An Introduction to Linux

1. Overview of Unix System
2. Basic Commands
3. Relative & Absolute Path
4. Redirect, Append and Pipe
5. Permission
6. Process Management
7. Install Software
8. Text Editor
9. Foreground and Background Jobs

Overview of Unix System

Kernel & Shell
 Unix/Linux is operating system (OS).
 Unix system is described as kernel & shell.

 Kernel is a main program of Unix system. User
it controls hard wares, CPU, memory, hard
disk, network card etc. input

 Shell is an interface between user and Shell
kernel. Shell interprets your input as
commands and pass them to kernel.
Kernel

Unix Overview (cont.)

Multi-user & Multi-process
 Many people can use one machine at the same time.

File & Process
 Data, directory, process, hard disk etc (almost everything)
are expressed as a file.
 Process is an running program identified by a unique id
(PID).

Directory Structure
 Files are put in a directory.
 All directories are in a hierarchical structure (tree
structure).
 User can put and remove any directories on the tree.
 Top directory is “/”, which is called slash or root.
 Users have the own directory. (home directory)

Directory Structure


Important Directories
 /bin This contains files that are essential for correct
operation of the system. These are available for use by all
users.

 /home This is where user home directories are stored.

 /var This directory is used to store files which change
frequently, and must be available to be written to.

 /etc Various system configuration files are stored here.


Important Directories
 /dev This contains various devices as files, e.g. hard
disk, CD-ROM drive, etc.

 /sbin Binaries which are only expected to be used by
the super user.

 /tmp Temporary files.


Normal user and Super user
 In Unix system, there is one special user for administrator, which
can do anything.
 This special user is called root or superuser.

Case Sensitivity
 Unix is case-sensitive.
 MYFILE.doc, Myfile.doc, mYfiLe.Doc are different.

Online Manual
 Unix has well-written online manuals.

Basic Commands

How to run commands
 Finder => Application => Utilitaires => Terminal
 When you log on Unix machine, you will see,

[someone]$

 One command consists of three parts, i.e. command
name, options, arguments.

Example)
[someone~]$ command-name optionA optionB argument1 argument2

Basic Commands

How to run commands
 Between command name, options and arguments, space is
necessary.

 Opitions always start with “-”

 Example:
cd ..
ls –l .bashrc
mv fileA fileB

Basic Commands

Commands
 ls show files in current position
 cd change directory
 cp copy file or directory
 mv move file or directory
 rm remove file or directory
 pwd show current position
 mkdir create directory
 rmdir remove directory
 less, more, cat display file contents
 man display online manual

Basic Commands

Commands
 su switch user
 passwd change password
 useradd create new user account
 userdel delete user account
 mount mount file system
 umount unmount file system
 df or du show disk space usage
 shutdown reboot or turn off machine

Basic Commands

1. Type following command in 3. In your home directory,
your directory. ls .bash_profile
cp .bash_profile sample.txt
ls
less sample.txt (note: to quit less, press “q”)
ls –a
rm sample.txt
ls –la
ls -Fa
4. check disk space usage
2. Make a directory
df
mkdir linux df -h
pwd
cd linux
pwd
cd
pwd
rmdir linux

Relative & Absolute Path

 Path means a position in the directory tree.
 To express a path, you can use relative path or
absolute path.
 In relative path expression, the path is not defined
uniquely, depends on your current path.
 In absolute path expression, the path is defined
uniquely, does not depend on your current path.

Absolute Path

 Address from the root
/home/linux/
~/linux
~: ~: Alt+N

 Similar to:
Lausanne University/Lausanne/Canton de Vaud/
Switzerland/Europe/Earth/Solar System/

Relative Path

 Relative to your current location
. : your current location
.. : one directory above your current location
pwd: gives you your current location

 Example
ls ./linux : lists the content of the dir linux
ls ../../ : lists everything that is two dir higer

 Similar to:
Go Left/turn right/take the TSOL/go

Relative & Absolute Path

 Relative Path  Ablsoute Path
pwd cd
cd . mkdir mydir
pwd
pwd
cd /Users/invite
cd ..
pwd
pwd
cd /Users
cd .. pwd
pwd cd /
cd pwd
cd /Users/invite
cd ~/mydir

Redirect, Append and Pipe

Redirect and append
 Output of command is displayed on screen.
 Using “>”, you can redirect the output from screen to a file.
 Using “>>” you can append the output to the bottom of the file.

Pipe
 Some commands require input from a file or other commands.
 Using “|”, you can use output from other command as input to the command.
 On MacOSX, The Pipe sign: (Shift+Alt+N: franc, Alt+7)


Commands
 head show first several lines and omit other lines.

 tail show last several lines and omit other lines.

 grep XXX File show lines matching pattern XXX in File


 In home directory, type  Use pipe.
ls -1 > sample.txt less redirect.txt
less sample.txt grep Desk redirect.txt
 Use redirect. grep –n Desk redirect.txt
head -3 sample.txt man grep
head -3 sample.txt > redirect.txt tail redirect.txt | grep Desk
 Use append. rm sample.txt
tail -3 sample.txt rm redirect.txt
tail -3 sample.txt >> redirect.txt
less redirect.txt

Sorting

Commands
 sort Sorts using the first field of each line.

