Introduction to Linux

Introducing Linux and Unix

What is Unix?

• Unix is a family of operating systems
• Popular Unix-based OSs include:
  • Oracle Solaris (and Open Solaris)
  • FreeBSD
  • HP-UX
  • IBM AIX
  • Apple macOS

UNIX beginnings:

Linux’s beginnings:

Linux, use cases today:

• Android
• Supercomputers
• Data Centers and Cloud Servers
• PCs

Overview of Linux Architecture

Kernel

• Lowest-level software in system
• Starts on boot and remains in memory
• Bridge between apps and hardware
• Key jobs:
  • Memory management
  • Process management
  • Device drivers
  • System calls and security

Linux filesystem:

Linux Terminal Overview

Communicating with Linux System:

Introduction to Linux Commands

Overview of Common Linux Shell Commands

What is a shell?

• User interface for running commands

• Interactive language

• Scripting language

  Shell command applications:

• Getting information

  • whoami – username
  • id – user ID and group ID
  • uname – operating system name
  • ps – running processes
  • top – resource usage
  • df – mounted file systems
  • man – reference manual
  • date – today’s date

• Navigating and working with files and directories

• Printing file and string contents

• Compression and archiving

  • tar – archive a set of files
  • zip – compress a set of files
  • unzip – extract files from a compressed zip archive

• Performing network operations

  • hostname – print hostname
  • ping – send packets to URL and print response
  • ifconfig – display or configure system network interfaces
  • curl – display contents of file at a URL
  • wget – download file from a URL

• Monitoring performance and status

Customizing View of File Content

• sort — Sort lines in a file, -r will do the same in the reverse
• uniq — Filter out repeated lines
• grep (“global regular expression print”) — Return lines in file matching pattern
• grep -i — makes grep search case-insensitive
• cut — Extracts a section from each line
• paste — Merge lines from different files

Introduction to Shell Scripting

Shell Scripting Basics

What is a script?

• Script: list of commands interpreted by a scripting language

• Commands can be entered interactively or listed in a text file

• Scripting languages are interpreted at runtime

• Scripting is slower to run, but faster to develop

  What is a script used for?

• Widely used to automate processes

• ETL jobs, file backups and archiving, system admin

• Used for application integration, plug-in development, web apps, and many other tasks

  Shell scripts and the ‘shebang’

• Shell script – executable text file with an interpreter directive

• Aka ‘shebang’ directive

  #!interpreter [optional-arg]

• ‘interpreter’ – path to an executable program

• ‘optional-arg’ – single argument string

Example – ‘shebang’ directives

Shell script directive:

#!/bin/sh
#!/bin/bash

Python script directive:

#!/usr/bin/env python3

Filters, Pipes, and Variables

Pipes and filters:

Filters are shell commands, which:

• Take input from standard input

• Send output to standard output

• Transform input data into output data

• Examples are wc, cat, more, head, sort, …

• Filters can be chained together

  Pipe command – |

• For chaining filter commands

  commmand1 | command2

• Output of command 1 is input of command 2

• Pipe stands for pipeline

Shell variables:

• Scope limited to shell

• Set – list all shell variables

  Defining shell variables:

  var_name=value

• No spaces around =

  unset var_name

• deletes var_name

Environment Variables:

• Extended scope

  export var_name

• env — list all environment variables

Useful Features of the Bash Shell

Metacharacters

• # — precedes a comment
• ; — command separator
• * — filename expansion wildcard
• ? — single character wildcard in filename expansion

Quoting

• \ — escape special character interpretation
• "" — interpret literally, but evaluate meta-characters
• '' — interpret literally

I/O redirection

Input/Output, or I/O redirection, refers to a set of features used for redirecting

• > — Redirect output to file
• >> — Append output to a file
• 2> — Redirect standard error to a file
• 2>> — Append standard error to a file
• < — Redirect file contents to standard input

Command substitution

• Replace command with its output

  $(command) or `command`

• Store output of pwd command in here:

Command line arguments

• Program arguments specified on the command line

• A way to pass arguments to a shell script

  ./MyBashScript.sh arg1 arg2
  

Batch vs. concurrent modes

Bath mode:

• Commands run sequentially

  command1; command2

  Concurrent mode:

• Commands run in parallel

  command1 & command2

Scheduling Jobs using Cron

Job scheduling

• Schedule jobs to run automatically at certain times

  • Load script at midnight every night
  • Backup script to run every Sunday at 2 AM

• Cron allows you to automate such tasks

  What are cron, crond, and crontab?

• Cron is a service that runs jobs

• Crond interprets ‘crontab files’ and submits jobs to cron

• A crontab is a table of jobs and schedule data

• Crontab command invokes text editor to edit a crontab file

Scheduling cron jobs with crontab

Viewing and Removing cron jobs