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Why would I want to do that? because pulseaudio isn't needed (presumably) and pulseaudio does not want to run as root. In theory I should be able to run pulseaudio --system to fix the problem, but I can't get that to work.

The issue:

root@mc: arecord -l
XDG_RUNTIME_DIR (/run/user/1000) is not owned by us (uid 0), but uid 1000! (This could e.g. happen if you try to connect to a non-root pulseAudio as a root user, over the native protocol. Don't do that.)

Well Okay but how? And why? The listed reasons are not applicable to a single user machine. Surely sox runs on alsa (AUDIODRIVER=alsa) and does not need PulseAudio. How can I tell sox to do that?

1 Answer 1

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Okay so I had no success setting up a pi to run pulseaudio in system wide mode. As the aim is to use sox from within a c program that is portable, modifying the environment in complex ways is self defeating anyway.

On a pi there is a good chance it will be run single user and so malicious other users are simply a case of edge case poisoning.

Instead I have wrapped the use of the sox command in some code that checks who the user is using getuid, read who owns the directory specified by XDG_RUNTIME_DIR using stat and, if necessary, using chown to make root the owner of /run/usr/xxx directory while the program is running and then chowns the original user back at the end. Oh and used

sudo visudo /etc/sudoers

to put a '!' before the 'env_reset' so that environment variables get carried over when using sudo (thinking about it, that is not necessary but I do it for other reasons).

This is not the most cludgy thing I've ever done but...

I'd argue that irrespective of what pulseaudio people say, pis should run pulseaudio in system-wide mode by default.

The code (snippet) called before calling snprintf with the sox command and again at termination:

 void
ch_XDG_RUNTIME_DIR() {
        char * xrd = getenv("XDG_RUNTIME_DIR");
        //printf(">%s\n",xrd);
        if(saved_uid != 0) { // put it back
                int i = chown(xrd,saved_uid,saved_uid);
                if(i !=0 ) { perror("chown"); return; }
                saved_uid = 0;
        } else {
                uid_t p_uid = getuid(); // who is running the process
                struct stat sb;
                int n = stat(xrd,&sb);
                if( n == -1) {perror("stat"); return; }
                if( p_uid == 0 && sb.st_uid != 0 ) {
                        saved_uid = sb.st_uid;
                        int i = chown(xrd,0,0);
                        if(i !=0 ) { perror("chown"); return; }
                }
        }
}

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