oracle报错cat: /etc/oratab: No such file or directory

cat: /etc/oratab: No such file or directory
提示找不到这个文件时可这样处理。
在oracle安装目录上找到root.sh并执行，这个要在root用户下进行操作。

[[email protected] db_1]# ./root.sh 
Performing root user operation for Oracle 11g 

The following environment variables are set as:
    ORACLE_OWNER= oracle
    ORACLE_HOME=  /u01/app/oracle/product/11.2.0/db_1

Enter the full pathname of the local bin directory: [/usr/local/bin]: 
   Copying dbhome to /usr/local/bin ...
   Copying oraenv to /usr/local/bin ...
   Copying coraenv to /usr/local/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 script.
Now product-specific root actions will be performed.
Finished product-specific root actions. 
[[email protected] db_1]# pwd
/u01/app/oracle/product/11.2.0/db_1