ssh server: reasons for sudden "Connection closed by remote host"

  • One of my ec2 servers has stopped receiving ssh connections. The OS is Ubuntu server 8.04, and the ssh server is the standard openssh-server.

    After months of uptime, I tried to connet to it today, and got the following message:

    ssh_exchange_identification: Connection closed by remote host
    

    Any idea what could have went wrong?

    Update: After a reboot, the server started receiving new connections. Disks are below 50% usage.

    First thing to do when you see this: try again with `ssh -vvv`, and look carefully through the output (or post it all for someone else to analyse; your password won't appear, but IP addresses and user names will).

  • jasonwryan

    jasonwryan Correct answer

    9 years ago

    Now that you once again have access, check the log to determine what, if any, clues there are as to why you were blocked.

    tail -n300 /var/log/auth.log | grep ssh 1

    The other thing to remember is that, if it happens again, you can run ssh in verbose mode with the -vvv option, which will return more detailed diagnostic information. From man ssh:

    -v    Verbose mode. Causes ssh to print debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. The maximum is 3.



    [1] You may need to increase/decrease the amount you tail by (-n) to identify the relevant entries.

    so I shouldn't include the footnote (^1) in my command? ;-)

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Content dated before 6/26/2020 9:53 AM