sql> oradebug setmypid 

sql> oradebug dump controlf 3

1 ：only the file header

2 ：just the file header, the database info record, and checkpoint progress records 

3 ：all record types, but just the earliest and latest records for circular reuse record types 

4 ：as above, but includes the 4 most recent records for circular reuse record types 

5+ ：as above, but the number of circular reuse records included doubles with each level