Introduction to UNIX. 2 Introduction What is UNIX? UNIX is an operating system which was first...

Introduction to UNIX

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. .


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.


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.


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.


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 / )


The Directory StructureIn 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"


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/SSHSecureShellClient-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 146.245.252.11

atrium12.its.brooklyn.cuny.edu 146.245.252120acc2.its.brooklyn.cuny.edu 146.245.252.72 fldsun228.its.brooklyn.cuny.edu 146.245.252.228


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.cuny.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


UNIX at BC - SSH Now you’re connected at ready to roll


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


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 college’s SUN servers and prompt you for an id and password

When completed, you will see a prompt of the form $ atrium4:/users1/rudowsky>

Now you’re in business


UNIX at BC See David Arnow’s “Getting Started with UNIX” guide Basic commands:

ls [-a|-l] List files in the directory mkdir <dir name> make a directory rm <filename> remove a file mv <oldfilename> <newfilename> rename a file cat <filename> display a file cp <original_filename> <copy_filename> copy a

file command > <output_filename> redirect the output of a

command e.g., ls –l > list g++ xyz.cpp –o xyz compiles a C++ program named

xyz.c and saves the compiled progam as xyz exit


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


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)


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


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.


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 */


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 Code::Blocks 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).


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.


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

Introduction to UNIX. 2 Introduction What is UNIX? UNIX is an operating system which was first...

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