[Gllug] Multiple logins with NIS/YP

[Richard Cottrill]

Hmmm... I think I'll just go and quietly clean the egg from my face then.

Richard

> -----Original Message-----
> From: gllug-admin at linux.co.uk [mailto:gllug-admin at linux.co.uk]On Behalf
> Of Alan Peery
> Sent: Wednesday, February 13, 2002 8:12 PM
> To: gllug at linux.co.uk
> Subject: Re: [Gllug] Multiple logins with NIS/YP
>
>
>
>
> Richard Cottrill wrote:
>
> > I'm pretty sure that only one program can have a file open for
> writing at a
> > time.
>
> Nope.  Unix expects the applications to do the locking.  Try it.
> The following
> lines were constructed with two separate "cat >>fred" commands in
> different
> windows, typing alternate letters:
>
> a
> b
> c
> d
> e
> f
>
> File locking on Unix is up to the writing process.
>
> > I think you'll get some error about 'couldn't write to file' from any
> > decent program. NFS should enforce this sort of thing across an entire
> > network too.
>
> Too optimistic again.  If your program wants such locking, it
> uses the functions
> provided by the rpc.lockd and rpc.statd demons.
>
> > Now if a file is opened, written to, and closed; of course it
> can then be
> > overwritten.
>
> Absolutely.
>
>
> > I think a lot of common programs use their own lock files for
> > managing multiple instances; Navigator and pine certainly do.
>
> It's quite interesting what Netscape uses for the lock file--it makes
> ~/.netscape/lock a symlink pointing to "<ip_address>:process", which a new
> Nescape process will use *somehow* in determining if it should
> run and update
> files, or if it should complain about another process already running.
>
> Alan
>
>
>
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