来源：Ubuntu 20.04 Remote Desktop Access with VNC – Answertopia
The chapter entitled “Ubuntu Remote Desktop Access with Vino” explored remote access to the Ubuntu GNOME desktop using the Vino server, an approach that is intended solely for situations where the remote system is already running a GNOME desktop session. In this chapter we will cover launching and accessing GNOME desktop sessions that run in the background, allowing multiple desktop sessions to be accessed remotely, including on server based system that do not have a graphical console attached.
1.1 Installing the GNOME Desktop Environment
It is, of course, only possible to access the desktop environment if the desktop itself has been installed. If, for example, the system was initially configured as a server it is unlikely that the desktop packages were installed. The easiest way to install the packages necessary to run the GNOME desktop is via the apt command as follows:
# apt install ubuntu-gnome-desktop
To prevent the desktop from attempting to launch automatically each time the system reboots, change the default systemd target back to multi-user:
# systemctl set-default multi-user.target
If the system has a graphical display attached, the desktop can be launched using the following command:
$ startx
If, on the other hand, the system is a server with no directly connected display, the only way to run and access the desktop will be to configure VNC support on the system.
1.2 Installing VNC on Ubuntu
Access to a remote desktop requires a VNC server installed on the remote system, a VNC viewer on the system from which access is being established and, optionally, a secure SSH connection. While a number of VNC server and viewer implementations are available, this chapter will make use of TigerVNC which provides both server and viewer components for Linux-based operating systems. VNC viewer clients for non-Linux platforms include RealVNC and TightVNC.
To install the TigerVNC server package on Ubuntu, simply run the following command:
# apt install tigervnc-standalone-server
If required, the TigerVNC viewer may also be installed as follows:
# apt install tigervnc-viewer
Once the server has been installed the system will need to be configured to run one or more VNC services and to open the appropriate ports on the firewall.
1.3 Configuring the VNC Server
With the VNC server packages installed, the next step is to configure the server. The first step is to specify a password for the user that will be accessing the remote desktop environment. While logged in as root (or with superuser privileges), execute the vncpasswd command (where the user name is assumed to be demo):
# su - demo
demo@demoserver:~$ vncpasswd
Password:
Verify:
Would you like to enter a view-only password (y/n)? n
A view-only password is not used
The above command will create a file named passwd in the .vnc directory of the user’s home directory. Next, change directory to the .vnc directory and create a new file named xstartup containing the following:
#!/bin/sh
# Start Gnome 3 Desktop
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
vncconfig -iconic &
dbus-launch --exit-with-session gnome-session &
These are the commands that will be executed to start the GNOME desktop when the VNC server is launched.
1.4 Starting the VNC Server
With the necessary packages installed and configured for the user’s account, the VNC server can be started as follows (making sure to run the command as the user and without superuser privileges):
$ vncserver
This will start the first desktop session running on the system. Since this is the first session, it will be configured to use port 5901 (which may be abbreviated to :1). Running the command a second time while the first session is running will create a VNC server listening on port 5902 (:2) and so on. The following command may be used to obtain a list of desktop sessions currently running:
$ vncserver -list
TigerVNC server sessions:
?
X DISPLAY # PROCESS ID
:1 1607
:2 4726
To terminate a session, use the vncserver command with the -kill option referencing the corresponding port. For example:
$ vncserver -kill :2
Killing Xtigervnc process ID 4726... success!
Alternatively, use the following command to kill all currently running VNC server sessions:
$ vncserver -kill :*
Killing Xtigervnc process ID 1607... success!
Killing Xtigervnc process ID 5287... success!
To manually specify the port to be used by the VNC server session, include the number in the command-line as follows:
$ vncserver :5
In the above example, the session will listen for a remote connection on port 5905.
1.5 Connecting to a VNC Server
For details on remotely connecting to a desktop session from another system, follow the steps outlined in the sections titled “Establishing a Secure Remote Desktop Session” and “Establishing a Secure Tunnel on Windows using PuTTY” in the previous chapter.
1.6 Summary
In this and the preceding chapter we have explored two different ways to remotely access the GNOME desktop environment of an Ubuntu system. While the previous chapter explored access to an existing desktop session, this chapter has focused on launching GNOME desktop sessions as background processes, thereby allowing remote access to multiple desktop sessions. This is a particularly useful technique for running and remotely accessing desktop sessions on “headless” server-based systems.