[oracle@swnode1 ~]$ adrci

ADRCI: Release 12.2.0.1. - Production on Fri Jul  :: 

Copyright (c) , , Oracle and/or its affiliates.  All rights reserved.

ADR base = "/u01/app/oracle"

adrci> show homes

ADR Homes:

diag/clients/user_oracle/host_2908371209_107

diag/rdbms/orcl/gnnt1

[oracle@swnode1 ~]$ tail -f /u01/app/oracle/diag/rdbms/orcl/gnnt1/alert/log.xml

 <txt>Please see the VKTM trace file for more details:

 </txt>

</msg>

<msg time='2018-07-05T09:12:34.163+08:00' org_id='oracle' comp_id='rdbms'

 type='UNKNOWN' level='16' host_id='swnode1'

 host_addr='::1' pid='23141' con_uid='1'

 con_id='1' con_name='CDB$ROOT'>

 <txt>/u01/app/oracle/diag/rdbms/orcl/gnnt1/trace/gnnt1_vktm_23141.trc

 </txt>

</msg>

^C