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NX is an exciting new technology for remote display. It provides near local speed application responsiveness over high latency, low bandwidth links. The core libraries for NX are provided by NoMachine under the GPL. FreeNX is a GPL implementation of the NX Server and NX Client Components.

FreeNX - the free NX

1 Installation

package is split up into 2 parts:

  • freenx (the server)
  • nxclient (the client)

If you plan using freenx to connect to a headless PC, keep in mind that you'll also need an X server configured, so you should install any relevant xorg package.

2 Setup

2.1 Server

The free server is the 'freenx' package. The sshd daemon must be installed and running for it to function properly. Add 'sshd' to daemons array in /etc/rc.conf and ensure your hosts.deny/hosts.allow allows ssh services.

For freenx to authentication to work, sshd has to be setup properly. Verify the following entries in /etc/ssh/sshd_config:

RSAAuthentication yes
AllowUsers someuser nx

The main configuration file is located at:

If you are running your SSH daemon on a port other than the default port 22, you'll need to uncomment and update:
Note: As of OpenSSL 1.0.0, it is necessary to set proper md5sum command in /opt/NX/etc/node.conf:

If you use KDE or Gnome desktop environments you do not need to edit this file, as the defaults with the modified MD5SUM command should work in this case. If you use another window manager such as Fluxbox/Openbox or Xfce, you may need to edit this file slightly (see below).

After installing the freenx package, run /opt/NX/bin/nxsetup --help for an overview of the install and uninstall procedures.

Note: You should also install "xdialog" on the server or you will not see the "suspend/terminate" dialog when you try to close the window or hit "ctrl-alt-T":
pacman -S xdialog

2.1.1 Keys

Keys are used to authenticate the clients with the server. By default a new set of random keys are generated during the install, one for the server and one for the clients. You will need to copy this client key to each of your clients that want to connect (Windows and linux).

The client key can be found here:


Alternatively you can use the default key that is provided by NoMachine with all clients. In this case you do not need to copy a custom generated key to each client. To get the server to accept the default client keys run:

/opt/NX/bin/nxsetup --install --setup-nomachine-key

Recreation of random keys:

/opt/NX/bin/nxsetup --install

Transferring nx keys to another freenx server:

  • /opt/NX/home/nx/.ssh contains the key files
 -rw------- 1 nx root  697  9. Okt 12:55 authorized_keys
 -rw------- 1 nx root  668  9. Okt 11:48 client.id_dsa.key
 -rw------- 1 nx root  609  9. Okt 12:55
  • Save those files.
  • Add those files to your new server, they need the same permissions, names, group and directory!
 # cp authorized_keys client.id_dsa.key /opt/NX/home/nx/.ssh/
 # chmod 600 /opt/NX/home/nx/.ssh/*
 # chown nx /opt/NX/home/nx/.ssh/*
 # chgrp root /opt/NX/home/nx/.ssh/*
  • Recreate known_hosts file:
 # echo -n > /opt/NX/home/nx/.ssh/known_hosts
 # cat /etc/ssh/ >> /opt/NX/home/nx/.ssh/known_hosts
 # chmod 633 /opt/NX/home/nx/.ssh/known_hosts
 # chown nx /opt/NX/home/nx/.ssh/known_hosts
 # chgrp root /opt/NX/home/nx/.ssh/known_hosts

2.1.2 Starting the server

Once installed the server is effectively running and ready to go, you do not have to do anything manually The only thing that must be running in order to connect is the sshd daemon. This is because the nxserver is actually started by logging into sshd as the special user 'nx'. This user has been set up to use the nxserver as its shell, much like a normal user has bash as the default shell.

You can specify the local addresses sshd should listen for by editing /etc/ssh/sshd_config and adding them in the following format:

ListenAddress host|IPv4_addr|IPv6_addr

The original ListenAddress in sshd_config is This listens to all addresses, however adding any address will take precedent to this and and accept connections from the new address only.

Restart the sshd daemon to put any changes to its configuration into effect:

sudo /etc/rc.d/sshd restart

In actual fact, if you check the process list (ps aux) you may not see the nxserver running even though it is. This is because the nxserver is actually started by logging into sshd as the special user 'nx'. This user has been set up to use the nxserver as its shell, much like a normal user has bash as the default shell.

