ssh problem

[Chris Green]

On Tue, Jun 19, 2012 at 12:54:29PM -0700, rikona wrote:
> Saturday, June 16, 2012, 3:46:14 AM, Chris wrote:
> 
> >> What might be happening to ssh? What is the best way to diagnose
> >> this? Best of all, is there a way to keep this from happening? It
> >> has become a PITA. Before the last few updates, I do not recall
> >> this happening. I run 10.04, updated.
> >> 
> > It sounds a bit like there's some sort of timeout in the connection.
> > I used to suffer from this when I used ssh to connect through the
> > firewall at work (with permission!). The firewall would drop the
> > connection after several minutes of inactivity. Setting any/all of
> > the keepalive settings in ssh didn't help, I finally resorted to a
> > background script started from .profile which sent a NUL character
> > every few minutes.
> 
> I'd be interested in that script...
> 
On looking I find it's actually an almost trivial C program, as follows:-

    /*

        Program to echo NULs periodically
    */
    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>


    int main(int argc, char * argv[])
    {
        int delay;                  // time between outputting NULs
        int fd;
        char nul[] = { 0 };

        switch (argc)
        {
            case 1:
                delay = 600;        // default delay of 10 minutes
                break;

            default:
                delay = atoi(argv[1]);
                break;
        }

        while(1)
        {
            fd = open("/dev/tty", O_RDWR | O_NOCTTY);
            if (fd < 0)
            {
                fd = open("/tmp/kaexit", O_RDWR);
                write(fd, "ka exited\n", 10);
                exit(1);
            }
            write(fd, nul, 1);
            close(fd);
            sleep(delay);
        }
    }

Then in .profile (or .bash_profile) I have:-

    #
    # 
    # Run ka (keep alive) if this is a remote ssh login
    #
    if [ "$SSH_CLIENT" ]
    then ka&
    fi


> > The symptoms of the firewall dropping the connection were exactly as
> > you describe, connection stops working but no error message or other
> > symptoms, just silence.
> 
> Did terminal stop responding to any input?
> 
Yes.

-- 
Chris Green