Introduction to UNIX

1
Introduction to UNIX
2
Introduction

• What is UNIX?
• UNIX is an operating system which was first
  developed in the 1960s, and has been under
  constant development ever since. By operating
  system, we mean the suite of programs which make
  the computer work. It is a stable, multi-user,
  multi-tasking system for servers, desktops and
  laptops.
• UNIX systems also have a graphical user interface
  (GUI) similar to Microsoft Windows which provides
  an easy to use environment. However, knowledge of
  UNIX is required for operations which aren't
  covered by a graphical program, or for when there
  is no windows interface available, for example,
  in a telnet session.
• Types of UNIX
• There are many different versions of UNIX,
  although they share common similarities. The most
  popular varieties of UNIX are Sun Solaris,
  GNU/Linux, and MacOS X. .

3
The UNIX Operating System

• The UNIX operating system is made up of three
  parts the kernel, the shell and the programs.
• The kernel
• The kernel of UNIX is the hub of the operating
  system
• It allocates time and memory to programs and
  handles the filestore and communications in
  response to system calls.
• An illustration of the way that the shell and the
  kernel work together
• suppose a user types rm myfile (which has the
  effect of removing the file myfile)
• The shell searches the filestore for the file
  containing the program rm, and then requests the
  kernel, through system calls, to execute the
  program rm on myfile
• When the process rm myfile has finished running,
  the shell then returns the UNIX prompt to the
  user, indicating that it is waiting for further
  commands.

4
The UNIX Operating System

• The shell
• The shell acts as an interface between the user
  and the kernel.
• When a user logs in, the login program checks the
  username and password, and then starts another
  program called the shell.
• The shell is a command line interpreter (CLI) -
  it interprets the commands the user types in and
  arranges for them to be carried out.
• The commands are themselves programs when they
  terminate, the shell gives the user another
  prompt ( on our systems).
• The adept user can customize his/her own shell,
  and users can use different shells on the same
  machine.
• History - The shell keeps a list of the commands
  you have typed in. If you need to repeat a
  command, use the cursor keys to scroll up and
  down the list or type history for a list of
  previous commands.

5
Files and processes

• Everything in UNIX is either a file or a process.
  
• A process is an executing program identified by a
  unique PID (process identifier).
• A file is a collection of data. They are created
  by users using text editors, running compilers
  etc.
• Examples of files
• a document (report, essay etc.)
• the text of a program written in some high-level
  programming language
• instructions comprehensible directly to the
  machine and incomprehensible to a casual user,
  for example, a collection of binary digits (an
  executable or binary file)
• a directory, containing information about its
  contents, which may be a mixture of other
  directories (subdirectories) and ordinary files.

6
The Directory Structure

• All the files are grouped together in the
  directory structure. The file-system is arranged
  in a hierarchical structure, like an inverted
  tree. The top of the hierarchy is traditionally
  called root (written as a slash / )

7
The Directory Structure
In the diagram below, the home directory of the
undergraduate student "ee51vn" contains two
sub-directories (docs and pics) and a file called
report.doc. The full path to the file report.doc
is "/home/its/ug1/ee51vn/report.doc"
8
UNIX at BC SSH Secure Shell Client

• The preferred connection method is SSH (Secure
  Shell Client) which does not transmit your
  password in the clear across the internet, as
  telnet and ftp do.
• SSH includes sftp ( Secure File Transfer Protocol
  ) and scp ( Secure Copy ). See the Andersen
  textbook for more details.
• If you are running a Linux, Unix or Mac system,
  ssh is probably available on your system.
• For MS windows users install packages are
  available at
• http//acc4.its.brooklyn.cuny.edu/sysadm/ssh/win
  /SSHSecureShellClient-3.2.9.exe
• http//acc6.its.brooklyn.cuny.edu/sysadm/ssh/win
  /SSHSecureShellClient-3.2.9.exe
• ftp//acc5.its.brooklyn.cuny.edu/pub/sysadm/SSHSec
  ureShellClient-3.2.9.exe
• These Windows products are licensed for use by
  Brooklyn College only.
• Using one of the lab's Unix machines, the command
  "lab_machines" will return a list of available
  Unix machines. i.e.
• atrium11.its.brooklyn.cuny.edu 146.245.252.11atri
  um12.its.brooklyn.cuny.edu 146.245.252120acc2.its
  .brooklyn.cuny.edu 146.245.252.72
  fldsun228.its.brooklyn.cuny.edu 146.245.252.228

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UNIX at BC - SSH

• Once SSH is installed, click on the icon and SSH
  Secure Shell (left) will appear
• Click on the Quick Connect icon this will
  bring up the Connect to Remote Host popup
• Enter the Host Name (e.g., atrium96.its.brooklyn.c
  uny.edu) and User Name and click Connect
• You will be prompted for your password
• Another popup will allow you to name the profile
  information for future reference

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UNIX at BC - SSH

• Now youre connected at ready to roll

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UNIX at BC SSH Transfer

• To transfer files between your local PC and the
  Unix machines, click on the SSH Secure File
  Transfer icon
• Click on Quick Connect and follow the same
  procedure as in connecting with SSH Shell
• You will have two windows one for your local
  machine and one for the Unix server. Drag and
  drop files from one to the other

