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...