Remote Desktop in a PC

Ones_Zeros · Jul 24, 2020

When I remote desktop into my pc to check a PLC and after I disconnect, it always leaves the PC at a ctrl+alt+del state.

Is there a way to remote desktop into a pc but leave it on the desktop after disconnecting? Reason I have several pc's in the field that maintenance personnel uses but if i remote in to check things and after disconnecting they cant see the screen. Id rather them not know the password and they have to ctrl+alt+del to get back into the desktop.

thanks,

mk42 · Jul 24, 2020

I think that's just inherently how windows handles RDP.

You could try VNC instead. It uses screen mirroring, instead of stealing the session.

Ones_Zeros · Jul 24, 2020

Is VNC free or a paid software?

jkerekes · Jul 24, 2020

TightVNC is free.

Ken Roach · Jul 24, 2020

There are actually a couple of different versions of VNC. I often use TightVNC, which is definitely free.

https://www.tightvnc.com/

RealVNC has a paid / enterprise subscription, but I haven't used it.

My company pays for remote administration using TeamViewer because it gives us the security and VPN services we need. Not everyone will need that.

mk42 · Jul 24, 2020

VNC is a protocol. There are a ton of different packages that use it. In theory most of them should work together. Many vendors also use it as a feature for remote viewing their HMI systems, although their marketing teams call it something else.

I'd 2nd TightVNC, free and open source is the way to go.

I_Automation · Jul 24, 2020

As far as locking the computer at the end of a session there is a setting (in TeamViewer and VNC Server) to lock or not.

In VNC - Options - Expert - DisconnectAction you can set Lock, LogOff or None

In TeamViewer it is Lock Remote Computer and can be Always, Automatic (which is always too) or Disabled.

Ken Moore · Jul 24, 2020

I have run into this issue before. If you have autologon configured. You can reboot the PC at the end of your remote session. It will then reboot and be ready for the maint. users.

If you can RDP into a PC to see a PLC, why not just connect directly, bypass the PC.

KingPresident · Jul 24, 2020

Ken, will you write a book? I would buy it.

mk42 · Jul 24, 2020

Ken Moore said:
If you can RDP into a PC to see a PLC, why not just connect directly, bypass the PC.

Dunno if that's what is happening here, but there's at least one reason: systems with a maintenance PC that bridges the network airgap.

I've seen a lot of systems where a PC on the plant floor acts like a (non-routing) bridge between the plant network and the control network with a NIC going to each. The PC stores all the PLC projects and has full licenses for engineering software. Engineers can remote in from anywhere and are almost guaranteed to have the up to date project and the correct software versions. The PLCs aren't accessible directly. It costs more up front, but can simply things later on.

It's starting to get more common to VPN directly to a machine, but I saw this model a lot in years past.

Ben Pugh · Jul 26, 2020

If you want to stick with RDP, what you are asking for is actually possible. I found a way to do that with some creative googling a while ago and it works with Windows 10 at least. Save the text below all on one line as a file with a .cmd extension, and then when you are ready to disconnect, right click the file and select "Run as Administrator". You will get a message saying that you have been disconnected because another user connected, and your on site users will get their screen back without having to log back in.

@powershell -NoProfile -ExecutionPolicy unrestricted -Command "$sessionid=((quser $env:USERNAME | select -Skip 1) -split '\s+')[2]; tscon $sessionid /dest:console" 2> UnlockErrors.log

Ones_Zeros · Jul 27, 2020

Thanks a lot for the tip with RDP
I’ll give this a try

Thanks again

harryting · Jul 27, 2020

The term for what mk42 described above is a "Jump server" and it's a popular way of doing remote support.

We also uses it for doing a lab, using Server OS, it allow us to play with many different PLC, switches, and HMI remotely without being in the office and the Server OS allows multiple RDP sessions.

Remote Desktop in a PC

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