2. * 2
Operating System Concept
• An operating system (OS) is
a resource manager
• It is a set of software
routines:
– that allow users and
application programs to access
system resources
– in a safe, efficient and abstract
way
– CPU, memory, disks, modems,
printers network cards etc.
• A general operating system
architecture can be
understood by the figure
Users
Shell or GUI
Application
Programs
System Utilities
System Call Library
Operating System Kernel
Dual Processor with 2 GB RAM,
160 GB Hard Disk
3. * 3
Operating System Concept
• The kernel controls the hardware
• It provides functions like
– Handling of interrupts from the devices
– Allocation of memory to programs
– Sharing of CPU among the programs
• Basic kernel services are exposed to higher-level programs
through a library of system calls
• Application Programs and System Utility Programs
make use of system calls
– Launched using a shell/GUI
• The OS may differ from one another on the basis of:
– System calls
– System utilities
– User interface they provide
– Resource scheduling policies implemented by the kernel
4. * 4
A Linux Distribution
• A distribution comprises of:
– Kernel
• 2.6.9-89.0.11.EL.cernsmp
– System Utilities
• File copy, hard disk repair/defragment etc.
– GUI
• GNOME, KDE
– Application Programs
• Open office, evolution, firefox, gedit, gftp. konqueror,
evince, kdevelop, kview, emace, vim etc.
5. * 5
Typical Directory Structure
• Linux Filesystem is laid out in a hierarchical tree
structure.
• Top level directory is called root “/”
7. * 7
Summary: Directory Structure
• Home Directories: /root,/home/username
• User Executables: /bin, /usr/bin, /usr/local/bin
• System Executables: /sbin, /usr/sbin, /usr/local/sbin
• Other Mountpoints: /media, /mnt
• Configuration: /etc
• Temporary Files: /tmp
• Kernels and Bootloader: /boot
• Server Data: /var, /srv
• System Information: /proc, /sys
• Shared Libraries: /lib, /usr/lib, /usr/local/lib
8. * 8
Logging into a Linux System
• Two types of login screens
– virtual consoles (text-based)
– graphical logins (display managers)
• Login using login name and password
• Each user has a home directory for personal
file storage
9. * 9
Absolute & Relative Paths
• Absolute pathnames
– Begin with a forward slash
– Complete "road map" to file location
– Can be used anytime you wish to specify a file
name
• Relative pathnames
– Do not begin with a slash
– Specify location relative to your current working
directory
– Can be used as a shorter way to specify a file
name
10. * 10
Basic Linux Commands
• ls, listing files and directories
– ls –a
– ls –l
– ls -la
• clear, clears the screen
• echo, display a line or text
– echo “any text”, echo $HOSTNAME
• exit, exit the current session/shell
• file, determine file type
– file <file name/path>
11. * 11
Basic Linux Commands
• cd, change directory
– cd ..
– cd –
– cd ~/mydir
– cd /home/usman
– cd
• su, switch user, su – (complete user
environment)
• id, print user and group ids
• passwd, change password
– yppasswd
12. * 12
Basic Linux Commands
• man, manual pages
– man <command>
• info, information pages
– info <command>
• command --help, basic help by author
– ls --help, man --help
• pwd, present working directory
13. * 13
Basic Linux Commands
• cp, copy files and directories
– cp [options] file destination
• More than one file may be copied at a time if the
destination is a directory:
– cp [options] file1 file2 destination
• If the destination is a directory, the copy is placed
there
• If the destination is a file, the copy overwrites the
destination
• If the destination does not exist, the copy is renamed
14. * 14
Basic Linux Commands
• mv, move and/or rename files and directories
– mv [options] file destination
• More than one file may be moved at a time if
the destination is a directory:
– mv [options] file1 file2 destination
• In mv also, the destination works like cp
• mkdir, creates directories
– mkdir <directory name/path>
• rmdir, removes empty directories
– rmdir < directory name/path>
16. * 16
Basic Linux Commands
• whoami, print user id
• locate, finds files using a pre-built database.
• find, Finds files and directories in real-time.
– locate is faster but relies on an updated index; find
is slower but always accurate.
• whereis, Shows locations of executables,
source code, and manual pages
18. * 18
File Permissions in Linux
Octal Binary Permissions
0 000 _ _ _
1 001 _ _ x
2 010 _ w _
3 011 _ w x
4 100 r _ _
5 101 r _ x
6 110 r w _
7 111 r w x
20. * 20
Shell Scripting Basics
#!/bin/sh
echo "Welcome to Linux -- $USER"
echo "Today is: $(date)"
echo "You are working in: $(pwd)"
echo "Enter your last name:"
read LNAME
echo "Hello -- $LNAME"
echo "Enter the first number:"
read X
echo "Enter the second number:"
read Y
PRODUCT=$((X * Y))
echo "The product is: $PRODUCT"
echo "Bye Bye..."
![* 13
Basic Linux Commands
• cp, copy files and directories
– cp [options] file destination
• More than one file may be copied at a time if the
destination is a directory:
– cp [options] file1 file2 destination
• If the destination is a directory, the copy is placed
there
• If the destination is a file, the copy overwrites the
destination
• If the destination does not exist, the copy is renamed](https://image.slidesharecdn.com/linux-lhcschool-250419063402-d312596e/85/Linux-Commands-Basic-commands-for-Beginners-13-320.jpg)
![* 14
Basic Linux Commands
• mv, move and/or rename files and directories
– mv [options] file destination
• More than one file may be moved at a time if
the destination is a directory:
– mv [options] file1 file2 destination
• In mv also, the destination works like cp
• mkdir, creates directories
– mkdir <directory name/path>
• rmdir, removes empty directories
– rmdir < directory name/path>](https://image.slidesharecdn.com/linux-lhcschool-250419063402-d312596e/85/Linux-Commands-Basic-commands-for-Beginners-14-320.jpg)
![* 15
Basic Linux Commands
• touch, create empty files or update file
timestamps
– touch <file name/path>
• rm, remove files
– rm [options] <file name/path>
– rm -i file (interactive)
– rm -r directory (recursive)
– rm -f file (force)
• rm –r, recursively removes directory trees
– rm –rf <directory name/path>](https://image.slidesharecdn.com/linux-lhcschool-250419063402-d312596e/85/Linux-Commands-Basic-commands-for-Beginners-15-320.jpg)
