Operating Systems: Shell, Linux and Types

• Shell is the outermost layer of the Operating System
• The shell manages the interaction between the user and the operating system

Operating System Management

• The shell prompts the user to give input
• The shell interprets the input for the operating system
• The shell handles the output from the operating system

Types of Operating Systems

• Multitasking OS, also known as time-sharing operating systems, work efficiently by allocating time slots for each task
• Network operating systems run on a server, managing all networking functions
• Examples of Network operating systems include Microsoft Windows Server 2008 and Linux.
• Mobile OS is an operating system designed for smartphones, tablets, and PDAs

Linux

• Linux is an open-source and freely distributable operating system based on UNIX that can be installed on PCs

Linux Freedoms

• Linux provides the freedom to run the program for any purpose
• Linux provides freedom to study and change the program with access to the underlying source code
• Linux provides freedom to share copies with others
• Linux provides freedom to distribute copies of modified versions to others

Creator of Linux

• Linus Benedict Torvalds, a Finnish-American software engineer, is the creator and principal developer of the Linux kernel
• The Linux kernel serves as the foundation for Linux operating systems (distributions)
• The Linux kernel also provides services for other operating systems like Android and Chrome OS
• Linus Benedict Torvalds was born on December 28, 1969

Linux History

• Linux began in 1991 as a personal project by Finnish student Linus Torvalds.
• Torvalds created a new free operating system kernel.

Linux Distributions

• Fedora (Red Hat)
• OpenSUSE (SUSE)
• Ubuntu (Canonical Ltd.)
• Debian
• Slackware
• Gentoo
• Arch Linux
• CentOS

Debian Based Distributions

• MX Linux
• Linux Mint
• Ubuntu
• Deepin
• AntiX
• PureOS
• Kali Linux
• Parrot OS
• Devuan
• Knoppix
• AV Linux

Redhat Based Distributions

• Rocky Linux
• Alma Linux
• CentOS

Locate and Help Resources

• man pages an abbreviation of the manual or man page
• info pagesare used for programs without manual pages

Parts of a man Page

• NAME is the short description of the command
• SYNOPSIS describes syntax.
• DESCRIPTON provides detailed explanation
• OPTION explains all available options
• COMMANDS provides instructions that can be given to the program while it is running
• FILES defines the files connected in some way to the command.
• SEE ALSO provides hints on related commands
• DIAGNOSTICS explains the possible error messages of the program
• EXAMPLES provides examples of calling up a command.
• BUGS notes known errors and problems with the command.

GUI and CLI commands

• cd Change directory
• ls List directory contents
• pwd Print working directory

Create and View Files

• touch Create an empty file / change file time stamp
• cat Display file contents
• less Display file contents one page at a time
• head Display first 10 lines of a file
• tail Display last 10 lines of a file

Files and Directories

• mv Move files and directories
• cp Copy files and directories
• mkdir Create directories
• rm Delete files and directories
• rmdir Delete empty directories
• rm -i will ask before deleting each file
• Using rm -I instead will only ask once and if you are trying to delete three or more files.
• rm -r will recursively delete a directory and all its contents
• W it display the log-in session information of the user
• whoami it display the current user being use
• pwd is the Print working directory (current location)
• last used to display a list of users who have previously logged in to the system
• lastb used to display information pertaining to failed login attempts
• sudo is a command-line utility for Unix and Unix-based operating systems such as Linux and macOS

Linux Directories

• Essential Binaries for Use by All Users (/bin)
• /bin/bash - Bash shell
• /bin/cat - Displaying files
• /bin/cp - Copying files
• /bin/dd - Copying files byte-wise
• /bin/gzip - Compressing files
• /bin/mount - Mounting file systems
• /bin/rm - Deleting files
• /bin/vi - Vi editor

Hierarchical Structure of The File System

• The hierarchical structure of the file system May be depicted as an inverted tree
• Separation is with is slash "/"
• Relative path Starts from the current directory
• Absolute path Starts from the root of the entire file system tree
• Always begin with a slash "/"

Root Directory

• The highest layer of the file system tree
• Upon system boot up, the partition on which this directory is located is the first one mounted
• There must always be /bin, /dev, ect, lib, /sbin

Device Files

• Each hardware component in the system is represented as a file in /dev directory Hardware components are addressed via these files by writing or reading from one of these files
• The two device files are Character-oriented and Block-oriented

Other Partitions

• If YaST finds other , it creates mount points for each partition labeled

Boot Directory

• Contains static files of the boot loader GRUB
• Contains the kernel
• Also contains backed up information for the Master Boot Record (MBR) and system map files.

