Remote desktop¶

Exercise remote-desktop-annex.pdf · PDF

Aina phones you: "The invoice program shows a window with an error and a button I cannot read." You are at home. With SSH you can get a shell on her PC. But can you see her window?

No. A shell gives you letters, not windows. Sometimes the thing you must use is a window. For that you need a different tool, one that brings the whole screen of a far machine to yours. You have probably used one already, if a teacher or an IT person ever "took control" of your computer to help you.

Sitting on its chair from far away¶

A remote desktop draws the screen of a far machine on yours, and sends your keyboard and mouse to act there.

If SSH is a phone call to the machine (you say commands, it answers in words), a remote desktop is sitting on its chair from far away: you see its screen and move its mouse. Pictures weigh much more than letters, so a remote desktop needs much more network than a shell.

flowchart LR
    subgraph YOU ["Your Ubuntu PC (the client)"]
        REM["<b>Remmina</b><br>draws the far screen"]
    end
    subgraph FAR ["win11 or deb-lab (the host)"]
        HOST["<b>Remote desktop service</b><br>port 3389"]
    end
    REM -->|"keys and mouse"| HOST
    HOST -->|"the screen"| REM

The machine you control is the host; the program you use to control it is the client. On the Ubuntu PCs the client is Remmina, which speaks both families below.

Two families: RDP and VNC¶

GNOME on Linux now speaks RDP too, and shows both behaviours:

• Remote Login gives you a new session, like Windows does.
• Desktop Sharing shows the session that is already open: you and the person at the machine see the same screen.

RDP into Windows 11¶

First check the edition: Settings → System → About. It must be Pro, Enterprise or Education; Windows 11 Home cannot be the host.

1. In win11: Settings → System → Remote Desktop → switch it On → Confirm.
2. Find its address in PowerShell with ipconfig.

3. Check that Windows is listening:

   Get-NetTCPConnection -LocalPort 3389 -State Listen
   

   A line with LocalPort 3389 and State Listen means the service is waiting.

4. On the Ubuntu PC, open Remmina → new connection → protocol RDP → the address → your Windows user name and password → Connect → accept the certificate.

Now look at the win11 window in virt-manager: it shows the lock screen. RDP gives you your own session, and only one person uses the machine at a time.

Share the GNOME desktop¶

In deb-lab, logged in:

1. Settings → System → Remote Desktop → Desktop Sharing. Switch on Desktop Sharing and Remote Control.
2. Note the user name and password the panel shows. They are not your Linux account.

3. Find the address with ip -br a, and check the port:

   ss -tln | grep 33
   

   A listener on *:3389 (or 3390, if Remote Login is also on) is the GNOME remote desktop service.

4. On the Ubuntu PC: Remmina → RDP → that address (add :3390 if that was the port) → the user and password from the panel.

Move the mouse in Remmina and watch the deb-lab window in virt-manager: both show the same desktop and the mouse moves in both. This is sharing, not a new session: exactly what you need to help Aina find her button.

If there is no Remote Desktop entry in GNOME Settings, install it with sudo apt install gnome-remote-desktop and log in again.

Never open it to the Internet¶

Remember the online server from SSH remote access: programs were knocking on port 22 all day, guessing passwords. They knock on 3389 and 5900 too, and a remote desktop gives them a whole screen.

Rule: a remote desktop port is for the inside of the network. From outside, you first enter through a VPN (Unit 3) or through SSH, and then connect.

When you are done, switch Remote Desktop off again on win11 and deb-lab. A door you do not use is a door you close.

Shell or desktop?¶

A remote desktop feels easier, so it is tempting to use it for everything. Don't. On a server there is often no desktop to show (ubu-srv has none), a shell works over a bad connection, and commands can be written in your log and repeated. Use a desktop only when the job is a window.

Key takeaways¶

• A remote desktop brings a far machine's screen to yours; it needs much more network than a shell.
• RDP (Microsoft, 1998, port 3389) gives you a session; VNC (Cambridge, 1998, port 5900, protocol RFB) classically shows the screen in use.
• Windows 11 Pro, Enterprise and Education can be RDP hosts; Home can only connect. GNOME offers Desktop Sharing and Remote Login.
• Remmina is the client on the Ubuntu PCs and speaks both RDP and VNC.
• Never expose a remote desktop port to the Internet: enter through a VPN or SSH first, and switch it off when unused.
• Choose the tool by the job: a window needs a desktop; commands, files and bad connections need SSH and scp.

Quick check¶

Two ways to be on a machine without being there. Now the server starts doing what a server is for: giving files to everybody. Next: Samba file server.