That error means the OS doesn't support it that flag for fnctl, and that Perl doesn't emulate it. I don't know if that helps, but newer version of Net::SSH::Perl don't use F_SETFL.

Older version (<= 1.26):

    fcntl($sock, F_SETFL, O_NONBLOCK)
        or die "Can't set socket non-blocking: $!";
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Newer version (>= 1.27):

    defined($sock->blocking(0))
        or die "Can't set socket non-blocking: $!";
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