I am running Ubuntu 12.04 Server, updated, to run a webserver on Tomcat 7. I have about 1000 clients that are very very often using an RSYNC program to sync some file with this server. Those RSync are using SSH with a certain user to open connections on the server.

The result is that my server is, as normal, full of connections by the same user. About 5 connections per 1 second every day any time.

Then, when I try to open a regular SSH connection with my Putty client, the connection fails before login saying "Server unexpectedly closed network connection", about 6 times for 10 attemps, anbd for 4 attemps out of 10, it works normally and I am able to login as any user.

Is there a overload of connections here?

The server statistics are very calm saying less then 40% of network usage and less of 2% CPU.

How can I improve this?

Thank you for any help. V.