[Lxc-users] Dependencies Use Cases
Serge Hallyn
serge.hallyn at canonical.com
Fri Nov 4 16:00:23 UTC 2011
Quoting Alex Eagar (alexeagar at gmail.com):
> Can LXC use cgroups without libcgroup? For that matter, just to be
> clear, can LXC use cgroups without cgroup-bin?
LXC doesn't need anything from cgroup-bin, and, if it did, cgroup-bin
could not deliver. (see below)
> In what use case would
> using LXC without cgroups make sense? Aren't cgroups fundamental to
I think you misunderstand cgroup-bin. The point of cgroup-bin is to
try and catch applications/daemons as they start and classify them
into cgroups according to a configuration. However because tasks are
classified by placing their pids one at a time into a file, there are
cases where it misses tasks, and it's not entirely reliable.
LXC controls cgroups (the kernel feature) itself through the cgroup
filesystem. cgroup-bin is not needed for this. The cgroups just need
to be composed in a (set of) cgroup mount(s) somewhere.
> happening, but based on my presumptions, which presumptions I am
> actively asking you to correct, that is what appears to have occurred
> in Ubuntu.
Hopefully the above explained why that's not what happened.
> serge, as a fellow member of the Ubuntu community, please do not refer
> to others' efforts as 'papering over' even if it perhaps is in
I wrote lxcguest. 'Papering over' is not meant as a put-down. The
point is that there are things in a stock Ubuntu install which stop
a container from booting. For each of those, the right thing to do
is to update the packages involved so that they can work just as well
in a container as on hardware/kvm. But for a first step, I chose
to create a package to hide the problems. In part, that gave us a
better chance to figure out what the real problems were. Currently
there are (if I'm thinking right), at core, two: 1. the need for the
lxc-monitor to watch /run/utmp in the container to detect reboot/shutdown.
That means the guest can't mount tmpfs on /run, which suddenly creates
a whole set of issues. Daniel is hoping to resend a kernel patchset
this week or next which well let us not do that. 2. mountall needs
to not mount certain things in a container at boot. Here is where
I almost literally paper over :) : lxcguest just bind-mounts a different
file over /lib/init/fstab to make mountall do what we want. This
can break upgrades, when they want to overwrite /lib/init/fstab. So
I intend to fix mountall so we don't need that.
-serge
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