Permission notation (rwxrwxrwx) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the permission notation rwxr-xr-- mean?

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

beginner

What does each letter in rwxrwxrwx represent?

• r: read permission
• w: write permission
• x: execute permission

Repeated for owner, group, and others in that order.

beginner

How many permission sets are shown in rwxrwxrwx and who do they belong to?

There are three sets: owner (first 3 letters), group (middle 3 letters), and others (last 3 letters).

beginner

What does a dash - mean in permission notation like rw-r--r--?

A dash means that the permission is not granted. For example, - in place of x means no execute permission.

intermediate

How can you change file permissions using symbolic notation in Linux?

Use the chmod command with symbols like u (owner), g (group), o (others), and +, -, = to add, remove, or set permissions.

In rwxr-xr--, what permission does the group have?

A Write only

B Read, write, and execute

C Read and execute

D No permissions

The group has r-x which means read and execute permissions.

What does the x permission allow a user to do?

A Delete the file

B Write to the file

C Read the file

D Execute the file or enter the directory

The execute permission allows running a file as a program or entering a directory.

If a file has permissions rw-r--r--, who can write to it?

A Owner only

B Group only

C Others only

D Everyone

Only the owner has write permission indicated by w in the first set.

What does the first character in a long permission string like -rwxr-xr-x indicate?

A Owner permission

B File type (e.g., file or directory)

C Group permission

D Others permission

The first character shows the file type: - for file, d for directory.

Which command changes permissions using numeric notation?

A chmod 755 filename

B ls -l filename

C cat filename

D pwd

chmod 755 filename sets permissions using numeric notation.

Explain the meaning of the permission string rwxr-xr-- in simple terms.

Break it down into three groups of three letters.

Describe how you would change a file to allow only the owner to write, but everyone to read and execute.

Think about symbolic or numeric notation for permissions.

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