Mixxx is a powerful and free (open source) DJ program which allows you perform a live set with up to 4 virtual decks and optionally stream it to a broadcasting server. Common effects like echo, flanger, reverb, bitcrusher are available, and through its LV2 plugin interface you can use many more external effects to spice up your set.
Its master sync feature ensures that the music primed in all your decks stays locked to the beat. You can control pitch and key, or loop a stretch of audio. Quantize your cues and loops so that they start right on the beat all the time. And so on – and all of that with an attractive skinnable user interface.
You can plug in a MIDI controller and map its buttons/knobs/sliders to operate the Mixxx user interface so that you do not have to use your computer’s mouse & keyboard to cue, mangle and cross-fade the audio. There’s actually a lot of presets you can load for the most well-known MIDI controllers like the Novation LaunchPad Mini.
If the JACK daemon is running you can connect Mixxx to it, but it will perform just fine with ALSA as well.
This was a piece of software which was missing from my DAW package collection. Therefore I created packages for mixxx and its dependencies and added them to the repository. The liveslak scripts have been updated as well so that the next Slackware DAW Live will include Mixxx for you to try out.
If you use slackpkg you can download an updated template here: http://www.slackware.com/~alien/tools/templates/daw.template and use “slackpkg install-template daw” to have easy access to the full list of packages.
Welcome, music-making (Slackware) Linux-using friends. This article will be an interactive work and probably never finished. I am looking for the best possible setup of my Slackware system for making music without having to revert to a custom Linux Distro like the revered StudioWare.
Please supplement my writings with your expert opinions and point out the holes and/or suggest improvements/alternatives to my setup. Good suggestions in the comments section will be incorporated into the main article.
Your contributions and knowledge are welcomed!
What is a DAW?
In simple terms, a Digital Audio Workstation is a device where you create and manipulate digital audio.
Before the era of personal computing, a DAW would be a complex piece of (expensive) hardware which was only within reach of music studios or artists of name and fame. A good example of an early DAW is the Fairlight CMI (Computer Musical Instrument), released in the late 70’s of the previous century. This Fairlight was also one of the first to offer a digital sampler. The picture at the left of this page is its monitor with a light-pen input.
These days, the name “DAW” is often used for the actual software used to produce music, like the free Ardour, LMMS, or the commercial Ableton Live, FL Studio, Cubase, Pro Tools, etcetera.
But “Digital Audio Workstation” also applies to the computer on which this software is running and whose software and hardware is tailored to the task of creating music. To make it easier for musicians who use Linux, you can find a number of custom distributions with a focus on making electronic music, such as StudioWare (Slackware based), AV Linux (Debian based), QStudio64 (Mint based), so that you do not have to spend a lot of time configuring your Operating System and toolkits.
A ready-to-use distro targeting the musician’s workflow is nice, but I am not the average user and want to know what’s going on under the hood. What’s new… And therefore, in the context of this article I am going to dive into the use of a regular Slackware Linux computer as a DAW.
I wrote an earlier article where I focused on the free programs that are available on a Linux platform and for which I created Slackware packages: Explorations into the world of electronic music production.
That article provided a lot of good info (and reader feedback!) about creating music. What lacked, was a good description of how to setup your computer as a capable platform to use all that software on. Slackware Linux out of the box is not setup as a real-time environment where you have low-latency connectivity between your musical hardware and the software. But these capabilities are essential if you want to produce electronic music by capturing the analog signals of physical instruments and converting them to digital audio, or if you want to add layers of CPU intensive post-processing to the soundscape in real-time.
Achieving that will be the topic of the article.
Typical hardware setup
The software you use to create, produce and mix your music… it runs on a computer of course. That computer will benefit from ample RAM and a fast SSD drive. It will have several peripherals connected to it that allow you to unleash your musical creativity:
a high-quality sound card or external audio interface with inputs for your physical music instruments and mics, sporting a good Analog to Digital Converter (DAC) and adding the least amount of latency.
an input device like a MIDI piano keyboard or controller, or simply a mouse and typing keyboard.
a means to listen to the final composite audio signal, i.e. a monitor with a flat frequency response.
In my case, this means:
USB Audio Interface: FocusRite Scarlett 2i4 2nd Gen
Voice and instrument recording mics connected to the USB audio interface:
Rode NT1-A studio microphone with a pop-filter, or
Behringer C-2 2 studio condenser microphones (matched pair)
Monitor: I use Devine PRO 5000 studio headphones instead of actual studio monitors since i am just sitting in the attic with other people in the house…
And a computer running Slackware Linux and all the tools installed which are listed in my previous article.
Configuring Slackware OS
We will focus on tweaking OS parameters in such a way that the OS essentially stays ‘out of your way’ when you are working with digital audio streams. You do not want audio glitches, drop-outs or experience out-of-sync inputs. If you are adding real-time audio synthesis and effects, you do not want to see delays. You do not want your computer to start swapping out to disk and bogging down the system. And so on.
Note that for real-time behavior of your applications, you do not have to install a real-time (rt) kernel!
The ‘audio’ group
The first thing we’ll do is decide that we will tie all the required capabilities to the ‘audio’ group of the OS. If your user is going to use the computer as a DAW, you need to add the user account to the ‘audio’ group:
# gpasswd -a your_user audio
All regular users stay out of that ‘audio’ group as a precaution. The ‘audio’ members will be able to claim resources from the OS that can lock or freeze the computer if misused. Your spouse and kids will still be able to fully use the computer – just not wreck havoc.
