Which of the following commands is used to change file permissions in Linux?

The command used to change file permissions in Linux is "chmod." This command allows users to modify the access rights associated with files and directories, enabling the specification of who can read, write, or execute a file. Permissions in Linux are assigned to three categories: the owner of the file, the group associated with the file, and others.

By using the "chmod" command, one can set or modify these permissions using either symbolic (r, w, x) or numeric (octal) notation. For example, you might use chmod 755 filename to give the owner full permissions while granting read and execute permissions to both the group and others.

The other commands serve different purposes: "chown" is utilized to change the ownership of a file or directory, assigning a new owner or group; "chgrp" specifically changes the group ownership of a file; and "touch" is used to create new empty files or to update the timestamps of existing files. These commands do not affect the permissions of a file, which is the primary function of "chmod."