[ILUG] Showmount "completeness and accurary"

[Paul Jakma]

On Wed, 26 Jun 2002, Niall O Broin wrote:

> If I simply remove /var/lib/nfs/rmtab how can I make it be recreated
> correctly ?

you cant.

rmtab holds state of which clients have mounted fs's on your server.  
blow that file away and you've lost the info forever. a reboot of your
server will require all clients to remount. (exportfs -r will probably 
do the same - eg if you add a new dir to be exported).

you can try exportfs -u host:/....

might work. or 

- delete the specific lines you know arent valid anymore
- exportfs -r

> Niall

Quoting Neil Brown on the NFS list recently:

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Maybe a little explanation of how it all works will help:

/etc/exports contains information about how file systems should
     normally be exported.  This is only read by exportfs.

/var/lib/nfs/etab contains information about what filesystems should
     be exported to whom at the moment.

/var/lib/nfs/rmtab contains a list of which filesystems actually are
     mounted by certain clients at the moment.

/proc/fs/nfs/exports contains information about what filesystems are
     exported to actual client (individual, not subnet or whatever)
     at the moment.

/var/lib/nfs/xtab is the same information as /proc/fs/nfs/exports but
     is maintained by nfs-utils instead of directly by the kernel.  It
     is only used if /proc isn't mounted.

When a mount request arrives, mountd check .../etab to see if that
host is allowed access.  If it is, an entry is placed in .../rmtab and
the filesystem is exported thus creating an entry in
/proc/fs/nfs/exports.


When you run
    exportfs -io  options host:/dir

then the entry in ../etab is changed, or a new one is added.
If it is a subnet/wildcard/netgroup entry, then every line in ../rmtab
is checked to see if it matches.  When a match is found, a
host-specific entry is given to (or changed in) the kernel.

When you run
    exportfs -a

it makes sure that all entries in /etc/exports are properly reflected
in .../etab.  Any extra entries in etab are left alone.  Once the
correct content of etab has been determined, rmtab is examine to
create a list of specific-host entries for any new entries in etab.
This host-specific entries are given to the kernel.

When you run
    exportfs -r
it ignores the prior contents of .../etab and initialises etab to the
contents of /etc/exportfs.  Then it inspects rmtab and make an changes
to /proc/fs/nfs/export that are necessary.


In general, the safest thing to do is edit /etc/exports and run
   exportfs -r

If this leaves you will /proc/fs/nfs/exports containing something that
you didn't expect, please show me the details (exportfs,etab,rmtab)
and I will look again.

NeilBrown
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regards,

--paulj