[lug] Restart failure binding to/listening on recently used port

[David Ahern]

I believe you need to set the SO_REUSEADDR socket option.

David



On 10/11/2009 12:57 PM, Chris Riddoch wrote:
> My google-fu is failing me, and I suspect I'm not the first to run
> into this issue.  I've thrown together a little shell script to
> demonstrate the problem:
> 
> socket at cinnamon:~/tmp/> cat listen-test.sh
> #!/bin/sh
> port=10000
> 
> echo "Starting at: " `date`
> socat tcp-listen:$port gopen:read_data.txt &
> sleep 1
> socat ~/out.ps tcp:localhost:$port
> echo "Finished runnng socat... killing anyway, just in case"
> pkill socat
> sleep 3
> echo "Remaining socat processes:"
> pgrep socat
> echo "Waiting a while before starting again..."
> sleep 2
> echo "Trying to start listening on the same port at " `date`
> socat tcp-listen:$port gopen:read_data_2.txt
> 
> socket at cinnamon:~/tmp/> ./listen-test.sh
> Starting at:  Sun Oct 11 12:51:40 MDT 2009
> Finished runnng socat... killing anyway, just in case
> Remaining socat processes:
> Waiting a while before starting again...
> Trying to start listening on the same port at  Sun Oct 11 12:51:46 MDT 2009
> 2009/10/11 12:51:46 socat[6749] E bind(3, {AF=2 0.0.0.0:10000}, 16):
> Address already in use
> socket at cinnamon:~/tmp/>
> 
> The amount of time I have to wait before I can bind a server to the
> same port can vary from a few seconds to more than a minute.
> Strangely, the faster the system I'm using, the longer it seems to
> take.
> 
> Is there a /proc or /sys switch I can fiddle with that affects this?
> It *seems* that the kernel isn't cleaning up after listening processes
> very quickly.  I've run into this frequently, when developing scripts
> that listen on ports, and need to restart them for testing.  I've
> experienced this in many languages, on several distros, with rather
> high frequency.  What gives?
>