[oracle@testdb ~]$ sqlplus / as sysdba
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit

[oracle@testdb ~]$ lsnrctl stop
LSNRCTL for Linux: Version 11.2.0.4.0 - Production on 23-DEC-2016 14:44:52
Copyright (c) 1991, 2013, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=testdb)(PORT=1521)))
The command completed successfully

[root@testdb ~]# service httpd stop
Stopping httpd: [ OK ]

[root@testdb ~]# rm -rf /u01/app/oracle/
[root@testdb ~]# rm -rf /u01/app/oraInventory/

[root@testdb ~]# rm -rf /usr/local/bin/dbhome
[root@testdb ~]# rm -rf /usr/local/bin/oraenv
[root@testdb ~]# rm -rf /usr/local/bin/coraenv

[root@testdb ~]# rm /etc/oratab

[root@testdb ~]# rm /etc/oraInst.loc

[root@testdb ~]# userdel -r oracle

[root@testdb ~]# groupdel oinstall
[root@testdb ~]# groupdel dba

[root@testdb ~]# chkconfig