What are Linux permissions?

Linux Permissions

Linux permissions are a fundamental concept in the Linux operating system that control who can access and perform specific actions on files and directories. These permissions determine the level of access and the types of operations that users, groups, and the system can perform on a given resource.

Understanding File Permissions

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

Read (r): Allows the user to view the contents of a file or list the contents of a directory.
Write (w): Allows the user to modify the contents of a file or create, delete, or rename files and directories.
Execute (x): Allows the user to run a file as a program or access the contents of a directory.

These permissions are assigned to three different entities:

User (u): The owner of the file or directory.
Group (g): A group of users who have been granted specific permissions.
Others (o): All other users on the system who are not the owner or part of the group.

The permissions for a file or directory are typically represented in a string of 10 characters, such as -rw-r--r--. The first character indicates the file type (e.g., - for a regular file, d for a directory), and the remaining nine characters represent the permissions for the user, group, and others.

graph TD A[File/Directory] --> B(User) A --> C(Group) A --> D(Others) B --> E[Read] B --> F[Write] B --> G[Execute] C --> H[Read] C --> I[Write] C --> J[Execute] D --> K[Read] D --> L[Write] D --> M[Execute]

Changing Permissions

You can change the permissions of a file or directory using the chmod (change mode) command. The basic syntax is:

chmod [options] mode file_or_directory

For example, to give the user read and write permissions, the group read permissions, and others no permissions, you would use the following command:

chmod 640 file.txt

In this command, the mode 640 represents the permissions:

User: 6 (read and write)
Group: 4 (read)
Others: 0 (no permissions)

You can also use symbolic notation to change permissions, such as:

chmod u+x,g+r,o-w file.txt

This command adds execute permission for the user, adds read permission for the group, and removes write permission for others.

Practical Examples

Imagine you have a personal journal file that you want to keep private. You can set the permissions to allow only you to read and write to the file:

chmod 600 journal.txt

Now, let's say you have a shared directory where your team collaborates on project files. You can set the permissions to allow your team members (the group) to read and write to the files, while others have no access:

chmod 770 project_files/

In these examples, the permissions ensure that only authorized users can access and modify the sensitive information, helping to maintain the security and privacy of your files and directories.

Understanding Linux permissions is crucial for effectively managing and securing your files and directories, as well as collaborating with others in a multi-user environment.