Instance startup and configuration Log files are located for INST_TOP in Oracle Release 12.1.3
$INST_TOP/logs/appl/admin/log
Startup/Shutdown error message related to tech stack (10.1.2, 10.1.3 forms/reports/web)
$INST_TOP/logs/ora/ (10.1.2 & 10.1.3)
$INST_TOP/logs/ora/10.1.3/Apache/error_log[timestamp](Apache log files)
$INST_TOP/logs/ora/10.1.3/opmn/ (OC4J, oa*, opmn.log)
$INST_TOP/logs/ora/10.1.2/network/ (listener log)
$INST_TOP/apps/$CONTEXT_NAME/logs/appl/conc/log (CM log files)