Introduction to UNIX System
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Transcript of Introduction to UNIX System
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Learing outcomes Introduction to Unix system Unix commands
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What is a UNIX? UNIX is an operating system An operating system is the
program that controls all the other parts of a computer system, both the hardware and software.
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What is LINUX LINUX is a free UNIX-type operating
system originally created by Linus Torlvads with the assistance of developers around the world.
The source code for Linux is freely available to everyone.
The commands of linux are similar to unix.
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Features of UNIX UNIX is a multi-user, multi-tasking
operating system. Multi-users may have multiple tasks
running sumiltaneously. This is different than PC operating system
UNIX is a machine independent operating system. Designed from the beginning to be
independent of the computer hardware
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Introduction unix
Developed at Bell Laboratories in the late 1960s by Dennis Ritchie and Ken Thompson
Shell is simply a program that reads in the commands you type and converts them into a form that is more readily understandable by the UNIX system
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Introduction (continue.)
Shell includes some fundamental programming constructs that let you make decisions, loop, and store values in variables
“Bourne” shell was written by Stephen Bourne in Bell laboratories
“Bourne” shell is the “standard” shell
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UNIX System
The “UNIX system” is logically divided into two pieces: Kernel Utilities
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UNIX System (continue.)
Kernel is the heart of the UNIX system and resides in the computer’s memory. It allocates time and memory to programs and handle filestore and comunications
Utilities
disks
UNIX system kernel
Memory
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UNIX System (continue.)
Utility resides on the computer’s disk and are only brought into memory as requested.
Virtually every command under UNIX is a utility
Shell is a utility program loaded into memory for execution whenever you log into the system
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Logging in a UNIX system
Terminal is connected to a UNIX system through Direct wire Modem LAN
After you connect the UNIX system a login: message appears
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Logging in a UNIX system (continue.)
UNIXSYSTEMKERNEL
getty
getty
getty
login:
login:
login:
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Logging in a UNIX system (continue.)
init is the UNIX system init automatically starts up a getty
program on each terminal port whenever the system is allowing users to log in
After getty displays the message login: and some types the usernames followed by RETURN, it starts up a program called login to finish the process of logging in. Then getty disappears
/etc/passwd file has one line per user
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Logging in a UNIX system (continue.)
UNIXSYSTEMKERNEL
login
getty
getty
login: Skanpassword:
login:
login:
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Logging in a UNIX system (continue.)
After login begins execution, Password: message appears
User types the password and hits RETURN
The user name and the password will be checked against the corresponding entry in the file /etc/passwd
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Logging in a UNIX system (continue.)
Every line has seven fields separated by “:”.
The fields are :1. Login name2. Password (encrypted form).3. User ID4. Group ID5. User information which could be First and Last
name, etc…6. Home directory7. Program to start up when user logs in. Usually a
“shell” program
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Logging in a UNIX system (continue.)
Example$ cat /etc/passwd
root:x:0:1:Super-User:/:/sbin/sh
daemon:x:1:1::/:
bin:x:2:2::/usr/bin:
sys:x:3:3::/:
adm:x:4:4:Admin:/var/adm:
lp:x:71:8:Line Printer Admin:/usr/spool/lp:
uucp:x:5:5:uucp Admin:/usr/lib/uucp:
nuucp:x:9:9:uucp Admin:/var/spool/uucppublic:/usr/lib/uucp/uucico
listen:x:37:4:Network Admin:/usr/net/nls:
nobody:x:60001:60001:Nobody:/:
noaccess:x:60002:60002:No Access User:/:
nobody4:x:65534:65534:SunOS 4.x Nobody:/:
oracle:*:101:67:DBA Account:/export/home/oracle:/bin/csh
webuser:*:102:102:Web User:/export/home/webuser:/bin/csh
abuzneid:x:103:100:Abdelshakour Abuzneid:/home/abuzneid:/sbin/csh
$
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Logging in a UNIX system (continue.)
UNIXSYSTEMKERNEL
/bin/sh
/usr/lbin/ksh
/usr/data/bin/dat_entry
login: Skanpassword:$
login:
login:
login: Medpassword:$
login: slimpassword:$
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After Shell starts When shell starts up, it displays a
command prompt: $ in Bourne shell and Korn shell % in C shell
Shell goes to sleep after every command or program followed by RETUN until the program has finished
This copied program is called a process
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init
init
init
Login cycle
init
getty
login
initsh
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Login cycle (continue.)
