Operating Systems Quiz

CSC 209 UNIX Tools - Hierarchical Diagram

• A hierarchical diagram displays folders and files created in assignment 1
• The home directory contains the user account jdoel
• The jdoel folder contains multiple subfolders and files
• The csc209 folder contains subfolders asgn01 and asgn02
• The public_html folder is a subfolder under csc209
• The folder csc209 contains the folder esc209
• The root directory (/) is the top-level folder

Login and Bash Initialization

• Sign on as a new user using Net-ID (user ID) and password
• Verify password and establish user identity and group id
• Establish login (home) directory and shell
• Announce the presence of email (traditional)
• Customize terminal settings
• Publish message of the day (motd) (traditional)
• Initiate command interpreter (shell)
• Perform user-specified initialization (code)
• Display prompt and await commands

Password File

• The /etc/passwd file historically stores login information
• Each line within /etc/passwd represents a user
• Each line contains seven pieces of user data separated by colons
• Encrypts password in a hash
• Modern systems use /etc/shadow or similar mechanisms for security

Shell Initialization Files

• The C Shell is the default login shell at Brockport
• Initialization files .cshrc and .login are executed on startup of the C shell
• In Assignment 1, a .login file is set up to switch to Bash
• Bash initialization executes /etc/profile and ~/.bash_profile at login

Sample .bashrc File

• The ~/.bashrc file contains important configurations
• Sources global definitions from /etc/bashrc (if applicable)
• Contains user-specific aliases (e.g., cls, h, lo)
• Controls history parameters (e.g., HISTSIZE, HISTFILESIZE)
• Sets default access permissions (using umask)
• Protects files in redirection
• Defines shell prompt (PS1)

What is an Operating System?

• OS is a computer's system software in charge of the entire computer system
• Provides a convenient working environment and organization of files
• Management of computer resources are critical OS functions
• Examples of OS include MS-DOS, Windows 11, macOS 14, UNIX, Linux, Android, and iOS

Brief History of UNIX

• MULTICS project at MIT influenced early UNIX development
• UNIX originated at Bell Labs (AT&T) in 1969 by Ken Thompson and Dennis Ritchie
• UNIX System Laboratory (USL)
• UNIX extensions and communication protocols (TCP/IP) emerged in the 1980s
• Major flavors such as AT&T System 5 Release 4 (SVR4). USL (AT&T) → Novell → Santa Cruz Operations (SCO) BSD 4.4 and some from vendors

UNIX/Linux

• Linux is a multi-user, time-sharing, multi-tasking OS
• Kernel is the core of the operating system
• Shell acts as the user interface and command interpreter
• Features include hierarchical file structure and I/O device support.

Simple Linux Commands

• date: Displays date and time
• who: Lists currently logged-in users
• whoami: Displays current user ID
• logout: Logs out of the system
• pwd: Displays the current working directory
• mkdir: Creates a new directory
• rmdir: Removes an empty directory
• cd: Changes the current working directory
• ls: Lists directory contents
• chmod: Changes file permissions

Permissions in Linux

• The ls -l command provides detailed security information of files and directories
• Permissions are specified as three sets of three permissions (read, write, execute)
• Permissions are tied to the owner, group, and others

Ordinary File Permissions

• Displaying files requires read permissions
• Rewriting files requires write permissions
• Executing a file requires execute permissions

Directory File Permissions

• Moving to directories requires execute permissions
• List directories requires read and execute permissions
• Creating new directory entries requires write permission
• Removing directory entries requires write permissions

Default Access Permissions

• Default file permissions are 666 (for files) and 777 (for directories)
• umask (user mask) controls what permissions are removed
• Using ~/.bashrc to set umask to 077 changes default permissions

Superuser (root)

• Superuser (root) is the administrator account
• Can access, create, or delete any files or directories irrespective of permissions
• Superuser bypasses permission restrictions

Format of Linux Commands

• Commands typically follow the format command_name [options] [argument]
• Options are single characters preceded by a hyphen
• Arguments are often necessary to use the commands effectively

Handling errors while typing commands

• ctl-h or Backspace to delete previous character
• ctl-w to delete the previous word
• ctl-u to delete the entire command

On-line help (man command)

• Use man to display help for commands
• Example man cat provides documentation for the cat command

