Brother HL-2270DW on Linux

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The Brother HL-2270DW is one of the best budget laser printers around, with third party consumables readily available on eBay.

The printer has a network port on the back of it, which is great news for GNU/Linux users, because networked printers tend to speak standard protocols.

The fastest way to get this printer working without Windows is to plug it in and log in via the web. The default settings have DHCP enabled. Here are a few pieces of crytic voodoo magic that helped me:

  1. To reset the print server settings, hold “GO” on startup, then let go and press it 6 times.
  2. The default admin login is admin / access
  3. On my printer (Firmware 1.10), printing network settings by holding “GO” for 10 seconds caused the network card (Brother NC-7800w) activity lights to go off, requiring a reboot.

On Debian, there is no “Brother HL-220DW” CUPS driver on the list, but I found the following driver to work fine (and allow duplex):

Brother HL-2170W Foomatic/hpijs-pcl5e (recommended)

To use this driver, you will need to install the HP Linux Printing and Imaging printer driver:

apt-get install printer-driver-hpijs

Missile Launcher on Raspberry Pi

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This post covers a few setups to experiment with if you have a DreamCheeky USB missile launcher and a Raspberry Pi.

A newer version is being sold on ThinkGeek, but the one I used was:

DreamCheeky USB Missile Launcher

Setup 1: Direct to PC

The launcher comes with some software to let you connect it straight to a computer. Of course, USB can only go 5 metres, which is not much fun for cubicle warfare:

USB Missile Launcher setup with PC

I included this setup because it is the easiest way for Debian/Ubuntu users to test that they can use this driver, which is needed for the other setups.

Setup 2: Networked with Raspberry Pi

So for this setup, you need a Raspberry Pi Model B. They look like this:

Raspberry Pi Model B

Running Raspbian, upgrade to Debian Jessie, and compile the code:

apt-get install git libusb-1.0-0-dev libncurses-dev gcc g++
git clone --recursive https://github.com/mike42/missile
cd missile
make

You can then place the pi anywhere with network and power:

USB Missile launcher setup with Raspberry Pi

To operate the launcher remotely, use SSH to log in, and run missile/bin/keyboard-ctl.

Setup 3: Wireless with Raspberry Pi and Battery

Of course, network and power can be provided with a power bank and wifi adapter:

Power Bank for mobile phone
USB WiFi Adapter

The wifi adapter will take some work to set up (see Debian Wiki), so I wont document that here. You will need a power bank that has enough power for the Raspberry Pi with launcher and wifi. Mine had to be close to fully charged to work.

An obligatory diagram of this setup:

USB Missile launcher setup with Raspberry Pi (WiFi and Battery)

Wrap-up

The reason this helps with cubicle warfare is simple: The launcher, Raspberry Pi and battery can be fitted into a tissue box or other small space. Proof:

Box interior

On a desk you would see this as:

Box exterior
Box open

And a quick demo for completeness:

In the above, the Pi is connected to DC power, because the battery didn’t have enough juice to power the unit.

Enabling graphical boot on Debian GNU/Linux

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Unlike most desktop Linuxes around today, Debian’s default boot screen is still text:

Debian's text-mode booting

I imagine that this is because there is no distinction between “Desktop” and “Server” editions in the Debian world (see tasksel), so a text-mode boot will work on every type of installation.

Luckily, if you want a graphical boot screen, you can simply apt-get install a package called plymouth and configure it according to these instructions.

The result looks more suited to a desktop PC (screen capture from here):

Debian's plymouth boot screen

Plymouth install notes

There is a comment in /etc/default/grub which suggests checking supported graphics modes, which is a Good Idea(TM):

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480

The theme for “wheezy” was called Joy, so if you have desktop-base installed, you should:

/usr/sbin/plymouth-set-default-theme joy

I tried to get this working in a virtual machine to get an actual screen capture, but on KVM this appears to be quite tricky, due to emulated graphics.

