Lecture 17 - Introduction to UNIX

Objectives

To introduce the UNIX Operating System

History
The UNIX Network
Some Features of UNIX
The UNIX File System
General UNIX Commands
Simple File Maintenance Commands
UNIX Command Summary

1. History

Unix started about 1970, when Ken Thompson and Dennis Ritchie (at AT&T, Bell Labs) wanted a computer to use as a general productivity tool (word processing etc) that many users could use at the same time. They had a Digital Equipment PDP7, but were dissatisfied with the operating system. They were working on an OS called Multics which would have multiuser capabilities, but it became large and unwieldy so Bell Labs dropped the project. So they wrote the first version of Unix (The original name of Unix was Unics which is a pun on Multics). In the process, they also designed the C programming language.

Unix was made available to research and education and spread widely. It has been substantially enhanced over the years. It is available for most current computers (including versions for the PC and Macintosh). In 2001 Apple Computers introduced the latest version of the Macintosh operating system, MacOS 10 also called Mac OS X because the wonderful graphical interface of the Mac is built on top of a full Unix OS (that controls memory management, disk access, interfacing with peripheral devices etc.)

2. The UNIX Network

The System Administrator is Howard Cock (h.cock@latrobe.edu.au) located in DSSG. SITS can help with problems regarding the UNIX networks.
Mainly used in programming subjects
The main UNIX lab that we will be using is room B1.11 (Linux PCs). The other UNIX lab is 1.08 (Apple Macs)

Servers

There are two main servers, redgum for student use and ironbark for staff.

redgum & ironbark

Apple Xserve (these act as UNIX servers to any UNIX workstation, whether they be PCs, Macs,...)
Dual G5 processors
2GB RAM
Total disk capacity is in terabytes (1000's of gigabytes)
6000 student accounts
Disk space limited to 50MB per student account
Backed up to hard disk nightly
- the main purpose of this is to restore the system if there is a major failure - not to restore files accidentally deleted by students

Workstations

The UNIX workstations we will be using in this subject are located in lab B1.11 (Computer Lab 3, also known as itlab3) and are networked into redgum's disk drive where your files are stored. The CS & CE Department has a number of different types of UNIX workstations, running different flavours of UNIX.

24 Dell (IBM compatible) workstations (2GB RAM, 19in monitors, 256MB video memory, DVD burners)
- Operating System: Linux
- Named indya, indyb, ...
- Room B1.11
24 Apple iMacs (2GB RAM, 20in monitors, 256MB video memory, DVD burners)
- Operating System: Mac OS X
- Room B1.08

Logging On & Passwords

Students automatically have accounts on the Macs (B1.08) and on redgum. To log onto a Mac use your student on-line username (in lowercase) and password.

Registering for an account on the Linux Workstations

Before you can use the workstations in the Linux lab (B1.11) you need to register for an account.

To register for an account in the Linux lab. apply online at http://hopper.bendigo.latrobe.edu.au/unix_account (You will need your student online username and password). You will receive an email and you need to click on the link in that email.

Note: if you change your student on-line password after you create your account for the Linux lab, the password in the Linux lab will remain the same as it was.

3. Some Features of Unix

Unix has a fairly simple design philosophy. Understanding that philosophy helps to iron out any problems that you may have.

It is Multi-User:

Many users can use a Unix computer at the same time. They share it through what is called time sharing. The operating system (Unix) protects each user's data, programs, actions, etc from interfering with others.

It has individual user accounts:

Users have usernames and passwords which identify them when they log into the system. The username identifies the user and allows access to the files owned by the user.

Unix is command driven:

When you log into a Unix system, you are presented with a shell (a command interpreter).
This is a program which accepts commands from the user and then executes them.
A number of different shells are available, but commonly used shells here are csh or tcsh.
The user typically sees a prompt and types in a command. The shell reads the command, and causes the appropriate action to occur. Typically, a command is the name of a program which is to be executed, together with any arguments needed.
- The name of the shell program you are using is 'tcsh'.

Unix has a Hierarchical File System (see below)

4. The Unix File System

Unix has a Hierarchical File System:

The Unix file system is made up of directories, plain files (normally referred to simply as files) and special files.
Directories are a kind of file that contains information about where other files (including other directories) are.
So, to find a file, one must read the directory which contains its location information.
Of course, since the directory is a file, we must first read the directory which contains that location information etc.

There is a special root directory where it all starts:

The is a special directory called "/" (slash) which is well known by Unix.
- It, in turn, contains the location of other directories (an example is bin which contains some basic command programs).
Slash (/) contains the directory Users, which contains the directory of fjsmith, which in turn contains the location of user fjsmith files.
- This directory is referred to as fjsmith's home directory and is referenced as /Users/fjsmith

We refer to files by their absolute pathnames:

A file can be referred to by its full or absolute pathname: this is the list of directory names starting from the root directory (slash) needed to find the file.
So, if the user fjsmith wishes to refer to a file in her home directory called afile.txt, she would type the full pathname: /Users/fjsmith/afile.txt
This is a bit tedious, so we allow a simpler way.

