The Chubby lock service is a coarse-grained lock service (locks that are held for a long time).
Chubby normally is run in a cluster of 5 (1 master, 4 replicas) that use paxos to elect a master. DNS finds the replicas, which can connect to the current master.
The file interface exposed by chubby is simpler than UNIX -- moving files from one directory to another is not allowed, directory modified times are not kept, and last-access times are not kept either.
Writing to a file requires an exclusive lock, whereas reading from a file does not.