Introduction to Unix

Lesson 8

Introduction to UNIX

What is an operating system?

Operatingsystem

Communications

Accounting

Input/Output

CommandInterpreter

Security

Scheduling

MemoryManagement

ProgramDevelopment

Tools

The UNIX operating system• Scheduler

• Allows more than one person to use the system at the same time.

• Shares the system’s resources among the users, allowing each a slice of the resources.

• Programs running in memory are called processes• File system

• A directory structure used to organize files in UNIX• Shell

• The UNIX system’s command interpreter• A program that reads the lines you type and interprets them.• Sits between the user and the internals of the system

History of UNIX• In 1965 Bell joined GE and MIT in a project to develop a new

OS called Multics• Wanted to provide simultaneous computer access to a large community of

users• A smaller version written by some at Bell including Ken

Thompson and Dennis Ritchie for PDP-7, later ported to PDP-11 (in 1971).• Name came as play on Multics – Unics, or UNIX

• Thompson started to develop a Fortran compiler for Unix, but ended up developing B language.• B was an interpretive language with the inherent speed problems

characteristic of such languages• Decided to improve on it so created next language, C

• In 1973 Unix rewritten in C

Unix Popularity grows…• At the time (70’s) AT&T was not allowed to market computer

products.• Universities were requesting copies of Unix for educational

purposes.• By 1977 Unix system sites had grown to about 500 of which 125

were universities.• Unix popular in phone companies and you can see heavy

influence in phone equipment.• In 1982 AT&T combined several versions and created UNIX

System III. Other additions were made and System V was born in 1983.

• UC-Berkeley had developed a variant for VAX machines which was called BSD.

• By 1984 there were about 100,000 sites running UNIX

The variations of UNIX• BSD (Berkeley Software Distribution)• XENIX – version for microcomputers developed by MS • SunOS – UNIX variation by Sun• POSIX – an independent effort to define a standard OS

environment – actually a family of standards.• System V release 4 (SVR4) – combined elements of System V

release 3, BSD, SunOS, and Xenix to provide a common environment

• Solaris – a version for Sun, 2.3 was POSIX compliant.• Linux – PC version by Linus Torvalds in 1991. • IRIX – a proprietary version used by Silicon Graphics• HP-UX – variant developed and sold by HP• AIX – IBM’s version for use on IBM workstations

Some differences to be aware of for Microsoft OS users

• UNIX is case sensitive, thus• CC FILE1 is not the same as cc file1

• UNIX is open source, thus source code is readily available for it.

• UNIX is not proprietary (as a whole) so its evolution is not controlled by a single organization/corporation

• NT/2000 and UNIX are both multitasking, but UNIX also is multiuser (supports simultaneous users)

UNIX file system

/

bin etc usr dev home

sh date who hosts passwd hosts.equiv src bin games tty1 hda1 cdrom user1 user2 user3

Redhat file1 .rhosts

LINUX• A number of different versions

• Redhat• BSD• Slackware• Caldera• Debian

• Incorporates the use of shells• Bash (Bourne again shell) variation on traditional

Bourne shell – default.• pdksh (Public Domain Korn Shell) variation on original

UNIX Korn shell.• tcsh – an enhanced version of the original Berkley C

shell csh.

Some common Linux functions

Function ProgramEditors vi, emacs

Shells bash, tcsh, pdksh

Text processing tetex, troff

Tools awk (gawk– file/DB manipulation)

Network programs telnet, ftp

Electronic mail Elm, Pine

Programming languages available

• C/C++• JAVA• LISP• Prolog• Ada• Perl• Tcl/Tk• Fortran-to-C translator• Pascal-to-C translator• Compiler tools (lex and yacc (flex and bison))

Interacting with the Linux OS

• The Shell is the interface between the user and the Linux OS

• How you interact with the system will depend on how the system was configured.• Command Line Interpreter• GUI

• Gnome• KDE

Gnome

KDE

Some common CLI commands• ls – provide list of files in current directory

• ls -l provides additional info on each file• ls -a lists all files in the directory (hidden)• ls -al combines the above two• ls doc* lists files that start with doc

• Wildcards: * for any set of characters, ? for single character.

