To check the alert logfile of database?

1)to check the alert log of database?
connect to sqlplus in dbtier
sqlplus / as sysdba

SQL> show parameter background;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
background_core_dump                 string      partial
background_dump_dest                 string      /home/u12/d01/oracle/VIS/db/te
                                                 ch_st/11.1.0/admin/VIS_ebus/di
                                                 ag/rdbms/vis/VIS/trace


In trace directory there will be the alert logfile.

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.

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 a directory below the value of the DIAGNOSTIC_DEST parameter: DIAGNOSTIC_DEST/diag/rdbms/DB_NAME/ORACLE_SID/trace. If this later parameter is not set, the alert.log file is created in the ORACLE_HOME/rdbms/trace directory.