Course: CS211P - Operating System (1)
Faculty: Faculty of Computers and Information - Mansoura University
Semester: Fall 2024-2025
Grade: 2

Table of Contents

1. Echo and Cat Commands
2. Ownership of Linux Files
3. File Permissions
4. Archiving and Compression
5. System Information Commands
6. Lab Exercises

1. Echo and Cat Commands

1.1 The echo Command

The echo command is used to display text or strings on the terminal.

Basic Syntax:

echo string

Example:

echo "Hello, Operating Systems!"

Output: Hello, Operating Systems!

1.2 Redirecting Output to a File

Instead of displaying output on the terminal, you can redirect it to a file using the >> operator (append) or > operator (overwrite).

Append to a file:

echo "This is a new line" >> fileName.txt

Overwrite a file:

echo "This will replace all content" > fileName.txt

Note:

• > creates a new file or overwrites existing content
• >> appends to the end of an existing file or creates a new one if it doesn't exist

1.3 The cat Command

The cat (concatenate) command is used to read and display file contents.

Basic Syntax:

cat fileName

Example:

cat myfile.txt

1.4 Advanced cat Usage

Display contents with line numbers:

cat -n fileName

Example:

cat -n script.sh

Output:

     1  #!/bin/bash
     2  echo "Hello World"
     3  # This is a comment

View contents from multiple files:

cat fileName1 fileName2

Example:

cat file1.txt file2.txt

2. Ownership of Linux Files

In Linux, every file and directory has three types of ownership:

2.1 Owner (User - u)

• The user who created the file
• Has primary control over the file
• Can modify permissions

2.2 Group (g)

• A group can contain multiple users
• All users in the group share the same permissions for the file
• Useful for collaborative work

2.3 Others (o)

• Represents everyone else on the system
• Users who are neither the owner nor in the group
• Typically have the most restricted access

Example:

ls -l myfile.txt

Output:

-rw-r--r-- 1 mahmoud students 1234 Oct 12 10:30 myfile.txt

• Owner: mahmoud
• Group: students
• Others: all other users

3. File Permissions

Linux uses a permission system to control access to files and directories. There are three types of permissions:

3.1 Permission Types

3.2 Permission Structure

Permissions are displayed in the following format:

-rwxrwxrwx

Breaking it down:

- rwx rwx rwx
│  │   │   │
│  │   │   └─── Other permissions
│  │   └─────── Group permissions
│  └─────────── Owner permissions
└────────────── File type (- for file, d for directory)

Example:

-rw-r--r--

• Owner: read + write (rw-)
• Group: read only (r--)
• Others: read only (r--)

3.3 Numeric Permission Calculation

Permissions can be represented as three-digit octal numbers:

Example:

• chmod 755 means:
  • Owner: rwx (7)
  • Group: r-x (5)
  • Others: r-x (5)

3.4 Changing Permissions with chmod

The chmod (change mode) command modifies file permissions.

Method 1: Symbolic Method

Syntax:

chmod [who][operation][permission] filename

Who:

• u = user (owner)
• g = group
• o = others
• a = all (user, group, and others)

Operation:

• + = add permission
• - = remove permission
• = = set exact permission

Examples:

# Add execute permission for owner
chmod u+x script.sh
 
# Remove write permission for group
chmod g-w file.txt
 
# Add read and write for all
chmod a+rw document.txt
 
# Remove execute for others
chmod o-x program
 
# Set exact permissions: owner=rw, group=r, others=nothing
chmod u=rw,g=r,o= file.txt

Method 2: Numeric (Octal) Method

Syntax:

chmod [number] filename

Examples:

# Owner: rwx, Group: ---, Others: r--
chmod 704 file.txt
 
# Owner: rw-, Group: r--, Others: r--
chmod 644 document.txt
 
# Owner: rwx, Group: r-x, Others: r-x
chmod 755 script.sh
 
# Owner: rw-, Group: rw-, Others: ---
chmod 660 private.txt

Common Permission Patterns:

• 644 - Standard file permissions (owner can read/write, others can read)
• 755 - Standard executable/directory permissions
• 700 - Private file/directory (only owner has access)
• 777 - All permissions for everyone (rarely recommended)

4. Archiving and Compression

4.1 Archiving vs. Compression

Archiving:

• Collects multiple files and directories into a single file
• Does not reduce file size
• Uses .tar extension
• Useful for organizing and transferring multiple files

Compression:

• Reduces the size of files
• Saves disk space and bandwidth
• Uses extensions like .gz, .zip
• Useful for storing and transmitting large files

4.2 The tar Command (Archiving)

tar stands for "Tape Archive" and is used to create archive files.

