Permission types (read, write, execute) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the 'read' permission allow a user to do on a file?

The 'read' permission allows a user to open and view the contents of a file.

beginner

What action does the 'write' permission enable on a file?

The 'write' permission lets a user modify or delete the contents of a file.

beginner

What is the purpose of the 'execute' permission on a file?

The 'execute' permission allows a user to run a file as a program or script.

intermediate

How do permissions differ for directories compared to files?

For directories, 'read' lets you list files, 'write' lets you add or remove files, and 'execute' lets you enter the directory.

intermediate

What does the permission string 'rwxr-xr--' mean?

It means the owner can read, write, and execute; the group can read and execute; others can only read.

Which permission allows you to run a script?

A Execute

B Write

C Read

D Delete

Only the 'execute' permission lets you run a file as a program or script.

If you want to change the contents of a file, which permission must you have?

A Write

B Read

C Execute

D None

The 'write' permission allows modifying or deleting a file's contents.

What does the 'read' permission on a directory allow?

A Enter the directory

B Modify files inside

C List the files inside

D Delete files inside

'Read' on a directory lets you list the files it contains.

In the permission string '-rw-r--r--', who can write to the file?

A Group only

B Owner only

C Others only

D Everyone

Only the owner has 'write' permission in '-rw-r--r--'.

What permission is needed to enter a directory?

A All of the above

B Write

C Read

D Execute

The 'execute' permission on a directory allows you to enter it.

Explain the difference between read, write, and execute permissions for files.

Think about what you can do with a file when you open it, change it, or run it.

Describe how permissions work differently for directories compared to files.

Consider what actions you do inside a folder versus a file.

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