jackd won't run in realtime

[Igor Sakulin]

Was using jackd2 for ages, never had this issue. The usual limits.conf tweaks are present. Jackd won't run in realtime even as root. It's very easy to reproduce in Focal.

Before upgrade, was working:
Ubuntu 18.04.4 LTS
uname -r
kernel 5.3.0-51-generic
jackd --version
jackdmp version 1.9.12 tmpdir /dev/shm protocol 8

After upgrade:
Ubuntu 20.04 LTS
uname -r
5.4.0-29-generic
jackd --version
jackdmp version 1.9.12 tmpdir /dev/shm protocol 8

Simple test:
jackd -R -d dummy -r192000 -p2048

jackdmp 1.9.12
Copyright 2001-2005 Paul Davis and others.
Copyright 2004-2016 Grame.
Copyright 2016-2017 Filipe Coelho.
jackdmp comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
Cannot create RT messagebuffer thread: Operation not permitted (1)
Retrying messagebuffer thread without RT scheduling
Messagebuffer not realtime; consider enabling RT scheduling for user
no message buffer overruns
Cannot create RT messagebuffer thread: Operation not permitted (1)
Retrying messagebuffer thread without RT scheduling
Messagebuffer not realtime; consider enabling RT scheduling for user
no message buffer overruns
Cannot create RT messagebuffer thread: Operation not permitted (1)
Retrying messagebuffer thread without RT scheduling
Messagebuffer not realtime; consider enabling RT scheduling for user
no message buffer overruns
JACK server starting in realtime mode with priority 10
self-connect-mode is "Don't restrict self connect requests"
Cannot use real-time scheduling (RR/10)(1: Operation not permitted)
AcquireSelfRealTime error

I'm guessing that it's not jack itself (package ver. seems to be the same as bionic, without new feats), smth is missing in the kernel config. I would try RT kernel, but it usually does not boot at all thanks to Nvidia blob on that system.

[Sebastien Bacher (seb128)]

Thank you for your bug report, bug #1875665 has similar warnings

[Sebastien Bacher (seb128)]

Could you add a 'journalctl -b 0' log from a session having the issue?

[Igor Sakulin (moroznah)]

Please see attached systemd log