queues on NFS share

Stephane Lentz Stephane.Lentz at ANSF.ALCATEL.FR
Wed Aug 14 07:34:36 IST 2002

On Tue, Aug 13, 2002 at 01:37:04PM +0100, Julian Field wrote:
> At 12:32 13/08/2002, you wrote:
> >I want to have my mailscanner incoming and outgoing queues on an NFS
> >share. Do I need to anything special to make it work? Any help would be
> >appreciated.
> This is generally a really bad idea. I think you'll get away with doing
> this with Exim.
> You will not get away with it if you are using sendmail. The file locking
> sendmail uses doesn't work over NFS. Bad things will happen to your mail.
> --

On the topic of locking, The Unix Programming FAQ says :
flock()' originates with BSD, and is now available in most (but not all)
Unices.  It is simple and effective on a single host, but doesn't work
at all with NFS.  It locks an entire file. Perhaps rather deceptively, the
popular Perl programming language implements its own `flock()' where
necessary, conveying the illusion of true portability.

`fcntl()' is the only POSIX-compliant locking mechanism, and is
therefore the only truly portable lock.  It is also the most powerful, and the
hardest to use.  For NFS-mounted file systems, `fcntl()' requests are
passed to a daemon (`rpc.lockd'), which communicates with the lockd on
the server host.  Unlike `flock()' it is capable of record-level locking

On linux.kernel I noticed a post :
       flock(2) does not  lock  files  over  NFS.   Use  fcntl(2)
       instead:  that  does  work  over NFS, given a sufficiently
       recent version of Linux and a server which supports  lock­

       flock(2)  and fcntl(2) locks have different semantics with
       respect to forked processes and dup(2).


NFS sharing a queue sounds like headache & problems  .....


Stephane Lentz / Alcanet International - Internet Services

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