The purpose of this tutorial is to show how to use a Bash shell script or Python programming code to validate a credit card number on a Linux system.
Luke Reynolds
Extract email from text file
The Linux command line has many tools that we can use to extract information from text files. In this tutorial, we’ll use a few different methods to extract email addresses from a text file on Linux.
WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!
When you use SSH to login to a remote system, the host’s identification key is stored inside your user’s home folder. If you try to SSH into the remote system again in the future, your computer will check to make sure that you’re logging into the same system as before. Sure, the IP address or hostname might be the same, but maybe a different system has taken over that IP or hostname. If that’s the case, you wouldn’t want to enter your password into the foreign system.
When this is detected, you’ll receive a warning to the effect of WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!. Then again, sometimes a remote host’s keys could have changed for a perfectly legitimate reason. If you know this to be true, then you can ignore the warning.
In this guide, we’ll show you how to bypass the SSH remote host warning, as well as permanently remedy the problem on a Linux system. Read on to see how.
In this tutorial you will learn:
- How to remove invalid SSH host key from config
Fixing the remote host has changed warning message
Linux epoch time
Epoch time is a convention used on Unix and Linux systems that many applications rely on for calculating time between dates and other similar functions. Some Linux commands like date and perl have an epoch option built in. An epoch denotes the number of seconds that have passed since the date January 1st, 1970.
ssh_exchange_identification: connection closed by remote host
If you are trying to SSH into a remote host from a Linux system, the ssh_exchange_identification: connection closed by remote host error is one you might encounter when trying to log in. In this tutorial, we will go over a few different causes for this error and show you how to troubleshoot the connection on your system. Using one of our methods below will hopefully remedy the error and allow you to log in via SSH.
Turn off beep / bell on linux terminal
Working with the terminal using a command line interface is very fast and effective way of doing stuff on Linux systems. But have you tried working with the terminal, listening to some music via headphones and having a terminal warning or tab-completion beep / bell turned ON at the same time? Well, it can be very annoying. Listening to the PC Speaker beeps via headphones is very close to the feeling of hitting your head with a hammer. Even without headphones this beeping bell sound is very annoying.
In this guide, we’ll show you several ways to turn off the terminal beep / bell noise in Linux, without just turning your system volume completely off. These instructions have been tested to work with a variety of major Linux distros.
In this tutorial you will learn:
- Multiple methods to turn off the bell / beep terminal sound in terminal
- Turn off beep / bell sound in vim text editor
List all directories and sort by size
When it comes to tidying up your hard drive on Linux, either to free up space or to become more organized, it’s helpful to identify which directories are consuming the most storage space.
In this guide, we’ll show you how to list all directories and sort them by their total size on Linux, through command line examples, a Bash script, and GUI methods.
In this tutorial you will learn:
- How to list directories by size with
ducommand examples - How to list directories by size with a Bash script
- How to check directory sizes with Disk Usage Analyzer GUI utility
Install VirtualBox Guest Additions on Linux guest
If you’re running Linux inside a VirtualBox virtual machine, installing the Guest Additions software will help you get the most out of the system. VirtualBox Guest Additions will give the machine more capabilities, such as a shared clipboard with the host system, drag and drop file transfer, time synchronization, shared folders, automatic window resizing, and more.
How to configure shared VirtualBox folder on Linux
After installing a Linux distro into a VirtualBox virtual machine, you may be wondering how to share files between the host operating syste and the virtual machine itself. One of the easiest and most convenient ways to provide this function is by setting up a VirtualBox shared folder.
Essentially this means that a folder on your host machine can be mounted on the virtual machine, where both systems will be able to access files or drop them in the folder. It doesn’t matter what host operating system you’re using, as the instructions will be the same across Linux, Windows, etc.
In this guide, we’ll go through the step by step instructions to configure a shared VirtualBox folder. We’ll also show you how to mount the shared folder on your Linux system, allowing you to easily share files back and forth.
In this tutorial you will learn:
- How to configure a shared VirtualBox folder on Linux
- How to mount a VirtualBox shared folder
How to connect to VirtualBox via SSH
After installing a Linux distribution in Oracle VirtualBox, you may be wondering how you can SSH from the host operating system into the virtual machine. After all, SSH is a great way to access and manage the system on command line.
Rename all file names from uppercase to lowercase characters
As a Linux user, you’re likely already familiar with using the mv command to rename a file on a Linux system. The task becomes a little more difficult when you need to rename multiple files at the same time on Linux.
One of the most common batch renaming jobs that are performed is to change all file names to lowercase letters. There are several different ways to do this on Linux. One way is with the native mv utility and a bit of Bash scripting, and the other methods involve the rename and mmv tools, which may or may not already be installed on your Linux distro by default.
In this guide, we’ll go over various command line examples to rename all files from uppercase to lowercase letters on Linux. Some commands will work only for files, some for directories, and some commands work recursively. Take a look at all the different examples below to decide which command(s) to use that would best suit your needs.
In this tutorial you will learn:
- How to rename all files from uppercase to lowercase using mv, rename, or mmv commands
- How to install rename and mmv on major Linux distros
Remove or substitute space within a file name
The purpose of this tutorial is to show various methods on how to remove or substitute spaces within a file name. Some tools on a Linux system may not work properly with files that contain spaces, which would give some users motivation to replace the white space with underscores or just delete them completely, for example. Manipulating files without white space is much easier, as you do not have to worry about escaping the file name each time. In this tutorial, you will see how to remove or substitute the spaces in file names in Linux.