[lxc-users] Migrating a rootfs back-and-forth lxc 2.0 <=> 3.0

[Christian Brauner]

> Date: Thu, 15 Feb 2018 13:05:44 -0500 (EST)
> From: Adrian Pepper <arpepper at uwaterloo.ca>
> To: lxc-users at lists.linuxcontainers.org
> Subject: [lxc-users] Migrating a rootfs back-and-forth lxc 2.0 <=> 3.0
> 
> Should one expect to encounter subtle (or perhaps not-so-subtle)
> problems if one takes the rootfs of a simple container created under
> one major version of lxc and uses it to replace the rootfs of a
> container previously created under another major version?
> (Replacing while the target is stopped, and then starting
> the container after the replacement).

No, that shouldn' cause any problems.

> 
> Assume that due diligence was done to keep the hostname in the
> filesystem was consistent with lxc.uts.name (or its equivalent
> in the relevant version), etc.
> 
> Or should one expect this to work seamlessly?  (The question would be
> whether there are hooks of some sort under the rootfs which might get
> automatically migrated in one direction (presumably "forwards" to a
> higher version), but not in the other direction, or possibly not in
> either direction at all).
> 
> Somewhat similarly, but conversely, I would assume that there is never
> any situation where having the same rootfs used simultaneously by more
> than one executing container would not be disastrous.  (in my case just
> a foreseeable possible accident, not something I have visions of exploiting).

That is a bad idea yes. For example, with system container you'd have
two init system thinking that they are in control of the whole rootfs
and fstree.

Christian