linux file permissions

Linux Basics: File and Directory Permissions


Linux, being a multi-user system, requires a sophisticated permission structure to maintain security and integrity. Permissions play a vital role in controlling access to files and directories, defining who can read, write, or execute them. This article dives into the complexities of the Linux permission system, laying the foundation for anyone who wants to manage their system efficiently. From understanding user, group, and other permissions to special permissions like SUID, SGID, and the sticky bit, we’ll explore how Linux maintains control over file access.

Understanding Basic Permissions

  • User, Group, and Others:
    • Owner (User) Permissions
    • Group Permissions
    • Other (World) Permissions
  • Permission Modes:
    • Read (r)
    • Write (w)
    • Execute (x)
  • Viewing Permissions:
    • Using ls -l command
    • Interpreting the permission string (e.g., -rwxr-xr–)

Special Permissions

  • Set User ID (SUID):
    • Definition and use cases
    • How to set and unset SUID
  • Set Group ID (SGID):
    • Definition and use cases
    • How to set and unset SGID
  • Sticky Bit:
    • Definition and common usage (e.g., /tmp directory)
    • How to set and unset the sticky bit

Managing Permissions with chown and chmod

Understanding and managing file and directory permissions are essential, and tools like chown and chmod make this task manageable. Refer to our detailed guide on managing file ownership and permissions with chown and chmod.

Access Control Lists (ACLs)

  • Understanding ACLs:
    • Why and when to use ACLs
    • How to set, view, and modify ACLs
  • Default ACLs:
    • How to set default permissions for a directory


File and directory permissions are at the core of Linux’s security model. Whether you’re a system administrator managing multiple user access or a single user aiming to keep personal files private, understanding and implementing permissions is crucial. This guide offers a comprehensive look into the various facets of Linux permissions, equipping you with the knowledge to manage your system effectively and securely. Remember to utilize tools like chown and chmod, and don’t hesitate to delve deeper into special permissions to leverage the full potential of Linux’s control mechanisms.