Starting an LXC changes the volume (sound!) of the host

[Martin Albisetti]

This has been happening at least since 11.10 on several different computers.
Whenever I start an LXC, it changes the volume of the host computer. Sometimes it turns it up, sometimes down.
It's quite puzzling :)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: lxc 0.7.5-3ubuntu33
ProcVersionSignature: Ubuntu 3.2.0-18.28-generic 3.2.9
Uname: Linux 3.2.0-18-generic x86_64
ApportVersion: 1.94-0ubuntu2
Architecture: amd64
Date: Tue Mar 6 18:16:57 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120215.1)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: lxc
UpgradeStatus: No upgrade log present (probably fresh install)

[Serge Hallyn (serge-hallyn)]

This is due to the container running udevadm trigger --action=add. Those events also get sent to the host, causing some hardware to be reset. For me, in addition to sound levels being reset, my keyboard bindings are also reset.

This won't happen with a Precise guest as it won't run udev. At the next UDS we intend to discuss a design for a devices namespace to avoid this.

[Serge Hallyn (serge-hallyn)]

Actually, I believe this is fixed as of precise, as the apparmor policy refuses writes from the container into the /sys/devices/*/uevent files. (udevadm trigger --add writes 'add' into those files).