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Realtime (rt) kernel: How to use with Jack?

I fail to start jackd with real time permissions. I am in group audio, my kernel is custom 2.6.29.5-rt21

Slackbuils.org writes about:

1. /dev/shm -> done
2. setcap cap_sys_nice=ep /usr/bin/jackd (does not help)
3. I have also tried set_rlimits (does not help)

/etc/set_rlimits.conf

Code:

@audio /usr/bin/jackd nice=-1 rtprio=80

start command and result..

Code:

set_rlimits jackd -R -dalsa -dhw:1,0 -r44100 -p1024 -n2 -S -i2 -o2 -Xseq

jackd 0.116.1

[..bla-bla-bla]

creating alsa driver ... hw:1,0|hw:1,0|1024|2|44100|2|2|nomon|swmeter|-|16bit

[..bla-bla-bla]

JACK: unable to mlock() port buffers: Cannot allocate memory

JACK: unable to mlock() port buffers: Cannot allocate memory

When running as root, it starts ok but
1. I don't want to start as root (psychological problems :) )
2. fst-git-feb2009 wants to start jackd, but if jackd is already started as root, it fails (stupidly? ) to start.

I believe I have "permissions" problem, but I don't know which "permissions" to tweak.

Have you enabled Realtime Group Scheduling?
(zgrep CONFIG_RT_GROUP_SCHED /proc/config.gz)

Thank you, that was slap in my face. Recompiled my kernel.

zgrep _RT_ /proc/config.gz

CONFIG_RT_GROUP_SCHED=y
CONFIG_RT_MUTEXES=y
# CONFIG_DEBUG_RT_MUTEXES is not set
# CONFIG_RT_MUTEX_TESTER is not set

Code:

set_rlimits jackd -R -dalsa -dhw:1,0 -r44100 -p1024 -n2 -S -i2 -o2 -Xseq

jackd 0.116.1

(bla-bla)

cannot use real-time scheduling (FIFO at priority 10) [for thread -1212617888, from thread -1212617888] (1: Operation not permitted)

cannot create engine

Same message with setcap thingie.

Also I forgot to mention

Code:

ls -l /dev | grep shm

drwxrwxrwt 2 myuser  audio      40 2009-06-27 00:05 shm

Actually, I would have advised not to use realtime group scheduling, as it makes things quite more complicated (it's only user-friendly if you use PAM) :P
A few other things:
- you do not need set_rlimits if you want to use posix capabilities. If you want to use those, you will also want to set cap_ipc_lock additionally to cap_sys_nice (but there might be still one missing I haven't found yet, and it will not work on reiserfs)
- you do not need to set any posix capabilities if you want to use set_rlimits

After looking closer at your first post it's probably cap_ipc_lock, which is missing, but jackd worked fine even without it set on my machine.

I tried both methods since I don't understand the problem. You believe it's a kernel issue?