ssh使用golang中的交互式shell将nsenter作为远程命令执行以调试Docker容器

Question

I am trying to automate debugging of docker containers on coreos. I want to have a script that connects to a host via ssh and exectues nsenter. That would be very convenient to jump directly into a container from my OSX box without doing a lot of stuff manually. I know that entering containers that way can be nasty, but if things are getting tough I would like to use such a tool. So here is what I have so far in golang.

I am able to create a interactive shell. Here I have the problem that things like reverse searching bash history using ctrl+R breaks the session. That code is commented below, thus not executed.

However, I am also able to execute a single command, here nsenter, but I receive the error stdin: is not a tty and nothing more happens. I am interested to know why stdin in my programm is not a tty and how I can achieve this.

Thanks

package main

import (
  "code.google.com/p/go.crypto/ssh"
  "io/ioutil"
  "log"
  "os"
)

func privateKey() ssh.Signer {
  buf, err := ioutil.ReadFile("./id_rsa")
  if err != nil {
    panic(err)
  }
  key, err := ssh.ParsePrivateKey(buf)
  if err != nil {
    panic(err)
  }

  return key
}

func main() {
  privateKey := privateKey()

  // Create client config
  config := &ssh.ClientConfig{
    User: "core",
    Auth: []ssh.AuthMethod{
      ssh.PublicKeys(privateKey),
    },
  }

  // Connect to ssh server
  conn, err := ssh.Dial("tcp", "myhost.com:22", config)
  if err != nil {
    log.Fatalf("unable to connect: %s", err)
  }
  defer conn.Close()

  // Create a session
  session, err := conn.NewSession()
  if err != nil {
    log.Fatalf("unable to create session: %s", err)
  }

  session.Stdout = os.Stdout
  session.Stderr = os.Stderr
  session.Stdin = os.Stdin // How can session.Stdin be a tty?

  //////////////////////////////////////////////////////////////////////
  // Stuff for interactive shell
  // Set up terminal modes
  //modes := ssh.TerminalModes{
  //  ssh.ECHO:          1,     // enable echoing
  //  ssh.TTY_OP_ISPEED: 14400, // input speed = 14.4kbaud
  //  ssh.TTY_OP_OSPEED: 14400, // output speed = 14.4kbaud
  //}
  // Request pseudo terminal
  //if err := session.RequestPty("xterm-256color", 80, 40, modes); err != nil {
  //  log.Fatalf("request for pseudo terminal failed: %s", err)
  //}
  // Start remote shell
  //if err := session.Shell(); err != nil {
  //  log.Fatalf("failed to start shell: %s", err)
  //}
  //////////////////////////////////////////////////////////////////////

  //////////////////////////////////////////////////////////////////////
  // Stuff for executing remote command
  // 2202 in my example is actually the pid of a running container
  if err := session.Run("sudo nsenter --target 2202 --mount --uts --ipc --net --pid"); err != nil {
    panic("Failed to run: " + err.Error())
  }
  //////////////////////////////////////////////////////////////////////

  session.Wait()
}

Answer 1

Super cool, I got it working, but there is still a magic I cannot comprehend. However, I changed my code as followed. The basic change leading to the correct pty behaviour, was the usage of the package "code.google.com/p/go.crypto/ssh/terminal". Using its MakeRaw(fd) seems to lead to side effects that enable the correct pty behaviour. Also thanks to the fleet project where I found the working example https://github.com/coreos/fleet/blob/master/ssh/ssh.go.

// The following two lines makes the terminal work properly because of
// side-effects I don't understand.
fd := int(os.Stdin.Fd())
oldState, err := terminal.MakeRaw(fd)
if err != nil {
  panic(err)
}

session.Stdout = os.Stdout
session.Stderr = os.Stderr
session.Stdin = os.Stdin

termWidth, termHeight, err := terminal.GetSize(fd)
if err != nil {
  panic(err)
}

// Set up terminal modes
modes := ssh.TerminalModes{
  ssh.ECHO:          1,     // enable echoing
  ssh.TTY_OP_ISPEED: 14400, // input speed = 14.4kbaud
  ssh.TTY_OP_OSPEED: 14400, // output speed = 14.4kbaud
}

// Request pseudo terminal
if err := session.RequestPty("xterm-256color", termHeight, termWidth, modes); err != nil {
  log.Fatalf("request for pseudo terminal failed: %s", err)
}

if err := session.Run("sudo nsenter --target 2202 --mount --uts --ipc --net --pid"); err != nil {
  // if the session terminated normally, err should be ExitError; in that
  // case, return nil error and actual exit status of command
  if exitErr, ok := err.(*ssh.ExitError); ok {
    fmt.Printf("exit code: %#v
", exitErr.ExitStatus())
  } else {
    panic("Failed to run: " + err.Error())
  }
}

session.Close()
terminal.Restore(fd, oldState)