 -n Sorts considering the numeric value of the strings
 -k3 Sorts using the third field of each line
 -rnk3 Sorts in reverse order, using the numeric value of
the third field


 Identify the largest file in a directory:

ls –la /bin/ | sort –nk5 | tail -1

Permission

 All of files and directories have owner and permission.
 There are three types of permission, readable, writeable and
executable.
 Permissions are given to three kinds of group. owner, group
member and others.

Example:
ls -l .bash_profile
-rw-r--r-- 1 cnotred cnotred 191 Jan 4 13:11 .bash_profile

 r:readable, w:writable, x: executable

Permission

Command
 chmod change file mode, add or remove
permission
 chown change owner of the file

Example)
chmod a+w filename
add writable permission to all users
chmod o-x filename
remove executable permission from others
chmod a+x
Gives permission to the usser to execute a file

 u: user (owner), g: group, o: others a: all

Permission

 Check permission
ls –l .bash_profile
cp .bash_profile sample.txt
ls –l sample.txt

 Remove readable permission from all.
chmod a-r sample.txt
ls –l sample.txt
less sample.txt

 Add readable & writable premissions to file owner.
chmod u+rw sample.txt
ls –l sample.txt
less sample.txt
rm sample.txt

Process Management
 Process is a unit of running program.

 Each process has some information, like process
ID, owner, priority, etc.

Example) Output of “top” command

Process Management
Commands
 kill Stop a program. The program is
specified by process ID.
 killall Stop a program. The program is
specified by command name.
 ps Show process status
 top Show system usage statistics

Process Management

 Check your process.
ps
ps –u

 Check process of all
users.
top (To quit top, press
“q”)
ps –e
ps –ef

 Find your process.

ps –ef | grep cnotred

Install Software

Commands
 Zypper
 New installation command introduced first in 10.2 release
 Transparant and simple
 Function :
 Install
 Update
 Search
 Remove
 Reduced Dependency Problem

Install Software
 Common paramater:
 zypper # to print the list of available global options and

commands
 zypper help search # to print help for the search command

 zypper lp # to see what patch updates are needed

 zypper patch # to apply the needed patches

 zypper se sqlite # to search for sqlite

 zypper rm sqlite2 # to remove sqlite2

 zypper in sqlite3 # to install sqlite3

 zypper in yast* # to install all packages matching 'yast*'

 zypper up # to update all installed packages with newer

versions, where possible

Text Editor

pico
 Programs & configuration files are text file.
 There are two popular text editors, vi and Emacs.
 Although they are very powerful and useful, it is also true that
they are complicated for beginners and difficult to learn.
 pico is an easy and simple alternative.

Text Editor

Commands
 Arrow-keys Move cursor
 CTRL+a Move to the beginning of the current line.
 CTRL+e Move to the end of the current line.
 CTRL+v Move forward one page.
 CTRL+y Move backward one page.
 CTRL+w Search for text.
 CTRL+d Delete the current character.
 CTRL+k Remove (cut) current line or selected text.
 CTRL+u Paste (uncut) last cut text at the cursor position.
 CTRL+o Save (output) the file.
 CTRL+x Exit Pico, saving the file.

 Autre: xemacs, emacs

Text Editor

 Create the file Hello
pico hello.pl

 Write hello.pl as follows.

#!/usr/bin/perl
print “Hello Worldn”;

 Make il executable
chmod u+x hello.pl

 Run it!
./hello.pl

Foreground and
Background

 Running job has two modes, “foreground” and “background”

 If program is running as “background”,
the program keeps running even after your session was
closed

 If program is running as “foreground”,
Ctrl-C stop program
Ctrl-Z let program background

Foreground and
Background

 To run programs in background mode, use “&”
[nomura@ssc-1]$ command &

 To get background job back into foreground mode, use “fg”
command.
[nomura@ssc-1]$ fg

Remote Login & File
Transfer

• rshd, telnetd, ftpd, sshd are server program
and provide similar services, remote login & file
transfer.
• The major difference is security level.
rshd < telnetd + ftpd < sshd

Commands
Client Server
 rsh & rcp
 rshd
 telnet & ftp
 ssh & scp
 telnetd & ftpd
 sshd

Remote Login & File
Transfer

Remote login & file transfer system are based on
server and client model. client program on your
machine ask sever program certain service remote
machine.

For example, telnet server provides remote login
service. ftp server provides file transfer service.

Sample client programs;
WS FTP FTP client
Internet Exploror HTTP client
Eudora POP, SMTP client

Tutorial of Unix/Linux

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An Introduction to Linux

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