How do I decrease the ssh.net timeout when my ssh client disconnects from the ssh server?

Question

I wrote a small program in C# using ssh.net that connects to an SSH server, makes some changes, and restarts the SSHD service on the SSH server.

Unfortunately, the SSH server is being run on a slow embeded system, and the SSHD service is not restarted quickly enough to do so seamlessly (without disconnecting the client). The SSH service actually takes about a minute to restart. This is fine.

My code looks this:

Console.WriteLine("Restarting SSHD service on modem...");

try
{
    using (var client = new SshClient(IPAddress, "root", "PASSWORD"))
    {
        client.ConnectionInfo.Timeout = TimeSpan.FromSeconds(10);
        client.Connect();

        client.RunCommand("service sshd restart");

        client.Disconnect();
    }
}
catch (System.Net.Sockets.SocketException)
{
    //We got disconnected because we just restarted the sshd service
    //This is expected
    Console.WriteLine("\tSuccess");
}
catch
{
    //We got disconnected for some other reason
    Console.WriteLine("\tIt appears there was a problem restarting the sshd service");
}

The issue I'm having is that the ssh client takes up to a minute, or sometimes longer, to figure out that the SSH server is no longer responding, and throw a System.Net.Sockets.SocketException. Is there any way to shorten this timeout? I don't want it to reconnect - I just want it to throw the exception sooner. Would this be some sort of ssh.net specific timeout value, or a System.Net.Sockets timeout?

Answer 1

Thanks to Hang's suggestions, the following code has solved the problem:

Console.WriteLine("Restarting SSHD service on modem...");

try
{
    var client = new SshClient(IPAddress, "root", "PASSWORD")
    client.ConnectionInfo.Timeout = TimeSpan.FromSeconds(10);
    client.Connect();

    client.RunCommand("service sshd restart >/dev/null 2>&1 &");
    Console.WriteLine("\tSuccess");
}
catch (System.Net.Sockets.SocketException)
{
    //We got disconnected because we just restarted the sshd service
    //This is expected
    Console.WriteLine("\tSuccess");
}
catch
{
    //We got disconnected for some other reason
    Console.WriteLine("\tIt appears there was a problem restarting the sshd service");
}

The things to note are:

• The RunCommand line now uses >/dev/null 2>&1 to get rid of stdout and stderr
• The RunCommand line now uses & to run the command in the background
• The try block now contains a Console.WriteLine("\tSuccess");, because this is the most likely result of the RunCommand() - the fact that it will keep going instead of throwing any exceptions
• There is no longer a client.Disconnect() or a using statement, so nothing attempts to disconnect from the ssh server - the code just keeps going

The reason this works in my case is because my program basically does nothing else after this - it just exits. Others may want to wait until the SshClient becomes available again, and disconnect properly to clean up and release the resources.