The kernel
A Slackware kernel has ‘CONFIG_HZ_1000’ set to allow for a responsive desktop, and ‘CONFIG_PREEMPT_VOLUNTARY’ as a sensible trade-off between having good overall throughput (efficiency) of your system and providing low latency to applications that need it.
So you are probably going to be fine with the stock ‘generic’ kernel in Slackware. One tweak though is going to improve on low-latency. One important part of the ‘rt-kernel’ patch set was added to the Linux source code, and that is related to interrupt handling. Threaded IRQs are meant to minimize the time your system spends with all interrupts disabled. Enabling this feature in the kernel is done on the boot command-line, by adding the word ‘threadirqs’ there.
If you use lilo, open “/etc/lilo.conf” in an editor and add “threadirqs” to the value of the “append=” keyword, and re-run ‘lilo’.
If you use elilo, open /boot/efi/EFI/Slackware/elilo.conf and add “threadirqs” to the value of the “append = ” keyword
If you are using Grub, then open “/etc/default/grub” in an editor and add “threadirqs” to the (probably empty) value for “GRUB_CMDLINE_LINUX_DEFAULT”. Then re-generate your Grub configuration.
CPU Frequency scaling
Your Slackware computer is configured by default to use the “ondemand” CPU frequency scaling governor. The kernel will reduce the CPU clock frequency (modern CPU’s support this) if the system is not under high load, to conserve energy. However, much of the load in a real-time audio system is on the DSP, not on the CPU, and the scaling governor will not catch that. It could result in buffer underruns (also called XRUNs). Therefore, it is advised to switch to the “performance” governor instead which will always keep your CPU cores at max clock frequency. To achieve this, open the file “/etc/default/cpufreq” in an editor and add this line (make sure that all other lines are commented out with a ‘#” at the beginnning!):
SCALING_GOVERNOR=performance
After reboot, this modification will be effective.
Note: if you want to use your laptop as a DAW, you may want to re-consider this modification. You do not want to have your CPU’s running at full clockspeed all of the time, it eats your battery life. Make use of this “performance” feature only when you need it.
Real-time scheduling
Your DAW and the software you use to create electronic music, must always be able to carry out their task irrespective of other tasks your OS or your Desktop Environment want to slip in. This means, your audio applications must be able to request (and get) real-time scheduling capabilities from the kernel.
How you do this depends on whether your Slackware uses PAM, or not.
If PAM is installed, RT Scheduling and the ability to claim Locked Memory is configured by creating a file in the “/etc/security/limits.d/” directory – let’s name the file “/etc/security/limits.d/rt_audio.conf” (the name is not relevant, as long as it ends on ‘.conf’) and add the following lines.
# Real-Time Priority allowed for user in the 'audio' group:
# Use 'unlimited' with care,a misbehaving application can
# lock up your system. Try reserving half your physical memory:
#@audio - memlock 2097152
@audio - memlock unlimited
@audio - rtprio 95
If PAM is not part of your system, we use a feature which is not so widely known to achieve almost the same thing: initscript (man 5 initscript). When the shell script “/etc/initscript” is present and executable, the ‘init’ process will use it to execute the commands from inittab. This script can be used to set things like ulimit and umask default values for every process.
So, let’s create that file “/etc/initscript”, add the following block of code to it:
# Set umask to safe level:
umask 022
# Disable core dumps:
ulimit -c 0
# Allow unlimited size to be locked into memory:
ulimit -l unlimited
# Address issue of jackd failing to start with realtime scheduling:
ulimit -r 95
# Execute the program.
eval exec "$4"
And make it executable:
# chmod +x /etc/initscript
The ulimit and umask values that have been configured in this script will now apply to every program started by every user of your computer. Not just members of the ‘audio’ group. You are warned. Watch your kids.
Use sysctl tweaks to favor real-time behavior
The ‘sysctl’ program is used to modify kernel parameters at runtime. We need it in a moment, but first some preparations.
A DAW which relies on ALSA MIDI, benefits from access to the high precision event timer (HPET). We will allow the members of the ‘audio’ group to access the HPET and real-time clock (RTC) which by default are only accessible to root.
We achieve this by creating a new UDEV rule file “/etc/udev/rules.d/40-timer-permissions.rules”. Add the following lines to the file and then reboot to make your changes effective:
With access to the HPET arranged, we can create a sysctl configuration file which the kernel will use on booting up. There are a number of audio related ‘sysctl‘ settings that allow for better real-time performance, and we add these settings to a new file “/etc/sysctl.d/daw.conf”. Add the following lines to it:
The first line allows the user to access the timers at a higher frequency than the default ’64’. Note that the max possible value is 8192 but a sensible minimum for achieving lower latency is 1024. The second line is suggested by the ‘realtimeconfigquickscan‘ tool, and increases the maximum number of files that the kernel can track on behalf of the programs you are using (no proof that this actually improves real-time behavior). And the third line will prevent your system from starting to swap too early (its default value is ’60’) which is a likely cause for XRUNs.
