How to set file access authority in Linux?

Understanding File Access Permissions in Linux

In the Linux operating system, file access permissions are a fundamental concept that determine who can read, write, and execute a file or directory. These permissions are crucial for ensuring the security and integrity of your system. Let's dive into the details of how to set file access authority in Linux.

Understanding File Permissions

In Linux, every file and directory has three main types of permissions:

1. Read (r): Allows the user to view the contents of the file or directory.
2. Write (w): Allows the user to modify the contents of the file or directory.
3. Execute (x): Allows the user to run the file as a program or access the contents of the directory.

These permissions are assigned to three different user categories:

1. Owner: The user who created the file or directory.
2. Group: The group to which the owner of the file or directory belongs.
3. Others: All other users on the system who are not the owner or part of the group.

The permissions for each user category are represented by a combination of the "r", "w", and "x" letters. For example, the permission "rwx" means the user has read, write, and execute permissions.

Viewing File Permissions

To view the file permissions, you can use the ls -l command in the terminal. This will display the file permissions in the following format:

-rw-r--r-- 1 user group 1024 Apr 15 12:34 file.txt

The first 10 characters represent the file permissions:

• The first character indicates the file type (- for regular file, d for directory).
• The next 3 characters represent the owner's permissions.
• The next 3 characters represent the group's permissions.
• The final 3 characters represent the permissions for all other users.

Changing File Permissions

To change the file permissions, you can use the chmod (change mode) command. The basic syntax is:

chmod [permissions] [file/directory]

Here's an example of how to give the owner read and write permissions, the group read-only permissions, and deny all permissions for others:

chmod 640 file.txt

The numbers 6, 4, and 0 represent the combination of permissions for the owner, group, and others, respectively. The number 6 represents rw- (read and write), 4 represents r-- (read-only), and 0 represents --- (no permissions).

You can also use symbolic notation to change permissions. For example, to give the owner read and write permissions, the group read-only permissions, and deny all permissions for others, you can use:

chmod u=rw,g=r,o=- file.txt

Here, u stands for the owner, g stands for the group, and o stands for others.

Changing Ownership and Group

In addition to setting file permissions, you can also change the owner and group of a file or directory using the chown (change owner) and chgrp (change group) commands, respectively.

chown user:group file.txt
chgrp group file.txt

Visualizing File Permissions with Mermaid

Here's a Mermaid diagram that illustrates the different file permission levels in Linux:

Real-World Example

Imagine you have a sensitive financial report that you want to share with your accounting team, but you don't want anyone else in the company to access it. You can set the file permissions to give the accounting group read-only access, while denying all permissions for other users. This way, the accounting team can view the report, but they can't modify or share it with unauthorized individuals.

By understanding and properly managing file permissions in Linux, you can ensure the security and privacy of your important files and directories, while still allowing authorized users to access the information they need.