Fix full Ubuntu /boot partition

Linux kernel images are stored on a separate partition mounted under /boot. This partition can fill up, at which point you can no longer install any software updates.

Ubuntu (and possibly Debian and Mint) has a command called purge-old-kernels that helps to prevent you from ever getting in that situation. Similarly, RHEL/CentOS/Fedora have a command called package-cleanup.

However, if your /boot partition is already full, purge-old-kernels won’t work. You will need to run something like the following:

dpkg --list 'linux-image*' | cut -d' ' -f3 | grep linux-image | grep -v "$(uname -r)" | grep "[0-9]" | xargs dpkg -r --force-depends

apt-get -fy install

purge-old-kernels -y



#DUTO2015 conference

I’m at the Data Unconference in Toronto today. Jarred Gaertner just gave a through-provoking keynote on the ethics of big data, and I’m about to dig my hands into some open data sets in Richard Pietro’s hands-on session.

My colleague Polong Lin will be on a panel about IBM’s data science tools this afternoon, which should be interesting if only because it’s hard to keep track of everything that’s out there.

#DUTO2015 is sponsored by my friends at Big Data University

Encrypt Gmail, Facebook emails with OpenPGP and Mailvelope

Facebook just released a great use case for OpenPGP encryption in Gmail and other web email providers. You can now configure Facebook to encrypt all email it sends you with OpenPGP.

Whether or not you use Facebook, it’s surprisingly easy to use Mailvelope to integrate OpenPGP with Gmail and other email providers. Mailvelope is a browser extension for Chrome and Firefox that lets you encrypt messages that you write and decrypt messages that you receive.

The encryption can be done externally to the web email interface, so your email provider does not have access to the plain text of your email message.

OpenPGP is based on public key cryptography. You have two keys — a public key you can share with everyone, and a private key that you keep secret. Everyone can use your public key to encrypt messages they send you, but only you can decrypt them using your private key.

Why encrypt email? Email is generally transmitted in plain text across the internet, meaning a hostile party can intercept it. With the web (http) moving to encrypted connections for everything, email is left as an insecure communication medium. You as a user have to take active steps to make it secure.

Here’s how you can transparently integrate OpenPGP encryption with Gmail and Facebook:

  1. Install Mailvelope
  2. Generate a new key in Mailvelope options
  3. Go to Display Keys, click on a key, go to Export, and copy the public key
  4. Open your Facebook profile, go to About > Contact and Basic Info, and paste in the key in the PGP Public Key field
  5. Facebook will send you an encrypted notification. Mailvelope should turn your browser cursor into a golden key when you hover your cursor over the encrypted contents
  6. Tada!

You may also want to share your public key on keyservers like the MIT PGP Key Server or the PGP Global Directory. In principle, that will allow other people to send you encrypted email messages that only you can decrypt.

How I made my Android Galaxy S3 phone run faster

My primary phone is a Samsung Galaxy S3 running Android 4.4.2 Kit Kat. It’s a little old at this point, but I’m disinclined to upgrade for the sake of upgrading. It was getting slower, so I’ve recently taken a number of steps to tune and optimize its performance.

Things I’ve done to make Android slower

1. Enable device encryption

If someone were to steal my phone without encryption, they would be able to hijack any number of my online accounts through email password resets. This is a frightening possibility, and the surest way to protect against it is to encrypt your device.

Device encryption would be mandatory if I chose to access work email on phone, but that is something I choose to avoid.

2. Encrypt microSD storage

Samsung Galaxy S2 through S5 were fantastic phones in that they have replaceable batteries and expandable storage. I’ve recently added a high performance 32GB microSD card to my phone, and sensibly encrypted it.

Things I’ve done to make Android faster

1. Replace Samsung keyboard with anything else

Ever since I purchased my phone, it’s had an infuriating multi-second delay in bringing up the Samsung touch keyboard. I’ve recently switched to the Google Keyboard available in the Google Play app store, and the difference is night and day. The Keyboard comes up instantaneously.

I’ve also heard great things about Swype.

2. Clear caches with CCleaner

Back when I was a Windows user, CCleaner was the one reputable, malware free application for tuning Windows. They have an Android version that does a good job of clearing the many caches and temporary files of your Android apps.

