Permission notation (rwxrwxrwx) in Linux CLI - Step-by-Step Execution

Concept Flow - Permission notation (rwxrwxrwx)

Start: File Permissions

↓

Divide into 3 groups

↓

Owner permissions

→Group permissions

↓

Read? Write? Execute?

↓

Combine letters: r,w,x or - for none

↓

Final notation: rwxrwxrwx

Permissions are split into three groups: owner, group, and others. Each group has read (r), write (w), and execute (x) permissions shown as letters or '-' if missing.

Execution Sample

Linux CLI

ls -l example.txt
-rwxr--r-- 1 user group 0 Apr 27 12:00 example.txt

Shows file permissions for example.txt in rwxr--r-- format.

Execution Table

Step	Permission Group	Permission Letter	Meaning	Resulting Symbol
1	Owner	Read	Owner can read the file	r
2	Owner	Write	Owner can write to the file	w
3	Owner	Execute	Owner can execute the file	x
4	Group	Read	Group can read the file	r
5	Group	Write	Group cannot write to the file	-
6	Group	Execute	Group cannot execute the file	-
7	Others	Read	Others can read the file	r
8	Others	Write	Others cannot write to the file	-
9	Others	Execute	Others cannot execute the file	-
10	Combine	All groups	Combine all symbols in order	rwxr--r--

💡 All permission bits checked and combined into final notation.

Variable Tracker

Variable	Start	After Owner	After Group	After Others	Final
Permission String		rwx	rwxr--	rwxr--r--	rwxr--r--

Key Moments - 3 Insights

Why do some permission letters show '-' instead of 'r', 'w', or 'x'?

A '-' means that permission is NOT granted. For example, in row 5, group write permission is '-', meaning group cannot write.

How do the three groups relate to different users?

Owner permissions apply to the file owner, group permissions apply to users in the file's group, and others apply to everyone else. See steps 1-9 in the execution table.

Why is the permission string always 9 characters long?

Because it shows 3 permissions (r,w,x) for each of the 3 groups (owner, group, others). Each missing permission is shown as '-'.

Visual Quiz - 3 Questions

Look at the execution table, what is the permission symbol for group execute at step 6?

A -

B x

C r

D w

💡 Hint

Check row 6 in the execution_table where group execute permission is evaluated.

At which step does the permission string become 'rwxr--r--'?

A Step 3

B Step 10

C Step 9

D Step 6

💡 Hint

Look at the combine step where all symbols are joined into the final string.

If the owner did NOT have execute permission, how would the permission string change?

A rwxr--r--

B r--r--r--

C rw-r--r--

D rwxrwxrwx

💡 Hint

Check the owner execute permission at step 3 and see what happens if it is removed.

Concept Snapshot

Permission notation shows file access as rwxrwxrwx.
Three groups: owner, group, others.
Each group has read (r), write (w), execute (x).
Use '-' if permission is missing.
Example: rwxr--r-- means owner full, group read only, others read only.

Full Transcript

This visual execution shows how Linux file permissions are represented as rwxrwxrwx. Permissions are split into three groups: owner, group, and others. Each group has three possible permissions: read (r), write (w), and execute (x). If a permission is not granted, it is shown as a dash '-'. The example traces a file with permissions rwxr--r--, meaning the owner can read, write, and execute; the group can only read; and others can only read. The execution table shows each permission checked step-by-step and combined into the final string. Key moments clarify why dashes appear and how groups relate to users. The quiz tests understanding of permission symbols and their positions. This helps beginners see exactly how permission notation is built and read.

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