GNU/Linux, Open Source, Cloud Computing, DevOps and more...

Linux remote control from your smatphone via SSH button widgets

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hot-button-ssh-command-widget-iconIn this post I will tell you about an Android app that is extremely useful to run commands remotely on a Linux computerHot Button SSH Command Widget. This application allows you to launch conveniently any command you want on a remote computer through SSH only with the push of a button on the screen of your mobile phone or tablet. This not only will facilitate automation of repetitive tasks, but also is very interesting from the perspective of security for the same reasons I exposed in my Automatically lock/unlock your screen by Bluetooth device proximity post. It will allow you for example to lock and unlock the screen without having to type your password again and again in sight of other people.

DanielLinux remote control from your smatphone via SSH button widgets

Partitioning and resizing the EBS Root Volume of an AWS EC2 Instance

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One of the few things I do not like about the AWS EC2 service is that all available images (AMIs) used to to launch new instances require a root volume of at least 8 or 10 GB in size and all of them also have a single partition where the root filesystem is mounted on.

In my post The importance of properly partitioning a disk in Linux I discussed why in my opinion this approach is not appropriate and now I will address in a practical way how to divide those volumes into multiple partitions keeping the 8-10 GB base size or making them even smaller to save costs in case you want to deploy smaller servers that do not need as much storage space.

DanielPartitioning and resizing the EBS Root Volume of an AWS EC2 Instance

Differences between ASLR, KASLR and KARL

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Following the release of the Linux Kernel 4.12, which for the first time brings the KASLR feature enabled by default, and almost simultaneously the announcement of a feature called KARL in OpenBSD, I found it interesting to clarify the differences between these security techniques, since I think that the combination of both will be very important in the future of system security as they will prevent exploiting vulnerabilities related to memory corruption (buffer-overflow).

DanielDifferences between ASLR, KASLR and KARL

How to create a Sentilo AWS EC2 instance from an OVA file

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Sentilo is an open source software designed by openTrends for the exchange and processing of information from thousands of sensors and actuators, acting as an interface between them and the various applications that want to collect and make use of the information they provide. Thus, it fits well within the Smart City architecture and has the city of Barcelona as the main promoter. But Sentilo is not only made by and for the cities, but also for any organization that wants to implement an IoT application that requires deploying a smaller number of sensors and actuators, such as inside buildings or in the open field.

In this article I will detail how to deploy a Sentilo 1.6 server in a Cloud Computing environment such as Amazon Web Services by creating an EC2 instance from an AMI that will be created by importing an image in Open Virtual Appliance (OVA) format which can be downloaded from Sentilo’s website at http://www.sentilo.io/xwiki/bin/view/Sentilo.Community.Documentation/Use+a+Virtual+Machine.

DanielHow to create a Sentilo AWS EC2 instance from an OVA file

How to exclude your own [dynamic] ip from Google Analytics

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In my 5 ways to exclude your own visits from Google Analytics post I discussed the 5 main methods that exist to prevent visits you make to your own websites are tracked by Google Analytics, each with its pros and cons. However, I found it necessary to further expand the first of those methods, which in my opinion is the best possible way to exclude your own internal traffic from Google Analytics based on your IP address, whether fixed or dynamic. It allows you not only to block yourself but also filter the activity of all members on your own team or company, which is of utmost importance to avoid any interference with data collected from real user activity.

And I say Google Analytics because it is the main actor in this market, but this same method is perfectly suitable for any other web analytics tool like Piwik, Clicky, OWA, Clicktale, StatCounter, Kissmetrics, Mouseflow and many others.

DanielHow to exclude your own [dynamic] ip from Google Analytics

How to prevent the .xsession-errors file from growing to a huge size

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Xorg iconThe .xsession-errors file is where the X Window system logs all errors that occur within the Linux graphical environment. All desktop environments, whether Gnome, KDE, Cinnamon, XFCE, LXDE, etc., and all lighter window managers like FVWM, IceWM or Window Maker make use of the X Window system. Therefore any graphical application running on your computer can cause that error messages are written to the .xsession-errors file, reason why it can grow wildly until reaching very big sizes of tens of GB or even hundreds if your disk capacity allows it.

DanielHow to prevent the .xsession-errors file from growing to a huge size

Fatrace command: how to know in real time which processes are writing to a file

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It is usually easy to know which process or processes are writing to a given file in Linux, since we either know its origin and its nature beforehand (for example the Apache access_log), or we can easily find it out with the fuser or lsof commands. However, sometimes it will happen that although we know the role and purpose of a file, there are so many applications accesing it simultaneously that it is very difficult to know which of them is the one that reads/writes the most or does so in a precise moment. Knowing this would be very useful to learn for example why a log file is growing excessively or which application is making an abusive use of system resources, either by mistake or intentionally.

DanielFatrace command: how to know in real time which processes are writing to a file

Automatically lock/unlock your screen by Bluetooth device proximity

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One of the most basic and common security measures that you can adopt in your working environment is to protect your computer by automatically locking the screen after a certain period of inactivity, so that it is necessary to enter a password to unlock. But there is a more effective way, and that is to configure your Linux machine so that the distance or proximity of a Bluetooth device you own, for example your cell phone or a smartwatch, automatically causes locking or unlocking the screen without having to enter any password on keyboard.

DanielAutomatically lock/unlock your screen by Bluetooth device proximity