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Connection closed by remote host: ssh_exchange_identification

Often when a process that uses SSH runs in a regular basis, you may get a “Connection closed by remote host” error.

For example, in my case I was using a Nagios based monitor that needed to connect to a group of hosts and, from time to time I got bursts of this error when trying to access the monitored machines.

This is an example of the log file:

10 13:43:02  hoard04 [2]: Protocol error. ssh is complaining, see next
message. #d83bb35 (ssh_common.c 427)
10 13:43:02  hoard04 [2]: ssh_exchange_identification: Connection
closed by remote host

Even though the problem solves automatically by just ingnoring it for a while (really) I prefer to fix the problem rather than the symptoms, so with a little help from google I came up with the right solution.

This problem happens when the server hits the MaxStartups limit in the /etc/ssh/sshd_config file. This value acts as a security measure if for example someone tries to compromise your server with a DoS attack. By default its set to 10 so its relatively easy for SSH to get stuck at 10 connections.

Anyway, to solve the issue you just have to edit the mentioned file and bump the MaxStartups limit to, say 25 or 50 if you need a lot of connections.

Categories: networking, ssh Tags:
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