• cp – copy a file• cp fileone filetwo copies fileone into filetwo, creating

filetwo if it needs to• cd – change directory

• cd docs changes current directory to docs• cd / changes to root directory• cd .. changes to parent directory

Some more commands

• rm – remove (delete) a file• rm fileone deletes fileone• rm file* deletes all files that begin with ‘file’• rm * deletes all files• rm * file deletes all files (space between * and file)

• cat – display contents of a file• cat fileone displays contents of fileone

• more – displays contents of a file screen by screen• more fileone displays contents of fileone

And just a few more commands

• mv – renames or moves a file• mv fileone newname renames ‘fileone’ to be ‘newname’• mv fileone docs/fileone moves fileone from current

directory to ‘docs’ directory• mv fileone docs/newname moves fileone from current

directory to ‘docs’ directory and renames it• mkdir – create a directory in current directory

• mkdir docs creates a directory called ‘docs’• mkdir /home/gwhite/docs creates a directory called ‘docs’

in directory /home/gwhite• rmdir – remove directory

• rmdir docs removes directory called ‘docs’

A couple more quick Linux commands

• pwd • lists current working directory

• chmod 777 <filename>• Changes permission of <filename> to allow

anybody to access it• chmod 700 <filename>

• Changes permission of <filename> to allow only the owner to access it

And more

• who – lists all users currently connected along with when, how long, and where they logged in.

• finger – provides information about other users on your network

• logout – logs you out of the system (ends your session)

• halt – shuts down Linux

Some commands everybody should know

• passwd – used to change your password.• man <topic> – used to obtain information

about a topic• apropos <keyword> – used to find commands

that are related to keyword

Devices

• Files and directories contained on different HW devices (e.g. floppy drives, CD’s) and hard disk partitions are called file systems.

• The Linux partition used to install the Linux system on is called the root partition.

• The root partition ( indicated by a single slash, /) contains the main file system and user subdirectories.

• To access files on another file system, say a CD-ROM, you need to attach that file system to your main system.

• Attaching a file system is called mounting the file system.

Mounting a file system• The first step is to set up an empty directory to which you

want to mount the file system.• Most Linux distributions, including Red Hat, have pre-created

directories for this purpose.• /mnt/cdrom• /mnt/floppy

• To mount a floppy, for example, you would:• mount device mountpoint

• mount /dev/fd0 /mnt/floppy

• When done, you need to unmount the device:• umount device-or-mointpoint (*** notice the spelling ***)

• umount /mnt/floppy• Make sure you aren’t still using that device or it won’t let you

unmount it.• These are sysadmin commands and not user commands!

Archive files

• The tar utility (tape archive) creates archives for files and directories.

• The tar utility is ideal for making backup copies of files or for combining several files into a singe file for transmission.

• Command examples:• tar cvf myarch.tar mydir

• Creates archive of mydir directory and calls the single file myarch.tar (the ‘v’ displays each filename as it is archived).`

• tar xf myarch.tar• Extracts all files and subdirectories from the file myarch.tar

Compressed Archives• A compressed archive is an archive file created

with tar and then compressed with gzip. It will generally have .tar.gz as extensions.

• To install such a file, you first need to uncompress it with gunzip, then extract it with tar.• gunzip savefile.tar.gz• tar xvf savefile.tar

• Instead of gunzip, you may also use gzip –d• You may also combine both with:

• tar xzvf savefile.tar.gz

Installation of software packages• rpm is used to manage and install software

packages.• The –i option is used to install software

• rpm –i newsoftwarefile

• RPM stands for “RedHat Package Manager”• An RPM software package operates as its own

installation program for a software application.• Linux software applications often consist of multiple

files that may need to be installed in different directories.

• The program is most likely installed in /usr/bin• Installation may also require changes to config files

C

• gcc (compiler for C), g++ (compiler for C++)• A sample C program (stored in file hello.c)#include <stdio.h>int main() { (void) printf(“Hello, World!\n”); return0; /* just to be nice */ }

• gcc –o hello hello.c• (-o says executable version to be called hello)

• now to invoke we type “hello”

Makefiles

game: main.o edit.ogcc –o game main.o edit.o

main.o: main.cgcc –c main.c

edit.o: edit.cgcc –c edit.c

$ make gcc –c main.cgcc –c edit.cgcc –o game main.o edit.o$

If we were to edit main.c, then

$ make gcc –c main.cgcc –o game main.o edit.o$

File named makefile

Editing -- the vi editor

• Still one of the most widely used editors in the UNIX world today

• A keyboard-based editor (emacs is another)• Uses the keyboard to specify commands and

receive user input• Certain keys perform certain functions

• Delete, insert, cursor movement, save, quit

vi commands

• To edit a file with vi• vi <filename>• If <filename> exists it will load that file, if it doesn’t it

will create it.• To exit, type ‘:’

• This moves the cursor to the command line at the bottom of the screen, then• ‘q’ quits the editor• ‘q!’ quits without saving• ‘w’ will save the file

vi commands• The vi editor in Linux (actually Vim) allows you to use

the arrow keys to move around.• To insert text

• ‘a’ enters text after the cursor• ‘i’ enters text before the cursor• To stop entering text, hit <esc>

• To delete text• ‘dw’ deletes the word the cursor is on• ‘dd’ deletes the line the cursor is on• ‘x’ deletes the character the cursor is on

• <del> and <backspace> also work

• To search• /<pattern> searches forward for <pattern>• ‘n’ repeats previous search