how to enable it.

1) Edit /etc/default/grub, adding “delayacct” as an option to the GRUB_CMDLINE_LINUX_DEFAULT entry. If you hadn’t already modified that line, it would go from


GRUB_CMDLINE_LINUX_DEFAULT=""

to


GRUB_CMDLINE_LINUX_DEFAULT="delayacct"

2) Run “sudo update-grub”
3) Reboot, and you should be good to go

CSG Meshing – BRL-CAD?

When doing cardiac simulations, you’d think heart-shaped models would be ideal. However, for many basic science projects, a slab-shaped model with various regions of various shapes is more desirable. This allows isolation of geometry to answer a specific question. Historically people have used all sorts of tools to do this. Recently I’ve actually been using OpenSCAD to mock things up and make flat images, which I then massage through ImageJ and GIMP until I get something I can feed into the voxel-based mesher Tarantula.

This is really suboptimal, though. There must be some sort of constructive geometry modeler out there like OpenSCAD that will do proper volume meshes. OpenSCAD is really for surface meshes, but it’s so very easy to make the shapes I want in it. To that end I’ve been searching for FOSS CSG software, and I’m now trying the first one I found that has promise — BRL-CAD. I’ll post more as I try it out.

EDIT: So far so good the MGED editor in BRL-CAD seems to be WAY more powerful than OpenSCAD, much as I love OpenSCAD. I will post some designs as I get the hang of it.