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UNIX

Dr. Emmanuel Shubhakar Pilli

Graphic Era University

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Unix History

q In early „60s, computers were expensive, had

minimal memory and were single user

u All activities were designed to make things easy for the

computer

q In the mid „60s, MIT, Bell Labs, and General

Electric teamed to build an OS for a large

computer, the GE-645 that would accommodate

1,000 simultaneous users

q Multics (Multiplexed Information and Computing

Service)

q In March „69, Bell pulled out of the project

u “Three people could overload it.”

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The Roots of Unix

q Ken Thompson had been using Multics to run

Space Travel but it cost $70 a run

q Thompson found a cast-off PDP-7 with the intent

to write a file system

q This file system became the roots of Unix

q Unix was originally called UNICS, a pun on

Multics (Uniplexed Information and Computing

Service)

q Unix struggled along on an obsolete, under-

powered machine until the PDP-11 was released

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Lessons Learned From Multics

q Tree-structured file system

q Separate, identifiable program to do command

interpretation (the shell)

q Structure files with no structure except as a

sequence of bytes, in most cases with no

interpretation by the OS

q Text files as simple sequences of characters

separated by new-lines

q Semantics of I/O operations (read and write) as

referring to a file handle, buffer, and a count, thus

concealing the underlying structure of the device

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The Birth of Unix

q In 1970, Thompson and Ritchie convinced the

Bell Labs Patent department to fund purchase of

a PDP-11/20 for use in text processing

q This ruse allowed them to develop Unix

q “We knew there was a scam going on--we‟d

promised a word processing system, not an

operating system.” Dennis Ritchie

q BTL Patent department became first users of

Unix, taking over the machine but giving

Thompson and Ritchie enough funds to purchase

a PDP-11/45

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Thompson, Ritchie with PDP-11

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Unix Philosophy

q Write programs that do one thing and do it well

q Write programs that work together, allowing the

output of one to become the input of another

u Write programs that handle text streams, because that

is a universal interface

q Don‟t hesitate to build new programs to do a job

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The Unix Explosion

q February 1973, the Third Edition of the UNIX

PROGRAMMER‟S MANUAL appeared, along

with a C compiler and debugger

q Thompson and Ritchie submitted an abstract for a

presentation to the ACM Symposium on

Operating Systems Principles

q When the paper was published in

Communications of the ACM in July 1974, Unix

took off

q In 1983, they shared the ACM‟s Turing Award for

their work

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The Law

q January, 1949 DOJ filed an antitrust complaint

against Western Electric and AT&T

q In January, 1956, a “consent decree” was entered

u AT&T and Western Electric were enjoined “from

commencing ... manufacture for sale or lease any

equipment [other than that used in providing telephone

or telegraph services],”

u “from engaging ... in any business not of a character or

type engaged in by Western Electric or its subsidiaries”

u AT&T was enjoined “from engaging in any business

other than the furnishing of common carrier

communications services”

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Results of Consent Decree

q AT&T was required to reveal what patents it held

and to license to anyone at nominal fees

q The lawyers at Bell Labs, a wholly owned

subsidiary of AT&T and Western Electric were

conservative

u “No business but phones and telegrams”

q Thompson‟s presentation at the ACM SOSP put

them in a quandary

u Suddenly requests started flowing in for Unix licenses

u Computers weren‟t “phones and telegrams” thus putting

them in danger of antagonizing the Justice Department

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AT&T Unix Policy

q To preclude any conflict with the Consent Decree,

AT&T would license Unix but make it clear that it

had no intention of pursuing software as a

business

q Bell System support policy:

no advertising

no support

no bug fixes

payment in advance

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The Growth of Unix

q May 1974 - “nearly a dozen”

q Spring „75 - “three dozen”

q June „75 - “plus 20 new installations”

q October „75 - 60 installations

q March „76 - 80 installations

q September „76 - 138 installations• Canada 13

• Great Britain 10

• Australia 4

• Israel 3

• The Netherlands 3

• Austria 1

• Belgium 1

• Germany 1

• Venezuela 1

• United States 101

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Berkeley Unix

q Robert Fabrey, of UC Berkeley, was on the SOSP

program when Thompson presented his paper

q Together with the Math department, he purchased

a PDP-11/45 and had Unix running by Jan „74

q By „78 Bill Joy had produced a Pascal compiler

and began producing the Berkeley Software

Distribution (BSD) for $50 containing:

u Unix Pascal System

u Ex Text Editor

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BSD Unix and the Internet

q DARPA wanted its contractors on a common

computer system

q In late 1980, Bill Joy convinced DARPA that the

software platform should be Unix, DARPA had

already decided on the DEC VAX for the

hardware

q TCP/IP, the language of the internet, was added

to BSD 4.2 at DARPA‟s request, along with the

Berkeley Fast File System

q Unix emerged from this as the machine that

fueled the original internet (ARPANET)

