I'm trying to build cluster computer system using redhat linux enterprise 5.5. And I'm on the step to set up the NFS mounting. (step 3 of part VI on this paper: http://www.cs.uiowa.edu/~jni/HowTo/H...dAClusterG.pdf)

However, I kept getting "permission denied" when I used the command "mount -t" to mount the slave node onto the hard drive of the master node. Even when I edited /etc/fstab file to make it automatically set up during booting, I still receive the same result. By the way, I've already logged in as a root user on both slave and master nodes.

I'll first say that when running a clustered environment, I wouldn't recommend having one of the essential components of a service, in this case the NFS mount point, be located on one of the nodes within the cluster. Instead, have a NAS or SAN to handle this aspect. But looking at the guide you're following, I'll go ahead and guess that this is just for research in general. That being said, if you're getting a permission denied error when trying to mount the NFS share, then it means exactly that...you don't have proper permissions. Here's what you can check:

1. /etc/hosts (make sure the entries in here match up to what the IP address and hostname for the machines actually are)
2. Check /etc/exports to make sure that you haven't denied access due to the ipaddress restriction. To make sure it's working, you can just replace the IP address with a "*" to allow all users momentarily. Restart the NFS service afterwards to pick up the changes. (you can also 'exportfs' instead of restarting NFS, but whatever...)
2. Run the following command to determine if you have your firewall setting up (you may be blocking NFS traffic. Remember that with NFS3 mounts, there are more ports that need to be allowed to go through. NFS4 simplified this part:

# iptables -L (this will list out your current rules in place)

To test if it's your firewall blocking traffic, temporarily flush them:

# iptables -F

Now try mounting the NFS share again (this is for NFS3):

# mount -t nfs xxx.xxx.xxx.xxx:/export /mnt

Obviously change the "/export" to the actual exported directory from the NFS server. If none of this seems to get you further, provide the following:

/etc/exports
/etc/hosts
# ifconfig
# iptables -L