How to resolve ora error ORA-00823?

ORA-00823: Specified value of sga_target greater than sga_max_size

This error tells us that there is configuration error:
*.sga_target was set to a value that is larger than value of *.sga_max_size
so that after you reboot Oracle server, database won't been brought up automatically even you've configured to auto start/restart when server reboot.

How to resovle such error?

Step 1: use sqlplus to connect to idle instance and create a temporary pfile.

• sqlplus /nolog
• conn / as sysdba
• create pfile=’$ORACLE_HOME/dbs/init_temp.ora’ from spfile;

Step 2: Exit sqlplus and edit init_temp.ora file to correct wrong configuration parameters: set value of sga_target to a smaller amount that is less than or equal to value of *.sga_max_size

Step 3: start oracle database with this pfile:
startup PFILE='/$ORACLE_HOME/dbs/init_temp.ora';

Step 4: after database has been started up and opened, shut down it by shutdown immediate;

Step 5: Create SPFILE:
reate spfile from pfile='$ORACLE_HOME/dbs/init_temp.ora';

Step 6: start up database in normal way by executing startup;