Session 1 : Operating System: Programming Concepts : Lab 1 : File System

Operating System : Programming Concepts

Young Man Asked A Rich

Old Man , How He Made

His Money

The Old Guy Said

Son, It was 1932, The depth

of the Great Depression

I Was Down To My Last Nickel

I Invested That In An Apple

And Spent The Entire Day

Polishing It & At The End Of The

Day, I Sold The Apple For 10 Cents

The Nxt Day ,I Invested Those

10 Cents In 2 Apples. I Spent The

Entire Day Polishing Them &

Sold Them For 20 Cents

I Continued This 4 A Month, By The

End Of Which I Had Accumulated

A Fortune Of $.1.37

Then My Wife's Father Died &

Left Us 2 Million Dollars

MORAL :

Hard Work Is Just Shit

Find A Chick Whose Father Is Rich

Lab 1 : FileSystem

Q?what are files

/>files are just the collection of bytes

Q?what is filesystem hierarchy

/> → Oridinary files : this are the files in which system imposes no particular structure. They are used for text documents(also program source code)

→Directory files : this are the container into which other files 

and directories can be placed

→ Special files : this are the files which communicate with running processes and also allow other processes to communicate with hardware devices

Q?what are special filesystem commands

/> “/” → root directory

“.” → current directory

“..” → parent directory

“/home/myfile/file.txt” → absolute path

“myfile/file.txt” → relative path

“name.extension” → files

Note *: hidden files name start with “.”

Q?what is the datastructure of the file

/>File are represented in a datastructure and it is called Inode

/>It consist of :

              >unique identification number type of file : ordinary / directory / special file

>owner id (UID) and group id (GID)

>size and path

>times for last access/modification/status change 

 >permissions >number of links to the Inode

Q?what are the types of link

/>there are two main types of links

/1>hard links : command → ln

/2>soft links : command → ln -s

Q?what are hard links

/>always pointes to the same Inode of the file

/>hard links only works for files and not directories

/>If the real copy is deleted the link will work

Q?what are soft links

/>contains absolute or relative path to a file or directory

/>if real copy is deleted the link will not work

Q?what kind of permission exists for accessing the file

/>we have mostly three kinds of permissions

/1>Read(r) : file listing can be done

/2>Write(w) : we can create or delete a file here

/3>Exec(x) : we can run , directory scanning can be done here

this permissions are grouped into Owner, Group, Others

Commands :

shows the manual page of the linux commands

$ man man

print current working directory

$ pwd

change directory

$ cd <NewDirectoryName>

$ cd / → go to root directory

$ cd → go to your home directory

files and directoires listing

$ ls

$ ls -a → list also the hidden files

create directories

$ mkdir <list of directories name>

copy files and directories

$ cp <source> <destination>

moving or rename files and directories

$ mv <source> <destination>

remove files and directories

$ rm <file name>

$ rm -r <directory name>

 

common options that can be used for rm, cp , mv are :

-r → recursive (delete the content of directory and subdirectory)

-i → interactive (ask conformation to delete each file)

-f → force (doesn't ask confirmation)

change directory/file permission

There are two modes for this action :

Numeric mode :

r: 4

w: 2

x: 1

$ chmod 644 test.txt

644 → 1(r)1(w)0(x)(user)-1(r)0(w)0(x)(group)-1(r)0(w)0(x)(other)

Symbolic mode :

$ chmod u+x

//i.e. we add for user the executable permission

displaying files

$ cat <files> → concatenate files and print on the standard output

$ head [-n <#rows>] <file> → output the first part of files

$ tail [-n <#rows>] <file> → output the last part of files

Editing softwares are :

gedit- emacs - vi

file statistics:

$ wc → print newline, word, and byte counts for each file

Q?What is gcc compiler

/>GNU compiler collection includes the front ends for C and C++

$ gcc [options] source_code -o executable_file_name

$ gcc -Wall myprogram.c -o mycommand

Lab 1 Exercise – Files, directories and permissions

try this out “Do You Like Me ... ?

Breathe For 'YES',

Lick Your Elbow For 'NO' ”

Learning goals: this laboratory activity is meant to practice with the most common commands

for interacting with the file system. The commands are: ls, cd, mv, cp, rm, chmod, less, mkdir, wc. Other commands introduced are gcc, man.

1.Create the following directory tree in your home directory (man

mkdir for details about how to create a directory).

Remarks:

• Work on the local disk. Do not use flash drives or similar storage devices; 

• Use the TAB key to exploit the auto completion feature of the shell;

2.Move inside the src directory and perform the following actions:

1.Create a simple C program, main.c, able to get the number of words of a text file. Text file has to be passed as parameter in the command line, and copy it in the src directory.

2.Copy the main.c file you have just created into test, script and result directories staying in the current src directory. Once done, 

verify the existence of the file using the less command

(man less for details about the less command) and then delete them without moving from the current directory. Then, move to the parent directory so_es1 

and redo the same actions

(copy, verify existence and delete);

3.In point 2.2 you used the cp command for copying files. What’s the difference with the mv command? (type man mv for more details about the mv command)

4.Compile the main.c file using the following command line: gcc –Wall main.c –o myWC .

What’s the purpose of the –Wall option?

5.Correct any compilation error and verify the existence of the myWC executable file.

6.Verify also that the file execute permission is set for the owner of the file. If the executable permission is not set, use the proper command 

to make it executable (man chmod for details about changing file permissions). 

Once done, move the binary file myWC into the bin directory;

3.Move inside the test directory and perform the following actions:

1.Download the test01.txt file. Save it inside the test directory and then edit it adding your student details

2.Execute the myWC executable you generated through gcc in step 2.4, passing it the test01.txt file you have just downloaded; The command for running the myWC executable is the following: ../bin/myWC test01.txt

3.The output should be the number of words of the test01.txt file. Why do you need to specify a full pathname (../bin/myWC) to the executable file in order to execute it?

4.Execute the following command: wc test01.txt

5.Compare the output of this command with the output you obtained in step 3.2. How we can only get the number of words using wc command?