[libvirt-users] [libvirt] LXC, user namespaces and systemd

[Daniel P. Berrange]

On Tue, Mar 04, 2014 at 05:16:42PM +0100, Dariusz Michaluk wrote:
> On 03.03.2014 16:26, Daniel P. Berrange wrote:
> 
> >That looks really bizarre. The same two directory names nested over
> >and over again. I can't reproduce this kind of thing on my own host.
> >Libvirt only ever creates the first two levels as expected
> >
> >/sys/fs/cgroup/systemd/machine.slice
> >/sys/fs/cgroup/systemd/machine.slice/machine-lxc\x2dmycontainer.scope
> >
> >The fact that the libvirt_lxc process itself ends up in the right
> >place suggest that this isn't libvirt, but rather something else
> >is creating these extra levels and moving systemd into them.
> 
> On arch linux mailing lists I found similar things:
> https://mailman.archlinux.org/pipermail/arch-general/2014-February/035077.html
> Behavior can be reproduced. After re-taking a look at the topic, it
> seems to me that the cause of the problem is the behavior of
> systemd.
> Systemd create first level
> (machine.slice/machine-lxc\x2dmycontainer.scope) during
> /usr/lib/systemd/systemd execution, and the second level during
> /usr/lib/systemd/systemd --user execution.
> 
> #cat /proc/1/cgroup
> 2:name=systemd:/machine.slice/machine-lxc\x2dmycontainer.scope/machine.slice/machine-lxc\x2dmycontainer.scope
> 
> #cat /proc/28/cgroup
> 2:name=systemd:/machine.slice/machine-lxc\x2dmycontainer.scope/machine.slice/machine-lxc\x2dmycontainer.scope/machine.slice/machine-lxc\x2dmycontainer.scope/user.slice/user-0.slice/user at 0.service
> 
> Maybe the problem is that the libvirt itself creates machine.slice /
> machine-lxc \ x2dmycontainer.scope
> According to:
> http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface/
> "Container managers should stay away from the "name=systemd" cgroup
> hierarchy. That's private property of systemd, and no other code
> should interfere with it. "

Libvirt honours that actually. When starting a guest it invokes a
DBus API call to systemd-machined, which talks to systemd to create
the cgroups. Libvirt isn't actually creating these in the filesystem
itself.

Regards,
Daniel
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