Logic Exception

Modern Time Technology That was it... I was finally fed up with amount of time I was spending to SSH into each host manually. I was repeating the same procedure probably hundreds of times every day... Typing the ssh command and the host name, waiting for the initial prompt, entering my password, typing the sudo -i command to get root access, and entering my password again. Just as expected from a modern time worker. But wait, there was more to deal with... Working with a lot of servers, I need to use my favorite terminal emulator to organize and manage the number of sessions. This means that every window has to be properly named and assigned to a specific session. So before logging into each server, I had to switch to the correct TMUX session (or create a new one), create a new TMUX window, name the window properly, and finally move on to the SSH stage. I was aware of a script that was created by an ex-colleague. The script automated the process by storing the credentials in a ...

It has been quite a while since I have written my last article. After pondering what to write for a couple of days, I have decided to share a couple of /proc filesystem tricks. Here is a list of real-life scenarios that illustrate how you can exploit this filesystem: Environment Variables Let's start with a simple example. You have a Java process that is misbehaving and you would like to make sure that the JAVA_HOME environment variable for the process context is pointing to the correct JDK installed on the system. Just cat the /proc/[pid]/environ file to view the list of environment variables for the process. File Descriptors To get the list of file descriptors opened by a process run an ls command for /proc/[pid]/fd. This directory would list the file descriptors as symbolic links to files or sockets with inode numbers. This is a particularly useful trick in case you are dealing with a long strace output and you have a system call with an associated file descriptor. If t...

Overview (R)?ex , according to its website, is a tool written in Perl for configuration management and software deployment. The only requirement to have is an SSH connection to the remote server(s). Alternative Uses (R)?ex is a very capable tool to automate system administration tasks. For example, I have recently built an RPM build script that copies my local code/files to a build server, builds an RPM package, and downloads the finished RPM to my RPM repository on my local box. I have also used it to generate reports. One recent report was required to see how many of our servers were able to access a certain DNS view. In fact, the use cases are pretty much unlimited. You can use (R)?ex for any process that requires some sort of automation on a remote server. That said, as powerful as it is, (R)?ex still requires some initial setup to become usable. I have included a couple of my tips below. Tips and Tricks Code Structure Rexify.org Wiki recommends using revision control s...

IT Support I showed up to work on my first day a couple of weeks ago and the first thing that I was given was a company Mac... A Mac! My absolutely brilliant idea was to ask IT support if I was allowed to wipe the hard-drive clean and install my favorite Linux distribution. After giving me the classic thousand-yard stare that every IT dude gives every time you ask for something, he told me that "it was not supported". Long story short, at the end of the first week, I was left with this piece of brushed Aliminum brick running some applications that does not even run on Linux but required by my new company. Virtualization Solution? Of course virtualization. Needless to say, this was a complex setup with multiple requirements: * I want to run a Fedora guest for every day use. There is nothing that can match Konsole running on a bleeding edge distribution out there. * I also need to run a CentOS guest for certain tasks such as building RPMs and other production related tas...

Overview In this article, I will try to explain how to design an Android OAuth2 client that can interact with a Smyfony2 back-end implementation using Spring for Android and Spring Social. Before we start, I need to emphasize a couple of points. First of all, I am not an Android expert; I am still learning. Secondly, I like to leverage existing tools so I have chosen Spring Social for Android for this article. It satisfies my requirements for this tutorial but it may not be suitable for every case. Finally, I will not be explaining the server side implementation in this article. Read my previous FOSRestBundle and FOSOAuthServerBundle articles if you need starters. Raw Data Let's first look at the raw data that we will fetch from the server. Because I have been using the Conversation and Message examples for a while now, I will stick with the same pattern in this article. Let's say we would like to retrieve a list of conversations by a specific user from a REST endpoi...

Parcelable Interface Overview In one of my earlier posts, I mentioned writing an article about FOSOAuthBundle integration with an Android client. To keep that article to the point, I need to explain some concepts beforehand. One of the important concepts is the Android Parcelable interface that allows data to be transferred between different processes/threads. Certain network operations with Android such as authentication with OAuth2 and then fetching data from a REST endpoint should be performed in the background in order not to block the UI thread. This requires data to be fetched by a service (I have opted for Intent Services in my implementation) in the background and then passed back to the calling activity/fragment with a result callback. This is where the Parcelable interface comes into play. Basically, the Parcelable interface allows your classes to be flattened inside a message container called a Parcel to facilitate high performance inter process communication. The rece...

I had to deal with an unexpected problem recently. In my setup, I have a Conversation document which contains multiple Message documents embedded inside - a one-to-many mapping basically - and I need to atomically push a new Message when a user replies to a conversation. Below is the initial code that I implemented: public function reply($conversationId, Message $message, $flush = true) { $this->dm->createQueryBuilder($this->class) ->update() ->field('archivers')->unsetField() ->field('repliedBy')->set($message->getUserId()) ->field('repliedBody')->set($message->getBody()) ->field('repliedAt')->set(new \DateTime()) ->field('modifiedAt')->set(new \DateTime()) ->field('messages')->push($message) ->field('id')->equals(new \MongoId($conversationId)) ->getQuery() ->execut...