Disable scheduled tasks of the OS and your DE
The suggestions above are mostly kernel related, but your own OS and more specifically, the Desktop Environment you are using can get in the way of real-time behavior you want for your audio applications.
General advice:
Disable your desktop’s Compositor (KWin in KDE Desktop, Compiz on XFCE and Gnome Desktop). Compositing requires a good GPU supporting OpenGL hardware acceleration but still this will put a load on your CPU and in particular on the application windows.
Desktop-specific:
Plasma 5 Desktop
The most obvious candidate to mess with your music making process is Baloo, the file indexer. The first time Baloo is started on a new installation, it will seriously bog down your computer and eat most of its CPU cycles while it works its way through your files.
If you really want to keep using Baloo (it allows for a comfortable file search in Plasma5) you could at least disable file content indexing and merely let it index the filenames (similar to console-based ‘locate’).
Go to “System Settings > Workspace > Search > File search” and un-check “also index file content”
If you want to completely disable Baloo so that you can not re-enable it anymore with any command or tool, do a manual edit of ${HOME}/.config/baloofilerc and make sure that the “[Basic Settings]” section contains the following line:
Indexing-Enabled=false
In KDE, the Akonadi framework is responsible for providing applications with a centralized database to store, index and retrieve the user’s personal information including the user’s emails, contacts, calendars, events, journals, alarms, notes, etc. The alerts this framework generates can interfere with real-time audio recording, so you can disable Akonadi if you want by running “akonadictl stop” in a terminal, under your own user account. Then make sure that your desktop does not auto-start applications which use Akonadi, Also, open the configuration of your desktop Clock and uncheck “show events” to prevent a call into Akonadi.
Read more on https://userbase.kde.org/Akonadi/nl#Disabling_the_Akonadi_subsystem
Compositing is another possible resource hog, especially when your computer is in the middle-or lower range. You can easily toggle (disable/re-enable) the desktop compositor by pressing the “Shift-Alt-F12” key combo.
Note that if you use Latte-dock as your application starter, this will not like the absence of a Compositor. You’ll have to switch back to KDE Plasma’s standard menus to start your applications.
Selecting your audio interface
You may not always have your high-quality USB audio interface connected to your computer. When the computer boots, ALSA will decide for itself which device will be your default audio device and usually it will be your internal on-board sound card.
You can inspect your computer’s audio devices that ALSA knows about. For instance, my computer has onboard audio, then the HDMI connector on the Nvidia GPU provides audio-out; I have a FocusRite Scarlett 2i4, an old Philips Web Cam with an onboard microphone and I have loaded the audio loopback module. That makes 5 audio devices, numbered by the kernel from 0 to 4 with the lowest number being the default card:
$ cat /proc/asound/cards
0 [NVidia_1 ]: HDA-Intel - HDA NVidia
HDA NVidia at 0xdeef4000 irq 22
1 [NVidia ]: HDA-Intel - HDA NVidia
HDA NVidia at 0xdef7c000 irq 19
2 [USB ]: USB-Audio - Scarlett 2i4 USB
Focusrite Scarlett 2i4 USB at usb-0000:00:02.1-2, high speed
3 [U0x4710x311 ]: USB-Audio - USB Device 0x471:0x311
USB Device 0x471:0x311 at usb-0000:00:02.0-3, full speed
4 [Loopback ]: Loopback - Loopback
Loopback 1
Note that these cards can be identified when using ALSA commands and configurations, both by their hardware index (hw0, hw2) and by their ‘friendly name‘ (‘Nvidia_1’, ‘USB’).
Once you know which cards are present, you can inspect which kernel modules are loaded for these cards – The same indices as shown in the previous ‘cat /proc/asound/cards‘ command are also listed in the output of the next command:
You’ll notice that some cards use the same kernel module. If you want to deterministically number your sound devices instead allowing the kernel to probe and enumerate your hardware, you’ll have to perform some wizardry in the /etc/modprobe.d/ directory.
Using pulseaudio you can change the default audio output device on the fly.
First you determine the naming of devices in pulseaudio (it’s quite different from what you saw in ALSA) with the following command which lists the available outputs (called sinks by pulseaudio):
You see which device is the default because that will be the only one that is in ‘RUNNING’ state and not ‘SUSPENDED’. Subsequently you can change the default output device, for instance to the FocusRite interface:
You can use these commands to help you deciding which to use as your default device if you un-plug your USB audio interface, or if you want to let your system sounds be handled by an on-board card while you are working on a musical production using your high-quality USB audio interface – each device with their own set of speakers.
Connecting the dots: ALSA -> Pulseaudio -> Jack
The connecting element in all the software tools of your DAW is the Jack Audio Connection Kit, or Jack for short. Jack is a sound server – it provides the software infrastructure for audio applications to communicate with each other and with your audio hardware. All my DAW-related software packages have been compiled against the Jack libraries and thus can make use of the Jack infrastructure once Jack daemon is started.
Once Jack takes control, it talks directly to ALSA sound system.
Slackware uses the ALSA sound architecture since replacing the old OSS (open sound system) with it, many years ago. ALSA is the kernel-level interface to your audio hardware combined with a set of user-land libraries and binaries to allow your applications to use your audio hardware.
