If you are using Oracle RAC (doesn't matter how many nodes you have) You need to know where log files are located.
The Cluster Ready Services Daemon (crsd) Log Files
Log files for the CRSD process (crsd) can be found in the following directories:
CRS home/log/hostname/crsd
Oracle Cluster Registry (OCR) Log Files
The Oracle Cluster Registry (OCR) records log information in the following location:
CRS Home/log/hostname/client
Cluster Synchronization Services (CSS) Log Files
You can find CSS information that the OCSSD generates in log files in the following locations:
CRS Home/log/hostname/cssd
Event Manager (EVM) Log Files
Event Manager (EVM) information generated by evmd is recorded in log files in the following locations:
CRS Home/log/hostname/evmd
RACG Log Files
The Oracle RAC high availability trace files are located in the following two locations:
CRS home/log/hostname/racg
$ORACLE_HOME/log/hostname/racg
Core files are in the sub-directories of the log directories. Each RACG executable has a sub-directory assigned exclusively for that executable. The name of the RACG executable sub-directory is the same as the name of the executable.
You can follow below table which define locations of logs files:
Oracle Clusterware log files
Cluster Ready Services Daemon (crsd) Log Files:
$CRS_HOME/log/hostname/crsd
Cluster Synchronization Services (CSS):
$CRS_HOME/log/hostname/cssd
Event Manager (EVM) information generated by evmd:
$CRS_HOME/log/hostname/evmd
Oracle RAC RACG:
$CRS_HOME/log/hostname/racg
$ORACLE_HOME/log/hostname/racg
Oracle RAC 11g Release 2 log files
Clusterware alert log:
$GRID_HOME/log/<host>/alert<host>.log
Disk Monitor daemon:
$GRID_HOME/log/<host>/diskmon
OCRDUMP, OCRCHECK, OCRCONFIG, CRSCTL:
$GRID_HOME/log/<host>/client
Cluster Time Synchronization Service:
$GRID_HOME/log/<host>/ctssd
Grid Interprocess Communication daemon:
$GRID_HOME/log/<host>/gipcd
Oracle High Availability Services daemon:
$GRID_HOME/log/<host>/ohasd
Cluster Ready Services daemon:
$GRID_HOME/log/<host>/crsd
Grid Plug and Play daemon:
$GRID_HOME/log/<host>/gpnpd:
Mulitcast Domain Name Service daemon:
$GRID_HOME/log/<host>/mdnsd
Event Manager daemon:
$GRID_HOME/log/<host>/evmd
RAC RACG (only used if pre-11.1 database is installed):
$GRID_HOME/log/<host>/racg
Cluster Synchronization Service daemon:
$GRID_HOME/log/<host>/cssd
Server Manager:
$GRID_HOME/log/<host>/srvm
HA Service Daemon Agent:
$GRID_HOME/log/<host>/agent/ohasd/oraagent_oracle11
HA Service Daemon CSS Agent:
$GRID_HOME/log/<host>/agent/ohasd/oracssdagent_root
HA Service Daemon ocssd Monitor Agent:
$GRID_HOME/log/<host>/agent/ohasd/oracssdmonitor_root
HA Service Daemon Oracle Root Agent:
$GRID_HOME/log/<host>/agent/ohasd/orarootagent_root
CRS Daemon Oracle Agent:
$GRID_HOME/log/<host>/agent/crsd/oraagent_oracle11
CRS Daemon Oracle Root Agent:
$GRID_HOME/log/<host> agent/crsd/orarootagent_root
Grid Naming Service daemon:
$GRID_HOME/log/<host>/gnsd