I login as "oracle" user in unix machine. I am able to login as another user
But when another unix user tries to use sqlplus he gets following
error:SQL*Plus: Release - Production on Mon Oct 7 10:50:21 2002
(c) Copyright 2000 Oracle Corporation. All rights reserved.
Enter user-name: hra
Enter password:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
SVR4 Error: 2: No such file or directory
But if use /userid/passwd@service_name then it log in correctly. Also if I set

TWO_TASK sqlplus does not give error. But I am logging to directly server,
therfore without servicename I should be able to login to sqlplus.
Puzzle is that I am able to work fine when I login as unix user "ORACLE" but
get errors when try to login as another unix user. I also checked that
ORACLE_SID is in proper case. (ps -ef | grep SMON)
I want to login without using vNet8.