Important Device Files - devices and device file directories

• Terminals /dev/console OR /dev/tty1
• Serial Ports /dev/ttys0... /dev/ttys*
• Parallel Ports /dev/lp0... /dev/lp*
• Floppy disk drives /dev/fd0 /dev/fd*
• IDE Hard drives /dev/hda... /dev/hd*
• IDE CD-ROM drives /dev/hd*
• SCSI Hard drives /dev/sda... /dev/sd*
• SATA Hard drives /dev/sda /dev/sd*
• SCSI CD-ROM drives /dev/scd0... /dev/scd*

Configuration Files

• /etc/SuSE-release
• /etc/passwd
• /etc/inittab
• /etc/shadow
• /etc/init.d/*
• /etc/group
• /etc/modprobe.conf
• /etc/cups/*
• /etc/DIR COLORS
• /etc/hosts
• /etc/X11/xorg.conf
• /etc/motd
• /etc/fstab
• /etc/issue
• /etc/profile
• /etc/sysconfig/*

User Directories

• .profile - Private login script of the user
• .bashrc -Configuration file for bash
• .bash history - List of command previously run in bash

Libraries

• Contains the libraries that are used by programs in the /bin and /sbin directories
• Kernel modules are located in /lib/modules directory.
• Additional libraries may be found in the /usr directory

Mount Points for Removable Media

• /media/floppy/
• /media/cdrom/
• /media/cdrecorder/
• /media/dvd/
• /media/usbdisk/
• /media/media name

Application Directory

• Installed programs can store their static files in this directory First, a directory with the name of the application is created The files are then stored in that address
  • For GNOME: /opt/gnome
  • For KDE: /opt/kde3

Root's Home Directory

• The home directory of the system administrator
• Not located in /home
• Preferably, it should be in the same partition as the root directory ("/")

System Binaries

• /sbin/SuSEconfig
• /sbin/fsck*
• /sbin/conf.d/*
• /sbin/init
• /sbin/yast
• /sbin/mkfs*
• /sbin/fdisk
• /sbin/shutdown

Data Directories for Services

• Contains subdirectories designed for containing data for various services
  • For Apache web server: /srv/www/
  • For FTP server: /srv/ftp/

Temporary Area

• Various programs create temporary files that are stored in /tmp/until they are deleted

The Hierarchy Below

• /usr - Unix Specific Resources OR Unix System
• /usr/X11R6/ -> Files for the X Window System
• /usr/bin/ -> Almost all executable programs
• /usr/lib/ -> Libraries
• /usr/local/ -> Locally-installed programs
• /usr/sbin/ -> Programs for system administration
• /usr/share/doc/ -> Documentation
• /usr/share/man/ -> The manual pages
• /usr/src/ -> Source files of all programs and the kernel

Variable Files

• /var/lib/ -Variable libraries
• /var/log/ -Log files for most services
• /var/run/ -Files with information on running processes
• /var/spool/ -Directory for queues
• /var/lock/ -Lock files to protect devices from multiple use

Windows Partitions

• If YaST finds any partitions with a Microsoft file system it creates a /windows directory automatically Inside this directory there are subdirectories labeled with Windows drive characters

Process Files

• /proc/cpuinfo
• /proc/mounts
• /proc/dma
• /proc/net/*
• /proc/interrupts
• /proc/partitions
• /proc/ioports
• /proc/bus/pci
• /proc/filesystems
• /proc/bus/scsi/
• /proc/modules
• /proc/sys/*
• /proc/version
• /sys

System Information Directory

• provides information in the form of a tree structure on:
• various hardware buses;
• hardware devices;
• active devices;
• and their drivers

Mount Point for Temporarily Mounted File Systems

• The standard directory for integrating file systems is /mnt .It should only be used for temporary purposes To mount the partition to unmount the partition: umount

Locally-available File Systems

• /bin
• /boot
• /dev
• /etc
• /lib
• /sbin

Filesystem Hierarchy Standard

• Describes the standard structure of a file system.
• Defines a two-layered hierarchy: The directories in the top layer A second layer, the directories under /usr and /var
• More information may found over the Internet at http://www.pathname.com/fhs/ The Hierarchical Structure of the File System
• May be depicted as an inverted tree
• The separation character between individual directory names is a slash "/"
• Relative path starts from the current directory
• Absolute path starts from the root of the entire file system tree
• Always begin with a slash "/"