[LAU] How to recover from a JACK freeze?

[James Harkins]

Hi, been inactive for a while.

I just up/cross-graded to Ubuntu Studio 16.04 -- very much enjoying it so far! I'm getting better USB audio performance than I could ever manage under plain Ubuntu (provided WiFi is off, but I can live with that for shows).

One problem that the upgrade didn't solve is that sometimes jackd gets stuck and it can't be killed.

Initial symptom: No audio, in or out.

Secondary symptom: In qjackctl, the CPU usage number is frozen -- never changes.

At that point:

$ ps x | grep jackd
 3140 ?        SLsl   0:16 /usr/bin/jackd -dalsa -r44100 -p1024 -n2 -D -Chw:Set,0 -Phw:Set
 4458 pts/1    S+     0:00 grep --color=auto jackd
$ kill -9 3140
$ ps x | grep jackd
 3140 ?        SLsl   0:16 /usr/bin/jackd -dalsa -r44100 -p1024 -n2 -D -Chw:Set,0 -Phw:Set
 4460 pts/1    S+     0:00 grep --color=auto jackd

"kill -9" has no effect.

"sudo kill -9" has no effect.

If I reboot, it takes several minutes for the system to shut down -- i.e., jackd is even preventing a clean shutdown.

So, the question: How do I regain control when this happens? (Ideally, without having to close everything.)

Thanks,
hjh