Linux file permissions are a fundamental aspect of system security and file management, dictating how users can interact with files and directories.

Each file or directory has an associated set of permissions that determine the actions permitted for the owner, the group, and others.

These permissions are typically represented in a symbolic notation, such as -rwxr-xr--, where the first character indicates the type (e.g., - for a regular file, d for a directory), and the subsequent characters are divided into three triads representing the permissions for the owner, group, and others, respectively.

Within each triad, the characters r, w, and x denote read, write, and execute permissions, respectively, while a hyphen (-) signifies the absence of a permission. ​

To modify these permissions, the chmod command is commonly used. This command allows users to change the permissions of a file or directory using either symbolic or numeric (octal) notation.

In numeric mode (octal notation), permissions are represented by a three-digit value, where each digit corresponds to the permissions for the owner, group, and others.

Each permission is assigned a numeric value: read (r) is 4, write (w) is 2, and execute (x) is 1. By summing these values, one can determine the appropriate permission digit.

For example, a permission set of rwxr-xr-- translates to 755 in numeric notation, where the owner has read, write, and execute permissions (4+2+1=7), the group has read and execute permissions (4+1=5), and others have only read permission (4).

User roles in Linux are categorized into three distinct classes:​

• User (u): The owner of the file or directory.​
• Group (g): A set of users who share the same group privileges.​
• Others (o): All other users who are neither the owner nor part of the group.

Managing file ownership is crucial for maintaining proper access controls. The chown command is utilized to change the ownership of a file or directory, allowing administrators to assign a new owner and group to a file.

For example, sudo chown user2:group2 filename changes the owner to user2 and the group to group2.

Similarly, the chgrp command specifically modifies the group ownership of a file or directory. Properly setting ownership ensures that only authorized users can access or modify sensitive files. ​StationX

Understanding and correctly setting file permissions and ownership are vital for system security and efficient collaboration among users.

By leveraging commands like chmod, chown, and chgrp, administrators can finely tune access controls, ensuring that users have the appropriate permissions necessary for their roles while safeguarding critical system resources.​

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