When working in a multi-user Linux environment, not everything is open to everyone—and that’s for a reason. File permissions are a cornerstone of Linux security, ensuring that only the right people can access or modify critical files. Whether you're a budding sysadmin or a curious developer, understanding how Linux handles file access is crucial to maintaining control and security.

Let’s break it down 👇

🔑 Introduction to File Permissions

Linux file permissions determine who can read, write, or execute files and directories. Each file or directory is governed by three levels of access:

  • Owner (User) – The creator of the file.
  • Group – Users who belong to the assigned group.
  • Others – Everyone else.

Permissions are represented in two ways:

  • Read (r or 4) – View file contents.
  • Write (w or 2) – Modify file contents.
  • Execute (x or 1) – Run the file as a program or script.

🛠️ Changing Permissions with chmod

🔹 Symbolic Mode

You can modify permissions using symbols:

  • + to add
  • - to remove
  • = to set exactly

Examples:

chmod u+x filename        # Add execute for user  
chmod g-w filename        # Remove write for group  
chmod o=r filename        # Set read-only for others  
chmod u=rwx,g=rx,o= filename  # Full for user, read/execute for group, none for others

🔢 Numeric (Octal) Mode

Each permission has a value:

  • Read = 4
  • Write = 2
  • Execute = 1

Add the values to define access levels.

Examples:

chmod 755 filename  # User (rwx), Group (r-x), Others (r-x)  
chmod 644 filename  # User (rw-), Group (r--), Others (r--)  
chmod 700 filename  # User (rwx), No access for group/others

👤 Changing Ownership with chown

The chown command is used to modify the file owner and group.

Examples:

chown newuser filename             # Change owner  
chown newuser:newgroup filename   # Change owner and group  
chown :newgroup filename          # Change only group

Recursively change ownership:

chown -R newuser:newgroup directory/

👥 Changing Group Ownership with chgrp

To change only the group without affecting the owner:

Examples:

chgrp newgroup filename           # Change group  
chgrp -R newgroup directory/      # Recursively change group

🚀 Ready to Take Full Control of Your Files?

Linux file permissions may seem daunting at first, but with a little practice, they become second nature—and a powerful part of your system toolkit.

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