Linux permissions are a fundamental aspect of the operating system's security model, determining who can access files and directories and in what manner. These permissions are crucial for maintaining system integrity and security.

File and Directory Permissions

In Linux, every file and directory is associated with an owner and a group, and permissions are set for three categories of users: the owner, the group, and others. Permissions are represented symbolically as 'r' for read, 'w' for write, and 'x' for execute. For directories, these permissions have specific meanings:

• Read: List the contents of the directory.

• Write: Add or remove files from the directory.

• Execute: Access the directory and its metadata.

Viewing Permissions

To view permissions, you can use the ls -l command, which displays a long listing format including file permissions. For example:

The first character indicates the file type, with '-' for a regular file and 'd' for a directory. The next nine characters show the permissions for the owner, group, and others.

Changing Permissions

To change permissions, the chmod command is used. Permissions can be modified using either symbolic mode or numeric mode (octal values). For example, to add execute permission for the group and others to a file, you would use:

In numeric mode, permissions are represented by numbers: 4 for read, 2 for write, and 1 for execute. To set permissions to read and write for the owner, and read-only for the group and others, you would use: