RSH scaling problems...

Jeff Layton jeffrey.b.layton at
Tue Dec 17 03:09:07 PST 2002

Jesse Becker wrote:

> On Sun, 15 Dec 2002, Mike S Galicki wrote:
> > I believe the default pty's in 2.4.20 is 1024, but when I list /dev/pty
> > I only see 256 entries.  MAKEDEV -m 1024 didn't seem to do anything past
> > 256.
> The default number of ptys is 254 in 2.4.x Linux kernels.  This is
> hardcoded, and you need a kernel recompile if you need more.

   The way it was explained to me is that the function rcmd(), which
is invoked by rsh, attempts to gobble up two ports between 512 and
1024.  Simple math: you can only EVER have 256 rshs running on a
machine at the same time.  It usually is a lot less than this since other
programs are gobbling up some of these ports. (Courtesy of Dan Nurmi
of Argonne).
   So, even if you patch the kernel to give you more than 256 ptys,
you also need to patch rcmd() to use a wider range of ports (at least
in theory).
   Any comments?


> --Jesse
> _______________________________________________
> Beowulf mailing list, Beowulf at
> To change your subscription (digest mode or unsubscribe) visit


Jeff Layton
Senior Engineer
Lockheed-Martin Aeronautical Company - Marietta
Aerodynamics & CFD

"Is it possible to overclock a cattle prod?" - Irv Mullins

This email may contain confidential information. If you have received this
email in error, please delete it immediately, and inform me of the mistake by
return email. Any form of reproduction, or further dissemination of this
email is strictly prohibited. Also, please note that opinions expressed in
this email are those of the author, and are not necessarily those of the
Lockheed-Martin Corporation.

More information about the Beowulf mailing list