[I wish I knew how to get the mailing list to thread my replies properly in the archives; I subscribe to the daily digest, and replying to that doesn't do it.] Greg Lindahl wrote: > On Thu, Jan 15, 2015 at 03:40:08PM -0300, Glenn Eychaner wrote: > > > My only theory is that this has something to do with non-ephemeral ports and > > socket reuse, but I'm not sure what. > > If you want a quick detection that the link is dead, have the server > occasionally send bytes to the dos box. You will get an immediate > error if the dos box is up and knows that connection is kaput. What if I am sending bytes to the DOS box, but it never reads the socket? (Let us assume, for the sake of argument, that I can't change the DOS box software. In fact, I can, but it's more difficult than changing the Linux end.) Won't that either result in my detecting the socket as "dead" when it is not, or eventually overflowing the socket buffering? > Given that the port numbers of the new connection are the same, I'm > kind of surprised that the behavior changed from 6.5 to 6.6, but, I > always use defensive programming (sending those extra bytes). I was super-surprised by the change, in that I fully tested the upgrade on my simulator system before deploying, and still got bit on deployment. Of course, the simulator doesn't have a real DOS box, just a simulation process that sends the images. [And, I also recently got bit by this http://www.macstadium.com/blog/osx-10-9-mavericks-bugs/ after upgrading some Macs. Sigh, network issues.] Alex from Germany wrote: > Since you always use the same local port - > maybe you need to set SO_REUSEADDR option. I assume I would have to set that on the client (DOS) side (the box which is using the same local port 1025 each time); setting it on the bound-listener socket on the Linux side doesn't seem like it would do anything to resolve the issue, based on my reading of SO_REUSEADDR on the net: http://www.unixguide.net/network/socketfaq/4.5.shtml http://stackoverflow.com/questions/14388706/ -G. -- Glenn Eychaner (geychaner at lco.cl) Telescope Systems Programmer, Las Campanas Observatory