What are common Linux file permissions?

Linux File Permissions

Linux file permissions are a crucial aspect of system security and file management. They determine who can perform various actions on a file or directory, such as reading, writing, or executing. Understanding these permissions is essential for effectively managing and securing your Linux system.

File Permissions Structure

In Linux, file permissions are represented by a series of nine characters, which can be divided into three sets of three characters each. The first set represents the permissions for the file's owner, the second set represents the permissions for the file's group, and the third set represents the permissions for all other users (often referred to as "others" or "world").

The three characters in each set represent the following permissions:

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

For example, the file permissions rwxr-xr-- can be interpreted as follows:

• The owner has read, write, and execute permissions.
• The group has read and execute permissions.
• All other users have read-only permissions.

Viewing File Permissions

You can view the permissions of a file or directory using the ls -l command in the terminal. This will display the file permissions, along with other information such as the file owner, group, size, and modification date.

$ ls -l
-rwxr-xr-- 1 user group 1024 Apr 1 12:34 example.txt

In the example above, the file example.txt has the following permissions:

• The owner has read, write, and execute permissions.
• The group has read and execute permissions.
• All other users have read-only permissions.

Modifying File Permissions

You can change the permissions of a file or directory using the chmod (change mode) command. The chmod command takes two arguments: the new permissions and the file or directory name.

Here's an example of how to change the permissions of a file to allow the owner to read, write, and execute, the group to read and execute, and all other users to only read:

$ chmod 754 example.txt

In this example, the permissions are represented in octal notation, where:

• 7 represents rwx (read, write, execute) for the owner.
• 5 represents r-x (read, execute) for the group.
• 4 represents r-- (read-only) for all other users.

Mermaid Diagram: File Permissions

Real-World Examples

Imagine you have a script that automates a daily backup process. You want to ensure that only the system administrator can run this script, and no one else can modify it. In this case, you would set the permissions to rwx------ (700 in octal notation), which grants the owner full access while denying read, write, and execute permissions to the group and other users.

Another example could be a shared document folder in your office. You want everyone in the "finance" group to be able to read and write to the files, but you don't want other users to have any access. In this case, you would set the permissions to rw-rw---- (660 in octal notation), which grants read and write permissions to the owner and group, while denying all access to other users.

Understanding and properly managing file permissions is crucial for maintaining the security and organization of your Linux system. By mastering these concepts, you can ensure that your files and directories are accessible to the right users, while protecting sensitive information from unauthorized access.