chmod (change permissions) in Linux CLI - Step-by-Step Execution

Concept Flow - chmod (change permissions)

Start

↓

Input chmod command

↓

Parse permissions and target file

↓

Check user rights to change permissions

Yes No↓

Apply new permissions

↓

Permissions updated

↓

End

The chmod command takes user input, checks permissions, and updates file permissions if allowed.

Execution Sample

Linux CLI

chmod u+x script.sh
ls -l script.sh

Adds execute permission for the user on script.sh and then lists its permissions.

Execution Table

Step	Command	Action	Permissions Before	Permissions After	Output
1	ls -l script.sh	Show current permissions	-rw-r--r--	-rw-r--r--	-rw-r--r-- 1 user user 0 date script.sh
2	chmod u+x script.sh	Add execute permission for user	-rw-r--r--	-rwxr--r--
3	ls -l script.sh	Show updated permissions	-rwxr--r--	-rwxr--r--	-rwxr--r-- 1 user user 0 date script.sh
4		End of commands	-rwxr--r--	-rwxr--r--

💡 Permissions updated successfully after chmod command

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Permissions of script.sh	-rw-r--r--	-rw-r--r--	-rwxr--r--	-rwxr--r--	-rwxr--r--

Key Moments - 2 Insights

Why does the execute permission only change for the user and not for group or others?

Because the command uses 'u+x' which means add execute permission only for the user, as shown in step 2 of the execution_table.

What happens if you try to change permissions without proper rights?

The system will show a 'Permission denied' error and permissions won't change, as indicated in the concept_flow where 'No' leads to an error.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what permission is added to script.sh?

A Read permission for others

B Write permission for group

C Execute permission for user

D Execute permission for others

💡 Hint

Check the 'Permissions After' column at step 2 in the execution_table.

At which step does the permissions of script.sh change?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Permissions After' column to see when the change happens.

If the command was 'chmod g+x script.sh', how would the permissions change compared to the example?

A Add execute permission for group instead of user

B Add execute permission for others

C Remove execute permission for user

D No change

💡 Hint

Refer to the meaning of 'u+x' vs 'g+x' in the key_moments and execution_table.

Concept Snapshot

chmod changes file permissions.
Syntax: chmod [who][+/-][permission] file
Who: u=user, g=group, o=others, a=all
Permissions: r=read, w=write, x=execute
Example: chmod u+x file adds execute for user.

Full Transcript

The chmod command changes file permissions by adding or removing rights for user, group, or others. In the example, 'chmod u+x script.sh' adds execute permission for the user only. Before the command, the file had '-rw-r--r--' permissions. After, it changed to '-rwxr--r--'. The ls -l command shows these permissions before and after the change. If you lack rights to change permissions, chmod will show an error and not update the file. This visual trace shows each step and how permissions update.