The command to set the SUID permission on a file named rider is "chmod u+s rider". This command will set the SUID permission on the file, which means that the file will be executed with the permissions of the owner of the file, rather than the permissions of the user who is executing it. This is useful for programs that need to run with elevated privileges, such as those that manage system resources. If you are unsure of how to set the SUID permission on a file, you can consult the man page for the chmod command for more information.