Procedure 13.1. Configuring a VNC Display for a Single User

1. A configuration file named /etc/systemd/system/vncserver@.service is required. To create this file, copy the /usr/lib/systemd/system/vncserver@.service file as root:

   ~]# cp /usr/lib/systemd/system/vncserver@.service /etc/systemd/system/vncserver@.service

   There is no need to include the display number in the file name because systemd automatically creates the appropriately named instance in memory on demand, replacing '%i' in the service file by the display number. For a single user it is not necessary to rename the file. For multiple users, a uniquely named service file for each user is required, for example, by adding the user name to the file name in some way. See Section 13.1.2.1, “Configuring VNC Server for Two Users” for details.
2. Edit /etc/systemd/system/vncserver@.service, replacing USER with the actual user name. Leave the remaining lines of the file unmodified. The -geometry argument specifies the size of the VNC desktop to be created; by default, it is set to 1024x768.

   ExecStart=/usr/sbin/runuser -l USER -c "/usr/bin/vncserver %i -geometry 1280x1024"
   PIDFile=/home/USER/.vnc/%H%i.pid
   

3. Save the changes.
4. To make the changes take effect immediately, issue the following command:

   ~]# systemctl daemon-reload

5. Set the password for the user or users defined in the configuration file. Note that you need to switch from root to USER first.

   ~]# su - USER
   ~]$ vncpasswd
   Password:
   Verify:

   Important

   The stored password is not encrypted; anyone who has access to the password file can find the plain-text password.

Procedure 13.2. Accessing the GDM login window and logging in

1. Set up GDM to enable XDMCP by editing the /etc/gdm/custom.conf configuration file:

   [xdmcp]
   Enable=true
   

2. Create a file called /etc/xinetd.d/xvncserver with the following content:

   service service_name
   {
   disable = no
   protocol = tcp
   socket_type = stream
   wait = no
   user = nobody
   server = /usr/bin/Xvnc
   server_args = -inetd -query localhost -once -geometry selected_geometry -depth selected_depth securitytypes=none
   }
   

   In the server_args section, the -query localhost option will make each Xvnc instance query localhost for an xdmcp session. The -depth option specifies the pixel depth (in bits) of the VNC desktop to be created. Acceptable values are 8, 15, 16 and 24 - any other values are likely to cause unpredictable behavior of applications.
3. Edit file /etc/services to have the service defined. To do this, append the following snippet to the /etc/services file:

   # VNC xinetd GDM base
   service_name 5950/tcp
   

4. To ensure that the configuration changes take effect, reboot the machine.
   Alternatively, you can run the following. Change init levels to 3 and back to 5 to force gdm to reload.

   # init 3
   # init 5
   

   Verify that gdm is listening on UDP port 177.

   # netstat -anu|grep 177
   udp        0      0 0.0.0.0:177                 0.0.0.0:*
   

   Restart the xinetd service.

   ~]# systemctl restart xinetd.service

   Verify that the xinetd service has loaded the new services.

   # netstat -anpt|grep 595
   tcp        0      0 :::5950                     :::*                        LISTEN      3119/xinetd
   

5. Test the setup using a vncviewer command:

   # vncviewer localhost:5950
   

   The command will launch a VNC session to the localhost where no password is asked. You will see a GDM login screen, and you will be able to log in to any user account on the system with a valid user name and password. Then you can run the same test on remote connections.