Multiple (multiplexed) simultaneous ssh connections - Cygwin bug?

Damien Miller djm at
Sat Sep 9 09:43:05 EST 2006

On Fri, 8 Sep 2006, Goldburt, Dan wrote:

> I set MAX_SESSIONS to 128.
> I think I'm definitely overrunning the fd_set. Running the test again
> with a just started sshd instance, I get the error fcntl(31, F_GETFL,
> 0). So the limit seems to be 30 fds, or 10 connections (3 fd per
> connection).
> Where is FD_SETSIZE set in cygwin? Any chance this can be bumped up?

OpenSSH dynamically allocates its fd_sets, so using more file descriptors
than can be represented in a single fd_set is OK as long as the platform's
select() implementation supports it. You might be running into a Cygwin


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