Permission types (read, write, execute) in Linux CLI - Step-by-Step Execution

Concept Flow - Permission types (read, write, execute)

Start

↓

Check Permission Type

↓

Read?

Yes→Allow reading file

↓

Check Write

↓

Write?

Yes→Allow writing file

↓

Check Execute

↓

Execute?

Yes→Allow execute

↓

Deny Access

↓

End

The system checks if a user has read, write, or execute permission on a file and allows or denies access accordingly.

Execution Sample

Linux CLI

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

Shows the permission types for the file example.txt

Execution Table

Step	Permission String	Check	Result	Action
1	-rwxr--r--	Read permission (r) for owner?	Yes	Allow reading
2	-rwxr--r--	Write permission (w) for owner?	Yes	Allow writing
3	-rwxr--r--	Execute permission (x) for owner?	Yes	Allow execute
4	-rwxr--r--	Read permission for group?	Yes	Allow reading
5	-rwxr--r--	Write permission for group?	No	Deny writing
6	-rwxr--r--	Execute permission for group?	No	Deny execute
7	-rwxr--r--	Read permission for others?	Yes	Allow reading
8	-rwxr--r--	Write permission for others?	No	Deny writing
9	-rwxr--r--	Execute permission for others?	No	Deny execute
10	-	All checks done	-	End

💡 All permission checks completed for owner, group, and others.

Variable Tracker

Permission Type	Start	Owner	Group	Others
Read	?	Yes	Yes	Yes
Write	?	Yes	No	No
Execute	?	Yes	No	No

Key Moments - 3 Insights

Why does the group have read permission but no write or execute?

Because in the permission string '-rwxr--r--', the group section 'r--' means read only, no write (w) or execute (x). See execution_table rows 4,5,6.

What does the first character '-' mean in the permission string?

It indicates the file type; '-' means a regular file. This is important but separate from permission bits. See execution_sample.

Why can others read but not write or execute?

Because the last three characters 'r--' in the permission string show read permission only for others. See execution_table rows 7,8,9.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, does the owner have execute permission?

A Yes, owner can execute

B No, owner cannot execute

C Only group can execute

D Only others can execute

💡 Hint

Check the 'Result' column at step 3 in execution_table

At which step does the group fail to have write permission?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look at the 'Check' and 'Result' columns for group write permission in execution_table

If the permission string changed to '-rwxrwxr-x', what would be true?

A Owner has no read permission

B Group has no write permission

C Others have execute permission

D Others have write permission

💡 Hint

Compare the permission string pattern with the original in variable_tracker

Concept Snapshot

Permission types control file access:
- Read (r): allows viewing file contents
- Write (w): allows modifying file
- Execute (x): allows running file
Permissions shown as rwx for owner, group, others
Check permissions with 'ls -l' command

Full Transcript

This lesson shows how Linux file permissions work using read, write, and execute types. The system checks each permission type for owner, group, and others. The permission string like '-rwxr--r--' shows which permissions are granted. For example, owner has read, write, execute; group has read only; others have read only. We traced each permission check step by step. Key points include understanding the permission string layout and what each letter means. The visual quiz tests your understanding of permission checks and changes.