Permission types (read, write, execute) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of the permission check command?

You run the command ls -l file.txt and see the permissions as -rw-r--r--. What does this mean for the file's owner?

A The owner can only read the file.

B The owner can read, write, and execute the file.

C The owner can read and write the file, but cannot execute it.

D The owner cannot access the file at all.

💡 Hint

Look at the first three permission characters after the dash.

The first three characters after the dash represent the owner's permissions. 'rw-' means read and write are allowed, but execute is not.

💻 Command Output

intermediate

What permission does 'chmod u+x file.sh' add?

You run chmod u+x file.sh. What permission is added to the file for the owner?

A Removes read permission for the owner.

B Adds execute permission for the owner.

C Adds write permission for the owner.

D Adds execute permission for everyone.

💡 Hint

The 'u' stands for user (owner), and '+x' means add execute.

The command adds execute permission (+x) only for the user (owner) of the file.

📝 Syntax

advanced

Which command correctly removes write permission for group?

You want to remove write permission for the group on a file named data.txt. Which command does this correctly?

A chmod g-w data.txt

B chmod -w g data.txt

C chmod w-g data.txt

D chmod g+w data.txt

💡 Hint

The syntax is 'chmod [who][+/-][permission] file'.

Option A uses the correct syntax to remove (-) write (w) permission for group (g).

💻 Command Output

advanced

What is the output of 'stat' showing permissions in octal?

You run stat -c '%a' script.sh and get 755. What does this mean for the file permissions?

A Owner has read, write, execute; group and others have read and execute.

B Owner has read and write; group and others have execute only.

C Owner, group, and others all have read, write, and execute.

D Owner has execute only; group and others have no permissions.

💡 Hint

Octal 7 means read+write+execute; 5 means read+execute.

Octal 7 = 4+2+1 = read+write+execute; 5 = 4+1 = read+execute. So 755 means owner rwx, group rx, others rx.

🚀 Application

expert

How many files have execute permission for others?

You run ls -l and see these permissions for files:
-rw-r--r--
-rwxr-xr-x
-rw-rw-r--
-rwxrwxrwx
How many files have execute permission for others?

A 0

B 1

C 3

D 2

💡 Hint

Look at the last character in the permission string for others.

Files 2 and 4 have 'x' in the last position, meaning others have execute permission.

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