[CentOS] nfs cannot see mount points on other machine

Kai Schaetzl maillists at conactive.com
Fri Jun 27 14:31:31 UTC 2008

Toby Bluhm wrote on Fri, 27 Jun 2008 08:54:56 -0400:

> I don't understand your talk about "fake" directories. They are not
> fake, they truly exist in the filesystem.

They are nevertheless fake. Consider the following:
- system A has mount points / and /home
- system B nfs mounts / on A without nohide at /nfs/A

Result is that you see *all* directories of A on B, including /home. There 
is no way to know that it doesn't exist on A, unless you compare the 
directories on both machines. There is no indication that you are not 
writing to A:/home when you write to /nfs/A/home. That is what I call 
"fake". It's definitely not "hidden". "hidden" comes from "hiding" = you 
don't see it. I consider this behavior *very* misleading.

> That NFS only exports a single partition at a time is probably due to
> the duplicate inode problem - maybe other stuff - I don't know. At any
> rate, just export the additional fs and mount it where you like. Again,
> nothing mysterious and it has been done that way since NFS was invented.

That may be so. I'm quite happy with this behavior as long as nfs doesn't 
pretend that something is there that isn't.

I was asking "where" that faked directory actually exists as it is gone 
when I unmount. If I understand your explanation correctly if I write to 
/nfs/A/home I'm actually writing to A, but not to the /home filesystem (as 
I think) but to a home directory on the / filesystem. Is that correct?
That makes clear why it is gone when I unmount. Further, if I unmount 
/home on A I should still get /home when I list / on A. Just now that 
"faked" home on /. Correct?

I understand that this directory *does* exist on A (just not where one 
would think) *after* nfs mounting. However, from the standpoint of machine 
B it is a fake. It is artificially being created because an ls on A shows 
it. The correct behavior would be to *not list* any other mount points in 
the nfs mount.


Kai Schätzl, Berlin, Germany
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