[Lxc-users] systemd inside LXC

[Serge Hallyn]

Quoting Michael H. Warfield (mhw at wittsend.com):
> Serge,
> 
> On Mon, 2012-10-22 at 09:12 -0500, Serge Hallyn wrote:
> > Quoting Serge Hallyn (serge.hallyn at canonical.com):
> > > Quoting Michael H. Warfield (mhw at WittsEnd.com):
> > > > On Sun, 2012-10-21 at 14:49 -0500, Serge Hallyn wrote:
> > > > > Quoting Michael H. Warfield (mhw at WittsEnd.com):
> > > > > > Serge,
> > > > > > 
> > > > 
> > > > ...
> > > > 
> > > > > > Short of building a custom systemd, I don't know how to fix that problem
> > > > > > and I suspect this OP is going to run into this same thing (container
> > > > > > taking over host's console) and might explain some of what he's seeing.
> > > > > > Several of these look like they could cause problems (like /dev/pts in
> > > > > > there).  I've really reached an impasse at getting systemd (at least
> > > > > > Fedora 16 and 17) to work in a container without screwing up the host.
> > > > > > Prohibiting mounts entirely in the container might work but I suspect
> > > > > > (having read some systemd error messages) systemd is going to have some
> > > > > > serious heartburn there.
> > > > > > 
> > > > > > Thoughts?
> > > > > 
> > > > > IIRC, simply having apparmor(/selinux) refuse the mount of /dev by the
> > > > > container should work, i.e. systemd was not going to fail as a result.
> > > > 
> > > > Hopefully, you've seen the message from Kay Sievers cc'ed to this list
> > > > from my post to the systemd-devel list.  Looks like they have a
> > > > mechanism in place to do this...
> > > > 
> > > > http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
> > > 
> > > Saw the email, haven't yet read the page, thanks.
> 
> > So based on that page, what we do (set 'container=lxc') should already be
> > sufficient.
> 
> Thanks to the dude asking a libvirt-lxc question on the list, I was let
> to a page that let to a page that led to some discussion you were having
> back in March with Ramez Hanna on this very subject, "Re: [Lxc-users]
> f16 update"...
> 
> http://www.mail-archive.com/lxc-users@lists.sourceforge.net/msg03263.html

thanks, I knew we'd been over some of this, but couldn't find my logs of
it.

> This would look to be the kludge to make a workaround for this problem,
> I'm just not sure how to make it happen.  Given you already found the
> answer that the device for /dev has to be different than the device for
> the parent, what should we do.
> 
> I tried this in the config...
> 
> lxc.mount.entry=tmpfs /var/lib/lxc/private/Alcove/dev tmpfs defaults 0 0

How about just a devtmpfs?  We actually now do this by default (as of very
recently) in ubuntu by adding

devtmpfs        dev          devtmpfs defaults 0 0

to /var/lib/lxc/$container/fstab

Or, are you on an older kernel which doesn't have devtmpfs?

> Maybe I got that entry wrong but it didn't do anything (and would have
> resulted in other failures later as I found out).  A similar mount entry
> for a shared filesystem worked just fine.
> 
> Trying an empty /dev fails because it's missing EVERYTHING so starting
> out with a tmpfs without populating it is not the answer either.
> 
> The correct answer would be to mount a tmpfs file system and then
> populate it before firing up systemd in the container.  I don't see how
> to do that.  A bind mount isn't going to work either, for the reasons
> you stated in that thread, it ends up on the same device.  Having
> another mount on another real device would be a workaround but a really
> bad kludge that would complicate things immensely.
> 
> > -serge
> 
> 
> -- 
> 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!