Permission types (read, write, execute) in Linux CLI - Mini Project: Build & Apply

Understanding Permission Types (read, write, execute) in Linux CLI

📖 Scenario: You are managing files on a Linux system. Each file has permissions that control who can read, write, or execute it. Understanding these permissions helps you keep files safe and control access.

🎯 Goal: You will create a file, set permissions, and check the permission types using Linux commands.

📋 What You'll Learn

Create a file named example.txt

Create a variable called permissions to store permission info

Use the ls -l command to get permission details

Print the permission types for the file

💡 Why This Matters

🌍 Real World

Managing file permissions is essential for protecting data and controlling access on Linux systems.

💼 Career

System administrators and developers often need to check and modify file permissions to secure systems and applications.

1

Create a file named example.txt

Use the touch command to create a file called example.txt.

Linux CLI

# Use the touch command to create example.txt
# Your code here

Hint

Use touch example.txt to create an empty file named example.txt.

2

Create a variable called permissions to store permission info

Use the command ls -l example.txt and assign its output to a variable called permissions.

Linux CLI

touch example.txt
# Assign the output of ls -l example.txt to permissions
# Your code here

Hint

Use permissions=$(ls -l example.txt) to save the file details into the variable.

3

Extract the permission types from permissions

Use the echo command with cut to extract the first 10 characters (permission string) from the permissions variable and save it to a variable called perm_types.

Linux CLI

touch example.txt
permissions=$(ls -l example.txt)
# Extract permission string and save to perm_types
# Your code here

Hint

Use perm_types=$(echo "$permissions" | cut -c1-10) to get the permission characters.

4

Print the permission types for example.txt

Use echo to print the value of the variable perm_types.

Linux CLI

touch example.txt
permissions=$(ls -l example.txt)
perm_types=$(echo "$permissions" | cut -c1-10)
# Print the permission types
# Your code here

Hint

Use echo "$perm_types" to display the permission string.

Practice

1. Which permission allows you to open and view the contents of a file in Linux?

easy

A. Read permission

B. Write permission

C. Execute permission

D. Delete permission

Solution

1. Step 1: Understand the meaning of read permission

   Read permission allows a user to open and view the contents of a file without changing it.

2. Step 2: Compare with other permissions

   Write permission allows changing the file, execute permission allows running the file as a program, and delete is not a standard permission type.

3. Final Answer:

   Read permission -> Option A

4. Quick Check:

   Read = open/view file [OK]

Hint: Read means open and see file contents [OK]

Common Mistakes:

• Confusing write with read permission
• Thinking execute lets you open files
• Assuming delete is a permission type

2. Which of the following is the correct symbolic representation for write permission in Linux file permissions?

easy

A. w

B. e

C. x

D. r

Solution

1. Step 1: Recall symbolic letters for permissions

   In Linux, 'r' stands for read, 'w' for write, and 'x' for execute permission.

2. Step 2: Identify the write permission symbol

   The letter 'w' is used to represent write permission.

3. Final Answer:

   w -> Option A

4. Quick Check:

   Write permission symbol = w [OK]

Hint: Write permission is always 'w' in Linux [OK]

Common Mistakes:

• Mixing 'r' and 'w' symbols
• Using 'e' which is not a permission symbol
• Confusing execute 'x' with write

3. What will be the output of the command ls -l script.sh if the permissions shown are -rwxr--r--?

medium

A. Owner can read only; group can write only; others can execute only

B. Owner can read and write only; group can execute only; others can write only

C. Owner can execute only; group can read and write; others can execute only

D. Owner can read, write, execute; group can read only; others can read only

Solution

1. Step 1: Break down the permission string

   The string '-rwxr--r--' means: owner has read (r), write (w), execute (x); group has read (r) only; others have read (r) only.

2. Step 2: Match permissions to options

   Owner can read, write, execute; group can read only; others can read only correctly describes these permissions. Other options incorrectly assign write or execute permissions to group or others.

3. Final Answer:

   Owner can read, write, execute; group can read only; others can read only -> Option D

4. Quick Check:

   rwx r-- r-- = Owner rwx, group r, others r [OK]

Hint: r = read, w = write, x = execute in order [OK]

Common Mistakes:

• Misreading group or others permissions
• Confusing execute with write
• Ignoring the first dash meaning file type

4. You run chmod u+x file.txt but still cannot execute the file. What is the most likely reason?

medium

A. The file is not owned by you

B. The file does not have execute permission for others

C. The file is not a script or executable program

D. You forgot to add read permission

Solution

1. Step 1: Understand what chmod u+x does

   This command adds execute permission for the file owner (user).

2. Step 2: Consider why execution might still fail

   If the file is not a script or executable program, adding execute permission won't let you run it.

3. Final Answer:

   The file is not a script or executable program -> Option C

4. Quick Check:

   Execute permission needs executable content [OK]

Hint: Execute permission needs executable content, not just flag [OK]

Common Mistakes:

• Assuming ownership blocks execution
• Thinking others' execute permission is needed
• Confusing read permission with execute

5. You want to allow a group to modify a file but not execute it. Which chmod command sets read and write permissions for the group only, leaving others unchanged?

hard

A. chmod o=rw file.txt

B. chmod g=rw file.txt

C. chmod g+rwx file.txt

D. chmod u=rw file.txt

Solution

1. Step 1: Understand chmod symbolic mode

   "g=rw" sets group permissions to read and write only, removing execute if present.

2. Step 2: Check other options

   chmod g+rwx file.txt adds execute permission, which is not wanted. chmod o=rw file.txt changes others' permissions, and chmod u=rw file.txt changes user permissions.

3. Final Answer:

   chmod g=rw file.txt -> Option B

4. Quick Check:

   g=rw sets group read/write only [OK]

Hint: Use g=rw to set group read/write without execute [OK]

Common Mistakes:

• Using g+rwx adds execute permission
• Changing user or others instead of group
• Using + instead of = to overwrite permissions