问题1.sqlplus login -- SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory 

在/etc/profile最后加入:

      export ORACLE_HOME=/u01/app/oracle/product/11.2.0/dbhome_1
export PATH=/u01/app/oracle/product/11.2.0/dbhome_1/bin:$PATH
    

source /etc/profile

问题2.

Enter user-name: system
Enter password:
ERROR:
ORA-12162: TNS:net service name is incorrectly specified

解决方案：sqlplus 加入上实例名，例如以下所看到的

sqlplus system/Hello54987663@localhost:1521/orcl