GNU/Linux

Linux remote control from your smartphone 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 smartphone via SSH button widgets

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 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

How to enlarge the size of an EBS volume in AWS and extend an ext4 partition

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Logo AWS EBSWhen we completely fill up an ext4 filesystem mounted on a partition hosted in an EBS volume of Amazon Web Services and we can not do anything to free space because we do not want to lose any of the stored data, the only solution is to grow up the volume and extend the associated partition up to 100% of its capacity to obtain free space again.

DanielHow to enlarge the size of an EBS volume in AWS and extend an ext4 partition

What is the true meaning of system average load and CPU utilization in Linux?

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The CPU average load value is a very important metric to understand the behavior of a Linux system, and especially its current and recent past status. Many times there is confusion between this term and percentage of CPU usage, but differences are important. In this article I will try to explain the true meaning of both and how to tell if a Linux box is overloaded or underutilized.

DanielWhat is the true meaning of system average load and CPU utilization in Linux?

The importance of properly partitioning a disk in Linux

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Linux disk partitionI am a strong supporter of simplicity and the principle that less is more, but as far as security and performance of information systems is concerned, we must be able to strike a balance between keeping things simple and exposing ourselves as little as possible to potential threats while trying to obtain the maximum performance of all system elements involved.

It is a common practice that the various distributions of Linux, and even the images used to launch Linux virtual server instances as in the case of AWS AMI’s, implement by default an extremely simple partitioning scheme consisting in a single partition that covers the entire disk. It is in this only partition where the root filesystem (/) is mounted and in which all the directories that configure the file hierarchy of a Linux operating system are placed.

But one of the features of Linux is precisely that it allows you to be highly flexible in placing each of these directories on different partitions or on different disks if necessary.

DanielThe importance of properly partitioning a disk in Linux

15 most useful Linux commands for file system maintenance

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One of the most common and tedious tasks of a sysadmin is to prevent file systems become completely full, because when a server runs out of space the consequences are unpredictable. Depending on how you structured the root file system and if it is divided into different partitions or volumes, those consequences will be more or less severe, but in any case undesirable.

Daniel15 most useful Linux commands for file system maintenance