Archive for May, 2008

ubuntu 8.04, real-time kernel, jack is working

Ubuntu 8.04 is out, and it’s out about a while ago. What I have working stable up till now is worth starting this blog. The programs I will talk about, I’ve been using with success on older versions of linux, but this time is different, because I made notes. So here we go:

After I installed the new version in its standard way, my internal sound card was working fine, I wouldn’t have liked to see (hear) anything else. One needs to be aware of a few things to get the jack audio connection kit (jack) to work properly. Live performance only works, if the audio demon has higher priorities than the usual programs. Running jack as root would work but it is an ugly solution. Apart from being a security problem by itself it requires all programs using jack to run as root as well.

Gathering information from the internet I ended up with the following: First, I installed the real-time kernel which comes with the standard packages. No compiling is needed, everything easy to do. Second, I added a user group with the name audio and added myself to that group. Then one has to allow that group certain limits. Add to /etc/security/limits.conf the lines

@audio - rtprio 99
@audio - memlock 250000
@audio - nice -10

which will do the job. The last bit, which I still do not understand completely, is a change in /etc/fstab. I added

shmfs /dev/shm tmpfs defaults 0 0

(When I know what this is about, I’ll tell you.) Now, whenever I boot the computer, I have to chose the real-time kernel. Than I start qjackctl and run the jack demon!

To be continued…

PS: There seems to be a problem related with the real-time kernel. Sometimes the login doesn’t work, the window manager (xfce) does not get started. Restarting the x-server (CTRL-ALT-BACKSPACE) the next login (most of the time) works. Running the normal kernel this problem doesn’t occur and I’m not yet sure, what does it cause.

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