Installing Debian on a HP dm-1

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Getting Debian working on different hardware is always a challenge. This week I am using a HP Pavilion dm1 4306AU.

lspci shows that it has the following hardware:

00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 14h Processor Root Complex
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Wrestler [Radeon HD 7310]
00:01.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Wrestler HDMI Audio
00:10.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB XHCI Controller (rev 03)
00:11.0 SATA controller: Advanced Micro Devices, Inc. [AMD] FCH SATA Controller [AHCI mode]
00:12.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB OHCI Controller (rev 11)
00:12.2 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB EHCI Controller (rev 11)
00:13.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB OHCI Controller (rev 11)
00:13.2 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB EHCI Controller (rev 11)
00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller (rev 14)
00:14.2 Audio device: Advanced Micro Devices, Inc. [AMD] FCH Azalia Controller (rev 01)
00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridge (rev 11)
00:14.4 PCI bridge: Advanced Micro Devices, Inc. [AMD] FCH PCI Bridge (rev 40)
00:15.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] Hudson PCI to PCI bridge (PCIE port 0)
00:15.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Hudson PCI to PCI bridge (PCIE port 1)
00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 0 (rev 43)
00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 1
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 2
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 3
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 4
00:18.5 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 6
00:18.6 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 5
00:18.7 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 12h/14h Processor Function 7
02:00.0 Network controller: Ralink corp. RT3290 Wireless 802.11n 1T/1R PCIe
02:00.1 Bluetooth: Ralink corp. RT3290 Bluetooth
06:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)

The Debian installer worked fine, but it booted to a blank screen with a blinking underscore. Steps below to get a working machine.

Fix graphics and wifi

Debian 7 running on a HP dm-1

You need the nonfree firmware in firmware-linux-nonfree. First select ‘recovery mode’ from the boot menu.

From the root terminal, nano /etc/apt/sources.list, and add non-free. Plug in a network cable, then:

apt-get update && apt-get install firmware-linux-nonfree firmware-ralink

After a reboot, you can now get a working desktop and use wifi.

The beep problem

On shutdown, my computer gave a loud PC speaker beep, which could not be muted. The GNOME sound control doesn’t provide a volume bar for the PC speaker, so I installed the gnome-alsamixer package, which has it:

Muting the PC speaker with gnome-alsa-mixer

Strangely, the beep returned after a few reboots, but was no longer as loud.

Brightness keys

The brightness keys did not work originally, but upgrading to “testing” (jessie) fixed this.

Overall

This laptop requires two non-free packages to run, both of which are just firmware blobs.

Writing in Ancient Egyptian with HieroTeX

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When I started learning Ancient Egyptian, I wanted to be able to type hieroglyphs alongside regular text, for printing translations. There is a package for the typesetting system LaTeX which does this, called “HieroTeX“. It took me a while to figure out how to use it, but the results are top-notch:

Example of HieroTex output

Because I’ve installed this on quite a few computers, I’m writing up this blog post to make it easier for other GNU/Linux users who are trying to figure it out.

Installation

This is tricky, because:

  • There is no Debian package! Uh oh.
  • Debian is phasing out tetex in favour of texlive
  • The variables.mk file needs to be edited for the install to work (diff to apply / how to apply it). This is because the default installation target is the user’s home directory.

I put togethter this script, hierotex-install-3.5.sh, which will get a working HieroTeX install on any recent version of Debian.

#!/bin/sh
# Script to download and install HieroTeX on a Debian computer.
# Use at your own risk.
#
# Some packages you should install first:
# 	apt-get install texlive make gcc

# Get and extract the files
wget -c "http://webperso.iut.univ-paris8.fr/~rosmord/archives/HieroTeX-3.5.tgz" && 
tar xvzf "HieroTeX-3.5.tgz" && 
cd HieroTeX && 
wget -c "http://webperso.iut.univ-paris8.fr/~rosmord/archives/HieroType1-3.1.4.tgz" && 
tar xvzf "HieroType1-3.1.4.tgz"

# Patch variable.mk to install for the whole system
wget http://mike42.me/blog/files/variable.patch && 
patch variable.mk < variable.patch

# Run the installer
sudo make tetex-install

Note: This page is great, but the variables.mk suggested for Debian/Ubuntu does not include the documentation folder, which will cause the installer to crash. It also suggests using tetex, which will not exist in future Debian releases! This is probably fine if you are on a .rpm-flavoured distro.

