CentOS - Jun 2008 - nfs cannot see mount points on other machine

I'm having a bit of a problem with what I can "see" over nfs.
I have two machines that nfs their root to each other and it seems to 
work. However, I now found out that some of the root directories that are 
listed are "fake" ones. A comparison of the root on both machines
shows
that some directories are the same and I can access those files on the 
other machine. However, there are some directories that are different.

That is true for all the "special" directories like dev, proc, sys
(which
makes some sense), but also for directories that are mount points on the 
other machine. Does nfs not give me access to those mount points? Do I 
have to create a second nfs mount to that machine which mounts only that 
mount point? Or do I need some parameter to mount these mount points under 
the normal mount?

What's weird is that if I create a file in these "fake"
directories I can
do that and it's listed like it actually were created on the other 
machine. But it gets created on *this* machine. When I then unmount, it's 
gone (like the whole nfs mount) and when I remount it's back. Where is it 
actually getting created and how can I remove it? Is there some nfs cache 
that holds it?

Kai

-- 
Kai Sch?tzl, Berlin, Germany
Get your web at Conactive Internet Services: http://www.conactive.com

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Kai Schaetzl
> Sent: Thursday, June 26, 2008 10:24 AM
> To: centos at centos.org
> Subject: [CentOS] nfs cannot see mount points on other machine
> 
> I'm having a bit of a problem with what I can "see" over nfs.
> I have two machines that nfs their root to each other and it 
> seems to work. However, I now found out that some of the root 
> directories that are listed are "fake" ones. A comparison of 
> the root on both machines shows that some directories are the 
> same and I can access those files on the other machine. 
> However, there are some directories that are different.
Was having a similar problem this morning, just listed them too as mounts on top
of the other mounts.
> 
> That is true for all the "special" directories like dev, 
> proc, sys (which makes some sense), but also for directories 
> that are mount points on the other machine. Does nfs not give 
> me access to those mount points? Do I have to create a second 
> nfs mount to that machine which mounts only that mount point? 
> Or do I need some parameter to mount these mount points under 
> the normal mount?
> 
>From man exports
nohide 

This option is based on the option of the same name provided in IRIX NFS.
Normally, if a server exports two filesystems one of which is mounted on the
other, then the client will have to mount both filesystems explicitly to get
access  to  them.   If  it just  mounts the parent, it will see an empty
directory at the place where the other filesystem is mounted.  That filesystem
is "hidden".

Setting the nohide option on a filesystem causes it not to be hidden, and an
appropriately authorised client will  be  able  to move from the parent to that
filesystem without noticing the change.

However,  some  NFS clients do not cope well with this situation as, for
instance, it is then possible for two files in the one apparent filesystem to
have the same inode number.

The nohide option is currently only effective on single host exports.  It does
not work  reliably  with  netgroup,  subnet,  or wildcard exports.

This  option  can  be  very  useful in some situations, but it should be used
with due care, and only after confirming that the client system copes with the
situation effectively.

The option can be explicitly disabled with hide.

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