The UPDATEC command rebuilds an updated control data set and combines the entries in the specified journal data set with the restored backup copy of the backup control data set (BCDS), migration control data set (MCDS), or offline control data set (OCDS). You use the UPDATEC command to fix any major problems that occur in the control data sets.
When you issue the UPDATEC command, DFSMShsm places itself in emergency mode and does not write in the journal data set.