Introduction to Unix and Cygwin – Practical 1

CS240 Operating Systems, Communications and Concurrency

Introduction to Unix and Cygwin – Practical 1
The operating systems course practicals involve learning aspects of Unix/Linux operating system.
Over the course of the labwork you will become familiar with Linux commands and utilities, writing
command scripts for the shell, using some C and/or Java programming to test various features of the
operating system such as process management and interprocess communication and working on
some concurrency problems. The practicals focus on the Unix process model and interprocess
communication mechanisms. Access to these mechanisms both at the shell level(command prompt)
and from within a running program(API library calls) are examined. Using the command line
interface allows us to extend the command interface using scripts unlike the fixed commands
offered by a GUI.
You should keep the practical handouts for reference as each practical builds on previous work.
Always read the handout and carry out the instructions contained therein to accumulate credits for
each practical. The University Library contains many texts on Unix operating system versions which
provide useful supplementary reading and some of these are identified on the course' Moodle page.
During the COVID-19 pandemic, we are unable to use our laboratories which have the Unix
operating system installed, so the simplest solution for you to do practical work is for you to install
the Cygwin software on your windows PC or laptop. It doesn’t take up very much disk space and will
allow us to teach various aspects of unix and do some unix programming.
Cygwin is an open source collection of tools that allows Unix or Linux targetted applications to be
compiled and run on a Windows operating system from within a Linux-like interface. It provides a set
of commands and utilities that behave as they might on a unix system and allows programs to use
unix operating system abstractions and communication mechanisms.
Refer to the separate document “Installing Cygwin software on your PC for CS240” and follow the
instructions to set up the software before continuing with this practical document.
Unix Commands - (Note: Commands are case sensitive)
A shell program is a command parser that interprets the commands of a shell scripting language.
Under the GNOME Applications/System Tools menu you can open a new Xterm(inal) which is then
automatically attached to a shell command parser process.
The commands listed below represent binary executable utility programmes located somewhere in
the shell’s search path. The shell locates the executable binary image and creates a child process to
execute the command. These commands can be included as part of shell script programs. These
scripts can be invoked with command line parameters and the syntax of the scripting language
allows the use of variables, selection and iteration statements as well as redirecting the source and
destination of data used by the processes. More on this later.
TRY OUT SOME OF THE COMMANDS LISTED BELOW.
Open an Xterminal or Gnome Terminal window (Under Applications/System Tools from the Gnome
desktop menu at the top) and enter some commands after the $ prompt when the terminal window
appears. Note you may get occassional software warnings for window based applications launched
from the command line which can be ignored. You also need some user files to be created first
before you can examine them in editors or process with some of these utilities.
General Utility Commands
1. Type the command “date” at the $ prompt and hit enter - Prints date and time
2. Type “pwd” at the $ prompt. -Prints the current directory (path to working directory – pwd)
It will give something like /home/yourname
This is the path to your home directory within the Cygwin filespace.
3. Now make a new directory for files relating to this course with the command
mkdir cs240 - Make a directory called cs240
4. Type “ls” to see the listing of files in your home directory. You should see the directory cs240 you
just created.
5. To make that directory your current directory use the command
“cd cs240” - Change directory to the directory cs240 in the current directory
6. The nano editor is a handy text editor that can be used if a graphical interface is not available.
At the $ shell prompt, type “nano myfile.txt”
This will create a file called myfile.txt in your current directory “/home/username/cs240”
Using the arrow keys to navigate, enter some text into myfile.txt
“Here is some text”
When done press CTRL+X to exit
It will ask to save the modified buffer and you select Y for yes.
It asks you to confirm the File Name to Write: myfile.txt and then press enter and the editor should
terminate.
7. To see the contents of the file myfile.txt on screen type “cat myfile.txt”
8. The command “who” - Lists the current users of the system, not very interesting when you are
home alone
9. The “man” or manual command gives you access to online documentation about unix commands
and utilities and the parameters that they can take.
For example if you wanted to know more about the who command you would type
“man who” - Print entries from the on-line manual
You exit the manual by entering q
Note the scroll bar for the Xterminal is on the left side of the window if you want to go back over
your history of commands.