Pulseaudio is a software layer which was added to Slackware 14.2. Basically it is a sound server (similar to Jack) which interfaces between ALSA and your audio applications, providing mixing and re-sampling capabilities that expand on what ALSA already provides. It deals with dynamic adding and removing of audio hardware (like head-phones) and can transfer audio streams over the network to other Pulseaudio servers.
Musicians and audiophiles sometimes complain that Pulseaudio interferes with the quality of the audio. Mostly this is caused by the resampling that Pulseaudio may do when combining different audio streams but this can be avoided by configuring your system components to all use a single sample rate like 44,1 or 48 KHz. Also, in recent years the quality of the Pulseaudio software has improved quite a bit.
When Jack starts it will interface directly to ALSA, bypassing Pulseaudio entirely. What that means is that all your other applications that are not Jack-aware suddenly stop emitting sound because they still play via Pulseaudio. Luckily, we can fix that easily, and without using any custom scripting.
All it takes is the Jack module for Pulseaudio. The source code for this module is part of Pulseaudio but it is not compiled and installed in Slackware since Slackware does not contain Jack. So what I did is create a package which compiles just that Pulseaudio Jack module. You should install my “pulseaudio-jack” package from my repository. The module contains a library responsible for detecting when jack starts and then enables ‘source’ and ‘sink’ for Pulseaudio-aware applications to use.
The main pulseaudio configuration file “/etc/pulse/default.pa” already contains the necessary lines to support the pulseaudio-jack module:
### Automatically connect sink and source if JACK server is present
.ifexists module-jackdbus-detect.so
.nofail
load-module module-jackdbus-detect channels=2
.fail
.endif
The only thing you need to do is ensuring that jackdbus is started. If you use qjackctl to launch Jack, you need to check the “Enable D-Bus interface” and “Enable JACK D-Bus interface” boxes in “Setup -> Misc”. See next section for more details on using QJackCtl.
In 2020 this is all it takes to route all output from your ALSA and Pulseaudio applications through Jack.
Easy configuration of Jack through QJackCtl
The Jack daemon can be started and configured all from the commandline and through scripts. But when your graphical DAW software runs inside a modern Desktop Environment like XFCE or KDE Plasma5, why not take advantage of graphical utilities to control the Jack sound server?
DAW-centric distros will typically ship with the Cadence Tools, which is a set of Qt5 based applications written for the KXStudio project (consisting of Cadence itself and also Catarina, Catia and Claudia) to manage your Jack audio configuration easily. Note that I have not created packages for Cadence Tools but if there’s enough demand I will certainly consider it, since this toolkit should work just fine in Slackware:
For a Qt5 based Desktop Environment like KDE Plasma5, a control application like QJackCtl will blend in just as well. While it’s more simplistic than Cadence, it does a real good job nevertheless. Its author offers several other very nice audio programs at https://www.rncbc.org/ like QSampler and the Vee One Suite of old-skool synths.
Like Cadence, QJackCtl offers a graphical user interface to connect your audio inputs and outputs, allowing you to create any setup you can imagine:
QJackCtl can be configured to run the Jack daemon on startup and enable Jack’s Dbus interface. Stuff like defining the samplerate, the audio device to use, the latency you allow, etcetera is also available. And if you tell the Desktop Session Manager to autostart qjackctl when you login, you will always have Jack ready and waiting for you.
Turning theory into practice
The reason for writing up this article was informational of course, since this kind of comprehensive detail is not readily available for Slackware. With all the directions shared above you should now be able to tune your computer to make it suited for some good music recording and production, and possibly live performances.
A secondary goal of the research into the article’s content was to gain a better understanding of how to put together my own Slackware based DAW Live OS. All of the above knowledge is being put into the liveslak scripts and Slackware Live Edition now has a new variant next to PLASMA5, SLACKWARE, XFCE, etc… it is “DAW“.
I am posting ISO images of this Slackware Live DAW Edition to https://martin.alienbase.nl/mirrors/slackware-live/pilot/ and hope some of you find it an interesting enough concept that you want to try it out.
Note that you’ll get a ~ 2.5 GB ISO which boots into a barebones KDE Plasma5 Desktop with all my DAW tools present and Jack configured, up and running. User accounts are the same as with any Slackware Live Edition: users ‘live‘ and ‘root‘ with passwords respectively ‘live‘ and ‘root‘.
Why KDE Plasma5 as the Desktop of choice? Isn’t this way too heavy on resources to provide a low-latency workflow with real-time behaviour?
Well actually… the resource usage and responsiveness of KDE Plasma5 is on par or even better than the light-weight XFCE. Which is the reason why an established distro like Ubuntu Studio is migrating from XFCE to KDE Plasma5 for their next release (based on Ubuntu 20.10) and KXStudio targets the KDE Plasma5 Desktop as well.
You can burn the ISO to a DVD and then use it as a real ‘live’ OS which is fresh and pristine on every boot, or use the ‘iso2usb.sh’ script which is part of liveslak to copy the content of the ISO to a USB stick – which adds persistency, application state saving and additional storage capability. The USB option also allows you to set new defaults for such things as language, keyboard layout, timezone etc so that you do not have to select those everytime through the bootmenus.
If your computer has sufficient RAM (say, 8 GB or more), you should consider loading the whole Live OS into RAM (using the ‘toram’ boot parameter) and have a lightning-fast DAW as a result. My tests with a USB stick with USB-3 interface was that it takes 2 to 3 minutes to load the 2.5 GB into RAM, which compares to nothing if your DAW session will be running for hours.