Hierarchical File System

• Organizes files and directories in a tree-like structure
• Root directory (/) is the top-level directory
• cd command navigates between directories
• pwd displays current working directory

Absolute and Relative Path Names

• Absolute paths start with a forward slash (/) or a tilde (~)
• Relative paths are relative to the current working directory

File Manipulation Commands

• cat: Concatenates files and prints to the standard output
• od: Displays content in octal format
• more: Displays files one screen at a time

Other File Commands

• head: Displays the first part of a file
• tail: Displays the last part of a file
• cmp: Compares two files; shows the first difference
• diff: Compares two files; shows all differences
• cal: Displays a calendar

File System Commands

• piico, nano, emacs: Editors for file manipulation
• cp: Copies files
• mv: Moves or renames files
• rm: Removes files
• rm -i: prompts before deleting files

Directory Listing Commands

• ls: Lists files and directories in the current working directory
• ls -a: Includes hidden files in listing
• ls -l: Displays file information in long format
• ls -ld: Lists directory information in long format

Directory Manipulation Commands

• mkdir: Creates a new directory
• rmdir: Removes an empty directory
• rm -r: Recursively removes a directory (be cautious)
• cd: Changes the current working directory
• pwd: Shows current working directory

Bash Special Characters

• Special characters define actions such as input/output redirection, variable substitutions, and more

Shell Substitutions and Quoting

• The shell performs input processing of various substitutions
• Three methods are available to quote
• Use \ (backslash) to quote a character
• Use single quotes to disable substitutions entirely
• Use double quotes to allow certain substitutions but restrict wildcard expansion

History Substitution

• Accessing previously entered commands or parts
• Variables like HISTSIZE and HISTFILESIZE influence command history management

Aliases Substitution

• Alias commands to shorten the names for frequently used tasks
• A list of all aliases can be obtained with the alias command
• An alias is undone using unalias

Shell Variable Value Substitution

• Accessing the values stored in shell variables using the "$" symbol
• Using set displays all current shell variables
• Removing particular variables using unset

Command Output Substitution

• Performing a command, and using the output as a value
• Enclosing the command in backticks

File Name Expansion

• Wildcards and file name expansion
• Example: ls -l * will generate a listing of all entries in the current directory
• Use \ or single quotes to disable wildcards

Special Characters and Quoting

• Backslash escapes the effect of special characters inside the quotes
• Single and double quotes both prevent certain interpretations

Redirection and Pipe

• Redirecting input from a file with input_file < or redirecting output to a file with >output_file
• Using a pipe to chain commands (e.g., command1 | command2)

Linux Filenames and Shell Substitutions

• Filename length and character restrictions
• Standard usage for creating and deleting files
• Filename wildcards and usage, e.g., "*and?`

Linux Directories, Inodes, Links

• Information of file and directories that describe the Linux file system
• Inode number is central to Linux structure to maintain all file attributes
• Hard and soft links

Shell Working and Process Control

• Shell activities and commands (e.g. ps, jobs, fg)

Process Control Commands

• Using ps and kill to manage running processes

Locating Files in File System

• Using find command to locate files
• Use criteria for location

Selection Criterion

• find command criteria to meet when listing files

Regular Expressions

• Method of describing a set of text strings using meta characters

Stream Editor (sed)

• sed is used for repetitive editing tasks
• Editing instructions can be in a separate file or given inline
• sed performs edits on each line

Bash Scripts

• Shell scripts are programs for the shell
• How to execute code in files

Bash Script Basics

• User-defined variables, use of $ symbol for accessing variables, arithmetic operations, string handling

Test Expressions

• Logical conditions to check whether a variable is true or false

File Queries

• Examine file types, permissions, sizes with find command

Multivalued Variables (Arrays)

• Array variables and how to access them

Command Line Arguments

• Accessing command line arguments passed to a script (e.g., $1, $2, $@ , $#).

Bash Control Structures

• Conditional statements and loops for Bash scripts (like if, elif, else, case, while, and for).

Examples of Bash Scripts

• Practical demonstrations of using the discussed concepts

Test your knowledge on Operating Systems with this quiz that covers key concepts, commands, and characteristics of different systems. From shell configurations to directory management, assess your understanding of both Linux and general Operating System principles.