Attention log file is used to check the critical events in the Oracle database quickly. One instance of the database has one attention log file. Attention log is a structured, externally modifiable file that contains information about critical and highly visible database events.

Example of the Attention log file:

{
  "NOTIFICATION" : "Shutting down ORACLE instance (immediate) (OS id: 24084)",
  "URGENCY"      : "INFO",
  "INFO"         : "Shutdown is initiated by oradim.exe. ",
  "CAUSE"        : "A command to shutdown the instance was executed",
  "ACTION"       : "Check alert log for progress and completion of command",
  "CLASS"        : "CDB Instance / CDB ADMINISTRATOR / AL-1001",
  "TIME"         : "2022-10-26T17:09:00.201+05:30"
}

{
  "NOTIFICATION" : "Starting ORACLE instance (normal) (OS id: 45728)",
  "URGENCY"      : "INFO",
  "INFO"         : "Additional Information Not Available",
  "CAUSE"        : "A command to startup the instance was executed",
  "ACTION"       : "Check alert log for progress and completion of command",
  "CLASS"        : "CDB Instance / CDB ADMINISTRATOR / AL-1000",
  "TIME"         : "2022-10-26T17:09:25.857+05:30"
}

Check the location of the Attention log in Oracle Database 21c

set line 200
col value for a70
col name for a15
select name, value from v$diag_info where name = 'Attention Log';
NAME          VALUE
------------- ---------------------------------------------------------------
Attention Log  C:\APP\PRODUCT\21C\diag\rdbms\xe\xe\trace\attention_xe.log

View Attention Log file critical error as used message_level=1:

SELECT container_name, message_id, message_type, message_text, version, host_id, component_id FROM V$DIAG_ALERT_EXT WHERE message_level = 1;

Refer:

https://docs.oracle.com/en/database/oracle/oracle-database/21/admin/diagnosing-and-resolving-problems.html#GUID-633CC0D9-8FA8-4D98-8BE2-967D1CBEE266

https://docs.oracle.com/en/database/oracle/oracle-database/21/admin/diagnosing-and-resolving-problems.html#GUID-4A484D86-ED31-45CE-AECE-4384882A5A7A