To reboot a single cluster element on a COB board, use the rms_boot command.
For example, assume a COB board is installed in slot 3 in a shelf named 'everest'. To reboot cluster element 5 on that board, issue the following command:
rms_boot 5 3 everest
A cluster element warm reset takes approximately X seconds. Use the rms_ip command to retrieve the IP address of an element, then attempt a connection with telnet or ssh: if the reboot is complete, the element will respond to the connection request.