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Dueling Unixes

q Up until „78, Unix meant AT&T‟s operating system

q After this, there were two principle flavors of Unix

u BSD

u System V

q Commercially, both were a success but were not

totally compatible with each other

q This led to the formation of the Open Software

Foundation and the competing Unix International

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Why Unix Instead of Other OSs?

q Portability

u Written in C, only a small portion is in assembly

u Runs on micros, minis, main frames, and super

computers

q Ran on (relatively) inexpensive hardware

q Designed to be adaptable to changing user

environments

q It was inexpensive

q Source was available

q Permits access to its operating features

u Wonderful programmer‟s environment

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Challenges of Unix

q Powerful system with many tools and capabilities

u Takes considerable effort and time to master

q Most commands are short, terse, and non-

descriptive

q Relatively unforgiving of user mistakes

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Major Personalities

q Ken Thompson

q Dennis Ritchie

q Joe Ossanna

q Rudd Canaday

q Robert Fabrey

q Steve Johnson

q Stephen Bourne

q Doug McIlroy

q Kirk McKusick

q Armando Stettner

q Heinz Lycklama

q Bill Joy

q Co-Inventor of Unix

q Co-Inventor of Unix

q Author of troff

q Original file system collaborator

q Obtained DARPA funding for BSD

q Author of lint and yacc

q Author of the Bourne shell, sh

q Originator of pipe concept

q Wrote Berkeley Fast File System

q Got DEC to acknowledge Unix

q Chaired first Unix standards group

q Author of csh, ex, vi, termcap, and

much of BSD

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Ken Thompson and Dennis Ritchie

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What‟s An Operating System?

q A program that acts as an intermediary between

the computer hardware and the user

q Primary goal is to make the computer system

convenient to use

q Secondary goal is to use the hardware resources

efficiently

q Unix can be divided into roughly four components

u the hardware

u the kernel, the hardware interface unique to a platform

u the shell and other system utilities

u the application programs

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The System View of Unix

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So Why Unix?

q Unix is a multi-tasking operating system based

around a hardware specific kernel

u Multi-tasking/multi-processing means more than one

command, program, process can seemingly be in

simultaneous execution

q Hardware specific kernel means that a small core

piece of functionality is coded specifically for the

platform

u All the rest of Unix remains unchanged

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Unix Shells

q A shell is the user interface or set of programs

user to interact with Unix and process commands

q Common shells are:

u Bourne

u C

u Korn

q When a shell is executed, it

u inherits environmental variables set by the previous

shell

u stops the previous shell

u becomes the current shell

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Bourne Shell (sh)

q Written by Dr Steven Bourne of Bell Labs

q Both a command interpreter and a high-level

programming language

q Typically the default Unix shell

q Fast

u Approximately 20 times faster than C shell because it is

simpler and doesn‟t carry as much baggage

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C Shell (csh)

q Written by Bill Joy at University of California at

Berkeley

q Slower and more complex than Bourne shell, but

has facilities to make it more user friendly

u alias

u history

u job control

u filename completion

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Korn Shell (ksh)

q Written by David Korn of AT&T, released in 1986

q Includes features of both the Bourne and C shell

q Introduces several new user interface features

including command line editing

q Adds features that improve its usefulness as a

programming language

u report formatting capabilities

u built-in arithmetic

u data types

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Superuser

q A user with essentially all privileges

u Often referred to as root privileges

q Allowed access to all files

q Allowed to run all commands

q System administrator has superuser privileges

q Can be very dangerous, all the Unix built in

protections are by-passed

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Password Security

q Unfortunately, password security is a necessity

q Good passwords have several characteristics

u Minimum of six (6) characters

u Mixture of alpha and numeric characters

u Mixture of upper and lower case

u No real words

l Susceptible to a dictionary attack

q It is also good practice to avoid:

u Family names

u Birthdates

u Pet‟s names

u Any other personal data

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Logging In and Out

q login: username

q password: your_password

u To change your password

l clyde% passwd

l Changing password for ??? on clyde.

