Keeping OpenSSH connections alive

From: JCA (1.41421_at_gmail.com)
Date: 06/17/05

  • Next message: G Lehnert: "64bit-compiled sshd fails on IBM/AIX"
    Date: Fri, 17 Jun 2005 08:28:23 -0700
    To: secureshell@securityfocus.com
    
    

      I inquired about this in comp.security.ssh, with limited success;
    hopefully somebody in this mailing list can provide further feedback.

      I have two Linux boxes, A and B, running OpenSSH versions 3.6.1p2
    and 3.9p1, respectively. I connect from B to A by means of ssh. That
    is, on B I am running X windows, and I open xterms that create a shell
    on A by means of the ssh command.

      The thing is, I have to bring B down on a regular basis. "Bring
    down" means suspend my running session to disk, by means of the
    suspend software available in www.suspend2.net. When I wake B up,
    after being suspended for a few hours, I retrieve my setup all right,
    including the xterms where I have my ssh connections to A. However, as
    soon as I press any key when the pointer is in any such windows, the
    following message is printed out:

        Read from remote host xxx.xxx.xxx: Connection reset by peer
       Connection to xxx.xxx.xxx closed.

    And the xterm window disappears (it had been created as xterm -e ssh
    xxx.xxx.xxx, so it just exits when the ssh connection terminates.)

       In an attempt the get around this, I added the following lines to
    the global sshd_config file on
    A:

       KeepAlive no
       ClientAliveInterval 30
       ClientAliveCountMax 1540

    My intention here was to make sure that the OpenSSH daemon on A would
    mantain connections open for up to 12 hours, regardless of what the
    clients are doing. As it happens, after such changes (and after
    restarting the OpenSSH daemon on A) I noticed that the sshd daemons
    forked in A for each ssh connection from B stay alive for just a few
    minutes (between 2 and 30; I hope I'll be able to measure this more
    accurately soon) after B gets suspended to disk.

       Somebody suggested to use autossh on B. With this, when B is
    brought back from hibernation, pressing a key on any of the ssh xterms
    on B elicits the same message as above, but a new ssh connection is
    automatically opened instantly. This is fine, but if I had something
    like, say, a debugging session running within the original ssh
    connection, that debugging session gets lost.

       The bottom line is, is there a way to coax A to keep its OpenSSH
    forked processes alive for a prespecified time, no matter what their
    matching ssh clients in B are doing? Why is it the case that the three
    lines I added to the sshd_config file do not pull it off? Something to
    do with the TCP stack overriding them perhaps?


  • Next message: G Lehnert: "64bit-compiled sshd fails on IBM/AIX"

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