Files can be referred to by relative pathnames:

When you login, your working directory is set to your home directory.
If a pathname is typed without a leading slash, it is taken from the working directory, rather than from the root directory (slash).
So, a filename on its own (without any slashes) refers to a file in the present working directory (pwd). eg:
afile.txt

Not all files are stored on the local machine:

The PC environment differentiates files from different physical locations with a volume letter. eg. A: for a floppy, C: for the local hard disk, H: for your home directory. Each of these volumes has its own directory tree.
Unix supports only one directory tree. However, branches of the tree can refer to files on another computer, or even to files on an attached floppy disk.
Files from one computer are mounted (by the system administrator) onto the file system of another computer using NFS (the Network File System).
Your home directory and your files are stored on redgum and all of the workstations have these files from redgum mounted in the same structure as they appear on redgum. This means that if you work on one machine and then move to another, the files are the same.
Every workstation has its own copy of the OS. Therefore, changes that are required to the OS have to be replicated across all UNIX workstations of that type

Structure of LTUB's Unix files as you see them from a workstation:

Directory	Description
/	Root directory
/dev	device drivers for terminal, printers etc.
/etc	local - commands (normally this holds the including the password file 'passwd' )
/proc	local - list/data of currently running processes
/sbin	local - Unix command files
/tmp	local - directory for temporary files
/Users	NFS redgum - directory for all students' stuff
/Users/fjsmith	NFS redgum - student fjsmith's home directory

5. General Unix Commands

As noted above, Unix is basically a command driven operating system. This means that users get the actions they want by giving commands. Commands all follow the same basic form: the first word is the name of the command. This is followed by options and arguments. Options are usually the minus sign "-" followed by some letters which change the action of the command. Arguments are usually the names of files on which the command is to act. Some useful commands are set out below:

exit: closes the current session (logs out of the session) - you can also use Ctrl+D to logout.

ls [-al]: lists the files in the current directory, similar to the old DOS 'DIR' command. eg:; ls -a all option lists all files, including any whose name start with a dot (which are normally hidden).; ls -l long option lists more information about each file.; ls -al all and long options (same as: ls - a -l)

pwd: gives the full pathname for the working directory

cd pathname: changes the working directory to the new directory specified by the pathname argument given. Note that "." (a dot on its own) refers to the current working directory, and ".." (two dots) refers to the parent directory - the directory which contains the location information for the current working directory.

less filename: copies the contents of the file to the terminal screen, one page at a time. Note that if this produces odd results, or complaints about the computer not knowing what kind of terminal you are using, you may need to set your environment - see the tutorial.

cat filename1 filename2 filename3 ....: prints the contents of the files onto stdout (the screen), one file immediately after the other.

man commandName: shows the online manual entry for the command.

man -k keyWord: lists the commands that may have to do with the keyWord given. eg:; man -k copy lists all commands that have anything to do with copying
man -k copy file lists all commands to do with copying and/or files (whew!)

ps [-ef]: shows all current processes - including the ps process that generates the list.; '-e' option shows all processes, '-f' provides a full listing; so, 'ps -ef' lets you see what everyone is doing:-).

who: lists the users who are currently logged onto the system

whoami: identifies the current user (useful if you find an unattended machine)

file pathname: tells you what kind of file the argument is

df: shows the NFS mountings including the amount of disk free on your system

du: shows how much disk usage you have consumed.

6. Simple File Maintenance Commands

To maintain an account a user needs to know how to create, delete, copy, move and rename files.
For good house-keeping the user also needs to know how to create subdirectories and how to move files between them.
Simplified versions of some file maintenance commands are shown below

Listing your files

Command: ls
Options are -a for all files and -l for a longer listing. eg:
ls -al
The long listing provides extra information such as whether a file is a directory of an ordinary file, permissions, owner, size and last date modified.
ls actually has 28 different options! Read all about them by 'man ls'
Use 'ls [-al] fileName1 fileName2 ...' to only view specified files' information

Creating a file

Usually performed by an application program, in the same way that your word processor creates files in the PC environment
Text editors are useful for creating text files:-).
- common text editors are called nedit, pico, ee (for easy-editor), and vi. eg:
  nedit myfile.txt creates the file myfile.txt that you can edit within nedit
Graphics files can be created with graphics programs, such a xv and gimp

Deleting files

Description: Removes (deletes) a file or files
Command Format: rm filename
Example: rm myholidays.txt

Copying a file

Description: copies a file or files. .
Command Format: cp oldFileName newFileName
Example: cp test1.java test2.java
Note: Requires two arguments. specifying only one file name is an error

Moving or Renaming files

Description: moves or renames a file or files..
Command Format: mv oldFileName newFileName
Examples: mv test1.java test2.java
Warning: the oldFileName no longer exists.
Note: Requires two arguments. specifying only one file name is an error

Viewing the contents of a file

Description: views the contents of a file. The command to use depends on the type of file e.g.: a graphical file requires a graphics program
To view the contents of text files use less or cat:
Command Format:
- less fileName
- cat filename
Examples:
- less test1.java
- cat test1.java

Changing Directories

Description: Change the current working directory. The directory can be a relative or absolute pathname
Command Format: cd dirName
Examples:
- cd public_html
- cd /Users/tjwhitfort
Note: all accounts have a public_html directory that is your home web page directory

Executing (or Running) a Program

Simply type the name of the program at the command line.
Unix does not really differentiate between programs and commands. In fact, commands are stored as programs!

Editing a text file

text files contain only standard text characters (or keyboard characters)
are edited by a text editor
terminal-based text editors available include:
- nedit filename
- pico filename
- vi filenamevi is a very powerful, universal command-based text editor that requires knowledge of the commands to work. As it is fast it is ideal for text editing through a modem connection.
Program source files are simply text files and can be edited by the above text editors
Other types of files are edited by a corresponding program. eg.:
- graphics files by graphics programs
- sound files by some multimedia program

6. Web Browsers

Firefox and Konqueror are two of the web browsers that are available on the workstations in the Linux lab.

7. UNIX Command Summary

A UNIX Command Summary listing commands relevant to Programming Environment is available.

Key Points

redgum: a Server is mainly for student use
ironbark: Server used for staff accounts and CS&CE Department web pages
workstations: IBM Compatibles running Linux in the UNIX lab, and Apple Macs
Unix
- is Multi-User
- has individual user accounts:
- is command driven
- has a Hierarchical File System
Unix can be accessed from The PC Network