[arch-general] lxc: systemd-udev-trigger resets host kbd & mouse settings

[Carl Schaefer]

On Fri, 2014-04-18 at 17:45 -0400, Daniel Micay wrote:
> On 18/04/14 05:40 PM, Carl Schaefer wrote:
> > I've just started playing with lxc, and found that if I create a
> > container with:
> > 
> > # lxc-create -n arch -t archlinux
> > 
> > and then start it:
> > 
> > # lxc-start -n arch
> > 
> > it resets my X keyboard map and mouse acceleration settings (which are
> > set by setxkbmap/xset/xinput), though mouse button remapping done by
> > xmodmap is not affected.
> > 
> > I tracked it as far as the execution of:
> > 
> >   /usr/bin/udevadm trigger --type=devices --action=add
> > 
> > in /usr/lib/systemd/system/systemd-udev-trigger.service, which seems to
> > write "add" to most of the "uevent" files under /sys/devices.  I don't
> > know the reason for this, especially in a container, but disabling the
> > whole udev trigger service in the container keeps the host X input
> > settings intact without breaking anything obvious in the container (and
> > the container boots a lot faster now, too).
> > 
> > I'd appreciate any thoughts on what systemd-udev-trigger is doing,
> > whether it's appropriate in a container, and if there's a better way to
> > keep a container from changing X input settings on the host.
> > Carl
> 
> Do you have these issues with systemd-nspawn?

no, systemd-nspawn does not reset host X input settings; the nspawn
container makes /sys read-only, so "udevadm trigger" in the container
can't succeed, and in fact the unit file's condition keeps it from even
trying: 

nspawn# systemctl status systemd-udev-trigger
* systemd-udev-trigger.service - udev Coldplug all Devices
   Loaded: loaded (/usr/lib/systemd/system/systemd-udev-trigger.service; static)
   Active: inactive (dead)
           start condition failed at Fri 2014-04-18 20:21:24 EDT; 28s ago
           ConditionPathIsReadWrite=/sys was not met

> Containers are not yet completely solid. One of the most notable flaws
> is the complete lack of namespacing for the cgroup filesystem. These
> kind of things are worked around by systemd via various hacks, so
> perhaps lxc is missing something.

I agree it seems something is missing, but I'm less clear about what &
from where...  :-)
Carl