How to use

Firstly, you will need to know a little bit about the LaTeX typesetting system. See wikibooks.

HieroTeX accepts markup in Manuel de Codage format, which you will either need to learn, or get a tool which helps you mark up text in it. This Linux for Egyptologists page has some excellent suggestions.

The block of LaTeX code below is from my tex-examples repo, and was used to generate the image of Tutankhamun’s cartouche above.

\documentclass[a4paper]{article}
\usepackage{hiero}
\usepackage{egypto}
\begin{document}
	\section*{Egyptian hieroglyph example}

	\begin{hieroglyph}zA ra < i-mn:n-t-G43-t-S34 HqA-iwn-Sma >\end{hieroglyph} \\
	{\em Tutankhamun Hekaiunushema} \\
	Living Image of Amun, ruler of Upper Heliopolis
\end{document}

To build the file, you need to filter it through sesh command. Something like this would work:

cat hierotex-example.tex | sesh > hierotex-example-2.tex
latex hierotex-example-2.tex

The actual example uses a Makefile to do this.

Update May 2016: The original website for HieroTeX has gone offline, but is available via the Internet Archive: webperso.iut.univ-paris8.fr/~rosmord/archives/

Infinite loop in a Makefile

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I had to kick myself for writing this bug into a Makefile today. I am writing it down so that I remember to use &&, and not ; next time.

The Makefile had this target in it:

clean:
	cd folder; \
		make clean
	rm -f file

The problem here is that the statement cd folder; make clean counts as one "line", and make wont notice a problem (and stop) until that line has executed.

Unfortunately, the folder name had a typo, so this script had a chance to call make clean without changing directory, calling itself and becoming stuck in an infinite loop.

So long story short, this is why Makefiles should be littered with the "and" operator.

clean:
	cd folder && \
		make clean
	rm -f file

How to liberate your myki data

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myki logo

myki is the public transport ticketing system in Melbourne. If you register your myki, you can view the usage history online. Unfortunately, you are limited to paging through HTML, or downloading a PDF.

This post will show you how to get your myki history into a CSV file on a GNU/Linux computer, so that you can analyse it with your favourite spreadsheet/database program.

Get your data as PDFs

Firstly, you need to register your myki, log in, and export your history. The web interface seemed to give you the right data if you chose blocks of 1 month.

Export myki data for each month

Once you do this, organise these into a folder filled with statements.

A folder filled with myki statements

You need the pdftotext utility to go on. In debian, this is in the poppler-utils package.

The manual steps below run you through how to extract the data, and at the bottom of the screen there are some scripts I’ve put together to do this automatically.

Manual steps to extract your data

These steps are basically a crash course in "scraping" PDF files.

To convert all of the PDF’s to text, run:

for i in *.pdf; do pdftotext -layout -nopgbrk $i; done

This preserves the line-based layout. The next step is to filter out the lines which don’t contain data. Each line we’re interested in begins with a date, followed by the word “Touch On”, “Touch Off”, or “Top Up”

18/08/2013 13:41:20   T...

We can filter all of the text files using grep, and a regex to match this:

cat *.txt | grep "^[0-3][0-9]/[0-9][0-9]/[0-9][0-9][0-9][0-9] [0-9][0-9]:[0-9][0-9]:[0-9][0-9] *T"

The output looks like:
Filtered output, showing data

So what are we looking at?

  1. One row per line
  2. Fields delimited by multiple spaces

To collapse every double-space into a tab, we use unexpand. Then, to collapse duplicate tabs, we use tr:

cat filtered-data.txt | unexpand -t 2 | tr -s '\t'

Finally, some fields need to be quoted, and tabs need to be converted to CSV. The PHP script below will do that step.