Shout out
A big help was the information in the Linux Audio Wiki, particularly this page: https://wiki.linuxaudio.org/wiki/system_configuration. In fact, I recommend that you absorb all of the information there.
On that page, you will also find a link to a Perl program “realtimeconfigquickscan” which can scan your system and report on the readiness of your computer for becoming a Digital Audio Workstation.
Today, 28th of May 2020, the Audacity multi-track audio recorder turns 20 years old! This is a nice moment to also release the Slackware packages (only targeting -current, sorry) for their latest and greatest, Audacity 2.4.1 which was released a week ago as a quick bug-fix to the long-awaited 2.4.0.
Along with this new Audacity release, I also have new packages for wxGTK3 (3.0.5.1) which you’ll need for Audacity to show its graphical user interface:
Get the packages here and note that you will also need to install jack2, ladspa_sdk and vamp-plugin-sdk packages: http://www.slackware.com/~alien/slackbuilds/(rsync://slackware.nl/mirrors/people/alien/slackbuilds/)
I do regular updates of packages in my repository. I focus on the software that is popular, or relevant to Slackware. For the software with a high visibility I usually write a blog post to alert people to the new stuff.
During the last couple of weeks I have not been writing so much about updates due to personal circumstances, some of it has to do with the Corona outbreak.
I was also affected the death of Erik Jan Tromp (Slackware’s alphageek) early March just after I visited him for a final time in his apartment in Leeuwarden.
Anyway, here is a summary of what was refreshed during these weeks.
The new KDE-5_20.03 batch is now available for download from my ‘ktown‘ repository. As always, please remove KDE4 first (check the README for instructions if you still need those). These packages will not work on Slackware 14.2.
This March release contains the KDE Frameworks 5.68.0, Plasma 5.18.3 and Applications 19.12.3. All this on top of Qt 5.13.2.
Deps:
The most interesting event this month is of course the addition of qt5 and its dependencies to Slackware-current itself. I could remove several packages from my own ktown ‘deps’ section: OpenAL (renamed to openal-soft in Slackware), SDL_sound (integrated to Slackware’s sdl package), brotli, hyphen, libxkbcommon, socat, qt5, qt5-webkit, wayland, wayland-protocols and woff2.
I also updated the sip package so its version matches again with that in Slackware (the ktown version has Qt5 support which the Slackware version still needs to pick up). The qca-qt5 package was updated to the latest version.
Plasma-extra;
In plasma-extra I updated latte-dock.
Applications;
Applications 19.12.3 is a stability and bugfix update for the 19.12 cycle. Remember that I still call this ‘Applications‘ but KDE folk prefer the new name ‘Releases‘. See https://kde.org/announcements/releases/2020-03-apps-update/
Applications-extra:
In applications-extra I updated kstars and added a new package: labplot.
Telepathy:
KDE Telepathy is no longer part of my ‘ktown’ distribution of KDE Plasma5.
PAM support
My ‘ktown’ has two sub-repositories. The ‘latest‘ sub-repository is always meant to be used with the official Slackware-current packages. and the ‘testing‘ sub-repository is where I test stuff that is not yet ready to be adopted by the larger population.
Since last month, Slackware’s own ‘/testing’ area contains a set of packages that add PAM support to Slackware. My regular ktown aka ‘latest’ repository content is meant for an up-to-date Slackware-current without PAM. The ‘testing’ repository on the other hand is compiled against a pam-ified Slackware and can be used if you have added the new ‘testing’ PAM packages of Slackware-current to your system.
The packages that picked up PAM support are: kscreenlocker and plasma-workspace (in the ‘plasma’ directory), and sddm-qt5 (in ‘plasma-extra’). A new package has been introduced as well: kwallet-pam (in the ‘plasma’ directory).
A new Plasma5 Live ISO is available at https://slackware.nl/slackware-live/latest/ (rsync://slackware.nl/mirrors/slackware-live/latest/) with user/pass being “live/live” as always.
While I was working on new Plasma5 packages, Pat Volkerding released packages for gcc 9.3.0for Slackware-current. When I told him I did not have the time to compile multilib versions for the new gcc because I was busy, Pat responded by updating the gcc-multilib.SlackBuild script and compiling a set of multilib gcc packages for me. So what you download from my multilib repository was actually built by Pat this time.
For those who still use the older Java7, I updated my openjdk7/openjre7 packages to 7u251_b02 with the help of IcedTea 2.6.21 release. This is a security bugfix release, as these Java releases always are I guess.
I get questions from time to time why I do not release packages for Java 11, and my answer always is: I do not see the need. I build my packages using IcedTea framework and when they add support for newer Java versions than 8, I will release packages for that too.
There were several Chromium 80 updates in rapid succession during the last month, and the most recent version you can get from my repository now is 80.0.3987.132. I realize that there’s even a slightly newer release available but there’s only so much time to work on Slackware.
The advantage of having Qt5 in Slackware nowadays, is that it becomes a lot easier to compile a Calibre package for slackware-current. Nevertheless, the calibre package for Slackware 14.2 is still big because my Calibre packages contain all the dependencies inside and the version for Slackware 14.2 includes qt5 libraries.
