Mastering Linux File Permissions: Read, Write, Execute Explained

Linux RSH Network November 30, 2025 2 mins read

Learn how Linux file permissions work, why they matter, and how to use chmod, chown, and symbolic or numeric modes to control access securely.

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๐Ÿ” Why File Permissions Matter

Linux is a multi-user operating system. Without proper permissions:

  • Anyone could read sensitive files

  • System files could be modified or deleted

  • Applications may break

  • Security risks increase

Permissions ensure privacy, security, and stability.

๐Ÿ“ The Three Basic Permissions

Every file and directory has three types of permissions:

Symbol Meaning What It Allows
r Read View file contents / list directory items
w Write Modify file / add or delete files inside a directory
x Execute Run file / enter or access a directory

๐Ÿ‘ฅ Permission Categories

Linux divides permissions into three groups:

  • Owner (u) → The creator/owner of the file

  • Group (g) → Users belonging to the same group

  • Others (o) → Everyone else on the system

A typical ls -l permission looks like:

 
-rw-r--r--

Breakdown:

  • rw- → Owner permissions

  • r-- → Group permissions

  • r-- → Others permissions

๐Ÿงฎ Numeric (Octal) Permission Mode

Linux also represents permissions using numbers:

  • r = 4

  • w = 2

  • x = 1

Example

 
chmod 755 file.sh

Meaning:

User Value Permission
Owner 7 rwx
Group 5 r-x
Others 5 r-x

๐Ÿ”ง Essential File Permission Commands

Command Purpose Example
chmod Change permissions chmod 644 notes.txt
chown Change file owner/group chown user:group file.txt
ls -l View file permissions ls -l /home/user

Symbolic Mode Examples

 
chmod u+x script.sh chmod g-w file.txt chmod o+r notes.txt

 

๐Ÿง  Pro Tips

  • Use chmod +x script.sh to make a script executable

  • Run ls -l often to audit file permissions

  • Avoid using chmod 777 — it exposes your system

  • Assign groups properly to simplify access control

๐Ÿš€ What’s Next?

In Post #4, we’ll explore Linux process management, including:

  • ps

  • top

  • kill

  • nice / renice

You’ll learn how to monitor and control running tasks like a pro.

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