Telecommunications Command Line Basics

Chapter 2: Accessing the Command Line

• Topic: Introduction to the Bash Shell
• Presenter: Hasnaa Sleiman
• Course: Master in telecommunications, Networks and Security
• Institution: UA-USJ-UL

Objectives

• Understand how to log in to a Linux system
• Learn how to run commands using Bash shell
• Explore the structure of commands and options

What is the Command Line?

• A text-based interface to input instructions into a system
• The shell is a program that provides the command line
• Bash (Bourne-Again Shell) is the default shell

Shell Prompts Explained

• Regular user prompt: [user@host ~]$
• Superuser prompt: [root@host ~]#
• Indicates whether logged in as a normal user or root (superuser)

Understanding Shell Commands

• Command: The program to run
• Options: Adjust command behavior (e.g., -L)
• Arguments: Targets or files for the command (e.g., user01)

Logging in Locally

• Physical console supports multiple virtual consoles
• Switch between them with Ctrl+Alt+F1 through F6
• Graphical login screen might be available on tty1

SSH - Logging in Over the Network

• SSH (Secure Shell): Allows secure remote login to another machine
• Command Example: ssh remoteuser@remotehost
• Encrypts communication to prevent eavesdropping

Public Key Authentication in SSH

• Uses a private key on the user's system and a public key on the server for secure login without a password
• Example: ssh -i mylab.pem remoteuser@remotehost

Logging Out

• Use the exit command or Ctrl+D to close the session
• In an SSH session, exit logs out and closes the connection to the remote machine

Key Takeaways

• Bash is the default shell in Linux for accessing the command line
• Basic shell commands include commands, options, and arguments
• You can log in to a system either locally or remotely using SSH

Understanding GNOME 3 and Linux Shell Commands

• Objectives: Log in to the Linux system using the GNOME 3 desktop environment; Run commands from a shell prompt in a terminal program

Introduction to GNOME Desktop Environment

• GNOME 3 is the default desktop environment in Red Hat Enterprise Linux 8
• Integrated user interface and unified development platform
• Built on Wayland or X Window System

GNOME Shell

• Core user interface functions for the GNOME desktop environment
• Customizable appearance
• Red Hat Enterprise Linux 8 uses the "Standard" theme
• Red Hat Enterprise Linux 7 used a "Classic" theme

First-Time Login

• Initial setup configures basic account settings
• GNOME Help starts with the Getting Started screen
• Access GNOME Help through the Activities button or the life ring icon

GNOME Shell Parts

• Top bar: Provides access to Activities, system settings, and volume control
• Activities overview: Organizes windows and starts applications
• Dash: Displays favorite and running applications
• Windows overview: Shows active windows
• Workspace selector: Switch between different workspaces
• Message tray: Displays notifications and system messages

Workspaces

• Organize windows by task in separate workspaces
• Switch workspaces with Ctrl+Alt+UpArrow or DownArrow
• Move windows between workspaces in the Activities overview

Starting a Terminal

• Start GNOME Terminal from the dash or using the Alt+F2 command
• Displays a shell prompt with the user name, host, and current directory

Locking the Screen or Logging Out

• Lock the screen via the system menu or with Super+L
• Log out via the system menu, under the user's name

Powering Off or Rebooting

• Power off from the system menu or use Ctrl+Alt+Del
• Automatic shutdown after 60 seconds if no choice is made

Overview of Basic Commands and Shortcuts

• Commands consist of the command name, options, and arguments
• Example: command -option argument
• Press Enter to execute a command
• Use ; to run multiple commands on one line
• Example: command1; command2

Examples of Simple Commands

• date: Displays date and time
• Example: date, date +%R

passwd

• Changes user's password
• Example: passwd

file

• Identifies file types
• Example: file /etc/passwd

cat

• Displays file contents
• Example: cat /etc/passwd

less

• Pages through file contents
• Example: less /etc/passwd

head and tail

• Shows beginning or end of files
• Example: head /etc/passwd, tail -n 3 /etc/passwd

wc

• Counts lines, words, and characters
• Example: wc /etc/passwd

Tab Completion

• Completes commands or file names
• Press Tab once to complete, twice to list options
• Example: Typing pas and pressing Tab shows passwd, paste, etc.

Continuing Long Commands

• Use \ to split commands across lines
• Example: head -n 3
  /usr/share/dict/words
  /usr/share/dict/linux.words

History Command

• history: Lists previously executed commands
• Use !number or !string to repeat commands
• Example: !ls, !26

Command-Line Editing

• Editing Shortcuts:
  • Ctrl+A: Beginning of line
  • Ctrl+E: End of line
  • Ctrl+U: Clear to beginning
  • Ctrl+K: Clear to end
  • Ctrl+LeftArrow: Previous word
  • Ctrl+RightArrow: Next word
  • Ctrl+R: Search history

Summary

• Bash Shell as a Command Interpreter: Bash (Bourne Again Shell) is a command-line interface (CLI) program that interprets user-typed commands, options, and arguments, executes them, and displays results.
• For example, when you type ls in the shell and press Enter, Bash interprets this as a request to list directory contents.

Using --help for Command Assistance

• Many commands in Linux come with a built-in help option (--help). This displays useful information about how to use the command, including available options and syntax
• For instance, typing ls --help provides details on how to use the ls command

Workspaces for Organizing Windows

• Workspaces are a feature that allows you to organize multiple open windows on a single desktop by spreading them across multiple virtual desktops. This reduces clutter and aids in organizing tasks
• You can switch between workspaces to organize related applications together, such as keeping a terminal in one workspace and a web browser in another

Using the Activities Button to Organize and Launch Applications

• The Activities button, typically located in the top-left corner of the GNOME screen, provides an overview of open windows and applications. It enables quick switching between windows, moving them to different workspaces and starting new applications.

The file Command to Identify File Types

• The file command is used to determine the type of a file based on its contents; it does not rely on file extensions like .txt or .jpg, but scans the file's internal structure to identify its type
• For example, file myfile might return "ASCII text" or "JPEG image data" depending on file contents.

Using head and tails commands

• The head command displays the first few lines (default is 10) of a file.
• Similarly, tail displays the last few lines.
• Example: head myfile.txt shows the first 10 lines; tail -n 5 myfile.txt shows the last 5 lines.

Tab Completion for Efficiency

• Tab completion automatically completes command or file names after typing part of the name and pressing the Tab key
• This saves time and reduces typing errors
• If multiple completions are possible (e.g., multiple files with similar names), pressing Tab twice shows a list of available matches

Lab - Performance Checklist

• In this lab, you will use the Bash shell to execute commands
• Outcomes: Successfully run simple programs using the Bash shell command line; Execute commands used to identify file types and display parts of text files; Practice using some Bash command history "shortcuts".

Before You Begin

• Log in to workstation as student using student as the password
• Run the lab cli-review start script

Lab Instructions (Page 42)

• List of specific commands and tasks to perform in the lab, including the date +%r format.

This quiz focuses on Chapter 2 of the course regarding the Bash shell and command-line interface. Participants will learn how to log into a Linux system, run commands, and understand the structure of commands and options. Enhance your knowledge of shell prompts and command usage effectively.