[Beowulf] Concurrently open sockets limit on Linux system

Galton, Simon galtons at aecl.ca
Sun Jun 17 14:37:46 PDT 2007

Mark -- more good thoughts!

Ulimit doesn't seem to be an issue here, and the darn thing is definitely
only holding open one connection per client (according to lsof, that is).

Interestingly, /proc/sys/fs/file-nr reports something odd:
	cat /proc/sys/fs/file-nr
	1605    0       65535

This suggests that there are 0 free allocated file descriptors.  I'm not
clear on the implications here.  I can certainly continue to open files on
this box, and make new remote connections via ssh...


-----Original Message-----
From: Mark Hahn [mailto:hahn at mcmaster.ca]
Sent: 2007 Jun 17 3:20 PM
To: Galton, Simon
Cc: 'beowulf at beowulf.org'
Subject: Re: [Beowulf] Concurrently open sockets limit on Linux system

> The vendor feels that they have not coded a specific limit; I'm wondering

in cases like this, I tend to do things like replace the license
manager by a script that first does "ulimit -a" before execing 
the actual program.  if the license manager is being execed through
su to run unprivileged, for instance, it's not always obvious whether
some ulimit is in effect.  similarly, I often cut to the chase and 
run such a daemon under strace, to see what it's doing that fails.

128-clients is such a low number that it doesn't sound like something
more exotic like an ephemeral-port-range limit.  128 is remarkably low,
though - you'd expect a multi-connection daemon might burn one fd 
per connection, but even a very desktop-y setting of NOFILE to 1024
would imply that the daemon is keeping ~8 fd's open per connection.

> it's file descriptors or somesuch.  I raised the limit of FDs on the
> to 65000+ and verified that the change took effect; no change to the

the system-wide (/proc/sys) setting is not likely to be the issue.

> This e-mail, and any attachments, may contain information that

are you aware that this nonsense has _no_ legal standing?

regards, mark hahn.

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