遇到这样一个情况，之前做过将/u01/app/Oracle下所有文件拷备、还原的操作，现在想删除已存在的数据库时，发现dbca中delete database选项是灰色的。但实际是存在一个数据库的，因此我怀疑是配置文件没有匹配的原因。在网上找了些看，看到有说直接修改/etc/oratab内容就可以的，实际操作后也可以：
以下为/etc/oratab中的原始内容：
$ cat /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::
#
# 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.
#
#
# *:/u01/app/oracle/product/9.2:N
# *:/u01/app/oracle/product/9.2:N
# *:/u01/app/oracle/product/9.2:N
# *:/u01/app/oracle/product/9.2:N
# *:/u01/app/oracle/product/9.2:N
# *:/u01/app/oracle/product/9.2:N
# *:/u01/app/oracle/product/9.2:N
*:/u01/app/oracle/product/9.2:N
只需要将最后一条前面的*号改成你所想删除的ORACLE_SID即可。