Introduction to Linux

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Introduction to Linux
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Overview

• Linux Overview
• Accessing Linux System
• Managing User and Group
• How Linux Organize Data

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Linux Overview

• What is Linux
• Features and Performance
• Linux Distributions
• Red Hat Linux Distribution

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What is Linux

• 3 major components of Linux OS
• Kernel
• Manage hardware devices
• Environment
• An Interface for the user
• File Structure
• Organized the way files are stored on storage
  device

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Features and Performance

• Technical characteristics of Linux
• Cross-platform
• Cost
• Power
• Availability
• Reliability

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Linux Distributions

• Linux distribution a package that includes all
  the softwares needed to install and run Linux
• Popular Distribution
• Debian
• Fedora Core
• Red Hat Enterprise Linux

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Red Hat Linux Distribution

• Red Hat recognize two different types of clients
  
• Business Clients
• Experimental Clients
• Red Hat decided to offer multiple distributions
• "Fedora Core" is freely downloadable version of
  the distribution
• "Red Hat Enterprise" is licensed software

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The Fedora Core

• Maintained and developed by an Open Source
  project (Fedora Project)
• Release will be issued every 6 months on average
• Designed for experimental clients

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Red Hat Enterprise Linux

• Focus on reliability and stability
• Releases issued every 2 years
• 3 Enterprise versions
• RHE AS
• RHE ES
• RHE WS
• Designed for business clients

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Accessing Linux System

• Accessing Your Linux System
• The Display Manager GDM
• Using Command Line Interface
• Logging In and Out
• Shutting Down Linux
• Starting a GUI from the CLI
• Terminal Windows and Pop Up Menu
• Mouse Operations
• Virtual Desktop

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Accessing Your Linux System

• The normal procedures are
• Turn on computer
• Choose Linux OS in GRUB Boot Loader
• Enter user id and password on Login screen using
• Command line login prompts
• Graphical interface (default)

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The Display Manager GDM

• Graphical logins/logout are handled by the GNOME
  Display Manager
• Combination key related with GDM Login window
• CTRL-ALT-BACKSPACE
• CTRL-ALT-F1
• CTRL-ALT-F7

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The Display Manager GDM (cont)

• 4 pop-up menus at the Login screen
• Session
• Language
• Shutdown
• Restart

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The Display Manager GDM (cont)

• 3 choice in GDM Logout window
• Logout
• Shutdown
• Reboot

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Using Command Line Interface

• Command line interface facilities
• Logging In and Out
• Shutting Down Linux
• Starting a GUI from the Command Line

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Logging In and Out

• 2 kinds of prompts in the CLI after login
• (regular user)
• (root)
• To end session use these command
• logout, or
• exit

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Shutting Down Linux

• To turn off your computer, shut down Linux first
• 2 ways to shut down Linux
• halt
• Shutdown h now
• To force Linux to reboot
• CTRL-ALT-DEL

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Starting a GUI from the CLI

• 2 related commands to start X Window from CLI
• startx or
• switchdesk

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Terminal Windows and Pop Up Menu

• X enables you to open a console session using
  Terminal window
• To access terminal window
• right-click on the desktop
• select Terminal from the pop-up menu

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Mouse Operations

• To copy text Click and drag the mouse across the
  text to be copied
• Text copied automatically into buffer
• With some Windows-compatible window manager,
  press Ctrl-C
• To paste text Click middle mouse button
• Or, simultaneously click the left and right
  buttons

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Virtual Desktop

• Desktop can be scrollable larger than the size of
  the monitor using virtual desktop
• Use Pager to move around the virtual desktop
• Provides a thumbnail view of your virtual desktop

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Managing User and Group

• User Account
• Adding and Removing Users
• Adding and Removing Group
• The Red Hat User Manager
• User Private Groups (UPG)

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User Account

• 2 kinds of users in Linux
• Root
• Regular user
• For safety, log in as the root user only when
  performing privileged operations

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Adding and Removing Users

• useradd
• Enter username and user-specific values (e.g.
  group, user ID) as options on the command line
• Get default values from /etc/login.defs
• Copies the /etc/skel directory to users new home
  directory
• Password is not set
• The new user must be given a password using the
  passwd command

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Adding and Removing Users(cont.)

