How are file permissions changed in a Linux system?

In a Linux system, file permissions can be modified using the chmod command. This command allows users to change the read, write, and execute permissions for files and directories. The syntax of chmod includes representing permissions either numerically or symbolically, enabling fine-grained control over the access privileges assigned to users, groups, and others.

For instance, when using the numerical method, permissions can be set using a three-digit octal representation, where each digit corresponds to user, group, and others, respectively. Each permission is represented by a specific value: read (4), write (2), and execute (1). By combining these values, users can effectively alter the permissions of a file.

Using chmod is standard practice in Linux environments, and it is a fundamental command that system administrators and users must understand for managing file security. The other options provided do not represent valid commands in Linux for changing file permissions, which makes them irrelevant in this context.