l Old password: your_current_password

l New password: your_new_password

l Retype new password: your_new_password

l clyde%

q To logout

u clyde% exit

u or clyde% logout

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To connect via internet

q telnet your.favorite.computer

q or telnet 127.0.0.0

q Your favorite computer may respond with

something like:

SunOS UNIX (yof)

login: username

Password: your_password

Last Login: Sat Aug 7 10:15:50 on ttyp0

SunOS Release 4.1.3_U1 (GENERIC) ..........

yof%

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What happens when you login?

q Unix runs the login program

u If it exists, .login script is executed

q Then the shell specified in /etc/passwd is

executed and user is placed in his HOME

directory

u If it exists, .cshrc (if csh is your default shell) is

executed

q So what‟s the difference? Why two initialization

files?

u .login is executed only at login

u .cshrc is executed every time a new shell is spawned

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exit or logout

q exit terminates your current shell

u if it is also your login shell, exit will exit and logout

q logout terminates a login shell

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Process Concepts

q Early or simple (DOS) computer systems allowed

only one program to be executed at a time

q Modern computer systems like Unix are multi-

tasking, allowing multiple programs to be loaded

and executed concurrently

q This requires more control of programs, leading to

the notion of a process

q A process is a program in some stage of

execution

q A modern computer system is a collection of

processes

u Operating system processes and User processes

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Unix Processes

q Every command executed on Unix is a process

q Unix processes are hierarchical

u Parent and child processes

q Every process is automagically assigned three

standard files

u input

u output

u error

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Process Blocks

q Each process has a process block that includes

u a process identifier

u the process state

u the value of the process‟s program counter

u other information specific to the process such as

l memory limits

l files in use

l processor time used

l ....

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Command Components

q Commands consist of:

u Command name

u Options, or flags

u Arguments

q Arguments are the “things” that the command will

operate on

q Options modify the behavior of the command

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Command Notation

q command name

q [ ] optional arguments or options

u can be nested

l [ arg1 [ arg2 ] ]

l [...]

q | is an OR condition

u arg1 | arg2

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who

q Who is on the system and info about their login

u User_name, terminal_name, login_time

q Syntax: who [am i]

q Example:

clyde% who

root console Jul 22 09:36

krf ttyp0 Aug 7 10:32 (dal-tx2-33.ix.ne)

q am i option lists requestor info only

q Related command: whoami

u Lists requestor‟s user_name only

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CALendar - cal

q Prints a calendar for the specified year

u Default is current year

q Syntax: cal [ [ month ] year ]

u month - number from 1 to 12

u year - number from 1 to 9999

q Note: September 1752 is odd, 11 days were

skipped to make up for lack of prior leap year

adjustments

q Examples:

clyde% cal

clyde% cal 9 1752

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date

q Display or set the date

q Syntax:date [-u] [-a [-] sss.fff] [yymmddhhmm [.ss]]

u u - display date in GMT, default is local time

u a - slowly adjust system clock

u yymmddhhmm [.ss] - set system date and time

l Only superuser can set the date and time

q If the argument begins with a +, the output of date

is under user control

q Examples:

clyde% date

clyde% date -u

clyde% date +%T

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finger

q Displays information about users

q Syntax: finger [options] user_name

q By default, finger displays user_name‟s:

u login name

u full name

u terminal name

u idle time

u login time

u location

u first line of .plan file

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mail

q Read or send electronic mail messages

q Syntax: mail [-deHinNUv] [-f [filename | +folder] ]

[-T file]

or: mail [-dFinUv] [-h number] [-r address] [-s

subject] recipient ...

q First form is for reading mail, second is for

sending mail

q For this class:

u Read mail: mail

u Send mail: mail -s “subject” recipient

u or: mail -s “subject” recipient < file_name

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MANual pages - man

q Read online documentation or find reference

pages by keyword

q Syntax: man [[section] title]

or: man [[-k keyword] | [-f filename]]

q Examples:

clyde% man ps

clyde% man -k compile

clyde% man -f /var/spool/mail

clyde% man link

clyde% man 2 link

clyde% man 8 link

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whois

q Internet „white pages‟

u Searches for a TCP/IP directory entry

u Used to find people or domain owners/contacts

q Syntax: who [-h host] identifier

u host - name of host computer to use for lookup

l Default is nic.ddn.mil, which no longer supports

anything but MILNET, Current host is rs.internic.net

l Names are stored as

– last name, first name, titles

q Examples:

clyde% whois -h rs.internic.net Earthlink.com

clyde% whois -h rs.internic.net „Krol, Ed*‟

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show ProcesSes - ps

q Displays the status of current processes

q Syntax: ps [ [-] acCegjklnrSuUvwx] [-tx] | [num]

