ORA-27121 unable to determine size of

퍼미션 에러인듯 싶더군요.

ORACLE_HOME/bin] chmod 6751 oracle
잘돌아갑니다.
위처럼 하면

-rwxr-xr-x   1 oracle     dba        77762776 1월 29일 13:15 oracle
->>> 이렇게 권한이 바뀝니다. s로 바뀌지요. s에 대한 자세한 설명은 유닉스나 리눅스 사용 권한을 참조하세요.
-rwsr-s--x   1 oracle     dba        77762776 1월 29일 13:15 oracle

Make sure file 'oracle' has the following permissions:
cd $ORACLE_HOME/bin
6751
If not...
1. Login as oracle user
2. Shutdown (normal) the db
3. Go to $ORACLE_HOME/bin
4. Execute the following
chmod 6751 oracle
5. Check the file permissions on oracle using the following
ls -l oracle
they should be:
-rwsr-s--x
Startup the db and try connecting as dba or non-oracle user.
if this will not work:
- make sure permisions on oracle filesystems are set correctly ( set to 755)
- filesystem must be mounted with correct setuid