[arch-proaudio] Introducing: dedicated realtime group (not only for jack/jack2)
dave at sleepmap.de
Mon Jul 30 11:34:59 UTC 2018
On 2018-07-29 18:52:36 (-0400), bill-auger wrote:
> can you explain why a new group was needed? why remove functionality
> from the audio group - that is the commonly expected purpose of the
> audio group on every distro i have used that caters to A/V use-cases -
> conversely, what purpose would the audio group now serve?
The audio group is installed via syusers.d with the systemd package
(defined in /usr/lib/sysusers.d/basic.conf).
It's one of the system's default groups, which grants access to
/dev/audio and /dev/snd/*  (/dev/rtc0, mentioned last, got dropped in
by jack/jack2 a few years back). The accompanying udev rule can be found
in /usr/lib/udev/rules.d/50-udev-default.rules (also part of the systemd
package). Traditionally, other software installing own rules, relies on
this group and its settings (e.g. libffado, as found in
The compromise introduced a long time ago for the jack and jack2
packages (as described upstream on the realtime topic ) also relies
on the audio group.
However, acquiring realtime privileges and accessing audio hardware are
two separate things. Note, that while acquiring realtime privileges can
be benificial for pro-audio applications, it is not the only use-case!
To make things more clear:
audio - access specific audio hardware
realtime - acquire realtime privileges (which you can use for pro-audio)
> most such distros (including the arch derivative i use) also have a
> package which is usually named similarly to 'proaudio-settings', that
> depends on JACK and the kernel-rt and provides optimizations for
> real-time audio use - but the JACK package should not require the
> kernel-rt nor any privileges or optimizations; simply because JACK
> itself does not require those and is intended to be fully usable
> without them
That's exactly why the realtime group will exist and realtime-privileges
will become an optional dependency for jack and jack2.
It doesn't make any sense to have realtime-privileges depend on linux-rt
and or jack/jack2, as realtime-privileges is meant to extend the
capabilities of what a certain user group is allowed to achieve with the
system (and the system's hardware) and therefore is an extension of what
said group can achieve with linux-rt and/or jack/jack2.
> i proposed before the idea of maintaining a consistent
> 'proaudio-settings' optimizations package in the arch upstream - does
> this 'realtime-privilege' package do nothing more than create
> 'realtime' group, with no other optimizations? - if it also has other
> general optimizations for real-time audio, then i suggest it be
> renamed to a commonly recognizable name like: 'proaudio-settings' - if
> not, then i still propose such a 'proaudio-settings' optimization
> package - such a package would necessarily depend on JACK and the
> 'realtime-privilege' package - but that would make it clear that it is
> the optimization package that provides realtime privileges and not the
> JACK package
The "optimizations" (which are more capabilities given to the realtime
group) are now all in the realtime-privileges package, instead of
redundantly packaged in jack/jack2 and being bound to the audio group
(which is there for accessing audio hardware, not for acquiring realtime
Again: Acquiring realtime is not a pro-audio only thing.
jack/jack2 can work without acquiring realtime (mind ). However, one
can extend reliability of some software by acquiring realtime
privileges. Therefore it makes no sense to have separate settings for
pro-audio, as realtime-privileges is a more general approach to whatever
one wants to achieve with that.
In other words: You wouldn't want to have to install jack/jack2 just to
acquire realtime privileges for another piece of software, that is non
pro-audio related, but you can now optionally extend jack/jack2's
capabilities by using realtime-privileges (with a more clear
distinction as to what the groups you're in actually stand for).
I hope this answers your questions.
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