Hey John, On Thu, 2013-04-04 at 09:07 +0100, John wrote: > On 03/04/13 23:15, Michael H. Warfield wrote: > > On Wed, 2013-04-03 at 23:03 +0100, John wrote: > >> On 02/04/13 23:59, Michael H. Warfield wrote: > >>> On Tue, 2013-04-02 at 16:02 +0100, John wrote: > >>>> If my understanding is correctl, to stop systemd trying to launch udev > >>>> and generally make a mess of everything inside a container, you need to > >>>> remove the mknod capability from the container. > >>> Ah... That's kind of old information and not really effective. > >>> > >>>> But what if I want > >>>> (need) to be able to use mknod inside a container, how can I do that > >>>> with a systemd container? > >>> 1) Get the latest lxc. lxc 0.8 might suffice for systemd in a container > >>> but not with systemd in the host and I wouldn't recommend it. 0.9.0 is > >>> being pulled and bundled now. It's not up yet but 0.9.0.rc1 is. > >>> > >>> 2) You'll have to add "lxc.autodev = 1" to your configuration file. > >> I already do that. I am running "lxc version: 0.9.0.alpha3" > > That's strange. What stops systemd from mounting devtmpfs and firing up > > udev is having a tmpfs mounted on /dev. That's part of what autodev = 1 > > is doing. > I'm taking my understanding from here: > http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface > where it says "The udev unit files will check for CAP_SYS_MKNOD, and > skip udev if that is not available."
> But it sounds like you're saying that "lxc.autodev = 1" should prevent
> systemd from firing the udev systemd unit anyway.
Well, sort of. I may have been a little off there. I do find that
"systemd-udevd" is running in my systemd containers but that the actual
udevd process itself is not (as opposed to the host systems and other
systems). I can run mknod in those containers. So it is possible to do
this.
But... A hint may be in the lxc-fedora template where there is
specifically a "configure_systemd_fedora" function that does this:
configure_fedora_systemd()
{
unlink ${rootfs_path}/etc/systemd/system/default.target
touch ${rootfs_path}/etc/fstab
chroot ${rootfs_path} ln -s /dev/null //etc/systemd/system/udev.service
chroot ${rootfs_path} ln -s /lib/systemd/system/multi-user.target
/etc/systemd/system/default.target
#dependency on a device unit fails it specially that we disabled udev
sed -i 's/After=dev-%i.device/After=/'
${rootfs_path}/lib/systemd/system/getty\@.service
}
Something similar does exist in the lxc-archlinux template:
# disable services unavailable for container
ln -s /dev/null /etc/systemd/system/systemd-udevd.service
ln -s /dev/null /etc/systemd/system/systemd-udevd-control.socket
ln -s /dev/null /etc/systemd/system/systemd-udevd-kernel.socket
ln -s /dev/null /etc/systemd/system/proc-sys-fs-binfmt_misc.automount
# set default systemd target
ln -s /lib/systemd/system/multi-user.target /etc/systemd/system/default.target
The lxc-archlinux template script seems very badly broken for me,
expecting an fixed bridge name of br0 and not using the defaults
from /etc/lxc/default.conf and looking for things that are not present
on my Fedora host. So I haven't been able to build an archlinux
container on my host systems.
Did you build yours from lxc-create or did you roll your own? Maybe you
might want to check those /dev/null links in that container. Looks like
udevd should not even start if those have been set correctly.
> > What distro is running in the container and what version of systemd?
> > I've seen this with Fedora 16 but the latest systemd and Fedora 17 in
> > the container are fine.
> >
> I am running Arch Linux on both host and container:
> Linux 3.7.10-1-ARCH #1 SMP PREEMPT Thu Feb 28 09:50:17 CET 2013 x86_64
> GNU/Linux
>
> On my host, "systemctl --version" reports:
> systemd 197
> +PAM -LIBWRAP -AUDIT -SELINUX -IMA -SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ
> And on the container, it's systemd 196
Those versions are congruent with what I'm running.
> I've just checked and the latest version in the Arch repo is 198. I
> wonder if I should try and update to that?
Proabably won't make a difference.
This did give me some place to look over my headaches with Fedora 15 and
Fedora 16 upgraded containers though. :-)=)
> >> I found that, without the removal of mknod capability, everything went
> >> crazy. I have working containers with systemd both on host and inside
> >> the container (I even run my full desktop inside a container). To get a
> >> systemd container working I found I needed three things:
> >> lxc.autodev = 1
> >> lxc.cap.drop = mknod
> > I'm not having to do that but I'm avoiding F15 and F16 because they
> > don't seem to play nice and start reliably. F17 is doing well for me.
> >
> >> lxc.pts = 1024
> >>
> >> It's alll working well except for the fact that I might need to allow a
> >> container to have mknod capability. Are you saying that with 0.9.0 there
> >> are changes that negate the requirement for "lxc.cap.drop = mknod"? The
> >> way I understood it was that it was systemd that behaved differently
> >> based on the availability of that capability...
> >>
> >>
> >>> I have found that this works to get recent systemd containers (Fedora
> >>> 17) to work but Fedora 15 and Fedora 16 (neither of which are supported
> >>> any longer) work due to udev / systemd interaction.
> >>>
> >>> I would recommend waiting a couple of days until 0.9.0 is up and then
> >>> pulling it down and building it. That's your best shot with systemd.
> >>>
> >>>> I have this container that is a builder of system images for other nodes
> >>>> (containers and/or metal boxes). In order to correctly do this it needs
> >>>> to execute mknod inside the image as it builds it. (note, device nodes
> >>>> created doesn't need to be usable in the context of the image being
> >>>> built - the builder just needs to be able to create it).
> >>>>
> >>>> I've been doing this for ages under sysvinit and it's been fine. I have
> >>>> just migrated this builder container to systemd and hit this problem...
> >>>> Is there another way to keep systemd in line other than removing the
> >>>> mknod capability ?
> >>>>
> >>>> Thanks,
> >>>> John
Regards,
Mike
--
Michael H. Warfield (AI4NB) | (770) 985-6132 | m...@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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