Creating an Archive

Syntax:

tar cvf archive_name.tar file1 file2 directory_name

Options:

• c = create a new archive
• v = verbose (show progress)
• f = specify filename

Example:

tar cvf backup.tar file1.txt file2.txt documents/

Extracting an Archive

Syntax:

tar xvf archive_name.tar

Options:

• x = extract files from archive
• v = verbose
• f = specify filename

Example:

tar xvf backup.tar

Viewing Archive Contents

Syntax:

tar tvf archive_name.tar

Options:

• t = list contents
• v = verbose
• f = specify filename

Example:

tar tvf backup.tar

4.3 The gzip Command (Compression)

gzip compresses a single file and adds .gz extension.

Compressing a File

Syntax:

gzip filename

Example:

gzip largefile.txt
# Creates: largefile.txt.gz (original file is removed)

Note: By default, gzip removes the original file after compression.

Decompressing a File

Syntax:

gzip -d filename.gz
# OR
gunzip filename.gz

Example:

gzip -d largefile.txt.gz
# Restores: largefile.txt

Combining tar and gzip

You can create compressed archives using both commands together:

Method 1: Two-step process

tar cvf archive.tar files/
gzip archive.tar
# Creates: archive.tar.gz

Method 2: Single command

tar czf archive.tar.gz files/
# c = create, z = compress with gzip, f = filename

Extracting compressed tar archives:

tar xzf archive.tar.gz
# x = extract, z = decompress with gzip, f = filename

4.4 The zip Command (Compression)

zip compresses files and directories into a .zip archive (Windows compatible).

Creating a Zip Archive

Syntax:

zip -r archive_name.zip file1 file2 directory_name

Options:

• -r = recursive (include directories)

Example:

zip -r backup.zip file1.txt file2.txt documents/

Extracting a Zip Archive

Syntax:

unzip archive_name.zip

Example:

unzip backup.zip

Extract to specific directory:

unzip backup.zip -d /path/to/destination/

View contents without extracting:

unzip -l backup.zip

5. System Information Commands

5.1 Disk Space Commands

df - Disk Filesystem Usage

Shows disk space usage for all mounted filesystems.

Syntax:

df -h

Options:

• -h = human-readable format (KB, MB, GB)

Example Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       50G   20G   28G  42% /
/dev/sda2       100G  75G   20G  79% /home

du - Directory Usage

Shows disk space used by directories.

Syntax:

du -hs directory_name

Options:

• -h = human-readable format
• -s = summary (total size only)

Example:

du -hs /home/mahmoud/documents/
# Output: 2.3G    /home/mahmoud/documents/

5.2 Memory Usage

free - Memory and Swap Usage

Shows memory (RAM) and swap space usage.

Syntax:

free
# OR for human-readable format
free -h

Example Output:

              total        used        free      shared  buff/cache   available
Mem:           7.7G        2.1G        3.2G        256M        2.4G        5.1G
Swap:          2.0G          0B        2.0G

5.3 System Information Commands

Hostname and Network

# Show computer name
hostname
 
# Show IP address
hostname -I

Date and Time

# Show current date and time
date
 
# Show calendar for current month
cal
 
# Show calendar for specific year
cal 2025

User Information

# Show current username (Method 1)
echo $USER
 
# Show current username (Method 2)
whoami
 
# Show user ID and groups
id

Example Output:

$ whoami
mahmoud
 
$ id
uid=1000(mahmoud) gid=1000(mahmoud) groups=1000(mahmoud),27(sudo),999(docker)

5.4 Command History

# Show recently used commands
history
 
# Save history to a file
history > commands.txt
 
# Execute a specific command from history
!123    # Runs command number 123
 
# Execute the last command
!!
 
# Search command history
history | grep "chmod"

5.5 Network Testing

ping - Check Network Connection

Tests connectivity to a server or IP address.

