How to use the pulseaudio API as root? - c

Question

I am currently trying to use the pulseaudio simple API to record microphone data from my USB sound card with my raspberry pi 3. I used the example program parec-simple from pulseaudio in my own program and it works quite nice.
The program i used this code for is accessing gpio's so i need to run this as root. However, when i try to execute the program as root, i get the following errors:
Home directory not accessible: Permission denied
W: [pulseaudio] core-util.c: Failed to open configuration file '/root/.config/pulse//daemon.conf': Permission denied
W: [pulseaudio] daemon-conf.c: Failed to open configuration file: Permission denied
pa_simple_new() failed: Connection refused
the code is used is the following:
static const pa_sample_spec ss = {
.format = PA_SAMPLE_S16LE,
.rate = 44100,
.channels = 1
};
pa_simple *s = NULL;
int ret = 1;
int error;
/* Create the recording stream */
if (!(s = pa_simple_new(NULL, argv[0], PA_STREAM_RECORD, NULL, "record", &ss, NULL, NULL, &error))) {
fprintf(stderr, "pa_simple_new() failed: %s\n", pa_strerror(error));
goto finish;
}
while(1)
{
uint8_t buf[BUFSIZE];
/* Record some data ... */
if (pa_simple_read(s, buf, sizeof(buf), &error) < 0) {
fprintf(stderr, __FILE__": pa_simple_read() failed: %s\n", pa_strerror(error));
goto finish;
}
/* And write it to STDOUT */
if (loop_write(STDOUT_FILENO, buf, sizeof(buf)) != sizeof(buf)) {
fprintf(stderr, __FILE__": write() failed: %s\n", strerror(errno));
goto finish;
}
}
ret = 0;
finish:
if (s)
pa_simple_free(s);
return ret;
I already tried chown pi:pi /home/pi as suggested here to try to fix it but it doesn't work. changing the owner of /home/pi from pi to root didn't work for me either.
I also tried a clean reinstall of pulseaudio but unfortunately it didn't fix it.
So what can i do to fix these errors?

Answer 1

If you need to run your program as user root, then you must impersonate root. I don't know if pulseaudio looks at the username in order to find configuration files, or it looks at the $HOME variable. In the second case, maybe that by setting HOME to the home of a "working" user helps.
Anyway what you told about the situation is clear: pulseaudio does not find a file:
'/root/.config/pulse//daemon.conf'
Place a correct "daemon.conf" in that directory - probably you can copy it from somewhere (like /home/auser/.config/pulse/daemon.conf).
Consider that directories with name starting with a dot are normally hidden; if using a file manager you must enable "show hidden files", if you use the shell, ls -a can help.
Your first target is to confirm that the file is there, and your program should not complain about a missing/unreadable config file. Then, maybe other errors will show up but, one after another, you can eliminate them.

Answer 2

When you run process with sudo it does not change Home directory to /root - sudo echo $HOME # /home/username. You need to specify HOME directory with by running sudo HOME=/root executable.
When you want to access pulseaudio from root you need to run it system wide with command - sudo pulseaudio --system=true.
Then you will receive an error from pulseaudio:
W: [pulseaudio] protocol-native.c: Denied access to client with invalid authentication data.
Which can be solved by adding root user to audio-pulse group - sudo adduser root pulse-access.