[kernel-name] [c-dump-file] [swap-file]

q Default is to display only processes with your

effective user ID

q We will only use the following options:

u a - include processes that are not owned by you

u x - show processes that don‟t have a controlling

terminal

u r - show only running processes

q Example:

clyde% ps -a

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talk Example

clyde% talk krf

Message from Talk_Daemon@clyde at 17:39 ...

talk: connection requested by krf@clyde.dcccd.edu.

talk: respond with: talk krf@clyde.dcccd.edu

q Respond as shown and a split screen will be

displayed with your input in one half and your talk-

mate‟s output in the other

q To end the session, type Control-c

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MESsaGe - mesg

q Permit or deny messages on your terminal

q Syntax: mesg [n] [y]

u default reports current state without changing it

u n - forbids messages to be sent to you from talk or write

u y - reinstates permission

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Print Working Directory - pwd

q Displays the pathname of the current working

directory

q Syntax: pwd

q Example:

clyde% pwd

/home/clyde/krf

clyde%

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Set TTY - stty

q Display and set terminal options

q Syntax: stty [-ag] [option] ...

u a - Report all option settings

u g - Report current settings in a format that can be used

as an argument to another stty command\

q Most common user use is to remap control keys,

such as erase

u To set the erase command to be a backspace:

clyde% stty erase ^h

u Key mapping good candidate for inclusion in your .login

file

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mail(pine)

PINE 4.10 MAIN MENU Folder : INBOX No Messages

? HELP - Get help using Pine

C COMPOSE MESSAGE - Compose and send a message

I MESSAGE CHECK - View messages in current folder

L FOLDER LIST - Select a folder to view

A ADDRESS BOOK - Update address book

S SETUP - Configure Pine Options

Q QUIT - Leave the Pine program

? Help P PrevCmd R RelNotes

O OTHER CMDS > [ListFldrs] N NextCmd K KBlock

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File System

q Unix provides a hierarchical, or tree-like, file

system

u Supports two main objects

l Files

l Directory files, or directories

u From Unix‟s view, there is no difference between the

two

q From the user‟s view, files are data that you want,

directories are containers of files

q In reality, files are simply a stream of bytes

u Critical design philosophy of Unix

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Tree Structure

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Files and Directories

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File Names

q Every file has a filename

q Current versions of Unix allow up to 255

characters, older versions limit to 14

q Almost any character can be used in a filename

u Sticking with the following will save many problems

l Uppercase letters (A-Z)

l Lowercase letters (a-z)

l Numbers (0-9)

u Period ( . ) can be used as any other character and

may denote special files

u Exception is the root directory, which is always named /

l No other file can use this name

lComma ( , )

lDash ( - )

lUnderscore ( _ )

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Other File Name Rules

q Other characters may be used by “escaping” them

with a “\” character

u Willie\*Weasil - displays as Willie*Weasil

u Much confusion can result from this

q File names are case sensitive

u my_file, My_File, and MY_FILE are all unique names

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File Access Controls

q Unix provides file security with access levels and

permissions

q Access levels define who specific permissions

belong to

u user (u)

u group (g)

u other (o)

q Permissions define what the members of an

access level are allowed to do

u execute (x)

u read (r)

u write (w)

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Access Controls Provide Security

q Generally accepted that there are files users

cannot access or modify

q This provides security for:

u System

u Work groups

u Individual users

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Unix Has Many Filesystem Types

Use AIX DigitalUnix

HPUnix

SCOUnix

SunOS

Solaris IRIX Linux

Native ifs ufs hfs EAFS 4.2 ufs efs ext2

NFS nfs nfs nfs nfs NFS nfs nfs nfs

CD cdrfs cdfs cdfs HS hsfs hsfs iso9660

iso9660

Swap ufs swap

DOS DOS pcfs dos msdos

/proc procfs proc proc proc

other advfs vxfs S51K s5 hfs sysv

lofs minux

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MaKe DIRectory - mkdir

q Creates new directories

q Syntax: mkdir [ -p ] dirname

u p - allows “missing” parent directories to be created as

needed

q Requires write permission in the parent directory

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ReMove file(s) - rm

q Removes (deletes) files

q Syntax: rm [ - ] [ -fir] filename ...

