案例環境：
操作系統 ：Oracle Linux Server release 5.7 64 bit
數據庫版本：Oracle Database 10g Release 10.2.0.4.0 - 64bit Production
案例介紹： 在一個剛剛安裝實例的服務器，使用dbca創建新的數據庫時，在指定全局數據庫名（Global Database Name）後，點擊下一步時。報如下錯誤：The Oracle system identifier(SID) "SCM2" alread exits. Specify another SID
出現這個錯誤，是因為在/etc/oratab文件中已經指定了$ORACLE_SID（上次刪除數據庫時，沒有徹底清除/etc/oratab），此時只需要將SCM2:/u01/app/oracle/product/10.2.0/db_1:N 這一行刪除或注釋即可。
[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
