A transaction log is a file that stores
information about DECdtm transactions performed on a node. It is
of file type .LM$JOURNAL.
Before a node can execute DECdtm transactions, you must create
a transaction log for the node. In an OpenVMS Cluster, create a
transaction log for each node in the cluster. Use the Log Manager
Control Program (LMCP) utility to create and manage transaction
logs.
DECdtm services use
the logical name SYS$JOURNAL to find transaction logs. You must
define SYS$JOURNAL to point to the directories that contain transaction
logs.
HP OpenVMS System Manager's Manual, Volume 2:... 
Managing DECdtm Services