I am regularly updating packages that are part of my ‘Digital Audio Workstation’ collection.
During the past weeks I updated the MuseScore package (Musescore can create, playback and print music scores) and along with that I updated the Qt5 based JackQtl graphical interface to the Jack2 audio server.
For my own laptop and desktop, I am now starting qjackctl in Plasma5 on login and all my ALSA and Pulseaudio sound pipes through Jack into my speakers now, without the need to change anything to Slackware’s default ALSA and Pulseaudio configurations.
I think I am not the only one who runs a graphical Linux desktop environment somewhere on a server 24/7.
I hear you ask: why would anyone want that?
For me the answer is simple: I work for a company that runs Linux in its datacenters but offers only Windows 10 on its user desktops and workstations. Sometimes you need to test work related stuff on an Internet-connected Linux box. But even more importantly: when I travel, I may need access to my tools – for instance to fix issues with my repositories, my blog, my build server, or build a new package for you guys.
This article documents how I created and run such a 24/7 graphical desktop session and how I made it easily accessible from any location, without being restricted by firewalls or operating systems not under my control. For instance, my company’s firewall/proxy only allows access to HTTP(S) Internet locations; for me a browser-based access to my remote desktop is a must-have.
How to run & access a graphical Linux desktop 24/7 ?
VNC or Virtual Network Computing is a way to remotely access another computer using the RFB (Remote Frame Buffer) protocol. The original VNC implementation is open source. In due time, lots of cross-platform clients and servers have been developed for most if not all operating systems. Slackware ships with an optimized implementation which makes it possible to work in a remote desktop even over low-bandwidth connections.
There’s one thing you should know about VNC. It is a full-blown display server. Many people configure a VNC server to share their primary, physical desktop (your Linux Xserver based desktop or a MS Windows desktop) with remote VNC clients.
VNC is also how IT Help Desks sometimes offer remote assistance by taking control over your mouse, keyboard and screen.
But I want to run a VNC server ‘headless‘. This means, that my VNC server will not connect to a physical keyboard, mouse and monitor. Instead, it will offer virtual access to these peripherals. Quite similar to X.Org, which also provides what is essentially a network protocol for transmitting key-presses, mouse movements and graphics updates. VNC builds on top of X.Org and thus inherits these network protocol qualities.
Start your engines
Get a computer (or two)
First, you will have to have a spare desktop computer which does not consume too much power and which you can keep running all day without bothering the other members of your family (the cooling fans of a desktop computer in your bedroom will keep people awake).
Next, install Slackware Linux on it (any Linux distro will do; but I am biased of course). You can omit all of the KDE packages if you want. We will be running XFCE. Also install ‘tigervnc’ and ‘fltk’ packages from Slackware’s ‘extra’ directory. The tigervnc package installs both a VNC client and a VNC server.
You can store this server somewhere in a cupboard or in the attic, or in the basement: you will not have a need to access the machine locally. It does not even have to have a keyboard/mouse/monitor attached after you have finished implementing all the instructions in this article.
You may of course want to use a second computer – this one would then act as the client computer from which you will access the server.
In my LAN, the server will be configured with the hostname “darkstar.example.net”. This hostname will be used a lot in the examples and instructions below. You can of course pick and choose any hostname you like when creating your own server.
I also use the Internet domain “lalalalala.org” in the example at the end where I show how to connect to your XFCE desktop from anywhere on the Internet. I do not own that domain, it’s used for demonstrative purposes only, so be gentle with it.
Run the XFCE desktop
Let’s start a VNC server and prepare to run a XFCE graphical desktop inside.
alien@darkstar:~$ vncserver -noxstartup
You will require a password to access your desktops.
Password:
Verify:
Would you like to enter a view-only password (y/n)? n
New 'darkstar.example.net:1 (alien)' desktop is darkstar.example.net:1
Creating default config /home/alien/.vnc/config
Log file is /home/alien/.vnc/darkstar.example.net:1.log
What we did here was to allow the VNC server to create the necessary directories and files but I prevented its default behavior to start a “Twm” graphical desktop. I do not want that pre-historic desktop, I want to run XFCE.
You can check that there’s a VNC server running now on “darkstar.example.net:1”, but still without a graphical desktop environment inside. Start a VNC client and connect it to the VNC server address (highlighted in red above):
alien@darkstar:~$ vncviewer darkstar.example.net:1
TigerVNC Viewer 64-bit v1.10.1
Built on: 2019-12-20 22:09
Copyright (C) 1999-2019 TigerVNC Team and many others (see README.rst)
See https://www.tigervnc.org for information on TigerVNC.
...
The connection of the VNC client to the server was successful, but all you will see is a black screen – nothing is running inside as expected. You can exit the VNC viewer application and then kill the VNC server like this:
alien@darkstar:~$ vncserver -kill :1
The value I passed to the parameter “-kill” is “:1”. This “:1” is a pointer to your active VNC session. It’s that same “:1” which you saw in the red highlighted “darkstar.example.net:1” above. It also corresponds to a socket file in ” /tmp/.X11-unix/”. For my VNC server instance with designation “:1” the corresponding socket file is “X1”. The “kill” command above will communicate with the VNC server through that socket file.
Some more background on VNC networking follows, because it will help you understand how to configure noVNC and Apache later on.
