[LAU] systemd woes with jackd and its permissions (raspbian)

Marc Joliet marcec at gmx.de
Tue Jan 21 18:18:02 CET 2020

(For some reason I never sent this, and while it's almost a year later, I
think it might be useful just to have it on record in the ML, to make things
easier for people reading this thread in the archives.)

Am Montag, 28. Januar 2019, 12:26:54 CET schrieb David Runge:
> On 2019-01-28 01:12:52 (+0100), Peter P. wrote:
> > Now this took me four hours so far without success and I wonder what
> > is a functional way to use jackd via systemd on a headless computer in
> > 2019. All comments are very welcome!
> I recommend going the systemd user service way. I have a templated
> unit [1], that I use with specific preset device configurations [2].
> If this should start automatically on boot, you need to enable linger
> for your user (using loginctl)!

The other thing that I don't think was mentioned in this thread is that you
will need to add your user to the audio group (if that's not already the case)
because systemd-logind normally gives your user access to certain devices
(including audio devices) by setting ACLs on the device node in /dev/ *when
you login*, e.g.:

  % getfacl /dev/snd/seq
  getfacl: Removing leading '/' from absolute path names
  # file: dev/snd/seq
  # owner: root
  # group: audio

Since you're not logging in, that won't get triggered, so even with lingering
enabled, anything requiring access to these devices won't work.

The device access concepts are documented in [0] and also in sd-login(3), from
which one could deduce the above, but it's not explicitly pointed out anywhere
AFAICT (I think I had it pointed out to me on a Gentoo ML).

[0] https://www.freedesktop.org/wiki/Software/systemd/multiseat/

Marc Joliet
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup
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