这种原因是安装oracle的时候，忘记去执行 一个root.sh文件了，当然，需要用root用户执行：
解决办法：
[root@localhost 10.2.0]#cd /oracle/product/10.2.0/db_1
[root@localhost 10.2.0]# ./root.sh
The following environment variables are set as:
ORACLE_OWNER= oracle
ORACLE_HOME= /opt/oracle/product/10g
Enter the full pathname of the local bin directory: [/usr/local/bin]:
Copying dbhome to /oracle/product/10.2.0/db_1/bin
./root.sh: line 155: [: too many arguments
./root.sh: line 175: [: too many arguments
Copying dbhome to Copying dbhome to /oracle/product/10.2.0/db_1/bin ...
./root.sh: line 175: [: too many arguments
Copying oraenv to Copying dbhome to /oracle/product/10.2.0/db_1/bin ...
./root.sh: line 175: [: too many arguments
Copying coraenv to Copying dbhome to /oracle/product/10.2.0/db_1/bin ...
Creating /etc/oratab file...
Entries will be added to the /etc/oratab file as needed by
Database Configuration Assistant when a database is created
Finished running generic part of root.sh script.
Now product-specific root actions will be performed.