Scripts to get your data

myki2csv.sh is a script which performs the above manual steps:

#!/bin/bash
# Convert myki history from PDF to CSV
#	(c) Michael Billington < michael.billington@gmail.com >
#	MIT Licence
hash pdftotext || exit 1
hash unexpand || exit 1
pdftotext -layout -nopgbrk $1 - | \
	grep "^[0-3][0-9]/[0-9][0-9]/[0-9][0-9][0-9][0-9] [0-9][0-9]:[0-9][0-9]:[0-9][0-9] *T" | \
	unexpand -t2 | \
	tr -s '\t' | \
	./tab2csv.php > ${1%.pdf}.csv

tab2csv.php is called at the end of the above script, to turn the result into a well-formed CSV file:

#!/usr/bin/env php
<?php
/* Generate well-formed CSV from dodgy tab-delimitted data
	(c) Michael Billington < michael.billington@gmail.com >
	MIT Licence */
$in = fopen("php://stdin", "r");
$out = fopen("php://stdout", "w");
while($line = fgets($in)) {
	$a = explode("\t", $line);
	foreach($a as $key => $value) {
		$a[$key]=trim($value);
		/* Quote out ",", and escape "" */
		if(!(strpos($value, "\"") === false &&
				strpos($value, ",") === false)) {
			$a[$key] = "\"".str_replace("\"", "\"\"", $a[$key])."\"";
		}
	}
	$line = implode(",", $a) . "\r\n";
	fwrite($out, $line);
}

Invocation

Call script on a single foo.pdf to get foo.csv:

./myki2csv.sh foo.pdf

Convert all PDF’s to CSV and then join them:

for i in *.pdf; do ./myki2csv.sh $i; done
tac *.csv > my-myki-data.csv

Importing into LibreOffice

The first field must be marked as a DD/MM/YYYY date, and the “zones” need to be marked as text (so that “1/2” isn’t treated as a fraction!)

These are my import settings:

Options to import the myki data into LibreOffice

Happy data analysis!

Update 2013-09-18: The -nopgbrk option was added to the above instructions, to prevent page break characters causing grep to skip one valid line per page

Update 2014-05-04: The code for the above, as well as this follow-up post are now available on github.

Backing up from a hosting provider

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Backups are great, and they’re not rocket science. I’m writing up how we do backups, not because I think it’s a cool or unique setup (because it’s not), but to highlight how effective a simple solution can be.

We use rsync to take a local copy of whatever is on our web host without wasting bandwidth downloading files that aren’t needed. The layout looks like this:

Our hosting provider is accessible via ssh, and the backup box we use is a Raspberry Pi model B, costing (more or less) 50 AUD to get running.

On the server

On the server, we back up databases with mysqldump. To do this, you need to enter user details into a .my.cnf file, and then something like this will do the trick:

#!/bin/sh
# Remove old dump
rm -f database.sql.gz

# Dump and compress database
mysqldump -h sql.example.com --all-databases > database.sql
gzip database.sql

The above script is called database-dump.sh, and is called from the backup box, to dump the databases to a file before grabbing all the files.

On the backup box

First, a script to get the files. You should use password-less login with ssh-copy-id for this to work non-interactively:

#!/bin/sh
# Update the database dump
ssh user@host.example.com './database-dump.sh'
# Get files
rsync -avz --delete-during user@host.example.com:/home/user .

We save a copy of the files at this date in a dated archive, so we can back-date to find deleted things. At the end of the above script:

mkdir -p archive
now=$(date +"%Y-%m-%d")
tar -czf archive/backup-$now.tar.gz user

There aren’t a huge number of changes to record daily, so we got cron to run the above script weekly on the backup box. Read man crontab for how to do this.

