问题：
On a client machine:

[root@xxx]# mount -t nfs machine1:/opt/Oracle /opt/Oracle/
mount: machine1:/opt/Oracle failed, reason given by server: Permission denied


解决办法：

1)修改 /etc/exports on server machine

/opt/Oracle        192.168.5.2(rw)

note: 192.168.5.2 is client's ipaddress

2)然后重启服务

service nfs restart

note:
1) if you meet an error about "service: Command not found",go to /sbin directory run "./service nfs restart".
2) if you meet an error about "ifconfig: Command not found.", go to /sbin directory run "./ifconfig".