[systemd-devel] Unable to run systemd in an LXC / cgroup container.

[Michael H. Warfield]

On Mon, 2012-10-22 at 02:53 +0200, Kay Sievers wrote:
> On Sun, Oct 21, 2012 at 11:25 PM, Michael H. Warfield <mhw at wittsend.com> wrote:
> > This is being directed to the systemd-devel community but I'm cc'ing the
> > lxc-users community and the Fedora community on this for their input as
> > well.  I know it's not always good to cross post between multiple lists
> > but this is of interest to all three communities who may have valuable
> > input.
> >
> > I'm new to this particular list, just having joined after tracking a
> > problem down to some systemd internals...
> >
> > Several people over the last year or two on the lxc-users list have been
> > discussions trying to run certain distros (notably Fedora 16 and above,
> > recent Arch Linux and possibly others) in LXC containers, virualizing
> > entire servers this way.  This is very similar to Virtuoso / OpenVZ only
> > it's using the native Linux cgroups for the containers (primary reason I
> > dumped OpenVZ was to avoid their custom patched kernels).  These recent
> > distros have switched to systemd for the main init process and this has
> > proven to be disastrous for those of us using LXC and trying to install
> > or update our containers.
> >
> > To put it bluntly, it doesn't work and causes all sorts of problems on
> > the host.
> >
> > To summarize the problem...  The LXC startup binary sets up various
> > things for /dev and /dev/pts for the container to run properly and this
> > works perfectly fine for SystemV start-up scripts and/or Upstart.
> > Unfortunately, systemd has mounts of devtmpfs on /dev and devpts
> > on /dev/pts which then break things horribly.  This is because the
> > kernel currently lacks namespaces for devices and won't for some time to
> > come (in design).  When devtmpfs gets mounted over top of /dev in the
> > container, it then hijacks the hosts console tty and several other
> > devices which had been set up through bind mounts by LXC and should have
> > been LEFT ALONE.
> >
> > Yes!  I recognize that this problem with devtmpfs and lack of namespaces
> > is a potential security problem anyways that could (and does) cause
> > serious container-to-host problems.  We're just not going to get that
> > fixed right away in the linux cgroups and namespaces.
> >
> > How do we work around this problem in systemd where it has hard coded
> > mounts in the binary that we can't override or configure?  Or is it
> > there and I'm just missing it trying to examine the sources?  That's how
> > I found where the problem lay.

> As a first step, this probably explains most of it:
>   http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface

A very long ways, yeah.  That looks like it could be just what we've
been looking for.  Just gotta figure out how to set that environment
variable but that's up to a couple of others to comment on in the
lxc-users list.  Then we'll see where we go from there.

Many thanks!

> Kay

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
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