how to start jackd with -R (realtime) as a regular user (non root)

[marcelbonnet]

Hi, folks.

The jackd man page affirms that is possible to start jackd with realtime scheduling "in several ways" [1].

So, does anybody knows some way to do it without being root or, at least, to start it as root but in a way a regular user can connect its clients to that instance?

If I start jackd with realtime as root, like above:
[CMD=""]# /usr/local/bin/jackd -R -doss -r44100 -p1024 -n3 -w16 -C/dev/dsp2.1 -P/dev/dsp2.1[/CMD]
then a regular user running a simple app like [CMD=""]$ jack_lsp[/CMD] is noticed that "JACK server not running".

Otherwise, if try to start jackd with the same params above as a regular user, it says I do not have enough privileges:

JACK compiled with System V SHM support.
cannot use real-time scheduling (FIFO at priority 10) [for thread 675300096, from thread 675300096] (1: Operation not permitted)
cannot create engine

I realized a big latency reduction running jackd with realtime scheduling, but when I did it I had to start all clients (like ardour and linuxsampler) as root too, which is no good!

Thanks in advance.

1. From:
[CMD=""]man jackd[/CMD]

-R, --realtime
Use realtime scheduling (default = true). This is needed for
reliable low-latency performance. On many systems, it requires
jackd to run with special scheduler and memory allocation privi-
leges, which may be obtained in several ways.

 

[marcelbonnet]

doing some testing

Hello.

I don't know if I'm on the right direction, but here is my thought:

After [CMD=""]$ man 2 mkfifo[/CMD], I was wondering if the problem was only permissions relative to the FIFO.

[CMD=""]# fstat | grep jackd [/CMD]

USER CMD PID FD MOUNT INUM MODE SZ|DV R/W
root jackd 4256 text /usr 782 -r-xr-xr-x 19188 r
root jackd 4256 ctty /dev 172 crw--w---- pts/2 rw
root jackd 4256 wd / 23562 drwxr-xr-x 2048 r
root jackd 4256 root / 2 drwxr-xr-x 512 r
root jackd 4256 0 /dev 172 crw--w---- pts/2 rw
root jackd 4256 1 /dev 172 crw--w---- pts/2 rw
root jackd 4256 2 /dev 172 crw--w---- pts/2 rw
root jackd 4256 3* pipe c5610af0 <-> c5610bac 0 rw
root jackd 4256 4* pipe c5610bac <-> c5610af0 0 rw
root jackd 4256 5* local stream c5817a14
root jackd 4256 6* local stream c5fd3560
root jackd 4256 7 /tmp 17798 prw-r--r-- 0 rw
root jackd 4256 8 /tmp 17799 prw-r--r-- 0 rw
root jackd 4256 9 /dev 176 crw-rw-rw- dsp2.1 rw


[CMD=""]# sockstat | grep jackd [/CMD]

USER COMMAND PID FD PROTO LOCAL ADDRESS FOREIGN ADDRESS
root jackd 4256 5 stream /tmp/jack-0/default/jack_0
root jackd 4256 6 stream /tmp/jack-0/default/jack_ack_0


So, I tried to change the permissions to that files, expecting that maybe a regular user could connect to that jack server instance:

[CMD=""]# cd /tmp/jack-0/default[/CMD]
[CMD=""]# chmod a+wrx *[/CMD]

As root, it still working:
[CMD=""]# jack_lsp [/CMD]
system:capture_1
system:capture_2
systemlayback_1
systemlayback_2

But as regular user, nothing changed:
[CMD=""]$ jack_lsp[/CMD]
JACK server not running

Any suggestion, please?