3. Delete all photos

Dropbox automatically backs up all of my photos, so there’s absolutely no reason to keep them on disk. Having a full file system on your Android phone reduces file system and encryption performance.

I went into the Gallery app and bulk-deleted all my old photos.

4. Move applications to external storage

The built-in storage on your phone is not as performant as a quality microSD card. Many applications will let you relocate them after installation to the microSD storage.

5. Disable animated transitions

You can enable developer mode on Android without jailbreaking.

Once you do, you can go into Settings > More > Developer options and disable all useless animations. This is something I’ve done in the past on other operating systems. On Android, I again got better responsiveness and minimal difference in visual experience.

6. Get an extended battery

Samsung phones other than the newest Galaxy S6 have user-serviceable batteries. That means you can easily purchase a replacement battery, an external spare battery charger, or an extended battery.

Since I’ve gotten an extended battery, my phone lasts two whole days on a single charge. This is fantastic for my user experience.

Going beyond

One thing I haven’t done is root or jailbreak my device. If you do jailbreak, you can uninstall all the bundleware cruft that Samsung puts on the phone.

Note that if you do intend to use your phone to access work email, there may be a policy against jailbreaking your device.

Installing DB2 on Mac OS X

It’s useful to have a local installation of the DB2 on Mac for development and test purposes. I have a local installation on my Macbook to develop DB2-backed Ruby on Rails applications.

IBM DB2 is a mature relational database server. It supports lots of neat things like SQL, XQuery for XML, SPARQL for RDF, full text search, and so on.

DB2 on Mac using DockerDB2 on Mac logo

A quicker option for getting running with DB2 on Mac is to use the DB2 docker image. It should get you started quickly with DB2 by running it in a virtualized Linux environment on your Mac.

DB2 on Mac natively

Here are the current instructions for installing DB2 10.1 on Mac OS X, courtesy of my colleague Kevin Rose:

Instructions to install DB2 v10.1 on Mac OS X Yosemite:

Prerequisite: XCode developer tools must be installed. These can be installed from the Mac App Store.

1. Ensure the following entries are in the /etc/sysctl.conf. Create the file /etc/sysctl.conf if it does not exist.


Restart your Mac after creating the file to make the values take effect.

2. Open a terminal with a shell for the the user that will become instance owner.

3. Ensure that otool is in the path. Execute otool:


If the error is “command not found” then run the following

     export PATH=$PATH*:*/Applications/

4. Extract the DB2 install image from the tar archive:

     tar -xzvf db2_v101_macos_expc.tar.gz

The image will be extracted into an expc directory.

5. Enter the expc directory and run the installer and perform a non-root install:

     cd expc
  # *** DO NOT RUN db2_install AS ROOT ***

This will install DB2 to the following default location: /Users/$(whoami)/sqllib

Execute step 6 if you need to enable connections for a userid other than the instance owner:

6. Enable OS authentication. (You need to be an Admin user to run these commands):

cd /Users/$(whoami)/sqllib/security
sudo chown root /Users/$(whoami)/sqllib/security/db2ckpw
sudo chmod u+rxs /Users/$(whoami)/sqllib/security/db2ckpw 
sudo chmod o+rx  /Users/$(whoami)/sqllib/security/db2ckpw

The instructions for starting DB2 and configuring remote access are the same as before.

Dockerize all the things

Dockerize all the things As my team creates new web apps and microservices in Rails, Meteor JS, and other stacks, we dockerize them. Docker is great because it enforces loose coupling, modular design, and process isolation.

A Docker container can be thought of as a very lightweight VM that shares a Linux kernel with its host. The infrastructure and tooling around it makes configuration management, scaling, and efficient use of resources easier.

My team’s also dockerized the Informix and DB2 database servers. The direct hardware access that Docker allows will give you better performance than you’d have seen with a VM equivalent in the past, while the container format allows for easy automation, operation, and management. cannot open shared object file: No such file or directory – …

Got this error while deploying a Rails app on Nginx: cannot open shared object file: No such file or directory - ...