Shell name UtilityDeveloped
by
Bourne shell shStephen Bourne
Korn shell ksh David Korn
C shell csh Bill Joy
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Responsibilities of Shell Program Execution Variable and File Name Substitution I/O Redirection Pipeline Hookup Environment Control Interpreted Programming Language
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Program Execution
Format: program-name arguments The shell scans the command line
and determines the name of the program to be executed and what argument to pass to the program
Multiple occurrences of white spaces characters are simple learned
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Program Execution (continue.)
$ mv oldfile newfile
$ echo Smile, you are in Bridgeport City Smile, you are in Bridgeport City $
oldfile
newfilemv
arguments
Smile,you arein
BridgeportCity
echoarguments
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Program Execution (continue.)
Shell has some built_in commands which execute them directly without searching the disk
cd, pwd and echo are built_in commands
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Variables and File Name Substitution
assign values to variables$ list=ls$ lsCarthageDamas$ $listCarthageDamas
file name substitution on the command line * ? []
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Variables and File Name Substitution (continue.)
• Examples
$ ls
Documents Memos mail personal
$
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DocumentsMemos
mailpersonal
echoarguments
Variables and File Name Substitution (continue.)
$ echo *
Documents Memos mail personal
$
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Variables and File Name Substitution (continue.)
$ ls Documents mail
Documents:
a.doc c.doc p1 p11
mail:
p1 p2
$
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Input/Output Redirection
< Input Input From a file
<< Here Document
Read From Shell Script
> Output Direct to a File
>> Output Append to a File
• Examples$ wc -l list
2 list
$ wc -l < list
2
$
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Input/Output Redirection (continue.)
-l
userswc
arguments
-lwcarguments
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Input/Output Redirection (continue.)
In the first command line, two arguments where passed to wc (word count) utility: -l and users
In the second command line, one argument is passed to wc utility: -l. This gives the indication that the number of lines appearing on standard input is to count
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Pipeline Hookup
Connects to commands Pipe characters:
| ^
Connects the standard output from the command preceding | to the standard input of the one following the |
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Pipeline Hookup (continue.)
Example:$ who | wc -l
Counts the number of users login to the system by connecting the standard output of who to the standard output for wc
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Basic Unix commands
cat file Concatenate or type out a file cat file1 file2 ... Type out a number of files cd directory1 Change current directory to directory1 cd /usr/bin Change current directory to /usr/bin cd Change back to your home directory clear Clear the current screen cp file1 file2 Copy file1 to file2 cp file1 file2 ... dir Copy a number of files to a directory ls List the files in the current directory ls /usr/bin List the files in the /usr/bin directory lpr file1 Print file1 out lpr file1 file2 ... Print a number of files out more file Look at the content of a file with paging, use ‘q’ to get out mkdir directory Create a directory mv file1 file2 Move file1 to file2, like rename. mv file1 file2 ... dir Move a number of files into a directory mv dir1 dir2 Move or rename a directory
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Basic Unix commands (continue)
• rm file Remove a file
rm file1 file2 .. Remove a number of files
rm -r directory Remove a directory include the sub-directory
• rmdir directory Remove a directory
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DOS Command Unix Command Descriptions
CD cd Change directoryCHKDSK du Disk usageCLS clear Clear the current screenCOPY cp Copying filesDEL rm Removing files or directoriesDIR ls File listing of directoriesMD mkdir Create a directoryMORE more Type out a file with pagingPRINT lpr Print out a fileRD rmdir Remove a directoryRENAME mv Moving files aroundTYPE cat Type out files
Unix commands vs DoS
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Who, When, Why, What and Where?
man cp Display on-line manual for the “cp” command man -k keyword Display manual help file related to the keyword passwd Change your login password pwd Display the path name of where you are uptime Tell you how long the machine has been up and running users Tell you who is logging in who Tell you who is logging-in in detail w Tell you who is logging in and doing what! whoami Show you the owner of this account finger user Find out the personal information of a user finger name Try to find the person’s info. by his/her name finger email-address Try to find the person’s info across the network write user Write a message on somebody’s screen talk user Talk to the person logging in the same system with you talk email-address Talk to somebody logging in the network date Display today’s time and date cal year Display the calendar of the specified year (e.g. 1997)
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References http://info.ee.surrey.ac.uk/Teaching/
Unix/ UNIX SHELLS BY EXAMPLE BY ELLIE
QUIGLEY UNIX FOR PROGRAMMERS AND USERS
BY G. GLASS AND K ABLES UNIX SHELL PROGRAMMING BY S.
KOCHAN AND P. WOOD