On saturday I made some tests and found the root CAUSE of the issue, and
the SOLUTION.
The reason "aplay" is called, is because it is used to enumerate sound cards,
(with the -l argument as in "aplay -l"), by ubuntu-drivers, to find ye-old
software modems.
The "ubuntu-drivers-common" package scripts are called by the
"kubuntu-driver-manager"
package scripts on login to KDE's desktop. Aplay is also called when going to
AdditionalDrivers
or running "ubuntu-drivers list".
The reason why the "pulseaudio" process created by 'aplay' remains running, is
because "aplay" and thus
"pulseaudio" receive an empty environment (no environment variables).
Since "pulseaudio" receives an empty environment, it cannot know from which
session or
DISPLAY it was called, and whether another pulseaudio is already running for
that session.
Because of that, we end up with two different pulseaudio processes, and thus
one interferes with the
other, producing "device busy" errors while plugging our USB
headsets/mics/webcams,
resulting in them not getting fully recognized.
The solution is as follows: Edit this file:
/usr/share/ubuntu-drivers-common/detect/sl-modem.py
and replace this line:
aplay = subprocess.Popen(['aplay', '-l'], env={},
with this line:
aplay = subprocess.Popen(['aplay', '-l'],
By removing the named 'env={}' argument, the "aplay -l" receives the environment
and can distinguish the correct pulseaudio process.
Another way to workaround this, but quick and dirty, is to simply add a line:
return None
right above the aplay line, with the same spacing (indentation level),
to disable looking for software modems at login if you don't plan on
using dial-up modems :-)
Details:
--------
I obtained the process list by adding redirecting 'aplay' temporarily to a
script, which had a "sleep 30" delay, so
that I could get it in "ps axf".
The process list at the time of calling aplay is:
\_ init --user
[...]
\_ dbus-daemon --fork --session
--address=unix:abstract=/tmp/dbus-l0CdfJrRGy
| \_ [dbus-daemon] <defunct>
[...]
\_ python3 /usr/lib/kde4/libexec/DriverManager_DBus
\_ /usr/bin/aplay -l
\_ /usr/bin/pulseaudio --start --log-target=syslog
Looking by the process number, for the second pulseaudio instance,
cat /proc/NNNN/environ
is empty.
I found by tracing the python calls that the file which runs aplay is:
/usr/share/ubuntu-drivers-common/detect/sl-modem.py
(if I skip/comment the call to aplay on that file, the issue dissapears).
The file "sl-modem.py" belongs to the package:
ubuntu-drivers-common
and the DriverManager_DBus script which runs at logon belongs to the
package:
kubuntu-driver-manager
which explains why this issue only affects us Kubuntu users, but in reality,
it also affects all Ubuntu users, because any time they enter the
driver manager (either by softwarke-properties-gtk or "Additional Drivers", or
by running "ubuntu-drivers list" in the console) they are going to get a
duplicate process for "pulseaudio" until they restart.
Many Thanks to all the guys in this thread: you pointed me in the right
direction.
My Zoom H2n is now correctly recognized with the solution I explained at the
top of this post.
Maintainers:
Please evaluate if removing 'env={}' from the aplay line at the "sl-modem.py"
file
of the ubuntu-drivers-common package is a worthy and safe patch so that
everyone benefits.
Cheers,
Juan Manuel Cabo
** Also affects: ubuntu-drivers-common (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1296425
Title:
pulseaudio is started twice - effectively making device management
impossible.
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https://bugs.launchpad.net/ubuntu/+source/alsa-plugins/+bug/1296425/+subscriptions
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