Sometimes if we display a very long file on the screen, it scrolls past faster than we can read it. The
more utility can help with that, it just displays one page at a time using the space bar to advance to
the next.
The command is “more filename”
You can try it on longer files later.
Some useful File Management Commands for copying, renaming, deleting files and directories are
given below:
File Management
cp filename1 filename4 - Copy filename1 to filename4
mkdir dirname - Create a new directory called dirname within the current directory
mv filename4 filename5 - Move or rename filename4 to filename5, different name or location
rm filename1 - Remove (Delete) filename1
rmdir dirname - Remove (Delete) directory dirname
Process Management
The ps command gives you a process listing of all active processes. Many of the processes listed are
associated with implementing the graphical user interface but some of the processes will belong to
you.
10. If you type the command “ps” it display a list of processes, process ids, executable commands
that initiated the processes, and I/O devices associated with them.
In the process list just generated look for processes with pty0 associated with them. Pty0 is the
psuedo-terminal that you are using (your xterm window) to enter commands. There should be two
processes listed associated with pty0. One was triggered by the command /usr/bin/ps and the other
is the shell program that accepted that command /usr/bin/bash.
11. Look up the PID or process ID of these processes in the list and make note of them.
12. Using the processid associated with the bash shell type the command
kill -9 processid Send a terminate signal to a process with id processid
What happened?
13. The bash process you terminated (by sending it signal 9 – the terminate signal) was your shell
command interpreter operating in the Xterm window. When the process is terminated the
associated Xterm window, used for its input and output streams, closes.
You can start a new Xterm window from the Gnome Applications/System Tools menu.
14. Another useful utility is the time utility used for timing process execution.
Try the command “time ls”
It gives a readout of the time taken to execute the ls command.
To find out more about the option settings and parameters to some of these commands, make use
of the online manual facility mentioned earlier.
SOME FURTHER EXERCISES TO TRY
First make the directory “/home/username/cs240” your current directory if it is not already. How do
you know what your current directory is?
15. To begin with, using the commands given earlier, create a directory called p1 within your cs240
directory for this course and then make p1 your current directory. Type pwd to check your current
directory is /home/username/cs240/p1.
16. Using nano from the command line or using Gedit from the Gnome/Applications/Accessories
menu - Create four files called file1, file2, file3, file4 in the directory p1. Enter a line into
each of the n files of the form 'This is file n' where n is the appropriate file number. You can
use the “save as” option in Gedit to just change the file and use a different number.
Make sure you save it in the right place
On your Xterminal when you execute ‘ls’, you should see your 4 files listed.
17. Copy the four files to four files of the same name but with the extension .bak
e.g. cp file1 file1.bak
18. Edit file1.bak and change its contents to 'This is a copy of file1'
19. Using the cmp command in the Xterm window, compare file2 with file2.bak and file1 with
file1.bak
i.e. cmp file1 file1.bak
cmp file2 file2.bak
So the file you changed differs from the original at byte 9 line 1. The other two files have no
differences.
20. Get a list of files in the root directory '/'. Give / as a parameter to the ls command.
ls /
21. What does the command ls /d* do? Try it and explain.
22. Remove all files with .bak extension from directory p1. You can use the wildcard symbol ‘*’
to match all file names beginning with f, for example rm f*.bak removes all files beginning with f and
ending with .bak
23. Make a directory called text.
24. Move all the files beginning with the name file, file* into directory text.
25. List files in directory text.
Steps 23-25 shown below.
The objective today is to ensure Cygwin is installed and working properly and to familiarise you with
some unix commands and utilities, how to create and edit files and navigation of the filesystem.
If you are satisfied that you are comfortable with these things, then that’s great, otherwise you can
go back over these exercises in your own time on Cygwin at home.
What to submit on moodle?
Take a full screen capture of your Gnome desktop showing your machine and user name in the top
right, showing an open Xterm with your last commands and an open Gedit window showing one of
the files you created earlier (remember they are now in a different directory, so you need to find
one to open). Save it as a .png format image and upload to the moodle Practical 1 assignment for
your group.