Friday, February 06, 2015

Setting DISPLAY variable to avoid No protocol specified Error: Can't open display: :# Selenium UnknownError: unknown error: Chrome failed to start: exited abnormally

If Selenium server cannot open the current display the client will fail with an error similar to "UnknownError: unknown error: Chrome failed to start: exited abnormally". This is a common issue many people ask about when they try to either run X applications (like tests against selenium in a remote server) remotely or when they are logged in via VNC, XRDP etc. Basically the DISPLAY variable is assigned to the local terminal console and not really to the remote session. You need to find the proper DISPLAY variable for your remote session in order to resolve this problem.

Setting DISPLAY variable will avoid the typical problem "No protocol specified Error: Can't open display: :#" where # is usually 0.

If this variable is set incorrectly your session will have no access to run X applications in the visible display. Perhaps the fastest way to find out if your DISPLAY is correctly set is to run the xclock application. The commands below should be self explanatory about how it fails and how it should be corrected at least in Debian/Ubuntu: So all you really need to do in order to make sure your selenium server spawns the chrome browser successfully is to set the DISPLAY variable to the correct value. Keep that in mind specially after restarting.

Saturday, December 27, 2014

ITPalooza Kanban and Continuous Delivery presentation

This was definitely a great event to share Kanban and Continuous delivery experiences with other agile practitioners in South Florida. I thank IT Palooza and the South Florida Agile Association for the opportunity.

Friday, December 26, 2014

On security: news without validation - The case of ntpd for MAC OSX

It is a shame that even Hacker News reported as many many others inaccurate information about the recent several NTP vulnerabilties affecting the ntpd daemon in *NIX systems.

Apple computers are not patched automatically if the users do not select to do so, a feature that was added with Yosemite so most likely not even available in many MACs in use out there.


Sysadmins should be encouraged to reach out their user base so the MACs are patched. As a difference with Ubuntu and other linux distros where most likely ntpdate is being used to synchronize time in MACs the ntpd daemon is used. Yes, this is not just a server issue when it comes to MAC OS-X.

BTW back to ntpd vulnerabilities. Follow apple instructions for correct remediation. As explained there 'what /usr/sbin/ntpd' should be run to check the proprietary OSX ntpd version.

What is interesting here is that 'ntpd --version' still returns 4.2.6 after the patch which according to the official ntpd distribution communication does not contain the patch. Version 4.2.8 does.

Thursday, December 25, 2014

Do you practice careful and serious reading?

Do you practice careful and serious reading? This is the ultimate question I have come to ask when someone claims to have read the book and clearly I find out s(he) meant to say "eyes went" instead of "mind went" through the content of the book.

When you carefully read a book you take notes. I personally do not like to highlight books as the highlighters I have seen so far as of December 2014 will literally ruin the book. I think taking notes not only help with deep understanding of the content but ultimately it becomes a great summary for further "quick reference".

When you seriously read a book you know what you disagree and agree upon, you are not in a sofa distracted by familiar sounds. You are in a quite space, fully concentrated in receiving a message, processing the message and coming up with your own conclusions, questions and ultimately must importantly answers to the unknown which now suddenly becomes part of your personal wisdom.

It is discouraging to sustain a debate around a book content when there is not careful and serious reading. In my opinion "reading" when it comes to a specific subject matter means "studying" and of course you can only claim you have studied a subject if you have carefully and seriously read the related material. Seeing a book is not the same as looking into a book. Listening to an audio book content is not the same as hearing it.

Thursday, December 18, 2014

How to SVN diff local agaist newer revision of item

From command line I would expect that a simple 'svn diff local/path/to/resource' will provide differences between local copy and subversion server copy. However that is not a case as a spacial '-r HEAD' needs to be added to the command instead:

Tuesday, December 16, 2014

NodeJS https to https proxy for transitions to Single Page applications like AngularJS SPA

If you are working on a migration from classical web sites to Single Page Applications (SPA) you will find yourself dealing with a domain where all the code lives, mixed technologies for which you are forced to run the backend server and bunch of inconveniences like applying database migrations or redeploying backend code.

You should be able to develop the SPA locally though and consume the APIs remotely but you probably do not want to allow cross domain requests or even separate the application in two different domains.

A reverse proxy should help you big time. With a reverse proxy you can concentrate on just developing your SPA bits locally while hitting the existing API remotely and yet being able to remotely deploy the app when ready. All you need to do is detect where the SPA is running and route through the local proxy the API requests.

Node http-proxy can be used to create an https-to-https proxy as presented below:

Wednesday, December 10, 2014

Adding ppid to ps aux

The usual way BSD style ps command is used does not return the parent process id (ppid). To add it you need to use the "o" option as follows:

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