File Permissions Complete Guide with Examples

Introduction

Suppose that you own a house. You decide who can enter, who can stay, and who can make changes inside. Some people may only visit, while others may have full control. Computers work in a very similar way through file permissions.

File permissions determine who can read, modify, or execute files and folders. They are one of the most important security features in Linux, Unix, and even Windows systems. Proper file permissions help protect sensitive information, prevent accidental changes, and improve overall system security.

In this guide, you’ll learn what file permissions are, how they work, and how to manage them with practical examples.

What Are File Permissions?

File permissions are rules that define what actions users can perform on files and directories.

These permissions determine whether a user can:

• Read a file
• Edit or modify it
• Run it as a program
• Access a directory

Without permissions, anyone could delete or modify important system files, making the operating system unstable.

Why File Permissions Matter

File permissions help:

• Protect sensitive data
• Prevent unauthorized access
• Reduce accidental deletion
• Improve system security
• Manage multi-user environments

For example, in a company, employees should not be able to modify payroll files.

Example

Imagine a school library.

There are three groups of people:

• Librarian
• Teachers
• Students

The library contains different books and records.

Permissions work like this:

This is exactly how file permissions work.

Different users receive different access levels.

Three Basic Permissions

Linux uses three basic permissions.

1. Read (r)

Allows viewing the contents of a file.

Example:

You can open a PDF or text file but cannot edit it.

Permission:

r

2. Write (w)

Allows modifying the file.

You can:

• Edit
• Rename
• Delete
• Save changes

Permission:

w

3. Execute (x)

Allows running the file as a program or script.

Example:

backup.sh

Without execute permission:

Permission denied

After adding execute permission:

./backup.sh

The script runs successfully.

File Permission Groups

Linux divides permissions into three categories.

Owner (u)

The person who created the file.

Example:

saqib

Group (g)

Users belonging to the same group.

Example:

developers

Others (o)

Everyone else on the system.

Example:

Guests or normal users.

Permission Structure

Run:

ls -l

Example output:

-rwxr-xr–

Let’s break it down.

–

rwx

r-x

r–

Meaning:

File Type

Owner:

Read

Write

Execute

Group:

Read

Execute

Others:

Read

Understanding the Symbols

Numeric Permission Values

Linux also uses numbers.

Add the values.

Example:

Read + Write + Execute

4 + 2 + 1 = 7

Common Permission Numbers

Example

Permission:

755

Means:

Owner

Read ✔

Write ✔

Execute ✔

Group

Read ✔

Write ✘

Execute ✔

Others

Read ✔

Write ✘

Execute ✔

Viewing Permissions

Command:

ls -l

Example:

-rw-r–r– notes.txt

Meaning:

Owner:

Read

Write

Group:

Read

Others:

Read

Changing Permissions

Linux uses the chmod command.

Symbolic Method

Give execute permission.

chmod +x script.sh

Remove write permission.

chmod -w file.txt

Add read permission.

chmod +r file.txt

Numeric Method

Example:

chmod 755 script.sh

Example:

chmod 644 notes.txt

Example:

chmod 700 secret.txt

Changing File Ownership

Use:

chown

Example:

sudo chown ali file.txt

Now the owner becomes:

ali

Changing Group Ownership

sudo chgrp developers project

Now the file belongs to:

developers

Directory Permissions

Directories also have permissions.

For directories:

Read:

Allows listing files.

Write:

Allows creating or deleting files.

Execute:

Allows entering the directory.

Example:

cd Documents

Without execute permission:

Permission denied

Secure Permission Practices

Recommended permissions:

Dangerous Permissions

Never use:

chmod 777

unless absolutely necessary.

Reason:

Everyone can:

• Read
• Edit
• Delete
• Execute

This creates serious security risks.

Example

Suppose you have:

salary.xlsx

You don’t want coworkers to edit it.

Set:

chmod 600 salary.xlsx

Now only you can read and modify the file.

Example

Imagine a company’s HR department.

The folder contains employee records.

Permissions:

• HR Manager: Read, Write, Execute
• HR Staff: Read and Write
• Other Employees: No Access

Linux permissions enforce this same level of controlled access, ensuring confidential information remains protected.

Best Practices

• Follow the principle of least privilege (give only the permissions needed).
• Avoid using 777 on production servers.
• Regularly audit file permissions.
• Keep sensitive files restricted with 600 or 640.
• Assign users to groups instead of giving permissions individually.
• Review permissions after software installations or migrations.

Advantages of File Permissions

• Protects sensitive information
• Prevents unauthorized modifications
• Supports secure multi-user systems
• Reduces accidental file deletion
• Enhances server security
• Simplifies access management

Disadvantages

• Incorrect settings may block legitimate users.
• Overly permissive access can create security vulnerabilities.
• Managing permissions on large systems requires planning and regular maintenance.

Conclusion

File permissions are a fundamental part of operating system security. By controlling who can read, modify, or execute files, they help protect data, support collaboration, and keep systems stable. Whether you’re managing a personal Linux computer, a web server, or an enterprise network, understanding file permissions is an essential skill. Learning to use commands like ls, chmod, chown, and chgrp will enable you to manage files securely and confidently.