Numeric permission mode (755, 644) in Linux CLI - Step-by-Step Execution

Concept Flow - Numeric permission mode (755, 644)

Start with numeric mode

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Split digits: Owner, Group, Others

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Convert each digit to rwx

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Apply permissions to file/folder

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Check permissions with ls -l

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End

This flow shows how numeric permission modes like 755 or 644 are split into owner, group, and others, then converted to read/write/execute permissions and applied to files.

Execution Sample

Linux CLI

chmod 755 file.txt
ls -l file.txt

Set file.txt permissions to 755 and then list its permissions.

Execution Table

Step	Action	Input Numeric Mode	Owner Permission	Group Permission	Others Permission	Resulting rwx	Command Output
1	Start	755
2	Split digits	755	7	5	5
3	Convert 7 to rwx		7			rwx
4	Convert 5 to r-x			5		r-x
5	Convert 5 to r-x				5	r-x
6	Apply chmod	755	rwx	r-x	r-x	rwxr-xr-x
7	Check permissions						-rwxr-xr-x 1 user group 0 date file.txt
8	Start	644
9	Split digits	644	6	4	4
10	Convert 6 to rw-		6			rw-
11	Convert 4 to r--			4		r--
12	Convert 4 to r--				4	r--
13	Apply chmod	644	rw-	r--	r--	rw-r--r--
14	Check permissions						-rw-r--r-- 1 user group 0 date file.txt
15	End

💡 Execution stops after permissions are applied and verified with ls -l.

Variable Tracker

Variable	Start	After Step 2	After Step 3/4/5	After Step 6	Final
Numeric Mode		755	755	755	755
Owner Digit		7	7	7	7
Group Digit		5	5	5	5
Others Digit		5	5	5	5
Owner rwx			rwx	rwx	rwx
Group rwx			r-x	r-x	r-x
Others rwx			r-x	r-x	r-x
Permission String				rwxr-xr-x	rwxr-xr-x

Key Moments - 3 Insights

Why does the digit 7 translate to rwx?

Because 7 in binary is 111, which means read (4) + write (2) + execute (1) permissions are all set, as shown in execution_table rows 3 and 6.

Why does 5 translate to r-x and not rwx?

5 in binary is 101, meaning read (4) and execute (1) are set, but write (2) is not, as shown in execution_table rows 4, 5, and 6.

What does the permission string rw-r--r-- mean for 644?

It means owner can read and write, group and others can only read, matching digits 6 (rw-), 4 (r--), and 4 (r--) in execution_table rows 10-13.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what permissions does the owner get for digit 7?

A rwx

B rw-

C r-x

D r--

💡 Hint

Check the 'Owner rwx' column at step 3 in execution_table.

At which step does the group permission get converted for mode 755?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Group Permission' and 'Resulting rwx' columns in execution_table.

If the numeric mode changed from 644 to 600, what would be the others permission?

A r--

B rw-

C ---

D rwx

💡 Hint

Refer to how digit '4' maps to 'r--' and '0' maps to '---' in execution_table rows 11-12.

Concept Snapshot

Numeric permission mode uses three digits: owner, group, others.
Each digit is a sum of read(4), write(2), execute(1).
Example: 7 = rwx (4+2+1), 5 = r-x (4+0+1), 4 = r-- (4+0+0).
Use chmod <mode> <file> to apply.
Check with ls -l to see permissions.

Full Transcript

Numeric permission modes like 755 or 644 are three-digit numbers representing file permissions for owner, group, and others. Each digit is a sum of read (4), write (2), and execute (1) permissions. For example, 7 means read, write, and execute are all allowed. The process starts by splitting the numeric mode into three digits, converting each digit to its rwx form, applying these permissions to the file using chmod, and then verifying with ls -l. This visual execution shows step-by-step how digits 7, 5, and 4 translate to rwx, r-x, and r-- respectively, and how the final permission string looks. Understanding this helps control who can read, write, or execute files on Linux systems.