Download Lesson 8

Introduction to Unix
Lesson 8
Introduction to UNIX
What is an operating system?
Input/
Output
Command
Interpreter
Accounting
Communications
Operating
system
Security
Program
Development
Tools
Memory
Management
Scheduling
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
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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
UNIX Variants
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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
Debian—released by the Debian project Sept 1993
Ubuntu – based on Debian, released 2004
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
sh date who
hosts passwd hosts.equiv
usr
src bin games
Redhat
dev
tty1 hda1 cdrom
home
user1 user2 user3
file1 .rhosts
LINUX
• A number of different versions
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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
Editors
Program
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
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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—historical:
• Gnome
• KDE
Gnome
KDE
Some common CLI commands
• ls – provide list of files in current directory
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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
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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
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(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
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(-o says executable version to be called hello)
• now to invoke we type “hello”
Makefiles
File named makefile
game: main.o edit.o
gcc –o game main.o edit.o
main.o: main.c
gcc –c main.c
edit.o: edit.c
gcc –c edit.c
$ make
gcc –c main.c
gcc –c edit.c
gcc –o game main.o edit.o
$
If we were to edit main.c, then
$ make
gcc –c main.c
gcc –o game main.o edit.o
$
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
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Questions