Dreamhost, DreamCompute(OpenStack) ssh login


You have just created your first instance in Dreamhost’s new service DreamCompute using OpenStack and you would like to login with ssh, but you get ‘Permission Denied’.


The solution is described here, and it’s the fact that the user name that you need to use is not your Dreamhost account name, or the DreamCompute dashboard user anme but the the username called:


NOTE: It seems that is also described here, at the bottom.

Using Elixir with Docker

In order to be able to use Elixir with the help of Docker, so that you can run different containers with different versions, and to have a shared code folder, you could follow the steps below:

  • Install docker in your system. Installation instructions for different systems are here
  • Download the elixir image from the Docker Hub:
    sudo docker pull trenpixster/elixir
  • List the images on your host:
    sudo ps docker images
  • Start a specific version of the elixir docker container (ie elixir 1.0.3):
    sudo docker run -t -i trenpixster/elixir:1.0.3 /bin/bash
  • Use a shared folder with code between the docker container and your host:
    sudo docker run -v /home/user/Prog:/Prog -t -i trenpixster/elixir:1.0.3 /bin/bash

    where the folders after the -v option are /home/user/Prog (host) and /Prog (docker)

  • Use a port forwarding:
    sudo docker run -p 8000 -v /home/user/Prog:/Prog -t -i trenpixster/elixir:1.0.3 /bin/bash

Some useful docker commands

Having started to use docker recently, some of the commands that are needed are a bit difficult to remember. I’m sure that this will change the more that I use it, but as a quick reminder/look up for this initial phase, I’m just going to list some of them here.

List current images:

sudo docker images

List currrent running containers:

sudo docker ps

Saving the state of a container by using the id from above command:

sudo docker commit -m "latest state comment" -a "John Somebody" 7ed30_id_no new_name_of_container:v2

Starting a container with port forwarding:

sudo docker run -p 8000 -t -i new_name_of_container:v2 /bin/bash

Sharing a directory from the host system (/home/user/Prog) inside the container (Prog):

sudo docker run -p 8000 -v /home/user/Prog:/Prog -t -i new_name_of_container:v2 /bin/bash

No PostgreSQL clusters exist; see “man pg_createcluster”


After installing postgresql in a new Ubuntu 14.04 installation you get the error:

No PostgreSQL clusters exist; see "man pg_createcluster"

and when you try to start the server with:

sudo service postgresql start

you get the error that the server does not exist:

psql: coud not create to server: No such file or directory ...


The solution can be found in the article here, and is to create manually the first cluster by:

sudo pg_createcluster 9.3 main

Fixing a broken sudoers file without rebooting


If by accident you make a mistake in your sudoers file then you won’t be able to run sudo command after saving the file.


Following the answer here, you can simply run the command pkexec visudo, supply your password and provided you already had sudo permissions, fix the sudoers file, make sure that you save it using the Q when prompted, and you should be able to use sudo commands again.

Docker error – error response from daemon: Cannot start container….is not within /var/lib/docker/aufs/mnt


You are trying to use an image from Docker in your Ubuntu 14.04 system, but you are getting a error like the following:

014/12/13 17:10:23 Error response from daemon: Cannot start container 4023610855c0551bdc44d0e602f20999c0527da3cfe010169707248887b3a1f0: /var/lib/docker/aufs/mnt/4023610855c0551bdc44d0e602f20999c0527da3cfe010169707248887b3a1f0 is not within /var/lib/docker/aufs/mnt/4023610855c0551bdc44d0e602f20999c0527da3cfe010169707248887b3a1f0


Your docker version is outdated (ie 1.0.1) so you would need to upgrade your docker installation.
There is a script for this (information from here):

After running the following you should be able to use your images as normal with: sudo docker run -t -i image/name bin/bash:

$ curl -s https://get.docker.io/ubuntu/ | sudo sh

Project ERROR: Unknown module(s) in QT: webkitwidgets


You are trying to bundle install a Gemfile that includes the capybara-webkit gem, in an Ubuntu system but you get the following error:

ERROR:  Error installing capybara-webkit:
ERROR: Failed to build gem native extension.
Project ERROR: Unknown module(s) in QT: webkitwidgets


It seems that the latest ubuntu versions are using QT version 5 instead of 4. So in order to be able to install the gem you would need to install the qt development libraries for version 5 like:

sudo apt-get install libqt5webkit5-dev

minitest assert_routing with method included in path


When trying to use the minitest assert_routing with the first parameter representing the path as a hash that includes both the path and the method, and run the tests rails complains about SyntaxErrors.

When trying to use it as suggested in the ‘Rails 4 Test Prescriptions’ Pragmatic Programmers book (p. 172 – Minitest and Routing) which is:

assert_routing({ path: "/projects", method: "post" }, 
controller: "projects", action: "create")

the error is:

syntax error, unexpected ',', expecting ')'
... '/projects', method: 'post' },  controller: 'projects', act...

even when trying to have the second parameter as a hash:

assert_routing({ path: "/projects", method: "post" }, 
{ controller: "projects", action: "create" })

the error is similar:

 syntax error, unexpected ',', expecting ')'
... '/projects', method: 'post' }, 
{ controller: 'projects', ac...


Seems that you need to pass the parameters enclosed in brackets, so the following would work:

assert_routing  ({ path: '/projects', method: 'post' }), 
({ controller: 'projects', action: 'create' })

Book Review: BDD in Action by John Ferguson Smart (Manning)

As the subtitle of the book ‘Behavior-driven development for the whole software lifecycle’ suggests, this is a book describing Behaviour Driven Development for the different phases of software development.

It starts with a very general description of BDD, the problems that it addresses, the general principles and the origins of it, as well as the pros and cons in different organisations and team scenarios. Throughout this general description there are plenty of references and links for anyone wishing to have more details.

This is followed by a real life project, that goes through the phases of requirement analysis, creation of the features, stories and examples and the distinction and differences between each of them. There are various techniques described, including Feature Injection for identifying business goals and supporting features, Impact Mapping for high-level requirement visualisation, Purpose-Based Alignment Model for judging how much effort you should put into different features, and the identification of stakeholders and their roles. There is also a description about Real Options and Deliberate Discovery principles.

There are more detailed examples to automating scenario steps, described in different languages (Java, Python, .NET, Javascript) and diffent tools (JBehave, Cucumber-JVM, Behave, SpecFlow and Cucumber-JS). These are used to go from executable specifications to automated acceptance tests. There two separate chapters following that, describing the two different ways for automating the acceptance criteria depending on whether they are for the UI layer or the non-UI requirements.

Last but not least, there is a chapter dedicated to explaining the relationship between BDD, TDD and Unit Testing, another one describing the idea of living documentation, as well as reporting and project management, and finally the role of BDD in continuous integration (CI) and continuous delivery.

Throughout the text there are a lot of diagrams to help explain the ideas better, as well as a lot of references for more detail. Even though most of the examples are based in Java, the principles, ideas and techniques are easily applied to other languages and tools.

So, in summary this is a very useful book for anyone wanting to learn how Behaviour Driven Development can be used in practise. There are different sections that are targeted to different roles from business stakeholders, to testers and to developers. Hopefully when your whole team reads this book, the whole idea of BDD can be understood better, and used to build the software right as well as build the right software.

Disclaimer: This book was reviewd under the Manning reviewers program.