This means that the ibm_db adapter is installed, but it can’t find the DB2 libraries. The issue is that IBM_DB_HOME and some other environment variables are not set.

The best solution is to make sure all users have db2profile loaded. Edit /etc/profile and add:

. /opt/dsdriver/db2profile

You should now reload your profile (. /etc/profile) and restart Nginx.

This assumes that you already have IBM Data Server Driver installed under /opt/dsdriver.

JRuby for the Java .class is .java_class

I’ve been having a lot of fun working with a Apache jclouds in JRuby. All the examples for the API are in Java and Clojure, while online JRuby docs could be better, so there’ve been some interesting translation challenges.

I just had to re-Google what .class becomes in JRuby, so a quick note for the future.



JRuby: "bluforcloud-test"


Circular dependency detected while autoloading constant

I recently ran into this frustrating and intermittent error in Ruby on Rails 4 (JRuby, actually):
Circular dependency detected while autoloading constant

Googling turned up several articles advising one to abide by the Rails conventions, but that was not the issue.

The application I’m writing uses background threads. The problem shows up when trying to instantiate a Rails controller in one of them. Rails searches for object definitions dynamically, so when multiple threads are trying to instantiate the same object, there’s a race condition.

The fix is define a mutex for access control:

$thread_mutex =

And then use it in the threads when instantiating the controller, model, or some Ruby class:

mc = nil
$thread_mutex.synchronize do
  mc =

Userscript to make banning MediaWiki spammers easier

Somehow, I’ve come to be responsible for administering two MediaWiki-powered wikis. The main burden is having to ban spammers, which sometimes sign up in batches of 20 at a time.

To help with process, I’ve put together the following browser userscript. On Firefox, you can easily set it up using the Greasemonkey extension. Opera and Chrome have their own facilities.

The script basically makes the default values on the user ban form sane, so I can just click through without fiddling with dropdown and checkboxes. Obviously, the ban has to be permanent. Obviously, I don’t want spammers emailing anyone.

// ==UserScript==
// @name           Blocker
// @namespace
// @include*
// ==/UserScript==

// Set default expiry to 'infinite' or 'indefinite', depending on MediaWiki version
function makeExpiryInfinite () { "use strict";
  // Get the element
  var elExpiry = document.getElementById('wpBlockExpiry');
  if (!elExpiry) { elExpiry = document.getElementById('mw-input-wpExpiry'); }

  // Abort if element not found
  if (!elExpiry || !elExpiry.children) { return; }

  // Find the infinite option
  var expiryNodes = elExpiry.children;
  var index = 0;
  for (var i in expiryNodes) {
    if (expiryNodes[i].label && expiryNodes[i].label in {infinite:1, indefinite:1}) {
      index = i;

  // Set dropdown to the infinite option
  elExpiry.selectedIndex = index;

// Automatically prevent user from sending e-mail
function preventEmail() { "use strict";
  // Find check box
  var elEmailBan = document.getElementById('wpEmailBan');
  if (!elEmailBan) { elEmailBan = document.getElementById('mw-input-wpDisableEmail'); }

  // Abort if it's not there
  if (!elEmailBan) { return; }

  // Check the box
  elEmailBan.checked = true;

// Automatically prevent user from sending e-mail
function reallyBanThatIP() { "use strict";
  // Find check box
  var elHardBlock = document.getElementById('mw-input-wpHardBlock');
  if (!elHardBlock) { elHardBlock = document.getElementById('mw-input-wpHardBlock'); }

  // Abort if it's not there
  if (!elHardBlock) { return; }

  // Check the box
  elHardBlock.checked = true;


I’ve been hearing wonderful things about userscripts for years, but this is the first one I’ve put together for myself. It’s actually very easy to write these, assuming you know Javascript and have tools like Firefox’s Web Console and the Web Developer extension handy.

I’m planning to enhance it a little so that it handles the slightly different form for banning anonymous users, but I’m not sure if it makes sense to submit to any official repository. It helps with running small wikis that have open memberships, so there isn’t any one site I can identify it with. Obviously, it’s not suited for Wikipedia, as they have a very different set of problems.

Edit: Updated the script with better handling for banning anonymous users by IP address.