[arch-general] systemd sessions, su -l, and access to /dev/

[Fons Adriaensen]

On Fri, Nov 23, 2012 at 01:15:29AM +0300, MSal wrote:
> Hello.
> 
> I asked about this in the forum. But it looks like this is a better
> place to discuss systemd-related issues.
> 
> If I login to user1 or user2 then try to play audio which requires
> access to /dev/snd/* , proper access to the logged in user is set by
> the session and everything works correctly.
> 
> But, if I login to user1 then su to user2, audio wouldn't work because
> access permissions are assigned to the session user only (user1).
> 
> Any idea how to fix this issue?

This is not really systemd but logind meddling with device permissions
to enforce its 'seat' and 'session' security scheme.

Quoting Tom G.:

  A brute-force way to avoid all of that is to "mask" it. I.e., symlink
  /etc/udev/rules.d/70-uaccess.rules to /dev/null.

Then use udev to assign group rights on audio devices to the 'audio'
group, make sure that users who need audio are members of that group,
and things will work as you want.

Ciao,

-- 
FA

A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)