The “:1” number does not only correspond to a socket; it translates directly to a TCP port: just add 5900 to the value behind the colon and you get the TCP port number where your VNC server is listening for client connections.
In our case, “5900 + 1” means TCP port 5901. We will use this port number later on.
If you had configured VNC server to share your physical X.Org based desktop (using the ‘x11vnc’ extension), then a VNC server would be running on “:0” meaning TCP port 5900.
And if multiple users want to run a VNC server on your computer, that is entirely possible! Every new VNC server session will get a new TCP port assigned (by default the first un-assigned TCP port above 5900).
It’s also good to know that the VNC server binds to all network interfaces, including the loop-back address. So the commands “vncviewer darkstar.example.net:1” and “vncviewer localhost:1” give identical result when you start a VNC client on the machine which is also running the VNC server.
Enough with the theory, we need that XFCE session to run! When a VNC server starts, it looks for a script file called “~/.vnc/xstartup” and executes that. This script should start your graphical desktop.
So let’s create a ‘xstartup’ script for VNC, based on Slackware’s default XFCE init script:
alien@darkstar:~$ cp /etc/X11/xinit/xinitrc.xfce ~/.vnc/xstartup
alien@darkstar:~$ vi ~/.vnc/xstartup
Edit that ‘xstartup’ script and add the following lines. They should be the first lines to be executed, so add them directly before the section “Merge in defaults and keymaps“:
Add the following lines immediately before the section “Start xfce Desktop Environment” to ensure that your desktop is locked from the start and no-one can hi-jack your unprotected VNC session before you have a chance to connect to it:
# Ensure that we start with a locked session:
xscreensaver -no-splash &
xscreensaver-command -lock &
In order for these commands to actually work, you may have to run “xscreensaver-demo” once, the first time you login to your desktop in VNC, and configure the screensaver properly.
Into the future
This ends the preparations. From now on, you will start your VNC server (hopefully once per reboot) with the following simple command without any parameters:
alien@darkstar:~$ vncserver
That’s it. You have a XFCE desktop running 24/7 or until you kill the VNC server. You can connect to that VNC server with a VNC client (on Slackware that’s the vncviewer program) just like I showed before, and configure your XFCE desktop to your heart’s content. You can close your VNC client at any time and reconnect to the VNC server at a later time – and in the meantime your XFCE desktop will happily keep on running undisturbed.
You can connect to your VNC server from any computer as long as that computer has a VNC client installed and there’s a network connection between server and client.
How to make that graphical desktop available remotely ?
So now we have a VNC server running with a XFCE desktop environment inside it. You can connect to it from within the LAN using your distro’s VNC viewer application. And now we will take it to the next level: make this Linux XFCE desktop available remotely using a browser based VNC client.
We will require NoVNC software and a correctly configured Apache httpd server. Apache is part of Slackware, all we need to do is give it the proper config, but NoVNC is something we need to download and configure first.
noVNC
The noVNC software is a JavaScript based VNC client application which uses HTML5 WebSockets and Canvas elements. It requires a fairly modern browser like Chromium, Firefox, and also mobile browsers (Android and i/OS based) will work just fine.
With your browser, you connect to the noVNC client URL. Apache’s reverse proxy connects the noVNC client to a WebSocket and that WebSocket in turn connects to your VNC server port.
Some VNC servers like x11vnc and libvncserver contain the WebSockets support that noVNC needs, but our TigerVNC based server does not have WebSocket support. Therefore we will have to add a WebSockets-to-TCP proxy to our noVNC installation. Luckily, the noVNC site offers such an add-on.
Installing
Get the most recent noVNC ‘tar.gz’ archive (at the moment that is version 1.1.0) from here: https://github.com/novnc/noVNC/releases .
As root, extract the archive somewhere to your server’s hard disk, I suggest /usr/local/ :
The symlink “/usr/local/novnc” allows you to create an Apache configuration which does not contain a version number, so that you can upgrade noVNC in future without having to reconfigure your Apache. See below for that Apache configuration.
We also need to download the WebSockets proxy implementation for noVNC:
# cd /usr/local/novnc/utils/
# git clone https://github.com/novnc/websockify websockify
Running
You will have to start the WebSockets software for noVNC as a non-root local account. That account can be your own user or a local account which you specifically use for noVNC. My suggestion is to start noVNC as your own user. That way, multiple users of your server would be able to start their own VNC session and noVNC acccess port.
I start the noVNC script in a ‘screen‘ session (the ‘screen’ application is a console analog of VNC) so that noVNC keeps running after I logoff.
Whether or not you use ‘screen‘, or ‘tmux‘, the actual commands to start noVNC are as follows (I added the output of these commands as well):
$ cd /usr/local/novnc/
$ ./utils/launch.sh --vnc localhost:5901
Warning: could not find self.pem
Using local websockify at /usr/local/novnc/utils/websockify/run
Starting webserver and WebSockets proxy on port 6080
websockify/websocket.py:30: UserWarning: no 'numpy' module, HyBi protocol will be slower
warnings.warn("no 'numpy' module, HyBi protocol will be slower")
WebSocket server settings:
- Listen on :6080
- Web server. Web root: /usr/local/novnc
- No SSL/TLS support (no cert file)
- proxying from :6080 to localhost:5901
Navigate to this URL:
http://baxter.dyn.barrier.lan:6080/vnc.html?host=baxter.dyn.barrier.lan&port=6080
Press Ctrl-C to exit
I highlighted some of the output in red. It shows that I instruct noVNC (via the commandline argument “–vnc”) to connect to your VNC server which is running on localhost’s TCP port 5901 (remember that port number from earlier in the article when we started vncserver?) and the noVNC WebSockets proxy starts listening on port 6080 for client connection requests. We will use that port 6080 later on, in the Apache configuration.
