terminal

VSZ and RSS columns in the ps command output

ps output – Difference between VSZ vs RSS memory usage

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The ps command on Linux systems is a default command line utility that can give us insight into the processes that are currently running. It can give us a lot of helpful information about these processes, including their PID (process ID), TTY, the user running a command or application, and more.

There are two columns in the output of the ps command that don’t get talked about a lot. These are the VSZ (Virtual Memory Size) and RSS (Resident Set Size) columns. Both columns give us information about how much memory a process is using. In this guide, we’ll go over their meanings and how to interpret the data they show us in the ps command on Linux.

In this tutorial you will learn:

  • How to interpret VSZ and RSS numbers in the ps command output

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Viewing an Excel formatted xlsx file in LibreOffice Calc

Converting xlsx Excel format files to CSV on Linux

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Files with the xlsx extension have been formatted for Microsoft Excel. These documents contain columns and rows of data, just like those found in Google Sheets or LibreOffice Calc. This data can be stored as CSV (comma separated values), making it easily readable by various applications or even plain text editors. Due to their proprietary nature, Excel spreadsheets can be difficult to open on Linux systems, making CSV files a much more cross compatible format.

In this guide, we’ll show you a few different methods to convert Excel spreadsheets into comma separated files. This can be done from the command line, or you can open the spreadsheets with LibreOffice and resave them in the desired format, as you’ll see below.

In this tutorial you will learn:

  • How to convert xlsx files to csv via command line with ssconvert
  • How to convert xlsx files to csv via command line or GUI with LibreOffice

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Changing the MAC address with the macchanger command on Linux

Change mac address with macchanger Linux command

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A Media Access Control (MAC) address is a unique number that gets assigned to every network interface, including Ethernet and wireless. It’s used by many system programs and protocols in order to identify a network interface. One of the most common examples would be in the case of DHCP, where a router assigns an IP address to a network interface automatically. The router will know which device it has assigned an IP address to by referring to the MAC address.

Unlike an IP address, which is temporary and can be changed easily, MAC addresses are hardcoded into a network interface from the manufacturer. However, it’s still possible to change or “spoof” a MAC address temporarily. On Linux systems, one of the easiest ways to do this is with the macchanger command line program. There are both legitimate and shady reasons for why a Linux user may find the need to change a MAC address.

In this guide, we’ll show how to install the macchanger program on major Linux distros and then use the macchanger command to change the MAC address of a network interface either to a random value or some specific number. Follow the examples below to learn how.

In this tutorial you will learn:

  • How to install macchanger on major Linux distros
  • How to identify current MAC address and network interface
  • How to change an interface’s MAC address
  • How to change interface to a specific MAC address

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Listing environment variables

How to set and list environment variables on Linux

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Environment variables are part of the Linux system shell that contain changing values. They help facilitate scripts and system programs, so that code can accommodate a variety of scenarios. Unlike regular shell variables, environment variables can be accessed system-wide, by any user or process.

Let’s look at a very simple example to see how environment variables work and why they exist. There are many system programs and user made scripts that need to access a current user’s home directory. This can be done reliably through the HOME environment variable. Therefore, a script that contains the following line can be used by any user on the system and it will generate the same result.

$ echo $SHELL > $HOME/current-shell.log

$ cat $HOME/current-shell.log
/bin/bash

In this guide, we’ll show how to list all the environment variables on a Linux system, as well as set new ones. Setting new environment variables can either be done temporarily, or permanently if you need them to survive a reboot. We’ll show instructions for both methods below.

In this tutorial you will learn:

  • How to list environment variables on Linux
  • How to set a temporary environment variable on Linux
  • How to set a permanent environment variable on Linux

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Changing the hostname in AlmaLinux

Change hostname on AlmaLinux

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The hostname of a Linux system is important because it’s used to identify the device on a network. The hostname is also shown in other prominent places, such as in the terminal prompt. This gives you a constant reminder of which system you’re working with. It’s a real life saver when you’re managing multiple systems through SSH and those command line terminals start to blend together in your mind.

Of course, IP addresses are used when devices need to communicate with each other, but those can change frequently. Hostnames give us a way to know which device we’re interacting with either on the network or physically, without remembering a bunch of numbers that are subject to change. Thus, it’s important that your system bears a hostname which helps you to identify it quickly. For example, “backup-server” is much more informative than “server2.” If you can’t easily identify a system’s purpose from the hostname, it’s time to change it.

In this guide, we’ll show you how to change the hostname on AlmaLinux. This can be especially useful if you’ve recently migrated from CentOS to AlmaLinux and need to update the hostname accordingly. Changing the hostname can be done either by command line or GUI, and we’ll show you the steps for both methods below.

In this tutorial you will learn:

  • How to change the AlmaLinux hostname from command line
  • How to change the AlmaLinux hostname from GNOME GUI
Changing the hostname in AlmaLinux

Changing the hostname in AlmaLinux

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Split window terminal multiplexer

An introduction to terminal multiplexers

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April 20, 2016
by Rares Aioanei

Introduction

If you’re new to server administration and command-line, perhaps you haven’t heard of terminal multiplexers or what they do. You want to learn how to be a good Linux sysadmin and how to use the tools of the trade. Or perhaps you’re a seasoned administrator already and administer quite a few machines, and want to make your life a little easier. Or maybe you’re somewhere in between.

Either way, this article will explain what terminal multiplexers are, what they do and most importantly, how you can benefit from using them.

A terminal multiplexer is nothing more than a program that allows its user to multiplex one or more virtual sessions, so the user can have several sessions inside one single terminal. One of the most useful features of such programs is the fact that users can attach and detach such sessions; how is this useful will become clear shortly.

Use cases

Persistent sessions

Let’s say you have to administer a remote server via ssh/command-line but your connection is not very stable. That means you have to reconnect often and don’t want to start work all over again. Terminal multiplexers offer the feature of saving your sessions between connections so you can continue just where you started.

Please note that such sessions are not persistent between reboots (in our case above, reboots of the server you’re connecting to) so it’s best to know this in order not to expect such a feature. The reason for this is the fact that the multiplexer runs shell sessions, from which you may be running a text editor, a monitoring tool and whatnot. Since all those processes will not be there anymore after a reboot, there is no reason why this feature should be implemented as it would not have any real use.

We spoke in our introduction about attaching and detaching : this is exactly what this feature does. Continuing with our use case, where you have an unstable connection, once you get disconnected, you can just ssh into the server again and reattach to the running session (or choose between sessions to reattach to) and you’ll be right where you
left off.

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Best Terminal Games on Linux

Best Terminal Games on Linux

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Intro

GNU/Linux gaming has come a long way over the past decade. We are lucky to live in an age where there are a number of native linux games including AAA titles to choose from on the platform. Steam has also vastly increased the number of games available on Linux. Despite the vast availability of GUI based games, sometimes it can be more relaxing and entertaining to play terminal based ones. This is not so surprising considering the fact that most Linux users spend a lot of time on the command line and feel at home there. Luckily, there are a number of great terminal based games available on the platform as well.

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Using GNU screen with examples

Using GNU screen with examples

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Have you even been in the situation where you were running a 3 hour copy or script on a remote machine, only to find that it broke at 2h 45min because your network connection or SSH connection dropped momentarily? If so, you know how painful that feels 🙂 Welcome to GNU screen, the utility which allows you to start a separate shell which will not be interrupted if your network connection breaks. Read on to discover how to use it and more!

In this tutorial you will learn:

  • How to install and use the GNU screen utility
  • How to configure the GNU screen utility to function better
  • Basic usage examples on how to use the GNU screen utility from the Bash command line

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