We use CentOS VMs at work to emulate our production environment - and it took me a while to figure out how to get the VirtualBox Guest Additions to build reliably on CentOS 6.4/5. This is what I’ve currently settled on as a reliable method.

First, make sure that you’ve got the kernel headers and tools installed that you need to build stuff:

$ sudo yum update -y
$ sudo yum install gcc kernel-devel kernel-headers dkms make bzip2 perl

Make sure that you’ve only got the current set of kernel headers installed - the one for the kernel you’re actually running. Having more than one set installed prevents this working properly. Running this should show you one version of each kernel package:

$ rpm -qa | grep kernel | sort

It should look something like this:

dracut-kernel-004-336.el6_5.2.noarch …

To create image thumbnails from a PDF document, run this in a terminal window:

$ convert -thumbnail x300 -background white -alpha remove input_file.pdf[0] output_thumbnail.png

The parameters to convert do the following things:

If you want larger thumbnails, just change the x300 parameter to match. If you want to output .jpg’s (or anything else, like .gif), just change the file …

I had a feature request for automatic figure numbering, like latex. I was revamping this plugin for Pelican 3.3 anyway - and this didn’t seem too hard - so I decided to add it.

So, the Better Figures & Images plugin now supports automatic figure numbering. To enable this for all posts, just add this to your config file:

FIGURE_NUMBERS = True

If you want to enable this per post, just add this to the metadata at the top of the post:

for restructuredText add this:

:figure_numbers: true

and for Markdown add this:

figure_numbers: true

There are quite a few changes in Pelican 3.3 - most of them minor, but a few which might mean making some changes to your site in order to upgrade. This is what I did to move my site from Pelican 3.2 to 3.3.

The change that had the biggest impact and took the most work was around image linking - caused by a combination of things. I think I was doing it wrong before and things changed in a way that meant this no longer worked. I also had to update my Better Figures & Images plugin to take this into account.

Previously, I’d been linking to my images like this, both in my theme:

/* Theme CSS Image Link */
background: #2C71B8 url(/static/images/blueprint-background.png) repeat;

{# Theme HTML/Jinja image link #}
<meta name="twitter:image" content …

I’ve recently been corresponding with Denny Dias, from Brazil, who’s converted his blog over to Pelican - and we’ve been helping each other out a bit with building themes and whatnot.

He’s written up his conversion & theme building process - and was generous enough to credit me after he borrowed some of my theme’s logic, from this blog’s GitHub repo.

As he’s such a nice guy - and as I’ve just borrowed his tagsort jinja filter for my blog’s tag page, I though I’d return the favour - cheers Deny! :)

I recently needed to convert some FLAC music files from the increasingly common 48 bit encoding, down to 16 bit at 44100 kHz, so that they’ll play on my Sonos. Here’s how to do it:

If you don’t already have sox installed, do this to install it:

$ sudo apt-get install sox

Then run this to do the conversion, in the folder with music in:

$ mkdir resampled
$ for flac in *.flac; do sox -S "${flac}" -r 44100 -b 16 ./resampled/"${flac}"; done

And that’s it - it will convert all the .flac files in that folder to 16 bit at 44100 kHz and put the result into the ./resampled subfolder, preserving the metadata.

Thunar - XFCE & XUbuntu’s small but perfectly formed file manager - has a simple mechanism that allows you to easily add new commands to the right click menu of files and folders. These are called Custom Actions and are easy to create…​ here’s how to do it.

Click the Edit menu, then click ‘Configure custom actions…​‘. This will take you to the Custom Actions Manager, where you can create, edit or delete your custom actions.

You can enter anything into the command box, including complex bash scripts, names of scripts or executables on the PATH, or the full path and filename of the command you want to run.

On the ‘Appearance Conditions‘ tab, you tell Thunar when you want your item to appear in the right click menu: