Given the command 
  condor_off hostname2
an error message of the form 
  Can't find address for master hostname2.somewhere.edu
appears. Yet, when looking at the host names with 
  condor_status -master
the output is of the form 
  hostname1.somewhere.edu
  hostname2
  hostname3.somewhere.edu

To correct this incomplete host name, add an entry to the configuration file for {DEFAULT_DOMAIN_NAME} that specifies the domain name to be used. For the example given, the configuration entry will be 

  DEFAULT_DOMAIN_NAME = somewhere.edu

After adding this configuration file entry, use condor_restart to restart the HTCondor daemons and effect the change.