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Support use of xrootd by HEP experiments

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Subject:
From:
Peter Elmer <[log in to unmask]>
Date:
20 Aug 2004 07:04:24 +0200Fri, 20 Aug 2004 07:04:24 +0200
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  Hi Andy,

On Thu, Aug 19, 2004 at 10:07:16PM +0200, Andrew Hanushevsky wrote:
> Creating a pid file in /tmp (or in /var/run) is standard practice of almost
> all system services. This file *is* used by processes that have to notify
> the olbd.

  xrootd itself doesn't create any such file.

  This presumably permits one to run only one olbd on any given machine
at a time, no? That would seem to disallow the separate "test system"
that we have discussed in the past from running on the same set of hardware.

  What exactly uses this file to notify the olbd? The xrootd on the redirector
finds its olbd via the "odc.manager" directive, correct?

  Ah, what happens on the data servers? If I have understood correctly the
default is that the xrootd there does _not_ connect to its olbd on its
data server. If the "-t" option is used with xrootd (config directive 
"ofs.redirect target") it _will_ connect with the olbd and if the olbd in
addition has "-w" ("olb.wait") enabled it won't actually agree to have 
anything redirected at it unless an xrootd is in fact connected. Since
"ofs.redirect target" doesn't in fact take a port argument, how does the
xrootd on the data server find the olbd? Is it using the /tmp/olbd.pid file? 
Besides enabling this mechanism, what else does the data server xrootd 
connecting with its olbd allow?

                                   Pete


> ----- Original Message ----- 
> From: "Peter Elmer" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, August 19, 2004 5:00 AM
> Subject: /tmp/olbd.pid
> 
> 
> >   Hi Andy,
> >
> >   I see that the olbd creates a small turd file when it is started:
> >
> > shire01> ls /tmp/olb*
> > /tmp/olbd.pid
> >
> >   Why is this file needed? (i.e. who or what uses it?)
> >
> >   I'm not particularly fond of these sorts of files in /tmp if they aren't
> > absolutely critical (even if they have the pid in the name to make it more
> > unique, which this one doesn't). They usually just cause headaches as one
> > user can trip over something some other user has done at some point in the
> > past on the same machine...
> >
> >                                  thanks,
> >                                    Pete



-------------------------------------------------------------------------
Peter Elmer     E-mail: [log in to unmask]      Phone: +41 (22) 767-4644
Address: CERN Division PPE, Bat. 32 2C-14, CH-1211 Geneva 23, Switzerland
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