[LAD] Jackd & Real Time Kernel

Len Ovens len at ovenwerks.net
Fri Jan 12 16:57:02 UTC 2018

On Fri, 12 Jan 2018, Benny Alexandar wrote:

> I just compiled simple_client.c and things starts to work.
> My doubt is do I need to install linux real-time kerel update for JACK.

It depends... personally, I use the lowlatency kernel with no problems 
using an ice1712 based PCI card audio interface. Your situation may 

> How do I know if jack is running real time, is it by checking for xruns ?

Jack runs in real time mode by default. If you are running jackd2 (version 
1.9*) then check ~/.log/jack/jackdbus.log

for the line:
Thu Dec 28 10:38:26 2017: JACK server starting in realtime mode with 
priority 10

Otherwise the same line will appear in jackd terminal output when started.

Do note that part of the jackd instalation process sometimes gets missed 
by some installers. There should be a file 
/etc/security/limits.d/audio.conf If this is missing or named as disabled, 
you may not be able to get jackd to start in realtime mode. The two lines 
of importance in that file are:
@audio   -  rtprio     95
@audio   -  memlock    unlimited
  Depending on your distro the group may be other than audio. Whatever that 
group is, your user needs to be a part of it. Most audio distributions get 
this right already (even ubuntustudio), but non-audio distros generally 
need this to be fixed. After adding yourself to the audio (or whatever) 
group you will need to logout and back in before that will have any 

Len Ovens

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