Ruby Net / SSH-启动远程Python脚本并分离

Question

I need to launch a remote Python script through SSH. The Python script on the remote machine needs to perform some file manipulation, launch an executable for a simulation (from a few hours to days), collect the results and write to a file.

I am launching the script from Ruby using Net-SSH exec! . I use channels to capture STDERR and STDOUT .

The script works fine, but now I would like to detach the running script on the remote machine from my local Ruby script. I will then check directly on the remote machine the state of the simulation.

I have tried to run the script using nohup .

Net::SSH.exec!("nohup python script.py args > out.log 2> err.log < /dev/null &")

The script is detached and I get back control immediately, but the script on the remote machine gets killed and I cannot find the process in background.

Ideally I would launch the simulation executable directly from Ruby, but I have to use Python because I need some libraries that are not available in Ruby.

Is the approach above correct? Can I use nohup with Net-SSH?

Is there a better approach?

EDIT:

  def self.ssh_exec!(ssh, cmd, log = nil)

    ssh.open_channel do |ch|

      ch.request_pty do |chan,success|
      end

      ch.exec(cmd) do |chan, success|
        raise "could not execute command" unless success

        # "on_data" is called when the process writes something to stdout
        chan.on_data do |c, data|
          log ? (log << data) : (puts data) 
        end

        # "on_extended_data" is called when the process writes something to stderr
        chan.on_extended_data do |c, type, data|
          log ? (log.error data) : (puts data) 
        end

        chan.on_close do
           puts 'Done'
        end
      end
    end    
   end  

then I call

  Net::SSH.start(aws_ip, user, options = aws_options) do |ssh|

    script = File.join(path, 'pyfoam_scripts', 'run_case.py')
    cmd = "source...; python #{script} #{dst_case}"
    RG::Utils.ssh_exec!(ssh, cmd, @logger)

    ssh.loop
  end

where

:options => {:keys => path_to_key, 'key.pem'), 
                        :keepalive => true,
                        :timeout => 3000, 
                        :compression => true,
                        :compression_level => 6},

Answer 1

After a bit more testing and thanks to the comments I realised that there were three errors in my code:

1. I was using channels . Channels are used to establish a communication with the remote machine, capture the output, use callbacks. In this case, I didn't need any of this.
2. Net::SSH.exec! waits for the command to complete. I needed to launch and forget. (Silly mistake)
3. ssh.loop is not needed. See 1.

After fixing the errors above, it works like a charm.