Alert log

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The alert log file (also referred to as the ALERT.LOG) is a chronological log of messages and errors written out by an Oracle Database. Typical messages found in this file is: database startup, shutdown, log switches, space errors, etc. This file should constantly be monitored to detect unexpected messages and corruptions.

Oracle will automatically create a new alert log file whenever the old one is deleted.

[edit] Location of the ALERT.LOG file

Oracle will write the alert.log file to the directory as specified by the BACKGROUND_DUMP_DEST parameter. If this parameter is not set, the alert.log will be created in the ORACLE_HOME/rdbms/trace directory.

SQL> show parameter BACKGROUND_DUMP_DEST

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
background_dump_dest                 string      /app/oracle/diag/rdbms/o11gr1/
                                                 o11gr1/trace

[edit] Writing to the ALERT.LOG file

Users can write messages to the alert.log file. Example:

 -- Write message to alert.log
 exec dbms_system.ksdwrt(2, 'Look Ma, I can write to the alert.log file!');
 PL/SQL procedure successfully completed.

 -- Flush the buffer
 exec dbms_system.ksdfls;
 PL/SQL procedure successfully completed.