In the normal case, heartbeat generates a UUID[1] for each node in the system as a way of uniquely identifying a node - even if it should change nodenames. This UUID[1] is typically stored in the file /var/lib/heartbeat/hb_uuid.
For certain kinds of installations (those booting from CDs or other read-only media), it is impossible for heartbeat to save a generated to disk as it normally does. In these cases, one can use the uuidfrom directive to instruct heartbeat to use the nodename as though it were a UUID[1], by specifying uuidfrom nodename.
All possible legal uuidfrom directives are shown below.
uuidfrom file uuidfrom nodename
| [1] | http://en.wikipedia.org/wiki/UUID |
This information provided courtesy of the Linux-HA project at http://linux-ha.org/