案例环境：
操作系统 ：Oracle Linux Server release 5.7 64 bit
数据库版本：Oracle Database 10g Release 10.2.0.4.0 - 64bit Production
案例介绍： 在一个刚刚安装实例的服务器，使用dbca创建新的数据库时，在指定全局数据库名（Global Database Name）后，点击下一步时。报如下错误：The Oracle system identifier(SID) "SCM2" alread exits. Specify another SID
出现这个错误，是因为在/etc /oratab文件中已经指定了$ORACLE_SID（上次删除数据库时，没有彻底清除/etc/oratab），此时只需要将SCM2:/u01 /app/oracle/product/10.2.0/db_1:N 这一行删除或注释即可。
[root@DB-Server ~]# more /etc/oratab
#
# This file is used by ORACLE utilities. It is created by root.sh
# and updated by the Database Configuration Assistant when creating
# a database.
# A colon, ':', is used as the field terminator. A new line terminates
# the entry. Lines beginning with a pound sign, '#', are comments.
#
# Entries are of the form:
# $ORACLE_SID:$ORACLE_HOME:<N|Y>:
#
# The first and second fields are the system identifier and home
# directory of the database respectively. The third filed indicates
# to the dbstart utility that the database should , "Y", or should not,
# "N", be brought up at system boot time.
#
# Multiple entries with the same $ORACLE_SID are not allowed.
#
#
SCM2:/u01/app/oracle/product/10.2.0/db_1:N
