注释部分已经说的比较清楚 ，主要是可以设置为自动启动实例，当linux os启动的时候 。 还有DBCA的时候升级，删除数据库时找到相关实例 。
epd2db$cat 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/product/oracle:N
*:/u01/product/oracle:N
epd2:/u01/product/oracle:N
ibml6rma:/u01/product/oracle:N
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