expectperl-discuss

[Expectperl-discuss] Limit on number of Expect sessions?

[Richards, K. <Kei...@Co...>]

Hi,

I'd like to maintain a number of simultaneous ssh connections from one host
to maybe 300 others. I've been looking at using Perl Expect for this, and
it's been working well for small numbers of connections.

This script:

#!/usr/local/bin/perl -w
use Expect;
@exps = ();
for $i (1 .. 300) {
  print "$i\n";
  my $exp = new Expect;
  $exp->log_stdout(0);
  $exp->spawn("ssh gend51");
  my $match = $exp->expect(30, "gend51> ");
  push(@exps, $exp);
}

falls over when it hits 251, with the error:

Cannot open pipe: Illegal seek at
/usr/local/lib/perl5/site_perl/5.6.0/Expect.pm line 105.

I guess this is something to do with limited file descriptors, but I've
upped my fd limit (as reported by ulimit -n and limit descriptors) to 1024,
and no change.

I'm on Solaris 8, perl 5.6.0, Expect 1.15, 2GB RAM, 8GB swap.

Any thoughts about how to avoid the above problem?

Many thanks,

Keith.


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Re: [Expectperl-discuss] Limit on number of Expect sessions?

[Roland G. <Ro...@Gi...>]

> I'd like to maintain a number of simultaneous ssh connections from
> one host to maybe 300 others. I've been looking at using Perl
> Expect for this, and it's been working well for small numbers
> of connections.
> 
> This script:
> 
> #!/usr/local/bin/perl -w
> use Expect;
> @exps = ();
> for $i (1 .. 300) {
>   print "$i\n";
>   my $exp = new Expect;
>   $exp->log_stdout(0);
>   $exp->spawn("ssh gend51");
>   my $match = $exp->expect(30, "gend51> ");
>   push(@exps, $exp);
> }
> 
> falls over when it hits 251, with the error:
> 
> Cannot open pipe: Illegal seek at
> /usr/local/lib/perl5/site_perl/5.6.0/Expect.pm line 105.
> 
> I guess this is something to do with limited file descriptors, but
> I've upped my fd limit (as reported by ulimit -n and limit
> descriptors) to 1024, and no change.

Are you sure about that?  Have you tried with a simple script that just 
opens files and counts how many can be opened?

Let's count the fds: stdin/out/err are 3, plus 250 open ptys gives 253; 
when spawning, Expect creates a pty/tty pair, makes 255, and then 
creates an anonymous pipe with 2 fd, which pushes the total count over 
256, so this seems to be the limit, and it looks like a system limit. 
As the default Solaris fd limit is 256, this seems the most plausible 
explanation, as I don't think that there is a hard limit like that in 
the perl interpreter (there is definitely no limit in Expect). Maybe 
you are running under a different user with a different limit?

> I'm on Solaris 8, perl 5.6.0, Expect 1.15, 2GB RAM, 8GB swap.
> 
> Any thoughts about how to avoid the above problem?

Upgrading to 5.6.1 might help, but this is a rather long shot.

Hope this helps,

Roland
--
Ro...@Gi...