[Lxc-users] systemd inside LXC

[Michael H. Warfield]

On Mon, 2012-10-22 at 18:05 -0400, Michael H. Warfield wrote:
> On Mon, 2012-10-22 at 16:21 -0500, Serge Hallyn wrote:
> > Quoting Michael H. Warfield (mhw at WittsEnd.com):
> > > On Mon, 2012-10-22 at 15:14 -0500, Serge Hallyn wrote:
> 
> <Trimming some overhead we've seen enough of...>
> 
> > > > 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
> > > 
> > > NO!  That's the problem!  That leads to the container connecting to the
> > > hosts console and other devices and committing random acts of terrorism.

> > No, it shouldn't, because lxc sets up the console after doing the mounts.

> Damn, dude!  That worked!  That kludge rang da bell.  Of course, I also
> discovered the boneheaded typo I had in attempting the tmpfs mount in
> the process.  :-P  I now have a container running systemd up and running
> with Fedora 17 in it.

> I'm not sure I'm totally happy with it.

> Because of doing the devtmpfs thing, the guest can immediately see
> things like removable drives coming and going and might, presumably, be
> able to mount them.  Not thrilled with that from a security standpoint.
> Would also mean the guests could access things like my permanent
> forensic CDs that are in the CD drives.  I guess that can be restricted
> in the config but still makes me a bit uncomfortable that the guest has
> complete visibility into the hosts dev system.

Another downside.  Container does not shut down cleanly...

init 0 inside the container...

In lxc-start -

Unmounting file systems.
Could not remount as read-only /: Device or resource busy
Not all file systems unmounted, 1 left.
Detaching loop devices.
Could not delete loopback /dev/loop7: Operation not permitted
Could not delete loopback /dev/loop6: Operation not permitted
Could not delete loopback /dev/loop5: Operation not permitted
Could not delete loopback /dev/loop4: Operation not permitted
Could not delete loopback /dev/loop3: Operation not permitted
Could not delete loopback /dev/loop2: Operation not permitted
Could not delete loopback /dev/loop1: Operation not permitted
Could not delete loopback /dev/loop0: Operation not permitted
Not all loop devices detached, 8 left.
Cannot finalize remaining file systems and devices, giving up.
Exiting container.
lxc-start: Device or resource busy - failed to remove cgroup '/sys/fs/cgroup/systemd/Alcove'

Not good.  The tasks file is empty but...  Can't get rid of it.
"Operation not permitted".

Sigh...

Getting closer though.  Much closer.

> Another gotcha, albeit a much more minor one...  When systemd drops into
> this mode, you no longer have vty consoles available so lxc-console
> won't work.  That's actually on their page.

> I remember seeing this:
> 
> -- 
> If systemd detects it is run in a container it will spawn a single shell
> on /dev/console, and not care about VTs or multiple gettys on VTs
> -- 
> 
> Suboptimal but a small price to pay I suppose.
> 
> > -serge
> 
> 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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