Syntax:

ping server_name
# OR
ping IP_address

Example:

ping google.com
ping 8.8.8.8

Stop ping with: Ctrl + C

Limit number of pings:

ping -c 5 google.com
# Sends only 5 ping packets

5.6 Exit Terminal

exit
# OR press Ctrl + D

6. Lab Exercises

Exercise 1: Echo and Cat Commands

1. Create a file named greeting.txt with the text "Hello from FCIS" using echo
2. Display the contents of greeting.txt using cat
3. Append "Mansoura University" to the file
4. Display the file with line numbers
5. Create another file info.txt with your name and student ID
6. Display both files together using a single cat command

Solution:

echo "Hello from FCIS" > greeting.txt
cat greeting.txt
echo "Mansoura University" >> greeting.txt
cat -n greeting.txt
echo "Name: Mahmoud Abas" > info.txt
echo "Student ID: 12345" >> info.txt
cat greeting.txt info.txt

Exercise 2: File Permissions

1. Create a file named script.sh with some text
2. Check its current permissions using ls -l
3. Give the owner execute permission using symbolic method
4. Remove write permission from group using symbolic method
5. Set permissions to 755 using numeric method
6. Create a directory and set its permissions to 700

Solution:

echo "#!/bin/bash" > script.sh
echo "echo 'Test script'" >> script.sh
ls -l script.sh
chmod u+x script.sh
chmod g-w script.sh
chmod 755 script.sh
mkdir mydir
chmod 700 mydir
ls -ld mydir

Exercise 3: Archiving and Compression

1. Create three text files with different content
2. Create a tar archive containing all three files
3. List the contents of the archive
4. Extract the archive to verify
5. Compress one of the files using gzip
6. Create a zip archive of all files
7. Check the size difference between original and compressed files

Solution:

echo "File 1 content" > file1.txt
echo "File 2 content" > file2.txt
echo "File 3 content" > file3.txt
 
tar cvf myarchive.tar file1.txt file2.txt file3.txt
tar tvf myarchive.tar
tar xvf myarchive.tar
 
gzip file1.txt
ls -lh
 
zip myfiles.zip file2.txt file3.txt file1.txt.gz
ls -lh

Exercise 4: System Information

1. Display your computer's hostname
2. Show your IP address
3. Display current date and time
4. Show this month's calendar
5. Check disk space usage in human-readable format
6. Check the size of your home directory
7. Display memory usage
8. Show your username using three different methods
9. Ping google.com 5 times

Solution:

hostname
hostname -I
date
cal
df -h
du -hs ~
free -h
echo $USER
whoami
id
ping -c 5 google.com

Exercise 5: Comprehensive Challenge

Create a script that:

1. Creates a directory named "lab3_project"
2. Inside it, creates three subdirectories: "docs", "scripts", "data"
3. Creates sample files in each directory
4. Sets appropriate permissions (755 for directories, 644 for files)
5. Creates a compressed tar archive of the entire project
6. Shows the size comparison between the directory and the archive

Solution:

# Create directory structure
mkdir -p lab3_project/{docs,scripts,data}
 
# Create sample files
echo "Documentation file" > lab3_project/docs/readme.txt
echo "#!/bin/bash" > lab3_project/scripts/run.sh
echo "echo 'Running script'" >> lab3_project/scripts/run.sh
echo "Sample data: 1,2,3,4,5" > lab3_project/data/data.csv
 
# Set permissions
chmod 755 lab3_project lab3_project/*
chmod 644 lab3_project/docs/* lab3_project/data/*
chmod 755 lab3_project/scripts/*
 
# Create compressed archive
tar czf lab3_project.tar.gz lab3_project/
 
# Show size comparison
echo "Directory size:"
du -hs lab3_project/
echo "Archive size:"
ls -lh lab3_project.tar.gz

Summary

In this lab, you learned:

✅ Echo and Cat Commands: Display text and read file contents
✅ File Ownership: Understanding user, group, and others
✅ File Permissions: Reading, writing, and executing files using symbolic and numeric methods
✅ Archiving: Using tar to bundle files together
✅ Compression: Reducing file sizes with gzip and zip
✅ System Commands: Checking disk space, memory, network connectivity, and user information

Additional Resources

• Linux Manual Pages: man command_name (e.g., man chmod)
• Linux Command Help: command_name --help (e.g., chmod --help)
• Online Resources:
  • Linux Journey
  • Ubuntu Documentation
  • GNU Core Utilities

Tips for Success

1. Practice regularly - Linux commands become easier with repetition
2. Use tab completion - Press Tab to auto-complete filenames and commands
3. Read error messages - They usually tell you what went wrong
4. Use man pages - They contain detailed information about commands
5. Be careful with permissions - Wrong permissions can make files inaccessible
6. Backup before compression - Always keep a copy of important files

End of Lab 03