Operating Systems An Introduction to Operating Systems Using UNIX CMSC 104, Lecture 03

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Operating Systems

An Introduction to Operating Systems

Using UNIX

CMSC 104, Lecture 03 1

What is an Operating System (OS)?

• A computer program

• Performs many operations:

• Allows you to communicate with the computer

(tell it what to do)

• Controls access (login) to the computer

• Keeps track of all “processes” currently running

• At this point, your main concern is how to communicate with the computer using the OS

CMSC 104, Lecture 03 2

How Do I Communicate With the

Computer Using the OS?

• You communicate using the particular OS’s

user interface

• Graphical User Interface (GUI) - Windows

• Command-driven interface - DOS, UNIX,

Linux

• We will be using Linux, which is very similar to

UNIX

CMSC 104, Lecture 03 3

How Do I Communicate With the

Computer Using the OS?

• When you

log in user prompt

to the Linux system here, a will be displayed: linux1[#]% _ where # is the “number” of the command that you are about to type

• If this prompt is not on the screen at any time, you are not communicating with the OS

CMSC 104, Lecture 03 4

UNIX Overview

Files

Directories

Commands

Resources o books o links from course homepage

CMSC 104, Lecture 03 5

UNIX Files

A file is a sequence of bytes

Created by text editor (emacs, pico)

Created by other programs

May contain a program, data, a document, or other information (but all are text)

Files which contain other files are called

“directories” (sometimes called folders)

CMSC 104, Lecture 03 6

Filenames

Restrictions o no blanks, no

metacharacters

, length o case sensitive

Wildcards

: * ?

CMSC 104, Lecture 03 7

Directories

• Directories can contain files or other directories called

subdirectories

• Directories are organized in a

hierarchical

fashion

• They help us to keep our files organized

CMSC 104, Lecture 03 8

Directories

/afs/umbc.edu/users/b/o/bob junk pie recipes cookie apple peach

CMSC 104, Lecture 03 choc_chip

9

Directories

Your

home directory

is where you are located when you log in

The

current directory

is where you are located at any time while you are using the system

Files within the same directory must be given unique names

paths

allow us to give the same name to different files located in different directories

Each running program has a current directory and all filenames are implicitly assumed to start with the name of that directory unless they begin with a slash

CMSC 104, Lecture 03 10

Subdirectories

Organizing your files

For example o make a subdirectory for CS104 o make subdirectories for each project

CMSC 104, Lecture 03 11

Moving in the Directory Tree

.

(dot) is the current directory

. .

(dot-dot) is the

parent directory

UNIX command

cd

“change directory”

Use dot-dot to move up the tree

Use directory name to move down

Use complete directory name (path name) to move anywhere

CMSC 104, Lecture 03 12

Commands

• cp, mv, ls, rm, more, cat, cd, pwd mkdir, rmdir, passwd, man, lpr redirection: | < > ctl-c, ctl-d

CMSC 104, Lecture 03 13

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