nixCraft Linux & Unix Sysadmin/DevOps Tutorial Newsletter

[nixCraft]

Welcome to nixCraft Linux/Unix newsletter for Friday, 27 August 2021. I hope you will enjoy this version of the newsletter.

• FreeBSD bhyve, OpenSSL, GEOM & libfetch security fixes released
  All supported versions of FreeBSD are affected by various security bugs that need to be applied ASAP.
   
• How to find a path of a Linux command like a pro
  One of the most common questions I get is how can I find a Linux command path that I just installed on Linux using a package manager such as apt/dnf command. We have many new developers coming from the Windows world. Many are first-time Linux users. Some are using Linux from WSL, and others are directly dealing with cloud servers over ssh. Let us see some common commands to list or find a path for Linux commands.
   
• How to switch boot target to text or GUI in systemd Linux
  Most modern Linux distro uses systemd as init replacement. It is a suite of basic building blocks for Linux distros such as RHEL/CentOS & co, OpenSUSE/SUSE, Fedora, Arch, Debian, Ubuntu, and more. By default, most distro boot into GUI, but you can change to text or vice versa.
   
• How to upgrade Debian 10 to Debian 11 Bullseye using the CLI
  I have Debian 10.10 installed on the AWS EC2 and Linode server. How do I upgrade Debian 10 Buster to Debian 11 Bullseye using the apt command or apt-get command safely? How can I upgrade Debian 10 to Debian 11 using ssh client?
   
• How to disable core dumps in Linux including systemd
  Core dumps created for diagnosing and debugging errors in Linux apps. They are also known as memory dump, crash dump, system dump, or ABEND dump. However, core dumps may contain sensitive info—for example, passwords, user data such as PAN, SSN, or encryption keys. Hence, we must disable them on production Linux servers.
   
• How to define multiple when conditions in Ansible
  Sometimes we need to evaluate multiple when conditions in Ansible playbooks. Let us see how to define multiple when conditions in Ansible for a single task.
   
• How to repeat a character 'n' times in Bash
  Let us say you want to repeat a character such as '-' OR '=' multiple times while writing bash script. Please note that I needed a quick script to work on Linux, macOS, and FreeBSD server to repeat a string/character n times.
   
• How to install Redis server on Ubuntu Linux
  How do I install the Redis server on the Ubuntu Linux version 18.04/20.04 LTS server to speed up database caching in memory?
   
• How to convert man page to HTML on Linux and Unix
  We can easily convert all Linux man pages to HTML, text, or pdf format. To display online manual documentation pages in terminal on Linux, macOS, *BSD, and Unix-like systems, we use the man command. However, some man pages are long and might be hard to search when using less or most as a pager. Hence, we can convert them to HTML format and skimmed them in a web browser such as Firefox.
   
• How to copy and transfer files remotely on Linux using scp and rsync
  In Linux, how do I copy and transfer files remotely between two Linux machines? What command do I need to use to transfer files between Unix/macOS and Linux computers securely?
   
• How to see what packages updates available on Alpine Linux
  On Debian or Ubuntu Linux, one can run ‘apt list --upgradable‘ command to see and list available package updates. On RHEL, we can use ‘dnf check-update‘ to list available updates on screen. However, the apk command does not have an option to show and list available security software updates. But fear not. Some other tricks can list, and you can see what packages updates are available on Alpine Linux using the apk command.
   
• How to find the number of RAM Slots in Linux
  Sometimes Linux sysadmins or developers need to determine the number of RAM slots on their servers or desktop/laptop without opening the case. Then, it is helpful to upgrade or install new RAM. Let us see how to find the number of RAM slots and supported max memory on Linux using command-line options.
   
• How to find and replace ALL IP addresses with a new one
  At a certain point, I needed to change the VLAN IP address such as 172.0.0.2 with 172.0.0.1 for ease of use. As you know, Linux and Unix-like operating system stores all IP addresses and config in plain text files. This page explains my little adventure where I had to find and find and replace ALL IP addresses with a new one on Linux.
   
• Linux Find Out BIOS Version Using a Command Line Option
  How do I find out BIOS version using a Linux command line option? How do I check the motherboard BIOS version using Linux command line option?
   
• OpenSSH Change a Passphrase With ssh-keygen command
  How do I change OpenSSH passphrase for one of my private keys under Linux, OpenBSD, FreeBSD, Apple macOS/OS X or Unix-like operating systems?
   
• What Does ‐‐ (double dash) Mean In SSH Shell Command?
  This page explains the use of the double-dash ('‐‐') in Linux, macOS, and Unix shell commands. For example: lxc exec container ‐‐ sh -c 'apt update && apt -y upgrade'. First, let us see what it does and when we might need it.
   
• Linux commands to check the Laptop battery's status via the terminal
  How do I find out details about my Linux Laptops temperature, battery status and other information from the command prompt? How can I check battery status using the terminal on Linux?
   
• Cut command in Linux with examples
  The Unix or Linux cut command is an extremely useful tool for filtering information. Here is a brief overview for new Linux, macOS, *BSD and Unix users.
   
• Linux help command examples and syntax
  You can use the help command to display help about built-in Bash commands. A shell builtin is nothing but a command or a function, called from a shell, that is executed directly in the shell itself.
   
• How To: Linux Find Large Files in a Directory
  There is no single command that can be used to list all large files. But, with the help of find command command and shell pipes, you can easily list all large files. This page explains how to find the largest files and directories in Linux using various commands.

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• How To Set Up SSH Keys With YubiKey as two-factor authentication (U2F/FIDO2)
  All Linux and Unix servers are managed manually or by automation tools such as Ansible using ssh. For example, say you have a server at Linode or AWS. Then you copy your public ssh key to a remote cloud server. Once copied, you can now login to those servers without a password as long as ssh keys are matched. It is the best practice. Unfortunately, you are not protecting ssh keys stored on a local desktop or dev machine at $HOME/.ssh/ directory. If your keys are stolen, an attacker can get access to all of your cloud servers, including backup servers. To avoid this mess, we can protect our ssh keys stored on local dev/desktop machines using physical security keys such as YubiKey.
   
• How to set up Redis sentinel cluster on Ubuntu or Debian Linux
  This guide explains how to set up 3-node Redis sentinel failover cluster for caching database or any other data type in high availability config.