[Jackit-devel] [linux-audio-user] pam modules / non root users can't get realtime privileges.

Ken Restivo ken at restivo.org
Sun Feb 4 23:35:02 EST 2007


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On Sun, Feb 04, 2007 at 09:40:11PM -0600, Jack O'Quin wrote:
> On 2/4/07, Ken Restivo <ken at restivo.org> wrote:
> >On Sun, Feb 04, 2007 at 04:54:01PM -0800, Fernando Lopez-Lezcano wrote:
> 
> >> It looks like the package was built to use capabilities. I don't know
> >> what jackd does when it does not find the proper capabilities (which
> >> will not be found if you are using pam), whether it still tries to get
> >> SCHED_FIFO or if it just gives up, it looks like the later.
> 
> I think we handle that correctly, i.e. go ahead and try to set SCHED_FIFO
> anyway and use it if available.
> 
> The current JACK engine implementation fails if -R is selected and
> realtime scheduling is not available.  That changed fairly recently,
> IIRC, so an older version might continue running in that case.
> 
> >What the....  I certainly hope not.
> >
> >I thought that was a spurious error message to be disregarded, since jackd 
> >definitely *is* running with RT priorities, at least on my machine, it 
> >reports:
> >
> >FreeBoB MSG: Streaming thread running with Realtime scheduling, priority 74
> >FreeBoB MSG: Registering capture port dev1c_MicIn1 left
> >
> >And ps says...
> >  PID CLS RTPRIO  NI PRI %CPU STAT COMMAND
> > 3423 TS       -   0  20  0.0 SLl  jackd
> > 3423 TS       -   0  24  0.0 SLl  jackd
> > 3423 TS       -   0  24  0.0 SLl  jackd
> > 3423 TS       -   0  19  0.0 SLl  jackd
> > 3423 FF      80   - 120  0.0 SLl  jackd
> > 3423 FF      70   - 110  1.5 SLl  jackd
> > 3423 FF      73   - 113  5.6 SLl  jackd
> > 3423 FF      73   - 113  5.0 SLl  jackd
> > 3423 FF      84   - 124  0.0 SLl  jackd
> > 3423 FF      74   - 114  5.4 SLl  jackd
> >
> >Although, I just noticed now that some of those jackd threads aren't 
> >running with any RT prio at all. And, I also noticed that the little 
> >yellow "RT" in qjackctl isn't lit up either... Is that OK? Or is this a 
> >problem?
> 
> Several JACK threads are not supposed to run RT.
> 
> >I'm standing by and waiting to hear from the jackd developers before 
> >filing this with the Debian bug tracking system...
> >
> >And also waiting to hear back before I go out and blow $400 on a 2.4Ghz 
> >CPU....
> 
> I can't say what you should do.  Looks like it ought to work to me.

I just rebuilt the package from the Debian package source, but edited it to take out the --enable-capabilities. Seems to work just fine as it did before.

So, at least on my system, --enable-capabilities looks like a red herring. I have PAM 0.79-4 which is the standard in Debian Etch (which I'm running right now), which means I don't need the "capabilities" module. jackd 0.101.1-2  seems to be fine without it, regardless of whether it's compiled with or without --enable-capabilities.

- -ken
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