Code Vamping

Working on a Remote VM

crostini virtualbox win10 ssh

Logging into a remote VM from a local VM. Getting from here to there isn’t all that hard.

The Problem

My main development system is ArchLinux running in a VirtualBox VM on a Windows 10 machine.

My mobile platform is a crostini VM running on a Samsung Chromebook.

For now, if I want to work on my main system while mobile, I do so by using Chrome Remote Desktop.

This works reasonably well, but there are two problems:

  1. My desktop screen has a vastly different Aspect Ratio from my chromebook. The resulting letterboxing makes the desktop tiny and hard to deal with.

  2. If I have to work tethered to my cell phone, bandwith limitation can do weird things to the screen and cause usability problems.

My main “IDE” is vim, so I really don’t need graphics that much.

The Goal

Use ssh (or something) to get from the crostini VM on my chromebook to the VirtualBox VM on my desktop. Major extra credit if X can be tunnelled back. But I’m comfortable with plain old tmux/vim.

The Journey

I decided to tackle this a small step at a time. I assumed that the two biggest pieces were going to be making the Win10 box visible on the internet and forwarding from there to the Virtualbox VM.

Step 1 - Chromebook to Win10

Chromebook client Google makes an SSH client for the chrome OS. So that is easy.

Windows 10 Server Windows 10 has an SSH server available, but it is a bit of a task to install. I finally found a microsoft document that gave the following two commands.

They need to run in a powershell window with admin privileges. Note also that this takes a while.

Get-WindowsCapability -Online | ? Name -like 'OpenSSH*'
Add-WindowsCapability -Online -Name 'Server name from above'

You’ll need to reboot afterwards, even though the output of the command says you don’t.

Now, go to the services settings and start the server. And then immediately stop it. This is needed to get it to create some directories.

Then from an elevated shell - do -

cd C:\windows\system32\OpenSSH
ssh-keygen -A

The permissions on the key files need to be set. Fortunately, Microsoft has provided a hack for that:

Install-Module -Force OpenSSHUtils
Repair-SshdHostKeyPermission -FilePath C:\ProgramData\ssh\ss_host_ed25519_key

Now, back to the services menu and restart the server.

And boom! we’re in.

Note, to get the local area IP for your Win 10 box, you can use ifconfig.

Step 2 - crostini to Windows 10

I figured this would be a no brainer. Just fire up ssh in crostini and do it.

Sure enough, No brainer.

Step 3 - crostini to virtualbox

I also thought this would be easy. I could get to the VM from the Win10 box, so, this shouldn’t be any different.

As it turns out, this was a little painful. The VM had its network set in NAT mode. Which means the the Win10 was doing the routing and the VM’s Ip was local.

After consulting the VirtualBox manual, I realized I could put the VM’s network in Bridge mode and it would talk pretty much directly to world. And so it did. As a side benefit, I noticed that the VM was actually visible to my router/modem as a connected device. This will come in handly in the next step.

I spent about an hour working the kinks out of my various tools to talk to the VM from the Win10 box to handle this brave new world. Then, from that experience, it was time to try from crostini to virtualbox.

And Boom! We’re in.

And after fixing a silly mistake in my .bashrc and adding the -X option to the ssh command, I had X forwarding working as well.

Nirvana! At least all on the local network.

The silly .bashrc mistake? I was overwriting the $DISPLAY variable. When ssh/putty are asked to forward X (via the -X option), they set $DISPLAY for you on the remote side so that the X protocol messages get forward. My .bashrc was trying to be helpful and set DISPLAY based on $SSH_CONNECTION. This works locally on the win10 box (and is actually faster), but it defeats the forwarding. The clients are directly talking to the X server.

Step 4 - World Dominance

My ISP provides a router/modem that automatically does NATing. So, all the boxes on the inside have private IPs that can’t be seen from the outside.

After a bit of research, I discovered that my ISP allows me to define port forwarding rules in the router. So, I could set it up so that, say, port 42 on the external IP routes to port 42 of the Win10 box or the VirtualBox VM.

Lets go directly for the goal and try to talk to the VB VM.

So, lets pick a port (2121 for this discussion) and do the following.

First define the port forward rule (however you need to do that with your ISP).

Then stop the sshd process on the VM, edit the config file to talk on the new port, and restart the sshd service.

On my ArchLinux Vm, it looks like the following:

systemctl stop sshd.service

vim /etc/ssh/sshd_config

# Uncomment the line with:
#   #Port 22
# and set it to our new port
#   Port 2121

systemctl start sshd.service

Now, go back to the router and figure out the external IP. It should be listed as the WAN IP or similar.

ssh -C -X user@1.2.3.4 -p 2121

and BOOM! We’re in.

Now, I’ve accomplished the goal AND the stretch goal.

I was going to stop there but decided that I actually wanted to get to the Win10 box as well. If nothing else, it would be a quick way to restart the VM - using virtualbox’s CLI - when needed.

This turned out be (almost) exactly the same as the configuring the VM. 1. Update the router with yet another port to forward. 2. Go to the service settings widget and stop the service 3. edit C:\ProgramData\ssh\sshd_config to change the port 4. drill a hole in the firewall New-NetFirewallRule -Name sshd -DisplayName ‘OpenSSH SSH Server’ -Enabled True -Direction Inbound -Protocol TCO -Action Allow -LocalPort “our-new-port” 4. Restart the service in the widget.

And done.

Well, not quite. I want to set up publickey encryption and disable password login, but I won’t bore you with that.

Wrap up.

Of course, one final touch would be to go to any of the multitude of dynamic DNS services and assign a nice name to that IP.

When I started this, I thought it was going to be journal of things tried and frustrating setbacks. But it actually turned out to be a reasonably simple 1 day task.

Resource

Here are some articles I found helpful while doing the research for this.

windows 10 ssh server https://winscp.net/eng/docs/guide_windows_openssh_server https://docs.microsoft.com/en-us/windows-server/administration/openssh/openssh_server_configuration https://winaero.com/blog/enable-openssh-server-windows-10/ https://poweruser.blog/enabling-the-hidden-openssh-server-in-windows-10-fall-creators-update-1709-and-why-its-great-51c9d06db8df

virtualbox docs https://www.virtualbox.org/manual