What backup is not

If you think you shouldn’t be doing backups, you’re wrong. The following are not good excuses:

  1. Trust — Whoever is looking after the data wont lose it.
    Our host is pretty good, but their terms of service say they wont be responsible for any data loss. Even providers which have support agreements can make mistakes. You’ll also be able to work faster if you’re not paranoid about any mistake being unrecoverable.
  2. Expense — It’s a nice idea but not worth it.
    It’s dirt cheap, you can learn to do it yourself, and once set up requires virtually no administration. If your organisation can’t afford some kind of backup solution, then it should probably stop using data in any form.
  3. RAID — I invested money in RAID, so I don’t need backups.
    If you accidentally delete something, or notice that some your files have been tampered with, then RAID will not help you. If there is a problem (eg. fire) at the hosting location, then you will be in trouble regardless of disk redundancy.

Debian & XFCE quirks on Toshiba NB550D

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Today I re-installed Debian wheezy on my Toshiba netbook and realised how useful it might be to collate the hurdles into one tidy reference blog post (to save looking everything up next time).

This just covers everything I had to configure or work around to get a working setup.

Install & hardware issues

From linux, use dd to write your disk image onto a flash drive:

dd if=debian-wheezy-DI-rc1-amd64-netinst.iso of=/dev/sdX bs=4M

If you don’t know your flash drive device, then locate ‘Disk Utility’ or use sudo fdisk -l and choose the likely candidate.

Now boot up the netbook. If you’ve disabled the splash screen, then F12 will get you a boot menu and F2 will let you enable USB booting (if you don’t see the flash drive).

The installer gives you a warning about needing non-free firmware. You can safely ignore this, it’s just bluetooth.

When you get the option to, Install openssh. You will have graphics issues later, and your computer will be next to useless if you don’t have some way to log in.

Follow the installer as usual, and boot into the new system.

Graphics

From GNOME, everything initially worked okay out of the box for me, but logging out would predictably corrupt the graphics like so:

Pro-tip(TM): Write down your IP address before this happens and follow the rest of the steps via ssh.

These steps on the Debian wiki suggest getting xserver-xorg-video-radeon and xserver-xorg-video-ati, but they are already installed (and xserver-xorg-video-radeonhd does not appear to exist in wheezy). The free firmware also didn’t work for me:

root@mikebook:~# apt-get install firmware-linux-free

So it looks like we need firmware-linux-nonfree, which means we need to allow non-free packages. Edit the end of each line in /etc/apt/sources.list to add contrib and non-free:

After this, update your package list, install the non-free firmware, and restart X (rebooting is shown here but not really necessary):

apt-get update
apt-get install firmware-linux-nonfree
reboot

Next time you log in, GNOME will report that it is running in full-bloat mode, which is a good sign. If you still have issues, then the output of lspci is what you need to google:

02:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI RV710 [Radeon HD 4350] (prog-if 00 [VGA controller])

Touchpad / two-finger scroll

The Laptop’s Synaptics touchpad will work just fine on the default settings. I only wrote this up because the version of XFCE in wheezy has no options for tapping, two-finger scroll, or other fancy things (unlike the screenshots on xfce.org).

GNOME will let you set up per-user mouse preferences, but these don’t affect gdm (the login screen), so you can’t tap the login buttons (how annoying!)

The solution is to configure the mouse using Xorg’s configuration. The Debian wiki page on the topic gives an example file to dump in /etc/X11/xorg.conf.d/. I swapped two values to get two-finger right-click:

Section "InputClass"
        Identifier      "Touchpad"                      # required
        MatchIsTouchpad "yes"                           # required
        Driver          "synaptics"                     # required
        Option          "MinSpeed"              "0.5"
        Option          "MaxSpeed"              "1.0"
        Option          "AccelFactor"           "0.075"
        Option          "TapButton1"            "1"
        Option          "TapButton2"            "3"     # multitouch
        Option          "TapButton3"            "2"     # multitouch
        Option          "VertTwoFingerScroll"   "1"     # multitouch
        Option          "HorizTwoFingerScroll"  "1"     # multitouch
        Option          "VertEdgeScroll"        "1"
        Option          "CoastingSpeed"         "8"
        Option          "CornerCoasting"        "1"
        Option          "CircularScrolling"     "1"
        Option          "CircScrollTrigger"     "7"
        Option          "EdgeMotionUseAlways"   "1"
        Option          "LBCornerButton"        "8"     # browser "back" btn
        Option          "RBCornerButton"        "9"     # browser "forward" btn
EndSection

After saving this file, reboot or run killall Xorg as root.