2.2 Client

Get the client from pacman:

pacman -S nxclient

2.2.1 Configuration

As mentioned above, the client must contain the correct key to connect to the server. If you are using the custom keys generated during install, you need to copy the client key to the following location:

  • Arch Linux: /opt/NX/share/keys/client.id_dsa.key

After moving the keys you may have use the nxclient GUI to import the new keys. From the configuration dialog press the 'Key...' button and import the new client key.

3 Running

After installing nxclient on Arch Linux, executables are available in /opt/NX/bin. At the first run of /opt/NX/bin/nxclient, the user will be led through a wizard.

3.1 Keyboard shortcuts

CTR+ALT+F          Toggles full-screen mode. 
CTRL+ALT+T         Shows the terminate, suspend dialog.
CTRL+ALT+M         Maximizes of minimizes the window 
CTRL+ALT+Mouse     Drags the viewport, so you can view different portions 
                   of the desktop. 
or                 Moves the viewport by an incremental amount of pixels. 
CTRL+ALT+S         It will activate "screen-scraping" mode, so all the GetImage
                   originated by the clients will be forwarded to the real
                   display. This should make happy those who love taking
                   screenshots ;-). By pressing the sequence again, nxagent
                   will revert to the usual "fast" mode.
CTRL+ALT+E         lazy image encoding
CTRL+ALT+Shift+ESC Emergency-exit and kill-window

3.2 Leaving fullscreen

There is a magic-pixel in the top right corner of nearly every nx-application in fullscreenmode. Right-click the pixel and application-window gets iconified.

3.3 Tips on resume

  • Resume is a bit experimental, crashes might appear after session has resumed. You have to find out which apps like resuming and which do not ;) .
  • If resume fails let it time out and don't use the cancel button, else sessions will stay open and consume RAM on server. To kill such sessions use the Session Admin program to kill them.

3.4 Fix DPI settings

If you like to have the same font-sizes/dpi sizes on all your client session, set the X resource "Xft.dpi". For example putting the following line into a user's "~/.Xresources" makes her/his "desktop" a 100dpi. Xft.dpi: 100

4 FreeNX to existing display

Usually, when connecting to a NX server, a new X session is created. Sometimes it might be useful, to connect to an existing X session, e.g. the root session. This is not possible with NX in default setup, but can be reached, using tightvnc and x11vnc. Do the following steps on the NX server system.

# pacman -S tightvnc x11vnc

x11vnc will serve the X session, we have to create a file $HOME/.x11vncrc to give x11vnc some options, e.g.:

display :0
rfbauth /home/USER/.x11vnc/passwd

Create the VNC password file:

$ mkdir $HOME/.x11vnc
$ x11vnc -storepasswd PASSWORD $HOME/.x11vnc/passwd
$ chmod 600 $HOME/.x11vnc/passwd

Create a shell script, which starts the x11vnc service, if not running and starts the vncviewer provided by the package tightvnc.

Note: The variable $VNC_PORT in the following script defines the X display, which is configured as display :0 under $HOME/.x11vncrc, 5900 is the root session, if you want to use display :1 use the port 5901 and so on

if [ -z "$(pgrep ${VNC_SERVER})" ]; then
	echo $VNC_SERVER not running, starting...
	exec $VNC_SERVER &
	sleep 5

exec $VNC_VIEWER -geometry $VNC_RESOLUTION -passwd $VNC_PASSWD localhost::$VNC_PORT

Save this script with a texteditor of your choice, e.g. under $HOME/shell/ Make it executable and create a symbolic link, e.g:

$ chmod +x $HOME/shell/
# ln -s /home/USER/shell/ /usr/local/bin/nxvnc

At this point, you might want to test the current configuration: $ /usr/local/bin/nxvnc

If the x11vnc service and a vncviewer session is started, you configuration works well. You are now able to connect to the current X session using your NX client with following options:

Login, Password, Host, Port: your default entries
Desktop: Unix -> Custom
 - Settings:
   - Run the following command: /usr/local/bin/nxvnc
   - New virtual desktop
  - Fullscreen or Custom with you preferred resolution

You are able to connect to your current X session via NX client now.

FreeNX to existing display (

5 Setting up non-KDE or Gnome desktop managers

Before following anything in this part, make sure the server working setup and accepting connections. This section only deals with problems once NXClient has logged on.

