What is Linux file permission?

Linux File Permissions

Linux file permissions are a set of rules that determine who can access, modify, or execute a file or directory. These permissions are essential for maintaining the security and integrity of the Linux file system.

Understanding File Permissions

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

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

These permissions are assigned to three different categories of users:

Owner: The user who created the file or directory.
Group: A group of users who have been granted specific permissions to the file or directory.
Others: 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 using a 10-character string, where 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 owner, group, and others.

For example, the file permission -rw-r--r-- can be interpreted as follows:

The first character (-) indicates that this is a regular file.
The next three characters (rw-) represent the permissions for the owner, which are read and write.
The next three characters (r--) represent the permissions for the group, which is only read.
The last three characters (r--) represent the permissions for others, which is also only read.

Modifying File Permissions

You can use the chmod (change mode) command to modify the permissions of a file or directory. The syntax for the chmod command is as follows:

chmod [options] mode file(s)

Here, mode can be specified in two ways:

Symbolic mode: Uses letters to represent the permissions, such as u for user (owner), g for group, o for others, and a for all. The permissions can be set using + to add, - to remove, and = to set the permissions.

Example: chmod u+x file.txt will add execute permission for the owner.
Octal mode: Uses a three-digit number to represent the permissions, where each digit represents the permissions for the owner, group, and others, respectively.

Example: chmod 755 file.txt will set the permissions to rwxr-xr-x.

graph TD A[File Permissions] --> B[Read (r)] A --> C[Write (w)] A --> D[Execute (x)] B --> E[Owner] B --> F[Group] B --> G[Others] C --> E C --> F C --> G D --> E D --> F D --> G

By understanding and properly managing file permissions, you can ensure the security and integrity of your Linux system, allowing only authorized users to access and modify files and directories as needed.