Unix File Permissions Explained - Octal Mode Decoder
Understand Unix/Linux file permissions. Enter any octal mode and see what each digit means in human-readable format.
-rw-r--r--
Owner (6)
✅read
✅write
❌execute
Group (4)
✅read
❌write
❌execute
Others (4)
✅read
❌write
❌execute
0
---
No permissions
1
--x
Execute only
2
-w-
Write only
3
-wx
Write + Execute
4
r--
Read only
5
r-x
Read + Execute
6
rw-
Read + Write
7
rwx
Full permissions
How Unix Permissions Work
Every file and directory in Unix/Linux has permissions that determine who can read, write, or execute it. These permissions are represented as a 3 or 4 digit octal number, where each digit controls a different user category.
The Three Categories
- Owner: The user who owns the file (first digit)
- Group: Users in the file's group (second digit)
- Others: Everyone else on the system (third digit)
Permission Values
- 4: Read permission (r)
- 2: Write permission (w)
- 1: Execute permission (x)
- 0: No permission (-)
Add values together: 4+2+1=7 (rwx), 4+2=6 (rw-), 4+1=5 (r-x)
Common Permission Patterns
- 755: Owner full, others read/execute (scripts, programs)
- 644: Owner read/write, others read (documents)
- 600: Owner read/write only (private files, SSH keys)
- 777: Everyone full access (avoid for security)
Setting Permissions
chmod 755 script.sh # Octal chmod u+rwx,go+rx file # Symbolic ls -la # View permissions