Numeric permission mode (755, 644) in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to set permissions to 755 for the file named script.sh.

Linux CLI

chmod [1] script.sh

Drag options to blanks, or click blank then click option'

A644

B777

C755

D700

Attempts:

3 left

💡 Hint

Common Mistakes

Using 644 instead of 755 will remove execute permissions.

Forgetting to specify the filename after the mode.

The numeric mode 755 sets read, write, and execute for owner, and read and execute for group and others.

2fill in blank

medium

Complete the command to set permissions to 644 for the file named document.txt.

Linux CLI

chmod [1] document.txt

Drag options to blanks, or click blank then click option'

A644

B755

C600

D700

Attempts:

3 left

💡 Hint

Common Mistakes

Using 755 instead of 644 will give execute permissions unnecessarily.

Not specifying the filename after the mode.

The numeric mode 644 sets read and write for owner, and read-only for group and others.

3fill in blank

hard

Fix the error in the command to set permissions to 755 for the file named app.sh.

Linux CLI

chmod [1] app.sh

Drag options to blanks, or click blank then click option'

A755

B700

C644

D777

Attempts:

3 left

💡 Hint

Common Mistakes

Using 644 which lacks execute permissions.

Using 700 which restricts permissions too much.

755 is the correct numeric mode to give execute permission to owner, group, and others as needed.

4fill in blank

hard

Fill both blanks to create a command that sets permissions to 644 for file.txt and 755 for script.sh.

Linux CLI

chmod [1] file.txt && chmod [2] script.sh

Drag options to blanks, or click blank then click option'

A644

B755

C700

D600

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the numeric modes between the two files.

Using 700 or 600 which restrict permissions too much.

644 is for file.txt to allow read/write for owner and read for others; 755 is for script.sh to allow execute permissions.

5fill in blank

hard

Fill all three blanks to create a script that sets permissions 755 on run.sh, 644 on data.txt, and 700 on secret.txt.

Linux CLI

chmod [1] run.sh
chmod [2] data.txt
chmod [3] secret.txt

Drag options to blanks, or click blank then click option'

A755

B644

C700

D600

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up numeric modes for different files.

Using 600 instead of 700 for secret.txt which removes execute permission.

755 for run.sh to allow execution, 644 for data.txt for read/write owner and read others, 700 for secret.txt to restrict access to owner only.

Practice

1. What does the numeric permission mode 755 mean for a file in Linux?

easy

A. User can read, write, execute; group and others can read and execute

B. User can read and write; group and others can only read

C. User, group, and others can read, write, and execute

D. User can read and execute; group and others have no permissions

Solution

1. Step 1: Understand numeric permission digits

   Each digit represents permissions for user, group, and others respectively. 7 means read(4)+write(2)+execute(1)=7, 5 means read(4)+execute(1)=5.

2. Step 2: Decode 755

   User (7) has read, write, execute; group (5) and others (5) have read and execute only.

3. Final Answer:

   User can read, write, execute; group and others can read and execute -> Option A

4. Quick Check:

   755 = rwx r-x r-x [OK]

Hint: 7 means full rights; 5 means read+execute only [OK]

Common Mistakes:

• Confusing 5 with write permission
• Thinking 7 means read+write only
• Mixing group and others permissions

2. Which of the following is the correct command to set a file named script.sh to permission mode 755?

easy

A. chmod 644 script.sh

B. chmod 700 script.sh

C. chmod 777 script.sh

D. chmod 755 script.sh

Solution

1. Step 1: Identify the command to change permissions

   The command to change file permissions is chmod followed by the numeric mode and filename.

2. Step 2: Match the mode 755 with the command

   To set mode 755, use chmod 755 script.sh.

3. Final Answer:

   chmod 755 script.sh -> Option D

4. Quick Check:

   chmod + numeric mode + filename = chmod 755 script.sh [OK]

Hint: chmod + mode + filename sets permissions [OK]

Common Mistakes:

• Using wrong numeric mode
• Swapping filename and mode
• Using chmod without mode

3. If a file has permissions set to 644, what will be the output of ls -l filename showing the permission part?

medium

A. -rw-r--r--

B. -rwxrwxrwx

C. -rwxr-xr-x

D. -rw-rw-r--

Solution

1. Step 1: Decode numeric mode 644

   6 = read(4)+write(2), 4 = read only, so user has read/write, group and others have read only.

2. Step 2: Translate to symbolic permissions

   Permissions are -rw-r--r-- where '-' means regular file, 'rw-' user, 'r--' group, 'r--' others.

3. Final Answer:

   -rw-r--r-- -> Option A

4. Quick Check:

   644 = rw- r-- r-- [OK]

Hint: 6 = rw-, 4 = r-- in permissions [OK]

Common Mistakes:

• Confusing 4 with execute permission
• Mixing user and group permissions
• Assuming 644 includes execute

4. You ran chmod 755 myfile but ls -l myfile shows -rw-r--r--. What is the likely problem?

medium

A. The chmod command syntax is incorrect

B. You forgot to specify the filename

C. You do not have permission to change the file mode

D. The file is a directory, not a regular file

Solution

1. Step 1: Understand chmod effect and output

   chmod 755 should set execute permission, but output shows no execute bits.

2. Step 2: Identify permission issue

   If permissions did not change, likely user lacks rights to modify file mode (not owner or no sudo).

3. Final Answer:

   You do not have permission to change the file mode -> Option C

4. Quick Check:

   chmod no effect = permission denied [OK]

Hint: No change after chmod? Check your ownership rights [OK]

Common Mistakes:

• Assuming syntax error
• Thinking file type blocks chmod
• Ignoring user permissions

5. You want to make a script file executable only by the owner and readable by everyone else. Which numeric mode should you use?

hard

A. 644

B. 744

C. 700

D. 755

Solution

1. Step 1: Define required permissions

   Owner: executable + read + write (7), group and others: read only (4 each).

2. Step 2: Construct numeric mode

   Owner = 7 (rwx), group = 4 (r--), others = 4 (r--), so mode is 744.

3. Final Answer:

   744 -> Option B

4. Quick Check:

   744 = rwx r-- r-- [OK]

Hint: Owner full, others read only = 744 [OK]

Common Mistakes:

• Choosing 755 which allows execute for others
• Using 700 which denies read for others
• Confusing 644 with execute permission