u - Treat following arguments a filenames, so you can

remove files starting with a minus sign

u f - Force files to be removed without displaying

permissions, asking questions, or reporting errors

u i - Interactive, ask before removing each file

u r - Recursively delete the contents of a directory, its

subdirectories, and the directory itself

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ReMove DIRectory - rmdir

q Removes empty directories

q Syntax: rmdir directory...

q An error will be reported if the directory is not

empty

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LiSt directory - ls

q List the contents of a directory

q Syntax: ls [-aAcCdfFgilLqrRstu1] filename

u a - List all entries, without this, files beginning with a .

are not listed

u c - Sort on time of last edit

u l - List in “long” form, giving mode, number of links,

owner, size, and time of last modification

u R -Recursively list subdirectories encountered

u s - Give size of file in kilobytes

u t - Sort by time modified, latest first

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Change Directory - cd

q Change current working directory

q Syntax: cd [directory]

u Without argument, changes to your login directory

u Otherwise changes to directory

6666

Absolute Pathnames

q Every file has a pathname

q A pathname is built by tracing a path from the root

directory, through all intermediate directories, to

the file

q String all the filenames in the path together,

separating them with slashes ( / ) and proceeding

them with the root directory ( / )

q Example: /usr/src/cmd/date.c

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Path Names

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Relative Pathnames

q Every directory has two intrinsic directories

u . (this directory)

u .. (the parent directory)

q These make using relative pathnames easy

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inode

q inodes (or index nodes) contain information about

files

q inodes do not contain path or file name

information

owner krf

group 300

type regular file

permissions rwxr-xr-x

last accessed Aug 23 1999 1:45 PM

last modified Jul 4 1999 9:17 AM

size 6030 bytes

number of links 2

disk addresses

7070

LiNk - ln

q Create a pseudonym for an existing file

q Syntax: ln [-fs] filename [linkname]

u f - force a hard link to a directory, only available to

supersuser

u s - create a symbolic (soft) link

q Hard links are default, they create a pointer to the

file

q Symbolic, or soft links, create an indirect pointer

to the file via the pathname

u Although only the superuser can create a hard link to a

directory, any user can create a soft link

u Soft links also work across file systems

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Why Hard and Soft Links?

q Hard links all have equal status

u When a file with hard links is deleted, the actual file

remains until all of the hard links have been deleted

q Soft links can have the original file deleted while

soft links still remain

q Soft links can also be confusing when used to

change directories

u Suppose you have a soft link called My_Dir that points

to your home directory, /home/krf and you cd My_Dir

u Then, if you execute pwd, it shows /home/krf!

u pwd shows the name of the linked-to directory rather

than the name of the link

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Why Not Just cp?

q ln creates a pseudonym for the given file

u No new inode is created

u Only one copy of the actual file exists

u Modifications via either filename affect the file

q cp creates a new copy of the given file

u A new inode is created

u Twice as much disk space is used

u Modifications to the copy are not reflected in the

original

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touch

q Update the access and modification times of a file

q Syntax: touch [-c] [-f] filename ...

u -c - Do not create filename if it doesn‟t exist, default is

to create filename

u -f - Attempt to force the update in spite of read/write

permissions associated with filename

q Why would you want to do this?

u This is particularly useful in software development

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conCATenate file(s) - cat

q Concatenate files to standard output

q Syntax: cat [ -benstuv ] [filename...]

u b - number all lens except blanks

u e - display non-printing characters and $ at end-of-line

u n - number all lines

u s - substitute a single blank line for multiple adjacent

blank lines

u t - display non-printing and tab characters

u u - unbuffered

u v - display not printing characters

l ^X for Control-X

l M-X for non-ASCII characters with high bit set

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more

q Page through a text file

q Syntax: more [-cdflsu] [-lines] [+linenumber]

[+/pattern] [filename...]

u c - clear screen before displaying

u d - display error message rather than ringing bell if an

illegal command is used

u f - do not fold long lines

u l - do not treat formfeed characters as page breaks

u s - squeeze multiple adjacent blank lines into one

u u - suppress underlining escape sequence

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head

q Display the first few lines of a specified file

q Syntax: head [-n] [filename...]

