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This document is a WORK IN PROGRESS.
This is just a quick personal cheat sheet: treat its contents with caution!

VNC

Virtual Network Computing (VNC) is an open source graphical desktop sharing system to remotely control another computer. VNC is platform independent - there are clients and servers for many GUI based operating systems.

Note

Two common alternative protocols are: RDP (a Microsoft proprietary protocol), and NX (a NoMachine proprietary protocol). But nothing proprietary will be discussed here.

At this point, you might think that ssh X11 forwarding ($ ssh -X ...) might be enough, but in a lot of cases it isn't, a dedicated tool is relevant.

  • TODO: compare with xpra
  • TODO: compare with x2go

A popular tool to use VNC is tigervnc which will be presented here.

This tool can be used in two ways:

  1. By duplicating the screen of a remote computer in order to control a remote user's desktop: in this cheat sheet this will be referred as the mirror way.
  2. By opening a new remote desktop on the remote computer, in order to use it potentially in parallel (like on another graphical server) of a user physically present on the computer without interfering with him: in this cheat sheet this will be referred as the parallel way.
Reference(s)

Table of contents

Install

Install tigervnc on both local and remote PC:

# pacman -S tigervnc

# vi /etc/portage/package.use/tigervnc
    > net-misc/tigervnc server
# emerge -a net-misc/tigervnc

# apt install tigervnc

# yum install tigervnc

# dnf install tigervnc

Config

on remote side

Setup a VNC password: 

$ vncpasswd

Edit ~/.vnc/xstartup (think of it as the .xinitrc file that the graphical server vncserver will run), depending on the remote side windows manager used:

~/.vnc/xstartup

#!/bin/sh
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid blue
gnome-session & # if not working try `gnome-session --session=gnome-classic &`
gnome-terminal &

#!/bin/sh
startkde &

#!/bin/sh
startxfce4 &

#!/bin/sh
startlxde &

See https://gist.github.com/Musinux/8e6c4752ed3c143d49764311a504c1e9 

#!/bin/sh

# Uncomment the following two lines for normal desktop:
# unset SESSION_MANAGER
# exec /etc/X11/xinit/xinitrc

#[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
#[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
#xsetroot -solid grey
#vncconfig -iconic &
#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
#x-window-manager &

export XKL_XMODMAP_DISABLE=1
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS

[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
gnome-session & # if not working try `gnome-session --session=gnome-classic &`
gnome-panel &
gnome-settings-daemon &
metacity &
nautilus &
gnome-terminal &


#!/bin/sh
startfluxbox &

#!/bin/sh
dwm &

Create a host white list (for secure mirror only): 

$ vi ~/.vnc/hosts
    > +127.0.0.1

Use

Let's consider that the remote user name is resu with IP 123.123.42.42

on remote side

Choose one way:

  1. parallel secure way: 

    $ vncserver -localhost :1

  2. parallel unsecure way: 

    $ vncserver :1

Tip

Run $ vncserver -kill :1 to gracefully shutdown the VNC server.

  1. mirror secure way: 

    $ x0vncserver -display :0 -rfbauth ~/.vnc/passwd -HostsFile ~/.vnc/hosts
    with older versions of x0vncserver you might want to try this command instead: 
    $ x0vncserver -display :0 -PasswordFile ~/.vnc/passwd -localhost

  2. mirror unsecure way: 

    $ x0vncserver -display :0 -rfbauth ~/.vnc/passwd
    with older versions of x0vncserver you might want to try this command instead: 
    $ x0vncserver -display :0 -PasswordFile ~/.vnc/passwd

Tip

You can specify a window size for your parallel desktop when running the VNC server: $ vncserver -geometry 1920x1080.

Tip

You can look at the currently running VNC servers: $ vncserver -status.

Note

If running $ vncserver :42 you will get a message like the following: 

> New 'HOSTNAME:42 (USERNAME)' desktop is HOSTNAME:42
>
> Starting applications specified in /home/USERNAME/.vnc/xstartup
> Log file is /home/USERNAME/.vnc/servoche:1.log
You just create a VNC server with id 42, you can now check it's logs in ~/.vnc/HOSTNAME:42.log.

If just run $ vncserver you will get similar message with automatically choosed vncserver id.

Also note that 5900+id (e.g. 5942 with id 42) is the default port to connect to the vncserver.

on client side

Choose one way:

  1. parallel secure way (through ssh tunneling): 

    $ ssh -fL 9901:127.0.0.1:5901 resu@123.123.42.42 sleep 10; vncviewer 127.0.0.1:9901

  2. parallel unsecure way: 

    $ vncviewer 123.123.42.42:5901 # you might need to open port 5901 of the remote side

  3. Mirror (for secure and unsecure x0vncserver) way: 

    $ ssh -fL 9900:127.0.0.1:5900 resu@123.123.42.42 sleep 10; vncviewer 127.0.0.1:9900

comments

  • Using the previously presented secure ways have multiple advantages:

    • they are secure: they are not vulnerable to man in the middle attacks because they are ciphered (thanks to ssh tunneling).
    • they don't require to open new ports, just the ssh port will be used.

  • tigervnc might not be available in the package manager and you might not want to install it manually (from https://tigervnc.org/) , in this case...

    • ... x11vnc is a common mirror alternative, it can be used as a drop in replacement for x0vncserver: just replace x0vncserver with x11vnc in the commands presented previously and it should run well.
    • ... vnc4server is a common parallel alternative, it can be used as a drop in replacement for vncserver: just use the same commands presented previously (vncserver is in deed the command used by vnc4server).
    • ... A lot of alternative can replace the vncviewer tool, like graphical ones: gtk-vnc, krdc, vinagre, remmina.

troubleshooting

  • No mouse pointer / no cursor: the cursor might seems invisible when using vncviewer, in this case, just add the -DotWhenNoCursor=1 option to your vncviewer command (see https://serverfault.com/a/560853).

  • After running the following: 

    $ x0vncserver -display :0 -PasswordFile ~/.vnc/passwd -localhost
    If you get a similar error: 
    Fri Jun  4 17:27:32 2021
 main:        XTest extension present - version 2.2
 main:        unable to bind listening socket: Address already in use (98)
~ImageCleanup called
    Then just restart x0vncserver: 
    $ killall x0vncserver
$ x0vncserver -display :0 -PasswordFile ~/.vnc/passwd -localhost

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