X server with sound inside an OpenVZ / Proxmox container

on August 24, 2009 in Linux with 3 comments by

Generally when using X-based applications inside an OpenVZ or Proxmox container, the host node will run the X server and the container will use X forwarding through SSH to run the application. An article at the Open VZ Wiki explains this in more detail.

However, I wanted to have an X server inside the container itself. Moreover, it should also have support for sound (ALSA). The reason behind this is to have a container capable of running FreeSWITCH (a high performance VoIP switch similar to Asterisk) with the Skypiax trunk (for Skype connectivity) fully independent.

There are various methods of implementing the X server inside an OpenVZ or Proxmox container, especially if no direct video output is required. However, there is very little information available on how to enable sound inside an OpenVZ or Proxmox container. This article will explain how to do this.

Preparing the host node

The host node requires the proper sound modules installed. For example, on a server that does not require actual output through attached speakers, snd_dummy is sufficient. Enter the following command to load the snd_dummy module:

modprobe snd_dummy

You can verify if everything went well with:

lsmod | grep snd

Which will  display an output similar to:

snd_dummy              23168  0
snd_pcm                97288  1 snd_dummy
snd_timer              35464  1 snd_pcm
snd                    79784  3 snd_dummy,snd_pcm,snd_timer
soundcore              18208  1 snd
snd_page_alloc         19984  1 snd_pcm

If this is the case, then you’d want to make sure the snd_dummy will be loaded at boot time. Simply issue the following command:

echo "snd_dummy" >> /etc/modules

Preparing the container

Setting device privileges

The next step is preparing the OpenVZ or Proxmox container. By default, the container does not have access privileges to the sound device, so this needs to be setup from the host node (assuming “100” is the actual container ID):

vzctl set 100 --devices c:116:all:rw --devices c:4:all:rw --save

Cloning the sound devices

The following step involves recreating the  /dev/snd layout from the host node in the container. Let’s first see what the layout looks like on the host node:

ls -la /dev/snd

This will give an output similar to:

crw-rw----  1 root audio 116, 6 2009-08-14 20:42 controlC0
crw-rw----  1 root audio 116, 5 2009-08-14 20:42 pcmC0D0c
crw-rw----  1 root audio 116, 4 2009-08-14 20:42 pcmC0D0p
crw-rw----  1 root audio 116, 3 2009-08-14 20:42 seq
crw-rw----  1 root audio 116, 2 2009-08-14 20:42 timer

It is important that the same device IDs are being recreated in the container. I.e., the device ID for seq is 116,3 in the above example.

Enter the container and start and issue the following commands, depending on the output given on the host node:

vzctl enter 100
rm -r /dev/snd
mkdir /dev/snd
mknod /dev/snd/controlC0 c 116 6
mknod /dev/snd/pcmC0D0c c 116 5
mknod /dev/snd/pcmC0D0p c 116 4
mknod /dev/snd/seq c 116 3
mknod /dev/snd/timer c 116 2
chmod 660 /dev/snd/*
chown :audio /dev/snd/*

At this point you have cloned copy of the host node’s sound devices and are ready to be used.

Please note that the application that wishes to use the sound devices require the proper privileges. The easiest method is to add the UID to the audio group. For example, if Skype runs under uid “skype”, issue this command:

adduser skype audio

Installing Xorg Server

There are various X server variants that can be installed in the container, especially if no video output is required. The most popular one is undoubtedly Xvfb.

I have opted for using the Xorg Server with a dummy video, mouse and keyboard driver instead (as this was dedicated server without any of these devices). This section details how I have installed it on Debian-based distributions.

Prior to installation

First step, inside a container, is to soft-link TTY1 to TTY0:

rm /dev/tty0
ln -s /dev/tty1 /dev/tty0
This assumes you are accessing the container using vzctl, not SSH !

If nscd is installed, remove this first:

aptitude remove nscd

Download and install packages

Next we install the required packages for Xorg and some device drivers, incuding ALSA for sound support:

aptitude -R install xorg xserver-xorg-video-dummy xserver-xorg-input-kbd xserver-xorg-input-mouse alsa-base linux-sound-base libaudiofile0 dbus udev-

Edit the configuration

The last step is configuring Xorg, by editing the /etc/X11/xorg.conf file as following:

Section "InputDevice"
        Identifier      "Dummy Input"
        Driver          "void"

Section "Device"
        Identifier      "Dummy Video"
        Driver          "dummy"

Section "Monitor"
        Identifier      "Configured Monitor"

Section "Screen"
        Identifier      "Default Screen"
        Monitor         "Configured Monitor"
        Device          "Dummy Video"

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Dummy Input"

You can now start X instances using:

/usr/bin/X :<DISPLAY#>

where <DISPLAY#> is the display to be used (without the brackets, or omit entirely for default settings). X-based applications will now be able to run on any of these displays. For example, to run Skype (for Skypiax) on a specific display and under UID “skype”:

su skype -c "echo secret:password | DISPLAY=:1 /usr/bin/skype --pipelogin 2>>skype_errors.log &"

Remote access using Nomachine NX

Even though you are using a virtual framebuffer (such as with Xvfb) or dummy video driver, you will still be able to do visual tasks on the server. One method is to use an X forwarding tunnel (ssh -X). I prefer to use Nomachine’s NX server instead.

To install the Nomachine NX server on a Debian-based distribution, issue the following command:

dpkg -i nxclient_3.3.0-6_i386.deb
dpkg -i nxnode_3.3.0-17_i386.deb
dpkg -i nxserver_3.3.0-22_i386.deb

This assumes you are running a 32-bits version of Linux and the versions listed above are still correct. Please verify this at Nomachine’s website and change as appropriate before issuing the command.

Now you are ready to connect to your Xorg server using Nomachine’s NX Client and do visual tasks (ie., browse the internet if a browser is installed).

vzctl set 105 –devices c:116:all:rw –devices c:4:all:rw –save
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  1. Eric
    posted on Apr 24, 2016 at 12:45 AM  |  reply

    Something interesting, when no X11 server is installed or running, but a VNC server (like TightVNCserver) is installed and started, NoMachine will show the the same display as the VNC server.

    For example, run tightvncserver, which will start a listening port on 5901. Connect to the server with a VNC viewer on port 5901. Then, use NX client to connect to the NoMachine server listening on port 4000. Compare the VNC viewer with the NX viewer; and you’ll see the same output

    I had thought NoMachine 5.x has a built-in X11 service for headless Linux servers, but it NX client hangs on “Connecting…” after password authentication.

  2. Zoobab
    posted on Apr 21, 2011 at 3:47 PM  |  reply

    I added it with:

    mknod tty1 c 4 1

    then tried to start the X:

    Fatal server error:
    xf86OpenConsole: Cannot open virtual console 7 (No such file or directory)

  3. Zoobab
    posted on Apr 21, 2011 at 3:45 PM  |  reply

    I tried to run the X server:

    xf86OpenConsole: Cannot open /dev/tty0 (No such file or directory)

    ls -l tty*

    crw-rw-rw- 1 root tty 5, 0 Nov 12 12:07 tty
    lrwxrwxrwx 1 root root 9 Apr 21 15:38 tty0 -> /dev/tty1

    But there is no tty1.

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