Re: [TCLUG:15107] nfs exports

["Eric M. Hopper" <hopper@omnifarious.mn.org>]

On Thu, Mar 23, 2000 at 12:29:30PM -0800, Carl Wilhelm Soderstrom wrote:
>         I'm trying to devise a recovery-from-backup scheme for my network. 
>         the theory is; if a machine dies; all I should have to do is insert
> a tomsrtbt disk into the new machine; boot from that; nfs-mount the tape
> drive on a server; and restore from the last backup tape over nfs.
>         this is what I thought I had heard of people doing.
> 
>         however, I can't seem to export the tape drive (/dev/st0) as an nfs
> export. the client always says:
> mount: <serverIP>:/dev/st0 failed, reason given by server; Permission denied.
> 
> on the server:
>         /var/lib/nfs/xtab seems to show it as an available mount point;
>         but /proc/fs/nfs/exports shows nothing. :(
> 
>         if I do a exportfs -av <IPaddress of client>:/dev/st0; it complains
> about /dev/st0 not being a directory.
>         I've chmod'ed /dev/st0 to 664 (instead of the 660 it used to be);
> wondering if that would make a difference.
>         I've made sure portmapper is running; and allowed connections to it
> (from our subnet) in /etc/hosts.allow
>         I've started and stopped and restarted nfs several times
> 
> this is using knfsd on a RH 6.1 box.
> 
> could it be that nfs refuses to export a device?
> 
> my only other experience with NFS has been on a RH 5.2 box... which
> seemed to be infinitely easier. (then again, I wasn't trying the same
> thing...)

	I believe you are correct in that NFS refuses to export a
device.  It also doesn't do UNIX domain sockets, and it doesn't handle
two processes on different machines trying to communicate through a fifo
mounted on the same place.

	The reason for this is that NFS is 'stateless'.  Most devices
have a lot of state associated with them being opened by something.
Most files don't.

	Actually, it really isn't stateless.  NFS slings i-node numbers
around your network with wild abandon, thereby making your entire
filesystem part of it's state.  This is why you can't export an NFS
directory and have all the directories mounted from different places
also be exported.  Each filesystem has to be NFS exported and mounted
seperately.

	It also causes ReiserFS endless difficulties because it makes
assumptions about directories just being normal files who's contests
have special meaning to the filesystem.  This isn't the case under
ReiserFS, and requires a kludgey patch to allow ReiserFS filesystems to
be mounted via NFS.

	NFS is an evil kludge, and should be expunged and replaced with
something better.

Have fun (if at all possible),
-- 
Its name is Public Opinion.  It is held in reverence. It settles everything.
Some think it is the voice of God.  Loyalty to petrified opinion never yet
broke a chain or freed a human soul.     ---Mark Twain
-- Eric Hopper (hopper@omnifarious.mn.org  http://omnifarious.mn.org/~hopper) --

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