Linux Operating System

Most virtual machines in the cloud and devices on the edge run Linux operating systems. Moreover, these systems typically run in “headless” mode, meaning that there is no attached monitor or graphical output by default.

Because of this, you must have a good understanding of the Linux operating system and how to use the operating system from the command line. Some of the important aspects for this training are covered below, but you should investigate the linked resources for a fuller understanding of Linux.

Shells

Use of Linux through the command line always takes place through a “shell”. This is a special program that allows interactive use of a Linux system and that provides features that simplify interactions with the operating system.

The Bourne shell (sh) is the original UNIX shell. All recent Linux distributions support this shell and have it installed by default. Most system level shell utilities target the command line syntax of the Bourne shell to maximize portability between Linux flavors. Details on this shell can be found on the web, for example, in the Bourne Shell Scripting book on Wikibooks.

The most common shell for interactive use is the Bourne Again Shell (bash). This version, provided by the GNU Project, provides some additional features that make it easier to use than the plain Bourne Shell, while still being fully compatible with the Bourne Shell syntax. This is the default shell for most Linux distributions, although it may not be present on embedded Linux distributions that aim for a small footprint. Shell examples in this training use bash. A bash scripting book is also available in Wikibooks.

There are many other shells that can be used. The Z shell (zsh), C shell (csh), tcsh, and Korn shell (ksh) are a few of them. These may or may not be installed by default by a Linux distribution. In all cases, use of these shells requires explicit configuration of your user account. Documentation for these shells can be found on the web. Unless you are already familiar with one of these shells, you would be better served with sh or bash.

Scripting

Automation of common actions or processes is often done by creating a “shell script”. This is simply a text file that starts with a “shebang” line followed by the shell commands to execute. An example that prints “Hello World” to the terminal is:

#!/bin/bash

echo "Hello World"

The “shebang” line (first line starting with ‘#!’) indicates what shell or program to start to interpret the subsequent commands.

You should review the Guide to UNIX and the documentation for the shell that you use.

System Administration

Before creating cloud applications, it is necessary that you understand a bit about system administration, specifically package and service management.

The instructions are given below for Ubuntu 18.04 and CentOS 7, two common operating systems. Choose the operating system with which you are most comfortable, although it is useful to look through the information for both systems.

Ubuntu 18.04

Administrator

System administration commands must be run from the “root” (super user or administrator) account.

Normally with Ubuntu, you will log into the “ubuntu” account, which is a normal user account, not an administrator account. To run system administration commands from the “ubuntu” account, there are two options:

• Prefix each command with sudo. This command will switch temporarily to the super user account and execute the command given to sudo.

• Switch into the “root” account with the command sudo su -. This creates a new session with the “root” account. System administrator accounts can be run with a sudo prefix. To close the “root” shell and return to the “ubuntu” account, just type exit.

On many cloud providers, there is also a third option. Many Ubuntu cloud images are configured so that you can SSH directly into the root account. Just change the command: ssh ubuntu@ipv4-address to ssh root@ipv4-address.

Package Management

Understand how all these commands work. If you have access to an Ubuntu machine, try searching, installing, and removing the “nginx” package. Nginx is one of the standard web servers.

Editors

To administer services on a virtual machine, you will need to be able to edit configuration files. The editors that are installed by default on Ubuntu 18.04 are: nano and vi. You need to be familiar with one of them. If you’re not already familiar with vi, choose nano. It has a very short learning curve. You can also install emacs (package name “emacs-nox”) if you’re familiar with it.

Service Management

Services are normally managed with the systemctl command (and friends). The full service management subsystem is called systemd. Earlier Ubuntu operating systems used a different service management system.

To understand how these commands work, reinstall the “nginx” package on an Ubuntu machine. When the service is started, you should be able to see the default landing page with the command:

curl http://localhost

This will dump the raw HTML content. In the HTML, you should see a header element like <h1>Welcome to nginx!</h1>.

Try the various service management commands to understand how they affect the nginx service.

IP Address

You will often need to find the IP address of your virtual machine. You can always get this from Exoscale, but it often easier to get this from within the VM itself. There are many ways to do this, but the easiest is just ifconfig. Look for the “inet” value assigned to the “eth0” interface.

CentOS 7

Administrator

System administration commands must be run from the “root” (super user or administrator) account.

Normally with CentOS on Exoscale, you will log into the “centos” account, which is a normal user account, not a super user account. To run system administration commands from the “centos” account, there are two options:

• Prefix each command with sudo. This command will switch temporarily to the super user account and execute the command given to sudo.

• Switch into the “root” account with the command sudo su -. This creates a new session with the “root” account. System administrator accounts can be run with a sudo prefix. To close the “root” shell and return to the “centos” account, just type exit.

On many cloud providers, there is also a third option. Many CentOS cloud images are configured so that you can SSH directly into the root account. Just change the command: ssh ubuntu@ipv4-address to ssh root@ipv4-address.

Package Management

The CentOS yum configuration only includes packages that are strictly part of the RedHat Enterprise Linux distribution. Many useful packages are in a separate package repository called EPEL.

To include the EPEL repository, install the package “epel-release”:

yum install epel-release

Unless you want to run a very minimal system, you will almost certainly want to systematically include the EPEL repository.

Try all of the package management commands to understand how they work. Try searching, installing, and removing the “nginx” package. Nginx is one of the standard web servers. The package for this is in EPEL, not the core CentOS repositories.

Editors

To administer services on a virtual machine, you will need to be able to edit configuration files. The vi editor is installed by default on CentOS 7.

If you’re not already familiar with vi, you may want to install nano. It has a very short learning curve. Just run yum install nano. You can also install emacs (package name “emacs-nox”) if you’re familiar with it.

Service Management

Services are normally managed with the systemctl command (and friends). The full service management subsystem is called systemd. Earlier CentOS operating systems used a different service management system.

To understand how these commands work, reinstall the “nginx” package on an Ubuntu machine. When the service is started, you should be able to see the default landing page with the command:

curl http://localhost

This will dump the raw HTML content. In the HTML, you should see a title element like <title>Test Page for the Nginx HTTP Server on Fedora</title>.

Try the various service management commands to understand how they affect the nginx service.

IP Address

You will often need to find the IP address of your virtual machine. You can always get this from Exoscale, but it often easier to get this from within the VM itself. There are many ways to do this, but the easiest is just ifconfig. Look for the “inet” value assigned to the “eth0” interface.