• usermod
• Takes the same options as useradd
• Enables you to change the values for any user
  features (e.g. group, user ID, etc.)
• userdel
• Delete the user's login
• With the -r option, the user's home directory
  will also be removed
• userdel -r chris

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Adding and Removing Group

• groupadd
• Used to create new groups
• Only creates the group category. Users must be
  added individually
• groupdel
• Deletes a group
• groupmod
• Change the name of a group or its ID

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The Red Hat User Manager

• Add, remove, and modify any user and groups
  easily with the Red Hat User Manager

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User Private Groups (UPG)

• Traditionally, all users are assigned into one
  group named users
• With UPG, a new user is assigned into a special
  group with the same name as the user
• E.g., new user dylan is given a default group
  also called dylan

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How Linux Organizes Data

• Devices
• Filesystems
• Directories and Paths
• File Permissions

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Devices

• Linux receives data from, sends data to, and
  stores data on devices
• Generally corresponds to a hardware unit
  (keyboard, hard disk)
• A device may have no hardware counterpart
  (pseudodevices)
• Example
• /dev/fd0
• /dev/cdrom
• /dev/hda1

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Filesystems

• Main Task of Filesystem
• Organizes the available space
• Provides directories and files which is a set of
  stored data
• Every storage device has a filesystem
• Common process for new drives
• Format
• Create Partition
• Create File System
• Examples
• ext2, ext3, reiserfs, ntfs, vfat, nfs, smbfs

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Directories and Paths

• Files and directories work as they do under
  MS-DOS
• Userss current directory after login process is
  called home directory

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Directories and Paths (cont)
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Directories and Paths (cont)

• 2 kinds of pathnames
• Absolute
• Relative
• 2 special directory name
• Single dot (.) current directory
• Two dots (..) parent directory

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System Directories

• The / is the topmost parent directory
• In Windows, we may call it C\
• 3 Linux system directories
• Program directories where applications are kept
• Configuration directories where most
  configuration files are placed
• System log directory that holds the system logs

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Program Directories

• Program directories are where installed programs
  usually store their executables
• /bin basic user programs
• /sbin file system management and system
  operations
• /usr/bin program files designed for user tasks
• /usr/sbin user-related system operation

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Configuration Directories

• Configuration directories hold most Linux
  configuration files
• /etc common configuration files
• /etc/sysconfig more specific device service
  configuration files

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Configuration Files /etc

• /etc holds your system, network, server, and
  application configuration files
• Sample contents
• fstab a list of file systems
• grub.conf boot systems supported by GRUB

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The /usr Directory

• Contains subdirectories used to support users
• Some important subdirectories
• /usr/bin holds user-accessible applications
  utilities
• /usr/sbin holds user-accessible administrative
  utilities
• /usr/share directory holds architecture-independen
  t data, including documentation

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The /mnt Directory

• Contains the mount points for your CD-ROM, DVD,
  floppy, Zip drives, and other partitions
• These are file systems you may be changing
  frequently
• Example
• /mnt/floppy
• /mnt/cdrom

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The /home Directory

• Contains users home directories
• A subdirectory with same name as user name will
  automatically be created when a user account is
  set up
• System administrators can access any users home
  directory

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The /var Directory

• Contains subdirectories for tasks whose files may
  change frequently
• Sample subdirectories
• /var/www holds Apache web server files
• /var/tmp holds any temporary files programs may
  need to perform a task

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The /proc Directory

• /proc is a special file system that is generated
  in system memory
• Does not actually exist on any disk
• Its files are interfaces to the kernel
• Sample files
• /proc/devices lists devices currently
  configured with the kernel
• /proc/cpuinfo holds information about the
  computers CPU processor

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The /dev Directory

• Contains device files that represents interfaces
  to actual system devices
• Floppy devices (/dev/fd0)
• Hard Disk devices (/dev/hda1, /dev/sdb1)
• CD-ROM devices (/dev/cdrom)
• Other devices
• To mount a file system, you have to specify its
  device name

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File Permissions

• Restricts access to directories and files based
  on
• The identity of the user
• Access modes assigned to each directory and file
• 3 kinds of permission

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File Permissions (cont)
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Permissions on GNOME

• With GNOME you can set permissions graphically

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Summary

• In this module, you have learned about
• Linux Overview
• Accessing Linux System
• Managing User and Group
• How Linux Organize Data