Today I had the issue that I could not login as sysoper on one database, despite being in the dba and oper groups.
The problem is that the osoper group was -probably- not selected during installation
e.g. in 12c /AIX
it may be called differently on your system
$ sqlplus -L -s / as sysoper
ERROR:
ORA-01017: invalid username/password; logon denied
$ awk '/H.17.*, 3/,/End/{print}' $ORACLE_HOME/rdbms/lib/config.s
.csect H.17.NO_SYMBOL{RO}, 3
.string ""
# End csect H.17.NO_SYMBOL{RO}
The string is empty. Let’s change this to oper or dba. Stopping any processes using that home is strongly recommended before relink.
$ vi $ORACLE_HOME/rdbms/lib/config.s
.string "dba"
$ relink
$ sqlplus -s -L / as sysoper
sho user
USER is "PUBLIC"
quit
$