Permission notation (rwxrwxrwx) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of ls -l permission part for a file with mode 754?

Given a file with permission mode 754, what will the permission notation rwxrwxrwx part look like in ls -l output?

A -rwxr-xr--

B -rwxr-xr-x

C -rwxr--r--

D -rwxrwxr--

💡 Hint

Remember that 7 means rwx, 5 means r-x, and 4 means r-- for user, group, and others respectively.

The permission 754 means: user=7 (rwx), group=5 (r-x), others=4 (r--). So the notation is '-rwxr-xr--'.

🧠 Conceptual

intermediate

What does the permission notation -rw-r--r-- mean?

Interpret the permission notation -rw-r--r--. Which of the following is true?

A Owner can read and write; group and others can only read

B Owner can read, write and execute; group and others can read and execute

C Owner can read only; group and others have no permissions

D Owner, group, and others all have read and write permissions

💡 Hint

Look at the letters for each user category: rw- means read and write, r-- means read only.

The first character '-' means a regular file. Then owner has 'rw-' (read and write), group has 'r--' (read only), others have 'r--' (read only).

📝 Syntax

advanced

Which command sets permissions to rwxr-x--- on a file named script.sh?

Choose the correct chmod command to set permissions to rwxr-x--- on script.sh.

A chmod 755 script.sh

B chmod 700 script.sh

C chmod 750 script.sh

D chmod 754 script.sh

💡 Hint

Convert rwxr-x--- to numeric: rwx=7, r-x=5, ---=0.

rwxr-x--- corresponds to 7 (rwx), 5 (r-x), 0 (no permissions). So chmod 750 sets this correctly.

🔧 Debug

advanced

Why does chmod 777 file.txt pose a security risk?

Select the main reason why setting permissions to 777 on a file is risky.

A It disables all permissions for group and others.

B It allows anyone to read, write, and execute the file, which can lead to unauthorized changes or execution.

C It restricts the owner from modifying the file.

D It only allows the owner to execute the file.

💡 Hint

Think about what rwxrwxrwx means for all users.

Permission 777 means everyone can read, write, and execute the file, which can cause security issues if unauthorized users modify or run it.

🚀 Application

expert

After running chmod u=rwx,g=rx,o= file.txt, what is the permission notation?

What is the exact permission notation shown by ls -l for file.txt after running chmod u=rwx,g=rx,o= file.txt?

A -rwxr--r--

B -rwxrwxrwx

C -rwxr-----

D -rwxr-x---

💡 Hint

u=rwx means owner has rwx, g=rx means group has r-x, o= means others have no permissions.

The command sets owner to rwx, group to r-x, and others to no permissions, resulting in '-rwxr-x---'.

Practice

1. What does the permission notation rwxr-xr-- mean for the group?

easy

A. No permissions

B. Read, write, and execute permissions

C. Write and execute permissions only

D. Read and execute permissions only

Solution

1. Step 1: Identify the group permission segment

   The permission string is divided into three groups: user (rwx), group (r-x), others (r--). The group segment is the middle three characters: r-x.

2. Step 2: Interpret the group permissions

   In r-x, r means read, - means no write permission, and x means execute permission.

3. Final Answer:

   Read and execute permissions only -> Option D

4. Quick Check:

   Group = r-x = read + execute [OK]

Hint: Look at the middle three letters for group permissions [OK]

Common Mistakes:

• Confusing user permissions with group permissions
• Assuming dash means write permission
• Mixing up execute (x) with write (w)

2. Which of the following is the correct permission notation for a file where others have only execute permission?

easy

A. rwxrwx--x

B. rwxrwxr--

C. rwxrwxrwx

D. rwxrwx---

Solution

1. Step 1: Understand the position of others' permissions

   The permission string has three groups of three characters: user, group, others. The last three characters represent others' permissions.

2. Step 2: Identify execute-only permission for others

   Execute permission is x, and no read or write means dashes -. So others' permissions should be --x.

3. Step 3: Match the options

   rwxrwx--- ends with --- (no permissions).
   rwxrwxr-- ends with r-- (read only).
   rwxrwxrwx ends with rwx (all permissions).
   rwxrwx--x ends with --x (execute only).

4. Final Answer:

   rwxrwx--x -> Option A

5. Quick Check:

   Others execute permission = last x in string [OK]

Hint: Others' permissions are the last three characters [OK]

Common Mistakes:

• Confusing read (r) with execute (x)
• Ignoring the position of others' permissions
• Assuming dashes mean execute permission

3. What is the numeric (octal) permission equivalent of rw-r--r--?

medium

A. 664

B. 644

C. 755

D. 777

Solution

1. Step 1: Convert each permission group to octal

   Permissions are grouped as user (rw-), group (r--), others (r--).
   For each group, read = 4, write = 2, execute = 1, dash = 0.
   User: r(4) + w(2) + -(0) = 6
   Group: r(4) + -(0) + -(0) = 4
   Others: r(4) + -(0) + -(0) = 4

2. Step 2: Combine the octal digits

   Combine user, group, others digits: 6 4 4

3. Final Answer:

   644 -> Option B

4. Quick Check:

   rw- = 6, r-- = 4, r-- = 4 [OK]

Hint: Add 4 for r, 2 for w, 1 for x in each group [OK]

Common Mistakes:

• Mixing up write and execute values
• Adding execute permission when not present
• Confusing group and others positions

4. You see the permission string rwxr-xr-x on a file, but the owner cannot write to it. What is the likely cause?

medium

A. The write permission is missing for the owner

B. The file is a directory, not a file

C. The file is owned by a different user

D. The execute permission is missing for the owner

Solution

1. Step 1: Analyze the permission string for owner

   The first three characters rwx mean the owner has read, write, and execute permissions.

2. Step 2: Understand why owner cannot write despite permissions

   If the owner cannot write, but permissions show write allowed, the likely cause is that the current user is not the owner of the file. Permissions apply to the file's owner, group, and others accordingly.

3. Final Answer:

   The file is owned by a different user -> Option C

4. Quick Check:

   Owner write permission present but user mismatch [OK]

Hint: Check if you are the file owner when permissions seem correct [OK]

Common Mistakes:

• Assuming permission string always matches current user rights
• Confusing execute with write permission
• Ignoring file ownership

5. You want to set a file permission so that the user has all permissions, the group can read and execute only, and others have no permissions. Which permission notation should you use?

hard

A. rwxr-x---

B. rwxrwxr--

C. rwxr-----

D. rwxr-xr-x

Solution

1. Step 1: Define permissions for each group

   User: all permissions = rwx
   Group: read and execute = r-x
   Others: no permissions = ---

2. Step 2: Combine the permission groups

   Concatenate user, group, others: rwx + r-x + --- = rwxr-x---

3. Final Answer:

   rwxr-x--- -> Option A

4. Quick Check:

   User=all, Group=read+execute, Others=none [OK]

Hint: Write permissions group by group: user, group, others [OK]

Common Mistakes:

• Giving others permissions when none required
• Confusing write and execute for group
• Mixing order of permission groups