April 20, 2023 CIS 118 Intro to UNIX

What’s a Unix?

• Unix is an Operating System

• Designed for high-traffic usage

• Many variants– Linux, BSD: free versions

• Spelled either Unix or UNIX

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

Multi-Computer, Multi-User

Servers

Clients

April 20, 2023 CIS 118 Intro to UNIX

The Shell

Person

Operating System

SHELL

User types commands into shell

Run progra

m

Shell translates commands to machine code

1100101

0110010

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

Interesting Commands

• Communication– write– mail– talk

• Useful– man– who– date– cal

• Printing– lpr– printer rm# file

• Network– ping– traceroute– nslookup– hostname

April 20, 2023 CIS 118 Intro to UNIX

E-mail Commands

• mail: read/send mail

• pine: read mail

• forwardmail: forward mail

• blockmail: block mail

• procmail: proc[ess] mail

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

What’s on your server?

• List users online– users– who– last [user]– finger [user]

• FAS-specific– ph [full name]– rwho [user]

• What are people doing?– w– ps [aux]

• Managing your own processes– fg/bg– kill [process #]

April 20, 2023 CIS 118 Intro to UNIX

Communicating on UNIX

• write user[@machine]: send a one-way message

• talk user[@machine]: have a conversation

• mesg [y | n]: let people talk to you

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

Hierarchical File System

b in

b in lo ca l

u sr e tc

a b

cd u an

d e

c

h o m e

/

/home/c/d/cduan

April 20, 2023 CIS 118 Intro to UNIX

Remote Home Directories

home05

home06

home07

is01

is02

smtp

webmail

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

File System Commands

• Browsing commands

• File Manipulation Commands

• File Viewing/Editing Commands

April 20, 2023 CIS 118 Intro to UNIX

File Browsing

pwd print working directory

% pwd/home15/c/d/cduan

cd change directory

cd .. up 1 directory

% cd /usr/bin% pwd/usr/bin

ls list files

ll “long” listing

% lsfile1 file2 file3file4 file5 file6

April 20, 2023 CIS 118 Intro to UNIX

File Manipulation

• mv: move file(s)– mv file1 file2 rename file1 to file2– mv [file…] dir move files to directory

• cp: copy file(s)

• rm: remove file(s)

• mkdir: create a directory

• rmdir: remove a directory

April 20, 2023 CIS 118 Intro to UNIX

File Viewing/Editing

• cat, more, less, head, tail: view (parts of) files

• grep word [file…]: find words in files

• vi: edit files (see tutorial)– Or use that pico program

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX

• Basic Concepts

• Common Commands

• Multi-User Functions

• File System– Structure– Commands– Security

UNIX>_

April 20, 2023 CIS 118 Intro to UNIX

File System Security

Problem: multiple users, one machine

1. How do we keep data private?

2. How do we make data public?

3. How do we make data partially public?

April 20, 2023 CIS 118 Intro to UNIX

File System Security

Solution: UNIX permissions scheme

• Three levels of people– Self, group, others

• Three levels of protection– read, write, execute

April 20, 2023 CIS 118 Intro to UNIX

File Permission Types

Level For Files For Directories

read Able to read file contents

Able to list files in

directory

write Able to modify file contents

Able to create/

remove files

execute

Able to run file as a program

Able to use files in

directory

April 20, 2023 CIS 118 Intro to UNIX

User Permission Levels

• Self: yourself

• Group: members of pre-defined system groups (student, ua, etc.)– Generally not treated specially

• World: every user on the system

• Root can read/write everything!

April 20, 2023 CIS 118 Intro to UNIX

Viewing File Permissions: ll

-rwxr-xr-x 1 cduan ua ...

self grou

p

world

owner

group

read

write execut

e

No write permission for world

April 20, 2023 CIS 118 Intro to UNIX

Changing Permissions: chmod

Level Self Group World

read 4 4 4

write 2 2 2

execute 1 1 1+

chmod 755 [file…]

April 20, 2023 CIS 118 Intro to UNIX

Common chmod Values

Private file

Private directory

Public file

Public directory

Public directory, no listing files

600

700

644

755

711

April 20, 2023 CIS 118 Intro to UNIX

Using UNIX: Final Remarks

• Where to get help– man pages– Internet– User Groups