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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 files with this server. Those RSyncs are using SSH with a certain user to open connections on the server.

The result is that my server is normally full of connections by the same user. About 5 connections per second at any given time.

Often, when I try to open a regular SSH connection with my Putty client, the connection fails before login with the error, "Server unexpectedly closed network connection". This happens about 6 times for 10 attempts, and for the other 4 attempts, it works normally and I am able to log in 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?

--

I found the solution. There was a limit in terms of connections allowed.

To increase this limit, I simply activated the setting MaxStartups and set its value to 1000. Now there is no more problem.

I will however check the network and server usage to verify that the traffic is not too much.

Thank you anyway.

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It's good to use something like fail2ban, if you are using that many connections, because it's rises number of possible attempts to break your password. –  week Dec 3 '12 at 12:20
    
Well done for finding it! Could you please post your solution as an answer and accept it? It makes it easier to read for the next person with this problem. –  terdon Dec 3 '12 at 12:23

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