openSUSE 12.3: Chapitre 5. Remote Access with VNC

Chapitre 5. Remote Access with VNC¶

Table des matières

5.1. One-time VNC Sessions
5.2. Persistent VNC Sessions

Virtual Network Computing (VNC) enables you to control a remote computer via a graphical desktop (as opposed to a remote shell access). VNC is platform-independent and lets you access the remote machine from any operating system.

openSUSE supports two different kinds of VNC sessions: One-time sessions that « live » as long as the VNC connection from the client is kept up, and persistent sessions that « live » until they are explicitly terminated.

	Session Types
A machine can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.

5.1. One-time VNC Sessions¶

A one-time session is initiated by the remote client. It starts a graphical login screen on the server. This way you can choose the user which starts the session and, if supported by the login manager, the desktop environment. Once you terminate the client connection to such a VNC session, all applications started within that session will be terminated, too. One-time VNC sessions cannot be shared, but it is possible to have multiple sessions on a single host at the same time.

Procédure 5.1. Enabling One-time VNC Sessions¶

Start YaST+Network Services+Remote Administration (VNC).
Check Allow Remote Administration.
If necessary, also check Open Port in Firewall (for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via Firewall Details.
Confirm your settings with Finish.
In case not all needed packages are available yet, you need to approve the installation of missing packages.

Available Configurations

	Available Configurations
The default configuration on openSUSE serves sessions with a resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are available on ports `5901` for « regular » VNC viewers (equivalent to VNC display `1`) and on port `5801` for Web browsers. Other configurations can be made available on different ports. VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, it automatically gets a free X display number.

The default configuration on openSUSE serves sessions with a resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are available on ports 5901 for « regular » VNC viewers (equivalent to VNC display 1) and on port 5801 for Web browsers.

Other configurations can be made available on different ports.

VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, it automatically gets a free X display number.

5.1.1. Initiating a One-time VNC Session¶

To initiate a one-time VNC session, a VNC viewer must be installed on the client machine. The standard viewer on SUSE Linux products is vncviewer, provided by the package tightvnc. You may also view a VNC session using your Web browser and a Java applet.

To start your VNC viewer and initiate a session with the server's default configuration, use the command:

vncviewer jupiter.example.com:1

Instead of the VNC display number you can also specify the port number with two colons:

vncviewer jupiter.example.com::5901

Alternatively use a Java-capable Web browser to view the VNC session by entering the following URL: http://jupiter.example.com:5801

5.1.2. Configuring One-time VNC Sessions¶

You can skip this section, if you do not need or want to modify the default configuration.

One-time VNC sessions are started via the xinetd daemon. A configuration file is located at /etc/xinetd.d/vnc. By default it offers six configuration blocks: three for VNC viewers (vnc1 to vnc3), and three serving a Java applet (vnchttpd1 to vnchttpd3). By default only vnc1 and vnchttpd1 are active.

To activate a configuration, comment the line disable = yes with a # character in the first column, or remove that line completely. To deactivate a configuration uncomment or add that line.

The Xvnc server can be configured via the server_args option—see Xnvc --help for a list of options.

When adding custom configurations, make sure they are not using ports that are already in use by other configurations, other services, or existing persistent VNC sessions on the same host.

Activate configuration changes by entering the following command:

rcxinetd reload

Firewall and VNC Ports

	Firewall and VNC Ports
When activating Remote Administration as described in Procédure 5.1, « Enabling One-time VNC Sessions », the ports `5801` and `5901` are opened in the firewall. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Chapitre 13, Masquerading and Firewalls (↑Security Guide) for instructions.

When activating Remote Administration as described in Procédure 5.1, « Enabling One-time VNC Sessions », the ports 5801 and 5901 are opened in the firewall. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Chapitre 13, Masquerading and Firewalls (↑Security Guide) for instructions.

5.2. Persistent VNC Sessions¶

A persistent VNC session is initiated on the server. The session and all applications started in this session run regardless of client connections until the session is terminated.

A persistent session can be accessed from multiple clients simultaneously. This is ideal for demonstration purposes where one client has full access and all other clients have view-only access. Another usecase are trainings where the trainer might need access to the trainee's desktop. However, most of the times you probably do not want to share your VNC session.

In contrast to one-time sessions that start a display manager, a persistent session starts a ready-to operate desktop that runs as the user that started the VNC session.

Access to persistent sessions is protected by two possible types of passwords:

a regular password that grants full access or
an optional view-only password that grants a non-interactive (view-only) access.

A session can have multiple client connections of both kinds at once.

Procédure 5.2. Starting a Persistent VNC Session¶

Open a shell and make sure you are logged in as the user that should own the VNC session.
If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the port used by your session in the firewall. If starting multiple sessions you may alternatively open a range of ports. See Chapitre 13, Masquerading and Firewalls (↑Security Guide) for details on how to configure the firewall.
vncserver uses the ports 5901 for display :1, 5902 for display :2, and so on. For persistent sessions, the VNC display and the X display usually have the same number.
To start a session with a resolution of 1024x769 pixel and with a color depth of 16-bit, enter the following command:
```
vncserver -geometry 1024x768 -depth 16
```
The vncserver command picks an unused display number when none is given and prints out its choice. See man 1 vncserver for more options.

When running vncviewer for the first time, it asks for a password for full access to the session. If needed, you can also provide a password for view-only access to the session.

The password(s) you are providing here are also used for future sessions started by the same user. They can be changed with the vncpasswd command.

	Security Considerations
Make sure to use strong passwords of significant length (eight or more characters). Do not share these passwords. VNC connections are unencrypted, so people who can sniff the network(s) between the two machines can read the password when it gets transferred at the beginning of a session.

Security Considerations

Make sure to use strong passwords of significant length (eight or more characters). Do not share these passwords.

VNC connections are unencrypted, so people who can sniff the network(s) between the two machines can read the password when it gets transferred at the beginning of a session.

To terminate the session shut down the desktop environment that runs inside the VNC session from the VNC viewer as you would shut it down if it was a regular local X session.

If you prefer to manually terminate a session, open a shell on the VNC server and make sure you are logged in as the user that owns the VNC session you want to terminate. Run the following command to terminate the session that runs on display :1: vncserver -kill :1

5.2.1. Connecting to a Persistent VNC Session¶

To connect to a persistent VNC session, a VNC viewer must be installed. The standard viewer on SUSE Linux products is vncviewer, provided by the package tightvnc. You may also view a VNC session using your Web browser and a Java applet.

To start your VNC viewer and connect to display :1 of the VNC server, use the command

vncviewer jupiter.example.com:1

Instead of the VNC display number you can also specify the port number with two colons:

vncviewer jupiter.example.com::5901

Alternatively use a Java-capable Web browser to view the VNC session by entering the following URL: http://jupiter.example.com:5801

5.2.2. Configuring Persistent VNC Sessions¶

Persistent VNC sessions can be configured by editing $HOME/.vnc/xstartup. By default this shell script starts an xterm and the twm Window Manager. To start either GNOME or KDE instead, replace the line starting twm with one of the following:

/usr/bin/gnome     # GNOME
/usr/bin/startkde  # KDE

	One Configuration for Each User
Persistent VNC sessions are configured in a single per-user configuration. Multiple sessions started by a user will all use the same startup and password files.