Sleep

I haven’t investigated this properly, but I would steer clear of suspend-to-RAM, and set your power settings to hibernate (ie suspend-to-disk) instead. This is one error you might get on wake (if you are lucky enough to get a display after it wakes):

This is not a kernel thing, as a no-X install can pm-suspend without issue.

Sudo

By default, the user you create during the Debian setup is not in the sudo group. To change this:

su
adduser joebloggs sudo

You need to log out then again for this to affect your session.

Making XFCE more useable

XFCE was my desktop of choice, so at this point, you can either stop reading or run this:

apt-get install xfce4 xfce4-goodies

Appearance

Because it runs GTK-2 and not GTK-3, GNOME apps will look ugly beside XFCE apps if you don’t choose settings which work well for both toolkits. I chose these ones but there are other good combinations:

  • Window Manager -> Theme: Default-4.6
  • Appearance -> Style: Anquita

If you use it, then you should open gnome-terminal now. It defaults to black-on-black under XFCE, which you will want to swap out for something less stupid.

Replacing Thunar with Nautilus

Thunar is great, but Nautilus is more familiar to me, and can easily be set up as the preferred file browser:

  • Preferred Applications -> Utilities -> File Manager: Nautilus

Thunar will hold onto your desktop unless you remove it from Session and Startup (tab over to ‘Session’ and delete xfdesktop)

To tell Nautilus to handle the desktop, install gnome-tweak-tool, and check the box labelled ‘Have file manager handle the desktop’. Next time you start Nautilus, it will give you a working desktop.

Disable screensavers

XFCE has some very cool screensavers, but personally I think this part of desktop computing is a bit last-century:

  • Settings -> Screensaver: Blank screen only

The program XScreenSaver itself is a bit of an eyesore. If you don’t like it, this forum post has some suggestions for alternatives.

Getting a calendar

The default clock on the panel is not clickable. Simply remove it and add the ‘DateTime’ widget — This can show a clock with a drop-down calendar, which is basically standard.

Getting ‘Print Screen’ to work

XFCE makes this super easy to set up (once you turn up this thread on google):

  • Settings manager -> Keyboard -> Application shortcuts

Add a new shortcut to this command:

xfce4-screenshooter -f

Then hit Print, and you should get this:

External monitor

When you use an external monitor and switch off the laptop display, you can get stuck without a screen if you pull out the cable! The XFCE screen-switching app (mapped to Fn-F5 on my keyboard) is not really navigable by keyboard, so I added this shortcut as well:

The command xrandr --auto will switch on any connected monitor with a sane default resolution, fixing your display without rebooting.

Update 2013-03-15: I changed this to Shift+Alt+F5, because some programs use the above shortcut, rendering it useless when said programs have focus.

Pyrocket and Ubuntu

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I have a great USB rocket launcher, it’s more useful than a computer mouse most of the time actually. I spotted a moth on the roof the other day, and hadn’t installed pyrocket on this computer yet.

A quick apt-get install pyrocket is all it takes to solve that though, right? No such luck.

Apparently, the quality control in the Ubuntu repos are such that this package has been broken for several months now, despite the dependency issue being fixed by an upstream fork.

So this is the error you get at the moment anyway:

Traceback (most recent call last):
  File "/usr/bin/pyrocket", line 17, in 
    from rocket_frontend import RocketWindow
  File "/usr/lib/pymodules/python2.7/rocket_frontend.py", line 11, in <module>
    from rocket_webcam import VideoWindow
  File "/usr/lib/pymodules/python2.7/rocket_webcam.py", line 2, in <module>
    from opencv import cv, highgui
ImportError: No module named opencv

The solution, beyond complaining about it, is to read the bug report here and do this:

git clone https://github.com/stadler/pyrocket
cd pyrocket/src
./pyrocket.py

But the moth had escaped by then.