It is quite simple (once the server is setup) to connect to Gnome and KDE sessions, however connecting to other window managers (fluxbox, xfce, whatever) is slightly different.

Choosing "custom" and using a command like startx of startfluxbox will either result in a blank screen after the !M logo or the Client to present an error complaining about lack of a X server. A way around this is open a session with the command "startx", and the another with the command to start your window-manager-of-choice.

If you do not want to do this, you can start X by [installing a login manager like SLIM or XDM]. I would recomend using SLiM because of it's small size.

(Authors note: This is how I got fluxbox, xfce and others to work on my arch installation- however, I have now removed slim from inittab and set the run level back to 3, and yet I can still login perfectly with NXClient. Possibly try this if you get your system working this way, if like me you have a low memory machine.)

5.1 Alternative fix

A simple fix without resorting to the above seems to involve a simple edit to the config file. This should work for fluxbox/openbox/xfce or any other window manager that uses the .xinitrc startup file in a call to startx.

Simply edit the config file (as root):


and change




Remember to remove the # symbol from the start of the line.

Then in the client under configuration settings, choose Custom as the desktop, and click on settings:

  • In the first group select - Run the default X client Script on server
  • In the second group select - New virtual desktop

6 Problems

6.1 Debug problems

Edit the nxserver config file:

 vi /opt/NX/etc/node.conf





Then you can look/debug the log files in:


For succesfull connections and:


For failed ones.

6.2 Authentication OK, but connection fails

If you are trying to startkde

 vi /opt/NX/etc/node.conf

And search for:


Replace for:


6.3 Key changes

Change the key in GUI setup to new generated key.

6.4 Xorg 7

Be aware that you have to remove the /usr/X11R6 directory, else strange things can happen.

6.5 Wrong password / No connection possible

  • If you have changed your ssh daemon to run on an alternate port, be sure to modify SSHD_PORT within /opt/NX/etc/node.conf.
  • If you get always wrong password or no connection after authentication was done and you are sure that you typed it correct, check that your server can connect to itself using localhost by ssh and that it is not blocked either by /etc/hosts.deny or not allowed by /etc/hosts.allow.

You must allow local access for sshd. Example /etc/hosts.deny file :

# /etc/hosts.deny
sshd: localhost.localdomain: ALLOW
  • If you messed up your key files, create new ones or fix the old ones, it's probably caused by a wrong known_hosts file.
  • If you get wrong password or login, put ENABLE_PASSDB_AUTHENTICATION="1" in /opt/NX/etc/node.conf and add a user by
# /opt/NX/bin/nxserver --adduser [username]
# /opt/NX/bin/nxserver --passwd [username]

6.5.1 NX Crashes on session startup

If your NX Client shows the NX logo then disappears with a Connection Problem dialog afterwards.

Then it could be due to missing fonts. Mostly applies if you have installed Arch Linux base and then installed freenx after without the whole X11 set.

Solution until FreeNX Dependencies is fixed is to install xorg-fonts-misc on your NX Server (pacman -S xorg-fonts-misc) and your NX should work.

Note: This does not apply to freenx 0.6.1-3 and above, fix has been incorporated in it and following versions.

6.6 NX logo then blank screen

If you see the NX logo (!M) then a blank screen.

This problem can be solved by running a login manager- The problem is that X11 is not started, and it appears that "startx" or similar do not work from the freenx client. Follow these instructions to setup a login manager and load it at startup: Display Manager

Blind: If this does not resolve your issues, be aware that freenx and bash_completion do not play well together. I only got things to work after removing bash_completion from the .bashrc.

6.7 GDM/XDM Session Menu Error with non-KDE or Gnome Desktop Managers (more common with non-Arch Linux users)

Problem: A session menu comes up talking about "chooseSessionListWidget." A window manager never loads.

Fix :

Double check to see if ~/.xinitrc is executable.

 ls -la ~/ | grep .xinitrc

If the file is not executable, simply

 chmod +x ~/.xinitrc

Keep in mind this command should be executed along with pertinent instructions on this page about "Setting up non-KDE or Gnome desktop managers"

6.8 Cannot connect because command sessreg not found

If you get the following error while connecting

 /opt/NX/bin/nxserver: line 941: sessreg: command not found
 NX> 280 Exiting on signal: 15

then you have to install the package xorg-server-utils.