u -n - number of lines to display, default is 10

u filename... - list of filenames to display

q When more than one filename is specified, the

start of each files listing displays

==>filename<==

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tail

q Displays the last part of a file

q Syntax: tail +|-number [lbc] [f] [filename]

or: tail +|-number [l] [rf] [filename]

u +number - begins copying at distance number from

beginning of file, if number isn‟y given, defaults to 10

u -number - begins from end of file

u l - number is in units of lines

u b - units are blocks

u c - units are characters

u r - print in reverse order

u f - if input is not a pipe, do not terminate after end of file

has been copied but loop. This is useful to monitor a

file being written by another process

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Word Count - wc

q Display a count of lines, words, and characters

q Syntax: wc [ -lwc ] [ filename ... ]

u l - count lines

u w - count words

u c - count characters

q Example:

clyde%wc testfile

7 43 168 testfile

clyde%

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Metacharacters

q Characters with special meaning to the shell

q *, ?, [...],

q * matches any grouping of zero or more

characters

q ? matches any single character

q [...] allows matching a range of characters

u [0-9] matches any digit

u [A-Z] matches any capital letter

u [a-d] matches a, b, c, or d

u [aeiou] matches any vowel

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history

q Display the history list in the C or Korn shells

q Syntax: history [ -hr ] [ n ]

u h - display history list without leading numbers

l used to produce files for input as a script

u r - display the history list in reverse order with most

recent command first

u n - number of previous commands to display

l if n is omitted, the entire history list is displayed

where the entire list length is determined by the

value of the shell variable history

Example:

set history = 40

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PaGe - pg

q Page through a file

q Unlike more, pg allows you to back up in the file

q Syntax:/usr/5bin/pg

q After each screen is displayed, it pauses, displays

a : prompt, and awaits a command

q Perusal commands

u Return or Enter - display next screen

u (+|-)number - simulate scrolling forward or backwards

number of screens

u . or CTRL-L - redisplay current screen

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Searching with pg

q [i]/pattern/ - search forward for the ith occurrence

(default i=1) of pattern

q [i]^pattern^ or [i]?pattern? - search backwards for

the ith occurrence (default i = 1) of pattern

q After searching, pg will normally display the line

containing pattern at the top of the screen

q h displays summary of commands

q q or Q exits

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CoPy file(s) -cp

q Syntax: cp [ -ip ] filename1 filename2

cp -rR [ -op ] directory1 directory2

cp [ -iprR ] filename ... directory

u i - interactive, prompt for confirmation whenever the

copy would overwrite an existing file

u p - preserve, duplicate not only the file contents but

also modification time and permission modes

u r or R - recursive, if any of the source files are

directories, copy the directory along with its files,

including any subdirectories and their files

8484

Forms of cp

q cp [ -ip ] filename1 filename2

u copies filename1 onto filename2

q cp -rR [ -op ] directory1 directory2

u recursively copies directory1, along with its contents

and subdirectories, into directory2

q cp [ -iprR ] filename ... directory

u copies filename(s) into directory

q cp refuses to copy a file on top of itself

q Beware of a recursive cp like this

clyde%cp -r /home/krf/src /home/krf/src/backup

u Why?

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MoVe file - mv

q Move or rename files

q Syntax: mv [ - ] [ -fi ] filename1 filename2

mv [ - ] [ -fi ] directory1 directory2

mv [ - ] [ -fi ] filename ... directory

u - - interpret all following arguments as filenames. This

allows filenames that begin with a minus sign

u f - force, overriding mode restrictions and the -i option.

Also suppress warning messages about modes that

would restrict overwriting

u i - interactive, displays the name of the file or directory

with a ? if the move would overwrite an existing file or

directory

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cp Versus mv

q mv simply changes the filename or absolute

pathname of the affected files, the file‟s inodes

are not changed

q cp creates new files so new inodes are created,

unless the copy is overwriting an existing file

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Line Print - lp, cancel

q lp arranges for the named files and associated

information (called a request) to be printed on a

line printer

q cancel lp requests

q Syntax: lp [-ddest] [-nnumber] [-ooption] [-ttitle]

filename

cancel [ids]

q lp displays an id that identifies the print request

u cancel uses this id to cancel a specific print request

8888

lpr

q lpr sends a job to the printer via the print spooler

q Syntax: lpr [-Pprinter] [-#copies] [-Ttitle] [-h]

filename

u -P - desired printer as listed in /etc/printcap

u -# - number of copies

u -T - title

u -h - suppress burst page

u filename - file to print

q lpr has many more options and capabilities

u See the man page for more info

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Line Printer Queue - lpq

q Displays the queue of printer jobs

q Syntax: lpq [-Pprinter] [-l] [+[interval] [username...]

