Unable to login to Sqlplus as sysdba: "ORA-01031: insufficient privileges"

Question

I can't login to sqlplus using:

sqlplus / as sysdba

All the time, it gives me:

ERROR: ORA-01031: insufficient privileges

If someone could help me, that would be awesome.

Answer 1

When you login like sqlplus / as sysdba i'm under the impression you are saying use the default login, and I do not want to enter a password.
In a linux unix environment the ORACLE_SID must be set to a value:

export ORACLE_SID=xxxdb

If this is not enought, look at sqlnet.ora in oracle_home/network/admin and make sure you do NOT have SQLNET.AUTHENTICATION_SERVICES=NONE (if you do -- you will get the ora-01031).