[pulseaudio-discuss] Strange "Root privileges required" error

[Lennart Poettering]

On Thu, 21.05.09 14:29, interim_descriptor (interim.descriptor at gmail.com) wrote:

> Hi.
> 
> I'm trying to configure pulseaudio in Ubuntu 9.10, such that it runs as a
> system instance with realtime priority, upon boot.
> 
> I've encountered something strange.
> 
> After running...
> 
> chmod a+s /usr/bin/pulseaudio
> 
> ...I would expect invoking pulseaudio would do so with root-level
> permissions. And yet, here's what I get when I try that:
> 
> id at kos-mos:~ $ pulseaudio -v
> (   0.000|   0.000) I: main.c: We're in the group 'pulse-rt', allowing
> high-priority scheduling.
> (   0.000|   0.000) I: main.c: We're in the group 'pulse-rt', allowing
> real-time scheduling.
> (   0.000|   0.000) I: main.c: RLIMIT_RTPRIO is set to 99, allowing
> real-time scheduling.
> (   0.000|   0.000) I: main.c: RLIMIT_NICE is set to 40, allowing
> high-priority scheduling.
> (   0.000|   0.000) I: core-util.c: Successfully gained nice level -11.
> (   0.000|   0.000) I: main.c: Giving up CAP_NICE
> (   0.000|   0.000) E: main.c: Root privileges required.
> 
> 
> ...Am I misunderstanding what the SUID bit does, or is pulseaudio
> incorrectly reporting that it doesn't have root privleges?

After starting up PA will quickly drop all priviliges it gained from
being SUID and become a normal user process, with the exception for
scheduling related priviliges which it will keep.

Please read up about difference between the UID and the EUID of a
process on Unix systems. suid only changes the latter, sudo changes
both.

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4