12
UNIX at BC - Telnet

• Open a browser and enter the url
  telnet//atrium4.its.brooklyn.cuny.edu/
• This will open a DOS window, connect you to the
  colleges SUN servers and prompt you for an id
  and password
• When completed, you will see a prompt of the form
  atrium4/users1/rudowskygt
• Now youre in business

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UNIX at BC

• See David Arnows Getting Started with UNIX
  guide
• Basic commands
• ls -a-l List files in the directory
• mkdir ltdir namegt make a directory
• rm ltfilenamegt remove a file
• mv ltoldfilenamegt ltnewfilenamegt rename a file
• cat ltfilenamegt display a file
• cp ltoriginal_filenamegt ltcopy_filenamegt copy a
  file
• command gt ltoutput_filenamegt redirect the output
  of a command e.g., ls l gt list
• g xyz.cpp o xyz compiles a C program named
  xyz.c and saves the compiled progam as xyz
• exit

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UNIX at BC

• ls does not, in fact, cause all the files in your
  home directory to be listed, but only those ones
  whose name does not begin with a dot (.)
• Files beginning with a dot (.) are known as
  hidden files and usually contain important
  program configuration information. They are
  hidden because you should not change them unless
  you are very familiar with UNIX!!!
• To list all files in your home directory
  including those whose names begin with a dot,
  type ls -a

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UNIX at BC

• When you type ls -a in a directory, two special
  directories called (.) and (..) appear
• In UNIX, (.) means the current directory, so
  typing cd . means stay where you are
• NOTE there is a space between cd and the dot
• (..) means the parent of the current directory,
  so typing cd .. will take you one directory up
  the hierarchy
• Note typing cd with no argument always returns
  you to your home directory. This is very useful
  if you are lost in the file system.
• Pathnames enable you to work out where you are in
  relation to the whole file-system.
• For example, to find out the absolute pathname of
  your home-directory, type cd to get back to your
  home-directory and then type pwd
• pwd (print working directory)

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UNIX at BC

• Home directories can also be referred to by the
  tilde character. It can be used to specify
  paths starting at your home directory.
• ls /unixstuff will list the contents of your
  unixstuff directory, no matter where you
  currently are in the file system
• ls will list the contents of your home
  directory no matter where you currently are in
  the file system
• ls /.. will list the contents of the parent of
  your home directory no matter where you
  currently are in the file system

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Your Directory Structure

• Your assignments should be maintained in a
  directory tree with the following structure
• Directly beneath your home directory, there
  should be a subdirectory named cis15.
• Directly beneath cis15, there should be a
  subdirectory named homework
• Within homework, there should be a subdirectory
  for each assignment.
• Thus, your files for homework 3 will be in the
  directory home/cis15/homework/hw-3 (where home is
  your home directory
• Put all C code, input and output files in that
  directory. Subdirectories can be created as
  needed.

18
Formatting Your Code

• Please use proper indentation-- reading code is
  like reading and essay-- improperly indented code
  is like text without punctuation, capitalization,
  and the other conventions of proper writing. You
  must develop the habit of proper indentation.
• Please give some thought to your identifier and
  function names-- single letters such as i or x
  are fine for loop/array indexes or symbols in a
  mathematical equation, but beyond that, the
  variables should be names reflecting the
  data/function they hold/perform.
• The first line of output from your program should
  contain your name, Unix id, course number and
  homework number.
• Each source file you submit should have a comment
  at the top containing the same information as
  above plus the name of the file. For example
• / Ira Rudowsky /
• / rudowsky /
• / CIS 15 EM6 Spring 07 /
• / Assignment hw-1 /
• / hw-1.cpp /

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C IDEs

• One way to work on your assignments is to code
  and debug on your local machine using an IDE
  (Dec/C http//www.bloodshed.net/devcpp.html
  or CodeBlocks http//www.codeblocks.org are
  two possibilities) and then transfer you code to
  the Atrium servers. (SSH Secure File Transfer or
  Core FTP LE http//www.coreftp.com/download.html
  and selecting the SSH/SFTP option.
• To edit files on the Unix server, two possible
  editors are vi or pico (shows you useful commands
  in the editor window). The Andersen book explains
  both or you can Google tutorials for either
  editor and find numerous sources of information
  online.
• The Unix compiler is invoked by the g command
  (see below for more).

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UNIX at BC

• Most of the machines are running Solaris 9, the
  rest Solaris 8.
• The GUIs available are Sun's openwin, CDE and
  gnome.
• Both gcc and sun's compilers are available. Only
  the command line compilers are usually used.
• cc and CC are the front ends to Sun's C and C
  compilers. gcc and g are the front ends to
  gcc's C and C compilers.
• cc  -flags  or CC -flags prints available
  compiler options
• Use an editor to write the code, save the file 
  e.g., abc.c
• g test1.cpp -o test1 produces file test1 if
  there are no errors
• Run the program by its name test1 
• The default output name is a.out is you omit the
  o option.

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UNIX at BC

• A lot of information regarding the Unix servers
  can be found at http//acc6.its.brooklyn.cuny.edu/
  AtriumSunGuide/Table_of_Contents.html
• This includes
• General Information
• Unix Commands
• Korn Shell
• Regular Expressions
• Floppies, Mtools
• Tar
• Editing Vi, Pico
• Compilers, Debuggers
• OpenWindows
• Email, Pine, Talk
• MailTool
• Browsers Netscape, Lynx
• Gopher
• NewsReaders Trn, Xrn
• NcFtp
• Rules