On my computer audio works sometimes and sometimes not. I want to troubleshoot this. First I verified I am using pulseaudio. I did this by strace'ing the pulseaudio process:
[pid 2289] send(28, "\0\0\0\24\377\377\377\377\0\0\0\0\0\0\0\0\0\0\0\0L\0\0\0=L\377\377\377\377L\0"..., 40, MSG_NOSIGNAL) = 40
At the same time the application speaker-test receives data from process 2289, pulseaudio. Many lines like this:
[pid 29146] recvmsg(7, {msg_name(0)=NULL, msg_iov(1)=[{"\0\0\0\0\377\377\377\377\0\0\0\20\0\0\0\0@\0\0\0", 20}], msg_controllen=24, {cmsg_len=24, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS{pid=2289, uid=0, gid=0}}, msg_flags=0}, 0) = 20
Now I can see the sockets are neighbors:
# ll /proc/29146/fd/7
lrwx------ 1 root root 64 Apr 4 16:46 /proc/29146/fd/7 -> socket:[114414]
# ll /proc/2289/fd/28
lrwx------ 1 root root 64 Apr 4 15:13 /proc/2289/fd/28 -> socket:[114415]
Which leads me to two questions:
- why is pulseaudio sending data and speaker-test is receiving data? I would expect it to be the other way round.
- where can I find that socket 114414 and 114415 are connected? Can I sniff their traffic?
BTW I am blogging this adventure on http://www.linuxintro.org/wiki/Sound_troubleshooting#strace.27ing_sound_II
