How Octal Permissions Work in Linux (With Examples)

Understanding Octal Permissions in Linux

Linux file permissions are often represented in two ways:

1. Symbolic notation → e.g., rwxr-xr--

2. Octal (numeric) notation → e.g., 754

Octal notation is simply a numeric shorthand for symbolic permissions.

1. Symbolic Permissions (The Long Form)

Linux permissions operate on three categories:

And each category can have these three permission types:

Example:

rwx r-x r--

Breaks down as:

2. The Numeric (Octal) System

For each of the permissions (r, w, x), Linux assigns a numeric value:

To convert symbolic to octal, add the values:

Examples:

• rwx → 4 + 2 + 1 → 7
• rw- → 4 + 2 + 0 → 6
• r-x → 4 + 0 + 1 → 5
• r-- → 4 + 0 + 0 → 4
• --- → 0 + 0 + 0 → 0

3. Putting It Together: Octal Notation

A full permission set requires 3 octal digits (user, group, others):

• (user)(group)(others)

Example:

• 754

Breaks down to:

• 7 = rwx (owner)
• 5 = r-x (group)
• 4 = r-- (others)

Symbolically:

Rwx r-x r--

4. Common Octal Permission Values

For Files

For Directories

5. Special Bits (Setuid, Setgid, Sticky Bit)

Sometimes you’ll see 4 digits (e.g., 4755).

The first digit is for special permissions:

Examples:

• 4755 → setuid bit + rwx r-x r-x
• 1777 → sticky bit + rwx rwx rwx (used on /tmp)

6. Setting Permissions with chmod

Use octal notation directly:

1. chmod 754 filename 

2. chmod 700 private_script.sh

3. chmod 1777 /shared/tmp

7. Why Use Octal Instead of Symbolic?

Octal is:

• faster (chmod 755 file)
• unambiguous
• very common in scripts and system admin work

Symbolic mode is better for tweaking permissions:

1. chmod g+w file

2. chmod o-rwx file 

But octal mode is perfect for resetting permissions.