u -P printer queue to display, default is

defined by environmental variable

PRINTER, or system default printer if

PRINTER isn‟t set

u -l display queue information in long format

u + interval displays the queue every interval

seconds until queue is empty

u username… displays jobs for username(s)

q Example of lpq output

Rank Owner Job Files

active krf 143 test.txt

9090

Line Print ReMove - lprm

q Remove files from the specified print queue

q Syntax: lprm [-Pprinter] [-] [job# …]

u -P specifies which printer queue

u - remove all jobs owned by you

u job#… remove specified job numbers, or ids

q Example

lprm -Pps 144 removes job # 144 from ps queue

lrpm -Pversatec - removes all my pending jobs from

versatec queue

lprm 144 removes job # 144 from default

printer queue

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file

q Attempts to determine the type of a file by

examining it‟s contents

q Syntax: file [-ffile] [-L] filename…

u -ffile get list of filenames to check from file

u -L if filename is a link, check the link

references rather than the link itself

u filename... name of file(s) to check

q file is good when you have no idea what a file is

u listing an executable or binary file to see what is in it

can mess up your terminal display, and using an editor

is more work

9292

CHange file MODe - chmod

q Changes access permissions (mode) of a file

q Syntax: chmod [-R] mode filename…

u -R recursively descend through directory

arguments, changing the mode for each file

u mode new value for file access permissions

mode, either octal or symbolic

u filename… filename(s) or directory(s) name to

modify

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Access Permissions

q Each file and directory has a set of access

permissions associated with it

q You can see them by using the long form of ls

(ls -l)

q Format is srwxrwxrwx

u s is special, l for links, d for directories, t for sticky bit

u r is read permission

u w is write permission

u x is execute permission

q Three access levels exist, in order

u User, Group, Other

9494

Access Permissions

q Only the owner (or superuser) can change the

access permissions of a file

q The execute bit must be set in order to cd into a

directory

q The shell variable umask sets the default access

permissions when you create a new file

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Octal Access Permissions

q Octal notation consists of the numbers 0-7

u In bit positions, the values of the bits are 4 2 1

u To determine the octal value, multiply the bit position

value by its contents and add them up

l 101 = 1*4 + 0*2 + 1*1 = 5

l 110 = 1*4 + 1*2 + 0*1 = 6

u To use octal access permissions, you do the same

thing for each level of permissions

l -rwxrw-r-- =(0*0)

(1*4+1*2+1*1) (1*4+1*2+0*1) (1*4+0*2+0*1) =0764

l Leading zeros can be ignored

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Symbolic Access Permissions

q Symbolic access permissions have the form

[who] op permission [ op permission] …

q Where who is

u u user

u g group

u o other

u a all

q If who is omitted, all is assumed

q op is +, -, or = for add, remove, or explicitly set

q permission is r (read), w (write), or x (execute)

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Symbolic Permissions Examples

q chmod o-w file remove write permission

from other

q chmod g+x file add execute permission to

group

q chmod u=wr file explicitly make permissions

for user read and write only (all other

bits for group are reset when = is used)

q chmod u=rwx g+rw o-w file

explicitly gives user all permissions,

adds read and write to group and

removes write from other

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Background Processes Using &

q The simplest way to create a background

process is to invoke the command with a trailing &

q Example:

% sort addresses > mail_list &

[1] 21885

%

u This will sort the file addresses in the background and

place the results in the file mail_list

u 21885 is the unique pid of this instance of the sort

process

u [1] is the job number that is assigned by the current

shell

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wait

q What if you initiate several background processes

and then you decide that you need to wait until

they have all finished before doing something?

q wait will make the shell wait on all the background

processes to complete before giving you another

prompt

u If wait immediately returns a prompt, there are no

processes executing in the background

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kill - signal a process

q kill is somewhat strangely named

q Syntax: kill [-sig_no] pid

kill -l (display list of signals)

u -sig_no - signal number to send

u pid - process id of process to receive signal

q Default sig_no is 15, or request-process-

termination

q kill -9 pid terminates the process with extreme

prejudice

q As usual, you can only kill your own processes

unless you are the superuser