Linux

Linux is a popular choice for a server environment. There are a variety of open-source distributions each with a large community of hobbyists and professionals supporting them. Unique development tools are widespread and simple to install, use, and maintain. And most distributions are very capable without the resource overhead of a graphical desktop user interface.

Unix Philosophy

1. Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new “features”.
2. Expect the output of every program to become the input to another, as yet unknown, program. Don’t clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don’t insist on interactive input.
3. Design and build software, even operating systems, to be tried early, ideally within weeks. Don’t hesitate to throw away the clumsy parts and rebuild them.
4. Use tools in preference to unskilled help to lighten a programming task, even if you have to detour to build the tools and expect to throw some of them out after you’ve finished using them.

Shell

On a headless server (without a graphical interface), the most popular way to interact with a server is through a terminal interface. The most widespread is a shell known as Bash, the Borne Again Shell.

A shell is a program that interprets user input. Emulating the look and feel of an old mainframe terminal interface, many shells like Bash provide their users access to several command-line interface (CLI) tools as well as useful conveniences such as auto-completion, a scripting language syntax, and I/O redirection.

To use a CLI tool a user types the name of a program followed by any parameters or flags.

Scripting

Text files saved with the .sh extension are commonly used as shell scripts - a manifest of commands for Bash to run automatically line by line. To write a script, a shebang is commonly used on the first line to denote the shell program of choice. To execute a script, either pass the file as an argument to the sh or bash command, or make the file executable using chmod and call the file in the shell.

Example script.sh

#!/bin/bash

# Updating the system with the yum package manager
sudo yum update -y

# Uninstalling prior versions of Java
sudo yum remove -y java

# Installing JDK 8
sudo yum install -y git java-1.8.0-openjdk-devel

# Adding external yum repository for Maven
sudo wget http://repos.fedorapeople.org/repos/dchen/apache-maven/epel-apache-maven.repo -O /etc/yum.repos.d/epel-apache-maven.repo
sudo sed -i s/\$releasever/6/g /etc/yum.repos.d/epel-apache-maven.repo
sudo yum update -y

# Installing Maven
sudo yum install -y apache-maven

Sudo

The sudo command elevates the shell prompt with root permissions. Root is the default administrator account and is rarely stopped by the system from doing anything. Whlie some programs require root access and thus must be used together with sudo, it is dangerous to use carelessly.

Package Management

Linux distributions maintain a variety of public and private repositories of program installation scripts. These repositories and their related CLI tool makes quick work of installing, updating, and uninstalling programs with simple commands. The program yum is commonly used on Amazon Linux and any Red Hat derived systems (RHEL, Fedora, CentOS), while apt is popular on Debian-based systems (Debian, Ubuntu).

Examples (using yum)

# To update all packages
sudo yum update

# To install a program (git)
sudo yum install git

# To uninstall a program (java)
sudo yum remove java

# To install OpenJDK Java 8
sudo yum install java-1.8.0-openjdk-devel

GNU Core Utilities

The coreutils are a collection of standard Unix tools available on most Linux distributions. They include utility programs for a variety of tasks on the command line. A few examples include:

• echo: print a line of text
• cd: change directory
• mkdir: make directories
• rm: remove files or directories
• cp: copy files and directories
• mv: move (rename) files
• ls: list directory contents
• cat: concatenate and write files
• echo: print output of aonther command to stdout
• chmod: change access permissions
• chown: change file ownership and group
• df: shows disk free space on file systems

Man

The man command will seek and display the manual page for most CLI tools installed through a package manager. Used like sudo, it takes a CLI command as an argument.

# Will display the manual page for yum
man yum

Grep

The global regular expression print tool (grep) processes files and standard output text to search for an expression matching what was passed to the command.

# Will search for lines with 'tim' inside users.txt
grep tim users.txt