Linux File Permissions and Access Control Lists
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File permissions and access control lists are mechanisms used to control access to files and directories in a computer system. They determine who can read, write, or execute files and directories, as well as who can modify the permissions themselves.
File Permissions: File permissions are a set of attributes associated with a file or directory that specify the actions that can be performed on it. These permissions are typically categorized into three levels of access: read (r), write (w), and execute (x).
Read (r): It allows a user to view the contents of a file or list the contents of a directory.
Write (w): It grants the ability to modify or delete a file, as well as create, rename, or delete files within a directory.
Execute (x): It allows the user to run or execute a file if it is an executable program or script. For directories, it permits the user to access and traverse the directory.
Each file or directory has permissions assigned to three different entities: the owner, the group, and others.
Owner: The owner of a file or directory is the user account that created it. The owner typically has the most control over the file, including the ability to modify permissions and change ownership.
Group: A group is a collection of user accounts. The group permissions determine the access rights for all users who are members of that group.
Others: "Others" refers to all users who are neither the owner nor members of the group associated with the file or directory.
For each entity (owner, group, and others), the file permissions can be set to allow or deny read, write, and execute access.
Access Control Lists (ACL): Access Control Lists (ACLs) are an extension to file permissions that provide more fine-grained control over access rights. While traditional file permissions allow permissions to be set for three entities (owner, group, and others), ACLs allow for additional entities to be defined, and specific permissions to be assigned to each entity.
ACLs are more flexible and can be used to grant or deny access permissions to specific users or groups on a file or directory. For example, with ACLs, you can grant read access to a specific user, even if they are not the owner or part of the group associated with the file.
ACLs can be managed through command-line tools or graphical interfaces provided by the operating system or file system.
In summary, file permissions and access control lists are security mechanisms that determine who can perform specific actions on files and directories in a computer system. They help protect sensitive data, enforce privacy, and ensure proper access control.