From this moment on, you can already access your VNC session in a browser, using the URL provided in the command output. But this only works inside your LAN, and the connection is un-encrypted (using HTTP instead of HTTPS) and not secured (no way to control or limit access to the URL).
The next step is to configure Apache and provide the missing pieces.
Apache
Making your Apache work securely using HTTPS protocol (port 443) means you will have to get a SSL certificate for your server and configure ‘httpd’ to use that certificate. I wrote an article on this blog recently which explains how to obtain and configure a free SSL certificate for your Apache webserver. Go check that out first!
Once you have a local webserver running securely over HTTPS, let’s add a block to create a reverse proxy in Apache. If you are already running Apache and have VirtualHosts configured, then you should add the below block to any of your VirtualHost definitions. Otherwise, just add it to /etc/httpd/httpd.conf .
Alias /aliensdesktop /usr/local/novnc
# Route all HTTP traffic at /aliensdesktop to port 6080
ProxyRequests Off
ProxyVia on
ProxyAddHeaders On
ProxyPreserveHost On
<Proxy *>
Require all granted
</Proxy>
# This will not work when you use encrypted web connections (https):
#<Location /websockify>
# Require all granted
# ProxyPass ws://localhost:6080/websockify
# ProxyPassReverse ws://localhost:6080/websockify
#</Location>
# But this will:
# Enable the rewrite engine
# Requires modules: proxy rewrite proxy_http proxy_wstunnel
# In the rules/conditions, we use the following flags:
# [NC] == case-insensitve, [P] == proxy, [L] == stop rewriting
RewriteEngine On
# When websocket wants to initiate a WebSocket connection, it sends an
# "upgrade: websocket" request that should be transferred to ws://
RewriteCond %{HTTP:Connection} Upgrade [NC]
RewriteCond %{HTTP:Upgrade} =websocket [NC]
RewriteRule /(.*) ws://127.0.0.1:6080/$1 [P,L]
<Location /aliensdesktop/>
Require all granted
# Delivery of the web files
ProxyPass http://localhost:6080/
ProxyPassReverse http://localhost:6080/
</Location>
Again, I highlighted the bits in red which you can change to fit your local needs.
The “Alias” statement in the first line is needed to make our noVNC directory visible to web clients, since it is not inside the Apache DocumentRoot (which is “/srv/httpd/htdocs/” by default). I do not like having actual content inside the DocumentRoot directory tree (you never know when you accidentally create a hole and allow the bad guys access to your data) so using an Alias is a nice alternative approach.
You will probably already have noticed that Apache’s reverse proxy will connect to “localhost”. This means you can run a local firewall on the server which only exposes ports 80 and 443 for http(s) access. There is no need for direct remote access to port 6080 (novnc’s websocket) or 5901 (your vncserver).
Check your Apache configuration for syntax errors and restart the httpd if all is well:
Password: the password string you defined for the VNC server
Token: leave empty
Then press “Connect”. You will get forwarded to your XFCE session running inside the VNC server. Probably the XFCE screen lock will be greeting you and if you enter your local account credentials, the desktop will unlock.
You can expand this Apache configuration with additional protection mechanisms. That is the power of hiding a simple application behind an Apache reverse proxy: the simple application does what it does best, and Apache takes care of all the rest, including data encryption and access control.
You could think of limiting access to the noVNC URL to certain IP addresses or domain names. or you can add a login dialog in front of the noVNC web page. Be creative.
Configure your ISP’s router
My assumption is that your LAN server is behind a DSL, fiber or other connection provided by a local Internet Service Provider (ISP). The ISP will have installed a modem/router in your home which connects your home’s internal network to the Internet.
So the final step is to ensure that the HTPS port (443) of your LAN server is accessible from the internet. For this, you will have to enable ‘port-forwarding’ on your Internet modem/router. The exact configuration will depend on your brand of router, but essentially you will have to forward port 443 on the router to port 443 on your LAN server’s IP address.
If you have been reading this far, I expect that you are serious about implementing noVNC. You should have control over an Internet domain and the Internet-facing interface of your ISP’s modem/router should be associated with a hostname in your domain. Let’s say, you own the domain “lalalalala.org” and the hostname “alien.lalalalala.org” points to the public IP address of your ISP’s modem. Then anyone outside of your home (and you too inside your home if the router is modern enough) can connect to: https://alien.lalalalala.org/aliensdesktop/vnc.html and enter the following data into the connection box in order to connect to your VNC session:
Host: alien.lalalalala.org
Port: 443
Password: the password string you defined for the VNC server
Token: leave empty
That’s it! I hope it was all clear. I love to hear your feedback. Also, if certain parts need clarification or are just not working for you, let me know in the comments section below.
Cheers, happy holidays, Eric
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